Instability of solid–liquid interface in transitional metal–carbide systems

The instability of solid–liquid interface (ISLI) during the liquid-phase sintering was studied using carbide–Ni composites. Of the various transitional metal carbides TiC of 4th period is the only carbide that exhibits a strong ISLI with negative curvatures in molten Ni. No ISLI was observed for other carbides in the 5th and 6th periods. The origin of ISLI is strain developed at the interface between the carbides and the newly formed solid solutions. The difference in the size of the atoms involved can be used to predict the formation of a carbide–Ni solid solution when the Hume-Rothery rules are applied. Aside from the size factor, other factors in the rules are not effective in predicting this phenomenon.     

Reduction of optical beat interference using gain-saturated RSOA in upstream WDM/SCM optical links

A new scheme for reducing optical beat interference (OBI) noise in optical network units is proposed for subcarrier multiplexing-based access network applications. The optical spectrum of the transmit lasers is broadened by using a radio frequency (RF) clipping tone with a modulation depth greater than one. This reduces the impact of the OBI noise. The distortions caused by an RF clipping tone are also suppressed by introducing a gain-saturated reflective optical amplifier, which shows the characteristics of high-pass filter. The proposed scheme has been verified by measuring the error vector magnitude of 16QAM signal with 20 Mbps. Error-free transmission has been achieved even when the light of OBI-noise-causing lasers is stronger than that of the signal laser by 7 dB     

Analysis of matrix damage evolution in laminated composite plates

A new model has been developed to investigate matrix cracking in laminated fibrous composite structures. The model can predict matrix cracking and its effect on stiffness reduction. It can also compute the load transfer from the cracked matrix to surrounding fibers. The model is based on the micromechanical concept of the fiber and matrix as well as the matrix material degradation concept as matrix cracking progressed. The micromechanical concept uses a rectangular cell geometry representing a fiber and its surrounding matrix while the material degradation concept uses an empirical expression of a Weibull type function. Two material constants are required for matrix cracking. The constants were obtained from an experiment on matrix cracking. With those constants, the present model predicts the matrix cracking in other cases. The predicted solutions were comparable to the experimental data.     

Strength of Al-Zn-Mg-Cu matrix composite reinforced with SiC particles

The AA7075 alloys reinforced with SiC and without SiC particles were fabricated by a pressureless infiltration method, and then, their tensile properties and microstructures were analyzed. The spontaneous infiltration of molten metal at 800 °C for 1 hour under a nitrogen atmosphere made it possible to fabricate 7075 Al matrix composite reinforced with SiC, as well as a control 7075 Al without SiC. A significant strengthening even in the control alloy occurred due to the formation of in-situ AlN particle even without an addition of SiC particles. Composite reinforced with SiC particles exhibited higher strength values than the control alloy in all aging conditions (underaged (UA), peak-aged (PA), and overaged (OA)), as well as a solution treated condition. Spontaneous infiltration was further prompted owing to the combined effect of both Mg and Zn. This may lead to an enhancement of wetting between the molten alloy and the reinforcement. Consequently, strength improvement in a composite may be attributed to good bond strength via enhancement of wetting. The grain size of the control alloy is greatly decreased to about 2.5 μm compared to 10 μm for the commercial alloy. In addition, the grain size in the composite is further decreased to about 2 μm. These grain refinements contributed to strengthening of the control alloy and the composite.     

Acidogenic fermentation of blended food‐waste in combination with primary sludge for the production of volatile fatty acids

The performance of a laboratory‐scale anaerobic acidogenic fermenter fed with a mixture of blended kitchen food‐waste and primary sludge from a sewage treatment plant was investigated for the production of volatile fatty acids (VFA). The operating variables for acidogenic fermentation were kitchen food‐waste content (10 and 25 wt %), hydraulic retention time (HRT: 1, 3 and 5 days), temperature (ambient: 18 ± 2 °C, and mesophilic: 35 ± 2 °C) and pH (varied from 5.2 to 6.7). The experimental results indicated that effluent VFA concentrations and VFA production rates were higher at ambient temperature than at mesophilic conditions. The net amount of VFA with 10 wt % food‐waste increased up to 920 mg dm^?3 with an increase of HRT, but contrasting results (a decrease of 2610 mg dm^?3) were found due to the conversion of VFA into biogas in the case of 25 wt % food‐waste, which increased significantly at HRT of 3–5 days. In terms of biogas composition (CO₂ and CH₄), the organic matter was converted into CO₂ through the oxidative pathway by facultative species at low temperature while mesophilic temperature and optimum pH (6.3–7.8) played a pivotal role in increasing rate of conversion of VFA into biogas by methanogenesis. Rates of VFA production and their conversion are dependent on the food‐waste content in the mixture. Yet, the higher concentration of food‐waste (25% compared with 10%) did not produce VFA proportionally due to the increased rate of conversion of VFA into gaseous products. The maximum VFA production rate (0.318 g VFA_produced g^?1 VS_fed day^?1) was achieved in the 10 wt % food‐waste at ambient temperature and at a 5‐day HRT. Copyright © 2005 Society of Chemical Industry     

Use of a neural network to link AFM etch patterns to plasma parameters

Plasmas play a critical role in depositing thin films or etching fine patterns while manufacturing integrated circuits. A new model for plasma diagnosis is presented. This was accomplished by linking atomic force microscopy (AFM) to plasma parameters using a neural network. Experimental AFM data were collected during the etching of silicon oxynitride films in C₂F₆ inductively coupled plasma. Surface roughness of etched patterns was characterized by means of discrete wavelet transformation. This led to the construction of three vertical (type I), diagonal (type II), and horizontal (type III) wavelet coefficient-based models. The performance of diagnosis models was evaluated in terms of the prediction and recognition accuracies. Both accuracies were optimized as a function of the number of hidden neurons. Comparisons revealed that the type I model yielded the largest recognition and the smallest prediction error. This was demonstrated even under stricter monitoring conditions. More improved diagnosis is expected by enhancing AFM resolution.     

Effects of reducing and oxidizing atmospheres on the PTCR characteristics of porous n-BaTiO3 ceramics by adding polyethylene glycol

Donor doped BaTiO₃ (n-BaTiO₃) ceramics were fabricated by adding polyethylene glycol (PEG) at 20 wt %. The effects of reducing and oxidizing atmospheres on the PTCR characteristics of the porous n-BaTiO₃ ceramics were investigated. The PTCR characteristics of the porous n-BaTiO₃ ceramics is strongly affected by chemisorbed oxygen at the grain boundaries and are recovered as the atmosphere is changed from the reducing gas to oxidizing gas. The low room-temperature resistivity of the porous n-BaTiO₃ ceramics in reducing atmospheres may be caused by the decrease in potential barrier height, which originates from an increase in the number of electrons owing to the desorption of chemisorbed oxygen atoms at the grain boundaries. In addition, the high room-temperature resistivity of the porous n-BaTiO₃ ceramics in oxidizing atmospheres may be caused by the increase in potential barrier height, which results from the adsorption of chemisorbed oxygen atoms at the grain boundaries.     

Strength and fracture toughness of nano and micron-silica particles bidispersed epoxy composites: evaluated by fragility parameter

In this study, we discuss the composition effect of 240 nm and 1.56 μm-silica particles on strength and fracture toughness by examining two parameters, fragility and glass transition temperature, that were derived from the thermo-viscoelasticity measurements. Experimental results showed that the composites had a lower fragility with higher strength and fracture toughness as the content of nanoparticles was increased regardless of glass transition temperature. The improvement in mechanical properties from adding nanoparticles was definitely explained by the fragility represented the heterogeneity in polymer matrix, and this was related to the interaction between particles and matrix. The fragility was found to be an effective parameter for evaluating strength and fracture toughness of epoxy composite containing a bidispersion of nano and micron-silica particles.