The Experts below are selected from a list of 14595 Experts worldwide ranked by ideXlab platform
Keith P Watson - One of the best experts on this subject based on the ideXlab platform.
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the tensile strength and free volume of cohesive powders compressed by gas flow
Powder Technology, 2001Co-Authors: Keith P Watson, J M Valverde, A CastellanosAbstract:We report measurements of tensile strength and average free volume for a set of cohesive powders as a function of consolidation stress. Powders with average particle size between 7.8 and 19.2 μm were made from a styrene/butadiene Copolymer, and were subsequently surface-treated with different concentrations of a submicron fumed silica. This silica acts as a flow control additive by controlling interparticle forces. The measurement technique consists of initialization of the sample by fluidization and subsequent consolidation by compression under a given gas flow while continuously monitoring the sample volume. By reversing the gas flow, a tensile stress is applied to the sample. For each consolidation state, we determine the tensile strength and the average free volume of the powder. We find that the relation between the free volume and the consolidation stress follows a logarithmic form. The magnitude of the interparticle forces is estimated from bulk measurements. At high consolidation stresses, the average tensile force per contact increases proportionally to the square root of the consolidation force per contact. Physical implications of these results are discussed.
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the tensile strength of cohesive powders and its relationship to consolidation free volume and cohesivity
Powder Technology, 1998Co-Authors: J M Valverde, A Castellanos, Antonio Ramos, Keith P WatsonAbstract:The tensile strength of a powder is related to the interparticle force and to the free volume, which, in turn, are related to consolidation stress. The relationship between stress and free volume is described by the state diagram that has been measured at zero shear for a set of cohesive powders (xerographic toners) with a range of concentrations of a flow control additive. The toners are 12.7 μm diameter particles of styrene/ butadiene Copolymer, and the surface additive is a submicron fumed silica that is used to control the interparticle forces. To overcome problems of sample non-uniformity, powder samples are initially fluidized and then allowed to settle under gravity. The tensile strenghts, σt, of these powders have been measured by means of a powder bed technique in which gas flow through the bed is increased until the bed fractures due to the tensile stress produced by the gas flow. The overpressure required to fracture the bed then provides a measure of σ1. The consolidation stress in the bed, σe, can be altered by varying the weight of the powder per unit area. Tensile strength is found to be linearly related to the consolidation stress in the limited range of stresses we have investigated, and the slope of this relationship is the same for all additive concentrations below 0.1%; above this concentration the slope decreases, consistent with a change from polymer-dominated to silica-dominated contacts between the particles. From the ratio σt/σe, we show that the contacts are fully plastic event at zero load, and that hardness of the contacts increases with increasing additive concentration.
A Castellanos - One of the best experts on this subject based on the ideXlab platform.
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the tensile strength and free volume of cohesive powders compressed by gas flow
Powder Technology, 2001Co-Authors: Keith P Watson, J M Valverde, A CastellanosAbstract:We report measurements of tensile strength and average free volume for a set of cohesive powders as a function of consolidation stress. Powders with average particle size between 7.8 and 19.2 μm were made from a styrene/butadiene Copolymer, and were subsequently surface-treated with different concentrations of a submicron fumed silica. This silica acts as a flow control additive by controlling interparticle forces. The measurement technique consists of initialization of the sample by fluidization and subsequent consolidation by compression under a given gas flow while continuously monitoring the sample volume. By reversing the gas flow, a tensile stress is applied to the sample. For each consolidation state, we determine the tensile strength and the average free volume of the powder. We find that the relation between the free volume and the consolidation stress follows a logarithmic form. The magnitude of the interparticle forces is estimated from bulk measurements. At high consolidation stresses, the average tensile force per contact increases proportionally to the square root of the consolidation force per contact. Physical implications of these results are discussed.
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the tensile strength of cohesive powders and its relationship to consolidation free volume and cohesivity
Powder Technology, 1998Co-Authors: J M Valverde, A Castellanos, Antonio Ramos, Keith P WatsonAbstract:The tensile strength of a powder is related to the interparticle force and to the free volume, which, in turn, are related to consolidation stress. The relationship between stress and free volume is described by the state diagram that has been measured at zero shear for a set of cohesive powders (xerographic toners) with a range of concentrations of a flow control additive. The toners are 12.7 μm diameter particles of styrene/ butadiene Copolymer, and the surface additive is a submicron fumed silica that is used to control the interparticle forces. To overcome problems of sample non-uniformity, powder samples are initially fluidized and then allowed to settle under gravity. The tensile strenghts, σt, of these powders have been measured by means of a powder bed technique in which gas flow through the bed is increased until the bed fractures due to the tensile stress produced by the gas flow. The overpressure required to fracture the bed then provides a measure of σ1. The consolidation stress in the bed, σe, can be altered by varying the weight of the powder per unit area. Tensile strength is found to be linearly related to the consolidation stress in the limited range of stresses we have investigated, and the slope of this relationship is the same for all additive concentrations below 0.1%; above this concentration the slope decreases, consistent with a change from polymer-dominated to silica-dominated contacts between the particles. From the ratio σt/σe, we show that the contacts are fully plastic event at zero load, and that hardness of the contacts increases with increasing additive concentration.
J M Valverde - One of the best experts on this subject based on the ideXlab platform.
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the tensile strength and free volume of cohesive powders compressed by gas flow
Powder Technology, 2001Co-Authors: Keith P Watson, J M Valverde, A CastellanosAbstract:We report measurements of tensile strength and average free volume for a set of cohesive powders as a function of consolidation stress. Powders with average particle size between 7.8 and 19.2 μm were made from a styrene/butadiene Copolymer, and were subsequently surface-treated with different concentrations of a submicron fumed silica. This silica acts as a flow control additive by controlling interparticle forces. The measurement technique consists of initialization of the sample by fluidization and subsequent consolidation by compression under a given gas flow while continuously monitoring the sample volume. By reversing the gas flow, a tensile stress is applied to the sample. For each consolidation state, we determine the tensile strength and the average free volume of the powder. We find that the relation between the free volume and the consolidation stress follows a logarithmic form. The magnitude of the interparticle forces is estimated from bulk measurements. At high consolidation stresses, the average tensile force per contact increases proportionally to the square root of the consolidation force per contact. Physical implications of these results are discussed.
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the tensile strength of cohesive powders and its relationship to consolidation free volume and cohesivity
Powder Technology, 1998Co-Authors: J M Valverde, A Castellanos, Antonio Ramos, Keith P WatsonAbstract:The tensile strength of a powder is related to the interparticle force and to the free volume, which, in turn, are related to consolidation stress. The relationship between stress and free volume is described by the state diagram that has been measured at zero shear for a set of cohesive powders (xerographic toners) with a range of concentrations of a flow control additive. The toners are 12.7 μm diameter particles of styrene/ butadiene Copolymer, and the surface additive is a submicron fumed silica that is used to control the interparticle forces. To overcome problems of sample non-uniformity, powder samples are initially fluidized and then allowed to settle under gravity. The tensile strenghts, σt, of these powders have been measured by means of a powder bed technique in which gas flow through the bed is increased until the bed fractures due to the tensile stress produced by the gas flow. The overpressure required to fracture the bed then provides a measure of σ1. The consolidation stress in the bed, σe, can be altered by varying the weight of the powder per unit area. Tensile strength is found to be linearly related to the consolidation stress in the limited range of stresses we have investigated, and the slope of this relationship is the same for all additive concentrations below 0.1%; above this concentration the slope decreases, consistent with a change from polymer-dominated to silica-dominated contacts between the particles. From the ratio σt/σe, we show that the contacts are fully plastic event at zero load, and that hardness of the contacts increases with increasing additive concentration.
Rosemarie Plonka - One of the best experts on this subject based on the ideXlab platform.
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nanocomposite coatings for healing surface defects of glass fibers and improving interfacial adhesion
Composites Science and Technology, 2008Co-Authors: Shanglin Gao, Edith Mader, Rosemarie PlonkaAbstract:Abstract Surface defects of brittle materials cause actual tensile strength much lower than the ultimate theoretical strength. Coatings can be used to ‘heal’ surface flaws and modify surface properties. Here, we describe an online process by which a nanometer-scale hybrid coating layer based on Styrene-Butadiene Copolymer with single or multi-walled carbon nanotubes (SWCNTs, MWCNTs) and/or nanoclays, as mechanical enhancement and environmental barrier layer, is applied to alkali-resistant glass (ARG) and E-glass fibers. Our data indicates that the nanostructured and functionalised traditional glass fibers show significantly improved both mechanical properties and environmental corrosion resistance. With low fraction of nanotubes in sizing, the tensile and bending strength of healed glass fiber increases remarkably. No apparent strength variation appears for nanoclay coated fiber subjected to alkaline attack. We introduce a healing efficiency factor and conclude that the coating modulus, thickness and roughness are responsible for the mechanical improvement of fibers. Besides, nanocomposite coatings result in enhanced fiber/matrix interfacial adhesion, indicating nanotube related interfacial toughening mechanisms.
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nanostructured coatings of glass fibers improvement of alkali resistance and mechanical properties
Acta Materialia, 2007Co-Authors: Shanglin Gao, Edith Mader, Rosemarie PlonkaAbstract:Abstract Surface defects cause the measured tensile strength of glass and other brittle materials to be significantly lower than their theoretical values. Coatings can be used to “heal” surface flaws and modify surface properties. Here, we describe an online process by which a nanometer-scale hybrid coating layer based on styrene–butadiene Copolymer with multi-walled carbon nanotubes (MWCNTs) and/or nanoclays, as a mechanical enhancement and environmental barrier layer, is applied to alkali-resistant glass (ARG) and E-glass fibers. Our data indicate that the nanostructured and functionalized traditional glass fibers show significant improvements in both mechanical properties and environmental corrosion resistance. With low fractions of nanotubes (0.2 wt% in sizing), the strength of healed glass fiber increases by up to 70%. No apparent strength variation appears for nanoclay-coated fiber subjected to alkaline attack. The adsorption isotherms of moisture vapor on the fiber surface have been analyzed and an assessment of changes in the nanomechanical properties of the fiber surface is provided. It is shown that the sorption of moisture is reduced by the presence of nanoclay particles in the coating. We introduce a healing efficiency factor and conclude that the coating modulus, thickness and roughness are responsible for the mechanical improvement of fibers.
Andrew J Daugulis - One of the best experts on this subject based on the ideXlab platform.
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improved reactor performance and operability in the biotransformation of carveol to carvone using a solid liquid two phase partitioning bioreactor
Biotechnology and Bioengineering, 2008Co-Authors: Jenna L E Morrish, Andrew J DaugulisAbstract:In an effort to improve reactor performance and process operability, the microbial biotransformation of (� )-trans-carveol to (R)-(� )-carvone by hydrophobic Rho- dococcus erythropolis DCL14 was carried out in a two phase partitioning bioreactor (TPPB) with solid polymer beads acting as the partitioning phase. Previous work had demon- strated that the substrate and product become inhibitory to the organism at elevated aqueous concentrations and the use of an immiscible second phase in the bioreactor was intended to provide a reservoir for substrates to be delivered to the aqueous phase based on the metabolic rate of the cells, while also acting as a sink to uptake the product as it is produced. The biotransformation was previously underta- ken in a two liquid phase TPPB with 1-dodecene and with silicone oil as the immiscible second phase and, although improvement in the reactor performance was obtained relative to a single phase system, the hydrophobic nature of the organism caused the formation of severe emulsions leading to significant operational challenges. In the present work, eight types of polymer beads were screened for their suitability for use in a solid-liquid TPPB for this biotrans- formation. The use of selected solid polymer beads as the second phase completely prevented emulsion formation and therefore improved overall operability of the reactor. Three modes of solid-liquid TPPB operation were considered: the use of a single polymer bead type (styrene/butadiene copo- lymer) in the reactor, the use of a mixture of polymer beads in the reactor (styrene/butadiene Copolymer plus Hytrel 1 8206), and the use of one type of polymer beads in the reactor (styrene/butadiene Copolymer), and another bead type (Hytrel 1 8206) in an external column through which fermentation medium was recirculated. This last configura- tion achieved the best reactor performance with 7 times more substrate being added throughout the biotransforma- tion relative to a single aqueous phase benchmark reactor and 2.7 times more substrate being added relative to the best two liquid TPPB case. Carvone was quantitatively recovered from the polymer beads via single stage extraction into methanol, allowing for bead re-use. Biotechnol. Bioeng. 2008;101: 946-956.
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oxygen transfer in a gas liquid system containing solids of varying oxygen affinity
Chemical Engineering Journal, 2007Co-Authors: Jennifer V Littlejohns, Andrew J DaugulisAbstract:Abstract An air sparged, mechanically agitated bioreactor containing spherical solids was studied in order to determine the effect of the solid phase on oxygen mass transfer. It was found that both nylon 6,6 and glass beads cause an enhancement of the volumetric mass transfer coefficient of up to 268%, whereas particles of silicone rubber and styrene–butadiene Copolymer reduce the volumetric mass transfer coefficient by up to 63%, relative to a system without a solid phase. A simple transport in series model has been proposed to account for the observed phenomena, which includes both the physical enhancement effects of particles on gas–liquid mass transfer as well as absorption of oxygen into the polymer. Even though volumetric mass transfer coefficient reductions were observed in the system containing silicone rubber, it was demonstrated that an increased oxygen transfer rate into the working volume of a two-phase system occurs relative to a system without a solid phase. This study provides an explanation for previous results regarding the enhanced effect of the presence of a styrene–butadiene Copolymer phase in reducing oxygen limitations in a solid–liquid two-phase partitioning bioreactor. Results from this study can be applied to two-phase aerobic fermentation systems that will benefit from reducing oxygen limiting conditions.
