Silicon Oxide Content Research Articles

Synthesis and Structural Characterization of Silica-Hybridized Hydroxyapatite with Gas Adsorption Capability

Silica-hybridized hydroxyapatite powder was prepared from a calcium hydroxide and phosphoric acid together with a tetra-n-butyl orthosilicate as the silica source in order to apply it as a gas adsorbent. According to the X-ray diffraction patterns, all peaks were assigned to the hydroxyapatite. No secondary phases, such as calcium hydroxide and silicon oxides, were observed. Moreover, the transmission electron microscope observations indicated that the crystallite size hardly changed by increasing the silicon oxide content. However, the adsorption areas of nitrogen, water and benzene were remarkably dependent on the silicon oxide content. In this paper, in order to explain the change in the adsorption areas, the lattice structure of the silica-hybridized hydroxyapatite is discussed based on the results obtained by the 29Si and 31P magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR).

The Influence of Silicon Oxide on the Mechanical Properties of Metaphosphate Glasses

The possibility of improving the mechanical properties of potassium aluminum metaphosphate glasses through the introduction of silicon oxide into the glass composition is analyzed. It is shown that the elastic moduli (Young modulus, shear modulus, Poisson ratio) and the hardness remain almost unchanged with an increase in the content of silicon oxide in the glass. At the same time, the structural strength increases by a factor of 1.7 and the fracture toughness increases by a factor of 1.3. The assumption is made that the observed increase in the structural strength is associated with the incorporation of silicon ions into the structure of the metaphosphate glass in the octahedral coordination.

Nature of visible luminescence and its excitation in Si–SiOx systems

Photoluminescence (PL) spectra and their temperature dependence, as well as PL excitation and Raman spectra of Si–SiOx systems prepared by RF magnetron sputtering were investigated as a function of Si content. It was shown that PL spectrum of such systems consists of several bands. The correlation of shift of peak position of the lower-energy band from 1.38 to 1.54eV with the change of size of Si nanocrystallites from 5 to 2.7nm was observed. It was assumed that this PL band is connected with carrier recombination inside Si nanoparticles or with radiative transitions between a Si band and an interface level. It was shown that peak positions of the other observed bands (at 1.7, 2.06 and 2.32eV) do not depend on the sizes of Si nanocrystallites. It was suggested that they are connected with silicon oxide defects based on the increase of intensities of these bands with increasing silicon oxide content. It was also shown that the excitation of PL is mainly due to light absorption in silicon nanocrystallites. Participation of hot carriers in excitation of defect-related bands was assumed.

Investigation of PEMFC operation above 100 °C employing perfluorosulfonic acid silicon oxide composite membranes

Various perfluorosulfonic acid membranes (PFSAs) were studied as pure and silicon oxide composite membranes for operation in hydrogen/oxygen proton-exchange membrane fuel cells (PEMFCs) from 80 to 140 °C. The composite membranes were prepared either by impregnation of pre-formed PFSAs via sol–gel processing of a polymeric silicon oxide, recasting a film using solubilized PFSAs and a silicon oxide polymer/gel. All composite membranes had a silicon oxide content of less than or equal to 10% by weight. Decreasing the equivalent weight and thickness of the PFSAs, in addition to the incorporation of silicon oxide helped improve water management in a PEMFC at elevated temperatures. Fourier transform-infrared spectroscopy–attenuated total reflectance (FT-IR–ATR), and scanning electron microscopy (SEM) experiments indicated an evenly distributed siloxane polymer in all of the composite membranes. At a potential of 0.4 V the Aciplex 1004/silicon oxide composite membrane in a humidified H 2/O 2 PEMFC at 130 °C and a pressure of 3 atm delivered six times higher current density than unmodified Nafion 115 under the same conditions, and 1.73 times the current density when unmodified Nafion 115 was operated with humidified gases at 80 °C and 1 atm of pressure. Furthermore, the PEMFC performances with the PFSA/silicon oxide composite membranes were physically more robust than the control membranes (unmodified PFSAs), which degraded after high operation temperature and thermal cycling.

Silicon Oxide Nafion Composite Membranes for Proton-Exchange Membrane Fuel Cell Operation at 80-140°C

Silicon oxide/Nafion composite membranes were studied for operation in hydrogen/oxygen proton-exchange membrane fuel cells (PEMFCs) from 80 to 140°C. The composite membranes were prepared either by an impregnation of Nafion 115 via sol-gel processing of tetraethoxysilane or by preparing a recast film, using solubilized Nafion 115 and a silicon oxide polymer/gel. Tetraethoxysilane, when reacted with water in an acidic medium, undergoes polymerization to form a mixture of and siloxane polymer with product hydroxide and ethoxide groups. This material is referred to as When Nafion is used as the acidic medium, the /siloxane polymer forms within the membrane. All composite membranes had a silicon oxide content of less than or equal to 10 wt %. The silicon oxide improved the water retention of the composite membranes, increasing proton conductivity at elevated temperatures. Attenuated total reflectance-Fourier transform infrared spectroscopy and scanning electron microscopy experiments indicated an evenly distributed siloxane polymer of in the composite membranes. At a potential of 0.4 V, silicon oxide/Nafion 115 composite membranes delivered four times the current density obtained with unmodified Nafion 115 in a PEMFC at 130°C and a pressure of 3 atm. Furthermore, silicon oxide-modified membranes were more robust than the control membranes (unmodified Nafion 115 and recast Nafion), which degraded after high operation temperature and thermal cycling. © 2002 The Electrochemical Society. All rights reserved.

Clay Shale from the Dzherdanakskoe Deposit: A High-Quality Ceramic Material

The properties of clay shale from the Dzherdanakskoe deposit (Uzbekistan) are investigated. It is established that a mullite-resembling phase with an elevated silicon oxide content is formed in thermal treatment. The possibility of producing refractories, porcelain, and faience based on material from this deposit is demonstrated.

Potassium determination by slurry technique

A variety of soil types (lime, clay, sandy-clay-loam, stream-deposits, and sandstone) were analysed by the slurry technique. The samples were dried, homogenized, ground, sieved, weighed, suspended in nitric acid solution and calibrated against aqueous standards. The results obtained by this technique were then compared with those from digested samples of the same soil. In order to establish optimum conditions for the slurry method, the following variables were studied: slurry concentration, acid concentration, aspiration rate, time and temperature of the ultrasonic agitation bath. The results have shown that only for soils with a high content of silicon oxide are there significant differences between the two methods.

Photoluminescence of Anodically Oxidized Porous Silicon

AbstractA photoluminescence (PL) study is carried out on porous silicon (PS) layers of 50 to 60% porosity which are anodically oxidized in ethylenglycol NH4NO3 electrolyte. Such oxidation is found to make the PL intensity stronger and the peak wavelength shorter. The emission of partially linearly polarized light is observed for PS samples under linearly polarized light excitation. Transmission IR and reflectance spectra are recorded to characterize porous silicon. As a result, a strong shift of the absorption band edge and high silicon oxide content are found in PS sampl. This shift is supposed to be due to the quantum confinement mechanism, but the features of PL speak in favour of the important role of oxide in the light emission from PS. In particular, the polarization of the emitted light can be due to the oxide‐induced elastic strains.

Infrared Spectroscopy Experiment on the Mariner 9 Mission: Preliminary Results

The Mariner 9 infrared spectroscopy experiment has provided goodquality spectra of many areas of Mars, predominantly in the southern hemisphere. Large portions of the thermal emission spectra are significantly affected by dust with a silicon oxide content approximately corresponding to that of an intermediate igneous rock, thus implying that Mars has undergone substantial geochemical differentiation. Derived temperature profiles indicate a warm daytime upper atmosphere with a strong warming over the south polar cap. Atmospheric water vapor is clearly observed over the south polar area and less strongly over other regions.