Shouren Gu

Oxidation protection of mild steel by zirconia sol–gel coatings

Abstract Zirconia coatings were deposited on a mild steel substrate by the sol–gel method. The interface between the coating and substrate was analyzed by Auger electron spectroscope (AES). The oxidation kinetics during iron oxide formation was investigated by measuring weight gain in the temperature range of 450–550°C. The sample surfaces after oxidation were characterized by scanning electron microscopy and X-ray diffraction (XRD). The experimental results showed that the zirconia coatings at moderate temperature increased the activation energy of oxidation from 32 to 58 kJ mol −1 , suppressed the growth of iron oxides, and substantially reduced the oxidation rate of the substrate.

Effects of CeO2 on phase transformation towards cordierite in MgO–Al2O3–SiO2 system

Abstract The properties of cordierite ceramic depend upon additives and phase transformation in sintering. XRD and DTA techniques are used to study the effects of CeO2 upon the transformation towards cordierite. As the experimental results show, with an increase of CeO2 content, the temperature drops at which cordierite forms through diffusion in solid state; when liquid has occurred, the crystallization temperature first drops with CeO2 content and then rises, the lowest measured temperatures being at 2–4 wt.% of CeO2. The effect of CeO2 can be associated with the alteration of ion diffusion.

Evaluation of cordierite–ceria composite ceramics with oxygen storage capacity

Abstract Oxygen storage capacity (OSC) is an important parameter in three-way-catalysts (TWCs) for the purification of exhausts from gasoline engines of automobiles. Beciuse CeO2 possesses the unique performance, it is added into catalytic coatings of converters to adjust the oxygen concentration of the exhausts. However, small amounts of CeO2 existing in the coating is insufficient in this when air-fuel ratio fluctuates in a relatively wide range. In the present work, a kind of cordierite–CeO2 ceramic was prepared through sol-gel method so as to append the OSC to the support on which the catalyst is coated. Advanced measurement techniques such as XRD, SEM and gas chromatograph were employed to evaluate the microstructure and properties of the composite ceramics. Results show that the composite ceramics consist both phases of cordierite and CeO2. CeO2 particles are uniformly and separately distributed in the cordierite matrix, their number and granularity dependent on the amount of Ce4+ addition. The cordierite and 10 wt.% CeO2, possesses an apparent OSC, appropriate porosity, flexural strength and thermal expansion coefficient. It will be helpful to enhance the OSC of the catalytic converters and so improve the purification effects to the exhausts.

Effect of Ce4+-modified amorphous SiO2 on phase transformation towards α-cordierite

Abstract The sintering temperature of cordierite ceramic is dependent on the transformation temperature to α-cordierite. In the present work, the effect of Ce 4+ -modified amorphous SiO 2 on the transformation behavior of the ceramics were studied using the techniques such as X-ray Diffraction, Differential Thermal Analysis (DTA) and Infrared Spectrometry so as to decrease the sintering temperature. Experimental results show that, Ce 4+ -free amorphous SiO 2 has no effect on the transformation, while Ce 4+ -modified amorphous SiO 2 can obviously decrease the onset temperature. This is correlated to that Ce 4+ addition, which makes the structure of tetragonal SiO 2 loosened and decreases the transformation temperature of SiO 2 to tetragonal and so, improves the condition of solid solution of Al 3+ and Mg 2+ into tetragonal SiO 2 . Moreover, Ce 4+ addition has little effect on the conversion rate, because it cannot effectively promote the diffusion of Al 3+ and Mg 2+ into tetragonal SiO 2 .

Effect of cerium addition on phase transformation and microstructure of cordierite ceramics prepared by sol-gel method

Low-temperature sintering of cordierite ceramic depends on the phase transformation into cordierite and the properties depend on its microstructure. In the present work, the effect of cerium on the phase transformation and microstructure of cordierite ceramics prepared by sol-gel method is studied by X-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM) in order to lower the sintering temperature and improve the properties of cordierite ceramic with the addition of cerium. It is observed that the cerium addition obviously lowers the crystallization temperature of α-cordierite while slightly raises that of μ-cordierite. The lowest temperature for μ → α cordierite transformation, which approaches the crystallization temperature of μ-cordierite, is achieved in the sample containing 4 wt% of cerium, implying a possibility to lower the sintering temperature of cordierite ceramics. The Ce-contained ceramics show a biphasic microstructure that is dependent on sintering temperature. Sintered below 1300°C, a cordierite-CeO2 microstructure is present; while sintered at the temperature above 1300°C, appears a cordierite-glass microstructure, of which the amount of glass phase is limited to a small extent. Since the addition of 4 wt% cerium to this MgO-Al2O3-SiO2 system substantially enhances the densification of cordierite ceramics and lowers the sintering temperature to the level of around 1000°C, it makes the ceramics suitable for such applications, where the low-temperature sintering is required, as the substrates for electronic circuit and the catalytic supports (with oxygen storage capacity) for cleaning of automotive exhaust emissions.

Influence of different TiO2 content on crystallization of CaO–MgO–P2O5–SiO2 system glasses

Abstract The kinetic parameters including the activation energy ( E ) of crystallization and the Avrami parameter ( n ) of CaO–MgO–P 2 O 5 –SiO 2 system glasses with various TiO 2 content were studied by means of differential thermal analysis (DTA) techniques. The results show that the more TiO 2 content was, the lower the crystallization peak temperature ( T p ) was. But the low value of T p did not also mean that value of E was small. The most effective addition of TiO 2 was about 8.7 wt% in this system glass. The activation energy difference between the base glass (no TiO 2 added) and the glass containing most effective addition of TiO 2 was more than 100 kJ/mol. The experimental results suggest that in the studied samples, TiO 2 can promote crystallization effectively.