TWI Frequently asked questions
In general the method and extent of cleaning depends on the ceramic and final product requirements. However, a suggested general cleaning approach is detailed below.
Typically, the contaminants that may be found on ceramics are ceramic powders (usually the same as the ceramic) from post sintering operations (i.e. cutting) and organics from fingerprints/handling.
The first cleaning operation would be to remove the powder contaminants and soluble organics. This can be achieved by immersion in a solvent (a few of which may be heated to increase their activity) and by agitation in an ultrasonic cleaner (for at least 15 minutes). The next step would be to rinse the solvent and any loose contaminants off the surface. A rinse in de-ionised water would be best, otherwise distilled or tap water (note tap water may leave scale on the surface). Leave to dry, ensuring no debris/contaminants can be picked up.
After drying, the cleaned parts should be placed on clean supports (that have been cleaned and fired as described here). Typically, the parts would then be fired in a clean air furnace to a temperature of at least 1000°C for >1 hour. Note that the furnace atmosphere and temperature is dependent on the ceramic being cleaned. On cooling, the parts must be handled with clean ceramic tweezers (metal implements may contaminate the ceramic). If the parts need to be picked-up, then powder-free gloves should be used. Note that plastic gloves generally contain plasticisers which can re-contaminate the parts again. Cotton gloves could be used, but there is the risk of introducing lint onto the parts, plus cotton is hygroscopic.
If the parts are to be stored, then it is recommended that they should be placed into a clean dessicator (can be vacuum-based).
