Nelson D G, Barry J C
Chemistry Department, Victoria University of Wellington, New Zealand.
Anat Rec. 1989 Jun;224(2):265-76. doi: 10.1002/ar.1092240217.
The application of high resolution electron microscopy, computer image processing, and image simulation techniques to the investigation of synthetic nonstoichiometric apatites has provided new details of apatite crystal growth mechanisms. Under certain precipitation conditions, calcium-deficient apatites with distinct octacalcium phosphate (OCP)-apatite intergrowths have been observed. Apatite crystals with unit-cell thick overgrowths of OCP on their surfaces confirmed the stepwise hydrolysis crystal growth mechanism initially proposed by Brown (Nature 196:1048-1050). However, many crystals also contained a central two-dimensional OCP inclusion one to two unit cells thick, embedded in an apatite matrix. Similar planar defects have been observed in dental enamel, dentin, and bone crystals. We have developed a modified version of Brown's stepwise OCP hydrolysis apatite crystal growth mechanism to explain the formation of crystals with OCP central planar defects. The mechanism involves the nucleation of an OCP seed that grows until it reaches a critical size, rh, before OCP hydrolysis occurs. Apatite subsequently grows epitaxially on the OCP seed, thereby embedding it in the center of an apatite crystal. Apatite growth is facilitated by partial screw dislocations emanating from the planar defect.
将高分辨率电子显微镜、计算机图像处理和图像模拟技术应用于合成非化学计量磷灰石的研究，为磷灰石晶体生长机制提供了新的细节。在某些沉淀条件下，已观察到具有明显的磷酸八钙（OCP）-磷灰石共生结构的缺钙磷灰石。表面具有OCP单位晶胞厚过度生长的磷灰石晶体证实了Brown最初提出的逐步水解晶体生长机制（《自然》196:1048 - 1050）。然而，许多晶体还包含一个嵌入磷灰石基质中的、厚度为一到两个单位晶胞的中心二维OCP夹杂物。在牙釉质、牙本质和骨晶体中也观察到了类似的平面缺陷。我们已经开发了Brown逐步OCP水解磷灰石晶体生长机制的改进版本，以解释具有OCP中心平面缺陷的晶体的形成。该机制涉及OCP晶种的成核，在OCP水解发生之前，OCP晶种生长直至达到临界尺寸rh。随后磷灰石在OCP晶种上外延生长，从而将其嵌入磷灰石晶体的中心。平面缺陷产生的部分螺型位错促进了磷灰石的生长。
