GROWTH AND MECHANICAL DEFORMATION OF ALPHA-LACTOSE MONOCRYSTALS

This project set out to use monocrystals as the starting point in the study of the mechanical properties and deformation behaviour of alpha-lactose crystals. Chapter 2 conducts a detailed investigation into the crystallisation and growth kinetics of alpha-lactose monohydrate crystals by an agar-gel suspension technique. A large number of morphologically well-formed alpha-lactose crystals of various sizes and habits were successfully grown using different agar types, different gel concentrations and the addition of ethanol. The fundamental mechanical properties of alpha-lactose monohydrate and anhydrous alpha-lactose monocrystals were assessed by microindentation (Chapter 3), compressive deformation (Chapter 4) and acoustic emission techniques (Chapter 5). The mechanical properties of crystal faces (Oil) and (110) of both lactose types were quantified by microindentation. The indentation data reveals the anisotropic nature of alpha-lactose monohydrate crystal. This observation is related fundamentally to the orientation of the crystal planes. This anisotropy was greatly reduced by an increase in growth rates and the process of dehydration. The indentation data shows that the anhydrous crystals are much softer, less elastic and much more deformable compared with the monohydrate form. This was confirmed by the crushing strength and acoustic emission measurements, which also revealed a distinct difference in the deformation behaviour of the two lactose types. Alpha-lactose monohydrate crystals deformed by spalling fracture whereas the anhydrous form was much more friable. The acoustic emission data shows that the fragmentation process of the monohydrate crystals is more energetic and that a different type of fragmentation may be involved in the case of the anhydrous lactose. The mechanical behaviour of the anhydrous crystals is in agreement with their polycrystalline nature. Differences in crystal habit and size have also been shown to influence the crushing strength and acoustic activity of the crystals. The data generated from single crystals of alpha-lactose correlates very well with existing data on the compression characteristics of alpha-lactose. Mechanical testing has provided both visual and quantitative confirmation of the previously observed bulk compression behaviour of the two lactose types. The acoustic emission study further provides valuable information regarding the microprocesses which occur within the crystal during deformation. Through this study, a better insight into the fundamental deformation characteristics of individual alpha-lactose crystals is obtained, thus giving a clearer picture of how the lactose crystals will interact with each other during bulk compression.

Name dc:type.qualificationname

PhD

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

De Montfort University

Year dc:date.issued

1989

Author dc:creator

• WONG, D. Y. T.

Licence

• https://dora.dmu.ac.uk/bitstreams/54e3e0de-4690-4736-bfa1-730d70f69d20/download