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102.jpg (3709 bytes)  Molybdenum Disilicide Heating Element Type MOSI2


ZIRCAR Molybdenum Disilicide Heating Element Type MOSI2 is an electric element principally containing molybdenum disilicide for use in industrial and laboratory furnaces. Elements fabricated of this unique material support high power densities on their surface (e.g. 20 W/cm of element surface area at an element temperature of 1700C, 14 W/cm at  1800C and 5 W/cm at 1900C), can be cycled rapidly, and  provide up to 10KVA / sq. ft. power density in rapid cycle and continuous furnace applications. 3 grades are available with maximum element temperatures of 1700C, 1800C and 1900C in air.

The element's "U" shaped heating shanks are supported by larger non-heating terminals. Aluminized ends are provided for positive connection to electrical straps.  

Made of molybdenum disilicide based cermets MOSI2 heating elements withstand oxidation at very high temperatures. Their surface is  protected by of a thin layer of silica glass that forms when they are exposed to oxygen at elevated temperatures. Although the base cermet is consumed in the formation of the silica "skin" the rate of decomposition is minimal. They provide long performance at elevated temperatures while delivering high power. 


Element resistance increases slowly over time as the cermet decomposes and the diameter of the heating shank is reduced. MOSI2 heating elements do not exhibit the rapid aging of silicon carbide or metallic iron-chrome-aluminum alloy elements.  MOSI2 heating elements operate at the highest temperatures and give longest life in oxidizing atmospheres. They can operate in other atmospheres but have reduced maximum temperatures. 




Tensile Strength, N mm2, 1800 K

> 190 

Bending Strength, N mm2 ,300 K

> 350

Impact Strength, N/mm2, 300 K


Hardness, mohs, 300 K


Density, g/cm3

5..5 - 5.6

Porosity, %




Resistivity, ohm mm2/m


Coefficient of linear expansion, 10-6/K, 300 K



Resistivity vs. Element Temperature for Grade 1700 and 1800 Elements Maximum Surface Load vs. Furnace Temperature for Grade 1700 (red) and 1800 (black) Elements.







1700 (3092)

1800 (3272)



1600 (2912)

1700 (3092)

1800 (3270)

     Argon, Helium

1600 (2912)

1700 (3092)

1800 (3270)


     *Temperature is dependent on dew point. 




    Nitrogen/Hydrogen   95/5%*




    (e.g. 10% CO, 5% CO, 15% H)

1600 (2912)

1700 (3092)

1700 (3092)

    (e.g. 40% H, 20% CO)

1400 (2552)

1450 (2642)

1450 (2642)

    Cracked and partially burnt  ammonia (~8%H )

1400 (2552)

1450 (2642)

1400 (2552)


Heating source in furnaces and industrial process equipment operating to 1800C (3272F).

Elements in production, laboratory and research furnaces for annealing, heat treating,

forging, ceramic and metal sintering, glass and metal melting, holding & refining, testing and gem enhancement.


For highest temperature and power performance plus longest life MOSI2 Heating Elements  should be installed in a free hanging manner. The elements should be positioned far enough away from furnace walls to allow for their natural movement as they deflect due to relief of internal stress and bowing & twisting due to electromagnetic interaction with neighboring elements. The use of  ZIRCAR furnace accessories including Type H Heating Element Holders and Heating Element Straps to support and electrically connect the element terminal shanks is recommended. At low temperatures MOSI2 heating elements are brittle and should be handled with care. At temperatures above 1200C they become ductile and sag under their own weight and assume a "Coke Bottle" shape as the sections of the element's heated length repel each other. 

MOSI2 Heating Elements with bent terminals can be installed through the side walls of a furnace lining. Type K Heating Element Holders should be used to secure the terminals. When the elements are installed in a manner where they are directly supported by refractories or touch insulation, they should be installed in a manner where they are free to move. When this application method is used their maximum temperature is lowered as reactions with the silica "skin" and the development of stresses causing catastrophic failure may occur.

MOSI2 heating elements exhibit a significant positive temperature coefficient of resistivity. As the element temperature increases so does its electrical resistance.  Typically a phase angle fired SCR with current limit capability is used to control the high currents established when the element is first fired. After warming up, it's resistance increases and limits the flow of current by itself. see the Furnace Module User's Guide for additional information about the electrical specifications for custom heating elements, how to electrically connect elements and the components required to build a furnace temperature controller.

Freely suspended MOSI2 Heating Elements installed around perimeter in 1700C bottom loading laboratory box furnace.

3/6 mm MOSI2 Heating Elements in octagonal  bottom loading box furnace used in multi-layer capacitor production. 6/12 mm MOSI2 Heating Elements with right angle bend in Terminal section after use in 1800C crucible furnace.
3/6 mm MOSI2 Heating Elements stapled in split clam shell heating cartridge with insulation assembly for use at 1600C. 6/12 mm MOSI2 Heating Elements in 12 sided bottom loading box furnace used for sintering of powder metal parts. 4/9 mm MOSI2 Heating Elements installed in rapid cycle front loading laboratory box furnace for extended use at 1750C.
6/12 mm MOSI2 Heating Elements showing "Coke Bottle" shape after extended production use at  1700C. 6/12 mm MOSI2 Heating Elements with 45 bend in Terminal section installed in 5  zone vertical  1700C furnace chamber. Interior view showing dense, even heating array of 6/12 mm MOSI2 Heating Elements in 5  zone 1700C furnace chamber.



MOSI2 Heating Elements are described by:

   Grade: 1700, 1800 or 1900

   Diameter: D1/D2, mm/mm

   Heated Length: Le*, in. or mm

   Terminal length: Lu*, in. or mm

   Shank Spacing: A*, in. or mm 

*Specify Le, Lu and A with the same units (e.g. all 3 as in. or mm).



Grade 1800, D1=3mm, D2=6mm, Le=5.5in., Lu=5in., A=.98in.

Specify as: MOSI2, 18-3/6-5.5-5-0.98in.


Grade 1700, D1=6mm, D2=12mm, Le=300mm, Lu=250mm, A=50m

Specify as: MOSI2, 17-6/12-300-250-50mm

Grade 1700 1800 1900
D1/D2 6/12 9/18 3/6 6/12 9/18 3/6 6/12
Le, max in. 25 49 12.5 25 49 12.5 14
Lu, max in. 25 25 12.5 25 25 12.5 14
A, typical mm 50 60 25 50 60 25 50
t, mm 45 75 25 45 75 25 45
n, mm 25 30 15 25 30 15 25




SHIP WT. (lb.)



 MOSI2, 18-3/6-5.50-5.00-0.98in. $202.50 1
 * Note: Prices shown apply to sales within the United States. Contact us for information regarding international commerce.

To place your order, please click the respective "ORDER" button next to the item you wish to purchase. To view your shopping cart click the button to the right. For more info -click here-

Standard Heating Elements are available for immediate shipment from stock.
Custom heating elements are available on request.
MOSI2 Heating Elements are typically produced in an "U" shaped form, but a wide variety of sizes and shapes can be made. Straight dual shank elements are available in the types and variety of sizes listed above. Elements with metric sizes, special size diameters, such as D1/D2 =1.5/3 mm and 12/24 mm and A dimensions  are available. Special shapes such as elements with multiple shanks, bends (e.g. 90, 45, 30, etc.) in their heating and terminal sections plus flat panel and wafer heaters, can be fabricated. The techniques used to produce MOSI2 elements permit the production of an almost unlimited variety of custom element shapes and sizes. Custom shapes include, 90 bends, 45 bends, multi-shank, cylindrical and more. 

Flexible leads attached to 3/6 mm MOSI2 Heating Elements.

3/6 mm elements in semi & full cylinder heating muffles.

Array of MOSI2 Heating Elements with holders and accessories.

2/4 mm MOSI2 Heating Elements used in analytical  apparatus.

Element accessories on a 1700C vertical tube furnace. 

9/18 mm MOSI2 Heating Elements in HR-3 Element Holder.

Please contact us with your special requirements.  We are pleased to contact you if you would like more information or want to discuss custom product availability and pricing.

To Order

Standard elements: order online or specify quantity, item # and description.

Custom "U" shape elements: specify quantity, product type, grade, diameters ( D1/D2), heated length (Le), terminal length (Lu) and shank spacing (A). Specify Le, Lu and A with the same units (e.g. all 3 as inches or mm).

Custom shape elements: specify quantity, product type, grade, and description (by supplying drawings, sketches, written descriptions or material specifications).

Copyright 2007  ZIRCAR Ceramics, Inc.