Prediction of the effective coefficient of thermal expansion of heterogeneous media using two-point correlation functions

Statistical continuum mechanics is used to predict the coefficient of thermal expansion (CTE) for solid oxide fuel cell glass-ceramic seal materials with different morphology and crystallinity. Two-point correlation functions are utilized to represent the heterogeneous microstructure morphology and phase distribution. The model uses two-point correlation functions in conjunction with local properties to predict the effective CTE. Prediction results are comparable to experimental CTE results. The advantage of using the statistical continuum mechanics model in predicting the effective properties of anisotropic media is shown, using the ability to take the microstructure into consideration.     

Rehydration activity of hydrated cement paste exposed to high temperature

Subjected to the wet surrounding, hydrated cement paste (HCP) exposed to high temperature may exhibit rehydration behavior. This paper presents the influence of the dehydration temperature and the initial water/cement ratio on the rehydration activity of dehydrated cement paste (DCP). Original HCPs were prepared with two water/cement ratios of 0.3 and 0.5, respectively, and cured under the fog‐spraying standard condition for 30thinspacedays. The DCP powders used were obtained by grinding dry HCP less than 75µm and then subjecting to different temperatures, up to 900^°C. The rehydration properties of DCP were evaluated by the required water for standard consistency, the setting time, the rehydrated compressive strength and the microstructure evolution. X‐ray diffraction (XRD) was employed to identify the crystalline phases before and after rehydration. Experimental results showed that the coupled rehydration effect from the dehydrated hydration products and the initially unhydrated cement determined the rehydration behavior of DCP. The rehydration of DCP strongly depended on the dehydration temperature and the water/cement ratio of the original HCP. Copyright © 2010 John Wiley & Sons, Ltd.     

Triacylglycerol Composition Profiling and Comparison of High‐Oleic and Normal Peanut Oils

Oilseed plants produce huge amounts of fatty acids (FA) stored as triacylglycerols (TAG) in seeds that give a great variation in their composition. The variety and content of TAG directly affect the nutrition and function of lipids. TAG composition of 12 high‐oleic and normal peanut oil samples were profiled by two‐dimensional liquid chromatography (2D LC) coupled with atmospheric pressure chemical ionization mass spectrometry (APCI‐MS). The statistical evaluation of the TAG profiles determined was conducted on the basis of multidimensional data matrix using Principal Component Analysis (PCA). The technique enabled the differentiation of high‐oleic oils from normal peanut oils—as results illustrated TAG of high‐oleic peanut oil were clearly different from those of normal peanut oils. High‐oleic and normal peanut oils had different profiles mainly in the contents of OOO, OPO and POL. This finding provided theoretical foundation for detecting the adulteration of edible oils and analyzing the nutrition and function of high‐oleic peanut oils.     

Electrochemical behaviour of Ti–25Nb–3Mo–3Zr–2Sn biomedical alloy in different simulated physiological environments

The electrochemical corrosion behaviour of biomedical Ti–25Nb–3Mo–3Zr-2Sn (TLM) alloy was investigated in various simulated body fluids at 37±0·5°C utilising potentiodynamic polarisation and current–time curves. The Ti–6Al–4V (TC4) alloy was also investigated to make a comparison. The different simulated body fluids comprised of 0·9%NaCl saline, Hank’s and Ringer’s solution were employed. The effect of heat treatment on the electrochemical behaviour of the TLM alloy was also considered. It was discovered that all the test specimens were passivated once immersed into the simulated body fluids. It was also found that the TLM alloy has poorer corrosion resistance in Hank’s solution, due to the chemical composition of the Hank’s. After different heat treated, the TLM alloy had different phases and microstructure, and the corrosion behaviour of the TLM alloy was different. In this study, after the heat treatment of 760°C/1 h/AC+550°C/6 h/AC, the TLM alloy had better corrosion resistance. Owing to the corrosion resistance of the TLM alloy was influenced by numerous factors, such as microstructure and the chemical composition of electrolyte, the corrosion behaviour of the TLM alloy is complex. By comparing with the corrosion behaviour of the TC4 alloy, the TLM alloy has poorer corrosion resistant than the TC4 alloy under the same conditions. But the current–time curves of the TLM alloy were more stable than these of the TC4 alloy with further experiments, because of the more passivation film on the surface of the TLM alloy.     

Wettability and biomineralisation of laser cladded Si doped TiCN biocoating

Surface textured Si doped TiCN coatings were synthesised on Ti–6Al–4V alloy by laser cladding technique. Phase constituent examination by X-ray diffraction revealed the formation of similar phases of TiC_0.2N_0.8 and Ti₅Si₄ within all coated samples. Laser coated samples presented much higher surface free energy compared to Ti–6Al–4V control due to the textured structure, which in turn demonstrated a better wettability and improved biomineralisation. Variation of silica content presented no significant influence on surface free energy, indicating that the silica content can be varied in a large range. The mineralised samples obtained after immersion in simulated body fluid were characterised to understand the mechanism and kinetics of Ca–P precipitation. The results confirmed that the precipitation kinetics of Ca–P was influenced by the substitution of silica.     

Acceleration of regeneration treatment for nanostructured bainitic steel welding by static recrystallisation

Abstract

In order to accelerate bainite transformation during regeneration treatment following nanostructured bainite steel welding, static recrystallisation mechanism is adopted to refine the coarse grain size during two-pass welding. Large mechanical deformation was introduced into the coarse grain zone of the first weld pass, where static recrystallisation would occur with thermal effect of the second weld pass. Static recrystallisation kinetics of nanostructure bainite was studied by two-pass hot deformation experiments. The explicit temperature function of two-pass welding was presented, and effect of welding parameters on static recrystallisation of the deformed coarse grain zone was analysed. Experimental results showed that grains in original coarse grain zone were greatly refined and that nanostructured bainite regeneration was remarkably accelerated.     

Relationships of diboride phases in Al–Ti(Zr)–B alloys

Abstract

The relationships of diboride phases in Al–Ti(Zr)–B alloys with a variable Ti/B ratio close to the stoichiometry of TiB₂ were studied. The formation of diboride solid solutions was confirmed. A grain refinement mechanism is proposed as that diboride particles in the Al–Ti–B master alloys reacting with aluminium upon adding into an aluminium melt and release titanium into the melt through forming a (Ti,Al)B₂ solid solution and maintain a thin dynamic Ti rich layer on the surfaces of the (Ti,Al)B₂ particles, which nucleates α-Al grains in solidification. The poisoning effect of zirconium on grain refinement of aluminium by Al–Ti–B master alloys is also discussed.