Q: I have an application where I need pan head, insulating, high vacuum compatible, screw. It will also need to be usable at a service temperature up to 150C. Do I need a ceramic?

A: Though ceramics are excellent insulators, they are usually only used for high temperature applications, where polymers are not compatible. For example Alumina ceramic has a usable limit of 1650°C. Since this is a relatively low temperature, your best bet is a polymer like PEEK or PVDF screws. Depending on the strength, inertness and chemical resistance needed will determine which polymer PEEK or PVDF is best for your fasteners.

Q: Why does Zirconia cost more than Alumina?

A:  1) Raw material cost: Aluminia is far more abundant, whereas Yttrium oxide which is a stabilizer for Zirconia ceramic, is a rare earth element.

2) Shaping costs: Due to its higher density it takes approximately 10x longer to grind down and shape Zirconia into parts.

3) Higher sintering temperatures:  The thermal shock resistance for Zirconia is poor so it requires a more costly sintering process.

Q: What advantages does Zirconia have over Alumina?

A:   Usually for most high temperature or electric insulator applications where ceramics are needed, alumina ceramic fasteners are the most popular choice due to their properties and relatively affordable price compared to zirconia fasteners. However sometimes the extreme properties of zirconia fasteners are needed which include:

• Higher material density provides greater wear and corrosion resistance
• Higher strength
• Higher temperature resistance

Q: I’m using a high temperature vacuum furnace at 2500F. What type of material do you suggest using and is there any advantage of using a metal over a ceramic?

A:   Under vacuum conditions with little to no oxygen present, there are some metallic options for fasteners which include molybdenum and tantalum. These metals are considered referactory metals and could be used up 2900F and 3600F for molybdenum and tantalum fasteners respectively. In addition to metals, alumina and zirconia ceramics could be used as well.

The advantages of each come from what is most important and the conditions of your application. For example, if quenching is involved, you might not want to use ceramic fasteners due to the thermal shock which will cause failure. However if having low thermal conductivity through the fastener is important, then ceramics are a good choice. If the fasteners are to hold higher loads, the molybdenum and tantalum metals might be more robust.

Q: Why does Zirconia cost more than Alumina?

A:   1.) Raw material cost. Alumina is far more abundant, whereas Yttrium oxide which is a stabilizer for Zirconia ceramic, is a rare earth element.

2.) Shaping costs. Due to its higher density it takes approximately 10x longer to grind down and shape Zirconia into parts.

3.) Higher sintering temperatures.  The thermal shock resistance for Zirconia is poor, so it requires a more costly sintering process.