Open AccessProcess of epitaxial crystal growth for CaSO 4 · 0.5H 2 O on a surface of dissolving fluorapatite crystals studied by scanning electron microscopy
Author(s) -
Dorozhkin S. V.
Publication year - 1996
Publication title -
scanning
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.359
H-Index - 47
eISSN - 1932-8745
pISSN - 0161-0457
DOI - 10.1002/sca.1996.4950180206
Subject(s) - fluorapatite , dissolution , epitaxy , scanning electron microscope , crystallization , crystal (programming language) , materials science , crystal growth , crystallography , chemical engineering , isotropic etching , etching (microfabrication) , nanotechnology , mineralogy , chemistry , composite material , apatite , layer (electronics) , computer science , engineering , programming language
A process for the epitaxial crystal growth for CaSO 4 · 0.5H 2 O on a surface of dissolving natural fluorapatite (FAP) crystals under conditions of wet‐process phosphoric acid production has been studied by scanning electron microscopy (SEM). With the SEM working in a secondary electron mode, we were able to establish the main stages of the coating formation, including direct measurements of its thickness and growing rate values for individual needle‐like CaSO 4 · 0.5H 2 O crystals. Confirmation of an aggregate mechanism for CaSO 4 · 0.5H 2 O epitaxial crystals growth, established earlier under conditions of chemical crystallization, was achieved for the first time. The mechanism includes the following steps: (1) ultramicrocrystals of CaSO 4 · 0.5H 2 O were formed, (2) they coalesced into needle‐like crystals by means of mutual aggregation, (3) the needle‐like crystals united into star‐like and besom‐like aggregates, and (4) the latter formed macro‐aggregates. We have found that these steps occur simultaneously, resulting in multilayer coating formation. During the investigation, the phenomenon of FAP crystals aggregation by means of mutual intergrowing of epitaxial CaSO 4 · 0.5H 2 O coatings and the peculiarities of the etching process for the FAP crystal surface under conditions of CaSO 4 · 0.5H 2 O coatings formation were also studied.