Standard Reference Materials

Abstract

The relative enthalpy of NBS Standard Reference Material No. 781 (99.95 mass-percent pure, polycrystalline molybdenum: a metallic, hightemperature enthalpy and heat-capacity standard) has been measured with two differently designed, receivingtype calorimeters in the temperature ranges 273 to 1173 K and 1173 to 2100 K, respectively. The smoothed enthalpy data derived from these measurements are believed to have an inaccuracy not exceeding 0.6 percent at any temperature in these ranges. The heat capacity of Standard Reference Material No. 781 has also been measured in the temperature range 1500 to 2800 K using a millisecondresolution pulse technique with resistive self-heating. This technique measured, in addition, hemispherical total emittance. In this highest temperature range, the smoothed heat-capacity data are believed to be in error by no more than 3 percent. A complete description of all the NBS experimental techniques and a detailed analysis of all suspected sources of errors are presented.Equations representing the smoothed NBS enthalpy and heat-capacity data for SRM-781 molybdenum in the range 273.15 to 2800 K are presented along with a table of these data calculated from the equations at selected temperatures. A bibliography of all known publications on the enthalpy and heat capacity of molybdenum has been compiled. The NBS-measured enthalpy and heat-capacity data for molybdenum have been compared with those of all the principal investigators and compilers reported in the literature.

Standards, calibration, and guidelines in microcalorimetry. Part 2. Calibration standards for differential scanning calorimetry* (IUPAC Technical Report)

“…σ fit = 0.0048 J K -1 mol -1 , σ red = 0.016 % for 74 values between 273.15 and 1000 K. Statement of the authors of ref. [35]: Chapter 6.2, second paragraph: " Figure 1 indicates that two enthalpy measurements at 323.15 and 373.15 K deviate considerably from all the others in the series (up to three times the standard deviation of residues). A re-calculation of the standard deviation of the ice-calorimeter data, neglecting these two measurements, yields 0.06 percent for this index of the imprecision of the measurements.…”

“…σ fit = 0.0048 J K -1 mol -1 , σ red = 0.007 % for 101 values between 1000 and 2000 K. Statement of the authors of ref. [35]: Page 38, first paragraph: "Addition of the observed standard deviation of residues for the enthalpy data (from equation (3), taken at a 99-percent confidence level) to the maximum estimated inaccuracy in enthalpy due to temperature error (0.15 percent at 2000 K) and the estimated inaccuracy due to sample impurity (0.05 percent) yields an estimate of the overall inaccuracy in the enthalpy measurements of 0.6 percent. The inaccuracy in the heat-capacity values derived from equation (3) by differentiation is believed to be about 1 percent".…”

“…[35]. σ fit = 0.0048 J K -1 mol -1 , σ red = 0.007 % for 101 values between 1000 and 2000 K. Statement of the authors of ref.…”

Enthalpy and Heat-Capacity Standard Reference Material: Synthetic Sapphire (Alpha-Al2O3) From 10 to 2250 K

“…Some physical and operational details of this apparatus have been given in [5] and [6]. These experiments were carried out with the calorimeter and furnace containing purified argon gas at about 0.1 atm.…”

Specific Heat Capacity Measurement of Single-Crystalline Silicon as New Reference Material

“…To measure the specific heat capacity of materials correctly, a reference material is essential. In the National Institute of Standards and Technology (NIST), USA, as is shown in Table I, three kinds of standard reference materials (SRMs) for enthalpy and heat capacity (SRM720: synthetic sapphire, [1][2][3][4][5] SRM781D2: molybdenum, [6][7][8][9] and SRM705a: polystyrene 10) ) have been developed. 11) For SRMs measurement, however, the uncertainty was not fully evaluated because they were developed in the old days.…”