Nano VC whiskers were prepared by using ammonium metavanadate,xylose,etc.as precursor materials with carbothermal reduction method.The effects of type and dosage of halogenation agents on the preparation of nano VC whiskers were studied by SEM,TEM and XRD.The results show that nano VC whiskers with about 100 nm diameter,smooth surface and good morphology can be prepared at 1000℃for 2 h by adding 10%NaF as the halogenation agent.NaF is the most ideal halogenation agent for preparing VC whiskers in six kinds of halogenation agents.The dosage of halogenation agents has an important influence on the preparation of nano VC whiskers.The optimal dosage of NaF is 10%.Too little NaF cannot promote the growth of VC whiskers,while too much NaF will inhibit the growth of VC whiskers.

The graphite/VO_2.5-xcomposite powders were successfully prepared by carbothermic reduction at atmospheric pressure.The influence of reduction temperature,reduction time and graphite/V2O5 mass ratio on the phase composition of the reduction product was studied by XRD,and the resistivity of gra-phite/VO_2.5-xcomposite powders was measured.The results show that reduction temperature is a key factor affecting phase composition of the product,while reduction time and graphite/V₂O₅mass ratio have little influence.Under the conditions of reduction time of 60 min and graphite/V2O5 mass ratio of 22∶100,the vanadium-containing phase transition sequence of the reduction product is V₂O₅→V₆O₁₃→VO₂→V₅O₉→V₂O₃with reduction temperature increasing from 450℃to 950℃.The graphite content and vanadium-containing phase composition in the reduction product are the key factors affecting the resistivity of gra-phite/VO_2.5-xcomposite powders,and the appearance of VO₂and V₂O₃is conducive to resistivity reduction of the composite powders.The product reduced at 650℃for 60 min with 40∶100 graphite/V2O5 mass ratio has the minimum resistivity of 0.08Ω·cm.

Ti(C,N)-based cermets were prepared by low pressure sintering.The effect of boron carbide(BN)content on the microstructure and mechanical properties of Ti(C,N)-based cermets was studied.The results show that the microstructure of sintered cermets shows a typical core-rim structure.The size of black cores in cermets decreases and the amount of white core-gray rim structure is improved with the increase of BN content.BN addition leads to more homogenous microstructure.Besides,the results reveal that the wettability between hard phase and binder phase is decreased,and the porosity of cermets improves with the BN content increasing.However,the modified microstructure by the appropriate addition of BN results in higher mechanical properties of the cermets.Hardness of Ti(C,N)-based cermets is improved to the maximum of 1710 HV₃₀,when the content of BN is 1.5%.With 2.0%BN addition,the cermet has the maximum toughness of 9.4 MPa·m^1/2,improved by about 10.59%compared with the samples without BN.More than 1.5%BN decreases the transverse rupture strength,and less transgranular fracture and more intergranular fracture are observed.In conclusion,when the content of BN is 1.5%,Ti(C,N)-based cermet samples have the best comprehensive mechanical properties.

By testing the micro-yield strength,thermal expansion coefficient,and dimensional changes of the isostatically pressed beryllium material,its dimensional stability against load and temperature changes was studied.The results show that the micro-yield strength of isostatically pressed beryllium material is relatively high,with an average value of 127.4 MPa,which is 53.5%higher than the equivalent beryllium materials published in the United States.Isostatically pressed beryllium material has a relatively low thermal expansion coefficient,and its longitudinal and horizontal average linear expansion coefficients in the temperature range of 25~100℃are 12.02×10^-6/℃and 11.89×10^-6/℃,respectively.The total axial resi-dual strain of isostatically pressed beryllium material is small after repeated cooling and heating cycles,about-18×10^-6after 15 cycles,and its dimensional thermal stability is excellent.

The preparation process of magnesium-lithium mixed oxide by calcining magnesite and lithium hydroxide monohydrate as raw materials was studied.Through differential thermal-thermogravimetric analysis of raw materials during calcination and X-ray diffraction phase analysis of calcined products,the decomposition process of lithium hydroxide monohydrate in the mixture was discussed.The results show that lithium hydroxide monohydrate is melted at first and then decomposed during direct calcination,while part of Li₂CO₃is generated during calcination of the mixture of lithium hydroxide monohydrate and magnesite,making subsequent decomposition difficult.The calcination process of the mixture of lithium hydroxide monohydrate and calcined magnesite produces a small amount of magnesium hydroxide,but the magnesium hydroxide is quickly decomposed into magnesium oxide,which has no effect on decomposition of lithium hydroxide.When calcination temperature is above 950℃and calcination time reaches 120 min,the decomposition ratio of lithium hydroxide monohydrate in the mixture is over 98%,and the main phases of calcined materials are MgO and Li₂O.

Taking 38 CrMoAl steel as the research object,its surface was treated with nitriding,iron plating and boronizing,respectively.The nitrided layer,iron-plated layer and boronized layer were characterized and analyzed by X-ray diffractometer,optical microscope and microhardness tester.The results show that the boronized layer with thickness of 100μm can be obtained by the method of combining iron plating and boronizing,and it is composed of Fe₂B single phase,which is wedged into the matrix in the shape of needle teeth and firmly combined with the matrix.The surface hardness of nitrided 38 CrMoAl steel is significantly improved to 1700 HV after iron plating and boronizing treatment,which is much higher than that of 38 CrMoAl steel with ordinary nitriding treatment,thus achieving the purpose of improving the surface performance of the repaired material.

Taking WC-8%Co carburized cemented carbide as the research object,it is quenched and cryogenically cooled after re-firing by hydrogen decarburization process with filling method.Metallographic microstructure,HRA hardness,coercivity,transverse fracture strength and other physical and mechanical pro-perties of cemented carbide samples were tested and analyzed.And the influences of quenching and cryogenic cooling processes on the mechanical properties and microstructure of re-fired cemented carbides were studied.The results show that both quenching and cryogenic cooling can increase the transverse fracture strength of re-fired cemented carbides(by 35.26%and 11.54%,respectively),refine their WC grains,and reduce the average WC grain size by 6.28%and 5.86%,respectively,but they cannot effectively eliminate the pores and non-combined carbon in the microstructure of re-fired cemented carbides.

用筷子进餐,同桌合食,交箸换盏,私筷入口再入合盘,虽则历史悠久、幸福快乐,但也存在巨大健康隐患。为了防范和减少交叉感染及食源性疾病传播,切断"口口相传"的疫情传播途径,倡导健康、卫生、文明的用餐方式,有必要启动"使用公筷,健康你我"行动。当然,现在仍有一部分人对使用公筷公勺存在争议,在他们的观念里,使用公筷公勺会显得自己失礼,有不信任、嫌弃别人的倾向,有的人还认为在家使用公筷太夸张了,有点过分讲究。要知道,在中国传统饮食文化中,筷子扮演着重要的角色。"莫道筷箸小,日日伴君餐;千年甘苦史,尽在双筷间。"筷子的一头连着嘴巴,另一头连着的可不只是美味佳肴,还有病毒和疾病。虽然使用公筷公勺缺失了那么一点人情味,但这才是对所有人健康的尊重和保护。

The freezing crystallization method was adopted to recover sodium carbonate in the sodium tungstate liquid,achieving the reuse of sodium carbonate as the production raw material and reducing the discharge of salty wastewater.The effects of liquid concentration,freezing temperature,freezing time and seed crystal addition amount on the freezing crystallization process were studied.The results show that when the simulated leaching liquid containing 200g/L WO3and 200g/L Na2CO3is processed,Na2CO3crystallization rate reaches 75%and WO3loss rate is only 1.9%under the conditions of freezing time of 2h,freezing temperature of 4~5℃and seed crystal addition amount of 0.5%.Under the above conditions,the actual leaching liquid containing 200g/L WO3and 200g/L Na2CO3and obtained by Na2CO3pressure lea-ching of low-grade tungsten ore is processed,and Na2CO3crystallization rate is 74%and WO3loss rate is 6.6%.When Na2CO3recovered by freezing crystallization is returned to the pressure leaching process of tungsten ore,the obtained leaching residue contains 0.52%WO3,and the leaching rate is up to 94.99%,which can meet the requirements of industrial recycling production.

Tungsten can be efficiently leached from low grade scheelite by sodium phosphate-sodium hydroxide-calcium fluoride synergistic leaching,but the crude sodium tungstate leaching solution contains a certain amount of impurities of fluorine and phosphorus.Magnesium chloride was used as impurity removal agent to remove fluorine and phosphorus from the crude sodium tungstate solution in the form of precipitate.The effects of magnesium chloride dosage,temperature,pH value,initial fluorine concentration and reaction time on impurity removal were investigated.The experimental results show that increasing the amount of MgCl2,reaction temperature and reaction time is beneficial to improving the removal effect of fluorine and phosphorus,but too large or too small pH value is not conducive to the removal of impurities.When initial fluorine concentration is 1.35~2.85g/L and initial phosphorus concentration is 0.18g/L,the optimal process conditions are as follows:the molar ratio of magnesium to fluorine is nMg/nF=0.9,the temperature is 80℃,the pH value of solution is 11.8,and the reaction time is 30min.The removal rates of fluorine and phosphorus reach 98.3%and 97.2%,respectively,while the loss rate of tungsten in the precipitation slag is about 0.15%.Therefore,magnesium chloride precipitation method can effectively remove fluorine and phosphorus from sodium tungstate solution with low tungsten loss.