Volume Fraction Of Powder Research Articles

Electrosteric Stabilization of Al2O3, ZrO2, and 3Y–ZrO2 Suspensions: Effect of Dissociation and Type of Polyelectrolyte

The mechanisms of eight anionic polyelectrolytes stabilizing colloidal sized α-Al2O3, pure ZrO2, and Y2O3-doped ZrO2 particles in aqueous solution are discussed. The polyelectrolytes studied were the Na+ and NH4+ salts of polyacrylic acid and polymethacrylic acid having different molecular weights. The particle–dispersant interactions were studied by measuring adsorption isotherms, particle size, thickness of adsorbed layer, and zeta potentials by elektrokinetic sonic analysis at different powder volume fractions (φ=0.01–0.3), pH, and electrolyte (KCl) content. The dissociation of the polyelectrolytes was studied by potentiometric titrations. The dissociation constant of the polymethacrylates was found to be 0.6 pH unit higher than that for the polyacrylates. High-affinity adsorption isotherms were observed over the pH range when the polyelectrolytes were fully ionized. The results show good correlation between adsorption isotherms and zeta potential data in systems of dispersed, dilute alumina particles. When particles and polymers were of equal charge (the same sign of charge) the polymer shell was thicker. At higher volume fractions (φ=0.3), and when alumina particles/added ammonium polyelectrolyte were of equal charge, a maximum in the absolute value of zeta potential resulted. Due to adsorption all the anionic polyelectrolytes studied provided electrosteric stabilization of the α-Al2O3, and Y2O3-doped ZrO2 suspensions by enhancing the zeta potential to 40 mV or over and by shifting the isoelectric point to lower pH, the low-molecular-weight polyelectrolytes decreasing the isoelectric point more than the polyelectrolytes having higher molecular weight. The polyelectrolytes studied failed to stabilize pure monoclinic ZrO2 particles. Due to the shortness of the chain of polyelectrolytes studied, no bridging was observed between oppositely charged polyelectrolyte/alumina particles.

Preparation and Characterization of Barium Titanate Suspensions for Stereolithography

Ferroelectric photoactive suspensions for stereolithography have been developed by dispersing a high volume fraction of barium titanate powder in hexanediol diacrylate (HDDA) with the aid of effective photoinitiators and dispersants. Rheological properties showed a shear thinning behavior and a low viscosity at a shear rate adequate for the recoating process. The barium titanate–HDDA suspension showed poor curing behavior due to the large refractive index difference between the ceramic and the resin. The coarse barium titanate–HDDA suspension showed a smaller surface reflectance and a larger cure depth than the fine barium titanate–HDDA suspension.

Composite rotor for high-speed induction motors

In order to improve the dynamic characteristics of 3-phase AC induction motors, the squirrel cage rotor for a high speed built-in type motor spindle system was designed and manufactured with powder containing epoxy composite material and an aluminum squirrel cage. The Young’s modulus, coefficient of thermal expansion (CTE), resistivity and magnetic permeability of the epoxy containing ferrite powder and iron powder were measured with respect to powder volume fraction to determine the optimum powder volume fraction. Then the epoxy powder composite rotor was manufactured by embedding the aluminum squirrel cage into the composite. Finally, the dynamic and electrical performances of the AC induction motor equipped with the developed composite rotor were measured and compared with those of a conventional AC induction motor.

Room‐Temperature Solubility Behavior of Barium Titanate in Aqueous Media

In the present study, the incongruent dissolution of barium from barium titanate (BaTiO3) has been studied as a function of dispersion pH and powder volume fraction for two different BaTiO3 powders. In alkaline dispersions, the barium solubility strongly increases as the pH increases, as suggested by thermodynamic considerations. At pH <7, the barium solubility reaches a plateau, the height of which is dependent on the surface area of the powder and the solids loading of the slip. The BaTiO3 surface is completely depleted of barium in this region.

Cold Compaction of Composite Powders

Densification behavior of composite powders was investigated under cold compaction. Experimental data were obtained for mixed copper and tungsten powders with various volume fractions of tungsten powder under cold isostatic pressing and die compaction. A model was also proposed for densification of mixed—soft and hard—metal powders under cold compaction. Theoretical predictions from the proposed model and models in the literature were compared with experimental data. The agreements between experimental data and theoretical predictions from the proposed model are very good for composite powders at initial stage under cold isostatic pressing. Theoretical predictions, however, underestimate experimental data under cold die compaction. [S0094-4289(00)01901-0]

ZrO2/ZrO2 Layered Composites for Crack Bifurcation

Laminates containing a thin layer (5 to 200 µm thick) sandwiched between two thick layers (2 mm thick) were fabricated by sequential slip casting in order to study crack bifurcation. The thin layer was formed with a mixture of a pure ZrO2 powder (MZ) and a Zr(Y)O2 powder containing 3 mol% Y2O3 (TZ). The thick layers were formed with TZ powder containing 0.05 volume fraction of Al2O3 powder to distinguish the interfaces between the different layers in the scanning electron microscope. Dilatometry data for monolithic specimens formed with the mixed MZ and TZ powders (0.30 to 1.00 volume fraction MZ) showed that the monoclinic‐to‐tetragonal transformation temperature and strain varied with the MZ content, suggesting the yttria in the TZ powder diffused into the MZ powder during processing at 1500°C/2 h. These data also showed that large compressive stresses developed in the thin layer due to the transformation. Conditions (thin layer composition and thickness) for observing edge cracks produced along the center line of the thin layer and for observing crack bifurcation during flexural failure were determined. Delamination occurred during cooling for layers fabricated with greaterthan equal to0.40 volume fraction of the MZ powder when the thin layers were 200 µm thick. Edge cracking, which occurred during cooling, and crack bifurcation, which occurred during flexural loading, occurred for thin layer compositions containing greaterthan equal to0.40 volume fraction MZ powder, when the thickness of the thin layer was between similar/congruent50 and 150 µm. Crack bifurcation was not observed in thinner layers. With decreasing layer thickness, thin layers fabricated with >0.60 volume fraction of the MZ powder contained multiple microcracks, parallel to the center line, on the surface, instead of a single edge crack. The flexural strength of all specimens depended on the strength of the thicker Zr(Y)O2 layers, regardless of whether bifurcation occurred.

磁石・磁性材料の化学 Ｉ 耐熱性Ｎｄ‐Ｆｅ‐Ｂ系異方性ボンド磁石の圧縮成形技術

Thermostable compression-molded bonded magnets, composed of anisotropic Nd-Fe-B powder, epoxy resin and thermosetting resin with volatile component, were developed. The influence of the thermosetting resin with volatile component on the thermostability and the mechanical strength of bonded magnets were investigated. The results show that thermal deterioration of bonded magnets is decreased by using the thermosetting resin with volatile component. Bonded magnets made by this method have a powder volume fraction and degreee of magenetic orientation of 77% and 96%, respectively. Bonded magnets with a high mechanical strength can be obtained by improvement in the compounding process.

Evaluation of Mechanical Properties of Sintered Alumina with Recycling Powder.

Recycling alumina powder was used to prepare sintered alumina. Virgin alumina samples were fabricated by atmospheric sintering and were crushed into powder under 500μm in grain size by thermal shock treatment and automatic mortar crushing. Then, the crushed alumina powder was mixed with virgin alumina powder and was subjected to re-sintering to renewed alumina. The renewed alumina samples were subjected to four-point bending test and SEM observation of microstructure. Relative density and bending strength of renewed alumina decreased as the volume fraction of recycled alumina powder increased. Samples over 200MPa of average bending strength, however, were obtained by mixing 50vol% recycled alumina powder with grain size<32μm, which was much larger than that of virgin alumina powder. SEM observation indicated that pore distribution was inhomogeneous and pores were located along large polycrystal grain boundaries. Pores, consequently, formed cracks which markedly decreased bending strength. Furthermore, 10vol%-glass containing renewed alumina samples were fabricated by a procedure similar to that of monolithic alumina. These samples showed higher bending strength than monolithic renewed alumina.

シナジー磁石と磁性材料 温間圧縮成形法による希土類ボンド磁石の高密度化

Rare earth bonded magnets with versatility on shaping and high density, composed of isotropic Nd-Fe-B powder and thermoplastic resin (Nylon-12, PBT and PPS), were developed with warm compression molding.(1) Compounds with magnet powder volume fraction of 80vol.%, composed PBT or Nylon-12, have versatility on shaping and compressibility at relatively low pressure. Coin-shaped magnets with a thickness of 0.3mm and ring magnets with a wall-thickness of 0.4mm were moldable with these compounds at the pressure of 250MPa. The properties of these bonded magnets were as follows: pore=0vol.% in substance, density =6.2Mg/m3 and (BH)max=97.9kJ/m3 (12.3MGOe).(2) Compounds with magnet powder volume fraction of 90vol.% have higher compressibility than the compounds for compaction molding at high pressure. This is because that viscosity of resin during the molding is easy to optimize and spring-back after molding is small in warm compression molding. The properties of the magnet were as follows: density=6.7Mg/m3 and (BH)max=115kJ/m3 (14.4MGOe) at pressure of 1250MPa.In this way, warm compression molding is applicable to extensive compounds through adjusting the molding condition.

UV Curable Systems for Tape Casting

The substitution of solvents by photopolymerizable binders in the tape casting process allows to achieve high ceramic loading and to eliminate the drying stage which is a critical step of the tape casting process. After the rapid UV polymerization of the resin, the high strength green tapes can be debinded and sintered. Ceramic suspensions containing alumina or zirconia powder, dispersant, UV curable binder and photoinitiator have been prepared. The use of a low viscosity organic vehicle allows to prepare low viscosity ceramic suspensions, containing about 50 vol% powder, which have a shear thinning behaviour. Because of the rapid attenuation of the incident light in UV curing systems containing ceramic particles it is important to estimate the thickness of the tape that can be treated. The effect of incident energy, of photoinitiator concentration and of powder volume fraction was studied. There is an optimal photoinitiator concentration which maximizes the cured depth and which depends on the volume fraction of solid. A theoretical model based on the Beer–Lambert’s law enables the prediction of cured depth for any volume fraction of solid. To prove the ability to manufacture ceramic sheets by tape casting, some suspensions were tape cast.

Dynamic viscoelastic properties and thermal properties of Ni powder-epoxy resin composites

The composite materials containing metal Ni powder of 5–15 μm in size were prepared by use of the matrix epoxy resin of glycidyl amine crosslinked with bis-4-amino-3-methylcyclohexyl methane and 2,4-diamine 3,5-dimethyltoluene. Dynamic viscoelastic properties of the composites at various volume fraction (Φp) of Ni powder have been measured over the temperature range from 30 to 300°C. The peak temperatures in dynamic loss modulus–temperature diagrams of the composite increased with increasing Φp, although the peak position was abruptly shifted to lower temperatures in the range of Φp more than 0.245. At this high concentration of Φp, agglomeration of the particles occurring in the composite lead to reduction of the interaction between Ni particle and epoxy resin. Parallel studies on the thermal conductivity (λ) of the composites materials showed that the value of λ at Φp = 0.245 increased by approximately 7 times that of the original epoxy resin. The shape of Ni particles also affected the thermal durabilities of the composites; the rough surface of Ni powder yields a higher storage modulus of the composite than that of the materials containing the powder with a smooth surface, which had been brought through a ball-milling process. The finding suggested that the increasing in specific surface area of the powder improved the thermal durability of the composites as well as their mechanical properties. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2593–2598, 1998

Magnetomechanical coupling and elastic moduli of polymer-bonded Terfenol composites

The dependence of coupling coefficient (k) and elastic moduli (EH and EB) on particle size and volume fraction of Terfenol powder in polymer-bonded composites has been investigated. Materials were prepared with powder in five size ranges between 106 and 710 μm and in three volume fractions (VF). The moduli show a ΔE effect, which is negative for small bias fields and positive for larger fields. EH is found to be independent of particle size and to vary with VF in agreement with model predictions. The maximum value of k, for each sample, is found to be independent of both particle size and VF and a simple model is presented which predicts this behavior and indicates that the low values of kmax arise mainly from the low modulus of the epoxy binder.

Uniaxial elongational flow of particle-filled polymer melts

Polymer processes which employ elongational flows have been successfully used for shaping ceramics by using crowded (50–60 vol %) suspensions of ceramic particles, but the full realization of their potential rests on an understanding of the extensional flow behavior of filled polymer systems. A uniaxial rheometer was constructed to evaluate the extensional flow properties of crowded suspensions based on polyisobutylene. The shear viscosity was evaluated for comparison using a Weissenberg rheometer and correlated with published literature values for a similar molecular weight polyisobutylene. Trouton’s Law was verified for the unfilled polymer. The shear and elongational viscosities of filled polyisobutylene, containing up to 42 vol % and 45 vol % ceramic, respectively, were measured. The dependence of shear and elongational relative viscosities on powder volume fraction were compared. In uniaxial flow, Trouton’s Law was obeyed for crowded suspensions containing up to 42 vol % ceramic powder.

High- Tc superconductor-polymer composites: YB 2Cu 3O 7− x-polyester polymer and YBa 2Cu 3O 7− x-Teflon

The YBa 2Cu 3O 7− x (YBCO) superconductor powder-polyester polymer (Polimal 109) and YBCO-Teflon composites were investigated. The volume fraction of YBCO powder ranged from 0.05 to 0.8. D.c. electrical conductivity of the composites increased exponentially with increase of YBCO volume content. The I–V characteristics showed transition from ohmic to highly nonohmic behaviour at electric field intensities of about 100 V/cm. Although these composites do not show zero resistance below the superconducting transition temperature T c of YBCO, the intrinsic diamagnetic properties of superconductor are observed. The magnetic field shielding effect indicates the superconducting transition at 90 K. The investigated composites have, at liquid nitrogen temperature, levitation properties similar to those of ceramic superconductors. The levitation force is proportional to the YBCO volume content.

Dielectric tunability of barium strontium titanate/silicone-rubber composite

The dielectric tunability, which is defined as the percentage change of the permittivity under DC biasing, is over 30% for polycrystalline barium strontium titanate (BST) under a field of at around the Curie peak. Various volume fractions (18%, 40%, 52%, and 64%) of BST powder are mixed with silicone rubber to obtain a multi-phase dielectric composite. The effective permittivity of the composite follows the Maxwell-Garnett relation with a shape parameter of about 14 for volume fractions below 52%. The dielectric tunabilities at for the samples made with 52% and 64% powder are about 0.7% and 7.4%, respectively. The results are compared to the dielectric tunabilities obtained on the basis of series, parallel, and logarithmic models. It is suggested that the dielectric tunability is enhanced when a sample with a more continuous BST powder phase is obtained. An increase of the permittivity with a small DC field applied to the composite is attributed to the effect of polarization of the interface between the BST and silicone-rubber phases.

Ultrasonic propagation in metal powder-viscous liquid suspensions

The need to measure the volume fraction of metal powder during the slurry casting synthesis of metal matrix composites has stimulated a new interest in ultrasonic propagation in metal powder-viscous liquid suspensions. Using model slurries, a systematic series of ultrasonic tests have been conducted to experimentally identify the frequency dependent relationships between ultrasonic velocity/attenuation and the particle volume fraction, the suspending liquid’s viscosity and the particle’s shape. For slurries with the compositions and viscosities typical of those used in slurry casting, the velocity decreases and the attenuation increases with particle fraction. The data have been compared to predictions of the Harker–Temple hydrodynamic model for these systems. The velocity measurements were well predicted by the model with a difference between measured and predicted velocities of about 0.25%. The ultrasonic attenuation was underpredicted by this model in part by its use of a rule of mixtures and by its failure to incorporate the intrinsic absorption/scattering within the powder phase.

Effect of silicone on dynamic mechanical properties of epoxy resin filled with imide powder

Abstraet-The dynamic mechanical properties of epoxy resin and epoxy-silicone alloy filled with thermoplastic polyimide powder have been studied over a temperature range of -150 to 250°C at the frequencies of 35 and 110 Hz and related to the morphological structure of composites observed by scanning electron microscopy. The incorporation of polyimide raised the glass transition temperature (Tg) of both epoxy resin and epoxy-silicone alloy. The storage modulus (E') of composites increased with increasing volume fraction of imide powder. E' of epoxy-silicone alloy composites was higher than that of epoxy resin though the silicone had a low storage modulus. This fact was explained by assuming that below Tg, the presence of silicone in the matrix facilitated molecular rearrangement during cooling from the cure temperature and above Tg, increased the interaction between filler particles and the matrix.

Influence of particle size distribution on colloidal processing of alumina

Two commercial alumina powders with different particle size distribution (PSD) shapes were blended in different proportions, and the rheological behaviour of the aqueous slurries was analysed. Slip casting experiments were performed in order to correlate the flow properties of the alumina slips with the green density. It was observed that the coarser alumina powder component which exhibits a bimodal PSD near to that predicted by the Furnas model, leads to slips with lower viscosity and green compacts with higher density. In order to reduce particle segregation phenomena and further increase the packing density of green compacts, the solid volume fraction of the bimodal powder with the highest packing ability was increased and maximised. Suspensions with a total solids loading as high as 70 vol% could be achieved by using a polyelectrolyte dispersant and milling to deagglomerate the powders. The results obtained show that the green density in the slip cast body continuously increases with increased solids loading, reaching a maximum value of about 78% of the theoretical density.

Porous Al Alloys by Local Melting and Diffusion of Metal Powders

ABSTRACTA novel method exploiting local melt and diffusion induced porosity is described for producing porous Al alloys. Aluminum powder and zinc powder were blended and cold-compacted to a near net shape. A porous AI-Zn alloy component was then formed by annealing the material above the melting point of zinc but below the solidus temperature of the alloy. Pores were generated by the diffusion of molten Zn into the solid Al grains. The pore structure is shown to be determined by the volume fraction, distribution, and size of the Zn powders in the powder mixture, and by time and temperature of the annealing heat treatment. The pores can be further expanded by incorporating small amounts of titanium hydride into the powder blend and conducting the annealing treatment above the decomposition temperature of the titanium hydride (T&gt;447°C). Porosity levels of 45 vol.% have been achieved to date. This processing approach appears amenable to the production of sandwich panels with a gradient porosity core and fully dense face sheets, and is applicable to other solid solution systems.

Synthesis of BaTiO3 fine powders and determination of the critical size of the tetragonal crystal

BaTiO3 fine powders were hydrothermally synthesized. The maximal size of cubic crystallite at room temperature was estimated by comparision of the size distributions on TEM and the x-ray powder diffraction intensities of the synthesized powders. The volume fraction of tetragonal powder in a batch was calculated from the x-ray diffraction pattern by the peak profile fitting method and the size distribution was counted on TEM micrographs of the powder. The critical size between cubic and tetragonal BaTiO3 powder at room temperature was calculated as 0.23μmlm