PSZ Ceramic information

Hello,
I have some technical development where we want to use PSZ (Ytrium type). However, in the application, temperature will have a temperature cyclic
between 150 to 300c. I heard problem of phase transformation but without clear information for such temperature level (phase tetragonal & monoclinic)
If youhave some information on this phenomena & case of problem, please let me know, Cheers, Philippe
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the best is to contact the producer, for example have a look at (lead zirconate titanate):
http://www.staveleyndt.com/products/ebllzt.html

monoclinic)
let
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Guerin Philippe wrote:

Did you notice sci.materials.ceramics?
Michael Dahms
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Since you are trying to use partially stabilized zirconia I am assuming you have some knowledge of the tranformation toughening effect. Partially stabilized zironia is also referred to as transformation toughened zirconia in which a dopant, typiclly 3mol% yttria, is used to partially stabilize the cubic phase resulting in a mix of stable cubic phase zirconia and metastable tetragonal zirconia. Microstructurally this appears as elliptical tetragronal precipitates in a cubic matrix. Dont confuse this with tetragonal zirconia polycrystal in which the entire material consists of metastable tetragonal phase at low temperatures with precise control of yttria content and cooling rates. Heres where it gets interesting. As the PSZ is cooled the tetragonal phase wants to expand into the monoclinic form below 1000C, however, the stabilized cubic phase provides a compressive stress that prevents this expansion. When a propagating crack hits one of these precipitates, the energy of the crack is dissipated by the energy of the phase transformation back into the monoclinic form. Here is where your problem lies. Typically, PSZ ceramics are used at elevated temperatures where the thermodynamic driving force for the phase transformation is not so great. Your problem is referred to as low temperature degredation of PSZ, and is due to the spontanteous transformation of tetragonal zirconia to the monoclinic phase in the 100 - 300C range. The interaction of microcracks accompanied by the spontaneous phase transformation results in larger macrocracks, which significantly lowers the strength of PSZ which can initially have a bending strength of 1200MPa. This low temperature degredation has been noted when using PSZ in bio applications. I believe the addition of alumina particles or Nb as a co-dopant with yttria have been used to alleviate low temperature degredation. There may even be zirconia suppliers of PSZ for medical applicaitons that could solve your problems.
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