The term "porcelain" refers to a wide range of ceramic products that are manufactured at high temperatures. Their distinguishing features are a smooth surface and low porosity. These properties of porcelain are widely in demand today. It is difficult to find any industry or national economy, wherever it is used.
The most common decorative porcelain, as well as chemical glassware, dental crowns and electrical insulators. Usually white or off-white, for “baking” this wonderful material arrives with an unpresentable piece of ceramics, which will take on our usual form only after frying in high-temperature ovens.
Benefits of Chinese Services
In this article, we will discuss the properties and types of porcelain. You will understand why all over the world this material was so popular that huge expeditions were equipped for its purchase. For a beautiful service that you can buy in any store today, you could have been killed.
Oddly enough, but the products of Chinese masters with current ceramics are only relatives, but not direct. To make sure of this, it is enough to recall the basic properties of porcelain, which came from the workshops of the Middle Kingdom. The materials are very similar to each other: both current and ancient porcelain can be glazed or “natural”. But simple ceramics are much softer. And a high-quality service cannot be made from it.
Why is this happening?
Such properties of porcelain as strength and heat resistance are the fruit of high temperatures at which true Chinese ceramics are produced. It is produced at a temperature of 2,650 degrees Fahrenheit (1,454 degrees Celsius). Compare this to 2,200 degrees Fahrenheit (1,204 degrees Celsius) for plain china. Since the second material is of lower quality, it is not used in the chemical industry and other technological branches of science. In addition, it is Chinese porcelain of the highest quality that is transparent to the lumen. Coarse ceramics cannot give such an effect.
Spy passions
"Hard paste", or true china, first appeared in China during the Tang Dynasty (618-907). But really high-quality products, whose properties are not inferior to modern ones, became known to the world only during the Yuan Dynasty (1279-1368). Early Chinese porcelain consisted of kaolin (porcelain clay) and pegmatite - a coarse type of granite.
He was unknown to European potters before importing Chinese equipment during the Middle Ages. Europeans tried to duplicate the properties of porcelain, but did not succeed in this matter. Since they were not able to analyze its chemical composition, the products manufactured by them resembled elegant, fragile and at the same time durable dishes only externally. It turned out so-so. In order to get the secret of true china production, real espionage wars unfolded, but the Chinese cherished their secret more than life.
Why was this material so popular? The reason is the excellent physical properties of porcelain. It is stronger than ordinary ceramics, has a high thermal conductivity, which makes it possible to brew excellent tea in teapots from it. In addition, due to the glaze, porcelain has an extremely small mark, staining only under the influence of synthetic pigments. Cups from ancient Chinese services many centuries later remain white.
Erzatsi
After mixing glass with tin oxide to obtain an opaque material, European artisans tried to combine clay and frosted glass. These alternatives became known as soft pasta, or artificial porcelain. But two unpleasant circumstances upset: all these materials turned out to be too soft, it was impossible to make really thin, elegant products from them, and the production costs were too high. In short, the properties of porcelain “ersatz-type” were very far from perfect.
There is evidence that our masters also owned the art of producing true porcelain, but all the secrets of Russian ceramics were lost during the Tatar-Mongol invasion, when entire cities were burned along with all their inhabitants. The British were also able to achieve a definite breakthrough. They created a "bone" type of material.
But what is bone china, the basic properties of which provided him incredible popularity in old Europe?
History of creation
In 1707, two Germans named Ehrenfried Walter von Chimhaus and Johan Friedrich Bottger discovered a more “sane” production method that uses clay and finely ground feldspar. In the XVII century, English artisans learned during experiments that almost identical to Chinese porcelain can be obtained by adding finely ground burnt bones to this mixture.
And later it turned out that the English version allows the production of transparent ceramics at much lower temperatures, which significantly reduced the cost of production. In addition, porcelain from Misty Albion fought much worse, was much stronger. So it is not surprising that the British soon filled up half of the Old and almost the entire New World with their services.
What are the properties of bone china? Firstly, products made of it are characterized by high strength with low weight and thinness. Secondly, this type of ceramics cannot be used in the chemical industry, since the substances that make up its composition react with acids and alkalis.
Raw materials
As we have already said, the main components of this material are extremely simple: clay, feldspar, minerals with calcium content. Until now, various companies are competing with each other, as it was quickly established that the properties of porcelain and faience can be radically changed by adding new elements to its composition. Of course, if the experience is successful.
Despite the fact that the composition of clay varies depending on the place of its extraction, it still turns into glass (due to which the final product is smooth) only at extremely high temperatures. But this is true only for those cases when clays are not mixed with materials whose vitrification threshold is lower. Unlike glass, clay, however, is thermostable, that is, it retains its shape even with strong heating.
So this material is really unique because it combines the low porosity of glass with the stability and relative strength of simple ceramics. At all times, kaolin and hydroaluminosilicate were used as the main type of raw material.
Feldspar (containing aluminum silicate) and flint, a type of hard quartz, are extremely important components of any type of porcelain. They melt during heating, linking the material into a single whole.
Quartz - the "heart" of porcelain
This is the key to strength. The properties of porcelain (and its application) are largely due to this very characteristic: it does not beat well (when compared with glass), and the small distances between the particles ensure the impermeability of the material to air, water, and other compounds.
Quartz is an “alloy” of oxygen and silicon - the two most common elements in the earth's crust. It has three functional forms: directly quartz (crystals), opal (amorphous variety) and sand (mixed, dirty fraction). In general, quartz has long been used in craftsmanship. Porcelain may also contain alumina and steatite, better known as soapstone.
Manufacturing process
After the raw material is selected and weighed, it goes to production. Firstly, it is cleaned and ground to very fine fractions. After that, all components are mixed in the required proportion, depending both on the production conditions and on the characteristics of the final products. Once the latter are formed, they can be sent to the oven immediately, or they are subjected to preliminary cleaning and further application of a layer of glaze.
Of course, its role is first played by ground glass. And only after that the future vases, cups, toilets and dental crowns are sent to the furnace mouth. And now we will consider each stage separately. After all, the properties of porcelain and its application depend on their success!
Crushing raw materials
Perhaps this is one of the most important operations, since the quality of the final product depends on the thoroughness of its implementation. Grinding is done with huge mechanical drum crushers. In the second pass, the particle size is brought to 0.25 cm. To turn the feedstock into fine dust, special ball crushers are used. These are huge steel cylinders filled with metal balls. When the whole structure rotates, the particles of raw materials turn into a homogeneous mass of extremely fine grinding.
Cleaning and mixing
The mixture is passed through fine filters, and then fed to a special "conveyor", which is an inclined steel sheet. They vibrate, as a result of which the raw materials are not only automatically mixed, but also sorted, since the largest particles are pushed up. If wet material is required, water is automatically sprayed on the line.
Filters with powerful magnets are sometimes used, since the latter can remove the smallest impurities of iron. The latter, if it falls into the finished product, will inform it of an undesirable red tint. After this, the finished products are sent to the furnace, where they are fired at the temperatures already indicated by us.
What production conditions can the product properties depend on?
It should be noted that during the final firing there are many processes that directly affect the properties of cold porcelain. Firstly, all carbon organic impurities are burned, excess water is evaporated, various gaseous fractions come out from the thickness of the future product. If the temperature is not brought up to 1100 degrees Celsius, then silicon and other components of the glaze will not be able to melt, and therefore will not form a smooth and chemically neutral layer on the ceramic surface.
In addition, these compounds are necessary to reduce the distance between the particles of materials, for a more reliable connection with each other. After the desired density is reached, the product cools, as a result of which the glaze “contracts”, becomes smooth and especially durable.
Summary
So why did we all describe this? The thing is that the properties of this material are closely dependent on the features and conditions of its manufacture. For example, strength depends on the percentage of content in the mass of feldspar, and the number of pores in porcelain is less, the more the spar. As the quartz and the residue obtained from the decomposition of the clay substance dissolve in the glass, the skeleton of the porcelain material becomes weaker, and deformations increase. Depending on the fineness of grinding of quartz, mass composition, temperature and duration of firing, the vitreous phase contains from 15 to 40% of all quartz introduced into the mass. The more it is, the porcelain is thinner and “airier”.
The properties of ceramic materials as dielectrics are characterized mainly by the resistance to the passage of electric current in the material and on the surface of the insulator. Distinguish between specific volume and specific surface resistance of porcelain.
In addition, the chemical properties of porcelain are of great practical importance. More precisely, their absence. Glazed ceramics with the addition of a large amount of feldspar and quartz is chemically neutral. You think, why mortars of pharmacists and chemists are made of this material? It is much stronger than glass, but does not react.
Current state of affairs
Today, ceramics (and porcelain in particular) is undergoing a rebirth. It turned out that these materials can be used in the production of various types of microelectronics. The importance of this for modern civilization does not need to be explained. Scientists also found that when certain additives are added, the strength of porcelain increases exponentially. Currently, even promising studies are being conducted in the field of creating new types of armor based on it. So not single toilets!
Finally, this material is becoming increasingly important in medicine. Various prostheses and excellent dental crowns - for them demand is increasing every year. So the ancient Chinese invention will remain relevant for a very long time.