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Principles of Simultaneous Thermal Analysis (STA) and Case Analysis
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- Universallab
- @universallab
Simultaneous Thermal Analysis (STA) is a technique that combines thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) to provide comprehensive information about a material's thermal behavior. By measuring both weight changes (via TGA) and heat flow (via DSC) simultaneously, STA offers insights into the material's composition, thermal stability, phase transitions, and reaction kinetics.
Principles of STA
Thermogravimetric Analysis (TGA):
Function: Measures changes in the mass of a sample as it is heated, cooled, or held at constant temperature.
Purpose: Identifies decomposition temperatures, moisture content, oxidation, and reduction reactions.
Differential Scanning Calorimetry (DSC):
Function: Measures the amount of heat required to increase the temperature of a sample compared to a reference.
Purpose: Detects phase transitions such as melting, crystallization, and glass transitions, as well as exothermic and endothermic reactions.
By using STA, researchers can correlate mass changes with thermal events, leading to a better understanding of material properties and behaviors.
Case Analysis
Excellent Stability
Heating alumina powder to 400°C (initial mass of 120.0 mg) results in a weight loss of 16.50 mg, primarily due to water evaporation, which corresponds to the endothermic peak on the DSC curve. During a 50-hour isothermal process, the mass change is only 11 micrograms, demonstrating the excellent stability of the balance system.
Reduction of Manganese Oxide
Manganese oxide (MnO2) is commonly used as an oxidizing agent in chemistry and as a cathode material in the battery industry. In the following STA measurement spectrum, there are two weight loss steps at around 600°C and 950°C due to the reduction of MnO2 to Mn2O3 and finally to Mn3O4. The corresponding weight losses of 9.20% and 3.07% match well with the theoretical values, reflecting the high precision of the weighing system. Corresponding to the DSC curve, there are two endothermic peaks with enthalpies of 432 J/g and 180 J/g. The endothermic peak at 1200°C on the DSC curve is a reversible structural transformation with no corresponding weight loss, and the exothermic peak at 1148°C during the cooling process (dashed line) corresponds to the reverse transformation.
Decomposition of Basic Ferric Sulfate Basic ferric sulfate (Fe(OH)SO4) is a basic raw material for synthesizing ferric oxide, used as pigments or magnetic storage media. The so-called ferrofluid typically contains superparamagnetic ferric oxide nanoparticles, which can be used as contrast agents for magnetic resonance imaging. Below 600°C, according to STA-MS combined test results, there are two dehydration steps corresponding to the peaks with a mass number of 18 on the mass spectrum. Between 600°C and 800°C, SO2 and O2 are generated, corresponding to the peaks with mass numbers 64 and 32. The final product is Fe2O3 (hematite).
Building Materials: Gypsum and Quartz Sand Gypsum and quartz sand are often used in plaster and mortar. In this example, the gypsum dihydrate (CaSO42H2O) component in the sample undergoes two dehydration steps before 200°C, forming hemihydrate (CaSO41/2H2O) and eventually anhydrous gypsum (CaSO4), with a total endothermic enthalpy of 122 J/g. Quantitative analysis shows the sample contains 23.4% gypsum dihydrate. Anhydrous gypsum releases 18.3 J/g of heat between approximately 300°C and 450°C, forming β-CaSO4. The endothermic effect at an onset temperature of 573°C is due to the α→β structural transition of quartz (crystalline SiO2).
Phase Diagram of Alloy Pt0.89Au0.1OIr0.01 is a dental alloy commonly used for inlays, crowns, and bridges. Dental alloys must be strong, easy to form, corrosion-resistant, and biocompatible. The test results show an endothermic phenomenon at an extrapolated onset temperature of 1659°C during heating, primarily due to the melting process with an enthalpy value of 88 J/g. During cooling, the DSC curve (dashed line) shows an exothermic peak at an onset temperature of 1685°C (peak temperature 1684°C), primarily due to the crystallization process of the alloy with an enthalpy value of -87 J/g. At the highest temperature, there is a weight loss of 0.05%, mainly due to the start of volatilization.
Plastics Plastic bottles, textile fibers, and films (e.g., food packaging) are common applications of the polymer PET (polyethylene terephthalate). STA test results show a step before 100°C on the DSC curve, primarily due to the glass transition, accompanied by an increase in specific heat of 0.35 J/(g*K). The endothermic peak at 81°C is mainly due to relaxation phenomena. The exothermic peak at 131°C is primarily due to the cold crystallization process. The endothermic peak at 255°C is the melting process. After 360°C, the sample begins to decompose, accompanied by a weight loss of 79.5%.
