Paul Barnes

Professor in Applied Crystallography

Direct Telephone: London (020)-7631-6817
FAX: London (020)-7631-6803
Departmental Secretary: London (020)-7631-6800
College Telephone: London (020)-7631-6000
(UK international code is 44)

Here is an untypical picture of me in 1995; I am almost teetotal, but found a rare excuse here to celebrate!

Brief Academic CV

Scientific Interests

I call myself an applied crystallographer which means almost anything. My interests are X-ray and neutron diffraction (especially fast in-situ powder diffraction with synchrotron/neutron sources), computer simulation and a bit of electron microscopy; all applied to materials like zeolites, ceramics, cements, hydrates, particularly those with an industrial application.

Recent Research Highlights

  1. Simulation of Water and Hydrates
    this work started with one of the first attempts to write an algorithm in which each particle is dynamically and individually polarised through the ionic/dipolar/quadrupolar/octapolar field of its environment, and was applied (see Ref. 1 and illustration) to many fundamental properties of water and ice structure. These days the applications are more to inorganic hydrate systems (see topic 5).
  2. Synthesis and Structure of Ultramarine or Goodbye Lowenstein
    Our first real attempt to follow complex solid state high temperature syntheses (see Ref. 2) using in-situ time-resolved diffraction: The biggest surprise was that neutron diffraction and magic angle NMR both confirmed (see Ref. 2) that the Al,Si-ordering was random in striking contrast to the Lowenstein rule applied to an aluminosilicate with equal numbers of aluminiums and silicons.
  3. Polytypism and One-dimensional Disorder in Silicon Carbide
    Using a unique batch of large vapour-grown silicon carbide crystals, this has been studied in SiC by synchrotron X-ray topography (see Ref. 3) giving detailed spatial information on the phenomenon. A new variant, synchrotron edge-topography, illustrated with one example here, has been pioneered which provides depth-profiles on >100 crystals and a unique database of nearest neighbour relationships for polytypism and thin one-dimensionally disordered layers.
  4. Synthesis of Tetragonal/Monoclinic Zirconia
    This project was fuelled by interest in zirconia-based high performance ceramics and sponsored by Alcan Chemicals/MEL Co. In-situ studies (see Ref. 4) using X-ray diffraction (see illustration), Zr-EXAFS and neutron scattering, on the synthesis (from initial compounds or amorphous hydroxides) have provided a structural model of how the nuclei evolve during calcination. Also the complex relationship between the all important tetragonal to monoclinic transformation and synthesis parameters (heating/cooling rate, top temperature, heating time, initial pH) have been determined.
  5. The double cation valve in Ca/K-clinoptilolite-zeolite
    This project was sponsored by British Gas as part of a general study into the use of zeolites to separate impurities from natural gas. The partial ion-exchange of Ca2+ by K+ cations in clinoptilolite was chosen as a prototype project for study by synchrotron EXAFS and diffraction data but also, crucially, combined with computer-simulation as well. A new simulation exchange-annealing schedule has revealed an intriguing sequence in which the Ca-cations are hydrated away from the framework well into the main channel, exchanged by the K-cations which are then guided by the water molecules towards their future sites which project more and more from each side of the main channel as the water molecules are removed. The resulting constriction to the flow of gas molecules has been termed a double cation valve and is illustrated in the schematic. This forms part of an ongoing study (see Ref. 5) into the synthesis and behaviour of functional zeolites.
  6. In-situ studies on the hydration of cements
    Our understanding of the behaviour and mechanisms of cement hydration has been transformed (see Ref. 6) by means of fast in-situ diffraction studies on bulk cement hydrating systems, using synchrotron energy-dispersive and neutron diffraction. The temperature-product scenario for Portland cements up to 190°C, with and without autoclave conditions, has been resolved (see Ref. 6a-f) a fleeting (50 - 200 seconds) intermediate in the rapid hydration of tricalcium aluminate has been captured (see Ref. 6g) using the ESRF-synchrotron (see illustration); the time-dependent solid solution changes during the formation of ettringite (a calcium sulpho-aluminate hydrate) have been measured and explained (see Ref. 6h) and the high temperature conversion of calcium aluminate (high alumina) cements has been elucidated (see Ref. 6i,j), again involving the temporary appearance of an intermediate hydrate. The work is sponsored by several companies, notably Schlumberger C.R.Ltd., Castle Cement, and Cementa AB.
  7. In-situ studies on the synthesis of zeolites
    It is our belief that we conducted the first in-situ diffraction studies on the hydrothermal synthesis of zeolites using either neutron or synchrotron sources (see Ref. 7). This has been particularly useful in the case of synthesis under autoclave conditions where conventional analysis, involving "before and after" methods, gives misleading results.
  8. And many more ......
    Basically if it diffracts, we'll try to look at it; if it doesn't diffract we might even still look at it. Our mission is to understand the structure and kinetics of functional materials; how they behave during synthesis or during performance. So if the price is right we'll look at anything. In our time we have occasion to also study for example bulk rock analysis (see Fig. and Ref. 8a-b), drug polymorphism (see Ref. 8c-d), rubber-based materials (see Ref. 8e), micro-mechanical structures (see Figure and Ref. 8f), We are concerned with the general application (see Ref. 8f-l) of all applied crystallography techniques to modern materials.

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