Zirconium plasma

Decomposition of Zircon. Zircon sand is inert and refractory. Therefore the first extractive step is to convert the zirconium and hafnium portions into active forms amenable to the subsequent processing scheme. For the production of hafnium, this is done in the United States by carbochlorination as shown in Figure 1. In the Ukraine, fluorosiUcate fusion is used. Caustic fusion is the usual starting procedure for the production of aqueous zirconium chemicals, which usually does not involve hafnium separation. Other methods of decomposing zircon such as plasma dissociation or lime fusions are used for production of some grades of zirconium oxide. 

Analyses of alloys or ores for hafnium by plasma emission atomic absorption spectroscopy, optical emission spectroscopy (qv), mass spectrometry (qv), x-ray spectroscopy (see X-ray technology), and neutron activation are possible without prior separation of hafnium (19). Alternatively, the combined hafnium and zirconium content can be separated from the sample by fusing the sample with sodium hydroxide, separating silica if present, and precipitating with mandelic acid from a dilute hydrochloric acid solution (20). The precipitate is ignited to oxide which is analy2ed by x-ray or emission spectroscopy to determine the relative proportion of each oxide. 

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). 

Zirconium(IV) oxychloride estrone, 17- -estradiol and estnol, plasma lipids heat to 150 to 180°C for 5 min Fluorescent zones are produced — sometimes only after heating for longer penod [178]... 

The first experiments on the plasma chemical decomposition of fluoride solutions containing tantalum or niobium to obtain tantalum and niobium oxides were reported about fifteen years ago [524]. Subsequent publications were devoted to further development and expansion of the method for other refractory rare metals such as titanium and zirconium [525 - 532]. 

The high temperatures attainable in a plasma furnace, with no restrictions with regard to factors such as the furnace atmosphere or the crucible material, has made processing by thermal decomposition a practicable and useful method. A good example is the thermal decomposition of low-cost zircon (ZrSi04) to produce zirconium dioxide (Zr02). The fur-... 

In addition to the Alloy 625 of the autoclave itself, the materials or material junctures examined were nickel (Ni) 201, platinum, platinum to Hastelloy C-276 weld in Zone 3, the YSZ supports, and arc-plasma sprayed YSZ on zirconium (thermal cycling only). The nickel, YSZ supports, and YSZ coating on zirconium exhibited poor performance (high corrosion, fracture, and delamination, respectively) in Zone 1 and Zone 2. Platinum was deemed to be satisfactory in Zones 1 and 3 but exhibited corrosive attack, including pitting and the formation of a platinum-sulfur compound, at the grain boundaries in Zone 2. The platinum/Hastelloy C-276 weld was determined to be satisfactory in Zone 3. 

Many attempts have been made to quantify SIMS data by using theoretical models of the ionization process. One of the early ones was the local thermal equilibrium model of Andersen and Hinthome [36-38] mentioned in the Introduction. The hypothesis for this model states that the majority of sputtered ions, atoms, molecules, and electrons are in thermal equilibrium with each other and that these equilibrium concentrations can be calculated by using the proper Saha equations. Andersen and Hinthome developed a computer model, C ARISMA, to quantify SIMS data, using these assumptions and the Saha-Eggert ionization equation [39-41]. They reported results within 10% error for most elements with the use of oxygen bombardment on mineralogical samples. Some elements such as zirconium, niobium, and molybdenum, however, were underestimated by factors of 2 to 6. With two internal standards, CARISMA calculated a plasma temperature and electron density to be used in the ionization equation. For similar matrices, temperature and pressure could be entered and the ion intensities quantified without standards. Subsequent research has shown that the temperature and electron densities derived by this method were not realistic and the establishment of a true thermal equilibrium is unlikely under SIMS ion bombardment. With too many failures in other matrices, the method has fallen into disuse. 

Eoex 21) reports the successful formation of borides in a rotating batch melting furnace, fired by an RE induction plasma. An amount of 0.8 kg from a stoichiometric mixture of Zr02 and boron, previously compressed in the rotating vessel to a pressure of 40 kg/cm, is treated by the action of an argon plasma (1 m /hr) for 0.5 hr. Zirconium diboride is formed by the reaction,... 

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