MoSi2 molybdenum disilicide heater

Multiple models of MoSi2 heaters manufactured according to customer requirements

MoSi2  molybdenum disilicide heater (1700-1800 °C)

Disilicide-molybdenum electric heating element is a kind of resistive heating element made of molybdenum disilicide based on high temperature resistance and oxidation resistance. When used in a high-temperature oxidizing atmosphere, like other Si-based high-temperature resistant materials, the surface of MoSi2 will quickly form a layer of bright and dense quartz glass film (SiO2) at high temperature and oxygen atmosphere, which can protect the inner layer of  disilicide molybdenum resistance from further oxidation,  So the element  molybdenum silicon resistance has a unique resistance to high-temperature oxidation.  

The resistivity of MoSi2 increases rapidly as temperature increases with increasing temperature to a maximum operating temperature of approximately 1700°C in an oxidizing atmosphere. Under normal circumstances, the strength of the element does not change with the duration of use, so old and new disilicide molybdenum heating elements can be mixed.

According to the structure, working atmosphere and temperature of the heating equipment device, the correct selection of the surface load of the electric heating element is the key to the service life  of  molybdenum silicon resistor. 

Physical and chemical properties

1.Density: 5.6~5.8g/cm3

2.Bending strength: 20MPa (20°C).

3.Vickers hardness (HV): 570kg/mm2

4.Porosity: 0.5~2.0%.

5.Water absorption: 0.5%.

6.Thermal elongation: 4%.

7.Emissivity: 0.7~0.8 (800~2000°C).

Product Applications

Disilicide molybdenum electric heating element products are widely used in metallurgy, steelmaking, glass, ceramics, refractories, crystals, electronic components, semiconductor materials and other fields, especially for the production of high-performance precision ceramics, high-grade intraocular crystals, precision structural cermets, glass fibers, optical fibers and high-quality alloy steel. 

 Molybdenum silicon heater is a non-metallic electric heating element, which is made of high-purity green hexagonal silicon carbide as the main raw material, recrystallized at a high temperature of 2200°C, the normal use temperature can reach 1450°C, and under reasonable use conditions, it can be used continuously for more than 3000 hours and is used in the air without any protective atmosphere. It is suitable for all types of electric ovens. 

MoSi2 heaters have high oxidation resistance, and a dense protective layer of SIO2 quartz is formed on the surface of the original to prevent MOSI2 from continuing to oxidize in a high-temperature atmosphere. When the protective layer of SIO2 with a temperature above 1700 degrees and a melting point of 1710 degrees melts, SIO2 melts into droplets due to surface tension and loses its protective effect. The SIO2 protective layer regenerates when the element is still used in an oxidizing atmosphere. 

Application of MoSi2 heaters

Due to the high temperature of disilicide molybdenum heater,  it has the characteristics of high temperature resistance, oxidation resistance, corrosion resistance, fast heating, long service life, small high-temperature deformation, and convenient installation and maintenance. It has good chemical stability. 

If combined with an automatic power supply system, it can not only get an accurate constant temperature, but also can automatically adjust the temperature according to the curve and the actual needs of the production process. Now it has been widely used in machinery, metallurgy, light chemistry, ceramics, semiconductors, analysis and testing, scientific research and other fields, and has become an electric heating element for various electric furnaces tunnel furnaces, roller furnaces, glass furnaces, vacuum furnaces, muffle furnaces, smelting furnaces and all kinds of heating equipment,  Using molybdenum silicon resistors for heating is convenient, safe, and reliable. 

Installation

The  disilicide-molybdenum strength softens a little at high temperature (more than 1500 degrees), hard and brittle at low temperature, in order to avoid stress during temperature change, which favors the thermal expansion and contraction of the component, it is better to use the installation method of free vertical suspension. It is also more convenient to disassemble and replace the lifting elements, and it is not necessary to wait for the oven to cool down, but can be hot-swapped. 

The following steps should be taken into account  when hanging  silicon-molybdenum resistors:

1. The furnace lining material should be corundum brick, and its mass fraction of Fe2O3 should be less than 1%, as it interacts with the protective film to form fusible silicate, thus accelerating the destruction of the element. 

2. The hot furnace gas escaping from the cold end will not only increase the heat loss of the furnace, but also burn the conductive tape mandrel and lead clamp, so it is better to use an asbestos mandrel. 

3. Because  disilicide-molybdenum strength is a brittle material, the bending strength is low, and it cannot withstand impact, protective measures should be taken during the installation process to prevent breakage. When connecting the conductive belt, the asbestos mandrel (or porcelain mandrel)  must first be installed and the force must not be too great when clamping. 

4. Load the  disilicide-molybdenum heater into the plug brick, in order to avoid the mechanical stress caused by loading and unloading, the plug brick should be made of a separate brick made of foam corundum brick. 

5. Insert the cap brick filled  with  silicon and molybdenum heater into the prepared space at the top of the kiln,and the plug brick should protrude from the top of the kiln so that it is easy to disassemble. 

6. Connect the conductive tape to the prepared connection bracket, but avoid conductive tape tension and unnatural twisting mechanical stress. 

7. In order to prevent the  disilicide -molybdenum strength from sinking and deforming due to the thermal expansion and cold shrinkage of the asbestos mandrel, the refractory mud mixed with water glass can be coated on the gasket to fix it firmly.  

8. When hoisting, the cone junction of the heating part is about 25mm-30mm from the oven wall, the cold end should be exposed 75mm outside the oven ceiling, and the bottom end of the heating part should not be less than 50mm from the bottom of the oven. 

9. The spacing of the  disilicide -molybdenum resistors in the furnace should not be less than the center spacing of the element itself.  

10. When hoisting, it is necessary to pay attention to the gravity balance of the two cold ends and the wiring part, otherwise it will cause the heating part to bend and deform.