电致发热SiC多孔陶瓷制备研究

采用一种新方法制备了具有2种孔隙结构的电致发热SiC多孔陶瓷.根据SEM,X射线分析,气孔率与电阻率等测试结果可知,试样主孔道直径在300μn左右,微孔道直径在30～40μm,气孔率可达55%,电阻率在0.0007～0.00195Ω·m.研究了烧结温度和烧结时间与电阻率的关系,并根据机械性能的测试结果,探讨了试样的强度与烧结温度的关系.     

电致发热多孔碳化硅陶瓷的绝缘涂层

以异丙醇铝{Al[OCH(CH3)2]3}为原料,用溶胶-凝胶法制备氧化铝(Al2O3)溶胶,然后再以碳化硅(SiC)多孔陶瓷为基体,用浸渍提拉法对陶瓷进行涂层,涂覆完成后进行热处理即可在陶瓷表面和孔隙内部形成致密的Al2O3涂层.当涂层后的陶瓷用作电加热元件时,就可以达到陶瓷和流体绝缘的目的.从扫描电镜照片可以看出:在陶瓷表面及其孔隙内部确实涂覆了Al2O3涂层.Al2O3具有高电阻系数、高介电常数,抗氧化、耐腐蚀性等优异性能,所以,涂层后陶瓷的电阻率明显增加,可以弥补电致发热过程可能引起危险性的缺陷.Al2O3的涂覆也很好地改善了陶瓷成分SiC的氧化问题.结果表明:涂层中Al2O3的质量分数(下同)为43.1%,二氧化硅(SiO2)为38.8%,硅(Si)为18.1%.Al2O3是涂层物质的主要成分,SiO2有两种来源,一是作为基体的多孔陶瓷在渗硅过程中的剩余硅在陶瓷冷却过程中氧化生成存留于陶瓷中;二是陶瓷中的剩余硅在涂层的热处理过程中再次氧化形成.所以SiO2的含量相对较高,其中的硅显然就是陶瓷中的残留硅.     

不同铝源对SiC/堇青石复相多孔陶瓷的制备及性能影响

以碳化硅、氮化铝、层析氧化铝、氢氧化铝、氟化铝、滑石为主要原料,石墨为造孔剂通过原位反应烧结技术制备碳化硅/堇青石复相多孔陶瓷.研究了含铝化合物种类、烧结温度、石墨含量对SiC/堇青石复相多孔陶瓷相组成、微观结构、气孔率和抗折强度的影响,同时对S0组在1200℃烧结温度下制得的SiC/堇青石复合多孔陶瓷的孔径分布进行了测试分析.结果表明:以AlN为铝源在1200℃下烧结,石墨含量在15％时,堇青石结合SiC多孔陶瓷的抗弯强度和气孔率两项综合性能达到最优,气孔率为31.99％,相应的弯曲强度86.20 MPa.S0组的平均孔径大小在3.0191 μm.     

硅锭线切割回收料制备SiC多孔陶瓷的研究

以硅锭线切割回收料为主要原料、Al2O3为烧结助剂、石墨粉为造孔剂.用普通烧结工艺制备了SiC多孔陶瓷.着重研究了Al2O3添加量对SiC多孔陶瓷的形貌、热膨胀系数、气孔率以及力学性能的影响.结果表明:当Al2O3和石墨添加量分别为30wt%和10wt%,在1450℃温度下烧成的多孔陶瓷的气孔率高达42.21%、弯强度达到30.5Mpa、热膨胀系数为6.64×10-6K-1,可以满足在熔融金属过滤等方面的应用.     

高温除尘用微粉SiC多孔陶瓷的制备和性能研究

本文以平均粒径为2.4 μm微粉SiC颗粒作为多孔陶瓷的主要原料,活性炭和石墨为造孔剂,再添加陶瓷粘结剂和羧甲基纤维素钠(CMC)溶液,采用逐层包覆工艺混料成型.将成型后的胚体在1300℃下烧结出不同陶瓷粘结剂含量(5～ 15wt％)(下同)以及不同成型压力(5～20 MPa)下的多孔陶瓷并研究了其气孔率、收缩率、过滤压降及抗压强度随陶瓷粘结剂含量以及不同成型压力下的变化.研究表明多孔陶瓷的气孔率随着成型压力由12.2MPa增加到48.8 MPa和粘结剂含量5％增加到15％气孔率逐渐降低,其抗压强度分别随着胚体成型压力的增大和粘结剂含量的增加而增加,烧结后胚体收缩率随粘结剂含量有先降低后增加的趋势.在粘结剂含量为10％时,成型压力19.52 MPa下多孔陶瓷的抗压强度和显气孔率都取得了较高的值,分别为31.75 MPa和29.87％,室温下空气流量为0.016 m3·h-1时,过滤压降为21.23 hPa.     

低温制备SiC多孔陶瓷及性能

采用SiC微粉为骨料,聚碳硅烷为粘结剂,混合后溶于THF中干燥过筛,经模压成型后于1000℃保护气氛下低温烧结制备SiC多孔陶瓷。运用XRD、SEM及孔隙率测定手段对陶瓷样品的物相结构、微观形貌及孔隙率进行研究,考察了不同聚碳硅烷含量对SiC多孔陶瓷抗弯强度、线收缩率及气孔率的影响。结果表明,随着聚碳硅烷含量的增加,SiC多孔陶瓷的线收缩率和失重比均增加,抗弯强度和显气孔率均先增加后下降,抗弯强度在聚碳硅烷含量为13%时达到最大值为58.45MPa,开口气孔率在PCS含量为5%时达到最大值为37.2%。     

气孔率对多孔质SiC氧化的影响

在２０ｋＰａ和１ｋＰａ的氧气分压下研究了气孔率对多孔质ＳｉＣ化性状的影响,使用四极质谱仪测定了氧化期间所产生气体的发生速度。     

SiC多孔陶瓷预成形坯的制备

本文采用真空烧结方法制备SiC多孔陶瓷预成形坯,研究了不同助烧结剂Al2O3-Y2O3、Si、Co和高岭土以及造孔剂羧甲基纤维素(CMC)含量对SiC多孔陶瓷预成形坯气孔率和形貌的影响。结果表明,多元助烧剂Al2O3-Y2O3有利于降低烧结温度和形成液相烧结,并有利于提高SiC多孔陶瓷的孔结构稳定性;羧甲基纤维素含量对烧结预成形坯气孔率和体积密度的影响较大,随着造孔剂CMC含量的增加,SiC多孔陶瓷的气孔率也相应地增加,其体积密度相应减少。     

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.     

Wood-Derived Porous SiC Ceramics by Sol Infiltration and Carbothermal Reduction

A new method for transforming wood structures into ceramic by carbothermal reduction of silica and carbonized wood has been developed. Application of this technique allows the preservation of wood microstructures in the ceramic state and the conversion of wood components without constraints in component size. The chosen infiltration technique of silica sol incorporation into carbonized wood structures is examined in terms of sol and wood type, carbonization conditions of the wood, and thickness of the infiltrated carbon body. Ceramization conditions were optimized, and the reaction mechanism is discussed.     

Thermal conductivity mapping of oxidized SiC/SiC composites by time-domain thermoreflectance with heterodyne detection

Silicon carbide/silicon carbide (SiC/SiC) composites are often used in oxidizing environments at high temperatures. Measurements of the thermal conductance of the oxide layer provide a way to better understand the oxidation process with high spatial resolution. We use time-domain thermoreflectance (TDTR) to map the thermal conductance of the oxide layer and the thermal conductivity of the SiC/SiC composite with a spatial resolution of 3 μm. Heterodyne detection using a 50-kHz-modulated probe beam and a 10-MHz-modulated pump suppresses the coherent pick-up and enables faster data acquisition than what has previously been possible using sequential demodulation. By analyzing the noise of the measured signals, we find that in the limit of small integration time constants or low laser powers, the dominant source of noise is the input noise of the preamplifier. The thermal conductance of the oxide that forms on the fiber region is lower than the oxide on the matrix due to small differences in thickness and thermal conductivity.     

Effect of Interfacial Reaction on the Thermal Conductivity of Al–SiC Composites with SiC Dispersions

The effect of interfacial reactions between Al and SiC on the thermal conductivity of SiC-particle-dispersed Al-matrix composites was investigated by X-ray diffraction and transmission electron microscopy (TEM), and the thermal barrier conductance ( h _c) of the interface in the Al–SiC composites was quantified using a rule of mixture regarding thermal conductivity. Al–SiC composites with a composition of Al (pure Al or Al–11 vol% Si alloy)–66.3 vol% SiC and a variety of SiC particle sizes were used as specimens. The addition of Si to an Al matrix increased the thermal barrier conductance although it decreased overall thermal conductivity. X-ray diffraction showed the formation of Al₄C₃ and Si as byproducts in addition to Al and SiC in some specimens. TEM observation indicated that whiskerlike products, possibly Al₄C₃, were formed at the interface between the SiC particles and the Al matrix. The thermal barrier conductance and the thermal conductivity of the Al–SiC composites decreased with increasing Al₄C₃ content. The role of Si addition to an Al matrix was concluded to be restraining an excessive progress of the interfacial reaction between Al and SiC.     

Cf/SiC复合材料的制备及性能的研究

采用料浆渗积-有机前躯体裂解工艺制备碳纤维增强碳化硅陶瓷基复合材料.制备材料的抗弯强度达283 MPa,断裂韧性达12.1 MPa·m1/2.     

SiC Nanowires Synthesized by Rapidly Heating a Mixture of SiO and Arc-Discharge Plasma Pretreated Carbon Black

SiC nanowires have been synthesized at 1,600 °C by using a simple and low-cost method in a high-frequency induction furnace. The commercial SiO powder and the arc-discharge plasma pretreated carbon black were mixed and used as the source materials. The heating-up and reaction time is less than half an hour. It was found that most of the nanowires have core-shell SiC/SiO₂ nanostructures. The nucleation, precipitation, and growth processes were discussed in terms of the oxide-assisted cluster-solid mechanism.     

SiC纳米粉体悬浮液导热系数研究

本文作采用非稳态热丝法,测量了水中加平均粒为25nm的碳化硅粉（简称n-SiC),乙二醇中加n-SiC,水中加平均粒径为0.6μm的碳化硅粉（简称μ-SiC）和乙醇中加μ-SiC等4个系列不同固体积含量悬浮液的有效热系数,实验结果表明：对于所研究的悬浮液,其有效导热系数相对增加量随固相加入量的增加而线性增加;固相颗粒形貌对有效导热系数相对增加量有显著影响;基体液体虽对有效导热系数相对增加量无明显影响,但有效导热系数的绝对量由基体液体的导热系数决定。     

Relationship Between Electric Properties and Temperature of ZrB,-SiC Composite Ceramic Heating Element

ZrB2 -SiC composite ceramic has been successfully introduced as heating element in super high temperature .field. This paper further investigated the microstructure of ZrB2 - SiC composite ceramic heating element and the relationship between electric properties and temperature. SEM photos show that the heating element consists of SiC grains and ZrBz grains smaller than 10 μm. The voltage and current gradually increase and the furnace tempera- ture rises lineally with heating time prolonging. The electric resistance increases linearly with the temperature rising. The service temperatltre of the heating element can reach 1 800 ℃ and 2 150 ℃ in air and argon at- mosphere, respectively.     

Nanowire-decorated SiC foam from tissue paper and silicon powder by filter-pressing

A facile and scalable method for the preparation of low-density SiC foam from tissue paper and silicon powder is reported. The co-dispersion of pulp-containing tissue paper micro-ribbons and silicon powder is coagulated by adjusting the pH to 3.5. The silicon particles adhere to the tissue paper micro-ribbons during the coagulation. The coagulated co-dispersion on filter-pressing consolidates the silicon particle-decorated tissue paper micro-ribbons and orients them perpendicular to the filter-pressing direction. The filter-pressed body on drying followed by heat treatment at 1600°C in inert atmosphere produces SiC foam. The tissue paper micro-ribbons retain their morphology during carbonization as well as high-temperature reaction with the silicon. The enormous growth of carbon-rich SiC nanowires is observed on the SiC micro-ribbons. The random orientation of SiC micro-ribbons in the X-Y plane with the hairy nanowires on the surface and their stacking in the Z-direction produces a porosity of ~94 vol.% with pore sizes in the range of 0.08 to 20 µm. The SiC foam shows a compressive strength and Young's modulus of 0.22 and 5.5 MPa, respectively. The thermal conductivity decreases from 0.11 to 0.07 W m⁻¹ K⁻¹ when temperature increases from 25°C to 350°C.