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Reports on Industrial Group Meetings in 2000
A Breath of Fresh Air - Specimen Preparation Workshop It was a welcome relief to attend the Industrial Group Meeting during Tuesday afternoon at the BCA Spring Meeting. I find the challenge to understand the organic structures and mathematical methods employed are becoming more comple x as I get older. Therefore, the Specimen Preparation Workshop was a welcome change in which I could relate in the real world. I believe if all meetings were based on a formal agenda but with some, controlled, informality where all participants could interrupt the proceedings and make the subject more interactive. The meeting was chaired by Steve Norval and started with an introduction to Jeremy Cockcroft (Birkbeck College). The title encompassed the A ~ Z of specimen p reparation which made attendees aware of the pitfalls associated with varying samples requiring different approaches. Typical effects occurring during sample mounting are as follows:-
There was plenty of discussion regarding the use of fillers for samples that requires additional bulk if the sample did not meet the requirements of sample holder volume. Examples that were mentioned are as follows:-
Although, apparently if you can get it there is an amorphous adhesive on 'Scotch' pressure sensitive tape. When rubbed between the thumb and forefinger it resembles snot. This four-letter word was delivered with such dexterity from a Rolls Royce attendee. < p>The next presentation was made by Stephen Hillier (Macauley Institute) who explained the virtues of an up-turned conical dustbin with a spray-gun held at the apex. This novel and practical design enabled his co-workers to spray-dry mud samples (clays) onto paper. This method of sample preparation alleviates preferred orientation, with no measurable cross contamination and an output of up to thirty samples per/day. The Institute now markets this fine example of design ingenuity.After the tea break Steve Norval reported on his Round-Robin exercise. The results compared various methods of sample preparation. The methods included front-filled, back-filled with moderate and light pressure, side filled and iso-propyl alcohol dispersion. The results concluded that a spray-dried sample gave the ideal performance and using sample rotation did not effect peak intensity. The following talk was done with great dexterity and imagination because Colin Small had no overheads, images, sp readsheets or slides to show the audience. However, he still managed to captivate the gathering on how we should prepare metallic specimens for texture analysis. Finally, Phil Lake (Glaxo Wellcome) was invited to start a discussion period concerning a sample that generated two different diffraction patterns. The meeting then became a 'free-for-all' when everybody gave possible explanations and reasons - why? Could the answer be the position of the x-ray tube, automatic divergence slits, sam ple position etc., I believe Phil did promise an answer by the next I. G. newsletter. The 'Workshop' format did provide the opportunity for the attendees to interact and made for a good open discussion. I believe everybody feels intimidated by different facets of crystallography beyond their depth of understanding. Therefore, identify a common ingredient in the real world of I. G. crystallography and I believe it will propagate self-interest. Steve Spratt. BCA Spring MeetingHeriot Watt University 5 April 2000Controlled environment XRDThis final group session of the BCA 2000 spring meeting at Heriot Watt University rewarded those attending with a number of excellent presentations on techniques using different diffraction experiments in various controlled environments. The last but one timetabled session of the three day event was expertly chaired by Dave T aylor to accommodate six 20 minute talks (of which one delegate remarked "It was good to hear so much pertinent science being discussed….." with reference to the succinct and witty delivery of the invited speakers). Simon Redfern (Cambridge University) opened the afternoon with a description of novel instrumentation designed to collect X-ray diffraction data from mechanically stressed crystals. Using a three-point bend arrangement with a 120 degree position sensitive detector he desc ribed how it would be possible to study ferroelastic materials under conditions where the applied stress is varied. He told the audience that the apparatus was still under construction and showed slides of the computer generated design stage of the manufacturing process. The equipment will be particularly useful in following changes in the elastic shear modulus as materials undergo phase transitions on heating. Simon rescheduled his talk so that he could catch a waiting taxi and was followe d by John Loveday (Edinburgh) with an absorbing talk on neutron diffraction at high pressure with particular emphasis on boron nitride. John informed the audience of the development of the Paris-Edinburgh cell (low mass, large volume) which had now extended the pressure range for neutron diffraction experiments by an order of magnitude up to 30 GPa (300kbar). He also mentioned the high pressure phase behaviour of ammonia monohydrate and explained its importance for formation models of Jupiter's moon Titan and other planetary satellites. Few of us present will forget without a smile John's last cartoon of two hungry polar bears astride adjoining holes in the Arctic ice. One seen smashing its fist into the water beneath one hole, while the other catches a fish ejected from the other hole with the caption: IF YOU WANT RESULTS FAST, USE HIGH PRESSURE ! Following on and also from Edinburgh University, Andrew Harrison speculated on the claims that the rate or even the course of a reaction may be influenced by microwave heating effects. Although using microwaves has become a routine reaction method in preparative chemistry "the jury is still out". Andrew produced some outstanding, clear transparencies showing the progress of hydrothermal experiments (involving microwaves as the heating source), which caught the attention of one of my colleagues who is working with more conventional hydrothermal treatments. This was real state of the art stuff and exhilarating too. To conclude the first part of the afternoon Christopher Frampton (Roche Discovery, Welwyn) warned of the dangers of polymorphic transformations that pharmaceuticals are suspect to in the field, due to variable humidity and temperature. Chris' first slide adequately stressed the importance of storage by depicting a typical pharmacy in a third world country and noting the difference in conditions from off the shelf preparations to the possible phase transitions caused by environmental stressing. His t alk concentrated on two compounds creatine monohydrate and Zopiclone and his XRPD patterns clearly illustrated the difference environmental conditions can have on the structure through hydration/dehydration processes. Trials are still under way. The crisp management of the first part of the afternoon allowed discussion and debate to continue over tea and on return Martin Soar (BP Amoco Chemicals, Sunbury) employing corporate design in his lecture slides (yellow on green) reminded us of the role of in-situ X-ray diffraction in catalyst development. Knowledge of structure and crystallite size is important in understanding activity as well as deactivation of many well-known catalysts. The experiments that Martin described were attempts, albeit sometimes disastrous to the equipment, to study materials under realistic reaction conditions and he managed to chronicle the industrial facility from the mid 1980's to the present day. And so last but not least John Evans (Durham Univers ity) rounded off with a tour de force considering it was the penultimate lecture of the entire three-day conference, he applauded the remaining audience for their "fortitude" in staying the course. John's eloquent discussion of the phase transitions that ZrV2O7 undergoes on cooling from a high temperature simple cubic phase via an incommensurately modulated phase to a room temperature 3 x 3 x 3 cubic superstructure were linked to the negative thermal expansion behaviour of the material. Laboratory based X-ray equipment and powder neutron diffraction were the mainstay of John's variable temperature investigation, similar he noted to that used by the other presenters whom we had the pleasure of listening to. Thanks also go to the organisers of the BCA conference Georgina Rosair and Chick Wilson for arranging a stimulating three days of scientific discussion and exchange of ideas. If this has whet your appetite for more you might be pleased to make a note in your d iary of a follow up workshop on 21st June organised by Dave Taylor and Jeremy Cockcroft at Birkbeck College on non-ambient diffraction techniques. Jim Kelly Industrial Group Pharmaceutical Sessions Mon 3rd - Wed 5th April 2000 Monday - Pharmaceuticals and Alun Bowen Lecture The meeting was opene d by Steve Norval, the chairman of the BCAIG and was subsequently run by the session organiser, Philip Lake. The lectures were on the theme of crystallisation methodology and practice. Stephen Byrn (Purdue University) chair-elect of the Pharmaceutical Sciences Advisory Committee to the FDA presented the Alun Bowen Industrial lecture on 'Crystallisation of Pharmaceuticals'. Crystallisation of pharmaceuticals is a critical step in a drugs development and the solid state form, together with t he method of synthesis, is the intellectual property of the discovering party. The lecture represented an excellent overview of polymorphism and crystallisation. Stephen discussed the recent problem that Abbott experienced with Ritonavir, where precipitation of a less soluble form forced a product recall, in the context of polymorph screening and the ICH polymorph decision tree. He covered crystallisation monitoring, crystallisation of amorphous systems, finding the most stable form using energy/tem perature diagrams, effects of impurities on crystallisation, salt selection, factors influencing particle size and even 'factors' such as site specific solid-state stability of drugs. Three non-solvated polymorphic systems, ROY (and the 4-methyl analogue) and methyl nitroacetanilide (WAY), were studied with the aid of energy temperature diagrams. 'Tunnel' hydrates of caffeine, theophylline and thiamine hydrochloride were also cited. Christian Lehmann (Max Plank Institute) described a multi- well crystallisation plate for simultaneous crystallisation and subsequent examination using a micro-diffractometer and sample translation stage (GADDS). Temperature controlled evaporative or vapour diffusion crystallisation is possible. Para-methyl chalcone, a system of several polymorphs, was cited as the example used to evaluate the equipment. Graeme White (Heriot-Watt) described an on-line analytical approach to monitoring and understanding batch crystallisation of organic speciality c hemicals. The 'Chemicals Behaving Badly' project was described. On-line techniques discussed included IR, ultra-sonic spectroscopy, UV, laser Doppler anemometry as well as XRD. Understanding growth and nucleation kinetics is key to the project and consideration of scale-up factors such as hydrodynamics and solid-liquid interactions was discussed. Urea and glutamic acid were sited as examples. The afternoon sessions comprised a series of plenary lectures on the theme of refinement. Peter Erk (BASF) provided an excellent lecture on behalf of the industrial group. Modelling of structures and the simulation and predictions of properties has recently gained momentum. The relationship between structure and solid-state properties eg. Crystal form, solubility, habit, density was discussed using examples from the organic pigment industry (copper phthalocyanine, diphenyl perylene. The need for a high degree of geometric and thermodynamic accuracy was stressed if any computational predictive app roach is to be successful. Robert Lancaster Tuesday - Pharmaceuticals Norman Shankland (Strathclyde University) gave an excellent overview of the methods available for growing crystals of suitable size for X-ray and neutron diffraction studies; this focussed on the use of slow evaporation techniques, non-ambient extremes, and the problems encountered when crystallising natural products. Nick Blag den (UMIST) described how solvents and additives could be used to control the formation of specific polymorphs by inhibiting progression towards the thermodynamically most stable form and how crystallisation conditions could be designed to yield a predicted polymorph. Finally, Steef Boeringter (Nijmegan University) outlined the current state-of-the-art in the area of crystal habit prediction highlighting that although it is possible to calculate morphologies the incorporation of growth conditions, s uch as solvent, temperature and kinetics, is highly desirable. Clare Anderton Controlled Environment WorkshopNon Ambient XRD Workshop, 21st June 2000 The summer solstice was celebrated in the school of crystallography at Birkbeck college with a one day controlled environment workshop jointly chaired by Dave Taylor (e-mail: [email protected]) & Jeremy Cockcroft (e-mail: [email protected]). The morning sessions on high and low temperature X-ray diffraction techniques (HTXRD) concentrated on instrumentation & environmental stages (Martin Vickers) while the afternoon dealt with data handling (Andrew Jupe) & use of synchrotron/neutron sources. The programme was delivered completely electronically via a superb MS PowerPoint presentation & internet web-pages, the programme was projected onto a screen in the relaxed atm osphere of the Glaxo-Wellcome multi-media seminar room located in the basement of the school of crystallography. The morning opened with the factors influencing the development of HTXRD which include sources & x-ray optics, solid state electronics particularly detectors & the ease of automation through computers & software, all of which were introduced to study in-situ dynamic processes. Possible reasons for wishing to employ the techniques can be broadly divided between chemical: oxida tion, reduction, corrosion, hydration, phase transitions, reaction kinetics and physical: crystallite size, thermal expansion, strain, reorientation, structure analysis. The sessions were introduced by the chair(s) alternatively in a lively jovial manner and they encouraged active audience participation and involvement (although perhaps not by as much as had been hoped by the organisers) by discussion & question prompt. The use of HTXRD was compared with a range of complementary methods : differential scanning calorimetry, thermogravimetric & thermo-mechanical analysis, mass spectrometry & optical investigations ‘all which identify the temperature at which a change occurs without phase identification’. Needless to say a wide choice of settings are possible for a particular experiment and compromise can often be reduced to speed versus cost, dynamic studies inevitably require rapid data acquisition which in turn can be translated into high photon flux, fast effic ient detectors and some special optics including parabolic focussing mirrors. In summary sealed tube can be used at <3kV whereas rotating anodes at <18kV with various elemental anodes, in comparison a synchrotron with a white beam has ~1012 x intensity of a conventional laboratory source. Moving onto detectors Dave noted that scintillation / proportional detectors were slow but offered good resolution with pulse height discrimination. While on the other hand solid state en ergy dispersive (EDD for short) devices are stationary, require liquid N2 (which is expensive) and invariably have a long dead time t. We were also reminded that position sensitive detectors (PSD) provided fast data acquisition with a 1D wire. But for state of the art it was all down to 2D image plate Charge Coupled Devices (CCD’s similar to those in digital cameras) despite being very fast they are also expensive. Rounding off with a few tips "…don ’t run a Cu tube above 45kV (it’s inefficient) & remember that for Imax with a conventional diffractometer remove the secondary Soller slit" On the topic of heating methods the advantages of using ribbon heaters over induction methods was pointed out, this was well illustrated with graphics and a specific example presented in a poster (1998 Denver – Andrew Paysant, ORNL, USA) that people could catch over coffee. Temperature gradients associated with the stri p seemed to be the main problem with reaction of the strip and peaks from strips also causing problems. A microwave stage in development by Andrew Harrison, Edinburgh (reported in Crystallography News no. 73 June 2000 p. 45) was shown to be used for solid state reactions & sintering processes. Other systems included Lasers, Induction & Quartz lamps all very much in development / research & not yet on the market. Problems with control invariably included overshoot, ramp rate & mainten ance of pre-set temperature. For those of us new to it PID temperature control (Proportional band, Integral time constant, Derivative time constant) is the smart way of overcoming some of these problems. The other major concern is validation & calibration of the attained temperature by comparison with the ITS-90 fixed points, some useful phase transitions are given below (these & others are available in an updated list on the BCA website):
Moving to the other extreme Jeremy stressed the advantages of collecting data at low temperature "are principally to reduce the thermal scatter and as a result improve the high angle data for materials of pharmaceutical interest. Two different ways of achieving this are by using either a cryostream or cryostat. However before collecting data decide the object of the experiment, a different sample geometry may be required for structure refinement, e.g. in the case of ibuprofen (which stro ngly shows preferred orientation when measured on a Bragg-Brentano diffractometer) you may require a capillary geometry". Capillaries are needless to say the best sample holders for low temperature manipulation. Illustrations for the talk were taken from the in house powder diffraction web course, an example (cryostat) web address used is http://pd.cryst.bbk.ac.uk/pd/web-ad/lowtemp.htm. On the topic of environmental stages the Bard (1564-1616) himself would have been proud of the midsummer night&rsq uo;s dream as presented by Dave, the comedy not lost on the well-versed audience:
Over a sumptuous poached salmon lunch participants were given a guided tour of the industrial materials group X-ray facilities by Martin Vickers who said of the tour "We showed everybody the helium cryostat (1.6K) & how we had adapted it to laboratory powder diffraction. The kit we use in house is based on the STOE Stadi-P transmission machine. We also got to see the Linkam high-temperature arrangement on the SIEMENS D500 reflection diffractometer". Previously the theoretical bu llet points concerning trade off between intensity (counts per second under the unfavourable conditions) & resolution (peak width) had been emphasised but were brought in to sharp focus during a practical demonstration by Martin (e-mail: [email protected].). While on the subject of data handling Andrew Jupe (e-mail: [email protected]) remarked that "If you want to present bulk graphical data the best way to do this is with a 2D contour plot routine, because it shows th e crucial details. The freely distributed FORTRAN graphics library PGPLOT is easy to use & well equipped to create this type of data plot ". Contributions from the audience included a presentation by Chris Frampton on the importance of combined PXRD and humidity studies and an illustration by Clare Anderton on a problem pharmaceutical powder which gave a different PXRD pattern 18 months after the initial one was taken. The longest day of the year rounded off with a brief discussion of s ynchrotron & neutron sources. Jim Kelly BCA IG STRUCTURAL MATERIALS WORKSHOPRESIDUAL STRESS IN CONTEXT. HOW TO CHOOSE A TECHNIQUE12th September 2000, ManchesterThe meeting took place in the Manchester Materials Science Centre. Unfortunately, the severe fuel shortage in the Northwest, and prob lems with trains meant that a couple of people weren't able to make it to Manchester. The meeting started with an introduction to the Manchester Materials Science Centre from Judith Shackleton. After welcoming the delegates to the meeting, Judith presented an outline of the facilities available in the Centre and emphasised the wide range of equipment now in place, including the recently installed Bruker D8 with XYZ stage, laser alignment and 2D detector for residual stress measuremen t. Other methods for residual stress measurement based on magnetic and Raman techniques were also described. Judith concluded by mentioning the Network for Strain Measurement by Neutron and Synchrotron Techniques, which has been set up to help new users to gain access to major facilities Phil Holdway from DERA Farnborough introduced X-ray diffraction methods. This is a surface technique, confined to the top 100 or so microns, even when successive layers of material are removed by El ectro-polishing. Phil went on to describe the many different parameters which influence X-ray residual stress measurements (aside form the principal problems of obtaining enough intensity and dealing with heavy, awkward shaped samples!) including, grain size, texture, stress gradients, sheer stresses, and instrument misalignments. The relative merits of laboratory based and portable instruments were also considered. A great many accessories are now available for laboratory instruments, for example mirrors and poly-capillaries. However, lab instruments are limited in the size of sample which they can accept, it's a bit difficult to get an engine block into one. Phil illustrated his talk by describing some examples including some stress measurements around cold expanded holes. Jerry Lord form NPL was next up speaking about Hole Drilling. This is a widely used technique and work on virtually anything which you can drill a hole in. Jerry started by outlining the basics an d some of the sources of errors. A new ASTM standard has recently become available. Jerry went on to talk about the merits and disadvantages of hole drilling and finished off discussing some recent developments including taper hole drilling, modelling and data analysis, (e.g. non-uniform stress fields) and new applications such as thin coatings and thermal barrier coatings. Mike Fitzpatrick from the Open University gave the next presentation on Neutron Diffraction methods. The abilit y of neutrons to penetrate several centimetres into a material is a unique property of the technique, although the sample has to be taken to a suitable source rather than the other way round. It's definitely not portable! Although the technique is expensive compared to laboratory x-rays, it allows the non-destructive determination of residual stresses in large components not available by any other method. Primarily neutron measurements are used to validate other techniques, for example finite elemen t calculations. Mike spoke about the differences between reactor sources and pulse sources and discussed about advances in methods for measuring surface stresses. Mike concluded that although the cost of neutron measurements are very high, a new instrument, currently being built should enable data collection times (and hence the cost) to be reduced. The next presentation was by Andrzje Wojtas from AST on the portable stress measuring equipment. This was set up in the basement. A bri ef outline of the equipment was given along with a demo (no x-rays were being produced), showing how the equipment can be configured to operate on almost any sample. No need to cut it up! An excellent buffet lunch (wine supplied by Philips) was provided, during which it was possible to see a demo of the new stress software from Philips Analytical. Having been suitably refreshed, it was now the turn of Angus Wilkinson from the Materials Department at Oxford to speak on the u se of EBSD (Electron Back-Scattered Diffraction) to investigate strains in semiconductor devices. Angus explained that defects such as dislocations and the presence of residual stresses could either be beneficial or detrimental to the performance of the device. A brief explanation of the EBSD technique was followed by an example of texture measurement normally associated with this technique. Angus then went on to talk about both plastic and elastic strains, the former giving rise to a reduction in p attern quality and the latter shifts in Kikuchi line position or zone axis. Some recent work on SiGe on Si substrate was used as an example. Phil Withers from Manchester Materials Science Centre talked about the use of synchrotron x-rays to measure residual stresses. These x-rays can have path lengths in materials such as Aluminium of 5 - 100 mm. In addition they are very much higher intensity which allows fast data collection. Phil listed a number of examples of recent work such as machining, shot peening, and friction stir welding. A case study on welding distortion was then presented showing the rapid data collection (4000 points in 8 hrs), that can be used to map strain. These measurements could be used to optimise the processing parameters and validate weld modelling. The last speaker was Brian Shaw from Newcastle University who talked about magnetic techniques, (Barkhausen noise). Brian showed the relationship between hardness/residual stress and the leve l of BN. This was followed by the benefits and limitations and its application to the investigation of grinding damage in gear steels. On of the principal advantages is that the equipment is easily portable and can be used on very large components, quote "You don't have to cut it up to prove that it was OK". Examples such as industrial gear manufacture, burn detection for gear quality control and gear failure investigation were then presented. Brian finished off with a demo of the kit and how calibr ation might be made. A lively discussion period, with a good exchange of ideas, hints and tips ended the meeting in which a number of topics were raised including ideas for a future meeting, data collection issues and standards. Judith closed the meeting, thanking those who attended. A tour of the x-ray diffraction facilities took place for those who wished to stay. Overall this was a very good meeting, with a good attendance despite the difficulties and uncertainty for those comin g by car. Phil Holdway & Judith Shackleton |
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Industrial Group of the BCA