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. Scope 1.1 This method is specifically designed for the determination of the true specific gravity of solid materials, particularly those that are prone to water absorption, deliquescence, or hydration. These types of substances are not suitable for testing using methods such as C135, C128, or C188. 1.2 When applying this standard, it is essential for users to develop and implement appropriate safety measures and health precautions based on the specific conditions of the 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. Key Points of the Method 3.1 The sample must be 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 powdered sample should be dried to remove any free moisture and 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 represents the true specific gravity, which is the ratio of the material’s density to that of water at 4°C. 3.2 The gas density meter operates based on two chambers and two pistons. When the connecting valve is closed, any movement of one piston causes an imbalance in pressure. To maintain equilibrium, the other piston must move proportionally. 3.3 If a sample with volume Vx is placed in chamber B, and the connecting valve is closed, moving both pistons from position 1 to 2 will cause a pressure imbalance. However, if only piston B moves to position 3, the pressure can be balanced. The displacement dx between positions 2 and 3 is proportional to the sample volume. This displacement is calibrated and can be directly read in cm³ via a digital display. 4. Purpose and Application 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 is a fundamental physical property that reflects the chemical composition and mineral structure of the material. 4.2 This method is especially useful for hydrated materials, as they cannot be accurately tested using the C135 method. 4.3 For refractory materials, specific gravity is a key parameter used to classify materials, detect differences in composition, assess porosity, and support various analytical calculations. 4.4 This method serves as a primary measurement technique suitable for quality control, research, product development, and arbitration in material procurement agreements. 4.5 Basic requirements include: - Representative sampling - Proper particle size reduction - No contamination during processing - Removal of moisture without altering the sample structure - Use of helium as the gas medium - Careful and accurate execution of the procedure 4.6 Due to potential closed-cell pores in samples, the results obtained are very close to the true specific gravity but may not be perfectly accurate. Therefore, when comparing similar materials, careful analysis is required to distinguish between inherent material differences and minor variations caused by the method itself. 5. Equipment 5.1 Analytical balance (200g capacity, 10mg sensitivity) 5.2 Drying oven with magnesium perchlorate desiccant 5.3 Muffle furnace (up to 1000°C) 5.4 Crushing equipment (particle size less than 45μm) 5.5 Dry helium cylinder with regulator and pressure gauge 5.6 Gas comparison densitometer with external cleaning valve system 6. Sample Preparation 6.1 Grind the sample to pass through a 45μm sieve, typically requiring about 100g per test. 6.2 Burn the sample at high temperatures to remove moisture and organic matter without causing agglomeration. 6.3 Cool the sample in a desiccator containing magnesium perchlorate. 7. Measurement Procedure 7.1 Calibrate the densitometer with a standard volume. 7.2 Weigh the sample quickly after removal from the desiccator to prevent hydration. 7.3 Place the sample in the densitometer and clean the system with dry helium. 7.4 Measure the sample volume following the instrument instructions with a 60-second equilibrium time. 7.5 Repeat the measurement until the difference between two consecutive values is less than 0.05 cm³. 8. Calculation 8.1 Calculate true density using the formula: S = W / V Where S is the true density, W is the sample mass in grams, and V is the sample volume in cm³. 9. Reporting 9.1 For three samples, if the results differ by no more than 0.01, take the average as the final result. 10. Precision and Bias 10.1 Interlaboratory tests were conducted on two materials (granular alumina and MULCOA 47), showing repeatability and reproducibility values. 10.2 No bias was found due to the lack of a reference material. 11. Keywords Gas comparison densitometer, hydrated material, refractory material, true specific gravity

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