basic knowledge

brief introduction

Clay clay is an important mineral raw material. It consists of various hydrated silicates and a certain amount of alumina, alkali metal oxides and alkaline earth metal oxides, and contains impurities such as feldspar, mica, sulfate, sulfide and carbonate. The particles of clay minerals are fine, often in the range of colloid size, crystalline or amorphous, most of them are flaky, and a few are tubular and rod-shaped. Clay minerals are plastic when wetted by water, can be deformed under small pressure and can remain unchanged for a long time, and have large specific surface area and negatively charged particles, so they have good physical adsorption and surface chemical activity, and have the ability to exchange with other cations.

characteristic

Soil containing clay is very easy to combine water, minerals and organic nutrients, because clay with very small particles has a large relative surface area and its surface is conductive. In production, clay has the characteristics of retaining fertilizer and water, and is known as "wet in a big mess, dry in a knife", so its arable property is poor.

clay

form

Clay is generally formed by weathering silicate minerals on the earth's surface. Generally, it is called primary clay or primary clay, which is weathered in situ, with large particles and composition close to the original stone. This kind of clay is mainly composed of tin oxide and aluminum oxide, which is white and fire-resistant, and is the main raw material for preparing porcelain clay.

Clay continues to weather and become young, and then it is transported by running water and wind, and a thick layer of clay is formed downstream, which is called secondary clay or secondary clay. Because of pollution, this kind of clay contains many metal oxides, dark color and low fire resistance. Because of its good viscosity and plasticity, it is the main raw material for preparing clay.

Kaolin is a kind of soft clay with kaolinite subfamily minerals as the main component. Mainly composed of kaolinite minerals. In nature, the minerals that make up kaolin are clay minerals and non-clay minerals. The color is white, the highest whiteness is more than 95%, and the hardness is 1~4.

Containing minerals

Some clay minerals are:

Kaolinite: alumina, silica, ·2h2o

Gasoline: Al2 (OH) 4 | Si2O3 * NH2O

Montmorillonite: (al, mg) 2 (oh) 2 | si4o 10 (na, ca) x * nh2o.

Vermiculite: (magnesium, calcium) 0.3 1(H2O)n {titanium 0. 1.08 aluminum 0.03 iron (III) 1.09 magnesium 1.25 silicon 2.80 aluminum 1.20.

Illite: K0, 65al2, 0Al0, 65Si3, 35O 10 (OH) 2.

Diaspore: Al2O3. Silicon dioxide ·5h2o

Edit this paragraph

High liquid limit clay

abstract

The three indexes to distinguish high liquid limit soil in engineering are: the soil with particle content less than 0.074mm is more than 50%, the liquid limit is more than 50%, and the plasticity index is more than 26. At present, the design idea of expansive high liquid limit soil in slope engineering is basically based on expansive soil. The high liquid limit soil not only has the characteristics of swelling and shrinking when it meets water, but also has poor compactness, and the compacted soil still has great compressibility and obvious strain softening. The failure of many slope projects is due to the recognition of the essential characteristics of high liquid limit soil.

Mineral composition and engineering properties of high liquid limit clay

High liquid limit soil usually contains a large number of clay components, such as montmorillonite, illite and kaolinite. Among them, montmorillonite is a mineral composed of water-containing aluminosilicate with extremely fine particles, and its lattice unit is composed of two silicon-oxygen tetrahedral layers sandwiched by an alumina octahedral layer. Van der Waals force makes the interlayer connection weak, makes water molecules easily enter between cells, and increases the distance between cells. It will shrink after dehydration, and its liquid limit can reach 140 ~ 7 10%, and its plastic limit range is 50 ~. Between crystal lattices, due to isomorphic substitution, montmorillonite has strong adsorption capacity, and a large number of Na+ and Ca2+ are filled in, resulting in electric double layer effect, which leads to the expansion between grains. Similarly, illite also has a three-layer crystal structure of 2: 1, but the cations it absorbs are mainly Na+ and K+, and the bonding force between crystal lattices is strong, so water molecules are not easy to enter, so illite is not hydrophilic and expansive like montmorillonite, with liquid limit ranging from 80 ~ 120% and plastic limit ranging from 45 ~ 60%. The structural unit of kaolinite is a unit cell composed of aluminum hydroxide flakes and oxidized silicon wafers. The connection between crystal cells is a hydrogen bond between oxygen atoms and hydroxyl groups, which has strong binding force, the distance between crystal cells is not easy to change, water molecules can not enter, and the hydrophilicity and expansibility are better than those of the first two mineral components. The engineering properties of high liquid limit soil are related to its parent rock composition, water content, compactness, external load and its action mode. According to a large number of engineering practices, the permeability of high liquid limit soil is poor; High strength when dry and hard, hard and not easy to dig and compact; Capillary phenomenon is obvious, which can retain water for a long time after water absorption, so the bearing capacity is small and the stability after water absorption is poor; High plasticity, weak expansibility and high viscosity.

Edit this paragraph

App application

Clay ceramics

Industrial clay minerals include kaolin, bentonite (mainly composed of montmorillonite) and activated clay (with uncertain composition). China first mined kaolin in Gaoling Village, Jiangxi Province to make ceramics. 1888 bentonite was mined in Wyoming, USA, and 1906 activated clay was first mined in Texas, USA.

Cement manufacturing

Mix with limestone to make cement.

Various applications

Modeling in industry, model making and art, artists use clay as a model, but it is also suitable for directly molding works of art with clay.

Clay acts as an ion exchanger in drinking water treatment and other chemical processes.

Kaolinite is the raw material of porcelain.

Kaolinite can also make the paper surface particularly smooth and absorb ink.

Ceramsite is used as isolation layer in construction industry and soilless culture.

Sealed landfill

Used as filler in pigment industry and pharmaceutical industry.

Used for catalytic converter

Edit this paragraph

Types of clay used in manual creation

List of clay types

Clay-type kaolin ball clay refractory clay

The generation time is mostly Cenozoic, and the Cenozoic is mostly Paleozoic.

Order degree of kaolinite

(Cover thickness) is mostly disordered.

(thin or none) is mostly disordered.

(very thin) basically orderly

(Very thick)

Kaolinite crystal form

(current treatment) often self-forming, semi-self-forming.

(not carrying) often irregular.

(Long-term handling) is often irregular

(Long-term handling)

Crystalline particle size/micron is greater than 5+/-less than 2 and greater than 2-5.

Poor plasticity, good and good (soft)

Poor adhesion, good, good (soft)

Illite content/%is usually 5 ~ 45, and 5 ~ 45 is usually less than 5%.

Fire resistance/℃ can be greater than or less than 1580, greater than or less than 1580 and greater than 1580.

Sintering temperature range

(Example/℃) Narrow

(1500 ~ 1570) width

(1320 ~ 1550) is slightly wider.

( 1300~ 1390)

Iron and titanium content

Usually less (whiteness)

(greater than 70 ~ 80) is often more.

(less than 50 ~ 80) is often more.

(less than 50 ~ 70)

organic matter

(plasticity) not often containing a small amount.

(can be improved) often contains a small amount.

(unable to improve)

Main genetic residual deposits

Paper clay

Also known as "pulp clay" in China. The ingredients include pulp, gum, feldspar and fiber. There is no need to barbecue, and the texture after drying is between clay and gypsum, which will not be broken and can be preserved permanently without deformation. It can not only be carved, but also attached to various objects for pasting and shaping, and can be well matched with stone, wood, glass and so on, so it is widely used. Ordinary paper clay is white and can be colored after drying. Waterborne and oily pigments can be used, and watercolor, acrylic and oil painting pigments can be used, which is non-toxic and tasteless.

In recent years, with the development of technology, paper clay is more delicate, lighter and more viscous, which can be used to make more delicate handicrafts, and colored paper clay appears. This kind of clay has been popularized in some foreign countries since 1970s, and is usually used in children's sculpture classes. In recent years, it has become a popular hand-molded material, and many works have become fashionable decorations and have been integrated into daily life.

wheat clay

There are two kinds of resin paste, one is bread flower (flour paste). A saying that bread flowers originated in Latin America, local people collect leftover bread crumbs, dry them and grind them into powder, and add white mucus to make "flour clay". But this kind of flour clay is not malleable enough and strong enough. Air-dried works are easily broken and cannot be placed for a long time. Later, this simple process spread to Japan, and the Japanese improved it by adding preservatives and other chemicals to make the present flour clay. This kind of flour clay itself is translucent and soft, and can be stretched to be very thin without cracking. Even after drying, it can maintain elasticity and make fine products freely. Strong plasticity, strong texture and simple use. You can use oil painting pigments and acrylic pigments to color, then shape the image in your mind and dry it naturally. The finished works can keep the same shape and can be used to make flowers, small animals, dolls, ornaments and other works. Clay is most suitable for flowers, which can be stretched to a very thin thickness to make a light and natural feeling. However, the produced works are relatively dull, and after drying, oil painting pigments must be coated on the surface of the works to increase their aesthetic feeling and three-dimensional sense.

There is also a kind of resin clay, which is very dry and hard to take out, but it feels broken. But after adding color, it becomes softer and softer, and the works made are very hard, suitable for making some mini-utensils, such as bowls, plates and flowerpots.

grease

Sludge is generally used as an auxiliary after the work is completed. For example, to make a clay flower bonsai, just take out a proper amount of soil and put it in the basin, so as to make the work stable. The characteristic of oil sludge is that soft/hard sludge will not harden even if exposed to air. Generally, you only need to choose soft sludge or hard sludge according to your own preferences.

Stone powder clay

Fine texture, good ductility, high strength after drying and stone texture. Easy to mold and carve. It is most suitable for human form and wall decoration.

Woody clay

Made of natural wood, it becomes hard after drying and can be carved into a sharp shape, which is suitable for products with wooden style.

Cloth clay

Liquid clay, delicate and soft. Very suitable for all kinds of fabrics. The surface of the finished product is treated with cloth mud, and the effect is completely different.

Silver clay

Also known as sterling silver clay, it can be widely used in DIY manual combination of jewelry, clay and metal, and can be easily burned into fashionable and beautiful sterling silver jewelry and gifts of various shapes.