Prolonged Calcination Research Articles

A novel high-entropy rare-earth hydroxycarbonate synthesized via facile hydrothermal synthesis with superior decomposition temperature

This study presents for the first time the synthesis of a novel high-entropy rare-earth hydroxycarbonate, specifically (Sm₀.₂La₀.₂Y₀.₂Nd₀.₂Gd₀.₂)(CO3)OH, by using a simple hydrothermal treatment. The resulting rare-earth hydroxycarbonate exhibits superior thermal stability compared to the related single-component rare-earth hydroxycarbonates, and a distinctive rod-like morphology, maintained even after prolonged calcination (i.e. 800 °C for 12 h), suggesting its potential as a “sacrificial template” for high-entropy bixbyite-structured oxides. Thus, our pioneering work opens new possibilities for the application of a novel class of high-entropy hydroxycarbonates in the field of catalysis, luminescence, and sensing technologies.

Synthesis and study of the impact of calcination duration on the properties of Al4(ZnO)96 nanoparticles

Aluminium doped zinc oxide (Al4(ZnO)96) nanoparticles were synthesized using new sogel method at 40 °C, with zinc acetate dihydrate (Zn(CH3COO)2·2 H2O) and aluminium nitrate nonahydrate (Al(NO3)3·9 H2O) as precursors. The samples underwent analysis using various structural and optical techniques to investigate the effect of calcination duration on the properties. Prolonged calcination durations led to a significant reduction of oxygen at the grain boundaries, influencing particle size and crystallization. According to TEM-histogram analysis, the most probable size for 28.5 % of nanoparticles fell within the range of 15–20 nm, which aligns closely with the estimated particle size determined by XRD analysis. The material displayed a significant direct bandgap of approximately 3.283 eV, which increased with the duration of calcination. The band gap was affected by changes in phase, strain, and particle size, attributed to the presence of defect states and a substantial concentration of localized states. Additionally, the material exhibited excellent chemical stability and a significantly high binding energy. Moreover, the optical bandgap widened as the width of the Urbach tails in the localized states decreased with an increase in the duration of calcination.

Direct and rapid regeneration of spent LiFePO4 cathodes via a high-temperature shock strategy

The requirement for lithium-ion batteries is rising sharply in recent years due to rapid development of electric vehicles and new energy storage. However, this increase in number of lithium-ion batteries also leads to the production of a significant number of spent batteries. Considering the potential environment pollution and waste of resources, it is absolutely imperative to recover these spent lithium-ion batteries. Conventional direct regeneration method always undergoes a slow heating rate and prolonged calcination process, which consume high energy and time. Herein, we presented an efficient, low-cost and ultrafast regeneration strategy for rapid regeneration of the spent LiFePO4 in only 20 s. Compared of traditional method, this ultrafast method consumes less energy and takes shorter time. As a result, the lithium is completely replenished and the structure of LiFePO4 is well repaired, and it demonstrates excellent initial capacity of 152 mAh g−1 at 0.1C. Furthermore, RLFP-800 exhibits a good rate performance and long-cycling stability (400 cycles at 2C without capacity recession). It is expected that this rapid regeneration strategy can be developed for practical spent LiFePO4 regeneration at low cost.

Features of Phase Formation of Pyrochlore-type Ceramics Bi2Mg(Zn)1-x Ni x Ta2O9.

The phase formation of complex pyrochlores (space group Fd-3m) Bi2Mg(Zn)1-x Ni x Ta2O9 was investigated during solid-phase synthesis. It was found that the pyrochlore phase precursor in all cases was α-BiTaO4. The pyrochlore phase synthesis reaction proceeds mainly at temperatures above 850-900 °C and consists in the interaction of bismuth orthotantalate with a transition element oxide. The influence of magnesium and zinc on the course of pyrochlore synthesis was revealed. The reaction temperatures of magnesium and nickel (800 and 750 °C, respectively) were determined. The change in the pyrochlore unit cell parameter depending on the synthesis temperature was analyzed for both systems. Nickel-magnesium pyrochlores are characterized by a porous dendrite-like microstructure with a grain size of 0.5-1.0 microns, and the porosity of the samples reaches 20 percent. The calcination temperature does not significantly affect the microstructure of the samples. Prolonged calcination of the preparations leads to the coalescence of grains with the formation of larger particles. Nickel oxide has a sintering effect on ceramics. The studied nickel-zinc pyrochlores are characterized by a low-porous dense microstructure. The porosity of the samples does not exceed 10%. The optimal conditions for obtaining phase-pure pyrochlores (1050 °C and 15 h) were determined.

Preparation and characterization of submicron-cerium oxide by hypergravity coprecipitation method

Submicron-cerium oxide particles were synthesized by applying hypergravity using ammonium bicarbonate (precipitant) and cerium nitrate hexahydrate (precursor). The influence of the concentration, pH, dispersant loading, flow rate, rotation speed of the hypergravity rotating bed, calcination temperature, and time on the cerium oxide particle size were examined by zeta potential, solid–liquid contact angle, thermo-gravimetry–differential scanning calorimetry, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The cerium oxide particles were highly dispersed, with an average particle size of 200 nm. Calcining at 650 °C for 1.5 h afforded the smallest particles. The crystallite size and fraction crystallinity increased with prolonged calcination. Crystalline cerium dioxide grew along three crystal planes, forming a complete face-centered cube, affording high hardness and activity of the polishing powder. The optimal conditions were: cerium nitrate concentration: 0.7 mol/L, cerium nitrate/ammonium bicarbonate molar ratio: 1:3, dispersant mass fraction: 3%, cerium nitrate initial pH: 4–5; the precursor solution was adjusted to pH 9 with ammonia water. Hypergravity coprecipitation with 1.5 h calcination afforded submicron-sized cerium oxide with a uniform size distribution using ammonium bicarbonate in an industrially viable process. The simple and low-cost manufacturing process may enable the development of hypergravity-assisted chemical synthesis technology.

Hierarchical TiO2 Nanoflower Photocatalysts with Remarkable Activity for Aqueous Methylene Blue Photo-Oxidation.

This study systematically evaluates the performance of a series of TiO2 nanoflower (TNF) photocatalysts for aqueous methylene blue photo-oxidation under UV irradiation. TNF nanoflowers were synthesized from Ti(IV) butoxide by a hydrothermal method and then calcined at different temperatures (T = 400–800 °C) for specific periods of time (t = 1–5 h). By varying the calcination conditions, TNF-T-t photocatalysts with diverse physicochemical properties and anatase/rutile ratios were obtained. Many of the TNF-T-1 photocatalysts demonstrated remarkable activity for aqueous methylene blue photo-oxidation at pH 6 under UV excitation (365 nm), with activities following the order TNF-700-1 > TNF-600-1 > TNF-500-1 > TNF-400-1 ∼ P25 TiO2 ≫ TNF-800-1. The activity of the TNF-700-1 photocatalyst (99% anatase, 1% rutile) was 2.3 times that of P25 TiO2 at pH 6 and 14.4 times that of P25 TiO2 at pH 4. Prolonged calcination of the TNFs at 700 °C proved detrimental to dye degradation performance due to excessive rutile formation, which reduced the photocatalyst surface area and suppressed OH• generation. The outstanding activities of TNF-700-1 and TNF-600-1 are attributed to their hierarchical nanoflower morphology which benefitted UV absorption, a near-ideal anatase crystallite size for efficient charge separation, and their unusually low isoelectric point (IEP = 4.3–4.5).

Relationship Between Microstructure and Properties of Limestone Calcined Rapidly at High Temperatures

The relationship between microstructure and physicochemical properties of limestone including, porosity, bulk density, pore size distribution, specific surface area and activity were studied under the condition of rapid heating from room temperature to 1350–1550 °C. The results showed that complete decomposition of limestone (diameter 12.5–15 mm) at 1350 °C, 1450 °C and 1550 °C took 11.7 min, 9.2 min and 6.9 min, respectively. With the prolongation of calcination, lime porosity first increased and then decreased. The peak value of lime porosity was found roughly at the end of limestone decomposition. The variation of bulk density, however, was just the opposite compared to porosity. When calcination temperature increased, the pore size of lime became larger, and the number of micropores decreased correspondingly; furthermore, while calcination time increased, micropores disappeared fast, and macropores increased rapidly. The specific surface area of lime decreased with prolonged calcination time. The best activity of lime could be obtained with high porosity and high specific surface area at the same time. The maximum activity values of lime were 379 mL, 365 mL and 267 mL at the temperatures of 1350 °C, 1450 °C and 1550 °C, respectively.

Investigation of decomposition of dolomite and distribution of iodine migration during the calcination-digestion process of phosphate ore

In this work, the thermal decomposition and digestion of dolomite during the calcination of medium and low grade phosphate ore were investigated. Moreover, the migration distribution of co-associated iodine in gas, liquid and solid phases was also examined. The effects of calcination temperature and time, digestion temperature and time, and liquid-solid ratio on the P2O5 grade, MgO removal rate and iodine migration distribution of phosphate ore were systematically studied. The results showed that the main phase Ca5(PO4)3F remained almost no change during calcination-digestion process of phosphate ore. The impurity dolomite was decomposed into magnesium and calcium oxides, and carbon dioxide was precipitated. With the thermal decomposition of dolomite, most of the accompanying iodine adsorbed in phosphate ore was oxidized to iodine and sublimated to the gas phase. A small amount of iodine continued to exist as an isomorph in the fluoroapatite lattice. Increasing the temperature and prolonging the time accelerated the decomposition rate of dolomite in phosphate ore. However, excessively, high calcination temperature and prolonged calcination time affected the decomposition reaction and led to the reduction of effective CaO and MgO content. This was not conducive to the removal of calcium and magnesium, or to the improvement of phosphate grade. Appropriate digestion temperature, time and water volume facilitated the digestion reaction and increased the MgO removal rate. During calcination and digestion progress, 80%~90% of the associated iodine migrated to the gas phase in the form of elemental I2. Under the optimized calcination conditions, the removal rate of MgO reached (85.0 ± 0.1)%, the grade of phosphate concentrate increased up to (32.5 ± 0.1)%, and the content of MgO was (1.02 ± 0.1)%.

Phase transition of BiNb1−xMnxO4−δ: Thermal analyse, NEXAFS, XPS and ESR-study

Abstract The manganese-doped polymorphs of bismuth orthoniobate were studied using thermal analysis, ESR, XPS and NEXAFS spectroscopy. It was shown that the phase transition from the orthorhombic (α) to the triclinic (β) modification can be reversible and it can be achieved by prolonged calcination of samples at 750°C. The DSC curves revealed no thermal effects associated with the phase transformation from the triclinic to the orthorhombic modification near 750°C. In the ESR spectra, the absorption band with g = 3.8 characterized by sextet structure disappeared during the phase transformation from the - to the -form and only the broad component with average intensity was observed at g = 2.2-2.0. According to NEXAFS spectroscopy data, the content of oxidized Mn(III) atoms increased and the content of Mn(II) decreased in the orthorhombic polymorph obtained at 750°C from the tri-clinic modification.

In Situ “Chainmail Catalyst” Assembly in Low‐Tortuosity, Hierarchical Carbon Frameworks for Efficient and Stable Hydrogen Generation

AbstractThe chainmail catalysts (transition metals or metal alloys encapsulated in carbon) are regarded as stable and efficient electrocatalysts for hydrogen generation. However, the fabrication of chainmail catalysts usually involves complex chemical vapor deposition (CVD) or prolonged calcination in a furnace, and the slurry‐based electrode assembly of the chainmail catalysts often suffers from inferior mass transfer and an underutilized active surface. In this work, a freestanding wood‐based open carbon framework is designed embedded with nitrogen (N) doped, few‐graphene‐layer‐encapsulated nickel iron (NiFe) alloy nanoparticles (N‐C‐NiFe). 3D wood‐derived carbon framework with numerous open and low‐tortuosity lumens, which are decorated with carbon nanotubes (CNTs) “villi”, can facilitate electrolyte permeation and hydrogen gas removal. The chainmail catalysts of the N‐C‐NiFe are uniformly in situ assembled on the CNT “villi” using a rapid heat shock treatment. The high heating and quenching rates of the heat shock method lead to formation of the well‐dispersed ultrafine nanoparticles. The self‐supported wood‐based carbon framework decorated with the chainmail catalyst displays high electrocatalytic activity and superior cycling durability for hydrogen evolution. The unique heat shock method offers a promising strategy to rapidly synthesize well‐dispersed binary and polynary metallic nanoparticles in porous matrices for high‐efficiency electrochemical energy storage and conversion.

Towards high-performance cathode materials for lithium-ion batteries: Al2O3-coated LiNi0.8Co0.15Zn0.05O2

Zn-doped LiNi0.8Co0.2O2 exhibits impressive electrochemical performance but suffers limited cycling stability due to the relative large size of irregular and bare particle which is prepared by conventional solid-state method usually requiring high calcination temperature and prolonged calcination time. Here, submicron LiNi0.8Co0.15Zn0.05O2 as cathode material for lithium-ion batteries is synthesized by a facile sol-gel method, which followed by coating Al2O3 layer of about 15 nm to enhance its electrochemistry performance. The as-prepared Al2O3-coated LiNi0.8Co0.15Zn0.05O2 cathode delivers a highly reversible capacity of 182 mA h g−1 and 94% capacity retention after 100 cycles at a current rate of 0.5 C, which is much superior to that of bare LiNi0.8Co0.15Zn0.05O2 cathode. The enhanced electrochemistry performance can be attributed to the Al2O3-coated protective layer, which prevents the direct contact between the LiNi0.8Co0.15Zn0.05O2 and electrolyte. The escalating trend of Li-ion diffusion coefficient estimated form electrochemical impedance spectroscopic (EIS) also indicate the enhanced structural stability of Al2O3-coated LiNi0.8Co0.15Zn0.05O2, which rationally illuminates the protection mechanism of the Al2O3-coated layer.

Synthesis and characterization of Mn intercalated Mg-Al hydrotalcite

Mn intercalated hydrotalcite was prepared using a reconstruction method. And Mn intercalation was confirmed by XRD, FTIR, and thermal analyses. The different valences of Mn were present as determined by XPS. Calcination slightly promoted the isomorphic replacement of Mn2+ and Mn3+ for Mg2+ and Al3+, especially the replacement of Mn2+ for Mg2+ and Al3+, and to some extent, reduced Mn intercalation. Ultrasonic treatment significantly increased Mn intercalation in permanganate form (Mn7+), and promoted the replacement of Mn2+ for Mg2+ and Al3+. XRF analysis showed that ultrasonic treatment decreased the unbalanced layer charge of Mn intercalated hydrotalcite, while prolonged calcination increased it. These results may provide guidance on the preparation and application of Mn intercalated hydrotalcite. Extended calcination time and ultrasonic vibration increased the interlayer spacing of hydrotalcite, as a result of reduction in layer charge. As the layer charge was not completely balanced after Mn intercalation, a certain amount of CO32− was re-adsorbed into the interlayer space. Mn-hydrotalcites with different layer charges, different contents of Mn with varying valences are expected to have different performances in the process of adsorption, degradation, and catalysis.

Rapid Synthetic Route to Nanocrystalline Carbon-Mixed Metal Oxide Nanocomposites with Enhanced Electrode Functionality

A rapid synthetic route to nanocrystalline carbon-incorporated mixed metal oxide nanocomposites with enhanced electrode performance for lithium ion batteries is developed by applying a very short heat-treatment of layered double hydroxide (LDH) precursor under C2H2 flow. Employing C2H2 atmosphere makes possible the rapid synthesis of nanocrystalline C–NiO–NiFe2O4 nanocomposite via the calcination of the Ni–Fe–LDH precursor at 300 °C in a very short period of 5 min. In the case of ambient atmosphere, a prolonged calcination time of several hours is demanded to induce a complete phase transformation from Ni–Fe–LDH to electrochemically active NiO–NiFe2O4 nanocomposite, highlighting the usefulness of C2H2 atmosphere in promoting the formation of mixed metal oxide nanocomposite. The present C–NiO–NiFe2O4 nanocomposite shows much better anode performance for lithium ion batteries with greater discharge capacity and better cyclability than do the NiO–NiFe2O4 nanocomposites prepared by the prolonged calcination of LDH under ambient atmosphere. The superior electrode activity of the present C–NiO–NiFe2O4 nanocomposite is attributable to the optimization of charge transfer induced by the enhanced electrical conductivity and a short diffusion length of Li ion. The present C2H2-assisted phase transition of LDH precursor provides a convenient, economic, and scalable synthetic way to carbon–mixed metal oxide nanocomposites with promising electrode performance for lithium ion batteries.

Phase evolution and morphology of nanocrystalline BaCe0.9Er0.1O3−δ proton conducting oxide synthesised by a novel modified solution combustion route

Pure BaCeO3 and 10mol% Er2O3 doped BaCeO3 (BCE) was synthesised by a novel modified solution combustion synthesis (MCS) route wherein the pH of the precursor solution was varied and the phase formation and morphology were compared with those obtained in conventional solution combustion synthesis (SCS). X-ray diffraction (XRD) studies confirmed the presence of the undesirable BaCO3 phase in the calcined powders prepared using SCS route whereas the powders synthesised with the modified (MCS) route exhibited a single perovskite phase after calcination. Variation in the pH of the precursor solution resulted in a morphology change from a mix of irregular and globular at pH 4 to more spherical at pH 6 and 8. Fourier transform infrared spectroscopy (FT-IR) studies revealed that calcination time has more pronounced effect on phase formation than calcination temperature. A calcination time of 10h at 1000°C resulted in negligible amount of BaCO3. Such prolonged calcination treatment resulted in substantial grain growth in the SCS sample while the MCS samples were still in the nanocrystalline form. Absence of the ceria peak (464cm–1) in the Raman spectra confirmed the presence of a single perovskite BaCeO3 phase in the sintered pellets as well.

Thermally Modified Graphite Electrodes for the Positive Side of the Zinc-Cerium Redox Flow Battery

In this study, thermal modification of graphite electrodes for the positive side of the Zinc-Cerium redox flow battery is found to enhance their performance and stability by providing a larger and more chemically active surface area to carry out the Ce(III)/(IV) reaction. Prolonged calcination (>9.5 h) and firing temperatures greater than 600°C lead to a physical deterioration of the samples while at 300°C no effect on the cerium reaction within the investigated reaction temperature range (25–55°C) is evident. When treated at 600°C for 6 h, the milder oxidation conditions result in a porous graphite electrode (7.13 m2 g−1) with a low charge transfer resistance (0.14 mΩ cm−2) and negligible weight loss (WTL = 6%). This thermally treated electrode is robust under repetitive cycling (300 cyclic voltammograms) with no degradation occurring within the time frame of the experiment (20 h). The quasi-reversible kinetics of the Ce(III)/(IV) reaction improve with elevated temperatures (ko = 6.0 × 10−3 cm s−1, D = 8.5 × 10−6 cm2 s−1 and jo = 2.91 × 10−3 A cm−2) and are comparable to the present electrode of choice on this flow battery, the Pt-Ti mesh electrode.

Synthesis and luminescent properties of trivalent rare-earth (Eu3+, Tb3+) ions doped nanocrystalline AgLa(PO3)4 polyphosphates

The AgLa(PO3)4 phosphors activated with trivalent rare-earth (Eu3+, Tb3+) ions were prepared by a sol–gel synthesis method. The crystal structure of the compound was studied by X-ray diffraction patterns and found to be crystallized in the monoclinic system with a space group P21/c, indicating the calculated lattice parameters of a=10.08Å, b=13.12Å, and c=7.314Å. The Fourier-transform infrared spectrum, photoluminescence excitation/emission spectra, and decay curves were examined to study the optical properties. The analysis of the Eu3+ ions related emission spectrum revealed the presence of highly symmetric sites for the activator ions. The Tb3+ ions related emission spectrum exhibited a 5D3 emission due to the prolonged calcination at high temperatures, which reduces the residual hydroxyl ions. The optical properties show that this host material is suitable for phosphor materials and laser crystals.

Growth behavior of nanograins in NiO fibers

The growth kinetics of nanograins in NiO nanofibers has been investigated. Individual NiO nanofiebrs synthesized by electrospinning consist of nanograins. The nanograins coalesce and grow at the expense of smaller ones under higher calcination temperatures and prolonged calcination times. The growth kinetics of nanograins makes a transition during growth at a critical size of ∼30 nm in diameter. At the early stage of growth, the activation energy and the growth exponent are found to be 10.94 kJ mol −1 and 9.09, respectively. They change to 137.58 kJ mol −1 and 2.04 at the later stage of growth at the critical size of nanogrians. In that growth stage, bamboo-like grains start to evolve.

Low-temperature thermal removal of template from high silica ZSM-5. Catalytic effect of zeolitic framework

Topochemical and catalytic effects of ZSM-5 zeolite framework in the course of thermal degradation of tetrapropyl ammonium (TPA +) template upon calcination under oxidative (air) and inert (nitrogen, N 2) atmosphere was analyzed using elemental analysis, X-ray Photoelectron Spectroscopy (XPS) and absorption UV–Vis–NIR spectroscopy. It has been demonstrated that template residues were selectively removed from the interior of the crystals. The concentration of (N (C)-containing template species was ⩽1 atom per unit cell (u.c.)) by prolonged (24 h) calcination in air already at temperature T max = 310 °C (N-containing template species) and T max = 330 °C (C-containing template species). Calcination in N 2 requires temperatures higher by about 20 °C. The surface region of ZSM-5 crystals contained, however, a substantial amount of template residua (20–30% of N-containing and ∼60% of C-containing species) even at T max = 430 °C. This effect is associated with conversion of propylene, originating from TPA + degradation, into low volatile products by their dehydrogenation on acidic centers and defect sites of ZSM-5. The dehydrogenation reaction was enhanced under oxidative conditions. The volatility of carbonaceous and N-containing residues was further reduced by their strong interaction with defect sites of ZSM-5.

Purification of Laser Synthesized SWCNTs by Different Methods: A Comparative Study

A comparison of different purification procedures for single walled carbon nanotubes (SWCNTs) synthesized by laser-vapourization has been presented. The methods involved gas-phase oxidation by calcination, liquid-phase oxidation by H2O2, hydrothermal treatment and acid refluxing in HCI. Sample purity is documented with Raman spectroscopy, Transmission electron microscopy, Scanning electron microscopy and thermogravimetric analysis. Multi-spot analyses were done to check the homogeneity of the purified samples. Different purification processes produced SWCNT material with purity in the range of 48-78%. Raman and TEM results suggested that prolonged calcination results in selective etching of larger diameter nanotubes. SEM and TGA analyses showed increase in density of SWCNTs with better oxidation resistance after purification.

Structural and Morphological Control in the Preparation of High Surface Area Zirconia

The methods for the formation of zirconia including precipitation from aqueous salts, sol–gel synthesis from zirconium alkoxides, and the templated synthesis using surfactants are described in this review. The surface areas obtained vary widely but invariably decrease upon prolonged calcination. Digestion of hydrous zirconia and incorporation of dopants such as lanthanum, yttrium, or sulfate ions can increase the surface area and thermal stability. However, these methods also affect the crystal phase of zirconia. The transformation from the metastable tetragonal to the monoclinic phase occurs during the cooling phase of calcination. Mechanisms for the stabilization of the tetragonal phase are discussed. Zirconia with well-ordered mesopores or in the form of hollow spheres can be prepared but lack thermal stability, unless doped with phosphates, silicates or sulfates.