Thermogravimetric And Differential Thermal Research Articles

Differential thermal analysis of mullite formation from Algerian kaolin

In the present work, the kinetics of mullite (3Al2O3.2SiO2) formation from Algerian kaolin was investigated using differential thermal analysis (DTA). The raw kaolin was wet ball milled for 5 h followed by attrition milling for 1 h. Differential thermal and thermogravimetric (DTA/TG) experiments were carried out on samples between room temperature and 1350°C at heating rates of 5, 10, 20 and 40°C min−1. The temperature of mullite crystallisation was found to be ∼1005°C. The activation energies measured from isothermal and non-isothermal treatments were around 1290 and 1260 kJ mol−1 respectively. The growth morphology parameters n (Avrami parameter which indicates the crystallisation mode) and m (a numerical factor which depends on the dimensionality of crystal growth) were found to be almost equal to 1˙5. Analysis of the results showed that bulk nucleation was dominant in mullite crystallisation followed by three-dimensional growth of mullite crystals with polyhedron-like morphology controlled by diffusion from a constant number of nuclei.

Radiation damage of variscite in historic crafts: Solarization, decolouration, structural changes and spectra from ionoluminescence

X-ray diffraction measurements, during halogen lamp illumination to simulate sunlight, (TXRD) show a phase transition from variscite (AlPO 4·H 2O) Messbach to variscite Lucin and a loss of the dark green colour. The differential-thermal and thermo-gravimetric (DTA-TG) analyses and thermoluminescence (TL) peaks all depict this first-order phase transition which takes place under sunlight. From the water vaporization temperature up to circa 650 °C, a second-order phase transition progressively occurs from variscite to berlinite (AlPO 4) by loss of a second unit of water with hydrogen bonded to the lattice. The ion beam luminescence (IBL) spectra of the Zamora variscite display a spectral band from 500 to 570 nm attributed to [UO 2] 2+ in phosphates, and another spectral band from 670 to 740 nm is linked with Cr(VI) 3+ defects situated in octahedral Al(VI) 3+ positions. In the hydrous variscite lattice, the Al–O and P–O chemical bonds are mainly covalent; with the degree of covalency of the P–O chemical bond significantly larger than of Al–O. This open structure of variscite, which has a crystal field of reduced strength, involves small shifts of the absorption bands which intensify the blue–green transmission producing the characteristic emerald colour of the dark green variscite of Zamora. These data provide a valuable basis for detection of solarization damage in historic crafts with inlaid variscite in the Museo del Prado (Madrid, Spain).

Sintering of Cu-Al2O3 nano-composite powders produced by a thermochemical route

This paper presents the synthesis of nano-composite Cu-Al2O3 powder by a thermochemical method and sintering, with a comparative analysis of the mechanical and electrical properties of the obtained solid samples. Nano-crystalline Cu-Al2O3 powders were produced by a thermochemical method through the following stages: spray-drying, oxidation of the precursor powder, reduction by hydrogen and homogenization. Characterization of powders included analytical electron microscopy (AEM) coupled with energy dispersive spectroscopy (EDS), differential thermal and thermogravimetric (DTA-TGA) analysis and X-ray diffraction (XRD) analysis. The size of the produced powders was 20-50 nm, with a noticeable presence of agglomerates. The composite powders were characterized by a homogenous distribution of Al2O3 in a copper matrix. The powders were cold pressed at a pressure of 500 MPa and sintered in a hydrogen atmosphere under isothermal conditions in the temperature range from 800 to 900 ?C for up to 120 min. Characterization of the Cu-Al2O3 sintered system included determination of the density, relative volume change, electrical and mechanical properties, examination of the microstructure by SEM and focused ion beam (FIB) analysis, as well as by EDS. The obtained nano-composite, the structure of which was, with certain changes, preserved in the final structure, provided a sintered material with a homogeneous distribution of dispersoid in a copper matrix, with exceptional effects of reinforcement and an excellent combination of mechanical and electrical properties.

In situ synthesis of ammonium salt of 12-molybdophosphoric acid on iron phosphate and the ammoxidation functionality of the catalyst in the transformation of 2-methylpyrazine to 2-cyanopyrazine

The ammonium salt of 12-molybdophosphoric acid (AMPA) on iron phosphate was synthesized via in situ interaction between the phosphate species of the support and the molybdenum component of ammonium heptamolybdate. The concentration of AMPA was varied such that the nominal MoO 3 content of the catalysts was in the range of 5–20 wt.%. The formation of AMPA, possessing the typical Keggin structure, was confirmed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and FT-Raman spectroscopy. Thermo-gravimetric and differential thermal (TG/DT) analyses were used to establish the stability of these catalysts. Whereas the support, FePO 4, displayed low activity but maximum selectivity to 2-cyanopyrazine (CP), the in situ synthesized catalysts exhibited higher activity during the ammoxidation of 2-methylpyrazine (MP). At lower reaction temperatures and particularly, at lower AMPA loading, the in situ synthesized catalysts have shown higher activity and retained substantially high selectivity.

Incorporation of fullerene derivatives into smectite clays: a new family of organic-inorganic nanocomposites.

Three fulleropyrrolidine derivatives, characterized by the presence of positive charges, were introduced in the interlayer space of montmorillonite. The composites were characterized by powder X-ray diffraction and differential thermal and thermogravimetric (DTA-TGA) analysis, in conjunction with FTIR, UV-Vis, Raman, and (57)Fe-Mössbauer spectroscopies. Organophilic derivatives were intercalated into organically modified clays, while water-soluble fulleropyrrolidines were introduced into the clay galleries through ion exchange. The experiments, complemented by computer simulations, show that not all the clay-clay platelets are intercalated by the fullerene derivatives and that a sizable amount of charge transfer takes place between the host and the guests.

Fabrication and Properties of PDMDPS-Based Inorganic/Organic Hybrid Sheets

Flexible and homogeneous inorganic/organic hybrid sheets were fabricated from silanol-terminated polydimethyldiphenylsiloxane (PDMDPS), phenyltriethoxysilane (PhSi(OEt) 3 ) and chemically modified zirconium n-butoxide (Zr(OBu n ) 4 ), Fourier transform infrared (FT-IR) spectroscopic, nuclear magnetic resonance (NMR) speetroscopic and differential scanning calorimetric (DSC) studies revealed that species derived from PhSi(OEt) 3 and Zr(OBu n ) 44 reacted with the silanol-terminated end groups of PDMDPS chains and connected each PDMDPS chains as a cross-linkage agent. Monophenylsiloxane species derived from Phsi(OEt) 3 were also found to act as an inhibitor of the micro-Brownian of POMDPS chains and affect the mechanical properties such as the tensile strength and elongation. Thermogravimetric and differential thermal (TG-DTA) analysis revealed that the thermal decomposition occurred above 400°C, which was higher than that of PDMS-based inorganic/organic hybrids. The addition of FeCl3 was not remarkably effective in thermal stabilization but affected both tensile strength and elongation to fracture.