Applied Mechanics and Materials Vol. 483

Abstract: A novel and one-pot route for the synthesis of O-glycosyl-5′-H-phosphonate diesters of d4T has been developed. This analogs were synthesized by controlling tandem substitution reaction on PCl₃ with 2,6-lutidine as suitable base.

Abstract: A novel and efficient method for the synthesis of 4-hydroxy-6-substituted-pyrazolo [3,4-d] primidines with acetic acid via phenol esters intermediate has been developed. Compared to the results obtained from the base substituted conditions, acetic acid catalyzed synthesis afforded target products in good yields.

Abstract: A new method for the preparation of Fe₃O₄ NPs from byproduct of titanium dioxide-copperas was studied in this study. Core-shell structures and chemical composition of the nanoparticles have been investigated by TEM, XRD and FTIR techniques. The results indicated that the Fe₃O₄ NPs can be synthesized and obtained from copperas by chemical co-precipitation method and have a uniform spherical morphology with an average diameter of about 10 nm. The mole ratio of Fe²⁺ to Fe³⁺was one of the most important factors during the chemical co-precipitation processing, which has a great effect on the yield and size distribution of precipitations. The recommended mole ratio f Fe²⁺ to Fe³⁺ was 1.75:1. The saturated magnetization of Fe₃O₄ NPs was 52.8emug^-1 at 25°C and this material exhibited excellent magnetic properties. A new way was therefore provided for the comprehensive utilization of the unmarketable copperas. Moreover, the Fe₃O₄ NPs obtained from the copperas have a big potential in environmental decontamination, medical technology and biological science.

Abstract: Elemental thermocouples are capable of meeting the demanding requirements of high temperature measurement with high accuracy, wide temperature measurement range, and long operational life. With an ever increasing need for more accurate, more precise temperature measuring devices over a wide spectrum of temperatures, elemental thermocouples show great promise when compared with its counterparts. The Au/Pt thermocouple, one of the more effective elemental metal combinations, is the ideal standard thermometer in the range of 0°C - 1000°C due to its reproducibility, accuracy, stability, and durability, causing the US and Korea to standardize its use. Much academic work has been done on the accuracy, stability, thermoelectric properties, structural design, and calibration methods of Au/Pt thermocouples to develop it to its current state. This paper summarizes research done on Au/Pt thermocouples, both domestically and internationally, in order to provide a foundation for future improvement.

Abstract: The effects of near β heat treatment on the microstructure of TC18 alloy during three temperature stages were studied. The results show that the microstructure of the sample is tri-modal microstructure after near β heat treatment, and the size of α_p does not significantly, but dispersible α_s increases and has a tendency to merge, and then it would not grow up anymore ; β phase would grow up, but the grain boundary has some broken. The experiment result shows that the tri-modal microstructure could obtain high damage tolerance properties of titanium alloy in theory.

Abstract: The polymer composites consist of phenolic resin, natural graphite, carbon fiber and copper powder, are fabricated by hot compression moulding or compression moulding followed by post-curing. The density, electrical conductivity and flexural strength of composites are analyzed to determine the influences of post-curing temperature and preparing method on the physical, electrical and mechanical properties of composites. It is found that the density, electrical conductivity and flexural strength of composites increase with increasing post-curing temperature for composites prepared by compression moulding followed by post-curing. The flexural strength is more strongly dependent on post-curing temperature. At 170 °C, the density, electrical conductivity and flexural strength of composites were 1.85 g/cm³, 2.94 × 10³ S/m and 40 MPa respectively. The cross-linking skeleton structure well established in the composites could be the main reason for the largely increasing of flexural strength as post-curing temperature increases. The results also show that the properties of composites prepared by hot compression moulding are higher than those of composites prepared by compression moulding followed by post-curing.

Abstract: Nitro humic acid was extracted from lignite of Guizhou Anshun, which production condition and process were studied. The results show that the optimum conditions of dry process are concentration of nitric acid of 40%, reaction temperature of 95°C, reaction time of 5 min. The optimum conditions of wet process production are concentrations of nitric acid of 20% ~ 25%, the solid-liquid ratio of 1:1.25 (weight ratio), reaction temperature of 80 ~ 85°C, and reaction time of 30 min.

Abstract: Electronic properties and configuration of rare-earth orthoferrites TbFeO₃ with perovskite-type structure was calculated using pseudo-potential method basing on density function theory. TbFeO₃ with ferromagnetic structure and antiferromagnetic structure are investigated. By comparing calculated values with experimental results, the antiferromagnetic structure is more stable at normal condition, and its configuration optimization results is closer to the experimental measurement. In addition, TbFeO₃ with antiferromagnetic structure should be a semiconductor having a band gap at the Fermi energy, while for TbFeO₃ with ferromagnetic structure, there is no gap at the Fermi energy.

Abstract: Electric-current induced electroresistance effect has been investigated in epitaxial Pr_0.7Sr_0.3MnO₃ thin film grown on the (100) SrTiO₃ substrate. A significant change ~38% in the ratio of the peak resistance at different currents with a current density up to ~3.3×10³ A/cm² was achieved. Such an ER effect is more remarkable in comparing with that reported in other manganite oxides with similar current densities. Compared with that of the as-grown films, the electroresistance of the post-annealed films is smaller, while the ER effect (~14%) is obtained. Although the nature behind such an electroresistance effect has not been well understood, the field tunability of the metal/insulator transition and the electroresistance effect induced by currents might be of potential for various applications such as filed effect devices.

Abstract: SBA-15 supported phosphotungstic acid has been synthesized under hydrothermal conditions via pH adjustment and characterized with various analytical and spectroscopic techniques including X-ray diffraction (XRD), N₂ adsorption, transmission electron micrographs (TEM). XRD results indicate that the substitution of tungsten occurs in the silicate framework structure of SBA-15. Study on the catalytic activity of mesoporous PW/SBA-15 catalyst through the isomerization of the a-pinene was investigated. The best reactive conditions of a-pinene isomerization were follows: reaction temperature 130°C, dosage of PW/SBA-15 catalyst 2 %, reactive time 2 h. Then the rate of a-pinene conversion could achieve 94.56 %, the selectivity of camphene could achieve 48.5%.