95 alumina ceramic specific comprehensive properties.

　　I. Electrical properties of 95% alumina

　1. Volumetric resistivity of bulk resistivity insulating material is the ratio of DC electric field strength in the direction of Bulk current to current density at that point. _= EV/jv (_cm). In the formula, EV is the strength of DC electric field and JV is the current density. 95% alumina ceramics are excellent electronic insulating materials with high volume resistivity. According to the national standard GB/T5593-1999, at 100 C, p_is greater than 1 1013_cm; at 300 C, P is greater than 1 1010_cm; and at 500 C, P is greater than 1 1089; In fact, the volume resistivity of 95 ceramics produced in China is 1-2 orders of magnitude higher than that stipulated above. Instruments for measuring volume resistance usually use high resistance meters.

　2. DC breakdown strength of electrical insulating materials refers to the change of DC breakdown strength under the action of external DC electric field, which is mainly caused by the change of internal structure. When the electric field strength reaches a certain value, it will promote the further change of its internal structure and lead to insulation breakdown. According to the national standard GB/T5593-1999, 95% alumina ceramics are tested under DC voltage. When DC voltage is applied to the sample, the sample breakdown occurs. The ratio of the breakdown voltage value to the average thickness of the sample is called DC breakdown strength in KV/mm. The national standard GB/T5593-1999 stipulates that it is larger than 18KV/mm. In fact, we can generally reach 30-40 KV/mm.

　　3. A parameter of dielectric polarization of dielectric constant insulating material under AC electric field is the ratio of capacitance of capacitor filled with some insulating material to capacitor with the same electrode size when vacuum is used as medium. It represents an inherent property of materials. The dielectric constant of 95% alumina ceramics ranges from 9 to 10 when the test frequency is 1 MHz according to the national standard.

　　4. The tangent value of dielectric loss angle indicates that polarization or absorption occurs under the action of alternating current electric field, resulting in electric energy loss, and usually heating occurs on dielectric materials. The magnitude of dielectric loss is expressed by the tangent value of dielectric loss angle. The national standard GB/T5593-1999 stipulates that when the frequency is 1MHz, 95% alumina ceramics meet the requirement of 4 x 10-4.

　　II. THERMAL PROPERTIES OF 95% ALUMINA

　　1. The relative elongation of ceramics with average linear expansion coefficient at elevated unit temperature, i.e. average linear expansion coefficient, is one of the main properties of 95% alumina ceramics. The national standard GB/T5593-1999 stipulates that the test temperature is 20-500 C and a is 6.5*10-6-7.5*10-6/. When the test temperature is 20-800 C, A is 6.5*10-6-8*10-6/. Ceramic parts are usually sealed with metal parts, so the expansion coefficient of ceramic parts is required to match the expansion coefficient of metal materials.

　2. Thermal shock resistance refers to the ability of ceramic materials to withstand rapid cooling and heat. 95% alumina ceramics have good thermal shock resistance and can withstand the test of high temperature, rapid cooling and heat without damage. National Standard GB/T5593-1999 stipulates that 10 ceramic specimens are put into a heating furnace at 800 +10 (?) C for 30 minutes, then taken out and placed on asbestos board, cooled to room temperature naturally, and then put into a heating furnace at 800 (?) C. According to the above stipulations, the specimens are carried out 10 times, and then immersed in magenta solution of 1% concentration for 3 minutes. Wash and dry with tap water and observe the sample under lamp. If all 10 samples have no cracks and cracks, the performance is qualified.

　Mechanical properties of 95% alumina

　Mechanical properties refer to the ability of materials to be damaged under mechanical forces. Usually according to the direction of force and the point of force, the tensile strength, flexural strength and compressive strength are different. The tensile strength of 95% alumina ceramics is generally more than 160 Mpa, and the sealing strength of 95% alumina ceramics is usually higher than that of other ceramics. There is no technical index of tensile strength and compressive strength of 95% alumina ceramics in national standard GB/T5593-1999. The national standard GB/T5593-1999 stipulates that the flexural strength of 95% alumina ceramics is 280 MPA.

　4. Other Properties of 95% Alumina

　　1. The volume density of 95% alumina ceramics is closely related to the selection of raw materials and the process of making ceramics. According to the national standard GB/T5593-1999, the volume density of 95% alumina ceramics is more than 3.60g/cm3. In fact, the forming method of porcelain is different. The density of 95% alumina ceramics is quite different. Usually, the density is 3.60-3.70 g/cm3 when molding by hot die-casting and grouting. When isostatic pressing is formed, 3.70 g/cm3; gel forming can reach 3.73 g/cm3.

　　2. Air tightness 95% alumina ceramics are used in microwave devices, vacuum switch tubes and so on, which requires high vacuum tightness. According to SJ/T standard of electronic industry, the leakage rate of sealing parts QK is less than 1*10-11Pa.M3/S. In fact, it is stipulated that the leakage rate of ceramics itself should also meet the above standard.

　　3. The chemical stability of 95% alumina ceramics is a characterization of their resistance to various chemical agents. The ability of acid resistance is called acid resistance, and the ability of alkaline resistance is called alkaline resistance. The national standard GB/T5593-1999 stipulates that the sample is placed in 1:9 hydrochloric acid or 10% sodium hydroxide solution, which is heated to 100 C for 1 h. The requirement of acid resistance is Kh < 7mg/cm2, and the requirement of alkali resistance is Kn < 0.2mg/cm2.

　　4. The micro-structure of ceramics refers to the composition, content, distribution, morphology, particle size distribution, uniformity, defects, interphase substances and domain structure of crystalline phases (main and secondary phases), glass phases, vapor phases and grain boundaries. Microstructure is closely related to ceramic manufacturing process, which directly affects the properties of ceramics. It is a research method to improve the quality and process of ceramics.

　　V. Sealing Properties of 95% Alumina Ceramic-Metal

　　95% alumina ceramics, as a kind of structural ceramics, should be sealed with metal to form a component. Especially 95% alumina ceramics used in microwave devices and vacuum development tubes usually take the sealing performance of ceramic-metal as an important index to evaluate. Assessment content: Ceramic-metal sealing performance requires high strength and good air tightness. According to the standard SJ/T "Ceramic Tubes and Shells for Vacuum Switch Tubes", the average sealing strength is a (>90Mpa) when standard porcelain is used for sealing, and a (>90Mpa) when three-point method is used for testing. Gas tightness of seals, helium leakage rate Qk < 1 *10-11 PaM3/S