Papers by Author: Guan Jun Qiao

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Authors: Shun Jian Xu, Yu Feng Luo, Wei Zhong, Guan Jun Qiao
Abstract: A novel counter electrode has been fabricated at low temperature using nanoporous carbon (NC) with about 35 nm pore size as based catalysis materials and silver conductor paste (SCP) as connecting adhesive. The efficiency of dye-sensitized solar cells (DSCs) employing this SCP/NC electrode reaches to 5.91%, which is 15% higher than that of DSCs with NC electrode. The improved efficiency is attributed to the enhancement in the fill factor and the short circuit photocurrent density. Electrochemical impedance spectroscopy reveals that all of charge transfer resistance, ohmic serial resistance and Nernst diffusion impedance of SCP/NC electrode decrease compared with NC electrode. Especially, the efficiency of 5.91% is comparable to that of DSCs with Pt electrode.
Authors: Ying Han, Guan Jun Qiao, Dong Na Yan, De Ning Zou
Abstract: The hot deformation behavior of super 13Cr martensitic stainless steel was investigated using artificial neural network (ANN). Hot compression tests were carried out at the temperature range of 950°C to 1200°C and strain rate range of 0.1–50s–1 at an interval of an order of magnitude. Based on the limited experimental data, the ANN model for the constitutive relationship existed between flow stress and strain, strain rate and deformation temperature was developed by back-propagation (BP) neural network method. A three layer structured network with one hidden layer and ten hidden neurons was trained and the normalization method was employed in training for avoiding over fitting. Modeling results show that the developed ANN model can efficiently predict the flow stress of the steel and reflect the hot deformation behavior in the whole deforming process.
Authors: Guan Jun Qiao, Zhi Hao Jin, Jun Min Qian
Abstract: Dense SiC/Si ceramics were prepared by a silicon melt infiltration method. Highly porous SiC ceramics with a wood-like microstructure were prepared by silica sol infiltration and carbothermal reduction reaction. Furthermore, laminated SiC/Si composites were also prepared by the carbonization and silicon melt infiltration of stacked papers. The microstructure and characteristics for this series of materials were determined and compared.
Authors: Guan Jun Qiao, Hong Jie Wang, Ji Qiang Gao, Zhi Hao Jin
Abstract: High purity alumina ceramic and Kovar alloy were brazed by Nickel and Titanium foils stacked as Ni/Ti/Ni layer structure. Airtight joints were achieved with shear strength more than 30MPa, after brazing at 995oC for 30min. A sandwich structure was observed in solder, which means an a-Ti solid solution belt at mid part and Ti2Ni intermetallics belts at both sides. The main reaction product at alumina/solder interface was Ni2Ti4O, a complex oxide with structure similar to Ti2Ni, which is the bonding agent and transition from the solder’s metallic crystal lattice to alumina crystal lattice. To simulate the actual serving conditions, a thermal cyclic experiment was undertaken at the 200oC-600oC temperature range. The results showed that shear strength of joint increased dramatically after thermal cycles. This interesting phenomenon is attributed to the annealing effects of thermal cycles, which released residual stress in brazed joints remarkably.
Authors: Dong Yun Li, Guan Jun Qiao, Zhi Hao Jin
Authors: Yong Feng Li, Ping Liu, Xiang Dong Wang, Hai Yun Jin, Guan Jun Qiao
Abstract: Porous silicon nitride ceramics with various amounts (25, 35, and 45 vol %) of hexagonal boron nitride (h-BN) were fabricated at 1800°C for 2h by the pressureless sintering process. With FESEM and TEM, the effects of h-BN on the microstructure and mechanical properties of Si3N4 ceramics were investigated. Results of the microstructure and mechanical properties of Si3N4/BN composites showed that the growth of the elongated β-Si3N4 were hindered by h-BN additive, which resulted in the decrease of fracture toughness of Si3N4/BN ceramics with increasing h-BN content. The morphologies of the fracture surfaces by FESEM revealed the fracture mode for Si3N4/BN composites to be intergranular. However, phase analysis by XRD indicated that the effect of h-BN on the α- to β- Si3N4 phase transformation of Si3N4/BN composites was negligible.
Authors: Xiao Juan Zhang, Guan Jun Qiao, Xiao Zhang
Abstract: High purity Al2O3 powder was used as raw material and MgO was used as additive to sinter alumina transparent ceramics in hydrogen atmosphere. EBSD image showed that, with the increase of the MgO content, the grain size decreased from 200μm (when no Mg was doped) to about 20μm (when the Mg doping amount was 1.0wt%), indicating that MgO had an inhibition effect on the grain growth. XRD analysis showed that the doping of MgO did not lead to the formation of new phases. A further refinement of cell parameters revealed that, when the doping amount reached 1.0wt%, lattice distortion occurred and the cell volume increased by about 80%, which was attributed to the formation and diffusion of oxygen vacancies. The Eg mode at ν=575cm-1 revealed by Laser Raman Spectroscopy suggested that AlO6 octahedra were distorted with the increase of the MgO content. And the frequency change of the A1g mode at ν=642cm-1 reflected the combined effect of ion mass and mechanical constant. Measurement of the optical transmittance indicated that, after the doping of MgO, a small amount of MgAl2O4 phase formed at the grain boundary, causing the transmittance to increase first and then decrease with the increase of the MgO content. And analysis of the dielectric properties showed that the change of the dielectric constant and loss with the frequency at room temperature resulted from ion relaxation polarization induced by the weakly bound ions in the AlO6 octahedron.
Authors: Wan Li Yang, Zhong Qi Shi, Zhi Hao Jin, Guan Jun Qiao
Abstract: The three kind of oxides such as 3Y-ZrO2, Fe2O3 and MgO were used as catalyst in reaction bonded silicon nitride (RBSN) with low-purity silicon powder as raw materials. The oxides can strongly promoted the nitridation ratio of RBSN, and the catalysis effects of these oxides for RBSN were investigated. After 4h nitridation, the degree of nitridation increased from 43% to 96% by adding 10wt% of 3Y-ZrO2 additive comparing with the sample without additive, and the catalystic effects of Fe2O3 and MgO were slightly less than 3Y-ZrO2 additive. XRD patterns revealed that the main phases of the reaction products were α-Si3N4, β-Si3N4 and Si-N-O intermediation. SEM micrographs show that the hexagonal columnar β-Si3N4 separated from acicular α-Si3N4.
Authors: Gui Wu Liu, Jie Li, Guan Jun Qiao, Shun Jian Xu, Tian Jian Lu
Abstract: A hierarchical porous carbon derived from phenolic resin (PF) was processed using ethylene glycol (EG) and starch as double porogens. The influences of composition of starting mixture, including the two porogens and PF, on morphological properties and microstructure of the porous carbon were investigated. It was demonstrated that the content of starch and the relative content of EG to PF played key roles in determining the number, size and formation of the hierarchical pores, which in turn led to changes in the properties and the microstructure of the porous carbon. In particular, the number of the first-level pores (diameter ~10–40 μm) increased with the content of starch increasing, and the high relative content of EG to PF contributed to the formation of the second-level pores (diameter ~0.5–2 μm), which were closely related to the formation mechanisms of the two-level pores, respectively. Under the present experimental conditions, sufficiently high starch content can result in the microstructural abnormalities, such as the incomplete decomposition of starch and the formation of the third-level pores which originated from the stack of discrete carbon particles.
Authors: Guang Wei Fan, Jie Liu, Pei De Han, Guan Jun Qiao, Jian Feng Yang
Abstract: Effect of the warm processing parameters (the strain rate, forming temperature and deformation degree ) on the γ' metastable phase transformation in 2205 duplex stainless steel has been studied. The γ' metastable phase was located within the ferrite phase. Dynamic recovery took place only within the γ phase, and dynamic recrystallization underwent for the ferrite phase. The γ' metastable phase transformation was affected by the deformation degree and about 15% deformation led to appearance of the γ' metastable phase. γ' metastable phase formation by the precipitation of intragranular γ' was favored by increasing ageing time, and the size and content of γ' metastable phase were related to deformation temperature and strain rates.
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