A novel method to synthesize vanadium carbonitride nanopowders by thermal processing precursor

Vanadium carbonitride nanopowders were successfully synthesized by a novel method to thermal processing precursor of ammonium vanadate (NH₄VO₃) and nanometer carbon black. The phase evaluation, microstructure and synthesization process were investigated by simultaneous thermogravimetric and differential thermal analysis (TG–DTA), X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). These results show that single-phase VC_0.61N_0.39 nanopowder can be obtained at 1050 °C holding for 1 h in N₂ atmosphere, which is much lower than those of the conventional synthesis methods and the particle size of product distribute homogeneously exhibiting sphere shape with average particle size of 60 nm. With reaction temperature increase, the lattice parameter of V(C_1−xN_x) increases gradually and the nitrogen content decreases continuously. When heated up to 1150 °C, V(C_1−xN_x) would transferred to V₈C₇ and a free carbon, and the particle sizes increase along with hard agglomerates.     

Effect of alumina precursor on the synthesis of LaAlO3 nanopowders by reverse micelle processing

The effect of alumina precursor on the synthesis of nanosized LaAlO₃ powders by reverse micelle process has been studied. The synthesized and calcined powders were characterized by thermogravimetry-differential thermal analysis, X-ray diffraction analysis and transmission electron microscopy. Differential thermal analysis showed that LaAlO₃ phase transformation occurs at 830 °C and 866 °C for Al(NO₃)₃ and AlCl₃ precursor respectively. With Al(NO₃)₃ as starting precursor, well-crystallized LaAlO₃ phase was formed at lower temperature. Use of AlCl₃ as precursor resulted in bigger particle formation (∼41 nm) while Al(NO₃)₃ forms much smaller particles (∼28 nm) as confirmed by transmission electron microscopy.     

纳米WC对热喷涂涂层耐磨性的影响

在喷涂材料Fe/WC中添加少量的纳米Ni、纳米CeO2以及不同含量的纳米WC,采用亚音速火焰喷涂方法在Q235钢上制备涂层,通过对涂层组织及性能的检测,探讨纳米WC对涂层显微组织、显微硬度以及耐磨性的影响。结果表明,添加适量的纳米WC可以改善涂层组织,提高涂层的显微硬度及其耐磨性。     

Effects of additives on synthesis of vanadium carbide (V8C7) nanopowders by thermal processing of the precursor

Vanadium carbide (V₈C₇) nanopowders can be synthesized by thermal processing of the precursor of ammonium vanadate (NH₄VO₃) and nanometer carbon black. Effects of additives (CaF₂, CeCl₃·7H₂O and LaCl₃·7H₂O) on the phase composition and microstructure of the synthesized powders were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that additives (CaF₂, CeCl₃·7H₂O and LaCl₃·7H₂O) can accelerate the solid state reaction during synthesis of V₈C₇, and these additives play a vital role in determining the phase composition and microstructure. V₈C₇ powders with basically single phase can be synthesized at 1100 °C for 0.5 h with the addition of additives (CaF₂, CeCl₃·7H₂O and LaCl₃·7H₂O), and the powders show good dispersion and are mainly composed of uniformly-sized spherical particles with a mean diameter of 50 nm. Further experiment shows that V₈C₇ powders can be prepared at 950 °C for 1 h with 1.0 wt% CaF₂ as additive.     

纳米WC粉氢处理脱除游离碳的研究

将高碳含量的纳米WC粉末在氢气流中进行热处理脱除游离碳,研究处理温度、保温时间和H2流量等工艺参数对WC粉碳含量及粒度的影响.结果表明,在温度为940℃,H2流量为3.5L/min,保温时间为100min的工艺条件下,可以将碳含量由9.74%降低至6.20%,处理后纳米WC颗粒无明显长大.当处理温度高于970℃会导致WC化合碳损失而生成W2C相,并造成WC颗粒长大.     

纳米结构WC/Co涂层精密加工及其磨损性能的研究

纳米结构WC／Co涂层是一种重要的纳米涂层材料,工程上对其的应用常常基于其高耐磨性和强抗腐蚀性。关干WC／Co涂层的精密磨削以及耐磨性能,已有学者对其进行丁一定的研究。对于其耐磨性能的研究主要是基于喷涂参数对它的影响;对于其磨削后耐磨性能以及磨削参数对耐磨性能的影响规律研究极少。本文综述了纳米结构WC／Co涂层制备方法、WC／Co涂层机械性能和摩擦磨损性能以及其精密加工等方面的研究现状,同时对陶瓷磨损预报做了简单的介绍。目的就是在后续的工作中对比研究磨削后纳米结构WC／Co涂层的耐磨性能以及并分析磨削参数对其耐磨性能的影响并建立预报模型。     

Effect of C and milling parameters on the synthesis of WC powders by mechanical alloying

In the current study, the amount of carbon and the effects of milling parameters in production of tungsten-carbide (WC) powder were evaluated. Mechanical alloying (MA) of elemental W and C powders at different carbon-rich and carbon-deficient compositions was studied. XRD results showed that the higher the carbon content the longer the milling period for the formation of WC powder. We also report on the effect of milling parameters on the phase formation. In stoichiometric composition, WC was synthesized faster than in compositions with higher carbon amount. Furthermore, W₂C phase was observed in compositions with higher carbon content milled at low speed and ball-to-powder ratio (BPR), as well as in carbon-deficient composition milled for shorter period. The ab initio calculations were performed in attempt to explain the destabilization of W₂C on further milling.     

利用碳等离子体热处理方法在钨金属和单晶硅片表面制备站立式石墨烯

利用等离子体热处理方法,分别在W金属和单晶Si基底表面直接制备了站立式石墨烯。利用X射线衍射仪(XRD)、扫描电镜(SEM)、拉曼光谱(Raman)对获得的样品进行了结构和成分的表征,并用硬度计对样品表面硬度进行了测量。结果表明,在W金属和单晶Si基底表面分别形成了成分为W₂C-WC/石墨烯和SiC/石墨烯的复合层,且均匀的分布在相应的基底上。W₂C-WC/石墨烯复合层制备成功后,金属W的表面硬度为502.95 HV0.01,与纯金属W基底的硬度450.41 HV0.01相比,表面硬度增加52.54 HV0.01,提高了11.6%;SiC/石墨烯复合层制备成功后,SiC/石墨烯表层的硬度为836.76 HV0.025,与单晶Si基底的硬度812.74 HV0.025相比,表面硬度增加24.02 HV0.025,提高了2.95%。     

水溶化学法制备纳米WC/Co复合粉工艺探索

本文通过实验探索了水溶化学法制备纳米WC/C0复合粉工艺,研究了影响喷雾转换、锻烧、碳化和调碳的工艺因素,找到了满足纳米WC/Co复合粉制备的工艺参数。在Kear等人的经典合成技术中,碳化钨钴纳米复合材料是由喷雾转化水溶液的化学计量量的水溶性钨源和钴源,然后用流化床通氢将钨钴氧化物还原为金属钨和钴,之后在一个充满CO/CO2的气体环境中将金属钨和钴碳化成纳米WUCo复合粉末。本研究不同于Kear等人的处理方法,涉及的WC/C0使用水溶性溶液钨、钴和碳前躯体加工的纳米复合材料,大量的WGCo纳米复合粉体是将钨、钴和碳在分子级水平上混合制备成一个复杂的前驱体粉末的独特方案,前驱体粉末在煅烧炉充满惰性气体约100撕00cC的温度下转化成一个含有W-Co-C-0的预复合粉粉末,随后在碳化炉低于1000℃的温度下碳化。实验表明,水溶化学法生产的纳米WC/Co复合粉较常规方法,具有晶粒细而均匀、流动性好等特点,更适于高性能硬质合金的生产。     

WC颗粒对激光熔覆高熵合金SiFeCoCrTi涂层的组织及性能的影响

采用激光熔覆技术,在Q235钢基体上制备了高熵合金SiFeCoCrTi涂层,并研究了WC颗粒对高熵合金涂层的组织及性能的影响。通过OM,XRD,SEM,硬度试验,磨损试验等手段探究了高熵合金涂层的微观形貌,相结构,硬度及磨损性能。结果表明,高熵合金SiFeCoCrTi涂层组织为胞状树枝晶,主要由bcc相和金属间化合物构成。添加WC后,涂层中形成了致密细小的枝状晶,而且形成了大量的金属间化合物,如TiCo_3、Co_(1.07)Fe_(18.93)。同时WC添加使得基材的稀释率降低,涂层的性能明显提高,其涂层平均硬度提升23%,涂层摩擦系数和磨损率都明显减小,耐磨性能显著提高。     

超细WC颗粒对纳米CeO2增强激光镍基涂层的显微组织和耐磨性影响

CO₂激光器熔覆1wt.%纳米CeO₂和20wt.%WC添加的镍基合金涂层的磨损、显微组织与1wt.%纳米CeO₂添加镍基合金涂层进行对比。上述两种涂层均熔覆在基体30CrMnSiNi2A上并呈优良冶金结合。超细碳化物WC对WC-CeO₂/Ni涂层的显微组织影响由X射线衍射(XRD),扫描电镜(SEM)连同能量色散谱(EDS),电子探针(EPMA)进行分析。添加WC后M₂₃C₆增多,而M₇C₃减少。通过维氏硬度计和磨损测试系统对有WC添加和无添加CeO₂镍基合金涂层进行综合机械性能比。得出结论WC-CeO₂/Ni涂层明显优于CeO₂/Ni涂层。极少数热裂纹出现于WC-CeO₂/Ni涂层,萌生并扩展于熔池凝固过程中,对此做了SEM和EDS分析。裂纹机理可归因为铁稀释和WC添加导致的涂层与基体30CrMnSiNi2A间线膨胀系数间差异。     

水热法合成树枝状PbSe的影响因素研究

无表面活性剂条件下以甘油为溶剂采用简易的水热法合成了树枝状结构PbSe。水热温度、时间以及Pb源对PbSe形貌调控及形状影响很大。得到的PbS分别用XRD、SEM、TEM进行了表征分析。这一合成方法为高通量制备不用纳米结构及微观形貌的半导体纳米材料开辟了一条崭新的技术路线。同时也探讨了不同微观形貌PbSe的形成机理,主要取决于晶面<100>和<111)的生长速率比(R)。     

热处理对电渣熔铸WC颗粒增强钢基复合材料组织和性能的影响

采用电渣熔铸技术制备了以5CrNiMo模具钢为基体,WC颗粒为硬质相的钢基复合材料。用金相分析方法研究了该颗粒增强钢基复合材料熔铸原始态、锻造退火态和淬火回火态的显微组织,进行了洛氏硬度和冲击试验。结果表明,复合材料钢基体的WC颗粒分布较为均匀,组织致密。白色WC颗粒周围包裹着一圈黑色条带的Fe₃W₃C和WMoC₂复合碳化物。经过热处理后,材料的洛氏硬度和冲击韧度均较原始态有明显提高。     

化学法制备片状纳米银粉的研究进展

片状纳米银粉由于小尺寸效应、表面积大、导电性高等显示出其独特的性能,在电子、催化、能源和生物等方面有着广阔的应用前景.近年来,采用化学法来制备片状纳米银粉备受人们关注.本文从制备方法、制备机理、影响因素等方面评述了化学法制备片状纳米银粉的最新研究进展,展望了今后研究的方向.     

预置法对V-EPC铸渗制备复合材料组织和质量的影响

通过涂覆预制块法和压制预制块法两种预置体的预置方法,利用V-EPC铸渗工艺制备了WC增强铁基表面复合材料,着重研究了两种预置法对复合材料的表面质量和组织的影响。结果表明,压制法制备的复合材料表面质量较涂覆法好,复合层厚度均为3 mm左右,表面较平整,复合位置对铸渗件表面质量影响不大,且随着WC颗粒体积分数的增加,复合材料铸件的铸渗层表面质量呈下降趋势。对显微组织的研究表明,两种方法制备的复合材料过渡层都较平缓,在压制法制备的复合材料靠近复合层处的过渡层组织中没有石墨出现。压制法制备的复合材料复合层中WC的分布较涂覆法均匀,WC颗粒体积分数较高,WC的大小不一,一些WC颗粒产生裂纹、破碎和搭接现象,随着WC颗粒体积分数的增加,WC颗粒将变均匀。     

碘输运剂对CVT法制备ZnSe单晶的性能影响研究

采用I2作为输运剂,以单质Zn和Se为原料运用化学气相输运法制备了ZnSe晶体。比较了不同I2含量下所生长ZnSe晶体的性能,借助XRD、SEM和EDS检测方法分析了ZnSe晶体的结构、形貌和成分。结果表明:I2含量对ZnSe晶体性能具有重要的影响,通过比较3组I2含量所制备的ZnSe晶体,确定出当I2含量为4 mg/cm3时,所生长的ZnSe晶体具有较好的结晶质量,其晶格常数为5.668 nm。测定ZnSe中Zn与Se的原子分数比为1:0.99,且只有1个衍射峰(2θ=27.2°),其晶面指数为(111)。SEM图像表面比较平滑,没有明显气孔。在此条件下,ZnSe晶体的红外透过性能最好,红外透过率为53.07%~62.61%。其他两种I2含量下所生长的ZnSe晶体结晶质量较差,XRD图谱显示有多个衍射峰,SEM图像表面凹凸不平,有明显气泡和孔洞,并且其红外透过率较低。     

Effect of processing parameters on the microstructure and thermal conductivity of diamond/Ag composites fabricated by spark plasma sintering

Diamond/metal composites with 50 vol.% diamond have been produced by spark plasma sintering (SPS) using pure Ag as a matrix and diamond particles as reinforcement. Three kinds of powder mixing processes were used to prepare the mixture of diamond/Ag powders: dry mixing without milling medium, wet mixing and magnetic blending. Subsequently, they were all consolidated by SPS at various processing parameters to produce bulk diamond/Ag composites. Then samples were heat treated in order to obtain a higher thermal conductivity. The effect of processing parameters on the morphologies of the mixed powders, the microstructure and the thermal conductivity of the composites were investigated by comparing the experimental data. It reveals that particles were easy to agglomerate and the distribution of mixed powders was inhomogeneous by dry mixing method, and wet mixing method is too complex. The most favorable mixing process is magnetic blending by which the powders can be homogenously mixed and the composites prepared by optimized SPS processing parameters can obtain the highest relative density and the best thermal conductivity among the composites prepared by different processes. The magnetic blending diamond/Ag composites even have a 23% increase in thermal conductivity compared with pure silver sintered by SPS.     

Effect of modification by Pt and manufacturing processes on the microstructure of two NiCoCrAlYTa bond coatings intended for thermal barrier system applications

Few studies have already shown that Pt influences the diffusion of aluminium and therefore the microstructure of β-NiAl or γ-Ni/γ′-Ni₃Al materials. Besides, several works have revealed that the addition of Pt to MCrAlY (M = Ni and/or Co) improves the oxidation/corrosion behavior of the material. Nevertheless, very few data have been published on the microstructure of such modified MCrAlYs. Then, the present work deals with the addition of Pt to two NiCoCrAlYTa coatings that differ by their manufacturing process. Characterization is carried out in order to understand the influence of Pt diffusion but also the effect of the manufacturing process on the final microstructure. The collected data from XRD, SEM, EDS and TEM analyses reveal that an Al uphill diffusion occurs during heat treatment due to the presence of the Pt layer. The Al diffusion from the NiCoCrAlYTa bulk to the Pt-rich surface is so extensive that no more β-phase remains within the core of the coating. Pt may also dissolve TaC, precipitates largely present in the non-modified NiCoCrAlYTa coatings. In addition to Pt, the microstructure of the NiCoCrAlYTa prior to Pt deposition and heat treatment, dependent on the NiCoCrAlYTa manufacturing process, greatly influences the final microstructure.     

柠檬酸与乙二醇对无机盐溶液热解制备铱锡氧化物涂层结构及性能的影响

在铱锡氯化物溶液中加入柠檬酸和乙二醇等助剂,采用刷涂-热分解法制备出钛基铱锡氧化物涂层。借助扫描电镜、电子探针、计时电流等技术研究柠檬酸与乙二醇对铱锡氧化物涂层表面形貌、结构、粗糙度和成分分布等表面性质的影响,采用循环伏安、阳极极化、交流阻抗等方法分析柠檬酸与乙二醇对铱锡氧化物涂层在硫酸溶液中电催化性能和化学稳定性的影响。结果表明:涂液中添加柠檬酸和乙二醇可细化电极表面涂层中的氧化物晶粒,明显减小涂层表面中的裂纹,显著改善锡元素的分布;在0.5mol/L硫酸溶液中,柠檬酸乙二醇助剂改性涂层的循环伏安电荷增加1.71倍,Tafel曲线斜率减小37%,析氧反应的电荷转移阻抗降低66%,开路电位提高0.13 V。