氟聚物和氟化石墨促进TiC低温高效固相合成机理研究

发布时间：2018-01-31 23:18

本文关键词： 低温固相合成碳化钛聚四氟乙烯聚偏二氟乙烯氟化石墨　出处：《南京航空航天大学》2015年博士论文　论文类型：学位论文

【摘要】：Ti C陶瓷属于超硬工具材料,具有高熔点、高硬度和优良的化学稳定性,其粉体主要用于制备金属陶瓷,耐热合金和硬质合金,同时Ti C具有优良的导电性,亦是电极的优选材料。Ti C的粉体合成方法亦随之得到广泛研究,目前已被报道的制备合成技术主要有碳热还原法、直接碳化法、高能球磨法、化学气相沉积法、溶胶凝胶法和微波合成法。然而,这些方法存在合成温度高、反应周期长、工艺复杂等缺点。本论文探索在较低的温度下固相合成Ti C陶瓷粉体,并初步分析了以聚四氟乙烯(PTFE)和聚偏二氟乙烯(PVDF)分别作为促进剂时对钛与碳反应过程的影响,同时对不同氟化度氟化石墨(CFx)n作为碳源与钛反应低温合成Ti C粉体的机理进行了研究。主要工作内容概括如下:(1)对Ti/C/PTFE、Ti/C/PVDF及Ti/(CF1.0)n三种反应体系分别进行了反应热力学计算,从各反应的吉布斯自由能、反应焓及绝热燃烧温度三个方面对各反应体系的可行性进行判断。结果表明:各体系中的子反应吉布斯自由能均为负值,且作为诱发反应的Ti/PTFE及Ti/PVDF体系在500℃反应时释放的能量均达到850k J/mol以上,远高于Ti/C体系反应的激活能364k J/mol,绝热燃烧温度高达1800℃,高于自维持反应温度1527℃,利于整个体系的完全反应;对于Ti/(CF1.0)n体系在600℃时释放的能量高达2100k J/mol,绝热燃烧温度高达1810℃,足以维持整个体系反应完全。(2)采用PTFE作为钛与碳体系反应合成Ti C的促进剂,在530℃成功制备出Ti C纳米粉体。从热-质联用测试及产物XRD物相结果分析得知:随着PTFE含量的增加,Ti/C/PTFE体系中的钛与PTFE体系反应温度向低温移动,当PTFE添加量达到3wt%时,钛与PTFE体系反应释放的热量足以激活整个体系的反应,并且在瞬间完成,制备出来的Ti C粉体平均粒径为81nm,颗粒形貌主要类似球状,有少部分颗粒在长大的过程中体现出了多面体状。当PTFE含量为4wt%时,产物中则会引入一定量的Ti F3降低了Ti C的纯度。反应过程中随着温度的升高,在524℃左右钛与PTFE开始反应并释放热量,进而激发钛与PTFE分解出来的高活性碳及原料中碳反应生成Ti C。(3)针对Ti/C/PVDF体系,通过分析得知:Ti/C/PVDF体系的初始反应温度为500℃左右,远高于单纯Ti/PVDF体系的反应温度440℃。当PVDF添加量为20wt%时,Ti/C/PVDF体系反应放热峰开始变得尖锐,反应起始温度为499℃,高于Ti/PVDF体系反应温度约50℃,同时较添加3wt%PTFE的Ti/C/PTFE体系反应温度低20℃左右。但由于体系中过多副产物Ti F3和Ti H1.5的生成,稀释了钛的浓度,降低了钛与碳的接触几率,导致产物中仅生成少量的Ti C0.625相。(4)采用不同氟化度的氟化石墨(CFx)n作为碳源与钛反应,在610℃制备出不同粒径等级的Ti C粉体。通过分析得知:当采用F/C原子比0.5的氟化石墨作为碳源时,氟化石墨与钛体系的反应在DSC曲线上体现为两步弱的反应,产物中含有Ti C粉体和残留的碳,残留的碳为(CFx)n分解时产生的低活性碳;当F/C原子比≥0.5时,反应在610℃瞬间完成,随着氟化度的升高,固相合成的Ti C粉体粒径由纳米级向微米级转变。其反应过程中随着温度升高,氟原子得到激活脱离对碳原子的依附而与钛反应生成中间相Ti F3,同时释放热量促使碳与钛及Ti F3反应生成Ti C。
[Abstract]:Ti C ceramic belongs to superhard tool materials with high melting point, high hardness and excellent chemical stability, the powder is mainly used for the preparation of metal ceramic, heat-resistant alloy and hard alloy, while Ti C has good conductivity, is also the powder synthesis material.Ti C electrode was also widely study has been reported to synthesize technology mainly carbon thermal reduction method, direct carbonization method, high-energy ball milling method, chemical vapor deposition, sol-gel method and microwave synthesis method. However, these methods have high reaction temperature and long reaction cycle, shortcomings of the complex process. This paper explores the solid phase synthesis of Ti C ceramic powder at low temperature, and a preliminary analysis using polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF two) respectively as accelerant of titanium and carbon reaction process, at the same time on different degree of graphite fluoride fluoride (CFx) n as carbon source The research and the reaction mechanism of titanium low temperature synthesis of Ti C powder. The main contents are as follows: (1) on Ti/C/PTFE, Ti/C/PVDF and Ti/ (CF1.0) n three reaction systems were calculated from the reaction thermodynamics, reaction Gibbs free energy, enthalpy and adiabatic combustion temperature burning feasibility in three aspects the reaction system of judgment. The results showed that the system of the Gibbs free energy of reaction were negative, and as the release of Ti/PTFE and Ti/PVDF system evoked responses at 500 DEG C when the reaction energy reached 850k more than J/mol, much higher than the Ti /C reaction activation energy 364k J/mol, adiabatic combustion temperature is as high as 1800 C higher than self sustained reaction temperature is 1527 DEG C, the reaction to the whole system completely; for Ti/ (CF1.0) release of n system in 600 degrees of energy up to 2100K J/mol, the adiabatic combustion temperature of 1810 DEG C, sufficient to maintain the whole body The Department reacted completely. (2) accelerator using PTFE as titanium and carbon reaction synthesis of Ti C at 530 DEG C, successfully prepared Ti C nano powder. From thermal mass spectrometry testing and product XRD phase results: with the increase of PTFE content, titanium and PTFE system in Ti/C/PTFE system the reaction temperature shifts to low temperature, when the PTFE content reaches 3wt%, the release of titanium and PTFE reactions heat sufficient to activate the system response, and in a moment, the synthesized Ti C powder with an average particle size of 81nm, particle morphology is mainly similar to spherical, a few particles in the process of growing up reflects the polyhedron shape. When the PTFE content is 4wt%, the product will introduce a quantity of Ti F3 decreased the purity of Ti C. The reaction process with the increase of temperature at 524 degrees Celsius, titanium started to react with PTFE and the release of heat, and thus stimulate the decomposition of titanium with high PTFE Generate Ti C. carbon reaction of activated carbon and raw materials (3) for the Ti/C/PVDF system, through the analysis of that: the initial reaction temperature of Ti/C/PVDF system is 500 degrees Celsius, the reaction temperature is much higher than that of pure Ti/PVDF system 440 degrees. When the amount of PVDF is 20wt%, Ti/C/PVDF reaction exothermic peak becomes sharp, the initial reaction temperature at 499, higher than the Ti/PVDF reaction temperature is about 50 DEG C, and add Ti/C/PTFE 3wt%PTFE reaction temperature is 20 DEG C lower. But due to the formation of many byproducts of Ti F3 and Ti H1.5 in the system, the dilution of the titanium concentration, reduce the probability of contact between titanium and carbon, lead to generate only a small amount of Ti C0.625 in the product phase. (4) with different degree of graphite fluoride fluoride (CFx) n as the carbon source and titanium reaction, 610 degrees in the preparation of Ti C powders with different particle size classes. The results show that when the atomic ratio of F/C 0.5 as carbon graphite fluoride The source, fluoride graphite and titanium system for the two step reaction reflects weak reactions on the DSC curve, the product contains Ti C powder and the residual carbon, the residual carbon (CFx) low carbon n produced during the decomposition; when the atomic ratio of F/C = 0.5, reaction instantaneously at 610 DEG C with the increase of salinity, fluoride, solid phase synthesis of Ti particle size of C powder by nano to micron. The reaction process with the increase of temperature, the fluorine atoms are activated from dependence on carbon atoms and Ti and titanium intermediate reaction F3, while the release of heat to make carbon and titanium and Ti F3 reaction Ti C.

【学位授予单位】：南京航空航天大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ174.1

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