High solubility of hydrogen in the beta-phase of the alloy is preventing hydrogen from precipitating into TiH. All implants, even those lacking TiH at the surface, were enriched with hydrogen. In all implants, hydrogen concentration was within the normative limit of 130 ppm.

The microabsorption of X-rays diffracted from planar granular powder specimens is caused by bulk porosity and surface roughness of the material. Methods of stochastic geometry are used to describe the geometrical characteristics of powder by volume fraction, mean chord length of powder particles, and density-density correlation function (covariance). Towards the surface of the specimen, the volume fraction of powder particles decays continuously from the bulk value to zero. Within the framework of the kinematic theory, analytical expressions are derived for both bulk and surface contributions to the microabsorption of symmetrically diffracted X-rays in randomly packed powder specimens with particles of irregular shape. Previous theoretical estimates and empirical formulae are discussed as limiting cases of the present more general results. IntroductionThe granular structure of powder specimens causes an angle-dependent contribution to the absorption of the incident and diffracted beams. This effect has been studied experimentally by de Wolff (1956) and by Suortti (1972; referred to as S) who measured the reduction of specimen fluorescence radiation due to granularity. Trucano & Batterman (1970) investigated the effect of porosity of amorphous powders, analysing diffuse scattering. Though the experimental results differ in some details, the intensity reduction due to granularity is described by a constant term proportional to volume fraction of pores, linear absorption coefficient, and mean chord length of particles, whereas the contribution of surface roughness is a smooth function of scattering angle. To our knowledge, the paper of S essentially represents the actual level of understanding of the effect of microabsorption.Previous theoretical work on X-ray absorption in powder specimens suffers from a fragmentary description of porosity and surface roughness. Harrison & Paskin (1964) analysed the case of an isolated cubic pore and estimated correction terms for a dilutely porous solid. Otto (1984) calculated numerically the absorption of a special two-dimensional 0108-7673/87/030401-05501.50 computer model, in which the grains of the powder are simulated by circles of equal diameter. He was able to reproduce the experimental results of S qualitatively. On the other hand, a quantitative correction of X-ray scattering from granular specimens is desirable in certain cases (e.g. Valvoda & Capcovfi, 1984).For these reasons, a refined analytical treatment of porosity and surface roughness seems to be useful.In the present paper, we calculate the kinematical X-ray power reflected from a plane powder sample. The powder sample is described by the very general and variable three-dimensional Boolean model that has been developed within the framework of stochastic geometry (Stoyan, 1979;Stoyan, Kendall & Mecke, 1986). Contrary to the models of Harrison & Paskin (1964) and Otto (1984), our theory is not restricted to powder particles of certain regular shape. We derive analytical expressions for the contribution of...

The violet pigment methylbenzimidazolonodioxazine, C22H12Cl2N6O4 (systematic name: 6,14-dichloro-3,11-dimethyl-1,3,9,11-tetrahydro-5,13-dioxa-7,15-diazadiimidazo-[4,5-b:4',5'-m]pentacene-2,10-dione), shows an X-ray powder diagram consisting of only ca 12 broad peaks. Indexing was not possible. The structure was solved by global lattice energy minimizations. The program CRYSCA [Schmidt & Kalkhof (1999), CRYSCA. Clariant GmbH, Pigments Research, Frankfurt am Main, Germany] was used to predict the possible crystal structures in different space groups. By comparing simulated and experimental powder diagrams, the correct structure was identified among the predicted structures. Owing to the low quality of the experimental powder diagram the Rietveld refinements gave no distinctive results and it was difficult to prove the correctness of the crystal structure. Finally, the structure was confirmed to be correct by refining the crystal structure of an isostructural mixed crystal having a better X-ray powder diagram. The compound crystallizes in P1, Z=1. The crystal structure consists of a very dense packing of molecules, which are connected by hydrogen bridges of the type N-H...O=C. This packing explains the observed insolubility. The work shows that crystal structures of molecular compounds may be solved by lattice energy minimization from diffraction data of limited quality, even when indexing is not possible.

Separation of size and strain effects on diffraction line profiles has been studied in a round robin involving laboratory instruments and synchrotron radiation beamlines operating with different radiation, optics, detectors and experimental configurations. The studied sample, an extensively ball milled iron alloy powder, provides an ideal test case, as domain size broadening and strain broadening are of comparable size.

The absorption of X-rays in a heterogeneous material depends on the linear absorption coefficients and volume fractions of the components, and on die geometrical peculiarities of their distribution. The latter is called the microabsorption effect, it can be separated into a bulk and a surface contribution. Within the framework of a well-defined stochastic structure model, the bulk contribution to the microabsorption is calculated for arbitrary random multiphase systems in terms of dependence on volume fractions and mean chord lengths of particles. Expressions are derived which are suitable for eliminating the experimental errors of scattering intensities caused by the bulk contribution of microabsorption.If only one wavelengtii of radiation is used, the mean chord lengths of the phases of the sample must be determined by other experimental techniques. A method is proposed to overcome this difficulty by using two or more wavelengths of radiation; this correction procedure works without the knowledge of the particle sizes of the phases.