Advanced Materials Research Vols. 197-198

Abstract: N-doped SiC whiskers with diameters of about 0.2 μm and length of 3-7 μm were synthesized via combustion reaction of Si/C system in Ar atmosphere, using NH₄Cl as the dopant and polytetrafluoroethylene (PTFE) as the chemical activator. These whiskers are straight and curved morphologies. X-Ray powder diffraction pattern and energy-dispersive spectroscopy (EDS) confirm that the lattice constant of prepared whiskers is smaller than standard value of β-SiC due to the N doping arising.

Abstract: With stearic acid (SA) as phase change material, waste polyacrylonitrile fiber (PAN) as framework material, N,N-dimethylformamide (DMF) as solvent, form-stable PAN/SA blends phase change materials (PCM) are prepared by solution blending process. Phase change temperature and latent heat and the thermal stability of the PAN/SA PCM are characterized using Differential Scanning Calorimetry (DSC). The structure, crystalline morphology, and thermal insulation properties of the PAN/SA PCMs are investigated using Fourier transformation infrared spectroscope (FTIR), polarizing optical microscopy (POM), and temperature-recording instrument. The FTIR and POM results show that PAN and SA are combined by intermolecular forces, and SA is homogeneous distribution in the PAN matrix. The DSC results indicate that PAN/SA PCMs have high latent heat storage capacity of more than 115J/g, the phase transition temperature and phase transition enthalpy of the PCMs increase with increasing the mass percent of SA. Cooling curve of PAN/SA PCMs show that the PCMs have good insulation properties, the soaking time is continued for about six minutes, and the thermal insulation properties remain unchanged after five and ten times of thermal cycling. The best process condition is obtained by the soaking time and orthogonal experiment.

Abstract: Strontium Bismuth Niobium (SBN) ceramics was prepared successfully using the powders synthesized from molten salt method. The evolution of microstructure with temperature increasing was studied and the influences of abnormal grain growth on dielectric properties were also presented in this paper. The results showed that pure strontium bismuth niobium ceramics without abnormal grain growth could be formed at 1150°C while the density was almost 95% of the theoretical density. Further investigations on dielectric properties indicated although abnormal grain growth did not shift the Curie point obviously, they lowered the dielectric constant corresponding to the Curie point. The dielectric loss was found to change with the frequency remarkably.

Abstract: Ba(Zn_0.3Co_0.7)₂Fe₁₆O₂₇ hexagonal ferrites have been prepared by sol-gel method. Effects of polyvinyl pyrrolidone (PVP) on crystalline phase, natural surface and electromagnetic properties were analyzed. The XRD patterns of samples with and without PVP added both showed the single phase of hexagonal ferrite. The particle thickness increased when PVP was added. Moreover, Ferrites prepared with 2.0g PVP added into the sol solution had lower complex permittivity. Addition of PVP can be an effective way to obtain the electromagnetic match of hexagonal ferrites.

Abstract: Some novel trigonal Schiff base compounds with aromatic core and different substituted groups have been designed and synthesized from the reaction of trigonal aromatic amine with different aldehydes. It has been found that depending on the molecular structures and substituted groups, the formed trigonal Schiff base compounds showed different properties, indicating distinct regulation of molecular design. UV and IR data confirmed commonly the formation of Schiff base as well as aromatic segment in molecular structures. Thermal analysis also clarified the structural influence of these compounds in different temperature ranges. The difference of thermal stability is mainly attributed to molecular structures, formation of Schiff base group and different substituted groups. The present results have showed that the special properties of Schiff base compounds could be turned by modifying molecular structures and substituted groups, which show potential application in fields of functional material and catalyst.

Abstract: Electrolysis method was used to prepared stannous methanesulfonate by using tin plate as the anode and graphite as the cathode in the methylsulfonic acid solution. Based on the uniform design experimental program, the multivariate nonlinear regression equation, which described quantitatively the inherent law of experiment, was established. The optimal conditions of synthesis were determined by data mining technology. The conversion rate was 97% when in optical conditions. From the results, it was shown that the influence degree of each factor is as follows: current density > electrolyte concentration > stirring speed > reaction temperature.

Abstract: Some functional luminol derivatives with aromatic substituted groups have been designed and synthesized from the reaction of the corresponding aromatic acyl chloride precursors with luminol. It has been found that depending on the size of aromatic groups, the formed luminol derivatives showed different properties, indicating distinct regulation of molecular skeletons. UV and IR data confirmed commonly the formation of imide group as well as aromatic segment in molecular structures. Thermal analysis showed that the thermal stability of luminol derivatives with p-phthaloyl segment was the highest in those derivatives. The difference of thermal stability is mainly attributed to the formation of imide group and aromatic substituent groups in molecular structure. The present results have demonstrated that the special properties of luminol derivatives can be turned by modifying molecular structures of objective compounds with proper substituted groups, which show potential application in functional material field and ECL sensor.

Abstract: The effect of MnO₂ addition (0–2.0 mol%) on the densification, crystal structure, and ionic conductivity of Ce_0.8Sm_0.2O_1.9 (SDC) was studied. The addition of MnO₂ promotes densification, reducing sintering temperature by ~150°C. X-ray diffraction analysis showed that all the samples exhibit a fluorite structure. Impedance spectroscopy measurements indicated that SDC with appropriate ratio of MnO₂ addition has higher ionic conductivity and lower activation energy compared with that of SDC. As the addition amount of Mn increases up to 1.0 mol% [(Ce_0.8Sm_0.2O_1.9)_0.99+(MnO₂)_0.01], the sample attains the highest ionic conductivity, about 35% higher than that of SDC at 600°C. In addition, Mn addition has little effect on bulk conductivity, but a marked influence on grain boundary behavior is observed.

Abstract: TiC_xN_1-x whiskers were prepared using TiO₂ and carbon mixed powder as the starting powder at the atmosphere of nitrogen by the carbothermal reduction process. NaCl and NiCl₂ were added into the starting powder as the cosolvent and growth adds of impurities, respectively. An effect of the content of TiO₂ and carbon in the starting powder on the TiC_xN_1-x whiskers was investigated. It is found from SEM and XRD observations that three types of TiC_x N_1-x whiskers are obtained when the different mol ratios of C and Ti are applied. The growth of whiskers is not only urged by the droplet on the top of whiskers, but also initiated by the helical dislocations. The growth of TiC_xN_1-x whiskers is controlled by the vapor-liquid-solid mechanism as well as vapor-solid mechanism.

Abstract: Some functional Schiff base derivatives with azobenzene substituted groups have been designed and synthesized from the reaction of aminoazobenzene with different aromatic aldehydes. It has been found that depending on the size of aromatic groups, the formed Schiff base derivatives showed different properties, indicating distinct regulation of molecular skeletons. UV and IR data confirmed commonly the formation of Schiff base as well as aromatic segment in molecular structures. Thermal analysis showed that the thermal stability of Schiff base molecules with naphthalene segment increased slightly in comparison with other derivatives. The difference of thermal stability is mainly attributed to the formation of Schiff base group and aromatic substituent groups in molecular structure. The present results have demonstrated that the special properties of Schiff base derivatives can be turned by modifying molecular structures of objective compounds with proper substituted groups, which show potential application in functional material field.