Firing is the name given to a wide variety of thermal processes in the manufacture of materials and the manufacture of semi-finished products . The term is widely used in the manufacture of ceramic materials, powder metallurgy, and alcohol manufacture.
When burning, a chemical reaction or a remodeling of the crystal structure of a material is achieved through the addition of energy . Firing is used to change material properties , possibly also as a separation process (material extraction ), or can be included in thermal primary and reshaping ( shaping ). It is also a post-treatment procedure.
Firing of ceramics
Firing processes for ceramic tiles , porcelain and other ceramic products take place in thermoprocessing systems ( melting furnace , kiln , etc.). Temperature ranges depend on the materials and can range from boiling temperatures below 100 ° C to melting points above 3000 ° C (special ceramics). The firing temperature required for a process is then usually limited to a very narrow range.
In the manufacture of ceramic material, one speaks of sintering when the focus is on the physico-chemical reactions, of firing when it is more about the specific furnace operation. A distinction must be made as to whether the sintering process takes place with the formation of a liquid phase, as is the case with clay and feldspar- containing silicate ceramics , or as solid phase sintering, as with oxide and non-oxide ceramics. The firing of silicate ceramics usually takes place at temperatures between 900 ° C and around 1400 ° C, whereby the clay-containing substances release water from around 600 ° C, which escapes through pores. The reaction of a part of feldspar with the other components of the molding compound can result in phases that become molten at 925 ° C. These molten phases solidify like glass when they cool down again, so that the structure of silicate ceramics generally also has an amorphous glass phase in addition to crystalline components, the proportion of which depends on the starting materials and the firing temperature. Oxide and non-oxide ceramics are generally fired at high temperatures above 1400 ° C (oxide ceramics 1600 ° C to 1800 ° C, non-oxide ceramics up to 1500 ° C). A liquid phase does not occur, so that the structure of the sintered body is purely polycrystalline. Oxide ceramics can be sintered in an oxidizing atmosphere, which is also suitable for burning out organic binder additives before the actual sintering process. The sintering of carbide and boride ceramics requires an inert gas atmosphere in the furnace and the sintering of nitride ceramics is carried out as reaction sintering in a nitrogen atmosphere, silicon nitride increasingly being formed as a result of the reaction with the nitrogen . During the sintering process, the powder grains grow together through diffusion processes. On the whole, a porous solid is converted into a denser and more solid state.
When burning lime , calcium carbonate , the main constituent of limestone , is heated to over 1000 ° C, where it decomposes and calcium oxide (quicklime) is formed with carbon dioxide being split off .
When burning is called the separation of ethanol to enjoy purposes of a mash by distillation . In contrast to distillation in the context of the isolation and purification of chemicals, the goal here is not to obtain the purest possible substance, but to obtain a tasty solution from ethanol, other alcohols, water and flavorings.
In cheese production , burning is the term used to describe the heating of the curd to expel water. The temperature and duration differ depending on the type of cheese (hard cheese: 52–56 ° C, soft cheese: 35–39 ° C). During this process, the syneresis and the whey discharge are further promoted by the increase in temperature.
- Degassing / calcining
- Removal of the crystal water
- Pigments (mostly conversion of iron-based yellow pigments into reddish pigments): burnt ocher , burnt umber , burnt sienna , iron oxide red
- of alcohol, see burning (spirit)
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