Hi everyone,
I'm confused about nanostructured coatings.
Say I have a material those grain size is of micron order ~ 10um, but consists of primary nanosized particles ~3nm and mean pore diameter ~30nm; will the thermally sprayed coating formed by such feedstock material be considered as a nanostructured one?
However, to keep the nano-structural characteristics, I'm thinking of agglomerating it with another ceramic with micron-sized grain. In that case, will this be a nanostructured coating?
I would really appreciate for any clarifications.
Thank you.
Lets us see whether you are able to understand this. Suppose your material is in bulk state, means no confinement, grain size of micrometer, etc. You can coat this material on any substance, what we call in older days as simply 'coating' (like painting wall surfaces, car, etc.) using conventional simple method like brushing or even some chemical methods like dip coating etc. Look here that method we employ does not deposit atom by atom and hence coating surface thickness will also looks high and we call this as a thick film coating. Now if you employ a sophisticated coating technique like sputtering or MBE etc. using the same material in bulk form, will coat the layer atom by atom. For eg. carbon deposited atom by atom with 100 times will give you thin film of carbon with thickness of 22 nm. Now I hope you understand the difference. If you have nanostructured material, you have to do even carefully to preserve the nanostructure on the coated surface. You can add specific agent to inhibit the agglomeration while coating.
Well, IMHO I would say that it depends on the deposition process. What You define as grain size in my opinion is particle size (~ 10um) and the grain size inside of the particles is 3nm. If that is the case, in the process of thermal spraying the spraying temperature is a critical factor. I would assume that heating of the 10um particles to a sufficiently high temperature will induce diffusion inside of them, potentially creating larger size grains inside the particles. As higher the temperature, as bigger the grains will get. If You can create the coating with thermal spraying at a sufficiently low temperature to hinder the grain growth trough diffusion, You would probably obtanin a coating with nanometer size grains, so id would be a nanostructured coating.
The agglomeration of the material with an other ceramic (possibily nanostructured also in raw form), and succesfully depositing it without significant grain size increase in both of the materials would result in a nanocomposit coating.
I would be rather conservative in pronouncing the result as nanostructured or nanocomposite however without proper investigation of the obtained coating. Such investigations can be lead with various procedures, however I would recommend XTEM (Cross Section Transmission Electron Microscopy).
Just my two cents,
Laci
Thank you both.
Laci, actually by grain size, I meant the granule size or powder size (um) which in turn consists of primary particles of nano-sized dimensions.
I believe if I thermal spray the above micron-sized powder, a bimodal coatings may be obtained, rather than a nanostructured one.
Please correct me if I am wrong.
p.s: I am a newbie in this field.
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