Tungsten

About: Tungsten is a research topic. Over the lifetime, 35225 publications have been published within this topic receiving 456213 citations. The topic is also known as: W & element 74.

Hydrothermal synthesis of transition metal oxides under mild conditions

Abstract: A notable development in mild (≤ 200°C) hydrothermal synthesis in the past few years has been the extension of the synthesis technique from zeolites and metal phosphates to binary and ternary transition metal oxides. This low-temperature technique is critical to the formation of metastable phases not obtainable using traditional high-temperature methods. New phases, as well as known materials, of the oxides of tungsten, molybdenum, vanadium and manganese have been formed, often in highly crystalline form. One enhancement of the technique is microwave heating, which appears to accelerate nucleation, producing very uniform particles in a few hours.

Stress, strain, and microstructure in thin tungsten films deposited by dc magnetron sputtering

Abstract: Tungsten thin films were deposited on glass substrates by direct‐current planar magnetron sputtering. The induced thickness‐averaged film stress within the plane of the film was determined with the bending‐beam technique and changed from compressive to tensile on increasing working‐gas pressure. The microstructure of these films was investigated by cross‐sectional transmission electron microscopy. Compressively stressed films consisted of tightly packed columnar grains, whereas in films with a maximum value for the tensile stress the onset of a void network surrounding the columnar grains was observed. High‐pressure conditions resulted in dendritic‐like film growth, which brought about complete relaxation of internal stresses. The α phase was predominantly found in films under compression, while an increasing amount of β‐W coincided with the transition to the tensile stress regime. Special attention was focused on stress‐depth dependence and the development of two overlapping line profiles in x‐ray diffra...

Reactions of pulsed‐laser evaporated uranium atoms with molecular oxygen: Infrared spectra of UO, UO2, UO3, UO2+, UO22+, and UO3–O2 in solid argon

Abstract: Uranium atoms from the Nd:YAG laser ablation of a uranium target were codeposited with molecular oxygen and excess argon at 12 K. Infrared spectra following the U+O2 reaction revealed a wide range of reaction products. The 776.0 cm−1 band due to UO2 was the strongest product absorption, strong UO3 bands were observed at 852.5 and 745.5 cm−1, and a weak UO absorption appeared at 819.8 cm−1. These product absorptions are in agreement with earlier work, which evaporated UO2 from a tungsten Knudsen cell at 2000 °C. The 16O2/18O2 reaction gave only U 16O2 and U 18O2, which verified an insertion mechanism. New product absorptions were observed at 952.3, 892.3, and 842.4 cm−1. The 842.4 cm−1 absorption due to the UO3–O2 complex and the 892.3 cm−1 band assigned to the charge‐transfer complex (UO2+)(O2−) grew markedly at the expense of the other uranium oxides during annealing the matrix to allow diffusion and reaction of O2. With 25% 16O2, 50% 16O18O, and 25% 18O2 samples, the 952.3 cm−1 band became a sharp tripl...

Characterization of zirconia-supported tungsten oxide catalyst

Abstract: Tungsten oxide−zirconia catalysts were prepared by drying powdered Zr(OH)4 with ammonium metatungstate aqueous solution, followed by calcining in air at high temperature. Characterization of prepared catalysts was performed by using Fourier transform infrared (FTIR), Raman, and X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) and by measuring surface area. The addition of tungsten oxide up to 20 wt % to zirconia shifted the phase transition of ZrO2 from amorphous to tetragonal to higher temperature due to the interaction between tungsten oxide and zirconia, and the specific surface area and acidity of catalysts increased in proportion to the tungsten oxide content. Since the ZrO2 stabilizes the tungsten oxide species, for the samples equal to or less than 5 wt %, tungsten oxide was well dispersed on the surface of zirconia, but for the samples containing 13 wt % or above 13 wt %, the triclinic phase of WO3 was observed at any calcination temperat...