Electrothermal Ageing of Epoxy Nanocomposites

Constant stress accelerated ageing experiments were conducted on unfilled epoxy and epoxy alumina nanocomposites with different filler loadings of 0.1, 1 and 5 wt%. Electrical (6 kV/mm), thermal (60 degrees C) and combined electrothermal (6 kV/mm and 60 degrees C) ageing experiments were performed for a duration of 250 h. The leakage current through the samples were continuously monitored and the variation in the tan delta values with ageing duration was also monitored. It was observed that the increase in the tan delta value with ageing duration was less for the epoxy alumina nanocomposites as compared to the unfilled epoxy. Dielectric spectroscopy measurements were performed on the samples before and after the ageing in the frequency range of 10(-2) to 10(6) Hz. The permittivity and tan delta values were found to increase in the low frequency range. The volume resistivity of unfilled epoxy and epoxy alumina nanocomposites were also measured before and after the ageing. The volume resistivity improved marginally for the thermally aged samples, but reduced for the electrically aged and the electrothermally aged samples. The decrease in the value of volume resistivity was more for the multistress aged unfilled epoxy samples as compared to the multistress aged epoxy alumina nanocomposites. It was also observed that the unfilled epoxy samples having a higher value of tan delta failed first. The time to failure of the samples showed an increasing trend with an increase in the nano filler loading of epoxy alumina nanocomposites.

Influence of nature of support on the catalytic activity of supported molybdenum-oxo species in benzyl alcohol conversion

Supported catalysts containing 15 wt.% of molybdenum have been prepared by the incipient wetness impregnation method. CaO, MgO, Al2O3, Zr(OH)4 and Al(OH)3 have been used as supports for the preparation of supported Mo catalysts. Characterisation of all the materials prepared has been carried out through BET surface area measurement, X-ray diffractometry and FT-IR spectroscopy. Catalytic activity measurements have been carried out with reference to structure-sensitive benzyl alcohol conversion in the liquid phase. The percentage conversion of benzyl alcohol to benzaldehyde and toluene varied over a large range depending on the support used for the preparation of catalysts, indicating the importance of the support on catalytic activity of Mo catalysts. Al(OH)3 has been found to be the best support for molybdenum among all the supports used. Support–metal interaction (SMI) has been found to play an important role in determining the catalytic activity of supported catalysts.

Photocatalytic degradation with combustion synthesized WO3 and WO3-TiO2 mixed oxides under UV and visible light

The photocatalytic activity of commercial titanium dioxide under UV and visible radiation was improved by composites of tungsten trioxide (WO3) with TiO2. WO3 was prepared by solution combustion synthesis and the mixed oxides/composites of WO3-TiO2 were prepared in different weight ratios (0, 0.10, 0.15, 0.20, 0.25, 0.50, 0.75, and 1) by physical mixing. These catalysts were characterized by XRD, DRS, BET, SEM, TEM, pH drift method, TGA and photoluminescence. The photocatalytic activity varies with the WO3 loading in the composites. The optimum loading of WO3 in the composites was found to be 15 wt% for both UV and visible radiation. This loading showed faster dye degradation rate than commercial TiO2 (TiO2-C) and WO3 (WO3-C). The effect of initial concentrations of methylene blue (MB) and orange G (OG) and the effect of the functional group on dye degradation was studied with both anionic and cationic dyes with 15 wt% WO3-TiO2. (C) 2012 Elsevier B.V. All rights reserved.

Fabrication and characterization of micro-arc oxidized fluoride containing titania films on Cp Ti

The present study is focussed at establishing an appropriate electrolyte system for developing electrochemically stable and fluorine (F) containing titania (F-TiO2) films on Cp Ti by micro-arc oxidation (MAO) technique. To fabricate the F-TiO2 films on Cp Ti, different electrolyte solutions of chosen concentrations of tri-sodium orthophosphate (TSOP, Na3PO4 center dot I2H2O), potassium hydroxide (KOH) and various F-containing compounds such as ammonium fluoride (NH4F), potassium fluoride (KF), sodium fluoride (NaF) and potassium fluorotitanate (K2TiF6) are employed. The structural and morphological characteristics, thickness and elemental composition of the developed films have been assessed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques. The in-vitro electrochemical corrosion behavior of the films was studied under Kokubo simulated body fluid (SBF) environment by potentiodynamic polarization, long term potential measurement and electrochemical impedance spectroscopy (EIS) methods. The XRD and SEM-EDS results show that the rutile content in the films vary in the range of 15-37 wt% and the F and P contents in the films is found to be in the range of 2-3 at% and 2.9-4.7 at% respectively, suggesting that the anatase to rutile phase transformation and the incorporation of F and P into the films are significantly controlled by the respective electrolyte solution. The SEM elemental mapping results show that the electrolyte borne F and P elements are incorporated and distributed uniformly in all the films. Among all the films under study, the film developed with 5 g TSOP+2 g KOH+3 g K2TiF6 electrolyte system exhibits considerably improved in-vitro corrosion resistance and therefore best suited for biomedical applications. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Chromite-silicate chemistry of the Neoarchean Sittampundi Complex, southern India: Implications for subduction-related arc magmatism

The Neoarchean layered anorthositic complex at Sittampundi in southern India is known for its chromitite layers that are mostly associated with anorthosite (An(90-100)). The chromitites contain FeAl-rich chromites concentrated in layers between amphibole-rich layers with a dominant mineralogy of amphibole-spinel-plagiocase+/-sapphirine. The chromite-rich layers contain only amphibole and plagioclase. Mineral compositions illustrated by X-ray composition maps and profiles show subtle chemical differences. The chrome spinels are of refractory grade with Cr2O3 and Al2O3 contents varying between 34-40 wt.% and 23-28 wt.%. The chromite compositions are noticeably different from those in layered igneous intrusions of the Bushveld-Stillwater type. The existence of original highly calcic plagioclase, FeAl-rich chromite, and magmatic amphibole is consistent with derivation from a parental magma of hydrous tholeiitic composition that was most likely generated in a supra-subduction zone arc setting. In terms of mineralogy and field relations, the Sittampundi chromitites are remarkably similar to anorthosite-hosted chromitites in the Neoarchean Fiskensset anorthositic complex, Greenland. We propose that the Sittampundi chromitites formed by partial melting of unusually aluminous harzburgite in a hydrated mantle wedge above a subduction zone. This melting process produced hydrous, aluminous basalt, which fractionated at depth to give rise to a variety of high-alumina basalt compositions from which the anorthositic complex with its cumulate chromite-rich and amphibole-rich layers formed within the magma chamber of a supra-subduction zone arc. (C) 2011 Elsevier B.V. All rights reserved.

Gene expression in osteoblast cells treated with submicron to nanometer hydroxyapatite-mullite eluate particles

The present research focused on determining the effect of hydroxyapatite-20 wt% mullite (H20M) particle eluates on apoptosis and differentiation of human fetal osteoblast (hFOB) cells. The H20M particles (257 +/- 37 nm) were prepared, starting with the production of a nanocomposite using a unique route of spark plasma sintering, followed by a repeated grinding-cryo treatment and elution process. Tetrazolium based cytotoxicity assay results showed a time-and dose-dependent effect of H20M particle eluates on hFOB cytotoxicity. In particular, the results revealed statistically reduced cell viability after hFOB were exposed to the above 10% H20M (257 +/- 37 nm) eluates for 48 h. The apoptotic cell death triggered by H20M treatment was proven by the analysis of molecular markers of apoptosis, that is, the Bcl-2 family of genes. hFOB expression of Bcl-xL and Bcl-xS significantly increased 25.6- and 25.2-fold for 50% of H20M concentrations, respectively. The ratio of Bcl-xL/Bax (4.01) decreased 2-fold for hFOB exposed to 100% of H20M eluates than that for 10% H20M eluate (7.94) treated hFOB cells. On the other hand, the Bcl-xS/Bax ratio for the 10% H20M eluate was 4.15-fold, whereas for 100% H20M eluates, it was 11.55-fold. Specifically, the anti-apoptotic effect of the H20M particle eluates was corroborated by the up-regulation of bone cell differentiation marker genes such as, collagen type I, cbfa, and osteocalcin. In summary, the present work clearly demonstrated that H20M submicron to nanometer composite particle eluates have a minimal effect on hFOB apoptosis and can even up-regulate the expression of bone cell markers at the molecular level.

Accelerated multistress aging of polymer nanocomposites and its condition monitoring

In recent years, the time dependant maintenance of expensive high voltage power equipments is getting replaced by condition based maintenance so as to detect apriori an impending failure of the equipment. For condition based maintenance, most monitoring systems concentrate on the electrical quantities such as measurement and evaluation of partial discharges, tan delta, tip-up test, dielectric strength, insulation resistance, polarization and depolarization current. However, in the case of equipments being developed with novel nanodielectric insulating materials, the variation in these parameters before an impending failure is not available. Hence in this work, accelerated electrothermal aging studies have been conducted on unfilled epoxy as well as epoxy nanocomposite samples of 5 wt% filler loading, and the tan d values were continuously monitored to obtain the condition of the samples under study. It was observed that those samples whose tan d increased at a rapid rate failed first.

In vitro cytotoxicity and in vivo osseointergration properties of compression-molded HDPE-HA-Al2O3 hybrid biocomposites

The aim of this study was to investigate the in vivo biocompatibility in terms of healing of long segmental bone defect in rabbit model as well as in vitro cytotoxicity of eluates of compression-molded High density polyethylene (HDPE)hydroxyapatite (HA)-aluminum oxide (Al2O3) composite-based implant material. Based on the physical property in terms of modulus and strength properties, as reported in our recent publication, HDPE-40 wt % HA and HDPE-20 wt % HA-20 wt % Al2O3 hybrid composites were used for biocompatibility assessment. Osteoblasts cells were cultured in conditioned media, which contains varying amount of composite eluate (0.01, 0.1, and 1.0 wt %). In vitro, the eluates did not exhibit any significant negative impact on proliferation, mineralization or on morphology of human osteoblast cells. In vivo, the histological assessment revealed neobone formation at the bone/implant interface, characterized by the presence of osteoid and osteoblasts. The observation of osteoclastic activity indicates the process of bone remodeling. No inflammation to any noticeable extent was observed at the implantation site. Overall, the combination of in vitro and in vivo results are suggestive of potential biomedical application of compression-molded HDPE- 20 wt % HA- 20 wt % Al2O3 composites to heal long segmental bone defects without causing any toxicity of bone cells.

Fine scale characterization of surface/subsurface and nanosized debris particles on worn Cu-10 % Pb nanocomposites

The identification of the damage mechanisms involved in the wear process demands the finer scale characterization of the surface, as well as the subsurface region of the wear scar region, and to this end, this article discusses the results obtained with Cu-10 wt% Pb-based metallic nanocomposites using a host of characterization techniques, including transmission electron microscopy and ion milling microscopy. Apart from finer scale characterization to understand deformation and cracking during the wear process, X-ray photoelectron spectroscopy analysis of wear debris confirms the occurrence of oxidation of Pb phase to Pb3O4. In order to understand the role of oxides on friction and wear, sliding wear tests in argon were also carried out and such tests did not result in the formation of any tribo-oxides, as confirmed using electron probe microanalysis. Conclusively, oxidative wear is attributed as the dominant wear mechanism in ambient conditions for Cu-10 wt% Pb composite.

Microscopic and dielectric studies of ZnO nanoparticles loaded in ortho-chloropolyaniline nanocomposites

We have studied the preparation of zinc oxide nanoparticles loaded in various weight percentages in ortho-chloropolyaniline by in situ polymerization method. The length of the O-chloropolyaniline tube is found to be 200 nm and diameter is about 150 nm wherein the embedded ZnO nanoparticles is of 13 nm as confirmed from scanning electron microscopy as well as transmission electron microscopy characterizations. The presence of the vibration band of the metal oxide and other characteristic bands confirms that the polymer nanocomposites are characterized by their Fourier transmission infrared spectroscopy. The X-ray diffraction pattern of nanocomposites reveals their polycrystalline nature. Electrical property of nanocomposites is a function of the filler as well as the matrix. Cole-Cole plots reveal the presence of well-defined semicircular arcs at high frequencies which are attributed to the bulk resistance of the material. Among all nanocomposites, 30 wt% shows the low relaxation time of 151 s, and hence it has high conductivity.

Reactive hot pressing of Ti-B-C and Ti-C at 1200 degrees C

Stoichiometric and non-stoichiometric powder mixtures of Ti-B4C and Ti-C with 1 wt% Ni were reactively hot pressed at 40 MPa, 1200 degrees C for 30 min. In both systems, the combined presence of Ni and non-stoichiometry enabled complete densification. While in Ti-C, non-stoichiometry by itself plays a significant role in promoting densification, the formation of intermediate borides in Ti-B4C powder mixtures requires the additional presence of Ni which promotes full reaction through the formation of a transient liquid as established previously in Ti-BN powder mixtures.

Euglena sp as a suitable source of lipids for potential use as biofuel and sustainable wastewater treatment

Prolific algal growth in sewage ponds with high organic loads in the tropical regions can provide cost-effective and efficient wastewater treatment and biofuel production. This work examines the ability of Euglena sp. growing in wastewater ponds for biofuel production and treatment of wastewater. The algae were isolated from the sewage treatment plants and were tested for their nutrient removal capability. Compared to other algae, Euglena sp. showed faster growth rates with high biomass density at elevated concentrations of ammonium nitrogen (NH4-N) and organic carbon (C). Profuse growth of these species was observed in untreated wastewaters with a mean specific growth rate (mu) of 0.28 day(-1) and biomass productivities of 132 mg L-1 day(-1). The algae cultured within a short period of 8 days resulted in the 98 % removal of NH4-N, 93 % of total nitrogen 85 % of ortho-phosphate, 66 % of total phosphate and 92 % total organic carbon. Euglenoids achieved a maximum lipid content of 24.6 % (w/w) with a biomass density of 1.24 g L-1 (dry wt.). Fourier transform infrared spectra showed clear transitions in biochemical compositions with increased lipid/protein ratio at the end of the culture. Gas chromatography and mass spectrometry indicated the presence of high contents of palmitic, linolenic and linoleic acids (46, 23 and 22 %, respectively), adding to the biodiesel quality. Good lipid content (comprised quality fatty acids), efficient nutrient uptake and profuse biomass productivity make the Euglena sp. as a viable source for biofuel production in wastewaters.

Heat conduction mechanisms in hot pressed ZrB2 and ZrB2-SiC composites

Thermal diffusivity and conductivity of hot pressed ZrB2 with different amounts of B4C (0-5 wt%) and ZrB2-SiC composites (10-30 vol% SiC) were investigated experimentally over a wide range of temperature (25-1500 degrees C). Both thermal diffusivity and thermal conductivity were found to decrease with increase in temperature for all the hot pressed ZrB2 and ZrB2-SiC composites. At around 200 degrees C, thermal conductivity of ZrB2-SiC composites was found to be composition independent. Thermal conductivity of ZrB2-SiC composites was also correlated with theoretical predictions of the Maxwell Eucken relation. The dominated mechanisms of heat transport for all hot pressed ZrB2 and ZrB2-SiC composites at room temperature were confirmed by Wiedemann Franz analysis by using measured electrical conductivity of these materials at room temperature. It was found that electronic thermal conductivity dominated for all monolithic ZrB2 whereas the phonon contribution to thermal conductivity increased with SiC contents for ZrB2-SiC composites.

Multiple molecular alterations in phosphodegrons 1-3 within AAV2 capsid demonstrates higher hepatic gene transfer efficiency

The success of AAV2 mediated hepatic gene transfer in human trials for diseases such as hemophilia has been hampered by a combination of low transduction efficiency and a robust immune response directed against these vectors. We have previously shown that AAV2 is targeted for destruction in the cytoplasm by the host-cellular kinase/ubiquitination/proteasomal degradation machinery and modification of the serine(S)/threonine(T) kinase and lysine(K) targets on AAV capsid is beneficial. Thus targeted single mutations of S/T>A(S489A, S498A, T251A) and K>R (K532R) improved the efficiency of gene transfer in vivo as compared to wild type (WT)-AAV2 vectors (∼6-14 fold). In the present study, we evaluated if combined alteration of the phosphodegrons (PD), which are the phosphorylation sites recognized as degradation signals by ubiquitin ligases, improves further the gene transfer efficiency. Thus, we generated four multiple mutant vectors (PD: 1+3, S489A+K532R, PD: 1+3, S489A+K532R together with T251 residue which did not lie in any of the phosphodegrons but had shown increased transduction efficiency compared to the WT-AAV2 vector (∼6 fold) and was also conserved in 9 out of 10 AAV serotypes (AAV 1 to 10), PD: 1+3, S489A+K532R+S498A and a fourth combination of PD: 3, K532R+T251. We then evaluated them in vitro and in vivo and compared their gene transfer efficiency with either the WT-AAV2 or the best single mutant S489A-AAV2 vector. The novel multiple mutations on the AAV2 capsid did not affect the overall vector packaging efficiency. All the multiple AAV2 mutants showed superior transduction efficiency in HeLa cells in vitro when compared to either the WT (62-72% Vs 21%) or the single mutant S489A (62-72% Vs 50%) AAV2 vectors as demonstrated by FACS analysis (Fig. 1A). On hepatic gene transfer with 5x10^10 vgs per animal in C57BL/6 mice, all the multiple mutants showed increased transgene expression compared to either the WT-AAV2 (∼15-23 fold) or the S489A single mutant vector (∼2-3 fold) (Fig.1B and C). These novel multiple mutant AAV2 vectors also showed higher vector copy number in murine hepatocytes 4 weeks post transduction, as compared to the WT-AAV2 (∼5-6 Vs 1.4 vector copies/diploid genome) and further higher when compared to the single mutant S489A(∼5-6 fold Vs 3.8 fold) (Fig.1D). Further ongoing studies will demonstrate the therapeutic benefit of one or more of the multiple mutants vectors in preclinical models of hemophilia.

A novel adeno-associated virus serotype (AAV)-8 capsid mutant improves human coagulation factor IX expression in vivo

Recombinant AAV-8 vectors have shown significant promise for hepatic gene therapy of hemophilia B. However, the theme of AAV vector dose dependent immunotoxicity seen with AAV2 vectors earlier seem to re-emerge with AAV8 vectors as well. It is therefore important to develop novel AAV8 vectors that provide enhanced gene expression at significantly less vector doses. We hypothesized that AAV8 during its intracellular trafficking, are targeted for destruction in the cytoplasm by the host-cellular kinase/ubiquitination/proteasomal degradation machinery and modification of specific serine/threonine kinase or ubiquitination targets on AAV8 capsid (Fig.1A) may improve its transduction efficiency. To test this, point mutations at specific serine (S)/threonine (T) > alanine (A) or lysine (K)>arginine (R) residues were generated on AAV8 capsid. scAAV8-EGFP vectors containing the wild-type (WT) and each one of the 5 S/T/K-mutant(S276A, S501A, S671A, T251A and K137R) capsids were evaluated for their liver transduction efficiency at a dose of 5 X 1010 vgs/ animal in C57BL/6 mice in vivo. The best performing mutant was found to be the K137R vector in terms of either the gene expression (46-fold) or the vector copy numbers in the hepatocytes (22-fold) compared to WT-AAV8 (Fig.1B). The K137R-AAV8 vector that showed significantly decreased ubiquitination of the viral capsid had reduced activation of markers of innate immune response [IL-6, IL-12, tumor necrosis factor α, Kupffer cells and TLR-9]. In addition, animals injected with the K137R mutant also demonstrated decreased (2-fold) levels of cross-neutralizing antibodies when compared to animals that received the WT-AAV8 vector. To study further the utility of the novel AAV8-K137R mutant in a therapeutic setting, we delivered human coagulation factor IX (h.FIX) under the control of liver specific promoters (LP1 or hAAT) at two different doses (2.5x10^10 and 1x10^11 vgs per mouse) in 8-12 weeks old male C57BL/6 mice. As can be seen in Fig.1C/D, the circulating levels of h.FIX were higher in all the K137R-AAV8 treated groups as compared to the WT-AAV8 treated groups either at 2 weeks (62% vs 37% for hAAT constructs and 47% vs 21% for LP1 constructs) or 4 weeks (78% vs 56% for hAAT constructs and 64% vs 30% for LP1 constructs) post hepatic gene transfer. These studies demonstrate the feasibility of the use of this novel vector for potential gene therapy of hemophilia B.