In this day and age, green is good – green energy, going green and virtually every connotation associated with green is seen as a positive; so what about green ceramic?
In ceramic, green is not the colour, but a stage in the production process that takes its name from one of the earliest industrialists where the ceramic parts had been formed but needed to be dried prior to sintering. To accelerate the drying process without paying to heat them, greenhouses were used to dry the ceramic and hence the name stuck.
So why is green ceramic seen as good in the modern context? To understand that we have to revisit the process of manufacturing.
When ceramic powder is compacted into a shape, it has the consistency of chalk and can be easily machined. It is then sintered and the process of sintering at high temperature shrinks the part, allowing the density to increase and create the hard ceramic that we know. The shrinkage is typically 20%, so a part that is100 mm in diameter when it goes into the furnace comes out measuring 80mm and that part is now so hard that it can only be machined with diamond tools.
If the part has to be diamond ground to achieve a tight tolerance on the 80mm diameter, this adds considerably to the cost and consumes energy in diamond grinding. If, however, the original green part is made to higher specifications, this extra grinding cost can be significantly reduced …
If the pressing of the part is expertly controlled, the machining of the part before sintering is carried out by skilled and experienced staff and the actual sintering takes place in a controlled manner, then the shrinkage can be held to a tighter tolerance which can reduce the need for expensive grinding.
A good green component can therefore reduce the need for additional grinding. Green can be good in ceramics.