INDIRECT CALCULATIOK. OF THE PARTIAL FREE ENERGY OF ALBITE AND ORTHOCLASE IN ALKALI FELDSPAR. [l]

Transcription

1 INDIRECT CALCULATIO OF THE PARTIAL FREE ENERGY OF ALBITE AND ORTHOCLASE IN ALALI FELDSPAR. [] By R. ALLMANN ande. HELLNER Mineragica Institute f the University f ie, Germany Orvie in his thesis "Akai in exchange between vapr and feidspar phases" [2] suggests a methd fr cacuating the partia mar free energy f the pure akai phases in the mixed crysta regin. Orvie studied the equiibrium f subiity f + and N a+ in a vapr phase and in the akai fedspar crystas; the vapr phase cnsisted f a 2 n sutin f C and NaC with different ratis f and N a. The resuts fr different temperatures at 2000 bars are given in Figure 3 f his paper in this vume (page FFF). The cncentratin rati fr fedspar and cexisting chride +Na sutin is given in Tabe. Tabe. rati in akai fedspar and cexisting vapr phase (after Orvie). +Na t = fedspar % 700 c vapr % t = 600 c fedspar misc.gap % vapr % [] Manuscript submitted Nvember 21st [2] In press in the American Jurna f Science. We thank Dr. Orvie fr kindy making the manuscript f his paper avaiabe t us. [349]

2 350 R.ALLMANN, E.HELLNER Frm the equatin f chemica equiibrium a bite+ C ++ rthcase +NaC, () fws the reatin f the partia free energy: If ne assumes an idea mixture f the akai chride sutin, ne can cacuate the partia free energy as a functin f the me fractin x by F(x) = F() + RT nx where F() is the free energy f the pure end members. Frm the assumptins mentined abve ne can cacuate the eft side f equatin (2) which is demnstrated in Figure fr 700 ; the eft side f the figure shws the partia free energy fr NaC and C in the sutin f the H20phase, the right side F NaC F O=.dFchride The vaues f Tabe aw us t cnstruct the.dffedspar curve frm the knwn.dfchride vaues; fr instance at 700 the (2) (3} F =partiee m/are Freie Energie bei 700 C fur NaCICILsung (Bidung aus deneiementen) dF = F;;aCI CI F 4F 65 65, NaC + jna+ CI Fig.. NaC,. CI jna+

3 ENERGY IN ALALI FELDSPAR 351 F =partiee m/are Freie Energie be i 700 C fur Akaifedspate F ,7 80 (Tief} A/bit (aus Na(}fissig, f 2, J At2 3, 3 5i02J..::JF r 15 O df= ftbi r : : A/bit. /,_, Orthkas + 85,5 Orhkas /. Na+ 5 OT A/bi /. Orhkas Na+ Fig. 2. LIFchride fr x=0.28 is equa t the LIFfedspar f the cexisting fedspar with x = 0.58 (see Figure 2). Frm this LIFfedspar curve it is pssibe t cnstruct the Fa bite and F rthcase curves frm the free energy f the end members, remembering that the curve has t shw a cntinuus spe, because n miscibiity gap exists at 700. (The stipped ines give the curves fr an idea mixed crysta). The actua curves indicate by their neary hriznta spes in the range x = 0.20 O. 70 the prximity f a miscibiity gap at wer temperatures. In the same manner the cacuatins were dne fr 600 C (Figure 3). In the unstabe regin f the miscibiity gap the curves are dtted, because these vaues cannt be reaized in nature. The methd f Orvie seems we suited fr cacuating partia free energies fr ther mixed crysta mineras. The Fvaues fr the fedspars were cacuated frm the heat f frmatin f the xides, except fr Na20 and 20; the free energy f the chrides was cacuated frm the eements; an extrapatin

4 352 R. ALL:VIANN, HELLNER was made fr the hydratin energy f the chrides, because these vaues are nt knwn frm the iterature. The fwing data were used fr cacuating the frae energy vaues (Tabes 2 and 3). Tabe 2. Thermdynamic cnstants (after Handbk f Physics and Chemistry, 43th Ed ). Cp = a+b T+c T 2 +d T 2 cafgrad me a b 0 3 c 106 d O 5 S298 Na ca/grad me A Si02(f:) 11.22! NaA1Si i A1Si308 Na iquid iquid C2 NaC C \JO ! 8.\J , ;) i ;) Tabe 3(a). Frmatin frm xydes. LJH 2ti c LJF 700 c[ LJF 600 c w abite 41.2 i ca/me high abite rthcase Tabe 3(b). Frmatin frm eements (iquid metas).! LJH 25 c!lf 700 c LJF 600 c ina20 i20 NaC C i ca/me! Tabe 3(c). Hydratin energy. L1F [ 25 c 700 c 600 c NaC 2.15 \J.07! C ca/me The used LJF vaues f Figure are the sums f Ta be 3(b) and 3(c); the vaues f Figure 2 and 3 are the sums f the LJF vaues in Tabes 3(a) and 3(b).

5 ENERGY IX ALALL FELDSP,\B 353 F = partiee m arefreie Energie be i 600 C fur Akaifedspate F 79 M r B5 :.cc : 2,.1 1,, 1 Mischungsiicke \ \ \ Orhkas B6,7 """""= = :p= 1 // 90 1/,( / : : : : 95+: L 0.5 A/bi J. Orhkas Na+ Fig. 3. A/bi J. Orhk/as Na+ XGT 2a