C/C坯体对C/SiC复合材料组织结构和导热性能的影响

以无涂层、C+SiC复合涂层处理的炭布/网胎预制体,分别经过化学气相渗透、树脂浸渍/炭化制备了3种C/C坯体,熔融渗硅后获得不同的C/SiC复合材料,对其组织结构和导热性能进行了研究。结果表明:热解炭坯体的C/SiC复合材料存在集中分布的Si,混合基体炭的C/SiC中可见较多微裂纹,C+SiC涂层的材料中残留Si含量少,基体组织均匀;热解炭坯体的C/SiC复合材料热扩散率和导热系数最大;混合基体炭的坯体,纤维经过C+SiC涂层,可明显提高材料的热扩散率和导热系数,且随温度的升高,导热系数的下降速率增大。     

熔体浸渍技术制备SiCp/AlN复合材料

采用熔体浸渍技术，研究了在高纯氮气氛下Al—Mg—Si合金反应浸渍碳化硅预形体制备SiCp／AlN复合材料．借助XRD，SEM／EDS，EMPA等测试手段检测了产物的物相组成，观察了材料的微观形貌，并对复合材料微区成分进行了分析。结果表明：1200℃下，在氮气气氛中用Al—Mg—Si合金反应浸渍碳化硅形成了SiCp／AlN复合材料。在氮化温度下，Al—Mg—Si合金中的Mg元素极易蒸发，与气氛中的微量氧发生反应，起到深脱氧作用，而Si元素的存在使Al—Si熔体容易浸渍渗透进入SiC预形体中，同时氮化反应生成AIN，形成了以AIN／Si为三维骨架，SiC呈孤岛状结构的SiCp／AlN复合材料。生长前沿氮化铝以胞状方式生长，胞内由呈放射状生长排列的柱状晶氮化铝构成，柱晶之问有大量的通道间隙，Si元素在胞内呈不均匀分布，胞边缘部分的硅含量明显高于胞中心部分，这与柱状氮化铝的生长机理有关。     

C/SiC-MoSi_2复合材料微结构和力学行为研究

以三维针刺碳毡作为预制体,先采用树脂单向加压浸渍-热解工艺制备出C/C多孔体,然后采用反应熔体浸渗法将Si-Mo合金浸渗到C/C多孔体中制备C/SiC-MoSi_2复合材料。对C/SiC-MoSi_2复合材料的物相组成、显微结构以及力学性能进行了研究。结果表明,该复合材料由C、SiC、MoSi_2和Si组成;生成的SiC和MoSi_2分布在纤维束间和胎网层,Si-Mo合金并未渗入纤维束内部,束内碳纤维未受损伤;残余Si含量仅为4.2%,且被分散成小块。C/SiC-MoSi_2复合材料的弯曲断裂行为可分为三个阶段,从材料的断口形貌中可以观察到纤维的脱粘拔出、基体的台阶状断裂以及裂纹偏转和分叉,表明该复合材料呈现出塑性断裂特征。     

C/C多孔体对C/C-SiC复合材料微观结构和弯曲性能的影响

以4种纤维含量相同(32%,体积分数,下同),用化学气相渗透(chemical vapor infiltration,CVI)法制备了4种密度的碳纤维增强碳(carbon fiber reinforced carbon,C/C)多孔体,基体炭含量约20%～50%.利用液相渗硅法(liquid silicon infiltration,LSI)制备了C/C-SiC复合材料,研究了C/C多孔体对所制备的C/C-SiC复合材料微观结构和弯曲性能的影响.结果表明:不同密度的C/C多孔体反应渗硅后,复合材料的物相组成均为SiC,C及单质Si;随着C/C多孔体中基体炭含量的增加,C/C-SiC复合材料中SiC含量逐渐减少而热解炭含量逐渐增加.C/C-SiC复合材料弯曲强度随着材料中残留热解炭含量增加而逐渐增加,热解炭含量为约42%的C/C多孔体所制备的C/C-SiC复合材料的弯曲强度最大,达到320 MPa.     

沥青基C/C复合材料浸渍过程的模拟

研究了沥青基C／C复合材料的浸渍过程，把沥青对预制体的浸渍分为束间浸渍和束内浸渍两个阶段，并同时考虑了浸渍过程中沥青中的喹啉不溶物在预制体表面的沉积，建立了束间浸渍模型和束内浸渍模型。使用Matlab软件对模型进行求解并实现了模拟结果的图形化。结果显示：浸渍效率随浸渍压力、浸渍时间的增加而增加，速率逐渐变缓；浸渍效率随孔隙率的增加而增加，速率逐渐增大；浸渍效率以近似正比关系随纤维束平均半径的增加而增加，并随浸渍过程的进行逐渐减小。验证显示模拟结果较好地符合了实验数据，说明了该模型的合理性。     

外加磁场下C／C复合材料的Fe—Ni催化石墨化以及性能研究

在Fe—Ni存在下,外加磁场不但可以提高酚醛树脂炭的石墨化度而且对新生成的石墨层也具有很好的导向作用。实验以短切雕N基碳纤维为增强体,酚醛树脂为基体碳源,采用液相浸渍的方法制备c／c复合材料。主要研究了外加磁场对c／c复合材料的Fe—Ni催化石墨化、电性能和力学性能的影响。结果表明,磁场作用下对含有铁磁性催化剂Fe—Ni的C／C复合材料的石墨化具有较好的改善作用;C／C复合材料的石墨化度越高其电阻率越低,并且电阻率在不同的磁场方向上呈现出了显著的差异性,平行于磁场方向上比垂直方向上的电阻率更低;但是,随着复合材料石墨化度的提高其抗压强度发生显著的降低。     

致密化工艺对C/C复合材料性能的影响

以三种致密化工艺对2D炭布针刺预制体进行致密，得到三组C／C复合材料，对其进行力学、热学性能检测及微观结构分析，并用C／C复合材料抗热震指标对三种致密化工艺所制备试样的性能进行综合评价，考察并比较了不同致密化工艺对C／C复合材料性能的影响。结果表明，采用化学气相沉积、沥青高压浸渍炭化及树脂常压炭化工艺所制备的RLS试样具有较好的综合性能。     

c—SiC—B4C复合材料的制备及其抗氧化性能研究

以生石油焦为炭质原料,向其中掺入定量SiC、B4CN瓷相,以改质煤焦油沥青作为粘结剂,通过模压制备出C—SiC—B4C复合材料。通过XRD、SEM、DTA—TG、EDS等分析方法研究了SiC、B4CNJ瓷相对C—SiC—B4C复合材料结构和性能的影响。研究表明,C—SiC—B4C复合材料的高温抗氧化性与氧化温度、各陶瓷相含量、本身气孔率等有关。掺入的Sic、B4C能够在一定程度上降低炭材料的气孔率,同时,高温条件下陶瓷相形成硼硅酸玻璃覆盖炭基体表面,减少材料表面活性区域数量,提高炭材料的表观活化能。     

二维C/C复合材料层叠板制备工艺及其性能的研究

研究通过浸渍—炭化法制备二维C／C复合材料层叠板的工艺参数，分析了不同基体前驱体和增密次数对材料的密度、厚度和收缩率、体积电阻率和层间剪切强度的影响，并用扫描电子显微镜进行断口分析。结果表明：选用残炭率较高的基体前驱体和适当的增密次数是制备低成本二维C／C复合材料层叠板的关键；相同纤维体积的层叠板基体炭含量越高，电阻率越小，导电性能越好；单位体积含有炭纤维越多，纤维受损几率就越大，产生结构缺陷几率越高，导致电阻率增加，导电性能下降；本实验中二维C／C复合材料层叠板制备工艺简单可行，层叠板的密度达到1．40g／cm^3以上，剪切强度为1．5MPa，断口呈脆性断裂特征。     

采用在SiC毡上CVD—SiC涂层提高C／C复合材料抗氧化性能

最近发展起来的SiC纤维复合涂层，也就是SiC/SiC层与化学气相沉积（CVD）SiC结合形成复合涂层，已能够在高温下提高C／C复合材料的抗氧化性。形成的SiC纤维复合涂层约300μm厚，生产时先将SiC毡覆盖在3D－C／C基体材料上，然后浸渍一种碳粉与硅粉均匀分散的料浆进行化学气要沉积。通过化学气相沉积（CVD）过程，在复合材料上形成致密的涂层。在CO2－H2O－N2组成的混合气体（CO2 9％、N273％、H2O18％），1700℃下进行5h氧化实验，结果发现有SiC毡增强复合涂层比没有SiC毡增强复合材料失重率低。SiC纤维毡复合涂层由双层结构组成，里层是多气孔的SiC/SiC纤维层，外层为致密的SiC涂层。由于SiC/SiC纤维层热膨胀系数介于C／C复合基体材料与CVD－SiC涂层之间，因此，SiC/SiC中间层在复合材料中起了重要作用，从而由于热膨胀系数不同产生的热应力致使涂层开裂降低到最低程度。涂层试样氧化后，采用缓冲冲床（MSP）测试其残余强度。MSP测试结果表明氧化后C／C复合材料强度值呈发散性，从纤维折断面看有z轴方向分布纤维存在。然而，这种方法仅适用于测试小尺寸试样。从这篇论文中，可看出涂层后的C／C复合材料有高的抗氧化性，其氧化后仍能保持高的残余强度。     

Microstructural evolution and mechanical performances of SiC/SiC composites by polymer impregnation/microwave pyrolysis (PIMP) process

SiC/SiC composites were prepared by polymer impregnation/microwave pyrolysis (PIMP) process, and their microstructural evolution and the mechanical performances were characterized. Using non-coated Tyranno SA fiber preforms as reinforcement and impregnation with only allylperhydropolycarbosilane (AHPCS) into the preforms, Tyranno SA/SiC composite (TSA/SiC) with higher density was obtained. While using carbon-coated Tyranno SA fiber preforms, Tyranno SA/C/SiC composite (TSA/C/SiC) with lower density were also fabricated. In this composite, SiC particulate was loaded with polymer precursor (AHPCS) in the first cycle impregnation. Microstructural observation revealed that pore and crack formation was affected by processing conditions. Bending strength was also dependent on the microstructural evolution of the samples. In TSA/SiC composite, relatively strong interfaces contribute to effective load transfer so that higher bending strength could be reached. In the TSA/C/SiC composite, weak interfaces provide a relatively lower strength. Meanwhile, different microstructural evolution and interfacial properties of the composites lead to the variation of the fracture behaviors.     

Reactive melt infiltration fabrication of C/C-SiC composite: Wetting and infiltration

Reactive melt infiltration is a fast and economical fabrication process for high performance C/C-SiC composite. In order to help understanding reactive melt infiltration production of C/C-SiC composite by liquid silicon, wetting and infiltration of the porous C/C composite preform by liquid silicon were investigated using a sessile drop technique. The contact angle decreased with the increase of time while the drop base diameter increased. According to the variation of drop base diameter and contact angle as a function of time, four different stages corresponding to the interfacial reaction and infiltration of liquid silicon were identified during wetting of the porous C/C composite preform by the liquid silicon. The infiltration height based on wetting curve linearly increased with time, much smaller than that calculated according to Washburn equation, which strongly indicated the reaction control of silicon infiltration.     

致密工艺对C/C复合材料摩擦性能的影响

采用针刺全炭纤维网胎无纬布整体结构预制体为骨架，经化学气相沉积（CVD）、树脂浸溃（RD固化致密及炭化、石墨化制得C／C复合材料。研究了粗糙层（RL）和树脂炭（RC）对摩擦性能的影响。结果表明，RL结构的C／C复合材料的摩擦性能较好，稳定性较高，是用作飞机刹车材料的前提；采用CVD＋RI制备且石墨化后的C／C复合材料具有优良的摩擦磨损特性；CVD试样的密度较低时，摩擦系数较高，但磨损较大，较难形成完整的摩擦膜。     

炭/炭复合材料制造硅晶体生长坩埚初探

多晶硅用直拉法(CZ)或磁场直拉法(MCZ)拉制成单晶硅棒。晶体生长炉热场零件中的石墨发热体、坩埚等在机械应力和热应力的综合作用下发生变形或损坏造成失效,更换频繁。选用纯度高的炭纤维制成待制件的多孔坯体,经过增密、纯化处理制成炭／炭复合材料坩埚。试制的两体12″炭／炭复合材料坩埚进行了工业性试验。炭／炭复合材料机械强度高、耐热冲击性能和化学稳定性好,其使用寿命大大高于高纯石墨坩埚。两体的连接止口的氧化侵蚀限制了坩埚的使用寿命。单晶硅设备的大型化、炭／炭复合材料势必成为晶体生长炉热场零件的必选材料。     

Electro-oxidation of ethylene glycol on PtRu/C and PtSn/C electrocatalysts prepared by alcohol-reduction process

PtRu/C and PtSn/C electrocatalysts were prepared by the alcohol-reduction process with different atomic ratios. The electrocatalysts were characterized by EDAX, XRD, TEM and cyclic voltammetry and the electro-oxidation of ethylene glycol was studied by cyclic voltammetry and chronoamperometry using the thin porous coating technique. PtRu/C and PtSn/C electrocatalysts were found to be active for ethylene glycol oxidation, which starts at lower potentials by increasing the ruthenium and tin content. In the region of interest for direct alcohol fuel cell applications PtSn/C electrocatalysts were more active than PtRu/C electrocatalysts.     

高温热处理对C/C多孔体显微结构的影响

以三维针刺碳毡作为预制体,先采用树脂单向加压浸渍结合热压固化制备了CFRP复合材料,然后通过树脂热解碳化制备出C/C多孔体。文章重点研究了高温热处理对C/C多孔体显微结构的影响。通过扫描电子显微镜观察了材料的显微结构,使用阿基米德方法测定材料的密度和气孔率,并利用压汞仪分析了材料的孔隙分布,利用X射线衍射分析碳基体的石墨化程度。结果显示,高温热处理后材料的密度降低,孔隙率增大;高温热处理没有改变材料中孔隙的类型,但使材料中三类孔隙尺寸均增大;经过高温热处理材料的石墨化度提高,部分块状碳基体转变为片层状石墨碳结构。     

Microstructures and properties of Si-Zr alloy based CMCs reinforced by various porous C/C performs

C/C-SiC composites were fabricated via Si-Zr reactive alloyed melt infiltration using various C/C preforms with different porosities as reinforcements. The influence of preform porosities on the microstructure, mechanical strength and ablation resistance of the as-prepared composites were investigated. The results indicated that microstructure and properties of the C/C-SiC composites seriously depended on C/C preform porosities. The composites were mainly composed of carbon, SiC and ZrSi₂ phases, while some residual silicon still existed in the composites prepared with very large porosity preforms. Flexural strength of the composites firstly increased with increasing C/C preform porosities, then reached the highest value, 307?MPa, and finally turned to decrease with the further increasing of preform porosities. Densities of the composites increased with increasing preform porosities, while open porosities were generally small below 7%. Linear ablation rates of the composites firstly sharply decreased with increasing preform porosities and then slightly decreased to reach a balance value. In a word, C/C preform porosity was of great significance for reactive melt infiltration of C/C-SiC composites. Densities, microstructure, mechanical strength and ablation resistance of the resulting composites should be comprehensively taken into consideration to choose an optimal preform porosity for fabrication of C/C-SiC composites.     

MOF衍生的Yolk-Shell结构NiCo/C复合材料的电磁波吸收性能

金属有机框架(MOF)衍生的多孔金属/碳复合材料由于具有大的表面积和孔体积,引起了电磁波吸收领域研究者的广泛关注。本文采用溶剂热法合成双金属NiCo-MOF,再通过煅烧制备了具有Yolk-shell结构的NiCo/C复合材料,采用SEM、XRD、拉曼光谱以及磁强计(VSM)等分析方法对比研究了不同Ni、Co质量比对NiCo/C复合材料吸波性能的影响。结果表明,随着Ni、Co质量比的变化,吸波性能发生了显著的改变。在9.4 GHz的频率下,Ni₁Co₁/C复合材料的性能达到最佳,最小反射损耗为-56.8 dB,有效吸收带宽为5.5 GHz。分析该复合材料的吸波机理发现,电磁波的多重反射、界面极化损耗、自然共振和交换共振是导致其吸波性能提高的重要原因。本文的研究结果为纳米多孔双金属MOF复合材料的制备与性能研究提供了研究思路。     

Low-temperature fabrication of porous ZrC/C composite material from molten salts

In this work, biological ceramic-wood porous ZrC/C materials were prepared in a KCl-KF molten salt reaction medium, using Zr as a metal source and a C template as C source. The effects of reaction temperature and salts/Zr mole ratio on the formation of porous biomorphic ZrC/C ceramics were investigated. The phase compositions and morphological structures of the C templates and porous ZrC/C ceramics were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and pore size analysis. The results showed that the ZrC grains were equiaxed and enhanced the oxidation resistance of the material. Furthermore, a possible reaction mechanism for the formation of porous biomorphic ZrC/C ceramics in molten salt is proposed.