The pycnometer method is presented here. Density 10 refers to the mass of an object per unit volume, expressed in g/mL. Fill the tested product with the pycnometer, and calculate the density of the tested product from the mass of the product in the pycnometer and the known volume of the pycnometer.
The effect of temperature on density has a very significant relationship with packing performance and varies with the type of product. Usually the specified test temperature is (23 ± 0.5) ℃, and the test can also be carried out at other agreed temperatures. During the test, the product under test and the pycnometer should be adjusted to the specified or agreed temperature, and the temperature change during the test should not exceed 0.5°C
instrument
(1) pycnometer
①Metal pycnometer with a capacity of 50mL or 100mL, is a cylinder with a circular cross-section made of finely processed anti-corrosion material, with a cover fitted with a hole in the center. The inside of the cover is concave, as shown in Figure 21-11.
②The volume of glass pycnometer is 10mL or 100mL (Guy-Lussac pycnometer or Hubbard pycnometer is shown in Figure 21-12 and Figure 21-13),
(2) Analytical balance
The pycnometer below 50mL is accurate to 1mg, and the pycnometer of 50~100mL is accurate to 10mg.
(3) The graduation value of the thermometer is 0.1°C, accurate to 0.2°C, (4) The constant temperature room or Water Bath constant temperature room should be able to adjust and maintain the balance, pycnometer or the product under test at the specified or agreed temperature, and the Water Bath should be able to maintain The pycnometer and the sample to be tested are at the specified or agreed temperature.
(5) Dustproof chapter.
Steps
(1) General
Perform two assays, each assay should be resampled.
The pycnometer should be calibrated at regular intervals, for example, after approximately 100 tests or when a change in the pycnometer is found.
(2) Determination
If the test is carried out in a constant temperature room, place the pycnometer, sample, and balance in the dustproof cover in the constant temperature room so that they are at the specified or agreed temperature. If a constant temperature Water Bath is used instead of the test in a constant temperature room, then Put the pycnometer and the sample in the dust-proof cover into a constant temperature Water Bath to keep them at the specified or agreed temperature, and the temperature can reach equilibrium in about 30 minutes. Use a thermometer to test the temperature tT of the sample. During the whole test process Check that the temperature of the thermostatic chamber and Water Bath is maintained within the specified range.
Weigh the pycnometer and record its mass m, the pycnometer with a capacity of 50-100mL is accurate to 10mg, and the pycnometer with a capacity of less than 50mL is accurate to 1mg.
Fill the pycnometer with the product to be tested, and take care to prevent air bubbles in the pycnometer. Stopper or cap the pycnometer, wipe up the spill with absorbent material, and dry the outside of the pycnometer, then wipe gently with a cotton ball.
Record the mass m2 of the pycnometer filled with the product to be tested.
Note: The liquid adhering to the ground glass surface of the glass pycnometer or the contact surface between the lid and the cup of the metal pycnometer will cause the weighing reading to be too high. In order to minimize the error, the interface should be tightly sealed to prevent air bubbles.
calculate
Test precision
①Repeatability (r) The absolute value of the difference between two single test results measured on the same sample by the same operator in the same laboratory and within a short time interval using this test method is 0.00 lg/mL , the confidence level of the predictable result is 95%.
② Reproducibility (R) When the absolute value of the difference between two single test results measured on the same sample by different operators in different laboratories using this test method is 0.002g/mL, it is predictable The confidence level of the results is 95%.
Note: ① These data are taken from DIN 53217-2:1991, Determination of the density of paints, varnishes and related materials with a specific gravity cup.
② Some liquid paint products, especially those with structural viscosity or thixotropy, may not be able to achieve the above precision.
notes
(l) Calibration of the pycnometer
When using a metal pycnometer, carefully clean it inside and out with a solvent that evaporates without leaving a residue, and dry it completely. Avoid leaving fingerprints on the pycnometer as they will affect the balance reading.
In order to keep the pycnometer constant weight, put it in the dust cover for 30 minutes, weigh it after reaching room temperature (m,), fill the pycnometer with pre-boiled plain distilled water or the standard specified in GB/T6682-92 For deionized water, the water temperature should not exceed 1°C at the test temperature, and then stopper or cover the pycnometer, taking care to prevent the generation of air bubbles.
Put the pycnometer into a Water Bath or a thermostatic chamber to bring it to the test temperature. Wipe up spilled material with absorbent material (cloth or paper). Take the pycnometer out of the Water Bath or thermostatic chamber and dry its exterior. To prevent the pycnometer from reheating and to ensure that the water no longer overflows, immediately weigh the pycnometer (m3) filled with water.
Note: ① Due to the direct operation by hand, the pycnometer will increase the temperature and cause more overflow, and also leave fingerprints. Therefore, it is recommended to handle the pycnometer with pliers or hands protected by a fiber insert.
② Since water can evaporate through the overflow hole, in order to minimize the mass loss, it is recommended to weigh the pycnometer filled with water immediately and quickly, and calibrate the pycnometer at the temperature of the density measurement system of the product to be tested. Necessary, because the volume of the pycnometer changes with temperature. In other words, calibration should be performed as specified in Table 21-8.
