碳热还原结合熔盐法制备碳化钛粉末与表征

以NaCl为熔盐介质,采用锐钛矿型钛白粉和炭黑为原料,探索一种碳热还原结合熔盐法合成高纯碳化钛(TiC)的方法。借助XRD研究了反应温度和原料配比对合成碳化钛的影响,采用SEM、TEM、EDS、粒度分析仪、热力学分析等检测分析手段对合成产物的特性和过程进行分析。结果表明:相比传统的碳热还原合成碳化钛的方法,NaCl熔盐介质的引入可以有效地降低碳化钛的合成温度(从1700℃到1550℃)以及合成高纯碳化钛的时间(从10 h到3 h)。结合研究成果,提出了熔盐介质中溶解-沉淀的合成机理。     

电场作用下75wt%Fe-25wt%(Ti+C)体系燃烧合成的探讨

采用Gleeble热模拟机对75Fe-25(Ti+C)体系在电场作用下的燃烧合成进行探讨,结果表明:这种不能采用普通SHS技术进行燃烧合成的体系,当预设升温速度为600℃/s时,在电场作用下仍不能实现燃烧合成;而当预设升温速度提高到1 000℃/s时,在电场作用下该体系能在743℃发生燃烧合成反应,合成产物由TiC和Fe组成,其中细小的TiC颗粒有一定程度的团聚现象。     

电场诱导Fe-Ti-C体系低温燃烧合成显微组织演变

采用Gleeble-1500D热模拟机，通过对质量分数55％（Ti＋C）-45％Fe粉末压坯分别升温至250～800℃的解析实验，研究Fe-Ti-c体系在电场诱导下低温燃烧合成的显微组织演变。结果表明：在电场和大热流密度的共同作用下，体系的点火温度可大幅降低。当加热温度在250～350℃之间，体系虽未发生化学反应，但显微结构在一定程度随温度而发生变化；当加热温度在350-470℃范围内，体系被点燃发生“热爆”现象，而在燃烧合成反应前期，合成TiC的反应优先发生；当加热温度提高到470-670℃，合成TiC反应发生的同时还伴随有合成Fe2Ti的反应；然而随加热温度进一步提高到670-800℃，Fe2Ti会发生部分分解，进而使得合成TiC的反应继续进行。当温度达到800℃左右，该合成反应全部完成，产物由Fe、TiC和少量Fe2Ti组成。此外，通过合成反应所得呈圆球状、细小的TiC颗粒均匀地分布在Fe基体中，且随加热温度的提高而有所长大。     

电场作用下75wt％Fe-25wt％（Ti＋C）体系燃烧合成的探讨

采用Gleeble热模拟机对75Fe-25（Ti＋C）体系在电场作用下的燃烧合成进行探讨。结果表明：这种不能采用普通SHS技术进行燃烧合成的体系，当预设升温速度为600℃／s时，在电场作用下仍不能实现燃烧合成；而当预设升温速度提高到1000℃／s时，在电场作用下该体系能在743℃发生燃烧合成反应。合成产物由TiC和Fe组成，其中细小的TiC颗粒有一定程度的团聚现象。     

机械激活工艺对TiO2碳热还原合成纳米TiC的影响

以纳米TiO2/碳黑为原料,通过机械激活-碳热还原法合成纳米TiC粉末,研究了机械激活工艺对TiO2碳热还原反应的影响.产物经XRD分析表明,激活时间延长、球料比增大、球磨机转速加快都有利于促进纳米TiO2碳热还原反应进行得更完全,但最终TiC产物中(Fe,C)杂质含量也随之上升.综合考虑,球磨时间4～8h,球料比10:1,转速250r/min对后续碳热还原合成纳米TiC是较合适的工艺选择.     

预设升温速度对电场作用下Fe-Ti-C体系燃烧合成的影响

采用Gleeble-1500D热模拟机,研究电场作用下预设升温速度对55wt%(Ti C)-45wt?体系在从室温加热至800℃过程中燃烧合成的影响,结果表明:预设升温速度对体系燃烧合成有较大影响,当预设升温速度为5℃/s时,不能实现燃烧合成;而在10～1500℃/s范围内,体系能实现燃烧合成,且点火温度大幅度降低,在336～742℃之间;随预设升温速度提高,点火温度降低,点火延迟时间缩短;合成产物主要由TiC、Fe和少量C组成,且随预设升温速度提高,TiC颗粒变小,并出现少量Fe2 Ti,但较低和过高的预设升温速度的合成产物中不会出现Fe2Ti.     

不同钛碳摩尔比和铝含量对Ti－Al－C体系燃烧合成Ti3AlC2粉体的影响

以Ti，Al，C和TiC粉末为原料，研究了钛碳摩尔比和Al含量对Ti—Al—C体系燃烧合成产物相组成的影响。实验表明，不同的钛碳摩尔比和Al含量变化，对Ti-Al—C体系燃烧合成Ti3AlC2粉体有很大影响。当Ti／C=1或1．5时，燃烧产物主晶相是TiC，与原料中Al含量变化关系不大；Ti／C=2和Ti／C=3时，主晶相分别是Ti3AlC2和Ti2AlC，它们的衍射峰强度均分别随原料中Al含量增加而增强，当Al含量增加到一定量后，Ti3AlC2和Ti2AlC的衍射峰强度均又减弱；TiC是Ti-Al-C体系燃烧合成Ti3AlC2相的中间产物。     

Combustion Synthesis of Fe-Cu-TiC Composites under Electric Field

以配料比为15%(Ti+C)-65%Fe-20%Cu (质量分数)（Ti:C化学计量比为1:1）的Fe-Cu-Ti-C体系为研究对象,研究该体系在不同温度下的燃烧合成过程。Fe-Cu-TiC复合材料在759 ℃的点火温度下完成电场辅助燃烧合成,该电场辅助由Gleeble-3500D热模拟机提供。Fe-Cu-Ti-C体系燃烧合成的四步模型被提出,描述了Fe-Cu-TiC复合材料的在电场作用下的燃烧合成过程。它包括 (I) 预热阶段、(II)固相扩散阶段、(III) 燃烧合成阶段、(IV) 后续阶段。从阶段I到阶段II,反应物原子的固相扩散随着温度的增加而增加。从阶段II到阶段III,C原子扩散到Ti原子,直至紧密的与其接触。在III的初始阶段,Ti开始和C在界面处发生反应：Ti(s) + C(s) =TiC(s),并且Ti粒子周围形成一层很薄的固相产物TiC层。在III的后续阶段,C原子穿过固相产物TiC层,扩散到Ti粒子中,继续发生化学反应,直到TiC粒子析出。在第IV阶段,TiC颗粒逐渐的形核和长大,在SEM中可以看出TiC是球形颗粒。     

电场作用下Fe含量对Fe-Ti-C体系低温燃烧合成的影响

采用Gleeble-15001)热模拟机，对电场作用下Fe含量对Fe-Ti-C体系低温燃烧合成过程和产物显微结构特征的影响进行了研究。结果表明：在电场和大热流密度作用下，体系的点火温度可以大幅降低；Fe含量越高，其对体系低温燃烧合成过程的影响越大。随Fe含量增加，体系点火温度升高，点火延迟时间缩短，所达到的最高温度也升高；与高温燃烧合成类似，低温燃烧合成的产物由TiC，Fe，少量Fe2Ti组成；当Fe含量为45％时(质量百分数，下同)，产物中的TiC量最多，且颗粒细小。     

攀钢尾矿原位合成TiCN/Fe3Si复合材料

以攀钢选钛尾矿为主要原料,尝试采用碳热还原氮化法合成TiCN/Fe3Si复合材料.为探明复杂体系过程反应机理,对体系中可能发生的高温反应进行了热力学分析,并采用XRD和SEM对合成产物进行表征.计算结果表明,1500 ℃下产物主晶相为TiC0.3N0.7和Fe3Si,其中,TiC0.3N0.7颗粒大多呈弥散分布,平均尺寸约为5 μm.     

Combustion synthesis of fine TiFe series alloy powder by magnesothermic reduction of ilmenite

Fine TiFe series alloy powder was fabricated by magnesothermic reduction of ilmenite as main raw material. Adiabatic temperature of the FeTiO3-Mg system was studied through thermodynamic analysis. Meanwhile, the characteristics of TiFe series alloy were described by XRD, SEM and grading analysis. It is shown that combustion synthesis of the FeTiO3-Mg system can carry out due to its strong exothermic reaction through adiabatic temperature calculate. Ultrafine TiFe series alloy powder after leached for 5 h has reasonable phases and morphology with the particle distribution of 0.2 to 1 μm. It indicates that in-situ magnesothermic reduction of natural ilmenite is a feasible way to fabricate ultrafine powder with a relatively lower cost.     

Synthesis of TiC by Self-propagating High-temperature Synthesis with Reduction Stage

Fine powder of TiC was prepared by self-propagating high-temperature synthesis(SHS)method with re-duction stage.The influence of diluent and relative density of the sample on both combustion rate and combus-tion temperature has been studied.The combustion reaction in the system of TiO_2-Mg-C begins at the meltingof Mg.The propagation of combustion wave is related to the gasifying of Mg.The activation energy of theprocess has an approximate linear dependence on the porosity of the sample.     

钴粉粒度对超细硬质合金性能的影响

目前在硬质合金领域,钴粉是硬质合金最佳的粘结剂,钴粉性能对合金性能有一定的影响,但研究钴粉性能对硬质合金性能及结构影响的论文较少。实验选取了从0.78～4.61μm不同粒度级别的钴粉,按YF06合金牌号配料,从压坯压力、压坯中钴粉分布以及合金的物理性能和金相组织结构等方面探讨了钴粉粒度对超细硬质合金性能及结构的影响。结果表明:随着钴粉粒度增粗,压坯的压制压力增大,但钴粉粒度对超细混合料压坯中的整体钴分布影响不明显;粒度1.0～1.5μm钴粉比其他粒度级别的钴粉制备的超细硬质合金的整体物理性能更佳;钴粉粒度对超细硬质合金的组织结构也有一定的影响,大于3μm的粗钴粉容易造成超细合金中出现钴池,钴粉太细有则可能造成钴相分布不均。     

STUDY OF PREPARATION PROCESS OF TUNGSTEN POWDER BY SHS WITH A MAGNESIUM THERMIT STAGE

Tungsten powder was fabricated from the system CaWOrMg by self-propagating high-temperature synthesis (SHS) with a magnesium thermit stage. The physic-chemical change during heating and the effects of pressure of sample and diluents (W powder) on product have been studied. The experimental results show that the porosity of combustion product and the particle size of final tungsten powder decrease with increasing pressure of sample. Addition of diluents could increase the particle size of final tungsten powder. The purity of tungsten is improved by leaching in NaOH solution. The results of spectral analysis and particle size distribution of final tungsten powder show that the final Tungsten powder has a median diameter of 0.87μm, specific surface area of 1.09m^2/g and purity of above 99.0%.     

Phase Evolution during Carbothermic Reduction Process of Ilmenite for TiC_xN_(1-x) Composite Powders

As cutting materials and wear-resistant materials, the composites reinforced by Ti(C,N) have very high performances. The super-high cost of these composites, however, limits apparently their wider application to industry due to use of very expensive Ti(C,N) powders. Therefore, it is very necessary to develop a new process technology with low fabrication cost. In the present work, ilmenite (FeTiO3), which is very cheap and very rich in China, was used to fabricate the Ti(C,N) powder directly. The phase evolu...     

焊条成形工艺对手工自蔓延焊接的影响

系统研究了焊条成形工艺对手工自蔓延焊接燃烧过程和焊接质量的影响.结果表明,粉末粒度、装药密度和混料时间均对焊接有显著影响.粉末粒度增大,焊缝出现大量气孔,强度降低;粉末粒度减小,燃烧速度加快,焊接可控性降低;粒度在-260~+300目时,焊接效果最佳.焊条燃烧速度随装药密度呈先增后减并逐渐趋于平稳的变化趋势,当药粉密度ρ2.7 g/cm3时,焊条燃烧平稳,焊接可控性好.混料时间增长,燃烧合成反应加剧,燃烧速度加快,焊接飞溅增大;混料时间不足,粉末混合不均,焊接热量不足,制作燃烧型焊条以30 min混料时间为宜.焊条直径对于燃烧影响较小,宜根据焊件厚度选择合适的焊条直径.     

氮气催化燃烧合成纳米碳化硅粉体

以硅粉和炭黑为原料,在N2气氛中通过燃烧合成制备出纳米SiC粉体。利用XRD、SEM等手段研究了N2压力、球料比、研磨时间等因素对燃烧合成反应的影响。结果表明,球料比和研磨时间对物料的反应程度影响显著。在球料比≥12.5∶1、球磨时间≥4 h的条件下,原料粉体可实现完全燃烧,生成产物主要为β-SiC,平均颗粒尺寸小于100 nm。在实验基础上,结合热力学分析,研究指出SiC是在N2催化作用下通过Si-C燃烧合成得到的,反应历程为:Si粉首先与N2反应生成Si3N4,同时放出大量的热,随着反应温度的升高,先生成的Si3N4发生分解,释放出的游离Si与C反应生成SiC。     

Effect of powder particle size on gradient formation and grain growth in ultrafine crystalline gradient cemented carbide

Sinter-HIP combining vacuum and pressure in one-step sintering process has been applied to prepare ultrafine crystalline cemented carbide with a surface gradient layer enriched in binder. The effect of powder particle size on gradient formation and grain growth has been examined. The results show that the gradient layer thickness increases with decreasing WC and Ti(C,N) powder particle size. The number of abnormal WC grains increases with decreasing WC powder particle size. The formational mechanism of the gradient cemented carbide with ultrafine grains is discussed through analyzing the decomposability of nanoscale Ti(C,N), atomic diffusion and grain growth during one-step Sinter-HIP process.     

Self-propagating high-temperature synthesis in Ti-W-C system

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Effect of particle size of iron on reaction velocity of combustion synthesis of Ti-C-Fe system

Four Ti-C-Fe powder mixtures, with a same molar ratio but different particle sizes of Fe and Ti, were used to measure the reaction velocity of the combustion synthesis. The results show that in the case of the finer Ti powder used, the reaction velocity of mixture with the finer Fe powder is higher than that with the coarser Fe powder. However,in the case of the coarser Ti powder used, the reaction velocity of mixture with the finer Fe powder is lower than that with the coarser Fe powder. The effect of particle size of Fe powder on reaction velocity can be explained with the previously proposed mechanisms of the combustion synthesis of Ti-C-Fe system.