Electrically conductive ceramics are generally used in some form of electrochemical cell, in which interfacial conditions at the surface of the ceramic are critically important for obtaining optimum performance from the cell. To ensure optimum performance it is essential that when installed in the application the ceramic is clean and dry. Ionically-conductive ceramics such as sodium beta”- alumina are very sensitive to atmospheric humidity. Other beta”-aluminas e.g. silver, potassium, hydronium, strontium and barium tend to be less sensitive. Conditions in which the material can be safely stored are described below.

Storage

Ionotec ceramics are usually supplied wrapped in heat-sealed aluminium bags. As long as the bags have not been cut open or damaged, no special storage conditions are needed. The bags can be cut open using a sharp knife or scissors. After opening, the ceramics should be stored in dry conditions. There are a number of options, from which any one can be chosen according to convenience:

Long-term storage

• In glass tubes fitted with airtight rubber bungs
• In a desiccator cabinet or plastic box with dry inert gas supply, e.g. nitrogen
• In a freezer unit at around -20°C or lower. In this condition an airtight seal is not needed. However the ceramic should itself be wrapped in a plastic bag, so that when removed from the freezer the bag and its contents can thaw to room temperature before opening the bag. In this way condensation of water directly onto the ceramic surface is avoided. In any of the above conditions the shelf life of the ceramic will be several years.

Short-term storage

• In a dehumidified air cabinet at < 10% RH
• In a refrigerator at < 5°C, or in a freezer compartment at below 0°C (in a sealed bag as described above, to prevent condensation of water on removal from storage)
• In a hot air oven at around 80°C.

In any of these conditions the shelf life of the ceramic will be several weeks. Storage conditions which are not recommended are

• In a desiccator cabinet containing silica gel
• In a vacuum drying cabinet

These methods are not recommended because sodium beta”-alumina itself is a more powerful desiccant than other common drying agents such as silica gel, and vacuum cabinets are seldom leak-tight, resulting in continuous inward suction of fresh moist air. Handling Ionotec supplies the ceramics specially treated to ensure that the surface is free of contamination. They can be handled with most types of laboratory gloves e.g. cotton, lint-free, clean-room or disposable polyethylene. Contact with paper, plastic and other ceramics is generally not detrimental to the surface condition, but contact with metallic parts and with bare hands should be avoided since these will cause contamination which may seriously reduce the life of the ceramic in operation.

Cleaning

Provided that the ceramics have been stored and handled as recommended above, no cleaning operation is necessary. If the ceramic surface has become contaminated, one of the following non-destructive procedures is recommended.

• Washing in hot (70°C) demineralised water with ultrasonic agitation for 15 minutes maximum, followed by rinsing and drying in hot circulating air
• Heat treatment at a temperature in the range 600-1000°C for one hour, with a heat-up rate of not more than 300°C per hour. 1000°C is satisfactory for sodium and potassium beta”-aluminas; for other ion-exchanged beta”-aluminas 600°C may be the limit owing to the risk of thermal decomposition.

General Advice

Ionotec’s beta”-alumina ceramics have been operated successfully for periods of up to 10 years in demanding applications including batteries and electrochemical reactors. We can provide users with considerable expertise in obtaining the maximum performance with these products; please do not hesitate to discuss this with us.