碳纤维水泥基复合材料的正、负压敏性及其机理分析

对碳纤维水泥基复合材料的压敏特性进行了实验研究。结果发现, 在含水量不同的情况下, 碳纤维水泥基复合材料分别具有正、负两种压敏特性。含水量较高时, 碳纤维水泥基材料的电阻相对变化率随应力的增大而增大, 随应力的减小而减小, 表现出正压敏性。而含水量较低时, 电阻相对变化率随应力的增大而单调减小,随应力的减小而单调增大, 表现出负压敏性, 进而提出了一种双效应机理, 并对这一物理现象进行了合理解释。     

力敏导电橡胶中的应变和压阻效应及工作原理分析

分析了应变和压阻效应对"负压力-电阻特性"(NPC)的影啊程度,揭示出力敏导电橡胶的工作原理.当填料用量处在渗流区中心时,电阻率的减小在NPC效应中占主导,导电橡胶的工作原理主要为压阻效应.随着填料用量的增多,电阻几何系数的减小在NPC效应中起主导,其工作原理主要为应变效应.在某一特定填料用量范围,力敏导电橡胶的工作原...     

碳纤维水泥基复合材料的阻-温特性

研究了碳纤维水泥基复合材料的阻-温特性。发现当温度低于某一特定值时，电阻率随温度的升高而单调降低(NTC效应)。超过此值时，则表现为电阻率随温度升高而大幅度单调增加(PTC效应)。普通水泥基材料不具有相应的阻-温特性．     

炭黑填充导电橡胶的力敏传感器灵敏系数

以通用有效介质理论为基础, 给出了炭黑填充导电橡胶(炭黑/橡胶)的力敏传感器灵敏系数计算方程。采用该方程并结合应变和压阻效应对"负压力-电阻特性"(NPC)的影响程度, 分析了力敏导电炭黑/橡胶的灵敏系数和工作原理。结果表明: 炭黑体积分数在临界体积分数附近时, 力敏导电炭黑/橡胶的灵敏系数在2.5～13之间, 其工作原理主要为压阻效应。当炭黑体积分数在渗流区时, 灵敏系数在2.5～4.5之间, 其工作原理与接触压力的大小有关。压力较小时, 其工作原理主要为压阻效应; 压力较大时, 其工作原理主要为应变效应。炭黑体积分数在传导区时, 灵敏系数在2.0～2.5之间, 其工作原理主要为应变效应。      

金刚石薄膜压阻效应及相关问题的研究

P型金刚石薄膜具有压阻效应,是最近五六年才发现的新现象。利用压阻效应,可望将金刚石膜制成高灵敏度的新一类压阻传感器材料和压力微传感器,从而拓宽金刚石膜在电子学领域的应用范围。 对金刚石膜的压阻因子进行了测量,结果表明,P型定向生长的多晶金刚石膜室温压阻因子可达100O以上;金刚石薄膜的压阻效应比硅和金属显著得多;多晶金刚石膜的压阻效应不如单晶金刚石膜。金刚石膜具有显著的压阻效应,其理论原因和机制问题到目前一直不太清楚,本研究工作对此进行了系统和深入的研究。在能带结构和形变势理论的基础上,首次结合价带分裂模型和M-S多晶模型,分别推导出P型单晶和多晶金刚石膜压阻因子的近似计算公式。分析结果认为,金刚石薄膜的压阻效应是应力诱导价带分裂造成的。轻、重空穴有效质量之间的巨大差异,是导致P型金刚石具有显著压阻效应的主要原因之一。P型多晶材料的压阻效应,是应力诱导价带分裂和晶界散射联合作用的结果,晶界有阻碍电阻随应变发生改变的作用。从而,第一次从理论上阐明了导致P型多晶材料压阻效应不如同种的P型单晶材料的原因。 对负偏压热灯丝CVD系统下,金刚石膜核化过程进行了研究,结果认为.负偏压对金刚石膜核化的增强是离子对衬底的轰击与发射电子激发的等离子体联合作用于衬     

导电炭黑填充硅橡胶的电阻温度系数

以炭黑(CB3100)为导电相,硅橡胶为基质制备导电复合材料。研究导电橡胶中炭黑质量分数对电阻温度系数的影响,并用填料对电阻温度系数的影响。以隧道效应理论为基础,给出了导电炭黑填充橡胶的电阻温度系数计算模型,结合实验得到温度对导电炭黑/硅橡胶电阻温度系数的影响主要体现在对其电阻率的影响;基体的体积热膨胀提高复合材料的电阻率,提高了正电阻温度系数;炭黑粒子间的隧道效应降低复合材料的电阻率,增强了负电阻温度系数;在炭黑/硅橡胶中加入少量碳纳米管,利用碳纳米管和炭黑的协同补强效应,使复合材料的导电性和稳定性提高。     

基于炭黑填充导电橡胶的压力传感器非线性特性

通过分析力敏炭黑填充导电橡胶(力敏导电炭黑/橡胶)"负电阻-压力系数"(NPCR)的主因,研究了基于炭黑填充导电橡胶的力传感器非线性特性。研究表明,当炭黑体积分数接近临界渗流体积分数时,NPCR非线性的主因为电阻率的非线性减小;炭黑体积分数在渗流区时,NPCR非线性的主因为电阻率的非线性减小和导电橡胶应力-应变关系的非线性;若炭黑体积分数在传导区时,NPCR非线性的主因为应力-应变关系的非线性。随着炭黑体积分数的增大,力敏导电炭黑/橡胶的NPCR非线性逐渐减弱。此外,由于界面压阻效应以及导电橡胶近似不可压缩体的性质,用于获取NPCR效应的电极分布形式也对NPCR效应的非线性特性存在影响。     

炭黑填充型导电橡胶的压力/温度特性研究

分析了导电橡胶的压阻效应和温度效应,实验制备了导电橡胶试样,并研究了试样添加不同导电粒子后的压阻特性和温度特性。研究表明,导电橡胶添加不同导电材料时呈现出不同的温度特性,随温度的升高,单独添加乙炔炭黑的导电橡胶在30～70℃之间呈现负温度效应,在70～120℃之间呈现正温度效应;乙炔炭黑与N472并用的导电橡胶随温度的升高呈现正温度效应;添加纳米Al2O3的导电橡胶随温度的升高呈现正温度效应和负温度效应。探讨了压力变化时电阻率与温度的相关性,分析了产生不同温度特性的主要原因。     

巨磁电阻效应

介绍了巨磁电阻效应的概念和研究意义,对金属及其合金的磁电阻效应、负巨磁电阻效应以及正磁电阻效应产生的机理进行了简要分析,并展望了巨磁电阻效应未来的研究。     

Ti/TiO2多层膜的光电性能研究

用真空蒸发和自然氧化法在玻璃基底上制备了Ti／TiO2多层膜，并检测了薄膜的光电性能。电性能检测表明Ti／TiO2多层膜存在类负阻效应，多层膜的层间的类负阻效应比表面的更明显，薄膜的层间电阻率高于表面电阻率；用分光光度计测得试样退火前后的透射谱；用X射线衍射仪和扫描电镜检测了Ti／TiO2多层膜的晶体结构和表面形貌。     

Piezoresistivity in Carbon Fiber Reinforced Cement Based Composites

The results of some interesting investigation on the piezoresistivity of carbon fiber reinforced cement based composites (CFRC) are presented with the prospect of developing a new nondestructive testing method to assess the integrity of the composite. The addition of short carbon fibers to cement-based mortar or concrete improves the structural performance and at the same time significantly decreases the bulk electrical resistivity. This makes CFRC responsive to the smart behavior by measuring the resistance change with uniaxial pressure. The piezoresistivity of CFRC under different stress was studied, at the same time the damage occurring inner specimens was detected by acoustic emission as well. Test results show that there exists a marking pressure dependence of the conductivity in CFRC, in which the so-called negative pressure coefficient of resistive (NPCR) and positive pressure coefficient of resistive (PPCR) are observed under low and high pressure. Under constant pressures, time-dependent resisti     

高密度聚乙烯/石墨半导体复合物的压阻特性

研究了聚乙烯/石墨半导体复合物(HDPE/GP) 在轴向压力下的压阻特性。结果表明, 这种复合物的导电性有较显著的压力依赖性。在低压力范围内电阻随压力增加而降低, 在较高压力下则随压力增大而升高, 呈现出所谓的“电阻负压力系数(N PCR ) ”和“正压力系数(PPCR ) ”效应。电阻的压力依赖性, 以及在恒压力作用下表现出来的“电阻蠕变”行为, 被认为与导电粒子网络在应力作用下的破坏与重组有关。     

基于隧道效应的CFRC 材料的导电模型

从碳纤维增强水泥基(CFRC) 材料导电机理出发, 建立了一个描述CFRC 材料导电性的数学模型, 并推导了这种材料电导率与材料内部微观结构参数、载流子运动参数的关系。以该模型分析CFRC 材料的力敏性, 其理论规律与实验结果基本一致, 从而验证了CRFC 导电模型的合理性。     

Negative piezoresistivity in continuous carbon fiber epoxy-matrix composite

The negative and positive piezoresistivity in continuous carbon fiber epoxy-matrix composite has been clarified. The negative piezoresistivity associated with the increase of the through-thickness resistivity upon longitudinal tension and decrease in the through-thickness resistivity upon longitudinal compression is practically attractive for strain sensing and is attributed to the decrease in the degree of contact between fibers of adjacent laminae upon longitudinal tension. This effect is stronger, more reversible and less prone to causing minor damage for the tension case than the compression case. The positive piezoresistivity associated with the longitudinal resistivity increasing upon longitudinal tension is negligibly weak, if any, independent of the number of laminae. The previously reported negative piezoresistivity associated with the longitudinal resistivity decreasing upon longitudinal tension does not occur for a commercially manufactured composite in which the fibers are well aligned.     

碳纤维增强水泥基复合材料(CFRC)的电学特性

综述了碳纤维增强水泥基复合材料(CFRC)电学特性的研究进展,探讨了CFRC的电磁屏蔽性能和导电性能研究中的相关问题,阐述了原材料、配合比和表面处理对CFRC电磁屏蔽性能的影响,明确了碳纤维分散性和试验方法对CFRC导电性能的影响规律以及CFRC在工程结构中的应用状况,展望了CFRC的发展方向,指出碳纤维分散性、测试方法、温度和应力等多因素条件是CFRC电学特性将来的研究重点.     

碳纤维水泥基材料电阻的非线性研究

研究了碳纤维水泥基材料(CFRC) 非线性电阻的伏安特性,并着重讨论了不同的碳纤维掺量和温度对CFRC材料电压-电阻关系的影响.结果表明:在较小外加电压下(＜2V)CFRC材料的电压-电阻曲线会出现明显的平台区,随着电压的进一步增大,其电阻逐渐降低呈现非线性特性.相同纤维掺量的水泥基材料随温度的升高其电压-电阻曲线下降斜率基本保持不变,但初始电阻值下降;而在温度保持不变时,随碳纤维掺量的增加,电阻随电压下降的趋势逐渐减缓.     

Fixation of carbon fibre-reinforced carbon composite implanted into bone

The push-out test of three types of biomaterials: carbon fibre-reinforced carbon (CFRC), hydroxyapatite (HA), and surgical steel (SS) implanted into rabbits femurs was carried out. Hydroxyapatite was used as a positive control (good fixation expected in bone) and surgical steel was a negative one (potentially no fixation in bone). Regeneration of bone in contact with all implants was found three months after implantation. The shear strength between CFRC implants and bone was lower than with the HA implants and higher than the shear strength between the surgical steel and bone. Compressive strength of CFRC implants removed after the observation period was significantly lower than the compressive strength of non-implanted samples. It is concluded that the mechanical bonding between the CFRC implants and host tissues exists 3 months after intrabone implantation and is accompanied by a decrease of the strength of implants.     

碳纤维水泥基材料的电热效应

研究了碳纤维水泥基材料(CFRC)的电热效应,包括最大温升与外加功率的关系、升温规律和降温规律等。结果表明:CFRC材料的最大温升与其外加功率满足良好的线性关系;其升温曲线和降温曲线可由特定的表达式来描述,且外加功率越大,升温速率越大。这一研究对碳纤维水泥基材料在海工工程上的应用具有重要意义。     

碳纤维水泥基复合材料Seebeck效应研究现状

具有显著Seebeck效应的碳纤维水泥基复合材料(Carbon fiber reinforced cement-based composites,简写为CFRC)近年来受到广泛关注。综述了CFRC的导电机理、Seebeck效应强化途径及其工程应用前景。CFRC的载流子类型主要包括离子、电子和空穴,并以空穴为主。碳纤维/碳纳米管掺杂,CFRC的Seebeck系数可提高至约30μV/℃;钢纤维掺杂水泥基材料表现为n型半导体,其Seebeck可达68μV/℃;金属氧化物Bi_2O_3掺杂可将CFRC的Seebeck系数稳步提高到100.28μV/℃,而ZnO和Fe_2O_3掺杂可使CFRC的Seebeck系数分别增大到3 300μV/℃和2 500μV/℃。这些研究有效地促进了CFRC在城市室外热量的转换收集、工业余热能量收集和长寿命结构健康监测传感器等领域的研究与发展。     

On the contribution of carbon nanotube deformation to piezoresistivity of carbon nanotube/polymer composites

The change in electrical resistance due to mechanical deformation of carbon nanotube (CNT)/polymer composites can be rationalized in terms of two effects: (i) changes in the composite electrical resistivity due to changes in the CNT network configuration and (ii) deformation of the CNTs themselves. The contribution of CNT dimensional changes (ii) to the piezoresistivity of CNT/polymer composites is investigated here. An analytical model based exclusively on dimensional changes which describes the CNT change of electrical resistance in terms of its mechanical deformation is proposed. A micromechanics approach and finite element analysis are performed to correlate the macroscale composite strain to the individual CNT strain. The CNT change of electrical resistance is quantified for different matrix elastic moduli and CNT weight fractions. The CNT/polymer composite is also modeled as an effective continuum material in terms of both its electrical and mechanical responses so that the effect of dimensional changes on the global piezoresistivity can be investigated. Based on the modeling predictions and previous experimental results, it is estimated that the CNT change of resistance due to the macroscale composite strain is marginal (∼5%) compared to the total composite change of resistance commonly measured in the laboratory, suggesting that the dominant effect in the piezoresistivity of CNT/polymer composites is the change in the CNT network configuration.