固相法制备高纯纳米碳化硼

以聚乙烯醇为碳源,硼酸为硼源,利用固相热反应法制备了高纯度纳米碳化硼(B_4C)粉体,用红外光谱分析、X射线衍射仪、场发射扫描电子显微镜对产物的物相、结构与形貌做了表征,并研究了制备条件对碳化硼粉体的影响。结果表明,将聚乙烯醇与硼酸在250℃以下反应可制备聚合物前驱体;将该聚合物前驱体于750℃低温裂解2 h可以得到裂解前驱体;该裂解前驱体在1 450℃下反应2 h,可得到高纯纳米碳化硼。     

前驱物法低温合成六方氮化硼

本文以三聚氰胺和硼酸为原料,先采用湿化学法合成棒状前驱物,然后将其在空气气氛中高温培烧制得六方氮化硼.实验考察了反应原料配比,反应物浓度,高温培烧的时间及温度对产物的影响.采用IR、化学分析、XRD、粒度分析和SEM等方法对前驱物及产物进行了表征,确定了前驱物及产物的组成、物相、粒度分布及形貌.研究结果表明:合成前驱物的适宜原料配比是C3N6H6∶H3BO3=1∶2,浓度为0.4 mol/L,合成的前驱物是分子式为C3N6H6·2H3BO3的棒状超分子加合物;在温度950℃,空气气氛中培烧6h能得到晶型良好、平均粒径为15 μm的六方氮化硼粉体.     

碳热还原法合成硼化锆粉体影响因素探究

以氧化锆(ZrO2)、硼酸(H3 BO3)和碳(C)粉为原料,研究了不同碳粉(活性炭、石墨)与前驱体粒度、温度及保温时间对碳热还原法制备硼化锆(ZrB2)粉体的影响.通过X射线衍射(XRD)分析合成粉体物相,扫描电镜(SEM)观察合成粉体形貌,并通过化学方法分析了合成粉体中的C、O含量.结果表明:以活性炭为碳源合成的粉体形貌呈条棒状,以石墨为碳源合成的粉体形貌呈规则的块状;合成粉体的粒度随前驱体粒度减小而减小,形貌由规则的块状逐渐转变为圆滑的不规则形貌,合成ZrB2粉体最小平均粒度约为1.69μm,产物中C含量随前驱体粒度减小而减少,O含量随前驱体粒度减小而增加,氧含量最低为0.54wt％;碳热还原法合成ZrB2粉体在1500℃下是可行的,但直到1900℃碳热还原反应合成ZrB2才进行完全;碳热还原反应合成ZrB2粉体最佳的反应条件为1900℃保温30 min.     

季戊四醇磷酸蜜胺盐膨胀型阻燃剂的合成

采用磷酸、季戊四醇和三聚氰胺为原料,乙二醇为介质,在一定温度和搅拌下合成无卤膨胀型阻燃剂季戊四醇磷酸蜜胺盐,并对产物进行了差热、热失重及红外分析.根据该阻燃剂的膨胀度、剩炭率的测定结果,确定最佳合成条件为:n(磷酸)∶n(季戊四醇)∶n(三聚氰胺)=3∶1∶2;中间产物季戊四醇磷酸酯中间体的合成温度120 ℃,合成时间2 h;最终产物磷酸酯三聚氰胺盐阻燃剂合成温度100 ℃,时间4 h.     

硼碳比对碳热法制备碳化硼的影响

由于碳热还原法工艺制备碳化硼粉体的过程中,迅速的升温乃至高温会使硼酸迅速挥发,为确定合适的原料配比,避免原料的损失,以硼酸和石油焦为原料在感应炉中于1 800℃合成碳化硼,研究了不同硼碳比(n(B):n(C)分别为0. 65、0. 68、0. 71和0. 74)对碳热还原法制备碳化硼粉体的组成和显微结构的影响。结果表明:随着硼碳比的升高,碳的衍射峰明显降低;当n(B):n(C)=0. 71时,碳峰已经不再明显,物相组成较为理想,碳化硼粉体纯度较高,游离碳和氧化硼较少,且碳化硼晶体形貌比较规则,晶体表面也较为平滑;继续升高硼碳比,会有B_2O_3衍射峰的出现。     

碳热还原法合成TiB_2的热力学分析与研究

以30μm TiO2(w(TiO2)>99.8%,金红石型)、50 μm B2O3(w(B2O3)>99.5%)及10μm石墨粉(w(C)>99%)为原料,按n(TiO2):n(B2O3):n(C)=1:1:5进行配料后放入不锈钢球磨罐中抽真空球磨24 h,然后将反应混合物移入石墨坩埚内置于热压炉中,分别在1 250、1 350、1 400、1 500、1 600、1 700℃保温4 h进行反应.对以TiO2、B2O3、石墨粉为原料合成TiB2的反应体系进行了热力学计算,并对反应产物进行XRD与SEM分析.热力学计算表明,上述3种原料通过碳热还原反应合成硼化钛的反应开始温度为1 556 K.而合成产物的XRD分析表明,生成硼化钛的开始温度为1 350℃以上.碳热还原TiO2和B2O3合成TiB2的反应机理应为C还原TiO2,其中间产物为Ti3O5、Ti2O3、TiO,然后这些中间产物与B2O3一起逐渐被C还原生成TiB2.SEM分析表明,TiB2颗粒呈不规则短柱状,粒度为5～10m;当反应温度达到1 700℃以上时,硼化钛晶粒有长大的现象.     

碳化锆陶瓷有机前驱体的热解过程

合成了碳化锆陶瓷有机前驱体,研究了其在热解过程中化学成分和物相组成变化,探讨了从有机高分子向无机陶瓷转化的机理,对碳热还原反应进行了热力学分析。结果表明,前驱体在600℃以下完成了有机结构的断裂、裂解碎片的重排与挥发,600℃以上裂解产物不再具备有机特征;随热解温度升高,无定型碳和单斜相ZrO2逐渐生成,大于1200℃时可检测到立方相ZrC,1400℃时单斜相ZrO2基本消失;1500℃时完成碳热还原反应,在远低于热力学反应温度的条件下生成了高度结晶的纳米尺寸的立方相碳化锆陶瓷。     

碳化硼微粉的制备及其性能表征

为对比不同品质的碳化硼微粉在纯度、晶型、形貌和硬度上的差异,先采用Fact Sage软件对碳热还原法制备碳化硼的反应过程进行热力学计算理论合成温度;再以硼酸和石油焦为原料,采用电弧炉碳热还原法制备了碳化硼结晶块,并根据其品质的不同分为一级品和二级品;然后采用化学分析、XRD、SEM和显微硬度等分析其纯度、硼碳比、晶型、物相结构、表观形貌和显微硬度。研究表明:碳热还原法制备碳化硼的理论合成温度应为1 600~1 800℃;一级品碳化硼微粉的纯度高(B4C质量分数达98.35%),n(B)n(C)接近B4C化学计量比4,结晶好,致密度高,硬度高。     

以三乙醇胺硼酸酯为前驱体制备大颗粒六方氮化硼

以三乙醇胺和硼酸为原料,甲苯为带水剂,合成了三乙醇胺硼酸酯,在最佳工艺条件下以三乙醇胺硼酸酯为前驱体在氨气气氛中烧结制得六方氮化硼颗粒。采用IR、XRD、SEM、NMR等测试方法对中间物和产物进行了表征,确定了中间物及产物的组成、物相、粒度及形貌。研究结果表明：以三乙醇胺硼酸酯为前驱体在1200℃烧结4h,可制得高纯度、晶型良好,粒径在20μm左右的六方氮化硼颗粒。经过高温精制后的六方氮化硼颗粒具有较高的结晶度和致密度,其粒径可以达到30μm以上,纯度为98.5%。     

硬脂酸钠改性白硼钙石的水热合成及表面改性

以硼酸和氢氧化钙为原料,在硼酸和氢氧化钙物质的量比为4:1和反应温度160℃的条件下,水热反应4 h合成出一种硼酸钙.对合成产物进行了化学成分、X射线衍射、粒度、热重、扫描电镜等表征,结果表明产物为单一物相的白硼钙石(4CaO·5B2O3·7H2O).以硬脂酸钠为改性剂对白硼钙石进行湿法改性,考察了硬脂酸钠的用量等因素...     

Low-temperature synthetic route for boron carbide

Boron carbide is one of the hardest materials with diamond-like mechanical properties, and is already used for a variety of applications including armor plating, blasting nozzles, and mechanical seal faces, as well as for grinding and cutting tools. It is produced on an industrial scale by classical carbothermal reduction of boric oxides at high temperatures, but the formation of pure boron carbide in processed forms, such as films and fibers, is difficult. As an alternative to high-temperature powder techniques, there is recently great interest in the development of polymer precursors to produce ceramic materials. The aim of the present work is to develop a cost effective and low-temperature manufacturing process to synthesize boron carbide from cheap and easily available raw materials. The initial objective of our research is the design and synthesis of a new type of boron–carbon polymer, which would serve as precursor for boron carbide. The polymeric precursor is synthesized by the reaction of boric acid and polyvinyl alcohol that after pyrolysis at 400 °C and 800 °C gives boron carbide. The polymeric precursor and its pyrolyzed products are characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). X-ray diffraction shows that boron carbide (B₄C) obtained from this method has an orthorhombic crystal structure. It is a unique low-temperature (∼400 °C) synthetic route for boron carbide.     

Processing factors influencing the free carbon contents in boron carbide powder by rapid carbothermal reduction

High quality boron carbide powder without free carbon is desired for many applications. In this study, the factors that influence free carbon content in boron carbide powders synthesized by rapid carbothermal reduction reaction were evaluated. The dominant factors affecting free carbon contents in boron carbide powder were reaction temperature, precursor homogeneity, the particle size of reactants, and excess boron reactant amount. The reaction temperature at 1850 °C was sufficient to synthesize boron carbide with low free carbon content. Depending on process conditions, precursor homogeneity was also affected by the calcination temperature and time. Smaller particle size of reactants contributed to less carbon content and more uniformity in synthesized boron carbide. Excess boric acid effectively compensated for B₂O₃ volatilization. In the optimal sample, using 80 mol% excess nano boric acid and calcined at 500 °C, the free carbon in the synthesized boron carbide was negligible (0.048 wt.%).     

前驱体转化法制备碳化硼粉体的研究进展

碳化硼材料具有优良的物理和化学性能,被广泛应用于各个领域。目前,传统的碳热还原方法生产碳化硼粉体存在温度高、产率低、环境污染重等问题。相比之下,前驱体转化法具有能耗低、工艺简便、原料易得、产品尺寸小等特点,在制备碳化硼粉体方面有明显的优势。详细介绍了前驱体转化法合成碳化硼粉体的制备过程,综述了使用不同碳源经前驱体转化法合成碳化硼粉体的最新研究进展,并展望了前驱体转化法合成碳化硼的研究方向。     

Preparation of nanocrystalline MoSi2 with enhanced lithium storage by sol–gel and carbonthermal reduction method

Herein nanocrystalline MoSi₂ with enhanced lithium storage was successfully synthesized via a sol-gel and carbonthermal reduction method. Reduction of the gel mixture of Mo precursor and Si precursor by carbon at a desired temperature resulted in the formation of MoSi₂ nanoparticles. The gel mixture was obtained through the hydrolysis of TEOS and ammonium molybdate and the polymerization of hydrolysis products of TEOS. The reducing agent carbon was produced via decarburition of sucrose's hydrolysis products, which have been wrapped in the gel during its formation process. Addition of HCl to the mixed solution controlled the hydrolysis and polymerization rate, and enabled the formation of a gel mixture with homogeneously distributed hydrolysis products of ammonium molybdate, TEOS and sucrose. This achievement likely generates a novel route to synthesize non-oxide compounds such as silicide, carbide through the sol–gel and carbonthermal reduction process. In addition, the as-received MoSi₂ nanoparticles showed considerable activities in the reversible lithiation and delithiation process. When using as an anode for Li-ion batteries, MoSi₂ nanoparticles delivered a specific capacity of 325 mAh g^?1 at C/12 and showed an increasing capacity with cycling.     

Ti-N-C-O系的热力学分析与相平衡

本文从热力学的角度分析了TiO2碳热还原反应制备TiC、TiN在不同的PCO、PN2下的最佳温度范围,并绘制了各相稳定存在与PCO、PN2的关系图.     

溶胶-凝胶法在SiC纤维表面制备ZrO2界面层的研究

采用溶胶凝胶法(sol-gel)在SiC纤维表面制备氧化锆(ZrO2)界面层,考察了前驱体溶胶和烧结温度对界面层的影响。采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)等测试手段对ZrO2界面层的晶体结构和表观形貌进行了分析。结果表明:当烧结温度为1 000℃,Zr4+金属离子浓度为1.0 mol/L,聚乙烯醇(polyvinylalcohol,PVA)质量分数为30%时,能够制备出完整致密的ZrO2界面层。     

纳米碳纤维/碳毡负载碳化钨和碳氮化钨的肼分解性能

以纳米碳纤维/碳毡(CFF)为载体,分别采用碳热氢气还原法和碳热氨气还原法制备了负载型碳化钨、碳氮化钨整体催化剂,XRD结果表明催化剂的活性相分别为W₂C和WC_xN_y, TEM表征发现其粒子尺寸分别为2～40 nm和2～20 nm。采用1 N肼分解推力器评价了上述催化剂的反应性能,W₂C/CFF和WC_xN_y/CFF表现出了相比于Ir/CFF更好的肼分解综合性能:除了初活性略低以外,启动加速性、稳态燃压以及比活性均高于贵金属Ir催化剂。此外,W₂C/CFF和WC_xN_y/CFF催化剂的稳定性明显优于Ir/CFF,这主要是由于CFF载体在贵金属Ir的作用下发生了更显著的甲烷化反应。     

二硼化锆-碳化硅复相陶瓷纤维的制备与表征

分别采用八水合氧氯化锆、硼酸、蔗糖、正硅酸乙酯为锆源、硼源、碳源和硅源,柠檬酸为络合剂,聚乙烯醇为纺丝助剂,通过干法纺丝制备了前驱体纤维,然后在氩气氛围下逐渐升温至1600℃并保温2 h,获得了二硼化锆-碳化硅复相陶瓷纤维。通过红外光谱、热失重分析、X射线衍射、扫描电镜等对前驱体纤维和陶瓷纤维进行了表征。结果表明:原料之间发生了相互反应,前驱体纤维具有良好的稳定性,硅源参与反应生成了碳化硅并细化了晶粒,提高了陶瓷纤维的致密度,并且使陶瓷纤维具有更好的高温抗氧化性。     

A low cost,low energy,environmentally friendly process for producing high-purity boron carbide

Boron carbide with purity levels higher than that achievable by traditional manufacturing processes using an electric arc furnace (EAF) was produced by a novel low cost, low energy, environmentally friendly process of carbothermic reduction of boric acid (H₃BO₃) with carbon using a self-designed temperature-controllable electric resistance furnace (ERF). The process is divided into three stages: the pelleting stage, the low-temperature pre-dehydration stage, and the high-temperature reduction stage. The optimal conditions are determined as a pelleting pressure of 20?MPa, pre-dehydration temperature of 400?°C, H₃BO₃/C ratio of 3.38, and reduction temperature of 1900–2300?°C. The formation of boron carbide changes from liquid-solid reactions to gas-solid reactions with increasing temperature. Furthermore, the decreasing CO partial pressure is verified to be beneficial for the synthesis of boron carbide. The proposed process circumvents the disadvantages caused by the evaporation of large quantities of water steam and unstable reduction temperature and B/C ratios exhibited by the traditional EAF process. Moreover, it provides a more stable and controllable reduction temperature for producing high-purity boron carbide that leads to improved energy consumption, product quality, and cost efficiency and reduces air pollution mainly caused by volatilization and condensation of boron oxides.     

Morphological evolution of boron carbide particles: Sol-gel synthesis of nano/micro B4C fibers

Herein we present a novel non-catalytic sol-gel route to synthesize nano/micro boron carbide fibers. By in-situ decoration of the precursor surface with boric acid crystals during the thermal decomposition stage, the growth kinetics of boron carbide particles was manipulated. Therefore, the formation of anisotropic crystals instead of polyhedral-equiaxed ones was successfully enabled. The results indicated that highly crystalline boron carbide (B₄C) particles with a low amount (<1 ± 5 wt%) of free carbon were obtained. The SEM and HR-FESEM micrographs revealed that B₄C particles with fully polyhedral-equiaxed morphology were obtained from the precursors, which were thermally decomposed with 2 h holding time at 675 °C. As a result of increased thermal decomposition duration of precursor, B₄C particles with various morphologies, such as rhomboid-plate, nanobelt, and fiber were formed beside the polyhedral-equiaxed particles. The yield of boron carbide fiber formation was increased, and polyhedral-equiaxed particles were decreased in the final products by tailoring the structure of the preceramic precursor. The products containing at least 50% of boron carbide fiber were achieved using 12 h of thermally decomposed precursors. The formation and growth mechanisms of boron carbide particles were speculated and comprehensively discussed.