Colloidal processing and sintering of nanosized transition aluminas

Abstract

Abstract. The dispersion of nanosized gamma aluminas with high specific surfaces areas (100 m 2 /g) and primary particle sizes around 20 nm, using polyacrylic acid has been investigated. The effect of pH and polymer concentration showed that the highest density green bodies were produced using high polymer concentrations (6% wt) and pH of 6. Interparticle potential calculations have been made and help explain the underlying dispersion mechanism at least on a qualitative level. The dispersions were then used to slip cast green bodies followed by drying and sintering. The types of gamma alumina powder have been investigated, the pure gamma alumina, doped with MgO and also with the addition of alpha alumina seeds. The high degree of agglomeration of the gamma alumina powders led to very low densities (60%) even the alpha seeded alumina reached only 85 % theoretical density. Attrition milling with zirconia media improves both green density and sintered densities significantly with all powders showing sintered densities > 97%. Mictrostructural analysis on polished and etched surfaces show, however, that the grain sizes are well above 1 micron over 50 times greater than the initial gamma alumina primary particles. A two step sintering cycle was investigated with the Mg doped powder and average grain sizes around 580 nm were achieved.

Fuerzas de repulsión de aditivos superplastificantes en sistemas de escoria granulada de horno alto en medios alcalinos, desde medidas de AFM a propiedades reológicas

“…In the present study, α-Al 2 O 3 substrates and probes have been used as a non reactive model system for slag. At pH=10 the zeta potential of α-Al 2 O 3 suspensions is low (around -5 mV) and similar to slag suspensions (26). With this model, force curves can be recorded without the interference of chemical reactions and the findings for the blast furnace slag can be validated.…”

“…Por esta razón, en el presente trabajo se han utilizado sustratos y sondas de α-Al 2 O 3 como un modelo inerte de la escoria. A pH=10, el potencial zeta de suspensiones de α-Al 2 O 3 es bajo y próximo a -5 mV, siendo similar al potencial zetal de suspensiones de escoria (26). Utilizando este modelo se pueden obtener las curvas de fuerza sin interferencia de reacciones químicas y validar los resultados obtenidos para la escoria.…”

Evaluation of dispersability of gamma alumina prepared by homogeneous precipitation

“…Thus, the ¦-potential is affected by changes in pH, nature of the electrolyte used, and its ionic strength. 13), 14) In this paper the effect of pH is evaluated according to the rheological behavior of dispersions of anisotropic £-Al 2 O 3 particles synthesized by homogeneous precipitation, compared with morphologically more uniform (spherical) £-Al 2 O 3 particles (TM-300·).…”

Hamaker 2: A Toolkit for the Calculation of Particle Interactions and Suspension Stability and its Application to Mullite Synthesis by Colloidal Methods

“…[8] In all of these cases, one would like to tune experimentally accessible parameters of both the powder and suspension medium in order to obtain either good dispersion or coagulation for the entire system or parts of it. The interplay of the different parameters is, however, often difficult to understand without resorting to theoretical approaches, which has led to many publications, [7,[9][10][11][12][13][14] where interparticle interaction calculations were used to predict or explain experiment.…”