Alumina Powder (alumina + powder)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science


Selected Abstracts


Synthesis of Nanocrystalline ,-Alumina Powder Using Triethanolamine

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2001
Ranjan K. Pati
Nanocrystalline ,-Al2O3 powders have been prepared by pyrolysis of a complex compound of aluminum with triethanolamine (TEA). The soluble metal-ion,TEA complex forms the precursor material on complete dehydration of the complex of aluminum-TEA. The single-phase ,-Al2O3 powder has resulted after heat treatment at 1025C. The precursors and the heat-treated final powders have been characterized by X-ray diffractometry, thermogravimetric and differential thermal analysis, and transmission electron microscopy (TEM). The average particle sizes as measured from X-ray line broadening and TEM are ,25 nm. The powder has crystallite sizes of the same order indicates the poor agglomeration of crystallites. [source]


Air Current Segregation of Alumina Powder

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 2 2007
Stefan Zigan
Abstract This paper outlines the industrial problem of air current segregation in alumina storage silos which occurs with the handling of the feedstock alumina in aluminium plants and investigates the parameters that affect the severity of the segregation. Bates [1] stated that the feeding rate influences segregation which we can confirm with own experimental findings. Higher powder flow rates tend to reduce air current segregation. Cooper et al. [2] pointed out that the air extraction rate affects the content of fine particles (dust) in the circulating air currents and we confirm his finding. The importance of the effect of different feeding rates on air current segregation was discovered in a two dimensional apparatus. The investigation of the influence of air extraction rate was realised in a cylindrical silo. Both experiments show a strong relationship between the strength of the particle-air flow in the silo and air current segregation. It is found that an increase of the powder feeding rate or the air extraction rate reduces air current segregation in the experimental equipment. The aim of our experiments was to find all significant parameters and to apply dimensional analysis to develop a method which scales the findings from small scale experiments to large industrial alumina silos. Five dimensionless groups were obtained, which is unwieldy. To reduce the number of dimensionless groups, physical properties were lumped into the terminal velocity. This simplified approach gives three dimensionless groups. Experiments in a water model and an air model justify more research using this simplified scaling method. [source]


Coagulation of Concentrated Suspensions of Ultrafine Alumina Powders by pH Shift

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2006
Anne-Laure Pnard
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]


Preparation of Nanometer-Sized ,-Alumina Powders by Calcining an Emulsion of Boehmite and Oleic Acid

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2002
Chih-Peng Lin
This study proposes a method to form ultrafine ,-Al2O3 powders. Oleic acid is mixed with Al(OH)3 gel. The gel is the precursor of the Al2O3. After it is mixed and aged, the mixture is calcined in a depleted oxygen atmosphere between 25 and 1100C. Oleic acid evaporates and decomposes into carbon during the thermal process. Residual carbon prevents the growth of agglomerates during the formation of ,-Al2O3. The phase transformation in this process is as follows: emulsion ,,-Al2O3,,-Al2O3,,-Al2O3,,-Al2O3. This process has no clear , phase. Aging the mixed sample lowers the formation temperature of ,-Al2O3 from 1100 to 1000C. The average crystallite diameter is 60 nm, measured using Scherrer's equation, which is consistent with TEM observations. [source]


Sintering and Microstructure Modification of Mullite/Zirconia Composites Derived from Silica-Coated Alumina Powders

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2001
Viktor Yaroshenko
This paper addresses the densification and microstructure development during firing of mullite/zirconia composites made from silica-coated-alumina (SCA) microcomposite powders. Densification occurs in two stages: in the presence of a silica,alumina mixture and after conversion to mullite. The first stage of densification occurs through transient viscous phase sintering (TVS). This is best promoted by rapid heating, which delays the crystallization of silica to higher temperatures. A further sintering stage is observed following mullitization. The introduction of seeds promotes solid-state sintering, most probably due to refinement of the mullite matrix. For seed concentrations up to about 1% the sintering kinetics depend on seed concentration. This suggests that nucleation still remains the rate-controlling mullitization step. Above this concentration the reaction becomes growth controlled. Introduction of seeds also promotes direct mullitization without transient zircon formation that was observed in a previous study of the same process without seeding. Seeding also promotes the development of elongated grains by way of a solid-state recrystallization process. [source]


Microwave Assisted Synthesis of Yb:Y2O3 Based Materials for Laser Source Application,

ADVANCED ENGINEERING MATERIALS, Issue 3 2010
Anna Luisa Costa
Yb:Y2O3 submicrometric particles were synthesized through co-precipitation of Yb and Y nitrate in water. Microwave heating and controlled release of ammonia through urea decomposition at reaction temperature leaded to the formation of disaggregated, monosized spherical particles of carbo-hydroxy-nitrate precursors. Pure crystalline Yb:Y2O3 powder that preserved the described morphology was obtained after calcination in air at 800,C for 30,min. This powder mixed with commercial alumina powder was used to produce transparent Yb:YAG ceramics. Improved properties in terms of powder morphology and reactivity were presented in comparison with powders obtained by traditional heating. [source]


Near Zero Shrinkage of an Low-Temperature Co-Fired Ceramic Package by Constrained Sintering Using Screen Printed Alumina Paste

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2010
Sang Myoung Lee
Conventional free sintering of low-temperature co-firing ceramic (LTCC) technology has several merits such as sintering temperature below 1000C that enables co-firing with electrode materials of silver or copper metal and multilayer structure formation. But due to the free sintering process, large shrinkage occurs. To fabricate electronic devices and components with near zero shrinkage within x, y directions constrained sintering (CS) technology is required. In this study a constrained sintering paste (CSP) utilizing alumina powder, which has a higher sintering temperature than LTCC powders, was fabricated for CS technology. The effect of CSP formulated using alumina powder on shrinkage was studied according to variation in paste composition. As a result ceramic package structure with a cavity was fabricated with shrinkage control of 0.028%, which is far smaller than the current CS technology shrinkage of approximately 0.1%. [source]


The influence of the particle size distribution on fluidized bed hydrodynamics using high-throughput experimentation

AICHE JOURNAL, Issue 8 2009
Renske Beetstra
Abstract The goal of the described project is to design mixtures of particles with optimal fluidization properties. Using high-throughput experimentation, a novel approach to study hydrodynamics in fluidized beds, the relevant properties can be obtained in a limited period of time. This approach is demonstrated by assessing the influence of particle size distribution on fluidized bed hydrodynamics of Geldart A powders. By manipulating the width of the particle size distribution of alumina powder, the bubble diameter is reduced up to 40%. The addition of fines to a given particle size distribution also decreases the bubble diameter up to 40%, whereas the addition of coarse particles hardly influences the bubble size. At low gas velocities, the bubble size was found to increase with fines addition or increasing standard deviation. 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]


Effect of Activated Carbon Bed on Binder Removal from Ceramic Injection Moldings

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2001
Martin Trunec
Weight losses during the binder removal from ceramic injection moldings that have been placed in beds of activated carbon powder and two types of alumina powder were compared. The effect of the specimen size and shape on debinding in a bed of activated carbon was investigated. Because of the structure of its particles, activated carbon powder allowed binder losses in ceramic moldings that consisted of submicrometer-sized particles to increase at a temperature of 130C. The binder loss in a bed of activated carbon was dependent on the ratio of surface area to volume of the body that was extracted. Renewal of the sorption abilities of the bed of activated carbon after saturation with binder increased the rate of binder removal. [source]


Effect of Aluminum Oxide Addition on the Flexural Strength and Thermal Diffusivity of Heat-Polymerized Acrylic Resin

JOURNAL OF PROSTHODONTICS, Issue 6 2008
Ayman E. Ellakwa BDS
Abstract Purpose: This work was undertaken to investigate the effect of adding from 5% to 20% by weight aluminum oxide powder on the flexural strength and thermal diffusivity of heat-polymerized acrylic resin. Materials and Methods: Seventy-five specimens of heat-polymerized acrylic resin were fabricated. The specimens were divided into five groups (n = 15) coded A to E. Group A was the control group (i.e., unmodified acrylic resin specimens). The specimens of the remaining four groups were reinforced with aluminum oxide (Al2O3) powder to achieve loadings of 5%, 10%, 15%, and 20% by weight. Specimens were stored in distilled water at 37C for 1 week before flexural strength testing to failure (5 mm/min crosshead speed) in a universal testing machine. Results were analyzed by one-way analysis of variance and post hoc Tukey paired group comparison tests (p < 0.05). Weibull analysis was used to calculate the Weibull modulus, characteristic strength, and the required stress for 1% and 5% probabilities of failure. Cylindrical test specimens (5 specimens/group) containing an embedded thermocouple were used to determine thermal diffusivity over a physiologic temperature range (0 to 70C). Results: The mean flexural strength values of the heat-polymerized acrylic resin were (in MPa) 99.45, 119.92, 121.19, 130.08, and 127.60 for groups A, B, C, D, and E, respectively. The flexural strength increased significantly after incorporation of 10% Al2O3. The mean thermal diffusivity values of the heat-polymerized acrylic resin (in m2/sec) were 6.8, 7.2, 8.0, 8.5, and 9.3 for groups A, B, C, D, and E, respectively. Thermal diffusivities of the composites were found to be significantly higher than the unmodified acrylic resin. Thermal diffusivity was found to increase in proportion to the weight percentage of alumina filler, which suggested that the proper distribution of alumina powders through the insulating polymer matrix might form a pathway for heat conduction. Conclusion: Al2O3 fillers have potential as added components in denture bases to provide increased flexural strength and thermal diffusivity. Increasing the flexural strength and heat transfer characteristics of the acrylic resin base material could lead to more patient satisfaction. [source]


Coagulation of Concentrated Suspensions of Ultrafine Alumina Powders by pH Shift

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2006
Anne-Laure Pnard
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]


Conventional and nanometric nucleating agents in poly(,-caprolactone) foaming: Crystals vs. bubbles nucleation

POLYMER ENGINEERING & SCIENCE, Issue 2 2008
Carlo Marrazzo
The aim of this article was to investigate the nucleating ability of different nucleating agents for the foaming of poly(,-caprolactone), a biodegradable, semicrystalline polymer. In particular, the efficiency of the nucleating agent in inducing the formation of the gaseous phase has been compared to the efficiency in inducing the formation of the crystalline phase. In effect, in foaming of semicrystalline polymers, bubble nucleation and crystal nucleation are concurrent and somehow interacting phenomena. Here, these two aspects have been evidenced and clarified. Foams were prepared by using a batch process with the pressure quench method, with nitrogen and carbon dioxide as the blowing agents. Conventional and novel nucleating agents were used: talc has been compared to several novel nanometric particles of different geometries and dimensions, such as titanium dioxide and alumina powders, exfoliated and intercalated clays, and carbon nanotubes. Foam densities and morphologies, in terms of number of cells per initial unit volume, were measured and found to depend both on crystalline phase nucleation and gaseous phase nucleation. In fact, the different nucleating agents, depending on shape, dimension, and surface functionalization, selectively nucleated the crystallites and/or the bubbles, affecting, respectively, bubble growth (and, hence, final foam density) and bubble nucleation (and, hence, cell number density,morphology). POLYM. ENG. SCI., 2008. 2007 Society of Plastics Engineers [source]


Processing and Properties of a Porous Oxide Matrix Composite Reinforced with Continuous Oxide Fibers

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2003
Magnus G. Holmquist
A process to manufacture porous oxide matrix/polycrystalline oxide fiber composites was developed and evaluated. The method uses infiltration of fiber cloths with an aqueous slurry of mullite/alumina powders to make prepregs. By careful manipulation of the interparticle pair potential in the slurry, a consolidated slurry with a high particle density is produced with a sufficiently low viscosity to allow efficient infiltration of the fiber tows. Vibration-assisted infiltration of stacked, cloth prepregs in combination with a simple vacuum bag technique produced composites with homogeneous microstructures. The method has the additional advantage of allowing complex shapes to be made. Subsequent infiltration of the powder mixture with an alumina precursor was made to strengthen the matrix. The porous matrix, without fibers, possessed good thermal stability and showed linear shrinkage of 0.9% on heat treatment at 1200C. Mechanical properties were evaluated in flexural testing in a manner that precluded interlaminar shear failure before failure via the tensile stresses. It was shown that the composite produced by this method was comparable to porous oxide matrix composites manufactured by other processes using the same fibers (N610 and N720). The ratio of notch strength to unnotch strength for a crack to width ratio of 0.5 was 0.7,0.9, indicating moderate notch sensitivity. Interlaminar shear strength, which is dominated by matrix strength, changed from 7 to 12 MPa for matrix porosity ranging from 38% to 43%, respectively. The porous microstructure did not change after aging at 1200C for 100 h. Heat treatment at 1300C for 100 h reduced the strength for the N610 and N720 composites by 35% and 20%, respectively, and increased their brittle nature. [source]