GB/T 1425-2021 English PDF (GBT1425-2021)

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GB/T 1425-2021: Determination of melting temperature range for precious metals and their alloys -- Testing method of thermal analysis
GB/T 1425-2021
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.040.99
CCS H 21
Replace GB/T 1425-1996
Determination of melting temperature range for precious
metals and their alloys -- Testing method of thermal analysis
ISSUED ON: AUGUST 20, 2021
IMPLEMENTED ON: MARCH 1, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 5
4 Principles ... 6
5 Reagents or materials ... 6
6 Instruments and equipment ... 7
7 Samples ... 8
8 Calibration ... 8
9 Test steps ... 8
10 Experimental data processing ... 9
11 Test report ... 11
Appendix A (Normative) Temperature calibration methods for differential thermal
analyzers and differential scanning calorimeters ... 13
Appendix B (Normative) Thermal lag temperature correction method for thermal
resistance measurement ... 15
Determination of melting temperature range for precious
metals and their alloys -- Testing method of thermal analysis
Warning -- The personnel using this document shall have practical experience in
formal laboratory work. This document does not indicate all possible safety issues.
The user is responsible for taking appropriate safety and health measures and
ensuring compliance with the conditions stipulated by relevant national laws and
regulations.
1 Scope
This document specifies a method for determining the melting temperature range of
precious metals and their alloys by using differential thermal analyzers or differential
scanning calorimeters.
This document is applicable to the test of the melting temperature range of precious
metals and their alloys, and the test range is 25 °C~2000 °C.
2 Normative references
The following documents are essential to the application of this document. For the dated
documents, only the versions with the dates indicated are applicable to this document;
for the undated documents, only the latest version (including all the amendments) is
applicable to this standard.
GB/T 6425 Nomenclature for thermal analysis
GB/T 8170 Rules of rounding off for numerical values and expression and
judgement of limiting values
3 Terms and definitions
The terms and definitions defined in GB/T 6425 and the following are applicable to this
document.
3.1 Melting temperature range
The interval between the initial melting temperature Ti and the final melting
temperature Tf is expressed as Ti ~ Tf
5.2 Reference material
The reference material shall have no enthalpy change in the test temperature range and
shall be stored in a desiccator for later use. Typical reference materials include calcined
α-Al2O3, platinum sheets, glass beads, silicone oil, sample vessels, etc.
6 Instruments and equipment
6.1 Thermal Analysis Instruments
6.1.1 Differential thermal analyzer: the maximum heating rate shall be not less than
10 °C/min, with sufficient accuracy and adjustment ability, so that the melting peak
generated by the temperature difference between the sample and the reference material
when the sample is being melted can be automatically recorded in the 10%~90%
indexing range of the recorder. Reading accuracy of the temperature curve: the
deviation shall not exceed ±0.5 °C when the temperature is lower than 300 °C, ±1 °C
when the temperature is 300 °C~700 °C, ±2 °C when the temperature
is >700 °C~1600 °C, and ±3 °C when the temperature is >1600 °C~2000 °C.
6.1.2 Differential scanning calorimeter: the maximum heating rate shall be not less than
10 °C/min, with sufficient accuracy and adjustment ability, so that the melting peak
generated by the energy difference input between the sample and the reference material
when the sample is being melted can be automatically recorded within the 10%~90%
indexing range of the recorder. Reading accuracy of the temperature curve: the
deviation shall not exceed ±0.5 °C when the temperature is lower than 300 °C, ±1 °C
when the temperature is 300 °C~700 °C, ±2 °C when the temperature
is >700 °C~1600 °C.
6.2 Sample vessel
Made of aluminum or other high thermal conductivity metals, borosilicate glass, fused
alumina, fused silica and other materials, it (or the crucible) shall not occur any phase
changes within the test temperature range and not react with the reference materials or
the samples.
6.3 Pressure Conditions
If the test needs to be carried out under pressure conditions, then:
- the test pressure of the compressed air source shall be maintained at 0.1 MPa~1.27
MPa;
- the pressure regulating converter shall be able to measure and adjust the test
pressure to the specified value, and the error shall be less than 5%.
7 Samples
7.1 For liquid or slurry samples, take samples after mixing; for sheet metal samples,
take samples after shredding.
7.2 On the premise of not affecting the sample, vibration filling, molding, extrusion and
other methods can be used to improve the heat conduction between the sample and the
sample vessel.
7.3 Unless otherwise stated, the samples will be measured as received without any
pretreatment.
7.4 If it is required to perform mechanical processing or heat treatment on the sample
before analysis, the corresponding processing method, process and conditions shall be
indicated in the report; For heat treatment, the mass loss before and after treatment shall
also be recorded.
7.5 Samples shall not be diluted. If the sensitivity of the instrument and the stability of
the baseline allow, it is recommended to use a smaller amount of sample for the test.
The recommended sample volume should be 2 mg~20 mg, or less than 1/3 of the
volume of the sample vessel. If the sample has the potential to suddenly release a large
amount of latent heat, the amount of sample shall be appropriately reduced.
8 Calibration
8.1 In the calibrated temperature range, select the calibration material in Appendix A to
calibrate the temperature indication value of the instrument.
8.2 The instrument sensitivity, heating rate, ambient atmosphere, gas flow rate and other
conditions selected for calibration shall be consistent with the corresponding conditions
during the test.
8.3 Under the fixed-point temperature of a certain calibration material, the correction
value of the instrument temperature indication is determined by the difference between
the corresponding melting temperature in Appendix A and the extrapolated initial point
temperature of the melting peak of the calibration curve.
8.4 The instrument calibration cycle shall be carried out according to the requirements
of the selected equipment.
9 Test steps
9.1 Turn on the power supply of the thermal analysis instrument, and the preheating
time of the instrument shall be not less than 20 min.
9.2 Use an analytical balance to weigh the sample with a mass of 2 mg~20 mg, and
place it in the corresponding sample vessel; the weight shall be accurate to 0.01 mg.
9.3 According to the situation of the sample, select an appropriate reference material.
In order to ensure the thermal neutrality of the reference material, the reference material
used for the first time shall be carried out a calcination treatment at a temperature no
lower than 1000 °C for 2 h.
9.4 Place the crucibles containing the sample and the reference material respectively in
the corresponding positions on the clean support, and record the filling of the sample in
...