1. Introduction to Sialon ceramics
In the early 1970s, scholars found in the study of Si3N4 additives that in the Si3N4-Al2O3 system, when a large amount of Al2O3 is added, the Si-Al-O-N system is formed. Al2O3's AI and O atoms partially replace Si and N atoms in Si3N4, which effectively promotes the sintering of Si3N4 and forms β-Si3N4 solid solution. The solid solution is called "Silicon Aluminum Oxynitride", and its prefix is "Sialon", which is translated as "Sialon". The chemical formula for this ceramic, called Sialon, can be expressed as Si6-xAlxN8-xOx. Where X is the number of Al atoms replaced by Si atoms.
In addition to Si-Al-O-N systems, there are Mg-Si-Al-O-N systems, Y-Si-Al-O-N systems, and lanthanide metals The system formed by oxides (such as La2O3, Sm2O3, CeO2, etc.) and Si3N4.
The crystal structure of Sialon ceramics belong to hexagonal crystal system like Si3N4. Al2O3 infiltration into Si3N4 does not change the original β-SI3N4 structure, but the lattice constant and other properties vary with the amount of Al2O3 penetration.
2. Manufacturing process of Sialon ceramics
(1) Design Formula
Sialon ceramics should be formulated according to the requirements of product performance. Sialon ceramics are metal oxides and metal nitrides , the Sialon ceramic materials with excellent properties can be obtained by selecting a wide range of solid solution materials and adjusting the composition ratio of solid solution.
(2) Shape
Sialon ceramics can be formed by extrusion, molding, pouring or isostatic forming.
(3) Sintering
Sialon ceramics are usually sintered without pressure or hot pressure, in 1600~1800℃ inert atmosphere sintering, can be obtained Sialon ceramic sinter with approximate theoretical density. Sialon ceramics are usually sintered without pressure or hot pressure, and sintered in an inert atmosphere of 1600~1800℃, the Sialon ceramics with a theoretical density can be obtained.
The manufacturing process of atmospheric sintering Sialon ceramics is to mix Si3N4 powder with appropriate amount of Al203 powder and AIN powder to form the Si6-xAlxN8-xOx main crystal sintered in nitrogen atmosphere at 1700℃. The x in the equation is at β-si3N4 .The number of Si atoms replaced by AI atoms in the cell ranges from 0 to 4.2. The properties of solid solutions vary with their composition and temperature.
Sialon ceramic materials with high performance requirements should be prepared by hot pressing method.
3. Performance and application of Sialon ceramics
(1) performance
Sialon ceramics may reduce or eliminate the glass grain boundary with low melting point and exist in the form of solid solution with excellent properties, it has many excellent properties, such as great strength at high moderate temperature, excellent chemical stability at room temperature and high temperature, and High abrasion resistance, low thermal expansion coefficient, good thermal impact resistance, strong oxidation resistance, and low density, etc.
(2) Applications
Sialon ceramics has many excellent properties, it has a wide range of application prospects in military industry, aerospace industry, machinery industry and electronic industry, etc.
Sialon ceramics has been used in the mechanical industry as bearings, seals, welding tubes and positioning pins. The life of the general locating pin is 7, 000 times, while the Salem location pin can reach 5 million times. The performance of Sialon seals is superior to that of other materials.
It has been used as a split ring for continuous casting, a thermocouple protection bushing, a crystal growing appliance, a crucible, a lower lining for blast furnace, a copper and aluminum tube drawing mandrel, and a die material for rolling, extrusion and die casting.
It also has good high temperature mechanical properties, made into automotive internal combustion engine tappet, running 60000km, only wear 0.75 μm.
Sialon ceramics can also produce transparent ceramics, such as high pressure sodium lamp tube, high temperature infrared thermometer window. In addition, it can be used bioceramics, artificial joints, etc.
Sialon ceramic material
