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Dispersant
Terms modified by Dispersant Selected AbstractsNovel Coagulation Method for Direct Coagulation Casting of Aqueous Alumina Slurries Prepared Using a Poly(Acrylate) DispersantJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008Kuttan Prabhakaran Coagulation of concentrated aqueous alumina slurries prepared using an ammonium poly(acrylate) dispersant by MgO has been studied for direct coagulation casting (DCC). A small amount of MgO (0.2 wt% of alumina) increased the viscosity of the concentrated alumina slurry with time and finally transformed it into a stiff gel. The mechanism of coagulation is proposed such that the time-delayed in situ generation of Mg2+ ions from the sparingly soluble MgO forms Mg,poly(acrylate) with the unadsorbed ammonium poly(acrylate) molecules in solution that shift the poly(acrylate) adsorption equilibrium toward the left by depleting the poly(acrylate) molecules adsorbed on the alumina particle surface. This leads to insufficient dispersant coverage on the particle surface and coagulation of the slurry. DCC using MgO is possible only if the slurry is prepared at a dispersant concentration higher than that required for optimum dispersion as the slurries prepared at the optimum dispersant concentration underwent premature coagulation. The gelation time could be tailored within 20 min to a few hours by maintaining the temperature in the range of 70°,30°C. The wet coagulated bodies prepared from 50 vol% alumina slurry showed a compressive strength of nearly 0.05 MPa. [source] Cardanol: A New Dispersant for Alumina in TolueneJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2000Kuttan Prabhakaran Cardanol, which is a naturally occurring C15 unsaturated aliphatic chain-substituted phenol derived from cashew nut shell liquid, was used as a dispersant for alumina in toluene. Adsorption data, along with the results of sedimentation studies, green density, and slurry viscosity (as a function of dispersant concentration), suggest that cardanol adsorption initially proceeded through surface coverage by a phenolic group that lies flat on the surface and that the best powder dispersion occurred at surface saturation by more closely packed end-on adsorbed cardanol molecules. The alkyl-chain unsaturation significantly contributed to dispersion, such that the saturation by hydrogenation led to an increase in the slurry viscosity by a factor of ,2.5. Concentrated slurries generally showed shear-thinning flow behavior, and the measured viscosity of a highly concentrated (53 vol%) slurry was <1 Pa·s at a shear rate of 93 s,1. [source] Anaphylactic reaction to intralesional corticosteroid injectionCONTACT DERMATITIS, Issue 2 2007M. E. Laing We report the case of anaphylactic reaction to carboxymethylcellulose, a dispersant in corticosteroid preparation and contrast media. Skin prick testing in this patient revealed a positive response to carboxymethylcellulose at a dilution of 1/1000. Anaphylaxis secondary to carboxymethylcellulose has previously been reported. To avoid further problems, this patient was advised to alert medical staff for the presence of allergy to carboxymethylcellulose in the event of the need for further interventional procedures. Care should be taken when giving intradermal steroids to patients with a history of anaphylaxis after contrast media. [source] Slip Casting of ZrB2,SiC Composite Aqueous SuspensionsADVANCED ENGINEERING MATERIALS, Issue 3 2010Valentina Medri Slip casting of concentrated aqueous suspensions was set up as forming technique for the production of crucibles from ZrB2,SiC composite powder. The dispersion effectiveness and the effect on the final microstructures of two commercial ammonium polyacrylates (Duramax D3005 and Dolapix PC33) used as dispersants were investigated. The first goal was pursued by evaluating the zeta potential of the powders in water at different concentrations of additives, while the second one was assessed by analyzing the microstructure. Duramax D3005 resulted more effective than Dolapix PC33 in electrostatically stabilize the suspensions. Correspondently, almost homogeneous microstructures and lower final porosity of the sintered crucibles were obtained with Duramax D3005, while ZrB2 layers on the vertical surfaces initially in contact with the plaster molds were observed using Dolapix PC33. Moreover, the use of this latter dispersant did not allow the preparation of thick crucible walls due to the sample rupture during the binders pyrolysis stage. [source] Properties of Porous Si3N4/BN Composites Fabricated by RBSN TechniqueINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2010Ji-Xuan Liu Reaction bonding of silicon nitride (RBSN) technique combined with slip-casting shaping process was used to fabricate porous Si3N4/BN ceramic composites. Si/BN slurry with chemical stability, good dispersibility, and viscosity was prepared using glycerol trioleate (GTO) covering on Si surface and poly(acrylic acid) (PAA) as dispersant. The hydrolysis of Si was strongly prevented by GTO coating. The dispersibility of covered Si and BN suspensions were improved by PAA dispersant. Twenty volume percent covered Si/BN slurries with low viscosity were successfully casted. The cast bodies were dried at room temperature, debindered at 750°C and nitrided below 1450°C. The nitrided samples mainly consist of ,-Si3N4, ,-Si3N4, and h-BN. The composites exhibit homogeneous microstructure consisting of faceted particles, ,-Si3N4 nanowires and a large amount of pores. The porosity is 52.64% and the pore size is in the range of 60,300 nm. The composites show compressive strength of 16.6±1.5 MPa. The dielectric constant of the composite is about 3.1 and the dielectric loss is below 0.5% under different frequencies. [source] Stability study of inverse suspension copolymerization of 1,1,3,3-tetramethylguandium acrylate and N,N, -methylenebisacrylamideJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Jie Dong Abstract In a previous study, we synthesized crosslinked P(TMGA- co -MBA) via an inverse suspension copolymerization of 1,1,3,3-tetramethylguandium acrylate (TMGA) and N,N,-methylenebisacrylamide (MBA) and found that the product is a good SO2 sorbent. However, the polymerization stability appeared to be poor under some reaction conditions and is far from being elucidated. In this study, the inverse suspension copolymerization was carried out using cyclohexane as solvent, Span60 as dispersant, and ammonium persulfate (APS) as initiator. The effects of the reaction conditions such as stirring speed, dispersant concentration, and temperature on the polymerization stability and particle size were systematically examined. It is found that the polymerization stability is a strong function of these parameters. Stable crosslinked poly(TMGA- co -MBA) particles from micrometer to millimeter diameters were synthesized under optimized conditions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Enhanced photodegradation efficiency of polyethylene-TiO2 nanocomposite film with oxidized polyethylene waxJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010Wenjun Fa Abstract A novel photodegradable polyethylene-oxidized polyethylene wax-TiO2 (PE-OPW-TiO2) nanocomposite film was prepared by embedding the organically modified TiO2 nanoparticles into commercial PE in the presence of OPW. The photocatalytic degradation behavior under ultraviolet light or solar light was investigated by examining the weight loss of the composite films, UV,vis transmittance spectrum, scanning electron microscope (SEM), and gel permeation chromatogram (GPC). The results show that OPW, as a dispersant and a compatibiliser, markedly improves the dispersion and compatibility of TiO2 nanoparticles in PE resins. The PE-OPW-TiO2 composite film demonstrates much higher photodegradation efficiency and much better mechanical property than either the PE-TiO2 composite film or the pure PE film. The weight-average molecular weight (Mw) of the PE-OPW-TiO2 composite film decreased 94.3% and the number-average molecular weight (Mn) decreased 84.5% after 38 days solar light irradiation. The photocatalytic degradation mechanism of the film is briefly discussed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Dispersion of nanoscale BaTiO3 suspensions by a combination of chemical and mechanical grinding/mixing processesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Kuo-Liang Ying Abstract The colloidal stability of aqueous nanometer- and micrometer-scale barium titanate (BaTiO3) utilizing poly (methacrylic acid) (PMAA-Na) and polyacrylamide/(,- N,N -dimethyl- N -acryloyloxyethyl)ammonium ethanate (PDAAE) was investigated. In addition to chemical dispersants, the effects of mechanical milling using either conventional ball milling or nanogrinding/-mixing on the dispersion of BaTiO3 suspensions were also studied. Characterization of the particle size distribution (d50), viscosity, and morphology of BaTiO3 particles in the suspensions revealed that a sole chemical dispersant or mechanical milling was insufficient to achieve nanometer-scale dispersion. The best dispersion results were obtained with a combination of PMAA-Na dispersant and nanogrinding/-mixing, which could provide sufficient electronic repulsive force and shear force to disperse the 80-nm BaTiO3 powders uniformly in the aqueous suspension. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Effects of chemical structure on the properties of carboxylate-type copolymer dispersant for coal-water slurryAICHE JOURNAL, Issue 9 2009Renfu Xu Abstract In this study, a series of carboxylate-type copolymer dispersants were prepared. The effects of chemical structures of the copolymer dispersants, including the molecular weight, kind, quantity and ratio of hydrophilic/hydrophobic groups, and side chain length, on the solid loading, apparent viscosity, zeta potential, rheological behavior, and stability of coal-water slurry (CWS) prepared from Dongtan, Yima, and Datong coals were systematically investigated. The dispersion performance of the copolymer can be improved by adjusting its chemical structures, and the dispersion mechanism was discussed. In addition, a high solid loading CWS with excellent stability toward settling can be achieved by means of the copolymer dispersant and carboxymethyl cellulose sodium salt (CMC-Na). Experiments have proved that the copolymer has the potential to be developed as a new high-effective dispersant for CWS. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Dispersion polymerization of styrene in carbon dioxide stabilized by copolymers of poly(propylene glycol) methacrylate and 2-(perfluorooctyl)ethyl methacrylateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2003Lunhan Ding Abstract The dispersion polymerization of styrene in carbon dioxide with a series of copolymers of poly(propylene glycol) methacrylate (PPGMA) and 2-(perfluorooctyl)ethyl methacrylate (FOEMA) as the polymerization dispersants was examined. It was demonstrated that PPGMA and FOEMA copolymers and polymers containing 52,100% FOEMA could be used as effective dispersants for the polymerization, and the composition of the copolymeric dispersant had a dramatic effect on both the polymerization yield and the morphology of the resulting polystyrene. The effects of the concentrations of the copolymeric dispersants, the concentrations of the monomer, and the reaction pressure were also investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3804,3815, 2003 [source] Fabrication and Characterization of Anode-Supported Tubular Solid-Oxide Fuel Cells by Slip Casting and Dip Coating TechniquesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2009Lan Zhang High-performance anode-supported tubular solid-oxide fuel cells (SOFCs) have been successfully developed and fabricated using slip casting, dip coating, and impregnation techniques. The effect of a dispersant and solid loading on the viscosity of the NiO/Y2O3,ZrO2 (NiO/YSZ) slurry is investigated in detail. The viscosity of the slurry was found to be minimum when the dispersant content was 0.6 wt% of NiO/YSZ. The effect of sintering temperature on the shrinkage and porosity of the anode tubes, densification of the electrolyte, and performance of the cell at different solid loadings is also investigated. A Ni/YSZ anode-supported tubular cell fabricated from the NiO/YSZ slurry with 65 wt% solid loading and sintered at 1380°C produced a peak power output of ,491 and ,376 mW/cm2 at 800°C in wet H2 and CH4, respectively. With the impregnation of Ce0.8Gd0.2O2 (GDC) nanoparticles, the peak power density increased to ,1104 and ,770 mW/cm2 at 800°C in wet H2 and CH4, respectively. GDC impregnation considerably enhances the electrochemical performance of the cell and significantly reduces the ohmic and polarization resistances of thin solid electrolyte cells. [source] The Effect of Electric Field on Pressure Filtration of Ceramic SuspensionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2009Yoshihiro Hirata The consolidation behavior of Al2O3 and indium tin oxide (ITO, 90% In2O3,10% SnO2) particles 150,200 nm in size was examined using a pressure filtration apparatus at a constant compressive rate under an electric field. The relation of applied pressure (,Pt) with volume of dehydrated filtrate (Vf) was compared with the established filtration theory (theory I) for a well-dispersed suspension and the newly developed filtration theory (theory II) for a flocculated suspension. The experimental results without polyelectrolyte dispersant deviated from theory I when ,Pt exceeded a critical pressure (,Ptc). This deviation is associated with the phase transition from a dispersed suspension to a flocculated suspension at ,Ptc. A good agreement was shown between the developed theory II and experimental results after the phase transition. When a dispersant (polyacrylic ammonium, PAA) was added to alumina, ITO, or Al2O3,ITO mixed powder suspensions, the consolidation behavior of the particles was controlled by the dissociation and amounts of adsorbed and free PAA. The addition of a large amount of highly charged PAA enhanced the repulsive interaction between PAA-adsorbed particles, and the consolidation behavior was explained by theory I. The adsorption of neutral PAA on the particles reduced the repulsive interaction, and the consolidation behavior was well explained by theory II. The phase transition from dispersed to flocculated suspension was very sensitive to the electric field during the pressure filtration. The ,Ptc for the suspension with and without PAA decreased drastically when a low electric field was applied. The final packing density of the flocculated particles was greatly increased by the application of a weak electric field. However, the dense structure under high pressure was relaxed to a low-density structure when the stored elastic strain energy was released. [source] Tailoring Texture of ,-Y2Si2O7 by Strong Magnetic Field Alignment and Two-Step SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2008Z. Q. Sun In this study, a well-dispersed ,-Y2Si2O7 ethanol-based suspension with 30 vol% solid loading was prepared by adding 1 dwb% polyethylene imine dispersant, which allows feeble magnetic ,-Y2Si2O7 particles with anisotropic magnetic susceptibility to rotate in a 12 T strong magnetic field during slip casting, resulting in the development of a strongtexture in green bodies. Pressureless sintering gives rise to more pronounced grain growth in the textured sample than in the untextured sample prepared without the magnetic field due to the rapid migration of the grain boundaries of the well-oriented grains, which was revealed by constant-heating-rate sintering kinetics. It was found that the use of two-step sintering is very efficient not only for inhibiting the grain growth but also for enhancing thetexture. This implies that controlled grain growth is crucial for enhancing texture development in ,-Y2Si2O7. [source] Novel Coagulation Method for Direct Coagulation Casting of Aqueous Alumina Slurries Prepared Using a Poly(Acrylate) DispersantJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008Kuttan Prabhakaran Coagulation of concentrated aqueous alumina slurries prepared using an ammonium poly(acrylate) dispersant by MgO has been studied for direct coagulation casting (DCC). A small amount of MgO (0.2 wt% of alumina) increased the viscosity of the concentrated alumina slurry with time and finally transformed it into a stiff gel. The mechanism of coagulation is proposed such that the time-delayed in situ generation of Mg2+ ions from the sparingly soluble MgO forms Mg,poly(acrylate) with the unadsorbed ammonium poly(acrylate) molecules in solution that shift the poly(acrylate) adsorption equilibrium toward the left by depleting the poly(acrylate) molecules adsorbed on the alumina particle surface. This leads to insufficient dispersant coverage on the particle surface and coagulation of the slurry. DCC using MgO is possible only if the slurry is prepared at a dispersant concentration higher than that required for optimum dispersion as the slurries prepared at the optimum dispersant concentration underwent premature coagulation. The gelation time could be tailored within 20 min to a few hours by maintaining the temperature in the range of 70°,30°C. The wet coagulated bodies prepared from 50 vol% alumina slurry showed a compressive strength of nearly 0.05 MPa. [source] Dispersion Behavior of ZrB2 Powder in Aqueous SolutionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Sea-Hoon Lee Dispersion conditions of ZrB2 powder in water were investigated using poly(ethyleneimine) (PEI) as a dispersant. Pulverization of ZrB2 powder to submicrometer size was difficult and a substantial amount of large particles remained after an intensive planatery milling for 72 h. The isoelectric point (IEP) of ZrB2 powder was measured to be pH 5.8 by electrophoresis, which shifted to pH 6.2 after milling. The application of PEI changed the IEP of the boride slurry to ,pH 11. Well-dispersed aqueous ZrB2 slurries with a high solid loading (up to 45 vol%) were fabricated at pH 6.5,7.5 by the application of 1.5 wt% PEI. [source] Coagulation of Concentrated Suspensions of Ultrafine Alumina Powders by pH ShiftJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2006Anne-Laure Pénard Highly concentrated suspensions of ultrafine alumina powders are prepared using 2-phosphonobutane-1,2,4-tricarboxylic acid as dispersant. The coagulation of these suspensions is carried out at around 278 K by adding a blend of acetic anhydride plus ethylene glycol. Coagulation takes place through a pH shift because of a time-delayed hydration of the acetic anhydride. The coagulation kinetics are studied by viscosity measurements with respect to the temperature and composition of the coagulant blend. Finally, the method is used to produce complex 3D parts of large dimensions for bio-applications by direct coagulation casting and the fired bodies are characterized. [source] Improvement of the Dispersion of Al2O3 Slurries Using EDTA-4NaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2006Jingxian Zhang Polyacrylic acid (PAA) is known to be an effective dispersant for Al2O3 powder in aqueous media. However, at high solid loading (>55 vol%), the dispersion of the Al2O3 suspensions became difficult with only PAA as a dispersant. In this paper, ethylenediaminetetraacetic acid, tetrasodium salt, dihydrate (EDTA-4Na) was introduced to improve the dispersion of the Al2O3 suspensions. With the aid of EDTA-4Na, the adsorption amount of sodium polyacrylic acid (PAA-Na) increased, while the apparent viscosity of 60 vol% Al2O3 slurries decreased significantly. Particle size measurements showed that EDTA-4Na could help to reduce larger agglomerates, possibly by modifying the adsorbed layer thickness. The interactions between EDTA-4Na and PAA-Na were studied using Fourier-transform infrared spectroscopy analysis. Results showed that it was possible to introduce EDTA-4Na as the second dispersant to improve the dispersion of high solid content Al2O3 slurries. [source] Sulfanilic Acid: A Novel Consolidation Agent for Al2O3 in Aqueous MediaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006Jingxian Zhang A new solidifying agent, 4-aminobenzene sulfonic acid (sulfanilic acid), is reported in this paper. The consolidation process and mechanism were followed using on viscoelastic, FTIR, SEM, and Hg porosimetry measurements. It was shown that the Al2O3 slurries with PAA-Na as dispersant exhibited a high degree of particle stabilization. After the addition of sulfanilic acid, we observed an exponential increase in the storage modulus (G,) as a function of consolidation time. Correspondingly, Al2O3 slurries exhibited a transition from a viscous to an elastic state (in 62 min). FTIR analysis indicated that the consolidation process might follow two steps: first, the adsorption of sulfanilic acid on the Al2O3 particle surface; second, the acid,base interaction between the adsorbed PAA-Na molecules and the sulfanilic acid molecules. This interaction could possibly induce the formation of three-dimensional networks through a bridging or charge neutralization mechanism. The as-consolidated Al2O3 green samples were homogeneous, with the relative green density being 54.69%. Results showed that it was feasible to introduce sulfanilic acid for the consolidation of Al2O3 slurries in aqueous media. [source] Rapid Prototyping of Piezoelectric Ceramics via Selective Laser Sintering and GelcastingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2004Dong Guo This article presents a new lost mold rapid prototyping method which combines selective laser sintering (SLS) and gelcasting techniques for fabricating piezoelectric ceramics. SLS was used to fabricate sacrificial molds of the desired structure of the ceramic part. Then aqueous PZT (lead zirconate titanate) suspension was cast in the mold and solidified in situ through formation of a three-dimensional network gel. Because the polymer mold can be easily removed at the initial stage of sintering and the gelcast PZT body has a high green strength, the desired geometry of the PZT part can be completely retained after sintering of the ceramics. Complex-shaped PZT parts were successfully fabricated after using concentrated PZT suspension with low viscosity. Densities and electrical properties, such as the d33, the relative permittivity ,, the dielectric loss tg, and the electromechanical coupling factor Kp of the gelcast PZT parts were also compared with those of the die-pressed PZT samples. The results indicated that the gel-forming process did not deteriorate the electrical properties of the samples, if proper dispersant was selected in developing concentrated ceramic slurry. [source] Aqueous Processing and Stabilization of Manganese Zinc Ferrite Powders via a Passivation,Dispersion ApproachJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2002Michael M. Mandanas A dispersion scheme for aqueous processing of manganese zinc ferrite suspensions is presented. The addition of oxalic acid leads to the formation of a uniform negative charge on the surface such that a cationic polyelectrolyte, polyethyleneimine (PEI), adsorbs and provides electrosteric dispersion. At 0.5 w/w (weight percent with respect to the dry powder) oxalic acid addition, there is a relatively uniform negative surface charge (approximately ,30 mV) within the suspension pH range investigated (3,10), eliminating the isoelectric point (pH ,7.6) present for the as-received metal oxide powder. At the addition of 0.5 w/w PEI on an oxalate-treated surface, the surface charge is constant and positive (,20 mV) through a wide pH range, ,5,10. The resulting rheological data for passivation,dispersion of relatively high-solids manganese zinc ferrite suspensions (,80 wt%) demonstrate improved colloid stability with improved rheological properties. The resulting apparent viscosity and Bingham yield point is 0.01 Pa·s (12.0 cP) and 0.24 Pa (2.4 dynes/cm2), respectively. A sulfonated napthalene-based dispersant, typically used in industry, gives an apparent viscosity and Bingham yield point of 0.03 Pa·s (32 cP) and 3.1 Pa (31 dynes/cm2), respectively. [source] Aqueous Processing of Titanium Carbide Green SheetsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2001Jing-Xian Zhang TiC sheets were prepared by an aqueous tape-casting process. The zeta potential measurement showed that the isoelectric point for TiC powders in the absence of dispersant had a pH value of ,3.3. According to the surface properties of TiC powders, a cationic polymer PEI was selected as dispersant. In the presence of dispersant, the isoelectric point increased to a pH value of ,10.4. The slip stability was determined by visual observation of the fluidity of the slip as well as the settling of the powders. Results showed that the amount of dispersant required to achieve a minimum of viscosity for 50 vol% suspensions was equal to 1.2 wt%. In the absence and presence of dispersant, stable slips could be obtained in the pH ranges 7,9 and 11,12, respectively. The rheological measurements showed that with PEI as dispersant, TiC suspensions exhibited a small time dependent behavior. With polyvinyl alcohol as binder and glycerol as plasticizer, suspensions showed a thixotropic feature. As-cast tapes were dried in air at room temperature. The results showed that it was possible to fabricate homogeneous green tapes with smooth surfaces from these suspensions. [source] Lead Zirconate Titanate Particle Dispersion in Thick-Film Ink FormulationsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2000Erik S. Thiele Diverse device applications for lead zirconate titanate (PZT) ceramics in thick-film form are currently in active development. In the present study, the particle dispersion properties of thick-film ink formulations containing PZT powder have been determined using rheological measurements. Although all of the eight commercially available dispersants tested are more effective than the terpineol solvent alone in decreasing attractive interparticle forces in suspensions, the best dispersant identified for hard and soft PZT powders is a phosphate ester oligomer. This dispersant is extremely efficient, and its use in thick-film ink formulations results in viscosity decreases of 50% at low shear rates (10 s,1) and 30% at high shear rates (100 s,1) compared with current ink formulations containing no dispersant. The effects upon rheology of the order of addition of components in the processing of inks have been studied, with the most effective processing route using a fugitive solvent that probably facilitates uniform coverage of the particle surfaces by the dispersant molecules. Modeling of the rheological profiles of inks indicates that the use of a dispersant decreases the depth of the primary minimum in the interparticle potential by a factor of 3. Demonstrated advantages of the use of a dispersant in PZT thick-film inks include improved microstructural homogeneity in the green body and the ability to formulate printable inks with higher solids loadings. No adverse effects of the dispersant upon the dielectric and piezoelectric properties of bulk PZT samples are found following burnout and sintering. [source] Cardanol: A New Dispersant for Alumina in TolueneJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2000Kuttan Prabhakaran Cardanol, which is a naturally occurring C15 unsaturated aliphatic chain-substituted phenol derived from cashew nut shell liquid, was used as a dispersant for alumina in toluene. Adsorption data, along with the results of sedimentation studies, green density, and slurry viscosity (as a function of dispersant concentration), suggest that cardanol adsorption initially proceeded through surface coverage by a phenolic group that lies flat on the surface and that the best powder dispersion occurred at surface saturation by more closely packed end-on adsorbed cardanol molecules. The alkyl-chain unsaturation significantly contributed to dispersion, such that the saturation by hydrogenation led to an increase in the slurry viscosity by a factor of ,2.5. Concentrated slurries generally showed shear-thinning flow behavior, and the measured viscosity of a highly concentrated (53 vol%) slurry was <1 Pa·s at a shear rate of 93 s,1. [source] Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: II, Dispersion of the PowderJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2000Liwu Wang A novel dispersant,O-(2-aminopropyl)-O,-(2-methoxyethyl)-polypropylene glycol (AMPG),was developed to disperse submicrometer-sized Si3N4 powder in nonaqueous media, based on the surface chemistry of the powder. The dispersing phenomena and mechanisms have been studied systematically, both in model systems (using atomic force microscopy and ellipsometry) and in powder systems (using rheological behavior and adsorption isotherms). The results from the model systems correlated well with those from wet powder systems. It is demonstrated that highly concentrated (with a solids volume fraction of >0.50) and colloidally stable nonaqueous Si3N4 suspensions can be realized using AMPG. [source] Direct Synthesis of PVA- g -PDMS in MicrosuspensionMACROMOLECULAR RAPID COMMUNICATIONS, Issue 5 2008Emmanuel Pouget Abstract The synthesis of P(VA- co -VAc)- graft -PDMS copolymers has been achieved in microsuspension by direct reaction between an epoxy-terminated PDMS and some pendant alcohol groups in P(VA- co -VAc). In this synthesis, the copolymer is used both as dispersant and reactant. The hydrophilic/hydrophobic character of the final material can be varied at will by incorporating various contents of epoxy-functionalized PDMS through optimized reaction conditions. The final composition was determined by TGA and 1H NMR. Products prepared from monofunctional PDMS were easily redispersed in water whereas a film of crosslinked materials, arising from difunctional PDMS, showed the best waterproofing as shown by contact angle analysis. [source] The preparation and properties of dextrin-graft-acrylic acid/montmorillonite superabsorbent nanocompositePOLYMER COMPOSITES, Issue 7 2009Xin Ding A novel superabsorbent nanocomposite was synthesized through intercalation polymerization of partially neutralized acrylic acid, gelatinized dextrin, and an organic-montmorillonite powder using N,N -methylenebisacrylamide as a crosslinker, Span-60 as a dispersant, and ammonium persulfate together with sodiumsulfite as a type of mixed redox initiator. Effects of the amount of them on water absorbency of the superabsorbent were investigated. The structure and the morphology of the nanocomposite were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and transmission electron microscopy analysis. The blood compatibility of the composite was primarily measured. The results show that the acrylic acid monomer was successfully intercalated into the organic-montmorillonite layers and bonded with them. The superabsorbent nanocomposite synthesized under optimal conditions with an organic-montmorillonite powder content of 5 wt% exhibit an absorption of 725.3 g/g in distilled water and favorable blood compatibility. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source] Evaluation of fungal antagonists for grey mould management in early growth of pot rosesANNALS OF APPLIED BIOLOGY, Issue 1 2004D S YOHALEM Summary Several filamentous fungi can reduce disease incidence and suppress sporulation of Botrytis cinerea during early establishment and vegetative growth of pot roses. Two isolates of Ulocladium atrum were the most successful of those fungi tested, were consistently more effective than the fungicide, iprodione and not different from each other. Tween 80, added as a dispersant, had no effect on the efficacy of U. atrum. An isolate of Clonostachys rosea also gave better disease control than iprodione, although not to the levels given by isolates of U. atrum, nor was its behaviour consistent across experiments. Another isolate of C. rosea performed well in one trial, had no discernible effect in a second and was excluded from the third due to poor inoculum quality. Commercial Trichoderma harzianum preparations (Trichodex and Supresivit) failed to reduce disease incidence under the high disease pressure of these experiments, but did reduce sporulation of the pathogen relative to untreated controls. [source] Enhancement of Thermal Conductivity with CuO for NanofluidsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 1 2006M.-S. Liu Abstract The enhancement of the thermal conductivity of ethylene glycol in the presence of copper oxide (CuO) is investigated. CuO nanofluids are prepared in a two-step method. No surfactant is employed as a dispersant. The volume fraction of CuO nanoparticles suspended in ethylene glycol liquid is below 5,vol.-%. The crystalline phases of the CuO powders are measured with x-ray diffraction patterns (XRD). CuO nanoparticles are examined using scanning electron microscopy (SEM) to determine their microstructure. The thermal conductivities of the CuO suspensions are measured by a modified transient hot wire method. The viscosity was measured with a viscosity instrument. The results show that CuO nanofluids with low concentrations of nanoparticles have considerably higher thermal conductivities than the identical ethylene glycol base liquids without solid nanoparticles. The thermal conductivity ratio improvement for CuO nanofluids is approximately linear with the volume fraction of nanoparticles. For CuO nanoparticles at a volume fraction of 0.05 (5,vol-.%) thermal conductivity was enhanced by up to 22.4,%. CuO nanofluids thus have good potential for effective heat transfer applications. [source] Predicting survival of grass shrimp (Palaemonetes pugio) exposed to naphthalene, fluorene, and dibenzothiophene,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2008Michael A. Unger Abstract The composition and persistence of dissolved polycyclic aromatic hydrocarbons (PAHs) released to the water column during oil spills are altered by weathering, tidal transport, and addition of dispersants. Conventional toxicity effect metrics, such as the median lethal concentration (LC50), are inaccurate predictors of mortality from all toxicant exposure duration/concentration combinations likely to occur during spills. In contrast, survival models can predict the proportions of animals dying as a consequence of exposures differing in duration and intensity. Extending previous work with ethylnaphthalene, dimethylnaphthalene, and phen-anthrene, survival time models were developed that include exposure duration and concentration to predict time to death for grass shrimp (Palaemonetes pugio). Two additional PAHs (naphthalene and fluorene) and a heterocyclic aromatic hydrocarbon (dibenzothiophene) were evaluated for the present study. Preliminary explorations of these models confirmed that quantitative structure-activity regression models were possible for predicting survival model parameters from compound characteristics. Conventional 48-h LC50s also were calculated for the compounds and combined with published LC50s to predict relative PAH toxicity to P. pugio based on octanol-water partitioning. [source] Slip Casting of ZrB2,SiC Composite Aqueous SuspensionsADVANCED ENGINEERING MATERIALS, Issue 3 2010Valentina Medri Slip casting of concentrated aqueous suspensions was set up as forming technique for the production of crucibles from ZrB2,SiC composite powder. The dispersion effectiveness and the effect on the final microstructures of two commercial ammonium polyacrylates (Duramax D3005 and Dolapix PC33) used as dispersants were investigated. The first goal was pursued by evaluating the zeta potential of the powders in water at different concentrations of additives, while the second one was assessed by analyzing the microstructure. Duramax D3005 resulted more effective than Dolapix PC33 in electrostatically stabilize the suspensions. Correspondently, almost homogeneous microstructures and lower final porosity of the sintered crucibles were obtained with Duramax D3005, while ZrB2 layers on the vertical surfaces initially in contact with the plaster molds were observed using Dolapix PC33. Moreover, the use of this latter dispersant did not allow the preparation of thick crucible walls due to the sample rupture during the binders pyrolysis stage. [source] | ||||||||||||||||||||||||||||||||||