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Comparison of zirconia, magnesia and alumina ceramics
Zirconium oxide ceramics have the advantages of high hardness, good wear resistance, high toughness, low friction coefficient and good corrosion resistance. They are widely used in mechanical seals, ball milling media, cutting tools, ceramic bearings, automotive engine parts, paper machines. Dehydration equipment, etc. The wear resistance of zirconia ceramics is 15 times that of alumina ceramics. The friction coefficient of zirconia ceramics is only 1/2 of that of alumina ceramics, and the friction coefficient of alumina ceramics itself is very low. The density of zirconia ceramics is higher than that of alumina ceramics. The density of alumina ceramics is 3.5, the density of zirconia ceramics is 6, and the texture is finer. After grinding, the surface finish is higher, up to ▽9 or more. Mirror-like, extremely smooth, with a lower coefficient of friction. The surface finish is higher, mirror-like, extremely smooth, and the zirconia ceramic has excellent toughness, which overcomes the inherent brittleness of the ceramic itself and has higher wear resistance. The ceramic is mainly composed of magnesium oxide. It belongs to cubic crystal system and has NaCl structure. Pure magnesium oxide has a melting point of 2800 ° C ± 13 ° C. It has a Mohs hardness of 6, and its tensile strength, compressive strength and flexural strength are much lower than that of sintered Al2O3, and its high temperature strength is also low. MgO is a good insulator with a resistivity of >1014 Ω·cm at room temperature, and the resistivity decreases sharply with increasing temperature. Magnesium oxide ceramic is a typical alkaline refractory material, which can work stably to 2400 ° C under oxidizing atmosphere or nitrogen protection; in the reducing atmosphere, MgO will decompose, volatilize in the form of magnesium metal, and start to volatilize in a vacuum at 1600 ° C; Metals such as Fe, Zn, Pb, Cu, and M do not have a reducing effect on it. MgO ceramics can be used as a bismuth for smelting metals, and are also suitable for smelting high-purity uranium and plutonium in the atomic energy industry; they can also be used as thermocouple protection sleeves. It uses the nature of electromagnetic waves to pass through, and acts as a radome and transmission window material for infrared radiation. Alumina ceramic materials have excellent insulation properties, low frequency loss and high frequency insulation. Alumina ceramics are non-flammable, stainless, strong and not easily damaged, and have excellent properties unmatched by other organic materials and metal materials. The wear resistance of alumina ceramics is the same as that of corundum, reaching a Mohs hardness of nine grades, and the wear resistance is comparable to that of superhard alloys. The heat resistance of alumina ceramics has the characteristics of small thermal expansion coefficient, large mechanical strength and good thermal conductivity. Alumina ceramics are characterized by chemical resistance and molten metal. Alumina ceramic mechanical parts have been used in the chemical industry earlier, and have been greatly developed over the years, especially acid-resistant pumps, valves and other components, often used in the hydrochloric acid, sulfuric acid, nitric acid industries. Modified alumina ceramics are likely to be used in gas turbines and engines; plasma sprayed alumina is used on a variety of machine surfaces. It can improve the working temperature of the heat machine, save the strategic materials, avoid the environmental pollution of the zirconia ceramic ball valve product structure characteristics ◆ Anti-erosion and wear resistance - the ball, the valve seat and the inner lining are all made of zirconia structural ceramic material, Rockwell hardness Up to HRA87, it can withstand the erosion of high-speed fluids and hard-particle media. Excellent wear resistance. ◆ Strong anti-corrosion ability - Tested by the Institute of Metal Corrosion and Protection of the Chinese Academy of Sciences, in addition to glass solution and hydrofluoric acid, zirconia ceramic materials have excellent corrosion resistance. ◆Long service life - Through the static pressure life test of the Hefei General Machinery Department, the switch still does not leak after 10,000 times. Engineering ceramics, also known as structural ceramics, are essentially different from ordinary ceramics. The ceramic material used on the valve is mainly TZP. Its raw material is the raw material of zirconium gemstone. After spraying granulation, isostatic pressing, high temperature sintering and precision processing, the "brittleness" of ceramics is greatly improved, and its toughness and strength are obtained. Greatly improved, the industry called it "ceramic steel." TZP ceramics not only have high toughness, high strength, high hardness, high wear resistance and high corrosion resistance, but also have good self-lubricating properties, low thermal conductivity and excellent surface finish (Ra up to 0.01um). It is an excellent replacement material for valve metal materials.