NB/SH/T 0632-2014 Determination of specific heat capacity — Differential scanning calorimetry (DSC)

Summary page. This page is a compiled excerpt/summary of the standard — it is not the full standard text and does not replace it. Verify every value against the official standard and the product certificate before use.

NB/SH/T 0632-2014 specifies a differential scanning calorimetry (DSC) method for determining specific heat capacity, applicable to thermally stable solids and liquids, usually over a test temperature range of −100 °C to 600 °C.

Evidence note: the content of this page was compiled from the original text of this standard held in the Origin Standard library (points marked "[to be verified]" are "[source unclear]" in the original); for individual values and current status, refer to the original pages of the standard and the product certificate.

Scope: This standard specifies a method for determining specific heat capacity by differential scanning calorimetry (DSC). It applies to solids and liquids with good thermal stability. The usual test temperature range is −100 °C–600 °C. If the measuring instrument and sample crucible can meet the requirements for use at higher temperatures, the test temperature range may be extended to a wider range. Only computers or electronic instruments, techniques or data processing equivalent to the requirements of this standard may be used. Note: users of this standard should recognize that not all instruments or techniques are equivalent to this standard. Users of this standard are responsible for determining, before use, whether the relevant instruments and techniques meet the requirements of this standard. Not applicable: no explicit "not applicable" clause is provided in the available material.

Principle: The test is carried out using a DSC instrument. In the test region, the sample is heated under the protection of an inert gas. The inert gas flow rate and the furnace heating rate are both controllable. The DSC thermal curve is recorded, the differences between the DSC thermal curves of the sample, the reference material and the empty crucible are compared, and the specific heat capacity of the sample is calculated using software or manually. (Clause 4)

Apparatus: Differential scanning calorimeter (DSC): capable of providing the differential scanning calorimetry capability required by this standard. 7.1.1 DSC test region: 7.1.1.1 Furnace: provides controlled heating (or cooling) of the sample. Within this temperature range (−100 °C–600 °C) it can hold the sample at a particular constant value, or heat (or cool) the sample at a constant heating rate. 7.1.1.2 Temperature sensor: capable of indicating the sample temperature, temperature sensitivity ±10 mK, approximately 0.01 °C. 7.1.1.3 Differential thermal sensor: capable of measuring a heat flow difference of 1 μW (microwatt) between the sample and the empty crucible. 7.1.1.4 Capable of maintaining the inert gas flow in the test region at any value within 10 mL/min–50 mL/min, with fluctuation not exceeding 5 mL/min. 7.1.2 Temperature controller: realizes programmed temperature control of the furnace, can select a heating rate at any value from 10 °C/min–20 °C/min (accuracy ±0.1 °C/min), and can also realize constant-temperature control (accuracy 0.1 °C). 7.1.3 Recording device: digital or analogue signals are both acceptable, provided that all heat flow signals (DSC curve) can be recorded and displayed; the DSC curve includes signal noise. 7.1.4 The tester may use data processing software meeting the requirements of this standard. The dedicated software supplied by the instrument manufacturer is generally recommended. 7.1.5 Container: consists of a flat-bottomed crucible and a lid. It can hold the sample or reference material. It shall have a suitable external shape and structure and, in accordance with the specific requirements of this standard, be able to contain the sample or reference material completely. Aluminium crucibles supplied with the instrument are generally used. 7.1.6 The DSC instrument has the cooling capacity for rapid cooling, the cooling rate can be kept constant and can reach 10 °C/min. It can operate below room temperature, maintain a constant low temperature, and can realize combinations of the above temperature programmes. 7.2 Balance: used for weighing samples and crucibles, range not less than 100 mg, accuracy ±10 μg.

Reagents and reference materials: Specific heat capacity reference material: synthetic sapphire discs, 10 mg–100 mg. (Clause 8) Note: interlaboratory studies have shown that synthetic sapphire in other shapes gives lower precision and greater bias than discs. Inert gas: if there is concern that the sample may be oxidized in air, nitrogen, argon or ammonia of purity above 99% shall be used to protect the sample (the "ammonia" in the original is suspected to be "helium", [to be verified] ([source unclear])). In general, a dry purge gas is recommended. A dry purge gas should be used at low temperatures. (Note to 7.1.1.4) Specific heat capacity data for the reference material (synthetic sapphire, α-aluminium oxide) are given in Table A.1 of Annex A; specific heat capacity data for aluminium (crucible material) are given in Table A.2 of Annex A. Other reagents: not provided in the available material.

Key conditions: Heating rate: 20 °C/min (13.1.4, 13.1.6); other heating rates may also be used, but shall be noted in the report. Increasing the heating rate can improve the resolution of the instrument. Cooling rate: determined by the cooling capacity of the instrument (13.1.4). Purge gas: dry nitrogen (or another inert gas), flow rate at a constant value between 10 mL/min and 50 mL/min, accuracy ±5 mL/min (13.1.1). Initial temperature equilibration: at least 4 min to establish equilibrium (13.1.5); a pre-equilibration of 4 min is recommended, other pre-equilibration times may be used but shall be noted in the report (12.4). Highest test temperature point: record a steady-state constant-temperature baseline (13.1.7). The same heating rate shall be used for calibrating the instrument and testing the sample (9.2.1). Once the instrument has been calibrated, the instrument settings shall not be modified during the test (9.2.2).

Calculation and results: 14.1–14.2 Distance measurement 14.1 At temperature T, measure the distance between the thermal curve of the empty crucible and the thermal curve of the specific heat capacity reference material (i.e. at temperature T, the distance from the baseline to the reference material line), namely D_a in Figure 1. See Figure 1. 14.2 At temperature T, measure the distance between the thermal curve of the empty crucible and the thermal curve of the sample (i.e. at temperature T, the distance from the baseline to the sample line), namely D_s in Figure 1. See Figure 1. Figure 1: Specific heat capacity thermal curves of the sapphire reference material and the sample (figure omitted in the original). Formula (1) Calorimetric sensitivity E E = [b/(60·D_a)]·[W_a·Cp(a) + ΔW·Cp(c)] where: b—heating rate, in degrees Celsius per minute (°C/min); Cp(a)—specific heat capacity of the reference material, in joules per gram per kelvin (J/(g·K)); Cp(c)—specific heat capacity of the sample crucible, in joules per gram per kelvin (J/(g·K)); E—calorimetric sensitivity of the DSC instrument; D_a—vertical displacement at a given temperature between the thermal curve of the empty crucible and that of the reference material, in milliwatts (mW); W_a—mass of the reference material, in milligrams (mg); ΔW—mass difference between the empty crucible and the reference material crucible, in milligrams (mg), if the reference material crucible and the empty crucible are not the same. (Note: formula (1) in the original is [source unclear] and appears as "E=[b/(60 D.) [Wa Gp(a)+AW•GHo)", the above has been reconstructed from the context, [to be verified] ([source unclear]).) 14.3 If heat flow calibration is carried out periodically, the calorimetric sensitivity E can be calculated from the specific heat capacity values of the reference material given in Table A.1 of Annex A and the specific heat capacity values of the aluminium crucible given in Table A.2 of Annex A, as specified in formula (1). Note: if the crucible mass difference is ≤ 0.1% of the sample mass, the second correction term on the right-hand side of formula (1) may be neglected. Formula (2) Sample specific heat capacity Cp(s) = [60·E·D_s − ΔW·Cp(c)]/(W_s·b) where: Cp(s)—specific heat capacity of the sample, in joules per gram per kelvin (J/(g·K)); D_s—vertical displacement at a given temperature between the thermal curve of the empty crucible and that of the test sample, in milliwatts (mW); ΔW—mass difference between the empty crucible and the test sample crucible, in milligrams (mg), if the empty crucible and the sample crucible are not the same crucible; W_s—mass of the sample, in milligrams (mg); b—heating rate, in degrees Celsius per minute (°C/min); E—calorimetric sensitivity of the DSC instrument; Cp(c)—specific heat capacity of the sample crucible, in joules per gram per kelvin (J/(g·K)). (Note: formula (2) in the original is [source unclear] and appears as "Cp(e)=- 00•E•D._AW•Cp() (2) W.•b", the above has been reconstructed from the context, [to be verified] ([source unclear]).) 14.5 Simplified calculation, formula (3) Assuming that the masses of the sample crucible, the reference material crucible and the empty crucible are comparable, with differences within 0.1% of the sample mass, and that heat flow calibration is carried out before each specific heat capacity determination, calculate the specific heat capacity using formula (3): Cp(s) = Cp(a) · (D_s · W_a)/(D_a · W_s) where: Cp(s)—specific heat capacity of the sample, in joules per gram per kelvin (J/(g·K)); Cp(a)—specific heat capacity of the reference material, in joules per gram per kelvin (J/(g·K)); D_s—vertical displacement at a given temperature between the thermal curve of the empty crucible and that of the test sample, in milliwatts (mW); D_a—vertical displacement at a given temperature between the thermal curve of the empty crucible and that of the reference material, in milliwatts (mW); W_s—mass of the sample, in milligrams (mg); W_a—mass of the reference material, in milligrams (mg). (Note: formula (3) in the original is [source unclear] and appears as "Cpce) =Cp(a)• D.•Wa! Da•W.", the above has been reconstructed from the context, [to be verified] ([source unclear]).)

Quality control: Clause 16 Precision and bias: In 1990, 7 laboratories tested three materials (diphenyl ether, linear polyethylene and indium) over the temperature range 40 °C to 80 °C and determined their specific heat capacity values at 67 °C. Note: in 2011, diphenyl ether and 4 liquid petroleum products were tested in 3 laboratories to verify the precision of this method; the precision at the 67 °C point remains reliable. During the development of this standard, the specific heat capacity values of diphenyl ether and 4 liquid petroleum products at 87 °C were also determined, for reference by users of this standard. Judge the reliability of test results as follows (95% confidence level): 16.1.1 Repeatability r: the difference between two test results obtained by the same operator, in the same laboratory, using the same instrument, following the same method, on the same sample in successive determinations shall not exceed 6.2% of their mean. 16.1.2 Reproducibility R: the difference between two single, independent test results obtained by different operators, in different laboratories, using different instruments, following the same method, on the same sample shall not exceed 8.4% of their mean. Bias (16.2): 16.2.1 The estimated bias is obtained by comparing the mean specific heat capacity obtained for each material with the value reported in the literature; bias = mean specific heat capacity − literature value. 16.2.2 The mean specific heat capacity of diphenyl ether, 1.70 J/(g·K), compared with the literature value 1.683 J/(g·K), shows a bias of +0.95%. 16.2.3 For linear polyethylene, the mean specific heat value 2.18 J/(g·K), compared with the literature value 2.200 J/(g·K), is a bias of −1.1%. 16.2.4 For indium metal, the mean specific heat value 0.243 J/(g·K), compared with the literature values 0.241 J/(g·K) and 0.239 J/(g·K), is an error of +0.8% or +1.8%.

Normative references: Clause 2 Normative ASTM E967 Standard practice for temperature calibration of differential scanning calorimeters and differential thermal analyzers ASTM E968 Standard practice for heat flow calibration of differential scanning calorimeters and differential thermal analyzers References: [1] Furakawa, G. T., et al, Joural Res. National Bureau of Standards, Vol 46, 1951 (as in the original, [to be verified] ([source unclear])) [2] Ginnings, D. C., and Furakawa, C. T., J. Amer Chem Soc., Vol 75, 1053, p. 522 (as in the original, [to be verified] ([source unclear])) [3] Archer, D.G., J. Phys. Chem. Ref. Data, Vol 22, No. 6, pp.1441-1453 Annex A (normative): specific heat capacity of the reference material (synthetic sapphire, i.e. α-aluminium oxide) and of aluminium (crucible material) Table A.1 Specific heat capacity of the reference material (synthetic sapphire, α-aluminium oxide) (temperature range −123.15 °C–606.85 °C, specific heat capacity 0.3133–1.1986 J/(g·K)) Table A.2 Specific heat capacity of aluminium (crucible material) (temperature range −123.15 °C–800 °C, specific heat capacity 0.684–1.128 J/(g·K)) Note: the data in Table A.2 were obtained by least-squares calculation of the heat capacity and enthalpy values in the literature Downie, D.B.; Martin, J. F.; Ciauque, W.F.; Meads, P.F.; J Chem. Thermodynam, 12, 779-786 (1980) and Ditmars, D. A.; Plint, C. A.; Shukla, R. C. Int. J. Thermophys, 6, 499-515 (1985). (As in the original, [to be verified] ([source unclear]).) Annex B (normative): compressed gases B.1 Inert gases can reduce the oxygen concentration available for breathing. B.2 Keep containers closed. B.3 Ensure air circulation during use. B.4 Do not enter cylinder storage areas where there is no air circulation. B.5 Loosen the pressure reducing valve before opening the cylinder. B.6 Do not transfer to other cylinders. B.7 Do not mix gases in a cylinder. B.8 Do not knock over cylinders. B.9 When opening the cylinder valve, keep away from the cylinder outlet. B.10 Cylinders should be kept away from heat sources. B.11 Cylinders should be kept away from sources of corrosion. B.12 Do not use unlabelled cylinders. B.13 Do not use dented or defective cylinders. B.14 For laboratory use only; not for breathing.

Evidence note: [to be verified] and [source unclear] mark specific points that still require checking against the original text of the standard and do not indicate that they have been verified. Do not use these values or steps directly as a basis for work.

View public related products