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SiC Heater Property

SiC Heating Elements Rods

一、Introduction

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:

SiC heating elements tubular different types

Working temperature

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.

SiCheatingelementsrods

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
 Porosity rate <30%  Radiancy 0.85
  • 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 ℃)
0 / / 0.148
300 3.8 / /
400 / / 0.255
600 4.3 14-18 /
800 / / 0.294
900 4.5 / /
1100 / 12-16 /
1200 4.8 / 0.325
1300 / 10-14 /
1500 5.2 / /

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:

SiC Electric property

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:

SiC heating elements surface load

Our recommended surface load:

 Furnace Temp.(℃) 1100 1200 1300 1350 1400 1450
 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 
Vaccum 1204 3.8    
Oxygen 1310 3.8 SiC is oxidized  
Water(different content) 1090-1370 3.1-3.6 Reacting with SiC forms hydrate of Si