Refractory metals corrosion resistance

The industrial value of furfuryl alcohol is a consequence of its low viscosity, high reactivity, and the outstanding chemical, mechanical, and thermal properties of its polymers, corrosion resistance, nonburning, low smoke emission, and exceUent char formation. The reactivity profile of furfuryl alcohol and resins is such that final curing can take place at ambient temperature with strong acids or at elevated temperature with latent acids. Major markets for furfuryl alcohol resins include the production of cores and molds for casting metals, corrosion-resistant fiber-reinforced plastics (FRPs), binders for refractories and corrosion-resistant cements and mortars. 

Ruthenium and osmium have hep crystal stmetures. These metals have properties similar to the refractory metals, ie, they are hard, britde, and have relatively poor oxidation resistance (see Refractories). Platinum and palladium have fee stmetures and properties akin to gold, ie, they are soft, ductile, and have excellent resistance to oxidation and high temperature corrosion. 

Alumina—graphite refractories, almost all continuous casting ware, have come into much greater use as continuous casting has spread in steelmaking. These refractories are used in shrouds that conduct the molten metal from the ladle to the tundish, in the subentry tubes that take the metal from the tundish to the mold, in isostatically pressed stopper rods, and in shroud tubes for slab and bloom casters. The alumina—graphite compositions are used in these products because of the thermal-shock resistance and corrosion resistance they impart to the product. 

Other useful refractory nitrides for corrosion protection are silicon nitride (Si3N4) and boron nitride (BN). Silicon nitride has good corrosion resistance and is not attacked by most molten metals as shown in Table 17.6 (see Ch. 10). 

Hafnium is used in control rods for nuclear reactors. It has high resistance to radiation and also very high corrosion resistance. Another major application is in alloys with other refractory metals, such as, tungsten, niobium and tantalum. 

A completely novel approach to technical electrolysis for anodic oxygen evolution from alkaline solution is the use of amorphous metals, i.e. chilled melts of nickel/cobalt mixtures whose crystallization is prevented by the addition of refractory metals like Ti, Zr, B, Mo, Hf, and P (46-51). For this type of material, enhanced catalytic activity in heterogeneous catalysis of gas-phase reactions has been observed (51). These amorphous metals are shown to be more corrosion resistant than the respective crystallized alloys, and the oxides being formed at their surfaces often exhibit a higher catalytic activity than those formed on ordered alloys, as shown by Kreysa (52-54). 

Chromizing and Related Diffusion Processes. Chromizing is similar to aluminizing. A thin corrosion and wear resistant coaling is applied to low cost steels such as mild steel, or to a nickel-based alloy. In the related boroni/ing process, a thin boron alloy is produced for extreme hardness, wear, and corrosion resistance. Siliconizing is yet another process used especially lor coaling of the refractory metals Ti. Nb. Ta. Cr. Mo. and W. 

The key technological goals include replacement of environmentally toxic metal coatings, deposition of new alloys and semiconductors and new coating methods for reactive metals. The main driving force for non-aqueous electrolytes has been the desire to deposit refractory metals such as Ti, Al and W. These metals are abundant and excellent for corrosion resistance. It is, however, the stability of their oxides that makes these metals difficult to extract from minerals and apply as surface coatings. 

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