Electron microscope study of noncrystalline calcium phosphate

Abstract

The morphology of brushite, CaHPO4 · 2 H2O, provides some basic information on biological mineralization. The growth, morphology and surface structures of brushite crystals grown at fairly high growth rates in silica gel at 37°C in the initial pH range of 4 to 6 (the final pH range of about 3.2 to 4.7) have been investigated. Their preferred growth direction is [101]: there is a marked tendency for calcium and phosphate ions in the gel to attach to (111) or (101) surfaces; inclusions derived from silica gel are also incorporated, mainly along the [101] direction in the initial stage of crystal growth and at higher pH values. The following order of “edge strength”, which refers to a sort of resistance of crystal edge against getting out of its shape, was obtained experimentally for the edges parallel to the (010) face of brushite: [101] ⪆ [201] > [001] ⪆ [100]. The relationship between the above order and the structure of corrugated sheets with composition [CaHPO4] is also discussed.