Hafnium silicate

Zircon is synthesized by heating a mixture of zirconium oxide and silicon oxide to 1500°C for several hours (163). The corresponding hafnium silicate, hafnon, has been synthesized also. Zircon can be dissociated into the respective oxides by heating above 1540°C and rapidly quenching to prevent recombination. Commercially, this is done bypassing closely sized zircon through a streaming arc plasma (38). 

Atomic layer deposition of hafnium silicate thin films using... 

It was shown that hafnium silicate thin films could be deposited by ALD using HtCl2[N(SiMe3)2]2 with H2O in the temperature range of 150-40010. As the deposition temperature increased, the Si content in the film increased but growth rate linearly decreased. However at low temperature, the Si content was as low as Si/(Hf+Si)=0.05 at ISOU, which was close to hafnium dioxide [4]. The surface mechanism of this ALD process was analyzed by in-situ FT-IR [6]. 

In other studies, the combination of alkoxides and chlorides, or alkoxides and amides without oxidant have been used to deposit hafnium silicate thin films by ALD [3,7],... 

Fig. 3. SIMS depth profiles of hafnium silicate films deposited at 200 C (a) using HfCl2[N(SiMej)2]2 and H2O, (b) using HfCl2[N(SiMe3)2]2 and H2O2, and (c) HfCl2[N(SiMe3)2]2, TBOS and H2O...

The low temperature ALD process for hafnium silicate films using HfCl2[N(SiMe3)2]2 and H2O was modified to improve the film properties by two different methods. With hydrogen peroxide, the silicon content in the film increased to Si/(Hf+Si)=0.2 at 2001 and the impurity levels decreased due to its strong oxidation effect. By introducing TBOS as an additional Si precursor, the silicon content in the film increased to Si/(Hf+Si)=0.5 at 200 °C and the hafiiium silicate films became fully oxidized with O/(Hf+Si)=2.0. 

Wilk, G.D. Wallace, R.M. Electrical properties of hafnium silicate gate dielectrics deposited directly on silicon. Appl. Phys. Lett. 1999, 74,2854-2856. 

Felix, J. A. Fleetwood, D. M. Schrimpf, R. D. Hong, J. G. Lucovsky, G. Schwank, J. R. Shaneyfelt, M. R. 2002. Total-dose radiation response of hafnium-silicate capacitors. IEEE Transactions on Nuclear Science, 49(6) 3191-3196. 

Zirconium is extracted mainly from the siUcate mineral, zircon (ZrSi04), which is found as a beach sand, usually in association with other minerals of commercial value, in Australia, India, Madagascar, Malaya, Ceylon, parts of Africa and the United States. The mineral is obtained in a relatively pure condition by ore dressing methods, except that it is usually associated with about 2 per cent of the isomorphous, and chemically very similar, hafnium silicate. The sihcate has been used directly, in admixture with charcoal, for chlorination to zirconium tetrachloride. The reaction can be represented as,... 

Hafnium Silicate. A compound analogous to zircon, hence the suggested name hafnon. It can be synthesized from the oxides at 1550°C. Thermal expansion (150-1300°C), 3.6 x 10-6. Hafnium Titanate. Special refractory compositions have been made by sintering mixtures of Hf02 and Ti02 in various proportions. The m.p. of these... 

Glocker and Frohnmayer determined the characteristic constant c for nine elements (Reference 2, Table 4) ranging in atomic numbers from 42 (molybdenum) to 90 (thorium). They proved that identical results could be obtained with the sample in the primary (polychromatic) or in the diffracted (monochromatic) beam. The method was applied with good results to the determination of barium in glass of antimony in a silicate of hafnium in the mineral alvite and of molybdenum, antimony, barium, and lanthanum in a solution of their salts—for example, 5.45% barium was found on 90-minute exposure by the x-ray method for a glass that yielded 5.8% on being analyzed chemically. 

Silicates of zirconium, ZrSi04 (zircon), and hafnium, HfSi04, are the only crystalline phases in the M02-Si02 system. Their fusion with molten Na2Si03 yields double silicates, Na2MSi05 and Na4MSi20g. 

SNC meteorites (Harper et al., 1995 Borg et al., 1997). This isotopic anomaly requires early differentiation of mantle and crust. Because hafnium and mngsten fractionated into silicate and metal, respectively, the short-lived Hf- W system can be used to determine that martian core formation occurred within —13 milhon years of the planet s accretion (Kleine et al., 2002 Yin et al., 2002). Correlation between Nd and isotope anomalies, as well as the initial Os/ Os ratios for martian meteorites (Brandon et al., 2000), indicate synchronous differentiation of core, mantle, and cmst (Figure 14). On Earth, core formation took substantially longer, convection has stirred the mantle sufficiently to erase any evidence of early isotopic heterogeneity, and cmst formation continues throughout geologic history. 

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