Journal of the American Ceramic Society
In situ synthesis of bulk Al(3)BC(3) was achieved via a reactive hot-pressing method using Al, B(4)C, and graphite powders at 1800 degrees C for 2 h. The reaction path for synthesizing Al(3)BC(3) was investigated. It was found that Al(3)BC(3) formed via the reaction of C, B(4)C, and Al(4)C(3) above 1180 degrees C. Dense Al(3)BC(3) was prepared with a little B(4)C and graphite remained. Microstructure observations revealed the plate-like morphology of Al(3)BC(3) grains. Moreover, the mechanical properties of Al(3)BC(3) were characterized (Vickers hardness of 11.1 GPa, bending strength of 185 MPa, fracture toughness of 2.3 MPa.m(1/2), and Young's modulus of 163 GPa). Young's modulus decreased slowly with increasing temperature, and at 1600 degrees C remained 79% of that at ambient temperature. These results show that Al(3)BC(3) is a promising lightweight high temperature structural material.
关键词:
boron-carbide;high-temperature;youngs modulus;aluminum;al8b4c7;friction;ti3alc2;ti3sic2;composites;ceramics
赵梓年
,
周露露
,
贾士儒
膜科学与技术
以聚偏氟乙烯(PVDF)为基体材料,二甲基乙酰胺(DMAc)为溶剂,分别添加细菌纤维素(BC)及其BC/SiO2复合物,通过相分离法制备PVDF/BC共混膜.通过扫描电子显微镜(SEM)、膜性能测试仪对共混膜的结构和性能进行了表征.BC的加入使PVDF/BC共混膜的水通量增加、截留率下降;BC浓度为0.4％时,共混膜的综合性能较优.在PVDF膜中加入改性制备的BC/SiO2复合物,PVDF /BC/SiO2共混膜的水通量降低,截留率有所增加.添加了经HC1催化的BC/SiO2复合物的共混膜,截留率达到最大.
关键词:
细菌纤维素
,
细菌纤维素/二氧化硅复合物
,
共混膜
Physica B-Condensed Matter
Structural, elastic constants and anisotropy of the potential superhard orthorhombic structure boron carbonitride beta-BC(2)N under hydrostatic pressure up to 100 GPa have been studied using density functional theory within the local density approximation (LDA) as well as the generalized gradient approximation (GGA) for exchange and correlation. The results are in excellent agreement with available experimental data and other theoretical results. Changes of lattice constants, the cell volume, elastic constants, and elastic anisotropy of beta-BC(2)N under hydrostatic loading are examined, and the bulk modulus B(0) and its pressure derivative B'(0) are fitted from the volume-pressure relation. It is concluded that beta-BC(2)N is a brittle and hard material in nature up to 100 GPa and is next to diamond in hardness. An analysis for the calculated elastic constant has been made to reveal the mechanical stability of beta-BC(2)N up to 100 GPa. (C) 2010 Elsevier B.V. All rights reserved.
关键词:
Elastic properties;Anisotropy;Density functional theory;beta-BC(2)N;ab-initio;cubic bc2n;hexagonal bc2n;crystals;instabilities;dynamics;diamond;stress
M. Militzer The Centre for Metallurgical Process Engineering
,
University of British Columbia
,
Vancouver
,
BC
,
Canada V6T 1Z4
金属学报(英文版)
The microstructure evolution has been investigated for hot rolling of advanced low carbon steels containing Nb, Ti, V and Cu. The critical processing step to develop the properties of hot rolled steels is cooling after rolling when the austenite-to-ferrite transformation as well as precipitation takes place thereby determining the final mi- crostructure. Thus, the modelling work emphasizes the kinetics of errite formation. Ferrite growth rates can adequately be described by taking into account a solute-drag- like effect of Mn and Nb. The emphasis of the model is to predict the phase transfor- mation kinetics for the industrial practice of accelerated cooling. The ferrite grain size is essentially determined at the early stages of transformation and can be correlated to the trunsformation start temperature. Pcarbides and nitrides of Nb, Ti and V is controlled by Ostwald ripening of these particles. The ageing behaviour can then be described based on the Shercliff-Ashby model for precipitation hardening. The situa- tion is more complex for Cu precipitation where the ageing response is also related to a sequence of different precipitation types.
关键词:
low carbon steal
,
null
,
null
,
null
Journal of Applied Physics
The mechanical properties and electronic structure of diamondlike BC(5) are studied by ab initio method. The results for elastic moduli, stress-strain relationships, and ideal strengths are presented. The calculated properties agree well with the existing experiments. BC(5) possesses very large elastic moduli and ideal strengths, suggesting its intrinsical superhard nature. Its ideal tensile strengths are much larger than ideal shear strengths. Electronic structures show that strong covalent bond network through sp(3) hybridization is the origin of excellent mechanical properties of BC(5). The failure of BC(5) is attributed to the breaking of the B-C bond. BC(5) is predicted to be metallic and remains its electronic properties at finite strain. Our results show that BC(5) has good prospect in electronic application as a superhard material. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3195082]
关键词:
cubic bc2n;strength;boron
Journal of Solid State Chemistry
Al3BC3, an isostructural phase to Mg3BN3, experienced no pressure-induced phase transformation that occurred in the latter material (J. Solid State Chem. 154 (2000) 254-256). The discrepancy is not clear yet. Using the first-principles density functional calculations, we predict that Al3BC3 undergoes a hexagonal-to-tetragonal structural transformation at 24 GPa. The predicted phase equilibrium pressure is much higher than the previously reported pressure range, i.e., 2.5-5.3 GPa, conducted on phase stability of Al3BC3. A homogeneous orthorhombic shear strain transformation path is proposed for the phase transformation. The transformation enthalpy barrier is estimated to yield a low value, i.e., 0.129 eV/atom, which ensures that the transformation can readily take place at the predicted pressure. (c) 2006 Elsevier Inc. All rights reserved.
关键词:
Al3BC3;high pressure;phase transformation;density functional;calculations;equation of state;mg3bn3
Journal of Applied Physics
In situ Raman spectra of Al(3)BC(3) have been measured at elevated temperatures of up to 1000 degrees C and high pressures of up to 32 GPa. It is shown that there are no abnormal phonon shifts when the measurement conditions were up to 1000 degrees C or up to 27 GPa, which indicates a good structural stability of Al(3)BC(3) at high temperatures and pressures. The Raman active phonon modes were assigned comprehensively to the corresponding vibration modes by first-principles calculations. Interestingly, an abnormal softening of the E(1g)(559 cm(-1)) and E(2g)(578 cm(-1)) phonon modes were observed when the pressure was higher than 27 GPa. Correlating the results with previous theoretical predictions of polymorphism in Al(3)BC(3), the mode softening at higher pressures might originate from the structural transformation (from hexagonal to tetragonal symmetry) involving changes of Al and C coordination numbers. In addition, the phonon anharmonicity has been investigated by studying the temperature and pressure dependence of the Raman peak shifts and broadenings. Finally, the present work has highlighted that in situ Raman spectrometry study is a sensitive method for investigating the structural stability and phonon anharmonicity of complex ceramics. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3665197]
关键词:
boron-carbide;mechanical-properties;thermal-expansion;optical;phonons;dependence;aluminum;1st-principles;calibration;composites;crystal
王军朋
,
李凤
,
敖靖
,
焦丽娜
,
李春梅
,
陈志谦
无机材料学报
doi:10.15541/jim20140463
采用第一性原理计算研究了超硬材料z-BC2N的弹性各向异性性质、应力-应变关系、硬度及最小热导率性质.计算得到的晶体力学行为判据 B/G 为 0.87, 泊松比为 0.084, 普适弹性各向异性指数为 0.09992.[100]晶向上最大拉伸强度达到180 GPa,(100)[010]应变方向上最大剪切强度达到160 GPa,维氏硬度值为77.07 GPa.基于Cahill模型得到的最小热导率为6.811 W/(m·K).结果表明: z-BC2N是脆性材料且力学稳定性良好,有非常高的拉伸强度、剪切强度, 体弹模量为各向同性, 杨氏模量各向异性程度不大.z-BC2N 的最小热导率低于金刚石的最小热导率.
关键词:
超硬材料
,
弹性性质
,
各向异性
,
热导率
靳增雪
,
陈志强
,
张苏雅拉吐
,
刘建立
,
韩瑞
,
刘星泉
,
林炜平
,
任培培
,
贾宝路
,
石福栋
原子核物理评论
doi:10.11804/NuclPhysRev.31.04.494
研究了对BC501A液体闪烁体对γ射线的光输出响应特性。实验上利用γ放射源(60Co，137 Cs)测量了不同光电倍增管高压下，尺寸为Φ5.08 cm ×5.08 cm的BC501A液体闪烁体探测器的脉冲幅度谱。利用Geant4软件进行模拟，计算结果与实验数据很好地符合，得到了能量分辨函数及能量刻度曲线。利用Geant4研究了BC501A的脉冲幅度谱的康普顿边缘Ec、康普顿峰Emax及康普顿半高点E1/2与能量分辨率的关系。同时模拟结果显示，随γ射线能量(0.2～3 MeV)的增加，康普顿边缘位置Nc/Nmax从0.8至0.7线性减少。
关键词:
BC501A
,
光输出响应
,
Geant4
,
能量分辨函数
,
康普顿边缘
