Two‐Step Sintering of Ceramics with Constant Grain‐Size, I. Y₂O₃

Abstract

Isothermal and constant-grain-size sintering have been carried out to full density in Y 2 O 3 with and without dopants, at as low as 40% of the homologous temperature. The normalized densification rate follows Herring's scaling law with a universal geometric factor that depends only on density. The frozen grain structure, however, prevents pore relocation commonly assumed in the conventional sintering models, which fail to describe our data. Suppression of grain growth but not densification is consistent with a grain boundary network pinned by triple-point junctions, which have a higher activation energy for migration than grain boundaries. Long transients in sintering and grain growth have provided further evidence of relaxation and threshold processes at the grain boundary/triple point. Isothermal and constant-grain-size sintering have been carried out to full density in Y 2 O 3 with and without dopants, at as low as 40% of the homologous temperature. The normalized densification rate follows Herring's scaling law with a universal geometric factor that depends only on density. The frozen grain structure, however, prevents pore relocation commonly assumed in the conventional sintering models, which fail to describe our data. Suppression of grain growth but not densification is consistent with a grain boundary network pinned by triple-point junctions, which have a higher activation energy for migration than grain boundaries. Long transients in sintering and grain growth have provided further evidence of relaxation and threshold processes at the grain boundary/triple point.

Sintering behaviour of cobalt ferrite ceramic

“…The optimised sintering profile adopted for the cobalt ferrite in this work is not unlike the twostep sintering approach recommended by Barba et al [4], and carried out by Kim [7] and others [5,29]. The major advantage of two-step sintering, as conceived by Chen and Wang [6], is the ability to achieve dense, nanostructured materials of grain size 25-30 nm from powders of size range 5-10 nm.…”

Mechanisms of Microstructure Control in Conventional Sintering

“…The sintering temperature in this region results in elimination of residual porosity without grain growth at final stage of work. Suppression of grain growth but not densification is consistent with a network of grain boundaries anchored by triple junction points, which have higher activation energy for migration than grain boundaries (Wang et al, 2006a).…”

“…Suppression of grain growth in the final stage of sintering was achieved by exploiting the difference between the kinetics of diffusion in the grain boundary and controlled grain boundary migration rate. Chen and colleagues used the technique of twostep sintering nanosized powders of Y 2 O 3 (Wang et al, 2006a), BaTiO 3 ferrites and Ni-Cu-Zn (Wang et al, 2006b). Other studies are reported in the literature using the two-step sintering to post nanometric TiO 2 (Mazaheri, 2008a), yttria stabilized zirconia (Mazaheri, 2008b), zirconia (Tartaj, 2009), abrasive alumina with additions of MgO-CaO-SiO 2 (Li et al, 2008), alumina-zirconia (Wang et.…”

“…According to Chen and Wang (Chen & Wang, 2000;Wang et al, 2006a), in a temperature range called kinetic window, occurs by grain boundary or volumetric diffusion while the grain boundary movement is restricted, so that the densification occurs without, however, growth occurs grain. The sintering temperature in this region results in elimination of residual porosity without grain growth at final stage of work.…”

Characterization investigations during mechanical alloying and sintering of W–20 vol% SiC composites

“…Secondly, increasing MA duration causes more homogeneous distribution of SiC phase in the W-matrix which contributes to higher sinter densities. On the other hand, the fact that an almost constant sintering density (∼95%) value is achieved for all W20SiC samples sintered using the second sintering regime could be attributed to slower sintering kinetics [22,23,[33][34][35] due to the "frozen" microstructure as reported in the literature [22,23,[31][32][33][34][35].…”