Thermogravimetric AnalyzerStudying the thermal stability of materials by measuring the change in sample quality with temperature, where the crucible is crucial as a container for carrying the sample. Careful selection and use are still necessary for the practical application of inert crucibles, otherwise errors may be introduced and equipment may be damaged. The following is an analysis of key points.
The so-called "inertness" only refers to materials that do not react with most substances under specific conditions, and there are no absolutely inert materials. Common crucible materials have their limitations: although platinum is chemically stable, it can be reduced by carbon at high temperatures; Aluminum oxide has strong corrosion resistance, but may react with strong alkalis; Quartz glass is suitable for routine testing, but hydrofluoric acid can severely corrode its surface. A certain university laboratory once used a quartz crucible to melt fluorine-containing catalysts, resulting in crucible perforation and contamination of the furnace body.
The crucible material should be selected to match the experimental requirements:
1. Metal crucible: Platinum is suitable for most inorganic materials, but the cost is high; Nickel crucibles are cost-effective, but not suitable for chloride testing. When a certain enterprise was testing the thermal decomposition of PVC, the nickel crucible was corroded by the precipitated hydrochloric acid. The problem was solved by using alumina instead.
2. Ceramic crucible: Aluminum oxide can withstand various acids and bases, but alkaline oxides (such as K ₂ O) will react slowly with it; Zirconia is more suitable for highly corrosive environments, but it comes at a higher price.
3. Special coating treatment: For active metals, boron nitride coated graphite crucibles can be used to improve thermal conductivity and enhance corrosion resistance.
Potential risks and countermeasures:
1. Cross contamination risk: Residual previous samples may evaporate or decompose in new experiments. The standardized operation requires full cleaning and high-temperature burning of the crucible after each use. However, a quality inspection agency failed to clean the crucible in a timely manner, resulting in false weight loss peaks between different products.
2. Catalytic interference: Active sites on certain metal surfaces can accelerate decomposition reactions. Comparative experiments show that a blank platinum crucible will experience slight weight gain under the same conditions, which is due to the adsorption of air components.
3. Effects of thermal conductivity differences: Differences in thermal conductivity between different materials can lead to temperature hysteresis. Graphite crucible has a fast heating rate, suitable for rapid screening; Aluminum oxide crucible has good insulation performance and is more suitable for precise measurement.
Standardized operation suggestions:
1. Pre treatment steps: Before using a new crucible, it should be air burned to a constant weight at the target temperature to remove surface impurities during the manufacturing process.
2. Weighing accuracy control: The sample loading should not exceed the crucible volume, as excessive accumulation can affect the thermal conductivity efficiency. A certain research institute found that when the sample filling exceeds the volume, the actual temperature measurement point deviates by a specific range.
3. Regular maintenance and replacement: Observe the inner wall of the crucible for discoloration, deformation, or cracks, especially when testing corrosive samples frequently. It is recommended to replace the crucible with a new one after completing a specific number of experiments.