Abstract
The work described in this thesis is concerned with some physical and crystallographic aspects of the formation and properties of water formed scales. It consists mainly of a study of the growth and physical properties of calcite crystals formed under the special conditions of scale formation. Three main aspects of scale and its properties are dealt with. These are: Part 1) The initiation of scale formation at a heating surface where boiling is taking place. Part 2) The physical properties of calcareous scale when it has been allowed to grow beyond the initial stage. Part 3) Some crystallographic aspects of the further growth of calcite under the specially rapid conditions of scale formation. Part 1). concerned with the initiation of scale formation shows that the crystalline ring formations first observed by Partridge (1) with calcium sulphate solutions are also obtained when using a range of other solutions. A variety of other formations based on Partridge's rings were also discovered. A dynamic mechanism is advanced to explain these formations. Part 2) describes tests evolved to test the adherence, crystal size and other properties of scale in the bulk. The effect on these properties of varying the material and also the texture of the heating surface is investigated. The results lead to a theory of adherence based on mechanical interlocks and bonds between the scale and the heating surface, A section is concerned with cohering forces in the scale itself and a mechanism of cementitious action is proposed that is similar to the setting of gypsum plaster. Part 3) is concerned with the orientation effects on further scale growth of single calcite crystal substrates attached to a heating surface. A number of different faces of calcite (100), (111), and (211) were used as the substrate and further growth of scale on them was found to be orientated with respect to the substrate crystal and to exhibit different habit formations according to the crystal face. In two cases evidence indicated that the structure of the growths was not that of a simple parallel overgrowth, but was orientated at 90° to the structure of the substrate.