Abstract
A conceptual design for a handheld X-ray diffraction (HHXRD) instrument is proposed. Central to the design is the application of energy-dispersive XRD (EDXRD) in a back-reflection geometry. This technique brings unique advantages which enable a handheld instrument format, most notably, insensitivity to sample morphology and to the precise sample position relative to the instrument. For fine-grained samples, including many geological specimens and the majority of common alloys, these characteristics negate sample preparation requirements. A prototype HHXRD device has been developed by minor modification of a handheld X-ray fluorescence instrument, and the performance of the prototype has been tested with samples relevant to mining/quarrying and with an extensive range of metal samples. It is shown, for example, that the mineralogical composition of iron-ore samples can be approximately quantified. In metals analysis, identification and quantification of the major phases have been demonstrated, along with extraction of lattice parameters. Texture analysis is also possible and a simple example for a phosphor bronze sample is presented. Instrument formats other than handheld are possible and online process control in metals production is a promising area. The prototype instrument requires extended measurement times but it is argued that a purpose-designed instrument can achieve data-acquisition times below one minute. HHXRD based on back-reflection EDXRD is limited by the low resolution of diffraction peaks and interference by overlapping fluorescence peaks and, for these reasons, cannot serve as a general-purpose XRD tool. However, the advantages of in situ, nondestructive and rapid measurement, tolerance of irregular surfaces, and no sample preparation requirement in many cases are potentially transformative. For targeted applications in which the analysis meets commercially relevant performance criteria, HHXRD could become the method of choice through sheer speed and convenience.
Highlights
Energy-dispersive X-ray diffraction (EDXRD) in a backreflection geometry is uniquely insensitive to sample morphology and to the precise distance between instrument and sample (Hansford, 2011, 2013; Hansford et al, 2014, 2017)
Iron ore Eleven iron-ore samples from working mines were used to test the ability of the prototype handheld XRD (HHXRD) instrument to
The much lower excitation voltages required by the back-reflection EDXRD technique relative to XRF applications, up to $10 kV, means that 400 mA is achievable given the 4–5 W X-ray tubes commonly specified in modern handheld XRF devices. (The use of lower X-ray energies for EDXRD measurements means that the radiation shielding employed in handheld X-ray fluorescence (HHXRF) devices is expected to be effective in an HHXRD instrument.) Exploiting these three changes would bring the 2.5 h acquisition time down to $30 s
Summary
Energy-dispersive X-ray diffraction (EDXRD) in a backreflection geometry is uniquely insensitive to sample morphology and to the precise distance between instrument and sample (Hansford, 2011, 2013; Hansford et al, 2014, 2017). The potential to develop a handheld XRD (HHXRD) instrument based on back-reflection EDXRD is explored in this paper. The majority of EDXRD experiments use synchrotron radiation to access high flux at high energies, but some laboratory instruments have been developed to take advantage of the static geometry (Dicken et al, 2015; O’Dwyer et al, 2014; Garrity et al, 2007). Application of EDXRD at high angles in a reflecting geometry is much less common (Bjeoumikhov et al, 2005; Sun et al, 2007) because of greater overlap with XRF peaks
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