Metals zirconium

Tin reacts completely with fluorine above 190°C to form tin tetrafluoride [7783-62-2] SnF. Titanium reacts appreciably above 150°C at a rate dependent on the size of the particles the conversion to titanium tetrafluoride [7783-63-3] TiF, is complete above 200°C. Fluorine reacts with zirconium metal above 190°C. However, the formation of a coating of zirconium tetrafluoride [7783-64 ] ZrF, prevents complete conversion, the reaction reaching... 

Both zirconium hydride and zirconium metal powders compact to fairly high densities at conventional pressures. During sintering the zirconium hydride decomposes and at the temperature of decomposition, zirconium particles start to bond. Sintered zirconium is ductile and can be worked without difficulty. Pure zirconium is seldom used in reactor engineering, but the powder is used in conjunction with uranium powder to form uranium—zirconium aUoys by soHd-state diffusion. These aUoys are important in reactor design because they change less under irradiation and are more resistant to corrosion. 

Other Reductions. Ductile, pure zirconium has been made by a two-stage sodium reduction of zirconium tetrachloride (68) in which the tetrachloride and sodium are continuously fed into a stirred reactor to form zirconium dichloride [13762-26-0], heating with additional sodium yields zirconium metal. Leaching with water removes the sodium chloride from the zirconium. Bomb reduction of pure zirconium tetrafluoride with calcium also produces pure metal (69). 

Electrolysis. Electrowinning of zirconium has long been considered as an alternative to the KroU process, and at one time zirconium was produced electrolyticaHy in a prototype production cell (70). Electrolysis of an aH-chloride molten-salt system is inefficient because of the stabiUty of lower chlorides in these melts. The presence of fluoride salts in the melt increases the stabiUty of in solution, decreasing the concentration of lower valence zirconium ions, and results in much higher current efficiencies. The chloride—electrolyte systems and electrolysis approaches are reviewed in References 71 and 72. The recovery of zirconium metal by electrolysis of aqueous solutions in not thermodynamically feasible, although efforts in this direction persist. 

There are no industry-wide specifications for zirconium metal castings, or for zirconium chemicals. 

Zirconium metal is marketed in three forms zirconium-containing silicon—manganese, kon, ferrosiUcon, or magnesium master alloys commercially pure zirconium metal and hafnium-free pure zirconium metal. The use of zkcon for the production of zirconium metal of all three types is ca 5—8% of the total U.S. zkcon consumption. 

Hafnium-free zirconium is particularly weU-suited for these appHcations because of its ductiHty, excellent oxidation resistance in pure water at 300°C, low thermal neutron absorption, and low susceptibiHty to radiation. Nuclear fuel cladding and reactor core stmctural components are the principal uses for zirconium metal. 

Hydrides. Zirconium hydride [7704-99-6] in powder form was produced by the reduction of zirconium oxide with calcium hydride in a bomb reactor. However, the workup was hazardous and many fires and explosions occurred when the calcium oxide was dissolved with hydrochloric acid to recover the hydride powder. With the ready availabiHty of zirconium metal via the KroU process, zirconium hydride can be obtained by exothermic absorption of hydrogen by pure zirconium, usually highly porous sponge. The heat of formation is 167.4 J / mol (40 kcal/mol) hydrogen absorbed. 

Phosphides. Zirconium forms several phosphides ZrP [39318-19-9] 2 [ 12037-80-8] and ZrP g [12066-61 -4]-, they are part of the Zr—P phase diagram (137). The solubiUty of phosphoms in zirconium metal is low, ca 50 ppm, and at higher concentrations it collects as separate globules at the metal grain boundaries. Analysis indicates that this material is Zr P. 

Qua.driva.Ient, Zirconium tetrafluoride is prepared by fluorination of zirconium metal, but this is hampered by the low volatility of the tetrafluoride which coats the surface of the metal. An effective method is the halogen exchange between flowing hydrogen fluoride gas and zirconium tetrachloride at 300°C. Large volumes are produced by the addition of concentrated hydrofluoric acid to a concentrated nitric acid solution of zirconium zirconium tetrafluoride monohydrate [14956-11-3] precipitates (69). The recovered crystals ate dried and treated with hydrogen fluoride gas at 450°C in a fluid-bed reactor. The thermal dissociation of fluorozirconates also yields zirconium tetrafluoride. 

Zirconium tetrachloride, ZrCl, is prepared by a variety of anhydrous chlorination procedures. The reaction of chlorine or hydrogen chloride with zirconium metal above 300°C, or phosgene or carbon tetrachloride on zirconium oxide above 450°C, or chlorine on an intimate mixture of zirconium oxide and carbon above 700°C are commonly used. 

In the equilibrium technique for oxygen, potassium containing lOO-KXX) ppm oxygen is exposed to zirconium metal at 815°C, and the zirconium analyzed for oxygen... 

Then, contrary to what was reported previously, the olefin dissociates from the zirconium metal complex. This conclusion was further supported by other experimental observations. However, it cannot be completely excluded that competition between dissociative and direct rearrangement pathways could occur with the different isomerization processes studied up to now. Note that with cationic zirconocene complexes [Cp2Zr-alkyl], DFT studies suggest that Zr-alkyl isomerizations occur by the classical reaction route, i.e. 3-H transfer, olefin rotation, and reinsertion into the Zr-H bond the olefin ligand appears to remain coordinated to the Zr metal center [89]. 

The pyrochemical process of zirconium-hafnium separation is particularly attractive not only because it makes the entire process of nuclear-grade zirconium metal production from zircon more economical than that involving a hydrometallurgical separation stage, but also... 

Eliminations of functional groups from zirconacydes with the zirconium metal still attached to the organic molecule. 

Elimination of an alkoxy group or of a halogen in the case of zirconacyclopentenes has been investigated in combination with the (3, (3-carbon—carbon bond-cleavage reaction. As shown in Eq. 2.73, an OR group or a halogen at a (3-position is eliminated and trapped by the zirconium metal center [53],... 

Sequences 246 and 249 were tested for their ability to catalyze hydrolysis while in solution rather than while attached to a support. The Zr4 complex of sequence 246 was found to catalyze the hydrolysis of phosphate ester 243b five times faster than the complex of peptide 249. Since the control complex 249 does not catalyze hydrolysis it appears that the small amount of catalysis that was observed was due to free zirconium metal (Scheme 29). 

Zirconium metal is produced from its tetrachloride by reduction with magnesium by the Kroll process. The oxide obtained above is converted to zirconium tetrachloride by heating with carbon and chlorine. In practice, the oxide is mixed with lampblack, powdered sugar, and a little water, and pelletized. The dried pellet is then heated with chlorine in a chlorinator to produce ziro-conium tetrachloride ... 

Hydride also may be obtained by combining zirconium metal with hydrogen... 

Zirconium tetrachloride is obtained as an intermediate in recovering zirconium metal from zircon and other minerals (See Zirconium, Recovery). The tetrachloride is obtained by heating a mixture of zirconium hydroxide and car-... 

Zirconium tetrachloride is reduced by heating with sodium, potassium or magnesium at high temperatures. Such reduction of tetrachloride has been the commerical method of producing zirconium metal ... 

Research Focus Synthesis of curable poly(ethylene-co5-ethylidene-2-norbomene) copolymers using a catalyst pair consisting of iron and zirconium metal complexes. 

Suggest a procedure for the industrial production of hafnium-free zirconium metal from baddeleyite (Zr02), on the basis of information given in this chapter and in Appendix C. 

Zirconium Metal Powder Type 1 47% Potassium Perchlorate Granulation 1 1% Graphite Powder... 

Zirconium metal exhibits passivity in air due to the formation of adherent coatings of oxide or nitnde. Even without the coating, it is resistant to the action of weak acids and acicl salts, but dissolves in HC1 (warm) or H2SO4 slowly, and more rapidly if F is present, forming compounds of Zr02+ ions, or fluorozneonates in the last case. 

The most important ore for production of zirconium metal is zircon ZrSi04, which occurs in several regions in the form of a beach sand,... 

---