Heats of Transformations in Bismuth Oxide by Differential Thermal Analysis

Abstract

DTA was chosen as a convenient method for resolving differences in the reported heat of transition and heat of fusion of Bi₂O₃. The heat of the low to high transition of K₂SO₄ (at 583 °C) and the heat of fusion of Ag (at 960.8 °C) were used as internal standards. These standards were mixed directly with the Bi₂O₃ in three weight ratios. The heating schedule for each weight ratio was 3°/min, 9°/min, and 3°/min. For evaluating internal consistency, DTA determinations were made for mixtures of the two standards. Linearity was obtained within limits between the weight ratio of Bi₂O₃ and standard and the corresponding ratio of peak areas. The heat of transition of Bi₂O₃ $(\text{mon}\stackrel{{730}^{°}\text{C}}{\to }$ cubic was found to be 9.9 ± 0.5 kcal/mole and the heat of fusion $\left(\text{cubic}\stackrel{{825}^{°}\text{C}}{\to }\text{liq}.\right)$ 3.9 ± 0.2 kcal/mole. The uncertainties are estimated limits of error, based on internal consistency and on the values of the standards.

Figure 1.. Differential thermal analysis carve for third cycle of heat treatment of Bi₂O₃: K₂SO₄ mixtures of weight ratio 1.72 :1.

Approx. 0.2 g of sample in Pt tube was heated in air at 3°/min. The temperature of sample container was measured with Pt-90 percent Pt: 10 percent Rh thermocouple; reference material was compacted alumina powder. Areas under peaks were obtained by counting squares in tracings of the peaks on millimeter ruled graph paper α → β = transition of K₂SO₄ M → c = monoclinic to cubic transition of Bi₂O₃ c → I = fusion of cubic Bi₂O₃.

Figure 2.. Peak area ratios versus weight ratios for mixtures of Bi₂O₃ and K₂SO₄.

$g_{\text{B}{1}_2{\text{O}}_3}/g_{{\text{K}}_2{\text{SO}}_4}$ refers to the weight ratio. $A_{{\text{Bi}}_2{\text{O}}_3}/A_{{\text{K}}_2{\text{SO}}_4}$ for slope of line m_tr refers to area under transition of Bi₂O₃ ÷ area under transition of K₂SO₄. $A_{{\text{B}}_1{\text{O}}_3}/A_{{\text{K}}_2{\text{SO}}_4}$ for slope of line mf refers to area under fusion of Bi₂O₃ ÷ area under transition of K₂SO₄. Slopes calculated by method of least squares. $L_{{\text{Bi}}_2{\text{O}}_3}$ = 5.722m₁ (see eq (5), in text). L_trBi₂O₃ = 5.722 × 1.66₉ = 9.5₅ kcal/mole. S.D. m_tr = 0.031. L_fBi₂O₃ = 5.722 × 0.671 =3.8₄ kcal/mole. S.D. m_f= 0.020.

Figure 3.. Peak area ratios versus weight ratios for mixtures of Bi₂O₃ and Ag.

$g_{{\text{Bi}}_2{\text{O}}_3}/g_{\text{Ag}}$ refers to the weight ratio. $A_{{\text{Bi}}_2{\text{O}}_3}/A_{\text{Ag}}$ for slope of line m_tr refers to area under transition of Bi₂O₃ ÷ area under fusion of Ag. $A_{{\text{Bi}}_2{\text{O}}_3}/A_{\text{Ag}}$ for slope of line m_f refers to area under fusion of Bi₂O₃ ÷ area under fusion of Ag. Slopes calculated by method of least squares. $L_{{\text{Bi}}_2{\text{O}}_3}$ 11.274m₂ (see eq (6), in text). L_trBi₂0₃= 11.274 × 0.902₅ = 10.1₇ kcal/mole. S.D. m_tr = 0.019. L_fBi₂0₃= 11.27 × 0.342₃ = 3.8₆ kcal/mole. S.D. m_f = 0.015.

Figure 4.. Peak area ratios versus weight ratios for mixtures of K₂SO₄ and Ag.

$g_{{\text{K}}_2{\text{SO}}_4}/{\text{g}}_{\text{Ag}}$ refers to the weight ratio. $A_{{\text{K}}_2{\text{SO}}_4}/A_{\text{Ag}}$ for slope of line m_tr (DTA) refers to the area under the transition of K₂SO₄ ÷ area under the fusion of Ag. Slope for solid line calculated by method of least squares; slope for dashed line calculated from literature values. $L_{{\text{K}}_2{\text{SO}}_4}$ = 4.217_m3 (see eq (7), in text). L_trK₂SO₄ = 4.217 × 0.533 = 2.2₅ keal/mole. S.D. m_tr = 0.014. L_trK₂SO₄, from literature [3, 12] = 2.14 kcal/mole.