Sol-Gel Alumina Coating for Improved Cyclic Oxidation Resistance of Silicon Nitride

A 25 nm thick α-alumina layer was deposited on a turbine-grade silicon nitride by sol-gel dip coating and subsequent heat treatment in air at 1200°C. This layer had a nanometer grain structure. Silicon nitride protected by this thin layer showed a significant improvement in oxidation resistance over its uncoated counterpart after 200 cyclic exposures in air at 1250°C. The oxide layer grown on the coated silicon nitride also exhibited superior surface morphology, compared with the uncoated silicon nitride.     

Characterization and physical properties of polymethylphenylsilsesquioxane (PMPSQ) and hydroxyl‐functionalized polystyrene (PS–OH) hybrids

Polymethylphenylsilsesquioxane (PMPSQ–OH) and trimethylsilyl end‐blocked PMPSQ (PMPSQ–EC) were prepared. The thermal decomposition behavior of these polymers was studied by thermogravimetric analysis (TGA) and FT‐Raman spectroscopy. Hydroxyl‐functionalized polystyrene (PS–OH) was also prepared by anionic living polymerization. Thin hybrid films of PMPSQ/PS–OH with various blend ratios were obtained by spin‐coating on freshly cleaned glass. The surface morphology of the hybrid films was investigated by atomic force microscopy (AFM). In 80/20 PMPSQ/PS–OH hybrid film, the PS–OH component produced a very uniformly dispersed phase. This hybrid film contained small domains of PS–OH whose size ranged from 60 to 80 nm. As the content of PS–OH was increased, the domain morphology coarsened and phase inversion took place around 50 wt %. In the phase‐inversed system, the PMPSQ‐rich phase was uniformly distributed in the PS–OH‐rich continuous phase. In addition, temperature‐dependent dielectric properties of PMPSQ/PS–OH hybrids were investigated. Relaxation of the hybrids was observed with an increasing content of the PS–OH component due to the amorphous glass transition behavior of PS–OH. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2801–2812, 2003     

Honey bees mating optimization algorithm for process planning problem

Process planning is a very important function in the modern manufacturing system. It impacts the efficiency of the manufacturing system greatly. The process planning problem has been proved to be a NP-hard problem. The traditional algorithms cannot solve this problem very well. Therefore, due to the intractability and importance of process planning problem, it is very necessary to develop efficiency algorithms which can obtain a good process plan with minimal global machining cost in reasonable time. In this paper, a new method based on honey bees mating optimization (HBMO) algorithm is proposed to optimize the process planning problem. With respect to the characteristics of process planning problem, the solution encoding, crossover operator, local search strategies have been developed. To evaluate the performance of the proposed algorithm, three experiments have been carried out, and the comparisons among HBMO and some other existing algorithms are also presented. The results demonstrate that the HBMO algorithm has achieved satisfactory improvement.     

Thermal behavior and the determination of the polymer-polymer interaction parameter of polycarbonate and a thermotropic liquid crystalline polymer blends

Summary The surface modification of low-density polyethylene(PE) by liquid phase photograft polymerization with acrylic acid(AA), acrylamide(AM) and glycidyl methacrylate(GMA) was described. The grafting of AA and AM was proved and characterized by electron spectroscopy for chemical analysis(ESCA). It was found that fully hydrophilic surface can be obtained in very short irradiation time. With ESCA and attenuated total reflection infrared spectroscopy(ATR-IR), it can be confirmed that bifunctional monomer GMA was grafted onto the PE film surface. Through further reaction with GMA grafted film, heparin and protamine were immobilized onto the grafted film surface.     

The structure of model coatings: latex-bound plastic pigment coatings

The immobilization and consolidation of model coatings based on monodisperse polystyrene (plastic pigment) and S/B latexes of known particle sizes were studied in terms of their packing volumes and the extent of latex shrinkage, which was found to increase with increasing pigment volume up to the critical pigment volume concentration (CPVC). The maximum latex shrinkage was estimated from the CPVC. Then, the porosity of model coatings was calculated based on three proposed latex shrinkage models: maximum, minimum, and linearly decreasing latex shrinkage. The number of pores and the average equivalent spherical pore diameters were subsequently calculated. The opacity and gloss of model coatings on polyester films were measured and their porosity was also determined by a simple coat weight-thickness method. The CPVC values determined by the opacity, gloss, and porosity versus PVC relationships, respectively, agreed very well with each other. The CPVCs determined by the opacity and porosity versus PVC curves were identical. The comparison between the theoretically calculated and experimental porosity values showed that the linearly decreasing value between the maximum and minimum latex shrinkage would best fit the experimental porosity data. The effect of plastic pigment particle size on the optical properties and porosity of model coatings was also studied and it was observed that the coating opacity and porosity increased with increasing plastic pigment particle size, but the gloss decreased. Additionally, a minimum crack-free temperature (MCFT) of latex-bound coatings was proposed to better predict the behaviors of latexes as pigment binders. The wet state of model coating dispersions, the surfaces of consolidated model coatings, and their internal structure were examined by both electron and atomic force microscopy, and their micrographs were found to be consistent with our immobilization and consolidation models.     

Development of bond strength model for FRP plates using back‐propagation algorithm

For the flexural reinforcement of bridge and building structure, synthetic materials whose dynamic properties are superior and those containing the merit of corrosion‐proof are widely used as the substitute for a steel plate. Since FRP plate has improved bond strength owing to the fibers externally adhering to the plate, many researches regarding the bond strength improvement have been substantially performed. To search out such bond strength improvement, previous researchers had ever examined the bond strength of FRP plate through their experiment by setting up many variables. However, since the experiment for a research on the bond strength takes much of expenditure for setting up the equipment and is time‐consuming, also is difficult to be carried out, it is limitedly conducted. The purpose of this study was to develop the most suitable artificial neural network model by application of various neural network models and algorithm to the data of the bond strength experiment conducted by previous researchers. Many variables were used as input layers against bond strength: depth, width, modulus of elasticity, tensile strength of FRP plate and the compressive strength, tensile strength, and width of concrete. The developed artificial neural network model has been applied back‐propagation, and its error was learned to be converged within the range of 0.001. Besides, the process for the over‐fitting problem has been dissolved by Bayesian technique. The verification on the developed model was executed by comparison with the test results of bond strength made by other previous researchers, which was never been utilized to the learning as yet. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 5119–5127, 2006     

Mechanical properties and morphology of polymer blends of poly(ethylene terephthalate) and semiflexible thermotropic liquid crystalline polyesters

Two thermotropic liquid crystalline polyesters (TLCPs) with long flexible spacer groups in the main chain were prepared by melt polymerization: one was a homopolymer with only decane groups (LCPHO) and the other was a copolymer with hexane or decane groups (LCPCO) between mesogen units. These polyesters were blended with a matrix polymer of poly(ethylene terephthalate) (PET). Scanning electron microscopy (SEM) revealed the excellent interfacial adhesion between polyester and PET, and the large aspect ratio of polyester microfibrils in the blend fiber made by extruding and drawing the blend through a die. The aspect ratio was estimated by using the modified Halpin-Tsai equation. The fiber with LCPHO showed more extensive fibril formation than that with LCPCO.     

New Process for the Preparation of Monodispersed, Spherical Silica Particles

A new method is presented for preparing highly monodispersed silica particles using a two-stage semibatch/batch hydrolysis reaction of Si(OC₂H₅)₄. The slower rate of hydrolysis of the tetraethylorthosilicate (TEOS) that occurred during the semibatch process resulted in larger silica particles with a higher yield and narrower size distribution. This was in direct contrast to the batch process. In addition, the ability of four different mixed processes to produce silica particles with good packing density, narrower particle-size distribution, and higher yield were evaluated. These were batch/batch (B-B), batch/semibatch (B-S), semibatch/batch (S-B), and semibatch/semibatch (S-S) processes. The S-S system produced the largest particles with the highest yields. The size of the silica particles obtained by the S-B method decreased with increasing reaction time, while the particles obtained by the B-S process had the best particle-size distribution and packing density. In conclusion, a mixed batch/semibatch system was the best way to produce an extremely narrow particle-size distribution and a good packing density.