For the preparation of whole-coal briquettes the following items are required. Samples are prepared by fusion with lithium tetraborate flux, and silicate rock standards are used to construct calibration curves for each element. Extensive matrix correction techniques are not required because of the almost eightfold dilution of the sample by the flux. Fusion is the preferred method of preparation because it eliminates particle-size effects and mineralogical heterogeneity and thus allows for the highest precision possible. To this mixture is added 5 drops of a 15-percent hydrobromic acid solution, which acts as a nonwetting agent during the fusion.
Caution is advised here.
Preliminary evidence indicates that the higher temperature effected by the Meeker burner in the Claisse R fluxer may volatilize sodium from certain samples during the fusion process. Calibration of the instrument consists of plotting X-ray intensity versus concentration of the standard reference materials for each element and calculating slope and intercept through simple linear regression analysis. Silicate rock standards are used for every element except sulfur because of their availability and similarity to the composition of most coal ashes. Results from a typical calibration for iron are shown in table 13 in the form of accepted and calculated concentrations generated by the simple linear regression model. Because many coal ashes contain much higher levels of sulfur than do the available reference materials, the preparation of separate standards for use in determining sulfur is necessary.