Hafnium coatings

It has been reported that hafnium oxide nano pattern can be formed on hafnium coated Si substrate surface utilizing AFM tip. It has also been reported that nano meter scale lines and dots of titanium oxide can be formed directly on the water absorbed titanium surface. Figure 13.13(a) and (b) shows AFM image and height profile of Ti02 lines fabricated using different scanning speed of AFM tip at — 10 V [30]. Narrowest line width of 18 nm of titanium oxide is successfidly fabricated by AFM tip induced anodization. 

Kuznetsova, S.V, Glagolevskaya,A.L., and Kuznetsov, S.A. (1992) Electrodeposition of hafnium coatings from molten NaCl-KCl-HfCU mixtures using direct and reversible currents, Rasplavy 6,29-35. 

At certain parameters of electrolysis [17] it is possible to obtain five intermetallic compounds HfCu4, HfCus, Hf2Cus, Hf2Cu3, Hf2Cu between the copper substrate and the hafnium coatings. 

Kuznetsova, S.V., Kuznetsov, S.A., Polyakov, E G., and Stangrit, P.T. (1989). Cathodic current efficiency during electrodeposition of hafnium coatings, Rasplavy 3, 118-120. 

The heavy mineral sand concentrates are scmbbed to remove any surface coatings, dried, and separated into magnetic and nonmagnetic fractions (see Separation, magnetic). Each of these fractions is further spHt into conducting and nonconducting fractions in an electrostatic separator to yield individual concentrates of ilmenite, leucoxene, monazite, mtile, xenotime, and zircon. Commercially pure zircon sand typically contains 64% zirconium oxide, 34% siUcon oxide, 1.2% hafnium oxide, and 0.8% other oxides including aluminum, iron, titanium, yttrium, lanthanides, uranium, thorium, phosphoms, scandium, and calcium. 

Hafnium nitride s high, emissivity in the visible spectmm at high temperature has led to a proposed use (52) as a coating on incandescent light filaments to improve visible light output. 

Hafnium carbide [12069-85-1] can be used as surface coating on cemented-carbide cutting tools, shows promise as a stable field emission cathode... 

MIBK is a highly effective separating agent for metals from solutions of their salts and is used in the mining industries to extract plutonium from uranium, niobium from tantalum, and zirconium from hafnium (112,113). MIBK is also used in the production of specialty surfactants for inks (qv), paints, and pesticide formulations, examples of which are 2,4,7,9-tetramethyl-5-decyn-4,7-diol and its ethoxylated adduct. Other appHcations include as a solvent for adhesives and wax/oil separation (114), in leather (qv) finishing, textile coating, and as a denaturant for ethanol formulations. 

Specialized alloys are used for high temperature appHcations on turbine blades, furnace parts, thermocouples, etc. These coatings can be as simple as iron—silicon—chromium or as exotic as chromium—aluminum—hafnium (36,41,52). 

The oxidation rate of niobium in air from 800°C to above 1000°C can be decreased by alloying e.g. with hafnium, zirconium, tungsten, molybdenum, titanium or tantalum . However, the preferred fabricable alloys still require further protection by coating . Ion implantation improves thermal oxidation resistance of niobium in oxygen below 500°C . 

Apart from the reactions described above for the formation of thin films of metals and compounds by the use of a solid source of the material, a very important industrial application of vapour phase transport involves the preparation of gas mixtures at room temperature which are then submitted to thermal decomposition in a high temperature furnace to produce a thin film at this temperature. Many of the molecular species and reactions which were considered earlier are used in this procedure, and so the conclusions which were drawn regarding choice and optimal performance apply again. For example, instead of using a solid source to prepare refractory compounds, as in the case of silicon carbide discussed above, a similar reaction has been used to prepare titanium boride coatings on silicon carbide and hafnium diboride coatings on carbon by means of a gaseous input to the deposition furnace (Choy and Derby, 1993) (Shinavski and Diefendorf, 1993). 

As discussed in Section 15.5.2, the separation of two or more sublimable substances by fractional sublimation is theoretically possible if the substances form true solid solutions. Gillot and Goldberger(10°) have reported the development of a laboratory-scale process known as thin-hlm fractional sublimation which has been applied successfully to the separation of volatile solid mixtures such as hafnium and zirconium tetrachlorides, 1,4-dibromobenzene and l-bromo-4-chlorobenzene, and anthracene and carbazole. A stream of inert, non-volatile solids fed to the top of a vertical fractionation column falls counter-currently to the rising supersaturated vapour which is mixed with an entrainer gas. The temperature of the incoming solids is maintained well below the snow-point temperature of the vapour, and thus the solids become coated with a thin film (10. im) of sublimate which acts as a reflux for the enriching section of the column above the feed entry point. 

Hafnium is a ductile metal that looks and feels much hke stainless steel, but it is significantly heavier than steel. When freshly cut, metallic hafnium has a bright silvery shine. When the fresh surface is exposed to air, it rapidly forms a protective oxidized coating on its surface. Therefore, once oxidized, hafnium resists corrosion, as do most transition metals, when exposed to the air. Chemically and physically, hafnium is very similar to zirconium, which is located just above it in group 4 on the periodic table. In fact, they are so similar that it is almost impossible to secure a pure sample of either one without a small percentage of the other. Each will contain a small amount of the other metal after final refining. 

The stereoselectivity of polymerization depends on the transition metal and the structure of the initiator. Syndioselective polymerization is more common than isoselective polymerization. Some titanium phenoxy-imine initiators yield highly syndioselective polymerization by chain end control. For example the initiator with R2 = R3 = t-butyl yields polypropene with (rr) = 0.92 [Tian and Coates, 2000]. The initiator with R2 = t-butyl and R1 = C6Fs yields polypropene with (rr) = 0.98 [Saito et al., 2001 Tian et al., 2001], Moderately isoselective polymerization is obtained with some zirconium and hafnium phenoxy-imine initiators [Saito et al., 2002]. 

Finally, rod-like particles of indium hydrous oxide, dispersed in solutions of HfOCl2 and Na2S04, were coated with hafnium hydrous oxide by simply aging the entire system for 24 h at room temperature (149). 

Coating -by extrusion processes [PLASTIC PROCESSING] (Vol 19) -with LDPE [OLEFIN POLYMERS - POLYETHYLENE - LOW DENSITY POLYETHYLENE] (Vol 17) -PVC use piNYL POLYMERS - VINYLCITLORIDE POLYMERS] (Vol 24) -use ofhafmum [HAFNIUM AND HAFNIUM COMPOUNDS] (Vol 12) -use of lime and limestone QIME AND LIMESTONE] (V ol 15)... 

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