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GB/T 19466 consists of the following seven parts, under the general title Plastics — Differential Scanning Calorimetry (DSC):
— Part 1: General Principles;
— Part 2: Determination of Glass Transition Temperature;
— Part 3: Determination of Temperature and Enthalpy of Melting and Crystallization;
— Part 4: Determination of Specific Heat Capacity;
— Part 5: Determination of Characteristic Reaction-curve Temperatures and Times, Enthalpy of Reaction and Degree of Conversion;
— Part 6: Determination of Oxidation Induction Time (Isothermal OIT) and Oxidation Induction Temperature (Dynamic OIT);
— Part 7: Determination of Crystallization Kinetics.
This part is Part 4 of GB/T 19466.
This part is drafted in accordance with the rules given in GB/T 1.1-2009.
This part has been redrafted and modified adoption of International Standard ISO 11357-4:2014 Plastics — Differential Scanning Calorimetry (DSC) — Part 4: Determination of Specific Heat Capacity.
The technical deviations between this standard and the International Standard ISO 11357-4:2014, together with their justifications, are given below:
— For the normative references, adjustments with technical deviations have been made in this part to adapt to China's technical conditions. Clause 2 "Normative References" embodies a concentrated reflection of adjustments, specific adjustments are as follows:
● ISO 472 is replaced with GB/T 2035, which is identical with the international standard;
● ISO 11357-1 is replaced with GB/T 19466.1-2004, which is identical with the international standard;
● for the purpose of meet the need of calculation precision, GB/T 6379.2-2004 is added;
● normative reference ISO 80000-1 is changed to GB/T 8170, because of the method in ISO 80000-1 is generally not adopted in the rules for calculation and rounding off in China;
— In Clause 10, the ISO precision is deleted and replaced by the Chinese precision data.
This part was proposed by China Petroleum and Chemical Industry Federation.
This part is under the jurisdiction of the National Technical Committee 15 on Plastic of Standardization Administration of China (SAC/TC 15).
Plastics — Differential Scanning Calorimetry (DSC) — Part 4: Determination of Specific Heat Capacity
1 Scope
This part of GB/T 19466 specifies methods for determining the specific heat capacity of plastics by differential scanning calorimetry.
2 Normative References
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 2035 Terms and Definitions for Plastics (GB/T 2035-2008, ISO 472:1999, IDT)
GB/T 6379.2-2004 Accuracy (Trueness and Precision) of Measurement Methods and Results — Part 2: Basic Method for the Determination of Repeatability and Reproducibility of a Standard Measurement Method (ISO 5725-2:1994, IDT)
GB/T 8170 Rules of Rounding Off for Numerical Values & Expression and Judgement of Limiting Values
GB/T 19466.1-2004 Plastics — Differential Scanning Calorimetry (DSC) — Part 1: General Principles (idt ISO 11357-1:1997)
3 Terms and Definitions
For the purposes of this document, the terms and definitions given in GB/T 2035 and GB/T 19466.1-2004 and the following apply.
3.1
calibration material material of known specific heat capacity
Note: Usually, α-alumina (such as synthetic sapphire) of 99,9% or higher purity is used as the calibration material.
3.2
specific heat capacity (at constant pressure)
Cp quantity of heat necessary to raise the temperature of unit mass of material by 1 K at constant pressure
Note 1: It is given by the Equation (1):
Cp=m-1Cp=m-1(dQ/dT)p (1)
where,
m — the mass of material;
Cp — the heat capacity and is expressed in kilojoules per kilogram per K (kJ·kg-1·K-1) or in joules per gram per K ((J·g-1·K-1); subscript p indicates an isobaric process;
dQ — the quantity of heat necessary to raise the temperature of the material by dT;
Equation (2) is valid in a temperature range where a material shows no first-order phase transition.
(dQ/dT)=(dt/dT)×(dQ/dt)=(heating rate)-1 × heat flow rate (2)
Note 2: At phase transitions, there is a discontinuity in the heat capacity. Part of the heat is consumed to produce a material state of higher energy and it is not all used in raising the temperature. For this reason, the specific heat can only be determined properly outside regions of phase transitions.
4 Principle
4.1 General
Each measurement consists of three runs at the same scanning rate (see Figure 1):
a) a blank run (empty crucibles in sample and reference holders);
b) a calibration run (calibration material in sample holder crucible and empty crucible in reference holder);
c) a specimen run (specimen in sample holder crucible and empty crucible in reference holder).
?
Key:
X — temperature T or time t; 1 — blank test;
2 — calibration test;
3 — specimen test;
I — isothermal baseline at start temperature Ts;
II — isothermal baseline at end temperature Tf;
a Endothermic direction.
Figure 1 Schematic drawing of typical DSC curves for specific heat capacity measurement (blank, calibration and specimen runs) after baseline adjustment
4.2 Continuous-scanning method
Based on the DSC principle (see GB/T 19466.1-2004) and the definition of specific heat capacity given in 3.2, the Equations (3) and (4) can be obtained:
msp·Cpsp∝Psr-Pbr (3)
mcal·Cpcal∝Pcr-Pbr (4)
where,
P — the heat flow rate (dQ/dt); superscripts sp and cal represent specimen and calibration material, respectively (see Figure 1). Superscripts sr, cr and br represent specimen run, calibration run and blank run respectively.
When Psr, Pcr and Pbr are measured, Cpsp can be calculated using Equation (6), since the values of Cpcal, msp and mcal are known:
(5)
(6)
4.3 Stepwise-scanning method
In the stepwise-scanning method, the total temperature range to be scanned is divided into small intervals and a complete determination consisting of the three runs mentioned in 4.1 is performed for each temperature interval. Upon integration of the heat flow rate curve, the total heat ΔQ consumed in the interval can be obtained. Dividing ΔQ by the temperature interval ΔT and the mass of the specimen gives the specific heat [see Equation (1)]:
Foreword II
1 Scope
2 Normative References
3 Terms and Definitions
4 Principle
5 Apparatus
7 Test Conditions and Specimen Conditioning
8 Test Procedure
9 Determination of Specific Heat Capacities
10 Precision and Bias
11 Test Report
Annex A (Informative) An Approximate Expression of the Specific Heat Capacity of Pure α-Al2O3 [3] to [5]
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