气相反应渗入法制备多孔SiC的研究

以椴木木炭为生物碳模板,利用气相反应性渗入法制成了一种具有木材结构的多孔SiC陶瓷。采用X射线衍射分析,红外光谱和扫描电镜对其物相变化和显微结构进行了表征。实验结果表明：随反应时间的延长,木炭的转化率增大,弯曲强度显著提高,而气孔率变化不明显。在1600℃下反应8h,木炭几乎完全转变成β-SiC,并高度保持椴木的微观结构,弯曲强度和气孔率分别为41．6MPa和53．2％。对气相SiO在木炭中的渗入-反应机理进行了探讨。     

生物形态SiC陶瓷的研究

木材经1200℃高温真空碳化生成生物模板(木炭)，然后经气相Si、SiO的反应性渗入或经SiO2溶胶真空，压力浸渍工艺和碳热还原反应过程制成多孔SiC陶瓷。借助SEM、XRD和FT—IR等方法对转变为多孔SiC过程中的显微结构、物相组成和物理化学结构变化进行了表征。试验结果表明：在木炭转变为多孔SiC的高温处理过程中，木炭的显微结构很好地留在了多孔SiC陶瓷中；生成的SiC主要是β—SiC.介绍了木炭转变为SiC陶瓷的过程与机理。     

碳化硅/堇青石复相多孔陶瓷的制备及性能研究

采用碳化硅、烧高岭土、氢氧化铝、滑石为主要原料,石墨为造孔剂制备了碳化硅/堇青石复相多孔陶瓷.研究了烧结温度和烧结助剂二氧化铈对碳化硅/堇青石复相多孔陶瓷气孔率和强度的影响,并分别用XRD和SEM分析晶相组成和断面显微结构表明:制备出的SiC多孔陶瓷的主相是SiC,结合相是堇青石与方石英,多孔陶瓷具有相互连通的开孔结构;在1350℃烧结,并保温3h,当造孔剂含量为15％时,碳化硅/堇青石复合多孔陶瓷性能最佳,其气孔率31.80％,相应的弯曲强度为63.74 MPa.在1200℃下,添加不同含量的CeO2,对烧结样品的相组成有影响,能够降低生成堇青石的温度,在CeO2含量为3％的样品中,堇青石的峰最明显,但是过量的氧化铈会抑制了堇青石的生成;随着CeO2加入量的增加,其气孔率和弯曲强度也会随之变化,1200℃下,在CeO2加入量为4％时其弯曲强度最优.但随着CeO2的含量的增加,其气孔率逐渐下降.     

木炭添加量对多孔莫来石陶瓷性能的影响

为了改善以木炭为造孔剂的多孔莫来石陶瓷的性能,以烧结莫来石(0.25~0.3 mm)、SiO2微粉、Al2O3微粉、滑石粉、球黏土、膨润土、甲基纤维素、木炭粉(≤0.044 mm)为原料,研究了不同量的木炭粉(外加质量分数分别为0、2%、4%、6%、8%、10%、12%)对多孔莫来石坯体的成型外观、烘干后的常温耐压强度及1 400℃保温3 h热处理后的显气孔率和常温耐压强度的影响,并对不同木炭添加量的多孔莫来石试样进行了显微结构分析。结果表明:外加质量分数≤8%的木炭,制成的多孔莫来石坯体可较好成型;外加质量分数2%~8%木炭的莫来石坯体与不添加木炭的相比,烘干后试样的常温耐压强度明显提高;多孔莫来石热处理后的显气孔率随着木炭添加量的增加而增加,常温耐压强度随之降低。综合考虑多孔莫来石陶瓷各项性能,木炭外加质量分数不宜超过8%。     

利用煤矸石制备堇青石多孔陶瓷

为了综合利用煤矸石,以煤矸石、滑石等为原料,按堇青石的理论组成配料,分别外加质量分数为0、5%、10%、15%、20%的活性炭粉为造孔剂,在1 400℃下分别保温3和6 h烧结后制备了堇青石多孔陶瓷,通过检测显气孔率和常温抗折强度及其显微结构分析探讨了其合成工艺制度。结果表明:利用煤矸石为主原料,外加5%(w)的活性炭为造孔剂,在1 400℃下保温6 h可以合成性能优良的堇青石多孔陶瓷。所合成的堇青石多孔陶瓷的抗折强度为29.1 MPa,显气孔率为39.8%;显微结构分析显示,该多孔陶瓷中以堇青石相为骨架,内部形成了贯通气孔的多孔结构。     

碳化硼的热压、组织结构的形成及性能

介绍了将工业碳化硼粉用热压法于1600-2160℃压制为陶瓷。研究了陶瓷的强度及系数的变化与碳化硼的多孔状及颗粒状的组织结构之间的关系。查明,当于2000～2160℃进行热压时,当最高温度达到2060—2080℃及气孔率几乎稳定在1%～1.5%时,强度的变化是无规律性的。     

二元凝胶法制备Al2O3多孔陶瓷及其表面强化层

采用发泡注凝法制备Al_2O_3多孔陶瓷,研究了丙烯酰胺与明胶所组成的二元凝胶体系对陶瓷浆料黏度、发泡效果、坯体强度及陶瓷显微结构的影响,并对烧结陶瓷体的显气孔率、强度等进行了表征。结果表明:丙烯酰胺具有辅助分散作用,可降低明胶对浆料黏度的影响并改善浆料发泡效果;采用二元凝胶体系可制备具有均匀孔径分布的可适当机械加工陶瓷坯体;经1 600℃烧结2 h,可获得显气孔率为70%～90%的Al_2O_3多孔陶瓷,其中显气孔率最高为90.8%的多孔陶瓷其抗压强度高达3.3 MPa。在此基础上,对其进行了表面强化的研究。通过在其表面流延一层高强度多孔薄层,不仅使材料整体抗弯强度从6.4 MPa提高到10.8 MPa,而且可以有效降低高温气流对材料表面的烧蚀程度。     

Al2O3多孔陶瓷的制备和性能研究

采用乙基纤维素为成孔剂制备了Al2O3多孔陶瓷,探讨了工艺参数对其性能的影响。研究结果表明,造孔剂含量、球磨时间及烧结温度均对多孔陶瓷的气孔率和抗折强度有影响。烧结温度的升高使得气孔率降低,但变化不明显,抗折强度明显提高。随造孔剂含量的升高,使得气孔率逐渐上升,超过20％后变化趋于平稳。随着球磨时间的增加,试样呈现气孔率下降和抗折强度升高的趋势。以烧结温度为1580℃,造孔剂含量20％;球磨时间为2．5h的条件下,可获得高显气孔率、抗折强度较高的舢203多孔陶瓷。     

含Al,Si粉的不烧MgO—C砖的高温特性

本文研究了含Ａｌ、Ｓｉ粉的不烧ＭｇＯ－Ｃ砖在所选定的温度范围内机械性能,热性能和显微结构的变化。经５００℃热处理的试样发生收缩,并且比未经热处理的试样具有更高的显气孔率。经５００℃热处理的试样其弯曲强度,弹性模量大大低于未经热处理的试样,并且在５００℃热处理的试样随着热处理次数增加,显气孔率增大,机械性能降低。推断当不再产生挥发性物质时,显微结构的收缩将停止,机械性能将趋于稳定。在８００℃、１００     

利用硼泥制备镁橄榄石质多孔陶瓷

利用硼泥废渣、钾长石、羧甲基纤维素钠等原料在950～1200℃不同烧结温度下制备了具有一定强度和气孔率的多孔陶瓷样品。利用TG,DTA,XRD、气孔率、抗弯强度和抗压强度等方法对陶瓷样品进行测试分析。优选获得了抗弯强度达10～33MPa,抗压强度为10～40MPa,气孔率达30％的镁橄榄石质多孔陶瓷。     

黄杨木制备SiC木质陶瓷的性能与表征

SiC木质陶瓷是近年来应用前景广阔的新型陶瓷材料,以绿色可再生的木材为原材料,通过反应烧结工艺制备出的陶瓷具有优良的高温力学性能。为探究影响生物质陶瓷性能的因素,将黄杨木在800 ℃氮气保护下热解形成生物质炭坯,然后在1 650 ℃和1 900 ℃两种高温下进行熔融渗硅制备SiC木质陶瓷。利用X射线衍射仪(XRD)和扫描电子显微镜(SEM)研究SiC木质陶瓷的物相组成和微观结构,采用阿基米德排水法和三点弯曲法测定陶瓷的开孔率、密度和弯曲强度,再使用维氏硬度计测定SiC木质陶瓷的显微硬度。研究结果表明:在1 650 ℃下通过熔融渗硅可以得到微观结构均匀的SiC木质陶瓷,在1 650 ℃比在1 900 ℃下熔融渗硅制备陶瓷的力学性能更优异,陶瓷的密度更大,为2.27 g/cm³,此时弯曲强度为192.45 MPa;游离Si会提高SiC木质陶瓷的密度,增强陶瓷的弯曲强度。     

竹材制备SiC多孔陶瓷及吸波性能研究

以印度竹和竹炭粉为原料,采用溶胶凝胶法和液态渗硅法制备生物基SiC陶瓷块和陶瓷粉,并通过磁性金属担载制备了吸波材料。借助XRD、SEM、RAM反射率测试系统对材料的物相构成、微观构造、吸波反射率进行了分析。结果表明:竹材炭化及陶瓷化后均保持了多孔的骨架结构特征。溶胶凝胶法和液态渗硅法的陶瓷化反应都发生在竹炭孔道侧壁上,且溶胶凝胶法在竹炭孔道内部有硅基陶瓷晶须生成。要提高液态渗硅法竹炭向SiC的转化率和SiC的晶化程度,可以通过提高陶瓷化温度和延长保温时间的方法来实现。无论何种方法,竹炭粉比竹炭块的陶瓷转化率高。另外通过溶胶凝胶法制备的担载磁性金属的竹基陶瓷材料在低频波段有一定的电磁波吸收性能。草刺     

多孔碳化硅陶瓷的原位氧化反应制备及其性能

以SiC为陶瓷骨料,Al2O3作为添加剂,通过原位氧化反应制备了Sic多孔陶瓷,并对其氧化反应特性及性能进行了研究.结果表明:在1 300～1 500℃,随烧结温度的升高,SiC的氧化程度增加,SiC多孔陶瓷的强度逐渐增加,但开口孔隙率有所降低.莫来石相在1 500℃开始生成·当烧结温度升高到1 550℃时,莫来石大量生成,得到了孔结构相互贯通且颈部发育良好的莫来石结合SiC多孔陶瓷;由于在SiC颗粒表面上覆盖了致密的莫来石层,SiC的氧化受到抑制,开口孔隙率因而升高,SiC多孔陶瓷的强度因莫来石的大量生成而增加.由平均粒径为5.0um的SiC,并添加20%(质量分数)Al2O3,经1 550℃烧结2h制备的SiC多孔陶瓷具有良好的性能,其抗弯强度为158.7MPa、开口孔隙率为27.7%.     

硅液相浸渍反应制备TiC/SiC和TiN/SiC复相陶瓷

以滤纸、酚醛树脂和氧化钛为原料,经过模压成型、固化、碳化及不同条件下渗硅制备了TiC/SiC和TiN/SiC复相陶瓷。通过X射线衍射和扫描电子显微镜研究了TiC/SiC和TiN/SiC复相陶瓷的微观结构和物相组成,测量了复相陶瓷的弯曲强度和断裂韧性。结果表明:真空条件下液态渗硅获得的TiC/SiC复相陶瓷具有多孔的微观结构,其弯曲强度和断裂韧性较小。氮气气氛下液态渗硅制备的TiN/SiC复相陶瓷结构致密,有较高的弯曲强度和断裂韧性。不同反应生成的TiC,TiN陶瓷颗粒对液态硅的润湿性不同,使得生成的复相陶瓷具有不同的微观结构。TiN/SiC复相陶瓷中TiN颗粒的引入,在基体与第二相颗粒间的界面上产生拉应力和压应力,使达到这一区域的裂纹偏转,从而获得增韧效果。     

Conversion of Oak to Cellular Silicon Carbide Ceramic by Gas-Phase Reaction with Silicon Monoxide

Oak has been converted to a porous biocarbon template by annealing in an inert atmosphere above 800°C. Subsequent infiltration with gaseous SiO at 1550–1600°C under flowing argon of atmospheric pressure finally resulted in the formation of a porous, cellular β-SiC ceramic. The conversion retains the biomorphic cellular morphology of oak tissue. While pores in the cell walls with a diameter less than ∼1 μm vanished, two distinct pore channel maxima representing tracheidal cells and large vessels remained in the SiC ceramic. Depending on the cellular morphology of different kinds of wood, e.g., strut thickness and pore size distribution, gas-phase conversion to single-phase β-SiC can be used to manufacture cellular ceramics with a wide range of pore channel diameters.     

Effects of Fe addition on the mechanical and thermo-mechanical properties of SiC/FeSi2/Si composites produced via reactive infiltration

Remaining silicon in SiC-based materials produced via reactive infiltration limits their use in high-temperature applications due to the poor mechanical properties of silicon: low fracture toughness, extreme fragility and creep phenomena above 1000 °C. In this paper SiC–FeSi₂ composites are fabricated by reactive infiltration of Si–Fe alloys into porous Cf/C preforms. The resulting materials are SiC/FeSi2 composites, in which remaining silicon is reduced by formation of FeSi₂. For the richest Fe alloys (35 wt% Fe) a nominal residual silicon content below 1% has been observed. However this, the relatively poor mechanical properties (bending strength) measured for those resulting materials can be explained by the thermal mismatch of FeSi2 and SiC, which weakens the interface and does even generate new porosity, associated with a debonding phenomenon between the two phases.     

Application of the chemical vapor infiltration and reaction (CVI-R) technique for the preparation of highly porous biomorphic SiC ceramics derived from paper

Chemical vapor infiltration and reaction (CVI-R) is used to produce biomorphic high porous SiC ceramics based on biological structures such as paper. The paper fibers are first converted into a biocarbon (C_b) template by a carbonization step. In a second step methyltrichlorosilane (MTS) in excess of hydrogen is infiltrated into the C_b-template by CVI technique, depositing a Si/SiC layer around each fiber. The reaction (R) between biocarbon and excess silicon to form additional silicon carbide occurs during a subsequent thermal treatment as a third step of the ceramization process. Due to the mild infiltration conditions (850–900 °C) the initial micro- and macrostructure of the carbon preform is retained in the final ceramics. The applied characterization methods after every step of the ceramization process are X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy, Thermal Gravimetric Analysis (TGA), and Scanning Electron Microscopy (SEM). The bending strength of the resulting porous ceramics is measured by the double ring bending test. It is found that a slight excess of free Si in relation to the amount of carbon from the C_b-template must be deposited in the Si/SiC layer to achieve a nearly complete conversion of the C_b-templates into SiC ceramic. The weight gain after infiltration has to be at least 400 wt.%. Varying the infiltration conditions such as temperature, MTS concentration and infiltration time, ceramics in a wide range of porosity (55–80%) and mechanical properties (5–40 MPa) can be produced. A thermal treatment temperature of 1400 °C is found to be optimal for the reaction between the deposited Si and the biocarbon.     

Preparation and characterization of porous,biomorphic SiC ceramic with hybrid pore structure

Bio-carbon template (charcoal) was prepared by carbonizing pine wood at 1200 °C under vacuum, and was impregnated with phenolic resin/SiO₂ sol mixture by vacuum/pressure processing. Porous SiC ceramics with hybrid pore structure, a combination of tubular pores and network SiC struts in the tubular pores, were fabricated via sol–gel conversion, carbonization and carbothermal reduction reaction at elevated temperatures in Ar atmosphere. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) were employed to characterize the phase identification and microstructural changes during the C/SiO₂ composites-to-porous SiC ceramic conversion. Experimental results show that the density of C/SiO₂ composite increases with the number of impregnation procedure, and increases from 0.32 g cm⁻³ of pine-derived charcoal to 1.5 g cm⁻³ of C/SiO₂ composite after the sixth impregnation. The conversion degree of charcoal to porous SiC ceramic increases as reaction time is lengthened. The resulting SiC ceramic consists of β-SiC with a small amount of α-SiC. The conversion from pine charcoal to porous SiC ceramic with hybrid pore structure improves bending strength from 16.4 to 42.2 MPa, and decreases porosity from 76.1% to 48.3%.     

热处理对层状SiC/Si复合材料结构和性能的影响

牛皮纸浸酚醛树脂,经叠层、固化、碳化,最后,埋入硅粉中,在N2气保护下加热到1400℃,再抽真空并升温至1550℃,保温60min,使碳化样品与液态硅充分反应,制备了SiC/Si层状陶瓷复合材料.复合材料的密度、强度分别为2.20g/cm3和435MPa.将SiC/Si层状复合材料分别在氮气和真空中,于1440℃进行再热处理.研究了再热处理后材料的组成、显微结构和气孔率、强度等物理性能.结果表明:在氮气气氛下再热处理60min,样品的密度、强度分别达2.32g/cm3和455MPa,此时,因SiC/Si层状复合材料中Si与C经扩散迁移而反应形成更多的SiC,使材料的密度、强度提高.在真空环境中1400℃再热处理30min,样品的密度、强度分别为2.12g/cm3和430MPa,这是由于Si蒸发,样品的质量减少,气孔率大幅度增加,因此,密度和强度略有下降.     

Synthesis and characterization of Si/SiC ceramics prepared using cotton fabric

A Si/SiC ceramic was prepared from cotton fabric by the reactive infiltration of liquid silicon into the carbon template. A large density difference between the samples has been observed. This may be due to the variation in the pore size and its distribution within the sample. Scanning electron microscopy with energy dispersive spectroscopy shows the presence of three distinct phases, i.e., SiC, free Si and free carbon. X-ray diffraction pattern also confirms the presence of SiC and Si phases. However, there is no peak corresponding to carbon. So, it is inferred that the carbon exists in amorphous form. Micro-hardness, fracture toughness and bending strength of the ceramics were also studied. The values are lower than commercially available SiC ceramics. This may be due to the highly porous nature of cotton fabric-based SiC, as compared to commercially available SiC.