The Ternary System MgO-Alfi % -SiO v 315 



Point 3 is the quintuple point for ternary compound, 

 Al 2 3 .Si0 2 and spinel (MgO 16-1, A1 2 3 34-8, Si0 2 49-1). 

 Its melting temperature (1460° ±5°) is based on the 

 values obtained from various compositions as given in 

 Table 18. 



Table 18. 



Melting temperature: Quintuple point 3 for ternary compound, AL0 3 .Si0 2 

 and spinel as determined from various compositions. 



fMgO 15-3 160 160 16-5 



Composition, weight, per cent \ AL0 3 38-8 380 350 345 



[Si6 2 45-9 46-0 490 490 



Temperature 1460 1455 1465 1460 



Point 4 is the quintuple point for spinel, ternary com- 

 pound, and 2MgO.SiO (MgO 25-7, A1 2 3 22-8, Si0 2 51-5). 

 Its melting temperature (1370° ±5°) is based on the 

 values obtained from compositions as given in Table 19. 



Table 19. 



Melting temperature: Quintuple point 4 for ternary compound, spinel and 

 2MgO.Si0 2 as determined from various compositions. 



fMgO 260 290 25-0 



Composition, weight, per cent \ AL0 3 230 23-0 24-0 



[SiO, 51-0 480 51-0 



Temperature 1370 1370 1363 



• 



Point 5 is the quintuple point (eutectic?) for 

 2MgO.Si0 2 , MgO.Si0 2 , and ternary compound (MgO 

 25-0, A1 2 3 21-0, Si0 2 54-0. Its melting temperature 

 (1360° ±5°) is based on the values obtained from various 

 compositions as given in Table 20. 



Table 20. 



Melting temperature: Quintuple point 5 for ternary compound, MgO.Si0 2 , 

 and 2MgO.Si0 2 as determined from various compositions. 



fMgO 



22-0 



25.0 



26-0 



25-5 



250 



Composition, weight, per cent \ Al-O, 



25-0 



22-0 



210 



210 



210 



[ SiO, 



530 



530 



530 



53-5 



54.0 





1357 



1360 



1355 



1353 



1363 



Point 6 is the eutectic point for 2MgO.SiOo, MgO, and 

 spinel (MgO 56-0, A1 9 3 16-0, Si0 2 28-0). Its melting 

 temperature (1700° ±25°) is based on values obtained 

 from several compositions melted in the iridium furnace, 

 temperature measurements being made with an optical 

 pyrometer. 



Point 7 is the quintuple point for A1 9 3 , spinel and 

 Al,0 3 .Si0 2 (MgO 15-2, A1 2 3 42-0, Si0 2 42-8). Its melt- 



