Developments in Processing of Functionally Gradient Metals and Metal–Ceramic Composites:A Review

Functionally gradient/graded materials(FGMs), an emerging new class of materials, are the outcome of the recent innovative concepts in materials technology. FGMs are in their early stages of evolution and expected to have a strong impact on the design and development of new components and structures with better performance. FGMs exhibit gradual transitions in the microstructure and/or the composition in a specific direction, the presence of which leads to variation in the functional performance within a part. The presence of gradual transitions in material composition in FGMs can reduce or eliminate the deleterious stress concentrations and result in a wide gradation of physical and/or chemical properties within the material. Functionally graded metal–ceramic composites are also getting the attention of the researchers. Among the fabrication routes for FGMs such as chemical vapour deposition, physical vapour deposition, the sol–gel technique, plasma spraying, molten metal infiltration, self propagating high temperature synthesis, spray forming,centrifugal casting, etc., the ones based on solidification route are preferred for FGMs because of their economics and capability to make large size products. The present paper discusses and compares various solidification processing techniques available for the fabrication of functionally gradient metals and metal–ceramic composites and lists their properties and possible applications. The other processing methods are briefly described.     

Synthesis and characterization of bifunctional β-MnO2-based Pt/C photoelectrochemical cell for hydrogen production

A manganese dioxide (β-MnO₂) photocatalyst for light-induced water splitting and hydrogen generation is studied via the impregnation and heat treatment method. The phase and fluorescence characterizations are examined by X-ray diffraction (XRD) and photoluminescence. A series of peaks for its (110) and (200) planes are identified as those for pure β-MnO₂ crystals with lattice spacings of 3.11 and 2.19 Å, respectively. The photoluminescence shows that the primary signals are located in the blue-violet spectral region, corresponding to the band-edge emission of β-MnO₂ (376 nm). Furthermore, two types of photoelectrochemical cell with added Pt are constructed to compare hydrogen production rates. A significant enhancement of light-induced hydrogen generation by water splitting is observed on Pt/β-MnO₂/C, with a hydrogen generation rate of 194.67 μmol cm⁻¹ h⁻¹, greater than that on a Pt/TiO₂/C photocatalyst, which can be attributed to the effective inhibiting of CO poisoning, thus maintaining the catalyst's surface area in methanol oxidation.     

Using ADABOOST and Rough Set Theory for Predicting Debris Flow Disaster

Debris flow resulting from typhoons, heavy rainfall, tsunamis or other natural disasters is a matter of particular importance to Taiwan owing to the country’s unique geographical environment and exacerbated by poor slope management and global warming. With regard to these types of natural occurrences, recent global events have attracted the attention of experts in various fields, such as civil engineering, environmental engineering and information management. These experts have developed several techniques to study the various factors of debris flow. The ADABOOST and rough set theory (RST) are two emerging methods with regard to classification and rule provision. The ADABOOST, an adaptive boosting machine learning algorithm, uses very little memory during computation and can obtain robust classification results. RST is able to deal with uncertainties and vague information in generating rules for decision makers. Thus, this study develops an ADARST model which uses the unique strengths of the ADABOOST and RST in classification and rule generation and applies the proposed ADARST to analyze debris flow. Specifically, data from previous studies were obtained and used for the purposes of this study. Experimental results have shown that the proposed ADARST model is able to generate better results than those in previous investigations in terms of prediction accuracy. In addition, the designed ADARST model can provide rules including forward and backward reasoning ways for decision makers. Therefore, the proposed ADARST model is shown to be an effective methodology with which to analyze debris flow.     

Application of the generalized method of cells principle to particulate-reinforced metal matrix composites

A three-dimensional model based on the generalized method of cells (GMC) principle has been used to predict the effective properties of particulate-reinforced metal matrix composites (PMMCs). The effects of constituent phases on the elastic properties of PMMCs are predicted using GMC. The predictions are compared with an assortment of finite-element predictions and experimental results available in the literature. The accuracy and the computational efficiency of the GMC model are also discussed. Moreover, the effect of particle shape and orientation on the elastic properties of PMMCs has been predicted and analyzed. Cubical and parallelepiped shaped particles having different orientations are considered for this study. Significant variations are noted on the elastic properties of the PMMC systems by altering the shape and orientation of the particles.     

Roughness-enhanced reliability of MOS tunneling diodes

Both electrical and optical reliabilities of PMOS and NMOS tunneling diodes are enhanced by oxide roughness, prepared by very high vacuum prebake technology. For rough PMOS devices, as compared to flat PMOS devices, the Weibull plot of T_BD shows a 2.5-fold enhancement at 63% failure rate, while both the D₂ and H₂-treated flat PMOS devices show similar inferior reliability. For rough NMOS devices, as compared to flat NMOS devices, the Weibull plot of T_BD shows a 4.9-fold enhancement at 63% failure rate. The time evolutions of the light emission from rough PMOS and NMOS diodes degrade much less than those of flat PMOS and NMOS diodes. The momentum reduction perpendicular to the Si/SiO₂ interface by roughness scattering could possibly make it difficult to form defects in the bulk oxide and at the Si/SiO₂ interface by the impact of the energetic electrons and holes     

New voice over Internet protocol technique with hierarchical datasecurity protection

The authors propose a voice over Internet protocol (VoIP) technique with a new hierarchical data security protection (HDSP) scheme. The proposed HDSP scheme can maintain the voice quality degraded from packet loss and preserve high data security. It performs both the data inter-leaving on the inter-frame of voice for achieving better error recovery of voices suffering from continuous packet loss, and the data encryption on the intra-frame of voice for achieving high data security, which are controlled by a random bit-string sequence generated from a chaotic system. To demonstrate the performance of the proposed HDSP scheme, we have successfully verified and analysed the proposed approach through software simulation and statistical measures on several test voices     

Role of magnesium in cast aluminium alloy matrix composites

Wetting between the dispersoid and the matrix alloy is the foremost requirement during the preparation of metal matrix composites (MMC) especially with the casting/liquid metal processing technique. The basic principles involved in improving wetting fall under three categories: (i) increasing the surface energies of the solids, (ii) decreasing the surface tension of the liquid matrix alloy, and (iii) decreasing the solid/liquid interfacial energy at the dispersoid matrix interface. The presence of magnesium, a powerful surfactant as well as a reactive element, in the aluminium alloy matrix seems to fulfil all the above three requirements. The role played by magnesium during the synthesis of aluminium alloy matrix composites with dispersoids such as zircon (ZrSiO₄), zirconia (ZrO₂), titania (TiO₂), silica (SiO₂), graphite, aluminium oxide (Al₂O₃) and silicon carbide (SiC), has been analysed. The important role played by the magnesium during the composite synthesis is the scavenging of the oxygen from the dispersoid surface, thus thinning the gas layer and improving wetting and reaction-aided wetting with the surface of the dispersoid. The combinations of magnesium and aluminium seem to have some synergistic effect on wetting.