The Ternary System MgO-Al^O.-SiO^ 



311 



Of the 14 boundary curves in this system, all of which 

 are given in fig. 2,. there are three which are represented 

 by dotted lines to indicate that the compositions and 

 temperatures along these lines could not be accurately 

 determined, because direct methods could not be used. 

 The indirect methods employed will be described when 

 quintuple point 6 is considered. Two other boundary 

 curves, 2-3 and 1-5, are so fiat at their summits that from 

 temperatures of complete melting alone it has not been 

 feasible to determine whether or not either contains a 

 maximum. However, from crystallization curves a max- 

 imum is evident in 2-3 (see Table 14a), and must lie 

 between 53% and 60% Si0 2 . Several crystallization 

 curves for compositions near point 5 were run, but they 

 did not definitely indicate a maximum on line 1-5. 



Table 14. 

 Quenchings winch determine temperatures for points on the boundary curves. 

 Temp. Time Phases present Bound- 



Comp. Weight 



MgO A1A 

 30-0 6-0 



270 

 200 

 150 

 7-0 

 100 

 150 

 160 



8.0 

 190 

 20-0 

 22-0 

 24-0 

 32-0 

 350 



16-0 38-0 

 16-0 40-0 



17-0 

 20-0 

 25-0 

 21-0 



330 

 300 

 250 

 28-0 



26-0 230 



31-0 22-0 

 370 210 



Per 

 cent 

 Si0 2 



64-0 

 65.0 

 610 



650 



710 



660 



530 



490 



460 

 44-0 



500 



500 



500 



510 



51.0 



470 



420 



1482 

 1460 

 1475 

 1450 

 1365 

 1350 

 1400 

 1390 

 1485 

 1475 

 1435 

 1430 

 1460 

 1455 

 1465 

 1460 

 1490 

 1550 

 1525 

 1458 

 1456 

 1435 

 1425 

 1390 

 1375 

 1430 

 1425 

 1376 

 1375 

 1450 

 1435 

 1600 



m 

 hours 



5 

 



Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 

 Glass 



+ MgO.SiOo 



+ MgO.SiO, + SiO. 



+ SiO. 



+ Si0 2 + MgO.SiO. 



-j- cordierite 



-j- cordierite -\- SiO. 



-4- SiO. -f- cordierite 



+ AlA.SiO, 



+ Al A-SiO. + SiO, 



+ ALA-SiO, 



-j- Al,0,.SiO, + cordierite 



+ ALA.SiO, 



-j- Al.O3.SiOo + cordierite 



+ ALA.SiO. 



-j- ALOo.SiO, -f- cordierite 



+ AlA.SiOo 



+ AlA-SiO. + spinel (tr.) 



-f- cordierite 



-j- cordierite -|- spinel 



-j- spinel 



-j- spinel 4- cordierite 



-j- spinel 



-j- spinel -4- cordierite 



-j- cordierite 



-j- cordierite -|- spinel 



-j- spinel 



-j- spinel + 2MgO.SiO, 



+ 2MgO.SiO. 



-j- 2MgO.SiO., 4. spinel 



ary 



E-l 



1-2 



D-2 



2-3 



3-7 



3-4 



4-6 



