Showing papers on "Hafnium published in 1991"

Oxidation of hafnium carbide and hafnium carbide with additions of tantalum and praseodymium

Abstract: The oxidation behavior of HfC, HfC-25 wt. % TaC, and HfC-7 wt.% PrC2 has been studied between 1200–2200° C. Parabolic growth of the oxide layer has been observed for both HfC and HfC-TaC over the entire temperature range. A break in the temperature dependence of the oxidation kinetics occurs around 1600°C. At lower temperatures, the kinetics are limited by gaseous diffusion via pores in the oxide. Above 1800°C, gaseous diffusion through pores becomes less important as scale-growth kinetics are dominated by bulk (ambipolar) diffusion of oxygen and electrons through the oxide.

Method of manufacturing a semiconductor device comprising capacitors which form memory elements and comprise a ferroelectric dielectric material having multilayer lower and upper electrodes

Abstract: A method of manufacturing a semiconductor device comprising a semiconductor body (3) with a surface (10) on which capacitors (2) are provided, which form memory elements, with a lower electrode (11) including platinum, a ferroelectric dielectric material (12) and an upper electrode (13) is presented. In the method according to the invention, the electrodes (11, 13) including platinum are formed by the successive deposition on a surface of a first layer (19, 26) comprising a metal from the group titanium, zirconium, hafnium or an alloy of these metals, a second layer (20, 27) comprising platinum, and a third layer (21, 28) comprising a metal from the group titanium, zirconium, hafnium, or an alloy of these metals, upon which the semiconductor body is heated in an atmosphere containing oxygen. The first metal layer ensures a good adhesion of the electrode, the second layer acts as the electrode proper, while the third metal layer counteracts adverse effects of the first layer. Semiconductor devices having electrodes with good adhesion and a smooth surface can be manufactured in such a way. As a result, the semicondcutor device is reliable, while switching of the capacitors (2) acting as memory elements between two polarization states takes place at a positive and a negative voltage of equal value.

Liquid ion exchangers and their uses in the separation of zirconium, niobium, molybdenum, hafnium, tantalum and tungsten

Abstract: Important liquid ion exchangers and the applications of their cationic and anionic forms in the studies of separation of zirconium, niobium, molybdenum, hafnium, tantalum and tungsten through solvent extraction and RPEC systems have been reviewed.

Production of polycarboxylic acids with hafnium-activated cobalt catalyst

Abstract: The addition of hafnium to oxidation catalysts provided by a heavy transition metal-bromine ion catalyst combination containing cobalt-manganese-bromine or manganese-bromine or cobalt-bromine and a soluble source of hafnium uniquely increases catalytic activity of the said catalyst combination for converting methyl groups on the benzene nucleus. The presence of hafnium in the total reactor contents is equal to or less than 250 parts per million by weight of the total reactor mother liquor. The solubility of the hafnium in the reactor solvent is such that reactor product cake contains less than 0.3 ppm by weight. Bromine emissions can be reduced.

Calculations of the production cross sections of high-spin isomeric states in hafnium

Abstract: This paper reports on the {sup 178}Hf(16{sup +}) isometric state that has a 31-yr half-life and could pose serious radioactive activation problems in nuclear fusion reactors if its production in 14-MeV neutron induced reactions is significant. The relatively high excitation energy (2.447 MeV) of this state causes it to lie in the continuum region. If rotational band members above this state were populated in a reaction, they would gamma cascade into it. While the existence of such levels can be justified theoretically, they have not been experimentally resolved; therefore, it is necessary to reconstruct the rotational levels built on the isomeric state. Using preequilibrium and compound nucleus theories, the cross sections for this and other hafnium isomeric states are calculated and compared with experimental measurements where available.

Elastic properties of materials by pulsed neutron powder diffraction

Abstract: We describe the use of pulsed neutron powder diffraction to measure the mean-square thermal displacements of atoms in polycrystalline materials at various temperatures. Data for aluminum, Pu0.95Al0.05, Ce0.90Th0.10, titanium, hafnium and CeRh3B2 are presented. A simple Debye model accounts for the observations, and a Debye temperature ΘDW can be extracted from the data. ΘDW is atom-specific and anisotropic, and is related to the elastic constants of the material. This technique provides a means of obtaining information on the elastic behavior of materials for which the traditional methods are not applicable.

Metal halide high-pressure discharge lamp with a fill containing hafnium and/or zirconium

Abstract: To generate light output from a metal halide discharge lamp having a fill which includes mercury, at least one noble gas, cesium and a metal halide, such that the color temperature will be between 4000 and 9000 K., and the color rendering index Ra is greater than 90, while, for the red spectral range, the color rendering index R9 is at least 50, the metal of the metal halides comprises hafnium, preferably present between 0.02 to 6 mg, or zirconium, preferably present between 0.01 to 4 mg, each per milliliter of volume of the discharge vessel (2, 14, 28). Both hafnium and zirconium may also be added.

Zirconium-hafnium production in a zero liquid discharge process

Abstract: A simple, low cost continuous process for separating and purifying zirconium and hafnium which eliminates liquid waste and facilitates the management of RCRA and LLW wastes is provided. An aqueous zirconium and hafnium - containing feed solution is prepared and fed to a continuously rotating annular chromatograph containing a bed of acid exchange resin. An acid eluant, such as hydrochloric acid, nitric acid, phosphoric acid or the like, is fed through the acid exchange bed while the chromatograph is rotating, which separates the feed into substantially pure zirconium and hafnium fractions and into RCRA and LLW waste fractions. The zirconium and hafnium are processed further into nuclear quality zirconium and hafnium metals. The acid eluant is recycled for reuse in the chromatograph, and the RCRA and LLW waste fractions are disposed of in solid form.

Self-powered detector response to thermal and epithermal neutron flux

Abstract: This paper reports on theoretical and experimental studies of various self-powered neutron detectors that are carried out. Among the emitter materials studied are cobalt, hafnium, erbium, silver, rhodium, and gadolinium.

Hafnium-catalyzed transesterification

Abstract: An ester of a carboxylic acid is prepared via a transesterification reaction which comprises reacting a lower alkyl ester of carboxylic acid with a higher alkyl alcohol in the presence of a catalyst consisting of a hafnium chelate derived from hafnium tetrachloride, bis(alkoxide)hafnium dichlorides, or hafnium tetraalkoxides in the presence of 1,3-dicarbonyl compounds.

Metal halide lamp and method of making the same

Abstract: A metal halide lamp is made by coating the inner surface of a luminous tube made of quartz glass with hafnium oxide, uranium oxide, hafnium oxide partially stabilized with yttrium oxide or uranium oxide partially stabilized with yttrium oxide by introducing therein a vapour of metal chelate containing hafnium (Hf), uranium (U) or yttrium (Y) and oxygen (O₂), nitrogen suboxide (N₂O) or ozone (O₃) as a reaction gas, and sealing the inside of the luminous tube with a halogenide of alkali metal, mercury and argon.

Nickel-base superalloy

Abstract: To achieve a complete recrystallisation in profile parts and mouldings made of nickel-based super alloys and having a structure made up of columnar grains, the maximum heating rate @max depends on the ratio V of one or more of the metal carbide formers hafnium, niobium, tantalum, titanium and zirconium to one or both the metal carbide formers tungsten and molybdenum.

Kinetic study of the hafnium-hydrogen reaction

Abstract: The kinetics of hafnium hydride formation were studied utilizing conventional rate measurements (Sieverts system) combined with metallographic examinations of partially hydrided samples. The rate measurements were performed at 700 TorrH2 over a temperature range 200–550 °C. Two types of hafnium samples (polycrystalline and crystal bar) were compared. The progression of the massive stage of the reaction is characterized by a contracting-envelope morphology with a constant hydride front velocity. The anisotropy in the reaction front velocity regarding different crystalline orientations of the metal is small, resulting in similar results for the different types of hafnium. The temperature dependence of the front velocity obeys an Arrhenius-type relation over the temperature range 250–450 °C, with an apparent activation energy of 0.50 ± 0.05 eV. Considering a diffusion-controlled model, a diffusion activation barrier of about 0.4 eV is evaluated, which agrees with the average reported value for the diffusion of hydrogen in hafnium hydride. At temperatures above about 500 °C, deviations from the Arrhenius relation are displayed, possibly owing to a change of mechanism.

Preparation of uniform colloidal particles of hafnium compounds

Abstract: Spherical colloidal particles of amorphous hafnium hydroxysulphate of narrow size distribution have been prepared by ageing at room temperature acidic solutions of hafnium oxychloride in the presence of metal sulphates. On calcination the powders crystallized into monoclinic hafnia, yet retained their spherical shape. The effects of several parameters (concentration of reagents, nature of the acid and the sulphate salt) on the characteristics of the precipitated particles were studied in detail. A mechanism for the formation of such particles is suggested.

Morphologies of anodic oxide films deduced from dissolution studies

Abstract: Study of the chemical stripping of anodic oxide films on hafnium, zirconium, tungsten and aluminium has led to the deduction of the morphology of the respective oxides. Away from the boundary region hafnium oxide is a compact, smooth, homogenous and crystalline oxide. Zirconium oxide has a superficial disorder layer which constitutes about 17% of the entire film. Tungsten oxide deposits are composed of two defective partial layers the outer one being more disordered. Aluminium oxide is a porous film. A schematic representation of each film had been presented.

Process for depositing layers containing titanium, zirconium or hafnium

Abstract: A process for depositing layers containing titanium, zirconium or hafnium by decomposition of certain sandwich compounds of the particular metal is described. The decomposition is preferably effected by the CVD method.

Thermochemistry of alloys of transition metals: Part III. Copper-silver, -titanium, -zirconium, and -hafnium at 1373 K

Abstract: The enthalpies of mixing of liquid copper with liquid silver and with solid titanium, zirconium, and hafnium have been measured by high temperature reaction calorimetry at 1371 to 1373 K. A least squares treatment of the data for copper-silver alloys yields the following expression for the molar enthalpy of mixing: ΔHmix = ϰAgϰCu(17.66 − 5.46 ϰAg) kJ mol−1. The enthalpies of solution of solid titanium, zirconium, and hafnium in dilute solutions in liquid copper are all exothermic; the following values were found: -2.0 kJ mol−1 for Ti, -52.5 kJ mol−1 for Zr, and -46.3 kJ mol−1 for Hf. These values are all significantly less exothermic than predicted by the semiempirical theory of Miedema. The enthalpies of formation of congruent melting intermetallic phases in the systems Cu-Ti, Cu-Zr, and Cu-Hf were measured by drop calorimetry or by solution calorimetry in liquid copper. The enthalpies of formation of the solid alloys have been compared with corresponding data for the liquid alloys.