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  • Biochemistry and Biotechnology  (2)
  • silica glass  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of sol gel science and technology 8 (1997), S. 397-402 
    ISSN: 1573-4846
    Keywords: silica glass ; monolith ; sub-critical drying ; chlorination ; sintering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Over the last few years, the feasibility of fabricating near net shape silica glass components, using a sub-critical drying process for pure alkoxide gels, has been demonstrated in our laboratories. Cracking during drying, due to capillary forces generated in the gel body, was overcome through two particular innovations. The first was the development and optimization of a dual-catalyzed high strength gel. The second was a controlled atmosphere drying process that allowed the gel to dry utilizing a newly observed phenomenology, postulated to be due to cavitation of the pore fluid. Contrary to conventional wisdom, in this drying approach the smallest pore size gels are the easiest to dry. Details of the types of gels and the drying process are reported. Gels of small size were sintered into crack-free glasses, utilizing conventional sintering approaches. However, large size gels always developed visible surface cracks that formed above 800°C. To successfully dry and sinter large monolithic gels then required re-optimization of the entire process. A great number of micron-range defects were initially detected in these sintered bodies. After analyzing the defects, further steps were taken to improve glass quality to the level of optical glass produced by vapor deposition processes. This included mixing and filtering of sols in a clean room, varying the pore size distribution, and optimizing the pre-sintering and sintering processes. Data of relevant glass quality parameters attained so far in the laboratory are reported.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of sol gel science and technology 8 (1997), S. 397-402 
    ISSN: 1573-4846
    Keywords: silica glass ; monolith ; sub-critical drying ; chlorination ; sintering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Over the last few years, the feasibility of fabricating near net shape silica glass components, using a sub-critical drying process for pure alkoxide gels, has been demonstrated in our laboratories. Cracking during drying, due to capillary forces generated in the gel body, was overcome through two particular innovations. The first was the development and optimization of a dual-catalyzed high strength gel. The second was a controlled atmosphere drying process that allowed the gel to dry utilizing a newly observed phenomenology, postulated to be due to cavitation of the pore fluid. Contrary to conventional wisdom, in this drying approach the smallest pore size gels are the easiest to dry. Details of the types of gels and the drying process are reported. Gels of small size were sintered into crack-free glasses, utilizing conventional sintering approaches. However, large size gels always developed visible surface cracks that formed above 800°C. To successfully dry and sinter large monolithic gels then required re-optimization of the entire process. A great number of micron-range defects were initially detected in these sintered bodies. After analyzing the defects, further steps were taken to improve glass quality to the level of optical glass produced by vapor deposition processes. This included mixing and filtering of sols in a clean room, varying the pore size distribution, and optimizing the pre-sintering and sintering processes. Data of relevant glass quality parameters attained so far in the laboratory are reported.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 489-497 
    ISSN: 0006-3592
    Keywords: Bacillus licheniformis ; bacterial transport ; porous media ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The convective transport of concentrated suspension of bacteria in porous media is of interest for several processes such as microbial enhanced oil recovery and in situ bioremediation. The parameters which affect the transport of the bacterium Bacillus licheniformis JF-2, a candidate microorganism for microbial enhanced oil recovery, were investigated experimentally in sandpacks. Bacteria retention and permeability reduction occurred primarily in the first few centimeters upon entering the porous medium. In downstream sections of the sandpack, the permeability reduction was low, even in cases in which high cell concentrations (108 cfu/mL) were detected in the effluent. The effect of (i) addition of a dispersant, (ii) linear velocity of injection, (iii) cell concentration, (iv) salinity (v) temperature, and (vi) the presence of a residual oleic phase were determined experimentally. A lower reduction in permeability and a higher effluent bacterial concentration were obtained in the presence of dispersant, high injection velocities, low salinities, and at a higher temperature. Macroscopic measurements at different linear velocities and in the presence or absence of dispersants suggest that the formation of reversible microaggregates and multiparticle hydrodynamic exclusion may be the primary mechanisms for bacterial retention and permeability reduction. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 499-508 
    ISSN: 0006-3592
    Keywords: bacterial transport ; porous media ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A model is presented for the coupled processes of bacterial growth and convective transport of bacteria has been modeled using a fractional flow approach. The various mechanisms of bacteria retention can be incorporated into the model through selection of an appropriate shape of the fractional flow curve. Permeability reduction due to pore plugging by bacteria was simulated using the effective medium theory. In porous media, the rates of transport and growth of bacteria, the generation of metabolic products, and the consumption of nutrients are strongly coupled processes. Consequently, the set of governing conservation equations form a set of coupled, nonlinear partial differential equations that were solved numerically. Reasonably good agreement between the model and experimental data has been obtained indicating that the physical processes incorporated in the model are adequate. The model has been used to predict the in situ transport and growth of bacteria, nutrient consumption, and metabolite production. It can be particularly useful in simulating laboratory experiments and in scaling microbial-enhanced oil recovery or bioremediation processes to the field. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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