Electron probe microanalysis phase composition

To find out the phase composition of the intermetallic compound layers formed, X-ray patterns were taken immediately from the polished surfaces of the Ni-Zn and Co-Zn cross-sections. Annealing and subsequent cooling the specimens of the type shown in Fig. 3.12b in most cases resulted in their rupture along the interface between the zinc phase and the intermetallic layers, with the latter remaining strongly adherent to nickel or cobalt plates. Therefore, preparation of the cross-sections for X-ray analysis presented no difficulties. These could readily made by successive grinding and polishing the plate surface until the Ni or Co phase was reached. In total, four layer sections parallel to the initial interface were analysed for each cross-section. Simultaneously, layer composition on each section of the interaction zone was determined by electron probe microanalysis. 

In the example above, the phases are such that the chemistry is unambiguous and the phase quantification could have been derived by normative calculation from bulk elemental analysis (XRF). This is not often the case, but it is frequently possible to establish the composition of each phase within a system via electron probe microanalysis or similar and conduct the inverse of a normative calculation to derive the bulk chemistry from the XRD QPA. This can then be compared with the results of a standards based technique such as XRF to obtain a measure of the accuracy of the XRD analysis. Examples of such calculations are given later in the sections dealing with application in mineralogical and industrial situations. Where this is not possible or practical, it is better to consider XRD QPA as a semi-quantitative technique at best. 

The phase compositions of the SHS products were characterized by using XRD, XRF and EPMA techniques. The morphologies of the products were characterized by electron probe microanalysis (EPMA, CAMECA SX-100) with using three WDS (Wavelength Dispersive Spectrometer) units. X-ray analyses of obtained alloys and slags were performed with Thermo Scientific Niton XL3t XRF device and PANalytical X Pert Pro PW3040/60 XRD device. 

Electron probe microanalysis data for the CSH phases observed in the columns give Ca Si ratios ranging from approximately 0.5 close to the inlet, rising to 1.6 further into the column. These ratios are representative of both the CSH(I) and CSH(II) groups of minerals (Lea 1970), and are consistent with the composition of the phases used in the model predictions (i.e. hillebrandite, Ca Si = 0.5 foshagite, Ca Si = 0.75 tobermorite, Ca Si = 1.2). Many analyses showed the presence of up to 1 wt% A1 (i.e. CASH phases). Although the predicted CSH phases did not contain all the variations of Ca Si produced in the experiments, as a result of the restricted number of CSH (and CASH) phases in the models, they do demonstrate evolution of CSH phase compositions with time and with distance along the columns. 

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