Gas density meter for measuring refractory density - Huaqiang Electronic Network

American Standard ASTM C604 –98

Method for determining true specific gravity of refractory materials by gas density meter

1. Scope

1.1 This method is particularly suitable for determining the true specific gravity of solid materials that are prone to water absorption, deliquescence, and hydration. These types of materials are not well-suited for testing using methods C135, C128, or C188.

1.2 When applying this standard, users should establish appropriate safety measures and health precautions based on the situation and implement them during operation.

2. References

2.1 ASTM standards:

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. Gas Density Meter Method

3.1 The sample is ground into a fine powder to ensure that gas can penetrate all pore spaces within the particles. This can typically be achieved by passing the sample through a #325 test sieve. Before the experiment, the powder is dried to remove free moisture and any bound water. The volume of the sample is then measured using a gas densitometer, and the density is calculated by dividing the mass (in grams) by the volume (in cubic centimeters). This value corresponds to the specific gravity of the material relative to water at 4°C.

3.2 The gas density meter operates based on two chambers and two pistons. When the connecting valve is closed, movement of one piston causes an imbalance in pressure, which must be compensated by the other piston. This principle ensures accurate measurement when the system reaches equilibrium.

3.3 If a sample with volume Vx is placed in chamber B, and the connecting valve is closed, the pistons move from position 1 to 2, causing a pressure imbalance. By adjusting piston B to position 3, the pressure is balanced again. The displacement between positions 2 and 3 is proportional to the sample volume. This distance is calibrated and can be directly read as volume in cm³ using a digital display.

4. Significance and Use

4.1 True specific gravity is the ratio of the true density of a substance at a given temperature to the density of water at the same temperature. It reflects the material’s physical properties and is closely related to its chemical composition and mineral structure.

4.2 This method is especially useful for hydratable materials, as traditional methods like C135 may not be suitable for such substances.

4.3 For refractory materials, specific gravity serves as a key indicator. It helps classify similar-looking materials, distinguish different minerals, calculate porosity, and support various analytical calculations.

4.4 This is a fundamental method used in technical classification, quality control, research, and product development. It can also serve as an arbitration method in material purchase agreements.

4.5 The following conditions must be met:

4.5.1 The sample must be representative of the overall material.

4.5.2 All samples must be ground to the required particle size.

4.5.3 No contaminants should be introduced during preparation.

4.5.4 The sample must be dried without causing agglomeration or structural changes.

4.5.5 Helium must be used as the measurement gas.

4.5.6 The procedure must be carried out accurately and carefully.

4.5.7 Deviations from these conditions may affect the reliability of results.

4.6 Due to the presence of closed pores in some samples, the measured value may not be perfectly accurate. Therefore, comparisons between similar materials should be interpreted carefully to identify whether differences arise from material properties or measurement techniques.

5. Equipment

5.1 Analytical balance (200g capacity, 10mg sensitivity)

5.2 Drying oven with magnesium perchlorate desiccant

5.3 Muffle furnace (capable of reaching 1000°C)

5.4 Crushing equipment (to achieve particle size less than 45µm)

5.5 Dry helium cylinder with regulator and pressure gauge

5.6 Gas pycnometer with external cleaning valve line

6. Sample Preparation and Pretreatment

6.1 Grind the sample sufficiently to meet three measurements, ensuring it passes a 45µm sieve. Typically, 100g of sample is used per test.

6.2 After grinding, burn the sample at a high enough temperature to remove free and bound moisture without sintering. Hydratable materials should be heated to 600°C for over 3 hours.

6.3 Cool the sample in a desiccator containing magnesium perchlorate.

7. Measurement Procedure

7.1 Calibrate the densitometer using a standard volume as per the manufacturer’s instructions.

7.2 Remove the cooled sample from the desiccator and quickly place it in the sample cup. Weigh it to the nearest 10mg. Ensure the temperature difference between the sample and the instrument does not exceed 2°C.

7.3 Place the sample in the densitometer chamber and close it securely. Purge the system with dry helium, keeping pressure below 13.8 psi.

7.4 Measure the sample volume according to the instrument manual, allowing 60 seconds for temperature equilibrium.

7.5 Repeat the measurement until the difference between two consecutive values is less than 0.05 cm³. Take the average as the final volume.

8. Calculation

8.1 Calculate true density using the formula: S = W / V, where S is true density, W is sample mass (g), and V is sample volume (cm³).

9. Reporting Results

9.1 For three samples, if the results differ by no more than 0.01, take the average as the final result, reported to two decimal places.

10. Precision and Bias

10.1 Interlaboratory tests were conducted on granular alumina and MULCOA 47. Six labs tested alumina, and seven tested MULCOA 47. Each lab performed 3–8 measurements. Data was analyzed using E691, showing repeatability and reproducibility values.

10.2 Precision and average results:

Granular Alumina: Average 3.952, Repeatability 0.026, Reproducibility 0.053

MULCOA 47: Average 2.790, Repeatability 0.016, Reproducibility 0.048

10.3 No bias was detected due to lack of reference material.

11. Keywords

11.1 Gas pycnometer, hydrated materials, refractory materials, true specific gravity