Papers by Keyword: Diffractometer

Abstract: Lead hydroxyapatite (PbHAP, chemical formula Pb₁₀(PO₄)₆(OH)₂) has been synthesized by ceramic (solid-state reaction) and semi-ceramic (precipitation) methods. The samples were prepared through a solid-state reaction conducted at 830 °C for 60 hours, with the y values ranging from 0.95 to 1.00. We have developed and created the most efficient preparation methods. The well-known technique was used - semi-ceramic (precipitation) deposition of lead and hydroxyapatite. For this purpose, several advanced devices were used to obtain an accurate structural structure of lead hydroxyapatite compounds. It has been observed, as in the case of chemical synthesis, that the elements (lead, phosphorus, and oxygen) appear to be distributed homogeneously within the crystals, regardless of the method of composition, which indicates that the samples are homogeneous. More importantly, the "solid-state reaction" method favored a specific composition range, while the "precipitation" method performed well for other composition ranges. The above methods indicate an ideal method, according to the desired structure, that should be developed for lead hydroxyapatite, depending on its composition. This research aims to establish the first steps in developing a new method for preparing lead hydroxyapatite compounds with the desired properties to improve their purity and crystal structure for potential uses in the future.

Abstract: National Nuclear Energy Agency of Indonesia has several neutron beam instruments for materials science research. One of the instrument is Four Circle Diffractometer / Texture Diffractometer for study of crystal structure and texture measurement. Due to the instrument is fully occupied by many samples, the instruments has to be further developed in order to conduct experiment effectively and efficiently. For that reason, the instrument controller has been replaced with a new programmable controller that can handle all axis simultaneously. Since the controller has been replaced with the new one, a software for data acquisition and measurement also has been modified using a visual basic of programming language with an addition of function, i.e. an automatic measurement for either single-crystal or poly-crystal sample. The software calculates four peaks of Miller indices of the sample for determining the crystal position to be scanned. Then, the software performs the automatic measurement started from scanning the axis of θ-2θ, calculating the peak position by fitting the data obtained from sample diffraction data, then positioning the θ and 2θ axis to the peak position. Finally, the software performs the scanning of the π-χ axis for texture analysis, and save the experiment data into a certain format for the texture analysis software, i.e. Material Analysis Using Diffraction (MAUD).

Abstract: Most models based on continuum mechanics do not account for inhomogeneities at the micro-scale. This can be achieved by considering a representative volume of material and using (poly)crystal elasto-plastic deformation theory to model the effects of grain morphology and crystallographic orientation. In this way, the relationship between the macroscopic stress state and the stress state at the grain level can be investigated in detail. In addition, this approach enables the determination of the inhomogeneous fields of plastic strain, the identification of regions of localised plasticity (persistent slip bands), grain level shakedown, and the prediction of fatigue crack initiation using energy dissipation at the micro-scale. Elastic anisotropy is known to promote earlier onset of yielding, and to increase the magnitude of intergranular residual stresses. The effect of hardening behaviour of different slip systems on intergranular residual stresses is more subtle, as discussed in the text. The present study focuses on the analysis average intergranular residual strains and stresses that arise within the polycrystal aggregate following the application of single or cyclic external loading. These residual strains can also be evaluated experimentally using diffraction of penetrating radiation, e.g. neutrons or high energy X-rays, allowing comparisons with the model predictions to be made.

Abstract: The sin2ψ technique for near-surface and bulk stress evaluation is frequently considered to be the method of reference, largely due to the historical reason of being established early on in the development of experimental study of residual stress, and due to the widespread availability of laboratory X-ray facilities equipped with goniometers allowing ψ-tilting to be carried out. In recent years other diffraction-based techniques of residual strain and residual stress evaluation have been developed, some of them based at large facilities such as synchrotrons, neutron reactors or spallation sources, and others becoming available in the laboratory setting. It is therefore perhaps relevant and timely to review the strengths and shortcomings of the sin2ψ technique in today’s context. In the present study this task is addressed through the use of polycrystal elasto-plastic modelling that allows the determination of equivalent average elastic lattice strains following complex deformation history, and by post-processing of the model results in order to extract the parameters measurable in diffraction experiments. In particular, it is possible to extract the simulated strain values that would be measured at different tilt angles, and to build a family of sin2ψ plots for different reflections. It then becomes possible to assess the degree to which the hypotheses underpinning the principle of this method are enforced or violated; to select the most suitable reflections; and to discuss how the method could be improved or varied to provide more reliable residual stress measurement procedures.