Solid-state reactions in Y2O3:3Al2O3:4B2O3 system studied by FTIR spectroscopy and X-ray diffraction

In the Y₂O₃:3Al₂O₃:4B₂O₃ system infrared absorption spectroscopy and X-ray diffraction have been used to study the solid-state reactions in the 600–1300°C temperature range. The expected YAl₃(BO₃)₄ formation (whose optimum temperature is at about 1150°C) was proceeded and accompanied by the appearance of YBO₃ and Al₄B₂O₉ intermediate phases. At higher temperatures the Al₁₈B₄O₃₃ phase was also identified with both methods. Based on these results, some chemical reactions were suggested.     

Borate,lithium borate,and borophosphate powders by sol–gel precipitation

Borate, lithium borate and borophosphate powders were synthesized by the sol–gel method. Triethyl borate, lithium methoxide, and orthophosphoric acid were used as precursors for B₂O_3, Li₂O, and P₂O₅, respectively. Powders were characterized by FTIR, DTA, XRD and SEM techniques. Powders from the Li₂O–B₂O₃ system exhibited glassy features while borate and borophosphate powders contained mainly crystalline B₂O₃ according to XRD analysis. However, a 500 °C heat treatment transformed these crystalline powders into glass powders. Conversely, heat treatment of Li₂O–B₂O₃ powders transformed their structure from glassy to crystalline (Li₂B₄O₇). Chemical durability studies conducted in water at 60 °C showed that minor additions of P₂O₅ into borate and lithium borate powders improved their chemical durability significantly. Furthermore, Li₂O and P₂O₅ acted synergistically on the chemical durability when added simultaneously to borate compositions.     

Effects of doping with CeO2 and calcination temperature on physicochemical properties of the NiO/Al2O3 system

The effects of doping with CeO₂ and calcination temperature on the physicochemical properties of the NiO/Al₂O₃ system have been investigated using DTA, XRD, nitrogen adsorption measurements at −196°C and decomposition of H₂O₂ at 30–50°C. The pure and variously doped solids were subjected to heat treatment at 300, 400, 700, 900 and 1000°C. The results revealed that the specific surface areas increased with increasing calcination temperature from 300 to 400°C and with doping of the system with CeO₂. The pure and variously doped solids calcined at 300 and 400°C consisted of poorly crystalline NiO dispersed on γ-Al₂O₃. Heating at 700°C resulted in formation of well crystalline NiO and γ-Al₂O₃ phases beside CeO₂ for the doped solids. Crystalline NiAl₂O₄ phase was formed starting from 900°C. The degree of crystallinity of NiAl₂O₄ increased with increasing the calcination temperature from 900 to 1000°C. An opposite effect was observed upon doping with CeO₂. The NiO/Al₂O₃ system calcined at 300 and 400°C has catalytic activity higher than individual NiO obtained at the same calcination temperatures. The catalytic activity of NiO/Al₂O₃ system increased, progressively, with increasing the amount of CeO₂ dopant and decreased with increasing the calcination temperature.     

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.     

Synthesis of ultrafine yttrium aluminum garnet using sol-gel technology

Mesoporous yttrium aluminum garnet Y₃Al₅O₁₂ powders were prepared using sol-gel technology proceeding from solutions of metal alkoxoacetylacetonates. Xerogel microstructure was studied by SEM, and the fact of mesopores being formed was established. The temperature range within which Y₃Al₅O₁₂ crystallizes in a dynamic mode from the xerogel was determined to be 850?C950°C using an SDT Q600 TGA/DTA/DSC analyzer. A 1-h isothermal treatment of the xerogel was shown to reduce the garnet phase formation temperature to 800°C. At lower temperatures (400, 450 or 500°C), even long-term (6-h) calcination yielded X-ray amorphous powders with developed surfaces (specific surface areas were 230?C350 m²/g). Powder particle coarsening was studied upon sintering for 2 and 4 h at 1000, 1200, and 1400°C.     

Effect of Modifying Additives on the Sintering and Properties of SiC/SiC<Subscript>w</Subscript> Ceramic Composite Material

Spark plasma sintering and hot compaction methods were used to obtain experimental samples of a composite material of the SiC?SiC_w system with various modifying additives (AlN, B₄C, HfB₂, Y₂O₃, Al₂O₃, Si₃N₄). The effect of the modifying additives on the sintering process, physicomechanical, and thermal properties of the ceramic composite material was examined. The introduction of the modifying additives lowered the sintering temperature of silicon carbide produced by the hot compaction method by 200°C and that formed with spark plasma spark sintering by 300?450°C as compared with the sintering temperature of silicon carbide without additives.     

Use of Methods of Thermal Analysis in Studying Ceramic Materials on the Basis of Al2O3, ZrO2, Si3N4, SiC and Inorganic Binder

By thermoanalytical methods TG, DTG, DTA there have been investigated the processes occurring during the formation of ceramic materials on the basis of Al₂O₃, ZrO₂, Si₃N₄, SiC,and inorganic binder. IR spectroscopy has been an additional research method. It's been determined that with the use of H₃PO₄ as the binder for ceramic materials, the mechanisms of thermal decomposition are connected with the following processes: 1. removal of weakly tied and crystallized water in the temperature range of120–230°C, the removal being characterized by the endothermic effect, 2. interaction of the initial powder components of the ceramic materials with orthophosphoric acid conditioned by a strong exothermic effect on the DTA curve in the range of 230–530°C, 3. overlapping of endo- and exo-effects, testifying to a complex mechanism of thermal transformations, 4.oxidizing of the non-reacted silicon at the temperature of 720(760)°C, an increase of mass is observed on the TG curve as a result of the formation of SiO₂ – crystoballite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phase equilibria in the Bi2O3-BaB2O4-B2O3 system in the subsolidus region

The phase equilibria in the concentration triangle Bi₂O₃-BaB₂O₄-B₂O₃ of the BaO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction and DTA. Barium bismuth borates of the composition BaBi₂B₄O₁₀ and BaBiB₁₁O₁₉ have been found to exist. These borates melt at 730 and 807°C, respectively. The quasi-binary sections have been determined. It has been shown that the isothermal section of the Bi₂O₃-BaB₂O₄-B₂O₃ in the subsolidus region at 600°C is characterized by 13 triangles of coexisting phases.     

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.     

Synthesis of Y<Subscript>3−x</Subscript>Lu<Subscript>x</Subscript>Al<Subscript>3</Subscript>MgSiO<Subscript>12</Subscript> garnet powders by sol–gel method

Y_3−xLu_xAl₃MgSiO₁₂ (x = 0–3) garnet powders were synthesized by an aqueous sol–gel method based on metal chelates with 1,2-ethanediol in aqueous media. Target samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy and reflection spectra. XRD analysis revealed that sintering of polycrystalline Y_3−xLu_xAl₃MgSiO₁₂ powders at 1,600 °C results in single-phase garnet materials.     

Phase transition of YBO<Subscript>3</Subscript>

Yttrium orthoborate crystallizes in the vaterite-type structure and has two polymorphous forms, viz. a low- und a high temperature one. DTA measurements of YBO₃ confirmed a reversible phase transition with a large thermal hysteresis. The phase transition has been accurately characterized by the application of different heating and cooling rates (β). Consequently, the extrapolation of the experimental data to zero β yields the transition points at 986.9°C for the heating up and at 596.5°C for the cooling down cycle. These values correspond to samples just after treatment at 1350°C. For samples with a different ‘thermal history’ other phase transition temperatures are observed, (e.g. after having performed several heating and cooling cycles). The linear relationship between the associated DTA signal ΔT=T _onset–T _offset and the square root of the heating rate β was confirmed, but the relation between T _onset and square root of β is not found here. From the empirical data a good linear fitting between T _onset and ln(β+1) can be derived. From the kinetic analysis (Kissinger method) of the phase transformation of YBO₃ an apparent activation energy of about 1386 kJ mol^–1 for heating and of about 568 kJ mol^–1 for cooling can be determined     

High‐Pressure Synthesis of Cd(NH3)2[B3O5(NH3)]2: Pioneering the Way to the Substance Class of Ammine Borates

To date, the access to the substance class of borates containing nitrogen, for example, nitridoborates, oxonitridoborates, or amine borates, was an extreme effort owing to the difficult starting materials and reaction conditions. Although a number of compounds containing boron and nitrogen are known, no adduct of ammonia to an inorganic borate has been observed so far. A new synthetic approach starting from the simple educts CdO, B₂O₃, and aqueous ammonia under conditions of 4.7 GPa and 800 °C led to the synthesis of Cd(NH₃)₂[B₃O₅(NH₃)]₂ as the first ammine borate. We thoroughly characterized this compound on the basis of low‐temperature single‐crystal and powder X‐ray diffraction data, IR and Raman spectroscopy, and by quantum theoretical calculations. This contribution shows that the adduct of NH₃ to the BO₃ group of a complex B–O network can be stabilized, opening up a fundamentally new synthetic route to nitrogen‐containing borates.     

Phase equilibria in the BaO-Bi2O3-B2O3 system

Phase equilibria in the BaO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction analysis and DTA. Quasi-binary sections have been determined, and an isothermal section of the system in the subsolidus region has been constructed. The BaO-Bi₂O₃-B₂O₃ ternary system has been divided into 22 triangles of coexisting phases. It has been found that four bismuth barium borates exist, namely, Ba₃BiB₃O₉, BaBi₂B₄O₁₀, BaBiB₁₁O₁₉, and BaBiBO₄. Ba₃BiB₃O₉ undergoes a phase transition at 850°C and exists up to 885°C, where it decomposes in the solid state. BaBiB₁₁O₁₉ and BaBi₂B₄O₁₀ melt congruently at 807 and 730°C, respectively. BaBiBO₄ melts incongruently at 780°C. X-ray powder diffraction data for the low-temperature polymorph of Ba₃BiB₃O₉ are presented.     

B<Subscript>2</Subscript>O<Subscript>3</Subscript> additives on sintering and microwave dielectric behaviors of Mg<Subscript>4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics synthesized through the aqueous sol–gel Process

The relationships between the sintering temperatures and the microwave dielectric properties of (1−x)Mg₄Nb₂O₉-xB₂O₃ (x = 0.5–10 wt. %) compounds were investigated by the sol–gel method in order to reduce the sintering temperature in this study. A suitable amount of B₂O₃ doping was effective in allowing low sintering temperatures without a little detrimental effect on these dielectric properties of the Mg₄Nb₂O₉ compounds. The variations in the dielectric constant (ε _r ) and the quality factor (Q·f) of the Mg₄Nb₂O₉ compounds depended on the amount of B₂O₃ doping and the sintering temperature. As a result, a ε _r value of ~12.8 and a Q·f value of ~142,570 GHz were obtained when the Mg₄Nb₂O₉ compound with x = 3% was sintered at 1,200 °C for 4 h. The temperature coefficient of resonant frequency (τ _f ) of the 3%-B₂O₃ doping Mg₄Nb₂O₉ compound slightly changed from −33 to −48 ppm/°C with an increased sintering temperature.     

Phase Relations in The System Al2(MoO4)3–V2O5

The phase equilibria established in the system Al₂ (MoO₄ )₃ –V₂ O₅ throughout the whole component concentration range up to 1000°C were investigated by DTA and XRD methods. The results are presented in the form of a phase diagram. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of B<Subscript>2</Subscript>O<Subscript>3</Subscript> on the structure and crystallization of soil active glasses

Glasses of the SiO₂–P₂O₅–K₂O–MgO–CaO–B₂O₃ system acting as nutrients carriers in the soil environment were synthesised by the melt-quenching technique. Thermal properties were studied using DTA/DSC methods and the influence of B₂O₃ and P₂O₅ content on thermal stability and crystallization process of these glasses was examined. The structure of the glass network was characterized by FTIR, ³¹P, and ¹¹B MAS NMR. The chemical activity of the glasses in the 2 mass% citric acid solution was measured by the ICP-AES method. The analysis indicated that the formation of P–O–B units with chemically stable tetrahedral borate groups decreases the glass solubility in conditions simulating the soil environment.     

Structural investigation in the TiB2-(Na2O·B2O3·Al2O3) system

Composites in the TiB₂-Na₂O·B₂O₃·Al₂O₃ systems, TiB₂-MBA (MB stands for sodium metaborate and A is Al₂O₃), were prepared by self-propagating high-temperature synthesis (SHS), in simultaneous mode. Selection of these compositions was ruled by the interesting properties of both TiB₂ and double borates of alkali metal and aluminum. The structure of the obtained materials was evaluated by micro-Raman spectroscopy, from room temperature up to 600 °C, and X-ray photoelectron spectroscopy (XPS). Formation of the TiB₂ and TiO_2−xB_x phases along with TiO₂ as rutile were identified as titanium speciation in the grain phase embedded in a sodium aluminum borate matrix. Integration of the Raman spectra of the grain phases revealed a TiB₂ content of 16.99% and 23.32% for the two composite investigated 2TiB₂·2MBA and 3TiB₂·5MBA. A constrained-width model for the spectral deconvolution of the high-frequency Raman band was forwarded to calculate the proportion of tetrahedral boron atoms (7.424%) in the blank borate matrix Na₂B₂O₄·Al₂O₃ in solid phase.     

Formation of Cr(II) Species in the H2/CrO3 System. Parameter control

The thermal behaviour of CrO₃ on heating up to 600°C in dynamic atmospheres of air, N₂ and H₂ was examined by thermogravimetry (TG), differential thermal analysis (DTA), IR spectroscopy and diffuse reflectance spectroscopy (DRS). The results revealed three major thermal events, depending to different extents on the surrounding atmosphere: (i) melting of CrO₃ near 215°C (independent of the atmosphere), (ii) decomposition into Cr₂(CrO₄)₃ at 340–360°C (insignificantly dependent), and (iii) decomposition of the chromate into Cr₂O₃ at 415–490°C (significantly dependent). The decomposition CrO₃ → Cr₂(CrO₄)₃ is largely thermal and involves exothermic deoxygenation and polymerization reactions, whereas the decomposition Cr₂(CrO₄)₃ → Cr₂O₃ involves endothermic reductive deoxygenation reactions in air (or N₂) which are greatly accelerated and rendered exothermic in the presence of H₂. TG measurements as a function of heating rate (2–50°C min⁻¹) demonstrated the acceleratory role of H₂, which extended to the formation of Cr(II) species. This could sustain a mechanism whereby H₂ molecules are considered to chemisorb dissociatively, and then spillover to induce the reduction. DTA measurements as a function of the heating rate (2–50°C min⁻¹) helped in the derivation of non-isothermal kinetic parameters strongly supportive of the mechanism envisaged. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Ionic Conductivity of Ultrafine Solid Electrolytes for Li4.4Al0.4Si0.6O4‐xY2O3 Systems

The Li_4.4Al_0.4Si_0.6O₄‐xY₂O₃ (x = 0 to 0.5) ion conductors were prepared by the Sol‐Gel method and examined in detail. The powder and sintered samples were characterized by DTA‐TG, XRD, SEM, and AC impedance techniques. The experimental results show that the conductivity and sinterability increased with the amount of excess Y₂O₃ in the silicate. The particle size of the powder samples is about 0.12 μm. The maximum conductivity at 16 °C is 2.925 × 10^?5s·cm^?1 for Li_4.4Al_0.4Si_0.6O₄‐0.3 Y₂O₃.     

Kinetic studies of the crystallization process of glass-ceramics based on basalt

The crystallization kinetic of the basalt glass ceramic of the oxide composition, (%): SiO₂ − 50.82; Al₂O₃ − 12.05; Fe₂O₃ − 9.28; CaO − 15.48; MgO − 11.08; Na₂O+K₂O − 1.14; TiO₂ − 0.15, with addition of 10% TiO₂ as nucleating agent has been studied using thermal analysis under non-isothermal conditions. In this order, the non-isothermal DTA curves were obtained at different heating rates between 4 and 20°C min⁻¹ in the temperature range of 25–1000°C using a Derivatograph-C (MOM, Hungary). The kinetic parameters of the crystallization process were calculated on the basis of Ozawa-Flynn-Wall, Friedman, Budrugeac-Segal and non-parametric kinetic methods.