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NEI's Heating Element Products
Molybdenum Heating Elements
We make Moly heating elements of all sizes and types including:
- Rod, Bar, Strip, Wire, Cable
- New Designs, Replacements, Upgrades, Emergency Repairs
National Element Inc. stocks Pure Molybdenum and other specialty materials in a wide range of popular sizes for:
- Elements
- Hangars
- Connectors
- Terminals
We form, twist, coil, weld, braze, machine, grind Molybdenum components
Design of Moly heating elements, Electrical Specifications, Complete System Design
About Moly Heating Elements
Pure Molybdenum is the classic material for high temperature, or high powered heating elements; Heat furnaces to 1900 °C, (3452 °F); or power elements up to 100 watts per square inch (of element surface area). Moly elements frequently operate trouble free at high temperatures for years. The low vapor pressure of pure Moly allows it to be used in vacuum furnaces. Long life at high temperatures in vacuum is commonly achieved with Moly elements.
Molybdenum is a good conductor of electricity (see Resistivity of Molybdenum at Various Temperatures). Problems at connection points are rare due to Moly's low resistivity.
Moly is strong at high temperatures. It is resistant to sagging and breaking, even at very high temperatures. (Watch out at low temperatures; it may be brittle at room temperature) See Limitations of Moly.
Limitations of Moly Heating Elements:
- Moly reacts rapidly with oxygen, beginning at 250 °C. Therefore, it cannot be used in air. Oxides of Molybdenum vaporize at relatively low temperatures, leaving the material unprotected. The result of heating Moly in air is rapid loss of surface material. Fluffy white or yellowish "parachutes" of re-condensed oxides usually appear in the surrounding cooler areas.
- Moly reacts with Carbon Gases at temperatures of 1200 °C. or higher. Molybdenum carbides form, starting on the outer surface. The result is apparent thickening of the element cross section as Molybdenum carbide grows on the surface. This surface material is a poor conductor of electricity and heat-- often leading to early failure. Such carbide affected elements show increased electrical resistance as the remaining unaffected core material gets thinner.
Good element life for Moly elements requires that they be used in vacuum, or atmospheres containing less than 10 ppm of oxygen, water, CO, CO2, methane, or other gas sources of Oxygen or Carbon. Element designs using thicker sections can last much longer than thin sections, especially if these are present. Also note that methane can be formed from carbon or graphite items in Hydrogen atmospheres if traces of water or Oxygen is present.- Moly reacts with many solid substances at higher temperatures. Design and maintenance of equipment should keep hot Moly elements well clear of contact with ordinary furnace parts, dirt, dust, or any other substances.
Moly itself is the best element hangar material. Ceramics of high density and purity, that are known to be compatible with Moly are also acceptable for supports.
See the Reaction Temperature Chart for more information on Moly reactions with various substances- Molybdenum is frequently brittle at low temperatures. Thicker sections, and any pieces that have been formed or joined may sometimes break easily at room temperatures. Elements, hangars, terminals, and connectors that have once been heated may be very brittle at room temperatures.
Always handle Moly heating elements and parts very carefully; think of them as glass. Generally; used elements are difficult to re-install, or to bend, straighten, weld, etc.- Molybdenum has a very large increase of resistance between room temperature and operating temperatures. About 5 to 1. An electrical system designed for proper operation of Moly elements at high temperature might be overloaded at room temperature. See Resistivity of Molybdenum at Various Temperatures. It is therefore necessary to carefully design and specify the power control system to handle the high startup current. Also, when heating up from room temperature, always begin heating slowly; especially with new, potentially brittle Moly elements.
Pure Molybdenum Reaction Temperatures With Various Substances
GASES: Substance Temp. Description of Reaction Air or O2 : 250°C Slight Oxidation beginning Air or O2 : 600°C Rapid Oxidation Br 800°C Reacts Cl 300°C Reacts CO2 1200°C Oxidation Begins CO 1400°C No Reaction F 20°C Reacts H2 2600°C No Reaction H2S 1200°C MoS forms Hydrocarbons 1100°C Carbide formation begins Hydrocarbons 1300°C Rapid Carburization I 500°C No Reaction N2 1500°C Nitrides begin to form NOx 700°C Oxidation NH3 2500°C No Reaction SO2 700°C Oxidation Steam 700°C Rapid Oxidation
Other Elements: Substance Temp. Description of Reaction C 1100°C Carbide formation begins C 1300°C Rapid Carburization Hg 20°C No significant solubility P No Reaction, even at "higher temperatures" S 440°C Sulfides begin to form Si Silicides form at "higher temperatures"
MOLTEN OXIDIZING SALTS: KCl3, K2CO3, KNO2, KNO3 Violent Reaction at molten salt temperature Na2CO3, NaO2, PbO2 Violent Reaction at molten salt temperature
