Temperature-dependent vibrational (Raman and infrared) spectroscopy and X-ray diffraction studies have been performed on polycrystalline Na₂WO₄ṡ2H₂O and Na₂MoO₄ṡ2H₂O crystals. Raman data at low temperature 13-300 K for sodium tungstate Na₂WO₄ṡ2H₂O was compared with the sodium molybdate Na₂MoO₄ṡ2H₂O. The infrared and the X-ray diffraction obtained in the 80-300 K suggest that both crystals have undergone conformational changes connected with an increase in the Raman intensity of NaO₆ modes and the libration modes of water molecules at about 100-120 K. Additionally, Raman spectroscopy measurements of Na₂WO₄ṡ2H₂O under hydrostatic pressure (from 0 to 5 GPa) were performed. The pressure-dependent studies indicate the starting orthorhombic structure is stable in the 0.0-3.2 GPa pressure range, and undergoes a phase transition at about 3.9 GPa, associated with rotation of WO4-2 units.

 

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Sodium tungstate solution can be prepared by decomposing wolframite with sodium hydroxide. A new technique is developed for precipitating scheelite from the sodium tungstate solution by the addition of calcium hydroxide. In this study, the effects of several variables on the conversion of sodium tungstate are investigated. Results show that the effects of temperature and sodium tungstate concentration are significant. Specifically, 96.4% WO₄^2 − was converted to scheelite in 2 h at 100 °C with a calcium hydroxide stoichiometric ratio of 1.4 and a stirring speed of 350 rpm. The parent solution containing sodium hydroxide can be recycled as a leaching agent return to the wolframite decomposition process.

Highlights

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Synthesis of scheelite from sodium tungstate solution with addition of calcium hydroxide was successfully achieved.

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Effects of processing parameters on the conversion of sodium tungstate were presented.

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Optimal processing parameters in the process of synthesizing scheelite were selected.
 

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Diabetes mellitus leads to bone disorders such as osteopenia and osteoporosis that can increase fracture risk. On the other hand, sodium tungstate is an inorganic compound which exerts anti-diabetic activity in experimental studies due to its suggested insulin-mimetic or antioxidant activity. Therefore this study was designed to investigate the effect of tungstate on bone quality in diabetic rat femurs. The rats were divided into four groups: Control (C), tungstate-treated control (C+Tung), diabetes (STZ-D) and tungstate-treated diabetes (STZ-D+Tung). Diabetes mellitus was induced by single injection of streptozotocin (50 mg/kg). The treated rats received 150 mg/kg/day of sodium tungstate for 12 weeks. Sodium tungstate achieved a little (17%) but significant reduction on blood glucose levels, while it didn't recover the reduced body weights of diabetic rats. In addition, impaired bone mechanical quality was reversed, despite the unchanged mineral density. Sodium tungstate administration significantly lowered the 2-thiobarbituric acid reactive substances and restored the activity of tissue antioxidant enzymes such as glutathione peroxidase, catalase and superoxide dismutase in diabetic rats. On the other hand, glutathione levels didn't change in either case. These findings indicate that tungstate can improve the reduced mechanical quality of diabetic rat femurs due probably to reduction of reactive oxygen species and modulation of antioxidant enzymes as well as reduction in blood glucose levels.

 

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As mentioned in some researches, the cutting edge geometry could affect the deposition stresses around the tool tip in coating process, in addition, during the machining, the thermal and mechanical loads will be complicated and imposed as well. It is also indicated that chip formation and cutting processes could be severely affected by the radius edge, especially there is a size effect, which is referred to the thickness of the uncut chip is close to or smaller than the edge radius.

In general, for the coated tungsten carbide inserts,on which the cutting edge effects include, with the edge radius increasing, there is a noticeable decrease in deposition residual stresses. On the contrast, the increasing of edge radius will bring up the cutting forces and the with different edge radii and  combined effects, the coated tungsten carbide inserts’wear behavior are complicated.


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