高强度多孔氮化硅陶瓷的制备与研究

以氮化硅为基体，通过加入一定量的纳米碳粉等添加剂，成功的制备出了具有高强度和较高气孔率的氮化硅多孔陶瓷。采用阿摹米得法、一点弯曲法测试了材料的密度、气孔率及强度；用X射线衍射仪及扫描电镜对相组成及断口进行了研究。实验结果表明：加入的纳米碳粉同在Si3N4表面的SiO2或者同Si3N4颗粒本身反应，生成了极细的SiC颗粒，钉扎在β型氮化硅的晶界，可以有效的增加材料的强度。在含碳量为5％(质量分数)，1780℃下保温60min，可以制得强度大于100MPa，气孔率大于40％的氮化硅多孔陶瓷。     

微孔无机分离膜用多孔陶瓷支撑体的研制

以碳化硅为原料，通过调整骨料粒径等级，并添加造孔剂和粘结剂，制备了孔隙率在35％-45％，平均孔径为40～60μm，具有狭窄的孔径分布（PSD）和很高强度的用于无机分离膜的微米级多孔陶瓷材料。在一定的烧成温度下，多孔陶瓷的平均气孔孔径与平均骨料粒径成正比。随着保温时间的延长，气孔孔径趋向均一；平均孔径增大，PSD变窄。增加粘结剂用量有利于促进PSD的集中趋势。多孔陶瓷的强度取决于骨料颗粒间的颈部连接强度，并随粘结剂用量的增加和烧成温度的提高而上升。     

SiC多孔陶瓷的气孔率和强度

选用ＳｉＣ作为骨料,长石和粘土组成的陶瓷结合剂和活性Ｃ作为成孔剂,对不同的烧成温度下ＳｉＣ多孔陶瓷的气孔率和强度进行了研究,温度的提高使ＳｉＣ多孔陶瓷的显气孔率陶低,而体气也民率增大;气孔形状随陶瓷结合剂的高温性能变化而变化,１２８０℃烧成时的气孔形状多为圆形,尺寸分布较均匀;１２４０℃烧成时出现经度极大值,温度提高使固体气孔率增大而强度降低,但在大于１３００℃时,由于ＳｉＣ的高温氧化产物参与晶界     

利用废弃棉短绒制备多孔SiC陶瓷及其性能的研究

以废弃的棉短绒和酚醛树脂为原料,通过模压成型,固化,碳化和渗硅制备出微观结构均匀的多孔碳和多孔碳化硅.通过SEM照片可以看出,由棉短绒纤维的杂乱排列和碳化时不同的收缩率产生了相互连通不规则的孔,在多孔碳化硅结构中也得以保留.经过三点弯曲测试,多孔碳化硅的气孔率随着排硅时间的增加而增加,强度和韧性随着捧硅时间的增加而减小.     

铸铁用碳化硅质泡沫陶瓷过滤器的制备与性能

使用有机泡沫浸渍工艺制备碳化硅质泡沫陶瓷过滤器,探讨了复合粘结剂的比例、烧结助剂(Al2O3)的加入量及烧结性能。样品的抗压强度与Al2O3的含量之间存在最佳搭配关系,莫来石相的生成是材料强度提高的一个重要贡献因素。采用最佳配方在1400℃制得的碳化硅质泡沫陶瓷过滤器抗压强度达到1.9MPa,样品加热至1100℃,放入15℃水中急冷的热震次数高达15次。     

无压烧结制备YAG多孔陶瓷的工艺及性能

为了能够利用YAG优异的性能开发出更多的功能材料,通过调整无压烧结技术工艺参数成功制备YAG多孔陶瓷材料。结果表明:1500℃烧结的YAG多孔陶瓷的气孔率与1550℃烧结的陶瓷相近,但是1550℃制备的陶瓷具有较多烧结颈使抗压强度较高。保温2 h的样品与保温1 h的样品进行对比表明,保温2 h样品包裹气泡长大使气孔率高,液相较多颗粒联接牢固使抗压强度高。升温速度为5℃/min制备的陶瓷比升温方式10℃/min制备的陶瓷气孔率和抗压强度都高。在800℃排碳所制备的样品的气孔率和抗压强度都比1000℃排碳的高。通过分析工艺参数与性能之间的内在联系,得出烧结温度为1550℃,保温2 h,升温速度为5℃/min,800℃排碳时间1 h制备的YAG多孔陶瓷材料较为适合,其材料气孔率为59.4%,抗压强度为8.55 MPa。     

高强度多孔氮化硅陶瓷的制备及性能研究

以氮化硅为原料,以叔丁醇为溶剂,采用凝胶注模成型工艺和无压烧结工艺,制备出具有高强度和高气孔率的多孔氮化硅陶瓷。在浆料中初始固相含量固定为10vol%的基础上,研究烧结温度和保温时间对多孔氮化硅陶瓷材料的气孔率、孔径尺寸分布、物相组成及显微结构的影响,分析抗弯强度与结构之间的关系。结果表明,通过改变烧结温度和保温时间,可制备气孔率63.3%~68.1%的多孔氮化硅陶瓷;气孔尺寸呈单峰分布,平均孔径为0.97~1.42μm;抗弯强度随烧结温度提高或保温时间延长单调增大,在1750℃保温1.5h下达到最大值(74.2±8.8)MPa。     

挤压成形制备多孔氮化硅陶瓷

以甲基纤维素作粘结剂配制氮化硅泥料,利用柱塞式挤压模具通过挤压成形法制备多孔氮化硅陶瓷.研究了挤压、干燥、排胶、烧结等各个工艺阶段坯体的开气孔率、体积密度、弯曲强度、显微结构及相转变等的变化规律.结果表明:挤压成形是制备多孔氮化硅陶瓷的一种有效而实用的方法.最后利用蜂窝陶瓷模具,首次成功挤出具有广泛应用前景的氮化硅蜂窝陶瓷.在未来的汽车尾气处理领域,有望取代当前广泛使用的堇青石材质蜂窝陶瓷.     

纳米晶和纳米复合陶瓷制备工艺

在传统的纳米粉末致密化的合成方法中，通常由于晶粒间的高界面能对晶粒长大带来很强的驱动力，而很难得到纳米结构材料。美国纳米材料研究学者介绍了两种制备纳米结构陶瓷块材的方法。一种方法是通过热压使火焰合成的亚稳态纳米粉末致密化，利用压力以诱导相转变控制晶粒致密化过程。该方法称为TAC(Transtormation Assisted Consolidation)，通常用于制备单相纳米陶 瓷——纳米晶陶瓷。另一种方法是等离子熔化和快冷法。TAC的技术关键是保持低温(减少熔融)和高压(增大成核作用)，这两个因素促使大量稳定相晶核的形成，从而得到陶瓷的…     

莫来石-刚玉多孔陶瓷支撑体的制备与性能

以高岭土和氧化铝为原料,通过聚合物辅助挤出成型法制备了管状莫来石-刚玉多孔陶瓷支撑体.研究造孔剂添加量和烧结温度对支撑体相组成、机械强度、微观结构及孔结构的影响,结果显示通过优化制备条件可以获得高气孔率、高强度、孔径分布均匀、透气度好,且具有良好抗热震性能的多孔陶瓷支撑体.     

Electrochemical corrosion of silicon carbide ceramics

Recently, SiC‐based ceramics have been found to exhibit corrosion damage patterns, which can only be explained by electrochemical processes. Therefore, the current work focusses on the electrochemical test procedures to determine the corrosion behaviour of solid state sintered silicon carbide (SSiC) ceramics in acidic and alkaline media. The corrosion current densities have been determined from linear voltammetric scans. At anodic polarization potentials, electrochemically induced etching patterns were observed in alkaline solution. The formation of pores and crevices during electrochemical oxidation in acidic solution could be monitored by field emission scanning electron microscopy (FESEM) in addition to transmission electron microscopy (TEM). Impedance spectra measured after anodic polarization could be described by the assumption of a pore model equivalent circuit.     

Processing and mechanical properties of porous silica-bonded silicon carbide ceramics

A simple processing route for manufacturing highly porous, silica-bonded SiC ceramics with spherical pores has been developed. The strategy adopted for making porous silica-bonded SiC ceramics entails the following steps: (i) fabricating a formed body through a combination of SiC and polymer microbeads (employed as sacrificial templates) and (ii) sintering the formed body in air. SiC particles are bonded to each other by oxidation-derived SiO₂ glass. By controlling the microbead content and the sintering temperature, it was possible to adjust the porosity such that it ranged from 19 to 77%. The flexural and compressive strengths of the porous silica-bonded SiC ceramics with ≈40% porosity were ≈65 MPa and ≈200 MPa, respectively. The superior strengths were attributed to the homogeneous distribution of small (≤30 μm), spherical pores with dense struts in the porous silica-bonded SiC ceramics.     

Preparation and properties of continuous Al-containing silicon carbide fibers

Continuous SiC(OA1) fibers, named KD-A fibers, were prepared by the melt-spinning of ceramic precursor polyaluminocarbosilane, air-curing, and pyrolizing at 1 300℃. These fibers contained small amount of aluminum and 7%-9% oxygen. The KD-A fibers were converted into sintered SiC(A1) fibers, named KD-SA, by sintering at 1 800℃. The fibers were characterized by chemical analysis, tensile strength test, SEM and XRD. The tensile strength, elastic modulus and diameter of the KD-A fibers are 2.6 GPa, 210 GPa, 12- 14μm, respectively. The KD-A fibers have higher thermal stability, more excellent oxidation resistance than the Nicalon fibers. The properties of the KD-A fibers have reached the level of Hi-Nicalon fibers. The tensile strength, elastic modulus and diameter of the KD-A fibers are 2.1 GPa, 405 GPa, 10 - 12μm, respectively. The KD-SA fibers with nearly stoichiometric component have stable performance at high temperature, and better creep resistance than the Tyranno SA fibers.     

Preparation and dielectric properties of porous silicon nitride ceramics

Porous silicon nitride ceramics with difference volume fractions of porosity from 34.1% to 59.2% were produced by adding different amount of the pore-forming agent into initial silicon nitride powder. The microwave dielectric property of these ceramics at a frequency of 9.36 GHz was studied. The crystalline phases of the samples were determined by X-ray diffraction analysis. The influence of porosity on the dielectric properties was evaluated. The results show that α-Si3N4 crystalline phase exists in all the samples while the main crystalline phase of the samples is β-Si3N4, indicating that the αβ transformation happens during the preparation of samples and the transformation is incomplete. There is a dense matrix containing large pores and cavities with needle-shaped and flaky β-Si3N4 grains distributing. The dielectric constant of the ceramics reduces with the increase of porosity.     

Dynamic elastic modulus and vibration damping behavior of porous silicon carbide ceramics at elevated temperatures

The piezoelectric ultrasonic composite oscillator technique (PUCOT) has been used to measure the Young’s modulus, E, the mechanical damping, Q ⁻¹, and the strain amplitude, ε, of a sintered silicon carbide containing pores (Hexoloy-SP). The silicon carbide material used in this study had at least 14 vol% porosity. Young’s modulus was found to have a linear temperature dependence from room temperature to 740 °C. The damping was near 10⁻⁴ and was independent of strain amplitude above room temperature.     

Electrochemical corrosion of liquid phase sintered silicon carbide ceramics

Liquid‐phase sintered silicon carbide (LPS‐SiC) is silicon carbide ceramic which contains sintering additives forming a liquid phase during sintering. These additives segregate in the grain boundary phase during cooling. The usually used Al₂O₃ dissolves partially in the SiC‐grains and therefore changing the conductivity of the SiC (core rim structure). This study is focused on the electrochemical properties of LPS‐SiC with yttria and alumina as sintering additives. Electrochemical corrosion behaviour of LPS‐SiC has been determined by linear and cyclic voltammetry in acidic and alkaline solution. The effect of anodic oxidation on the material has been monitored by field emission scanning electron microscopy (FESEM) and energy dispersive X‐ray spectroscopy (EDX) as well as by atomic force microscopy (AFM). The core‐rim structure of the investigated materials plays a decisive role in the vulnerability towards corrosion. If oxidative attack was found to occur under anodic polarization, it happened preferentially in the rim region of the SiC‐grains, while the core of the SiC‐grains remained basically unaffected.     

微波烧结碳化硅的制备

以硅粉为硅源,乙炔炭黑为碳源,通过微波加热的方法制备碳化硅。研究反应物密实度和反应物粒度对产物碳化硅粒度和形貌的影响,利用SEM和TEM等手段观察碳化硅的形貌。结果表明:采用自由堆积的乙炔炭黑和硅粉为反应物时,硅粉、碳粉表面存在的氧与其发生反应生成的Si O和CO,再通过气-气反应生成Si C晶须,生成产物包括Si C颗粒和晶须。当反应物加压后,生成的Si O与Si和C反应生成Si C颗粒,产物中只包括Si C颗粒。乙炔炭黑和硅粉反应过程中Si C通过扩散机制生成,碳颗粒的粒度决定了生成的Si C的粒度。     

Preparation of porous hydroxyapatite ceramics with starch additives

Porous ceramics prepared from nano-sized hydroxyapatite powders by adding water soluble starch and insoluble starch were investigated. The results show that small pores of several micrometers or less can be produced by adding water soluble starch as a pore former. Two kinds of starch have different pore forming mechanisms. The permeability of the porous ceramics can be greatly improved by adding the insoluble starch to channel the small pores rather than solely using water soluble starch. The control of permeability can be achieved by adjusting the content ratio of water soluble starch to insoluble starch. Strength tests show the ceramics have rather high strength. Therefore a kind of porous filtering material with small pores, controllable permeability and good strength can be prepared by using starch additives.     

燃烧合成法制备的Al2O3基多孔陶瓷

研究了Al2O3-TiC和Al2O3-TiB2两个体系的多孔陶瓷的制备过程,分析和讨论了产物的相组成、显微结构及成型性以及影响多孔陶瓷性能,如孔径大小、耐腐蚀性能和压缩强度的诸多因素.实验结果表明:布料时有序地改变反应物料的化学组成,可以在产物中不同区域产生不同尺寸的孔洞,形成梯度多孔陶瓷.利用燃烧合成法,可制备出孔径尺寸为1～500μm、酸碱腐蚀质量损失率小于2%、压缩强度为10 MPa左右的多孔陶瓷.