SiC Heater Property
SiC Heating Elements Rods
Silicon Carbide(SiC) resistant electrical heating elements(also called Silicon Carbide(SiC)heater or Silicon Carbide(SiC)tubular/rods)is used for industrial high temperature furnaces or laboratory muffle furnace/oven
Different types and sizes:
up to 1400℃。The resistance is very important to elements’ life-time.
The resistance of the elements will change along with it’s application temperature,when below 800 degree C.,the resistance decrease when temperture increase;Wheras,>800 degree C.,the resistance increase along with the temperature increase.
二、Physical Properties of SiC heating elements rods
- General physical properties:
|Specific gravity||2.6 ～2.8g/cm³||Bend strength||>300kg|
|Hardness||>9 MOH’S||Tensile strength||>150kg/cm²|
- How the linear expensivity, heat conductivity and specific heat change with temperature:
|Temperature (℃)||Linear expansion coefficient (10-6m/℃)||Heat conductivity (Kcal/M hr ℃)||Specific heat (calg ℃)|
三、Chemical Properties of SiC heating elements rods
Antioxidant of SiC Heating Elements
The element start to being oxidized when heat to 800℃ in air atmosphere, when temperature up to 1000-1300℃, and a protect film will be generated in the surface of hot zone,when temperature up to 1270℃,SiO2 film will be crystallized into cristobalite .The protect film get into thicker when the temperature increase which makes the resistance increase and the elements’ life time shortened.
Though the element oxidized very slowly in heating processing, it also will make the resistance increased along with the working time continues, this phenomena called component aging, in order to slow aging speed,Microsupertech use special technique to coated elements surface with a kind of protect film, which make antioxidant stronger and then increase the SiC elements’ life time.
The alkali and alkaline metal oxide effect on elements
The alkali & alkaline metal oxide will react with SiC at about 1300℃ and generate silicate, which calls alkali-chemical corrosion, and can influence the SiC elements’ heating effect.
Melting metal effect on SiC elements
Some metals, such as Cobalt, Nickel, Chrome and so on, can corrade the SiC element when they are in melting state in high temperature,it also affects SiC elements’life time.
四、Electric property of SiC heating element
SiC heating elements rods have large resistance unit area .When it is heated in air and the surface temperature of the hot zone reaches 1050℃, its unit resistance is 600-1400Ω*mm²/m and its resistance changes with temperature,please see below drawing for details:
Surface load is very important for the life-time of SiC heating elements,so that a siutable surface laod choosing takes a key part when using the elements.
Here below shows the relation between furnace temperature,elements temperature,surface load,under elements fully radiation:
Our recommended surface load:
|Surface Load of Hot Zone（w/cm²)||<17||<13||<9||<7||<5||<4|
Surface load recommanded under different atmosphere:
|Atmosphere||Furnance Temp.(℃）||Surface Load (w/cm²)||Effect to the Element||Solution|
|Ammonia||1290||3.8||The chemical reaction with SiC generates methane which can reduce SiO2 protective film||Dew Point activation|
|CO2||1450||3.1||Corroding SiC||Protecting with quartz|
|18% CO||1500||4||No effect|
|20% CO||1370||3.8||Absorbing grains affects SiO2 pretective film|
|Halogen||704||3.8||Corroding SiC to reduce SiO2 protective film||Protecting with quartz|
|Hydrocarbon||1310||3.1||Absorbing C grains cause hot pollution||Filling with enough air|
|Hydrogen||1290||3.1||The chemical reaction with SiC generates methane which can reduce SiO2 protective film||Dew Point activation|
|Methane||1370||3.1||Absorbing C grains cause hot pollution|
|N||1370||3.1||React with SiC forms SIN insulating layer|
|Na||1310||3.8||Corroding SiC||Protecting with quartz|
|SO2||1310||3.8||Corroding SiC||Protecting with quartz|
|Oxygen||1310||3.8||SiC is oxidized|
|Water(different content)||1090-1370||3.1-3.6||Reacting with SiC forms hydrate of Si|