| Calibration of Differential Scanning Calorimeters
Differential Scanning Calorimeters are almost universally calibrated for temperature and enthalpy using the melting temperatures of highly pure metals. Recommended values for the melting temperature (Tm) and heat of fusion (Hf) are given below. Many of these substances will react with standard aluminium crucibles. This may be overcomes by annealing the empty crucible (and lid) air above 400°C in order to build up a protective layer of aluminium oxide. Aluminium crucibles cannot be used to calibrate with aluminium for obvious reasons! |
|
Material |
Tm (°C) |
Hf (J/g) |
|
Mercury |
-38.8344 |
11.469 |
|
Gallium |
29.7646 |
79.88 |
Indium |
156.5985 |
28.62 |
|
Tin |
231.298 |
7.170 |
|
Bismuth |
271.40 |
53.83 |
|
Lead |
327.462 |
23.00 |
|
Zinc |
419.527 |
108.6 |
|
Aluminium |
660.323 |
398.1 |
References: G. W. H. Höhne, H. K. Cammenga, W. Eysel, E. Gmelin, W. Hemminger; "The Temperature Calibration of Scanning Calorimeters", Thermochimica Acta, 160 (1990) 1-12 S. M. Sarge, E. Gmelin, G. W. H. Höhne, H. K. Cammenga, W. Hemminger, W. Eysel; "The Caloric Calibration of Scanning Calorimeters", Thermochimica Acta, 247 (1994) 129-168 M. L. Richardson, E. L. Charsley; "Calibration and Standardisation in DSC", in Handbook of Thermal Analysis and Calorimetry. Vol. 1: Principles and Practice, M. E. Brown (editor), Elsevier Science B.V. (1998) A number of other materials have well defined transition temperatures which make them useful calibration materials (particularly at low temperatures): |
|
Material |
Tm (°C) |
|
Toluene |
-95.01 |
|
Cyclohexane (solid-solid) |
-56.8 |
|
Octane |
-56.8 |
|
Decane |
-29.6 |
|
Dodecane |
-9.6 |
|
Water |
0.00 |
|
Cyclohexane (solid-liquid) |
6.7 |
|
Diphenyl Ether |
26.87 |
|
4-Nitrotoluene |
51.61 |
|
Biphenyl |
68.93 |
|
Napthalene |
80.23 |
|
Acetanilide |
114.34 |
|
Benzoic Acid |
122.34 |
|
Anisic Acid |
183.28 |
|
2-Chloroanthraquinone |
209.83 |
|
Caffeine |
236.1 |
|
Carbazole |
284.52 |
Organic substances which are liquids at room temperature may be volatile and thus difficult to handle. The solid-solid transitions of ammonium sulphate (-48.8°C) and ammonium dihydrogen phosphate (-121.4°C) are particularly useful for low temperature calibration. Reference: D. M. Price; "Temperature Calibration of Differential Scanning Calorimeters", Journal of Thermal Analysis, 45 (1995) 1285-1296 Sythethic sapphire (carborundum, aluminium oxide) is widely used as a calibrant for heat capacity determination. Values of the Cp (in J K-1g-1 at temperature T (in K) of this material are accurately given by the polynomial: Cp(T) = A + B * T + C * T 2 + D * T 3 + E * T 4 + F * T 5 + G * T 6 + H * T 7 The values of A-H are given for two temperature ranges: |
|
|
(T = 70 to 300 K) |
(T = 290 to 2250 K) |
|
A |
3.63245x10-2 |
-5.81126x10-1 |
|
B |
-1.11472x10-3 |
8.25981x10-3 |
C |
-5.38683x10-6 |
-1.76767x10-5 |
|
D |
5.96137x10-7 |
2.17663x10-8 |
|
E |
-4.92923x10-9 |
-1.60541x10-11 |
|
F |
1.83001x10-11 |
7.01732x10-15 |
|
G |
-3.36754x10-14 |
-1.67621x10-18 |
|
H |
2.50251x10-17 |
1.68486x10-22 |
Reference: S. M. Sarge, E. Gmelin, G. W. H. Höhne, H. K. Cammenga, W. Hemminger, W. Eysel; "The Caloric Calibration of Scanning Calorimeters", Thermochimica Acta, 247 (1994) 129-168 |
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