Basma A.A. Balboul

Thermal genesis course and characterization of lanthanum oxide

Abstract La(NO3)3·6H2O was used as a precursor to produce La2O3 at 650°C in an atmosphere of air. Thermal processes occurred were monitored by means of thermogravimetry, differential thermal analysis, and gas-mass spectrometry. Infrared (IR)-spectroscopy, X-ray diffractometry and scanning electron microscopy characterized the intermediates and final solid products. The results showed that, La(NO3)3·6H2O decomposes through nine endothermic weight loss processes. Five dehydration steps occurred at 90, 105, 150, 175 and 215°C, leading to the formation of crystalline nitrate monohydrate, which decomposes to La(OH)(NO3)2 at 410°C. The latter, decomposes to La2O3 at 640°C, via two different intermediates; LaO(NO3) at 440°C, and non-stoichiometric unstable, La(O)1.5(NO3)0.5 at 570°C. The gaseous decomposition products as identified by gas-mass spectroscopy were water vapor, nitric acid and nitrogen oxides (NO, NO2 and N2O5). The final product La2O3 has a large crystalline containing pores, voids and cracks, with a surface area of 23 m2 g−1. Also it possessed Lewis acidic and basic sites, as indicated by Pyridine adsorption.

Thermal genesis course and characterization of praseodymium oxide from praseodymium nitrate hydrate

Pr(NO3)36H2O was used as a precursor to produce PrO1.833 at 6008C in an atmosphere of static air. Thermal processes occurred were monitored by means of thermogravimetry, differential thermal analysis and mass spectrometry. IR-spectroscopy and X-ray characterized the intermediates and final solid products. The results showed that, Pr(NO3)36H2O decomposes through 11 endothermic weight loss processes. Five dehydration steps occurred at 130, 180, 200, 230 and 2508C, leading to the formation of crystalline nitrate monohydrate, Which decomposes to Pr(NO3)2 at 3408C. The latter, decomposes to PrO1.833 at 4658C, via four different intermediates PrO(NO3) at 4308C, and nonstoichiometric unstable, PrO0.25(NO3)2.5 at 3628C; Pr(O)0.5(NO3)2 at 3828C and Pr(O)0.75(NO3)1.5 at 4008C. The gaseous decomposition products identified by mass spectroscopy were water vapor and nitrogen oxides (NO, NO2 and N2O5). The activation energy was determined nonisothermally for the thermal processes monitored throughout the decomposition course. The final product PrO1.833 has a surface area of 46.3 m 2 /g. # 2001 Elsevier Science B.V. All rights reserved.

Physicochemical characterization of the decomposition course of hydrated holmium nitrate. Thermoanalytical studies

Abstract Ho(NO 3 ) 3 ·5H 2 O (HoNit) was used as a parent compound for the formation of Ho 2 O 3 at up to 800°C in atmosphere of air. Thermal processes occurring during the decomposition course were monitored by means of differential thermal analysis (DTA), thermogravimetry (TG) and gas-mass spectroscopy. The intermediates and final solid products were characterized by infrared (IR) spectroscopy, X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that, HoNit decomposes completely through eight endothermic weight losses processes. The dehydration occurs through the first four steps at 120°, 140°, 205° and 240°, forming crystalline nitrate monohydrate, which decomposes to Ho(OH)(NO 3 ) 2 at 265°C. The latter, decomposes immediately to form a stable and crystalline HoO(NO 3 ) at 368°C, then to nonstoichiometric unstable intermediates; Ho(O) 1.25 (NO 3 ) 0.5 at 500°C. Finally, Ho 2 O 3 was formed at 560°C. The decomposition course and surface morphology were supported and followed by SEM. The final product Ho 2 O 3 at 600°C has large crystalline with irregular sheet-shaped particles containing large pores, voids and cracks. The gaseous decomposition products as identified by gas-mass spectroscopy are water vapor, nitric acid and nitrogen oxides (NO, NO 2 and N 2 O 5 ).

Thermal decomposition study of erbium oxalate hexahydrate

Abstract The thermal decomposition of erbium oxalate hydrate (Er 2 (C 2 O 4 ) 3 ·6H 2 O) till 900°C, in air and nitrogen, is investigated by nonisothermal gravimetry and differential thermal analyses. The activation energy (Δ E ) is determined for each thermal decomposition step. The gaseous decomposition products are identified by infrared (IR)-spectroscopy. Intermediate and final solid products are characterized by IR-spectroscopy and X-ray diffraction (XRD). The results indicate that, in air atmosphere, following a stepwise dehydration at 90–370°C, the anhydrous product was noncrystalline and thermally unstable. An oxycarbonate Er 2 O 2 CO 3 is obtained at 450°C which decomposes near 600°C into crystalline Er 2 O 3 . The atmosphere has no affect on the decomposition pathway. The oxide proportion and crystallinity improved on increasing the temperature to 800°C. The volatile decomposition products were water vapor and carbon oxides.

Formation and surface characterization of thulium oxide catalysts

Thulium oxide, Tm2O3, was obtained as a final product of the thermal decomposition of Tm(CH3COO)3·4H2O. The decomposition steps up to 800°C were characterized by TG, DTA, XRD, SEM, GC-MS and gas- and solid-phase IR spectroscopy. The results showed that Tm(CH3COO)3 ·4H2O dehydrates completely in two overlapping steps at 90 and 110°C and decomposes to Tm2O3 at 540°C through a non-crystalline intermediate Tm(OH)(CH3COO)2 at 350°C, Tm(O)(CH3COO) at 375°C and Tm2O2CO3 at 400°C. The oxides obtained at 600 and 800°C were subjected to texture analysis and pyridine adsorption. The results revealed that the oxide obtained at 600°C has a higher surface area of 49.7 m2 g−1 with larger pores than that obtained at 800°C (SBET=32.8 m2 g−1). On the other hand, the oxide obtained at 600°C has a basic surface character and contains at least two different Lewis acid sites as indicated from pyridine adsorption. The gaseous decomposition products as identified by gas-phase IR and GC-MS are water vapour, acetic acid, ketene, acetone and methane.

Ytterbium oxide from different precursors: formation and characterization: Thermoanalytical studies

Abstract Thermal processes involved in the decomposition course of hydrated ytterbium acetate (Yb(CH 3 COO) 3 ·4H 2 O) and oxalate (Yb 2 (C 2 O 4 ) 3 ·6H 2 O) up to 900°C, in atmosphere of air, were monitored by non-isothermal gravimetry and differential thermal analyses. The gaseous decomposition products were identified by gas-mass spectroscopy. Intermediates and final solid products were characterized by X-ray and scanning electron microscopy. The results showed that Yb-acetate dehydrates in four steps and decomposes to Yb 2 O 3 at 560°C, through four non-crystalline unstable intermediates. For Yb-oxalate, the dehydration occurs in three steps. The anhydrous oxalate is thermally unstable and immediately decomposes to Yb 2 O 3 at 600°C through two unstable intermediates. The crystalline oxide obtained from the acetate contains large pores in comparison to that oxide obtained from oxalate as indicated from SEM results. The volatile decomposition products from the acetate are water vapor, acetic acid, ketene, acetone and methane.

Holmium oxide from holmium acetate, formation and characterization: thermoanalytical studies

Abstract Thermal processes involved during the decomposition course of hydrated holmium acetate (Ho(CH 3 COO) 3 ·3.5H 2 O) up to 800°C, in an atmosphere of air, were monitored by thermogravimetry and differential thermal analysis. The gaseous decomposition products were identified by IR- spectroscopy. X-ray diffraction and IR-spectroscopy characterized intermediates and final solid products. The results showed that, Ho-acetate, dehydrates completely in two steps then decomposes to Ho 2 O 3 at 570°C, through three noncrystalline unstable intermediates. The oxide obtained at 600 and 800°C possesses a surface area of 31 and 15.0 m 2 g −1 , respectively. The volatile decomposition products from the acetate were water vapor, acetic acid, ketene, acetone, methane and isobutene.

Probing the Phase Transition in Nanocrystalline TiO2 Powders by Positron Lifetime (PAL) Technique

Positron annihilation techniques (PAT) have recently been successfully employed for the characterization of phase transitions in metals and compounds. In the present study, positron annihilation lifetime (PAL) measurements have been carried out on a nanocrystalline titania (TiO2) in the form of powders that had been heat-treated at temperatures ranging from 300 to 1273K. The PAL spectra were analyzed into two lifetime components. The shorter lifetime τ1 (185-300 ps) is attributed to positron annihilation in vacancies and the longer lifetime τ1 (400-580 ps) to positrons in microviods at interfaces. The rutile phase of TiO2 powders was utilized as a reference in order to compare their behavior with the commercially supplied and widely available anatase phase (Degussa P25). The influence of the heat-treatment upon the nanostructure during the transition of the anatase to rutile phase were also investigated by X-ray diffraction (XRD), TEM and BET surface area methods. Understanding of this effect is expected to enhance our knowledge of the morphology and nanocrystallite size of TiO2 powders and their T-dependence, and hence their physical properties.