Classification of ceramics and ceramic raw materials

Table Of Content

• (1) Pottery
• (2) Porcelain
• (3) Stoneware

Ceramic products are divided into the following three types according to their raw material composition and process:

(1) Pottery

It is mainly made of pottery clay and river sand as the main raw materials with a small amount of porcelain clay or clinker, etc., and is fired at high temperature (about 1000C). It can be glazed or unglazed. Its products have the characteristics of large porosity, low strength, high water absorption, rough and matte cross section, opaque, and mute sound when knocked. Pottery is divided into two types: coarse pottery and fine pottery. Rough pottery is generally made up of one or more types of clay that contains a lot of impurities. The finished product after firing is usually colored. Bricks, tiles, pottery pipes, etc. used in construction projects all fall into this category. Fine pottery is generally fired twice by biscuit firing and glaze firing. It is usually white or ivory in color and has a water absorption rate of 9% to 12%, which can be as high as 18% to 22%. Painted pottery, art ceramics, etc. used for architectural decoration. Glazed tiles , etc. all fall into this category. Fine pottery can be divided into architectural fine pottery, daily fine pottery and fine art pottery according to its different uses.

(2) Porcelain

Porcelain products have a dense structure, basically do not absorb water, are white in color, and have a certain degree of translucency. Their surfaces are usually covered with a glaze layer. Porcelain is divided into two types: coarse porcelain and fine porcelain according to the chemical composition of its raw materials and the manufacturing process. Porcelain is mostly used for display porcelain, tableware and tea sets, art porcelain, high-voltage electrical porcelain, high-frequency device porcelain, etc.

(3) Stoneware

Stoneware is a type of ceramic product between pottery and porcelain, also known as semi-porcelain. Its structure is denser than ceramics, and its water absorption rate is generally smaller, but it is not as white as porcelain. Its body is mostly colored and has no translucency.

Stoneware is divided into the following two types according to the density of its body:

1. rough stoneware

The water absorption rate of rough stoneware is generally 4% to 8%. Exterior wall tiles, floor tiles and ceramic mosaics (mosaics) used for building decorations all belong to rough stoneware.

2. fine stoneware

The water absorption rate of fine stoneware is less than 2%. Daily utensils, chemical and electrical industry ceramics, etc. are all fine stoneware.

Ceramic raw materials are divided into three major categories: plastic clay raw materials, non-plastic quartz raw materials (barren raw materials) and flux raw materials.

Clay raw materials are one of the main raw materials for daily ceramic raw materials. The dosage of clay raw materials in fine porcelain ingredients often reaches 40~60%, and the dosage in pottery and stoneware can be increased. Clay is used as the main raw material for ceramic products because of its plasticity and sintering properties. The main minerals in clay used in ceramic industry include kaolinite, montmorillonite, illite (hydrous mica), and rare allophane.

Quartz raw materials (barren raw materials): There are several quartz raw materials and materials commonly used in the ceramic industry: vein quartz, sandstone, quartzite, quartz sand, chert, and diatomite.

The role of quartz in ceramic production is that it is added to the ceramic blank as a barren raw material. It is one of the main components of the ceramic body. Its role in ceramic production is not only during the shaping of the ceramic body but also during firing. have an important impact.

Flux raw materials: The most important ones are mineral raw materials containing alkali metal oxides. In addition, some minerals containing alkaline earth metals can also be used as flux raw materials. Among them, carbonate minerals containing calcium oxide and magnesium oxide are more common. Feldspar is the most commonly used fluxing raw material among ceramic raw materials. It is used as basic components such as blanks, glazes, and color fluxes in ceramic production. It is used in large amounts and is one of the three major raw materials for ceramics.

=================================

Classification of ceramics

There are many varieties of ceramic products, and their chemical compositions are different. Mineral composition, physical properties, and manufacturing methods are often close to each other, with no obvious boundaries, but there are great differences in application. Therefore, it is difficult to rigidly summarize it into several systems. Each company has different opinions on the detailed classification method. Up to now, there is no unified classification method in the world. There are two commonly used classification methods from different perspectives:

(1) Classification according to different uses

1. Daily ceramics: such as tableware, tea sets, jars, altars, basins, jars, plates, saucers, bowls, etc.

2. Art craft ceramics: such as vases, sculptures. Garden ceramics, utensils, furnishings, etc.

3. Industrial ceramics: refers to ceramic products used in various industries. It is divided into the following 6 aspects:

Building-sanitary ceramics: such as bricks, drainage pipes, facing tiles, exterior wall tiles, sanitary ware, etc.;

Chemical {chemical} ceramics: used in acid-resistant containers, pipes, towers, pumps, valves, and acid-resistant bricks and ash for lining reaction pots in various chemical industries;

Electrical porcelain: used for insulators on high and low voltage transmission lines in the electric power industry. Bushings for motors, pillar insulation, insulators for low-voltage electrical appliances and lighting, as well as insulators for telecommunications, radio insulators, etc.;

Special ceramics: Special ceramic products that are behind various modern industries and cutting-edge science and technology, including high-alumina porcelain, magnesia porcelain, titanite porcelain, zirconite porcelain, lithium porcelain, and magnetic porcelain , cermets, etc.

(2) According to the raw materials used and the density of the green body, it can be divided into:

Brickware or terra-cotta, fine pottery, stoneware, semivitreous china, and even porcelain, the raw materials are from coarse to fine, and the body is from coarse to loose and porous. gradually reaches density, sintering, and the sintering temperature gradually increases from low to high.

Stoneware is the most primitive and low-grade ceramic, generally made of a kind of fusible clay. In some cases clinker or sand can also be added to the clay to reduce shrinkage. The firing temperature of these products varies widely, depending on the nature and amount of impurities contained in the chemical composition of the clay. When making bricks and tiles with it, if the porosity is too high, the freeze resistance of the body will be poor, and if the fork is too low, it will be difficult to catch the mortar, so the water absorption rate should generally be maintained between 5-15%. The color of the green body after firing depends on the content of colored oxides in the clay and the firing atmosphere. It is mostly yellow or red when fired in an oxidizing flame, and cyan or black when fired in a reducing flame.

The green bricks in my country's building materials are made of yellow or red clay containing Fe2O3 as raw materials. They are calcined with a reducing flame when the fire is approaching to stop the fire, so that the Fe2O3 is reduced to FeON and becomes cyan. The pottery can be divided into two categories: ordinary pottery and refined pottery. . Ordinary pottery refers to clay pots. Pots, jars, urns. As well as products with porous colored bodies such as refractory bricks. The water absorption rate of the fine pottery body is still 4-12%, so there is penetration and no translucency. It is generally white, but there are also colored ones. The glaze is mostly fusible glaze containing lead and boron. Compared with stoneware, the amount of flux is less and the firing temperature does not exceed 1300C, so the green body is not fully sintered; compared with porcelain, the requirements for raw materials are lower, the plasticity of the blank is greater, and the firing temperature is higher Low. It is not easy to deform, so it can simplify the forming, bowling and other processes of products. However, the mechanical strength and impact strength of fine pottery are smaller than those of porcelain and stoneware. At the same time, its glaze is softer than that of the above-mentioned products. When its glaze layer is damaged, the porous body is easily stained, affecting hygiene.

Fine pottery can be divided into four types according to the composition of the body: clay, calcareous, feldspathic, and clinker. Clay fine pottery is close to ordinary pottery. Calcareous fine pottery uses limestone as a flux. Its manufacturing process is similar to that of feldspathic fine pottery, but its quality is not as good as that of feldspathic fine pottery. Therefore, it has been rarely produced in recent years and has been replaced by feldspathic fine pottery. Feldsparic fine pottery is also called hard fine pottery, using feldspar as a flux. It is the most perfect and widely used type of pottery. In recent times, many countries have used it to mass-produce daily tableware (cups, plates, etc.) and sanitary pottery to replace expensive porcelain. Hot material fine pottery is to add a certain amount of clinker to the fine pottery blank in order to reduce shrinkage and avoid waste products. This kind of blank is mostly used in large and thick products (such as bathtubs, large wash basins, etc.).

Stoneware is called "stone-bodied porcelain" in ancient Chinese books. The body is dense and has been completely sintered, which is very close to porcelain. But it has not yet been vitrified, and still has a water absorption rate of less than 2%. The green body is opaque, some are white, and most are allowed to show color after firing, so the requirements for the purity of the raw materials are not as high as those of porcelain, and the raw materials are easy to obtain. Stoneware has high strength and good thermal stability, is well adapted to modern mechanized washing, and can smoothly pass through sudden temperature changes from refrigerator to oven. In the international market, due to the development of tourism and the socialization of diet, Stoneware has a greater sales volume than enameled pottery.

The blank of semi-porcelain is close to that of porcelain, but it still has a water absorption rate of 3-5% after firing (for real porcelain, the water absorption rate is less than 0.5%), so its performance is not as good as that of porcelain, but better than fine pottery.

Porcelain is a higher stage of the development of ceramics. Its characteristics are that the green body has been completely sintered and completely vitrified, so it is very dense, impermeable to liquids and gases, the thinnest parts are translucent, and the cross-section is shell-shaped. When licked with the tongue, it feels smooth but not sticky. live. Hard porcelain has the best properties among ceramics. Used to make high-end daily utensils, electric porcelain, chemical porcelain, etc.

Soft porcelain has more flux and a lower firing temperature, so its mechanical strength is not as good as that of hard porcelain, and its thermal stability is also lower. However, it has high transparency and is highly decorative, so it is mostly used to make art display porcelain. . As for Fritted porcelain and bone china, their firing temperatures are similar to those of soft porcelain, and their advantages and disadvantages are also similar to those of soft porcelain, so they should both fall into the category of soft porcelain. Due to the difficulty in production of these two types of porcelain (the plasticity and dry strength of the green body are very poor, and the deformation is serious during firing), the cost is high, and the production is not common. The UK is a famous producer of bone ash porcelain, and China also produces bone ash porcelain.

Special ceramics have developed with the rapid development of modern electrical appliances, radio, aviation, atomic energy, metallurgy, machinery, chemistry and other industries, as well as cutting-edge science and technology such as electronic computers, space technology, and new energy development. The main raw materials used in these ceramics are no longer clay, feldspar, and quartz. Some ceramics also use some clay or feldspar. However, more of them use pure oxides and raw materials with special properties. The manufacturing process and performance requirements Also different.

=================

There are many ways to classify ceramics. Generally, people are used to classifying them according to the following four aspects:

1.According to the purpose, it can be divided into daily-use ceramics, art (display) ceramics, sanitary ceramics, architectural ceramics, electrical ceramics, electronic ceramics, chemical ceramics, textile ceramics, through-pass (gas transmission) ceramics, etc.

2.According to whether it is glazed or not, it can be divided into two categories: glazed ceramics and unglazed ceramics.

3.For the convenience of production, research and study, people sometimes divide ceramics into high-strength ceramics, ferroelectric ceramics, acid-resistant ceramics, high-temperature ceramics, piezoelectric ceramics, and high-toughness ceramics based on their performance rather than chemical composition. Electrolyte ceramics, optical ceramics (i.e. transparent ceramics), magnetic ceramics, dielectric ceramics, magnetic ceramics and bioceramics, etc.

4.It can be simply divided into three categories: hard porcelain, soft porcelain and special porcelain.

The porcelain produced in China is mainly hard porcelain. Hard porcelain has a small body composition and a high firing temperature. It is white and hard in color above 1360C, translucent, has good strength, high chemical stability and thermal stability, and has poor electrical conductivity. Body, such as electric porcelain, high-end tableware porcelain, chemical porcelain, ordinary daily-use porcelain, etc. all fall into this category, and can also be called feldspar glazed porcelain.

The difference between soft porcelain and hard porcelain is that the body contains more flux and the firing temperature is slightly lower, below 1300C. Therefore, its chemical stability, mechanical strength, and dielectric strength are low, and it is not used in general industrial porcelain. Soft porcelain is characterized by high translucency and is mostly made of art porcelain, sanitary porcelain, ceramic tiles and various decorative porcelain, etc. Usually bone ash porcelain and frit porcelain fall into this category.

There are many types of special porcelain, mostly based on various oxides, such as high-alumina porcelain, which is mainly alumina, magnesia porcelain, which is mainly magnesium oxide; talc porcelain, which is mainly talc; beryllium porcelain , mainly beryllium oxide or beryl; zirconium porcelain, mainly zirconium oxide; titanium porcelain, mainly titanium oxide.

Most of the characteristics of the above-mentioned special porcelain are that they are made of products that do not contain clay or contain a very small amount of clay. They are often formed by dry pressing and high-pressure methods. This type of porcelain is often used in the defense industry and heavy industry, such as rockets, baffles on missiles, and aircraft. , spark plugs used in cars, radios, internal semiconductors, porcelain knives for rapid cutting, etc.

===============================

There are 5 categories of ceramic tableware

Generally speaking, we can divide ceramic tableware into five categories, namely: 1. Magnesia porcelain tableware 2. Magnesium reinforced porcelain tableware 3. Reinforced porcelain tableware 4. Shell porcelain tableware 5. Colored glazed porcelain tableware.

1. Magnesium porcelain tableware

Magnesia porcelain is mainly made of talc, a magnesium-rich silicate mineral, as the main raw material of porcelain clay, and is fired at a high temperature of 1380 degrees Celsius. Therefore, magnesia porcelain tableware has outstanding characteristics such as high whiteness, high strength, and high thermal stability. It is as white as jade, crystal clear and moist, and is the best choice for tableware for star-rated hotels. It is now designated as the Great Hall of the People and Diaoyutai State Guesthouse. Porcelain is used for state banquets and has been selected as special porcelain by Beijing Wangfu Hotel.

Magnesia porcelain tableware has unique properties of high strength, acid and alkali resistance, lead-free poison, and easy to wash. It can withstand the bumps and collisions of kitchen operations and is not easily damaged. It is more suitable for mechanical washing, high-temperature cooking and sterilization, and continuous high temperature of electric ovens. and modern lifestyles such as microwave heating. Magnesia porcelain tableware is selected by large hotels in big cities such as Beijing, Tianjin, Shanghai, and Guangzhou, and is favored by foreign businessmen. It has become a "hot item" among tableware exported to Europe, America, Southeast Asia, and the Middle East.

2. Magnesium reinforced porcelain tableware

Magnesium reinforced porcelain tableware is made of magnesia stone powder and feldspar powder as the main raw materials, and is fired at a high temperature of about 1340 degrees Celsius. It has ultra-high strength, low brittleness, high whiteness, smooth glaze and long service life. It is 3-5 times that of ordinary ceramics. It is an ideal product suitable for sterilizing tableware among all daily-use porcelains. Although the cost of a single product is about 25% higher than that of white porcelain and ordinary strengthened porcelain, due to its long service life, low breakage rate, high grade and good image, the actual cumulative total investment in tableware is more than 50% lower. Porcelain is noble and elegant, with a smooth and soft glaze. It has the characteristics of high temperature resistance, rapid cooling resistance, high temperature resistance, and is not easy to scratch. It does not contain lead and other chemical substances. It is a pollution-free green tableware and environmentally friendly tableware. It is an ideal choice for modern hotels, guesthouses and Ceramic tableware products are the first choice of sterilizing tableware companies and are well received by users.

3. Reinforced porcelain tableware

Reinforced porcelain is made by adding aluminum and magnesium to high-quality porcelain clay and then firing it with a fire at about 1300 degrees Celsius, so that they can be re-crystallized and combined into a substance that is magnetized and is resistant to collisions. The glaze is milky white and feels delicate. The color glaze of strengthened porcelain is darker than that of magnesia-strengthened porcelain. The tableware currently used in the sterilized tableware market has been gradually replaced by magnesia-strengthened porcelain and magnesium-based porcelain.

4. Shell porcelain tableware

Shell porcelain uses a scientific formula of high white mud, high white glaze and shell powder, and is fired at a high temperature of more than 1,200 degrees Celsius. It is then painted, glazed again, and fired a second time at high temperature to make it non-toxic. , lead-free, harmless and never fade, not easily broken, suitable for dishwasher washing. The glaze of shell porcelain tableware is white with blue, which is suitable for users of medium and low-end ceramic tableware.

5. Colored glazed porcelain tableware

Colored glazed porcelain is painted directly on the embryo before the product is fired, and is fired at a high temperature. It belongs to underglaze colored ceramics. The patterns on the porcelain are artificially painted and have artistic value. It is a tableware product with a different style from the porcelain above, providing more choices for sterilization centers that require special tableware.

=============================================

Healthy life: How to choose ceramic tableware?

The firing and application of ceramic tableware has a long history in our country. It has various shapes, colorful colors, cool and smooth feel, and is easy to wash. It is deeply loved by Chinese people. As everyone knows, there is a lot of knowledge in selecting and using ceramic tableware. If we neglect it, the "guy style" that we must use every day and for every meal will gradually affect our health like a trace amount of poison.

There are three methods of making ceramic tableware: overglaze color, underglaze color, and in-glaze color.

Overglaze colored ceramics use pigments to make decorative paper and stick it on the glaze or paint directly on the surface of the product, and then bake it at low temperature. Since the baking temperature cannot reach the level of melting of the glaze layer, the flower surface cannot sink. into the glaze. When you touch the overglaze colored ceramics with your hands, you can feel the obvious concave and convex feeling on the flower surface;

The firing temperature of the glaze-in-glaze ceramics can melt the glaze, and the pigments can sink into the glaze and be covered by the glaze layer after cooling. The surface of the product is smooth and there is no obvious concave and convex feeling to the touch;

All the decorations of underglaze ceramics are carried out on the porcelain blank. After the glaze is applied, it is fired at high temperature. The flower surface is covered by the glaze layer, which looks bright, flat and feels smooth.

The heavy metal toxins we emphasize mainly come from overglaze pigments. Experts point out that the lead compounds in overglaze ceramics can be leached by acid. When food comes into contact with the picture, the lead may be leached out by the organic acid in the food. Of course, if the overglaze color design is reasonable and the barbecue technology is appropriate, excessive lead can be avoided. If ceramic products contain harmful ingredients, they may overflow at high temperatures of 600C to 800C. Therefore, when people use a microwave oven, it is best to put a white bowl or an underglaze bowl. In contrast, the underglaze, underglaze and white porcelain currently on the market do not contain lead and are relatively safe.

The reason for this situation is that in order to reduce costs, some small ceramic manufacturers purchase cheap raw materials with high lead and cadmium content and unstable performance. During the production process, due to factors such as excessive decoration area, insufficient baking temperature or improper processing by workers, the lead dissolution of ceramic products will not meet the standards. In order to make more profits, some individual and private enterprises arbitrarily shorten the baking time or lower the baking temperature, and even use old-fashioned baking ovens that rely entirely on the experience of workers, which seriously restricts the quality of ceramic tableware.

===============================

What is the difference between bone china and ceramics?

The main component of bone china is high-value natural bone powder. The production method is to add more than 30% of herbivore bone meal (component is tricalcium phosphate) into porcelain clay. The finished bone china is light, fine and hard (twice as much as daily porcelain), not easy to wear and crack, and has moderate permeability. The lightness, heat preservation and color are the unique natural milky white color of natural bone powder. The color of the utensils, which contain more than 40% bone powder, becomes milky white and belongs to high-grade bone china (fine bone china).

The color of bone china is the unique natural milky white color of natural bone powder. Generally speaking, porcelain containing 25% bone powder in raw materials can be called bone china. It is internationally recognized that the bone powder content is higher than 40%. The best bone china generally contains 51% high-quality bovine bone powder. The bone powder composition is more than 40%, and the color of the utensils is more milky white, which is a high-grade bone china.

During the firing process of bone china, the requirements for its regularity, whiteness, transparency, thermal stability and other physical and chemical indicators are extremely high, so the scrap rate is very high. Due to its exquisite materials, fine production and strict standards, its value is higher than other porcelain types. The unique firing process and the addition of bone carbon eliminate impurities in the porcelain clay. The bone china appears whiter, more delicate, transparent, lighter, with few flaws, and is thinner than ordinary porcelain, giving it a special visual cleanness. The texture and strength are higher than ordinary porcelain and twice as strong as daily porcelain. The higher the content of bone meal, the lower the composition of the clay, and the easier it is to crack during the production process. It requires higher technology in shaping and increases the difficulty of firing, so it is more precious.

Bone china has many outstanding advantages: the texture is fine, the whole body is milky white, and it is translucent under the light. The most valuable thing is that it is much lighter than ordinary ceramics. The maintenance of bone china is very simple. When it is stained with oil and needs to be cleaned, it does not need to be cleaned. With detergent, just clean with warm water. It can be placed in a sterilizing cupboard for high-temperature sterilization. If there are scratches, you can gently polish them with toothpaste. If there are tea stains, you can use lemon juice or vinegar to clean them. Bone china tableware is designed to be matched. Each set has a poetic and picturesque name, such as "Fragrance of Calligraphy", "Hundred Years of Love", "Moonlight over Lotus Pond", etc. The pattern of each set of tableware carries an expression. , to create an atmosphere. Therefore, which kind of decoration style of house and which style of bone china tableware to choose depends on the personality and style of the owner. Every meal of the day, before the feast, must be served with enough graceful bone china to show its extraordinary style.