Zum Problem des β‐Wolframs

Abstract

Aus KCl enthaltendem WO2 kann mittels H2 ein Gemisch von α‐ und β‐W, in Gegenwart von Wasserdampf jedoch röntgenreines β‐W hergestellt werden. Die Temperatur der β → α‐Modifikationsumwandlung kann durch Fremdstoffe innerhalb 520–820° C verschoben werden. In Gegenwart von 0,5% P/W entsteht aus WO3 ein grobkörniges β‐W mit einem Sauerstoffgehalt entsprechend WO<0,01 und mit auffallend scharfen Röntgeninterferenzen. Eine α → β‐Modifikationsumwandlung konnte nie verwirklicht werden. Durch die Verfeinerung der Untersuchungsmethoden ließ sich im β‐W, welches aus überwiegend röntgenamorphen WO3 mittels H2 bei 500°C erhalten wurde, 0,066 Atome Sauerstoff pro ein Atom Wolfram nachweisen. Das β‐W wurde bisher niemals ohne erheblichem Fremdstoffgehalt hergestellt.

Ternary Rare Earth Transition Metal Zinc Compounds Ln2T3Zn14 (T = Fe, Co, Rh, Ni, Pd, Pt) with Ordered Th2Zn17-Type Structure and Structure Refinement of the Corresponding Binary Compound La2Zn17

“…Only 6 at. % oxygen is needed to stabilize this structure, corresponding to the formula W 3 O 0.2 . Other well-known examples of impurity stabilization are the many compounds with “filled” Mn 5 Si 3 (Mo 5 Si 3 C- or Hf 5 CuSn 3 -type structure). − The final difference Fourier synthesis of the least-squares refinement of the structure of La 2 Zn 17 shows a residual electron density of 1.36 e/Å 3 at the origin of the cell.…”

Formation and Incorporation of Dopant Phases during Technical Reduction of NS-Doped Tungsten Blue Oxide

“…Figure 3 shows the various possible reduction paths, based on X-ray diffraction measurements beween 600 and 900°C, for an NS-doped and for an undoped TBO. Since the first description of ßtungsten by Neugebauer et al, 13 its formation and transformation have been thought to be of importance for the dopant incorporation during NStungsten powder manufacture. Since the first description of ßtungsten by Neugebauer et al, 13 its formation and transformation have been thought to be of importance for the dopant incorporation during NStungsten powder manufacture.…”

A New ( W , Mo ) C Electrocatalyst Synthesized by a Carbonyl Process: Activity Enhancement Resulting from Water Vapor Treatment in the Synthesizing Process

“…It is interesting to note that the average O/metals ratio between 20 and 100~ is about 0.3, which coincides with that in compound W:~O, or (W, Mo)30, known as B-W, though x-ray diffraction only revealed a pattern identical to W in the bulk of the film. Neugebauer et al (8) stated that fl-W can be prepared with less than 0.01 atoms of O per atom of W. It is conceivable, therefore, that the surface layer of water vapor-treated film is a B-W like compound of alloy.…”