Aluminium oxide mainly has three kinds of α-Al2O3, β-Al2O3 andγ-Al2O3. The structure of α-Al2O3 is the most closely and stable on high temperature. It also has low activity and good mechanical and electrical performance. So aluminium oxide ceramic is based on α-Al2O3.
Aluminium oxide has many diferent performances and uses because of diferent contents , such as:
——High mechanical strength, can be made of ceramic and other mechanical components.
——High resistivity and good electrical insulation properties, can be made of substrate, spark plug, socket, circuit, etc.
——High hardness and excellent abtasion resistance, can be used to make cutting tools, grinding wheels, wire drawing dies, bearings, etc.
——High melting point and corrosion resistance, can be used to make refractories, furnace tubes, hollow balls, glass wire drawing crucibles, etc.
——Excellent chemical stability and no reaction with composite sulfides, phosphides, chlorides and sulfuric acid, hydrochloric acid,etc. can be made into pure metal and single crystal growth of the crucibles, human joints, artificial bones, etc.
——Optical properties, can be made into transparent materials (transparent Al2O3 ceramics).
——Ionic conductivity, can be used as solar cell materials and battery materials.
Zirconium oxide (ZrO2) ceramic has been developed recently. And it is a very important structural ceramics only after aluminium oxide ceramic. ZrO2 ceramics is very difficult to be produced from pure zirconium oxide. Because the volume of ZrO2 can change and cause cracking with phase transformation. But by adding oxide (Y2O3,CaO,MgO, etc), ZrO2 can be made into stable cubic or tetragonal ZrO2 without abnormal expansion and contraction. Partially stabilized ZrO2 can be obtained by reducing 50% stabilizers (Y2O3,CaO,MgO,etc). Using stabilized ZrO2 and partially stabilized ZrO2 can produce good performance of ZrO2 ceramics.
Silicon nitride(Si3N4) is remarkable as high temperature engineering materials. France and Britain firstly developed Si3N4 ceramic in 1960s. China, USA, Japan and other countries began to research this area in 1970s. Si3N4 ceramics has a series of characteristics, such as light, hard, high strength, good oxidation resistance and corrosion resistance, high temperature creep, small friction coefficient, low thermal expansion coefficient, etc. Because of these excellent properties, Si3N4 ceramics has been widely used in many industrial fields and has many potential applications.