浸渍熔渗复合法制备C_f/HfC复合材料及其性能

采用液相浸渍结合反应熔渗法制备了Cf/HfC复合材料。研究了浸渍效果、抗氧化烧蚀微粒分布形貌、熔渗效果与熔渗组织,并考核了C_f/HfC复合材料的抗氧化烧蚀性能和力学性能。结果表明:经5次浸渍-碳化循环和1次高温处理工艺制备了含13wt%抗氧化烧蚀微粒的ZrB_2+HfO_2+TaSi_2改性C/C预制体,其密度和开孔率分别为1.41g/cm~3和24.84%,微粒主要分布在纤维束之间的基体碳中,且分布均匀。改性C/C预制体经过Hf35Zr10Si5Ta合金反应熔渗制备的C_f/HfC复合材料密度和开孔率分别为2.98g/cm~3和12.95%,其线烧蚀率为0.017 1mm/s,弯曲强度为173.76 MPa,断裂方式为假塑性断裂。     

Al/TiC composites produced by melt infiltration

Abstract

An Al/TiC composite has been developed using a melt infiltration technique. Green preforms of TiC were partially sintered to densities ranging from 50 to 85%. They were then infiltrated with molten aluminium in argon at atmospheric pressure, at temperatures ranging from 950 to 1350°C. The variations in mechanical properties of this composite material with ceramic content and fabrication conditions are presented and the resulting microstructures are discussed. The composite exhibited excellent tensile strength values of ~475 MN m^?2 and up to 5% elongation. Fracture behaviour mechanisms are also described in relation to the stress–strain curves. High infiltration temperatures were found to be detrimental to the mechanical properties since the TiC particle network, which formed during sintering, was broken down by the metallic phase.

MST/1601     

Synthesis of Al2O3 matrix composites by reactive infiltration

Reactive infiltration of a NiO-base blended powder with molten aluminium was attempted at 1673 K in order to obtain Al2O3 matrix composites containing a dispersion of Al3Ni, AlNi and/or AlNi3. The NiO powder was barely infiltrated by the molten aluminium after a 3600 s holding time at 1673 K. A continuous layer of Al2O3 was observed to exist at the infiltration front, which prevented any further infiltration. TiB2 particles were added to the NiO powder in order to absorb the heat of reaction between NiO and aluminium. When the TiB2 particle content in the [NiO+TiB2] powder blend was greater than 20 vol%, spontaneous infiltration occurred completely. Thus, it was shown that the addition of the TiB2 particles assisted in the spontaneous infiltration. The specimens produced by the in situ reaction consisted of Al2O3, TiB2 and Al3Ni. Al3Ni was mainly located between the TiB2 and Al2O3. The effect of the TiB2 addition on the infiltration kinetics was to decrease the maximum attainable temperature caused by the exothermic reaction. This in turn prevented the formation of a continuous Al2O3 film at the infiltration front. This resulted in the production of pathways for the infiltration of the molten aluminium and made possible the complete infiltration. This revised version was published online in November 2006 with corrections to the Cover Date.     

Fabrication and microstructural evaluation of ZrB2/ZrC/Zr composites by liquid infiltration

The microstructure of ZrB₂/ZrC/Zr composites was examined using scanning electron microscopy, optical microscopy, and X-ray diffraction techniques. Dense ZrB₂/ZrC/Zr composites could be fabricated by the reaction sintering of molten zirconium with ZrB₂ preform. The composites were made by infiltration of molten zirconium into ZrB₂ preform, which contained 0–40 vol% B₄C, at 1900C for 10 min. The average grain size of ZrB₂ in the reaction-sintered composites decreased slightly with an increase in the volume fraction of the B₄C. The volume fraction of the solid increased with further increase of B₄C contents. The mechanical properties were measured in accordance with B₄C contents. The composites exhibited a four-point bending strength of up to 570 MPa and a fracture toughness of up to 11.5 MPa m^1/2.     

ZrB_2基超高温陶瓷复合材料的高温拉伸损伤行为

开展了SiC(20vol%)-石墨(15vol%)/ZrB2复合材料室温及高温拉伸性能实验,发现高温时复合材料的拉伸强度和弹性模量有所降低,并且具有明显的非线性特征。引入热损伤来表征弹性模量随温度的衰减规律,利用强度统计分析方法确定单向应力状态下材料的机械损伤演化方程,建立了材料在热力耦合条件下的高温拉伸损伤非线性本构模型。分析表明:随着温度的升高,SiC-石墨/ZrB2复合材料的热损伤和机械损伤不断增加,延性增强,且脆性-延性破坏转变温度范围为1 250~1 350℃。     

Synthesis of an Al2O3/Al co-continuous composite by reactive melt infiltration

The route for the fabrication of an Al₂O₃/Al co-continuous composite by reactive melt infiltration was investigated using scanning electron microscopy, energy dispersive X-ray microanalysis and X-ray diffraction analysis. It was found that in the process of molten aluminium infiltration into the SiO₂ preform, the chemical reaction of 3SiO₂ + 4Al → 2Al₂O₃ + 3Si occurred at the infiltration front, and generated a transition zone containing a new type of continuous porosity about 100 μm in width. The reaction continued with further infiltration of molten aluminium alloy into this porosity which reacted with the residual SiO₂ until all the SiO₂ was transformed into Al₂O₃. A comparison was made between this route and that by direct infiltration of molten aluminium alloy into the open porosity of an Al₂O₃ preform. As a result of the increased wetting ability of the molten aluminium alloy by the chemical reaction, reactive melt infiltration took place at a higher rate for the SiO₂ preform than that for the direct infiltration of the Al₂O₃ preform. A fracture surface examination demonstrated a toughening effect provided by the continuous aluminium alloy in the composite.     

SiC引入方式对反应熔渗原位纳米SiC/MoSi_2复合材料组织性能的影响

探讨了SiC引入方式对反应熔渗原位20wt%纳米SiC/MoSi_2复合材料TEM组织及力学性能的影响。结果表明:完全原位反应熔渗硅可获得基体相和增强相均为纳米尺度的SiC/MoSi_2复合材料,其组织中存在大量晶内层错等缺陷,可能会使纳米SiC/MoSi_2复合材料力学性能的提高不十分显著;而部分原位反应熔渗法中,SiC初始粉末的引入可缓解剧烈物相反应,所得纳米SiC/MoSi_2复合材料晶内缺陷消失,断口出现大量撕裂棱,复合材料力学性能大幅提高。     

Preparation and characterization of ZrB 2 -SiC ultra-high temperature ceramics by microwave sintering

ZrB₂-SiC ultra-high temperature ceramic composites reinforced by nano-SiC whiskers and SiC particles were prepared by microwave sintering at 1850°C. XRD and SEM techniques were used to characterize the sintered samples. It was found that microwave sintering can promote the densification of the composites at lower temperatures. The addition of SiC also improved the densification of ZrB₂-SiC composites and almost fully dense ZrB₂-SiC composites were obtained when the amount of SiC increased up to 30vol.%. Flexural strength and fracture toughness of the ZrB₂-SiC composites were also enhanced; the maximum strength and toughness reached 625 MPa and 7.18 MPa·m^1/2, respectively.     

低温制备高致密度细晶W-10％TiC复合材料

采用高能球磨结合真空热压的手段制备了W-10％（质量分数）TiC复合材料。采用扫描电镜、透射电镜和x射线衍射等对复合粉体及复合材料进行表征。结果表明，通过高能球磨得到了粒径均匀，平均粒径约为100nm的纳米复合粉体，粉体经过1700℃真空热压烧结后致密度达到99．1％，并且保持细晶结构（平均晶粒尺寸为0．8gm）。热压和高能球磨导致的机械活化以及引入的Fe、Ni等杂质是复合材料低温烧结达到高致密度的重要原因。     

Fabrication of biphasic calcium phosphates/polycaprolactone composites by melt infiltration process

Synthesis and characterization of material properties of biphasic calcium phosphates (BCP)/polycaprolactone (PCL) composites, which were obtained by melt infiltration of PCL using porous BCP bodies, were investigated. Using 70 vol.% of poly methyl methacrylate (PMMA) powder as a pore-forming agent, porous BCP bodies were obtained by pressure less sintering depending on the temperature. The porous bodies obtained showed interconnected, spherical pores about 200 μm in diameter. Densification of the pore frame improved and grain growth increased remarkably as the sintering temperature increased. Molten PCL was infiltrated into porous BCP bodies to obtain the BCP/PCL composites. The material properties such as the relative density, hardness, bending strength, and elastic modulus of BCP/PCL composite, which was sintered at 1200 °C, were 95.7%, 11.2 Hv, 31.6 MPa and 10.2 GPa, respectively.     

原位水解低温制备ZnO-TiO2复合半导体光催化剂

以乙二醇作反应物和溶剂，通过原位水解低温晶化法在较温和的条件下制备出纳米复合ZnO-TiO2光催化剂．通过TEM、XR-D、UV-Vis、BET、粒度分析等技术手段对光催化剂进行了表征，发现ZnO-TiO2是由纳米级的ZnO和TiO2粒子组成，该光催化剂分散性好，并且可以吸收部分可见光，扩大了光吸收范围。光催化降解甲基橙实验表明，ZnO-TiO2纳米复合氧化物的光催化活性明显高于自制的TiO2和ZnO单一氧化物和商业P25TiO2．     

Optical, mechanical properties and infiltration rate of spinel/zirconia-glass dental composites prepared by melt infiltration

Spinel/zirconia-glass dental composites were prepared by melt infiltration to investigate the effect of zirconia addition on mechanical, optical properties and infiltration rate of the composites. The glass infiltration rate decreased with raising the zirconia content having a parabolic dependence of infiltration distance on time described by the Washburn equation due to the reduction in pore size. Although the optimum strength (308 MPa) of the spinel/zirconia-glass dental composite was observed when 20 wt% of zirconia was added, transmittance decreased with further increase in the zirconia content.     

熔融渗透工艺制备SiC-TiSi2复相陶瓷的反应机理

熔融Si渗透过程伴随着复杂的化学反应及多组分扩散,对该过程进行研究有助于更好地理解熔渗反应机理。本工作采用熔融渗透工艺制备SiC-TiSi2复相陶瓷,在生成SiC基体的同时原位生成TiSi2。通过扫描电子显微镜(SEM)、X射线能谱分析(EDS)和微区X射线衍射(micro-beam XRD)分别对熔融硅区域、Si/SiC界面以及SiC基体的微观结构和相组成进行表征和分析,研究了熔渗工艺制备SiC-TiSi2的反应机理。结果表明:高温下液Si渗入C-TiC预制体,发生化学反应生成SiC、TiSi2以及少量副产物Ti5Si3,其中Ti5Si3主要集中于Si/SiC界面处。随着反应进行,液Si与TiSi2形成液态Ti-Si共晶。该液态共晶通过流动扩散在Si区域中析出TiSi2。而预制体中的少量固态C在液Si中溶解、扩散,并在Si区域生成均匀分布的孤立SiC颗粒。     

Preparation of photosensitized nanocrystalline TiO(2) hydrosol by nanosized CdS at low temperature

A new method was developed for the fabrication of CdS-TiO(2) semiconductor nanoparticles as visible-light-excitable photocatalyst at low temperatures. Nanosized CdS acting as an effective and stable sensitizer was incorporated into TiO(2) by microemulsion-mediated solvothermal hydrolyzation followed by acidic peptization of the precipitate under 70?°C. The new method avoided the calcination or other pyrochemical treatments involved in traditional preparations, and thus eliminated the unwanted agglomeration of nanoparticles or the oxidation of CdS by oxygen. Compared to traditional methods, it was highly simplified, bypassing those miscellaneous steps like filtration, sintering, milling and redispersion in solutions. The crystal structure, configuration, element composition, as well as the light-absorption properties of the obtained CdS-TiO(2) hydrosol were characterized in detail. The hydrosol consisting of uniform and small crystalline particles of about 2?nm in diameter was thermodynamically stable and showed good dispersibility. The photocatalytic activity of the 'coupled' material was confirmed through the photocatalytic degradation of methylene blue (MB) dye under visible light irradiation, and the cooperative photocatalytic mechanism is discussed.     

Preparation of battery-grade Li2CO3 efficiently by high shear dispersion at low temperature

With the significant increase of market demand, battery-grade lithium carbonate has become an imperative research. However, it is difficult for commercially available battery-grade lithium carbonate to simultaneously meet all criteria such as dispersion, particle size, particle size distribution, and purity. Here, we proposed a flexible method to prepare battery-grade lithium carbonate with small particle size, uniform size distribution, high purity, and good dispersion by using a high shear dispersion reactor under low-temperature conditions. First, a numerical simulation model was established, and the feasibility of this proposed method was verified by computational fluid dynamics (CFD). Then, the factors of yield optimization on Li₂CO₃ were analyzed based on response surface methodology (RSM) by using a 3-level 4-factor Box-Behnken statistical design with a fixed lithium solution concentration as the input parameter. Moreover, the reaction kinetics, size distribution, crystal morphology, and purity of Li₂CO₃ were investigated. The obtained Li₂CO₃ possessed the average particle size in 5.85 μm and total particle size range from 1.56 to 12.97 μm, which both exhibited a ten-fold reduction compared with it prepared under conventional preparation conditions. Finally, the Li₂CO₃ products with 99.81% purity met the requirements of the Chinese non-ferrous metal industry standard (YS/T582-2013) for battery-grade Li₂CO₃. We anticipate that this work may shed light on developing efficient and controllable method for the preparation of battery-grade Li₂CO₃.     

两种先驱体低温裂解制备石英纤维增强氮化硅复合材料

以全氢聚硅氮烷( PHPS) 和聚甲基硅氮烷( PHMS) 为陶瓷先驱体, 通过循环浸渍和600 ℃低温裂解分别制备了三维石英纤维增强氮化硅复合材料, 对比研究了复合材料的力学性能和微观结构。结果表明: 由PHPS 制备的复合材料密度为1. 83 g/ cm3 , 气孔率10 % , 弯曲强度45. 4 MPa , 材料断口平整, 纤维基体界面结合强; 而由PHMS 制备的复合材料密度仅为1. 66 g/ cm3 , 气孔率16 % , 却具有更高的弯曲强度56. 3 MPa , 材料断面较粗糙,界面结合较弱。先驱体活性不同是导致复合材料界面结合强弱及力学性能不同的主要原因。      

低温镁铝尖晶石纳米粉末的制备与表征

以Mg(NO3)2.6H2O、Al(NO3)3.9H2O为原料,Na2CO3、NaOH为沉淀剂,采用化学共沉淀法制得MgAl2O4尖晶石前驱体。用TG、XRD、TEM及物理吸附仪研究了试样的热稳定性、物相组成、显微形貌和表面性能。结果表明:前驱体经800℃处理后,几乎全部转变成粒径为10nm左右的MgAl2O4尖晶石超细粉末,并且颗粒分散性好,比表面积大,为136.35m2/g,比传统制备镁铝尖晶石粉末的温度低600～700℃。