Thus, HCl may be added to BHF solutions in order to dissolve these insoluble products and produce a higher quality etch.
[3] Buffered oxide etch can be produced in laboratory quantities by dissolving NH4F powder into water, and adding a solution of HF.
[5] HF solution buffered with NH4F can be used to provide better etching of zeolite for the creation of larger pores, to improve the characteristically poor rate of diffusion in these microporous structures.
Simple HF solutions (and other acidic methods of etching) show high selectivity in removing aluminum from zeolites, reducing the number of potential Brønsted acid sites, and subsequently reducing certain catalytic performance.
However, the addition of a NH4F buffer results in a solution with more HF and HF−2 present, which removes Al and Si in more equal proportion.