A novel technique for fabrication of near-net-shape CMCs

A sol-gel vacuum infiltration technique has been developed for the fabrication of near-net-shape ceramic matrix composites (CMCs) using discontinuous mullite fibre preform with 15 vol.% of fibre content and ZrO₂.10 wt.% Y₂O₃ sol as the infiltrant. Effect of sol viscosity, number of infiltration and calcination temperature on physico-mechanical properties of fabricated CMCs were examined. Characterization of the fibre preform, matrix material (in the form of ceramic specimen without fibre) and the developed CMCs were performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD indicated the presence of cubic (c) and tetragonal (t) zirconia in both the CMCs and the ceramic specimens calcined even at 1400°C. Flexural strength of the CMCs and the ceramic specimens (calcined at 1400°C), determined by the three-point bending test, was found to be about 14 mPa and 1.40 mPa, respectively. SEM indicated multiple fracture of the matrix which gave rise to pseudo elasticity. This is also evident from the load-displacement curve of the three-point bend test. SEM studies also indicated fibre pull-out in the fracture surface of the CMCs.     

UV assisted stabilization routes for carbon fiber precursors produced from melt-processible polyacrylonitrile terpolymer

A low-cost route for producing PAN-based carbon fibers is being developed. The approach involves forming polyacrylonitrile terpolymers that can be melt-spun into fibers. The fibers are then stabilized and carbonized to yield carbon fibers. Melt-processibility, however, precludes direct thermal stabilization of these polymeric fibers. Therefore, a precursor terpolymer containing acryloyl benzophenone (ABP) is used. The UV sensitivity of ABP moiety enhances the UV crosslinkability of the precursor fibers. After a brief exposure to UV radiation, the melt-spun terpolymer fibers can be oxidatively stabilized at 320 °C without melting and subsequently carbonized. UV-visible and ATR-IR spectroscopic analyses suggest that UV radiation induces the formation of free radicals which, in turn, cyclize the PAN. Cyclized PAN was characterized by a strong absorbance in UV-visible region (300-500 nm) due to conjugated >CC< and >CN- bonds which were also detected by infrared spectroscopy.     

Understanding the influence of anti-reversion agent and metal oxide dose on natural rubber–carbon black system

Sulfidic linkages that are formed during the vulcanization process of natural rubber (NR) are unstable at a higher temperature and can be reversed into conjugated diene. To overcome such issue and to build a compound that is hostile to inversion and with increasing service life, anti-reversion agent (ARA), for example, N,N′-4,4′-diphenylmethyene bismaleimide (BMDM), is added into the formulation. This work explains the conjugation reaction mechanism of conjugated diene and BMDM by means of gas chromatography–mass spectrometry and Fourier transform infrared spectroscopy. The first phase of this study is associated with the change in ARA dosage keeping ZnO dosage the same. It is observed that 5 phr of BMDM and 2 phr ZnO combination (ARA4) shows lowest reversion at 160°C. The modulus value at 300% elongation increased 12% by the incorporation of BMDM as compared to the compound of no BMDM (ARA1). The second part is all about keeping BMDM dosage the same at 5 phr level and varying ZnO phr by 3, 4, and 5. From the overall results, it is observed that at a suitable dosage of BMDM and ZnO (5 phr BMDM and 3 phr ZnO combination [ARA5]), least reversion can be achieved and vulcanizates containing optimized BMDM and ZnO show better retention properties after aerobic aging as compared to ARA1.     

RFL coated aramid short fiber reinforced thermoplastic elastomer: Mechanical, rheological and morphological characteristics

Composite based on a new generation metallocene catalyzed thermoplastic elastomer ethylene-octene copolymer (EOC) and resorcinol formaldehyde latex (RFL) coated aramid short fiber was prepared by varying the short fiber loading from 1 to 10 phr. The mechanical, morphological and rheological characterizations were carried out. The impact of a low molecular weight maleic anhydride grafted 1, 2 polybutadiene (MA-g-PB) on various properties was also investigated. It has been observed that with increasing the short fiber content both the low strain modulus and modulus at 100% increase but the tensile strength and elongation at break decrease. The improvements in tensile strength coupled with elongation at break and good fiber dispersion particularly at high fiber loaded composite were achieved with the incorporation of MA-g-PB, which indicates that it acts as an interface modifier through compatibilization between the fiber and the EOC matrix as well as a good dispersing agent. The understanding of adhesion between the fiber and the polymer and the sticking of polymer traces on the tensile fractured fiber surface of the composite by scanning electron microscopic analyses further support the compatibilizing action of MA-g-PB. The melt rheological behavior such as storage modulus, loss modulus, complex viscosity and storage viscosity of the composites were investigated using a Rubber Process Analyser (RPA) under strain and frequency sweep mode.     

Influence of PVP buffer layer on the formation of NaA zeolite membrane

The support substrates were modified with the aqueous solutions of 1 and 3 wt% of polyvinyl pyrrolidine (PVP) as intermediate buffer layer followed by NaA zeolite seed (prepared hydrothermally at 85 °C for 2 h) coating with 2.5 wt% aqueous dispersion in each case. A better surface coverage with the oriented layer of NaA seed crystals was found with 1 wt% PVP buffer layer. The secondary crystallization of NaA membranes in the PVP-seed-coated supports was carried out hydrothermally at 65 °C for 2, 4, 6 h (single-stage each) and (2 + 2), (4 + 2)h (double-stage each) crystal growth processes. The crystallization behaviours of NaA membranes were studied by X-ray diffraction (XRD) while the microstructures of the same films were observed by scanning electron microscope (SEM). The single-stage secondary crystallization at 65 °C for 4 h showed highly interlocked and oriented NaA grains in the membranes and it rendered the permeance value of 2.2 × 10⁻⁸ mol m⁻²s⁻¹Pa⁻¹ for single gas, nitrogen (N₂) at ambient temperature (30 °C).     

Terpolymers from lactide and bisphenol a derivatives: Scale‐up,properties, and blends

Terpolymerization of L‐lactide (LA) and bisphenol A derivatives was performed on few hundred gram scale, and the resultant terpolymer (TP) was characterized by gel permeation chromatography, infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermogravimetric analysis. Moderate molecular weight (M_n ～ 12 kg/mol) TP was achieved with glass transition temperatures about 100°C (DSC and DMA). The TP exhibited improved thermal stability compared with polylactide (PLA), with a thermal degradation temperature of about 80°C higher than PLA. Although the TP exhibited distinctly different surface morphology compared with that of PLA, both showed similar contact angle and surface energy (ca. 40 mN/m) properties. Blends of PLA and TP showed enhanced glass transition (～ 5°C change in T_g) temperatures compared with PLA homopolymer. This is due to the compatibility of PLA and TP. Thus, TP could be used as an additive for PLA‐based blends to enhance compatibility with phenolic‐based resins. TP electrospun fiber morphology is also reported. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Physicochemical Characterization of Selected Sweet Potatocultivars and Their Starches

The uses of sweet potato tubers rely on the physicochemical and functional properties of its starch. The different properties studied from 14 lines include cooking quality, extractable starch, dry matter, starch, sugar, carotenoids, and anthocyanin. The properties of extracted starch like swelling volume, solubility, amylose content, clarity of paste, rheological properties were examined. The organic matter content of different lines almost remained the same. Starch content of the tubers was greater than 20% and the sugar content ranged from 1–3%. The extractable starch was in the range of 16–21%. The anthocyanin content was high for ST- 13, while ST- 14 was rich in carotene. The swelling volume was comparatively low and the solubility ranged from 8.81–13.65%. Most of the starches examined in this present study displayed excellent viscosity properties with peak viscosity greater than 3000 cP. This study revealed that many lines have excellent potential for use as nutritive and calorific food and as industrial raw material.     

Synthesis of Nanofiber‐like Mesoporous γ‐Al2O3 toward Its Adsorption Efficiency for Congo Red

Nanofiber‐like mesoporous γ‐Al₂O₃ was synthesized using freshly prepared boehmite sol in the presence of triblock copolymer, P123 following evaporation‐induced self‐assembly (EISA) process followed by calcinations at 400°C–1000°C. The samples were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X‐ray diffraction (XRD), N₂ adsorption–desorption, and transmission electron microscopy (TEM). The adsorption efficiency of the samples with Congo red (CR) was studied by UV – vis spectroscopy. XRD results showed boehmite phase in the as‐prepared sample while γ‐Al₂O₃ phase obtained at 400°C was stable up to 900°C, a little transformation of θ‐Al₂O₃ resulted at 1000°C. The Brunauer‐Emmett‐Teller surface area of the 400°C‐treated sample was found to be 175.5 m²g ^{? 1}. The TEM micrograph showed nanofiber‐like morphology of γ‐Al₂O_3. The 400°C‐treated sample showed about 100% CR adsorption within 60 min.     

Simulation-based SONET ADM optimization approach for dynamic traffic grooming in WDM optical networks

The article addresses a simulation-based optimization approach for allocation of ADMs in WDM optical networks with stochastic dynamic traffic. Since ADMs are expensive, it is desirable that if each node in WDM optical networks can use a minimum number of ADMs to achieve a near-ideal performance. In this article, first, the utilization statistics of ADMs are gathered by simulation. Then, ADMs are allocated based on the utilization statistics. In this respect, a simple sorting mechanism is used. The distinguished feature of the proposed approach is that it shows the way to allocate ADMs at the nodes of WDM optical networks with stochastic dynamic traffic. The experimental results ensure that the proposed approach can solve the problem of allocating ADMs in practical WDM optical networks considering stochastic dynamic traffic.

A survey of cellular automata: types,dynamics, non-uniformity and applications

Cellular automata (CAs) are dynamical systems which exhibit complex global behavior from simple local interaction and computation. Since the inception of cellular automaton (CA) by von Neumann in 1950s, it has attracted the attention of several researchers over various backgrounds and fields for modeling different physical, natural as well as real-life phenomena. Classically, CAs are uniform. However, non-uniformity has also been introduced in update pattern, lattice structure, neighborhood dependency and local rule. In this survey, we tour to the various types of CAs introduced till date, the different characterization tools, the global behavior of CAs, like universality, reversibility, dynamics etc. Special attention is given to non-uniformity in CAs and especially to non-uniform elementary CAs, which have been very useful in solving several real-life problems.