Pressureless Sintering of Carbon Nanofibre/SiC Composites and Their Properties

To enhance the fracture toughness of silicon carbide (SiC) ceramics and prevent the generation of cracks and chippings in the SiC ceramics during machining process, carbon nanofibres (CNFs) were compounded with SiC. The densification and microstructure development of the CNFs/SiC composites pressureless sintered in Ar atmosphere were investigated. The fracture toughness of SiC ceramics was enhanced by the addition of 1–3 wt% CNFs, which resulted from the pullout and/or bridging effect of CNFs bonded much more closely with SiC. The addition of 3 wt% CNFs prevented the chippings from generating in the composite during precision machining process.     

无压烧结制备Al2O3/SiC纳米复合陶瓷

用沉淀法包裹微米级SiC颗粒，通过常压、埋烧制备Al2O3／SiC纳米复合陶瓷。通过XRD、TG和SEM等分析了煅烧和烧结过程中相组成的变化、烧成收缩和显微结构。结果表明：利用SiC粉埋烧及碳粉制造还原气氛，含8wt％SiC(平均粒径为5mm)的复合粉末经800℃煅烧、成型，试样于1550℃，2h烧结，可制备Al2O3／SiC纳米复合陶瓷，其相对体积密度达95．2％，在烧结过程中由SiC氧化形成的无定形SiO2及与基质氧化铝反应形成的莫来石前躯体可大大促进烧结。     

无压烧结碳化硅复合材料的制备与性能研究

以部分碳化钛为增强相投入到碳化硅基体材料中,并投入微量炭黑和碳化硼为烧结活化剂,利用无压固相烧结技术制造了碳化硅基陶瓷复合材料。评测了其力学性能,凭借扫描电镜(SEM)观测了试样的断口形貌与表观形貌,并探讨了其氧化行为。结果表明:在碳化硅中投加部分碳化钛,对复合材料的力学性能有非常大地益处,于9 wt%时达到顶峰,弯曲强度497 MPa,相对密度98.9%,断裂韧性4.79 MPa·m^1/2。复合材料的显微组织构造紧致密实,TiC颗粒在SiC材料中的离散作用而激发的钉扎效果和裂纹偏移转向为其主要的增韧原理。在设定的氧化条件下(1200℃保温2 h),试样表面形成了一层较为致密并可以弱化氧化进程的氧化膜层。     

碳纤维增强聚丙烯复合材料的制备及性能

采用硝酸液相氧化法改性短切碳纤维(NCF),用以制备聚丙烯(PP)复合材料。以纤维含量和纤维种类为变量,通过万能力学试验机、熔体流动速率试验机、差示扫描量热、X射线衍射、扫描电子显微镜等研究它们对材料力学性能、流动性能、熔融温度以及结晶性能的影响。实验结果表明,纤维的含量影响纤维在基体中的分布,进而显著影响材料的性能,且含量在10%至20%区内时具有较好的增强效果;NCF与PP的界面具有更强的粘附力,这提升了复合材料的力学强度,降低了材料的断裂伸长率,降低了材料的熔融流动速率,提升了材料的结晶温度与结晶度,略微降低了材料的熔融温度;纤维含量与纤维种类均对材料的结晶晶型无明显影响。     

凝胶-注模成型技术制备碳纤维/HA复合材料的研究

本文研究了pH值、分散剂、有机单体和碳纤维含量对碳纤维/HA陶瓷浆料粘度的影响,观察了复相陶瓷浆料的凝胶固化过程,研究了烧结温度和碳纤维含量对复合材料烧结密度、抗弯强度和断裂韧性的影响.研究结果表明:当pH =9、有机单体含量为10wt％、分散剂含量为5wt％、固相含量为50wt％的碳纤维/HA陶瓷浆料具有良好的分散性.随引发剂、催化剂含量的增加,复相陶瓷浆料的凝胶固化时间缩短.复合材料的烧结密度、抗弯强度和断裂韧性均随烧结温度的升高而升高.复合材料的抗弯强度和断裂韧性均随着碳纤维含量的增加呈现先增加而后降低趋势.当碳纤维含量为2wt％和2.5wt％时,凝胶注模成型所制备的复合材料的抗弯强度和断裂韧性分别为80.6 MPa和1.87 MPa·m1/2,较干压成型样品提高了24.9％和19.8％.     

Photoluminescence Properties of Nanocrystalline ZnO Ceramics Prepared by Pressureless Sintering and Spark Plasma Sintering

Nanocrystalline ZnO ceramics with grain sizes of ∼100 nm were prepared by pressureless sintering at 800°C for 2 h and spark plasma sintering (SPS) at 550°C for 2 min, respectively. Excellent green emission properties were obtained in the ZnO ceramic prepared by the SPS process and in the pressureless-sintered ZnO ceramic prepared at 1000°C for 2 h, which are attributed to the vacuum ambience of the SPS process and the sublimeness of the interstitial Zn at >900°C in air, respectively.     

炭纤维增强中间相炭微球制备炭/炭复合材料

以中间相炭微球为炭源,沥青基磨切炭纤维为同质增强相,采用冷模压成型和气氛低温烧结制备出高性能炭/炭复合材料。研究了炭纤维表面处理对界面结合强度的作用机制和改善效果,分析了不同球磨时间下原始粉料的微观形貌。结果表明：炭纤维的添加有利于坯体各向均匀收缩,降低了总体积收缩率,使得复合材料密度下降;同时大幅度提升了复合材料的机械强度;添加10%（质量分数）炭纤维时弯曲强度最高,达到123.5MPa。     

Properties of ZrB2–SiC Ceramics by Pressureless Sintering

Pressureless sintering was used to densify ZrB₂–SiC ultra-high temperature ceramics. The physical, mechanical, thermal, electrical, and high temperature properties were investigated. This comprehensive set of properties was measured for ZrB₂ containing 20 vol% SiC in which B₄C and C were used as the sintering aids. The three-point flexural strength was 361±44 MPa and the elastic modulus was 374±25 GPa. The Vickers hardness and fracture toughness were 14.7±0.2 GPa and 4.0±0.5 MPa·m^1/2 respectively. Scanning electron microscopy studies of the microstructure of ZrB₂–SiC showed that SiC particles were distributed homogenously in the ZrB₂ matrix with little residual porosity.     

氮化硅陶瓷的无压烧结工艺优化及性能研究

以α-Si3 N4为原料,Y2 O3和MgO为复合烧结助剂,通过无压烧结制备出氮化硅陶瓷。为了优化实验配方和工艺参数,采用正交实验研究了成型压力、保压时间、保温时间、烧结温度、烧结助剂含量以及配比对氮化硅陶瓷气孔率和抗弯强度的影响规律。结果表明,影响氮化硅陶瓷气孔率的主要因素是烧结助剂含量和配比,而影响其抗弯强度的主要因素是烧结助剂配比和烧结温度。经分析得出,最佳工艺参数为成型压力16 MPa,保压时间120 s,保温时间2 h,烧结温度1750℃,烧结助剂含量12wt％,烧结助剂配比1∶1;经最佳工艺烧结后的氮化硅陶瓷,相对密度为94．53％,气孔率为1．09％,抗弯强度为410．73 MPa。     

SiC Matrix Structure–Function Composites Prepared by Pressureless Sintering and Their Microwave Attenuation Property in the X Band

For developing excellent microwave attenuation materials in a wide band, two series of SiC‐C (graphite) composites with different C additions were fabricated by pressureless sintering, using α‐SiC and β‐SiC green powder, respectively. β‐SBC composites were more suitable for microwave attenuation materials than α‐SBC composites. β‐SiC composites with 3 wt% C additions exhibited the best microwave absorption: The most significant microwave attenuation was ?40.5 dB, and most other attenuations were above ?30 dB in the whole X band. The composites were prepared with cost‐effective and easily controllable manufacturing process and can be considered as structure–function materials for particular applications.     

Pressureless Sintering of High-Density ZrB2–SiC Ceramic Composites

Ultra-high-temperature ceramic composites of ZrB₂ 20 wt%SiC were pressureless sintered under an argon atmosphere. The starting ZrB₂ powder was synthesized via the sol–gel method with a small crystallite size and a large specific surface area. Dry-pressed compacts using 4 wt% Mo as a sintering aid can be pressureless sintered to ∼97.7% theoretical density at 2250°C for 2 h. Vickers hardness and fracture toughness of the sintered ceramic composites were 14.82±0.25 GPa and 5.39±0.13 MPa·m^1/2, respectively. In addition to the good sinterability of the ZrB₂ powders, X-ray diffraction and scanning electron microscopy results showed that Mo formed a solid solution with ZrB₂, which was believed to be beneficial for the densification process.     

无压烧结硼化锆基ZrB2-SiC复相陶瓷的结构与性能

以钇铝石榴石-YAG为烧结助剂,通过无压烧结制备了ZrB2-SiC复相陶瓷。研究了烧结助剂含量对烧结材料力学性能和显微结构的影响,材料的显微结构由扫描电镜SEM及其能谱分析EDS测定。研究结果表明,烧结助剂(YAG)和原料中的杂质形成玻璃相填充在晶界上,显著促进了硼化锆基ZrB2-SiC复相陶瓷的致密化。     

羟丙基甲基纤维素对碳纤维增强环氧树脂力学性能的影响

为了提高短切碳纤维(CF)的分散性从而提高复合材料的力学性能,通过采用羟丙基甲基纤维素(HPMC)为分散剂的方法,研究了CF增强环氧树脂复合材料(EP/CF)的力学性能。利用扫描电子显微镜(SEM)研究了HPMC作为分散剂对CF在环氧树脂中分散的影响;并利用傅里叶红外光谱法(FTIR)和差示扫描量热法(DSC)分析了HPMC与基体的相互作用;采用动态热机械分析(DMA)和万能试验机表征复合材料的力学性能,通过SEM考察了材料断裂面的显微结构和断裂形态。研究表明:HPMC能有效分散CF,使得CF与环氧树脂E-51基体之间形成良好界面作用,复合材料的拉伸强度和冲击强度分别提高47.5%和62.7%。     

Pressureless Sintering and Mechanical and Biological Properties of Fluor-hydroxyapatite Composites with Zirconia

Fluor-hydroxyapatite (FHA) fabricated by a reaction between fluorapatite (FA) and hydroxyapatite (HA) was mixed with ZrO₂ to produce FHA–ZrO₂ composites. When the relative amount of FA to HA increased, the decomposition of the composite was decreased gradually because of the formation of thermally stable FHA solid solutions. With such suppression of decomposition, the FHA–ZrO₂ composites retained fully densified bodies. As a result, significant enhancements in mechanical properties, such as hardness, flexural strength, and fracture toughness, were achieved as the relative amount of FA to HA increased. The highest values in strength and toughness were 220 MPa and 2.5 MPa·m^1/2, respectively, with FHA–40 vol% ZrO₂ composites. In vitro proliferation of osteoblast-like cells (MG63) on the composites showed behavior similar to that observed on pure HA and FHA. Alkaline phosphatase (ALP) activity of the growing cells (HOS) on the composites was slightly down-regulated compared with that on pure HA and FHA at prolonged periods.     

固相剪切粉碎制备聚丙烯／碳纤维复合材料及性能研究

应用固相力化学反应器对聚丙烯(PP)和碳纤维(CF)颗粒进行固相剪切粉碎共碾磨制备复合粉体,研究了同相剪切粉碎对PP/CF复合粉体热压成型复合材料的力学性能、导热和导电性能的影响.拉伸断面的扫描电镜形貌表明,随着碾磨次数增加,CF呈微纤状均匀地分布在PP基体中,与PP基体的结合更加紧密,复合材料的缺陷减少,有利于提高复合材料的导热和导电性能.     

湿法混炼芳纶短纤维/丁腈橡胶复合材料的性能研究

用湿法混炼方法制备了芳纶短纤维/丁腈橡胶(NBR)复合材料,研究增稠剂和芳纶短纤维用量对复合材料性能的影响。结果表明:添加聚丙烯酸钠(PNaAA)和聚氧化乙烯(PEO)两种增稠剂有利于提高芳纶短纤维的分散性,添加质量分数为0.007 5 PNaAA的复合材料拉伸性能最好;随着芳纶短纤维用量的增大,复合材料的拉伸性能先提高后降低;芳纶短纤维用量为2份时,复合材料的拉伸性能总体最好,芳纶短纤维补强效果最佳。     

Tailoring Carbon Fiber/Carbon Nanotubes Interface to Optimize Mechanical Properties of Cf‐CNTs/SiC Composites

C_f/SiC composites were fabricated using fiber coatings including CNTs and matrix infiltration using the polymer impregnation and pyrolysis process. Interface between fiber and CNTs (CF/CNTs) was tailored to optimize mechanical properties of hybrid composites. The tailored interphases, such as Pyrocarbon (PyC) and PyC/SiC, protect fibers from degradation during the growth of CNTs successfully. Hybrid composites with well‐tailored CF/CNTs interface displayed significantly increased mechanical strength (352 ± 21 MPa) compared with that (34 ± 3 MPa) of composites reinforced with CNTs, which grown on carbon fibers directly. The interfacial bonding strength of hybrid composites was improved and optimized by tailoring the CF/CNTs interface. Interfacial failure modes were studied, and a firm interface bonding at the joint where CNTs grown was observed.     

纤维类型对C/SiC复合材料性能的影响

利用化学气相浸渗法制备了Cf-C/SiC复合材料,借助SEM、TEM等研究了纤维类型对Cf-C/SiC复合材料力学性能的影响.实验证明T300碳纤维增韧补强效果优于M40碳纤维,利用T300碳纤维制备出弯曲强度为459M,断裂韧性为20.0MPa*m1/2,断裂功为25170J/m2的Cf-C/SiC复合材料.2种碳纤维增韧效果的差异是由纤维的原始强度、热膨胀系数和弹性常数的不同决定的.