Fig. 1. Summary of nepheline determinations by quantitative X-ray diffraction. Table I. Comparison of Weight Percentage Nepheline Content Determinations by X-Ray and Lineal Analysis Sample X-ray analysis (~1 % ) Lineal analysis* (wt%) 1 2 3 4 5t 6t 7t 83.2t2.1 81.8a3.2 7 4 . 2 t 1.8 72.5 t 4.1 6 1 . 3 t 2 . 6 63.9-1-2.8 46.3C3.0 44.8 t 2.6 5 0 . 1 t 2 . 3 53.8 t 6.4 39.5-1-1.7 3 7 . 4 t 8.4 22.222.5 25.3 t 5.9 'Average of 10 micrographs each. tContains mixture of nepheline and sodium niobate.values of these samples, while standard deviations for measurements by the X-ray method remain fairly constant in all cases.) In sample 2, when the glass was completely etched away and the residue weighed, the weight percentage nepheline was 70%, in good agreement with the data in Table I .This analysis procedure allows measurement of various amounts of a given crystalline phase in a glass-ceramic regardless of the type or composition of the other phases present. Once a calibration curve for a given material is established, it can be used to determine the weight fraction of that phase in any matrix, provided the same experimental parameters are duplicated exactly. This fact is shown in the results reported in this note where the same calibration curve was used to determine the weight fraction of nepheline present in parent glasses of varying compositions as well as when other crystalline phases were present. Specifically, samples 1, 2, 3, and 4 contained <5% MgO.2Ti0, and samples 5,6, and 7 contained up to 40% NaNbO,.This method is, however, dependent on the availability of good quality reference standards of the phase under study. The use of the sol-gel technique has facilitated the synthesis of many useful reference materials (nepheline, cordierite, mullite, etc.); yet in cases where the crystalline phase of interest is a complex solid solution or a phase that is extremely difficult to synthesize, another technique may be preferable.The main sources of error in this type of measurement include preferred orientation effects, extinction, microabsorption, crystallite size in the powder, and poor mixing of the internal standard. But the random orientation of crystalline phases precipitated in most glass-ceramics and their generally fine crystallite size ( < 5 p m ) help minimize these effects, or at least cause them to affect each analysis in a more or less constant manner. The possible sources of error have been analyzed in detail, and the accuracy of this method is shown to be better than ?4%.l0 ALTHOUGH B,O,, P,O,, and CaO are technologically important, ternary phase relations in this system have not been studied in detail. Therefore, a preliminary investigation of the phase relations over a limited temperature interval was made: this study resulted in a tentative isothermal plot at 900°C. The 3 binary systems which bound this ternary system have been investigated by several workers.'+ Eleven binary compounds have been reported, and Bauer, established the existence of a ternary compound with the composition 2Ca0. P,O,. B203...
