2021年12月15日星期三

Tungsten Oxide Type

Tungsten oxide is a kind of tungstic anhydride, which is a tungstate product. Tungsten oxide type includes tungsten trioxide and tungsten dioxide. In actual industrial production, it is rare to have tungsten dioxide.

yellow tungsten oxide image

Tungsten dioxide is also known as brown tungsten oxide. The formula WO2 tungsten dioxide is an intermediate transition state of ammonium paratungstate into tungsten trioxide. Its appearance is tan monoclinic powder crystal, and tungsten dioxide is the most commonly known, the role is to manufacture tungsten powder and tungsten trioxide.

Tungsten trioxide, also known as yellow tungsten oxide, chemical formula WO3, is the main tungsten oxide product of our country before the eighties. Yellow powder is insoluble in water, soluble in alkali and slightly soluble in acid. Its density is 7.16 g / cm3; The melting point is 1473 ° C; the boiling point is about 1700 ° C. Mainly used in the system of high melting point alloys and cemented carbide, tungsten wire and fire gas sensitive materials, but also for photocatalyst materials.

blue tungsten oxide image

Blue tungsten oxide is also known as blue tungsten, chemical type W2.90. After the reform and opening up in 80s, China began to produce the blue powder in accordance with the requirements of international orders. Blue tungsten has a certain crystalline form, which is larger than the surface and is easy to be doped. The tungsten carbide powder and tungsten powder are better than those with yellow tungsten. Therefore, after 80s, blue tungsten has gradually replaced the mainstream of the yellow tungsten oxide in the market, and is the main product of the tungsten oxide market.

violet tungsten oxide image

Violet tungsten oxide, also known as purple tungsten, chemical formula 2.72, which in broad terms can be considered a branch of blue tungsten, the appearance is purple or purple red fine crystal powder. Compared with blue tungsten and tungsten, violet tungsten has a special surface and the highest chemical activity. Therefore, ultraviolet tungsten is the most suitable for the production of ultrafine tungsten powder. At the time of increasing the requirements for the performance of cemented carbide, the demand for nanometer tungsten powder is also contending. Therefore, the market of violet tungsten is becoming bigger and bigger.

At present, the tungsten oxide products that are mainly traded on the market are four kinds. Tungsten oxide can only be the final product of tungsten raw material in the whole process of tungsten application, and it is also the main product of China's exports at present.

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The Milling Guide Refinement of Tungsten Trioxide

Ball mill is a fine equipment used in industry and can also be used for mixing.

ball mill tungsten trioxide refinement image

The ball mill is composed of a cylinder and sphere, its working principle is when the cylinder rotates, installed in the cylinder body and the grinding body in grinding by centrifugal force and friction force with the cylinder to rotate to a height, and then automatically fall, the material in the cylinder impact and the grinding and grinding material.

The main factors affecting the efficiency of the ball mill are the speed of the ball mill, the quantity of the ball, the amount of water and electrolyte, the time and the loading. The normal milling time is about 24-72 hours, and the length of the ball milling time directly affects the quality of the ball milling product. Generally speaking, coarse grained material is easier to grind to coffee, and the time is shorter. However, the milling time of gal material to cut below is usually prolonged by several times or longer. However, with the prolongation of ball milling time, the cost of ball consumption and energy consumption will increase correspondingly, and the production capacity of the mill is decreased. Therefore, the appropriate ball milling time must be determined in the actual production.

In the process of ball milling, the ratio of solid to liquid is also a critical process parameter. During the process of mechanical milling, the solid liquid ratio, the shape and size of particles, and the interaction between particles will affect the rheological properties of slurry. The solid-liquid ratio is too low, medium ball received buoyancy, it will reduce the quality of the effective volume, the impact effect is bad, being a medium ball impact the opportunity will be less, so the production efficiency is low, high solid-liquid ratio is opposite, so too high or too low is not conducive to the refinement of tungsten trioxide.

The size of the material ratio directly determines the ball milling fineness, energy consumption, ball consumption and so on. In general, the larger the ratio of the material to the material, the more the relative quantity of the medium, the increase of the impact and the number of shearing of the material, and the enhancement of the effect of refining the crushing.

In summary, mechanical milling can produce high purity tungsten trioxide powder. But the milling conditions have a great influence on the particle size. The ball milling time and the ratio of pellet to particle size tend to be stable. It is better to prolong the time blindly and increase the ball size rather than the thinning effect. On the contrary, it will increase the introduction of impurities.

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Different Crystalline Forms of Tungsten Trioxide Gas Sensitivity Competition

Tungsten trioxide (WO3) is a kind of transition metal oxides, it is not only a kind of N type semiconductor material, is also a kind of "d0" oxide, this dual identity so it has many characteristics.

tungsten trioxide gas sensitive component image

The research shows that there is rod, plate and rod plate three kinds of nano tungsten oxide crystal, gas sensing properties of tungsten oxide with different crystal morphology is slightly different, some scholars use tungsten trioxide for four kinds of common harmful gases were tested and concluded.

(1) The best working temperature of WO3 sensor in ethanol, acetone, ammonia and formaldehyde is 350 ℃, 300 ℃, 325 ℃ and 250 ℃, respectively, and the sensitivity reaches the maximum at gas concentration of 1000 ppm. 21.29, 10.82, 24.32 and 9.68 respectively, and the lowest detection concentration of gas sensors for four gases are 100ppm, 50ppm, 25ppm and 100ppm, respectively.

(2) The best working temperature of nano-plate WO3 gas sensor is 350 ℃, 300 ℃, 325 ℃ and 250 ℃, respectively, and the sensitivity reaches the maximum when the gas concentration is 1000 ppm, which are respectively 25.4 and 18.52 , 30.29 and 18.31, respectively, the sensitivity value of ammonia is up to 30.29; The minimum detectable concentration of nano-plate tungsten trioxide gas sensor for the four gases is 50 ppm, 50 ppm, 25 ppm and 100 ppm, respectively, of which the sensitivity is 2.81 when the ammonia gas concentration is 25 ppm, indicating that the nano- Tungsten trioxide gas sensor is very sensitive to low concentration of ammonia.

(3) Nanoplate rod-shaped tungsten trioxide gas sensor The best working temperature of the four gases was 350 ℃, 300 ℃, 300 ℃ and 250 ℃, respectively, and the sensitivity reached the maximum when the gas concentration was 1000 ppm, the minimum detection concentrations for the four gases at 9.11, 8.73, 14.23 and 6.89 gas sensors were 200 ppm, 50 ppm, 50 ppm and 100 ppm, respectively.

Gas-sensitive test results show that the three kinds of crystal tungsten oxide have their own strengths. However, the overall comparison shows that the plate-shaped nano-tungsten trioxide is slightly better than the other two types of tungsten trioxide in terms of the lowest detection concentration or sensitivity.

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Preparation of Nano Tungsten Trioxide by Hydrothermal Synthesis

Nano tungsten trioxide is a typical N-type semiconductor gas sensing material, which has a large specific surface area, stable chemical properties, a variety of toxic gases have good sensitivity, can effectively improve sensitivity and responsiveness of gas sensors effectively reduce the harmful effects of harmful gases on human health.

tungsten trioxide hydrothermal reactor image

The preparation of nano tungsten trioxide by hydrothermal method can overcome the problems that the nano rods prepared in the prior art have larger diameters, uneven distribution of rods and other forms of particles. 

Using ammonium metatungstate as tungsten source, citric acid as the profile control agent, according to a certain proportion in the mixed solution, adding concentrated hydrochloric acid solution was adjusted by drops in pH magnetic stirring at room temperature is equal to 1.5, half an hour so that the magnetic stirring solution mixing, the mixed solution was transferred to a hydrothermal reaction kettle PTFE capacity of 100 mL in seal, placed in an oven and incubated at 180 ° C for 18 h. After completion of the hydrothermal reaction, the precipitate was collected by centrifugation, washed with deionized water and acetone, and centrifuged three times to remove residual Na2SO4 and organic impurities in the precipitate. The cleaned precipitate was placed in a watch glass, dried in an oven at 80 ° C for 24 h, and finally ground in an agate mortar to obtain a powder.

Through SEM and TEM observation, it is concluded that the best technological conditions for preparing nano structured WO3 are citric acid content of 2 mol, P H value of the system 1.5, hydrothermal reaction 180 degrees, and hydrothermal reaction time of 1D. The prepared nanorod WO3 nanorods have a maximum length of about 2.5 um, a diameter of about 30-60 nm, a maximum aspect ratio of about 1:80 and a growth direction of the nanorods of [002].

The gas sensor made of nano rod tungsten trioxide has the best working temperature of 350 ℃, 300 ℃, 325 ℃ and 250 ℃ in the gas of ethanol, acetone, ammonia and formaldehyde respectively. When the gas concentration is 1000 ppm sensitivity reached the maximum, respectively 21.29,10.82,24.32 and 9.68; Gas sensors for the four gases minimum detection concentrations were 100ppm, 50ppm, 25ppm and 100ppm, gas sensitivity is good, but to be higher than the working temperature of 150 ℃ to play a good gas sensitivity performance, so in the future to find the right of the material on the nano tungsten oxide doping is to improve the performance of gas sensors the main way.

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Tungsten Oxide Type

Tungsten oxide is a kind of tungstic anhydride, which is a tungstate product. Tungsten oxide type includes tungsten trioxide and tungsten d...