Pore former
02-14-2011, 12:20 AM,
#1
Pore former
Dear All ,

Just wondering if anyone can help me with the term "PORE FORMER" in thermally sprayed coatings.
What are the materials used for this particular purpose and how does it work in relation with a certain thermal spray technique ?

Any ideas from this forum are highly appreciated .... Smile

Thanks a lot,
~MaDiLa~
Reply
02-17-2011, 07:38 PM,
#2
RE: Pore former
Hi Madila

Should the term "PORE FORMER" mean producing a more open structured coating or increasing/controlling the amount/type of porosity above that which is normal then:

Increasing porosity can be achieved by "detuning" parameters Happy0193 Careful selection of spray powders with respect to particle size/distribution/form.

More control on amount, size, shape and distribution of porosity however, can be achieved by introducing a secondary sacrificial material ("PORE FORMER" may be a good name for this) into the coating. The pore former needs the property of being able to be removed from the coating in a post process such as heating to burn out constituent, or being water soluble so it can be dissolved out with water or selectively chemically removed. Materials that could be used are organic materials that can be burnt out later, polyester comes to mind for a few applications. Water soluble salts sound a reasonable idea, though I've not got round to doing enough work to know how practical it is. Producing pseudo alloy coatings by blending two dissimilar metals/alloys or arc spraying using two different wires and selectively leaching out the unwanted constituent.

Now it would be interesting to know the general application you have in mind for this, I know it could be commercially sensitive, but a general idea for coating function would be helpful.

(02-14-2011, 12:20 AM)Madila Awalini Wrote: Dear All ,

Just wondering if anyone can help me with the term "PORE FORMER" in thermally sprayed coatings.
What are the materials used for this particular purpose and how does it work in relation with a certain thermal spray technique ?

Any ideas from this forum are highly appreciated .... Smile

Thanks a lot,
~MaDiLa~

Reply
03-02-2011, 06:30 AM,
#3
RE: Pore former
Hi Gordon,

Thanks for replying to my question.
What we intend to do is to have a porous structure of the coating for an application such as biomaterial coating.
For one thing, as you've said "detuning" all the process parameters was also what we had in mind.
But introducing what's called a pore former into the coating is also our interest.
Thanks a lot for your explanation relating to the property of the applied pore former, very helpful to understand this as well.

Another thing that I want to ask you is the method to analyse the interconnected pores within the coating .
Have you heard anything about applying a fluorescent die for the epoxy resin , is it a common practice ?

Thanks a lot .
~MaDiLa~
Reply
03-03-2011, 06:42 AM,
#4
RE: Pore former
Hi MaDiLa,

I have been working on biomaterial coating for some years (actually got my Ph.D on this. I about half year or so, I need to start working on porous coatings (titanium or CoCr alloy) on metal implants by HVOF as well. I have a research grant that requires me to do this. I know a patent by, if I recall correctly, an aircraft engine manufacturer that said that they can thermal-spray porous metal/ceramics on a metal substrate using polyester as the sacrificial pore maker. We can exchange information in the future, if you are interested.

I had experience with both epoxy and fluorescence dye, but never mixed them. Pls clarify your question (what is needed? visualizing pores by fluorescence? my labmat worked on visualization of micro-cracks in bone by fluorescence dyes), and I might be of help.

rgds,




(03-02-2011, 06:30 AM)Madila Awalini Wrote: Hi Gordon,

Thanks for replying to my question.
What we intend to do is to have a porous structure of the coating for an application such as biomaterial coating.
For one thing, as you've said "detuning" all the process parameters was also what we had in mind.
But introducing what's called a pore former into the coating is also our interest.
Thanks a lot for your explanation relating to the property of the applied pore former, very helpful to understand this as well.

Another thing that I want to ask you is the method to analyse the interconnected pores within the coating .
Have you heard anything about applying a fluorescent die for the epoxy resin , is it a common practice ?

Thanks a lot .
~MaDiLa~

Reply
03-03-2011, 06:43 PM,
#5
RE: Pore former
Hi Madila

Quote:Another thing that I want to ask you is the method to analyse the interconnected pores within the coating .
Have you heard anything about applying a fluorescent die for the epoxy resin , is it a common practice ?

First, impregnation of the metallography samples with epoxy resin prior to grinding and polishing will greatly aid in retaining the "true microstructure". To be honest, I think it is easy enough to identify the epoxy filled porosity without colour dying or UV fluorescent microscopy. I have tried UV fluorescent dyes in epoxy resin, but without setting up your microscope with UV light source and special UV optics, it does not work. Colour dyes in the resin also appear not to give any benefit. Wink If you have a lab with UV microscopy set-up or the resources to do so, it may be a beneficial aid. When I was keen on this, I could not get the funding for upgrading microscope.
Reply
03-08-2011, 05:23 AM,
#6
RE: Pore former
Hi there.

Pulaunias, first of all , I'd like to thank you for your reply.
I really appreciate it ,
I will contact you by PM about this so that we can discuss it in more detail .
Thanks a lot ..

Gordon,
Yes , I did the vacuum impregnation first with my samples , but still wonder if I can have the right method to rate the connected pores within the structure.
Because in my opinion, the image analysis by SEM or OM only allows the characterization of porosity level but not the pore connectivity .
However, thanks for sharing the info on use of fluorescent dyes in epoxy resin and the need for the UV light source for its analysis.

Cheers,
~Madila~




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