Clay is a type of mineral found underneath hot and solid rock sediment. The mineral is formed from fine particles that move along the water, wind, and glaciers from a higher place and also affected by constant geothermal activity. The clay will lose some of its critical minerals during the formation process, thus degrading its purity. As a result, the clay’s color and composition will change from time to time.
The basic structure of clay consists of one or two silicon dioxide layers with a cushion of aluminum oxide or magnesium oxide. Within the silica layer, you will find a rich amount of silica tetrahedron, made of silicon atoms bonded to four oxygen atoms. If each tetrahedron shares three of the other four oxygens, it forms a hexagonal structure called a tetrahedral layer.
While clay minerals have many types and categories, in this article, we will focus on the ball clay, a kind of clay mainly composed of kaolinite minerals and carbon, which is widely used for industrial ceramic, mixed fodder, and refractory brick production.
What is Ball Clay?
Ball clay is a flexible, dark gray clay that can increase material flexibility when mixed with other types of clay. This material is generally used in porcelain production and combined with kaolin or stoneware clay to create a unique finish.
The clay is categorized as sedimentary clay. It has a melting point between 1250 °C to 1350 °C. Because of its plastic-like texture, the clay can only be used as a mixture of filler for commercial production.
Ball Clay Characteristics
Ball clay is typically sold in the form of balls (hence the name). The clay can be identified based on several characteristics, including:
- Fine-grained with plastic-like properties
- High dry strength
- Easy to shrink after drying and easy to lose volume after heating
- Higher iron content than kaolin
- Darker tone (sometimes it looks greyish) due to its high carbon content.
Furthermore, ball clay is known as having a high level of plasticity because it consists of beautiful particles. It also has excellent binding and flowability. The melting point of this mineral is somewhere between 1.250 °C to 1.350 °C.
Primary and Secondary Clay
Ball Clay is categorized as secondary or sedimentary clays. In general understanding, secondary clay is minerals formed from weathering of feldspathic rocks that move far from their primary sediment or gravel due to exogenous forces. The mineral is mixed with organic and inorganic materials during transit, causing severe chemical and physical change.
Primary clay (residue) is a type of clay produced from the weathering process of feldspathic rocks that is not separated from its primary sediment or rock. This type of clay is purer than the secondary clay as it does not move anywhere. Kaolin, feldspathic, quartz, bentonite, and dolomite are some of the primary types of clay easily found in the market.
Primary and secondary clay has its own unique characteristics. Look at the table below.
|Purer mineral content. The raw primary clay looks bright white or pale.
|A lot of impurities. The color usually looks darker. The secondary clay typically has cream, gray, brown, pink, yellow, light yellow, brownish yellow, reddish, and black color.
|Tend to have coarser or rougher grains and textures.
|Tends to be fine grained or has smooth textures
|More rigid and harder to mold.
|Flexible and easier to mold.
|High melting point
|Low to medium melting point
|Little to no shrinkage
|Fire resistant or require higher temperature to melt
|The combustion temperature is 1200 0C-1300 0C, some are up to 1400 0C (fireclay, stoneware, ball clay).
Moreover, just like other clay minerals, this clay is negatively charged, which means that the clay particles are stuck in a hydration state (surrounded by layers of water molecules called adsorbed water). This state generates a coating consisting of two molecules thick, referred to as a “double diffusion layer.” This layer attracts water molecules or cations around it and can only be diminished in higher temperatures, between 600 °C to 1000 °C.
The Use of Ball Clay in Various Industries
Clay is primarily used as filler for pottery, floor tiles, and the ceramics industry. Clay is also used to make sanitary ware and building materials (bricks, cement, and foundation). Traditionally, people from different civilizations and eras exploited clay as the main component to create various types of heat-resistant goods (refractories). In addition, for thousands of years, ball clay is better known as the main ingredient for making decorative ceramics or porcelain.
Apart from these utilities, clay also has many other benefits. Based on the current research, the mineral within raw clay is beneficial for human health and skin treatment. The study found no less than 67 essential minerals (including calcium, iron, magnesium, manganese, potassium, and silica) within clay that are good for human skin and the body.
Regardless of modern research, history shows that clay for health purposes was carried out more than four millennia ago by the Indians from the Andes, Native Mexicans, Aborigines, and people from Central Africa. They used clay as medicine to relieve stomach pain, treat leprosy, treat tuberculosis, mycobacterium, and other diseases.
Furthermore, clay is an excellent body detox agent. Natural clay has a big, porous texture similar to sponge. It is good to absorb toxins, bacteria, and harmful metals from the human body.
In the modern world, ball clay is generally used in the ceramics industry. This clay is needed for:
- Add flexibility to ease the shaping process and solidify the color of ceramics, making it appear thicker and tougher by reducing its translucent properties.
- Add strength to one of several components before they are burned. The clay protects the primary material so it will not easily be damaged after being processed.
- Add binding strength in the glazing process.
While ball clay is commonly used in the ceramics and porcelain industry, we can get many other benefits from its utilization. Aside from this mineral, you can also find different clay with similar properties widely used within the industry, such as kaolin, bentonite, fuller’s earth, and fire clay.