Si3N4-SiC-TiN陶瓷燃烧合成工艺研究

以TiSi2和SiC为原料,利用SHS方法合成Si3N4-SiC-TiN复相陶瓷.在不同稀释剂含量及氮气压力下进行燃烧合成,计算了毛坯转化率和产物相对密度,并对产物进行了XRD分析.结果表明,氮气压力增高有利于提高转化率及产物相对密度.反应物转化率随稀释剂含量增加而增大.孔隙率为53%(体积分数)毛坯,稀释剂SiC含量为35%(质量分数)压坯相对密度达到最大值,且当稀释剂含量高于35%(质量分数)时,SiC发生氮化反应,生成Si3N4和C.     

氧化铝基复合陶瓷物理和力学性能的研究

采用热压烧结致密化工艺,在1 550,1 600,1 650℃3个不同的烧结温度下,烧结制备了Si3N4含量从0.25w%到6w%的Al2O3/Si3N4纳米复相陶瓷.对所制备的试样进行了密度、硬度、断裂韧性的测试.实验结果表明,所有试样达到了较高的致密度,且致密度随烧结温度的升高而增加.硬度在Si3N4含量为0.75w%和3w%时达到峰值.韧性在Si3N4含量3 w%达到峰值.材料的性能较纯Al2O3陶瓷有较大幅度提高.     

以Al-B-C为烧结助剂的SiC陶瓷热压烧结工艺

以SiC超细粉末为原料,Al粉、B粉和碳黑为烧结助剂,采用热压烧结工艺制备了SiC陶瓷,重点研究了烧结助剂含量(4～13 wt％)对SiC陶瓷物相组成、致密度、断面结构及力学性能的影响.除SiC主晶相外,X射线衍射图还显示了Al8B4C7相的存在;当烧结助剂的含量从4 wt％增至13 wt％时,扫描电镜照片显示陶瓷断面形貌从疏松结构变成致密结构,存在晶粒拔出现象;陶瓷力学性能随着烧结助剂含量的增加先升高后降低.当烧结助剂含量为10 wt％时,SiC陶瓷的力学性能达到最高,抗弯强度为518.1 MPa,断裂韧性为4.98 MPa·m1/2.Al、B和C烧结助剂在1850℃烧结温度下形成的Al8B4C7液相促进晶粒间的重排和传质,并填充晶粒间的气孔,提高了陶瓷致密度.     

SPS原位反应制备TiSi2基复合材料的微观结构和性能研究

以工业用硅粉、碳粉和碳化钛粉为原料,利用放电等离子烧结技术原位反应制备了TiSi2-SiC两相复合材料和TiSi2-SiC-Ti3SiC2三相复合材料.利用XRD、FESEM和TEM对复合材料的相组成和微观结构进行了研究.结果表明,基体相TiSi2的晶粒尺寸在1um以上,反应生成的SiC颗粒尺度在200～300nm,且均匀弥散分布在TiSi2基体中.TiSi2-SiC材料的硬度、断裂韧性和抗弯强度随着SiC含量的增加都有一定程度的提高.Ti3SiC2三元相的引入大大提高了TiSi2-SiC-Ti3SiC2复合材料的力学性能. SiC和Ti2SiC2的引入对TiSi2-SiC复合材料在高温下的电导率和热导率影响较小.     

利用传统电炉低温烧结致密Si3N4陶瓷

Si3N4陶瓷具有高硬度、高耐磨以及高抗弯强度等优异特性,常常被应用于冶金、化工以及航空航天等现代化领域.Si3 N4的强共价键使其难以致密化,因此热压烧结和气压烧结是目前制备致密Si3 N4陶瓷最常见的方法.然而极高的烧结温度以及较大的N2压力需求等极其苛刻的制备条件限制了致密Si3 N4陶瓷的基础探索研究和工业化生产应用.因此,本工作提出设计以传统空气电炉作为烧结装置,通过埋碳低温制备致密Si3 N4陶瓷,研究该工艺条件下实验用坩埚、填埋Si3 N4粉体以及烧结试样的物相变化和微观结构,结果表明:(1)Si3 N4的分解使得坩埚表层生成不规则的SiC纤维堆积,较低的氧分压使所埋Si3 N4粉体经烧结后仍存在较多Si3 N4和少量Si2 N2 O;(2)烧结后的试样仅表面存在少量Si2 N2 O,而试样内部并未出现Si2 N2 O相;(3)1650℃低温烧结后试样致密度达到98％以上,显微组织均匀,且具有良好的性能.     

SiC含量对机械合金化-热压制备B4C-SiC复合陶瓷的影响

以B₄C、SiC粗粉为原料, 采用机械合金化辅助热压烧结工艺, 在不添加任何助烧剂的情况下于1950℃制备出致密的B₄C-SiC复合陶瓷。通过对烧结样品进行相对密度、维氏硬度、抗弯强度和断裂韧性测试, 研究SiC含量对复合陶瓷力学性能的影响; 结合XRD、SEM和TEM对样品进行组分和微观结构分析, 研究其微观结构与力学性能之间的关系。结果表明: 复合陶瓷的相对密度和断裂韧性随SiC含量的增加而增大, 当SiC含量为50wt%时获得最大值为96.1%和4.6 MPa•m^1/2; 复合陶瓷的硬度和抗弯强度随SiC含量的增加呈先增大后减小的趋势, 在SiC含量为20wt%时获得最大值25.5 GPa和480 MPa。SiC相均匀分布在B₄C基体中使得复合陶瓷具有较高的强度; B₄C与SiC之间好的界面相容性以及SiC的高断裂韧性是该B₄C基复合陶瓷韧性得到显著提高的原因。     

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。     

反烧结Si3N4复合陶热力学分析

以TiSi2-SiC—N2体系反应制备Si3N4-TiN—SiC复相陶瓷材料进行理论分析和理论计算,通过对TiSi2-SiC—N2体系的DSC试验和XRD检测来研究TiSi2与N2的反应温度区间。结果表明：TiSi2和N2在2000K以下在热力学上可以发生反应,而TiSi2不分解;DSC结果发现在1105℃以上TiSi2与N2开始反应。     

无压烧结Ti3SiC2/铝基复合材料组织与性能

MAX相具有独特的层状晶体结构,不但具备常用铝基复合材料外加陶瓷颗粒的性能特征,同时具有可与石墨媲美的摩擦性能.本文以Al粉、Si粉和典型MAX相Ti_3SiC_2为原料,采用冷压成型-无压烧结方法制备了Ti_3SiC_2/Al-Si复合材料,并通过金相显微镜、X射线衍射仪(XRD)、扫描电镜(SEM)、能谱仪(EDS)等分析手段,研究了烧结温度、Si元素含量对复合材料组织与性能的影响.研究表明:随着烧结温度从500℃提高到700℃,复合材料致密度先上升后下降,摩擦系数先降低后上升,硬度逐渐增大至最大值并基本保持稳定;随着Si质量分数从0增加到20.7%,复合材料的致密度逐渐降低,硬度逐渐增大,摩擦系数先降低后增大,晶粒尺寸随之下降,12.5%Si晶粒最为细小;烧结温度为650℃,Si元素质量分数为12.5%的铝基复合材料具有最低的摩擦系数0.18,相应的硬度为62 HV,致密度为92.12%.XRD物相和扫描电镜组织分析表明,复合材料的主要相组成为Al、Ti_3SiC_2,及由界面反应产生的Al_4C_3和Al的氧化产物Al_2O_3.     

ZnAl_2O_4和La_2O_3对Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷介电性能的影响

通过传统的固相反应合成掺杂ZnAl_2O_4和La~(3+)(来自La_2O_3)的Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷粉体,干压成型后在空气气氛下常压烧结制备ZnAl_2O_4和La~(3+)掺杂Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷样品。分别研究了La~(3+)和ZnAl_2O_4的掺杂量对复合陶瓷样品的微观形貌、相组成和介电性能的影响。结果表明:ZnAl_2O_4具有细化晶粒的作用;Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷样品的致密度随La~(3+)和ZnAl_2O_4含量的增加而增加;介电常数和谐振频率温度系数随ZnAl_2O_4含量的增加而减小,随La_2O_3添加量变化不大;品质因数值随ZnAl_2O_4含量的增加先增加后减小。制备出的ZnAl_2O_4和La~(3+)掺杂Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷致密度达到94%以上,介电常数在40~50之间,谐振频率温度系数小于40×10~(-6)℃~(-1),品质因数大于38 000GHz,可以用于通信技术领域。     

Effect of ball-milling time on mechanical properties of carbon nanotubes reinforced aluminum matrix composites

Carbon nanotubes reinforced pure Al (CNT/Al) composites were produced by ball-milling and powder metallurgy. Microstructure and its evolution of the mixture powders and the fabricated composites were examined and the mechanical properties of the composites were tested. It was indicated that the CNTs were gradually dispersed into the Al matrix as ball-milling time increased and achieved a uniform dispersion after 6 h ball-milling. Further increasing the ball-milling time to 8–12 h resulted in serious damage to the CNTs. The tensile tests showed that as the ball-milling time increased, the tensile and yield strengths of the composites increased, while the elongation increased first and then decreased. The strengthening of CNTs increased significantly as the ball-milling time increased to 6 h, and then decreased when further increasing the ball-milling time. The yield strength of the composite with 6 h ball-milling increased by 42.3% compared with the matrix.     

New procedure for preparation of highly stable and well separated carbon nanotubes in an aqueous modified polyacrylonitrile

Carbon nanotubes (CNTs) due to their nonreactive surface can not effectively disperse in polymeric matrix. Efficient exploitation of CNTs properties to improve material performance is generally related to the degree of dispersion, saturation by the matrix and interfacial adhesion. In order to obtain a suitable dispersion, the CNTs usually need treatment before they can be utilized. In this work, an easy procedure for preparation a stable dispersion of well separated and individual CNTs in an aqueous polymeric solution by using of Gum Arabic (GA) and modified polymer has been described. The applied polymer was a modified water soluble acrylonitrile polymer. The modification was carried out through functionalizing polyacrylonitrile by 2‐aminoethanol. Individual dispersion of the CNTs in the aqueous GA solution after two month can be observed. By incorporating the modified polyacrylonitrile to the solution, the stability of the individual CNTs dispersion several times was increased in such a way that after six month, the CNTs were still kept at their individual positions. According to the suggested mechanism of dispersion, hydrogen bonds between GA/CNTs and the modified polyacrylonitrile chains can be formed that increasing the dispersion ability. The effects of salts and temperature on dispersion ability of GA were also studied.     

正应力支配下混合顺序对PA6/HDPE/CNTs体系结构及性能的影响EI北大核心CSCD

利用自行研制的叶片式混炼装置,实现了正应力支配下聚合物复合体系的熔融共混。实验研究了混合顺序以及混合时间对高密度聚乙烯(HDPE)/尼龙6(PA6)/碳纳米管(CNTs)共混物的微观结构、流变特性、热性能及宏观力学性能的影响。结果表明:正应力支配作用能在短混合时间内实现PA6粒子和CNTs的均匀分散,分散效率高;相比于将HDPE,PA6,CNTs三者同时共混或者是先将PA6与CNTs混炼制成母料,再与HDPE共混这两种混合顺序,先将HDPE与CNTs混炼制成母料,再与PA6共混制得的共混物中分散相PA6粒径最小,分散更均匀,共混物的热性能以及力学性能更好。     

Toughening modification of polycarbonate/poly(butylene terephthalate) blends achieved by simultaneous addition of elastomer particles and carbon nanotubes

Small quantities of maleic anhydride grafted styrene-ethylene-butylene-styrene (SEBS-g-MAH) copolymer and carbon nanotubes (CNTs) were introduced into polycarbonate (PC)/poly(butylene terephthalate) (PBT) blends. The results demonstrated that simultaneously adding SEBS-g-MAH and CNTs greatly enhanced the fracture toughness of the samples and the impact strength increased with increasing CNT content. The morphologies, the dispersion of CNTs, the relaxation behaviors and the crystallization behaviors of samples were systematically investigated. SEBS-g-MAH formed the dispersed particles in the system. The particle diameter was decreased in the blend composites. CNTs exhibited homogeneous dispersion in the blend composites and they also formed a percolated network structure at relatively high content. The transesterification between PC and PBT components was suppressed by SEBS-g-MAH, and the crystallization ability of the PBT component was greatly enhanced. The toughening mechanisms were mainly related to the suppressed transesterification, the decreased elastomer particle size, and the formation of a CNT network structure.     

球磨对碳纳米管增强泡沫铝基复合材料压缩与吸能性能的影响

因碳纳米管（CNTs）具有优异的性能,被认为是金属基复合材料理想的增强体,因此如何制备得到CNTs增强体均匀分散的金属基复合材料一直是本领域的研究热点。本文通过原位化学气相沉积（CVD）、短时球磨和填加造孔剂的工艺成功制备了CNTs增强的泡沫铝基复合材料,着重研究了球磨过程对复合泡沫铝的微观形貌、压缩性能和吸能性能的影响规律。结果表明,随着球磨时间的延长,CNTs的分散性提高并逐步嵌入铝基体中,使复合泡沫铝的组织均匀性得到改善。相对于未球磨的含CNTs 3.0wt%的复合泡沫材料,当球磨时间增加至90 min时,复合泡沫铝的孔壁硬度、屈服强度和吸能能力分别提高了67%、126%和343%。     

Preparation and properties of the powder SBR composites filled with CNTs by spray drying process

Carbon nanotubes (CNTs) filled powder styrene-butadiene rubber (SBR) composites were prepared by spray drying of the suspension of CNTs in SBR latex. The powder was spherical like and uniform with an average diameter of less than 10 μm. The dispersion of CNTs in the rubber matrix was improved remarkably compared with that in the rubber composites obtained by the conventional mechanical mixing method. Further study about the effect of CNTs on the prepared SBR composites was performed by analyzing the vulcanization process of the SBR powder, thermal and mechanical properties of the vulcanized SBR composites. Differential scanning calorimeter (DSC) analysis indicated that the glass transition temperatures of SBR composites increased with the increasing ratio of CNTs. The vulcanization process showed that CNTs could decelerate the vulcanization of the SBR composites. Dynamic mechanical analysis indicated that the storage modulus of the composites was improved with the CNTs additions, especially when the CNTs addition exceeded 30 phr. Compared with pure SBR composites, the hardness, tensile and tear strengths of the composites filled with 60 phr CNTs enhanced 73.9%, 327.7% and 191.1%, respectively, which should be ascribed to the excellent mechanical properties of CNTs and uniform dispersion of CNTs in the rubber matrix.     

具有负温度系数效应的导电硬质聚氨酯泡沫

采用高能球磨分散方法制备了稳定的聚合物多元醇/碳纳米管分散液,并通过原位聚合制备了导电聚氨酯（PU）/碳纳米管（CNTs）硬质泡沫复合材料。采用扫描电镜（SEM）表征了泡沫复合材料的结构,研究了CNTs含量对泡沫材料导电性的影响以及泡沫材料的负温度系数（NTC）效应,通过压缩测试考察了泡沫材料的力学性能。结果表明,CN...     

Mechanical characterization of copper coated carbon nanotubes reinforced aluminum matrix composites

In this investigation, carbon nanotube (CNT) reinforced aluminum composites were prepared by the molecular-level mixing process using copper coated CNTs. The mixing of CNTs was accomplished by ultrasonic mixing and ball milling. Electroless Cu-coated CNTs were used to enhance the interfacial bonding between CNTs and aluminum. Scanning electron microscope analysis revealed the homogenous dispersion of Cu-coated CNTs in the composite samples compared with the uncoated CNTs. The samples were pressureless sintered under vacuum followed by hot rolling to promote the uniform microstructure and dispersion of CNTs. In 1.0 wt.% uncoated and Cu-coated CNT/Al composites, compared to pure Al, the microhardness increased by 44% and 103%, respectively. As compared to the pure Al, for 1.0 wt.% uncoated CNT/Al composite, increase in yield strength and ultimate tensile strength was estimated about 58% and 62%, respectively. However, in case of 1.0 wt.% Cu-coated CNT/Al composite, yield strength and ultimate tensile strength were increased significantly about 121% and 107%, respectively.     

KOH活化处理碳纳米管对其负载非晶态NiP催化性能的影响

经KOH活化处理和未经活化处理的碳纳米管分别用于负载非晶态NiP合金.以苯加氢为探针反应,研究了KOH活化处理温度和时间对碳纳米管的性质及其负载非晶态NiP催化剂活性的影响.研究结果表明:碳纳米管经KOH处理可以提高其负载非晶态NiP催化剂的催化活性,催化剂活性随活化温度升高和活化时间延长而增加.由于KOH处理改变了碳纳米管的微观结构,增加了其比表面积,所以非晶态NiP在碳纳米管上更易沉积分散,其负载的非晶态NiP合金催化剂的催化活性较高.     

Creep behavior of polyurethane nanocomposites with carbon nanotubes

The polyurethane (PU) nanocomposites containing carbon nanotubes (CNTs) were prepared through in situ polymerization for the creep study. The results show that the presence of CNTs leads to a significant improvement of creep resistance of PU. However, this creep resistance does not increase monotonously with increase of CNT contents because it is highly dependent on the dispersion of CNTs. Several theoretical models were then used to establish the relations between CNT dispersion and final creep and creep–recovery behaviors of nanocomposites. The as-obtained viscoelastic and viscoplastic parameters of PU matrix and structural parameters of CNTs further confirmed the retardation effect by CNTs during creep of the nanocomposite systems. Besides, the time–temperature superposition (TTS) principle was also employed in this work to make a further evaluation on the creep of PU/CNT nanocomposites with long-term time scale.