层厚比和硬夹层组成对B_4C-BNNTs/TiB_2-B_4C层状陶瓷复合材料性能的影响

以B_4C为基体层材料,BNNTs为基体层补强增韧剂,TiB_2为硬夹层,采用水基流延成型和热压烧结工艺制备了B_4C-BNNTs/TiB_2-B_4C层状陶瓷复合材料。研究了基体层与硬夹层的层厚比、硬夹层组成和烧结温度对层状陶瓷复合材料的显微结构和力学性能的影响。实验结果表明:当层厚比为1,硬夹层组份为80 wt%TiB_2+20 wt%B_4C,烧结温度为2050℃时,可以制备出力学性能良好的B_4C-BNNTs/TiB_2-B_4C层状陶瓷复合材料,其抗弯强度和断裂韧性分别达到570.54 MPa和7.74 MPa·m~(1/2)。     

SiC基层状复合材料界面层的选择

利用凝胶注模成型SiC基体层 ,以喷涂法、流延法、金属箔法、浸涂法分别加涂W ,W -2 % (质量分数 ,下同 )Co ,Ta,BN界面层 ,通过热压烧结制备了SiC/W ,SiC/W -2 %Co ,SiC/Ta ,SiC/BN层状复合材料 .在复合材料高温制备过程中 ,金属W ,W -2 %Co ,Ta与SiC反应生成了碳化物和硅化物 ,失去了金属塑性 ,未能实现裂纹尾流区桥接、残余应力增韧等金属界面层层状复合材料赖以大幅度提高其强韧性的增韧机制 ,其增韧效果仅与BN陶瓷界面层的增韧效果相当 .此外 ,研究表明 ,提高基体层力学性能可以显著提高层状复合材料的强韧性 .制备的SiC/BN层状复合材料的室温三点弯曲强度为 72 9.86± 114 .0 2MPa、室温断裂韧性为 2 0 .5 8± 2 .77MPa·m1 /2 ,其主要增韧机制包括裂纹分叉钝化、裂纹偏转、裂纹并行扩展以及裂纹尾流区片层拔出等     

热燃烧温度对超重力场自蔓延离心熔铸TiB_2-TiC-(Ti,W)C组织及性能的影响

通过在(Ti+B_4C)燃烧体系中引入WO_3+Al高能铝热剂,采用自蔓延离心熔铸方法制备TiB_2-TiC-(Ti,W)C复相陶瓷材料。结果表明,陶瓷是由规则的TiB_2片晶、TiC球晶以及(Ti,W)C固溶体组成,并发现少量Al_2O_3夹杂存在于陶瓷熔体中。随着铝热剂含量的增加,不仅提高了绝热燃烧温度,增进了陶瓷致密化,而且提高了陶瓷熔体中的W含量,提高了陶瓷硬度。TiB_2片晶诱发的裂纹偏转和桥接增韧大幅度提高了陶瓷的抗弯强度和断裂韧性。材料的硬度、抗弯强度和断裂韧性分别为24.6 GPa、584 MPa与20.3 MPa·m~(1/2)。当铝热剂添加过量,TiB_2相的含量下降,导致陶瓷力学性能有所下降。     

无压浸渗TiCx/Cu双连续复合材料的高温力学及抗烧蚀性能研究

以纳米乙炔炭黑和Ti粉为初始原料,利用原位反应烧结法制备了不同气孔率、非化学计量比的多孔TiC_x (x=0.7)预制体,然后通过无压浸渗制备了双连续相TiC_x/Cu复合材料。系统分析了TiC_x气孔率、陶瓷晶粒尺寸与形貌对TiC_x/Cu双连续复合材料物相和微观结构的影响,并测试分析了TiC_x/Cu复合材料的常温、高温力学性能以及耐烧蚀性能。研究发现,通过调控预压压力以及烧结温度可以对TiC_x预制体气孔率和晶粒尺寸进行调控。TiC_x/Cu双连续相复合材料的弯曲强度和断裂韧性随预制体气孔率增加而提高,1600℃/3 MPa制备的预制体对应的复合材料,室温弯曲强度达到1052 MPa±59 MPa,断裂韧性达到11.9 MPa·m^1/2±2.7MPa·m1/2,600℃时弯曲强度仍可达到387 MPa±11 MPa。用氧-乙炔火焰对1700℃/3 MPa制备的预制体对应的复合材料进行烧蚀,测得线烧蚀率为0.0485 mm...     

环氧树脂/纳米SiO_2复合材料的制备

制备了环氧树脂(EP)/纳米SiO2复合材料,研究了纳米SiO2用量对复合材料结构和力学性能的影响,采用扫描电子显微镜观察了复合材料的断面形貌,分析了纳米SiO2的增韧机理。添加适量的纳米SiO2可显著提高EP的力学性能,添加6 phr纳米SiO2时,EP/纳米SiO2复合材料的力学性能最佳,拉伸剪切强度、弯曲强度、悬臂梁缺口冲击强度分别为13.8 MPa,86.1 MPa,11.6 kJ/m2;适量的纳米SiO2能改善EP的内部结构,具有明显的增韧补强作用。     

连续CF增强PEEK复合材料层压板的制备工艺

采用熔融浸渍法制备了连续碳纤维(CF)增强聚醚醚酮(PEEK)复合材料预浸带,并层压成型制备复合材料层压板。研究了成型温度、成型压力、成型时间、纤维含量等因素对复合材料层压板力学性能的影响。结果表明,在成型温度为370℃、成型压力为12 MPa、成型时间为70 min、纤维含量为61%的工艺条件下,连续CF增强PEEK复合材料层压板的力学性能达到最优值,弯曲强度和弯曲弹性模量分别达到(1 750.76±49.13)MPa和(107.54±6.35)GPa,层间剪切强度达到(100.04±6.88)MPa,缺口冲击强度为(84.44±1.54)k J/m2。随着冷却速率的增大,复合材料层压板的弯曲性能和层间剪切强度下降,而缺口冲击强度提高。SEM分析表明,复合材料层压板的界面粘结良好。     

自蔓延离心熔铸TiB2-(Ti,W)C-TiC陶瓷研究

基于离心热爆反应、难熔液相分离与快速凝固原理,选取(WO3+Al+C)体系辅助(B4C+Ti)反应体系,采用自蔓延离心熔铸工艺可以成功制备出TiB2微纳米晶补强TiC-(Ti,W)C陶瓷基复合材料.将(B4C+Ti)、(WO3+Al+C)两种反应体系依次装填入坩埚中进行SHS离心熔铸实验,发现因W-Ti-C液相动力学粘度的降低、Al2O3液滴迁移路程减小,极大促进Al2O3液滴的Stokes上浮过程,故而显著减小残存于陶瓷基体上的氧化物夹杂含量与尺寸,进而TiB2微纳米片晶诱发的强烈自增韧机制与Al2O3微纳米晶产生的残余应力增韧效应,使得TiB2-(Ti,W)C-TiC陶瓷的弯曲强度、断裂韧性与维氏硬度分别达到(952±25)MPa、(12.6±2.5)MPa·m1/2与(28.6±1.2)GPa.     

Ti_2AlC/TiAl_3复合材料的制备及其性能研究

利用Ti-Al-TiC-CNTs体系的原位反应结合热压技术制备Ti2AlC/TiAl3复合材料。研究产物的相组成、结构和力学性能。结果表明:产物主要由TiAl3和Ti2AlC相组成,增强相Ti2AlC主要分布在基体晶界处,并形成了明显的搭接层状结构。产物的弯曲强度和断裂韧性分别为343.21 MPa和6.5 MPa·m1/2,远高于TiAl3合金的弯曲强度(162 MPa)和断裂韧性(2 MPa·m1/2),较TiAl3合金分别提高了111.86%和225%。     

B_4C-BNNTs/TiB_2-B_4C层状复合材料层间残余应力分析及界面组成优化

采用ANSYS软件对B_4C-BNNTs/TiB2-B_4C层状复合材料中硬夹层含不同体积分数B_4C时的残余应力进行了分析,结果表明,随着B_4C含量的增加,复合材料的层间残余应力呈下降趋势。基于分析结果,采用热压烧结工艺制备了硬夹层含不同体积分数B_4C的复合材料样品。研究了B_4C体积分数对B_4C-BNNTs/TiB_2-B_4C层状复合材料层间残余应力、界面结合情况、相对密度及力学性能的影响。结果表明:当B_4C含量为15 vol%时,可得到最佳结果,此时材料的相对密度、抗弯强度、断裂韧性和维氏硬度分别为99.1%、509 MPa、7.49 MPa·m~(1/2)和38.6 GPa。     

热解碳对先驱体浸渍裂解3D-C_f/SiC复合材料性能影响

以三维编织T300碳纤维为预制体,通过控制化学气相渗积(CVI)沉积时间制备厚度不同的热解碳界面相,采用先驱体浸渍裂解(PIP)工艺增密制备3D-C_f/SiC复合材料,研究界面相对先驱体浸渍裂解3D-C_f/SiC复合材料性能影响。结果表明:3D-C/SiC复合材料在合适的界面相厚度下能够获得更好的增韧效果。热解碳厚度为220±20 nm时,3D-C_f/SiC复合材料弯曲强度为388.8 MPa,弯曲断口处纤维呈台阶式拔出,拔出面参齐不齐,弯曲强度最大,增韧效果最佳。     

水镁石、水菱镁石和斜方云石资源、加工与应用

对水镁石、水菱镁石和斜方云石资源及其加工和应用进行了评述。包括上述资源的发展历史、化学组成和物性参数、资源储量和矿石品位、生产加工以及在不同领域(如镁质阻燃剂、中和剂、重金属离子脱除剂、镁肥、饲料添加剂等)的应用,并对它们的发展前景进行了展望。     

Pd-, Ni-, Fe-, and Co-Catalyzed Cross-Couplings Using Functionalized Zn-, Mg-, Fe-, and In-Organometallics

The development of new methods for preparing polyfunctional organometallics has made a broad range of such reagents available for various transition metal-catalyzed cross-couplings. An overview of the most general preparation methods will be presented. Applications to practical cross-coupling procedures will be covered, emphasizing the functional group compatibility and the reaction scope.     

Bioaerosol Science,Technology, and Engineering: Past,Present, and Future

Poor air hygiene as a result of bioaerosol contamination has caused diverse forms of adverse health effects and diseases. In addition, global biosecurity is threatened by purposeful use of biowarfare agents and the vulnerability of people to the infectious agents. Accordingly, developments in high-volume biosampling, including aerosol-to-hydrosol techniques with low cut-off size, real-time bioaerosol detection, adequate biological quantification, and exposure control, as well as the investigation of the link between disease outcome and bioaerosol exposure, are current areas of bioaerosol research. Although milestone progress has been achieved both in bioaerosol sampling and analysis techniques since late 1800s, compared to atmospheric chemistry the bioaerosol field is still understudied. This is partially because of the lack of both bioaerosol scientists and multidisciplinary collaboration. It is becoming necessary to develop a pool of scientists with different expertise, e.g., bioaerosol scientists, environmental engineers, biomedical engineers, epidemiologists, microbiologists, chemists, physicists, as well as researchers in other engineering fields, in mitigating bioaerosol-related adverse health effects, eliminating diseases, and preventing and controlling epidemic outbreaks. This work is conducted to broadly review current state-of-the-art sciences and technologies in the bioaerosol field. In tackling the challenges ahead, the review also provides perspectives for bioaerosol research needs, and further reminds bioaerosol scientists of those existing technologies in other fields that can be leveraged. In view of the past, forward-looking hypotheses and revolutional perspectives are needed to be formed in order to allow the bioaerosol research have major impacts in the academic community in this new millennium.     

Stable silyl, germyl, and stannyl cations, radicals, and anions: heavy versions of carbocations, carbon radicals, and carbanions

The rapidly growing chemistry of the cations, radicals, and anions based on the group 14 elements heavier than carbon (Si, Ge, Sn, and Pb) is one of the most important organometallic fields. Recent developments in this research area moved such species from the class of short-lived reactive intermediates to the class of easily accessible, isolable, and fully characterizable compounds. In this Account, we deal with the major accomplishments in the field of the stable representatives of "heavy" cations, radicals, and anions.     

Polystyrene nanocomposite materials: Preparation,morphology, and mechanical,electrical, and thermal properties

In this study, we prepared polystyrene (PS) resin nanocomposites with antistatic properties by melt‐blending PS with nanoscale zinc oxide (ZnO). The effects of nanoscale ZnO on the electrical and physical characteristics of the PS nanocomposites were investigated. Two kinds of nanoscale powders, spherical zinc oxide (s‐ZnO) and zinc oxide whisker (w‐ZnO), were selected. The coupling agents vinyltriethoxysilane (VTES) and phenyltriethoxysilane (PTES) were used to improve the compatibility between the nanopowders and PS resin. The addition of s‐ZnO and w‐ZnO improved the antistatic characteristics of the materials. The surface resistivities of the s‐ZnO and w‐ZnO nanocomposites were significantly reduced by modification with VTES and PTES. The addition of ZnO nanopowder increased the flexural modulus and reduced the flexural strength. The silane coupling agents improved the flexural properties of the nanocomposites. The glass‐transition temperatures and thermal degradation temperatures of the ZnO/PS nanocomposites increased with ZnO content. Treatment with silane increased the glass‐transition temperatures and thermal degradation temperatures of the composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2266–2273, 2005     

Sapindaceae,cyanolipids, and bugs

Scentless plant bugs (Heteroptera: Rhopalidae) are so named because adults of the Serinethinae have vestigial metathoracic scent glands. Serinethines are seed predators of Sapindales, especially Sapindaceae that produce toxic cyanolipids. In two serinethine species whose ranges extend into the southern United States,Jadera haematoloma andJ. sanguinolenta, sequestration of host cyanolipids as glucosides renders these gregarious, aposematic insects unpalatable to a variety of predators. The blood glucoside profile and cyanogenesis ofJadera varies depending on the cyanolipid chemistry of hosts, and adults and larvae fed golden rain tree seeds (Koelreuteria paniculata) excrete the volatile lactone, 4-methyl-2(5H)-furanone, to which they are attracted.Jadera fed balloon vine seeds (Cardiospermum spp.) do not excrete the attractive lactone. Loss of the usual heteropteran defensive glands in serinethines may have coevolved with host specificity on toxic plants, and the orientation ofJadera to a volatile excretory product could be an adaptive response to save time.Mention of a commercial product does not consititute an endorsement by the USDA.     

Self-crosslinked poly-L-ornithine and poly-L-arginine networks: Synthesis,characterization, pH-responsibility,biocompatibility, and AIE-functionality

A pH-responsive hydrogel consists of polypeptides only is a promising biomaterial with the advantages of good biocompatibility and non-toxicity. This work reports the synthesis of poly-L-ornithine(poc) (polyLOpoc) serving as the precursor for hydrogels of poly-L-ornithine (polyOrn) and poly(L-arginine-r-L-ornithine) (poly(Arg-r-Orn)). Their controllable degree of crosslinking, good mechanical properties, good biocompatibility, and pH-responsibility are detailedly investigated. The swelling ratio of polyOrn hydrogel in acidic aqueous solution is 5.7 times higher than that in a basic environment. In the deprotection of phenoxycarbonyl group, polyLOpoc releases amino pendant groups, which attack the remaining poc-protected amino groups to fulfill self-crosslinking without any crosslinking agent. In addition, the pH-responsive behavior of hydrogels is visualized by aggregation-induced emission phenomena with polyOrn and poly(Arg-r-Orn) containing tetrakis(4-aminophenyl)ethene moisture.