Size Reduction

The mechanical properties of spherical alumina and zeolite particles were measured to provide an insight to their susceptibility to milling in a pin - mill. Nanoindentation was applied to determine Young’s modulus and hardness, whilst microindentation and SEM observation were carried out to measure fracture toughness. Preliminary indents determined the suitable load to apply for each material. The Young’s modulus, hardness and fracture toughness were found to be greatest for alumina, and increased with size of zeolite particles. Large scatter was present in the measurements, as is typically the case. The scatter was greater for the zeolite particles than the alumina. The mechanical and physical properties of these particles lead to the prediction that the larger zeolite is more prone to impact breakage caused by a pin mill, with the alumina particles being least susceptible.

The impact breakage of the smaller zeolite particles was assessed in a single particle impact rig at a range of impact velocities and angles. The extent of breakage was shown to correlate with normal impact velocity, regardless of impact angle. This is expected to be the case for larger zeolite particles, however alumina particles should be subjected to similar tests to assess if impact angle is influential on the extent of breakage.

Executive Summary

The aim of the project is to establish a relationship between the product properties and feed material and the mill functions for milling of organic solids. The specific objectives are:

• a) To characterise the physical, mechanical, and thermal properties of organic feed materials (material function) at the single particle level, and to examine the effects of temperature and humidity on these properties,
• b) To investigate the breakage behaviour of single organic particles at quasi-static and dynamic conditions under the influences of temperature and humidity,
• c) To investigate the bulk milling behaviour of model organic solids and mill hydrodynamics (mill function),
• d) To characterise the properties of milled product, and to correlate the product properties to material and mill functions.

Model materials used in the work include aspirin, α-lactose monohydrate (α-LM), sucrose, sorbitol, starch, and microcrystalline cellulose (MCC). These materials cover a fairly wide range of physical, mechanical and thermal properties, hence ensuring generality of the results to be achieved. This report summarises the work done over the past three years, including the single particle breakage studies using the impact tester under both ambient and sub-ambient conditions, measurements of Young’s modulus, hardness and fracture toughness of single particles of some model materials using the nano-indentation method, characterisation of some product particles using the Dynamic Vapour Sortion (DVS), Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD), analysis of the bulk milling behaviour of the model materials in a single ball simulating mill under both ambient and sub-ambient conditions, theoretical analysis of the mill dynamics, distinct element modelling of particle and milling ball motion to establish the mill function, investigation into the use of a flow aid (Aerosil) on the bulk milling, and population balance modelling of the milling of aspirin in collaboration with Du Pont. The main findings are summarised in the following:

The Phase I Preliminary and Annual reports include the State of the Art Review for the following four research fields in Japan:

• A. Slurry Handling and Rheology
• B. Flow and Cohesion of Powders
• C. Agglomeration in Particulate Systems
• D. Deliquoring of Filter Cakes

This Phase II Preliminary Report includes a State of the Art Review for the following two additional research fields in Japan:

• E. Particle Characterisation
• F. Solid-Solid Separation

The previous Phase I reports were mainly compiled by use of the suggestions and advice of 5 consultant professors, who are specialists in each field. The critical opinion of the Phase I Annual Report is based on a general review and my own personal views.

However, this Phase II report has been written based on the results of questionaires mailed to individual principal research personnel. Therefore, it may contain better information than the Phase I reports, but the results might be exaggerated. Each research field was studied in several of the same laboratories as the ones in other fields. That is, some laboratories are listed in more than one field, because the same subjects have been studied by two or three researchers, or the subjects have some correlation with other fields. Especially, the fifth field "E Particle Characterisation" has many connections with other fields, because it is a fundamental scientific subject in particle technology.

The highly selective state of the art review has been assigned for the following four R and D project areas which are shown in Appendix III in detail.

A. Slurry Handling and Rheology

B. Flow and Cohesion of Powders

C. Agglomeration in Particulate Systems

D. Dsliquoring of Filter Cakes

I have selected five active professors in the above areas as consultants, and discussed with them the general outline of the projects. I have prepared the survey guideline and the questionnaire format in Japanese.

The five consultant professors have written the survey reports by use of the questionnaires. On the other hand, a post graduate student has listed up Japanese literatures recently published in the above four areas. I have also passed or sent the questionnaires to selected scholars and have visited several university laboratories and three government research institutes in Japan last March. Direct interviews with key personnels and making laboratory tours by travelling around were the best way to get adequate informations. It is difficult to say which laboratories are most highly trained and well equipped in Japan. However, I have listed their research activities each on a'separate page, which we think to be important ones, as follows.

Overall Objectives of Programme

TO develop:

1. means of predicting particle attrition in process equipment based on unambiguous small scale tests.
2. Insight into the influence of
• particle design and
• equipment design and operation on attrition.

This is the annual progress report on the Particle Attrition project which is being partially carried out at the University of Delft. The project is part of a collaborative effort, at present a complementary project is being carried out at the University of Birmingham. The project was started in February 1982.

The project follows the initial literature survey made by Dr. J. van Brake1 of this University of Technology. In that report the sub-division of the subject was identified as being basically in three parts:

1. Tests on Single Particles
2. Tests on Groups of Particles
3. The Attrition Behaviour of Particles in Kcal Systems

In this department we are currently concentrating on the relationship between the tests on single particles and the behaviour in real systems. This necessarily means that such a relationship will most easily be established for particle handling systems in which the particles are in diluted phase. The two systems in which we have made measurements of particle attrition are in a pneumatic conveying line, where the criteria of lean phase is maintained and in a fluidised bed where the process is more complicated. In defining the objects of this programme there is of course no real distinction between the attrition of particles and the fracture of particles. In our minds we basically perceive the fracture as being the splitting of particles to a number of fragments of roughly comparable size, while the attrition behaviour on the other hand is the gradual wearing away of one large particle. In real processes both features are occuring simultaneously.

At the Clausthal meeting in June 1982 the overall objectives were defined as follow:

• To develop
• means of predicting particle attrition in process equipment based on unambiguous small scale tests.
• insight into the influence of particle design and equipment design and operation on attrition.