Kaiming Liang

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.

Enhanced mechanical properties of oriented mica glass-ceramics

Abstract Oriented mica-containing glass-ceramics have been fabricated by hot-pressing the glasses after they were crystallized. X-ray diffraction analysis and scanning electron microscopy show that mica plates were aligned in the hot-pressed glass-ceramics, forming a (001) preferential texture. The formation of the oriented structure was attributed to the combination of viscous flow of residual glass and rolling of mica plates when hot-pressure was applied. By hot-pressing technique, the flexural strength and fracture toughness of the glass-ceramics were improved up to 380 MPa and 2.8 MPa m1/2, respectively, two to three times higher than traditional mica glass-ceramics.

Isothermal DTA study on crystallization of mica composition-based glass

Abstract Isothermal differential thermal analysis (DTA) was used to study the crystallization of a glass with a composition close to that of mica (NaMg 3 AlSi 3 O 10 F 2 ), with TiO 2 added as a nucleating agent. Two distinct crystallization exotherms in DTA were attributed to the formation of MgTi 2 O 5 followed by NaMg 3 AlSi 3 O 10 F 2 . By using the Johnson-Mehl-Avrami equation, the activation energy for precipitation of each crystalline phase was evaluated and the crystallization mechanism was analyzed. Results indicate that NaMg 3 AlSi 3 O 10 F 2 growth is a two-dimensional process, controlled by the crystal-glass interface reaction. The average value of activation energy is 256 ± 11 kJ/mol and 275 ± 7 kJ/mol corresponding to MgTi 2 O 5 and mica, respectively.

Effect of P2O5 on evolution of microstructure of MgO–Al2O3–SiO2 glass ceramics

Abstract MgO–Al2O3–SiO2 (MAS) cordierite based glass ceramics were prepared by volume crystallisation. X-ray diffraction, Scanning electron microscopy and Energy diffraction scanning were used to investigate crystallisation behaviour and the influence of P2O5 on microstructure MAS based glass ceramics. The results showed that P5+ could promote the phase separation of MAS glass and that the glass was divided into two areas, such as Mg4Al2Ti9O25 and the containing P5+ area at <900°C. Mg4Al2Ti9O25 and Mg3(PO4)2 in the area were both advantageous to the precipitation of μ cordierite, which further transformed to α cordierite due to P5+ in the residual glassy phase. However, P5+ inhibited the presence of cordierite when the heat treatment temperature was >900°C.

Microstructure research of glasses by impulse excitation technique (IET)

The stiffness and internal friction (Q−1) of a CaO–Al2O3 SiO2 glass and an Na2O–CaO–SiO2 glass have been measured from room temperature to their respective glass transition temperatures (Tg) using the impulse excitation technique (IET). Thermomechanical analysis (TMA) is used to confirm the analysis results for the CaO–Al2O3–SiO2 glass. IET samples of both glasses have a resonance frequency near 10 kHz. At this frequency and in the measured temperature range, the glasses are characterized by one Q−1 peak superimposed on an exponential background. The internal friction peak of the CaO–Al2O3–SiO2 glass occurs at a temperature of about 320°C. From the reversibility of the changes of stiffness, it is concluded that the peak is due to anelastic relaxation, i.e. that of Ca2+ and Na+ ions from the structure units of [AlO4]Ca[AlO4] and [AlO4]Na. In the case of the Na2O–CaO–SiO2 glass, Ca2+ and Na+ ions induce a Q−1 peak as well, but at about 230°C. In this glass, the cations diffuse through the network holes causing irreversible stiffness changes. For the CaO–Al2O3–SiO2 glass, the Al3+ ions within the structure units of [AlO4]Ca[AlO4] and [AlO4]Na start to anelastically relax at temperatures well above the Q−1 peak (such as 550°C). For the Na2O–CaO–SiO2 glass, the [SiO4] structure units begin to move slightly and rearrange at about 450°C. This corresponds to the beginning of the glass transition. If the temperature is lower than 600°C, the changes of the CaO–Al2O3–SiO2 glass microstructure are reversible. On the other hand, even below the temperature of 500°C the microstructure of the Na2O–CaO–SiO2 glass is not stable. IET is shown to be a very effective method to investigate these subtle changes of the microstructure of glasses.

Preparation of porous spodumene/zircon composite ceramics and its thermal and mechanical properties

Abstract Porous β-spodumene/zircon (ZrSiO4) composite ceramics were prepared by addition of zirconia to spodumene mineral using conventional solid reaction methods. The formation of the zircon was investigated by means of the differential scan calorimetry measurements and an X-Ray diffractometer. The microstructure of the composite ceramics was observed through a scanning electron microscope. The results show that the presence of zircon benefited the formation and stability of the porous structure and improved significantly the thermal endurance and mechanical properties of the spodumene matrix. The composites with 10–15% porosity exhibit an excellent thermal shock resistance, a low thermal expansion coefficient of approximately 1·4 × 10−6 K−1 in the range of 200–800°C and a high flexural strength about 100 MPa. It is found that the spodumene/zircon composites, widely used as a high temperature structure material, can be synthesised by a cost effective method.