Molybdenum mandrel

The refractory metals for which CVD is commonly used to produce free-standing shapes are tungsten, niobium, rhenium, tantalum, molybdenum, and nickelb lb lb l (see Ch. 6). Shapes presently produced include rods, tubes, crucibles, manifolds, ordnance items, nozzles, and thrust chambers. They are usually deposited on a disposable mandrel of copper, molybdenum, or graphite which is subsequently machined off or removed chemically by etching. 

Most incandescent lamps today exhibit a coiled-coil geometry of the filament (Fig. 6.7). Coiled-coils are made by winding the filaments on mandrels of molybdenum and subsequent winding of the coil on a larger mandrel to form a secondary coil [6.2]. The coil is then heated to about 1700°C to relieve the stresses formed during coiling and to stabilize the geometry [6.7]. The mandrels are then selectively dissolved in nitric acid or mixtures of nitric and sulfuric acid. 

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