Vaclav Pouchly

Sintering densification curve: A practical approach for its construction from dilatometric shrinkage data

This article summarizes the usage of high-temperature dilatometry in ceramic processing and powder technology with special attention on the description of the sintering process. A practical method for transformation of dilatometric shrinkage data into densification curves (the dependence of the sample density on sintering temperature or time) is described in detail. A new automatic procedure to recalculate sintering shrinkage data allowing the plot of the densification curve has been developed, which is presented here.

TWO-STEP SINTERING AND SPARK PLASMA SINTERING OF Al2O3, ZrO2 AND SrTiO3 CERAMICS

ABSTRACT The influence of Two Step Sintering and Spark Plasma Sintering processes on the microstructure of three kinds of oxide ceramics was studied. Al2O3 (with initial particle size of 240 nm), ZrO2 (60 nm, stabilized with 3 mol% Y2O3) and SrTiO3 (50 nm) powders were cold isostatically pressed and pressureless sintered with different heating regimes. It was found that the method of TSS does not bring about significant reduction of final grain size in Al2O3 and ZrO2 ceramics, but does reduce the grain size in perovskite SrTiO3 ceramics. Pressureless sintering of SrTiO3 leads only to 95%TD dense ceramics with the minimum grain size of 400 nm. In comparison, by SPS, with an applied uniaxial pressure of 200 MPa, SrTiO3 ceramic of 98%TD dense with grain size of 80 nm was prepared.

Master Sintering Curve - A Practical Approach to its Construction

The concept of a Master Sintering Curve (MSC) is a strong tool for optimizing the sintering process. However, constructing the MSC from sintering data involves complicated and time- consuming calculations. A practical method for the construction of a MSC is presented in the paper. With the help of a few dilatometric sintering experiments the newly developed software calculates the MSC and finds the optimal activation energy of a given material. The software, which also enables sintering prediction, was verified by sintering tetragonal and cubic zirconia, and alumina of two different particle sizes.

Intensive particle rearrangement in the early stage of spark plasma sintering process

Abstract The densification behaviors of 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) ceramics during spark plasma sintering (SPS) were analyzed both using the master sintering curve (MSC) approach and by evaluating the temperature dependent evolution of density and densification rate. It was found that densification curves could hardly be fitted using one apparent activation energy value by MSC conception, by which it indicated that more than one densification mechanisms were involved in SPS. Moreover, dependent neither on applied pressure (20–100 MPa) nor heating rates higher than 50 °C/min, the maximum densification rate had always been observed at rather similar ∼78% of theoretical density (TD) accompanied with negligible grain growth. An intensive particle rearrangement mechanism was proposed to dominate the rapid densification to 78% TD in early stage of SPS process, by which it yielded the considerable faster densification rate than those achievable by diffusion-related processes.

Master Sintering Surface – A Practical Approach to Its Construction and Utilization for Spark Plasma Sintering Prediction

The sintering is a complex thermally activated process, thus any prediction of sintering behaviour is very welcome not only for industrial purposes. Presented paper shows the possibility of densification prediction based on concept of Master Sintering Surface (MSS) for pressure assisted Spark Plasma Sintering (SPS). User friendly software for evaluation of the MSS is presented. The concept was used for densification prediction of alumina ceramics sintered by SPS.

A Practical Approach for the Calculation of the Activation Energy of the Sintering

Newly developed software for calculation of activation energy (Qs in the following) of sintering using the Wang and Raj model is presented. To demonstrate the practical potential of the software and to evaluate the behaviour of the Qs during the sintering process, alumina and cubic zirconia ceramic compacts were prepared from nanometric powders. The results obtained with both materials are in agreement with previously published data calculated by different approaches. In the interval of interest (relative densities from 60 % to almost 100 % of theoretical density), both materials show similar behaviour. Three distinct regions can be seen: the initial constant values of Qs 868 kJ/mol and 762 kJ/mol for alumina and cubic zirconia, respectively; a region containing linear drop of Qs and the final region of constant Qs values 625 kJ/mol and 645 kJ/mol for alumina and cubic zirconia, respectively.