Influence of molecular weight on the microhardness of poly(ethylene terephthalate)

 Poly(ethylene terephthalate) (PET) was annealed in vacuum at different temperatures (190–260 °C) for different times (10 min–24 h) in order to examine the mechanical properties (microhardness) of PET samples with a wide range of molecular weights (10 000–120 000). Short annealing times result in a twofold decrease in mol. wt. due to hydrolytic decomposition. However, long annealing times give rise to a substantial molecular weight increase. It is found that microhardness (H) rises linearly with the degree of crystallinity obtained during up-grading of mol. wt. and its extrapolation leads to H-values of completely crystalline PET, H ^PET _c=405 MPa for samples with conventional mol. wt. and of 426 MPa for samples with mol. wt. higher than 30 000. It is shown that the increase of mol. wt. for each set of samples with a given range of degree of crystallinity also causes a slight increase of H. The influence of mol. wt. upon hardness is discussed in the light of the changes in the physical structure (crystallinity, crystal thickness) which is formed at given heat treatment conditions. Received: 29 April 1997 Accepted: 23 September 1997     

Three-Dimensional Porous Network Structure Developed in Hydroxyapatite-Based Nanocomposites Containing Enzyme Pretreated Silk Fibroin

Chemically modified silk fibroin (SF) with an enzyme, Proteinase K, has been incorporated into hydroxyapatite (HAp)-based nanocomposite attempting to strengthen the interfacial bonding between the mineral phase and the organic matrix. Particular emphasis is laid on the microstructure and microhardness of the composite along with the crystallographic properties of HAp. The whisker-like HAp crystallites of nanometer size show the preferential self-assembly and anisotropic crystal growth along c-axis. There appears porous microstructure with 70% of open porosity and pore size distribution of 10–115 um in the composite. Attributed to the enzyme modification, the crosslinkage between HAp clusters and SF matrix is improved to form an enhanced three-dimensional network extending throughout the composites and an increase of 35% in microhardness of the composite is achieved as well.     

膜基组件微硬度量测的数值模拟

采用轴对称弹塑性有限元计算模拟了膜基组件的微硬度量测过程，得到了压头与膜体间无摩擦时组件的变形、塑性区和接触压力分布，针对Ａｌ／Ｓｉ与Ｓｉ／Ａｌ两种膜基组件得到了微硬度和压下量的关系曲线。     

Physical aging in poly(ethylene naphthalene-2,6-dicarboxylate) in relation to sorbed water,enthalpic relaxation,and mechanical properties

Amorphous poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) films (～ 220 μm thick), stored in ambient atmosphere for different periods of time and after annealing at different temperatures below T_g = 123°C, for different times, have been investigated by infrared spectroscopy (FTIR), microhardness, and differential scanning calorimetry (DSC). FTIR spectroscopy and weight measurements reveal the presence of water which is easily removed by annealing of the films. Films again recover their initial weight and absorption bands after 1-2 days storage in ambient atmosphere. Samples annealed at different temperatures T_a for different times t_a show an increasing microhardness for relatively short times of t_a. The microhardness passes through a maximum at an annealing time depending on T_a, and it decreases toward values somewhat larger than the initial ones. The changes observed in the microhardness and in the values of the excess enthalpy with storage time of the samples at room temperature depend on the physical aging as well as on the content of water of PEN films. © 1995 John Wiley & Sons, Inc.     

Phase transformation behavior of the SMA490BW weathering steel

In order to optimize the heat treatment schedule and the welding procedure of the SMA490BW weathering steel, a precise determination of the continuous cooling transformation and simulated heat affected zone continuous cooling transforming diagrams were carried out. Meanwhile, the hardnesses of the specimens with different cooling rates were measured and the microstructures were observed. The microstructures are composed of pearlite, polygonal ferrite, granular structure, acicular ferrite, and lath bainite depending on the cooling rates and transformation temperature. The experiment results provide a useful guide for the heat treatment and welding of this steel.     

深过冷条件下Co_7Mo_6金属间化合物的枝晶生长和维氏硬度研究

采用电磁悬浮和自由落体两种实验技术对二元Co-50%Mo过共晶合金中初生Co_7Mo_6金属间化合物的生长机理和维氏硬度进行了系统研究.电磁悬浮实验中,合金熔体获得的最大过冷度为203 K(0.12T_L),初生Co_7Mo_6枝晶生长速度与过冷度之间呈现幂函数关系.随着过冷度的增大,初生枝晶中Co元素含量单调递增,枝晶尺寸明显减小,并且其维氏硬度逐渐升高.在自由落体状态下,随着液滴直径的减小,合金熔体的过冷度和冷却速率均增大.当液滴直径减小到392μm以下时,初生Co_7Mo_6枝晶从小平面向非小平面形态进行转变.实验发现,深过冷条件下Co_7Mo_6化合物发生了显著的溶质截留效应,其维氏硬度与Co元素分布和形貌特征密切相关.     

Crystal growth,optical, mechanical and electrical properties of organic NLO material γ‐glycine

Single crystals of organic non‐linear optical material, γ‐glycine have been grown by gel method for the first time. The γ‐phase is confirmed by single crystal XRD. The presence of various functional groups of γ‐glycine are confirmed by FTIR. The UV‐Vis‐NIR spectrum reveals the high percentage of transmission of the sample in the entire visible region. The SHG of γ‐glycine is confirmed by Kurtz powder technique. TGA‐DTA studies indicate that the crystal is structurally stable upto 170 °C. Microhardness investigations are conducted on the grown crystals. The dielectric constant measurements are carried out and the nature of variation of dielectric constant ε′ and dielectric loss D in the frequency range of 50 Hz to 5 MHz is studied and reported. Photoconductivity studies of γ‐glycine crystals revealed the negative photoconducting nature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and mechanical properties of KН2PО4 single crystals with embedded nanoparticles and organic molecules

Single crystals of KDP crystals with embedded Urea molecules and TiO₂ nanoparticles have been grown from aqueous solution by the temperature lowering method. The effect of the organic molecules and nanoparticles on the structural and mechanical properties has been studied. It has been observed that addition of Urea molecules improves laser induced damage threshold and mechanical strength of the crystal, while TiO₂ nanoparticles have the opposite effect. The structure and composition of KDP:Urea crystal are studied by three‐crystal X‐ray diffraction analysis, which reveals the existence of a correlation between the increase of the microhardness value and the change of the crystal lattice parameter. The surface features of KDP:TiO₂ crystals are analyzed by scanning electron microscopy that reveals the presence of quasi‐equidistant growth bands caused by capture of the nanoparticles. It is shown that the rise of TiO₂ nanoparticles concentration up to 10⁻⁴ wt.% and higher resulted in 3‐fold reduction of the laser damage threshold of KDP:TiO₂ relative to pure KDP in [001] and [100] crystallographic directions. It is found that microhardness and fracture toughness decrease at the nanoparticles concentration of 10⁻³ wt.% due to crack formation at crystal lattice discontinuities. The grown crystals also have been subjected to dielectric studies.     

Comparison of physical properties of pure and doped new metal organic crystal Bisthiourea sodium nitrate (BTSN)

Single crystals of pure and Na⁺ doped Bisthiourea Sodium Nitrate (BTSN), semi organic crystal were grown by slow evaporation technique. The grown crystals were subjected to various studies such as single crystal X-ray diffraction (XRD), UV–vis studies, Fourier transform infrared (FTIR), TG–DTA, and Vickers's microhardness were also measured. Single crystal X-ray diffraction studies reveal the crystals belong to orthorhombic crystallographic system. The mechanical property of the grown crystal was determined by microhardness studies.     

Electronic structure and Mn<Emphasis Type="Italic">K</Emphasis> absorption spectra of MnO clusters in nanocomposites

The products of the thermobaric treatment (P = 1–4 GPa, T = 2000°C) of the ultrafine powder Re_0.67Rh_0.33 (crystallite size 50 Å) were studied. For one of the products, the (Vickers) microhardness is 1200 kg/mm², which is significantly higher than the literature values for alloys in the Re-Rh system. This effect is attributed to the formation of a binary carbide with an anti-NiAs type of structure.