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 substances may not be accurately measured using methods such as C135, C128, or C188.
1.2 Users should implement appropriate safety measures and health precautions based on the situation when applying this standard 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 Overview
3.1 The sample must be ground into a fine powder to allow gas to penetrate all pore spaces. This can typically be achieved by passing the material through a #325 sieve. Before testing, the powder is dried to remove free moisture and any bound water. The volume 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 relative to water at 4°C.
3.2 The gas density meter operates using two chambers and two pistons. When the connecting valve is closed, movement of one piston causes pressure imbalance, which is corrected by moving the other piston in the same direction and distance to restore balance.
3.3 If a sample with volume Vx is placed in chamber B, the pistons move from position 1 to 2, causing 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 and can be directly read from the instrument in cm³.
4. Significance and Use
4.1 True specific gravity is the ratio of the true density of a substance to that of water at the same temperature. It reflects the material’s chemical composition and mineral structure.
4.2 This method is especially useful for hydrated materials, as traditional methods like C135 may not be accurate for such samples.
4.3 For refractory materials, specific gravity is a key parameter used to classify, compare, and assess material properties, including porosity and composition differences.
4.4 This method serves as a fundamental technique for quality control, research, and product development. It can also act as an arbitration method in material procurement agreements.
4.5 The following conditions must be met for accurate results:
4.5.1 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 sample preparation.
4.5.4 Drying must remove moisture without altering the sample’s structure.
4.5.5 Helium must be used as the gas medium.
4.5.6 The procedure must be conducted carefully and precisely.
4.5.7 Deviating from these conditions may lead to inaccurate results.
4.6 Due to potential closed-cell pores in fine particles, the measured value is close to the true specific gravity but not exact. Differences between similar materials may arise due to measurement techniques or inherent material properties.
5. Equipment
5.1 Analytical balance (200g capacity, 10mg sensitivity)
5.2 Oven with magnesium perchlorate desiccant
5.3 Muffle furnace (up to 1000°C)
5.4 Milling equipment (grinds to less than 45µm)
5.5 Dry helium cylinder with regulator and pressure gauge
5.6 Gas pycnometer with cleaning valve system
6. Sample Preparation
6.1 Grind enough sample to perform three measurements, ensuring it passes through a 45µm sieve. Typically, 100g is sufficient.
6.2 After grinding, burn the sample at high temperature to remove moisture and organic matter without causing sintering. Hydratable materials should be heated to 600°C for over 3 hours.
6.3 Cool the sample in a desiccator containing magnesium perchlorate before testing.
7. Procedure
7.1 Calibrate the densitometer using a standard volume as per the manual.
7.2 Weigh the sample quickly after removing from the desiccator to avoid hydration. Ensure the temperature difference does not exceed 2°C.
7.3 Place the sample in the densitometer chamber and purge with dry helium at ≤13.8 PSI.
7.4 Measure the sample volume according to the instrument instructions, allowing 60 seconds for temperature equilibrium.
7.5 Repeat the test until two consecutive volumes differ by less than 0.05 cm³; take the average.
8. Calculation
8.1 Calculate true density using S = W/V, where S is density (g/cm³), W is mass (g), and V is volume (cm³).
9. Reporting
9.1 For three samples, if the results differ by no more than 0.01, report the average with one decimal place.
10. Precision and Bias
10.1 Interlaboratory tests were conducted on granular alumina and MULCOA 47. Results showed good repeatability and reproducibility, with standard deviations calculated accordingly.
10.2 No bias was observed due to the lack of reference materials.
11. Keywords
11.1 Gas pycnometer, hydrated material, refractory material, true specific gravity
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