Thermal Study of the Ceramic Pigments CoxZn(7−x)Sb2O12

Using the Pechini method, pigments with spinel structure (Zn₇Sb₂O₁₂)were synthesized by substitution of the cation Zn²⁺ by Co²⁺, in compounds with different concentrations of Sb₂O₃. The doping resulted in Co_xZn_(7–x)Sb₂O₁₂ phases(x=1–7) that were isomorphs to spinel, denominated as samples A and B. After thermal treatment at 400°C for 1 h, the powders were characterized by thermogravimetry(TG) and differential thermal analysis (DTA). The results indicate a different behavior whena higher amount of Sb₂O₃ is used, due to the presence of a secondary phase (ilmenite). This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal studies of ZnO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–TeO<Subscript>2</Subscript> glasses

The effect of TeO₂ additions on the thermal behaviour of zinc borophosphate glasses were studied in the compositional series (100 − x)[0.5ZnO–0.1B₂O₃–0.4P₂O₅]–xTeO₂ by differential scanning calorimetry, thermodilatometry and heating microscopy thermal analysis. The addition of TeO₂ to the starting borophosphate glass resulted in a linear increase of glass transition temperature and dilatometric softening temperature, whereas the thermal expansion coefficient decreased. Most of glasses crystallize under heating within the temperature range of 440–640 °C. The crystallization temperature steeply decreases with increasing TeO₂ content. The lowest tendency towards crystallization was observed for the glasses containing 50 and 60 mol% TeO₂. X-ray diffraction analysis showed that major compounds formed by annealing of the glasses were Zn₂P₂O₇, BPO₄ and α-TeO₂. Annealing of the powdered 50ZnO–10B₂O₃–40P₂O₅ glass leads at first to the formation of an unknown crystalline phase, which is gradually transformed to Zn₂P₂O₇ and BPO₄ during subsequent heating.     

The standard enthalpies of formation of mixed antimony and bismuth oxides

The Bi₂O₃-BiSbO₄ and BiSbO₄-Sb₂O₄ sections of the phase diagram of the Bi-Sb-O system were studied by the Knudsen effusion method with mass spectrometric analysis of the gas phase. The standard enthalpies of formation of the Bi₃SbO₆(g), Bi₂Sb₂O₆(g), BiSb₃O₆(g), Bi₃SbO₇(s), and BiSbO₄(s) mixed antimony-bismuth oxides and the standard enthalpies of some reactions with the participation of these oxides were calculated.     

Structure and Magnetic Properties of Nickel–Zinc Ferrite Nanoparticles Prepared by Glass Crystallization Method

The magnetic and microstructure properties of Fe₂O₃–0.4NiO–0.6ZnO–B₂O₃ glass system, which was subjected to heat treatment in order to induce a magnetic crystalline phase (Ni_0.4Zn_0.6-Fe₂O₄ crystals) within the glass matrix, were investigated. DSC measurement was performed to reveal the crystallization temperature of the prepared glass sample. The obtained samples, produced by heat treatment at 765°C for various times (1, 1.5, 2, and 3 h), were characterized by X-ray diffraction, IR spectra, transmission electron microscopy, and vibrating sample magnetometer. The results indicated the formation of spinel Ni–Zn ferrite in the glass matrix. Particles of the ferrite with sizes ranging from 28 to 120 nm depending on the sintering time were observed. The coercivity values for different heat-treatment samples were found to be in the range from 15.2 to 100 Oe. The combination of zinc content and sintering times leads to samples with saturation magnetization ranging from 12.25 to 17.82 emu/g.     

Unknown thermal properties of ZnSb2O6 and Zn7Sb2O12 compounds

The investigations by XRD, DTA/TG and IR methods show that two compounds: ZnSb₂O₆ and Zn₇Sb₂O₁₂ are formed in the ZnO-α-Sb₂O₄ system in air. Oxygen contained in the air participates in the synthesis of these compounds. ZnSb₂O₆ was observed as an intermediate phase, during the Zn₇Sb₂O₁₂ synthesis. The temperature of the β→α-Zn₇Sb₂O₁₂ transition was fixed at 1225±10°C. The mechanisms of the reactions of ZnSb₂O₆ and Zn₇Sb₂O₁₂ thermal decomposition have been proposed. The IR studies of α and β-Zn₇Sb₂O₁₂ have initially indicated that the structures of both polymorphous forms differ in the reciprocal connection of the SbO₆ and ZnO₆ octahedra and the ZnO₄ tetrahedra.     

Structure and Magnetic Properties of Nickel–Zinc Ferrite Nanoparticles Prepared by Glass Crystallization Method

Summary. The magnetic and microstructure properties of Fe₂O₃–0.4NiO–0.6ZnO–B₂O₃ glass system, which was subjected to heat treatment in order to induce a magnetic crystalline phase (Ni_0.4Zn_0.6-Fe₂O₄ crystals) within the glass matrix, were investigated. DSC measurement was performed to reveal the crystallization temperature of the prepared glass sample. The obtained samples, produced by heat treatment at 765°C for various times (1, 1.5, 2, and 3 h), were characterized by X-ray diffraction, IR spectra, transmission electron microscopy, and vibrating sample magnetometer. The results indicated the formation of spinel Ni–Zn ferrite in the glass matrix. Particles of the ferrite with sizes ranging from 28 to 120 nm depending on the sintering time were observed. The coercivity values for different heat-treatment samples were found to be in the range from 15.2 to 100 Oe. The combination of zinc content and sintering times leads to samples with saturation magnetization ranging from 12.25 to 17.82 emu/g.     

Pyrochlore phases in the system ZnOBi2O3Sb2O5: II. Crystal structures of Zn2Bi3.08Sb2.92O14+δ and Zn2+xBi2.96−(x−y)Sb3.04−yO14.04+δ

Rietveld refinement of combined X-ray and neutron diffraction data has, within errors, confirmed the stoichiometries of two, cubic pyrochlore phases in the ZnOBi₂O₃Sb₂O₅ system. Neither phase has the ‘ideal’ stoichiometry, Zn₂Bi₃Sb₃O₁₄. One phase, P₁, is a Zn-rich, Bi-deficient solid solution Zn_2+xBi_{2.96−(x−y)}Sb_3.04−yO_14.04+δ. The other, P₂, is a Bi-rich line phase, stoichiometry Zn₂Bi_3.08Sb_2.92O_14+δ. Both structures have a mixture of Bi, Zn on the A-sites and Zn, Sb on the B-sites. However, Zn is displaced off-centre in the A-sites to achieve lower co-ordination number with realistic ZnO bond lengths. Additional structural complexities arise from: displacement of O(2) atoms; partial occupancies of O(1) and O(2) sites; partial occupancy of a third, interstitial oxygen site, O(3). Since the multiplicities of the off-centre sites are much higher than those of the ideal positions, there is considerable possibility for correlated short range order throughout the structures.     

Preparation and characterization of bismuth silicate nanopowders

Bismuth silicate (Bi₄Si₃O₁₂) nanopowders were prepared by the sol-gel method. Tetraethyl orthosilicate (TEOS) and Bi₂O₃ were used as the starting materials. The precursors were heat-treated at 750°C for 2 h. The size distribution of Bi₄Si₃O₁₂ nanopowders is 40–100 nm. The thermogravimetry and differential thermal analysis (TG-DTA) curves, the X-ray diffraction (XRD) patterns and the transmission electron microscopy (TEM) microphotograph of Bi₄Si₃O₁₂ were discussed. Compared with crystal materials, the excitation and emission spectra of Bi₄Si₃O₁₂ nanopowders indicated a blue shift. Translated from Chinese Journal of Inorganic Chemistry, 2006, 22(7): 1327–1329 (in Chinese)     

Thermal behaviour and fragility of Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>-containing zinc borophosphate glasses

Thermal behaviour of the glass series (100-x)[50ZnO-10B₂O₃-40P₂O₅]·xSb₂O₃ (x=0-42 mol%) and (100-y)[60ZnO-10B₂O₃-30P₂O₅]·ySb₂O₃ (y=0-28 mol%) was investigated by DSC and TMA. The addition of Sb₂O₃ results in a decrease of the glass transition temperature and crystallization temperature in both compositional series. All glasses crystallize on heating in the temperature range of 522–632°C. Thermal expansion coefficient of the glasses monotonously increases with increasing Sb₂O₃ content in both series and varies within the range of 6.6–11.7 ppm °C⁻¹. From changes of thermal capacity within the glass transition region it was concluded that with increasing Sb₂O₃ content the ‘fragility’ of the studied glasses increases.     

Spektralphotometrische Ermittlung der Koordinationsverhältnisse in Kristallgittern, 2. Mitt.: Die Dimorphie von Zn7Sb2O12

Zusammenfassung Im System ZnO–Sb₂O₅ existieren zwei Spinellphasen (I) und (III) gleicher Zusammensetzung Zn₇Sb₂O₁₂. Außerdem konnte noch eine weitere Modifikation (II) mit einer niedrigsymmetrischen Struktur aufgefunden werden.In (II) und (III) wurden Cu²⁺, Ni²⁺ und Co²⁺ als farbgebende Kationen eingebaut. Die spektralphotometrische Untersuchung ergab, daß Zn²⁺ in (II) sowohl oktaedrisch als auch tetraedrisch koordiniert ist. Im Spinell (III) wird Cu²⁺ sowohl in Tetraeder-und Oktaederlücken, Ni²⁺ nur in Oktaeder- und Co²⁺ vorwiegend in Oktaederlücken eingebaut.In the system ZnO–Sb₂O₅ exist two phases (I) and (III) with the spinel structure and the same composition Zn₇Sb₂O₁₂. Besides these another modification (II) with a structure of lower symmetry could be found.The colouring cations Cu²⁺, Ni²⁺, Co²⁺ have been incorporated in (II) and (III). The spectrophotometrical investigation shows that Zn²⁺ occupies in (II) octahedral and tetrahedral sites. In the spinel (III) Cu²⁺ is incorporated tetrahedrally and octahedrally, Ni²⁺ only octahedrally and Co²⁺ predominantly octahedrally.Mit 4 Abbildungen1. Mitt.:H. Kasper, Z. anorg. allgem. Chem. (im Druck).     

Effect of CuO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> on low temperature sintered MnZn-ferrite by sol–gel auto-combustion method

A sol–gel auto-combustion method was investigated to incorporate small amounts of additives of Cu and Bi uniformly into soft magnetic MnZn-ferrite nanoparticles, which were prepared by Fe(NO₃)₃·9H₂O, Mn(NO₃)₂ and Zn(NO₃)₂·6H₂O dissolved in water and citric acid. The powder was characterized by the X-ray diffraction analysis and transmission electron microscope method. The effects of nano-particle sized powders in microstructure development and adding CuO–Bi₂O₃ into MnZn-ferrite on phase formation, densification process as well as magnetic properties were studied by scanning electron microscope and vibrating sample magnetometer techniques. The sample without additive can be sintered well at 930 °C, while the samples with a small amount of the additive can be sintered at less than 900 °C. Obviously, the micron-sized powders exhibited high sintering activity. It was also found that CuO–Bi₂O₃ additive promoted the growth of grains and improved magnetic properties. The permeability and the saturation magnetization were improved substantially by adding CuO–Bi₂O₃ into MnZn-ferrite and the sintering temperature was lowered to 875 °C, which may be associated with the redistribution of cations on the tetrahedral (A) sites and octahedral (B) sites within the spinel lattice.     

Phase transformation in spodumene–diopside glass

In situ developments of platelike spodumene–diopside grains were obtained by controlled devitrification of the complex system Li₂O–CaO–MgO–Al₂O₃–SiO₂ glass. The crystallization mechanisms of spodumene–diopside glass were measured by isothermal and non-isothermal processes using classical and differential thermal analysis techniques. The Avrami constant n was 2.0–2.1, indicating two-dimensional crystal growth and platelike grains. The crystalline phases precipitated first were high-quartz_s.s., then transformed to β-spodumene and diopside. The Flexural strength, fracture toughness and thermal shock resistance (in 20°C water) increased from 145 MPa, 1.3 MPa m^1/2, 800°C (pure spodumene) to 197 MPa, 2.9 MPa m^1/2 and 920°C (spodumene–diopside) with low thermal expansion coefficient (from 3∼9·10^–7 to 11.8·10^–7 K^–1). This mean in situ developments of platelike spodumene–diopside grains reinforced the low thermal expansion coefficient glass-ceramics.     

Phase relations up to the solidus line in the part of the Sb-Zn-O system

Phase relations up to the solidus line in part of the Sb-Zn-O system have been investigated over the entire concentration range of the α-Sb₂O₄-ZnO system in air (= 0.21 atm) using XRD and DTA/TG. The components of this system in air form ZnSb₂O₆ and Zn₇Sb₂O₁₂. The results allow division of the system into three subsystems, i.e. α-Sb₂O₄-ZnSb₂O₆; ZnSb₂O₆Zn₇Sb₂O₁₂ and Zn₇Sb₂O₁₂-ZnO. The temperature ranges over which the ZnSb₂O₆ and Zn₇Sb₂O₁₂ remain at equilibrium with other solid compounds depend on the gaseous atmosphere.      

Thermal stability and crystallization kinetics of Pb and Bi borate-based glasses

Glasses with compositions 60B₂O₃–40PbO, 60B₂O₃–40Bi₂O₃, and 60B₂O₃–30Bi₂O₃–10PbO have been prepared and studied by differential thermal analysis. The crystallization kinetics of the glasses was investigated under non-isothermal conditions. From dependence of the glass transition temperature (T _g) on the heating rate, the activation energy for the glass transition was derived. Similarly the activation energy of the crystallization process was determined. Thermal stability of these glasses were achieved in terms of the characteristic temperatures, such as the glass transition temperature, T _g, the onset temperature of crystallization, T _in , the temperature corresponding to the maximum crystallization rate, T _p, beside the kinetic parameters, K(T _g) and K(T _p). The results revealed that the 60B₂O₃–40PbO is more stable than the others. The crystallization mechanism is characterized for glasses. The phases at which the glass crystallizes after the thermal process have been identified by X-ray diffraction.     

Thermal Characterization and Physico-Chemical Properties of Fe2O3−Mn2O3/Al2O3 Systems

The effect of ferric and manganese oxides dopants on thermal and physicochemical properties of Mn-oxide/Al₂O₃ and Fe₂O₃/Al₂O₃ systems has been studied separately. The pure and doped mixed solids were thermally treated at 400–1000°C. Pyrolysis of pure and doped mixed solids was investigated via thermal analysis (TG-DTG) techniques. The thermal products were characterized using XRD-analysis. The results revealed that pure ferric nitrate decomposes into Fe₂O₃ at 350°C and shows thermal stability up to1000°C. Crystalline Fe₃O₄ and Mn₃O₄phases were detected for some doped solids precalcined at 1000°C. Crystalline γ-Al₂O₃ phase was detected for all solids preheated up to 800°C. Ferric and manganese oxides enhanced the formation of α-Al₂O₃ phase at1000°C. Crystalline MnAl₂O₄ and MnFe₂O₄ phases were formed at 1000°C as a result of solid–solid interaction processes. The catalytic behavior of the thermal products was tested using the decomposition of H₂O₂ reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Low Temperature WGS Catalysts for Hydrogen Station and Fuel Processor Applications

Generally, water gas shift (WGS) reaction is a very important step in the industrial production of hydrogen, ammonia and other bulk chemicals utilizing synthesis gases. In this paper, we are reporting WGS reaction carried out in our research group for the application of hydrogen station and fuel processor. We prepared various Mo₂C, Pt–Ni-based and Cu-based catalysts for low temperature WGS reaction. The characteristics of the prepared catalyst were analyzed by N₂ physisorption, CO chemisorptions, XRD, SEM and TEM technologies, and compared with that of commercial Cu-Zn/Al₂O₃ catalyst. It was found that prepared catalysts displayed reasonably good activity and thermal cycling stability than commercial LTS (Cu–Zn/Al₂O₃) catalyst. It was found that the deactivation of commercial LTS catalyst during the thermal cycling run at 250 °C was caused by the sintering of active metal even though it shows high activity at less than 250 °C. The deactivation of Mo₂C catalyst during the thermal cycling run was caused by the transition of Mo^δ+, Mo^IV and Mo₂C on the surface of Mo₂C catalyst to Mo^VI(MoO₃) with the reaction of H₂O in reactants. However, they showed higher stability than the commercial LTS catalyst during thermal cycling test. The Pt–Ni/CeO₂ catalyst after the thermal cycling shows slightly deactivation due to the sintering of Ni metal. Among Cu-based catalysts, it was found that Cu–Mo/Ce_0.5Zr_0.5O₂ catalyst has higher WGS activity and stability over commercial LTS catalyst. The results suggested that Pt–Ni/CeO₂ and Cu–Mo/Ce_0.5Zr_0.5O₂ catalysts are desirable candidates for application in hydrogen station and fuel processor system even though all other catalysts deactivated slowly during the thermal cycling run.     

Structural effects of Zn+2/Mg+2 ratios on crystallization characteristics and microstructure of fluorophlogopite mica-containing glass-ceramics

We report the effect of Mg⁺² substitution (by Zn⁺²) on crystallization kinetics, microstructure, thermal and mechanical properties of boroaluminosilicate glass. Zn²⁺ was selected for Mg²⁺ on the basis of similar ionic radius in six coordination system (Mg²⁺∼0.72 Å, Zn²⁺∼0.75 Å). The melt-quenched glasses with SiO₂–(1 − x) MgO–Al₂O₃–K₂O–B₂O₃–MgF₂ (BPAS)/x ZnO system, have been investigated to establish the effect of Zn⁺²/Mg⁺² ratios. It is found that the density of BPAS glass without zinc content is 2.52 g/cm³ and increased linearly on substitution of Mg²⁺ by 5–32 mol% ZnO. T_g and T_d of BPAS glass initially increased on adding 5 mol% ZnO and then decreased on further addition. From DSC study, it is found that the crystallization exotherm changes significantly in the temperature range 750–1000 °C, where different crystalline phases are formed, and the activation energy of crystallization (E_C) varies in the range of 254–388 kJ/mol. The crystalline phases formed in opaque BPAS glass-ceramic, derived by controlled heat treatment at 800 and 1050 °C (4 h), are identified as fluorophlogopite [KMg₃(AlSi₃O₁₀)F₂] mica and willemite (Zn₂SiO₄) by XRD technique, and confirmed by FTIR spectroscopy. The change of crystallization phenomena varying Zn⁺²/Mg⁺² ratios correspond to significant microstructural change. A wide range of thermal expansion (CTE) values are obtained for the BPAS glasses and corresponding glass-ceramics. CTE (50–500 °C) of BPAS glass without zinc content is 7.76 × 10⁻⁶/K, and decreased sequentially on increasing Zn⁺²/Mg⁺² ratio. The density of glass-ceramics after heating at 800 and 1050 °C increased linearly with increasing Zn⁺² substitution for Mg⁺². Microhardness of the BPAS glasses is in the range of 4.26–6.15 GPa and found to be increased to 4.58–6.78 GPa after crystallized at 1050 °C.     

Thermal analysis of pigments based on Bi2O3

The synthesis of new pigments based on Bi₂O₃ is investigated because they give interesting orange hues and can substitute the pigments problematic from the environmental point of view. Chemical compounds of the Bi_2–xZr_3x/4O₃ type were synthesized. The host lattice of these pigments is Bi₂O₃ that is doped by Zr⁴⁺ ions. The area of ZrO₂ solubility in Bi₂O₃ at 800°C forming solid solution of both oxides was studied. The incorporation of doped ions provides interesting colours and contributes to a growth of the thermal stability of these compounds. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments.     

EDTA assisted sol–gel synthesis of ZrW2O8

A novel sol–gel synthetic route using water-soluble precursor salts is presented as a synthetic path for a high-purity negative thermal expansion material, ZrW₂O₈. This synthetic route involves a sol–gel method with the use of EDTA as complexing agent. The aqueous solution is transformed into a ceramic material after a two-step heat treatment: gelation at 60 °C and reactive sintering at 1,180 °C. The decomposition of the gel is monitored with infrared spectroscopy and TGA. The high-temperature heat treatment results in ZrW₂O₈ with its characteristic negative thermal expansion behaviour α_{[75–130 °C]}: −9.8 ± 1.6 μm/m °C and α_{[175–300 °C]}: −1.2 ± 0.2 μm/m °C.     

Infrared absorption spectra of Er3+-doped Al2O3 nanopowders by the sol-gel method

The Er³⁺-doped Al₂O₃ nanopowders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC₃H₇)₃]-derived γ-AlOOH sols with addition of the erbium nitrate [Er(NO₃)₃·5H₂O]. The five phases of γ-(Al,Er)₂O₃, θ-(Al,Er)₂O₃, α-(Al,Er)₂O₃, ErAlO₃, and Al₁₀Er₆O₂₄ were detected with the 0–20 mol% Er³⁺-doped Al₂O₃ nanopowders at the different sintering temperature of 600–1200°C. The average grain size was increased from about 5 to 62 nm for phase transformation of undoped γ-Al₂O₃→α-Al₂O₃ at the sintering temperature from 600 to 1200°C. At the same sintering temperature, average grain size was decreased with increase of the Er³⁺ doping concentration. Infrared absorption spectra of γ-Al₂O₃ and θ-Al₂O₃ nanopowders showed the two broad bands of 830–870 and 550–600 cm⁻¹, the three broad bands of 830–870, 750–760, and 550–600 cm⁻¹, respectively. The infrared absorption spectra for the α-Al₂O₃ nanopowder showed three characteristic bands, 640, 602, and 453 cm⁻¹. The two characteristic bands of 669 and 418 cm⁻¹ for Er₂O₃ clusters were observed for the Er³⁺-doped Al₂O₃ nanopowders when Er³⁺ doping concentration was increased up to 2 mol%. The 796, 788, 725, 692, 688, 669, 586, 509, 459, and 418 cm⁻¹ are the characteristic bands of Al₁₀Er₆O₂₄ phase.