Using x-ray powder diffraction as a cost effective tool in cement industry

Rietveld Analysis of cement diffraction patterns have been used to determined the composition of cement since John Taylor's pioneering work in the 1990's. Since then many workers have used this techniques to analyse cement and supplementary cementitious materials and their hydration products, both for research and production control purposes. Nevertheless there are a number of factors, including the amorphous content of the cement and relative proportion of mineral polymorphs present in the initial clinker, whose impact on analysis are still not completely understood. X-ray powder diffraction beamlines from the Brazilian Synchrotron Light Laboratory (LNLS) and the Australian Synchrotron, which produce more intensity and better resolution than normal x-ray diffraction sources, were used to investigate cement diffraction patterns and the hydration products of a range of cement pastes cured for up to 28 days. This study highlights the information that can be obtained from X-ray diffraction analysis for controlling and optimizing cement production and concrete durability.

Stoichiometric changes in lithium conducting materials based on Li1+xAlxTi2−x(PO4)3: impedance, X-ray and NMR studies

The lithium fast-ion conductor, Li_1+xAl_xTi_2−x(PO₄)₃ (LATP) has been modified via changes in stoichiometry during the processing steps. The resultant changes have been followed using ²⁷Al MAS NMR, X-ray powder diffraction and impedance spectroscopy. The most important changes were those of the form Li_1.3+4yAl_0.3Ti_1.7−y(PO₄)₃. It was possible to remove the AlPO₄ phase (both tridymite and berlinite polymorphs), as monitored by X-ray diffractograms and ²⁷Al NMR spectra. Consequently, these changes appear to result in increased grain boundary conductivity of the LATP material.

Towards elucidating microscopic structural changes in Li-ion conductors Li1+yTi2–yAly[PO4 ]3 and Li1+yTi2–yAly[PO4 ]3–x [MO4 ]x(M=V and Nb) : X-ray and27Al and31P NMR studies

A combination of X-ray powder diffraction (XRD) and nuclear magnetic resonance (NMR) studies has demonstrated that attempted substitutions of Al, V and Nb into the framework of LiTi₂(PO₄)₃ yield several impurity phases in addition to direct substitutions of Al into Ti and V, Nb into P sites. Direct substitutions were confirmed by changes in the unit cell dimensions as indicated by the peak shifts observed in the X-ray diffractographs and by analyses of the ²⁷Al and ³¹P magic angle spinning (MAS) spectra. A major impurity phase was identified as AlPO₄ (found in at least two polymorphs) and the amount present increases with increasing Al additions. The formation of AlPO₄ appeared to be enhanced by further V but suppressed by Nb substitution. These results suggest that the presence of AlPO₄ , together with the non-stoichiometric modified LTP, may be the cause for the observed densification of this material upon sintering and the increased ionic conductivity.

High-pressure structural transitions of Sc2O3 by X-ray diffraction, raman spectra, and ab initio calculations

The high-pressure behavior of scandium oxide (Sc₂O₃) has been investigated by angle-dispersive synchrotron powder X-ray diffraction and Raman spectroscopy techniques in a diamond anvil cell up to 46.2 and 42 GPa, respectively. An irreversible structural transformation of Sc₂O₃ from the cubic phase to a monoclinic high-pressure phase was observed at 36 GPa. Subsequent ab initio calculations for Sc₂O₃ predicted the phase transition from the cubic to monoclinic phase but at a much lower pressure. The same calculations predicted a second phase transition at 77 GPa from the monoclinic to hexagonal phase.

An in situ method for the study of strain broadening using synchrotron X-ray diffraction

A tensonometer for stretching metal foils has been constructed for the study of strain broadening in X-ray diffraction line profiles. This device, which is designed for use on powder diffractometers and was tested on Station 2.3 at Daresbury Laboratory, allows in situ measurements to be performed on samples under stress. It can be used for data collection in either transmission or reflection modes using either symmetric or asymmetric diffraction geometries. As a test case, measurements were carried out on an 18 µm-thick copper foil experiencing strain levels of up to 5% using both symmetric reflection and symmetric transmission diffraction. All the diffraction profiles displayed peak broadening and asymmetry which increased with strain. The measured profiles were analysed by the fundamental-parameters approach using the TOPAS peak-fitting software. All the observed broadened profiles were modelled by convoluting a refineable diffraction profile, representing the dislocation and crystallite size broadening, with a fixed instrumental profile predetermined using high-quality LaB6 reference powder. The deconvolution process yielded `pure' sample integral breadths and asymmetry results which displayed a strong dependence on applied strain and increased almost linearly with applied strain. Assuming crystallite size broadening in combination with dislocation broadening arising from f.c.c. a/2〈110〉{111} dislocations, the variation of mechanical property with strain has been extracted. The observation of both peak asymmetry and broadening has been interpreted as a manifestation of a cellular structure with cell walls and cell interiors possessing high and low dislocation densities.

X-ray diffraction line broadening from gold and platinum thin films

X-ray diffraction line profile analysis has been used to study the microstructure of (Ill) oriented gold and platinum thin films deposited by thermal evaporation and DC magnetron sputtering. In addition to crystallite size broadening, the profiles from these films displayed broadening arising from dislocations. A parallel investigation, using transmission electron microscopy (TEM) was undertaken to study the nature of dislocations formed, and to provide information on the dimensions of the crystallite columns in the films. X-ray data were collected at room temperature to determine the anisotropy of the broadening with (hkl), using a Siemens D5000 powder diffractometer (CuKa radiation) and two high-resolution synchrotron instruments (BM 16 at the ESRF [A=0.35A] and station 2.3 at the Daresbury laboratory. Two approaches to instrument deconvolution were investigated; Fourier deconvolution and fundamental parameters profile fitting, using Lab6 as a reference material to determine the instrument profile function. After removal of the crystallite size broadening contribution from the measured integral breadths, the residual microstrain broadening was modelled assuming dislocations based on a FCC a/2<110>{ Ill} slip system. The results of the X-ray analysis agreed with dark field TEM micrographs, which showed that many of the crystallites contained dislocations of mixed character (screw- edge).

In-situ studies of X-ray diffraction line profiles from strained copper foils

The development of an in-situ tensometer is described along with preliminary results of x-ray line profiles from copper foils under tensile stress. The tensometer was designed and constructed on the high resolution diffraction instrument, Station 2.3 at the synchrotron radiation source (SRS) Daresbury Laboratory, and is capable of collecting data in either symmetric or asymmetric geometry including transmission and reflection modes. Experiments were carried out using 18 J..Lm thick copper foil up to strain levels of 5 % using both symmetric reflection and symmetric transmission diffraction. All profiles displayed diffraction broadening and asymmetry which increased with strain. In addition, the asymmetry observed in symmetric transmission was associated with extended tails on the low angle side of the profiles, but in symmetric reflection data the opposite asymmetry was observed. In the analysis, the measured profiles were fitted using the software TOPAS, a fundamental parameters approach to profile fitting. The instrumental profile function was characterised and modelled using annealed LaB6 powder. The diffraction broadening was then determined by refining the convolution of a Voigt function, an asymmetric exponential function and a fixed instrument function to reproduce the observed broadened profiles. The integral breadth and asymmetry results display a strong order dependence and increase almost linearly with strain. The results were interpreted by assuming crystallite size broadening in combination with dislocation broadening arising from fcc a/2( 110) {Ill } dislocations.