A Novel Approach to Sintering Nanocrystalline Barium Titanate Ceramics

Abstract

A novel approach to pressureless sintering based on the combination of rapid‐rate sintering, rate‐controlled sintering, and two‐step sintering under a controlled atmosphere is proposed. This combined sintering method facilitates control of grain and pore morphology. The application of this sintering approach for pure nanocrystalline barium titanate powder enables the suppression of grain growth during the intermediate and final stages of sintering and the production of fully dense ceramics with 108 nm grain size. The grain growth factor is 3.5, which is three and 17 times smaller than rate‐controlled and conventional sintering, respectively.

Sintering behaviour of cobalt ferrite ceramic

“…In the final stage of sintering, the open porosity network loses stability, forming closed spherical or ellipsoidal pores, which are located in triple junctions. Splitting of cylinder-shaped pores and localisation of spherical pores are accompanied by extended grain growth [10]. Some authors have gone to great lengths [5,10] to accurately determine the relative density boundary value at which to switch to the second stage of two-step sintering.…”

“…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. In Polotai et al's [10] study of nano-crystalline barium titanate, the goal of the first stage of two-step sintering was to produce and freeze in place a uniform pore microstructure while minimising grain growth. This fine and uniform microstructure minimises diffusion distance during constant grain-size sintering which maximises densi-fication kinetics leading to almost fully dense ceramics (99.7 %Dth).…”

“…According to Duran et al, the end of the intermediate stage of sintering occurred at 92 %Dth, and this is characterised by a transition from continuous pore channels to isolated pores. Polotai et al [10], in their study of nanosized BaTiO 3 , use the %Dth value of 94% as the point for switching to the two-step sintering regime. They claim that this density is the transition point between the open and closed porosity networks and the onset point for extended grain growth.…”

“…Some authors have gone to great lengths [5,10] to accurately determine the relative density boundary value at which to switch to the second stage of two-step sintering. For example, Polotai et al [10] found 94% to be optimum for the barium titanate system they studied.…”

“…If real density drops below the set density the temperature is raised, to achieve a higher densification rate and vice versa. Very recently, Polotai et al [10] employed a novel approach, combining two-step sintering and RCS, to sinter nano-crystalline BaTiO 3 . By fully optimising their sintering steps, a fully dense ceramic (relative density 99.7%) with an average grain size of 108 nm was produced.…”