Combined-stage Sintering Model Research Articles

Effective diffusion distance for isothermal sintering of hydroxyapatite

The microstructural evolution of hydroxyapatite (HAp) was quantified for isothermal sintering at 1100°C. The aggregated state of the powder particles is thought to be responsible for the relatively high value of the average pore separation throughout isothermal sintering. The measured grain size exponent of 6·7 is not compatible with the values expected for volume diffusion or grain boundary diffusion under the assumptions of the Combined Stage Sintering Model and hence the Master Sintering Curve. The measured exponent for a previously defined flux weighted effective diffusion distance gave a more reasonable value of 3·4. The theoretical exponent in the Combined Stage Sintering Model was then corrected to accommodate a non-linear relationship between the effective diffusion length and pore size. The results demonstrate how the effective lengthscale in the Combined Stage Sintering Model can be corrected to accommodate aggregation in the microstructure.

Densification behaviour and two stage master sintering curve in lithium sodium niobate ceramics

The Master Sintering Curve (MSC) has received much attention in recent years due to its ability to predict sintering behaviour of a given powder and green body process regardless of its thermal history. In this paper MSC, based on the combined stage sintering model is constructed for one of the most important lead-free piezoelectric viz. lithium sodium niobate, Na1-xLixNbO3 (x=0.12, LNN-12), ceramic using shrinkage data. The present study has been carried out to understand and control the densification behaviour during pressureless sintering. Two distinct stages of densification have been observed en route to the upper limit to sintering temperature. The activation energies of densification for the two temperature ranges viz. 800–1150°C and 1150–1300°C were found to be 365kJ/mol and 2530kJ/mol, respectively, through the construction of MSC. The MSC should be useful in predicting the densification behaviour and the final density and for designing a reproducible fabrication schedule for the LNN-12 ceramics.

Densification Process of WC-MgO Nanocomposite Based on Master Sintering Curve

The master sintering curve (MSC) of nanocomposite WC-MgO was constructed based on the combined-stage sintering model. Nano-sized WC-4.3wt%MgO powder with average particle size of 35nm was synthesized by high-energy ball milling, and then uniaxially pressed at the pressure of 500MPa to fabricate green compacts. The shrinkage response of the compacts, used to construct the master sintering curve, were studied by dilatometric runs at two constant heating rates of 5°C/min and 10°C/min up to 1900°C. Using the estimated activation energy, the master sintering curves were established and compared to acquire an optimum value (Q=361.8 kJ/mol). The obtained MSC was validated by non-isothermal sintering with the identical green compacts. The results demonstrate that the MSC can be applied successfully to predict and control shrinkage level and final density during heating up regardless of heating rates.

Master sintering curve of nanocomposite WC-MgO powder compacts

The master sintering curve (MSC) of nanocomposite WC-MgO was constructed based on the combined-stage sintering model. Nano-sized WC-4.3wt%MgO powder with an average particle size of 35nm was synthesized by high-energy ball milling and then pressed uniaxially at a pressure of 500MPa to fabricate green compacts. The shrinkage response of the compacts during heating was studied by dilatometric runs at constant heating rates of 5 and 10°C/min up to 1900°C. The master sintering curve with sintering activation energy Q=361.8kJ/mol was constructed between 600 and 1900°C. The MSC was validated by isothermal and non-isothermal sintering experiments with identical green compacts. The results demonstrate that the MSC can be successfully applied to predict and control densification evolution during heating, regardless of the heating path, and non-isothermal sintering in the high-temperature range.

DENSIFICATION AND GRAIN GROWTH OF NANOCRYSTALLINE NIAL POWDER DURING PRESSURELESS SINTERING

Nanocrystalline NiAl powder was prepared by mechanical alloying. The prepared powder was cold compacted and sintered at different temperatures and times. The crystallite size of green and sintered compacts was estimated from X-Ray Diffraction peak profile analysis. Thereafter, the Generalized Parabolic Grain Growth model and Master Sintering Curve concept based on Combined Stage Sintering model were employed to investigate the grain growth and densification behavior of nanocrystalline NiAl powder during sintering, respectively. The results of modeling were in a very good agreement to that of experiment. Finally, by comparing the modeling results the sintering parameters were optimized.

Prediction and control of microstructure evolution for sub-microscale α-Al 2O 3 during low-heating-rate sintering based on the master sintering curve theory

The master sintering curve (MSC) can sometimes be used for analyzing the shrinkage behaviour of ceramics. Densification of α-Al 2O 3 with the mean particle size of 350 nm was continuously recorded during heating at 0.5, 2 and 5 °C/min. A MSC was successfully constructed using dilatometry data with the help of combined-stage sintering model. The validity of the MSC has been verified by a few experimental runs. The microstructural evolution with densification during different heating-rate sintering was explored. The sintered microstructure is a function of the time–temperature sintering conditions, and it is verified that there exists a link between sintered density and microstructure. The MSC can be used to predict and control microstructure evolution during sintering of α-Al 2O 3 ceramics.

Prediction of densification during low heating rate sintering of microcrystalline alumina ceramics based on master sintering curve theory

The master sintering curve (MSC) approach is useful for analysing the shrinkage behaviour of ceramics. In this study, the shrinkage behaviour of α-Al2O3 of mean particle size 2·5 μm during constant heating rate sintering was evaluated. An MSC has been constructed using dilatometry data containing lower heating rates only with the help of a combined stage sintering model. The validity of the MSC has been verified from experimental data. A comparison between the predicted and the Archimedes densities showed good agreement, suggesting that it is possible to control shrinkage behaviour during processing using the MSC. The concept of the MSC has been used to evaluate the apparent activation energy for the above powder; a high value of 1148 kJ mol−1 was obtained.

Application of Master Sintering Curve Theory to Predict and Control the Sintering of Nanocrystalline TiO<sub>2</sub> Ceramic

Master sintering curve (MSC), in which the sintered density is a unique function of the integral of a temperature function over time, is insensitive to the heating path. In this paper, the densification of rutile TiO2 was continuously recorded at heating rates of 2 °C/min and 5 °C/min, respectively, by dilatometer. The MSC for rutile TiO2 was constructed for pressureless sintering using constant heating rate date based on the combined-stage sintering model. The construction and application of the MSC were described in detail for different thermal histories. The MSC can be used to predict and control the densification, final density, and microstructure evolution during the whole sintering. The final density can be predicted for an arbitrary temperature–time path. A good consistence exists between the predicted and experimental densification curve, confirming that it is possible to accurately predict and control the sintering behavior of TiO2 from the initial to final stage of sintering using MSC.

Prediction of densification and microstructure evolution for α-Al2O3 during pressureless sintering at low heating rates based on the master sintering curve theory

The master sintering curve (MSC), in which the sintered density is a unique function of the integral of a temperature function over time, is insensitive to the heating path. Densification of ?-Al2O3 with the mean particle size of 2.5?m was continuously recorded during heating at 0.5, 2 and 5oC/min. A MSC was successfully constructed using dilatometry data with the help of a combined-stage sintering model. The validity of the MSC was verified by seveal experimental runs. The microstructural evolution with densification during different heating-rate sintering was explored. The sintered microstructure is a function of the time-temperature sintering conditions, and it is verified that there exists a link between sintered density and microstructure. The MSC can be used to predict and control microstructure evolution during sintering of ?-Al2O3 ceramics.

The master sintering curve for pressure-less sintering of TiO2

A Master Sintering Curve (MSC) for rutile TiO2 was constructed for Pressure-less sintering using constant heating rate dilatometry data based on the combined-stage sintering model. Construction of the master sintering curve is described and the validation is proved with rutile TiO2 under different thermal histories. The concept of master sintering can be used to predict the sintering shrinkage and final density and calculate the activation energy, and a value of 105 KJ/mol for TiO2 was obtained. With one temperature dependent parameter determined experimentally, it became possible to describe accurately the densification behavior of TiO2 from the initial to final stages of sintering. .

Development of a master sintering curve for ThO 2

A master sintering curve for ThO 2 containing 0.5 wt% CaO has been constructed with the help of combined-stage sintering model. The concept of the master sintering curve (MSC) has been used to calculate the activation energy for sintering for the above composition, and a value of 520 kJ/mol was obtained. The validity of MSC has been verified by the data of a few experimental runs using a high temperature dilatometer. With one temperature dependent parameter determined experimentally ( Θ), it became possible to describe accurately the densification behavior of ThO 2 from the early to final stages of sintering. The sinterability of powder compacts made from different powders and fabrication procedures under different thermal histories, could be characterized through the master sintering curve.

Microwave Plasma Sintering of Alumina

AbstractMicrowave induced plasma provides an effective heating source for sintering of ceramics without the thermal instability that occurs in microwave sintering of some materials. In the present study, small cylindrical tubes were sintered in a microwave induced oxygen plasma inside a single mode (TM012) cavity. A dilatometer and an optical fiber thermometer (OFT) black body sensor were employed to follow the changes of shrinkage and temperature during the sintering process. A similar specimen setup was built inside a conventional rapid heating furnace for comparison. The estimated activation energies were 468 ± 20 kJ/mol for plasma sintering and 488 ± 20 kJ/mol for conventional sintering. An athermal effect due to the plasma was observed. Sintering data were analyzed using the combined stage sintering model and the results suggest that the athermal effect may be ascribed to an increase of aluminum interstitial concentration during plasma sintering.

Combined Stage Sintering Model: Review and Applications

ABSTRACTIn the combined stage sintering model previously introduced[l], a single equation was derived that quantifies sintering as a continuous phenomenon from beginning to end. The microstructure is characterized by two separate parameters representing the geometry (Γ) and the scale (G). Calculations of Γ from experimental data show the effect of surface diffusion and microstructural geometry on Γ. The model is reviewed and discussed with respect to the sintering of alumina and spherical nickel powder.