Effects of Solvent Exchange Period and Heat Treatment on Physical and Chemical Properties of Rice Husk Derived Silica Aerogels

In this study, hydrophobic silica aerogels were synthesized from rice husk ash-derived sodium silicate through sol-gel processing, solvent exchange, surface modification and ambient pressure drying. By volume, 10% of trimethylchlorosilane (TMCS) in 90% of n-hexane was used as a hydrophobic solution in the surface modification process. The physical and chemical properties of silica aerogels were characterized by density and porosity measurements, scanning electron microscopy (SEM), Fourier transforms infrared (FTIR) spectroscopy, Brunauer–Emmett–Teller theory (BET) and dynamic scanning calorimetry (DSC). The hydrogels prepared were in the form of 2.5 ± 0.5 mm beads and then converted into alcogels through solvent exchange with ethanol for repetition of 3, 6 and 9 days. It is found that the optimal quality of silica aerogels with the BET surface area as high as 668.82 m²/g was obtained from the alcogels of the solvent exchange period of 9 days. Depending on the size of the gel’s block, a longer solvent exchange period will ensure adequate removal of pore water. Post heat treatment on silica aerogels obtained from the 9 days of solvent exchange at 200, 300 and 400 °C for 2 h results in slight decreased of aerogel’s density from 0.048 g/cm³ to 0.039 g/cm³ and the hydrophobicity of the aerogels is decreased above 380 °C as confirmed by DSC analysis.

     

Aqueous and nonaqueous microemulsion systems with a palm oil-base emollient

Microemulsions with a palm oil-based emollient, i.e., medium-chain triglyceride (MCT), and water or glycerol, stabilized by two oppositely charged ionic surfactants and a medium-chain alcohol, were investigated. The results showed that only the water-in-MCT or the glycerol-in-MCT microemulsions were prominent. The maximum solubilization of the MCT emollient was higher in cetyltrimethyl ammonium bromide, i.e., the positively charged surfactant that contained a nitrogen atom, than the negatively charged surfactant sodium dodecyl sulfate. However, the results did not lend themselves for selecting any decisive factor that would explain the different solubilization behavior encountered in the investigated aqueous and nonaqueous systems.     

An analysis of an implicit finite element algorithm for geometrically nonlinear problems of structural dynamics part 2. Accuracy

In part 1¹ a series of implicit finite element algorithms for the geometrically nonlinear structural problem were proposed. These algorithms were shown to be computationally efficient because they require the solution of a linear system rather than a nonlinear system at each time point. In addition, because of the conservative nature of the algorithms, their stability properties are easily assessed. One algorithm was shown to be unconditionally stable.In part 2 the convergence of the proposed algorithms is demonstrated. It is shown that for the consistent algorithm, additional conditions must be satisfied to insure convergence. In fact, one of the proposed algorithms is shown to be unconditionally stable but conditionally convergent.     

An investigation of sound absorption coefficient on sisal fiber poly lactic acid bio‐composites

In this research, the mechanical, acoustical, thermal, morphological, and infrared spectral properties of untreated, heat and alkaline‐treated sisal fiber‐reinforced poly‐lactic‐acid bio‐composites were analyzed. The bio‐composite samples were fabricated using a hot press molding machine. The properties mentioned above were evaluated and compared with heat‐treated and alkaline‐treated sisal fibers. Composites with heat‐treated sisal fibers were found to exhibit the best mechanical properties. Thermo‐gravimetric analysis (TGA) was conducted to study the thermal degradation of the bio‐composite samples. It was discovered that the PLA‐sisal composites with optimal heat‐treated at 160°C and alkaline‐treated fibers possess good thermal stability as compared with untreated fiber. The results indicated that the composites prepared with 30wt % of sisal had the highest sound absorption as compared with other composites. Evidence of the successful reaction of sodium hydroxide and heat treatment of the sisal fibers was provided by the infrared spectrum and implied by decreased bands at certain wavenumbers. Observations based on scanning electron microscopy of the fracture surface of the composites showed the effect of alkaline and heat treatment on the fiber surface and improved fiber‐matrix adhesion. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42470.     

Detection of stressed oil palms from an airborne sensor using optimized spectral indices

Existing vegetation indices and red-edge techniques have been widely used for the assessment of vegetation status and vegetation health from remote-sensing instruments. This study proposed and applied optimized Airborne Imaging Spectrometer for Applications (AISA) airborne hyperspectral indices in assessing and mapping stressed oil palm trees. Six vegetation indices, four red-edge techniques, a standard supervised classifier and three optimized AISA spectral indices were compared in mapping diseased oil palms using AISA airborne hyperspectral imagery. The optimized AISA spectral indices algorithms used newly defined reflectance values at wavelength locations of 734 nm (near-infrared (NIR)) and 616 nm (red). The selection of these two bands was based on laboratory statistical analysis using field spectroradiometer reflectance data. These two bands were then applied to the AISA airborne hyperspectral imagery using the three optimized algorithms for AISA data. The newly formulated AISA hyperspectral indices were D2 = R ₆₁₆/R ₇₃₄, normalized difference vegetation index a (NDVIa)?=?(R ₇₃₄ – R ₆₁₆)/(R ₇₃₄?+?R ₆₁₆) and transformed vegetation index a (TVIa)?=?((NDVIa?+?0.5)/(abs (NDVIa?+?0.5))?×?[abs (NDVIa?+?0.5)]^1/2. The classification results from the optimized AISA hyperspectral indices were compared with the other techniques and the optimized AISA spectral indices obtained the highest overall accuracy. D2 and NDVIa obtained 86% of overall accuracy followed by TVIa with 84% of overall accuracy.     

Linking phosphorus sequestration to carbon humification in wetland soils by 31P and 13C NMR spectroscopy

Phosphorus sequestration in wetland soils is a prerequisite for long-term maintenance of water quality in downstream aquatic systems, but can be compromised if phosphorus is released following changes in nutrient status or hydrological regimen. The association of phosphorus with relatively refractory natural organic matter (e.g., humic substances) might protect soil phosphorus from such changes. Here we used hydrofluoric acid (HF) pretreatment to remove phosphorus associated with metals or anionic sorption sites, allowing us to isolate a pool of phosphorus associated with the soil organic fraction. Solution (31)P and solid state (13)C NMR spectra for wetland soils were acquired before and after hydrofluoric acid pretreatment to assess quantitatively and qualitatively the changes in phosphorus and carbon functional groups. Organic phosphorus was largely unaffected by HF treatment in soils dominated by refractory alkyl and aromatic carbon groups, indicating association of organic phosphorus with stable, humified soil organic matter. Conversely, a considerable decrease in organic phosphorus following HF pretreatment was detected in soils where O-alkyl groups represented the major fraction of the soil carbon. These correlations suggest that HF treatment can be used as a method to distinguish phosphorus fractions that are bound to the inorganic soil components from those fractions that are stabilized by incorporation into soil organic matter.     

On the location of different titanium sites in Ti–OMS-2 and their catalytic role in oxidation of styrene

Octahedral manganese oxide molecular sieves (OMS-2) modified by impregnation of TiO₂ exhibit a higher catalytic activity for oxidation of styrene with tert-butylhydroperoxide in comparison to titanium-incorporated OMS-2, where the styrene conversions were ca. 70% and 45–50%, respectively. The framework of titanium species has no effect on the enhancement of catalytic activity, while the non-framework of titanium species induces a synergetic effect that enhances the oxidation of styrene with tert-butylhydroperoxide.     

Magnesium substitution in brushite cements

The use of magnesium-doped ceramics has been described to modify brushite cements and improve their biological behavior. However, few studies have analyzed the efficiency of this approach to induce magnesium substitution in brushite crystals. Mg-doped ceramics composed of Mg-substituted β-TCP, stanfieldite and/or farringtonite were reacted with primary monocalcium phosphate (MCP) in the presence of water. The cement setting reaction has resulted in the formation of brushite and newberyite within the cement matrix. Interestingly, the combination of SAED and EDX analyses of single crystal has indicated the occurrence of magnesium substitution within brushite crystals. Moreover, the effect of magnesium ions on the structure, and mechanical and setting properties of the new cements was characterized as well as the release of Ca^2 + and Mg^2 + ions. Further research would enhance the efficiency of the system to incorporate larger amounts of magnesium ions within brushite crystals.     

Investigation of beta-amyloid peptide by on-line high-performance liquid chromatography coupled to electrospray ionization mass spectrometry

beta(1-39) amyloid peptide is one of the components of the cerebral amyloid deposits that are characteristic of Alzheimer's disease. Solid-phase synthesis of this peptide resulted in a fairly complex crude product containing both the target peptide and a number of side products. High-performance liquid chromatography coupled to electrospray ionization mass spectrometry allowed rapid and reliable identification of both the desired peptide and most of the side products which were found to have relative molecular masses above and below that of the target peptide.