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Gas Sensing Response Principle of WO3-based Gas Sensors (II)

Details: Category: Tungsten Information; Published on Thursday, 05 February 2015 17:23; Written by cq; Hits: 1863

The sensitivity (S) could be defined as the ratio between the respective variation of resistance in the air (ΔRair) and in the target gases (ΔRgas) according to

S = ΔRair / ΔRgas

ΔR represents the difference between the maximum and minimum values of the resistance during one complete period of aerating cycling. However, we prefer to express the sensitivity with a more simple calculation route like this

S = Rgas / Rair

or S = Rair / Rgas

Rair and Rgas are the resistance of sensor in dry air and target gases, respectively. Usually, in oxidizing atmosphere, the oxide surface is covered by negatively charged oxygen adsorbate and the adjacent space charge region is electron-depleted: the oxide layer presents therefore a high resistance (Rgas＞Rair). Under reducing conditions, the oxygen adsorbate is removed by the reaction with reducing gas species and the electrons are re-injected into the space charge layers: as a result, the oxide layer resistance decreases (Rgas＜Rair). Besides, the voltage change of oxide may be used to illuminate the gas sensitivity at times. Therefore, the change of resistance, conductivity or voltage could be used as the parameters to scale the sensitivity.

In addition, the response time is often defined as the time required for the conductance to reach 90% of the equilibrium value after the test gas is injected, and the recovery time is the time necessary for the sensor to attain a conductance 10% above the original value in air.

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Ammonium Paratungstate is Basic Material

Details: Category: Tungsten Information; Published on Thursday, 05 February 2015 17:23; Written by zsq; Hits: 568

Ammonium Paratungstate (NH₄)[H₂W₁₂O₄₂].4H₂O is the most important precursor for the majority of tungsten products. Exceptions are products of melting metallurgy and Menstrum WC produced directly from ore concentrates.

All other intermediates such as tungsten trioxide, tungsten blue oxide, tungstic acid and ammonium metatungstate can be derived from APT, either by thermal decomposition or chemical conversion.APT is a white crystallized powder having average crystal size between 30 and 100 µm. Especially crucial for the quality is the purity. Typical levels of todays commercial APT are (upper limits in µg/g):Al 1-7, As 5-10, Bi 0.5-1, Ca 1-10, Co 1-10, Cr 1-10, Cu 1-3, Fe 3-10, K 2-10, Mg 1-7, Mn 1-10, Mo 5-30, Na 5-10, Ni 1-7, P 5-7, Pb 1-5, S 5-7, Si 1-10, Sn 1-10, Ti 3-10, and U 3-10. APT is packaged in polyethylene-lined drums or woven bags up to 1 ton.

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Gas Sensing Response Principle of WO3-based Gas Sensors (I)

Details: Category: Tungsten Information; Published on Thursday, 05 February 2015 17:18; Written by cq; Hits: 1672

The WO3-based gas sensors operate on the principle that the sensor’s resistance or conductivity changes in the presence of target gases. When the gas sensing devices exposure under target gases, the gas molecules are adsorbed on the surface of WO3 and electron transfer occurs between WO3 and the adsorbent. As a result, a depletion or accumulation of charges occurs on the surface. Following that variation of surface potential barrier induces a change in the resistivity or conductivity. Thus, this change suggests that WO3 produces response to the target gases.

It is common to evaluate gas sensing characteristics by the parameters like sensitivity, response time, recover time, gas concentration and working temperature. The ideal sensor materials should be of high sensitivity to target gases, short response and recover time, low gas concentration and working temperature.

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What is Advantage of Dart Games?(II)

Details: Category: Tungsten Information; Published on Thursday, 05 February 2015 17:22; Written by xsh; Hits: 602

There are some advantages of dart game ,especially the aspect of psychological:

It can improve brain balance and coordination skills. Dart game can develop the mussel consistent with the physical and mental. Make the heart, eyes, hands, force coordination to the optimum point, it may enhance balance and coordination ability of the brain, brain activity slows brain full of fine bubbles decreased ability to work full-time.

Improve the psychological quality in the technical details of darts. It emphasize the movement, honed by a certain time, for them, it is a challengeto overcome the psychological process of self-tolerance and exercise, anti-jamming capability.

Build self-confidence, individuality.

Darts game advantages would easy to use compared to other sports easy progress and achievement, and better reflect the personality can develop their skills and
Establish a strong self-confidence, initiative, and a sense of achievement and satisfaction.

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Ammonium Paratungstate is Synthesis

Details: Category: Tungsten Information; Published on Thursday, 05 February 2015 17:17; Written by zsq; Hits: 591

When concentrating an ammoniacal solution of tungstic acid (i.e. hydrous WO3), the product obtained is ammonium paratungstate. Below 50 C, the hexahydrate is formed, whereas when the temperature of the solution is above 50 °C, the pentahydrate or heptahydrate is formed. The former crystallizes as triclinic plates or prisms, whereas the latter as pseudorhombic needles.If a calcined WO3 is used, refluxing the ammonia solution is advisable to speed up the dissolution of the oxide.

Ammonium paratungstate is a white, crystalline powder with a very high degree ofchemical purity. It is used as a universal intermediate product for a variety of applications such as manufacturing tungsten oxides and tungsten metal powder, tungstic acid, ammonium paratungstate and organometallic components as well as in catalysis and fine chemistry.

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