Heat Capacity (Specific Heat) and Thermodynamic Quantities

The specific heat, entropy, heat and Gibbs free energies of formation of alumina are given in Table 14, from [28]. Above 2,790°K, the boiling point of aluminum, there is a discontinuous change in the heat of formation of alumina.

Table 12 Densities of anhydrous and hydrated aluminas

Material

Density (g cm 2)

Sapphire (a-Al2O3)

3.96

T-A^

3.2

S-Al2O3

3.2

K-Al2O3

3.3

e-Al2O3

3.56

Al(OH)3 gibbsite

2.42

AlOOH diaspore

3.44

AlOOH boehmite

3.01

From [1]

Table 13 The coefficient of linear thermal expansion of a-alumina as a function of temperature

Temp. (°C)

da /dT (x106 per °C)

1,000

12.0

800

11.6

600

11.1

400

10.4

200

9.1

100

7.7

50

6.5

From [23]

Table 14 Specific heat and thermodynamic properties of a-alumina as a function of temperature

T (K)

Specific heat

Entropy

Heat of formation

Free energy of formation

J mol-1

K-1

kJ mol-

1

0

0

0

-1663.608

-1663.608

100

12.855

4.295

-1668.606

-1641.692

200

51.120

24.880

-1673.388

-1612.636

298.15

79.015

50.950

-1675.692

-1582.275

400

96.086

76.779

-1676.342

-1550.226

600

112.545

119.345

-1675.300

-1487.319

800

120.135

152.873

-1673.498

-1424.931

1,000

124.771

180.210

-1693.394

-1361.437

1,200

128.252

203.277

-1691.366

-1295.228

1,400

131.081

223.267

-1686.128

-1229.393

1,600

133.361

240.925

-1686.128

-1163.934

1,800

135.143

256.740

-1683.082

-1098.841

2,000

136.608

271.056

-1679.858

-1034.096

2,200

138.030

284.143

-1676.485

-969.681

2,327

138.934

291.914

Melting temperature

2,400

139.453

296.214

-1672.963

-905.582

2,600

140.959

307.435

-1669.279

-841.781

2,800

142.591

317.980

-2253.212

-776.335

3,000

144.474

327.841

-2244.729

-671.139

From [28]