Oxygen in zirconium

The behaviour of zirconium is very similar to that of titanium. It is obtained in the same way, mainly as sponge, and is melted into ingots under vacuum. 

In the unalloyed form, zirconium is used for the construction of chemical equipment. Of much higher importance are however the zirconium alloys, from which especially the types zircaloy-2 (1.5 % Sn, 0.1 IS Fe, 0.1 % Cr, 0.05 % Ni) and zircaloy-4 (1.5 % Sn, 0.1 % Cr, 0.2 % Fe) are of interest. They are used as fuel cladding materials in pressure and boiling water nuclear reactors and for structural elements in the reactor core. 

As it is the case for titanium, oxygen acts as an alloying element with very high solubility and influences mechanical strength (Table 1-2). 

Oxygen content (A g/g) Yield point (N/mm ) Tensile strength (N/mm ) Elongation %) Hardness (HV 30) (N/mm ) 

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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An entirely different selectivity principle known as phase equilibrium comes into play in high-temperature ionic conductors. Many important gases dissolve in ionic solids at elevated temperatures. However, the solubility is rather sharply defined for the gas and the solid by the lattice parameters and the size of the gas molecule. The best example is the solubility of oxygen in zirconium dioxide. When Z1O2 is doped with yttrium ions, it exhibits a high mobility for the O anion. The solubility and anion mobility then become the basis for several electrochemical gas sensors, using yttria-stabilized zirconia (YSZ). 

The results of this study are summarized in Table VI-8. The agreement is excellent. At the 30 /g/g level a precision and accuracy of the order of 5 % can be obtained. In 1980 these methods were used to certify nitrogen in three existing reference materials for oxygen in zirconium (41). 

THE DETERMINATION OF OXYGEN IN ZIRCONIUM. TITANIUM AND THEIR ALLOYS... 

Table VI1-9 Approved experimental conditions for the determination of oxygen in zirconium by inert gas fusion...

Revel and Albert (240) used helium-3 particles of 14.7 MeV, degraded to less than 14 MeV, for the instrumental determination of oxygen in zirconium. a-particles of 56 MeV were also used (240) for this determination. 

Alkyds. Alkyd resins (qv) are polyesters formed by the reaction of polybasic acids, unsaturated fatty acids, and polyhydric alcohols (see Alcohols, POLYHYDRic). Modified alkyds are made when epoxy, sUicone, urethane, or vinyl resins take part in this reaction. The resins cross-link by reaction with oxygen in the air, and carboxylate salts of cobalt, chromium, manganese, zinc, or zirconium are included in the formulation to catalyze drying. 

Sufficient heat is generated to ignite the hydrogen gas so that it can react explosively with the oxygen in air. Metals like magnesium, aluminum, titanium, and zirconium in pure form also react with water to release Hj, but heat must be supplied to initiate the reaction. The generalized representation is ... 

When zirconium is saturated with oxygen in solid solution, the vapor pressure of zirconium monoxide is 50 to 100 times higher than that of pure zirconium. The R value of zirconium remains at 3 to 4 up to 5 at-% oxygen, and then decreases to the limiting value of... 

No zirconium(III) complexes with oxygen donor ligands have been isolated. However, the electronic absorption spectra of aqueous solutions of Zrl3 have been interpreted in terms of the formation of aqua complexes (equation 4).29 The spectrum of a freshly prepared solution of Zrl3 exhibits a band at 24 400 cm-1, which decays over a period of 40 minutes, and a shoulder at 22000 cm-1, which decays more rapidly. The 24400 cm-1 band has been assigned to [Zr(H20)6]3+, and the 22000 cm-1 shoulder has been attributed to an unstable intermediate iodo-aqua complex. If it is assumed that the absorption band of [Zr(H20)6]3+ is due to the 2T 2Ee ligand-field transition, the value of A is 24 400 cm. This corresponds to a A value of 20 300 cm-1 for [Ti(H20)6]3+ 30 and 17 400 cm-1 for the octahedral ZrCl6 chromophore in zirconium(III) chloride.25... 

Brhacek, L., Kalandra, C. Determination of hydrogen, oxygen and nitrogen in zirconium and its alloys. Chem. Prumysl 18, 417 (1968). 

In the formation of metal oxides, both diffusion of oxygen inwards through the film on metal as well as diffusion of metal outwards may occur. Diffusion of oxide inwards to the metal/oxide interface is typified by titanium-oxygen and zirconium-oxygen systems. 

Fluidized-bed chlorination was started in 1950. The titanium raw material (with a particle size similar to that of sand) and petroleum coke (with a mean particle size ca. five times that of the Ti02) are reacted with chlorine and oxygen in a brick-Uned fluidized-bed reactor (c) at 800-1200 °C. The raw materials must be as dry as possible to avoid HCl formation. Since the only losses are those due to dust entrainment the chlorine is 98-100% reacted, and the titanium in the raw material is 95-100% reacted, depending on the reactor design and the gas velocity. Magnesium chloride and calcium chloride can accumulate in the fluidized-bed reactor due to their low volatility. Zirconium silicate also accumulates because it is chlorinated only very slowly at the temperatures used. All the other constituents of the raw materials are volatilized as chlorides in the reaction gases. 

Impurities in zirconium and zirconium alloys and compounds are often determined by emission spectroscopy. Both carrier distillation techniques and poiat-to-plane methods are available (91,92). Several metaUic impurities can be determined instantaneously by this method. Atomic absorption analysis has been used for iron, chromium, tin, copper, nickel, and magnesium (93). The interstitial gases, hydrogen, nitrogen, and oxygen are most often determiaed by chromatography (81). Procedures for carbon, chloride, fluoride, phosphorus, siUcon, sulfur, titanium, and uranium in zirconium are given in the hteiatuie (81,94—96). 

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