Tungsten Oxide/Graphene Composites

Tungsten oxide picture

Graphene is a two-dimensional planar material with a six-membered ring structure. Its unique electronic structure and atomic structure have made graphene a widespread concern in the field of gas sensors such as tungsten oxide sensors. Semiconductor materials produced by compounding graphene and tungsten oxide have excellent optical, electrical, and mechanical properties.

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Tungsten Oxide Activation Problem

Tungsten oxide picture

With the development of sensor technology, the research direction of semiconductor gas sensors is developing toward normal temperature, integration, and low power consumption. Tungsten oxide has attracted the attention of researchers because of its high sensitivity. Researchers have achieved room temperature detection by changing the activation mode. However, tungsten oxide room temperature sensors still have the disadvantages of low sensitivity, slow response recovery, and poor selectivity and stability. These defects are also the challenges faced by the practical use of room temperature tungsten oxide gas sensors.

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Tungsten Oxide Sensor Metal Activation

Tungsten oxide picture

Adding metal elements to the tungsten oxide sensor can significantly improve the sensor response characteristics and reduce the sensor operating temperature. Metal catalysts such as iron and titanium can increase the surface reaction sites of tungsten oxide sensors. However, precious metal catalysts such as silver and platinum can not only provide surface active sites, but also can change the electron concentration of the conduction band of the tungsten oxide sensor by doping, thereby improving the characteristics of the tungsten oxide sensor.

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Tungsten Oxide Sensor Gas Sensitivity

Tungsten oxide picture

A lead-containing tungsten oxide sensor is prepared by hydrothermal synthesis and the operating temperature is lowered to room temperature. The hydrothermally synthesized tungsten oxide gas-sensitive material has better gas-sensitivity than the tungsten oxide gas-sensitive material prepared by the mechanical mixing method and the pure tungsten oxide gas-sensitive material. The addition of lead effectively changed the response characteristics of the sensor. The sensitivity to hydrogen at room temperature was 34 and the response time was 24 s. And it has very good selectivity and repeatability.

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Tungsten Oxide Electrospinning

Tungsten oxide picture

Electrospinning is a special form of tungsten oxide polymer fluid electrostatic atomization. The tungsten oxide split by atomization at this time is not a tiny droplet, but a tiny jet of polymer, which can run for a long distance and eventually solidify into a tungsten oxide fiber.

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Tungsten Oxide Ceramics EDS Spectroscopy

Tungsten oxide picture

The leakage current of the tungsten oxide ceramic varistor under the action of the applied voltage is a decreasing process with time. This shows that the grain boundary barrier model of tungsten oxide varistors is different from conventional varistors such as zinc oxide.

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UV Light Affects the Gas Sensitive Properties of Tungsten Oxide

Tungsten oxide picture

Researchers have found that ultraviolet and visible light can provide energy for the surface chemical reaction of tungsten oxide gas-sensitive materials, thereby accelerating the rate of chemical reactions, thereby improving its gas-sensing properties. The study found that ultraviolet light affects the gas-sensitive properties of tungsten oxide gas mainly through two aspects:

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Sintering Densification of Tungsten Carbide

three stages of densification image
Sintering densification of tungsten carbide is the most prominent change in the sintering process. There are many kinds of statements about the mechanism of densification. Views include diffusion control, flow control, physical and chemical reaction process control, etc. At present, the mainstream view regards the whole densification process as a complex process of the three stages of diffusion - flow - rearrangement.

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Influence Factors of Sintering Densification

pore of tungsten carbide image
The sintering process of tungsten carbide is divided into pre-sintering (deforming agent), solid phase sintering, liquid phase sintering, cooling and so on. During the sintering, the volume of the block will shrink, and the pores decrease greatly, which is so called the sintering densification. Liquid phase flow and particle rearrangement during the stage of liquid sintering do contribute a lot to densification. The liquid-solid wetting angle and the content of cobalt are two of the most important influence factors.

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Influence Factors of η Phase

WC-Co tungsten carbide SEM image
As for WC-Co tungsten carbide, the nucleation and growth of its η phase is restricted by the composition and quantity of the alloy's γ phase. Therefore, the increase of carbon content and cobalt alloy amount and the WC grain refinement lead to the increase of η phase concentration distribution and size coarsening. The increase of sintering temperature and cooling rate will reduce the number and size of η phase.

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