BN纤维对石墨烯微片/聚丙烯复合材料导热绝缘性能的影响

采用熔融共混法制备BN纤维-石墨烯微片/聚丙烯（BN纤维-GNP/PP）高导热绝缘复合材料,结合有限元模拟、SEM、XRD、导热导电测试结果,探究了BN纤维含量和长度对BN纤维-GNP/PP复合材料导热绝缘性能的影响。结果表明:BN纤维-GNP/PP复合材料中BN纤维含量和长度的增加可增大GNP分布范围,增大BN纤维与GNP的接触概率;在GNP含量为7wt%、100 μm BN纤维含量为20wt%时BN纤维-GNP/PP复合材料的热导率较PP提高了4.2倍,同时电绝缘性略有提高。模拟结果表明,高含量100 μm BN纤维的加入使BN纤维-GNP/PP复合材料导热网络的构建趋于完整,局部热通量较低的区域减少。片状GNP与纤维状BN二相填料的"协同效应",使GNP和BN纤维分别作为"岛"和"桥"形成了一种特殊的"双网络"结构,BN纤维作为高导热"桥"阻隔了相邻GNP间导电通路的形成,从而提高了BN纤维-GNP/PP复合材料的导热绝缘性能。      

BN/SiC复合界面层对SiC纤维和PIP-Mini复合材料力学性能的影响

采用化学气相渗透(CVI)工艺,在SiC纤维表面沉积BN和BN/SiC复合界面层,对沉积界面层前后纤维的力学性能进行了评价。采用聚合物浸渍裂解(PIP)工艺进行致密化,制得以原纤维、BN界面层和BN/SiC界面层纤维增强的三种Mini-SiCf/SiC复合材料,研究其微观结构和拉伸性能。结果表明:采用CVI工艺制得的界面层厚度均匀、结构致密,其中BN界面层中存在六方相,晶体尺寸为1.76 nm; SiC界面层结晶性较好,晶粒尺寸为18.73 nm;沉积界面层后SiC纤维的弹性模量基本保持不变,拉伸强度降低。与SiCf/SiC相比, PIP工艺制备的SiCf/BN/SiC和SiCf/(BN/SiC)/SiC-Mini复合材料所能承受的最大拉伸载荷和断裂应变明显提升, BN界面层起主要作用。由断面形貌分析可以看出, SiCf/BN/SiC和SiCf/(BN/SiC)/SiC复合材料的纤维拔出明显,说明在断裂时消耗的能量增加,可承受的最大载荷增大。     

氮化物对增强线性酚醛树脂导热性能的对比研究

目的对比探讨氮化物陶瓷颗粒AlN和BN对热塑性酚醛树脂复合材料导热率的影响,制备高导热复合材料,并将其应用于电子塑封领域。方法首先,采用硅烷偶联剂对AlN和BN进行表面改性,以增强其在有机聚合物中的分散性。然后通过在线性酚醛树脂中添加不同粒径的陶瓷颗粒,对比粒径及填料含量对线性酚醛树脂复合材料导热率的影响,从声子角度分析,获取适合作为提高复合材料导热性能的填料。结果经过硅烷偶联剂表面改性后,陶瓷颗粒AlN、BN与水的接触角变大,与树脂的接触角变小,能够更好地分散在线性酚醛树脂中。在线性酚醛树脂中添加不同粒径、不同含量的AlN和BN,发现在不同含量范围内,填料粒径对复合材料导热率的影响不同。根据声子传递热量理论分析,BN较AlN在与C形成的界面上更容易传输热量,从而实现了较高的导热率。结论氮化物陶瓷颗粒能够很好地增强复合材料的导热率,尤其是BN,其态密度和C的态密度重叠率极高,更适合在BN与C的界面快速传递热量。     

电纺制备聚丙烯腈/氮化硼杂化复合纤维及其结构、性能研究

针对聚合物材料导热性差的问题,为了改善聚合物填充复合材料的导热和吸附等性能,以聚丙烯腈和氮化硼为原料,利用静电纺丝方法制备了聚丙烯腈/氮化硼(PAN/BN)有机无机杂化复合纤维。采用扫描电镜、热分析、红外光谱、X射线衍射仪、激光导热仪和比表面积及孔隙度分析仪对复合纤维进行了结构和性能表征。实验通过改变聚丙烯腈和氮化硼在纺丝溶液中的质量比,研究了纤维中不同氮化硼含量对复合纤维形态、结构和性能的影响。结果表明,通过静电纺丝能够把氮化硼包覆并均匀分散在聚丙烯腈聚合物中,可有效改善聚合物的导热和吸附性能。随着纤维中氮化硼含量的增加,材料的热导率增加,当BN质量分数为54.5%时,纺制得到的PAN/BN杂化复合纤维的热导率最高达到3.977 W/(m·K),比热导率为0.048 W/(m·K)的纯PAN纤维高82.8倍左右。     

混合溶剂分散法制备耐高温、高导热六方氮化硼/半芳香聚酰胺12T复合材料及其性能

制备兼具优异耐高温性能和导热性能的聚合物基复合材料对于电子元器件的封装保护、高效散热和稳定成型至关重要。本文通过混合溶剂分散法(MSD)制备了六方氮化硼(BN)/半芳香聚酰胺12T (PA12T)复合材料,并对复合材料的微观结构、导热、耐高温、介电和力学性能进行了表征。结果表明:混合溶剂分散法可以有效实现BN和PA12T粉末的均匀悬浮,并可协同真空辅助自组装法与真空热压法构筑具有均一分散和取向结构的复合材料。研究表明,当BN/PA12T复合材料中的BN含量为40wt%时,混合溶剂分散法制备的样品的平面导热率可以达到2.73 W/(m·K),是机械混合法(MM)制备的样品(1.59 W/(m·K))的1.72倍,同时其具有优异的力学性能、低介电常数(3.6)、介电损耗(0.016)和显著的耐高温性能(维卡软化点超过250℃且初始分解温度可达446℃)。综上所述,混合溶剂分散法制备的BN/PA12T复合材料在电子封装及热管理领域中具有广阔的应用前景。      

原位反应加工法制备氮化硼/聚甲基丙烯酸甲酯/聚乙烯导热复合材料的性能EI北大核心CSCD

以氮化硼(BN)为导热填料、聚甲基丙烯酸甲酯(PMMA)和高密度聚乙烯(HDPE)为基体,利用甲基丙烯酸甲酯(MMA)的原位反应加工成功制备了BN/PMMA/HDPE高导热复合材料。研究了PMMA与HDPE不同质量比时的相形态,通过扫描电子显微镜发现,当PMMA与HDPE的质量比为9:11时,复合材料构成了完善的双连续结构,BN选择性分散在原位反应加工法制备的BN/PMMA/HDPE高导热复合材料的PMMA相中,这种双连续结构及选择性分散的设计有利于提升材料的导热性能和耐热性能。导热性能测试结果表明,当BN的质量分数为40%时,原位反应加工法制备的BN/PMMA/HDPE导热复合材料的导热系数达到了0.92W/(m·K),相对于纯HDPE提升了283%,相对于简单熔融共混法制备的BN/PMMA/HDPE导热复合材料提升了接近20%。同时,动态力学热分析表明,在温度为40℃时,BN的质量分数为30%时,原位反应加工法制备的BN/PMMA/HDPE导热复合材料的储能模量比简单熔融共混法制备的BN/PMMA/HDPE导热复合材料的储能模量提升了46%,并且差示扫描量热分析及维卡软化点测试表明,其玻璃化转变温度、结晶温度和维卡软化点都有提升。其研究为制备高导热耐热复合材料提供了一种新的方法。     

不同粒径氮化硼对聚丙烯复合材料性能的影响

以聚丙烯(PP)为基体、不同粒径氮化硼(BN)为填充物,采用熔融共混的方法制备聚丙烯/氮化硼(PP/BN)复合材料。通过耐冲击性能、弯曲性能、拉伸性能分析和热分析,研究BN粒径对PP/BN复合材料性能的影响。结果表明：不同粒径BN均可提高复合材料的冲击强度,试验所用填充PP的两种粒径BN,在填充量为5%时均能让复合材料的冲击强度达到约3.65 kJ/m²,比纯PP基体的冲击强度增加了38.8%;与20μm粒径的BN相比,填充5μm粒径的BN可显著提高复合材料的抗弯折能力;填充两种粒径的BN,均能降低复合材料的拉伸强度和断裂伸长率,且在所研究范围内,复合材料的拉伸强度和断裂伸长率与BN粒径关系不大;复合材料的熔体流动速率随两种粒径BN填充量的增大而表现出先增大后逐渐减小的趋势;填充两种粒径BN,均能提高复合材料的结晶温度,降低复合材料的结晶度,但熔融温度变化不大。     

BN纤维补强ZrO_2材料的显微结构

研究了 BN 纤维补强 ZrO_2 材料中显微结构及界面特性,BN 纤维与 ZrO_2基体之间有一扩散区,经烧结后复合材料中 BN 以多晶形式存在。在 BN 纤维内扩散入较多 Y_2O_3 和 SiO_2,这些组分在纤维内形成玻璃相。聚集在 ZrO_2之间的 BN 形成细长结晶体,该晶体内有较多刃位错和反相畴区域。与 BN 相邻的 ZrO_2仍为四方相。     

CVD BN界面层对Si3N4/SiBN复合材料弯曲性能的影响

连续Si3 N4纤维以其优异的热稳定性、高温力学性能和介电性能,被认为是耐高温陶瓷基透波复合材料的候选材料之一.采用连续Si3 N4纤维为增强体,以BCl3+NH3+H2+Ar反应体系,利用化学气相沉积工艺在Si3 N4纤维表面制备了BN界面层,并以聚硅硼氮烷为陶瓷先驱体,通过先驱体浸渍裂解工艺制备了Si3 N4/SiBN复合材料.研究了CVD BN界面层的合成及其对Si3 N4/SiBN复合材料弯曲性能的影响.结果表明:在Si3 N4纤维表面获得了均匀致密的BN界面层,该界面层有效改善了复合材料中纤维/基体的界面结合力,复合材料显示出典型的韧性断裂特征.当界面层的厚度为200 nm时,Si3 N4/SiBN的弯曲强度和断裂韧性分别为182.3 MPa和17.3 MPa·m1/2,比无涂层的复合材料分别提高了59.6％和94.4％.     

脆性纤维分散混合技术现状研究

多个角度对脆性纤维分散混合技术的现状进行了综述。结合脆性纤维的特性、分散机理及脆性纤维在不同材料领域的应用,对功能助剂分散方法和物理分散方法分别进行了归纳,说明了每一种分散混合方法的优点及局限性。脆性纤维分散混合的均匀程度取决于混合的介质、混合物的黏度、纤维的加入量及纤维长度等因素。脆性纤维在高固含量及超高固含量的物料体系中的分散,仍然是目前及未来大力发展短碳纤维复合材料急需解决的一个重要课题。采用物理分散和化学分散并用是解决这一问题的有效途径。     

Fabrication and mechanical properties of oriented SiC short-fiber-reinforced SiC composite by tape casting

SiC fiber-reinforced SiC composites with nearly unidirectionally and randomly aligned SiC short fiber were prepared by tape-casting and hot-pressing (HP). Volume fractions of fibers were 10 and 20 vol.%. Three-point bending test was carried out at room temperature. The SiC short-fiber-reinforced SiC composites showed completely brittle fracture for any fiber volume fraction and orientation. The maximum strength increased with increasing sintering temperature regardless of orientation of short fiber. In the unidirectionally and randomly aligned composites sintered at 1700 °C containing 20 vol.% fiber, the maximum bending strength was about 390 and 280 MPa, respectively.     

Fabrication of toughened Cf/SiC whisker composites and their mechanical properties

In this paper, dense short carbon fiber reinforced silicon carbide matrix composites had been fabricated by hot-pressed (HP) sintering using Al₂O₃ and La₂O₃ as sintering additives. The results showed that the combination of Al₂O₃ and La₂O₃ system was effective to promote densification of short cut carbon fiber reinforced silicon carbide composites (Cf/SiC). The whisker structure of silicon carbide was formed during the annealed treatment at 2023 K for 1 h. However, it was noted that this structure was not observed in the as-received HP material. The mechanism of forming whisker structure was not clear, but this kind of whisker structure was helpful to improve mechanical properties. The combination of grain bridging, crack deflection and whisker debonding would improve the fracture toughness of the Cf/SiC composites.     

Comparative study of mechanical and wear behavior of Cu/WS_2 composites fabricated by spark plasma sintering and hot pressing

The mechanical and wear behavior of copper-tungsten disulfide(Cu/WS_2) composites fabricated by spark plasma sintering(SPS) and hot pressing(HP) was investigated, comparatively. Results indicated that the addition of lubricant WS_2 substantially reduced wear rate of the Cu matrix composites fabricated by SPS,and the optimum content of WS_2 is 20 wt% with regard to the wear behavior. However, it affected a little to the wear rate while dramatically decreased the friction coefficient of the composite fabricated by HP.This difference in friction behavior of the self-lubricating composites fabricated by the two techniques was closely related to their different mechanical properties. Severe interfacial reaction occurred during spark plasma sintering, leading to brittle phase formation at interface.     

Microstructures and mechanical behaviors of CVI-based C/C composites containing h-BN powdered additives

Hexagonal boron nitride(h-BN) powders were introduced into carbon fiber preform by powder addition and subsequent combined with chemical vapor infiltration(CVI) for densification to prepare carbon fiber reinforced/carbon and boron nitride dual matrix composites(C/C-BN). Microstructures and mechanical properties of C/C composites with three different volume contents of h-BN powders were investigated in comparison to pure C/C composites. Results indicated that the introduction of h-BN powders into C/C composites significantly reduced the size of Py C and the anisotropy of thermal contraction in matrix,leading to a gradual disappearance of ring defects as the h-BN content increased. In addition, an enhanced interfacial bonding between fiber and matrix obtained due to higher-textured Py C and rougher fiber surface. Thereby, the flexural strengths and modulus of as-prepared composites decreased firstly and then increased, while the impact toughness presented a decreasing tendency as the content of BN powders increased. Furthermore, with the increasing of h-BN content, anisotropies of compressive properties were weakened, and the compressive strength of C/C-BN composites were always higher than that of pure C/C composit. However, when C/C composites modified by 13.5 vol% content of h-BN, excessive loose BN aggregates appeared in C/C-BN composites, leading to a relatively slight reduction of compressive strength.     

Evaluating the effect of oxygen content in BN interfacial coatings on the stability of SiC/BN/SiC composites

Boron nitride was studied as a fiber–matrix interface coating for Nicalon™/SiC composites. The effect of initial O-impurity content within the as-processed BN coatings on the long-term interface stability was investigated at elevated temperatures in flowing oxygen. Two types of Nicalon™/SiC composites were used for this study; one composite had a BN coating with <2% oxygen (low-O BN) and another composite had BN with an oxygen concentration >11% (high-O BN) in the as-processed state. The high-O BN is actually most representative of BN coatings available commercially. The BN coatings in both the high-O and low-O BN containing composites were structurally similar. The samples used here were thinned to <200 μm before oxidation and the final preparation for electron microscopy examination of the interface region was done after the reactions were completed. Thin samples were used to simulate maximum corrosion effects that would occur at the surface of an actual part during service. Ech sample was exposed to flowing oxygen at temperatures as high as 950°C for times up to 400 h. After each oxidation experiment, the BN coatings were examined by TEM to quantify the extent of any reaction which occurred at either the fiber/BN and BN/SiC matrix interfaces. At 950°C for 100 h, there were no interface microstructural changes observed in the low-O BN but there was extensive silica formation at the fiber/BN interfaces in the high-O BN. After 400 h at 950°C, large voids formed at the fiber/BN interface in the high-O BN sample only. Oxygen present within the initial BN coating contributed significantly to the degradation of the interfacial properties of the composite. Several techniques, including transmission electron microscopy (TEM), Auger electron spectroscopy (AES), energy-dispersive spectrometry (EDS), and electron energy-loss spectroscopy (EELS) were used to characterize changes in structure and chemistry of the fiber–matrix interface region and to elucidate and quantify composite degradation mechanisms.     

BN/Al_2O_3/碳纤维填充MVQ导热复合材料的制备

以甲基乙烯基硅橡胶(MVQ)为基体,片层氮化硼(BN)、球形Al_2O_3、碳纤维为填料,通过共混的方法制备了导热硅橡胶复合材料。利用热重分析仪(TGA),扫描电子显微镜(SEM),电子拉力试验机以及导热系数仪对复合材料的结构和性能进行了表征。结果表明:复合材料的热导率、热稳定性、力学性能、交联密度随着填料量的增加而增加。填料量达50vol.%时,尤以片层BN对热导率增加的效果突出,热导率从0.168增至1.8W/(m·K);碳纤维对复合材料的力学性能贡献最大,拉伸强度从0.48增加到2.98MPa;片层BN在橡胶基体中以面-面接触的方式均匀分散,更易于形成有效的导热网链。     

Thermal conductivity of boron nitride reinforced polyethylene composites

The thermal conductivity of boron nitride (BN) particulates reinforced high density polyethylene (HDPE) composites was investigated under a special dispersion state of BN particles in HDPE, i.e., BN particles surrounding HDPE particles. The effects of BN content, particle size of HDPE and temperature on the thermal conductivity of the composites were discussed. The results indicate that the special dispersion of BN in matrix provides the composites with high thermal conductivity; moreover, the thermal conductivity of composites is higher for the larger size HDPE than for the smaller size one. The thermal conductivity increases with increasing filler content, and significantly deviates the predictions from the theoretic models. It is found also that the combined use of BN particles and alumina short fiber obtains higher thermal conductivity of composites compared to the BN particles used alone.     

SiC含量对SiCw/Cu复合材料组织与力学性能的影响

为了研究SiCw/Cu复合材料的制备工艺、形成机理,进一步研究SiC含量对材料的组织结构、力学性能的影响.采用热压法和热等静压法制备了不同SiCw含量的SiCw/Cu复合材料,并对复合材料的致密度、显微组织和物相组成、维氏硬度、拉伸和压缩性能进行了研究,对拉伸断口进行分析.结果表明:SiCw有效阻碍Cu基体晶粒的长大,随着SiCw含量的增加,热压制备的SiCw/Cu复合材料的致密度、断后伸长率、拉伸屈服强度下降,而气孔率、维氏硬度与压缩屈服强度显著增加,抗拉强度先增加后降低.热压制备得到的1wt%SiCw/Cu复合材料,具有相对最优的综合力学性能:抗拉强度为156.9 MPa,拉伸屈服强度为112.5 MPa.采用热等静压法制备的3wt%SiCw/Cu复合材料,各方面性能都要优于相同组分的热压材料,抗拉强度达到175.6 Mpa,拉伸屈服强度达到123.2 MPa,维氏硬度达到101.8 HV.复合材料的强度是SiCw的增强作用与孔隙的弱化作用共同作用的结果,SiCw/Cu复合材料的断裂行为既表现出一定的韧性特征,又表现出一定的脆性特征.