What type of FTIR experiment are you using, reflection or transmission? Sometimes it is much better to use KBr pellet than trying to measure on diamond.

Hi, what about XPS? it's very surface specific and gives you information about surface functional groups as well.

Michal Hegedus thanks for your suggestion. I already tried reflection and transmission mode but i am not getting reproducible data even for the same sample.

Agnieszka Suliga thanks. Actually the major content of basalt fiber is silica and my coating also contains Si, so my XPS data showed variable elemental composition.

This article may be useful to develop alternative coating on basalt fibers

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