GB/T 2539-1981 Determination of the melting point (cooling curve) of paraffin GB/T2539-1981 standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Method for determination of melting point (cooling curve) of paraffin wax
Petroleum waxes--Determination of melting point--Cooling curve This standard applies to the determination of melting point of paraffin wax, but not to microcrystalline wax and petroleum grease. 1 Method Overview
GB/T 2539-81
Cool the melted paraffin sample under the specified conditions. The temperature at the first stagnation period on the cooling curve is the melting point of the paraffin wax
During the cooling process of the wax sample, record the temperature once every 15 seconds. When the total difference of five consecutive numbers does not exceed 0.1℃, it is the first stagnation period. The average of the five consecutive numbers is the melting point of the tested sample. 2 Instruments
2.1 Test tube: Made of soda-lime glass. The outer diameter is 25 mm, the wall thickness is 2-3 mm, the length is 100 mm, and the bottom of the tube is hemispherical. Mark a ring-shaped sample loading line at a height of 50 mm from the bottom of the test tube, and a thermometer positioning line at a height of 10 mm from the bottom of the test tube. 2.2 Air bath: a cylinder with an inner diameter of 51 mm and a depth of 113 mm. 2.3 Water bath: an inner diameter of 130 mm and a depth of 150 mm. The air bath is placed in the water bath. It is required to maintain a 38 mm water layer around the air bath, the water bath wall and the bottom. The water bath temperature measuring hole should keep the thermometer 20 mm away from the water bath wall. 2.4 Melting point thermometer: meet the requirements of Appendix A. 2.5 Water bath thermometer: semi-immersed type, required to be accurate to 1°C within the use range. 2.6 Oven or water bath: overflow control can reach 93°C. 3 Test steps
3.1 Install the thermometer, test tube, air bath and water bath as shown in the figure: the test tube is equipped with a suitable cork, the middle hole is opened to fix the melting point thermometer, and the 79 mm immersion section of the thermometer should be inserted under the cork. The thermometer is inserted into the test tube, and the bottom of the thermometer is 10 mm from the bottom of the tube. Issued by the General Administration of Standards on March 26, 1981
Implementation on July 1, 1981
GB/T2539-81
Sampling line
Wall thickness 2~3
Outer 25
Inner 51
Inner 130
Paraffin melting point (cooling curve) tester
3.2 Inject 16~28℃ water into the water bath, and the distance between the water surface and the top is less than 15 mm. During the entire test, the water temperature is maintained at 16~28℃.
3.3 Place the sample in a clean beaker and heat it in an oven or water bath to 8°C above the estimated melting point, or heat it to 10°C after the sample melts, or heat it to 90-93°C. Do not use open flames or electric heating plates to directly heat the sample. 3.4 Place the melted sample in a preheated test tube, add it to the 50mm mark, insert a cork with a thermometer, and make the bottom of the thermometer reach the 10mm mark.
3.5 Place the test tube vertically in an air bath while ensuring that the wax temperature is at least 8°C higher than the estimated melting point. 3.6 Record the temperature every 15 seconds and estimate it to 0.05°C. When the total difference of five consecutive numbers does not exceed 0.1°C for the first time, a plateau appears on the sample cooling curve, which is the stagnation period. The test can be stopped at this time. If the above situation does not occur, continue to read until 38°C or 8°C below the freezing point, then stop the test and judge that this method is not applicable to the sample. 4 Calculation
Calculate the average of the five consecutive numbers of the stagnation period, and take it to 0.05 (. 5 Precision
The maximum difference between the two repeated measurement results shall not exceed 0.1℃. 6 Report
Take the smaller value of the two repeated measurement results as the melting point of the sample. Note: According to the statistical test results of different laboratories, this method is: ① Use the company's operator's instrument to measure the difference between the repeated test results of the same sample under the specified conditions and operate correctly. After long-term testing: only one of the differences in 20 tests exceeds 0.1℃. (2) Different operators in different laboratories measure the same sample under the specified conditions and operate correctly. The difference between the results has been verified over a long period of time: the difference in the 20 tests only exceeded 0.5°C once. 287
Half-rod type
Temperature range
Minimum division
Long line division
Engraved division
Indication error
Allowable heating temperature of expansion chamber
Insertion depth
Rod diameterbzxZ.net
Mercury ball length
Mercury ball diameter
Distance from bottom of mercury ball to 40°C line
Distance from bottom of mercury ball to 80°C line
Distance from mercury ball to top of contraction chamber
Additional instructions:
GB/T 2539-81
Appendix A
Technical conditions for melting point thermometers
(Supplement)
38 ~ 82℃;
Maximum 0.1℃;
100℃;
79mm;
377±5mm,
6.0~7.0mm,
18～28mm;
5.0~6.0mm,
116～125mm;
315～325mm;
Not more than 41mm.
This standard was proposed by the Ministry of Petroleum Industry of the People's Republic of China. This standard was drafted by the Shanfu Petroleum Refining Research Institute. This standard has been revised according to the national standard amendment sheet No. 288.
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