*Platinum Metals Rev.*, 2013, **57**, (2), 127

doi:10.1595/147106713x665030

## Crystallographic Properties of Ruthenium

### Assessment of properties from absolute zero to 2606 K

- John W. Arblaster
- Wombourne, West Midlands, UK Email: jwarblaster@yahoo.co.uk

### Article Synopsis

*The crystallographic properties of ruthenium at temperatures from absolute zero to the melting point at 2606 K are assessed following a review of the literature published between 1935 and to date. Selected values of the thermal expansion coefficients and measurements of length changes due to thermal expansion have been used to calculate the variation with temperature of the lattice parameters, interatomic distances, atomic and molar volumes and densities. The data is presented in the form of Figures, Equations and Tables.*

This is the sixth in a series of papers in this Journal on the crystallographic properties of the platinum group metals (pgms), following two papers on platinum (1, 2) and one each on rhodium (3), iridium (4) and palladium (5). Ruthenium exists in a hexagonal close-packed (hcp) structure (Pearson symbol *hP2*) up to the melting point which is a secondary fixed point on ITS-90 at 2606 ± 10 K (6).

The thermal expansion is represented by five sets of lattice parameter measurements, those of Owen and Roberts (7, 8) (from 323 K to 873 K), Hall and Crangle (9) (from 799 K to 1557 K), Ross and Hume-Rothery (10) (from 1793 K to 2453 K), Schröder *et al.* (11) (from 84 K to 1982 K) and Finkel’ *et al.* (12) (from 80 K to 300 K) and one set of dilatometric measurements, those of Shirasu and Minato (13) (from 323 K to 1300 K). The measurements of Hall and Crangle, Ross and Hume-Rothery and Finkel’ *et al.* were only shown graphically with actual data points as length change values being given by Touloukian *et al.* (14). Because there is a certain degree of incompatibility between the high-temperature measurements, and those obtained at low-temperature by Finkel’ *et al.*, the high- and low-temperature data were initially treated separately. Available thermal expansion data covers the range from 293.15 K to 2453 K with estimated values below the lower limit whilst in the high-temperature region the derived equations are extrapolated to the melting point.

## Thermal Expansion

### High-Temperature Region

Length change values derived from the measurements of Owen and Roberts (7, 8) and Ross and Hume-Rothery (10) agree satisfactorily and were combined to give Equations (i) and (ii) to represent the thermal expansion from 293.15 K to the melting point. On the basis ± 100δ*L*/*L*_{293.15 K} Equation (i) for the *a*-axis has an accuracy of ± 0.009 and Equation (ii) for the *c*-axis an accuracy of ± 0.025. Crystallographic properties derived from Equations (i) and (ii) are given in **Tables I** and **II**.

##### Table I

Temperature, K | Thermal expansion coefficient, α _{a}, 10^{−6} K^{−1} | Thermal expansion coefficient, α_{c}, 10^{−6} K^{−1} | Thermal expansion coefficient, α, 10_{avr}^{−6} K^{−1} | Length change, δa/a_{293.15 K} × 100, % | Length change, δc/c_{293.15 K} × 100, % | Length change, δavr/avr_{293.15 K} × 100^{a}, % |
---|---|---|---|---|---|---|

293.15 | 5.77 | 8.80 | 6.78 | 0 | 0 | 0 |

300 | 5.79 | 8.83 | 6.80 | 0.004 | 0.006 | 0.005 |

400 | 6.09 | 9.29 | 7.16 | 0.063 | 0.097 | 0.074 |

500 | 6.40 | 9.77 | 7.52 | 0.126 | 0.192 | 0.148 |

600 | 6.72 | 10.25 | 7.90 | 0.191 | 0.292 | 0.225 |

700 | 7.05 | 10.76 | 8.28 | 0.260 | 0.398 | 0.306 |

800 | 7.39 | 11.27 | 8.68 | 0.333 | 0.509 | 0.391 |

900 | 7.73 | 11.80 | 9.09 | 0.409 | 0.625 | 0.481 |

1000 | 8.09 | 12.34 | 9.51 | 0.488 | 0.746 | 0.574 |

1100 | 8.46 | 12.90 | 9.94 | 0.571 | 0.873 | 0.672 |

1200 | 8.83 | 13.47 | 10.38 | 0.658 | 1.006 | 0.774 |

1300 | 9.22 | 14.05 | 10.83 | 0.749 | 1.145 | 0.881 |

1400 | 9.61 | 14.65 | 11.29 | 0.844 | 1.291 | 0.993 |

1500 | 10.02 | 15.26 | 11.76 | 0.943 | 1.442 | 1.110 |

1600 | 10.43 | 15.88 | 12.24 | 1.046 | 1.600 | 1.231 |

1700 | 10.85 | 16.51 | 12.74 | 1.154 | 1.765 | 1.358 |

1800 | 11.28 | 17.16 | 13.24 | 1.266 | 1.936 | 1.489 |

1900 | 11.71 | 17.82 | 13.75 | 1.382 | 2.115 | 1.627 |

2000 | 12.16 | 18.49 | 14.27 | 1.503 | 2.300 | 1.769 |

2100 | 12.61 | 19.17 | 14.80 | 1.629 | 2.493 | 1.917 |

2200 | 13.08 | 19.86 | 15.34 | 1.760 | 2.693 | 2.071 |

2300 | 13.55 | 20.56 | 15.89 | 1.895 | 2.901 | 2.231 |

2400 | 14.03 | 21.28 | 16.44 | 2.036 | 3.117 | 2.396 |

2500 | 14.51 | 22.00 | 17.01 | 2.182 | 3.340 | 2.568 |

2600 | 15.01 | 22.74 | 17.58 | 2.333 | 3.571 | 2.746 |

2606 | 15.04 | 22.78 | 17.62 | 2.342 | 3.586 | 2.756 |

##### Table II

On the basis of the expression:

100 × (δ*L*/*L*_{293.15 K (experimental)} − δ*L*/*L*_{293.15 K (calculated)})

where δ*L*/*L*_{293.15 K (experimental)} is the experimental length change relative to 293.15 K and δ*L*/*L*_{293.15 K (calculated)} is the selected length change value, then length change values derived from the measurements of Hall and Crangle (9) deviate continuously from selected values and both axes are 0.14 low at the experimental limit 1557 K. Above room temperature the *a*-axis values of Schröder *et al.* (11) initially trend to be 0.080 low at 1300 K before increasing to 0.089 high at 1982 K. The *c*-axis values behave similarly, initially trending to 0.072 low at 1100 K before increasing sharply to 0.35 high at 1982 K. The dilatometric measurements of Shirasu and Minato (13) trend to 0.10 low. The deviations of these three sets of values are shown in **Figure 1**.

##### Fig. 1.

### Low-Temperature Region

The lattice parameter measurements of Finkel’ *et al.* (12), given as length change values by Touloukian *et al.* (14), were fitted to cubic Equations (v) and (vi) for the *a-* and c-axes respectively. Derived thermal expansion coefficients at 293.15 K of 6.5 × 10^{−6} K^{−1} for the *a*-axis and 11.5 × 10^{−6} K^{−1} for the *c*-axis are notably higher than those derived from Equations (i) and (ii) as given in **Tables II** and **III** and indicate the degree of incompatibility between the high- and low-temperature data. Various manipulations of subsets of the low-temperature measurements to try and reconcile the differences proved to be unsatisfactory and the measurements of Finkel’ *et al.* were rejected. Therefore in order to extrapolate below room temperature Equations (i) and (ii) were differentiated and derived values of the thermal expansion coefficient relative to 293.15 K, α*, were converted to thermodynamic thermal expansion, α, using α = α*/(1 + δ*L*/*L*_{293.15 K}). The α values obtained at 293.15 K and over the range 300 K to 800 K at 50 K intervals were then fitted to Equations (iii) and (iv) where the values of the specific heat used, *C _{p}*, are given by Equation (vii). Equations (iii) and (iv) were then extrapolated below the room temperature region using specific heat values given in the Appendix in order to represent the thermal expansion to absolute zero, although

*a*-axis thermal expansion coefficients above 240 K were slightly adjusted in order to give a smooth continuity with the high-temperature selected values. Crystallographic properties derived from Equations (iii) and (iv) are given in

**Tables III**and

**IV**.

##### Table III

##### Table IV

Temperature, K | Thermal expansion coefficient, α_{a}, 10^{−6} K^{−1} | Thermal expansion coefficient, α_{c}, 10^{−6} K^{−1} | Thermal expansion coefficient, α_{avr}, 10^{−6} K^{−1} | Length change, δa/a_{293.15 K} × 100, % | Length change, δc/c_{293.15 K} × 100, % | Length change, δavr/avr_{293.15 K} × 100, % |
---|---|---|---|---|---|---|

0^{a} | 0 | 0 | 0 | −0.113 | −0.172 | −0.132 |

10 | 0.04 | 0.06 | 0.05 | −0.113 | −0.172 | −0.132 |

20 | 0.09 | 0.16 | 0.12 | −0.113 | −0.172 | −0.132 |

30 | 0.32 | 0.48 | 0.37 | −0.112 | −0.171 | −0.132 |

40 | 0.70 | 1.07 | 0.83 | −0.112 | −0.171 | −0.131 |

50 | 1.25 | 1.91 | 1.47 | −0.111 | −0.169 | −0.130 |

60 | 1.85 | 2.82 | 2.17 | −0.109 | −0.167 | −0.129 |

70 | 2.39 | 3.66 | 2.56 | −0.107 | −0.163 | −0.126 |

80 | 2.88 | 4.40 | 3.39 | −0.105 | −0.159 | −0.123 |

90 | 3.30 | 5.04 | 3.88 | −0.102 | −0.155 | −0.119 |

100 | 3.66 | 5.58 | 4.30 | −0.098 | −0.149 | −0.115 |

110 | 3.95 | 6.03 | 4.65 | −0.094 | −0.144 | −0.111 |

120 | 4.20 | 6.42 | 4.94 | −0.090 | −0.137 | −0.106 |

130 | 4.42 | 6.74 | 5.19 | −0.086 | −0.131 | −0.101 |

140 | 4.60 | 7.02 | 5.40 | −0.081 | −0.124 | −0.096 |

150 | 4.75 | 7.25 | 5.58 | −0.077 | −0.117 | −0.090 |

160 | 4.88 | 7.44 | 5.73 | −0.072 | −0.109 | −0.084 |

170 | 4.98 | 7.61 | 5.86 | −0.067 | −0.102 | −0.079 |

180 | 5.08 | 7.76 | 5.97 | −0.062 | −0.094 | −0.073 |

190 | 5.17 | 7.89 | 6.07 | −0.057 | −0.086 | −0.067 |

200 | 5.25 | 8.01 | 6.17 | −0.052 | −0.079 | −0.061 |

210 | 5.32 | 8.12 | 6.25 | −0.046 | −0.070 | −0.054 |

220 | 5.38 | 8.22 | 6.33 | −0.041 | −0.062 | −0.048 |

230 | 5.45 | 8.31 | 6.40 | −0.036 | −0.054 | −0.042 |

240 | 5.50 | 8.40 | 6.47 | −0.030 | −0.046 | −0.035 |

250 | 5.58 | 8.48 | 6.55 | −0.024 | −0.037 | −0.029 |

260 | 5.63 | 8.56 | 6.61 | −0.019 | −0.029 | −0.022 |

270 | 5.68 | 8.63 | 6.66 | −0.013 | −0.020 | −0.016 |

280 | 5.71 | 8.70 | 6.71 | −0.008 | −0.011 | −0.009 |

290 | 5.75 | 8.77 | 6.76 | −0.002 | −0.003 | −0.002 |

293.15 | 5.77 | 8.80 | 6.78 | 0 | 0 | 0 |

There is the possibility of significant uncertainty in this procedure but it is noted that in comparison, using the same procedure as for the high-temperature data, the measurements of Finkel’ *et al.* (12) show a maximum deviation of only 0.006 low at 80 K for the *a*-axis and then converge towards the selected values. For the *c*-axis, there is initially agreement with the selected values and a maximum deviation of only 0.010 low at 220 K. These small differences would actually suggest agreement between the high- and low-temperature data; however, the fitting procedure is so sensitive that these differences represent incompatibility. The low-temperature measurements of Schröder *et al.* (11) are initially 0.027 low at 84 K for the *a*-axis and then converge towards the selected values, whilst for the *c*-axis the value is initially 0.026 low but there is agreement to better than 0.001 above 210 K.

Normally, as an alternative method of calculation, Equations (iii) and (iv) would be fitted to a series of spline fitted equations; however as there are two axes this could involve a significant number of equations and therefore the much simpler procedure has been adopted of substituting values of *C _{p}* from the

**Appendix**into the equations.

## The Lattice Parameter at 293.15 K

The values of the lattice parameters, *a *and* c*, given in **Table V** represent a combination of those values selected by Donohue (15) and more recent measurements. Values originally given in kX units were converted to nanometres using the 2010 International Council for Science: Committee on Data for Science and Technology (CODATA) Fundamental Constants (16, 17) conversion factor for CuKα_{1}, which is 0.100207697 ± 0.000000028 whilst values given in angstroms (Å) were converted using the default ratio 0.100207697/1.00202 where the latter value represents the old conversion factor from kX units to Å. Lattice parameter values were corrected to 293.15 K using the values of the thermal expansion coefficient selected in the present review. Density values given in **Tables II** and **III** were calculated using the currently accepted atomic weight of 101.07 ± 0.02 (18) and an Avogadro constant (*N*_{A}) of (6.02214129 ± 0.00000027) × 10^{23}mol^{−1} (16, 17). From the lattice parameter values at 293.15 K selected in **Table V** as: *a* = 0.27058 ± 0.00002 nm and *c* = 0.42816 ± 0.00007 nm, the derived selected density is 12364 ± 3 kg m^{−3} and the molar volume is (8.1743 ± 0.0018) × 10^{−6} m^{3} mol^{−1}. In **Tables II** and **III** the interatomic distance *d*1 = *(a*^{2}*/*3* + c*^{2}*/*4*)*^{½} and *d*2 = *a. *The atomic volume is *(√*3* a*^{2} *c)/*4 and the molar volume is calculated as *N*_{A} *(√*3* a*^{2} *c)*/4 which is equivalent to atomic weight divided by density. Thermal expansion is α_{avr} = (2 α_{a} + α_{c})/3 and length change is δavr/avr_{293.15 K} = (2 δ*a*/*a*_{293.15 K} + δ*c*/*c*_{293.15 K})/3 (avr = average).

##### Table V

#### Lattice Parameter Values at 293.15 K^{a}

Authors (Year) | Reference | Original temperature, K | Original units | Lattice parameter, a, corrected to 293.15 K, nm | Lattice parameter, c, corrected to 293.15 K, nm | Notes |
---|---|---|---|---|---|---|

Owen et al. (1935) | (18) | 291 | kX | 0.27044 | 0.42818 | (a) |

Owen and Roberts (1936) | (7) | 291 | kX | 0.27042 | 0.42819 | (a) |

Owen and Roberts (1937) | (8) | 293 | kX | 0.27040 | 0.42819 | (a) |

Ross and Hume-Rothery | (10) | 303 | Å | 0.27042 | 0.42799 | (a), (b) |

Finkel’ et al. (1971) | (12) | 293 | Å | 0.27062 | 0.42815 | (a), (b) |

Hellawell and Hume-Rothery (1954) | (19) | 298 | kX | 0.27058 | 0.42817 | |

Swanson et al. (1955) | (20) | 300 | Å | 0.27059 | 0.42819 | |

Hall and Crangle (1957) | (9) | rt^{b} | Å | 0.27058 | 0.42805 | |

Anderson and Hume-Rothery (1960) | (21) | 293 | kX | 0.27058 | 0.42814 | |

Černohorský (1960) | (22) | 295 | Å | 0.27059 | 0.42812 | |

Savitskii et al. (1962) | (23) | rt | kX | 0.27059 | 0.42819 | |

Schröder et al. (1972) | (11) | 284 | Å | 0.27056 | 0.42826 |

## Summary

Because there is disagreement between the high- and low-temperature measurements for ruthenium, satisfactory thermal expansion data is only available above 293.15 K with a novel approach being used to extrapolate below this temperature to derive values which must be considered to be tentative. Clearly further measurements are required for this element.

#### High-Temperature Thermal Expansion Equations for Ruthenium (293.15 K to 2606 K)

δ*a*/*a*_{293.15} = −1.56642 × 10^{−3} + 4.93471 × 10^{−6} *T* + 1.34455 × 10^{−9} *T*^{2} + 1.69158 × 10^{−13} *T*^{3} (i)

δ*c*/*c*_{293.15} = −2.39045 × 10^{−3} + 7.52727 × 10^{−6} *T* + 2.06251 × 10^{−9} *T*^{2} + 2.61425 × 10^{−13} *T*^{3} (ii)

#### Low-Temperature Thermal Expansion Equations for Ruthenium (0 K to 293.15 K)

α_{a} (K^{−1}) = *C _{p}* (1.92207 × 10

^{−7}+ 8.09046 × 10

^{−11}

*T*+ 7.16082 × 10

^{−6}/

*T*) (iii)

α_{c} (K^{−1}) = *C _{p}* (2.93088 × 10

^{−7}+ 1.24609 × 10

^{−10}

*T*+ 1.09421 × 10

^{−5}/

*T*) (iv)

#### Thermal Expansion Equations Representing the Measurements of Finkel’ et al. (12)

δ*a*/*a*_{293.15} = −1.40337 × 10^{−3} + 3.25082 × 10^{−6} *T* + 4.63332 × 10^{−9} *T*^{2} + 2.07266 × 10^{−12} *T*^{3} (v)

δ*c*/*c*_{293.15} = −1.87652 × 10^{−3} + 3.44170 × 10^{−6} *T* + 2.91501 × 10^{−9} *T*^{2} + 2.44946 × 10^{−11} *T*^{3} (vi)

#### High-Temperature Specific Heat Equation (298.15 K to 2606 K)

#### Appendix: Specific Heat Values for Ruthenium

Because of the large number of spline fitted equations that would be required to conform to Equations (iii) and (iv), a simpler approach is used for the non-cubic metals in that specific heat values are directly applied to these equations. However this would require that the Table of low-temperature specific heat values originally given by the present author (24) has to be more comprehensive and the revised Table is given as **Table VI**. The high-temperature specific heat values corresponding to the above reference is given as Equation (vii) and is derived by differentiating the selected enthalpy equation.

##### Table VI

#### Low-Temperature Specific Heat Values for Ruthenium

## References

- J. W. Arblaster,
*Platinum Metals Rev*., 1997,**41**, (1), 12 LINK https://www.technology.matthey.com/article/41/1/12-21/ - J. W. Arblaster,
*Platinum Metals Rev*., 2006,**50**, (3), 118 LINK https://www.technology.matthey.com/article/50/3/118-119/ - J. W. Arblaster,
*Platinum Metals Rev*., 1997,**41**, (4), 184 LINK https://www.technology.matthey.com/article/41/4/184-189/ - J. W. Arblaster,
*Platinum Metals Rev*., 2010,**54**, (2), 93 LINK https://www.technology.matthey.com/article/54/2/93-102/ - J. W. Arblaster,
*Platinum Metals Rev*., 2012,**56**, (3), 181 LINK https://www.technology.matthey.com/article/56/3/181-189/ - R. E. Bedford, G. Bonnier, H. Maas and F. Pavese,
*Metrologia*, 1996,**33**, (2), 133 LINK http://dx.doi.org/10.1088/0026-1394/33/2/3 - E. A. Owen and E. W. Roberts,
*Philos. Mag.*, 1936,**22**, (146), 290 LINK http://dx.doi.org/10.1080/14786443608561687 - E. A. Owen and E. W. Roberts,
*Z. Kristallogr.*, 1937,**A96**, 497 - E. O. Hall and J. Crangle,
*Acta Cryst.*, 1957,**10**, Part 3, 240 LINK http://dx.doi.org/10.1107/S0365110X57000742 - R. G. Ross and W. Hume-Rothery,
*J. Less Common Met.*, 1963,**5**, (3), 258 LINK http://dx.doi.org/10.1016/0022-5088(63)90031-6 - R. H. Schröder, N. Schmitz-Pranghe and R. Kohlhaas,
*Z. Metallkd.*, 1972,**63**, (1), 12 - V. A. Finkel’, M. Palatnik and G. P. Kovtun,
*Fiz. Met. Metalloved.*, 1971,**32**, (1), 212; translated into English in*Phys. Met. Metallogr.*, 1972,**32**, (1), 231 - Y. Shirasu and K. Minato,
*J. Alloys Compd.*, 2002,**335**, (1–2), 224 LINK http://dx.doi.org/10.1016/S0925-8388(01)01806-0 - Y. S. Touloukian, R. K. Kirby, R. E. Taylor and P. D. Desai, “Thermal Expansion: Metallic Elements and Alloys”, Thermophysical Properties of Matter, The TPRC Data Series, Vol. 12, eds. Y. S. Touloukian and C. Y. Ho, IFI/Plenum Press, New York, USA, 1975
- J. Donohue, “The Structure of the Elements”, John Wiley and Sons, New York, USA, 1974
- P. J. Mohr, B. N. Taylor and D. B. Newell,
*Rev. Mod. Phys.*, 2012,**84**, (4), 1527 LINK http://dx.doi.org/10.1103/RevModPhys.84.1527 - P. J. Mohr, B. N. Taylor and D. B. Newell,
*J. Phys. Chem. Ref. Data*, 2012,**41**, (4), 043109 LINK http://link.aip.org/link/doi/10.1063/1.4724320 - E. A. Owen, L. Pickup and I. O. Roberts,
*Z. Kristallogr*., 1935,**A91**, 70 - A. Hellawell and W. Hume-Rothery,
*Philos. Mag. Ser. 7*, 1954,**45**, (367), 797 LINK http://dx.doi.org/10.1080/14786440808520492 - H. E. Swanson, R. K. Fuyat and G. M. Ugrinic, “Standard X-Ray Diffraction Powder Patterns”, NBS Circular Natl. Bur. Stand. Circ. (US) 539, 1955,
**IV**, 5 LINK http://digicoll.manoa.hawaii.edu/techreports/PDF/NBS25-18.pdf - E. Anderson and W. Hume-Rothery.
*J. Less Common Met.*, 1960,**2**, (6), 443 LINK http://dx.doi.org/10.1016/0022-5088(60)90026-6 - M. Černohorský,
*Acta Cryst.*, 1960,**13**, (10), 823 LINK http://dx.doi.org/10.1107/S0365110X60001989 - E. M. Savitskii, M. A. Tylkina and V. P. Polyakova,
*Zh. Neorgan. Khim.*, 1962,**7**, (2), 439; translated into English in*Russ. J. Inorg. Chem.*, 1962,**7**, (2), 224 - J. W. Arblaster,
*CALPHAD*, 1995,**19**, (3), 339 LINK http://dx.doi.org/10.1016/0364-5916(95)00031-9

*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.*