2016年2月24日星期三

Analyzing Resulting of Violet Tungsten Oxide Cycle Reduction to Micro Tungsten Powder

Because violet tungsten oxide (VTO) producing process and process parameters are simple as well as equipment are easy to control and many advantages so many manufactures are like to use VTO to producing tungsten powder. VTO cycle reduction method can producing excellent performance submicron or micro tungsten powder particles, to further understand tungsten powder in the reactions process which is used cycle reduction method will conducive to the future development and maturity of this method.
Tungsten Powder

After studies, VTO is first hydrogen reduced to tungsten powder and the specific surface area of tungsten oxide is 0.141m2 • g-1 and particle size mainly between 4.72-12.13um. Compared with the original VTO particle size distribution, after first reduction the particle of VTO is significantly thinner, but still existing coarse particles. The tungsten powder in the air oxidation to tungsten trioxide for the first the specific surface area of it is 0.145m2 • g-1, which is 1.13 times of VTO. It can be seen, the first time oxidized to tungsten trioxide the particle are smaller than VTO particle size which is more uniform distribution, but still significant reunion.

Analyzing Blue Tungsten Oxide Appearance

Learning blue tungsten oxide (BTO) phase morphology, size and uniformity, help to improve the performance blue tungsten oxide, so that it can be applied in more areas. To produce blue tungsten oxide is boat loading ammonium paratungstate (APT) to the hot zone and during the process to control the hydrogen flow, temperature and holding time these three parameters to produced blue tungsten oxide.
Blue Tungsten Oxide SEM

By using hydrogen reduction method to produce blue tungsten oxide and the surface of it has a large number of cracks and voids star, breakage obviously, it has lost the characteristics of hexagonal grains, forming a loose rule like appearance. Blue tungsten oxide surface has cracks is due to a large amount of water molecules and ammonium molecules which is produced from APT decomposition during the reaction. So the crystal inside of APT will cause inner stress to make crystal lattice mutation, resulting in cracks. At the same time, the external hydrogen to penetrate APT inside promoted deepening and expanding of cracks. Because of this crack APT generating vacancies and in baking time it caused partial intense contractions to make further fragmentation then to produce a fine particle powder.

Analysizing Tungsten Oxide Pyrochlore Type

A purity of more than 99.9% WO3 into a porcelain crucible, porcelain crucible and then placed in a muffle furnace and calcined at 800℃ 1 hour coolish placed in a desiccator, cool room temperature. Accurately weighed 0.25g tungsten trioxide into 100ml beaker, with 20% NaOH20ml, heating completely dissolved, after cooling into 250ml volumetric flask, dilute to the mark and shake, this solution was transferred to a plastic bottle dry spare.

Standard curve: accurate absorption 1.00mg / ml solution 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0ml Guarantee 100ml flask were placed with 0.85N ~ NaOH complement to 10ml, plus 50 percent potassium thiocyanate 5ml, plus 1: 1HCL50ml, plus 1% TiCl32ml, diluted with water to the mark and shake for 10 minutes, measured at 721 spectrophotometer extinction 0.5cm cuvette with a wavelength of 420 nm, as a reagent blank reference, drawing working curve, the measured slope of the curve K.
YTO SEM

Solid phase analysis
Weigh a sample in 50ml of 0.200 ~ 0.500g iron crucible, adding sodium peroxide 4g, was stirred with dry round a glass rod, a small piece of filter paper Sassafras net glass rod, the filters were put in a crucible, in addition to the low temperature furnace H2O , add a muffle furnace at a temperature of 700 ~ 750 ℃ ​​burn for about 10 minutes until pink, remove coolish, leaching into the 250ml beaker containing 100ml of hot water, and washed with water crucible, cooled to room temperature later, into 250ml volumetric flask, dilute to the mark, shake, filtration.Imbibe filtrate G2ml (tungsten oxide content may be) in 100ml volumetric flask, fill 0.85N sodium hydroxide to 10ml, following the same standard curve drawing methods.

Analysis Using Blue Tungsten Oxide To Produce Tungsten Powder By Cyclic Oxidation

After analysis using blue tungsten oxide to produce tungsten powder by cyclic oxidation found the tungsten powder particle size is small, and good performance. From the experimental data show that after the first reduction tungsten powder‘s specific surface area is 0.119m2 / g which is 1.95times to blue tungsten oxide’s. From this we can see that tungsten powder particle size is smaller than the blue tungsten oxide and distribution is more concentrated, but there is a certain amount of coarse particles of tungsten powder. 
Tungsten Powder

In the second reduction which is using obtained tungsten powder in the air restore to tungsten trioxide then using hydrogen to make the second reduction. And the tungsten powder which obtained from the second reduction is finer. Comparing tungsten powder of the first reduction and the second reduction find in the second reduction there has more fine tungsten powder than first reduction, its particle size distribution is more uniform, but there are a small number of coarse particles of tungsten powder. The second reduction of tungsten powder specific surface area is 0.180m2 / g which is the first reduction of tungsten powder of 1.51 times and its diameter mainly in the 3 ~ 10um. It can be found using cyclic oxidation method obtained tungsten powder particles finer than directly by using hydrogen reduction, besides the distribution is more concentrated.