Sintering of viscous droplets under surface tension

Area of Science:

• Materials Science
• Physics
• Chemical Engineering

Background:

• Sintering is a crucial process in materials processing and geological formation.
• Understanding the densification of viscous materials under surface tension is key to controlling material properties.
• Existing models often do not account for time-dependent viscosity or residual porosity during sintering.

Purpose of the Study:

• To experimentally investigate the sintering of high-viscosity liquid droplets (glass beads).
• To test and extend existing sintering models by incorporating non-isothermal effects and initial pore size distributions.
• To determine the factors limiting late-stage densification and the equilibrium residual gas volume fraction.

Main Methods:

• Heating free-standing cylinders of spherical glass beads above their glass transition temperature.
• High-resolution measurement of evolving bead pack volume during sintering.
• Extension of theoretical models to include time-dependent viscosity and initial pore radii.
• X-ray computed tomography (CT) to determine residual gas volume fraction.

Main Results:

• Good agreement between experimental data and extended models for early-stage sintering (times less than capillary relaxation timescale).
• Increasing discrepancy between models and data at later stages, linked to decreasing permeability.
• Sintering inhibition at later stages due to decreasing permeability.
• Experimental determination of equilibrium residual gas volume fraction.

Conclusions:

• Decreasing permeability of the sintering system significantly inhibits late-stage densification.
• Extended models provide accurate predictions when accounting for non-isothermal conditions and initial pore size distributions.
• The study provides a comprehensive understanding of liquid droplet sintering, with implications for materials processing and geological modeling.