Tuula Leskelä

A thermoanalytical study of synthetic carbonate-containing apatites ☆

Abstract Two series of carbonate-apatites, Ca10(PO4)6 − x (CO3)x (F,OH)2, were synthesized by precipitating them from aqueous solutions followed by ripening at the precipitation temperature (20 or 80°C). Initial solutions contained Ca2+, Mg2+, NH4+, PO3−4, F−, CO2−3 and NO−3 ions; in the second series Na+ was added. The samples had low crystallinity but, nevertheless, showed the apatite structure as judged from XRD and IR. Thermal degradation was followed by simultaneous TG/DTA and TG/EGA (evolved gas analysis) methods and by ex situ studies. The NH4+-containing samples (A, 20°C and B, 80°C) and two Na+-containing samples (C and D, both at 80°C) were subjected to a detailed study. On the basis of EGA studies of sample A by FTIR, the first two exothermic peaks at 250– 300°C could be assigned to the release of H2O and H2O + NH3, respectively: the remaining three at 350– 710°C were due to CO2 evolution and changes in the apatite structure. For samples synthesized at 80°C, the DTA peaks were smaller than for sample A. The EGA peak due to NH3 was missing for Na+-containing samples (C and D). For all samples, the residue at 1000°C had the hydroxy-fluorapatite structure. The TA and XRD data indicate that the crystal structure of the precipitated apatites is relatively labile. After the release of volatiles, however, thermally induced rearrangements take place leading to a more stable and crystalline phase.

Thermal Decomposition of Copper(I) Thiocarbamide Chloride Hemihydrate

Two combinations of simultaneous thermoanalytical techniques (TG+DTA and TG+EGA) were used to study the thermal decomposition of the title compound in order to gain a better insight into the spray pyrolytic processes leading to Cu2-xS and CuInS2 thin films. After dehydration a complex sequence of reactions starts above 220°C leading through several intermediates to the formation of CuO in air at 1000°C. In an inert atmosphere Cu2S is formed which in helium above 800°C partly decomposes to Cu. XRD and FTIR were used to identify the intermediate solid phases which in air included CuCl, Cu2OSO4, Cu2OCl2 and CuSO4. EGA-FTIR confirmed the complex reaction mechanism with NH3, HCl, H2O, COS, CO2 and some HCN as main gaseous products under oxidative conditions.

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)2Cl2 (tu=thiourea), was studied up to 1200°C in dynamic inert (N2) 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 300°C in both atmospheres and is observed until 760°C, 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 revealed by an XRD analysis.

A Thermoanalytical Study of Copper(I) Thiocarbamide Compounds

Hydrated isostructural 1:3 complexes of copper(I) chloride and bromide with thiourea were synthesised and their thermal decomposition studied by simultaneous TG/DTA complemented by ex situ FTIR and XRD studies. The decomposition of Cu(tu)3Cl·H2O is initiated by dehydration around 100°C, followed by a total multi-step degradation of the structure in the temperature range of 200–600°C. The counter ion has some influence on the temperatures and composition of the solid residue. The results were compared with those obtained with the 1:1 complex Cu(tu)Cl·1/2H2O.

Evolved gas analysis of inorganic compounds with a quadrupole mass spectrometer coupled to a thermogravimetric analyzer

Abstract An inexpensive EGA system, based on a quadrupole MS and a standard PC, has been constructed and connected to a commercial thermobalance via a heated capillary. The system has been tested with various inorganic compounds including CaC 2 O 4 · H 2 O, CuSO 4 · 5H 2 O, Cu(NH 3 ) 4 SO 4 · H 2 O and [Pt(NH 3 ) 5 OH]CI 3 · H 2 O. The applicability of the TG-EGA-MS system is discussed.

Thermal behaviour of sulphato and nitrato complexes of cerium(IV)

Four sulphato and nitrato complexes of cerium(IV),viz. (NH4)4Ce(SO4)4·2H2O (1), (NH4)2Ce(SO4)3 (2), (NH4)2Ce(NO3)6 (3) and Cs2Ce(NO3)6 (4) were studied by simultaneous TG/DTA under various experimental conditions in order to establish their decomposition mechanism and to compare the results with the literature data which have been reviewed. In the case of the ammonium compounds (1, 2 and3) the decompositions are accompanied by changes in the oxidation state of cerium; the presence of Ce(III) and Ce(IV) were studied byex situ magnetic susceptibility and XPS measurements. The crystal structure of (1) was determined as well. It forms monoclinic crystals with space groupP21/c; the parameters of the unit cell are:a=12.638(18) Å,b=11.362(10) Å,c=13.607(11) Å, β=110.17(9)°,V=1834.05 Å3.ZusammenfassungZur Ermittlung des Zersetzungsmechanismus und zum Vergleich der Resultate mit den im Überblick angegebenen Literaturangaben wurden mittels simultaner TG/DTA unter verschiedenen Versuchsbedingungen vier Sulfato- und Nitratokomplexe von Zer(IV), nämlich von (NH4)4Ce(SO4)4·2H2O (1), (NH4)2Ce(SO4)3 (2), (NH4)2Ce(NO3)6 (3) und Cs2Ce(NO3)6 (4) untersucht. Im Falle der Ammoniumverbindungen (1, 2 und3) werden die Zersetzungen von Änderungen des Oxidationszustandes von Zer begleitet; die Gegenwart von Ce(III) und Ce(IV) wurde durch ex situ Messungen der magnetischen Suszeptibilität und durch XPS-Messungen untersucht. Weiterhin wurde auch die Kristallstruktur von1 ermittelt. Diese Verbindung bildet monoklinische Kristalle der Raumgruppe P21/c; die Parameter der Elementarzelle lauten:a=12.638(18) Å,b=11.362(10) Å,c=13.607(11) Å, β=110.17(9),V=1834.0.5 Å3.

Formation of CuInS_2 in Spray Pyrolisis Process as Simulated by Thermal Analysis

The formation of CuInS2 thin films was studied by simulating spray pyrolysis conditions through thermogravimetric experiments performed both in air and helium. The solid precursor containing Cu, In, Cl, thiourea and H2O in a ratio 1:1:5:3:2 was obtained by evaporation of the aqueous spray pyrolysis solution. Thermal degradation of the precursor was found to be a complex process where CuInS2 is formed as the main crystalline product already at 250 °C in both atmospheres. In air, however, InOCl is also readily formed and at 650 °C In2O3 and CuO appear as final products. In thin films prepared at 320 °C the Cu:In:S ratio is correct but there are 1.5 wt.% Cl residues as shown by RBS and EDS analyses, respectively.

Oxidation of alkaline-earth-metal sulfide powders and thin films

The oxidation of CaS and SrS powders and thin films was studied in situ up to 1300 °C by thermoanalytical techniques (TG, DTA and high-temperature XRD) while FTIR and powder XRD were used to analyse ex situ the solid reaction intermediates and products. CaS powder starts to oxidize to CaSO4 around 500 °C but the oxidation is not complete because of a competing reaction, i.e. the decomposition of CaSO4 to CaO, which is significant above 1000 °C. SrSO4 is more stable and therefore SrS completely oxidizes to SrSO4 before the decomposition starts. FTIR and XRD failed to detect CaSO3 or SrSO3 at any stage of the heating process. Particle size appears to have a marked effect on the decomposition of powders, while moisture plays only a minor role. Thin films appear to be more stable towards oxidation but they react around 1000 °C with the silicon substrate.

Thermoanalytical methods in the study of inorganic thin films

Thermoanalytical (TA) methods are relatively seldom applied for assessing the physical and chemical proeprties of thin films, but they can be used in studies of composition, phase transitions and film—substrate interactions. In the present paper the possibilities of TA methods in thin film studies are reviewed. The thermoanalytical methods considered are the classical TG and DTA/DSC methods but some complementary methods will also be briefly mentioned. The main emphasis is given to true thin films. Details of sample preparation are also given. An important application of TA methods is characterization of precursors for the CVD growth of thin films, and this is also discussed.ZusammenfassungThermoanalytische Methoden werden relativ selten zur Beurteilung der physikalischen und chemischen Eigenschaften von Dünnschichten verwendet, können aber zur Untersuchung von Zusammensetzung, Phasenum wandlungen und Dünnschicht-Substrat-Wechselwirkungen eingesetzt werden. Es wird hier ein Überblick über die Möglichkeiten der TA-Methoden bei der Untersuchung von Dünnschichten gegeben. Die in Betracht gezogenen thermo-analytischen Methoden sind die klassischen Methoden TG und DTA/DSC, aber auch einige ergänzende Methoden werden kurz beschrieben. Das Schwergewicht liegt bei echten Dünnschichten. Es werden auch Details der Probenvorbereitung beschrieben. Eine wichtige Anwendung von TA-Methoden besteht in der Beschreibung von Präkursoren für das CVD-Wachstum von Dünschichten und dies wird ebenfalls diskutiert.

Preparation of yellow and red iron oxide pigments from iron(II) sulfate by alkali precipitation

Abstract A study was made of the preparation of yellow α-FeOOH pigments from iron(II) sulfate solution by alkali precipitation and gas oxidation methods. The preparation of pure yellow pigments turned out to be difficult. Pigments of composition FeOOH were obtained under acidic (pH 3 O 4 was formed as well, and it stained the products greenish, brownish or black. At 70°C and pH 7–9 a pure black Fe 3 O 4 was formed. According to TG measurements, the needle-like FeOOH particles decomposed to red α-Fe 2 O 3 above 300°C and the pigments then obtained were light red. The preparation of dark red oxides required higher temperatures than the direct firing of FeSO 4 ·7 H 2 O to oxide.