Archive of Reports on Past meetings

BCA IG Reports on meetings 1990 - 1994

• 1994
• 1993
• 1992
  • 9 Jul 92 The Importance of Quality Assurance on X-ray Diffraction Laboratories
• 1991
  • 19 Jun 91Control of Structure and Mechanical Properties of Crystalline Materials
• 1990
  • 15 Feb 90Microstructural Properties From Line Profile Analysis
  • Sessions at BCA Spring meeting March 90

The Importance of Quality Assurance on X-ray Diffraction Laboratories.

The meeting, held at BP Research, Sunbury on Thames an 9th July, attracted delegates from over 30 industrial and academic X-ray laboratories. Of these, only 4 had some form of accreditation.

The meeting started with the reminder:

It is so easy "to do the right things" rather than "do things right." We are all consumers of measurements and the supplier should have some traceability to a nationally accepted standard - if one exists. Customers buy products which we, by virtue of x-ray measurements, have had input to. These measurements need not be of high accuracy but the result should be adequate for the intended purpose. Objectivity and subjectivity are both important in X-ray world. When obtaining results, is there a procedure that is followed to guarantee control of the experiment, so that we can demonstrate that all appropriately trained staff would obtain the same result - with in acceptable limits? If we resort to the use of software for obtaining these results have we fully validated the software - be it of in house or commercial origin?

Brian Kent (NAMAS) and Norman Deeley (British Standards) were invited to describe their own schemes and the requirements for accrediting the procedures in use in laboratories for obtaining results. Both stressed that their schemes were complementary. NAMAS specialise in testing and their emphasis is on measurement - whether it be by a well defined national standard or an in-house method. BS are more concerned with the product, its design and the management of its manufacture. This product can be information and knowledge. Each of these standards has a number of clauses that requires a procedure - if they are applicable. These procedures will show that one has a means of agreeing with ones customer what he/she wants, a policy for supplying him/her, a well defined method of how one proposes to do it, and a system of record keeping to demonstrate ones achievements. Inherent in these will be staff training, calibration, accuracy assessment, maintenance, standards, etc.. The procedures are the heart of accreditation, with validation methods, measurement traceability and reports of considerable importance.

The following questions were put to the delegates:

"Would another laboratory accept your in-house procedures?"

"What statement do you make at the end of the test - how sure are you that you h ave the right answer and what is the (justified) error in it?"

"Is your computer software fully validated and fully documented before use and by whom?"

"Can you demonstrate that appropriately trained staff will, within defined limits, obtain the same answer by following a set procedure?"

The last question is the one used to assess the subjective element in a test. We have few standard samples or nationally documented procedures and one suggestion was that we should excha nge amongst ourselves those that we have or have round robin test pieces. The "garbage in, garbage out" saying may be true about computer operations but good quality data gathered in an objective manner could still lead to the wrong answer if the software is unvalidated or there is a high subjective input into the result evaluation. Both organisations will accredit objectivity but not subjectivity.

QA, i.e. quality assurance and not quantitative analysis as one person thought, is probably p ractised in a non-formal way in most laboratories. Those who have achieved accreditation will confirm that although it is not easy it does have benefits. Not only does it make one think deeply about the claims that one makes but customer confidence and that of staff and management is boosted. There is less rework and the improved efficiency results in reduced operating costs.

D.J.Dyson.

CONTROL OF STRUCTURE AND MECHANICAL PROPERTIES 0F CRY STALLINE MATERIALS

ICI CHEMICALS AND POLYMERS, RUNCORN. 19th JUNE 1991

More then 80 delegates attended this one day meeting held in the Conference Centre at ICI in Runcorn. This meeting was jointly sponsored by the Particle Technology Group of the Institution of Chemical Engineers, the British Association for Crystal Growth and the industrial Group of the BCA with the general aim to addressing the role of structure and mechanical properties in the definition of particulate p rocesses.

The theme of the morning's talks were the structural aspects of crystallisation associated with such processes at the molecular level. The session was opened with a paper by J. Garside (Chemical Engineering, UMIST) who gave a detailed overview on the parameters that must be considered to obtain the desired structure and related properties of a material during crystallisation processes. Factors such as supersaturation, kinetics, polymorphism, crystal size distribution and mixing we re individually examined with relevant examples illustrating each point.

A comprehensive introduction to polymorphism was presented by T. Threlfall (Chemistry, University of York). Adopting a "practical approach" he described identification of polymorphism, production of phase diagrams using thermodynamic considerations, and a third structural approach trying to relate polymorphism with molecular structure. He laid the basis for the afternoon's discussion by outlining that, although regula tory bodies may not be demanding such information, the pharmaceutical scientist should be pursuing it in order to alleviate the range of formulation problems caused by polymorphism.

A talk by J. Anwar (Pharmacy. Kings College) followed and continued the morning's theme with a detailed examination of the mechanisms of polymorphic solid-state phase transformations Normal reaction kinetics are inapplicable in this area, with various factors that have to be considered, e.g. the spatial distrib ution of nuclei and the nucleation and growth mechanisms of the new solid phase. Ideally measurements may he based on large single crystals, however in practice this is not applicable for many systems and measurements must be based on polycrystalline and powder samples. Normally a reaction may only be followed by consideration of the fraction of a system transformed. Extraction of a rate constant for these reactions have been the subject of many theories, all of which assume that reactions will cont inue to completion if given sufficient time. Studies on sulphathiazole indicate that the solid- state transformation does not always continue to completion and that the rate and extent of reaction is dependent on temperature. This was explained in terms of nucleation in different sites characterised by different energies of activation.

N. Shankland (Pharmacy. University of Strathclyde) presented a paper on "Structural Control of Crystallisation in Chiral Systems". Initially describing the i mportance of investigation into the crystallisation of optical isomers, and the part that separation plays in the pharmaceutical and agrochemical industries he outlined the importance of the classical experiments undertaken by Pasteur. He then described how modern techniques were being employed to answer the question as to why mixtures of isomers can crystallise in three very distinct phases. These phases are, he explained, readily distinguished by single crystal x-ray diffraction and their thermo-s tability can now be related directly to crystal structure. This, he concluded, would result in a better understanding of any separation process which could be developed to gain optically pure materials.

The afternoon's talks, devoted to the relationship between structure and mechanical properties of a system, was opened by J. N. Sherwood (Chemistry, University of Strathclyde) who lectured on "Structure, Strain and Mechanical Properties in Relation to Crystal Grouth."

The two following presentations highlighted the growing relevance of an appr eciation of crystal form in relation to powder technology and therefore to the pharmaceutical sciences, hitherto described by some as an "art form".

J. J. Dijksterhuis (DMV. The Netherlands) gave a review of lactose as an excipient in the dry dosage form discussing the history for, and rationale of its use. By describing the differences between two commonly chosen forms of the material (spray dried and amorphous) he explained how the largely crystalline spray dried material, under compressi on will fragment and form good compacts because of the generation of many more inter-particulate binding sites. In contrast the amorphous material, being less brittle, will deform plastically but will also form good compacts under compression.

M. Aulton (Pharmacy, Leicester Polytechnic) expanded on this by noting that hard elastic materials would give rise to poor quality compacts in contrast to the better compacts produced by ductile, or fragmentary materials. He described methods for qua ntifying the crystalline nature of materials and drew on a -lactose as well as other pharmaceutically relevant materials to illustrate this argument.

Closing an excellent and stimulating meeting was a paper given by m. Ghadari (Chemical Engineering, University of Surrey) who spoke on "Studies of Attrition Processes in Crystalline Solids Using Controlled Rate Impact Fracture." Here he explored the link between the rate of attrition of particulate solids and the phy sical and mechanical properties of solids. By expanding on previous theories that the rate of attrition could be linked to the appearance of sub-surface lateral cracks, he described how these cracks could be used to describe the loss per impact from the particle properties and impact velocity. He highlighted his talk with results on cubic systems such as Mg0, NaCI and KCl as achieved on apparatus discussed comprehensively later in the talk.

Paul Fagan, Stephen Love, and Pau l Meenan
University of Strathclyde

INDUSTRIAL GROUP
SPECIAL INTEREST SYMPOSIUM
MICROSTRUCTURAL PROPERTIES FROM LINE PROFILE ANALYSIS

This symposium was held at ICI Runcorn on 15th February and was organised by Ian Langford and Steve Fletcher. The interest in the topic proved to be far greater than the organisers had expected: there were 60 applications to attend but unfortunately space only allowed 40 to be accommodated on the day.

The symposium began with lan Langford covering various aspects of background theory, including sources of line broadening, line profile shape functions, deconvolution and requirements for data quality. This was followed by Steve Fletcher discussing the various experimental factors involved in obtaining a "pure" line profile, including the choice of a standard for deconvolution. Steve went on to describe the Warren Averbach method and some single-line techniques for obtaining both crystallite sire and strain, using an ICI catalyst as an example to demonstrate the application of these approaches and the agreement between them.

In the final presentation before lunch, Steve Andrews (ICI) described the application of the Williamson-Hall approach to the determination of size and strain in a magnesium hydroxide sample.

The afternoon session began with lan Langord discussing the use of total pattern fitting to determine size and strain, particularly applicable wh ere it was difficult to measure individual reflections. Steve Andrews described the use of the Daresbury synchrotron source to obtain good quality pure line profiles, followed by Bill David of Rutherford Laboratory who demonstrated how the fundamental understanding of the line shape of the SNS was enabling precise fits to line profiles to be achieved. The art contribution, by Ivan Hall (UMIST) described attempts to obtain microstructural information on polymers (Kevlar and LDPE) by fitting a distrib ution function to higher order Fourier coefficients. Ian Ferguson (Springfields) then discussed some examples from the nuclear industry including surface coatings and corrosion layers. This talk finished

with a demonstration given by Tony Bell (Springfields) of an IBM PC program to determine crystallite size and shape.

The meeting concluded with presentations by the major instrument suppliers of the range and capabilities of their size-strain software. These were given by Reg Nicho lls (Philips) and Marcus Winter (Siemens).

One possible criticism of the symposium was that it did not offer the opportunity for those less experienced in line profile analysis to raise and discuss their problems. It is therefore likely that, in the future, the Industrial Group will hold two types of meeting on this subject:

1. A basic workshop which will be limited to small numbers and will take the form of a round-table discussion of individuals' specific problems and applic ations.
2. A symposium with prepared presentations and contributions on techniques and applications.

The success of this meeting and the unexpected demand has certainly demonstrated that there are many people using line profile analysis on a wide range of real problems and that there is a general and widespread interest in the topic throughout the industrial X-ray diffraction community.

Steve Fletcher