Structural, Mechanical, and Reactivity Properties of Tricalcium Aluminate Using First-Principles Calculations

Although tricalcium aluminate (C₃A) is one of the most important components of Portland cement, neither its reactivity nor its elastic moduli tensor have been fully determined yet. This work aims to shed some insights on these questions by means of ab-initio simulations. First our simulations have reproduced the details of its crystalline structure. Second, we have computed the full elastic moduli tensor of C₃A, where we found that our value for the Young modulus ( E =138.7 GPa) is in agreement with the values obtained by nanoindentation measurements. Finally, we have identified which atoms and sites are more suitable to suffer chemical attacks.     

First-Principles Investigation on Electronic Transport Properties of Tungsten Nitride Nanoribbon Based Molecular Device

The electronic transport property of tungsten nitride nanoribbon-based molecular device is investigated using density functional theory. The study on electronic transport properties are discussed in terms of device density of states and transmission spectrum of the nanoribbon. The scattering region of the nanoribbon is placed between the electrodes. For different bias voltages, the transport properties are studied. The contribution due to various orbitals leads to the peak maximum in device density of states. The transmission spectrum and transmission pathway provides insight to the transmission of charge under various bias conditions. The maximum peak in the transmission spectrum corresponds to the variation in transmission of charge with different bias voltage. The reported results will pave the way to improve the performance in the field of nanoelectronics.     

Investigation of Structural,Morphological, Mechanical,Thermal and Optical Properties of PVA-ZnO Nanocomposites

Glass Physics and Chemistry - In recent years, the production of composite films has been gained importance and composites consist of organic and nonorganic parts has been attracted particular...     

Structural and Thermo-Physical Properties of 3C-SiC: High-Temperature and High-Pressure Effects

Silicon - Based on the density functional theory (DFT), a systematic theoretical investigation on the structural parameters and finite temperature thermo-physical properties of cubic silicon...     

Structural and Mechanical Properties of Nanoporous Silica

Nanoporous silica systems with porosity between 30% and 70% were developed using two Molecular Dynamics (MD) simulation protocols to obtain structures with dissimilar pore morphologies. Short‐ and medium‐range structural characteristics including bond angle distributions and pair distribution functions were analyzed and found to be consistent with experimental results. Surface area to volume ratio and pore microstructures were characterized and compared with experimental observations. Mechanical properties including elastic, shear, and bulk moduli of these nanoporous silica systems were calculated and their change as a function of porosity was compared with experimental data and theoretical models. It was found that the elastic modulus of porous silica with 50% porosity is 5–14 GPa which is consistent with experimental results. The elastic moduli–porosity relationship was fitted by exponential and power functions, and analysis of coefficients was performed to obtain microstructure characteristics of the simulated nanoporous silica structures. This works confirms that two distinct nanoporous silica microstructures are generated with MD simulations which result in variations in mechanical properties and highlight the importance of selecting a nanoporous silica simulation method which approximates experimental systems.     

First-Principles Calculation of Electronic, Optical, and Structural Properties of α-Al2O3

The electronic structure, the linear optical properties, and the structural properties of α-Al₂O₃ in the corundum structure are studied by means of first-principles local density calculations. An indirect band gap of 6.29 eV is obtained, which is almost the same as the direct band gap of 6.31 eV at Γ. The calculated density of states are compared with X-ray photoemission and photoabsorption measurements. Real space charge density analysis shows Al,₂O₃ to be highly ionic with an effective charge formula of Al₂^+2.75O₃^−1.83. The calculated dielectric function is in general agreement with the experimental vacuum ultraviolet data. It is shown that the component with c-direction polarization is in better agreement with the experimental data because it is less affected by the exciton formation near the absorption edge. The intrinsic difference between the calculated local density approximation gap and the measured optical gap is pointed out. Various careful test calculations indicate that the remaining discrepancy in the optical spectra may be in the LDA approximation of the electronic structure theory. The total energy calculation for the ground-state structural properties of α-Al₂O₃ shows excellent agreement with experimental data: the calculated equilibrium volume, c/a ratio, bulk modulus, and internal parameters for Al and O atoms differ from measured values by 0.0, −4.3, −4.0,0.85, and 1.96 percent, respectively. The calculations for the electronic structure and the optical properties are repeated with crystal parameters obtained at 2000°C. The result shows only a slight reduction in the band gap (to 5.76 eV at Γ), with the optical spectra essentially unchanged.     

HDPE/木粉复合材料性能的研究

本文以高密度聚乙烯(HDPE)和木粉为原料,通过同向旋转双螺杆挤出机,制备HDPE/木粉复合材料。研究了木粉含量和螺杆结构对HDPE/木粉复合材料流变-形态-性能的影响。结果表明:木粉含量的增加增大了复合材料的储能模量和复数黏度,降低了冲击强度,而厚度大和错列角大的捏合块元件的加入有助于降低复合材料的储能模量和复数黏度,增加冲击强度。     

Investigation of SiC-AlN: Part II, Mechanical Properties

SiC/AIN composites with controlled interfacial solid solution were employed in the present work for investigating the effects of interfacial bonding and A1N polytypes on the mechanical properties. Platelike A1N polytypes and interfacial bonding were found to have substantial effects on the flexural strength, hardness, and fracture toughness.     

Theoretical Investigations on the Structural,Electronic, Mechanical,and Thermal Properties of MP2O7 (M = Ti,Hf)

A systematical ab initio analysis on MP₂O₇ (M = Ti, Hf) is presented in this work. Density functional theory (DFT) computations were performed for the electronic, mechanical, and thermal properties of MP₂O₇. Heterogeneous bonding nature of MP₂O₇ was revealed by examining the structural and electronic properties, M–O bonds were weaker than P–O bonds. The elastic constants and polycrystalline mechanical properties of MP₂O₇ were reported. Based on the low shear‐modulus‐to‐bulk‐modulus ratios and positive Cauchy pressure, MP₂O₇ ceramics were predicted to be “quasi‐ductile”. In addition, the minimum thermal conductivities were estimated to be 1.52 and 0.99 W·m^?1·K^?1 for TiP₂O₇ and HfP₂O₇, respectively. The ultra‐low thermal conductivities were contributed to the lattice phonon scattering due to the heterogeneous bonding nature. Our theoretical results emphasize the importance of weak M–O bonds in the determination of mechanical and thermal properties of MP₂O₇.     

Flame-Retardant,Thermal, Mechanical and Dielectric Properties of Structural Non-Halogenated Epoxy Resin Composites

First, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and epoxy resin (E-51) were employed to synthesize a structural non-halogenated epoxy resin (ED). And a novelphenolic aldehyde curing agent, 2,4,6-tri (phenol-methylene-amide)-triazine (MFP) was also synthesized for preparing high-performance MFP/ED composites. Results showed that, the flame-retardant and thermal stabilities of the composites were improved with the increasing phosphorus content. When the content of phosphorus was 3wt%, the initial decomposing temperature of the composite was over 325°C, and the charring rate was 30.3% at 650°C, could meet the requirements of UL 94-V0 rating. However, all the flexural and impact, dielectric constant and loss and the glass transition temperature (Tg) of the composites were decreased with the increasing phosphorus content.     

CdGeAs2晶体的结构、弹性和电子性能的模拟计算和分析

利用基于密度泛函理论的平面波赝势法对CdGeAs2晶体的结构,弹性和电子性能进行了研究.CdCeAs2晶体具有6个独立的弹性常数,利用计算的弹性性能可以判断晶体具有机械稳定性、延性和弹性各向异性等力学特点.通过总的和部分态密度分析了不同能带的贡献成分.计算的结构参数及弹性常数与实验值基本吻合.CdGeAs2晶体具有直接...     

熔体旋甩法制备Sr_8Ga_（16）Ge_（30）笼合物的微结构及热电性能

将熔体旋甩法（MS）用于制备Ⅰ-型Sr8Ga16Ge30笼合物,研究了MS对Sr8Ga16Ge30笼合物微结构及热电性能的影响。结果表明,MS得到的Sr8Ga16Ge30薄带自由面晶粒尺寸随冷却速率的增加而减小,接触面未有明显结晶现象。薄带经SPS烧结得到的致密块体结构中存在大量精细的层状结构。与熔融＋SPS制备的试样相比,熔融＋MS＋SPS制备的Sr8Ga16Ge30试样的电导率变化不大,Seebeck系数增加,热导率显著降低,其中铜辊转速为4 000 r/min的Sr8Ga16Ge30试样的ZT值在800 K达到0.74,相对于熔融＋SPS试样提高了45%。     

Effect of Si on Phase Equilibria,Mechanical Properties and Tribological Behaviour of Al-Cu Alloy

Silicon - In the current work, novel Al-rich Al90-XCu10Six (x = 2.5 at%, 5 at%, 7.5 at%) ternary alloys were used to evaluate the effect of Si on Al-Cu alloy in an effort to design and...     

Study of Structural and Mechanical Properties of Mineral Fertilizer Granules

Theoretical Foundations of Chemical Engineering - The results of a study of the structural–mechanical properties of granules of various types of mineral fertilizers prepared on the basis of...     

PVC/NE复合材料的结构流变学及力学性能

采用熔融共混法制备了聚氯乙烯/霞石复合材料(PVC/NE),并测试了其形态、结构流变学和力学性能。结果表明,NE用量存在最佳值,用量过多对复合材料介观结构的贡献不大;NE均匀分散在PVC基体中,且用量约为50phr时,复合材料的冲击强度和表面硬度最佳。     

Modeling the Electronic,Structural and Vibrational Properties of Cubic SiC Nanocrystals Built from Diamondoid Structures

Silicon carbide diamondoids are used as building blocks of cubic SiC nanocrystals. Density functional theory (DFT) at the generalized gradient approximation level of Perdew, Burke and Ernzerhof (PBE) with 6-31G(d) basis is used to investigate the electronic structure of these diamondoids up to 12 cages. The results show that the energy gap and bond lengths generally decrease with shape fluctuations as the number of atoms increases. Electronic and structural properties are in good agreement with both previous experimental and theoretical results. Vibrational modes converge to the SiC experimental bulk limit of the radial breathing mode while hydrogen related modes are nearly constant in their frequencies. It is suggested in this work to identify SiC-diamondoids from their hydrogen vibrational modes finger print in the range (1000-3000 cm^?1) and identify the size of the diamondoid from low frequency vibrational modes (0-1000 cm^?1) such as radial breathing modes.     

Molten Salt Synthesis,Polymorphism, and Microwave Dielectric Properties of Ba8NiTa6O24 Perovskite

Molten salt synthesis (MSS) of the eight‐layer hexagonal perovskite Ba₈NiTa₆O₂₄ was performed using mixed KCl–NaCl salts in comparison with solid‐state synthesis (SSS). In the SSS, the hexagonal Ba₈NiTa₆O₂₄ formed at 1300°C via a reaction between cubic Ba₃NiTa₂O₉ and hexagonal Ba₅Ta₄O₁₅. While the MSS did not lower the synthesis temperature of the hexagonal Ba₈NiTa₆O₂₄ but stabilized an unusual A‐ and B‐site‐deficient cubic perovskite polymorph of Ba₈NiTa₆O₂₄ below 1350°C as an intermediate phase prior to transforming into the hexagonal phase. This cubic polymorph contains ~3% A‐site and ~9.5% B‐site vacancies plus ~3% Ba cations in the B sites and demonstrated remarkable stability below 1350°C when without presence of the molten salt. The cubic polymorph displayed larger ε ~ 36 and τ_f ~ 110 ppm/°C than the hexagonal polymorph from the MSS (ε ~ 29 and τ_f ~ 67 ppm/°C). The hexagonal SSS‐processed ceramics showed advantageous dielectric properties (Q_f ~ 52 000 GHz, τ_f ~ 30 ppm/°C) over both cubic and hexagonal MSS‐processed ones (Q_f ~ 18 600–20 000 GHz), while displaying anisotropic grain growth. The anisotropic grain growth was suppressed significantly by the MSS processing.     

Preparation,structural and microstructural properties of Ba0.64Ca0.32Al2Si2O8 ceramics phase

Monoclinic celsian has been prepared from Ba-LTA zeolite precursor. The Ca²⁺-exchanged hexacelsian (HC_Ca) synthesized from Ba-LTA zeolite precursors was used for preparation of monoclinic celsian (MC_Ca). The partially ion exchange diphyllosilicate has a composition of Ba_0.64Ca_0.32Al₂Si₂O₈ (HC_Ca). It was found that prepared HC_Ca phase is stable between room temperature and 1300 °C. During prolonged heating this phase is polymorphic transformed to Ba, Ca-celsian feldspar. Synthesis of Ba, Ca-celsian and thermal behavior during transformation processes was observed by XRD method. The crystal structure and microstructural parameters were refined using Rietveld method. The crystal morphology of thermal treated samples was observed by SEM/EDAX analysis.     

Mechanical,Structural and Microstructural Properties of CFB Desulfurization Slag and Silico-Manganese Slag Based-Geopolymer Pastes

Silicon - Circulating fluidized bed desulfurization slag (CDS) and silico-manganese slag (SiMnS) are two kinds of industrial solid wastes. They both have rich Al2O3 and SiO2. In this paper, the...     

高聚物黏结炸药的力学性能研究进展

从材料的力学行为特性、实验方法、本构模型和强度理论4个方面对高聚物黏结炸药(PBX)的力学性能特征进行了归纳和评述。指出应变率和温度对材料应力状况的影响及动态力学性能分析是目前PBX研究的热点和难点。认为可以借鉴研究混凝土和高聚物的一些方法来建立PBX的本构模型和失效准则。指出选择和改进现有测试技术时,须考虑PBX的含能敏感性、大变形等特性。对PBX力学性能的理论研究、实验技术及数值模拟等方面需要开展的工作提出了一些看法。认为复杂环境下的力学响应和细观建模模拟应是今后研究的重点方向。附参考文献93篇。