What Elements Does Pure Molybdenum Plate Contain? Purity, Trace Limits and Properties
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The Base Element and the Purity Level
Pure molybdenum plate is, in substance, molybdenum. The material is produced by hydrogen reduction of molybdenum oxide to metal powder, pressing and sintering the powder into a bar or ingot, and then rolling the sintered compact to plate, sheet, strip or foil at high temperature. Commercial unalloyed plate is normally specified at 99.95 percent molybdenum minimum, with the remaining fraction comprising trace elements that are inherent to the raw material or picked up during powder handling and rolling. The applicable product specification for the flat-rolled forms is ASTM B386/B386M, which covers unalloyed molybdenum and molybdenum alloy plate, sheet, strip and foil and identifies grade Molybdenum 361 among the unalloyed grades; buyers sourcing plate should reference that specification and the required grade rather than relying on a purity statement alone.
The Trace Elements Normally Reported
Trace elements fall into two groups: substitutional metallic impurities originating from the ore and the reduction process, and interstitial elements dissolved in the lattice. The metallic group includes iron, nickel, copper, silicon, aluminium, calcium, magnesium, lead, bismuth, antimony, tin, cadmium and phosphorus. The interstitial group is carbon, oxygen and nitrogen, which occupy lattice sites and strongly influence ductility, recrystallisation behaviour and weldability. Suppliers report both groups as a certified chemical analysis for each lot, and the values below are representative of a controlled production analysis for unalloyed plate at 99.95 percent molybdenum minimum.
| Element | Typical value, % |
|---|---|
| Mo (molybdenum, base) | above 99.95 |
| Fe (iron) | 0.004 |
| Ni (nickel) | 0.002 |
| C (carbon) | 0.0028 |
| Al (aluminium) | 0.0005 |
| O (oxygen) | 0.005 |
| N (nitrogen) | 0.002 |
| Si (silicon) | 0.0013 |
| Ca / Mg | below 0.001 / below 0.0005 |
| Cu / Pb / Bi / Sb / Sn / Cd | below 0.001 each |
| P (phosphorus) | below 0.001 |
Why the Interstitial Elements Matter Most
Oxygen, nitrogen and carbon are present in parts per million rather than percent, but they dominate the practical behaviour of the plate. Oxygen and nitrogen in solution raise the ductile-to-brittle transition temperature, so a plate that meets the molybdenum content requirement can still crack during bending if the interstitial load is high. Carbon influences recrystallisation temperature and grain growth, which in turn sets the temperature at which a furnace component begins to sag under its own weight. For this reason purchase documents frequently specify maximum oxygen and maximum nitrogen in addition to the molybdenum minimum, and require the analysis to be determined on the finished plate rather than on the powder blend.
How the Analysis Is Verified
Molybdenum content and metallic trace elements are normally determined by inductively coupled plasma optical emission spectrometry on a dissolved sample, with mass spectrometric techniques used where very low detection limits are required. Carbon and sulphur are determined by combustion analysis, and oxygen and nitrogen by inert gas fusion. Because these methods measure different things, a complete certificate of analysis for a molybdenum plate reports the test method alongside each result, together with the lot number and the plate dimensions to which the certificate applies.
Properties That Follow From the Purity
Molybdenum melts at approximately 2,623 degrees Celsius and has a density of about 10.2 grams per cubic centimetre, a thermal conductivity of roughly 138 watts per metre-kelvin near room temperature and a coefficient of thermal expansion of about 4.8 parts per million per kelvin. Its elastic modulus is approximately 329 gigapascals. These properties, combined with the corrosion resistance of the metal, make pure molybdenum plate a standard material for high-temperature furnace hearths, heating elements and radiation shields in vacuum and hydrogen furnaces, for glass melting electrodes and stirrers, for sputtering targets, for chemical process equipment handling aggressive media, and for rocket nozzles and other aerospace hot-section components. In service the practical temperature ceiling is set not by melting but by recrystallisation and by oxidation, so components are normally used in vacuum, hydrogen or inert atmosphere above roughly 600 degrees Celsius.
Frequently Asked Questions
Q: What elements does pure molybdenum plate contain?
A: Molybdenum as the base element, normally above 99.95 percent, plus trace elements such as iron, nickel, carbon, aluminium, oxygen, nitrogen, silicon, calcium, magnesium, copper, lead, bismuth, antimony, tin, cadmium and phosphorus.
Q: Which specification covers molybdenum plate?
A: ASTM B386/B386M covers unalloyed molybdenum and molybdenum alloy plate, sheet, strip and foil, and identifies the unalloyed and alloy grades to which a purchase order should refer.
Q: Are the trace elements harmful?
A: In the permitted ranges they are not, but the interstitial elements oxygen, nitrogen and carbon are kept deliberately low because they control ductility, the ductile-to-brittle transition and recrystallisation behaviour.
Q: How is the chemical analysis of a molybdenum plate verified?
A: Molybdenum and metallic traces by inductively coupled plasma optical emission spectrometry, carbon and sulphur by combustion analysis, and oxygen and nitrogen by inert gas fusion, all reported with the method and lot number.
Q: Why does molybdenum work in high-temperature furnaces?
A: Its melting point of about 2,623 degrees Celsius, high thermal conductivity and low thermal expansion make it dimensionally stable at high temperature, provided it is used in vacuum, hydrogen or inert atmosphere to avoid oxidation.
