Ruifang Zhang

Ilmenite structure-type β-CdSnO3 used as an ethanol sensing material

Abstract This Letter reports for the first time that the ilmenite structure-type oxide, β-CdSnO3 semiconductor, can be used as a new material for detecting ethanol gas. The phase and microstructure of β-CdSnO3 powders were studied by XRD and TEM. The conductance-temperature, sensitivity-temperature and sensitivity-gas concentration properties of β-CdSnO3-based sensors were investigated. The sensors based on this phase have a high sensitivity and selectivity to ethanol gas and are promising for detecting ethanol.

Ammonia-sensing characteristics of Pt-doped CdSnO3 semiconducting ceramic sensor

Abstract The initial experimental results concerning the ammonia-sensing properties of Pt doped mixtures of α- and β-CdSnO 3 are reported. The mixtures of different β α ratios can be obtained by calcining the CdSnO 3 powder precursor prepared by coprecipitation under different experimental conditions. As compared with that of other samples, however, the 1 wt% Pt doped mixture with β α ratio of 2.0 exhibits a very high sensitivity and selectivity to NH 3 gas, moderate resistance and good response characteristic, as well as low operating temperature (240 °C) for this application.

The Influence of Train on the Smoke Movement in Subway Tunnel with Longitudinal Ventilations

The smoke movement in the subway tunnel with train under different longitudinal ventilations was simulated using Fire Dynamics Simulator (FDS) program in this paper. The influence of subway train on the characteristics of smoke flow, including the smoke temperature underneath the tunnel ceiling and back-layering length, were investigated. The results showed that the upstream smoke gas temperature was much lower with train than without when the ventilation velocity was lower than the critical value and the downstream dimensionless smoke gas excess temperature decayed exponentially. The subway train could contribute to reduce the back-layering length at low ventilation velocities. Meanwhile, the FDS simulated smoke back-layering length agreed well with the calculated values of the proposed model. However, the difference between train lengths of 20 m and 40 m was insignificant. The mechanism of the train influence was discussed in depth using hydrodynamics.

The Effect of Aspect Ratios on Critical Velocity in Tunnel Fires

The influence of aspect ratio, A s (height/width for a tunnel of rectangular cross section), on the critical velocity in tunnel fires was studied by computational fluid dynamics (CFD) simulation. According to previous researches, the influence of aspect ratio on critical velocity presents different tendencies. Someone believes the critical velocity increases with A s ; others think that the critical velocity decreases when A s is larger than unity. According to previous experimental results and CFD results, in this paper, it is inappropriate to use aspect ratio as the only factor which affects the critical velocity. Both A s and the tunnel width should be considered. By introducing the characteristic fire diameter, the difference of relationship between critical velocity and aspect ratio is unified, and a new critical velocity model is developed. The critical velocity varies with the one-fifth power of the heat release rate for under-medium fires.

Effect of Starch on Sintering Behavior for Fabricating Porous Cordierite Ceramic

Abstract Porous cordierite ceramics were prepared with starch as pore-forming agent by solid-state method. The green bodies were sintered at 1,100–1,400 °C for 2 h. The characterization was focused on thermal analysis, phase evolution, sintering behavior, porosity and micro-structural changes. The results show that cordierite becomes the main crystallization phase at 1,200 °C. The shrinkage behavior shows the most obvious dependence on the sintering temperature and starch content, and it can be divided into three stages. Moreover, the open porosity increases with the increase of starch content, but the pore-forming effectivity decreases. Nevertheless, compared with the open porosity curves, the bulk density curves are more in line with the linear rule. The microphotographs show the densification process with the sintering temperature and the variation of pore connectivity with the starch content.