Alumina ceramic is a kind of Al2O3 as the main raw materials, with corundum ( a - Al2O3 ) as main crystalline phase ceramic material. Because of its high mechanical strength, high hardness, high frequency dielectric loss of small, high temperature and high insulation resistance, chemical corrosion resistance and good thermal conductivity, excellent comprehensive performance, and wide source of raw materials, the price is relatively cheap, manufacturing technology is mature advantages, alumina ceramics have been widely used in electronics, electrical appliances, machinery, chemical, textile, automobile, metallurgy, aerospace and other industries, has become the world 's largest amount of oxide ceramic material. However, due to the high melting point of 2050 DEG C of alumina, alumina ceramic sintering temperature leads to higher (see Table 1 in the standard, so that the sintering temperature ) alumina ceramic manufacture require the use of high-temperature heating body or a high quality fuel and high-level refractory material for furnace and kiln, which to some extent, it limits the production and the more widespread application. Therefore, lower alumina ceramic sintering temperature, reduce energy consumption, shortening the firing cycle, reduce the loss of furnace and kiln, thereby reducing the production cost, has been a business concern and important issues need to be resolved.At present, on alumina ceramics low temperature sintering technology research work has very extensive and in-depth, from 75 to 99 porcelain porcelain of systematic research, has achieved remarkable results. The watch is realized all kinds of alumina ceramics sintered at low temperature condition.Table of low temperature sintering of alumina ceramics of the mechanical and electrical properties have reached the corresponding national standards or porcelain, alumina porcelain in some technical standards more than high aluminum porcelain GB, such as the CAS Shanghai Institute of silicate of 1360 DEG C firing 85 porcelain, the bending strength of more than 99%Al2O3 ceramic GB, the electric property is better than 95%Al2O3 porcelain GB; Al2O3 content are respectively 90% and 95% of the low-temperature sintered ceramics, its mechanical properties are better than the 95 porcelain and porcelain 99 gb.Looking at the current all kinds of alumina ceramics low temperature sintering technology, Baconian rise, mainly from the processing of raw materials, formulation design and firing technology from three aspects to take measures respectively, are summarized below.One, by raising the Al2O3 powder fineness and activity decreased porcelain sintering temperature.Compared with the lump, powder has a large specific surface area, which is outside of the powder work results. Using mechanical or chemical action preparation powder when consumed by mechanical or chemical energy, part of the surface energy and stored as a powder, in addition, in powder preparation process, can cause the powder surface and internal appear all sorts of lattice defects, so that the lattice activation. For these reasons, the powder has high surface free energy. The surface of powder which can be sintered intrinsic motivation. Therefore, Al2O3 powder particles finer and finer, the higher the degree of activation, powder more easily sintering, sintering temperature is low. In the alumina sintering technology, the use of highly active easily sintered Al2O3 powder as raw materials is one of important steps, so the powder preparation technology of low temperature sintering of ceramics technology become a basic link.At present, the preparation of ultrafine activated easily sintered Al2O3 powder method is divided into two categories, one category is mechanical method, another kind is the chemical method. Mechanical method is to use external mechanical force to make Al2O3 powder particle refinement, commonly used grinding process with milling and crushing, vibration mill, sand mill, airflow grinding etc.. Through the mechanical crushing method to improve powder specific surface area, though it is effective, but it has some limits, usually only the powder average particle size as small as 1 m or more detailed, and the particle size distribution range is wide, easy to impurities. In recent years, wet chemical method of manufacturing ultrafine high purity Al2O3 powder development is rapidder, is one of the more mature is the sol - gel method. The sol is highly stable, and can be a variety of metal ions is uniform, stable distribution in the colloid, by further dehydration to form homogeneous gel ( amorphous ), after appropriate treatment can obtain extremely active ultrafine powder mixed oxides or uniform solid solution. At present it has roughly the following 3 kinds of technological process. ( 1) formed of metal oxygen organic complexes, hydrolysis and condensation synthesis sol hydroxy containing three dimensional structure of polymer and sol gel - low temperature evaporation and dehydration is calcined into active oxide powder. ( 2) containing different metal ions and organic acid salt solution glue mixing into solution, sol gel, evaporation and dehydration of calcined into powder. ( 3) containing different metal ions by direct quenching, deposition or heated into a gel, low temperature calcined into powder. Wet chemical synthesis of Al2O3 powder particle size can be achieved nanometer particle size, narrow distribution range, high chemical purity, crystal defects. Therefore chemical powder surface energy and activity than mechanical powder is much higher. The ultrafine Al2O3 powder as raw materials not only can reduce alumina sintering temperature ( 150 degrees - 300 degrees C can be reduced, but also can obtain microcrystalline ) high strength high aluminum porcelain materials. Table two is the Japanese Sumitomo Chemical Company Limited production of sintered Al2O3 powder food chemical index.In addition, some experts recommend the following three kinds of ultrafine Al2O3 powder preparation method, for reference purposes only: ( 1) the ( NH4 ) SO4Al2 ( SO4 ) 3 2H2O ( MgCO3 ) and 4Mg ( OH ) 2 5H2O mixed, heated to 1200 DEG C decomposition, can be obtained with MgO 99% purity, particle size of 0. From 2 to 0. 5 u m alpha Al2O3 superfine powder. ( 2) two acetic acid anhydrous aluminum heating to 1200 deg.c for 3 hours or more, can obtain a particle size of less than 0 . 5 u m alpha Al2O3 superfine powder. ( 3) the iron tube ball, wet grinding hundreds of hours, slurry heating pickling iron removal, flotation, repeated several times, can be prepared from a size 0 . 3 - 0 . 5 u m alpha Al2O3 superfine powder.Two, through the ceramic composition design dopant lowers porcelain sintering temperatureAlumina ceramic sintering temperature mainly by its chemical composition and the content of Al2O3 in the decision, the higher Al2O3 content, the ceramic sintering temperature is high, in addition, also with porcelain composition system, the composition and additives on the type. For example, in the Al2O3 content is very, CaOAl2O3SiO2 Al2O3 porcelain than MgOAl2O3SiO2 system ceramic materials low sintering temperature, the mass production of CaOMgOAl2O3SiO2 system porcelain, for it has the advantages of low sintering temperature and good performance, should control its SiO2 / CaO is 1. 6 ~ 0. 6., MgO content does not exceed the flux oxide total 1 / 3, at the same time, introduced in the formula of small amounts of La2O3, Y2O3, Cr2O3, MnO, TiO2, ZrO2, Ta2O3 oxide can further reduce the sintering temperature, improve the porcelain body of the microstructure and properties of. Therefore, in ensuring the porcelain body meet product use and technical requirements under the premise, we can through the formulation design, reasonable choice of porcelain system, adding proper sintering additives, so that the sintering temperature of alumina is reduced as much as possible.At present in the formulation design of adding various additives, according to its promotion of alumina ceramics sintering mechanism is different, they can be divided to form new phase or solid solution additive and produces liquid additives two categories.In 1, and Al2O3 to form a new phase or solid solution additive.The additives are alumina lattice constant phase near the oxide, such as TiO2, Cr2O3, Fe2O3, MnO2 etc, during sintering, these additives can with Al2O3 to form solid solution, the solid solution or for mixing solid solution ( such as Ti4 replacement when Al3 ), or as a limited solid solution body, or as a continuous solid solution ( such as Cr2O3 and Al2O3 formed ), they can activate the lattice ( TI4, Al3 ionic radius difference caused by forming a hole or migration of atoms ), ( 3TiO2, AbO3 3Tia1Va160 ) and so that the lattice distortion, the action of the Al2O3 easy crystallization and sintering of ceramics. For example, adding 0 . 5 ~ 1 . 0% TiO2, can make the ceramic sintering temperature decreased from 150 to 200 DEG c.. With solid phase sintering based high alumina porcelain often uses this kind of additives, such as a black alumina ceramic formula follows ( wt% ): Al2O3 91, CoO 0 . 5, MnO2 3 . 7, Cr2O3 2 . 1, SiO2 0 . 4, TiO2 2 . 0, V2O3 0 . 3, the porcelain in the 1350 temperature insulation 2 hours firing.This kind of additive to promote the role of alumina ceramic sintering has certain regularity : 1 can be formed between Al2O3 limited solid solution additive is formed of continuous solid solution of the cooling effect of the additive is greater; the variable valency ion additives than changeless value of additive effect; the cationic charge much, electrovalency is tall the cooling effect of the additives of greater. Note that, because this kind of additives is in lack of liquid phase sintering conditions ( heavy crystallization sintering ), so the intracrystalline porosity is difficult to fill, poor air tightness, and electrical performance to drop more, to be considered in formulation design.2, the formation of liquid phase sintering additives.This kind of additive chemical composition are mainly SiO2, CaO, MgO, SrO, BaO, they can with other components in the firing process of the formation of two yuan, three yuan or a plurality of eutectic. As a result of liquid phase formation temperature is low, thus greatly reducing the alumina ceramic sintering temperature. When there is a considerable amount (about 12% ) of the liquid, solid particles in liquid phase and solid phase particles have certain solubility can be liquid wetting, its promote sintering effect is obvious. The mechanism is relatively solid liquid surface wettability and surface tension of the solid particles, both close to and fill the pores. In addition, the sintering process by small defective crystal surface activity, therefore in the liquid phase solubility than larger crystals of the much larger. Thus, sintering process and crystal growing, porosity decreases, appeared heavy crystallization. In order to prevent recrystallization grain too grown up, affect the mechanical properties of ceramics, in the formula design should be considered in selection of some of the grain increase without influence or even can inhibit grain increased additives, such as MgO, CuO and NiO etc..At present, in the liquid phase sintering of Al2O3 ceramic composition, sintering additives can adopt the following 3 materials form to join. The natural mineral form join. This kind of mineral raw materials mainly include: kaolin, bentonite clay mine. Quartz, talc, magnesite, dolomite, calcite and so on, they are the introduction of SiO2, MgO, CaO and other chemical constituents. Formula of kaolin and other clay minerals are used, in addition to meeting the porcelain body chemical composition requirements, more can improve the blank forming performance. This form of adding additives for Al2O3 content below 90% of aluminous porcelain ingredients, such as a low temperature sintering of 75 porcelain formula as follows ( wt% ): Al2O3 65, 24, calcined kaolin bentonite 2, BaCO3 4, 3, 2 talc calcite.The synthetic additives, to form join. It is in the CaOAl2O3SiO2, MgOAl2O3SiO2 CaOMgOAl2O3SiO2, three yuan, four yuan or other phase diagram in to find the lowest eutectic composition, advance in points CaO, MgO, SiO2 component, Al2O3 desired compounds were first ingredients, through ball milling, calcined made eutectic, namely" artificial synthesis additive", then according to a certain ratio of artificial synthetic additives and Al2O3 powder second ingredients, to meet the requirements of chemical composition and properties of alumina ceramics. The method has high purity, mainly used to reduce the chemical composition of accurate, high performance requirements of high aluminum porcelain sintering temperature, disadvantage is the complicated process, high energy consumption, product cost is high, only in exceptional cases by.The chemical raw material to form join. In the ingredients, directly to the various chemical raw materials as additive and Al2O3 powder with a complete ingredients, various sintering additives composition ratio remains the reference professional phase diagram in lowest eutectic point composition to set. Production practice proves, this method not only with artificial synthetic additive method has the same cooling effect, but also greatly simplifies the process, regardless of formulation design, ingredients and process are better than synthetic additive method is simple, but also more easily than the natural mineral form of porcelain, stable performance, energy-saving benefit. In practical production, from reduce cost and blank forming performance reasons, natural mineral raw materials and chemical raw materials are often used at the same time. For example, a sintered at low temperature (1500 degrees C x 2H ) high aluminum porcelain formula follows ( wt% ); alpha 93, Suzhou 3, Al2O3 soil burned bone stone 2, CaCO3 1 . 5, BaCO3 0 . 5, and ZrO2, CeO2, La2O3 2%.Three, using a special firing process to reduce porcelain sintering temperatureSintered by hot pressing process, in the billet heating and pressurizing sintering, so only by diffusion mass transfer to complete, the plastic flow plays an important role, blank sintering temperature than normal pressure sintering is much lower, thus reducing Al2O3 sintering is one of the important techniques of ceramic sintering temperature. The hot pressing sintering method with pressure sintering and hot isostatic pressing sintering method ( HIP ) two. The HIP method can make the body be isotropic pressure, the microstructure of ceramics sintering method is more uniform than pressure. Alumina porcelain, if under ordinary sinter must burn to high temperature more than 1800 DEG C, pressing 20MPa sintering, at about 1000 DEG C lower temperature has been densified.Hot pressing sintering technology not only reduce alumina sintering temperature, but also can restrain the grain growth, to obtain high strength dense microcrystalline alumina ceramic, especially for transparent alumina ceramic and porcelain sintered corundum ceramics.In addition, because the alumina sintering process with anion diffusion rate, and reducing atmosphere in favor of anion vacancies increases, can promote the sintering. Therefore, vacuum sintering, a hydrogen atmosphere sintering alumina porcelain sintered at low temperature is an effective auxiliary method.In production practice, in order to obtain the best comprehensive economic benefits, the fever techniques often used in conjunction, adding sintering additive method compared with other methods, has the advantages of low cost, good effect, simple process and practical characteristics. In the aluminum porcelain, high-alumina corundum porcelain production is widely used. In addition, from the material point of view, by doping modification technology, greatly improve the mechanical properties of alumina ceramic, porcelain body with low Al2O3 content instead of high content of Al2O3 of porcelain body, also is the enterprise commonly used to reduce the sintering temperature of alumina ceramic products is an effective technical means. For example, in the material properties to meet the product requirements, use 85 instead of 90 or 95 porcelain porcelain porcelain, 90 porcelain, 95 porcelain, 99 porcelain instead is feasible.Although the alumina ceramic fever technology has achieved good economic benefit, but still has the potential to be excavated, at present there are still some products, from the special properties of materials requirements and under the condition of high temperature device size stability considerations, still using high temperature sintering, how will this kind of product sintering temperature also falls, is the future of porcelain body doping such low fever technical direction.