Author: Ping LiPublisher:
ISBN:
Category :
Languages : en
Pages : 486
Book Description
Crystallization Behavior of Sol-gel Derived Lithium Disilicate Powders and Coatings
Author: Ping LiProcess Structure and Property Correlations in Sol-gel Derived Lithium Niobate Thin Films
Author: Vikram JoshiChemical Engineering
Author: Miguel A. GalanPublisher: John Wiley & Sons
ISBN:
Category : Science
Languages : en
Pages : 458
Book Description
Unlike extensive major reference works or handbooks, Chemical Engineering: Trends and Developments provides readers with a ready-reference to latest techniques in selected areas of chemical engineering where research is and will be focused in the future. These areas are: bioseparations; particle science and design; nanotechnology; and reaction engineering. The aim of the book is to provide academic and R&D researchers with an overview of the main areas of technical development and how these techniques can be applied. Each chapter focuses on a technique, plus a selection of applications or examples of where the technique could be applied.
Chemical Processing of Lead Metatitanate by Co-precipitation and Sol-gel Methods: The Role of Powder and Gel Characteristics on Crystallization Behavior
Author: Robert William SchwartzPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
This thesis reports on preparation of PbTiO$sb3$ by two chemical methods: (i) aqueous co-precipitation and (ii) organo-metallic sol-gel processing. The effects of chemical processing conditions on material properties were determined. Particular attention was paid to the evolution of structure on heat treatment, and crystallization. Materials prepared by the two methods were amorphous in the as-prepared state, but transformed to the stable perovskite structure on heat treatment. Crystallization kinetics for the chemically prepared materials were compared with another type of amorphous PbTiO$sb3$ prepared by rapid solidification. This comparison led to the identification of material parameters which aided in crystallization. Co-precipitation was carried out by spray-atomizing a solution containing inorganic salts of lead and titanium into a continuous flow constant volume reactor. Temperature, pH, and other reactor parameters were controlled. The precipitated powders, which were dried by spray-drying, had a uniform spherical morphology with particle sizes in the micron range, and surface areas $>$100 m$sp2$/g. Crystallization into the perovskite structure occurred at 375$spcirc$C. The second chemical method was sol-gel processing of PbTiO$sb3$ from metal alkoxide solutions. Effects of hydrolysis, additive (i.e., acid or base), and drying conditions on the physical, structural, and chemical nature of the material were characterized, as was the evolution of material properties with thermal processing. Results indicated that manipulation of preparation conditions gave a significant degree of control over material properties. Correlations of material properties with preparation conditions were explained by a model which related differences in gel network structure (and structural rearrangements on heat treatment) with the level of polymeric crosslinking. Differences induced in wet gels through control of preparation conditions persisted in the amorphous and crystalline states. TEM observations indicated that densification and crystallization occurred at relatively low temperatures (400-450$spcirc$C). Lead titanate was also prepared by a third physical method, rapid solidification. Compared with the rapidly solidified material, the co-precipitated and sol-gel derived materials exhibited enhanced crystallization kinetics and lower crystallization temperatures. The chemically prepared materials were also characterized by greater surface areas and free volumes than the rapidly solidified material. The enhanced crystallization behavior was therefore believed to be at least partially due to the internal surfaces present in the chemically prepared materials.
American Doctoral Dissertations
Author: Publisher:
ISBN:
Category : Dissertation abstracts
Languages : en
Pages : 896
Book Description
Characterisation of Sol-gel Derived Silica Powders
Author: Malcolm Andrew ButlerCeramics Technology
Author: Sol-gel Derived Ceramic Electrolyte Films on Porous Substrates
Author: Timothy Walter KueperPublisher:
ISBN:
Category :
Languages : en
Pages : 252
Book Description
Sol-Gel Processing and Crystallization of Yttrium Aluminosilicates
Author: James C. WalckPublisher:
ISBN:
Category :
Languages : en
Pages : 20
Book Description
Glasses in the yttria-aluminum-silica (YAS) system are candidate matrices for SiC reinforced composites because of their high elastic moduli and excellent chemical durability. Moreover, several compositions offer the potential for controlled crystallization into glass ceramics exhibiting low-thermal expansion and elevated temperature stability. In order to exploit the properties of these glasses and glass ceramics, improved processing techniques and detailed investigations of their crystallization behavior are required. Glass in the yttria-alumina-silica system was synthesized using sol-gel techniques. Crystallization behavior of the gel and the glass was examined using variable heating rate data obtained by differential thermal analysis (DTA). The reaction rate constants for crystallization followed an Arrhenius temperature dependence, and the activation energies for crystallization were readily determined. Surface nucleation/crystallization dominated but no appreciable difference in crystallization between the gel and glass powders was evident. In this system it was verified that densification of the gel occurred before the onset of crystallization. Isothermal heat treatment of the gels and glasses produced 3Al2O3-2SiO2 and various polymorphs of Y2O3.2SiO2. Yttrium pyrosilicates, Mullite.
Author: Hsin-Chun Lu