Calcination Conditions Research Articles

Microwave thermal pre-treatment and calcination of biomineralised sorbents for calcium looping

Waste eggshells have been investigated as biomineralised CO2 sorbents for the calcium looping cycle due to their high Ca content, low cost, availability, and high CO2 uptake. This work investigates a novel heat-pre-treatment using eggshells as raw material. The eggshells were simultaneously calcined and thermally pre-treated via microwave heating using different powers and times whilst maintaining the same input energy in a single mode cavity reactor. The calcined eggshells were characterised using standard characterisation techniques such as TGA and isotherms of N2 adsorption at 77 K. The dielectric properties were measured using the cavity perturbation technique at 2.45 GHz. Numerical electromagnetic simulations were performed using COMSOL Multiphysics and results were used to optimise the experimental setup. The treated materials were subjected to carbonation/calcination cycles in order to assess their suitability as a calcium-looping sorbent. The sorbent that exhibited a more stable CO2 uptake was the one treated at the highest power (800 W) 4.5 mmol CO2/g sorbent after 20 cycles under mild calcination conditions. Adsorbents prepared at 400, 600 and 800 W displayed similar CO2 uptake after 20 cycles when the calcination conditions were under more realistic conditions.

Acid leaching technology for post-consumer gypsum purification

Background Contaminants and water-soluble salts present in mechanically recycled gypsum from refurbishment and demolition (post-consumer) plasterboard waste limit its use as a secondary raw material in plasterboard manufacturing. This research addresses this limitation, developing a novel acid leaching purification technology combined with an improved mechanical pre-treatment for post-consumer gypsum valorization. Methods Laboratory-scale acid leaching purification was performed with a borosilicate beaker, hot plate, and overhead stirrer. Stuccos were produced after calcination of gypsum at 150 °C for 3 hours. Samples were characterized through X-ray fluorescence, X-ray diffraction, thermal gravimetric analysis, scanning electron microscopy and particle size analysis. Results Acid leaching at 90 °C for 1 h using a 5 wt% sulfuric acid solution was revealed to be the optimum purification conditions. Stuccos produced from purified gypsum under optimum conditions had similar initial setting times to that of a commercial stucco but with higher water demand, which could be reduced by optimizing the calcination conditions. A magnesium-rich gypsum was precipitated from the wastewater. Conclusions Purified post-consumer gypsum with > 96 wt% chemical purity and calcium sulfate dihydrate content was produced. The research recommends acid neutralization prior filtration, use of gypsum particles < 2 mm in size, and stirring speed of 50 rpm to reduce the economic and environmental impacts of the acid leaching purification process at industrial scale. The magnesium-rich gypsum could potentially be marketed as soil fertilizer.

Adsorption Mechanism and Regeneration Performance of Calcined Zeolites for Hydrogen Sulfide and Its Application.

Hydrogen sulfide (H2S) is a very toxic, acidic, and odorous gas. In this study, a calcined zeolite was used to investigate the adsorption performance of H2S. Among particle size, calcination temperature and time calcination temperature and time had significant effects on the adsorption capacity of H2S on the zeolite. The optimal calcination conditions for the zeolite were 332 °C, 1.8 h, and 10-20 mm size, and the maximum adsorption capacity of H2S was approximately 6219 mg kg-1. Calcination could broaden the channels, remove the adsorbed gases and impurities on the surface of zeolites, and increase the average pore size and point of zero net charge. As the zeolite adsorbed to saturation, it could be regenerated at the temperatures between 200 and 350 °C for 0.5 h. Compared with the natural zeolite, the adsorption capacities of dimethyl disulfide, dimethyl sulfide, toluene, CH3SH, CS2, CO2, and H2S were significantly higher on the calcined zeolite, while the adsorption capacity of CH4 was lower on the calcined zeolite. A gas treatment system by a temperature swing adsorption-regeneration process on honeycomb rotors with calcined zeolites was proposed. These findings are helpful for developing techniques for removing gas pollutants such as volatile sulfur compounds and volatile organic compounds to purify biogas and to limited toxic concentrations in the working environment.

Effects of Calcination Conditions on the Structural and Electrochemical Behaviors of High‐Nickel, Cobalt‐Free LiNi0.9Mn0.1O2 Cathode

AbstractEliminating cobalt from high‐nickel layered oxide cathodes lowers the cost of lithium‐ion batteries for electric vehicles. However, cobalt‐free cathodes with high Mn4+ and Ni2+ contents are prone to Li/Ni mixing after synthesis, potentially compromising battery energy density, rate capability, and cycling stability. Without cobalt facilitating cation ordering in the layered structure, the degree of Li/Ni mixing in cobalt‐free cathodes depends heavily on the calcination conditions. In this study, a systematic exploration of calcination temperatures and LiOH ratio for LiNi0.9Mn0.1O2 (NM‐90) provides detailed insights into the optimal synthesis conditions for high‐capacity cobalt‐free cathodes with extended cycle life. Surprisingly, high Li/Ni mixing does not necessarily lead to poor cycling stability whereas low Li/Ni mixing does not guarantee a long cycle life. More importantly, although excessive calcination temperature can further decrease Li/Ni mixing, it does not necessarily enhance capacity. Instead, the pernicious effects from the H2 → H3 phase transition are amplified due to a pronounced two‐phase reaction. An extensive suite of chemical and structural characterization methods uncovers a correlation between elevated calcination temperature, phase transformation, cation ordering, and capacity fading behavior: “overcooking” high‐nickel, cobalt‐free cathodes induce structural arrangement toward that of LiNiO2, with exacerbated lattice distortion and surface instability accelerating capacity fade.

Designing ultrastable P2/O3-type layered oxides for sodium ion batteries by regulating Na distribution and oxygen redox chemistry

P2/O3-type Ni/Mn-based layered oxides are promising cathode materials for sodium-ion batteries (SIBs) owing to their high energy density. However, exploring effective ways to enhance the synergy between the P2 and O3 phases remains a necessity. Herein, we design a P2/O3-type Na0.76Ni0.31Zn0.07Mn0.50Ti0.12O2 (NNZMT) with high chemical/electrochemical stability by enhancing the coupling between the two phases. For the first time, a unique Na+ extraction is observed from a Na-rich O3 phase by a Na-poor P2 phase and systematically investigated. This process is facilitated by Zn2+/Ti4+ dual doping and calcination condition regulation, allowing a higher Na+ content in the P2 phase with larger Na+ transport channels and enhancing Na+ transport kinetics. Because of reduced Na+ in the O3 phase, which increases the difficulty of H+/Na+ exchange, the hydrostability of the O3 phase in NNZMT is considerably improved. Furthermore, Zn2+/Ti4+ presence in NNZMT synergistically regulates oxygen redox chemistry, which effectively suppresses O2/CO2 gas release and electrolyte decomposition, and completely inhibits phase transitions above 4.0 V. As a result, NNZMT achieves a high discharge capacity of 144.8 mA h g−1 with a median voltage of 3.42 V at 20 mA g−1 and exhibits excellent cycling performance with a capacity retention of 77.3% for 1000 cycles at 2000 mA g−1. This study provides an effective strategy and new insights into the design of high-performance layered-oxide cathode materials with enhanced structure/interface stability for SIBs.

Amine-functionalized high-surface-area Al2O3 adsorbent for CO2 capture: Effect of the support calcination conditions

Porous alumina has garnered interest as a substrate in the development of solid amine adsorbents for CO2 capture. However, the calcination conditions of alumina can significantly alter its properties, which in turn affects the adsorption performance of the resulting adsorbents. In this study, high-surface-area alumina was synthesized using a reverse microemulsion method. The impact of the calcination conditions on the pore structure and surface properties of the alumina precursor was examined. Additionally, the porous alumina produced under various calcination conditions served as the support for tetraethylenepentamine (TEPA) loading, and the CO2 capture performance of the resultant adsorbents was assessed. The adsorption kinetics and activation energy were analyzed, emphasizing the cyclic stability when regenerated in a realistic CO2 atmosphere. Our findings indicate that alumina calcined under an air atmosphere with a lid exhibited the highest capture capacity (reaching 89.97 mg/g after a 40 wt% TEPA loading), compared to other alumina samples. The adsorption kinetics corresponded closely with the Avrami model, yielding an activation energy (Ea) of 4.75 kJ/mol. Both alumina samples calcined in air, with and without a lid, demonstrated robust cycling stability and resistance to urea formation. The underlying anti-urea mechanisms were also elucidated in the study.

Structural Order-Disorder Analysis of Thermally-Activated Water-Washed Kaolin Particles Using Fourier Transform Infrared Spectroscopy

During the calcination of kaolin particles, kaolinite is thermally activated at high temperatures, causing the crystal structure to collapse and yielding amorphous metakaolinite through dehydroxylation. This metakaolinite is used as a supplementary cementitious material, and one of the most important factors influencing the pozzolanic properties is calcination conditions. Fourier transform infrared spectroscopy (FTIR) has become useful in distinguishing and obtaining information about structural order-disorder and phase transformation following the calcination process. In this study, water-washed kaolin particles were thermally activated at elevated temperatures ranging from 600 to 800 °C for 3–4 h at a rate of 10 °C/min before being analyzed with FTIR to determine the optimum conditions for calcining kaolin particles by examining functional groups, and also to study structural order-disorder or crystallinity of calcined kaolin particles. The most reactive metakaolinite state of water-washed kaolin particles was achieved after 3 h of calcination at 800 °C. Using both empirical and numerical approaches, variations in the position and relative intensity of O-H stretching and deformation of hydroxyl groups in the infrared spectrum can be used to classify the degree of structural order of water-washed kaolin particles. By increasing the calcination temperatures and period, the well-ordered and partially-ordered structures of kaolin particles were transformed into well-ordered, partially-ordered, and poorly-ordered structures. These structural disorder and crystallinity have a significant impact on pozzolanic activity because well-ordered kaolinite can be transformed into less reactive metakaolinite, whereas poorly-ordered kaolinite with high defects can be transformed into more reactive metakaolinite. However, in this study, the structure of water-washed kaolin particles that achieved complete dehydroxylation was discovered to be partially-ordered to poorly-ordered and can be transformed into highly reactive pozzolans.

Pre-treatment through reductive calcination for CO2 mineralization and selective battery metal extraction from laterites

The world needs an increasing supply of nickel and cobalt production as battery materials for sustainable development. However, the complexity of laterite deposits and the need to control CO2 emissions challenge the enhanced global supply from laterites. This work investigates the effects of calcination as a pre-treatment for selective battery metal extraction from both limonite laterite and saprolite laterite together with concurrent achievement of CO2 mineralization. Calcination under a reducing atmosphere of CO-N2 or CO-CO2 gas mixtures can significantly enhance the extraction of critical metals from both limonite and saprolite laterites. With calcination, the hydrated silicate minerals and ferric oxides converted to reactive olivine and ferrous oxide. The calcines thus can participate in the CO2 mineralization process to stabilize CO2 as mineral carbonates and release nickel and cobalt arising from the CO2 mineral carbonation into solution as complex ions with a ligand (such as sodium nitrilotriacetate, NTA). The optimum calcination conditions are 20 ∼ 30 % CO in CO-CO2 gas mixture at 700 °C. Beyond the optimum range results in the inadequate conversion of ferric to ferrous at too low CO concentration or over calcination of ferric to metallic iron at too high CO concentration. At the optimum conditions, the nickel & cobalt extraction and CO2 mineralization can reach 90 %, 93 %, and 39 % from laterite. Each tonne saprolite with the pre-treatment of calcination can recover 20.5 kg nickel, 0.59 kg cobalt, and simultaneously sequester 142 kg CO2 as stable mineral carbonates. The pre-treatment through slightly reductive calcination enables the robust suitability of the developed process for all layers of laterites for both critical battery metal recovery and carbon mineralization.

Phase engineering of Ni-Mn binary layered oxide cathodes for sodium-ion batteries

Nickel-manganese binary layered oxides with high working potential and low cost are potential candidates for sodium-ion batteries, but their electrochemical properties are highly related to compositional diversity. Diverse composite materials with various phase structures of P3, P2/P3, P2, P2/O3, and P2/P3/O3 were synthesized by manipulating the sodium content and calcination conditions, leading to the construction of a synthetic phase diagram for NaxNi0.25Mn0.75O2 (0.45 ≤ x ≤ 1.1). Then, we compared the electrochemical characteristics and structural evolution during the desodiation/sodiation process of P2, P2/P3, P2/O3, and P2/P3/O3-NaxNi0.25Mn0.75O2. Among them, P2/P3-Na0.75Ni0.25Mn0.75O2 exhibits the best rate capability of 90.9 mA h g−1 at 5 C, with an initial discharge capacity of 142.62 mA h g−1 at 0.1 C and a capacity retention rate of 78.25% after 100 cycles at 1 C in the voltage range of 2–4.3 V. The observed superior sodium storage performance of P2/P3 hybrids compared to other composite phases can be attributed to the enhanced Na+ transfer dynamic, reduction of the Jahn-teller effect, and improved reaction reversibility induced by the synergistic effect of P2 and P3 phases. The systematic research and exploration of phases in NaxNi0.25Mn0.75O2 provide new sights into high-performance nickel-manganese binary layered oxide for sodium-ion batteries.

Effect of Flash Calcined Powders on the Properties of Spherical Alumina Granules

Three types of flash calcined powders with different specific surfaces and phases were selected to make alumina granules. The granulation was performed in a pan granulator as the spherical form. The hydrothermal and calcination conditions were applied to the granules. Physical, chemical and microstructural studies were applied to the hydrated and calcined granules. This study focussed on the thermal historical effects of the initial powders derived from bauxite on the granules. The least physical changes and the highest specific surface area were obtained for the granules prepared with flash calcined powder at 650°C. The hydrated granules can have boehmite, gamma and bayerite phases with rod, porous and plate morphologies, respectively. The presence of rod boehmite phase increases the strength of hydrated granules and plays an important role in the final strength. In the calcination stage, the phases transformed into the transition alumina and gamma phases with the growth of nanometer-sized crystals.

Optimising the acid-base ratio of Mg-Al layered double oxides to enhance CO2 capture performance: the critical role of calcination conditions.

The effect of calcination conditions (ramp rate, calcination temperature and time) on the formation of Mg2Al layered double oxides (Mg2Al LDOs) as well as their CO2 capture performance, has been systematically investigated. This study explores novel insights into the intricate relationship between these calcination conditions and the resulting surface characteristics, which play a vital role in CO2 capture efficiency. Notably, it is revealed that a rapid ramp rate (100 °C min-1) significantly increases surface area and hydroxyl concentration, leading to a 69% increase in CO2 capture efficiency compared to slower ramp rate. Conversely, short calcination times (1 h) and fast ramp rates (100 °C min-1) are observed to compromise CO2 adsorption due to the presence of dehydrated LDHs. A critical acid : base ratio of 0.37, achieved from a fast ramp rate (100 °C min-1) at 400 °C for 2 h, was found as a key threshold for optimising surface properties, effectively balancing favourable hydroxyl and less favourable strong acid sites, thereby maximizing CO2 capture performance.

Effect of impregnation strategy on structural characteristics of Ce-Mn/Al2O3 and its catalytic ozonation of benzoic acid.

Ce-Mn binary oxides supported on Al2O3 (Ce-Mn/Al2O3), with enhanced activity and stability for catalytic ozonation of benzoic acid, were synthesized using a facile impregnation method. The competitive synergetic effects between cerium and manganese significantly influenced the structural characteristics and catalytic performance of the catalysts depending on the impregnation sequence. Catalysts prepared via the one-step impregnation process exhibited a higher concentration of homogeneous Ce3+ species on the catalyst surface. This led to an increase in surface oxygen vacancies, thereby enhancing catalytic activity. In contrast, the two-step impregnation process resulted in fewer oxygen vacancies due to reduced competitive effects between cerium and manganese. Overall, the optimized Ce-Mn/Al2O3 catalysts demonstrated improved catalytic performance in ozonation reactions, highlighting the importance of impregnation method and calcination conditions in tailoring catalyst properties for enhanced activity and stability. Oxygen vacancies play a crucial role as active sites for ozone adsorption and dissociation into *O2 and *O, facilitated by the reduction of Mn4+ to Mn3+ and the oxidation of Ce3+ to Ce4+. This process forms an electron closed loop that maintains electron balance. The synergistic interactions between cerium and manganese enable rapid electron transfer between Ce4+ and Mn3+, facilitating the regeneration of Ce3+ and Mn4+. Due to the increase of the dual redox conjugate pairs and the surface reactive oxygen species, the catalytic ozonation activity and stability of Ce-Mn/Al2O3 was enhanced.

Comparative study on devolatilization behavior, microstructural evolution and resultant properties during calcination of petroleum coke with distinct mesophase texture

Petroleum coke as an affordable and abundant material represents significant opportunities for using in both traditional and emerging fields, whereas a lack of understanding transformation chemistry during essential calcination hampers its development. Herein, relevance among devolatilization behavior, microstructural evolution and resultant properties during calcination of green coke were investigated. Calcination is found to be roughly distinguished into three regimes according to average stacking height (Lc) and average interlayer spacing (d002) obtained by analysis of WAXS as well as appearance of D2 peak in Raman spectra. The first regime below 800ºC shows starting transformation from semi-coke to coke, mainly induced by volatilization of low-molecular-weight components, dealkylation and intramolecular dehydro-condensation. Simultaneously, progressive healing of in-plane defects, gradual increase of mesogen-layer size and decrease of interlayer spacing was accompanied, causing significant growth of real density. Thereafter, intermolecular dehydro-polymerization and heteroatoms elimination become dominant in 800–1400 °C, leading to removal of interstitial defects. Consequently, larger stacking height and more homogeneous stacking of well-developed hexagonal carbon layers are formed, further promoting microstrength and electric-conductivity of resultant coke. Next, graphite-like microcrystallites would be rearranged into polyhedral configuration in 1400–1600ºC, indicating a transition from coke to semi-graphite. Notably, the mode of arrangement of mesophase units in the green coke would largely predetermine the coke microstructure. This work could give a guidance for regulating structural evolution via selection of green coke and calcination condition according to application.

Eco-friendly, sustainable and porous eggshell/tea waste-derived CaO nanoparticles as a high-temperature CO2 sorbent: Fabrication and textural/morphological evaluation

The CaO-based sorbents suffer from a high-intensity sintering rate and require costly promoters to improve their CO2 capture capacity through the Calcium Looping (CaL) technique. Herein, for the first time, the eco-friendly and efficient eggshell-derived CaO sorbents were promoted with tea waste for the CO2 capture process. 0, 2.5, and 5 wt.% of ball-milled tea waste nanoparticles (NPs) were merged with sieved eggshell-based NPs throughly. Their CO2 capture activity was evaluated under severe calcination conditions, including calcination under 100 vol.% CO2 for 5 min at 950 °C. According to the textural/morphological data, 92 % and 89.8 % enhancement were seen for the prepared sample's surface area and pore volume, including 5 wt.% tea waste NPs. Additionally, the average grain size of as-prepared specimens decreased from 39.3 nm to 25.2 nm. Furthermore, the sorbent having 5 wt.% tea waste presented the multicyclic durability of 48.1 % and the average CO2 uptake capacity of 0.133 g CO2/g sorbent during fifteen multiple carbonation/calcination cycles under severe calcination conditions. The incorporation of 5 wt.% tea waste as the structural promoter resulted in 100 % and 58 % improvements in the capture potential of CaO at kinetically- and diffusion-controlled carbonation stages of the 15th cycle.

Acid leaching technology for post-consumer gypsum purification.

Contaminants and water-soluble salts present in mechanically recycled gypsum from refurbishment and demolition (post-consumer) plasterboard waste limit its use as a secondary raw material in plasterboard manufacturing. This research addresses this limitation, developing a novel acid leaching purification technology combined with an improved mechanical pre-treatment for post-consumer gypsum valorization. Laboratory-scale acid leaching purification was performed with a borosilicate beaker, hot plate, and overhead stirrer. Stuccos were produced after calcination of gypsum at 150 °C for 3 hours. Samples were characterized through X-ray fluorescence, X-ray diffraction, thermal gravimetric analysis, scanning electron microscopy and particle size analysis. Acid leaching at 90 °C for 1 h using a 5 wt% sulfuric acid solution was revealed to be the optimum purification conditions. Stuccos produced from purified gypsum under optimum conditions had similar initial setting times to that of a commercial stucco but with higher water demand, which could be reduced by optimizing the calcination conditions. A magnesium-rich gypsum was precipitated from the wastewater. Purified post-consumer gypsum with > 96 wt% chemical purity and calcium sulfate dihydrate content was produced. The research recommends acid neutralization prior filtration, use of gypsum particles < 2 mm in size, and stirring speed of 50 rpm to reduce the economic and environmental impacts of the acid leaching purification process at industrial scale. The magnesium-rich gypsum could potentially be marketed as soil fertilizer.

Identification of oxidized platinum single atoms on chlorinated γ–alumina support by density functional theory calculations and X-ray absorption spectroscopy

The existence and nature of oxidized Pt single atoms (SA) are unraveled on two γ-Al2O3 supported Pt catalysts (0.3 wt%) containing two chlorine contents (0.1 and 1.4 wt%) characterized by HR-HAADF-STEM and HERFD-XANES/EXAFS after a calcination treatment at 520 °C. Pt SA are revealed as PtOxCly complexes where the number of oxygen (x) and chlorine (y) ligands directly depends on the chlorine content. In order to interpret these experimental observations and provide coherent atomic structures for these PtOxCly complexes, the thermodynamic stability of the oxidized Pt SA species supported on the (100) surface model of γ-Al2O3 is determined by density functional theory (DFT) calculations as a function of the calcination conditions determined by the temperature, and partial pressures of H2O, HCl and O2. It is shown that various ligands such as Cl, OH, O (from the alumina surface or as extra-ligands) and H2O are coordinated to Pt depending on the conditions and chlorine content. Various square planar and square-based pyramidal PtOxCly species such as PtO2, PtOCl2, PtCl4 are found to be stable in calcination conditions, while octahedral Pt(OH)xCl4-x(H2O) are stabilized in XAS recording conditions. The features of these DFT simulated octahedral Pt SA species are successfully compared to XAS data. On one hand, based on thermodynamics arguments, we proposed models of supported complexes in agreement with EXAFS coordination numbers and distances (Pt-O, Pt-Cl and Pt-Al). On the other hand, the simulated XANES spectra at the Pt L3-edge for these complexes match well with the experimental HERFD-XANES and reveal that the bump feature observed between 11575 eV and 11585 eV (post-edge signal) is a tracer of the amount of Cl coordinated to Pt SA.

Tailoring self-pulverized low-calcium clinker for CO2 sequestration

To reduce energy consumption and greenhouse gas emissions in the cement industry, this study develops a novel low-calcium clinker with self-pulverization properties. The clinker is synthesized from limestone and sandstone raw materials and comprises dicalcium silicate (2CaO·SiO2 (C2S)) as the primary mineral and rankinite (3CaO·2SiO2 (C3S2)) as the auxiliary mineral. The influence of calcination temperature, cooling rate, and holding time on clinker pulverization and mineral formation is investigated through a series of experiments. The optimal calcination condition involves heating at 1240 °C for 1 h, followed by natural cooling, resulting in a self-pulverized low-calcium clinker (SPLCC) with main mineral is γ-C2S and contains β-C2S, C3S2, and C2AS (Calcium alumina feldspar (2CaO·Al2O3·SiO2)). The self-pulverized clinker exhibits a pulverization ratio of 93.0 %, a specific surface area of 666.4 m2/kg, and an average particle size of 8.2 μm. Additionally, the clinker displays excellent carbonation reactivity, with the compressive strength reaching 69.3 MPa and 82.2 MPa after 4 h and 24 h of CO2 curing, respectively. The carbonation products are identified as calcite and silica gel. SPLCC can reduce and sequester approximately 277.3 kg of CO2 emissions compared to the hydration of Portland cement clinker when considering the preparation and curing stages. The results highlight the potential of SPLCC as a sustainable cementitious material.

Effect of calcination temperature and duration on structural and dielectric properties of CaFeO3-δ

With its perovskite structure, CaFeO3-δ exhibits intriguing properties. It possesses remarkable dielectric properties that make it an attractive candidate for various technological applications such as capacitors, enhanced signal transmission, and other electronic components. The primary objective of this study is to optimize the dielectric properties of CaFeO3-δ perovskite material. For this purpose, an ideal combination of the duration and temperature of calcination was studied. The calcination conditions were variated, from 600 °C to 1100 °C for the temperature at different durations (4 h and 10 h). The XRD results were refined using the Rietveld refinement, showing a simple orthorhombic crystallographic structure. This structure was found for samples calcined at 900 °C, 1000 °C, and 1100 °C during 4 h and 10 h, according to the observed and calculated patterns (Rp ≤ 5 % - Rwp ≤ 7 %) of these ceramics. The sample calcinated at 1000 °C/4h has the closest χ2 factor to 1 which indicates an optimum crystallinity. the crystallite size goes from 70.8245 nm to 99.1266 nm with the increase of the calcination temperature and duration, this parameter was calculated using the XRD peak broadening analysis and the Scherrer equation. SEM analysis revealed, that high temperature and calcination time led to a larger grain size. Notably, samples calcined at 1100 °C/10 h had a larger particle size of 1.312 μm, confirming the crystallite size evolution determined by XRD. FT-IR and Raman analyses further confirmed the samples purity. Dielectric studies showed that the colossal dielectric constant (ε') reached a maximum of 105 for CaFeO3-δ calcined at 1000 °C for both durations. The lower transition temperature was found for the sample calcined at 1000 °C/10 h with a value of 257 °C. The maximum conductivity of 0.22 S/m at 1 MHz was recorded for the CaFeO3-δ calcined at 1000 °C/10 h. Furthermore, the dielectric constant exhibits relaxational behavior, which can be attributed to the strong correlation between the ferrite conduction mechanism and their dielectric behavior. The dielectric material does not follow the ideal Debye theory, according to Cole-Cole analysis, indicating a distribution of relaxation times instead. These obtained properties make this ceramic (CaFeO3-δ calcined at 1000 °C/10 h) a potential candidate for dielectric and electrical device applications such as batterie and electric capacitors.

Determinants and performance prediction on photocatalytic properties of hydroxyapatite by machine learning

Hydroxyapatite (HAP) have been widely used as photocatalysts in environmental remediation. However, the effects of crystallinity, crystal size, and purity of HAP on their photocatalytic performances have not been fully understood yet. In this paper, we synthesized HAP samples with different properties by controlling the calcination conditions and evaluated their photocatalytic performance in the degradation reaction of methyl orange. Combing the catalytic experiments with machine learning technique, we found that the crystallinity of HAP was the dominant parameter that determined the photocatalytic performance. And the developed machine learning method could predict the catalytic results with an error of only 2.2 %. Our work provides a route to predict material properties based its characters by experiment combined with machine learning.

Sintering Temperature Effect on Phase Formation, Microstructure and Electrical Properties of Modified KNLNTS Solid Solution Prepared via the Solid-State Combustion Technique

In this study, the effect of sintering temperature (1000–1100 °C for 2 h) on phase formation, phase transition, microstructure and electrical properties of lead-free piezoelectric (K0.44Na0.52Li0.04)(Nb0.84Ta0.10Sb0.06)O3 (KNLNTS) solid solution with 0.3 wt%Bi2O3 + 0.4 wt%Fe2O3 + 0.2 wt%CuO additive (abbreviate as modified KNLNTS) was investigated. Modified KNLNTS ceramics were synthesized by the solid-state combustion technique using glycine as fuel. The modified KNLNTS powders were prepared using the calcination condition of 650 °C for 2 h. The XRD pattern of all sintered ceramics exhibited a pure perovskite phase. Using Rietveld refinement to analyze the phase formation showed that the modified KNLNTS ceramics had co-existing phases of orthorhombic and tetragonal in all sintered ceramics and the orthorhombic phase increased when the sintering temperature increased. The average grain size, TO-T, Tc, Pr and Ec increased with increasing sintering temperature. At the sintering temperature of 1025 °C, the modified KNLNTS ceramic showed the best electrical properties (Cε ≈ 6745, Smax ≈0.274% and d*33 ≈ 548 pm/V). The good electrical properties of the modified KNLNTS ceramics makes them good candidates for lead-free applications to replace Pb-based ceramics.