水热合成法制备微纳米MnO_2晶体不同形貌的电磁特性

本文采用水热合成法,以(NH4)2S2O8作氧化剂,以MnSO4为锰源,在不同水热反应时间下制备了不同晶体结构和形貌的二氧化锰。利用X射线粉末衍射(XRD),扫描电子显微镜(SEM)和透射电子显微镜(TEM)对产物进行成分、晶型和形貌进行分析,并通过电磁参数的测试对产物的电磁特性以及电磁波损耗机制进行讨论。结果表明,水热反应时间由1h逐渐增加到48h后,二氧化锰晶体结构由纯γ型逐渐转变为纯β型,中间产物为γ、α和β的混合体,二氧化锰的形貌也由球状经团絮状后逐渐转变为直径约为5-10nm纳米线状。复介电常数随反应时间增加而增加,复磁导率却正好相反,由此最后分析了二氧化锰的电磁波损耗机制。     

Single crystal growth,structure and properties of TlHgBr3

High-quality inclusion-free single crystals of ternary thallium mercury bromide, TlHgBr₃, were successfully grown by Bridgman–Stockbarger method. For the pristine surface of the TlHgBr₃ single crystal, X-ray photoelectron core-level and valence-band spectra were measured. The comparison on a common energy scale of the X-ray photoelectron valence-band spectrum of TlHgBr₃ and the X-ray emission Br Kβ₂ band, representing peculiarities of the energy distribution of the Br 4p states revealed that the main contribution of the valence Br p states, occurred in the upper portion of the valence band, with also their significant contributions in other valence band regions. It has been determined that TlHgBr₃ is a semiconductor with the bandgap energy value of E_g = 2.51 eV at 100 K. The E_g value decreased up to 2.44 eV when temperature increased to 300 K.     

Growth, structural, optical, thermal and mechanical properties of glycine zinc chloride single crystal

The nonlinear optical single crystals of glycine zinc chloride were grown by the slow cooling method from aqueous solution. The title compound was synthesized and purified by repeated recrystallization process. Grown crystals were characterized by X-ray diffraction, FT-IR and FT-Raman spectral analysis. The range and percentage of optical transmission were ascertained by recording UV-Vis-NIR spectrum. Thermal properties were investigated by DTA and TGA analyses. Its second harmonic generation relative efficiency was measured by Kurtz and Perry powder technique using Nd:YAG laser and was observed to be 0.5 times that of potassium dihydrogen orthophosphate. Its mechanical hardness was estimated by Vickers microhardness method.     

Relationship between structure and mechanical properties for aramid fibres

The relationship between structure and mechanical properties for a series of twelve wellcharacterized aramid fibres has been determined. The fibres were produced under a variety of processing conditions and the fibre structure has been characterized using transmission electron microscopy. In particular, both the overall degree of molecular orientation in the fibres and the difference in structure between the fibre skin and core regions have been investigated in detail. The mechanical properties of the fibres have been evaluated using conventional mechanical testing and molecular deformation followed using Raman microscopy to monitor strain-induced band shifts. It has been shown that the mechanical properties of the fibres are controlled by the fibre structure. In particular, it is shown that the fibre modulus is governed by the overall degree of molecular orientation. It is also demonstrated that the fibre strength is controlled principally by the overall molecular orientation but may also be reduced by the presence of a highly-oriented skin region. It has been found that the rate of shift of the Raman bands per unit strain is proportional to the fibre modulus except for fibres with large differences in molecular orientation between fibre skin and core regions. For these fibres the rate of shift reflects the higher orientation of the skin.     

Comparison for the crystal structure,synthesis and microwave dielectric properties of alkaline earth orthophosphates

A₃(PO₄)₂ compounds have different crystal structures when A sites are occupied by Ca or heavy alkaline earth metal atoms (Sr or Ba). The compounds with isomorphous crystal structure were synthesized by solid-state reaction method when the A-site atoms were Sr or Ba, and their crystal structure and microstructure of the sintered ceramics were investigated by X-ray powder diffraction (XRD) and scanning electron microscope (SEM), respectively. The microwave dielectric properties were measured using a network analyzer. It was found that Ba₃(PO₄)₂ could be sintered at 1060 °C, while the α-Sr₃(PO₄)₂ ceramics that has a smaller Sr²⁺ ionic radius, could be sintered at 1200 °C, and higher relative densities were obtained. The dielectric constant (?) of the α-Sr₃(PO₄)₂ is higher than that of Ba₃(PO₄)₂, but Ba₃(PO₄)₂ has a higher Q × f value than that of β-Ca₃(PO₄)₂ and α-Sr₃(PO₄)₂, which could be interpreted by the differences in ionic polarizability and bond strength. The temperature coefficients of resonant frequency (τ_f) for all samples with isomorphous crystal structure have positive values, ranging between +11 and +66 ppm °C⁻¹.     

Relationship between structure and mechanical properties in high manganese alloyed ductile iron

Abstract

Measurements of ultimate tensile strength, 0·2% proof stress, elongation, and impact energy are reported for an alloyed ductile iron containing 3·52%C, 2·64%Si, 0·67%Mn, 0·007%P, 0·013%S, 0·25%Mo, 0·25%Cu, and 0·04%Mg,for a range of austempering temperatures and times after austenitising at 920°C for 120 min. It is shown that the mechanical properties satisfy the high strength grades of the standard AST MA897 M:1990, but fail to satisfy the higher ductility grades because of poor ductility. This is attributed to overlapping of the stage I and II reactions and the occurrence of the transformation induced plasticity mechanism during deformation, particularly in irons austempered at higher temperatures.

MST/3054     

Growth, thermal and mechanical properties of new nonlinear optical barium bis-paranitrophenolate paranitrophenol tetrahydrate single crystal

Barium bis paranitrophenolate paranitrophenol tetrahydrate, a new semiorganic nonlinear optical single crystal has been grown by slow evaporation solution growth technique at room temperature of 30 °C. Crystal of dimensions of 29 mm × 11 mm × 5 mm was obtained in a period of 30 days. X-ray diffraction analysis reveal the newness of the crystal structure belonging to the orthorhombic class with lattice parameters a = 19.899(5) Å, b = 28.019(8) Å, c = 10.745(4) Å and α = β = γ = 90°. The grown crystal is examined for its nonlinear optical nature with Kurtz powder technique after being sieved for particle sizes between 5 and 100 μm and analyzed for its thermal and mechanical properties. The effective nonlinear optical coefficient being 16 times greater than that of KDP crystal, good thermal stability up to 120 °C with the Meyer's constant n < 2 helps fashion the crystal towards device geometry.     

Relationship between mechanical properties and structure in austempered alloyed compacted graphite cast iron

Abstract

Austempering kinetic measurements and mechanical property measurements are presented for a compacted graphite iron of composition Fe-3.4C-3.5Si-0.25Mn-0.50Mo-0.50Ni (wt-%) austempered at 375°C after austenitising at 890 and 940°C. Analysis of the austempering kinetics shows that alloying elements have a similar effect on the processing window as in ductile irons. The mechanical properties show optimum values at austempering times within the processing window. However, the graphite morphology limits the mechanical property enhancement achieved by austempering. Nevertheless, it is possible to double the strength of the as cast compacted graphite iron without loss in ductility.     

Relationship between microstructure and mechanical properties in Nb–V microalloyed TRIP steel

Nb–V additions clearly affected the precipitation state, respective phase transformations and final microstructure, and in turn, resulting mechanical properties of an intercritically annealed transformation induced plasticity sheet steel. As the precipitation hardening played a limited role in the overall strengthening, the grain refinement was the prevailing strengthening mechanism associated with the addition of the Nb–V microalloying to a basic TRIP780 composition. In addition to this, the microstructural changes, resulting from the addition of microalloying, lowered the stability of retained austenite, which decreased the elongation of the steel. Nevertheless, using this microalloying concept, an exceptional product of R_mxA₈₀ exceeding 16?000 MPa % could be achieved.     

A study on optical, thermal, mechanical, dielectric, piezoelectric and NLO properties of unidirectional ammonium chloride added ammonium dihydrogen phosphate crystal

<0 0 1> directed ammonium dihydrogen phosphate single crystal with the addition of 1 mol% of ammonium chloride in the mother solution has been grown by Sankaranarayanan-Ramasamy method. The grown crystal has cylindrical morphology with good optical quality. It has good thermal stability up to 200 °C. Higher mechanical stability was observed in ammonium chloride added crystal compared to pure crystal. Moreover, the addition of ammonium chloride improves the quality and yields highly transparent crystal in minimum duration of growth. Good piezoelectric behaviour was observed for the grown crystal. Low dielectric loss shows that the grown crystal contains minimum defects. The optical transmission study and the powder SHG measurement show the suitability of the ingot for nonlinear optical applications.     

Optical,mechanical and transport properties of unidirectional grown l-tartaric acid bulk single crystal for non-linear optical application

Good optical quality bulk single crystal of l-tartaric acid has been grown by directional solidification crystal growth method from aqueous solution. Crystal of dimension 77 mm length and 12 mm diameter has been grown at a growth rate of 2.5 mm day⁻¹ which is the maximum size and growth rate achieved so far. The grown crystal was confirmed by powder XRD analysis and the presence of the functional groups in the crystal lattice was confirmed by Fourier transform infrared spectral analysis. Transmission spectral analysis shows that the crystal has more than 90% of transmittance in visible and near infrared region which exhibits the good optical quality of the crystal. The optical band gap was estimated to be 4.8 eV and it shows indirect optical transition. Thermal analysis shows the crystal to be thermally stable up to 172 °C and the load variation of the hardness has been explained on the basis of normal indentation size effect from microhardness study.     

Physicochemical properties of organic nonlinear optical crystal for frequency doubling: Glycine acetamide

Non-linear optical (NLO) crystal of glycine acetamide (GA) is synthesized and grown in aqueous solution by slow evaporation technique. The cell parameters of the grown crystal are identified from single crystal XRD and the functional groups are confirmed in vibrational analysis. Temperature dependence of the material is probed using TGA/DTA. Mechanical strength of the grown material is tested by Hardness studies. UV-VIS-NIR spectral study explains the transmission ability of the crystal in visible range also the photoluminescence spectrum explains the transition mechanism of ions. The NLO activity of the crystal is confirmed by Kurtz power technique.     

Effects of precursors on the crystal structure and photoluminescence of CdS nanocrystalline

A series of cadmium sulfide (CdS) nanocrystalline were synthesized by precipitation from a mixture of aqueous solutions of cadmium salts and sulfur salts without adding any surface-termination agent. Their crystal structures and particle sizes were determined by X-ray diffraction (XRD). The CdS nanocrystalline precipitated from different precursors exhibited three cases: cubic phase, hexagonal phase and a hybrid of cubic and hexagonal phases. The photoluminescence (PL) of cadmium salt precursors and CdS nanocrystalline is also analyzed. Similar spectral band structure of cadmium salt precursors and CdS nanocrystalline is found. The PL of 3.4, 2.4 and 2.0 nm sized CdS nanocrystalline with the same crystal structure indicated quantum confinement effect.     

Crystalline structure and magnetic and magneto-optical properties of MnSbBi thin films

Mn–Sb–Bi thin films were prepared by successive r.f. or d.c. sputter deposition of elements in a trilayer configuration with either Bi or Sb as the first layer. In-situ transmission electron microscopy (TEM) observations were conducted to investigate the morphology and structure of the films, both as-deposited and after annealing at 623 K for 5 h in a high vacuum furnace. The morphology and structure of all the films are highly dependent on the first-deposited layer. For the annealed film in the configuration of Mn/Bi/Sb// a well-defined hexagonal Mn–Sb–Bi NiAs type structure with the c-axis perpendicular to the film surface was observed. The grain size (100 nm) was two times larger than that of the film having Bi as the first layer. In both kinds of film the easy direction of magnetisation was very close to the film plane. The polar Kerr rotation from the two film structures was approximately 1.0°.     

Carbon fibres: structure and mechanical properties

The microstructure of six types of acrylic-based and hydrated cellulose-based carbon fibres of strengths from 1650 to 6120 MPa and elastic moduli from 97 to 228 GPa were studied by scanning electron microscopy (SEM). A ‘microcomposite’ structure of carbon fibres studied consisting of quasi-amorphous (‘matrix’) and orientated fibrillar carbon was revealed. This led to a new model of the fibre structure. The analysis of results of testing different carbon fibres defines the elastic modulus of ‘matrix’ carbon, and shows plastic drawing of fibrils. The model describes the properties of fibres and predicts ways to improve the fibre properties.     

Relationship between morphology and mechanical properties of tobacco leaf lamina

To optimize processing parameters, a study was done of the overall mechanical properties of tobacco leaf lamina. Stress-strain tests were performed to determine modulus, yield strength, and toughness (energy to break) of the lamina when deformed under tension and simple shear loads. The cellular morphology of the lamina was obtained by using scanning electron microscopy. Microscopic observation of deformed samples showed an uneven stress distribution and anisotropy. The macroscale phenomenological results indicated a harmony in its mechanical behaviour. Lamina isotropy and homogeneity in the plane of a leaf were determined by testing samples taken from different orientation and locations. Bright and burley tobacco were studied. The relationship between tension and shear properties was also obtained. Both in shear and tension, the lamina became softer with an increase in load. The stress-strain behaviour was characterized by a two-parameter power law equation. Statistically estimated results, obtained from several leaves, did not indicate any significant effect of sample location and orientation. Tobacco lamina appeared softer but tougher in shear than tension. It also showed sensitivity to the rate of deformation, indicating the viscoelastic nature of its behaviour. Material yield during manufacturing related well with mechanical properties. Burley lamina was stiffer and broke at lower strain than bright lamina. Thus, even though at the microlevel, tobacco lamina, is heterogeneous and anisotropic, at the macrolevel it displays homogeneous and uniform mechanical properties.     

草鱼鳞片的多级结构及力学性能

经过长时间的自然进化,硬骨鱼鳞片变得超薄、超轻,并具有很好的柔韧性。为研制新型柔性防护体系,对草鱼鳞片的多级结构及力学性能进行了研究。首先,按3个不同方向(0°、45°和90°)在鳞片中心区域裁取鳞片和胶原层2组试样;然后,进行了轴向拉伸测试并对不同含水量的鳞片以及不同应变率下鳞片和胶原层的力学性能进行了对比研究。结果显示:草鱼鳞片主要由坚硬的骨质外层和软质的胶原层组成,其中胶原层由胶原纤维层交错叠加组成,交错角约为28°~31°;鳞片的力学性能为平面内各向异性,而胶原层的力学性能为各向同性;脱水鳞片的弹性模量和拉伸强度显著增加,分别约为饱水鳞片的10倍和3倍,但极限应变减少了约50%。饱水鳞片和胶原层的力学性能与应变率有很大相关性。所得结论为新型仿生复合材料及柔性防护体系的研究提供了思路。      

多面体低聚倍半硅氧烷晶粒诱导的聚乳酸结晶行为及性能

通过溶液及熔融两步共混方法,用带有环氧基的多面体低聚倍半硅氧烷(EVOS)对聚乳酸(PLA)进行改性,并对复合材料的力学性能、结晶性能和相态等方面进行了表征。实验结果表明,随着EVOS的加入,PLA冷结晶温度降低,结晶和熔融温度变化不大,结晶热和熔融热下降。1%的EVOS在PLA中实现了纳米尺度的分散,随着EVOS含量增加,球晶尺寸明显增加。当EVOS的添加量为5%时,材料的拉伸强度比纯PLA增加26.2%,达到最大值。     

天然高分子泡沫材料的复合结构与力学性能

通过扫描电子显微镜和光学显微镜研究了2 种天然高分子泡沫材料, 即玉米秆芯和高粱秆芯切面的泡孔形态结构及胞体堆砌模式。测试了材料在轴向和径向的压缩杨氏模量和压缩屈服强度等力学性能, 探讨了泡沫材料的压缩变形机制, 建立了天然泡沫材料的复合结构模型, 并分析了力学性能与复合结构的关系。研究结果表明, 这2 种天然泡沫均由一种近似六棱柱和少量圆形管状胞体构成, 它们在轴向的杨氏模量和屈服强度分别比径向的大4 倍以上。导管增强的复合结构是引起天然泡沫材料具有明显各向异性的重要原因, 其中厚壁导管的轴向杨氏模量约为不规则六棱柱胞体的105 倍。