2021年9月6日星期一

Decoloration Mechanism of Double Doped Zinc Tungstate

The modification of zinc tungstate by doping rare earth elements is an effective way to improve its luminescent properties.

The single crystal of zinc tungstate is rose red, the color makes the luminous efficiency decrease and the decoloration effect is obvious.

After annealing for a long time, the ZnWo4 crystal will disappear gradually, but the annealing of the bulk crystal still has difficulties which can not be overcome. The main problem is that the defect is incomplete and the defects are introduced into the annealing process. 

double doped zinc tungstate image

In single doped rare earth crystals, only cerium doped Ce3+ can recede the color of the crystal, both doped cerium Ce3+ and lithium li3+ have obvious decoloration effect on zinc tungstate crystal, especially, the former can obtain colorless crystal by proper doping.

The removal mechanism of zinc tungstate may be due to the decomposition of CO2 in Li2CO3 crystals, CO2 molecules will be partially retained in the lattice, CO2 molecules and O2 molecules are linear molecules, and the radius of the two has little difference, can replace each other in the hole. Therefore, when the crystal grows, the CO2 molecules fill in the oxygen vacancies to make the crystal clear.

Through the mechanism of doped zinc tungstate, it can be seen that the segregation coefficient of Ce3+ and Sm3+ in ZnWo4 crystal increases after double doping, it is beneficial to obtain high content of crystals, thereby changing the short life of fluorescence and the quenching temperature of luminescence is too low.

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Toughening Properties of Silver and Nickel Contacts Evaluation by Tungsten and Tungsten Oxide

In life, silver-nickel contact materials are widely used in relays, circuit breakers for low current ratings because of their good ductility and low contact resistance.

When current levels exceed 20 A, conventional AgNi contact materials exhibit weaker resistance to soldering and erosion, limiting their range of application. However, by adding a small amount of additives, the electrical properties can be improved, thus expanding its application area. Some scholars have studied that adding tungsten or tungsten oxide can improve the performance of AgNi contact materials. 

silver nickel contact image

The W or WO3, which accounts for 1.5% of the total, was made into silver-nickel contacts (containing 85% of silver content) by powder mixing, isostatic pressing, sintering, extrusion, subsequent wire drawing and riveting. Each contact material was repeated 5 times using the same resistive load in the test. The current and mechanical structure ensured that all tests had comparable arcing energy with supply voltages and load currents of 220 V and 25 A, respectively. After the 5000 operation, the contact is removed from the equipment and cleaned by ultrasonic in alcohol. After drying, the weight is weighed and the weight loss is calculated. 

The comparison of test results shows that the two different additive silver and nickel contact materials with tungsten powder or tungsten oxide have no obvious difference in the microstructure of the material, but there are big differences in the electrical properties such as material transfer and arc erosion. In the simulation of electrical performance test, the tendency of the addition of WO3 is that the mass loss and the microstructure of arc-affected zone are worse than that of tungsten powder. 

The addition of 1.5% W in AgNi contact materials can reduce the maximum welding power and reduce the arc erosion compared with 1.5% WO3. Therefore, tungsten powder may be better applied at low current level AC contactors.

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Tungsten Phosphide Catalyst Desulfurization

The contradiction between the increase of organic nitrides and sulfides in oil and the heavy crude oil.

The strict environmental protection regulations are becoming more and more serious, so it is necessary to conduct deep hydrofining for oil products.

The research shows that although the traditional molybdenum sulfide based catalyst is effective in hydrotreating process, it is far from meeting the requirements of deep hydrodesulfurization. The current approach is to retrofit existing catalysts and find new catalysts that can be used to meet the need for deep hydrotreating of crude oils.

desulfurization of tungsten phosphide catalyst image

In 1990s, the synthesis and performance of tungsten nitride hydrodesulfurization catalyst have been reported abroad, and the structure and desulfurization performance of P, Ni, W catalyst with phosphorus as auxiliary agent have been studied. However, the research on tungsten phosphide seems to be few. Therefore, the Chinese scholars also try to use tungsten phosphide for hydrodesulfurization test, so as to evaluate the non phosphorus catalytic effect.

The catalyst active component tungsten phosphide was synthesized by the method of temperature programmed reduction of phosphotungstic acid with high purity hydrogen. The PW-r-Al2O3 catalyst was prepared by reduction and mixing with r-Al2O3 as the carrier and tested.

The results show that the specific surface area of the tungsten phosphide is 7.228m2/g, and the specific surface area of tungsten phosphide catalyst Al2O3 is 105.543m2/g, which has better thiophene desulfurization performance. When the pressure is 3.0MPa, the space velocity is 4h-1, the volume ratio of hydrogen to oil is 1000 and the temperature is 340 °C, the thiophene hydrodesulfurization rates of the catalysts are respectively 90.2%. In addition, the stability of the catalyst was investigated. When the mixture was injected (thiophene 0.8%, pyridine 1.2%, cyclohexane 76%, octane 2%, cyclohexene 20%), the quality of the catalyst was all mass fraction, under the same reaction conditions, the denitrification rate and the desulfurization rate of the catalyst were only decreased by about 2%, which indicated that the PW-r-Al2O3 catalyst had good stability after 105h.

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Nickel Tungsten Nitrogen Catalyst for Its Catalytic Strength

With the continuous strengthening of human environmental awareness, the quality of living environment has aroused widespread concern.

All countries have formulated strict standards for the quality indicators of sulfur, nitrogen and other harmful substances in petroleum products. The clean production process and green products have become the mainstream trend in the development of petroleum refining and chemical production. In recent years, the transition metal nitrides hydrotreating catalyst has become a hot topic in the field of new catalysts because of its excellent deep hydrodesulfurization, denitrification activity and selectivity.

Some scholars believe that the current research on oil desulfurization catalyst is too focused on the cobalt molybdenum series earlier, and has excellent mechanical and thermal stability and anti poisoning characteristics of nickel tungsten catalysts study less, but in fact, the nickel tungsten nitrogen catalyst has more potential applications. 

nickel tungsten nitrogen catalyst image

By using temperature programmed reduction technology and r-Al2O3 as carrier, the nickel tungsten hydrofining catalyst NiWN/r-Al2O3 with different metal loading was prepared by impregnation method, and its hydrodesulfurization test was carried out.

 The size of the desulfurization activity level and surface acidity of catalyst was correspondence, namely catalyst surface acidity high desulfurization activity of catalyst, desulfurization activity of small low surface acidity. The surface acidity of catalysts, in addition to direct hydrogenolysis and hydrogenation desulfurization desulfurization, isomerization and cracking degree of strengthening, for deep desulfurization, and high desulfurization activity. The test found in NiWN/r-Al2O3 than the surface of the product is 149.5, surface acidity was 0.205, in the process of cracking gasoline showed good catalytic performance, surface acidity of benzothiophene on two is enough to produce catalytic desulfurization effect, the desulfurization rate is only about 91.2%. In this regard, scholars believe that nickel tungsten nitrogen catalyst can be used for catalytic desulfurization of oil, but there is still room for improvement and improvement.

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Decoloration Mechanism of Double Doped Zinc Tungstate

The modification of zinc tungstate by doping rare earth elements is an effective way to improve its luminescent properties. The single cryst...