Spectroscopic study on peculiarities of fumed silica hydridesilylation with triethoxysilane under fluidized bed conditions

Fumed silica has found widespread application in industry due to variety of fascinating properties. Owing to its specific manufacturing process, it consists of finely dispersed particles and is featured with large specific surface area covered by profoundly reactive silanol groups which are available for chemical grafting. Spherical shape of fumed silica particles and lacking porosity provides a space-filling structure. These characteristics implement the fume silica’s utilization as high-surface-area carriers for various catalysts, i.e. metallic nanometer-sized particles, organic moieties, etc. Currently a great attention is called to on-surface grafting to improve the silica-based carrier. Most of research is carried out in area of liquid phase chemistry involving an abundance of expensive and often toxic solvents while the space-filling properties of silica are favoring reactions in fluidized bed conditions. In current research fumed silica (A-300) was a subject for hydridesilylation with triethoxysilane under fluidized bed conditions. In all synthesis reported in current research the insignificant amount of solvent (1.00 wt. % of the amount used in typical wet-chemical modifications method) was spent for the silica surface silylation. While the mass ratio of silica/TES was kept constant, other conditions, i.e. solvent/catalyst presence, surface pretreatment, additional treatment with water, and the fluidized bed heating mode have been varied. FTIR spectroscopy revealed the interaction between groups of triethoxysilane and silica surface silanol groups and demonstrated the effect of modification conditions on the density of the hydridesilyl groups coverage. The results of FTIR spectroscopic studies have confirmed the presence of grafted silicon hydride groups on the surface of modified silica, as well as the presence of ethoxy and/or silanol groups – either intact or formed due to hydrolysis of the ethoxy groups. Titrimetric and spectrophotometric analysis was performed to estimate the concentration of grafted SiH groups (in all samples prepared under fluidized bed conditions their concentration ranged within about 0.28–0.55 mmol/g as dependent on the reaction conditions). Other important aspects of fluidization such as the presence of solvent and/or hydrolyzing agent, bed heating mode and the effect of the silica sample thermal pre-treatment are also discussed.

Evaluation of silane effect as a coupling agent for metakaolin

This study aimed at evaluating the coupling effect of silane Si69 bis(triethoxysilylpropyl)tetrasulfide in metakaolin (MK) in automobile tire tread compounds based on a styrene–butadiene rubber/butadiene rubber blend. A reference compound of a typical tread recipe, filled with silica and carbon black, was used as a reference due to the acknowledged effect of TESPT in silica incorporation in elastomers. A silica sample without silane was also prepared. Silica was then completely substituted by MK, producing two samples, with and without silane. The samples were tested for crosslink density, rheometry, and morphology, and the vulcanization reaction parameters were determined and evaluated. Silane improved the interaction between MK and the polymer matrix, evidenced by the increase in crosslink density and vulcanization reaction rate, the same effect silane causes on silica-filled composites. Morphology also revealed that silane increased MK dispersion and adhesion to rubber. On the other hand, MK seems not to be as reinforcing as silica, considering that maximum torque is related to the stiffness of the material, with MK exhibiting lower values for this parameter.

Optical freeform generation by laser machining and plasma-assisted polishing

Tailored optical freeform lenses are required for different applications. Sub-aperture deterministic machining techniques such as plasma jet machining have shown great potential to generate freeform surfaces. However, depending on the required local slopes of the surface shape geometrical limitations occur due to the lateral tool function width. In the paper an alternative approach to fabricate freeform shapes exhibiting steep local slopes is presented. A first step involves a dwell time based fs-laser ablation process to generate the surface contour on a fused silica sample. Since the resulting roughness after laser machining lies in the range of 400 nm RMS which does not match optical requirements a subsequent plasma jet based polishing step is performed where micro-roughness is drastically reduced to values below 0.3 nm RMS.

Quantifying adsorption-induced deformation of nanoporous materials on different length scales

A newin situsetup combining small-angle neutron scattering (SANS) and dilatometry was used to measure water-adsorption-induced deformation of a monolithic silica sample with hierarchical porosity. The sample exhibits a disordered framework consisting of macropores and struts containing two-dimensional hexagonally ordered cylindrical mesopores. The use of an H2O/D2O water mixture with zero scattering length density as an adsorptive allows a quantitative determination of the pore lattice strain from the shift of the corresponding diffraction peak. This radial strut deformation is compared with the simultaneously measured macroscopic length change of the sample with dilatometry, and differences between the two quantities are discussed on the basis of the deformation mechanisms effective at the different length scales. It is demonstrated that the SANS data also provide a facile way to quantitatively determine the adsorption isotherm of the material by evaluating the incoherent scattering contribution of H2O at large scattering vectors.

Laser Induced Damage in Fused Silica for 248 nm

For the key-optical material, the laser induced damage character of fused silica is crucial for the application among the optical laser fitting. As the defect of each point of the silica sample is diverse, and the lasers focus point by point, we divided the sample block into three-dimensional structure for each laser-point to discuss the relationship between the LIDT of each points and the OH-content. The result shows that the LIDT of the center of the sample block is up to 10-11J/cm2 which is consistent after the treatment while the LIDT of border pieces is 9-10 J/cm2. The different temperature and the aggradation during the fusing process and the machine process caused the different OH content of different location of the sample.

Preparation and characterization of activated carbon & amorphous silica from rice husk

Activated carbon (AC) was prepared by the conventional carbonization and KOH activation and amorphous silica was extracted by alkali extraction followed by acid precipitation from rice husk on a laboratory scale. The performance of the produced activated carbon and amorphous silica were examined using I2 value measurement, methylene blue (MB) adsorption test, pH measurement, FTIR and SEM-EDX analysis. The optimum temperature for production of AC was obtained at 700 0C. The AC by alkali extraction method was show higher activity than KOH activation. The maximum I2 value, MB adsorption value & pH value shows at 700 0C followed by alkali extraction with 15% NaOH, which were 510.82 mg/g, 61.1 mg/g and 7.32 respectively. The FTIR analysis shows presence of Si-O-Si bond with a strong peak at 1078.28 cm-1. The SEM image of silica sample shows that the most of organic component is burnt out during combustion.Bangladesh J. Sci. Ind. Res. 50(4), 263-270, 2015

Measuring Microscopic Properties of a Single-Crystalline Diamond by Nano-Indentation Technology

Nano-indentation technology was brought to study microscopic mechanical properties of a single-crystalline diamond (SCD). Nano-indentation measurement was conducted on the {100} plane of SCD, and influences of various factors on measured results were analyzed, from which methods were confirmed to improve veracity of measurement. Properties of the indenter were checked with a fused silica sample both before and after indentation on diamond, which provided guarantee to veracity of results on diamond. It was found that tilt of diamond surface had so great influence that it could damage the indenter, and make the indentation curves anomalous. While damage of indenter could be avoided and valid measurement results could be obtained when tilt of diamondsurface was decreased below 0.10º and the maximal indentation force was less than 10 mN. Deformation of the diamond was almost full-elastic during indentation process. Indentation hardness of {100} plane of the SCD was about 70 GPa with standard deviation less than 3 GPa. And there had good reproducibility between two groups of measurements.

Plastic Strain Effect in Progressive Multi-Cycle Nano-Indentation Measurement

Properties of materials and their variations in depth direction in the same location could be measured directly by progressive multi-cycle (PMC) nanoindentation method. But influences of strain-hardening on measured results in this process haven’t been researched thoroughly. Measurements on an austenitic steel sample and a fused silica sample were conducted by PMC nanoindentation and standard nanoindentation methods, and differences of the results by two methods of the two materials were analyzed. It was found that hardness of austenitic steel measured by PMC method decreased monotonously with increased depth, while hardness measured by standard method decreased to stable value with increased depth. And properties of fused silica measured by both methods accorded much well. Based on analysis of plastic strain during indentation process, it was deduced that austenitic steel with high plasticity could introduce second convergence of plastic strain and stress in PMC indentation process, which made measured hardness decrease monotonously with increased depth.

Effect of Titania Loading on Properties and Catalytic Activity of Nanostructured Phosphate–Vanadia-Impregnated Silica–Titania Oxidative–Acidic Bifunctional Catalyst

Effect of titania loading on physical–chemical properties and bifunctional catalytic activity of phosphate–vanadia-impregnated silica–titania was investigated. Different concentrations of titanium were impregnated into fumed silica, followed by impregnation of vanadium and phosphoric acid simultaneously onto the prepared silica–titania. Results revealed that Ti amount did not have significant effect on crystallinity, surface area and particle size of the resulted materials. However, quantity of tetrahedrally coordinated Ti species increased with increasing Ti content in the sample. Pyridine adsorption study showed the presence of both Brønsted and Lewis acid sites in all the samples even in the titanium-free phosphate–vanadia-impregnated silica sample. The catalytic testing showed that phosphate–vanadia-impregnated silica–titania with the molar ratio of Si:Ti=33:1 was the best bifunctional catalyst in the transformation of 1-octene to 1,2-octanediol using aqueous hydrogen peroxide as oxidant.

Synthesis, Characterizations and Photocatalytic Activity of Mesoporous TiO2 Using Typha Latifolia as Template

Typha latifolia were successfully used as template to synthesize mesoporous titania and silica with efficient photocatalytic activity under solar and visible light. Both two titania and silica samples were characterized by a combination of various physicochemical techniques, such as, N2 adsorption/ desorption isotherm, diffuse reflectance UV-vis, and X-ray diffraction. It was found that both two synthesized samples exhibited similar morphologies to the original templates. The presence of the residual carbon species of mesoporous titania and silica strongly affects their photocatalytic activity. The photoactivity of P25 TiO2 could not almost exhibit while both mesoporous titania and silica samples exhibited varied photoactivities for dyes under visible light, due to the presence of the residual carbon species. Moreover, as a whole the titania sample enhanced the higher photocatalytic activity than the silica sample under both solar and visible light.