Issues in the Energetics of Metastable Oxides and Oxyhydroxides

1996 ◽  
Vol 432 ◽  
Author(s):  
Alexandra Navrotsky
Keyword(s):  
Low Temperature ◽  
Manganese Oxides ◽  
Sol Gel ◽  
Stable Phase ◽  
Gamma Alumina ◽  
Materials Synthesis ◽  
Crystalline Materials ◽  
Hydrothermal Reactions ◽  
Calorimetric Studies ◽  
Gel Processing

AbstractIn both low temperature materials synthesis (sol gel processing, chimie douce) and low temperature geochemistry (weathering, geothermal and hydrothermal reactions, diagenesis) metastable and/or poorly crystalline materials are encountered. Despite the lack of equilibrium, energetic considerations play a major role in the formation and transformation of such phases. Recent calorimetric studies on heats of formation of zeolites and related metastable frameworks, on nanophase alpha and gamma alumina, and on manganese oxides and hydroxides are summarized. These studies illustrate the effects of framework topology, cation content, hydration and surface energy on the formation, persistence, and eventual transformation to more stable phase assemblages of these environmentally important materials.

scholarly journals Preparation and Characterization of Nano-Cadmium Ferrite

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
S. M. Ismail ◽  
Sh. Labib ◽  
S. S. Attallah
Keyword(s):  
Particle Size ◽  
Low Temperature ◽  
Sol Gel ◽  
Stable Phase ◽  
X Ray Diffraction ◽  
Economic Point ◽  
Sol Gel Process ◽  
Pure Phase ◽  
Microstructural Studies

Nano-hematite (α-Fe2O3) and nano-cadmium ferrite (CdFe2O4) are prepared using template-assisted sol-gel method. The prepared samples are analyzed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Mössbauer spectroscopy techniques for structural and microstructural studies. Nano-α-Fe2O3 with particle size ~60 nm is formed at 500°C, while nano-CdFe2O4 with smaller particle size (~40 nm) is formed at 600°C. It is found that with a simple sol-gel process we can prepare nano-CdFe2O4 with better conditions than other methods: pure phase at lower sintering temperature and time (economic point) and of course with a smaller particle size. So, based on the obtained experimental results, a proposed theoretical model is made to explain the link between the use of the sol-gel process and the formation of nano-CdFe2O4 as a pure phase at low temperature. This model is based on a simple magnetostatic interaction between the formed nuclei within the solution leading to the formation of the stable phase at low temperature.

scholarly journals Hydrophobic silica thin films by sol-gel processing and spin coating technique at low temperature

2014 ◽  
Vol 8 (1) ◽  
Author(s):  
Nurul Huda Abu Bakar ◽  
Karim Deraman ◽  
R. Hussin ◽  
W. Nurulhuda W. Shamsuri ◽  
Faizal Mansor ◽  
...  
Keyword(s):  
Thin Films ◽  
Low Temperature ◽  
Spin Coating ◽  
Sol Gel ◽  
Contact Angles ◽  
Spin Coating Technique ◽  
Coating Technique ◽  
Hydrophobic Silica ◽  
Silica Thin Films ◽  
Gel Processing

Hydrophobic silica thin films were prepared by sol-gel processing and self-assembly by chemical vapor reaction with Trimethylchlorosilane (TMCS) at low temperature. The sols were divided into Sol A with ethanol, Polyethylene glycol (PEG) and water (H2O) while Sol B were contain precursor of silica Tetraethylorthosilicate (TEOS) hydrolyze with ethanol which was stirred for 15 minutes. HCl was added into the mixture and stirred for another 10 minutes. After deposition on 1 x 1 cm corning glass using spin coating technique (two-step timer), the films were heated at 60˚C for 10 minutes and finally annealed at 150°C for 1 hour. The films were characterized by using Rudolph/Auto EL Ellipsometer, Shimadzu Spectrophotometer, Perkin Elmer Fourier Transform Infrared (FTIR) and Atomic Force Microscope (AFM). The results showed that the films thickness and refractive index were in the range of 105.2 to 112.4 nm and 1.35 to 1.38, respectively. The films were transmitted 70-80% of light (in visible range) with various bondings of C-H, Si-O-Si, Si-C and Si-OH. Surface roughness of the films was increased from 30.6 nm (silica thin film) to 140.5 nm (hydrophobic silica thin films) after modification have been done on the films by using TMCS (heated at 40˚C). It was found that the water contact angles increased when time of reaction increased from 109° to 124°.

Low-temperature synthesis of ZrB2 nano-powders using a sorbitol modified sol–gel processing route

2014 ◽  
Vol 25 (3) ◽  
pp. 910-915 ◽  
Author(s):  
Huiming Ji ◽  
Ming Yang ◽  
Minmin Li ◽  
Guangyi Ji ◽  
Hongna Fan ◽  
...  
Keyword(s):  
Low Temperature ◽  
Sol Gel ◽  
Processing Route ◽  
Low Temperature Synthesis ◽  
Temperature Synthesis ◽  
Gel Processing

Photo-induced sol–gel processing for low-temperature fabrication of high-performance silsesquioxane membranes for use in molecular separation

2015 ◽  
Vol 51 (49) ◽  
pp. 9932-9935 ◽  
Author(s):  
Mai Nishibayashi ◽  
Hiroyuki Yoshida ◽  
Masamoto Uenishi ◽  
Masakoto Kanezashi ◽  
Hiroki Nagasawa ◽  
...  
Keyword(s):  
Low Temperature ◽  
High Performance ◽  
Sol Gel ◽  
Molecular Separation ◽  
Gel Processing

Silsesquioxane (SQ) membranes derived from 3-methacryloxypropyltrimethoxysilane and bis(trimethoxysilyl)ethane were successfully fabricated at low temperature via photo-induced sol–gel processing.

Low Temperature Selective Catalytic Reduction of NOx with NH3 over MnOx /TiO2 Catalyst

2013 ◽  
Vol 295-298 ◽  
pp. 364-369 ◽  
Author(s):  
Jun Lin Xie ◽  
Zheng Bing Fu ◽  
Feng He ◽  
De Fang
Keyword(s):  
Low Temperature ◽  
Selective Catalytic Reduction ◽  
Manganese Oxides ◽  
Catalytic Reduction ◽  
Sol Gel ◽  
Soft Template ◽  
Excess Oxygen ◽  
Narrow Slit ◽  
Transport Pathways ◽  
Scr Of Nox

Amorphous phase MnOx/TiO2 catalysts were prepared by two different methods, their catalytic activities for low temperature selective catalytic reduction (SCR) of NOx with NH3 in the presence of excess oxygen were investigated. The catalysts were characterized by XRD, XPS and HRTEM. The results showed that the catalyst prepared by soft template method had better catalytic active than those prepared by sol-gel method, its catalytic property could reach 98.2% at 200°C. From the microstructure characterization, it could be known that the catalyst prepared by soft template had the shape of nanorod, this shape was contributed to the dispersion of the manganese oxides and possessed higher surface lattice oxygen concentration. Furthermore, narrow slit-shaped pores associated with rod-like particles could provide efficient transport pathways to reactant molecules and products. Due to these, the catalyst performed catalytic active very well.

TiO 2 /SiO 2 /ORMOSIL hybrid material planar waveguides prepared at low-temperature by sol-gel processing

1999 ◽  
Author(s):  
Wenxiu Que ◽  
Yan Zhou ◽  
Yee Loy Lam ◽  
Yuen Chuen Chan ◽  
Shi De Cheng ◽  
...  
Keyword(s):  
Low Temperature ◽  
Hybrid Material ◽  
Sol Gel ◽  
Planar Waveguides ◽  
Gel Processing

The Chemical Processing of Silicates for Biological Applications - A Review

1990 ◽  
Vol 180 ◽  
Author(s):  
L. L. Hench ◽  
June Wilson
Keyword(s):  
Low Temperature ◽  
Sol Gel ◽  
Clinical Applications ◽  
Chemical Processing ◽  
Biological Applications ◽  
Application Area ◽  
Processing Methods ◽  
Bioactive Materials ◽  
Gel Processing ◽  
Glass Powders

ABSTRACTA new application area for sol-gel processing biomaterials and implant devices, is presented. The concepts of bioactive fixation of implants is reviewed. Conventional processing methods for bioactive materials are compared with low temperature chemical processing. Advantages of sol-gel processing include new bioactive compositional ranges of ultraporous CaO-P2O5-SiO2 biogel-glass powders. Clinical applications of bioactive implants are discussed.

The Study of the MnOx/TiO2-ZrO2 Used in the Sintering Flue Gas Low-Temperature Selective Catalytic Reaction

2013 ◽  
Vol 641-642 ◽  
pp. 551-556 ◽  
Author(s):  
Xi Ning Lu ◽  
Cun Yi Song
Keyword(s):  
Low Temperature ◽  
Manganese Oxides ◽  
Catalytic Reduction ◽  
Sol Gel ◽  
Surface Concentration ◽  
Space Velocity ◽  
X Ray Diffraction ◽  
Active Point ◽  
Reduction Of Nox ◽  
High Space

TiO2, 50%TiO2-ZrO2 and 80%TiO2-ZrO2 were prepared by sol-gel method. The manganese oxides were impregnated on the carrier and the catalysts were used for low-temperature selective catalytic reduction of NOx with ammonia (NH3-SCR) in the presence of excess O2. The samples were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The results showed that the particle size of 80%TiO2-ZrO2 is the smallest among the three kind of carrier and the particles are highly dispersed. By adding the ZrO2, the Zr4+ ions replaced the lattice Ti4+ ions, and thus caused lattice distortion in the TiO2 and an increase of the active point amount on the carrier. Furthermore, the Zr also promoted the dispersion of the active ingredients carried on the carrier, increased the surface concentration of Mn. The most active catalyst was obtained with a mass MnOx/80%TiO2-ZrO2 ratio of 0.1.The best MnOx/80%TiO2-ZrO2 catalyst yielded nearly 92.6% NO conversion at 130°C at a high space velocity of 67,000 h-1.

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