A size interval-by-size interval marching algorithm for modelling grain growth in the intermediate stage of sintering

An accurate and efficient numerical algorithm is presented for solving the grain population balance equation which describes the evolution of micro-structure as a function of time in solid-state sintering. The solution scheme is based on the postulate that in a class of physically realistic deterministic systems, the queue or the relative order of particles in size is maintained intact as they grow and or decay in time. The resulting size interval-by-size interval marching algorithm has been validated with the available asymptotic steady-state analytical solutions of grain growth/ripening model equations. It can be employed to simulate the sintering process in a more quantitative and realistic manner than what has been possible hitherto, especially in the intermediate stage of sintering, which is of practical interest in ceramic systems. A variety of simulations showing the effects of initial grain size distribution and sintering time are presented. Potential applications for optimizing the sintering process are discussed

Surface chemical studies on the competitive adsorption of poly(acrylic acid) and poly(vinyl alcohol) onto alumina

The adsorption of poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA) onto alumina has been studied as a function of pH, both individually and in the presence of each other. The adsorption density of PAA is found to decrease with an increase of pH while that of PVA shows the opposite trend. In a binary system containing PAA and PVA, the presence of PVA does not affect the adsorption of PAA onto alumina, but the addition of PAA diminishes the adsorption of PVA in the pH range investigated. The adsorption isotherm of PAA at acidic pH exhibits high-affinity Langmuirian behavior. The isotherms for PVA appear rounded and are of the low-affinity type. Once again the adsorption isotherms of PAA remain unaltered in the presence of PVA whereas those of PVA are significantly affected resulting in a lowering of the adsorption density consequent to PAA addition. A variation in the sequence of addition of PAA and PVA does not affect the adsorption behavior of either of the polymers. The electrokinetic behavior of alumina with PAA is hardly influenced by the addition of PVA. On the other hand, the electrophoretic mobility of alumina in the presence of PVA is significantly altered in the presence of PAA and closely resembles the trend observed with PAA alone. Desorption studies reveal that over 80% of PVA could be desorbed in the pH range 3-9 whereas in the case of PAA, the percent desorption increases from 20 to about 70% as the pH is increased from about 3 to 8. Solution conductivity tests confirm interaction of aluminum species and PAA in the bulk solution. FTIR spectroscopic data provide evidence in support of hydrogen bonding and chemical interaction in the case of the PAA-alumina system and hydrogen bonding with respect to the PVA-alumina interaction

Effect of polymer molecular weight on the absorption of polyacrylic acid at the alumina-water interface

The absorption and electrokinetic characteristics of alumina suspensions in the presence of polyacrylic acid as a dispersant have been studied. The adsorption isotherms exhibit high-affinity Langmuirian behaviour. The adsorption density decreases with increasing in pH, while it increases with increasing molecular weight of the polymer. Electrokinetic studies indicate specific adsorption at and above the isoelectric point of the alumina sample. Possible mechanisms of interaction between alumina and polyacrylic acid are discussed

Adsorption and electrokinetic studies on alumina suspensions using poly(vinyl alcohol)

The adsorption of poly(vinyl alcohol) (PVA) of molecular weight 25,000 onto alumina was studied as a function of pH. The adsorption isotherms were also determined. The adsorption density increases with increasing pH, while the isotherms are rounded and of the low affinity type. Electrokinetic studies indicate that the electrophoretic mobilities are reduced in magnitude in proportion to the PVA concentration, without any shift in isoelectric-point (iep). This resembles the influence of an indifferent electrolyte. The calculated values of the free energy of adsorption between alumina and PVA are suggestive of hydrogen bonding. FTIR spectroscopic data provide additional evidence in support of hydrogen bonding

Surface chemical studies on alumina suspensions using ammonium poly(methacrylate)

The interaction of \alpha-alumina with ammonium poly(methacrylate) (APMA) has been investigated through adsorption and electrokinetic measurements. The adsorption isotherms exhibit high affinity, Langmuirian behaviour at highly acidic pH and the adsorption density is found to decrease with increasing pH. On the contrary, the percentage desorption increases with increasing pH. Electrokinetic studies indicate specific adsorption between alumina and APMA resulting in a shift of the isoelectric point to acidic pH values. Electrophoretic mobility values indicate that the alumina suspension could be well dispersed in the pH range 5-11, consequent to polymer adsorption. These results were corroborated by the dispersion tests. Dissolution tests reveal the release of aluminium species from alumina while co-precipitation experiments confirm the chemical interaction of aluminium species with APMA in the bulk solution. Hydrogen bonding, electrostatic and chemical interactive forces are postulated to govern the adsorption process. FTIR spectroscopic data lend further support to the interaction mechanisms proposed

Adsorption and electrokinetic studies on alumina suspensions using poly(vinyl alcohol)

The adsorption of poly(vinyl alcohol) (PVA) of molecular weight 25,000 onto alumina was studied as a function of pH. The adsorption isotherms were also determined. The adsorption density increases with increasing pH, while the isotherms are rounded and of the low affinity type. Electrokinetic studies indicate that the electrophoretic mobilities are reduced in magnitude in proportion to the PVA concentration, without any shift in isoelectric-point (iep). This resembles the influence of an indifferent electrolyte. The calculated values of the free energy of adsorption between alumina and PVA are suggestive of hydrogen bonding. FTIR spectroscopic data provide additional evidence in support of hydrogen bonding

Investigation of the effects of pressure on the compaction and subsequent sintering of nanosize powders. Final report

With current technology and available raw materials, one knows that it is very difficult, if not impossible, to produce a monolithic ceramic material with an average grain size of less than 100 nm. The grains of ceramic materials cannot be refined by cold working as is typically done in metals. Hence, the starting ceramic powder must be of a smaller or similar particle size as the desired grain size for the final product. The availability of nanosize (<100 nm) ceramic powders, however, is limited. In many cases, the powders consist of polymorphic mixtures, precursors, or amorphous phases of the desired material. Phase transformation during sintering is difficult to control, and when it does occur it usually is accompanied by significant microstructural changes and grain growth. An example of such a powder is Al{sub 2}O{sub 3}. To the best of the authors` knowledge, high purity nanosize {alpha}-Al{sub 2}O{sub 3} powder is unavailable commercially. However, a variety of nanosize transitional forms of Al{sub 2}O{sub 3}, including the {gamma} and {delta} polymorphs, are commercially available in large quantities as mixtures. Results on the compaction and sintering of nanosize {gamma}-Al{sub 2}O{sub 3} powder are reported here