Advanced Search
RSS LinkedIn Twitter

Journal Archive

Johnson Matthey Technol. Rev., 2021, 65, (1), 54

doi:10.1595/205651320x15898131243119

锇的热力学性质再评估

熔化焓值得到改进

作者在1995年对热力学性质进行了综述。熔化焓为68.0±1.7 kJ mol-1的新评估导致液相热力学性质的修改,而且尽管在298.15 K条件下的升华焓仍为788±4 kJ mol-1,但一个大气压条件下的标准沸点修正为5565 K。

A Re-assessment of the Thermodynamic Properties of Osmium

Improved value for the enthalpy of fusion

SHARE THIS PAGE:

Article Synopsis

The thermodynamic properties were reviewed by the author in 1995. A new assessment of the enthalpy of fusion at 68.0 ± 1.7 kJ mol−1 leads to a revision of the thermodynamic properties of the liquid phase and although the enthalpy of sublimation at 298.15 K is retained as 788 ± 4 kJ mol−1 the normal boiling point is revised to 5565 K at one atmosphere pressure.

Introduction

The thermodynamic properties of osmium were reviewed by the author in 1995 (1) with a further review in 2005 (2) to estimate a most likely value for the melting point at 3400 ± 50 K to replace the poor quality experimental values which were being quoted in the literature. More recently Burakovsky et al. (3) have estimated a value of 3370 ± 75 K in good agreement with the above selected value. In the 1995 review the enthalpy of fusion was unknown but was estimated from a relationship between the entropy of fusion and the melting point which showed a high degree of correlation for the platinum group metals (pgms). However the derived entropy of fusion value for osmium was based on values for the other pgms available at that time but since then the values for both palladium and platinum have been revised so that the entropy of fusion value for osmium would also be revised leading to a new estimate of 68.0 ± 1.7 kJ mol−1 for the enthalpy of fusion. This would then require the thermodynamic properties of the liquid phase to also be updated. A comment is included on an independent much lower estimate of the enthalpy of fusion. Wherever possible measurements have been corrected to the International Temperature Scale (ITS-90) and to the currently accepted atomic weight of 190.23 ± 0.03 (4).

Low Temperature Solid Phase

Selected values in the normal and superconducting states are based on the specific heat measurements of Okaz and Keesom (0.18 K to 4.2 K) (5) including a superconducting transition temperature of 0.638 ± 0.002 K, an electronic specific heat coefficient (γ) of 2.050 ± 0.003 mJ mol−1 K−2 and a limiting Debye temperature (ΘD) of 467 ± 6 K. Specific heat values up to 5 K in both the normal and superconducting states are given in Table I.

Table I

Low Temperature Specific Heat Data Up To 5 K

Temperature, K Cºsa, mJ mol−1K−1 Cºnb, mJ mol−1K−1 Temperature, K Cºp, mJ mol−1 K−1
0.2 0.093 0.410 1.0 2.07
0.3 0.525 0.616 2.0 4.25
0.4 1.19 0.821 3.0 6.67
0.5 1.94 1.03 4.0 9.43
0.6 2.79 1.23 5.0 12.7
0.638 3.14 1.32

aSuperconducting state

bNon-superconducting state (in magnetic field)

Above 4 K selected specific heat values are initially based on the measurements by Naumov et al. (6 K to 316 K) (6). However above 280 K these measurements show an abrupt increase of 0.5 J mol−1 K−1 and a further abrupt increase of 0.3 J mol−1 K−1 above 300 K. Naumov et al. attempted to accommodate these values but the selected specific heat curve showed an unnatural sharp change in slope above 270 K. Therefore the selected values of Naumov et al. above 250 K were rejected and instead specific heat values to 298.15 K were obtained by joining smoothly with the high temperature enthalpy measurements of Ramanauskas et al. (7). In the original review of the low temperature data only the specific heat values were given consisting above 50 K of 10 K intervals to 100 K and then 20 K intervals above this temperature as well as the value at 298.15 K. This minimalist approach is now considered to be unsatisfactory and therefore comprehensive low temperature thermodynamic data are now given at 5 K intervals from 5 K to 50 K and at 10 K intervals above this temperature up to 290 K and then the value at 298.15 K as given in Table II.

Table II

Low Temperature Thermodynamic Data Above 5 K

Temperature, K pa, J mol−1K−1 T – Hº0 Kb, J mol−1 Tc, J mol−1 K−1 −GºT – Hº0 Kd, J mol−1 −(GºT – Hº0 K)/Td, J mol−1 K−1
5 0.0127 0.0286 0.0111 0.0266 0.00532
10 0.0417 0.153 0.0272 0.119 0.0119
15 0.116 0.519 0.0559 0.319 0.0213
20 0.290 1.475 0.110 0.719 0.0360
25 0.636 3.704 0.208 1.490 0.0596
30 1.252 8.302 0.374 2.910 0.0970
35 2.104 16.61 0.628 5.376 0.154
40 3.139 29.65 0.975 9.346 0.234
45 4.322 48.25 1.412 15.27 0.339
50 5.604 73.03 1.933 23.60 0.472
60 8.205 142.2 3.186 48.99 0.817
70 10.563 236.2 4.631 87.96 1.257
80 12.661 352.6 6.182 142.0 1.775
90 14.448 488.4 7.780 211.8 2.353
100 15.939 640.6 9.381 297.6 2.976
110 17.182 806.4 10.961 399.3 3.630
120 18.231 983.6 12.502 516.7 4.305
130 19.132 1170 13.997 649.2 4.994
140 19.912 1366 15.445 796.4 5.689
150 20.577 1568 16.842 957.9 6.386
160 21.085 1777 18.187 1133 7.082
170 21.533 1990 19.479 1322 7.774
180 21.975 2207 20.722 1523 8.459
190 22.377 2429 21.921 1736 9.136
200 22.695 2655 23.078 1961 9.804
210 22.928 2883 24.191 2197 10.463
220 23.178 3113 25.263 2445 11.111
230 23.441 3346 26.928 2702 11.749
240 23.715 3582 27.302 2970 12.377
250 23.929 3820 28.275 3248 12.993
260 24.119 4061 29.217 3536 13.599
270 24.290 4303 30.130 3832 14.195
280 24.444 4546 31.017 4138 14.780
290 24.584 4791 31.877 4453 15.355
298.15 24.688 4992 32.560 4715 15.816

aP is specific heat

bT – H0 K is enthalpy

cT is entropy

d−GºT – Hº 0 K and −(GºT – Hº0 K)/T are free energy functions

High Temperature Solid Phase

In the high temperature region, after correction for temperature scale and atomic weight, the enthalpy measurements of Ramanauskas et al. (1155 K to 2961 K) (7) were fitted to the following equation with an overall accuracy of ± 200 J mol−1 (0.4%) (Equation (i)):

(i)

This equation was used to represent selected enthalpy values from 298.15 K to 3400 K. Equivalent specific heat and entropy equations corresponding to the above equation are given in Table III, the free energy equations in Table IV, transitions values associated with the free energy functions in Table V and derived thermodynamic values in Table VI. The actual equation given by Ramanauskas et al. to represent the enthalpy measurements over the experimental temperature range agrees with Equation (i) to within 0.2%.

Table III

Thermodynamic Equations Above 298.15 K

Solid: 298.15 K to 3400 K
pa, J mol−1 K−1 = 26.1938 + 2.64636 × 10−4 T + 1.15788 × 10−6 T2 + 1.599912 × 10−10 T3 – 150378/T2
T – Hº298.15 Kb, J mol−1 = 26.1938 T + 1.32318 × 10−4 T2 + 3.85960 × 10−7 T3 + 3.99978 × 10−11 T4 + 150378/T – 8336.36
Tc, J mol−1 K−1 = 26.1938 ln(T) + 2.64636 × 10−4 T + 5.78940 × 10−7 T2 + 5.33304 × 10−11 T3 + 75189/T2 – 117.6597
Liquid: 3400 K to 5600 K
pa, J mol−1 K−1 = 50.0000
T – H298.15 Kb, J mol−1 = 50.0000 T + 816.2
Tc, J mol−1 K−1 = 50.0000 ln(T) – 281.5442

aP is specific heat

bT – H298.15 K is enthalpy

cT is entropy

Table IV

Free Energy Equations Above 298.15 K

Solid: 298.15 K to 3400 K
T – Hº298.15 Ka, J mol−1 = 143.8535 T – 1.32318 × 10−4 T2 – 1.92980 × 10−7 T3 – 1.33326 × 10−11 T4 + 75189/ T – 26.1938 T ln(T) – 8336.36
Liquid: 3400 K to 5600 K
T – Hº298.15 K, J mol−1 = 331.5442 T – 50.0000 T ln(T) + 816.2

aT – Hº298.15 K is the free energy function

Table V

Transition Values Involved with the Free Energy Equations

Transition Temperature, K ΔHM, J mol−1 ΔSM, J mol−1 K−1
Fusion 3400 68005.00 20.0014
Table VI

High Temperature Thermodynamic Data for the Condensed Phases

Temperature, K pa, J mol−1 K−1 T – Hº298.15 Kb, J mol−1 Tc, J mol−1 K−1 −(GºT – Hº298.15 K)/Td, J mol−1 K−1
298.15 24.688 0 32.560 32.560
300 24.711 46 32.712 32.560
400 25.555 2564 39.951 33.541
500 26.034 5145 45.709 35.419
600 26.386 7767 50.488 37.543
700 26.694 10,421 54.579 39.692
800 26.994 13,105 58.163 41.781
900 27.301 15,820 61.360 43.782
1000 27.626 18,566 64.253 45.687
1100 27.975 21,346 66.902 47.497
1200 28.351 24,162 69.352 49.217
1300 28.757 27,017 71.637 50.855
1400 29.196 29,914 73.784 52.417
1500 29.669 32,857 75.814 53.909
1600 30.178 35,849 77.745 55.339
1700 30.724 38,894 79.591 56.712
1800 31.308 41,996 81.363 58.033
1900 31.932 45,157 83.073 59.306
2000 32.597 48,383 84.727 60.536
2100 33.303 51,678 86.335 61.726
2200 34.053 55,045 87.902 62.880
2300 34.846 58,490 89.432 64.002
2400 35.684 62,016 90.933 65.093
2500 36.568 65,628 92.407 66.156
2600 37.499 69,331 93.859 67.193
2700 38.478 73,130 95.293 68.208
2800 39.506 77,028 96.710 69.200
2900 40.583 81,032 98.115 70.173
3000 41.712 85,147 99.510 71.128
3100 42.892 89,377 100.897 72.066
3200 44.125 93,727 102.278 72.988
3300 45.412 98,203 103.655 73.897
3400 (solid) 46.751 102,811 105.031 74.792
3400 (liquid) 50.000 170,816 125.032 74.792
3500 50.000 175,816 126.482 76.249
3600 50.000 180,816 127.890 77.664
3700 50.000 185,816 129.260 79.040
3800 50.000 190,816 130.594 80.379
3900 50.000 195,816 131.892 81.683
4000 50.000 200,816 133.158 82.954
4100 50.000 205,816 134.393 84.194
4200 50.000 210,816 135.598 85.403
4300 50.000 215,816 136.774 86.585
4400 50.000 220,816 137.924 87.738
4500 50.000 225,816 139.047 88.866
4600 50.000 230,816 140.146 89.969
4700 50.000 235,816 141.222 91.048
4800 50.000 240,816 142.274 92.104
4900 50.000 245,816 143.305 93.139
5000 50.000 250,816 144.306 94.152
5100 50.000 255,816 145.311 95.146
5200 50.000 260,816 146.276 96.120
5300 50.000 265,816 147.229 97.075
5400 50.000 270,816 148.164 98.012
5500 50.000 275,816 149.081 98.933
5600 50.000 280,816 149.982 99.836

aP is specific heat

bT – H298.15 K is enthalpy

cT is entropy

d−(GºT – Hº295.15 K)/T is the free energy functions

The only other enthalpy measurements were obtained by Jaeger and Rosenbohm (693 K to 1877 K) (8) and compared to the selected values vary from 1.6% low at 693 K to an estimated 1.2% low at 1600 K to 1.4% low at 1877 K.

Liquid Phase

Selected values of the enthalpies and entropies of fusion of the Groups 8 to 10 elements with a close-packed structure are given in Table VII. Only the enthalpy of fusion of osmium is unknown. References (1014) represent the latest reviews on the thermodynamic properties of the pgms by the present author. From an evaluation of the entropies of fusion of the elements, Chekhovskoi and Kats (15) proposed that the entropy of fusion (ΔSºM) and the melting point (TM) could be related by the equation ΔSºM = A TM + B. In the previous review (1) different values were proposed for the entropies of fusion of palladium (8.80 J mol−1 K−1) and platinum (10.45 J mol−1 K−1) leading to an estimate of the entropy of fusion for osmium of 20.6 J mol−1 K−1. With the revised values it is clear that, although of the right order, the entropy of fusion of nickel is discrepant and has therefore been disregarded. The other six values were fitted to the equation with A = 6.6954 × 10−3 and B = −2.7630 and a standard deviation of the fit of ± 0.193 J mol−1 K−1. However in order that the derived entropy of fusion of osmium has a similar accuracy to those of the input values then the accuracy is expanded to a 95% confidence level leading to an entropy of fusion of 20.0014 ± 0.387 J mol−1 K−1 and based on a melting point 3400 ± 50 K to an enthalpy of fusion of 68,005 ± 1653 J mol−1. Based on neighbouring elements then a liquid specific heat of 50 J mol−1 K−1 was proposed in the original paper (1) and therefore the enthalpy of liquid osmium can now be expressed as Equation (ii):

(ii)
Table VII

Enthalpies and Entropies of Fusion for the Groups 8 to 10 Elements

Element Melting point, K Enthalpy of fusion, J mol−1 Entropy of fusion, J mol−1 K−1 Reference
Cobalt 1768 16056 ± 369 9.08 ± 0.21 (9)
Nickel 1728 17042 ± 376 9.86 ± 0.22 (9)
Ruthenium 2606 39040 ± 1400 14.98 ± 0.54 (10)
Rhodium 2236 27295 ± 850 12.21 ± 0.38 (11)
Palladium 1828.0 17340 ± 730 9.48 ± 0.40 (12)
Iridium 2719 41335 ± 1128 15.20 ± 0.41 (13)
Platinum 2041.3 22110 ± 940 10.83 ± 0.46 (14)

Equivalent specific heat and entropy equations corresponding to the above equation are given in Table III, the free energy equation in Table IV and derived thermodynamic values in Table VI. It should now be possible to accurately determine the melting point and enthalpy of fusion of osmium since the metal is available in high purity in a coherent form whilst the enthalpies of fusion of other high melting point elements such as rhenium (3458 K) and tungsten (3687 K) have been successfully determined.

Gas Phase

Based on a standard state pressure of 1 bar the thermodynamic properties of the monatomic gas were calculated from the 295 energy levels listed by Van Kleef and Klinkenberg (16) and Gluck et al. (17) using the method outlined by Kolsky et al. (18) together with the 2018 Fundamental Constants (19). Derived thermodynamic values are given in Table VIII.

Table VIII

Thermodynamic Properties of the Gaseous Phase

Temperature, K pa, J mol−1 K−1 T – Hº298.15 Kb, J mol−1 Tc, J mol−1 K−1 −(GºT – Hº298.15 K)/ Td, J mol−1 K−1
298.15 20.788 0 192.579 192.579
300 20.788 38 192.707 192.579
400 20.810 2118 198.689 193.394
500 20.901 4203 203.341 194.936
600 21.102 6302 207.168 196.665
700 21.432 8428 210.444 198.404
800 21.887 10,592 213.334 200.093
900 22.453 12,809 215.944 201.712
1000 23.104 15,086 218.342 203.256
1100 23.812 27,431 220.577 204.731
1200 24.545 29,849 222.680 206.140
1300 25.278 22,340 224.674 207.489
1400 25.988 24,904 226.574 208.785
1500 26.659 27,537 228.390 210.032
1600 27.283 30,234 230.130 211.234
1700 27.854 32,991 231.802 212.395
1800 28.374 35,803 233.409 213.518
1900 28.844 38,665 234.956 214.606
2000 29.269 41,571 236.446 215.661
2100 29.656 44,517 237.884 216.685
2200 30.009 47,501 239.272 217.681
2300 30.337 50,518 240.613 218.649
2400 30.642 53,567 241.911 219.591
2500 30.931 56,646 243.167 220.509
2600 31.207 59,753 244.386 221.404
2700 31.473 62,887 245.569 222.277
2800 31.732 66,047 246.718 223.130
2900 31.986 69,233 247.836 223.962
3000 32.234 72,444 248.925 224.776
3100 32.480 75,680 249.986 225.573
3200 32.722 78,940 251.021 226.352
3300 32.961 82,224 252.031 227.115
3400 33.197 85,532 253.019 227.862
3500 33.430 88,864 253.984 228.595
3600 33.660 92,218 254.929 229.313
3700 33.885 95,596 255.855 230.018
3800 34.107 98,995 256.761 230.710
3900 34.323 102,417 257.650 231.389
4000 34.535 105,860 258.522 232.057
4100 34.742 109,324 259.377 232.713
4200 34.943 112,808 260.217 233.357
4300 35.138 116,312 261.041 233.992
4400 35.327 119,835 261.851 234.616
4500 35.510 123,377 262.647 235.230
4600 35.687 126,937 263.429 235.834
4700 35.858 130,514 264.199 236.430
4800 36.023 134,108 264.956 237.016
4900 36.182 137,719 265.700 237.594
5000 36.325 141,345 266.432 238.164
5100 36.483 144,986 267.153 238.725
5200 36.625 148,641 267.863 239.278
5300 36.762 152,311 268.562 239.824
5400 36.895 155,993 269.251 240.363
5500 37.022 159,689 269.929 240.894
5600 37.145 163,398 270.597 241.419

aP is specific heat

bT – H298.15 K is enthalpy

cT is entropy

d−(GºT – Hº295.15 K)/T is the free energy functions; Hº298.15 K – Hº0 K = 6197.4 J mol−1

Enthalpy of Sublimation

No temperature scales were given with the measurements of the vapour pressures by Panish and Reif (20) and Carrera et al. (21). Normally the experimental temperature values would therefore be accepted but in the case of such values above 2000 K the difference from the current scale, ITS‐90, becomes significant. Since the measurements were carried out in 1962 and 1964 then they would ultimately be associated with the International Practical Temperature Scale (IPTS-1948) and were therefore corrected to the ITS-90 scale on this basis. Derived enthalpies of sublimation are given in Table IX. The selected enthalpy of sublimation of 788 ± 4 kJ mol−1 is basically an unweighted average but slightly biased towards the measurements of Carrera et al. (21).

Table IX

Enthalpies of Sublimation at 298.15 K

Authors Reference Methoda Temperature range, Kb ΔHº298.15 K (II)c, kJ mol−1 ΔHº298.15 K (III)c, kJ mol−1
Panish and Reif (19) L 2376–2718 807 ± 35 784.3 ± 1.3
Carrera et al. (20) L 2159–2595 773 ± 13 790.7 ± 0.7
Selected 788 ± 4

aL: Langmuir free evaporation

bTemperature ranges corrected to temperature scale ITS-90

cΔHº298.15 K (II) and ΔHº298.15 K (III) are the Second Law and Third Law enthalpies of sublimation at 298.15 K

Vapour Pressure Equations

The vapour pressure equations are given in Table X. For the solid the evaluation was for free energy functions for the solid and the gas at 50 K intervals from 1700 K to 3400 K and for the liquid at 50 K intervals from 3400 K to 5600 K and were fitted to Equation (iii):

(iii)
Table X

Vapour Pressure Equationsa

Phase Temperature range, K A B C D E
Solid 1700–3400 26.82612 −1.17464 −95030.60 5.68917 × 10−4 −6.25849 × 10−8
Liquid 3400–5600 45.02206 −3.41958 −93542.51 2.64385 × 10−4 −5.78416 × 10−9

A review of the vapour pressure data is given in Table XI.

Table XI

Vapour Pressure

Temperature, K Pressure, bar ΔGºTa, J mol−1 ΔHºTb, J mol−1 Pressure, bar Temperature, K
298.15 2.03 × 10−130 740,290 788,000 10−15 1780
300 1.44 × 10−129 739,994 787,992 10−14 1861
400 2.81 × 10−95 724,059 787,554 10−13 1950
500 1.03 × 10−74 708,242 787,058 10−12 2048
600 5.14 × 10−61 692,527 786,535 10−11 2156
700 3.09 × 10−51 676,901 786,007 10−10 2277
800 6.59 × 10−44 661,350 785,487 10−9 2411
900 3.28 × 10−38 645,863 784,989 10−8 2563
1000 1.18 × 10−33 630,430 784,520 10−7 2736
1100 6.23 × 10−30 615,043 784,085 10−6 2934
1200 7.88 × 10−27 599,693 783,687 10−5 3163
1300 3.31 × 10−24 584,375 783,323 10−4 3435
1400 5.86 × 10−22 569,084 782,990 10−3 3792
1500 5.19 × 10−20 553,816 782,680 10−2 4235
1600 2.62 × 10−18 538,568 782,385 10−1 4804
1700 8.32 × 10−17 523,338 782,097 1 5559.70
1800 1.80 × 10−15 508,126 781,807 NBPc 5564.74
1900 2.81 × 10−14 492,929 781,508
2000 3.33 × 10−13 477,749 781,188
2100 3.12 × 10−12 462,586 780,839
2200 2.38 × 10−11 447,439 780,456
2300 1.52 × 10−10 432,312 780,028
2400 8.32 × 10−10 417,204 779,551
2500 3.97 × 10−9 402,117 779,018
2600 1.68 × 10−8 387,052 778,422
2700 6.36 × 10−8 372,012 777,757
2800 2.19 × 10−7 356,998 777,019
2900 6.92 × 10−7 342,011 776,201
3000 2.02 × 10−6 327,054 775,297
3100 5.51 × 10−6 312,129 774,303
3200 1.41 × 10−5 297,237 773,213
3300 3.39 × 10−5 282,381 772,021
3400 (solid) 7.75 × 10−5 267,563 770,721
3400 (liquid) 7.75 × 10−5 267,563 702,716
3500 1.58 × 10−4 254,788 701,048
3600 3.08 × 10−4 242,061 699,402
3700 5.78 × 10−4 229,380 697,780
3800 1.05 × 10−3 216,742 696,179
3900 1.84 × 10−3 204,146 694,601
4000 3.15 × 10−3 191,590 693,044
4100 5.23 × 10−3 179,073 691,508
4200 8.48 × 10−3 166,593 689,992
4300 1.34 × 10−2 154,148 688,496
4400 2.08 × 10−2 141,739 687,019
4500 3.15 × 10−2 129,363 685,561
4600 4.69 × 10−2 117,018 684,121
4700 6.84 × 10−2 104,706 682,698
4800 9.87 × 10−2 92,422 681,292
4900 0.140 80,169 679,903
5000 0.195 67,943 678,529
5100 0.269 55,745 677,170
5200 0.365 43,574 675,820
5300 0.490 31,428 674,495
5400 0.651 19,307 673,177
5500 0.854 7,210 671,873
5559.70 1.000 0 671,100
5600 1.110 −4,863 670,582

aΔGºT is the free energy of formation at 1 bar standard state pressure and temperature T

bΔHºT is the enthalpy of sublimation at temperature T enthalpy of sublimation at 0 K: ΔHº0 = 786.795 ± 4.000 kJ mol−1

cNBP is the normal boiling point at one atmosphere pressure (1.01325 bar)

Discussion of Alternative Estimates of the Enthalpy of Fusion of Osmium

Based on various assumptions Fokin et al. (22) proposed that the enthalpy of fusion for osmium was only in the range 30 kJ mol−1 to 40 kJ mol−1 or half of the above derived value. One of the main arguments was that by using the Chekhovskoi-Kats equation the entropy of fusion for rhenium was estimated to be 20.0 J mol−1 K−1 whereas the actual value is only 9.85 J mol−1 K−1 (23) and therefore if the estimate for rhenium was so completely wrong then it would also be possible that the estimate for the neighbouring element osmium at 19.0 J mol−1 K−1 could also be wrong. However, Fokin et al. completely misunderstood how the estimated values were arrived at. It was initially assumed that Group 7 rhenium would behave like Groups 8 to 10 (the pgms) whereas all that the experimental value proved was that Group 7 elements behaved completely independently of Groups 8 to 10 and therefore showed the same deviations as other transition metal groups. For example, the entropies of fusion of Group 5 elements vanadium, niobium and tantalum at 10.46 J mol−1 K−1, 11.13 J mol−1 K−1 and 10.25 J mol−1 K−1 (24) showed no trend with temperature whilst the entropies of fusion of the Group 6 elements chromium, molybdenum and tungsten at 13.89 J mol−1 K−1, 13.53 J mol−1 K−1 and 13.66 J mol−1 K−1 (24) were virtually identical. Therefore it would not be surprising if Group 7 elements would also behave completely independently. In fact for the transition metals only the Groups 8 to 10 elements showed a high degree of correlation with the Chekhovskoi-Kats equation. However in order to prove their point that osmium does behave differently to the other pgms, Fokin et al. used the equation: σM = Z ΔHM ρSM d where σM is the surface tension at the melting point, ΔHM is the enthalpy of fusion, ρSM is the density of the solid at the melting point and d is the interatomic distance. This equation was applied to a number of elements but there is virtually no correlation for the values of Z with values varying between 1.2 to 3.3. For osmium Fokin et al. selected an arbitrary rounded value of Z = 2 for osmium and values of surface tension and liquid density determined by Paradis et al. (25) to arrive at an enthalpy of fusion of only 32 kJ mol−1 which is considerably less than the value of 39.0 ± 1.4 kJ mol−1 (9) selected for the analogue element ruthenium whereas for the other pgms the enthalpy of fusion is always greater for the heavier analogue. This much lower value for the enthalpy of fusion would suggest that the thermal properties of osmium should then be distinct from those of the other pgms but this is not the case. For example, the specific heat values of ruthenium (10) and osmium at reduced temperature (T/TM) as indicated in Figure 1 are very similar and show virtually the same behaviour suggesting that they are genuine analogues of each other whilst the extrapolated melting point of osmium obtained by applying the same incremental difference as between iridium and platinum agrees closely with the selected value and again suggesting a common Groups 8 to 10 behaviour.

Fig. 1

The specific heat values of ruthenium and osmium at reduced temperature (T/TM)

The specific heat values of ruthenium and osmium at reduced temperature (T/TM)

Further, the chemical properties of ruthenium and osmium are virtually identical forming the same type of compounds with similar properties. These are examples where osmium behaves exactly like the other pgms and on these grounds it is suggested that the very low value for the enthalpy of fusion as suggested by Fokin et al. is inconsistent with this behaviour and that osmium would obey the same periodic trend as suggested by the other pgms and that its entropy of fusion can be determined by the Chekhovskoi-Kats equation. This would suggest anomalies in the input values selected by Fokin et al., especially in the selection of Z = 2 for osmium since the value for the analogue ruthenium is only 1.5 whilst the value for the neighbouring element iridium is only 1.2 where the selection of such values would lead to higher enthalpies of fusion for osmium. It is suggested that in view of the lack of any real correlation for Z that the value for osmium may well be independent and could even be 1.0 leading to an enthalpy of fusion similar to that obtained from the Chekhovskoi-Kats equation. Therefore until the actual enthalpy of fusion of osmium is determined it is assumed that it behaves as a normal Groups 8 to 10 element.

Conclusions

Estimated entropy and enthalpy values of fusion of osmium have been revised leading to corrections of the thermodynamic properties of the liquid phase and therefore to the vapour pressure curve above the melting point. The revisions are based on the assumption that osmium behaves as a normal Group 8 to 10 element and contradicts recent suggestions that its behaviour could be abnormal.

BACK TO TOP

References

  1. 1.
    J. W. Arblaster, Calphad, 1995, 19, (3), 349 LINK https://doi.org/10.1016/0364-5916(95)00032-a
  2. 2.
    J. W. Arblaster, Platinum Metals Rev., 2005, 49, (4), 166 LINK https://www.technology.matthey.com/article/49/4/166-168/
  3. 3.
    L. Burakovsky, N. Burakovsky and D. L. Preston, Phys. Rev. B, 2015, 92, (17), 174105 LINK https://doi.org/10.1103/physrevb.92.174105
  4. 4.
    ‘Standard Atomic Weights’, Commission on Isotopic Abundances and Atomic Weights (CIAAW), 2019 LINK www.ciaaw.org/atomic-weights.htm
  5. 5.
    A. M. Okaz and P. H. Keesom, Physica, 1973, 69, (1), 97 LINK https://doi.org/10.1016/0031-8914(73)90204-8
  6. 6.
    V. N. Naumov, I. E. Paukov, G. Ramanauskas and V. Ya. Chekhovskoi, Zh. Fiz. Khim., 1988, 62, (1), 25, translated into English in Russ. J. Phys. Chem., 1988, 62, (1), 12
  7. 7.
    G. Ramanauskas, V. D. Tarasov, V. Ya. Chekhovskoi, N. L. Korenovskii and V. P. Polyakova, Vysokochist. Veshchestva., 1988, (4), 149, in Russian
  8. 8.
    F. M. Jaeger and E. Rosenbohm, Proc. R. Acad. Amsterdam, 1931, 34, (1), 85
  9. 9.
    S. Stølen and F. Grønvold, Thermochim. Acta, 1999, 327, (1–2), 1 LINK https://doi.org/10.1016/S0040-6031(98)00613-3
  10. 10.
    J. W. Arblaster, Calphad, 1995, 19, (3), 339 LINK https://doi.org/10.1016/0364-5916(95)00031-9
  11. 11.
    J. W. Arblaster, Calphad, 1995, 19, (3), 357 LINK https://doi.org/10.1016/0364-5916(95)00033-b
  12. 12.
    J. W. Arblaster, Johnson Matthey Technol. Rev., 2018, 62, (1), 48 LINK https://www.technology.matthey.com/article/62/1/48-59/
  13. 13.
    J. W. Arblaster, Calphad, 1995, 19, (3), 365 LINK https://doi.org/10.1016/0364-5916(95)00034-c
  14. 14.
    J. W. Arblaster, Platinum Metals Rev., 2005, 49, (3), 141 LINK https://www.technology.matthey.com/article/49/3/141-149/
  15. 15.
    V. Ya. Chekhovskoi and S. A. Kats, High Temp.–High Pressures, 1981, 13, (6), 611
  16. 16.
    Th. A. M. Van Kleef and P. F. A. Klinkenberg, Physica, 1961, 27, (1), 83 LINK https://doi.org/10.1016/0031-8914(61)90023-4
  17. 17.
    G. G. Gluck, Y. Bordarier, J. Bauche and Th. A. M. Van Kleef, Physica, 1964, 30, (11), 2068 LINK https://doi.org/10.1016/0031-8914(64)90028-x
  18. 18.
    H. G. Kolsky, R. M. Gilmer and P. W. Gilles, “The Thermodynamic Properties of 54 Elements Considered as Ideal Monatomic Gases”, LA 2110, US Atomic Energy Commission, Washington, USA, 15th March, 1957, 138 pp
  19. 19.
    E. Tiesinga, P. J. Mohr, D. B. Newell and B. N. Taylor, ‘The CODATA Internationally Recommended 2018 Values of the Fundamental Physical Constants’, NIST Standard Reference Database 121, Version 8.0, National Institute of Standards and Technology, Gaithersburg, USA, May, 2019 LINK https://physics.nist.gov/cuu/Constants/index.html
  20. 20.
    M. B. Panish and L. Reif, J. Chem. Phys., 1962, 37, (1), 128 LINK https://doi.org/10.1063/1.1732934
  21. 21.
    N. J. Carrera, R. F. Walker and E. R. Plante, J. Res. Nat. Bur. Stand., 1964, 68A, (3), 325 LINK https://doi.org/10.6028/jres.068a.031
  22. 22.
    L. R. Fokin, E. Yu. Kulyamina and V. Yu. Zitserman, High Temp., 2019, 57, (1), 54 LINK https://doi.org/10.1134/s0018151x19010073
  23. 23.
    J. W. Arblaster, Calphad, 1996, 20, (3), 343 LINK https://doi.org/10.1016/s0364-5916(96)00036-3
  24. 24.
    M. G. Frohberg, Thermochim. Acta, 1999, 337, (1–2), 7 LINK https://doi.org/10.1016/s0040-6031(99)00159-8
  25. 25.
    P.-F. Paradis, T. Ishikawa and N. Koike, J. Appl. Phys., 2006, 100, (10), 103523 LINK https://doi.org/10.1063/1.2386948
 

The Author


John W. Arblaster is interested in the history of science and the evaluation of the thermodynamic and crystallographic properties of the elements. Now retired, he previously worked as a metallurgical chemist in a number of commercial laboratories and was involved in the analysis of a wide range of ferrous and non-ferrous alloys.

Read more from this issue »

BACK TO TOP

SHARE THIS PAGE: