CVI-PIP工艺制备C/SiC复合材料及其显微结构研究

采用化学气相渗透(CVI)与先驱体浸渍裂解(PIP)两种工艺方法联用制备C/SiC陶瓷基复合材料,通过与单纯PIP工艺的致密化效率比较,复合材料的扫描电子显微镜(SEM)、X射线衍射(XRD)分析,结果表明:采用CVI-PIP联用的方法制备C/SiC复合材料,致密化程度有明显的提高.CVI沉积SiC基体结晶性较好,为典型的β-SiC晶体结构;而PIP先驱体聚碳硅烷裂解基体为无定型结构,基体结构差异是决定材料结构与性能的关键因素.     

SiCf/SiC复合材料的制备与力学性能

分别采用先驱体裂解-热压和先驱体浸渍-裂解方法制备出了SiCf/SiC复合材料.重点探讨了不同制备工艺对复合材料纤维/基体间界面和断裂行为的影响.研究表明,采用先驱体裂解-热压工艺制备复合材料时,虽然烧结液相可以促进复合材料的致密化,但其同时导致纤维与基体间的界面结合强以及纤维本身性能的退化,因此复合材料表现为脆性断裂,具有较低的力学性能.而采用先驱体浸渍-裂解法制备复合材料时,由于致密化温度较低,复合材料中纤维与基体的界面结合较弱,而且纤维的性能保留率较高,因此,纤维能够较好地发挥补强增韧作用,复合材料具有较好的力学性能,其抗弯强度和断裂韧性分别为703.6MPa和23.1Pa.m1/2.     

制备工艺对Cf/SiC复合材料力学性能的影响

分别采用先驱体裂解-热压和先驱体浸渍-裂解方法制备出了Cf/SiC复合材料.重点探讨了不同制备工艺对复合材料纤维/基体间界面和力学性能的影响.研究表明,采用先驱体裂解-热压工艺制备复合材料时,由于制备温度较高,复合材料中纤维与基体间的界面结合强,同时纤维本身性能的退化严重,因此复合材料表现为脆性断裂,具有较低的力学性能.而采用先驱体浸渍-裂解法制备复合材料时,由于致密化温度较低,复合材料中纤维与基体的界面结合较弱,而且纤维的性能保留率较高.因此,纤维能够较好地发挥补强增韧作用,复合材料具有较好的力学性能, 其抗弯强度和断裂韧性分别为573.4MPa和17.2 MPa*m1/2.     

不同先驱体制备C/SiC复合材料及其浸渍行为

采用先驱体浸渍裂解工艺(PIP工艺)制备C/SiC复合材料, 研究了不同先驱体对复合材料浸渍行为的影响(三种先驱体分别为固态聚碳硅烷(PCS(s))、液态聚碳硅烷Ⅰ(PCS-Ⅰ(l))和液态聚碳硅烷Ⅱ(PCS-Ⅱ(l)), 制备的三种复合材料体系分别为C/SiC-0、C/SiC-Ⅰ和C/SiC-Ⅱ)。结合C/SiC复合材料的力学性能以及不同裂解周期C/SiC复合材料的微观形貌, 研究了不同先驱体制备的C/SiC复合材料对碳纤维织物浸渍行为的影响。研究结果表明: C/SiC-Ⅰ复合材料的室温弯曲强度最高, 达到336 MPa。不同裂解周期的微观形貌显示, C/SiC-0复合材料内部孔隙分布于碳纤维束间; C/SiC-Ⅰ复合材料内部较致密, 孔隙分布均匀; C/SiC-Ⅱ复合材料基体和束丝内部都存在孔隙, 说明三种聚碳硅烷浸渍液对C/SiC复合材料有不同的浸渍效果。凝胶渗透色谱(GPC)的分析结果显示, 由于浸渍液的分子量不同, 大分子无法浸渍到碳纤维束丝内部, 会造成裂解后的复合材料束内SiC基体较少, 造成其力学性能较低。     

C/SiC-SiB4复合材料的制备及氧化行为

在多孔C/SiC中渗入SiB4微粉后,采用先驱体浸渍裂解(PIP)结合化学气相渗透(CVI)法进行致密化制备C/SiC-SiB4复合材料.利用XRD、EDS、SEM分析了材料的组分及微结构.研究了材料在500～1000℃静态空气的氧化行为,并与致密C/SiC复合材料的氧化行为进行了比较.结果表明,SiB4主要渗入到纤维束间,它与随后PIP及CVI法引入的SiC较好地结合在一起.在氧化过程中,SiB4起自愈合作用,它能减缓碳纤维和界面的氧化.在600～900℃氧化10h后,C/SiC-SiB4的失重率均比致密C/SiC小,抗弯强度没有明显降低,且均比致密C/SiC高.     

活性填料在先驱体转化法纤维增强陶瓷基复合材料中的应用 Ⅰ.复合材料的致密化模型

在先驱体转化陶瓷基复合材料的制备中,坯体在裂解前后的体积发生变化。引入体系体积收缩率参数,对单一先驱体转化纤维增强陶瓷基复合材料致密化模型进行了修正。同时,分别对含惰性填料和/或活性填料的先驱体浆料浸渍-裂解纤维增强陶瓷基复合材料致密化进行了模型分析。从理论上揭示了复合材料的浸渍-裂解周期与材料的理论密度和理论孔隙率之间的关系。当先驱体浆料中含有活性填料时,复合材料的理论密度和理论孔隙率与活性填料的反应陶瓷产率、反应密度比、体积收缩率有密切的数学关系。在先驱体中引入活性填料比引入惰性填料能更为有效地提高材料的密度,降低材料的孔隙率。     

先驱体转化法制备连续纤维增韧陶瓷基复合材料的研究

综述了先驱体转化法制备连续纤维增韧陶瓷基复合材料在先驱体、填料、浸渍裂解工艺、热处理工艺以及微观结构(界面层、气孔)等方面的研究状况.先驱体主要有聚碳硅烷、聚硅氮烷、聚硅氧烷等,填料包括活性填料和惰性填料两种,温度、压力、时间等因素对浸渍裂解过程的影响很大,界面结合的强度关系到复合材料的性能,所以制备复合材料时,各方面的因素都得不断摸索,确定最佳的制备方案.最后,提出了目前该方法存在的问题以及未来的研究方向.     

先驱体转化法制备碳纤维增强碳化硅复合材料的研究

本文采用有机硅先驱体聚碳硅烷转化成碳化硅制备连续碳纤维增强的碳化硅基复合材料。对其制备工艺,如碳纤维体积分数的控制、液相浸渍聚碳硅烷热解转化成碳化硅基体的致密化等进行了研究。结果表明,该工艺对制备连续纤维增强的陶瓷基复合材料是一种有效的方法,易于实现纤维和基体的成型、复合。致密化过程不损伤纤维。对其C/SiC复合材料的性能进行了表征,C纤维具有明显增韧碳化硅的效果,其断裂机制表现为韧性特征。     

SiCf/SiC复合材料制备研究进展

随着科学技术的不断发展,人类对极端条件下应用的材料的需求持续上升.SiCf/SiC复合材料具有耐高温、高强高韧、耐氧化等优点,成为航空航天领域热端部件的理想候选材料;同时,SiCf/SiC复合材料还具有低活化、抗辐照、高温化学稳定性好等优异性能,在核电领域结构材料的应用具有广阔的前景.常用的SiCf/SiC复合材料的制备方法有化学气相渗透法、先驱体浸渍裂解法、热压烧结工艺和熔融浸渍法,其中化学气相渗透法和先驱体浸渍裂解法两种工艺已经应用于航空发动机静载热端部件的生产,但是这些工艺自身固有的不足在材料制备中依然无法较好地解决,于是近年来出现了混合采用多种工艺来制备SiCf/SiC复合材料的尝试.SiC纤维和基体间需要有一层界面层来偏转裂纹、保护纤维,目前常用的界面材料有热解炭和六方氮化硼涂层,由于单一涂层较难满足材料在多种复杂条件下的应用需求,针对涂层改进的新方法和新思路层出不穷.相对于传统烧结工艺,新型烧结方式如微波烧结和放电等离子烧结等在烧结速度、温度均匀性等方面展示出巨大的优势,为陶瓷基复合材料的制备提供了新的选择.为了进一步提升SiCf/SiC复合材料的性能,近年的研究工作主要集中在对SiCf/SiC复合材料的制备方法的优化、纤维/基体界面层的创新和对烧结技术的选择等方面.本文从这些方面对SiCf/SiC复合材料的研究进展进行了详细的归纳和介绍.     

炭纤维针刺预制体增强C/SiC复合材料的制备与性能研究

以炭纤维复合网胎针刺织物为预制体, 采用“化学气相渗透法+先驱体浸渍裂解法”(CVI+PIP)混合工艺, 制备了C/SiC陶瓷复合材料; 研究了针刺预制体的致密化效率以及复合材料的微观结构和力学性能, 并与目前常用的三维编织C/SiC复合材料和预氧丝针刺织物增强C/SiC复合材料进行了对比. 结果表明, 针刺预制体的致密化效率明显高于三维编织预制体, 在相同致密工艺条件下, 炭纤维针刺织物增强复合材料和预氧丝针刺织物增强复合材料的密度分 别达到2.08和2.02g/cm³, 而三维编织预制体增强复合材料的密度仅为1.81g/cm³. 炭纤维针刺复合材料的力学性能高于预氧丝针刺复合材料, 弯曲强度和剪切强度分别达到237和26MPa.     

Advances in piezoelectric thin films for acoustic biosensors,acoustofluidics and lab-on-chip applications

Recently, piezoelectric thin films including zinc oxide (ZnO) and aluminium nitride (AlN) have found a broad range of lab-on-chip applications such as biosensing, particle/cell concentrating, sorting/patterning, pumping, mixing, nebulisation and jetting. Integrated acoustic wave sensing/microfluidic devices have been fabricated by depositing these piezoelectric films onto a number of substrates such as silicon, ceramics, diamond, quartz, glass, and more recently also polymer, metallic foils and bendable glass/silicon for making flexible devices. Such thin film acoustic wave devices have great potential for implementing integrated, disposable, or bendable/flexible lab-on-a-chip devices into various sensing and actuating applications. This paper discusses the recent development in engineering high performance piezoelectric thin films, and highlights the critical issues such as film deposition, MEMS processing techniques, control of deposition/processing parametres, film texture, doping, dispersion effects, film stress, multilayer design, electrode materials/designs and substrate selections. Finally, advances in using thin film devices for lab-on-chip applications are summarised and future development trends are identified.     

Effect of boron waste and boric acid addition on the production of low energy belite cement

The effect of boron oxide addition on the production of low energy belite cements has been investigated. Three types of clinkers were prepared with 1.5 wt.% (BC_BA1.5) boric acid, and 1.0 wt.% (BC_BW1) and 6.5 wt.% (BC_BW6.5) boron waste addition. The design of the raw mixtures was based on modified Bogue equations. According to the free lime content and the evolution of the microstructure of the clinkers, firing was performed at 1330 °C, 1350 °C and 1310 °C for BC_BA1.5, BC_BW1 and BC_BW6.5, respectively. Boron addition favored the reduction of the clinkering temperature as well as the stabilization of upper belite polymorphs. According to the present results, late compressive strength development of belite cements depends mainly on the crystal type rather than on the content of belite in the clinker. The results indicate that controlled quantities of boron oxide can be beneficial in the production of belite cement.     

Recent advances in thermoelectric materials

Thermoelectric materials are crucial in renewable energy conversion technologies to solve the global energy crisis. They have been proven to be suitable for high-end technological applications such as missiles and spacecraft. The thermoelectric performance of devices depends primarily on the type of materials used and their properties such as their Seebeck coefficient, electrical conductivity, thermal conductivity, and thermal stability. Classic inorganic materials have become important due to their enhanced thermoelectric responses compared with organic materials. In this review, we focus on the physical and chemical properties of various thermoelectric materials. Newly emerging materials such as carbon nanomaterials, electronically conducting polymers, and their nanocomposites are also briefly discussed. Strategies for improving the thermoelectric performance of materials are proposed, along with an insight into semiconductor physics. Approaches such as nanostructuring, nanocomposites, and doping are found to enhance thermoelectric responses by simultaneously tuning various properties within a material. A recent trend in thermoelectric research shows that high-performance thermoelectric materials such as inorganic materials and carbon nanomaterials/electronically conducting polymer nanocomposites may be suitable for power generation and energy sustainability in the near future.     

The use of mindmapping software for patent search and management

Modern information technologies and in particular the internet have revolutionized the patent information professionals' work in terms of speed of access and information comprehensiveness from both company internal and external digital sources. Here, I describe how the digital mindmapping technique can be used to complement existing intellectual property management software solutions to meet the challenge of optimizing and managing patent search workflows as well as to rapidly organise and access highly dynamic, heterogeneous and scattered patent information sources. Both eye catching and highly memorable and at the same time self-explanatory mindmapping examples are presented. These were designed to include basic and advanced level digital mindmapping features tailored to significantly speed up and maintain a high work quality level of patent search professionals. A special emphasis is put on the great benefit of organising and accessing the plethora of internet-based worldwide online patent registers through mindmapping, both in terms of managing the constantly changing deep links to the actual search options for e.g., legal status information, and keeping track of the offered level of content.     

Effect of hypophosphite on electrodeposition of graphite@copper powders

The effect of sodium hypophosphite (NaH₂PO₂) on the electrodeposition of copper coated graphite powders (graphite@Cu) was investigated in this paper. The cathodic polarization curves were determined by potentiodynamic scanning method in the electrolyte containing various concentrations of NaH₂PO₂. Hypophosphite could reduce the overpotential of copper deposited on the graphite particles surface and accelerate electroless copper nuclei generated by the reduction reaction. The applied potential promoted the formation of copper nuclei on the surface of graphite powders. Uniform graphite@Cu powders were fabricated by optimizing the NaH₂PO₂ concentration in the range of 10–15 g dm⁻³. The residue of NaH₂PO₂ could be depleted to less than 0.25 g dm⁻³ by decomposition on the anode and chemical reduction in the bath during electrodeposition. The effect of hypophosphite on the electrodeposition of graphite@Cu is also discussed.     

Polymer/carbon based composites as electromagnetic interference (EMI) shielding materials

The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of applications, the quest for materials with high efficiency to mitigate electromagnetic interferences (EMI) pollution has become a mainstream field of research. This paper reviews the state-of-the-art research in the design and characterization of polymer/carbon based composites as EMI shielding materials. After a brief introduction, in Section 1, the electromagnetic theory will be briefly discussed in Section 2 setting the foundations of the strategies to be employed to design efficient EMI shielding materials. These materials will be classified in the next section by the type of carbon fillers, involving carbon black, carbon fiber, carbon nanotubes and graphene. The importance of the dispersion method into the polymer matrix (melt-blending, solution processing, etc.) on the final material properties will be discussed. The combination of carbon fillers with other constituents such as metallic nanoparticles or conductive polymers will be the topic of Section 4. The final section will address advanced complex architectures that are currently studied to improve the performances of EMI materials and, in some cases, to impart additional properties such as thermal management and mechanical resistance. In all these studies, we will discuss the efficiency of the composites/devices to absorb and/or reflect the EMI radiation.     

Drug self-assembly: A phenomenon at the nanometer scale with major impact in the structure–biological properties relationship and the treatment of disease

Under water-rich conditions, small amphiphilic and hydrophobic drug molecules self-assemble into supramolecular nanostructures. Thus, substantial modifications in their interaction with cellular structures and the ability to reach intracellular targets could happen. Additionally, drug aggregates could be more toxic than the non-aggregated counterparts, or vice versa. Moreover, since self-aggregation reduces the number of effective “monomeric” molecules that interact with the target, the drug potency could be underestimated. In other cases, the activity could be ascribed to the non-aggregated molecule while it stems from its aggregates. Thus, drug self-assembly could mislead from drug throughput screening assays to advanced preclinical and clinical trials. Finally, aggregates could serve as crystallization nuclei. The impact that this phenomenon has on the biological performance of active compounds, the inconsistent and often controversial nature of the published data and the need for recommendations/guidelines as preamble of more harmonized research protocols to characterize drug self-aggregation were main motivations for this review. First, the key molecular and environmental parameters governing drug self-aggregation, the main drug families for which this phenomenon and the methods used for its characterization are described. Then, promising nanotechnology platforms investigated to prevent/control it towards a more efficient drug development process are briefly discussed.     

Luminescence properties of long-lasting phosphor SrMg2(PO4)2:Eu2+, Ho3+, Zr4+

Novel long lasting phosphors SrMg₂(PO₄)₂:Eu²⁺, SrMg₂(PO₄)₂:Eu²⁺, Zr⁴⁺, SrMg₂(PO₄)₂:Eu²⁺, Ho³⁺ and SrMg₂(PO₄)₂:Eu²⁺, Ho³⁺, Zr⁴⁺ were synthesized by conventional solid-state reaction method. The luminescent properties were systematically characterized by X-ray diffraction, photoluminescent excitation and emission spectra, as well as thermoluminescence spectrum and decay curves. The XRD patterns indicated that the samples belonged to monoclinic phase and co-doping Eu²⁺, Ho³⁺ and Zr⁴⁺ ions had no effect on the basic crystal structure. These phosphors emitting purplish blue light is related to the characteristic emission of Eu²⁺. The afterglow time of Eu²⁺ activated SrMg₂(PO₄)₂ can be greatly enhanced by the co-doping of Ho³⁺, Zr⁴⁺. After the 365 nm UV light excitation source switching off, the Sr_0.92Mg_1.95(PO₄)₂:Eu²⁺_0.01, Zr⁴⁺_0.05, Ho³⁺_0.07 phosphorescence can be observed for more than 1013 s in the limit of light perception of dark-adapted human eyes (0.32 mcd/m²). Different kinds of TL peaks at 423, 448 and 473 K have appeared, and traps densities have increased compared with the Eu²⁺ single doped SrMg₂(PO₄)₂ phosphor. By analyzing the TL curve the depths of traps were calculated to be 0.846, 0.896 and 0.946 eV, respectively, which suggested that the co-doping of Ho³⁺, Zr⁴⁺ improved the electron storage ability of material. Besides, the mechanism was discussed in this report.     

Advances in metals and alloys for joint replacement

Metals, ceramics, polymers, and composites have been employed in joint arthroplasty with ever increasing success since the 1960s. New materials to repair or replace human skeletal joints (e.g. hip, knee, shoulder, ankle, fingers) are being introduced as materials scientists and engineers develop better understanding of the limitations of current joint replacement technologies. Advances in the processing and properties of all classes of materials are providing superior solutions for human health. However, as the average age of patients for joint replacement surgery decreases and the average lifespans of men and women increases worldwide, the demands upon the joint materials are growing. This article focuses solely on advances in metals, highlighting the current and emerging technologies in metals processing, metal surface treatment, and integration of metals into hybrid materials systems. The needed improvements in key properties such as wear, corrosion, and fatigue resistance are discussed in terms of the enhanced microstructures that can be achieved through advanced surface and bulk metal treatments. Finally, far reaching horizons in metals science that may further increase the effectiveness of total joint replacement solutions are outlined.     

Effects of microstructural heterogeneity on very high cycle fatigue properties of 7050-T7451 aluminum alloy friction stir butt welds

In this study, the very high cycle fatigue (VHCF) properties of 7050-T7451 aluminum alloy and its friction stir welding (FSW) butt welds have been investigated. The results show that the failure of FSW joints still occurs at 7.0 × 10⁸ cycles. The fatigue properties of the FSW joints are superior to those of the base material, especially in the super long life regime. Most fatigue cracks initiate at the thermo-mechanically affected zone and heat affected zone on the advancing side of the FSW joints, and the susceptibility of these zones to fatigue is attributed to the metallurgical heterogeneity.