Structural dependence of microwave dielectric properties of spinel structured Mg2(Ti1-xSnx)O4 solid solutions: Crystal structure refinement,Raman spectra study and complex chemical bond theory

Mg₂(Ti_1-xSn_x)O₄ (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg₂(Ti_1-xSn_x)O₄ average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg₂(Ti_1-xSn_x)O₄ compounds were obtained (${\epsilon }_r$= 12.18, $Q\times f$?=?170,130?GHz, ${\tau }_f$?=??53.1?ppm/°C, x?=?0.2).     

Optimised phase compositions and improved microwave dielectric properties based on calcium tin silicates

The Ca_(1+2y)Sn_(1-x)Si_(1+y)O_(5-2x+4y) low-permittivity microwave dielectric ceramics were prepared through solid-state reaction at 1350–1450 °C for 5 h. The relations between microwave dielectric properties and phase compositions for non-stoichiometric Ca_(1+2y)Sn_(1-x)Si_(1+y)O_(5-2x+4y) ceramics have been investigated. A single CaSnSiO₅ phase with abnormally positive temperature coefficient of resonant frequency (τ_f = + 62.5 ppm/°C) was synthesised at 1450 °C. This composition was an effective τ_f compensator of CaSiO₃ and Ca₃SnSi₂O₉ phases with typically negative τ_f value. The CaSiO₃ second phase was related to the Sn deficiency in the CaSn_(1-x)SiO_(5-2x) (0 < x < 1.0) composition, whereas the Ca₃SnSi₂O₉ second phase was obtained by controlling the Ca:Sn:Si ratios on the basis of the Ca_(1+2y)SnSi_(1+y)O_(5+4y) (0 < y < 1.0) composition. A promising low-permittivity millimetre-wave ceramic with most excellent microwave dielectric properties (ε_r = 10.2, Q×f = 81,000 GHz and τ_f = −4.8 ppm/°C) was produced from the Ca_(1+2y)SnSi_(1+y)O_(5+4y) (y = 0.4) ceramic.     

Sol-Gel Preparation and Luminescence Properties of BaMgAl10O17∶Eu2+ Phosphors

The synthesis of BaMgAl10O17∶ Eu2 (BAM) phosphors using the sol-gel method and their luminescence properties were reported. The blue-light emitting BAM was synthesized using citric acid and ethylene glycol as chelating materials. Emission of blue-light was obtained from these phosphors. The luminescent intensity increases as the temperature of heat treatment is increased. This study investigated the effects of the molar ratio of ethylene glycol to citric acid (Φ value), with respect to the phase formation and luminescence properties of BAM. The variation of the Φ value resulted in the change of the sol-gel reaction mechanism and the microstructures of the resultant powders. An increase in Φ value leads to an increase in the rate of BAM phase formation. The photoluminescent intensity of the prepared phosphors increases with heating temperatures because of enhanced crystallization.     

Effects of Rare Earths on Toughness of 31Mn2SiRE Wear-Resistance Cast Steel

The toughness of 31Mn2SiRE wear-resistance cast steel were increased by means of RE compound modification and high temperature austenitizing. The results show that the microstructures can be refined, needle and network ferrite are eliminated, the dislocation density and the quantity of dislocated martensite are increased remarkably, and the shape and distribution of inclusions are improved by the addition of RE. Therefore, the mechanical properties of the modified steel can be greatly increased, especially the toughness (αK) by 44%, yield strength (σs) by 10%, and elongation (δ5) by 42%.     

强捻棉纱针织产品的性能研究

通过对强捻棉纱针织产品进行服用性能测试，得出强捻纱织物具有良好的服用性能。     

基于压电陶瓷动态信息的结构裂纹识别方法

利用压电陶瓷的动态特性和压电系统的动态信息,对铝梁的裂纹损伤进行了分析研究。随着梁裂纹尺寸的增加,压电陶瓷片的导钠幅值下降,且系统固有频率减小。利用导钠幅值的变化和系统的动态信息,可以对裂纹的位置和尺寸大小进行识别。实验证明该方法的有效性。     

从PZT体系看无铅压电陶瓷的可能应用

总结了主要以(Bi0.5Na0.5)TiO3和NaNbO3为基的无铅压电陶瓷的性能，以Pb(Ti，Zr)TiO3基二元系、三元系压电陶瓷的性能与应用为参考，分析了无铅压电陶瓷可能的器件应用。此外，还对拓宽无铅压电陶瓷应用需要改进的性能提出了建议。     

Mechanical properties of polyethylene mixtures crystallized under high pressure

The mechanical properties of a medium molecular weight polyethylene (MMW‐PE) and an ultrahigh molecular weight PE (UHMW‐PE) binary mixture with different weight fractions crystallized from the melt at 0.1 and 450 MPa were studied. The tensile modulus, yield stress, and strain were obtained as a function of the weight fractions in the PE mixtures at 25 and 85°C. The tensile modulus in the sample crystallized at 0.1 MPa decreased from 1.5 GPa of pure MMW‐PE to about 0.4 GPa of pure UHMW‐PE with the UHMW‐PE content but it did not decrease with the UHMW‐PE in the sample crystallized at 450 MPa in testing at 25°C. A decreasing rate of the storage modulus E′ of UHMW‐PE in a dynamic measurement for the sample crystallized at 0.1 MPa with the temperature is larger than that of the sample crystallized at 450 MPa. These experimental facts are interpreted in relation to the molecular motion and crystallinity of the sample. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1962–1968, 2003