Clay is a fine-grained natural soil material made up of clay minerals. When wet, clays develop plasticity, or elasticity, due to the molecular film of water that surrounds each of the individual clay particles. When clays are dried, they lose this plasticity and become hard and brittle. Fired clays lose this plasticity and become non-plastic.
Table of Contents
Table of contents
Plasticity of clay
The plasticity of clay is a characteristic of some clay bodies. This property of clays relates to their electrolytic nature or the ability to hold opposite charges. The opposite charges of flat clay particles act as the glue that holds the particles together, and this property lends plasticity. However, the plasticity of clay is hard to measure with standard test equipment.
To make ceramic pieces, potters need to know the plasticity of clay. This property allows them to shape the clay into a variety of shapes and forms. Moreover, plastic clays tend not to revert to their original state of elasticity, even if they are subjected to moderate pressure. This property makes the clay useful for industrial and engineering applications.
The plasticity of clay is influenced by two processes: the clay’s composition and processing. The first step in the plasticity assessment process is the characterization of the sample using a compression test. The resulting test curve gives information on the modulus of elasticity, yield strength, maximum deformation, and rupture strength. The test curves show that the clay behaves elastically up to point A and plastically until point B.
Plasticity measurements can be performed using a variety of methods. The Atterberg limits are the most commonly used method to assess the plasticity of clay. However, these methods involve many variables, which makes them difficult to correlate with clay behavior. For example, the clay measurements using a falling cone do not clearly indicate the water content in the clay.
The size of the particles in clay has the most significant influence on the plasticity of clay bodies. Clay particles are approximately one micron in diameter and have a large surface area for their weight. One gram of kaolin, for example, has a surface area of twenty square meters. Similarly, clay particles that do not possess the ability to retain water have a surface area of approximately one square meter per gram.
Color
Clay is a warm color with a color code of #b66a50. It is made up of individual particles that are less than 0.002 millimeters in diameter. They are very small and can be sticky to the touch, not visible to the naked eye, and accumulate in lower layers of soil. They travel with the water and mechanical sorting down through the topsoil. Loam soil can vary in color from light yellow to dark brown.
Clay is used in numerous applications across the globe. The color of the clay is determined by where it’s mined, the amount of minerals in it, and its composition. Its properties include anti-aging and blemish-fighting properties. In addition, it can tighten and strengthen the skin. Some clays have been known to have a rusty hue.
Clay can be dyed using two main methods. The first one is by using a mason stain, and the other is by using a contrasting color called an oxide. Both types of stains have various ingredients to make the color more stable. Mason stains should be mixed into the clay evenly. Otherwise, chunks of stain will show up in the firing process, making it difficult to see the final product.
Another type of clay is called earthenware. Its color is brown-orange. It is a form of organic clay. Terra cotta is made by molding and firing clay. Terra cotta is made of organic clays, such as bentonite and caliche.
Porosity of clay
In soils, the amount of pore space is known as porosity. In general, the higher the porosity, the more water can flow through it. However, clays have low permeability and poor drainage properties. The degree of compaction in clay particles also affects their pore size.
Computer image processing technology has made it possible to analyze the microstructure of soils. In a study conducted by Tovey and colleagues, they applied several image-processing techniques to measure the porosity of clay particles. They developed a novel algorithm to segment high-resolution SEM images and estimate the porosity.
Porosity is an essential characteristic of soils, and estimating it accurately is crucial in addressing environmental and engineering problems. For example, soil porosity can help detect water seepage from dam axes or detect differential settlement problems in foundations. It can also help predict a potential earthquake problem.
The amount of calcium carbonate in soils can affect porosity. For example, sand and gravel are very porous. However, their pore size is small, so they will not absorb much water. For this reason, increasing the sand content in soils will decrease their porosity.
The depth to which a rock is buried also determines its porosity. Deeper in the earth, a rock’s porosity is lower, and its porousness is greatly diminished. In addition, the weight of overlying rocks reduces the size of pores at a great depth.
In the south of China, red clay is widely distributed and localized in Hubei and Anhui. It is mainly found on low mountain slopes and in depressions. Its high liquid limit and high porosity ratio make it a poor foundation soil.
Drying properties
The drying properties of clay are essential for ceramics. This characteristic allows for comparing different clays and determines their relative plasticity and particle size. The measurement is most useful when the sample preparation, water content, and drying conditions are controlled and the measurements are repeated over time. However, some clays are unsuitable for making shrinkage test bars and must be mixed with another clay or calcined substance to simulate their drying properties.
The Aptian clays in Tunisia contain mostly illite, kaolinite, smectite, and accessory minerals. The Aptian clays contain approximately 3.5 wt% aluminas, with varying amounts of lime and iron. These clays have a medium plasticity index (16-28 wt%). However, their shrinkage and cracking properties are affected by the finer particle size.
The drying properties of clay can be estimated through computations of their sorption isotherms at different temperatures. To do this, we conducted X-ray diffraction tests on two different clay types and measured their vapor pressures. Using these data, we could determine how much water each type of clay would bind to different liquids and gases at three different temperatures.
The drying properties of clay vary greatly. For example, plastic clay tends to shrink more when dried. This happens because of the finer particle size and greater water between the particles. As a result, it is more difficult to dry these clays. However, if you have the patience to test different types of clay, you can find the sweet spot where they dry well.
Depending on the ambient air temperature, the clay sand mixture reaches its maximum moisture content within a short period of time. This maximum moisture content is related to the mineralogy of the clay. Unlike in soil moisture, the decrease in electrical conductivity and moisture content are not linear. The two parameters vary according to the ambient temperature and the exposure time.
Dry form clay
Today’s desire for naturalness has created a new demand for eco-friendly design. This new demand has pushed architects and designers to embrace clay and explore the potential of this versatile material. From large, bulky construction to fine crafts, clay has an immense variety of uses. In fact, it has become more prevalent in recent years.
Its healing properties are widely known, and it has a wide variety of applications in medicine and cosmetology. For example, clay is used as a mask, wrap, and lotion. It helps the skin retain elasticity and protects against premature aging. It is also used internally for a variety of medical conditions, including multiple sclerosis and atherosclerosis.
While most clays have a similar composition, they can vary in porosity. Porosity refers to the amount of air or water that can pass through the material. This is largely determined by the type of rock in which the clay is formed. Typically, clay has a porosity of between twenty and sixty percent. Because clay is porous, it can collect liquid and can be used in watertight structures.
Clays can be classified according to their origin and use. Among the main types are clays that come from the sea and those that are transported by water. Clays from the sea can be classified into four sub-classes, each associated with where the soil was deposited and where the final rock formed. Coastal clay is formed near the water’s edge and is usually coarse with poorly sorted particles.