Silicon nitride impellers are better than graphite rotor.
STA sialon silicon nitride advanced ceramic impellers which are used in the Chemical & Process Industries often for mixing or stirring highly corrosive chemicals and abrasive slurries.
Traditionally, impellers have been made from metal or plastic coated metals. These suffer badly from wear, thus contaminating the chemical, which in clean environments is unacceptable. Also, corrosion, particularly for metallic impellers, also contaminates the chemical. This wear and corrosion results in often short lifetimes for these impellers.
Sialons are alloys of silicon nitride and are characterised by excellent mechanical properties, and thermal and chemical stability. Syalon 101 ceramic impellers possess excellent corrosion resistance and wear resistance. For example, Silicon nitride impeller is resistant to corrosion by many acids, such as boiling hydrochloric and sulphuric acid, and alkaline materials, such as sodium hydroxide. This chemical stability, combined with high strength, hardness and toughness make Silicon nitride impeller an ideal material for many demanding chemical applications.
Silicon nitride ceramic material with high thermal stability ,antioxidant ability,and product size excellent performance. Reaction bonded silicon nitride is made by direct nitridation of a compacted silicon powder, and because of the difficulty of ensuring complete reaction; it is hard to achieve a high component density. Usual densities are in the range 2.3 – 2.5g/cm3 compared with 3.29g/cm3 for gas pressured sintered silicon nitride. The higher density gives the HPSN, SSN & GPS-SSN materials better physical properties and means they are used in more demanding applications at very high temperature, especially for non-ferrous molten metal handling and thermocouple sheaths. The nitridation produces only a small volume change, which means that RBSN components do not need to be machined after fabrication and complex near net shapes can be produced in a single process stage.Key PropertiesApplications exploit the following properties of silicon nitridelow densityhigh temperature strengthsuperior thermal shock resistanceexcellent wear resistancegood fracture toughnessmechanical fatigue and creep resistanceExcellent non-wetting property with good oxidation resistance
SSN GPS-SSN HPSN RBSN
3.28 3.30 3.23 2.5
Young’s Modulus (GPa)
285 320 315 189
Bend Strength (MPa)
675 750 850 440
Fracture Toughness K1c (MPa.m0.5)
6 7 8 2.5
16 16 16 7.2
Thermal Expansion Coefficient (x 10-6/°C)
3.2 3.2 3.2 3.2
Thermal Conductivity (W/m.K)
25 30 30 14
Maximum Temperature (°C) for applicationDielectric ConstantAbrasive Wear resistance Parameter
1150 1150 1150 11009 9 9 7.51110 1130 1120 360
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