Centrifugal Gel Casting: A Combined Process for the Consolidation of Homogenous and Reliable Ceramics

Abstract

In this work, a combined process, called centrifugal gel casting (CGC), was proposed for the fabrication of homogenous and reliable monolithic and composite ceramics starting from submicrometer‐sized powders. This method exploits the advantages of both conventional gel casting (GC) and centrifugal slip casting (CSC), while overcoming the limitations associated with the two methods. Via this process, a relatively low centrifugal force is applied to form a highly concentrated slurry in the mold cavity, which is then followed by in situ polymerization of slurry during gelation. In this work, concentrated alumina slurries with different solid contents from 45 to 65 vol% were consolidated by the three forming methods mentioned above. Various properties of green and fired products were measured and compared. Shorter processing time, lower centrifugal force, higher green strength, and minimal segregation are observed to be the characteristics of CGC in comparison with CSC. In situ elimination of bubbles with no need for degassing and the ability to remove heterogeneities, on top of high reliability and the potential to process higher viscosity slurries, are the main advantages of this method over the conventional GC.

Netshape centrifugal gel-casting of high-temperature sialon ceramics

“…This is attributed to the increasing formation of compacted powders sedimentation in the colloidal system with the increase in the centrifugal force. The effect of this unique compaction mechanism of centrifugal compaction has been previously reported in the literature [11,13]. In such a process, the particles flow downwards, in the opposite direction of the medium in the colloidal system, to form densely packed and compacted sediment, resulting in a highly dense part.…”

“…These observations confirm that centrifugation lowered the level of porosity within the sample matrix. In fact, it can be rather difficult to remove the entrapped air in the ceramic slurry with the high solid loading by vacuum de-airing due to its high viscosity [11]. The addition of centrifugation to the conventional GC route was shown previously to have been greatly effective in eliminating entrapped air in concentrated ceramics slurries [12].…”

“…As such, the use of centrifugation during casting can overcome this issue compared with vacuum de-airing, since the residual bubbles will be forced out of the gel under the action of the centrifugal force. There are several studies that verified the utility of centrifugation on the elimination of the residual air bubbles within the slurry, resulting in an increase in strength following sintering [11]. The addition of centrifugation to the conventional GC route was shown previously to have been greatly effective in eliminating the entrapped air in concentrated ceramics slurries, alongside an enhanced consolidation and densification in the green component [11][12][13].…”

Developments in Processing of Functionally Gradient Metals and Metal–Ceramic Composites: A Review

“…Centrifugal casting is extensively used for gradation of ceramic powders containing two or more ceramics [41]. In polymer composites, graded structures were obtained by centrifugal casting method.…”

Microstructure and mechanical properties of ZrB2-SiC composites fabricated by the centrifugal gel casting

“…However, it must be noted that when the slurry viscosity increased as a consequence of the increase in the solid loading, the problem with air bubbles trapped in the suspensions become more critical [20]. Vacuum deairing would not work as efficiently as in the case of low viscosity slurries and it was essential to combine the mechanical stirring process with vacuum deairing to minimize the air bubbles [21].…”