冷却速率对Cu49Hf42Al9金属玻璃热膨胀的影响

研究冷却速率对Cu49Hf42Al9金属玻璃热膨胀行为的影响.为了得到较大范围的冷却速率,制备了5种不同尺寸的非晶样品(冷却速率范围为102107 K/S).淬火态样品的平均热膨胀系数(αaver)分布于6.14×10-6 K-1至9.20×10-6 K-1之间.在玻璃转变温度(Tg以下时,淬火态样品的平均热膨胀系数(...     

A study of the fluorescence spectra and dielectric properties of HDPE + x vol % TlGaSe2 composites

The results of studying the fluorescence spectra of HDPE + x vol % TlGaSe₂ (x = 0, 1, 5, 10, and 20) composite materials in the wavelength range of 400–600 nm are described. The fluorescence effect is revealed, and the wavelength-dependent qualitative relationship between the composition and the fluorescence spectrum of the composite is found. The temperature dependences of the dielectric permeability and the dielectric loss tangent of the HDPE + x vol % TlGaSe₂ (x = 0, 1, 3, 5, 7, and 10) composites in the temperature range of 300–500 K are studied.     

The Effect of Copper Addition on the Fluidity and Viscosity of an Al-Mg-Si Alloy

This study was undertaken to investigate the effect of Cu addition on the fluidity and viscosity of Al-%15Mg₂Si in-situ metal matrix composite. The flowability of the composites was studied by measuring strip fluidity, cast in a permanent mold. The effect of casting parameters such as casting and mold temperatures on fluidity was studied. After obtaining an optimum condition for casting and mold temperatures, the effect of Cu addition on the fluidity and viscosity was studied. DSC thermal analysis was applied for studying the effect of Cu on solidification characteristics. Also, composites were characterized by optical and scanning electron microscopy (SEM). The results showed that casting fluidity of composites increases with the increase of mold and melt temperatures, but decreases with increase of Cu addition. Similarly, the viscosity of composites was increased by adding Cu content. The main effect of Cu was on the solidification mode.     

Enhancement of the thermoelectric properties of directionally grown Bi–Ca–Co–O through Pb for Bi substitution

Thermoelectric performances on cobaltite ceramics can be changed by doping followed by grain orientation methods. This can be performed by the Laser Floating Zone (LFZ) method on samples with different substitutions in the Rock Salt sublattice. In this work, Bi_2?xPb_xCa₂Co_1.7O_y (x = 0.0, 0.2, 0.4 and 0.6) ceramics have been directionally grown at 30 mm/h. In all the cases, samples show a microstructure composed, mainly, of alternated grains of the thermoelectrical phase and the solid solution Bi(Pb)–Ca–O, with small CoO inclusions. It has been found an important improvement on the resistivity and thermopower for samples with 0.4 Pb substitution, leading to power factor values higher than usual in misfit cobaltites obtained by conventional solid state routes.     

Polyvinyl alcohol-collagen-hydroxyapatite biocomposite nanofibrous scaffold: Mimicking the key features of natural bone at the nanoscale level

Polyvinyl alcohol (PVA) nanofibers, PVA/Type I Collagen (Col) and their composites with hydroxyapatite nanoparticles (nano-HAp) were prepared by electrospinning techniques. The composite nanofibrous membranes were subjected to detailed analysis. Morphological investigations show that the generated nanofibers (NFs) have uniform morphology with an average diameter of ∼160 nm for pure PVA, ∼176 nm for PVA/n-HAp, ∼245 nm for PVA/Col and ∼320 nm for PVA/Col/n-HAp. It is of interest to observe that large numbers of HAp nanorods are preferentially oriented parallel to the longitudinal direction of the electrospun PVA and/or PVA/Col NFs. FTIR and thermal analysis demonstrated that there was strong intermolecular hydrogen bonding between the molecules of PVA/Col/n-HAp. Furthermore, the obtained PVA/Col/nHAp NFs scaffold (7 cm × 11 cm) has a porous structure with adjustable pore size and shape. The pore size is in the range of 650 μm with a porosity of 49.5%. On the other hand, mechanical characterizations revealed that the incorporating of 5 wt% n-HAp into the matrix of PVA/Col nanofibers could significantly improve the rigidity of the resultant biocomposite nanofibrous scaffold. These results strongly suggest a huge potential of the prepared scaffold for bone tissue engineering.     

Sintering and conductivity of Sc-doped CaZrO3 with Fe2O3 as a sintering aid

This paper reports the effect of 0.1–0.5 wt% Fe₂O₃ addition on sintering and electrical properties of CaZr_0.95Sc_0.05O_3-δ ceramics synthesized by combustion method. Addition of the sintering aid was shown to enhance ceramic densification and grain coarsening at a reduced sintering temperature and a shorter holding time (1430 °C, 2 h). Effect of the sintering aid on electrical conductivity of the ceramics was investigated using impedance spectroscopy. The highest total conductivity was achieved for the composition with 0.5 wt% Fe₂O₃; it was about an order of magnitude higher than that of the composition without Fe₂O₃. The effect of Fe₂O₃ addition on the conductivity of the grain interior and grain boundaries has been discussed. It was concluded that ceramic densification, grain coarsening and formation of small amounts of calcium ferrite at the grain boundaries upon Fe₂O₃ addition were responsible for the conductivity enhancement.     

铝合金点焊过程振动信号频谱分析

频谱分析是试验数据处理的重要方法之一。通过对铝合金点焊过程中电极振动信号的频谱分析，提取振动信号中的特征量，来判断点焊过程中熔核形成及飞溅发生。试验证明，利用振动信号的频谱分析能够有效地对铝合金点焊过程进行监控，是提高铝合金点焊质量的一种有效方法。     

Chromium combustion in nitrogen

Results of investigation of chromium combustion in nitrogen are presented. It is shown that the combustion proceeds in the solid state. In the combustion wave, chromium reacts with nitrogen in steps. The first step—the formation of Cr₂N—proceeds in the separation regime. The maximum combustion temperature is limited by the temperature of dissociation of CrN. Afterburning is observed behind the combustion front. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 5, pp. 40–45, September–October 1999.     

MAGMA-PROGNOZ system for evaluation and prediction of the state parameters of rotary furnaces for manufacturing magnesite powder

A MAGMA-PROGNOZ system created for rotary furnaces of the Magnezit Works JSC is considered. MAGMA-PROGNOZ makes a continuous prediction of the behavior of some very important measurable and nonmeasurable variables for a specified time interval in current and optimum control. MAGMA-PROGNOZ interacts with the MAIS and MAGMA systems created earlier in the furnaces.