Kaolin is one of the ingredients used in ceramics, paint, rubber, paper and many other products. Although it has plenty of use, not many people know exactly what it is and why it is used in a lot of products. This article will discuss everything about kaolin and kaolin 325 mesh as well as its use in a variety of industries.

What does Kaolin 325 Mesh Mean?

Kaolin, also commonly called china clay, is a soft white clay that is usually used in manufacturing porcelain, paint, rubber, paper, and a lot more. Its name is derived from the name of a hill in China called Kao-ling, the place where this material was mined for centuries. 

Mesh is the old imperial standard measuring system used to measure particle size. This measuring system is still widely used to this day for mineral measurement in countries such as China and India. The higher the number of the mesh size means the smaller the particles. 

From the two definitions above, kaolin 325 mesh is a type of kaolin with the size of 325 mesh or equal to 45 microns. This means that most of the particles of the materials are less than 45 microns. It is one of the international standards commonly used among a variety of kaolin users in various industries. 

Properties of Kaolin

Kaolin is naturally white, yellowish or greyish in color. It is soft, and powdery, which mostly consists of a mineral called kaolinite. However, it also contains other various types of minerals such as quartz, feldspar, muscovite, and anatase. or 

This material is usually odorless and is insoluble in water. When it is wet, however, kaolin will be darkened and develop an earthy odor.  While it is usually white in nature, crude kaolin often has a yellow stain due to iron hydroxide pigments. 

The yellowish kaolin is usually bleached to chemically remove the iron pigment. It is also washed in water to remove other minerals before commercial use to obtain the pure kaolin mineral. 

When it is mixed with water under 20 to 35 percent, kaolin becomes plastic and can be molded under pressure. However, the amount of water needed to create the plasticity and viscosity varied depending on the kaolinite particle’s size and other chemicals found in it. 

Calcined vs Washed Kaolin

Kaolin used in industry is usually either calcined or water-washed. When calcined, the original soil changed and formed crystals. Meanwhile, the water-washed kaolin means that it is only treated physically which will not change its original soil nature. Additionally, after a light burning, kaolin will become increasingly white. However, kaolin that is treated with water washing will not become whiter significantly. 

Calcined kaolin after being burned to certain temperatures can be used in the papermaking industry as additive and refractory aggregate. Meanwhile, the water-washed kaolin is usually used as filler in the papermaking industry. However, calcined in the papermaking industry generally has better whiteness but with a higher cost. 

The Use of Kaolin

As mentioned previously, kaolin 325 mesh is commonly used in various industries from paper, paint, to ceramics manufacturing. Here is how this mineral is used in said industries:

1. Paint and coatings

This material has a high refractive index with structure in the form of hexagonal crystal. This is one of the reasons why kaolin has excellent covering power and color payoff. It also creates a balanced fluidity and leveling of these products. Due to its flat particles, it will also provide great compressive adhesion.

Since this mineral is hydrophilic, it means that paint using kaolin will be easily spread and offer excellent suspension performance. Meanwhile, it also has strong chemical inert, smaller optical axis angle with higher crystal shape order. The combination of these three features allows paint using kaolin as ingredients to have great UV protection ability.

Related: All You Need to Know about Kaolin Clay as Paints & Coatings

2. Glazes and ceramics

In glazes manufacturing, kaolin is used to produce a vitreous material. AI2O3-2SiO2-2H20 is the ideal formula to form a vitreous material. This formula is similar to marble, quartz, and feldspar, which is glass formation’s main component.

This white mineral is mostly composed of AI2O3 with a few silicon dioxides. With a bigger amount of alumina, the glaze’s viscosity will also improve. This prevents the glaze that is stuck to flow and at the same time affects the glass diffusion. This makes crystallization harder to produce.

3. Paper industry

Kaolin is the necessary raw material in a huge variety of industries such as papermaking, rubber, ceramics, coating, chemical, medicine, and a lot more. The reasons lie within the properties of the pure kaolin, which are high whiteness, softness, ease to disperse, suspension in water, high adhesion, excellent plasticity and excellent performance of electrical insulation.

There are two ways of how this mineral is used in the papermaking industry. First, in the fillers used in the papermaking process, and second in the coating process for the surface that uses kaolin pigments. In fact, 60% of total kaolin consumption was used in the paper manufacturing industry.

4. Rubber industry 

For this industry, the kaolin mineral used is the raw and high-quality version produced through washing and refining process. It has a smaller particle size with low moisture. It also has stable PH and excellent DPG absorbency. 

With the features above, rubber made with refined kaolin usually has lower abrasion, good strength and great bending performance. It is also an excellent filler for rubber products variations.

5. Medical Industry

Last but not least is the medical industry. In the medical field, this mineral is used to treat mild to moderate cases of diarrhea, severe diarrhea, and cholera. When combined with other ingredients, this mineral also treats soreness and swelling inside the mouth and relieves swelling inside the mouth due to radiation treatment. 

Kaolin Mesh 325 is the common measurement of kaolin or china clay used in industries. Its properties allow for a wide variety of uses. With careful preparation this material is even used for medicine. Which means that this mineral is generally non-toxic. However, please remember to wear protective clothes and masks when handling this material.