Influence of the surface tension components of stainless steel on fouling caused by calcium phosphate

Abstract

In order to lengthen the processing time of dairy plants, research has been undertaken to study the deposition of calcium phosphate, one of the main components of milk fouling deposits. It is accepted that the surface tension of the solid material in contact with the liquid affects the fouling behaviour and, therefore samples with different surface tension characteristics were tested. These surfaces were non-modified stainless steel 316L food grade (2B and 2R finishes) and surfaces modified by ion implantation (SiF3+ and MOS2) DLC sputtering and coating (Ni-P-PTFE and SiOx). To understand the fouling process of calcium phosphate, its deposition on the different surfaces was followed by using a rotating disk apparatus and by characterising the deposits by contact angle measurements, image analysis and weighing. From these experiments it could be concluded that: In terms of the phenomenology of the build-up of calcium phosphate deposits, surface tension components do not seem to affect the sequence of steps involved in the deposition process. Three phases can easily be distinguished in the process: a) induction period, correspondent to the period of time passed until the start of particle formation in the bulk; b) adhesion and formation of the first layers of crystals and c) growth and compaction of the crystals. From a quantitative standpoint, the deposition process seems to depend on the gamma(-) component of the surface tension of the fouling support, which represents the electron donor part of the acid-base polar component of the solid surface tension. The initial deposition rate showed to be higher for lower values of the gamma(-) component while the amount of deposit obtained at the end of the deposition process increased for higher values of the gamma(-) component.