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. 1971 Sep-Oct;75A(5):401-420.
doi: 10.6028/jres.075A.031.

Measurement of the Relative Enthalpy of Pure α-AI2O3 (NBS Heat Capacity and Enthalpy Standard Reference Material No. 720) from 273 to 1173 K

David A Ditmars  1 , Thomas B Douglas  1
Affiliations

Measurement of the Relative Enthalpy of Pure α-AI2O3 (NBS Heat Capacity and Enthalpy Standard Reference Material No. 720) from 273 to 1173 K

David A Ditmars et al. J Res Natl Bur Stand A Phys Chem. 1971 Sep-Oct.

Abstract

The relative enthalpy of NBS Standard Reference Material No. 720 (99.98 percent pure, single-crystal α-Al2O3, a calorimetrie heat-capacity standard) was measured over the range 273 to 1173 K by the drop method using a highly precise Bunsen ice calorimeter. Enthalpy data over the same temperature interval were obtained also on the Calorimetry Conference Sample of this substance. These results are believed to be more accurate than similar NBS results on the latter sample published in 1956, and show no significant discontinuity with the NBS data on the same substance that covered the ranges 13 to 380 K and 1173 to 2257 K. The average deviation from the mean for all enthalpy measurements on the SKM 720 sample was 0.017 percent, and the smooth enthalpy values derived from the data were estimated to be accurate to 0.1 percent. The precautions observed in order to minimize measuring errors are described in detail. The data are compared with many sets of the most reliable published data available and new recommended values for the thermodynamic functions of α-Al2O3 are presented for the interval 0 to 1200 K.

Keywords: Alumina; aluminium oxide; corundum; drop calorimetry; enthalpy; heat capacity standard; specific heat; standard reference material; synthetic sapphire; thermodynamic functions.

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Figures

Figure 1.
Figure 1.. Sampling procedure followed to obtain four random specimens of SRM720.
See also text, section 3.4.a.
Figure 2.
Figure 2.. Schedule of measurements.
Each “X” indicates a single enthalpy measurement. Temperatures are spaced about 50 K apart from 0 to 900 °C. All measurements at any one temperature were completed before proceeding to another temperature.
Figure 3.
Figure 3.. Deviation of Pt10Rh blank enthalpy data from smoothing function (eq (1)).
●, Blank 1: ○, Blank 2.
Figure 4.
Figure 4.. Deviation of α-Al2O3 enthalpy data of the present investigation and of eq (3) from least-squares fit of SRM720 data alone (eq (2)).
SRM720 Sublots: ○, No. 1; ⦶, No. 2; ⊕, No. 3; ⊖, No. 4; ◓, Calorimetry Conference Sample. —————, eq (3).
Figure 5.
Figure 5.. Comparison with table 4 of α-Al2O3 On enthalpy relative to 0 °C for NBS ice-calorimeter data.
Base line is table 4; ●, SRM720 sample (this work); ◓, Calprimetry Conference sample (this work); ○, Calorimetry Conference Sample. Furukawa, Douglas et al. (1956) [2] : △, (Winnings and Corruccini (1947) [6]; – – – . Furukawa, Douglas et al. (smoothed values) (1956) [2];------ Smooth values of [2] (1956) as corrected by Ginnings (1963) [10]. The vertical bars (not error bounds) locate the common temperature of each group of points.
Figure 6.
Figure 6.. Comparison of NBS drop-calorimeter heat capacity results on α-Al2O3 with results of high-temperature adiabatic calorimetry.
The base line is the heat capacity function derived from eq (2): ●, average Cp, corrected for curvature, from SRM720 data of table 2, this work:------, NBS 1956 recommended values [2]; —————, NBS l970 recommended values (table 4, this work): ▲, West and Ginnings [16]; ○, Grønvold [17]; formula image Martin and Snowdon [40].
Figure 7.
Figure 7.. Comparison of α-Al2O3 enthalpy data relative to 0 °C with values derived from table 4.
Selected NBS data upon which table 4 was based are shown along with results of other high-temperature investigators.
Figure 7.
Figure 7.. Comparison of α-Al2O3 enthalpy data relative to 0 °C with values derived from table 4.
Selected NBS data upon which table 4 was based are shown along with results of other high-temperature investigators.
See this image and copyright information in PMC

References

    1. Schneider S. J., Pure Appl. Chem. 21, No. 1, 116 (1970).
    1. Furukawa G. T., Douglas T. B., McCoskey R. E., and Ginnings D. C., J. Res. Nat. Bur. Stand. (U.S.). 57, No. 2, 67 (1956) RP2694.
    1. West E. D., and Ishihara S., Advances in Thermophysical Properties at Extreme Temperatures and Pressures, 146–151. The American Society of Mechanical Engineers. N.Y., N.Y. (1965); also in Precision Measurement and Calibration (Heat), Ginnings D. C., Ed., Nat. Bur. Stand. (U.S.), Spec. Publ. 300. Vol. 6, 220–225 (1970).
    1. Verneuil A. V. L., U.S. Patent No. 1.004,505 Sept. 26. 1911.
    1. Douglas T. B., and King E. G., High Temperature Drop Calorimetry, Chapter 8 in Experimental Thermodynamics V.I, (Butterworths, London, 1968); also in Precision Measurement and Calibration (Heat), Ginnings D. C., Ed., Nat. Bur. Stand. (U.S.), Spec. Publ. 300, Vol. 6, 181–219 (1970).

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