Clay

See also: Clay (homonymy)

The clay (female name) is a Sedimentary rock, made up to a large extent of specific minerals, Silicate S in general of Aluminum more or less hydrated, which have a laminated structure (Phyllosilicate S) which explains to them Plasticité, or a fibrous structure (Sépiolite and Palygorskite) which explains their qualities of absorption.

One classifies them in three big families according to the thickness of the layers (0,7 or 1 or 1,4 Nm), which correspond to a number of oxide coatings tetrahedral (If) and octahedral (Al, Ni, Mg, Fe2+, Fe3+, mn, Na, K,…).

The interstice between layers can contain Eau as well as Ion S. It results from it from the variations of the distance between layers, and thus of the macroscopic dimensional variations of clay when it is hydrated (dilation) or is drained (contraction being able to cause cracks)

The most common minerals in clays are:

  • the Kaolinite (0,7 Nm) (in particular in the kaolin, in English, Clouded clay : “clay of China”), of formula Si2O5Al2 (OH) 4 is blanchâtre, pasty and fatty; one uses it out of ceramics and not only in the manufacture of the Porcelaine (historical layer, now exhausted, in the area of Limoges);
  • the minerals of the group of the Halloysite are composed by the same layer that kaolinite but their stacking is disordered, with random translations in the two directions has and B . There exist the two halloysite shapes:
    • dehydrated, with the same chemical formula as kaolinite and thickness close to that of kaolinite: 0,72 Nm;
    • hydrated, of which the thickness is approximately 0,1 Nm, which corresponds to that of kaolinite plus a layer of water (0,29 Nm);
  • the Montmorillonite, whose form, which has as a formula Si4O10Al5/3Mg1/3Na1/3 (OH) 2, is known under the name of ground of Sommière used like stain-remover or bentonite employed in civil engineering because of its colloidal properties (plasticizing in the mortar S). With the difference of halloysite, several layers of water can take seat between two layers of montmorillonite and consequently separation between two layers can go from 0,96 Nm to complete separation;
  • the Illite, (1 Nm) of formula KAl2 (AlSi3O10) (OH) 2 is spread, it is it which is used for manufacture of the objects out of terra cotta. The structure of the illites is close to that of the Mica S but remotely by the degree of Si/Al substitution (lower in the illite), the presence of potassium (lower in the illite) and for a certain degree of disorder in the stacking of the layers.
  • the Vermiculite S (approximately 1,4 Nm, like the Chlorite S, which drops to 1 Nm following warming). The layer has a composition close to the Talc; however, in talc it is neutral, while in vermiculites it has a negative charge, as in chlorites. This negative charge is compensated by hydrated ions magnesium placed between the layers. The water of hydration of the ions magnesium in the interfoliaceous area is eliminated by warming, which explains the reduction in the period.

To note that these minerals do not meet separately, but in rocks made up of a mixture of typical minerals of clays and other minerals or materials associated (sand, oxide iron, limestone, remains vegetable).

In Géotechnique, where one is interested above all in the soil mechanics behavior, one indicates by clay materials of Granulométrie lower than 2 Micromètre S (between 2 and 50 µm, one speaks about silt).

The argillaceous grounds are made up of very fine elements, coming from the mechanical and chemical degradation of preexistent rocks (in particular the Mica S and the Feldspath S). One finds the clay benches in the sediments deposited by the erosion of water since the era Tertiaire, with the foot of the mountains and in the river large valleys.

Characterization of clays

One in the manners of recognizing clays is the analysis by Diffraction of x-rays.

A simple analysis of diffraction does not give an interesting result: the crystalline phases in themselves are not different from one clay to another and because of structure in layers, clay is directed when one deposits it on a blade of glass; this preferential Orientation embarrassment analysis.

To differentiate clays, one carries out various treatments aiming at modifying space inter-layers: heating, acidification… By looking at the evolution of the peaks of diffraction to the weak angles according to the treatment, one can recognize clay. This analysis is done on a given particle shape, obtained by putting clay in suspension in water, while agitating and while taking with a depth given after a given rest period.

In addition to in Geochemistry, this technique is also used by the Scientific police to try to determine the origin of the ground traces which can constitute an index at the time of an investigation.

Colors

The clay particles are by no means responsible for the color of the ground. The color red, orange, yellow, green, blue of a ground (argillaceous or not) are due to the state of the Fer in the ground (oxidized in the first 3 cases and reduced in the two last). When the ground is of color tending towards the white, it is that this element was dissolved and evacuated out of the profile.

Formation

Clays indicate very fine matter particles torn off with the rocks by the erosion. Observed under the microscope, they have the shape of plates, which explains their plasticity. The majority of these particles come from the disintegration of silicated rocks: Granite (Mica and Feldspar), Gneiss or of the Schiste S. These particles are transported by the wind or the water in the form of Limon or of vase. The rivers convey clays which end up settling in Alluvion S, in the river itself, with its mouth, in a lake or the sea. The deposits can then form a deposit and form an argillaceous rock by Diagenèse: Dehydration and Compactation. As a sedimentary rocks, the argillaceous outcrops present a succession of layer S piled up the ones on the others, which resembles a layer.

Use

Clay is one of oldest materials used by the man. Kneaded with water, it gives a plastic paste which can be easily moulded or formatted. After cooking, it gives a resistant and impermeable object. These remarkable properties are at the origin of its very old use to carry out objects out of ceramics, out of porcelain… Brick and tiles are also manufactured starting from a mixture of clay and water moulded under pressure and cooked at sufficiently high temperature (1000 to 1200 °C).

Terra cotta

Hydrated clay is malleable, it can be formatted; put at the Four (“cooked”) it takes a solid consistency. These properties make of it a material of choice for the manufacture of objects.

An argillaceous ground intended for cooking is often called clay or loam .

One can call most of clays by the grounds terms with common Faïence or clays. These clays contain enough Fer and other mineral impurities to become hard, cooked from 950 to 1100 °C approximately. In a natural state, they are gray, greenish, red or brown because of other and iron oxide as the oxide of Titane which they contain.

Cooked, their color can go from the white, the pink to the black while passing by all the varieties of yellow, red, brown, following the particular quality of each clay and the conditions of cooking. The majority of the Poterie S in the world are made with this kind of clay, as well as the brick S, the Tuile S, the pipes and other productions similar.

Common red clay can be very plastic, and even too plastic and too sticking to be employed only; in addition, it happens that she is practically not it because of the presence of sand or other rock remains.

The potter and the sculptor seek a ground with soft and plastic earthenware, which they can possibly modify by adding a little nonplastic clay sand, of the Chamotte, or the Cellulose.

The brick-maker, him, research a less fine ground containing nonplastic sand and other remains, that it will be able to press, dry and cook, without fear of warping, slits or excessive withdrawal.

Finally one can practice a “Minéralurgie” to eliminate or add the elements undesirable or necessary on clays, in order to give them the characteristics necessary to their more or less industrial use.

Raw ground

See: Ground-clay in particular for the therapeutic uses of clay.

Other uses

Researchers in Science of the materials work on the clay integration in Polymère S. the clay plates can produce a reinforcement (deviation of the cracks in polymers “shock”, i.e. having to resist the shocks). In addition, they can obstruct the diffusion Gaz, and in particular of gases Combustible S resulting from the Pyrolyse at the time of a Feu, thus improving the fire resistance of polymer.

Certain very pure Kaolinites clays make it possible to make the paper pulp white, however this process is less and less used, it is replaced, by the Carbonate of precipitated calcium.

In the Painting S, the addition of mineral loads as the Bentonite makes it possible to obtain the Rhéologie wished and improves also the stability of the suspensions.

Certain clays are used in Fonderie, to build the moulds.

Clay was used by civilization summéro-akadienne (the Sumérien S of Mésopotamie). There small clay balls were flattened to form an approximate rectangle in order to be able to register wedge-shaped writing. Sumériens used kinds of cylinder seal. These cylinders were engraved in low-relief, and when one made them roll while pressing on clay, they left a print in high relief.

See too

External bonds

  • Preparation and collection of clay
  • Preparation of cellulose clay
  • " argilothérapie" , use of clay for health, it cosmetic or the house
  • chart of France of the clay soils

clay|Clay

Beats-smg: Muolis Simple: Clay

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