Zirconium sponge

The zirconium sponge thus obtained is highly pyrophoric. The industrial practice is to condition this sponge by the controlled admittance of air-argon mixtures at around 50 °C. Such a treatment results in the formation of a thin, protective oxide film on the sponge this eliminates any major fire hazard in subsequent handling and crushing operations. 

A mixture of powdered zirconium and carbon tetrachloride exploded violently while being heated [1], and immersion of zirconium sponge in the unheated solvent also caused explosion [2],... 

Figure 5. The final stages in the production of zirconium sponge (the Kroll process).

The Kroll process involves heating molten magnesium and zirconium tetrachloride vapor in a sealed furnace in the absence of air under a helium atmosphere. The reaction forms zirconium sponge and magnesium chloride ... 

Zirconium sponge (1.82 g., 0.020 mole) and resublimed sulfur (1.34 g., a slight excess over 0.040 mole) are charged into the transport tube. The procedures for adding iodine (5 mg./ml. of ampule volume) and heating that are described in the TiS2... 

Finely divided zirconium, such as the zirconium sponge produced in the Kroll process (Sec. 8.3), reacts sufficiently rapidly with water at ordinary temperatures to impair its mechanical properties. Thus it is not feasible to use water leaching to separate zirconium sponge from the magnesium chloride by-product of the Kroll process. 

The grades of zirconium and zirconium-base alloys commercially available in the United States are described in ASTM Special Technical Publication 639 [S2]. The most important of these are zircaloy-2, zircaloy-4, and Zr-2.5 Nb. Table 7.4 gives the ASTM composition specifications for these three alloys and zirconium sponge. 

Form Common name Sponge Zirconium sponge Ingots ... 

Vacuum distillatHm of MgClj. To remove MgClj from the zirconium sponge it is necessary to resort to vacuum distillation. Water leaching cannot be used because the finely divided zirconium sponge would become contaminated by oxide corrosion product. 

The crucible containing the zirconium sponge and MgClj is transferred to the vacuum distillation retort, shown in Fig. 7.13, where it is supported, upside down, over a perforated, stainless steel funnel. The air in the retort is evacuated, and the crucible is heated to 900 to 920°C to melt the MgGj. which partially drains off the sponge. Salt still wetting the sponge is distilled at this temperature to a water-cooled jacket inside the retort. 

Zirconium carbide powder is prepared by the reaction of Zr02 with carbon at 1800-2400 C in hydrogen by the carburization of zirconium sponge by the auxiliary bath technique, or by plasma-CVD. Zirconium carbide coatings are deposited by CVD, evaporation or sputtering (see Chs. 14 and 15). 

Reaction of Zr02 with carbon at 1800-2400 C in hydrogen Carburization of zirconium sponge... 

In 1945, development work on zirconium was initiated at the U.S. Bureau of Mines in Albany, Oregon imder Dr. Kroll s technical direction. Dr. Kroll had already developed a production process for titanium by the reduction of titanium tetrachloride with magnesium in an inert atmosphere before 1940. A similar process for zirconium was developed in 1947 as a pilot plant with a weekly capacity of 60 poimds of zirconium sponge. 

Semiproducts of pure zirconium, intended for the construction of chemical equipment, contain approx. 1000 g/g oxygen. Normal oxygen contents in remelted zirconium sponge amount to 600-1400 Aig/g, and to 200-600 a g/g or even lower for iodide zirconium. 

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