Rate Controlled Sintering - Application in Advanced ceramic process

E .SIVANAGI REDDY12ACPA02

OUTLINE 0F THE TALK

• Ceramics• Sintering• Types of sintering• Process of sintering• Consequence of sintering• Rate controlled sintering• Summary

ceramics

• A ceramic is an inorganic, non-metallic solid prepared by the action of heat and subsequent cooling

• Ceramics that with minor exceptions have been developed with in the last 50 years or so are called advanced ceramics.

• Advanced ceramics include ceramics for electrical, magnetic, electronic, and optical applications

Sintering

• Sintering is the process by which a powder compact is transformed to a strong, dense ceramic body upon heating.

• Sintering could eliminate most pores in porous green body and compress residual pores, and bring grain growth and improve binding among grains

• Driving force for sintering: Lowering of free energyI. The curvature of particle surface II. An extremely applied pressureIII. Chemical reaction

Stages of Sintering Three stages: 1. Initial stage :2. Intermediate Stage :3. Final stage:

• Temperature• Time duration• Green density• Uniformity of green density• Atmosphere• Impurities• Size distribution• Particle size

Factors effecting sintering

FE-SEM micrograph of Mg/1 wt% HAp sintered at different times, (a) 1 min, (b) 2 min, (c) 3 min and (d) 4 min

Material transport mechanisms

Transport mechanism

Material source

Material sink Related parameter

Lattice diffusion Grain boundary

Neck Lattice diffusivity, Df

Grain boundary diffusion

Grain boundary

Neck Grain boundary diffusion, Db

Viscous flow Bulk grain Neck Viscosity, ȠSurface diffusion Grain Surface Neck Surface diffusivity,

Ds

Lattice diffusion Grain Surface Neck Lattice diffusivity, D l

Gas phase transport 1. Evaporation/ condensation 2.Gas diffusion

Gas surface

Gas surface

Neck

Neck

Vapour pressure difference ΔpGas diffusivity, Dg

Rate-Controlled SinteringRate – controlled sintering is done in two waysI. controlling Heating rateII. controlling temperature

SEM images of KNN sintered samples at: a) 1060, b) 1080, c) 1100 and d) 1120°C for 2 h

FE-SEM micrograph of Mg sintered at different heating rate, (a) 200 °C/min, (b) 400 °C/min, (c) 500 °C/min and (d)1200 °C/min

Summary

• Sintering is the process by which a powder compact is transformed to a strong, dense ceramic body upon heating

• The driving force behind sintering is lowering of free energy.

• Three stages of sintering depends of different parameters.

• Rate controlled sintering basically done in Temperature and heating rate controlling methods.

References

• Suk-Joong L. Kang, Sintering : Densification, Grain growth and Microstructure Elsevier(2005)• M.N Rahaman, Ceramic processing and Sintering 2/e CRC Press(2007)• M.W Barsoum Fundamentals of Ceramics CRC Press(2003)