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1.
Diffusion kinetics of nitrogen in tantalum during plasma-nitriding   总被引:2,自引:0,他引:2  
1 INTRODUCTIONBecausetantalumhasstrongaffinitywithoxygenitisdifficulttonitridetantalumatrelativelylowtem perature (≤ 1 0 0 0℃ )ascomparedwithitshighmelt ingpoint ( 2 996℃ ) .TantalumwillbeoxidizedintoTa2 O5 ratherthannitridedontraditionalnitridingconditionsofironan…  相似文献   

2.
Solid-state synthesis of Sr-and Co-doped LaMnO_3 perovskites   总被引:5,自引:0,他引:5  
1 INTRODUCTIONAnimportantgoalinthedevelopmentofsolidoxidefuelcells (SOFCs)istoreducetheoperatingtemperatureofthefuelcellstackfrom 10 0 0℃tobe low 85 0℃ .Theprimarydriversare :1)togetanop timumtrade offbetweenperformanceandlifetimeofthestackand 2 )toreducetheoveral…  相似文献   

3.
Kinetic mechanism of anodic oxidation of tantalum in nitrate melts   总被引:3,自引:0,他引:3  
1 INTRODUCTIONTantalumcanbeoxidizedatlowtemperaturein toinactiveTa2 O5 withcompacttextureandspecificresistanceof 1 0 18Ω·cm[1],whichentitlestantalumgoodcorrosionresistanceandelectricresistance ,andalsomakesitimpossibletogetthickTa2 O5 filmsatlowtemperature .Theo…  相似文献   

4.
Modeling and optimizing of steel and mushy Al-28Pb alloy bonding   总被引:8,自引:0,他引:8  
1 INTRODUCTIONAtpresent,thetypicalmaterialofneotypebear ingissteel backedAl 2 0Snalloybonding plate[1 ] .Forsteel backedAl 2 0Snalloybondingplate ,steelbackhashighstrengthwhichcanbeartheexternalload ,andAl 2 0SnalloylayerisalubricatingoneinwhichAlsubstratehasexcel…  相似文献   

5.
1 INTRODUCTIONMoSi2 isoneoftheintermetalliccompoundswhichhavethepotentialinbeingusedasadvancedhightemperaturematerials[1] .Ithashighmeltingpoint(2 0 30℃ ) ,highductile/brittlenesstransitiontemperature(10 0 0℃ ) ,highoxidationtemperature(16 0 0℃ ) ,relativelylowdensity(6 .30…  相似文献   

6.
Deoxidization of CuCr25 alloys prepared by vacuum induction melting   总被引:12,自引:2,他引:10  
1 INTRODUCTIONLow gascontentisthebasicrequirementforCuCr2 5contactmaterialinvacuuminterrupters.Be causethereleasedgasduringcurrentinterruptioncouldinduceinterruptingfailure[1] .Sotheoxygencontentmustbelowerthan 0 .0 5% ,andnitrogencontentmustbelowerthan 0 .0 0 5%acc…  相似文献   

7.
Rare earth activated sintering of MoSi_2 and its electric conductivity   总被引:10,自引:0,他引:10  
1 INTRODUCTIONIntermetallicMoSi2 holdsconsiderable promiseforawidevarietyofelevatedtemperaturestructuralapplicationsattemperaturesabove10 0 0℃[1] .SinceMaxwellfirstputforwardthehypothesisthatMoSi2couldbeapotentialstructuralmaterialintheearly1950s,materialscien…  相似文献   

8.
1 INTRODUCTIONNanocrystallineAl richglassalloyshaveattract edgreatattentionasanewmaterialduetoitsmuchhigherspecificstrengththanthehigheststrengthofconventionalcrystallineAl basedalloys[1 ] .Refs.[2 ,3]reportedthatthefracturestrengthisabove 1 0 0 0GPaforAl richamo…  相似文献   

9.
1 INTRODUCTIONTi1 0V2Fe3Aland 3 0CrMnSiNi2Aaretypicalmaterialstomanufacturelanding gearofairplanewhichbearsdynamicloadingduringtakingoffandlanding[1].AerospacesparesdesignedbyNormalQuasi staticStrengthDesignCriterionfacethecon tradictoryofsafetyandeconomy .Dyn…  相似文献   

10.
1 INTRODUCTIONRoast leach purification electrowinningprocessisthemostcommonmethodforzincproductionintheworld[1 ] .Theremovalofcobaltfromzincsulphatesolu tionbycementationhasbeenthefocusofresearchformorethan 2 0yearsinthehydrometallurgyofzinc[1 ,2 ] .Thepresenceo…  相似文献   

11.
The electrochemical activity and stability of tungsten carbide gas diffusion electrode in different electrolytes were determined by galvanostatic charge method. It is shown that WC exhibits good electrocatalytic activity and stability for hydrogen oxidation in acidic solutions when the electrode potential is below about 800 mV (vs DHE), WC is firstly oxidized to an unstable blue tungsten oxides at 800-900mV which are closed to a composite stoichiometry of W2O5 in H2 SO4 solution and W8O23 in HCl solution calculated by charge consumed. Furthermore,the generated intermediate tungsten oxides can be further oxidized into WO3 at higher potentials. While in alkali solution, WC can not be used as anodic catalyst for its poor stability and catalytic activity due to the fact that WC will be directly oxidized into WO3.  相似文献   

12.
以剥离后的蒙脱石(Mnt)片层为载体、六氯化钨(WCl6)为钨源,通过浸渍负载及原位还原碳化获得了碳化钨(WC)与蒙脱石(Mnt)纳米复合材料,然后将氯铂酸(H2PtCl6)通过浸渍负载于复合材料上,并在氢气(H2)中还原得到Pt-WC/Mnt三元纳米复合催化材料。采用X射线粉末衍射和透射电子显微镜对三元纳米复合催化材料的物相、形貌和结构进行表征,采用三电极体系和循环伏安法测试了样品的电催化性能。结果表明:样品物相主要为WO3和WC,蒙脱石片层结构明显,铂(Pt)纳米粒子均匀分布于WC/Mnt复合材料的外表面。Pt-WC/Mnt三元纳米复合材料对甲醇电催化氧化具有较高的催化活性,并且在酸碱体系中均具有良好的稳定性。  相似文献   

13.
目的制备多壁碳纳米管负载碳化钨的纳米复合材料(WC_x/MWCNTs),探索微波加热温度对WC_x/MWCNTs合成的影响规律。方法利用分子自组装技术与微波加热技术相结合,以钨酸钠为W源,制备了WC_x/MWCNTs纳米复合材料。采用X射线衍射(XRD)和透射电子显微镜技术(TEM)对不同条件下制得样品的物相组成、结构及微观形貌进行了表征;采用循环伏安法在酸性环境下测试了WC_x/MWCNTs对氢和CH3OH的电催化性能。结果当微波加热温度为1000℃时,制备的WC_x/MWCNTs纳米复合材料由WC、WC2和C组成,碳纳米管的多壁结构保留较好,碳化钨颗粒均匀地分布在碳纳米管外表面,粒径为20~50 nm。循环伏安测试结果表明,制备的WC_x/MWCNTs在酸性环境下对氢具有一定的催化作用,但对甲醇没有明显的电催化作用。结论通过控制合理的微波加热温度,可制备出碳化钨粒径小、分布均匀、碳纳米管多壁结构完好的WC_x/MWCNTs纳米复合材料。制备的WC_x/MWCNTs在酸性环境下对氢具有一定的催化作用,可作为催化剂载体来负载其他金属制备复合催化剂。  相似文献   

14.
As part of an ongoing study of a new tungsten recycling process using a molten sodium hydroxide bath, in which tungsten is anodically dissolved in the melt from tungsten-containing secondary resources, the influence of the partial pressure of water vapor on the electrochemical behavior of tungsten, cobalt, nickel, and tungsten carbide was investigated. Cyclic voltammograms of cobalt suggested that the solubility of cobalt compounds increased with the partial pressure of water vapor, whereas tungsten and tungsten carbide underwent no significant changes during their oxidation step. In addition, the current attributable to the evolution of hydrogen gas was measured when the partial pressure of water vapor became higher than 0.5 atm. On the basis of the abovementioned results, anodic dissolution was carried out at a constant cell voltage using a super hard alloy tool. When water vapor was introduced into the system, the cell voltage and period required to dissolve the entire tip were reduced, even though the applied cell voltage was less than half that required under a pure argon atmosphere. These results indicate that the introduction of water vapor has the potential to improve the anodic dissolution step in the tungsten recycling process using a molten sodium hydroxide bath.  相似文献   

15.
研究了在传统氢还原工艺制备纳米碳化钨粉末过程中不同氧化钨的形貌结构对纳米W/WC粉末均匀性的影响,并对粉末及其WC-Co烧结体的性能进行了表征。结果表明,用具有疏松、多孔形貌结构的细小氧化钨颗粒更容易制备出结构较疏松、分散性较好的纳米W粉和WC粉。晶粒聚集和异常粗大颗粒的产生,主要与碳化过程中团聚纳米钨粉颗粒因烧结合并增粗有关。  相似文献   

16.
An understanding of the anodic behaviour of WC‐Co type hardmetals is vital for the functional behaviour of this class of materials. The anodic oxidation of WC‐13Co grade hardmetal in 0.1 M H2SO4 was investigated. This study is based on electrochemical (linear sweep voltammetry, cyclic voltammetry, impedance spectroscopy), compositional (energy dispersive spectroscopy), structural (X‐ray diffraction) and morphological (scanning electron microscopy) investigations. The potential range in which the oxidation of the Co‐alloy takes place with respect to the nobler carbide phase was defined. Within this potential interval a passivating behaviour for the binder alloy was shown. The potential threshold for WC oxidation was identified by monitoring the inception of the electrochromic loop. The anodic attack gives rise to the formation of hydrous WO3. The attack morphology is characterised by the alteration of the grain shape with formation of jelly‐like microscopic and flaky macroscopic structures.  相似文献   

17.
氩气保护下碳化钨对镍基合金熔覆层组织及耐磨性的影响   总被引:3,自引:3,他引:0  
杨勇  赵靖宇  李静  杨景凤  赵彬  孙玉福 《表面技术》2015,44(2):55-59,82
目的改善Q235钢板的耐磨性,以取代65Mn在振动筛筛板中的应用。方法采用电阻丝加热非真空熔覆技术,在氩气保护条件下于Q235钢表面制备碳化钨/镍基合金复合熔覆层。通过SEM和XRD观察分析熔覆层与基体的结合方式、碳化钨分布、熔覆层组织及相组成,通过硬度测试及磨损试验,分析碳化钨对熔覆层耐磨性的影响。结果熔覆层与钢基体达到冶金结合。熔覆层主要由奥氏体、碳化钨、碳化物及硼碳复合化合物等相组成,碳化钨弥散分布其中。当碳化钨用量为熔覆粉末总质量的35%时,熔覆层硬度为47.3HRC,磨损率为0.08 mg/m,约是钢基体耐磨性的5倍,65Mn耐磨性的4倍。结论采用氩气保护制备的碳化钨熔覆层与基体结合良好,提高了钢基体的耐磨性。  相似文献   

18.
Ceramic-WC coatings were prepared on AZ31 B Mg alloy by plasma electrolytic oxidation (PEO) from a phosphate based bath containing suspended tungsten carbide nanoparticles at various process times. Scanning electron microscope results indicated that increase of coating time and incorporation of tungsten carbide into the ceramic coating during the PEO process led to a decrease in the number and diameter of coating pores. Phase analysis showed that the nanocomposite coating was composed of MgO, Mg3(PO4)2 and WC. Tribological properties and corrosion behaviour of uncoated AZ31 B Mg alloy and ceramic coatings were evaluated using a pin-on-disc tribometer and potentiodynamic polarisation technique in 3.5% NaCl solution, respectively. The wear and electrochemical tests showed that wear and corrosion resistance of ceramic-WC nanocomposite coatings were better than ceramic only ones. In addition, wear and corrosion behaviour of coatings improved with increasing the coating time.  相似文献   

19.
Cemented tungsten carbide tool bits are widely used in cutting, oil and gas, tunneling, and mining industries there these materials exposed to extremely harsh environments that cause early stages of failure. Tungsten carbide hardmetals are suffering from tribocorrosion, which is a material degradation process that occurs due to the combined action of wear and corrosion. On the one hand, tungsten carbide materials composed of hard ceramics (WC grains) phase in a soft metal matrix binder (Co, Fe, and Ni) phase; hence, it leads to different tribological mechanisms. On the other hand, the different electrode potential of hard WC grains (act as a cathode) and soft binder phase (act as an anode) leads to the formation of the micro galvanic couples between these phases in many aqueous environments causing corrosion. Since tribocorrosion mechanisms are significantly influenced by the varying composition and microstructure of tungsten carbide hardmetals, the effect of size and morphology of the WC grains on tribocorrosion has also been reviewed. This review particularly highlighting the various tribological and electrochemical aspects and their possible degradation mechanisms that are generally encountered by the drill bits during operating conditions. Hence, the understanding of these mechanisms is, therefore, very essential for the selection, improvement, and development of high-performance hardmetals.  相似文献   

20.
A fine and platelet tungsten carbide patterned structure with fine yttrium containing dispersed phase was observed in liquid phase sintered WC-20% Co-1%Y2O3 cemented carbide with ultrafine tungsten carbide and nano yttrium oxide as starting materials. By comparing the microstructures of the alloy prepared by hot-press at the temperature below the eutectic melting temperature and by conventional liquid phase sintering, it is shown that hexagonal and truncated trigonal plate-like WC grains are formed through the mechanism of dissolution-precipitation (recrystallization) at the stage of liquid phase sintering. Yttrium in the addition form of oxide exhibits good ability in inhibiting the discontinuous or inhomogeneous WC grain growth in the alloy at the stage of solid phase sintering.  相似文献   

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