Preparation And Properties Research Of Dielectric Ceramic Derived From Pyrophyllite

Pyrophyllite is a kind of clay minerals, crystal structure is a 2:1 type layered aluminum silicate mineral aquifer, its water content in all aluminum silicate mineral in the aquifer at least, relatively stable water content. The chemical structures for the Al2 [Si4O10] (OH)2, the theoretical chemical composition of Al2O3 28.3%, SiO2 66.7%, H2O 5.0%.Pyrophyllite is a wide range of applications, which has drawn more and more concerns in recent years. It's not only because it has many advantageous properties, but also it is valued for its special advantages, such as 1. vast reserves, cost effectiveness and easy acquirement, 2. good insulation, low thermal expansion, 3. higher stability. Therefore, in this experiment to choose the main raw material for the production of pyrophyllite for dielectric ceramics, to explore its development. Pyrophyllite has low hardness, good mechanical processing and easily broken, and higher chemical stability. The stability of crystal structure is higher than the kaolinite . Under high-frequency , the loss of dielectric properties is little. It can be used as material of high - frequency insulation in the radio industry. The crystallization of pyrophyllite with less water, not the total contraction and expansion coefficient smaller, essentially linear in nature, is good material of high quality for dielectric ceramics.In this age of information, our country has focus on the development of integrated, a growing number of the current domestic semiconductor manufacturers have been set up .And the corresponding subsidiary IC products also has a broad prospect. On the electrical performance requirements in which a relatively low substrate materials and packaging materials that are used for semiconductor integrated circuits, such as organic plastics and rubber materials.But such materials is marked as a result of pollution of the environment and non-biodegradable nature, more importantly, plastic and single - thermal properties of crystalline silicon does not match, and water, which limits its use on large-scale integrated circuits.Later they were replaced by alumina ceramics. Ceramics on the market today are mainly this type of alumina-based ceramic. With the development of material technology, the performance so far has yet to give full play to strengths of materials, as a result of the synthesis of raw materials and manufacturing process development, become a high-performance, low-cost materials, and the possibility of practical is growing. And any type of material can not be a single. In the experiment, the dielectric ceramic based pyrophyllite, is produced by the materials from the earth. From its special nature and the modification effect of view, it is possible to achieve the practical us less than the cost of alumina. The pyrophyllite is produced in Inner Mongolia, without expansion and plasticity in the water, absorbent poor and structural stability. So take use of suppression method for the firing of ceramic. Natural non-metallic ores often contain different composition of the impurities, impact the utilization of the product. Therefore ,it is necessary for the structure to analysis components before purification . In order to facilitate the ore in accordance with the different nature of impurities, select the appropriate method of purification, so as to achieve the desired results.After the test ,we found that the original pyrophyllite contains a certain amount of ferrum, which would affect its dielectric properties. Due to the dielectric constant materials and materials of their respective properties and volume fraction of the relevant and in line with a certain degree of increase and the law. Because the dielectric constant of Fe2O3 is 14.2, impacts the whole ceramic dielectric property.In order to avoid impurities in the pyrophyllite impacts properties of ceramics, the experiment need the processes of Fe2O3 removing and preburning. In addition , Fe2O3 removing changes pyrophyllite layered structure to lead-like structure, improved the mechanical properties of ceramics. Because of hydroxyl in pyrophyllite, ceramic structures will be affected and even ceramic cracking in the process of firing. Therefore, the preburning process is significant .About ceramic raw materials, in addition to pyrophyllite after pretreatment, there are BaCO3, kaolin, MgO and SiC. Taking use of their performance, design appropriate formulations for ceramic firing. BaCO3 can improve the dielectric properties ,enhance the stability of ceramic, reduce the air bubbles and prevent signs of aging, kaolin can improve plasticity. Because this experiment does not contain quartz in kaolin , the introduction of impurities is less . MgO is as sintering aids to lower the sintering temperature, to make the scope of sintering wider and it inhibits the grain growth of microcrystalline structure to promote densification of the material, SiC with insulation, low thermal expansion , high thermal conductivity and high mechanical properties, improves the mechanical properties and thermal properties without affecting the ceramic dielectric properties.Papers with high temperature solid state reaction method using natural mineral pyrophyllite, kaolin,BaCO3, MgO and SiC as raw materials, through the rational design of formulations, raw material pre-processing, ball milling, such as hybrid and high-temperature sintering process, in 1100 ~ 1150℃quality pyrophyllite synthesized dielectric ceramics, the performance of the test analysis, the following conclusions:1. Removing Fe2O3 and hydroxyl, such as pretreatment can effectively improve the dielectric properties of ceramics and mechanical properties; the right amount of MgO and BaCO3 can reduce the sintering temperature of ceramics and improve the thermal expansion of ceramics; and the introduction of SiC can increase the strength of ceramics. 2. Through the tests, we can find that the dielectric constant can be maintained at between 2 to 8 (1kHz), dielectric loss is less than 0.01 (1kHz), the water absorption is less than 1% and porosity is about 1%,the coefficient of thermal expansion is 4 ~ 5×10-6K-1, the maximum compressive strength is 200Mpa, the largest bending strength is 132 Mpa.. Basically reached the requirements of dielectric ceramics.3. The optimal prescribe of ceramic is No.Ⅰpyrophyllite 75% ~ 80%, BaCO3 4% ~ 7%, Kaolin 5% ~ 8%, MgO 0.4 % ~ 1%, SiC 9% ~ 10%.4. Optimal conditions for preparation of ceramics is wet milling mixed for 90min, dry under 80℃, dry-pressed molding, sintering in 1100 ~ 1150℃, heat for 2h, cooling with the furnace.