Ammonium paratungstate is an important material for preparing ammonium metatungstate by a thermal decomposition - resin exchange method. This method overcomes the problems of some traditional processes such as APT - tungstic acid method, APT - acidification - alcohol precipitation method, and APT thermal decomposition - alcoholization crystallization method, etc. It has the advantages of simple process, high single pass yield and excellent product quality.

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Preparation of Ammonium Metatungstate with Ammonium Paratungstate

Place 100g of ammonium paratungstate in an enamel tray or white steel tray, and put it in a drying oven with a constant temperature of 240 °C for 25-30 min. After taking out, it was slowly poured into 60ml of pure water at 95 °C while stirring. When most of the solids are dissolved, add about 5-8 g of L-shaped resin, at this time, the pH value is between 3.5-4.0. Stir at a constant temperature for 30 min. The obtained Common Turning Inserts mixed liquid was passed through a stainless steel screen to remove resin and its impurities. The filtrate was placed for 12h and vacuum filtered to remove insoluble tungsten compounds and impurities. The prepared clear and transparent filtrate was heated and concentrated until a crystal film appeared on the liquid surface, then cooled and crystallized, and finally dried by airflow at 50-60 °C for 2 h to obtain ammonium metatungstate.

Nanowhiskers, nanowires and nanorods are nearly perfect materials, which have superior performance compared with metal materials. As a structural material, tungsten whiskers or tungsten nanowires are used to reinforce and toughen refractory alloys, ceramic materials, etc. Can significantly enhance the toughness and strength of the material.

In addition, tungsten nanowhiskers have excellent field emission properties and gas ionization properties, and can be used to fabricate field emission appliances, flat panel displays, and gas ionizers, such as nanoscale tungsten probes, which are lithography machines and chips. One of the important components of a manufacturing machine.

Deep Hole Drilling Inserts

The following technical solutions can be adopted for the preparation of tungsten nanowhiskers:

Weigh 200g of pure tungsten powder, the tungsten powder has a particle size of 2~5μm, and arrange 7wt% of nickel and iron metal powder, and mix by ball milling. The effect of mixing nickel and iron metal powders is to induce the growth of tungsten whiskers. Take 2.0g of mixed powder, tiling in the cleaned stainless-steel boat, push the stainless-steel boat into the tube-type reduction furnace with inner diameter of 60mm, ensure that the stainless-steel boat is placed in the high temperature center of the reduction furnace, close the furnace door, and pass nitrogen gas. And hydrogen. The N2 flow rate was 0.3 L/min, the H2 flow rate was 0.03 L/min, and nitrogen gas was introduced into the furnace through a three-necked flask to which deionized water was added, and the three-necked flask was placed in an electric heating jacket. The reduction furnace was heated at a rate of 3 ° C / min to raise the furnace from room temperature to 500 ° C. Turn on the electric heating power supply and set the temperature at 80 °C to slowly increase the deionized water to 80 °C (this temperature controls the water vapor flow rate). The furnace temperature was raised from 500 ° C to 800 ° C at a heating rate of 2 ° C / min, and then held for 6 hours. After the reaction is completed, the furnace temperature is lowered to room temperature, and the product is opened to remove the product. After washing, filtering and drying with ethanol, a uniformly distributed micro/nano tungsten whisker/wire/rod is obtained, and the product shape is good, and the whisker/rod length the aspect ratio is 5-200, wherein a small amount of tungsten nanowires having a diameter less than 100 nm and uniformly distributed can be seen.

The tungsten whisker prepared by the above process has a good shape, and can obtain tungsten nanowhiskers has an aspect ratio of 5 to 200, and a tungsten nanowire having a diameter of less than 100 nm and uniformly distributed. The process has low reaction temperature, short reaction time, easy control, high yield, good product shape and uniform distribution, and is a good mass production plan.

The photoelectric properties of bismuth tungstate are severely limited by its low quantum efficiency. Therefore, the study of bismuth tungstate composites is an effective way to improve the photoelectric properties. The common practice is to dope materials with complementary effects.

Porphyrins are a class of macromolecular heterocyclic compounds. Modified porphyrins can copolymerize carbon dioxide with epoxides under the co-catalysis of iron, cobalt and aluminium. Some scholars used tetracarboxyphenyl porphyrin as carrier to deposit bismuth tungstate on the carrier to make composite materials. It needs to go through the following process:

1)Preparation of flower-like bismuth tungstate: 0.79g bismuth nitrate pentahydrate and 0.23g sodium tungstate were added into 25 ml of water. The ultrasonic water bath was at 60 ℃, stirred evenly, and the pH was adjusted to 2-2.5. Hydrothermal reaction was carried out in the reactor for 28-30 hours, cooling, washing with secondary water and ethanol respectively. After 10-12 hours of drying, pale yellow solid samples were obtained. The product is bismuth tungstate, and then the product is ground into powder in a mortar and placed for use.

2)Composite materials were prepared by immersion self-assembly method. Firstly, flower-like bismuth tungstate was deposited on FTO conductive glass by grooving inserts electrophoretic deposition. The process of electrophoretic deposition was as follows: 6-8 mg flower-like bismuth tungstate, 2-4 mg iodine and 10-12 ml acetone were mixed. FTO conductive glass was added into the above-mentioned mixture, and DC current was 8-12 V for each. The time of secondary deposition is 2-4 minutes and 2-3 times. After deposition, the FTO conductive glass is dried at 50-60 ℃ for 10-12 hours, and then burned in a tubular furnace at 500 ℃. Then FTO conductive glass was immersed in ethanol solution containing 0.005mmol/L tetracarboxyl phenylporphyrin (TCPP) in dark for 20-24 hours to obtain flower-like bismuth tungstate-tetracarboxyl phenylporphyrin composite loaded on FTO conductive glass.

Because porphyrin has sensitization effect, it can improve light absorption ability and form heterojunction with bismuth tungstate, which can reduce the probability of electron hole recombination. It is proved that the photocurrent of bismuth tungstate-tetracarboxyl phenyl porphyrin composite is four times and six times higher than that of bismuth tungstate, respectively. The lower the probability of electron hole recombination after irradiation, the more effective the photoelectric response of bismuth tungstate is.