Sintering Kinetics at Constant Rates of Heating: Effect of Al₂O₃ on the Initial Sintering Stage of Fine Zirconia Powder

Abstract

The sinterabilities of fine zirconia powders including 5 mass% Y 2 O 3 were investigated, with emphasis on the effect of Al 2 O 3 at the initial sintering stage. The shrinkage of powder compact was measured under constant rates of heating (CRH). The powder compact including a small amount of Al 2 O 3 increased the densification rate with elevating temperature. The activation energies at the initial stage of sintering were determined by analyzing the densification curves. The activation energy of powder compact including Al 2 O 3 was lower than that of a powder compact without Al 2 O 3 . The diffusion mechanisms at the initial sintering stage were determined using the new analytical equation applied for CRH techniques. This analysis exhibited that Al 2 O 3 included in a powder compact changed the diffusion mechanism from grain boundary to volume diffusions (VD). Therefore, it is concluded that the effect of Al 2 O 3 enhanced the densification rate because of decrease in the activation energy of VD at the initial sintering stage.

Effect of alumina addition on initial sintering of cubic ZrO2 (8YSZ)

“…Tekeli et al proposed that for large amounts the alumina is deposited directly in the grain boundaries and reduces the contact points between zirconia particles. It is known [17,21,23] that the GBD is the predominant initial sintering mechanism for Zr 4+ and Y 3+ matter transport in alumina-free samples and this mechanism is affected by the presence of alumina particles. Alumina and zirconia (with no yttria) has very limited mutual solubility and the solubility of Al 2 O 3 in ZrO 2 increases as the temperature increase [25,26].…”

“…As previously mention we used the method described by Matsui et al [9,[21][22][23], where they have incorporated a combination of equations developed by Young-Cutler [17] and Wang-Raj [11] both based on the two-spheres shrinkage model.…”

Bioceramics for Hip Joints: The Physical Chemistry Viewpoint

“…The physicochemical origin of this effect has comprehensively been summarized in recent papers by Guo [108,109], and it is also of stoichiometry nature. The benefit in adding a small amount (typically a fraction of 0.25 wt%) of Al 2 O 3 to 3Y-TZP is twofold: (i) an easier densification ( i.e ., meaning a lower sintering temperature and, thus, a finer microstructure) [110,111]; and, (ii) a better environmental resistance in water-vapor environment [112]. However, it might prove difficult to solve problems related to the heterogeneity of such small alumina quantities when mixing with the 3Y-TZP raw powder, due to a generally strong tendency to agglomeration of raw nanometer-sized powders [113].…”

Apparent activation energy for densification of α-Al2O3 powder at constant heating-rate sintering

“…constant heating-rate method (Young and Cutler 1970). Although most of the sintering models can be used to evaluate the value of the activation energy of sintering, an Arrhenius plot of ln( T ε ) (where ε is the densification rate, T the absolute temperature) versus the reciprocal of the absolute temperature is usually used for the evaluation (Matsui et al 2005;Lahiri et al 2006).…”