Thermodynamic properties of magnesium oxide and beryllium oxide from 298 to 1,200 °K

As a step in developin g new sta ndard s of hi g h-temperature h eat cap acity and i n d etermi nin g accurate thermodynamic data fOl" simpl e s ubstances, t h e enthalpy (heat content) relative to 273 oK, of hi gh puri ty fu sed mag nesium oxide, MgO, and of s inte red b e ryllium oxide, BeO, was m eas ured up to 1,17 3 ole A B un sen ice calorimeter and the d rop m ethod were used. The two sa mples of BeO measured ha d s urface-to-volu me r atios differing by a fac tor of 15 or 20, yet agreed with each other closely enoug h to preclude app reciable error attributable to the considerab le surface a rea. The e nthalpies found for MgO arc several p e rcent highe r t han m ost previously r eported values . The values arc represen ted wi t hin t heir un ce rtain ty (estimated to ave ra ge 0 .25 % ) by t he foll owin g empirica l eq ua tion s 3 (cal mo le-I at l' OK ) MgO : T-f~-T-f;73 15= 10.74091'+ 1. 2177 (1 0-3) 7'2 -2.3183(10-7) 1'3 + 2.26151 (1 05) 1'-'-3847.94. BeO: Tl ~-II;73 1 5= 11.10841 '+ 7.1245 (10-4) 1'2 + 8.40705(105) 7'-1 -5.3 1245(10 7 ) T-2-5453.21. Valu e'S of rnt halpy, IwaL capacit.v, rnt ro py, a nd G ibbs free-energy function a rc tabu lated from 298. 15 to 1, 200 oK.