Thermogravimetric analysis

About: Thermogravimetric analysis is a research topic. Over the lifetime, 37248 publications have been published within this topic receiving 862144 citations. The topic is also known as: thermal gravimetric analysis & TGA.

The thermal decomposition of Mg-Al hydrotalcites: effects of interlayer anions and characteristics of the final structure.

Abstract: The thermal decomposition of hydrotalcites (HTs) with different interlayer anions in the 298 ± 523 K re- gion has been investigated by using transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and IR, 27 Al MAS-NMR and X-ray absorp- tion near-edge structure (XANES) spec- troscopy. The thermal stability of the HT with interlayer oxalate was remarkably higher than that of HTs with interlayer carbonate; the onset temperatures for decomposition were 523 K and 473 K, respectively. It is proposed that the basicity of the interlayer anion is the key factor in the onset of dehydroxyla- tion of the brucite-like layers: the lower the basicity, the more thermally stable the HT compound. After heat treatment at 723 K, small Mg(Al)O domains ( 5 nm) within the HT crystallites cause broadening of the XRD reflec- tions. The electron diffraction pattern consists of spots and rings, due to non- randomly oriented crystalline material. Formation of disordered bonds, caused by nonideal packing between the de- composing adjacent cation layers in the (1 1 1) direction, could explain the ex- panded d value in the resulting MgO- like phase observed with XRD and electron diffraction. The orientation of the Mg(Al)O domains in the heat-treat- ed material may be crucial for the so- called ™memory effect∫ of HTs.

Poly(Aryl ethers) by nucleophilic aromatic substitution. II. Thermal stability

Abstract: The thermal stability and degradation process for a specific poly(aryl ether) system have been studied. In particular, the polymer which is available from Union Carbide Corporation as Bakelite polysulfone has been examined in detail. Polysulfone can be prepared from 2,2-bis(4-hydroxyphenyl)propane and 4,4′-dichlorodiphenyl sulfone by nucleophilic aromatic substitution. Because of a low-temperature transition at − 100°C. and a glass transition at 195°C., polysulfone retains useful mechanical properties from −100°C. to 175°C. A number of experimental methods were utilized to study the thermal decomposition process for this polymer system. Polysulfone gradually degraded in vacuum above 400°C. as demonstrated by mass spectrometry. Thermogravimetric analysis in argon, air, or high vacuum indicated that rapid decomposition began above 460°C. From gas chromatography, mass spectrometry and repeated laboratory pyrolyses, a number of products from polymer decompositions were identified. The most important degradation process in vacuum or inert atmosphere was loss of sulfur dioxide. Several model compounds representative of portions of poly(aryl ether) molecules were synthesized and the relative thermal stabilities determined. Possible mechanisms for pure thermal decomposition of polysulfone were derived from the product analyses, model studies, and consideration of bond dissociation energies.