Degradation and Characterization of Resorbable Phosphate-Based Glass Thin-Film Coatings Applied by Radio-Frequency Magnetron Sputtering

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• 作者：Bryan W. Stuart ; Miquel Gimeno-Fabra ; Joel Segal ; Ifty Ahmed ; David M. Grant
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2015
• 出版时间：December 16, 2015
• 年：2015
• 卷：7
• 期：49
• 页码：27362-27372
• 全文大小：593K
• ISSN：1944-8252

文摘

Quinternary phosphate-based glasses of up to 2.67 渭m, deposited by radio-frequency magnetron sputtering, were degraded in distilled water and phosphate-buffered saline (PBS) to investigate their degradation characteristics. Magnetron-sputtered coatings have been structurally compared to their compositionally equivalent melt-quenched bulk glass counterparts. The coatings were found to have structurally variable surfaces to melt-quenched glass such that the respective bridging oxygen to nonbridging oxygen bonds were 34.2% to 65.8% versus 20.5% to 79.5%, forming metaphosphate (PO₃)^{鈭?/sup> (Q2) versus less soluble (P₂O₇)4鈥?/sup> (Q1) and (PO₄)3鈥?/sup> (Q0), respectively. This factor led to highly soluble coatings, exhibiting a t1/2 degradation dependence in the first 2 h in distilled water, followed by a more characteristic linear profile because the subsequent layers were less soluble. Degradation was observed to preferentially occur, forming voids characteristic of pitting corrosion, which was confirmed by the use of a focused ion beam. Coating degradation in PBS precipitated a (PO₃)鈭?/sup> metaphosphate, an X-ray amorphous layer, which remained adherent to the substrate and seemingly formed a protective diffusion barrier, which inhibited further coating degradation. The implications are that while compositionally similar, sputter-deposited coatings and melt-quenched glasses are structurally dissimilar, most notably, with regard to the surface layer. This factor has been attributed to surface etching of the as-deposited coating layer during deposition and variation in the thermal history between the processes of magnetron sputtering and melt quenching.}