Formation Of Intermediate Phase Research Articles

Multiscale investigation on the formation path of the apatite phase in bioactive glasses

Mesoporous bioactive glasses (MBGs) have been reported as promising biomaterials to stimulate and promote the growth of bones. When exposed to Simulated Body Fluid (SBF), MBGs develop an apatite phase called carbonate hydroxyapatite (H(C)A) on their surfaces that closely mimics the mineral phase of bones. In order to gain deeper insights into the key stages of the surface reactions of two different types of MBGs (58S and 70S30C) soaked in SBF, we have used high energy total X-ray scattering coupled to Pair Distribution Function (PDF) analysis, along with Raman spectroscopy and scanning electron microscopy. This type of coupled analytical approach can ultimately help to unravel the details of the reaction kinetics in the complex calcium phosphate environment around the BGs surfaces. The data obtained in our in-vitro study point to the formation of other intermediate phases like amorphous calcium phosphate (ACP) and calcite (CC), that transform after a specific time into H(C)A depending on the composition of the MBGs, their surface properties and their interaction times with SBF.

Reaction dynamics simulation of MoO2 cluster precursor with melting, deoxygenation and sulfuration for MoS2 growth by chemical vapor deposition

Chemical vapor deposition (CVD) is a promising strategy for achieving fascinating large-scale production of MoS2. During CVD, MoO2 exhibits high reactivity and can effectively inhibit intermediate phase formation. Although, the experiments qualitatively demonstrate the MoO2 sulfuration mechanism, the reaction dynamics process on the atomic level is not clear. Herein, according to our previous experimental results of pre-deposited MoO2 vapor–liquid-solid growth MoS2, we investigate microscopic reaction events, including melting, deoxygenation, and sulfuration by reactive molecular dynamics simulation as follow: Terminal oxygen in pre-melting zone on the cluster surface has high reactivity, leading to deoxygenation occurring during melting. The unsaturated coordination Mo atoms are more accessible to sulfuration. With a long simulation time, MoO2 is transformed into MoO0.27S1.95 in which MoS2-like clusters account for up to 92.45 % after annealing. We hope that our work will provide theoretical support for the controlled CVD synthesis of MoS2 and other transition metal dichalcogenides.

A Morphological Study and Effect of Intermediate Phase Formation on Hard and Wear Resistant SiC-Co Composite Coating on Low Carbon Steel via Arc Based Heat Source

A Morphological Study and Effect of Intermediate Phase Formation on Hard and Wear Resistant SiC-Co Composite Coating on Low Carbon Steel via Arc Based Heat Source

Nanosized Tungsten Powder Synthesized Using the Nitridation–Decomposition Method

A facile, one-step nitridation–decomposition method was developed for the synthesis of nanosized tungsten powder with a high surface area. This approach involved the nitridation of WO3 in NH3 to form mesoporous tungsten nitride (W2N), followed by in situ decomposition of W2N to directly yield single-phase W particles. The phase and morphology evolution during the synthesis were systematically investigated and compared with the carbothermal reduction of WO3. It was revealed that powdered tungsten product with single-phase particles was obtained after nitridation at 800 °C combined with in situ decomposition at 1000 °C, displaying an average particle size of 15 nm and a large specific surface area of 6.52 m2/g. Furthermore, the proposed method avoided the limitations associated with intermediate phase formation and coarsening observed in carbothermal reduction, which resulted in the growth of W particles up to ~4.4 μm in size. This work demonstrates the potential of the nitridation–decomposition approach for the scalable and efficient synthesis of high-quality, fine-grained tungsten powder.

Effect of cyclic mechanical treatment on the final properties of Nb + 2Si powder mixtures prepared for SHS

The mechanical pretreatment of a powder mixture of niobium and silicon was studied experimentally and theoretically using the new macrokinetic theory of mechanochemical synthesis. The method of organizing the operation mode of the ball mill affects the degree of grinding and activation of the powder composition, as well as the rate of formation of intermediate phases. The effect of cycling on the temperature inside the mill drum, particle size of the powder mixture, formation of mechanically synthesized niobium silicides, and structure of the initial components has been studied. Varying the cycling can lead to safe and emergency operation of the mill. The final mixtures' characteristics may vary significantly depending on the number of cycles of discontinuous mechanical treatment, even if the total operating time of the ball mill remains the same. The safe conditions for cyclic operation of the mill were determined. The effects of different mechanical treatment modes on the grinding, activation, and phase formation of a powder mixture were investigated. Various parameters were analyzed, including thermophysical, physico-chemical, and kinetic characteristics of the cyclic operation of the AGO-3 ball mill, the kinetics of grinding and activation of Nb and Si particles, and the rate of mechanochemical reaction in the mechanically activated mixture of Nb + 2Si.

Unraveling the influence of Sb dopant to reversible capacity and initial Coulombic efficiency of SnO2-graphene as anodes for sodium storage

Sodium storage materials based on conversion and alloying reactions often suffer from low initial Coulombic efficiency (ICE). Most of literature shows that the SnO2-based anode commonly reveals an ICE below 50 %, and the reasons could be attributed to the partial reversibility in conversion reaction by forming an intermediate phase. This work focuses on using an element doping strategy to suppress the formation of an inert intermediate phase and improves the ICE for SnO2-based anodes in sodium storage applications. Mechanisms of performance enhancement are also carefully investigated. The 3 % Sb doped sample is demonstrated with enhanced electrochemical performance. Specifically, it delivers an initial discharge capacity of 847 mAh g−1 at 50 mA g−1, combining an average enhanced ICE of 57.1 % (37.8 % for the undoped comparison), and it also presents a good rate performance of 206 mAh g−1 at a high current density of 1600 mA g−1. It is found that the Sb dopant reduces the specific capacity of active materials, but it enhances reaction reversibility; improves the overall conductivity of active materials, but does not directly enhance the Na+ diffusion coefficient; helps to restrain the formation of inert phase (the SnO phase) in sodium storage reactions to improve reversibility and initial Coulombic efficiency. Therefore, reversible capacities and initial Coulombic efficiencies can be effectively enhanced after introducing the Sb dopant at an optimized percentage. This work could provide valuable inspiration for designing conversion and alloying-type anodes for sodium storage applications via ion doping methods.

Tin dioxide coated rice husk silica as lead-acid battery positive additive for enhancing the performance under power-intensive applications

Lead-acid batteries rapidly response to instantaneous high-current, rendering them particularly effective for high-power applications, including power traction batteries, starter batteries, and start-stop systems. However, issues arise during intense working rate (6–10C), causing significant polarization that leads to severe oxygen evolution side reactions and softening and shedding of positive active material (PAM), limiting the battery's cycle life. This study introduces a tin dioxide (SnO2) coated rice husk silica (RH-SiO2) composite as an positive additive in lead-acid batteries. The composite (SnO2/RH-SiO2) has a hierarchical pore structure from RH-SiO2, provides a robust conductive framework. The lattice structure of the SnO2 is similar to that of PbO2, while induces the formation of a PbSnO3 intermediate phase during formation process. SnO2/RH-SiO2 can also accelerates lead dioxide deposition and improves the interphase conversion efficiency, while significantly enhances the transformation of α- and β-PbO2, leading to a 20.7% increase in discharge specific capacity. Compared to a standard battery, up to 3.7 times longer at 100% deep discharge cycle life and 4.7 times longer in start-stop-mode testing. In our finding the SnO2/RH-SiO2 composite serves as a highly effective additive for augmenting the performance and longevity of lead-acid batteries in high-power applications, presenting a significant advancement in battery technology.

Changing Template/Al2O3 Ratio in Reaction Gel-An Effective Way to Regulate Nature of Intermediate Phases and Properties of SAPO-11 Molecular Sieves during Crystallization.

A study has been conducted to investigate the formation of intermediate phases during the crystallization of SAPO-11 molecular sieves from reaction mixtures with a varying template (di-n-propylamine) DPA/Al2O3 ratio. It was found that changing the DPA/Al2O3 ratio from 1.0 to 1.8 in the initial reaction gels leads to the formation of different intermediate phases during crystallization into a SAPO-11 molecular sieve. It is shown that at the ratio template/Al2O3 = 1.0, an intermediate amorphous silicoaluminophosphate is formed; at 1.4, a mixture consisting of amorphous and layered phases forms; and at 1.8, a layered phase is present. A simple and innovative approach for controlling the morphology, size, and characteristics of primary crystals and the secondary porous structure in hierarchical SAPO-11 is proposed. The method is based on regulating the DPA/Al2O3 ratio in the reaction gel. The synthesized SAPO-11 molecular sieves with a hierarchical porous structure exhibited high selectivity in the hydroisomerization of n-hexadecane.

Impact of tannic acid on iron oxide nanoclusters synthesized by a polyol solvothermal method

Raspberry-shaped iron oxide nanostructures (RSNs) correspond to oriented aggregated and hollow clusters of nanograins exhibiting a high saturation magnetization and a superparamagnetic behaviour. These nanostructures are promising for a wide range of applications, such as magnetic separation, catalysis, pollution control, and nanomedicine. However, for most applications, particularly nanomedecine and depollution, high colloidal stability is required, and the isoelectric point of iron oxide is around 6–7. Therefore, these nanoclusters need to be coated with a surfactant to obtain colloidal suspensions in water. Here, we have developed a one-pot polyol solvothermal synthesis process to coat these promising nanoclusters with tannic acid (TA), a natural compound with antimicrobial properties, which has been little studied with these nanoclusters. Different parameters of the synthesis were adjusted, such as the molar ratio TA:Fe, the synthesis temperature and duration. We showed that TA interferes deeply in the RSNs synthesis mechanism with the observed reduction of iron(III) to iron(II), the complexation of TA with iron, the formation of intermediate phases, as well as the growth of a parasitic iron carbonate phase and the loss of the oriented aggregation and hollowness of the iron oxide RSNs. Considering all these parameters, the optimal synthesis conditions were thus established (TA:Fe ratio = 0.010, temperature of 200°C and duration of 10.5 h), leading to RSNs with small nanograins, a rather high surface area (82 m2/g), high saturation magnetization (74 emu/g) and good colloidal stability. By combining different characterization techniques, a new synthesis mechanism was proposed different from previously established for RSNs without TA, based on strong TA-iron oxide interfaces.

ИЗУЧЕНИЕ ВОЗМОЖНОСТИ ИСПОЛЬЗОВАНИЯ РАЗЛИЧНЫХ КАРБОНАТНЫХ ПОРОД ПРИ СИНТЕЗЕ КАЛЬЦИЕВО-АЛЮМОФЕРРИТОВОГО КЛИНКЕРА

The article considers the possibility of using carbonate rocks of limestone, marl and chalk in the synthesis of calcium-aluminoferrite clinker (CAFC). The analysis of the structure of carbonate rocks, as well as their influence on the physico-chemical processes occurring during the synthesis of calcium-aluminoferrite clinker, is given. Phase formation has been studied in the temperature ranges 900-1000 °C and 1100-1200 °C with an isothermal exposure of 20 minutes. The heat treatment mode has been selected to obtain the basic phase composition of calcium-aluminoferrite clinker. The dynamics of changes in the qualitative phase composition of firing products at various temperatures, ranging from 900 °C to the clinker sintering temperature of 1200 ° C, as well as quantitative characteristics of the intensity of formation of the main clinker phases are presented. It was found that during the firing of CAFC in the temperature range of 900-1000 °C, raw materials mixtures gradually undergo a number of physico–chemical transformations, the main of which are thermal dissociation of CaCO3, the formation of intermediate phases (CS, CF, Al2O3•4SiO2, Al2O3•SiO2), as a result of decomposition of accompanying minerals and solid-phase interactions, as well as the beginning of the formation of clinker compounds CA, C2AS and C2F. It is proposed to use for the limestone-bauxite composition a temperature of 1150 °C with an exposure of 40-60 minutes, marl-bauxite - 1100 °C with an exposure of 30-40 minutes and chalk-bauxite- 1100 °C with an exposure of 30-40 minutes.

Facile Hydrogen‐Bonding Assisted Crystallization Modulation for Large‐area High‐quality CsPbI2Br Films and Efficient Solar Cells

AbstractThe thermally stable inorganic cesium‐based perovskites promise efficient and stable photovoltaics. Unfortunately, the strong ionic bonds lead to uncontrollable rapid crystallization, making it difficult in fabricating large‐area black‐phase film for photovoltaics. Herein, we developed a facile hydrogen‐bonding assisted strategy for modulating the crystallization of CsPbI2Br to achieve uniform large‐area phase‐pure films with much‐reduced defects. The simple addition of methylamine acetate in precursors not only promotes the formation of intermediate phase via hydrogen bonding to circumvent the direct crystallization of CsPbI2Br from ionic precursors but also widens the film processing window, thus enabling to fabricate large‐area high‐quality phase‐pure CsPbI2Br film under benign conditions. Combining with stable dopant‐free poly(3‐hexylthiophene), the CsPbI2Br solar cells achieve the record‐high efficiencies of 18.14 % and 16.46 % for 0.1 cm2 and 1 cm2 active area, respectively. The obtained high efficiency of 38.24 % under 1000 lux illumination suggests its potential in indoor photovoltaics for powering the Internet of Things, etc.

Facile Hydrogen-Bonding Assisted Crystallization Modulation for Large-area High-quality CsPbI2 Br Films and Efficient Solar Cells.

The thermally stable inorganic cesium-based perovskites promise efficient and stable photovoltaics. Unfortunately, the strong ionic bonds lead to uncontrollable rapid crystallization, making it difficult in fabricating large-area black-phase film for photovoltaics. Herein, we developed a facile hydrogen-bonding assisted strategy for modulating the crystallization of CsPbI2 Br to achieve uniform large-area phase-pure films with much-reduced defects. The simple addition of methylamine acetate in precursors not only promotes the formation of intermediate phase via hydrogen bonding to circumvent the direct crystallization of CsPbI2 Br from ionic precursors but also widens the film processing window, thus enabling to fabricate large-area high-quality phase-pure CsPbI2 Br film under benign conditions. Combining with stable dopant-free poly(3-hexylthiophene), the CsPbI2 Br solar cells achieve the record-high efficiencies of 18.14 % and 16.46 % for 0.1 cm2 and 1 cm2 active area, respectively. The obtained high efficiency of 38.24 % under 1000 lux illumination suggests its potential in indoor photovoltaics for powering the Internet of Things, etc.

Highly Circularly Polarized Light‐Sensitive Chiral One‐Dimensional Perovskites Enabled by Antisolvent Engineering

AbstractChiral perovskites have emerged as promising next‐generation materials for polarization detection due to their excellent circularly polarized light (CPL) detection capabilities. However, they suffer from a low chiroptical response when fabricated as a polycrystalline thin film, limiting their potential range of applications. Herein, it is demonstrated that antisolvent dripping during the spin‐coating process can effectively improve the chiroptical properties of polycrystalline chiral perovskite thin films. Systematic analysis with different antisolvents reveals that the highly polar antisolvent chloroform interacts with dimethyl sulfoxide molecules via hydrogen bonding. This strong hydrogen bonding suppresses the formation of intermediate and secondary phases and accelerates the crystallization of chiral 1D perovskites, thus reducing the density of the iodine vacancies inside the perovskite thin films. The lower density of iodine vacancies also intensifies the asymmetric tilting inorganic distortion of PbI6 octahedrons, enhancing the chiroptical response of the fabricated chiral perovskite material. Photodetectors based on the chloroform‐treated chiral perovskite films achieve a remarkably high distinguishability of 0.31, outperforming previously reported photodetectors based on the chiral perovskites. The fabricated photodetectors also exhibit outstanding responsivity and detectivity with enhanced operational stability.

Elimination of buried interfacial voids for efficient perovskite solar cells

Establishing optimal interfacial contact is crucial for enhancing the efficiency of perovskite solar cells (PSCs). However, formation of voids at buried interface of perovskite films often hinders this critical objective. Our investigation reveals that these buried interfacial voids predominantly manifest at sites characterized by large-angle pits on rough substrate, due to their elevated nucleation barriers compared to their small-angle counterparts. To address this challenge and promote uniform nucleation and growth across all sites, regardless of their angles, we develop an innovative precursor regulation strategy to reduce the nucleation barrier discrepancy between different sites by introducing nonstoichiometric homologous ions or by facilitating the formation of intermediate phases. Notably, the incorporation of FACl additive into the FAPbI3 precursor combines the dual benefits of this approach, yielding high-quality perovskite film with intimate contact and reduced defect density. Consequently, this leads to a significant enhancement in the photovoltaic performance of PSCs.

Unraveling the Nanoscale Segregation Mechanism in N-Doped Niobium for Enhanced SRF Performance.

The nitrogen doping (N-doping) treatment for niobium superconducting radio-frequency (SRF) cavities is one of the key enabling technologies that support the development of more efficient future large accelerators. However, the N-doping results have diverged due to a complex chemical profile under the nitrogen-doped surface. Particularly, under industrial-scale production conditions, it is difficult to understand the underlying mechanism thus hindering performance improvement. Herein, a combination of spatially resolved and surface-sensitive approaches is employed to establish the detailed near-surface phase composition of thermally processed niobium. The results show that intermediate phase segregations, particularly the nanometric carbon-rich phase, can impede the nitridation process and limit the interactions between nitrogen and the niobium sub-surface. In comparison, the removal of the carbon-rich layer at the Nb surface leads to enhanced nitrogen binding at the Nb surface. Combining the RF test results, it is shown that the complex uniformity and grain boundary penetrations of impurity elements have a direct correlation with the mid-field quench behavior in the N-doped Nb cavities. Therefore, proper control of the nanometric intermediate phase formation in discrete thermal steps is critical in improving the ultimate performance and production yield of the Nb cavities.

Alumino-Silico-thermic synthesis of high purity ferroboron alloy and its characterization

High purity ferroboron (Fe–B) alloy is used as an alloying agent for making special grades of steels, Nd-Fe-B magnets etc. In this study, alumino-silico-thermic co-reduction of Fe2O3 and B2O3 was attempted to prepare high purity Fe–B. Extensive differential thermal analysis (DTA) studies were carried out to understand the reduction behaviour of Fe2O3 and B2O3 by Al and Si. DTA exothermic peaks indicated three step reduction of Fe2O3 (Fe2O3→Fe3O4→FeO→Fe) when reacted with Al and Si separately. B2O3–Si system did not show exothermic peaks while heating indicating sluggish or no reduction, however, B2O3–Al DTA peaks indicated two step reduction behaviour. Differential thermal analysis of Fe2O3–B2O3–Al–Si indicated completion of reduction of oxides, and formation of different intermediate phases. Specially designed reduction reactors were used to produce ferroboron alloy in bulk quantities. Thermal analysis results suggested that the formation of aluminium and silicon borides could be avoided using sub-stoichiometric amount of Al and Si, which was further confirmed from the bulk thermit product. Si acted as reducing agent as well as forming low melting slag comprising of Al(Si)–B–O type oxides. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and Particle Induced Gamma-ray Emission (PIGE) analysis confirmed the presence of 12 wt% boron in the alloy product with lower content (<1 %) of impurity elements like Al and Si. The relationship between the chemical homogeneity with the thermit process parameters was established. Microstructure and mechanical properties confirmed the formation of Fe2B and FeB phase in the thermit alloy.

High-pressure Raman spectroscopy study of α-quartz-like Si1-xGexO2 solid solution

Spontaneous α-Si1-xGexO2 single crystals were synthesized using the set of crystal growth techniques: hydrothermal (XGe = 0.09, 0.20), flux (XGe = 0.45, 0.70) and recycling (XGe = 0.96). The XRD and spectroscopic studies with non-negative matrix factorization show linear dependences of structural parameters and Raman shift on germanium content and confirmed the existence of a complete series of α-Si1-xGexO2 solid solution. The synthesized samples of the solid solution were studied by Raman spectroscopy at the ambient conditions and for the first time at high pressures up to ∼30 GPa. The obtained results suggest a phase transition “α-quartz → post-quartz” for Si1-xGexO2 in the examined pressure range. The formation of the possible intermediate phase (quartz-II) was detected for Si1-xGexO2 with XGe = 0.09, 0.20 and 0.45 at 11, 10 and 7.5 GPa, respectively. The linear dependences of the pressure value of phase transitions on germanium content were observed. At decompression, the post-quartz phase remained stable that was determined by Raman spectra for all compositions of solid solution. Obtained experimental results revealed the correlation of the chemical composition, spectroscopic characteristics, and structural deformations at ambient conditions and at high pressures.

Systematic in situ Investigation of the Formation of NH3 Cracking Catalysts from Precursor Perovskites ABO3 (A=La,Ca,Sr and B=Fe,Co,Ni) and their Catalytic Performance

AbstractThis work addresses the formation of ammonia (NH3) decomposition catalysts derived from perovskites ABO3 (A=La, Ca, Sr, and B=Fe, Co, Ni) precursors via operando synchrotron X‐ray diffraction experiments. During the reaction in NH3, the perovskite precursors are decomposed and the transition metals are reduced. Depending on their reduction properties, active metallic catalysts are formed in situ on La2O3 as support. The reduction behavior of the perovskites, formation of intermediate phases during activation, and catalytic performance was studied in detail. In addition, microstructure properties such as crystallite sizes and particle morphology were analyzed. Co‐/Ni‐based perovskites decomposed completely during activation to Co0/Ni0 supported on La2O3 while Fe‐based perovskites were fully stable but inactive in catalysis. This difference is due to varying electronic properties of the transition metals, e. g., decreasing electronegativity from Ni to Fe. With decreasing reducibility, the intermediate phases during activation formed more distinct. La3+ was partially substituted by Ca2+/Sr2+ in LaCoO3 to test for advantageous effects in NH3 decomposition. The best performance was observed using the precatalyst La0.8Sr0.2CoO3 with a conversion of 86 % (100 % NH3, 15000 mL g−1 h−1) at 550 °C.

Formation, conversion, and elimination of intermediate spinel phase in MgO/kaolin mixture firing for cordierite

AbstractCordierite ceramic is usually used for diesel particulate filter owing to its excellent low thermal expansion coefficient and high thermal shock resistance properties. However, the co‐exited intermediate spinel phase can deteriorate the thermal and mechanical performances of cordierite ceramic product, because the spinel phase has much higher thermal expansion coefficient comparing to that of cordierite. In this study, two methods are utilized to reduce the spinel impurity in the cordierite ceramic. On the one hand, rational reaction resources were introduced to decrease spinel production. The formation of intermediate spinel phase is systematically researched by X‐ray diffraction (XRD), scanning electron microscopy (SEM), Raman characterizations and the results clarified the preference of path “Enstatite + Mullite → Cordierite” for less spinel production in comparison to path “Enstatite + Al2O3 → Cordierite + Spinel.” Additionally, MgO was introduced as fluxing agent to promote liquid‐phase sintering, thus facilitating the conversion of spinel. On the other hand, the sintering schedule was improved by introducing a holding temperature gradient to promote the diffusion of Si4+ and further promote the conversion of spinel into cordierite. With these methods, the residual spinel phase is minimized, the resulting high‐purity cordierite has a 47% reduction in the thermal expansion coefficient from 3.07 × 10−6/K to 1.63 × 10−6/K compared to the original cordierite sample.

Synthesis, crystal structure and thermal behavior of tetra-kis-(3-cyano-pyridine N-oxide-κO)bis-(thio-cyanato-κN)cobalt(II), which shows strong pseudo-symmetry.

The title compound, [Co(SCN)2(C6H4N2O)4], was prepared by the reaction of cobalt(II)thio-cyanate with 3-cyano-pyridine N-oxide in ethanol. In the crystal, the cobalt(II) cations are octa-hedrally coordinated by two terminal N-bonded thio-cyanate anions and four O-bonded 3-cyano-pyridine N-oxide coligands, forming discrete complexes that are located on centers of inversion, hence forming trans-CoN2O4 octa-hedra. The structure refinement was performed in the monoclinic space group P21/n, for which a potential lattice translation and new symmetry elements with a fit of 100% is suggested. The structure can easily be refined in the space group I2/m, where the complexes have 2/m symmetry. However, nearly all of the reflections that violate the centering are observed with significant intensity and the refinement in P21/n leads to significantly lower R(F) values (0.027 versus 0.033). Moreover, in I2/m much larger components of the anisotropic displacement parameters are observed and therefore, the crystal structure is presented in the primitive unit cell. IR investigations confirm that the anionic ligands are only terminally bonded and that the cyano group is not involved in the metal coordination. PXRD investigations show that a pure crystalline phase has been obtained and measurements using simultaneously thermogravimetry and differential thermoanalysis reveal that the compound decomposes in an exothermic reaction upon heating, without the formation of a coligand-deficient inter-mediate phase.