Powder X-ray diffraction (XRD) is an established method for qualitative characterization of ceramic materials. Accurate quantitative information can be extracted from XRD data by a data processing method named Rietveld refinement (RR). However, profound knowledge in crystallography is required in order to master RR, which might be one reason why the method has not been adopted more widely for routine tasks in the field of bioceramics analysis. The program Profex[1], which is a graphical user interface for the RR kernel BGMN[2], has proven to be a valuable tool for phase analysis of bioceramics. Both programs are available under a liberal open-source license for all major operating systems and can be used for academic and commercial purpose without restrictions. Core features for general application were recently published[1]. Profex also has some advanced features of particular interest for the characterization of biomaterials, owing to its provenance from a bioceramics research environment. The distribution package includes phase templates for all major bioceramics such as Ca-phosphates, -sulfates, and -carbonates, all common ZrO2, Al2O3, and TiO2 polymorphs, and a variety of apatite phases, just to name a few. Traditionally, phase identification and quantification by RR are conducted manually, resulting in a high dependence on the operator’s skills and diligence. Profex’s refinement presets eliminate user dependence and allow for fully or semi-automatic refinements. For example, the phase purity of β-TCP, as specified in ASTM F 1088 and ISO 13175-3, can be determined automatically by quantifying β-CPP and HA contaminations, once a corresponding refinement preset has been created. User input thus can be reduced to non-critical actions like loading the raw data file, applying the preset, and launching the refinement. Results are presented in tabular form with realistic estimated standard deviations computed by BGMN’s sophisticated error propagation algorithms. Phase quantities below the detection limit are highlighted and can easily be removed from the refinement in order to avoid accumulation of artifact phase quantities. Quantification of amorphous contents by the internal standard method is supported by automatic correction of refined phase quantities for the internal standard quantity.
Despite a large number of convenience features and a workflow implementation focusing on efficiency, Profex does not restrict the user in any way. It gives access to BGMN’s flexible scripting features, and thus remains useful for advanced applications including: structure refinements, texture and micro-strain analyses, refinement of stacking faults, and many more. But its automatic single or batch refinement features (eliminating user dependence) enable its application in a validated XRD phase quantification procedure, as typically required for research and quality control of ceramic implants for surgical application.
References:
[1] Doebelin, N. and R. Kleeberg, Profex: a graphical user interface for the Rietveld refinement program BGMN. Journal of Applied Crystallography, 2015. 48(5).
[2] Bergmann, J., P. Friedel, and R. Kleeberg, BGMN - a new fundamental parameters based Rietveld program for laboratory X-ray sources, it's use in quantitative analysis and structure investigations. Commission on Powder Diffraction (IUCr). Newsletter, 1998. 20: p. 5-8.