Evolved gas analysis of dichlorobis(thiourea)zinc(II) by coupled TG-FTIR and TG/DTA-MS techniques

Identification and monitoring of gaseous species released during thermal decomposition of the title compound 1, Zn(tu)(2)Cl-2, (tu=thiourea, (NH2)(2)C=S) have been carried out in flowing air atmosphere up to 800degreesC by both online coupled TG-EGA-FTIR and simultaneous TG/DTA-EGA-MS. The first gaseous products of 1, between 200 and 240degreesC, are carbon disulfide (CS2) and ammonia (NH3). At 240degreesC, an exothermic oxidation of CS2 vapors occurs resulting in a sudden release of sulphur dioxide (SO2) and carbonyl sulphide (COS). An intense evolution of hydrogen cyanide (HCN) and beginning of the evolution of cyanamide (H2NCN) and isothiocyanic acid (HNCS) are also observed just above 240degreesC. Probably because of condensation and/or polymerization of cyanamide vapors on the windows and mirrors of the FTIR gas cell optics, some strange baseline shape changes are also occurring above 330degreesC. Above 500degreesC the oxidation process of organic residues appears to accelerate which is indicated by the increasing concentration of CO2, while above 600degreesC zinc sulfide starts to oxidize resulting in the evolution of SO2. All species identified by FTIR gas cell were also confirmed by mass spectrometry, except for HNCS

Thermally induced changes in the oxidation state of cerium(IV) - a study of carbonate and chloro complexes

Cesium hexachlorocerate(IV), Cs2CeCl6 (I) and sodium pentakis(carbonato)cerate(IV), Na6Ce(CO3)(5).12H(2)O (II) have been investigated in air by simultaneous TG/DTA, FTIR and XRD in order to follow the oxidation state of cerium during their thermal treatment. The thermal decomposition of the hexachloro compound (I) is accompanied by a double change in the oxidation state of cerium. First, in an inner reduction-oxidation reaction, chlorine is evolved and a Cs2CeCl5 phase is obtained. The immediately starting oxidation of this Ce(III) species caused various phase transitions in the CeCl3-CsCl system formed. The presence of Cs3CeCl6 above 400 degrees C can also be assumed and finally this phase also oxidizes into CeO2 with the formation of CsCl as by-product. In the case of the pentacarbonato complex (II), no Ce(III) species were detected. The final products of its decomposition were CeO2 and Na2CO3

Study of zinc thiocarbamide chloride, a single-source precursor for zinc sulfide thin films by spray pyrolysis

Thermal decomposition of the title compound, Zn(tu)(2)Cl-2 (tu=thiourea), was studied up to 1200degreesC in dynamic inert (N-2) and oxidative (air) atmospheres using simultaneous TG/DTA techniques. In addition, XRD and IR were employed ex situ to resolve the reaction mechanism and products. Cubic ZnS (sphalerite) is formed below 300degreesC in both atmospheres and is observed until 760degreesC, whereafter it transforms in nitrogen to the hexagonal ZnS (wurtzite). EGA by FTIR revealed the complexity of the decomposition reactions involving also the evolution of H2NCN, which reacts to form hexagonal ZnCN2 as shown by an XRD analysis

Microwave-assisted hydrothermal synthesis of zeolite Beta coatings on ALD-modified borosilicate glass for application in microstructured reactors

Stable zeolite Beta coatings with a thickness of 1–2 µm were synthesized on a borosilicate glass substrate by microwave-assisted hydrothermal synthesis. Prior to the synthesis, surface roughness of the substrate was increased to 1.0 µm. Then, two thin films of zirconia and titania were successively deposited at 300 °C on the glass substrate by atomic layer deposition using ZrCl4 as metal precursors for zirconia and TiCl4 for titania, respectively. Oxygen and H2O were used as oxygen precursors in the ALD process. The internal zirconia film protects the glass substrate from dissolution in a highly alkaline synthesis solution. The outer titania film was made superhydrophilic (>15 OH/nm2) by an UV irradiation, which enhances the nucleation and crystallization processes on the substrate. The duration of the zeolite nucleation period was decreased by using the additive effect between fluoride ions and the zeolite seed solution under microwave irradiation. A uniform zeolite Beta coating was obtained already after 8 h at 150 °C in a microwave from a precursor gel with SiO2/Al2O3 = 25, TEAOH/Al2O3 = 8.75, H2O/SiO2 = 11.6, NH4F/SiO2 = 0.2. This is almost six times faster comparing to conventional hydrothermal synthesis