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zirconia ceramics

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PKerEng

PKerEng

Chemical
Mar 31, 2011
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I am working on zirconia-3%yttria material cutting blades. The problem is that the blades have to be autoclave sterized. Under such conditions they may deteriorate. I am stuck with commercial 3%yttria material.
Is there a way to, say, surface modify the material in order to stabilize it without compromising good mechanical properties?
Also, what would be the optimum firing schedule for small size zirconia-3%yttria parts in order to fully develop best mechanical properties?

Slawomir
 
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Bruce,
I am trying to stay within the US-bounds. I have been exposed to bits and pieces of info regarding different types of zirconia ceramics. I made a number of commercial parts. One of the candidates is scandia-stabilized (or partially stabilized) material but it sets things back to the square one. Anyway, the general idea is: can we somehow figure-out how to make a standard, commercially available 3%yttria material to perform up to our expectations? Can we surface modify it? Is there another way to make it work?

Slawomir
 
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Do you have a failure mode for failed parts from the autoclave
exposure.?

Here are links to some information about various Zirconium Oxide
materials. Zircoa at one time has the best source for information. Both Dynamic Ceramics and Refractron make different Zirconium oxide formulations.




Addenda:
Problems with stabilized Zirconium Oxide in ball valves installed on polymer autoclaves nearly did us in. The problem was with 4" dia balls for valves that had worked alright during test started failing while holding 2000 lbs of polymer at 283C and 250 psig. Investigation revealed that operations had change their process in such a way to cause the valve to see an additional 40C differential when charging the autoclave. The Zirconium Oxide balls couldn't take the additional thermal shock.
 
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Hi Slawomir,

There was a fair body of research done in the 1980's during Reagan's Star Wars years. I no longer have the references but they may be available from the American Ceramic Society. They were compendiums of papers presented at the Cocoa Beach Symposia. I'll take a look through my paper files to see what I can find. In the meantime, here are two articles for your consideration. It looks like you might be trying to beat Mother Nature at her own game.

Bruce
 
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It is a new project. The idea is to make lasting, reuseable cutting instrument. It is for medical application so sterilization is a must. Obviously other means of sterilizing could be considered but in real life it is the customer who makes the specs. Regarding the mode of failure: the ceramics seems to become more brittle and looses its cutting edge.
I just wonder, in general terms: what could be possibly done to a regular 3%yttria material to improve it for this particular application. We are talking here pretty small, thin pieces with sharp cutting edge.

Slawomir
 
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This still doesn't answer your question about how to protect a regular 3%yttria material, but it's another interesting link which describes the most likely mechanism for the material degradation.


You could contact the author (that's his website) to see if he has any suggestions.

Everything I've read so far looks at reformulating the base material (see the linked article re: oxalic acid); nothing's come up about surface treating.
 
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Thanks for the link, PratsA. This gets, more or less, to the heart of the problem: the inherent instability of the tetragonal phase ready to get transformed into the monoclinic. As the other respondents indicated one possibly marginal gain could be realized thru controlled processing of the ceramics ( size of crystalites affected, among other things, by thermal treatment and "better", more perfect material thru HIPing ). Assuming that we start with "good" fine particle powder and subject it to proper ceramic treatment we may end-up with satisfactory quality ceramics, which we already know may deteriorate while exposed to elevated temperature steam treatment. The temperature itself (~130C) may not be so bad to trigger phase transformation. It certainly points to the water vapor. As much as it may not seem to be unusual at quite a bit higher temperatures, 130C makes it really tricky.
Here is what I have been thinking/hoping for: is it possible to surface treat a piece of decent PSZ zirconia in order to prevent it from deterioration coming from moderately overheated steam? Could it be some kind of CVD coat or pack cementation treatment the answer?

Slawomir
 
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Perhaps you can sputter a thin, dense monoclinic phase over the PSZ material to protect it from the water. I would give Jack Bradshaw at Atkinson Thin Film in New Hampshire a call and get his thoughts on the possibility. He does a lot of weird and unusual thin film work.


Bruce
 
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Yes Bruce, this is a kind of thinking I tried to pursue. Here, I rather thought of enriching the surface layer with yttria up to the level of full stabilization. The culprit here seems to be a depletion of yttria from tetragonal zirconia leading to monoclinic transformation. I would envision baking the ceramics in a bed of yttria ( kind of pack cementation process ) leading to surface yttria enrichment. Here the jury is still out. The biggest thing is to preserve good, long lasting cutting edge and , at the same time be able to steam sterilize the gadget. So the problem remains open: have an extra coating of the like material which is stable ( as you suggest ) or push the surface of the existing material well within the stability limits where it will remain despite gradual surface depletion of critical component ( yttria ).

Slawomir
 
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ould it be possible to get a blade made by people like the linked below. Or if practical you could get a standard blade and modify it.
I would try to get a few blades to actually check from one of several suppliers.
I would also look to Koycera and Kasumi for possible candidates for your blade.

The basic process.


m_content&view=article&id=113&Itemid=139

Some actual blades.


My ceramic knives have been through the dishwasher numerous times with no loss in quality.
 
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I appreciate the link, however I am not in buy-sell type of business. I make what I sell. Obviously, one has to buy powders from places like Tosoh, etc. I am trying to figure-out a fundamental process to make custom blades. We can not delegate everything to China. In addition, such approach quite often does not work as well as desired. So, the question remains essentially the same, unanswered: how to make good tetragonal zirconia blade, starting from a commercial powder which would work well for this specific application.

Slawomir
 
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Yes, HIPing seems to be one way to push it incrementaly to the higher level, for sure. It does not change the overall ball game, just pushes the microstructure closer to perfection. I appreciate the hint, however I am trying to bit bushes around with the hope to come-up with a better mousetrap. Here, we are just fighting the kinetics of the transformation triggered, most likely, by leaching-out of yttria. Certainly, denser more perfect ceramics will stand-up better, but how about some other approach?

Slawomir
 
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