Determination of Shell Thickness of Spherical Core-Shell Ni_xMn_1-x(OH)₂Particles via Absorption Calculations of X-Ray Diffraction Patterns

Abstract

Two core-shell materials were made in a continuously stirred tank reactor, one with a Ni(OH)2 core and a Ni1/2Mn1/2(OH)2 shell and the other with a Ni1/2Mn1/2(OH)2 core and a Ni0.17Mn0.83(OH)2 shell. X-ray diffraction measurements (Cu Kα radiation) of the core-shell materials were compared to reference materials which were physical mixtures with the same overall composition. The smaller core peaks in the XRD patterns of the core-shell materials were attributed to absorption of X-rays due primarily to the high manganese contents of the shells. Calculations were performed assuming spherical particles of radius matching results from SEM/EDS measurements. For a 5.5 μm radius particle with a Ni(OH)2 core, the shell thickness was calculated from XRD patterns to be 0.47 ± 0.03 μm. For a 7.9 μm particle of the material with the Ni1/2Mn1/2(OH)2 core, the shell was determined to be 1.77 ± 0.15 μm thick. Both these results were found to agree well with the overall composition of the samples as determined by elemental analysis and with spatial EDS measurements. This X-ray absorption modeling technique provides an experimentally simple way to measure the thickness of micron scale shell coatings while sampling all particles, unlike methods such as EDS.