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Concrete

Concrete

In construction, concrete is a composite building material made from the combination of aggregate and cement binder. The most common form of concrete is Portland cement concrete, which consists of mineral aggregate (generally gravel and sand), Portland cement and water. It is commonly believed that concrete dries after mixing and placement. Actually, concrete does not solidify because water evaporates, but rather cement hydrates, gluing the other components together and eventually creating a stone-like material. When used in the generic sense, this is the material referred to by the term concrete. Concrete is used to make pavements, building structures, foundations, motorways/roads, overpasses, parking structures, bases for gates/fences/poles, and cement in brick or block walls. An old name for concrete is liquid stone.

History

The Assyrians and Babylonians used clay as cement in their concretes. The Egyptians used lime and gypsum cement. In the Roman Empire, cements made from pozzolanic ash/pozzolana and an aggregate made from pumice were used to make a concrete very similar to modern portland cement concrete. In 1756, British engineer John Smeaton pioneered the use of portland cement in concrete, using pebbles and powdered brick as aggregate. In the modern day, the use of recycled/reused materials as concrete ingredients is gaining popularity due to increasingly stringent environmental legislation. The most conspicuous of these is pulverized fuel ash, recycled from the ash by-products of coal power plants. This has a significant impact in reducing the amount of quarrying and the ever-attenuating landfill space.

Characteristics

During hydration and hardening, concrete needs to develop certain physical and chemical properties, among others, mechanical strength, low permeability to ingress of moisture, and chemical and volume stability. Concrete has relatively high compressive strength, but significantly lower tensile strength (about 10% of the compressive strength). As a result, concrete always fails from tensile stresses - even when loaded in compression. The practical implication of these facts is that concrete elements that are subjected to tensile stresses must be reinforced. Concrete is most often constructed with the addition of steel bar or fiber reinforcement. The reinforcement can be by bars (rebars), mesh, or fibres to produce reinforced concrete. Concrete can also be prestressed (reducing tensile stress) using steel cables, allowing for beams or slabs with a longer span than is practical with reinforced concrete. The ultimate strength of concrete is related to water/cement ratio, the proportion and type of cement to fillers, and the size, shape, and strength of the aggregate used. Concrete with lower water/cement ratio (down to 0.35) makes a stronger concrete than a higher ratio. Concrete made with smooth pebbles is weaker than that made with rough-surfaced broken rock pieces for example. Certain shapes are very strong in compression, such as arches and vaults, and are therefore preferred for concrete construction. Concrete is placed in a wet or plastic state, and therefore can be manipulated and molded as needed. Hydration and hardening of concrete may lead to tensile stresses at a time when it has not yet gained significant strength, resulting in shrinkage cracks. However, when concrete mix is placed in accordance with the best recommended practice, cracking may be minimal. vault

Additives

Additives are organic or non-organic materials in form of solids or fluids that are added to the concrete to give it certain characteristics. In normal use the additives make up less than 5% of the cement weight. The most used types of additives are:
- Accelerators: Speed up the hydration (strengthening) of the concete.
- Retarders: Slow the hydration of concrete.
- Air-entrainers: Add and distribute air to the concrete.
- Plasticizers: Increase the workability of concrete.

Workability

Workability is the ability of a fresh (plastic) concrete mix to fill the form/mould properly with the desired work (vibration) and without reducing the concrete's quality. Workability depends on water content, additives, aggregate (shape and size distribution) and age (level of hydration). Raising the water content or adding plasticizer will increase the workability. Too much water will lead to bleeding (loss of water) and/or segregation (concrete starts to get heterogeneous) and the resulting concrete will have reduced quality. Workability is normally tested by slump measurement. High flow concrete, like self compacting concrete, are normaly tested by one of several flow measuring methods. Concrete slump is a simplistic measure of fresh (plastic) concrete's workability. Slump is normally determined by the ASTM C 143 or EN 12350-2 slump test standards, using the Abrams cone, into which concrete is placed for testing. When the cone is carefully lifted off the enclosed material, it will slump a certain amount due to its water content. A relatively dry sample will slump very little, and be given a slump of one or two inches (25 or 50 mm), while a relatively wet concrete sample may slump as much as six or seven inches (150 to 175 mm). To increase the slump, the rule of thumb is:
- US units :Add 1 US gallon of water per cubic yard of concrete in the mixer truck to increase slump by 1 inch. Adding 27 US gallons to 9 cubic yards of batched concrete will therefore increase the slump by about 3 inches.
- Metric units (converted from US rule of thumb) :Add 2 litres of water per cubic metre of concrete in the mixer truck to increase slump by 1 cm. Adding 54 litres to 9 cubic metres of batched concrete will therefore increase the slump by about 3 cm. Slump can also be increased by adding a plasticizer, without changing the water/cement ratio.

Self compacting concretes

During the 1980s a number of countries including Japan, Sweden and France developed a range of concretes that were self-compacting. These 'SCC's are characterised by their extreme fluidity (using plasticizers), behaving more like water than the traditional viscous concrete. SCCs are characterized by
- extreme fluidity measured by flow or slump, typically measured between 700-750 mm.
- no need for vibrators to compact the concrete, which can be noisy
- no or little need for expensive concrete pumping equipment
- no bleed water (excess water draining out of the concrete) SCC can offer benefits of up to 50% in labour costs, due to it being poured up to 80% faster and having reduced wear and tear on formwork. As of 2005, self compacting concretes account for 10-15% of concrete sales in some European countries.

Shotcrete / sprayed concrete

Main article: Shotcrete

Shotcrete uses compressed air to shoot (cast) concrete to a frame or structure. Shotcrete is mostly used for rock support, especially in tunnelling. Today there are two application methods for shotcrete: the dry-mix and the wet-mix procedure. In Dry-mix the dry mixture of cement and aggregates is filled into the machine and conveyed with compressed air through the hoses. The water needed for the hydration is added at the nozzle. In Wet-mix the mixes are prepared with all necessary water for hydration. The mixes are pumped through the hoses. At the nozzle compressed air is added for spraying. For both methods additives such as plasticizers and accelerators may be used. Shotcrete is normally reinforced by fibers.

External link

- [http://inventors.about.com/library/inventors/blconcrete.htm History of Concrete] Category:Concrete Category:Civil engineering Category:Materials Category:Construction Category:Pavements Category:Heterogeneous mixtures ms:Konkrit ja:コンクリート simple:Concrete

Composite material

Composite materials (or composites for short) are engineered materials made from two or more constituent materials that remain separate and distinct on a macroscopic level while forming a single component. There are two categories of constituent materials: matrix and reinforcement. At least one portion (fraction) of each type is required. The matrix material surrounds and supports the reinforcement materials by maintaining their relative positions. The reinforcements impart their special mechanical, electrical and physical properties to enhance the matrix properties. A synergism produces material properties unavailable from naturally occurring materials. Due to the wide variety of matrix and reinforcement materials available, the design potentials are incredible. The most primitive composite materials comprised straw and mud in the form of bricks for building construction. The most advanced examples perform routinely on spacecraft in demanding environments. The most visible applications pave our roadways in the form of either steel and aggregate reinforced portland cement or asphalt concrete. Those composites closest to our personal hygiene form our shower stalls and bath tubs made of fiberglass. Solid surface, imitation granite and cultured marble sinks and countertops are widely used to enhance our living experiences. There are the so-called natural composites like bone and wood. Both of these are constructed by the processes of nature and beyond the scope of this text. Engineered composite materials must be formed to shape. This involves strategically placing the reinforcements while manipulating the matrix properties to achieve a melding event at or near the beginning of the component life cycle. A variety of methods are used according to the end item design requirements, and they are commonly named molding or casting processes, as appropriate. The principle factors impacting the methodology are the natures of the chosen matrix and reinforcement materials. Another important factor is the gross quantity of material to be produced. Large quantities can be used to justify high capital expenditures for rapid and automated manufacturing technology. Small production quantities are accommodated with lower capital expenditures but higher labor and tooling costs at a correspondingly slower rate. Most commercially produced composites use a polymer matrix material often called a resin or resin solution. There are many different polymers available depending upon the starting raw ingredients. There are several broad categories, each with numerous variations. The most common categories are known as polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, and others. The reinforcement materials are often fibers but also commonly ground minerals. Fibers are often transormed into a textile material such as a felt, fabric, knit or stitched construction. Advanced composite materials constitute a category comprising carbon fiber reinforcement and epoxy or polyimide matrix materials. These are the aerospace grade composites and typically involve laminate molding at high temperature and pressure to achieve high reinforcement volume fractions. One component is often a strong fibre such as fiberglass, quartz, kevlar, Dyneema or carbon fibre that gives the material its tensile strength, while another component (called a matrix) is often a resin such as polyester, or epoxy that binds the fibres together, transferring load from broken fibers to unbroken ones and between fibers that are not oriented along lines of tension. Also, unless the matrix chosen is especially flexible, it prevents the fibers from buckling in compression. Some composites use an aggregate instead of, or in addition to, fibers. In terms of stress, any fibers serve to resist tension, the matrix serves to resist shear, and all materials present serve to resist compression, including any aggregate. Composite materials can be divided into two main categories normally referred to as short fiber reinforced materials and continous fiber reinforced materials. Continuous reinforced materials will often constitute a layered or laminated structure. Shocks, impact, loadings or repeated cyclic stresses can cause the laminate to separate at the interface between two layers, a condition known as delamination. Individual fibers can separate from the matrix e.g. fiber pull-out.

Examples of composite materials:

- Fibre reinforced plastics:
- Classified by type of fiber:
- Wood (cellulose fibers in a lignin and hemicellulose matrix)
- Carbon-fibre reinforced plastic or CRP
- Glass-fibre reinforced plastic or GRP (informally, "fiberglass")
- Classified by matrix:
- Thermoplastic Composites
- long fiber thermoplastics or long fiber reinforced thermoplastics
- glass mat thermoplastics
- Thermoset Composites
- Metal matrix composites or MMCs:
- White cast iron
- Hardmetal (carbide in metal matrix)
- Metal-intermetallic laminate
- Ceramic matrix composites:
- Cermet (ceramic and metal)
- concrete
- Reinforced carbon-carbon (carbon fibre in a graphite matrix)
- Bone (hydroxyapatite reinforced with collagen fibers)
- Organic matrix/ceramic aggregate composites
- Mother of Pearl
- Syntactic foam
- Asphalt concrete
- Chobham armour (see composite armour)
- Engineered wood
- Plywood
- Oriented strand board
- Wood plastic composite (recycled wood fiber in polyethylene matrix)
- Pycrete (sawdust in ice matrix) ms:Bahan komposit th:วัสดุผสม

Cement

In the general sense, a cement is any material with adhesive properties. The term cement is also commonly used to refer more specifically to powdered materials which develop strong adhesive qualities when combined with water. These materials are more properly known as hydraulic cements. Hydraulic limes, natural pozzolana and Portland cements are the more common hydraulic cements, with portland cement being the most important in construction. Gypsum plaster and common lime are not hydraulic cements.

History

Hydraulic cement was first invented by the Egyptians, and later reinvented by the Greeks and Babylonians, who made their mortar out of lime, much harder than the Roman mortars. Later, the Romans produced a good cement from pozzolanic ash. pozzolanic ash, Australia. The company is a member of the Boral Group of Companies]] Portland cement was patented in England by Joseph Aspdin in 1824.

Geology

In geology, the term is used to refer to the fine-grained minerals which bind the coarser-grained matrix in sedimentary rocks. Such cements are typically composed of calcite, quartz or clay minerals.

Another meaning

Cement is also the name of Chuck Mosley's post-Faith No More band. Additionally, CEMENT is an acronym for [http://comparametric.sourceforge.net Computer Enhanced Multiple Exposure Numerical Technique] in which multiple pictures of the same subject matter are "cemented" together to attain increased picture resolution or for artistic visual lightspaces. Category:Concrete ja:セメント

Gravel

] Gravel is rock that is of a certain size range. In geology, gravel is any loose rock that is at least two millimeters in its largest dimension (about 1/12 of an inch), and no more than 75 millimeters (about 3 inches). Sometimes gravel is restricted to rock in the 2-4 millimeter range, with pebble being reserved for rock 4-75 millimeters (some say 64 millimeters). The next smaller size class in geology is sand, which is 0.02 mm to 2 mm in size. The next larger size is cobble, which is 75 (64) millimeters to 256 millimeters (about ten inches). Gravel is an important commercial product, used in many applications. Some important types of gravel include:
- Crushed stone: This is generally limestone or dolomite that has been crushed and graded by screens to certain size classes. It is widely used in concrete and as a surfacing for roads and driveways, sometimes with tar applied over it. Crushed stone may also be made from granite and other rocks. A special type of limestone crushed stone is dense grade aggregate, or DGA, also known as crusher run. This is a mixed grade of mostly small crushed stone in a matrix of crushed limestone powder.
- Creek rock: This is generally rounded stones, potentially of a wide range of types, that are dredged or scooped from river beds and creek beds. It is also often used as concrete aggregate and less often as a paving surface. In Britain, gravel always refers to smooth, rounded, river-worn material, never to angular stones or crushed rock. British gravel ranges in size from 4 mm to about 30 mm, the smaller sizes up to 8 mm are usually called 'pea gravel'. Many roadways are surfaced with gravel, especially in rural areas where there is little traffic. Globally, far more roads are surfaced with gravel than with concrete or tarmac; Russia alone has over 400,000 km of gravel-surfaced roads. Large gravel deposits are a common geological feature, being formed as a result of the weathering and erosion of rocks. The action of rivers and waves tends to pile up gravel in large concentrations. This can sometimes result in gravel becoming compacted and concreted into the sedimentary rock called conglomerate. Where natural gravel deposits are insufficient for human purposes, gravel is often produced by quarrying and crushing hard-wearing rocks, such as sandstone, limestone, or basalt. Quarries where gravel is extracted are known as gravel pits. Southern England possesses particularly large concentrations of them due to the widespread deposition of gravel in the region during the Ice Ages. The word comes from the French gravelle, meaning "coarse sand".

Types of gravel

French]] Multiple types of gravel have been recognised by geologists. They include:
- Bank gravel: gravel intermixed with sand or clay.
- Bench gravel: a bed of gravel located on the side of a valley above the present stream bottom, indicating the former location of the stream bed when it was at a higher level.
- Fine gravel: gravel consisting of particles with a diameter of 1 to 2 mm.
- Lag gravel: a surface accumulation of coarse gravel produced by the removal of finer particles.
- Pay gravel: also known as "pay dirt"; a nickname for gravel with a high concentration of gold and other precious metals. The metals are recovered through gold panning.
- Piedmont gravel: a coarse gravel carried down from high places by mountain streams and deposited on relatively flat ground, where the water runs more slowly.
- Plateau gravel: a layer of gravel on a plateau or other region above the height at which stream-terrace gravel is usually found.
- River run gravel: naturally deposited gravel found in and next to rivers and streams.

Sand

Sand is an example of a class of materials called granular matter. Sand is a naturally occurring, finely divided rock, comprising particles or granules ranging in size from ¹⁄₁₆ to 2 millimeters. An individual particle in this range size is termed a sand grain. The next smaller size class in geology is silt: particles below ¹⁄₁₆ mm down to ¹⁄₂₅₆ mm (0.004 mm) in size. The next larger size class above sand is gravel, with particles ranging up to 64 mm (see grain size for standards in use). The most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide), usually in the form of quartz which because of its chemical inertness and considerable hardness is quite resistant to weathering. However, the composition of sand varies according to local rock sources and conditions. The bright white sands found in tropical and subtropical coastal settings are ground-up limestone. Arkose is a sand or sandstone with considerable feldspar content which is derived from the weathering and erosion of a usually nearby granite. Some locations have sands that contain magnetite, chlorite, glauconite, or gypsum. Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts. The chlorite-glauconite bearing sands are typically green in color, as are sands derived from basalts (lavas) with a high olivine content. The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, white color. Sand deposits in some areas contain garnets and other resistant minerals, including some small gemstones. Sand is transported by wind or water and deposited in the form of beaches, dunes, sand spits, sand bars, and the like. In most deserts, sand is a dominant constituent of the soil. The study of sand is called arenology.

Uses of sand

arenology Sand is often a principal component of the aggregate used in the preparation of concrete. Sand manufactured at rock crusher plants for use as an aggregate is called mansand. Graded sand is used as an abrasive in sandblasting and is also used in media filters for filtering water. Brick manufacturing plants use Sand as an additive with a mixture of clay and other materials for manufacturing bricks. Sandy soils are ideal for certain crops such as watermelons and peanuts and are often preferred for intensive dairy farming because of their excellent drainage characteristics. Sandbags are used for protection against floods and gun fire. They can be easily transported when empty, and filled with local sand. People, especially children, love to play with sand on a beach or in a sandpit. See sand art and play for details.

Hazards of sand

Bags of sand now typically carry labels warning the user to wear respiratory protection and avoid breathing the fine silica dust. There have been a number of lawsuits in recent years where workers have sought damages after they developed silicosis, a lung disease caused by inhalation of fine silica particles. People have been severely injured and even killed after digging sand "caves" in large dunes, sandhills, or even on beaches when the cave or tunnel collapsed upon them.

Water (molecule)

Water has the chemical formula H₂O, meaning that one molecule of water is composed of two hydrogen atoms and one oxygen atom. It is in dynamic equilibrium between the liquid and solid states at standard temperature and pressure. At room temperature, it is a nearly colorless, tasteless, and odorless liquid. It is often referred to in the sciences as the universal solvent and the only pure substance found naturally in all three states of matter.

Forms of water

:See the :Category:Forms of water Water may take many forms. The solid state of water is commonly known as ice (while many other forms exist, see amorphous solid water; the gaseous state is known as water vapor (or steam), and the common liquid phase is generally taken as simply water. Water may take many forms, and is the base molecule of aqueous solutions. Above a certain critical temperature and pressure (647 K and 22.064 MPa), water molecules assume a supercritical condition, in which liquid-like clusters float within a vapor-like phase. Heavy water is water in which the hydrogen atoms are replaced by its heavier isotope, deuterium. It is chemically almost identical to normal water. Heavy water is used in the nuclear industry to slow down neutrons.

A common substance

Water in the Universe

Water has been found in interstellar clouds within our galaxy, the Milky Way. It is believed that water exists in abundance in other galaxies too, because its components, hydrogen and oxygen, are among the most abundant elements in the universe. Interstellar clouds eventually condense into solar nebulae and solar systems, such as ours. The initial water can then be found in comets, planets, and their satellites. In our solar system, water, in liquid or ice form, has been found :
- on the Moon,
- on the planets Mercury, Mars, Neptune, and Pluto,
- on satellites of planets, such as Triton and Europa.

Water on Earth

The water cycle (known scientifically as the hydrologic cycle) refers to the continuous exchange of water within the hydrosphere, between the atmosphere, soil water, surface water, groundwater, and plants. Earth's approximate water volume (the total water supply of the world) is 1,360,000,000 km³ (326,000,000 mi³). Of this volume:
- 1,320,000,000 km³ (316,900,000 mi³ or 97.2%) is in the oceans
- 25,000,000 km³ (6,000,000 mi³ or 1.8%) is in glaciers and icecaps
- 13,000,000 km³ (3,000,000 mi³ or 0.9%) is groundwater.
- 250,000 km³ (60,000 mi³ or 0.02%) is fresh water in lakes, inland seas, and rivers.
- 13,000 km³ (3,100 mi³ or 0.001%) is atmospheric water vapor at any given time. Liquid water is found in bodies of water, such as an ocean, sea, lake, river, stream, canal, or pond. The majority of water on Earth is sea water. Water is also present in the atmosphere in both liquid and vapor phases. It also exists as groundwater in aquifers. Although water normally boils at about 100℃, in deep sea vents the pressurised superheated water reaches a natural temperature of 400℃, whereas at the top of Mount Everest, the low pressure allows water to boil at a mere 70℃.

Water in industry

Water is also used in many industrial processes and machines, such as the steam turbine and heat exchanger, in addition to its use as a chemical solvent. Discharge of untreated water from industrial uses is pollution. Pollution includes discharged solutes (chemical pollution) and discharged coolant water (thermal pollution). Industry requires pure water for many applications and utilizes a variety of purification techniques both in water supply and discharge.

Physics and chemistry of water

Density of water and ice

For most substances, the solid form of the substance is more dense than the liquid form; thus, a block of pure solid substance will sink in a tub of pure liquid substance. But, by contrast, a block of common ice will float in a tub of water because solid water is less dense than liquid water. This is an extremely important characteristic property of water. At room temperature, liquid water becomes denser with lowering temperature, just like other substances. But at 4°C, just above freezing, water reaches its maximum density, and as water cools further toward its freezing point, the liquid water, under standard conditions, expands to become less dense. The physical reason for this is related to the crystal structure of ordinary ice, known as hexagonal ice Ih. Water, gallium, bismuth, acetic acid, antimony and silicon are some of the few materials which expand when they freeze; most other materials contract. It should be noted however, that all forms of ice are not less dense than liquid water. For example HDA and VHDA are both more dense than liquid phase pure water. Thus, the reason that the common form of ice is less dense than water is a bit non-intuitive, and relies heavily on the unusual properties inherent to the hydrogen bond. Generally, water expands when it freezes because of its molecular structure, in tandem with the unusual elasticity of the hydrogen bond and the particular lowest energy hexagonal crystal confirmation that it adopts under standard conditions. That is, when water cools, it tries to stack in a crystalline lattice configuration that stretches the rotational and vibrational components of the bond, so that the effect is that each molecule of water is pushed further from each of its neighboring molecules. This effectively reduces the density ρ of water when ice is formed under standard conditions. The importance of this property cannot be overemphasized for its role on the ecosystem of earth. For example, if water was more dense when frozen, lakes and oceans in a polar environment would eventually freeze solid (from top to bottom). This would happen because frozen ice would settle on the lake and riverbeds, and the necessary warming phenomenon (see below) could not occur in summer, as the warm surface layer would be less dense than the solid frozen layer below. It is a significant feature of nature that this does not occur naturally in the environment, but under synthetic laboratory conditions where HDA and VHDA form, specialized forms of ice are more dense, and do sink to the bottom in liquid water. Nevertheless, the unusual expansion of freezing water (in ordinary natural settings in relevant biological systems), due to the hydrogen bond, from 4 °C above freezing to the freezing point offers an important advantage for freshwater life in winter. Water chilled at the surface becomes denser and sinks, forming convection currents that cool the whole water body, but when the temperature of the lake water reaches 4 °C, water on the surface, as it chills further, becomes less dense, and stays as a surface layer which eventually freezes and forms ice. Since downward convection of colder water is blocked by the density change, any large body of fresh water frozen in winter will have the coldest water near the surface, away from the riverbed or lakebed.

Density of saltwater and ice

The situation in salt water is somewhat different. Ice still floats to keep the oceans from freezing solid (see following paragraph). However, the salt content of oceans both lowers the colligative freezing point by about 2 °C and lowers the temperature of the density maximum of water to be about at the freezing point. Hence, in ocean water, because of the salt content, the downward convection of colder water is not blocked by an expansion of water as it becomes colder near the freezing point; thus the oceans' cold water near the freezing point continues to sink. For this reason, any creature attempting to survive at the bottom of such cold water as the Arctic Ocean generally lives in water that is 4 °C colder than the temperature at the bottom of frozen-over fresh water lakes and rivers in winter. As the surface of salt water begins to freeze (at -1.9 °C for normal salinity seawater, 35‰) the ice that forms is essentially salt free with a density approximately that of freshwater ice. This ice floats on the surface and the salt that is "frozen out" adds to the salinity and density of the seawater just below it. This more dense saltwater sinks by convection and the replacing seawater is subject to the same process. This provides essentially freshwater ice at -1.9 °C on the surface. The increased density of the seawater beneath the forming ice sinks towards the bottom, thus the deep ocean waters should have a minimum temperature of -1.9 °C also.

Triple point

The temperature and pressure at which solid, liquid, and gaseous water coexist in equilibrium is called the triple point of water. This point is used to define the units of temperature (the kelvin and, indirectly, the degree Celsius and even the degree Fahrenheit). The triple point is at a temperature of 273.16 K (0.01 °C) by convention, and at a pressure of 611.2 Pa. This pressure is quite low, about 150 times lower than the normal sea level barometric pressure of 101,300 Pa. The atmospheric surface pressure on planet Mars is remarkably close to the triple point pressure.

Mpemba effect

The Mpemba effect is the surprising phenomenon whereby hot water can, under certain conditions, freeze faster than cold water, even though it must pass the lower temperature on the way to freezing. However, this can be explained with evaporation, convection, supercooling, and the insulating effect of frost.

Surface tension

Water drops are stable thanks to the high surface tension of water. This can be seen when small quantities of water are put onto a nonsoluble surface such as glass: the water stays together as drops. This property is important for life. For example, when water is carried through xylem up stems in plants the strong intermolecular attractions hold the water column together. Strong cohesive properties hold the water column together, and strong adhesive properties stick the water to the xylem, and prevent tension rupture caused by transpiration pull. Other liquids with lower surface tension would have a higher tendency to "rip", forming vacuum or air pockets and rendering the xylem water transport inoperative.

Electrical properties

Pure water is actually a good insulator (poor conductor), meaning that it does not conduct electricity well. Because water is such a good solvent, however, it almost always has some solute dissolved in it, most frequently a salt. If water has even a tiny amount of such impurities, then it can conduct electricity much better, because impurities such as salt separate into free ions in aqueous solution by which an electric current can flow. Water can be split into its constituent elements, hydrogen and oxygen, by passing a current through it. This process is called electrolysis. Water molecules naturally dissociate into H⁺ and OH^- ions, which are pulled toward the cathode and anode, respectively. At the cathode, two H⁺ ions pick up electrons and form H₂ gas. At the anode, four OH^- ions combine and release O₂ gas, molecular water, and four electrons. The gases produced bubble to the surface, where they can be collected. It is known that the theoretical maximum electrical resistivity for water is approximately 182 kilohm-meters (or 18.2 MΩ·cm) at 25 degrees Celsius. This figure agrees well with what is typically seen on reverse osmosis, ultrafiltered and deionized ultrapure water systems used for instance, in semiconductor manufacturing plants. A salt or acid contaminant level exceeding that of even 100 parts per trillion (ppt) in ultrapure water will begin to noticeably lower its resistivity level by up to several kilohm-meters (a change of several hundred nanosiemens per meter of conductance).

Dipolar nature of water

An important feature of water is its polar nature. The water molecule forms an angle, with hydrogen atoms at the tips and oxygen at the vertex. Since oxygen has a higher electronegativity than hydrogen, the side of the molecule with the oxygen atom has a partial negative charge. A molecule with such a charge difference is called a dipole. The charge differences cause water molecules to be attracted to each other (the relatively positive areas being attracted to the relatively negative areas) and to other polar molecules. This attraction is known as hydrogen bonding, and explains many of the properties of water. Although hydrogen bonding is a relatively weak attraction compared to the covalent bonds within the water molecule itself, it is responsible for a number of water's physical properties. One such property is its relatively high melting and boiling point temperatures; more heat energy is required to break the hydrogen bonds between molecules. The similar compound hydrogen sulfide (H₂S), which has much weaker hydrogen bonding, is a gas at room temperature even though it has twice the molecular weight of water. The extra bonding between water molecules also gives liquid water a large specific heat capacity. This high heat capacity makes water a good heat storage medium. Hydrogen bonding also gives water its unusual behavior when freezing. When cooled to near freezing point, the presence of hydrogen bonds means that the molecules, as they rearrange to minimize their energy, form the hexagonal crystal structure of ice that is actually of lower density: hence the solid form, ice, will float in water. In other words, water expands as it freezes, whereas virtually all other materials shrink on solidification. An interesting consequence of the solid having a lower density than the liquid is that ice will melt if sufficient pressure is applied. With increasing pressure the melting point temperature drops and when the melting point temperature is lower than the ambient temperature the ice begins to melt. A significant increase of pressure is required to lower the melting point temperature by very much - the pressure exerted by an ice skater on the ice would only reduce the melting point by something like 0.09 °C.

Water as a solvent

Water is also a good solvent due to its polarity. When an ionic or polar compound enters water, it is surrounded by water molecules. The relatively small size of water molecules typically allows many water molecules to surround one molecule of solute. The partially negative dipole ends of the water are attracted to positively charged components of the solute, and vice versa for the positive dipole ends. In general, ionic and polar substances such as acids, alcohols, and salts are relatively soluble in water, and nonpolar substances such as fats and oils are not. Nonpolar molecules stay together in water because it is energetically more favorable for the water molecules to hydrogen bond to each other than to engage in van der Waals interactions with nonpolar molecules. An example of an ionic solute is table salt; the sodium chloride, NaCl, separates into Na⁺ cations and Cl^- anions, each being surrounded by water molecules. The ions are then easily transported away from their crystalline lattice into solution. An example of a nonionic solute is table sugar. The water dipoles make hydrogen bonds with the polar regions of the sugar molecule (OH groups) and allow it to be carried away into solution. The solvent properties of water are vital in biology, because many biochemical reactions take place only within aqueous solutions (e.g., reactions in the cytoplasm and blood).

Amphoteric nature of water

Chemically, water is amphoteric -- i.e., it is able to act as either an acid or a base. Occasionally the term hydroxic acid is used when water acts as an acid in a chemical reaction. At a pH of 7 (neutral), the concentration of hydroxide ions (OH^-) is equal to that of the hydronium (H₃O⁺) or hydrogen (H⁺) ions. If the equilibrium is disturbed, the solution becomes acidic (higher concentration of hydronium ions) or basic (higher concentration of hydroxide ions). Water can act as either an acid or a base in reactions. According to the Brønsted-Lowry system, an acid is defined as a species which donates a proton (an H⁺ ion) in a reaction, and a base as one which receives a proton. When reacting with a stronger acid, water acts as a base; when reacting with a weaker acid, it acts as an acid. For instance, it receives an H⁺ ion from HCl in the equilibrium: :HCl + H₂O ↔ H₃O⁺ + Cl^- Here water is acting as a base, by receiving an H⁺ ion. An acid donates an H⁺ ion, and water can also do this, such as in the reaction with ammonia, NH₃: :NH₃ + H₂O ↔ NH₄⁺ + OH^-

Acidity in nature

In theory, pure water has a pH of 7. In practice, pure water is very difficult to produce. Water left exposed to air for any length of time will rapidly dissolve carbon dioxide, forming a dilute solution of carbonic acid, with a limiting pH of about 5.7. As cloud droplets form in the atmosphere and as raindrops fall through the air minor amounts of CO₂ are absorbed and thus most rain is slightly acidic. If high amounts of nitrogen and sulfur oxides are present in the air, they too will dissolve into the cloud and rain drops producing more serious acid rain problems.

Hydrogen bonding in water

Water molecule can form a maximum of four hydrogen bonds because it can accept two and donate two hydrogens. Other molecules like hydrogen fluoride, ammonia, methanol form hydrogen bonds but they do not show anomalous behaviour of thermodynamic, kinetic or structural properties like those observed in water. The answer to the apparent difference between water and other hydrogen bonding liquids lies in the fact that apart from water none of the hydrogen bonding molecules can form four hydrogen bonds either due to an inability to donate/accept hydrogens or due to steric effects in bulky residues. In water local tetrahedral order due to the four hydrogen bonds gives rise to an open structure and a 3-dimensional bonding network, which exists in contrast to the closely packed structures of simple liquids. There is a great similarity between water and silica in their anomalous behaviour, even though one (water) is a liquid which has a hydrogen bonding network while the other (silica) has a covalent network with a very high melting point. One reason that water is well suited, and chosen, by life-forms, is that it exhibits its unique properties over a temperature regime that suits diverse biological processes, including hydration. It is believed that hydrogen bond in water is largely due to electrostatic forces and some amount of covalency. The partial covalent nature of hydrogen bond predicted by Linus Pauling in 1930s is yet be to proven unambiguously by experiments and theoretical calculations.

Quantum properties of Molecular Water

Although the molecular formula of water is generally considered to be a stable result in molecular thermodynamics, recent work, started in 1995 [http://physics.about.com/gi/dynamic/offsite.htm?site=http://www.aip.org/enews/physnews/2003/split/648%2D1.html] has shown that at certain scales, water may act more like H_3/2O than H₂O at the subatomic quantum level. This result could have significant ramifications at the level of, for example, the hydrogen bond in biological, chemical and physical systems. The experiment shows that when neutrons and protons collide with water, they scatter in a way that indicates that they only are affected by a ratio of 1.5:1 of hydrogen to oxygen respectively. However, the time-scale of this response is only seen at the level of attoseconds, and so is only relevant in highly resolved kinetic and dynamical systems. For more references see [http://prola.aps.org/abstract/PRL/v79/i15/p2839_1] and [http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000091000005057403000001&idtype=cvips&gifs=yes].

History

In 1742, Anders Celsius defined the Celsius temperature scale with the freezing point of water at 100 degrees and the boiling point at standard atmospheric pressure at 0 degrees. The scale was reversed in 1744. The first decomposition of water into hydrogen and oxygen, by electrolysis, was done in 1800 by William Nicholson, an English chemist. Gilbert Newton Lewis isolated the first sample of pure heavy water in 1933. Polywater was a hypothetical polymerized form of water that was the subject of much scientific controversy during the late 1960s. The consensus now is that it does not exist.

Systematic nomenclature and humor

Chemists sometimes jokingly refer to water as dihydrogen monoxide or DHMO, an overly pedantic systematic covalent name of this molecule, especially in parodies of chemical research that call for this "lethal chemical" to be banned. In 2004, the town of Aliso Viejo, California nearly banned foam cups after learning that DHMO was used in their production (see [http://slashdot.org/articles/04/03/16/1419252.shtml?tid=133&tid=186]). In reality, a more realistic systematic name would be hydrogen oxide, since the "di-" and "mon-" prefixes are superfluous. Hydrogen sulfide, H₂S, is never referred to as "dihydrogen monosulfide", and hydrogen peroxide, H₂O₂, is never called "dihydrogen dioxide". Some overzealous MSDSs for water list the following: Caution: May cause drowning! The systematic acid name of water is hydroxic acid or hydroxilic acid. Likewise, the systematic alkali name of water is hydrogen hydroxide – both acid and alkali names exist for water because it is able to react both as an acid or an alkali, depending on the strength of the acid or alkali it is reacted with (it is amphoteric). None of these names are used widely outside of DHMO sites.

External links

- [http://www.lsbu.ac.uk/water/ Water Structure and Behaviour]
- [http://www.dhmo.org/ A spoof site on the "dangers" of dihydrogen monoxide]
- [http://www.siwi.org/ Stockholm International Water Institute] (SIWI)
- [http://www.btinternet.com/~martin.chaplin/explan.html Explanation of the anomalous properties of water]
- [http://www.compchemwiki.org/index.php?title=Water Computational Chemistry Wiki] Category:Forms of water Category:Solvents Category:Hydrogen compounds Category:Oxygen compounds Category:Hydrides Category:Oxides Category:Hydroxides

Hydration

In chemistry, hydration is the condition of being combined with water. Hydration can create a hydrate from which water can be reextracted. When hydration occurs in a chemical reaction it is called a hydration reaction, in which water is permanently and chemically combined with a reactant in a way that it can no longer be reextracted. An example of a hydration reaction is acid-catalyzed hydration of the carbon-carbon double bond in an alkene. H⁺ and OH^- is added via Markovnikov's rule. Hydration can cause hydrolysis. An example of hydrate synthesis is hydration of a carbonyl group. Hydration also is used to mean getting water into an organism, usually human. This is important when large amounts of body fluid are lost, such as by sweating. In this context, it is also called rehydration. Category:Nutrition Category:Organic chemistry

Babylonian

Babylonia, named for the city of Babylon, was an ancient state in Mesopotamia (in modern Iraq), combining the territories of Sumer and Akkad. Its capital was Babylon. The earliest mention of Babylon can be found in a tablet of the reign of Sargon of Akkad, dating back to the 23rd century BC.

History

During the first centuries of the "Old Babylonian" period (that followed the Sumerian revival under Ur-III), kings and people in high position often had Amorite names, and supreme power rested at Isin. A constant intercourse was maintained between Babylonia and the West — with Babylonian officials and troops passing to Syria and Canaan, while "Amorite" colonists were established in Babylonia for the purposes of trade. One of these Amorites, Abi-ramu or Abram by name, is the father of a witness to a deed dated in the reign of Hammurabi's grandfather. The city of Babylon was given hegemony over Mesopotamia by their sixth ruler, Hammurabi (1780–1750 BC; dates highly uncertain). He was a very efficient ruler, giving the region stability after turbulent times, and transforming it into the central power of Mesopotamia. A great literary revival followed the recovery of Babylonian independence. One of the most important works of this "First Dynasty of Babylon", as it was called by the native historians, was the compilation of a code of laws. This was made by order of Hammurabi after the expulsion of the Elamites and the settlement of his kingdom. A copy of the Code of Hammurabi was found by J. de Morgan at Susa, where it had been taken as plunder, and is now in the Louvre. Ammiditana, the great-grandson of Hammurabi, still titled himself "king of the land of the Amorites", and his father and son bore the Canaanite names of Abieshuh and Ammisaduqa. The armies of Babylonia were well-disciplined, and they conquered the city-states of Isin, Elam, and Uruk, and the strong Kingdom of Mari. The rule of Babylon was even obeyed as far as the shores of the Mediterranean. But Mesopotamia had no clear boundaries, making it vulnerable to attack. Trade and culture thrived for 150 years, until the fall of Babylon in 1595 BC. The last king of the dynasty was Samsu-Ditana, son of Ammisaduqa. He was overthrown following the sack of Babylon in 1595 BC by the Hittite king Mursili I, and Babylonia was turned over to the Kassites (Kossaeans) from the mountains of Iran, with whom Samsu-Iluna had already come into conflict in his 6th year. The Kassite dynasty was founded by Kandis or Gandash of Mari. The Kassites renamed Babylon "Kar-Duniash", and their rule lasted for 576 years. With this foreign dominion — that offers a striking analogy to the contemporary rule of the Hyksos in Egypt — Babylonia lost its empire over western Asia. Syria and Canaan became independent, and the high-priests of Asshur made themselves kings of Assyria. Most divine attributes ascribed to the Semitic kings of Babylonia disappeared at this time; the title of "god" was never given to a Kassite sovereign. However, Babylon continued to be the capital of the kingdom and the 'holy' city of western Asia, where the priests were all-powerful, and the only place where the right to inheritance of the old Babylonian empire could be conferred.

Neo-Babylonian Empire

Through the centuries of Assyrian domination, Babylonia enjoyed a prominent status, or revolting at the slightest indication that it did not. However, the Assyrians always managed to restore Babylonian loyalty, whether through granting of increased privileges, or militarily. That finally changed in 627 BC with the death of the last strong Assyrian ruler, Ashurbanipal, and Babylonia rebelled under Nabopolassar the Chaldean the following year. With help from the Medes, Niniveh was sacked in 612, and the seat of empire was again transferred to Babylonia. Nabopolassar was followed by his son Nebuchadnezzar II, whose reign of 43 years made Babylon once more the mistress of the civilized world. Only a small fragment of his annals has been discovered, relating to his invasion of Egypt in 567 BC, and referring to "Phut of the Ionians". Of the reign of the last Babylonian king, Nabonidus (Nabu-na'id), and the conquest of Babylonia by Cyrus, there is a fair amount of information available. This is chiefly derived from a chronological tablet containing the annals of Nabonidus, supplemented by another inscription of Nabonidus where he recounts his restoration of the temple of the Moon-god at Harran; as well as by a proclamation of Cyrus issued shortly after his formal recognition as king of Babylonia. It was in the sixth year of Nabonidus (549 BC) that Cyrus, the Achaemenid Persian "king of Anshan" in Elam, revolted against his suzerain Astyages, "king of the Manda" or Medes, at Ecbatana. Astyages' army betrayed him to his enemy, and Cyrus established himself at Ecbatana, thus putting an end to the empire of the Medes. Three years later Cyrus had become king of all Persia, and was engaged in a campaign in the north of Mesopotamia. Meanwhile, Nabonidus had established a camp in the desert, near the southern frontier of his kingdom, leaving his son Belshazzar (Belsharutsur) in command of the army. In 538 BC Cyrus invaded Babylonia. A battle was fought at Opis in the month of June, where the Babylonians were defeated; and immediately afterwards Sippara surrendered to the invader. Nabonidus fled to Babylon, where he was pursued by Gobryas, the governor of Kurdistan, and on the 16th of Tammuz, two days after the capture of Sippara, "the soldiers of Cyrus entered Babylon without fighting." Nabonidus was dragged from his hiding-place, and Kurdish guards were placed at the gates of the great temple of Bel, where the services continued without interruption. Cyrus did not arrive until the 3rd of Marchesvan (October), Gobryas having acted for him in his absence. Gobryas was now made governor of the province of Babylon, and a few days afterwards the son of Nabonidus died. A public mourning followed, lasting six days, and Cambyses accompanied the corpse to the tomb. Cyrus now claimed to be the legitimate successor of the ancient Babylonian kings and the avenger of Bel-Marduk, who was assumed to be wrathful at the impiety of Nabonidus in removing the images of the local gods from their ancestral shrines, to his capital Babylon. Nabonidus, in fact, had excited a strong feeling against himself by attempting to centralize the religion of Babylonia in the temple of Merodach (Marduk) at Babylon, and while he had thus alienated the local priesthoods, the military party despised him on account of his antiquarian tastes. He seems to have left the defence of his kingdom to others, occupying himself with the more congenial work of excavating the foundation records of the temples and determining the dates of their builders. The invasion of Babylonia by Cyrus was doubtless facilitated by the existence of a disaffected party in the state, as well as by the presence of foreign exiles like the Jews, who had been planted in the midst of the country. One of the first acts of Cyrus accordingly was to allow these exiles to return to their own homes, carrying with them the images of their gods and their sacred vessels. The permission to do so was embodied in a proclamation, whereby the conqueror endeavoured to justify his claim to the Babylonian throne. The feeling was still strong that none had a right to rule over western Asia until he had been consecrated to the office by Bel and his priests; and accordingly, Cyrus henceforth assumed the imperial title of "king of Babylon." A year before Cyrus' death, in 529 BC, he elevated his son Cambyses II in the government, making him king of Babylon, while he reserved for himself the fuller title of "king of the (other) provinces" of the empire. It was only when Darius Hystaspis ("the Magian") acquired the Persian throne and ruled it as a representative of the Zoroastrian religion, that the old tradition was broken and the claim of Babylon to confer legitimacy on the rulers of western Asia ceased to be acknowledged. Darius, in fact, entered Babylon as a conqueror. After the murder of Darius, it briefly recovered its independence under Nidinta-Bel, who took the name of Nebuchadnezzar III, and reigned from October 521 BC to August 520 BC, when the Persians took it by storm. A few years later, probably 514 BC, Babylon again revolted under Arakha; on this occasion, after its capture by the Persians, the walls were partly destroyed. E-Saggila, the great temple of Bel, however, still continued to be kept in repair and to be a center of Babylonian patriotism, until at last the foundation of Seleucia diverted the population to the new capital of Babylonia and the ruins of the old city became a quarry for the builders of the new seat of government.

Science and mathematics

Among the sciences, astronomy and astrology occupied a conspicuous place in Babylonian society. Astronomy was of old standing in Babylonia, and the standard work on the subject, written from an astrological point of view, later translated into Greek by Berossus, was believed to date from the age of Sargon of Akkad. The zodiac was a Babylonian invention of great antiquity; and eclipses of the sun and moon could be foretold. Observatories were attached to the temples, and reports were regularly sent by astronomers to the king. The stars had been numbered and named at an early date, and we possess tables of lunar longitudes and observations of the phases of Venus. Great attention was naturally paid to the calendar, and we find a week of seven days and another of five days in use. In Seleucid and Parthian times, the astronomical reports were of a thoroughly scientific character; how much earlier their advanced knowledge and methods were developed is uncertain. The development of astronomy implies considerable progress in mathematics; it is not surprising that the Babylonians should have invented an extremely simple method of ciphering, or have discovered the convenience of the duodecimal system. The ner of 600 and the sar of 3600 were formed from the unit of 60, corresponding with a degree of the equator. Tablets of squares and cubes, calculated from 1 to 60, have been found at Senkera, and a people acquainted with the sun-dial, the clepsydra, the lever and the pulley, must have had no mean knowledge of mechanics. A crystal lens, turned on the lathe, was discovered by Austen Henry Layard at Nimrud along with glass vases bearing the name of Sargon; this could explain the excessive minuteness of some of the writing on the Assyrian tablets, and a lens may also have been used in the observation of the heavens. The Babylonian system of mathematics was sexagesimal, or a base 60 numeral system (see: Babylonian numerals). From this we derive the modern day usage of 60 seconds in a minute, 60 minutes in an hour, and 360 (60 x 6) degrees in a circle. The Babylonians were able to make great advances in mathematics for two reasons. First, the number 60 has many divisors (2, 3, 4, 5, 6, 10, 12, 15, 20, and 30), making calculations easier. Additionally, unlike the Egyptians and Romans, the Babylonians had a true place-value system, where digits written in the left column represented larger values (much as in our base ten system: 734 = 7×100 + 3×10 + 4×1). Among the Babylonians mathematical accomplishments were the determination of the square root of two correctly to seven places ([http://it.stlawu.edu/%7Edmelvill/mesomath/tablets/YBC7289.html YBC 7289 clay tablet]). They also demonstrated knowledge of the Pythagorean theorem well before Pythagoras, as evidenced by [http://www.tmeg.com/bab_mat/bab_mat.htm this tablet] translated by Dennis Ramsey and dating to c. 1900 BC: 4 is the length and 5 is the diagonal. What is the breadth? Its size is not known. 4 times 4 is 16. 5 times 5 is 25. You take 16 from 25 and there remains 9. What times what shall I take in order to get 9? 3 times 3 is 9. 3 is the breadth.

Literature

:Main article: Babylonian literature

Location

The city of Babylon, the main city of Babylonia, was found on the Euphrates River, about 110 kilometres south of modern Baghdad, just north of what is now the Iraqi town of al-Hillah.

External links

- [http://ancientneareast.tripod.com/Old_Kingdom_of_Babylonia.html The History of the Ancient Near East]
- [http://www.math.tamu.edu/~don.allen/history/babylon/babylon.html Babylonian Mathematics]
- [http://www-groups.dcs.st-andrews.ac.uk/~history/HistTopics/Babylonian_numerals.html Babylonian Numerals]
- [http://www.halloran.com/babylon1.htm Babylonian Astronomy/Astrology]
- [http://www.phys.uu.nl/~vgent/babylon/babybibl.htm Bibliography of Babylonian Astronomy/Astrology]
- [http://www.sacred-texts.com/ane/rbaa.htm The Religion of Babylonia and Assyria by Theophilus G. Pinches (Many deities' names are now read differently, but this detailed 1906 Work is a classic)]
- [http://fax.libs.uga.edu/BM530xK531l/ Legends of Babylon and Egypt in Relation to Hebrew Tradition], by Leonard W. King, 1918 (a searchable facsimile at the University of Georgia Libraries; DjVu & [http://fax.libs.uga.edu/BM530xK531l/1f/legends_of_babylon_and_egypt.pdf layered PDF] format)
- [http://fax.libs.uga.edu/BL1620xB7/ The Babylonian Legends of the Creation] and the Fight between Bel and the Dragon, as told by Assyrian Tablets from Nineveh, 1921 (a searchable facsimile at the University of Georgia Libraries; DjVu & [http://fax.libs.uga.edu/BL1620xB7/1f/babylonian_legends_of_creation.pdf layered PDF] format) Category:Former monarchies Category:Civilizations Category:Ancient Iranian provinces ja:バビロニア

Clay

:For the town in the United States, see Clay, New York. Clay, New York.]] Clay is a generic term for an aggregate of hydrous silicate particles less than 4 μm (micrometres) in diameter. Clay consists of a variety of phyllosilicate minerals rich in silicon and aluminium oxides and hydroxides which include variable amounts of structural water. Clays are generally formed by the chemical weathering of silicate-bearing rocks by carbonic acid, but some are formed by hydrothermal activity. Clays are distinguished from other small particles present in soils such as silt by their small size, flake or layered shape, affinity for water and high plasticity index. There are three main groups of clays: kaolinite-serpentine, illite, and smectite. Altogether, there are about thirty different types of "pure" clays in these categories, but most "natural" clays are mixtures of these different types, as well as other weathered minerals. Montmorillonite, with a chemical formula of (Na,Ca)_0.33(Al,Mg)₂Si₄O₁₀(OH)₂·nH₂O, is typically formed as a weathering product of low silica rocks. Montmorillonite is a member of the smectite group and a major component of bentonite. Varve (or varved clay) is clay with visible annual layers, formed by seasonal differences in erosion and organic content. This type of deposit is common in former glacial lakes from the ice age. Quick clay is a unique type of marine clay, indigenous to the glaciated terrains of Norway, Canada, and Sweden. It is a highly sensitive clay, prone to liquefaction which has been involved in several deadly landslides.

Historical and modern uses of clay

Clays are heavy in texture yet soft to the touch. Clay is a malleable substance when wet, which means it can be shaped easily with the hands. When dry, it becomes firm and when "fired," or hardened by intense heat, clay becomes permanently solid. A fireplace specifically designed for hardening clay is called a kiln. These properties make clay an ideal subtance for making pottery, stoneware and various other practical items. Early humans discovered the useful properties of clay in prehistoric times, and one of the earliest artifacts ever uncovered is a drinking vessel made of sun-dried clay. Depending on the content of the soil, clay can appear in various colors, from a dull gray to a deep orange-red. Clays sintered in fire were the first ceramic, and remain one of the cheapest to produce and most widely used materials even in the present day. Bricks, cooking pots, art objects, dishware, spark plug bodies, and even musical instruments such as the ocarina are all made with clay. Clay is also used in many industrial processes, such as paper making, concrete production, and chemical filtering.

Reference

- [http://www.minsocam.org/msa/collectors_corner/arc/nomenclaturecl1.htm Clay mineral nomenclature American Mineralogist] Category:Sedimentology Category:Silicate minerals Category:Natural materials Category:Art materials Category:Sediments ms:Tanah liat ja:粘土

Ancient Egyptian

Ancient Egypt was a civilization along the Lower Nile extending from as far south as Jebel Barkal, Napata [http://www.newadvent.org/cathen/05329b.htm], and then northward to the Mediterranean Sea, though varying in size throughout its history between circa 3200 BC and 343 BC, ending with the conquest of Alexander the Great. As a civilization based on irrigation it is the quintessential example of a hydraulic empire.

Geography

Most of Egypt is in North Africa; though the Sinai Peninsula is in Southwest Asia. The country has shorelines on the Mediterranean Sea and the Red Sea; it borders Libya to the west, Sudan to the south, and the Gaza Strip, Palestine and Israel to the east. Ancient Egypt was divided into two kingdoms, known as Upper and Lower Egypt. Somewhat counter-intuitively, Upper Egypt was in the south and Lower Egypt in the north, named according to the flow of the Nile. The Nile river flows northward from a southerly point to the Mediterranean rather than southward from a northerly point. The Nile river, around which much of the population of the country clusters, has been the lifeline for Egyptian culture since the Stone Age and Naqada cultures. Two kingdoms formed Kemet ("the black land", in Ancient Egyptian Kmt), the name for the dark soil deposited by the Nile floodwaters. The desert was called Deshret ("the red land"), c.f. Herodotus: "Egypt is a land of black soil.... We know that Libya is a redder earth" (Histories, 2:12).

People

Libya]] A recent genetic study links the maternal lineage of a traditional population from Upper Egypt to Eastern Africa . A separate study further narrows the genetic lineage to Northeast Africa () and reveals also that modern day Egyptians "reflect a mixture of European, Middle Eastern, and African." Champollion the Younger, who deciphered the Rosetta Stone, claimed in Expressions et Termes Particuliers ("Expression of Particular Terms") that Kmt did not actually refer to the soil but to a negroid population in the sense of "Black Nation." Modern day professional Egyptologists, linguists and historians, however, overwhelmingly agree that the term referred to the soil rather than the people. Herodotus wrote, "the Colchians are Egyptians... on the fact that they are black-skinned (melanchrôs) and wooly-haired (oulothrix)" (Histories Book 2:104). Later authors, including Aristotle and Diodorus Siculus, repeated Herodotus' description of "black-skinned". Melanchros is also used of the sunburnt complexion of Odysseus (Od. 16.176). Although analyzing the hair of ancient Egyptian mummies from the Late Middle Kingdom has revealed evidence of a stable diet , mummies from circa 3200 BC show signs of severe anemia and hemolitic disorders . A few teams of European scientists reported that cocaine, hashish and nicotine have been found in the skin and hair of Egyptian mummies . The results of these studies have been harshly criticized (e.g., ref. ) by mainstream scientists and Egyptologists as flawed and inaccurate.

History

:Main article: History of ancient Egypt The ancient Egyptians themselves traced their origin to a land they called Punt, or "Ta Nteru" ("Land of the Gods"). Once commonly thought to be located on what is today the Somali coast, Punt now is thought to have been in either southern Sudan or Eritrea. The history of ancient Egypt proper starts with Egypt as a unified state, which occurred sometime around 3000 BC. Though archaeological evidence indicates a developed Egyptian society may have existed for a much longer period (see Predynastic Egypt). Along the Nile, in 10th millennium BC, a grain-grinding culture using the earliest type of sickle blades had been replaced by another culture of hunters, fishers, and gathering peoples using stone tools. Evidence also indicates human habitation in the southwestern corner of Egypt, near the Sudan border, before 8000 BC. Climate changes and/or overgrazing around 8000 BC began to desiccate the pastoral lands of Egypt, eventually forming the Sahara (c.2500 BC), and early tribes naturally migrated to the Nile river where they developed a settled agricultural economy and more centralized society (see Nile: History). There is evidence of pastoralism and cultivation of cereals in the East Sahara in the 7th millennium BC. By 6000 BC ancient Egyptians in the southwestern corner of Egypt were herding cattle and constructing large buildings. Mortar (masonry) was in use by 4000 BC. The Predynastic Period continues through this time, variously held to begin with the Naqada culture. Some authorities however begin the Predynastic Period earlier, in the Lower Paleolithic (see Predynastic Egypt). Egypt unified as a single state circa 3000 BC. Egyptian chronology involves assigning beginnings and endings to various dynasties beginning around this time. The conventional Egyptian chronology is the accepted developments during the 20th century, but do not include any of the major revision proposals that have also been made in that time. Even within a single work, often archeologists will offer several possible dates or even several whole chronologies as possibilities. Consequently, there may be discrepancies between dates shown here and in articles on particular rulers. Often there are also several possible spellings of the names. Typically, Egyptologists divide the history of pharaonic civilization using a schedule laid out first by Manetho's Aegyptaica.
- List of pharaohs: The pharaohs stretch from before 3000 BC to around 30 BC.
- Dynasties (see also: List of Egyptian dynasties):
- Early Dynastic Period of Egypt (1st to 2nd Dynasties; until ca. 27th century BC)
- Old Kingdom (3rd to 6th Dynasties; 27th to 22nd centuries BC)
- First Intermediate Period (7th to 11th Dynasties)
- Middle Kingdom of Egypt (11th to 14th Dynasties; 20th to 17th centuries BC)
- Second Intermediate Period (14th to 17th Dynasties)
- Hyksos (15th to 16th Dynasties)
- New Kingdom of Egypt (18th to 20th Dynasties; 16th to 11th centuries BC)
- Third Intermediate Period (21st to 25th Dynasties; 11th to 7th centuries BC)
- Late Period of Ancient Egypt (26th to 31st Dynasties; 7th century BC to 332 BC)
- Achaemenid Dynasty
- Graeco-Roman Egypt (332 BC to AD 639)
- Ptolemaic Dynasty
- Roman Empire

Government

Nomes were the subnational administrative divisions of Upper and Lower Egypt. The pharaoh was the ruler of these two kingdoms and headed the ancient Egyptian state structure. The pharaoh served as monarch, spiritual leader and commander-in-chief of both the army and navy. The pharaoh was supposed to be divine, a connection between men and gods. Below him in the government, were the viziers (one for Upper Egypt and one for Lower Egypt) and various officials. Under him on the religious side were the high priest and various other priests. Generally, the position was handed down from father to eldest son. Sometimes this rule was broken, and occasionally a woman assumed power.

Language

The ancient Egyptians spoke an Afro-Asiatic language related to Chadic, Berber and Semitic languages. Records of the ancient Egyptian language have been dated to about 3200 BC. Scholars group the Egyptian language into six major chronological divisions:
- Archaic Egyptian (before 2600 BC)
- Old Egyptian (2600–2000 BC)
- Middle Egyptian (2000–1300 BC)
- Late Egyptian (1300–700 BC)
- Demotic Egyptian (7th century BC–4th century AD)
- Coptic (3rd–12th century AD)

Writing

For many years, the earliest known hieroglyphic inscription was the Narmer Palette, found during excavations at Hierakonpolis (modern Kawm al-Ahmar) in the 1890s, which has been dated to c.3200 BC. However recent archaeological findings reveal that symbols on Gerzean pottery, c.4000 BC, resemble the traditional hieroglyph forms . Also in 1998 a German archeological team under Gunter Dreyer excavating at Abydos (modern Umm el-Qa'ab) uncovered tomb U-j, which belonged to a Predynastic ruler, and they recovered three hundred clay labels inscribed with proto-hieroglyphics dating to the Naqada IIIA period, circa 33rd century BC , . Egyptologists refer to Egyptian writing as hieroglyphs, today standing as the world's earliest known writing system. The hieroglyphic script was partly syllabic, partly ideographic. Hieratic is a cursive form of Egyptian hieroglyphs and was first used during the First Dynasty (c. 2925 BC – c. 2775 BC). The term Demotic, in the context of Egypt, came to refer to both the script and the language that followed the Late Ancient Egyptian stage, i.e. from the Nubian 25th dynasty until its marginalization by the Greek Koine in the early centuries AD. After the conquest of Umar ibn al-Khattab, the Coptic language survived into the Middle Ages as the liturgical language of the Christian minority. Beginning from around 2700 BC, Egyptians used pictograms to represent vocal sounds -- both vowel and consonant vocalizations (see Hieroglyph: Script). By 2000 BC, 26 pictograms were being used to represent 24 (known) main vocal sounds. The world's oldest known alphabet (c. 1800 BC) is only an abjad system and was derived from these uniliteral signs as well as other Egyptian hieroglyphs. The hieroplyphic script finally fell out of use around the 4th century and began to be rediscovered after the 15th century (see Hieroglyphica).

Literature

- c. 2500 BC: Westcar Papyrus
- c. 1800 BC: Story of Sinuhe
- c. 1800 BC: Ipuwer papyrus
- c. 1800 BC: Papyrus Harris I
- c. 1000 BC: Story of Wenamun

Culture

The Egyptian religions, embodied in Egyptian mythology, were the succession of beliefs held by the people of Egypt, until the coming of Christianity and Islam. These were conducted by Egyptian priests or magicians, but the use of magic and spells is questioned. The religious nature of ancient Egyptian civilization influenced its contribution to the arts of the ancient world. Many of the great works of ancient Egypt depict gods, goddesses, and pharaohs, who were also considered divine. Ancient Egyptian art in general is characterized by the idea of order. Evidence of mummies and pyramids outside ancient Egypt indicate reflections of ancient Egyptian belief values on other prehistoric cultures, transmitted in one way over the Silk Road. Some scholars have speculated that Egypt's art pieces are sexually symbolic.

Ancient achievements

symbolic See Predynastic Egypt for inventions and other significant achievements in the Sahara region before the Protodynastic Period. The art and science of engineering was present in Egypt, such as accurately determining the position of points and the distances between them (known as surveying). These skills were used to outline pyramid bases. The Egyptian pyramids took the geometric shape formed from a polygonal base and a point, called the apex, by triangular faces. Hydraulic Cement was first invented by the Egyptians. The Al Fayyum Irrigation (water works) was one of the main agricultural breadbaskets of the ancient world. There is evidence of ancient Egyptian pharaohs of the twelfth dynasty using the natural lake of the Fayyum as a reservoir to store surpluses of water for use during the dry seasons. From the time of the First dynasty or before, the Egyptians mined turquoise in Sinai Peninsula. The earliest evidence (circa 1600 BC) of traditional empiricism is credited to Egypt, as evidenced by the Edwin Smith and Ebers papyri. The roots of the Scientific method may be traced back to the ancient Egyptians. The ancient Egyptians are also credited with devising the world's earliest known alphabet, decimal system and complex mathematical formularizations, in the form of the Moscow and Rhind Mathematical Papyri. An awareness of

Concrete

History

Characteristics

Additives

Workability

Self compacting concretes

Shotcrete / sprayed concrete

See also

External link

Composite material

Examples of composite materials:

Cement

History

Geology

Another meaning

Gravel

Types of gravel

See also

Sand

Uses of sand

Hazards of sand

See also

Water (molecule)

Forms of water

A common substance

Water in the Universe

Water on Earth

Water in industry

Physics and chemistry of water

Density of water and ice

Density of saltwater and ice

Triple point

Mpemba effect

Surface tension

Electrical properties

Dipolar nature of water

Water as a solvent

Amphoteric nature of water

Acidity in nature

Hydrogen bonding in water

Quantum properties of Molecular Water

History

Systematic nomenclature and humor

See also

External links

Hydration

Babylonian

History

Neo-Babylonian Empire

Science and mathematics

Literature

Location

See also

Further reading

External links

Clay

Historical and modern uses of clay

See also

Reference

Ancient Egyptian

Geography

People

History

Government

Language

Writing

Literature

Culture

Ancient achievements