Re: Zirconia

Posted by Joe on March 29, 2004 at 23:17:39:

In Reply to: Re: Zirconia posted by Gordon England on March 27, 2004 at 02:59:55:

: : Hello Mr. Gordon. I have another question for you. I am by no means a chemist, is Zirconia and Zirconium oxide powder the same? I'm under the understanding they are and have variations of them with added stabalizers, as in yttria, calcia. Why is there a need for a stabilizer and what exactly does oxide mean? I know some ceramics have the word oxide in the name and I want to know why. Thanks in advance for your reply. Joe

: Hi Joe

: Zirconia, zirconium oxide and zirconium dioxide are the same and refer to a compound ZrO2. Basically, oxide or oxide ceramic is a compound of a metal and oxygen.

: Pure zirconia can exist in three different crystalline phases; cubic (stable above 2380 C), tetragonal (stable above 1170 C) and monoclinic (stable below1170 C) On cooling from tetragonal phase to below 1170 C a martensitic type transformation occurs to monoclinic phase. This type of transformation is very rapid and similar to that found when hardening steel. This transformation also causes a sudden volume change of about 3%. Since zirconia is a brittle material this sudden expansion causes severe cracking and in the case of a coating complete failure. Not good for use as a high temperature thermal barrier coating in this state. Additions of some other metal oxides like calcium oxide (lime, calcia), magnesium oxide (magnesia)and yttrium oxide (yttria)suppress or stop this transformation to monoclinic and so stabilise the tetragonal or even cubic phase.

: Hope this makes sense.

: Regards Gordon

Thanks once again for your help, makes sense to me. Joe

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