Sintering Behavior and Hardness of Tungsten Prepared by Hard Metal Sludge Recycling Process without Ammonium Paratungstate

In this paper, we suggest a novel recycling process for hard metal sludge that does not use ammonium paratungstate. Ammonia, which in the conventional recycling process is essential for removing sodium and crystallized tungstate, was not used in the novel process. Instead of ammonia, acid was used to remove the sodium and crystallized tungstate resulting in the formation of tungstic acid (H2WO4). Tungsten powders were successfully synthesized by hydrogen reduction of the tungstic acid through H2O decomposition, WO3 to WO2 reduction, and tungsten metal formation. The tungsten powders prepared from tungstic acid were spherical in shape and had a higher sintering density than the facet-shaped tungsten powders prepared from tungsten oxide. The spherical shape of the tungsten powders enhanced their sinterability and resulted in an increase in the size of grains. This is a result of the high diffusion rate of the atoms along the particle surfaces. Despite having a higher density, the hardness of the sintered tungsten was lower than that of tungsten from tungsten oxide. High energy milling effectively reduced grain size and improved hardness. The hardness of the tungsten prepared from milled tungstic acid was enhanced to a value (max. 471 HV) higher than the best previously reported value (389 HV). In sum, tungsten can be hardened, thereby improving its sinterability and reducing grain size, with tungstic acid prepared using the proposed recycling process.

Tetraammonium μ-ethylenediaminetetraacetato-1κ3 O,N,O′:2κ3 O′′,N′,O′′′-bis[trioxidotungstate(VI)] tetrahydrate

The title compound, (NH4)4[W2(C10H12N2O8)O6]·4H2O, was obtained from a mixture of tungstic acid, ammonia and ethylenediaminetetraacetic acid (H4edta) in a 2:4:1 ratio. The anion of the complex contains two WO3 units and one bridging edta4− ligand. Each central metal atom is tridentately coordinated by nitrogen and two carboxylate groups of the edta4− ligand, together with the three oxido ligands, producing a distorted octahedral coordination environment around each tungsten atom. The center of the carbon–carbon bond of the ethylene bridge represents a crystallographic inversion center. The crystal structure consists of a three-dimensional supramolecular framework built up by the dinuclear cations, the ammonium counter-ions and the solvent water molecules via hydrogen bonds of the N—H...O and O—H...O type.

Growth of a Large, Single-Crystalline WS2 Monolayer for High-Performance Photodetectors by Chemical Vapor Deposition

2D WS2 is a promising candidate for the next generation nanoelectronics, spintronics, valleytronics, and optoelectronics. However, the uncontrollably large-area growth of WS2 nanosheets and their unsatisfactory performance of the photodetectors based on WS2 hindered its applications. Here, we proposed a CVD method using tungstic acid as the precursors to grow WS2 flakes. After being characterized by AFM, Raman, PL, and TEM, we found the as-grown WS2 flakes were high-quality structures. Then the photodetectors based on the as-grown WS2 were fabricated, which exhibited high responsivity (7.3 A W−1), a fast response rate (a response time of 5 ms and a recovery time of 7 ms), prefect external quantum efficiency (EQE) (1814%), and remarkable detectivity (D*) (3.4 × 1012 Jones). Our works provided a new CVD method to grow some high-quality WS2 nanosheets.

Biobased Aldehydes from Fatty Epoxides Through Thermal Cleavage of β-Hydroxy Hydroperoxides

The ring-opening of epoxidized methyl oleate by aqueous H₂O₂ has been studied using tungsten and molybdenum catalysts to form the corresponding fatty b-hydroxy hydroperoxides. It was found that tungstic acid and phosphostungstic acid gave the highest selectivities (92-93%) towards the formation of the desired products, thus limiting the formation of the corresponding fatty 1,2-diols. The optimized conditions were applied to a range of fatty epoxides to give the corresponding fatty b-hydroxy hydroperoxides with 30-80% isolated yields (8 examples). These species were fully characterized by ¹H and ¹³C NMR, HPLC-HRMS and their stability was studied by DSC. The thermal cleavage of the b-hydroxy hydroperoxide derived from methyl oleate was studied both in batch and flow conditions. It was found that the thermal cleavage in flow conditions gave the highest selectivity towards the formation of aldehydes with limited amounts of byproducts. The aldehydes were both formed with 68% GC yield and nonanal and methyl 9-oxononanoate were isolated with 57 and 55% yield, respectively. Advantageously, the overall process does not require large excess of H₂O₂ and only generates water as a byproduct.

Biobased Aldehydes from Fatty Epoxides Through Thermal Cleavage of β-Hydroxy Hydroperoxides

The ring-opening of epoxidized methyl oleate by aqueous H₂O₂ has been studied using tungsten and molybdenum catalysts to form the corresponding fatty b-hydroxy hydroperoxides. It was found that tungstic acid and phosphostungstic acid gave the highest selectivities (92-93%) towards the formation of the desired products, thus limiting the formation of the corresponding fatty 1,2-diols. The optimized conditions were applied to a range of fatty epoxides to give the corresponding fatty b-hydroxy hydroperoxides with 30-80% isolated yields (8 examples). These species were fully characterized by ¹H and ¹³C NMR, HPLC-HRMS and their stability was studied by DSC. The thermal cleavage of the b-hydroxy hydroperoxide derived from methyl oleate was studied both in batch and flow conditions. It was found that the thermal cleavage in flow conditions gave the highest selectivity towards the formation of aldehydes with limited amounts of byproducts. The aldehydes were both formed with 68% GC yield and nonanal and methyl 9-oxononanoate were isolated with 57 and 55% yield, respectively. Advantageously, the overall process does not require large excess of H₂O₂ and only generates water as a byproduct.

Biobased Aldehydes from Fatty Epoxides Through Thermal Cleavage of β-Hydroxy Hydroperoxides

The ring-opening of epoxidized methyl oleate by aqueous H₂O₂ has been studied using tungsten and molybdenum catalysts to form the corresponding fatty b-hydroxy hydroperoxides. It was found that tungstic acid and phosphostungstic acid gave the highest selectivities (92-93%) towards the formation of the desired products, thus limiting the formation of the corresponding fatty 1,2-diols. The optimized conditions were applied to a range of fatty epoxides to give the corresponding fatty b-hydroxy hydroperoxides with 30-80% isolated yields (8 examples). These species were fully characterized by ¹H and ¹³C NMR, HPLC-HRMS and their stability was studied by DSC. The thermal cleavage of the b-hydroxy hydroperoxide derived from methyl oleate was studied both in batch and flow conditions. It was found that the thermal cleavage in flow conditions gave the highest selectivity towards the formation of aldehydes with limited amounts of byproducts. The aldehydes were both formed with 68% GC yield and nonanal and methyl 9-oxononanoate were isolated with 57 and 55% yield, respectively. Advantageously, the overall process does not require large excess of H₂O₂ and only generates water as a byproduct.