Solid solubility of sodium oxide in tricalcium aluminate

The tie line connecting the compounds 3CaO·Al2O3 and Na2O·8CaO·3Al2O3 in the ternary system CaO-Al2O3-Na2O was studied at 1250° Celsius. It was determined that Na2O can exist in crystalline solution with 3CaO·Al2O3 in percentages of about 2.3% or less without any apparent change in the structure of 3CaO·Al2O3. X-ray diffraction peaks in the back-reflection region shifted to lower d-spacing values on increasing Na2O contents. At a Na2O content of about 2.7%, each major x-ray diffraction peak of 3CaO·Al2O3 splits into two peaks, indicating the appearance of a new phase. This new phase occurs on the tie line investigated with Na2O contents varying from 2.7% to 7.7%. Peaks corresponding to 3CaO·Al2O3 do not appear in the x-ray patterns for samples with Na2O content greater than 2.7%. The composition containing 2.7% Na2O shows x-ray diffraction peaks corresponding to both 3CaO·Al2O3 and the new phase. The new phase has d-spacing values very similar to the ternary compound Na2O·8CaO·3Al2O3 and might consist of this compound or a crystalline solution of Na2O·8CaO·3Al2O3 deficient with respect to Na2O”--Abstract, page ii