Injection moulding of thin walled zirconia tubes for oxygen sensors

Abstract

An injection moulding process has been developed for the production of net shaped zirconia tubes. A specially designed injection mould was used for shaping feedstocks containing a paraffin wax–oleic acid binder system with a mixture of ceramic powders. Many thousands of thin walled tubes were injection moulded to optimise the process parameters. Using a two stage wicking–thermal debinding process, the post-moulding processing time was decreased to approximately a seventh of the total required when binder removal was accomplished using only a thermal treatment. Characterisation of starting materials and zirconia tubes was conducted using thermogravimetric analysis, scanning electron microscopy, dilatometry and density and size measurements. Performance of the injection moulded tubes was tested using oxygen activity measurements in molten steel under industrial steelmaking conditions. Excellent results were obtained in terms of oxygen concentration, electromotive force and soluble aluminium content, with good reproducibility and high accuracy. The proposed injection moulding process is very promising and provides an important alternative for mass production of oxygen sensor tubes.

Keywords:

• INJECTION MOULDING
• OXYGEN ACTIVITY MEASUREMENTS
• SENSORS
• THERMAL SHOCK RESISTANCE
• ZIRCONIA