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Contact Angle Measurements of Steel on Waterglass-bonded Al2O3-SiO2 Composite Materials
Sebastian Weiss, Ingo Riehl, Jan Hantusch and Ulrich Gross

Measurements of the contact angle in a hot stage microscope by the sessile drop technique have been carried out for thermite steel on waterglass-bonded Al2O3-SiO2 composite materials and pure Al2O3 material in a temperature range from liquidus up to 1923K. High temperature contact angles of liquid thermite steel are needed as boundary conditions for numerical multiphase simulations of crucible discharge and mould filling the aluminothermic welding process. For waterglass-bonded materials, the contact angle was analysed at two fixed temperatures namely at 1723K and just below a critical temperature at which the waterglass binder is decomposing and the substrate is becoming unstable. Contact angles for substrates with high and low Al2O3 content are obtained as (134.0 +/- 5.6)° and (131.4 +/- 3.5)° respectively. On pure Al2O3, contact angles for a temperature range from 1665.8K up to 1779.3K have been found to be linearly decreasing and at 1921.5K to be nearly constant yielding (102.7 +/- 3.0)°.

Keywords: Wetting, contact angle, thermite, steel, waterglass-bonded substrate, oxygen activity

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