Gelcasting of aluminum titanate. Final report Page: 7 of 9
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Gelcasting Process Development
Initial gelcasting trials using Golden's slip casting slurry formulation in the MAM/MBAM
gelcasting system showed good gelling properties but poor drying characteristics.
Additives in the slurry formula apparently sealed off the pore structure at the surface of the
cast samples during the early stages of drying and strongly inhibited drying of the bulk
material. To address this difficulty, the individual starting materials were shipped from
Golden to prepare an alternate aluminum titanate composition for gelcasting which
eliminated some of the organic additives which had been used in the original formulation.
Using the altered formula, the slurries showed good viscosity and gelling characteristics,
and dried at rates similar to other gelcast materials.
Property Determination .
Samples in both plate and tubular form were cast and fired. The density of the samples
fired at ORNL was somewhat less than that observed in firings of the baseline material at
Golden. Particle size measurement of the milled slurry showed a particle size distribution
which was coarser than the baseline slip casting material. Samples were sent to Golden for
evaluation and comparison. Their tests showed results in agreement with the findings
obtained at ORNL. It was believed that correction of the particle size distribution would
improve the fired density. Approaches for improving the milling of the aluminum titanate
powder composition were discussed and alternative milling procedures were evaluated.
Milling all of the constituent powders simultaneously at the desired solids loading did not
result in adequate particle size refinement and narrowing of the particle size range.
Analysis of the individual starting powders showed that two of the components, titania and
silica, were very coarse and were skewing the particle size distribution in the batches. To
improve the milling, these two powders were milled separately to refine the particle size
before adding the remaining ceramic powders. This resulted in a significant change in the
overall particle size distribution of the slurry.
Gelcast samples from these batches were dried and fired. The target density for the fired
materials was 3.10 g/cm3. Two firing profiles were evaluated. The first was the normal
firing schedule used by Golden which had a 30 min. hold at the peak temperature. The
fired density under these conditions for the gelcast material was 2.85 g/cm . The second
firing schedule had a faster heating rate and a hold of 4 hours at the peak temperature.
Under these firing conditions, the density was 3.04 g/cm3. Sintering trials conducted at
Golden on gelcast samples prepared at ORNL confirmed the densification results which
had been observed at Oak Ridge. The aluminum titanate material fired to a density of about
3.05 g/cm3, comparable to the results typically obtained for the conventionally processed
Samples of thin-walled tubes were gelcast at ORNL for evaluation by Golden. The tubes
had a 1.25 in. outer diameter with a wall thickness of about 0.08 in. and were 4 to 5 in.
long. In firing trials at Golden, the tubes showed some distortion during the sintering
process. It was decided that the thicker-walled tubes (0.125 to 0.25 in.) which had been
prepared in earlier gelcasting trials would be used for the final evaluation of the gelcast
materials for use as exhaust port liners. After discussion with the principal investigator at
Golden, it was decided that the most desirable tube dimensions would be about 1.25 in.
outer diameter, 0.125 in. wall thickness, and 6.0 in. long. An appropriate mold was
prepared and the aluminum titanate tubes were gelcast. After drying, five tubes were
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Nunn, S.D. & Stephan, J.E. Gelcasting of aluminum titanate. Final report, report, August 1, 1997; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc693501/m1/7/: accessed July 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.