Carbonate formation on bioactive glasses.
Carbonate formation on bioactive glasses.
复制标题
生物活性玻璃上形成碳酸盐。
作者：
M. Cerruti;C. Morterra
这种名为58S的系统是一种由二氧化硅、氧化钙和五氧化二磷组成的溶胶-凝胶合成的生物活性玻璃，在医学上用作骨假体，因为当浸泡在生理液体中时，其表面会形成一层羟基碳酸盐磷灰石。以CO_2、H_2O和Cd_3CN为探针分子，用原位FTIR光谱研究了生物活性玻璃58S在真空中碳化的机理。在真空中的研究是必要的，以确定碳化过程中具体涉及的分子和形成的碳酸盐的类型。将生物活性玻璃58S与掺钙二氧化硅和CaO进行了比较。在CaO上，仅与CO2接触即可形成离子碳酸盐，而在58s和掺钙二氧化硅上，只有当样品上同时存在CO2和过量H2O时，才会发生碳化反应。H2O的作用不仅是封闭表面的阳离子中心，使CO2不能表现出其Lewis碱行为，而且还能形成一个允许碳酸盐离子形成的类液体(单)层。H2O的存在也被认为促进了钙离子从块体向表面的迁移。在CaO和含钙硅酸盐(包括生物活性玻璃)表面形成的碳酸盐是相同类型的，但通过两种不同的机制产生。生物活性玻璃上需要过量的水才能开始重碳化，这一发现似乎表明，在一个简化且易于复制的系统中，导致原位碳化的机制模拟了碳酸盐加入磷灰石层时在溶液中发生的情况，以及样品在货架老化过程中发生的情况。
The system termed 58S is a sol-gel-synthesized bioactive glass composed of SiO2, CaO, and P2O5, used in medicine as bone prosthetic because, when immersed in a physiological fluid, a layer of hydroxycarbonate apatite is formed on its surface. The mechanism of bioactive glass 58S carbonation was studied in the vacuum by means of in-situ FTIR spectroscopy with the use of CO2, H2O, and CD3CN as probe molecules. The study in the vacuum was necessary to identify both the molecules specifically involved in the carbonation process and the type of carbonates formed. Bioactive glass 58S was compared to a Ca-doped silica and to CaO. On CaO, ionic carbonates could form by contact with CO2 alone, whereas on 58S and on Ca-doped silica carbonation occurred only if both CO2 and an excess of H2O were present on the sample. The function of H2O was not only to block surface cationic sites, so that CO2 could not manifest its Lewis base behavior, but also to form a liquid-like (mono)layer that allowed the formation of carbonate ions. The presence of H2O is also supposed to promote Ca2+ migration from the bulk to the surface. Carbonates formed at the surface of CaO and of Ca-bearing silicas (thus including bioactive glasses) are of the same type, but are produced through two different mechanisms. The finding that a water excess is necessary to start heavy carbonation on bioactive glasses seemed to imply that the mechanism leading to in-situ carbonation simulates, in a simplified and easy-to-reproduce system, what happens both in solution, when carbonates are incorporated in the apatite layer, and during sample shelf-aging.