Investigation into the formation of silicate deposits in the steam sterilization process

A. Gassner*, W. Fuchs¹, L. Waidelich¹, H. Mozaffari-Jovein^2
1 Aesculap AG, Am Aesculap-Platz, 78532 Tuttlingen, Germany; ² Hochschule Furtwangen, STW Material-Technologie, 78532 Tuttlingen, Germany

Summary

The present study investigated the formation and fixation of silicate deposits during steam sterilization. First, transfer of silicic acid from the feed water into the sterilization steam onto the sterile supplies was analysed in theory by comparing the process parameters of all substeps of a typical steam sterilization process with a solubility diagram for silicic acid in water and in steam. Next, in furnace tests silicate deposits were selectively deposited onto test specimen made of non-rusting steel and with instrument-like surfaces. Deposit formation was visualized through digital photography and differential interference contrast (DIC) microscopy. In addition, topography images were obtained with atomic force microscopy (AFM) and the chemical composition of surfaces was determined with X-ray fluorescence analysis. Theoretical considerations supported the notion of a pressure- and temperature-dependent solubility of silicic acid in steam which, based on the steam sterilization process parameters, led to extensive entrainment of silicic acid into, and little removal from, the autoclave. Furthermore, experimental findings demonstrated that entrainment of silicic acid compounds gave rise to high, interlocking silicate margins on the test specimen, with a thin flat configuration within the dried drops. By combining the theoretical considerations and experimental findings, it was possible for the first time to add to the literature repository an explanation for the transfer of silicic acid to the sterile supplies and for the mechanism underling the transformation into visible deposits.

Citation:
Gassner A, Fuchs W, Waidelich L, Mozaffari-Jovein H. Investigation into the formation of silicate deposits in the steam sterilization process. Zentr Steril 2019; 27 (6): 380–386

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