Method for determining the true specific gravity of refractory materials by gas density meter - Master's thesis - Dissertation

American Standard ASTM C604 –98
Method for determining true specific gravity of refractory materials by gas density meter

1. range
1.1 For the determination of the true specific gravity of solid materials, it is particularly suitable for the determination of the density of substances that are easy to absorb water, deliquescent, and hydrate. These substances are not suitable for determining the true specific gravity by the C135 method, C128 method and C188 method.
1.2 When adopting this standard, users should formulate corresponding safety protection and health care items according to the situation and adopt them during operation.
2. references
2.1 ASTM standard
C128 Experimental method for specific gravity and absorption of fine aggregates
C135 Determination method of true specific gravity of refractory materials, water pycnometer method.
C188 Hydraulic cement density determination method
3. Method points
3.1 The sample is ground into a powder to ensure that the gas can enter all pore spaces of the sample particles. In fact, the purpose can be achieved by breaking the sample through the #325 test sieve. Prior to the experiment, the powder sample was first dried to remove free moisture and possibly bound water, and the volume of the sample was measured by a gas densitometer. The density of the sample was calculated from the mass (grams) of the sample divided by the volume (cubic centimeters). This density value is the same as the sample specific gravity (ratio to the density of water at a temperature of 4 ° C).
3.2 Gas Density The principle of the instrument is as follows: The instrument consists of two chambers and two pistons, as shown in Figure 1. To illustrate the principle, it is assumed that the two chambers are of equal volume and both chambers are empty. Under this condition, when the connecting valve is closed, any change of one piston will make the differential pressure indicator unbalanced, and in order to maintain the pressure balance on both sides of the pressure difference, the other piston must be moved in the same direction at the same distance.
3.3 If a sample of volume Vx is placed in chamber B, the connecting valve is in the closed state, and the two pistons move in the same direction, moving from position 1 to position 2, the pressure in the two chambers no longer remains equal. However, if the piston B is moved only to the position 3, the pressure of the two chambers can be balanced. At this time, the displacement amount dx from the position 3 to the position 2 is proportional to the sample volume (equal). If the position at which the piston A advances at each measurement is the same, when the pressure in the two chambers is equalized (equal), the difference in the displacement position of the piston A from the position 2 will necessarily be proportional to the sample volume Vx. The volume represented by the distance (dx) between position 2 and position 3 can be calibrated and can be read directly from a digital device in units of cm3.
4. Determination of meaning and use
4.1 The true specific gravity of a substance is the ratio of the true density measured at a certain temperature to the true density of water at a certain temperature. The true specific gravity of a substance is the main physical property of a substance, and the specific gravity is related to the chemical composition of the substance and the composition of the mineral phase.
4.2 This test method is particularly useful for the determination of specific gravity of substances that are easily hydrated, as such materials are not suitable for testing specific gravity using the C135 method.
4.3 For refractory raw materials and products, the specific gravity parameter is a useful indicator. It can be used to classify and test the chemical composition differences of materials that look very similar; distinguish (reflect) different minerals from each other; The porosity of the substance can also be calculated from the density value; some test items also need to use the specific gravity parameter to calculate the measurement result.
4.4 This method is a basic (primary) standard measurement method that can be used for technical index classification, quality control, scientific research, and product development. It can be used as an arbitration test method in the purchase and sale contracts and agreements of materials.
4.5 The experimental methods have the following basic prerequisites:
4.5.1 The sample is representative of the overall material (composition and properties),
4.5.2 All samples are ground to the specified particle size,
4.5.3 During the preparation and processing of the sample, no pollutants were introduced.
4.5.4 The sample is burned to remove free moisture and bound moisture without causing agglomerates or changing composition and structure.
4.5.5 Using helium as the medium gas during the experiment,
4.5.6 The test work should be carried out rigorously, conscientiously and accurately.
4.5.7 Deviation from any of the above preconditions will result in the use of the measurement results.
4.6 In the analysis and interpretation of the results of the method, it must be realized that the particle size of the experimental sample particles specified in this method is finer than the particle size required by the experimental method C135. Even with such fine particle size, it is not excluded that there may still be closed-cell pores in the sample particles, and the amount of residual closed-cell voids between different materials may be different, even in the different samples of the same material. There will also be differences in the amount of voids. Therefore, the value of the method measured by this method is a value that is very close to the true specific gravity of the material, rather than a very correct true specific gravity value. Therefore, when comparing the results of the specific gravity of similar materials measured by this method, it should be carefully and carefully analyzed and judged reasonably to confirm whether there is a potential inherent difference between the materials being compared, or in the details of the measurement method. Differences cause small differences in results.
5. instrument
5.1 Analytical balance, weighing range, 200g, minimum sensitivity 10mg;
5.2 dryer, equipped with magnesium perchlorate desiccant;
5.3 Mafu furnace, can be heated to 1000 ° C;
5.4 Fragmentation equipment, can crush the sample to a particle size of less than 45um (No: 325 experimental sieve);
5.5 Dry helium cylinders with pressure regulators and pressure gauges;
5.6 gas comparison density meter, equipped with an external cleaning distribution valve line;
6. Sample preparation and pretreatment
6.1 Grinding is enough for three measurements, representative samples, so that the same 45μ test sieve, different instruments require different sample sizes, generally 100g samples.
6.2 After grinding, all samples for analysis are burned at a sufficiently high temperature to remove any free water, combined with water and organic matter, etc., but the sample may not be sintered into agglomerates. For hydratable refractories, the minimum temperature should be burned at 600 ° C for more than 3 hours.
6.3 After burning, place the powder sample in a desiccator containing magnesium perchlorate and cool to room temperature.
7. Measuring step
7.1 Perform zero calibration of the densitometer and calibrate with a standard volume according to the instructions in the instrument manual.
7.2 Remove the cold sample from the desiccator and quickly place it in the sample cup that has been buckled so that the sample is close to the filled sample cup. Weigh the mass to the nearest 10mg. The temperature difference between the sample and the sample cup and the temperature of the instrument should not exceed 2 °C. For easily hydrated samples, once the sample is removed from the dryer, the subsequent measurement steps should be performed as quickly as possible to avoid hydration of the sample.
7.3 Place the sample cup containing the sample in the sample chamber of the densitometer and close the sample chamber to ensure it is in place. Clean the instrument system with dry helium and the gas pressure should not exceed 13.8 PSI.
7.4 The sample volume is determined using the standard procedure for the measurement of the volume of the cleaning atmosphere given in the instrument manual, but the temperature equilibrium waiting time used is 60 seconds.
7.5 Repeat the test volume for the same sample. When the difference between two consecutive test values ​​is less than 0.05 cm3, take the average of the two results as the sample volume.
8. Calculation
8.1 Calculate the true density of the sample at room temperature according to the following formula:
S = W/V
Where: S: true density
W: sample quality g,
V: sample volume cm3.
9. report
9.1 For the three samples, the difference between the results is not more than 0.01, the average of the three results is taken as the density result, and the result is taken to the decimal place.
10. Precision and deviation
10.1 Interlaboratory synergistic tests were performed on two randomly selected samples of material (granular alumina and MULCOA 47). Six laboratories used a gas density meter to determine the specific gravity of alumina and seven laboratory gas densities. The instrument measured the specific gravity of MULCOA47. The number of repeated measurements for each laboratory with alumina samples was from 3 to 6 times, with an average of 4 and 5 determinations; for Mulcoa, an average of 8 measurements per laboratory. The data was processed and analyzed according to the method specified in E691, and the following results were obtained:
10.2 Experimental results --- Method precision and measured average:
Granular alumina Mulcoa 47
The average laboratory result is 3.952 2.790
Repeatability (simultaneous room tolerance) 0.026 0.016
Reproducibility (different room tolerance) 0.053 0.048
The allowable error value is divided by 2.8 to obtain the standard error.
10.3 Deviation: There is no deviation from the method due to the absence of a suitable reference material.
11. Key words
11.1 gas comparison density meter, hydrated material, refractory material, true specific gravity