Synthesis of an Al/MgAl2O4 in situ metal matrix composite from silica gel

An aluminum/MgAl2O4 in situ metal matrix composite has been synthesized using silica gel containing B98% SiO2 in an Al–5Mg alloy. The thermodynamics and kinetics of MgAl2O4 formation have been discussed in detail. A transition phase of composition between MgO and MgAl2O4 has been detected in the SEM-EDS analysis of the particles extracted from the composite by a 25% NaOH solution. This confirms the gradual transformation of MgO to MgAl2O4 by the reaction 3SiO2(s)12MgO(s)14Al(l)-2MgAl2O4(s)13Si(l). The stoichiometry, n, of MgAl2O4 has been found to sustain close to 1 and the crystallite growth of MgAl2O4 has been stopped at DB30 nm in the composites held at 7501C up to 10 h.

Thermodynamics and kinetics of the formation of Al2 O3/ MgAl2O4/MgO in Al-Silica metal matrix composite

The formation of Al₂O₃, MgAl₂O₄, and MgO has been widely studied in different Al base metal matrix composites, but the studies on thermodynamic aspects of the Al₂O₃/ MgAl₂O₄/MgO phase equilibria have been limited to few systems such as Al/Al₂O₃ and Al/SiC. The present study analyzes the Al₂O₃/MgAl₂O₄ and MgAl₂O₄/MgO equilibria with respect to the temperature and the Mg content in Al/SiO2 system using an extended Miedema model. There is a linear and parabolic variation in Mg with respect to the temperature for MgAl₂O₄/MgO and Al₂O₃/MgAl₂O₄ equilibria, respectively, and the influence of Si and Cu in the two equilibria is not appreciable. The experimental verification has been limited to MgAl₂O₄/MgO equilibria due to the high Mg content (≥0.5 wt pct) required for composite processing. The study has been carried out on two varieties of Al/SiO₂ composites, i.e., Al/Silica gel and Al/Micro silica processed by liquid metallurgy route (stir casting route). MgO is found to be more stable compared to MgAl₂O₄ at Mg levels ≥5 and 1 wt pct in Al/Silica gel and Al/Micro silica composites, respectively, at 1073 K. MgO is also found to be more stable at lower Mg content (3 wt pct) in Al/Silica gel composite with decreasing particle size of silica gel from 180 micron to submicron and nanolevels. The MgO to MgAl₂O₄ transformation has taken place through a series of transition phases influenced by the different thermodynamic and kinetic parameters such as holding temperature, Mg concentration in the alloy, holding time, and silica particle size.

Analysis of self-assembled monolayer interfaces by electrospray mass spectrometry : a gentle approach

A general mass spectrometry technique for the characterization of alkanethiol-modified surfaces is presented. Alkanethiol self-assembled onto a gold surface (in this case, peptides were attached to the gold surface via a thiolate bond) was reductively desorbed in 0.05 M KOH in the presence of octadecyl-derivatized silica gel. The peptide adsorbed onto the silica gel, whereupon it could be filtered, washed to remove any salts, and then eluted using a mixture of 4:1 v/v methanol/water. The eluant containing the peptide was injected into a Fourier transform ion-cyclotron resonance mass spectrometer (FTICR/MS) via electrospray ionization. The spectrum showed no fragmentation of the peptide, demonstrating the gentleness of the technique. This simple procedure is not limited to FTICR/MS and could be adapted to other mass spectrometers.

Critical assessment of various techniques for the extraction of carotenoids and co-enzyme Q10 from the Thraustochytrid strain ONC-T18

A variety of techniques for extracting carotenoids from the marine Thraustochytrium sp. ONC-T18 was compared. Specifically, the organic solvents acetone, ethyl acetate, and petroleum ether were tested, along with direct and indirect ultrasonic assisted extraction (probe vs bath) methods. Techniques that used petroleum ether/acetone/water (15:75:10, v/v/v) with 3 h of agitation, or 5 min in an ultrasonic bath, produced the highest extraction yields of total carotenoids (29−30.5 μg g^-1). Concentrations up to 11.5 μg g^-1 of canthaxanthin and 17.5 μg g^-1 of β-carotene were detected in extracts stored for 6 weeks. Astaxanthin and echinenone were also detected as minor compounds. Extracts with and without antioxidants showed similar carotenoid concentration profiles. However, total carotenoid concentrations were approximately 8% higher when antioxidants were used. Finally, an easy-to-perform and inexpensive method to detect co-enzymes in ONC-T18 was also developed using silica gel TLC plates. Five percent methanol in toluene as a mobile phase consistently eluted co-enzyme Q10 standards and could separate the co-enzyme fractions present in ONC-T18.

Cerium acetylacetonates—new aspects, including the lamellar clathrate [Ce(acac)4]·10H2O

Reactions of CeCl₃·7H₂O and Ce(NO₃)₃·6H₂O with Naacac or NH₄acac in aqueous solution at 21 and 45 °C yielded the trihydrate [Ce(acac)₃(H₂O)₂]·H₂O and the dihydrate [Ce(acac)₃(H₂O)₂], respectively, whereas similar treatment of (NH₄)₂[Ce(NO₃)₆] gave the trihydrate at both temperatures. Desiccation of the hydrates over silica gel left the dihydrate unchanged, whereas the trihydrate underwent decomposition rather than dehydration. Aerial oxidation of [Ce(acac)₃(H₂O)₂] in CH₂Cl₂ and toluene yielded α-[Ce(acac)₄] and β-[Ce(acac)₄], respectively, the structure of the former being re-determined with improved precision. Careful treatment of aqueous (NH₄)₄[Ce(SO₄)₄] and Hacac (initially pH 1–2) with aqueous ammonia to pH 5 precipitated hydrated [Ce(acac)₄], from which [Ce(acac)₄]·10H₂O was isolated as unstable, light-sensitive single crystals, and the structure was determined. The complex is a laminar clathrate containing layers of Ce(acac)₄ molecules sandwiched between extensive hydrogen-bonded layers of water molecules which do not interact with the metal. Electrochemical experiments confirmed the unstable nature of hydrated Ce^III(acac)₃, while the reduction of [Ce(acac)₄] yielded well-defined cyclic voltammograms in acetonitrile and acetone, corresponding to a quasi-reversible process. For the [Ce^IV(acac)₄]/[Ce^III(acac)₄]⁻redox couple, a calculated reversible potential of 0.22±0.02 V versus SHE was obtained in acetone or acetonitrile (0.1 M Bu₄NPF₆) at both gold and glassy carbon electrodes. This potential is consistent with the ease of both oxidation and reduction of cerium acetylacetonate complexes as found in the synthetic studies.

Experimental investigation of the dissolution of quartz by a muscovite mica surface : implications for pressure solution

Using the surface forces apparatus, which can measure small changes in thickness occurring even at essentially geological timescales, we have measured dissolution of quartz sheets when pressed against muscovite mica surfaces in aqueous electrolyte solution, but no dissolution is observed under dry conditions. It is postulated that the dissolved quartz may reprecipitate outside the contact junction as a fragile silica gel, which could be the main factor limiting the rate of further dissolution.

Gel electrolytes based on lithium modified silica nano-particles

In this work lithium modified silica (Li-SiO₂) nano-particles were synthesized and used as a single ion lithium conductor source in gel electrolytes. It was found that Li-SiO₂ exhibited good compatibility with DMSO, DMA/EC (a mixture of N,N-dimethyl acetamide and ethylene carbonate) and the ionic liquid, N-methyl-N-propyl pyrrolidinium bis(trifluoromethylsulfonyl) amide ([C₃mpyr][NTf₂]). Several gel electrolytes based on Li-SiO₂ were obtained. These gel electrolytes were investigated by DSC, solid state NMR, conductivity measurements and cyclic voltammetry. Conductivities as high as 10⁻³ S/cm at room temperature were observed in these nano-particle gel electrolytes. The results of electrochemical tests showed that some of these materials were promising for using as lithium conductive electrolytes in electrochemical devices, with high lithium cycling efficiency evident.

Aggregation, ageing and transport properties of surface modified fumed silica dispersions

We have investigated the aggregation, ageing and transport properties of surface modified silica dispersions in DMSO by photon correlation spectroscopy and conductivity measurements. The surface modification introduces Li+-ions that dissociate in the dispersion creating a single Li+-ion conducting electrolyte. We show that the surface modification changes the aggregation and ageing properties of the material. There is a pronounced ageing observed for the modified silica dispersions. At high concentrations of fumed silica a gel state is found, which in the case of the surface modified silica is a very weak gel that can be rejuvenated by ultrasonic treatment. The key parameter controlling the aggregation in this system is hydrogen bonding and the surface modification results in a very low number of sites for hydrogen bonding. In addition there is a contribution from repulsive electrostatic interactions in the surface modified silica dispersions due to the highly charged surfaces of these particles. Furthermore, the Li+-ion diffusion, at low silica concentration, is three orders of magnitude faster than that of the silica particles and in the gel state the silica particles are immobile. We also find that the Li+-ion diffusion is virtually independent of the silica concentration in the dispersions.

Bioactivating the surfaces of titanium by sol-gel process

In the present study, titanium (Ti) samples were surface-modified by titania (TiO₂), silica (SiO₂) and hydroxyapatite (HA) coatings using a sol-gel process. The bioactivity of the film-coated Ti samples was investigated by cell attachment and morphology study using human osteoblast-like SaOS-2 cells. Results of the cell attachment indicated that the densities of cell attachment on the surfaces of Ti samples were significantly increased by film coatings; the density of cell attachment on HA film-coated surface was higher than those on TiO₂ and SiO₂ film-coated surfaces. Cell morphology study showed that the cells attached, spread and grew well on the three kinds of film-coated surfaces. It can be concluded that the three kinds of film coatings can bioactivate the surfaces of Ti samples effectively. Overall, Ti sample with HA film-coated surface exhibited the best bioactivity.

Superhydrophobic fabrics from hybrid silica sol-gel coatings: Structural effect of precursors on wettability and washing durability

Particle-containing silica sol was synthesized by co-hydrolysis and co-condensation of two silane precursors, tetraethylorthosilicate (TEOS) and an organic silane composed of a non-hydrolyzable functional group (e.g., alkyl, flourinated alkyl, and phenyl), and used to produce superhydrophobic coatings on fabrics. it has been revealed that the non-hydrolyzable functional groups in the organic silanes have a considerable influence on the fabric surface wettability. When the functional group was long chain alkyl (C16), phenyl, or flourinated alkyl (C8), the treated surfaces were highly superhydrophobic with a water contact angle (CA) greater than 170°, and the CA value was little affected by the fabric type. The washing durability of the superhydrophobic coating was improved by introducing the third silane containg epoxide group, 3-glycidoxypropyltrimethoxsilane (GPTMS), for synthesis. Although the presence of epoxide groups in the coating slightly reduced the fabrics' superhydrophobicity, the washing durability was considerably improved when polyester and cotton fabrics were used as substrates.

Robust, self-healing superamphiphobic fabrics prepared by two-step coating of fluoro-containing polymer, fluoroalkyl silane, and modified silica nanoparticles

A robust, superamphiphobic fabric with a novel self-healing ability to autorepair from chemical damage is prepared by a two-step wet-chemistry coating technique using an easily available material system consisting of poly(vinylidene fluoride-co-hexafluoropropylene), fluoroalkyl silane, and modified silica nanoparticles. The coated fabrics can withstand at least 600 cycles of standard laundry and 8000 cycles of abrasion without apparently changing the superamphiphobicity. The coating is also very stable to strong acid/base, ozone, and boiling treatments. After being damaged chemically, the coating can restore its super liquid-repellent properties by a short-time heating treatment or room temperature ageing. This simple but novel and effective coating system may be useful for the development of robust protective clothing for various applications.

Photostability of wool fabrics coated with pure and modified TiO2 colloids

The surface of wool fabrics was coated with TiO2 and TiO2-based nanocomposite colloids and the impact of this coating on the photostability of wool was investigated. TiO2 along with TiO2/Metal and TiO2/Metal/SiO2 sols were synthesized through a low-temperature sol-gel method and applied to fabrics. Composite colloids were synthesized through integrating the silica and three noble metals of silver (Ag), gold (Au) and platinum (Pt) into the synthesis process of sols. Four different molar ratios of Metal to TiO2 (0.01%, 0.1%, 0.5% and 1%) were used to elucidate the role of metal type and amount on the obtained features. Photostability and UV protection features of fabrics were evaluated through measuring the photo-induced chemiluminescence (PICL), photoyellowing rate and ultraviolet protection factor (UPF) of fabrics. PICL and photoyellowing tests were carried out under UVA and UVC light sources, respectively. PICL profiles demonstrated that the presence of pure and modified TiO2 nanoparticles on fabrics reduced the intensity of PICL peak indicating a lower amount of polymer free radicals in coated wool, compared to that of pristine fabric. Moreover, a higher PICL peak intensity as well as photoyellowing rate was observed on fabrics coated with modified colloids in comparison with pure TiO2. The surface morphology of fabrics was further characterized using FESEM images.