Agglomeration Of Particles Research Articles

Study on the inhibitory behavior of high-voltage electric field on the agglomeration and sedimentation of nanoparticles in suspension

Nanoparticles can improve the heat transfer effect of fluids, however, they are difficult to dissolve in the base fluid and are prone to fouling, agglomeration and sedimentation during flow, which affects their efficient heat transfer characteristics. In this paper, the inhibitory effect of high-voltage electric field on the agglomeration and deposition of TiO2 nanoparticles in suspension was comparatively studied by comprehensive gravity sedimentation, spectrophotometer, particle size analysis, and zeta potential method. Studies have shown that the absorbance of suspensions is basically the same in neutral and acidic environments. However, in a highly alkaline environment, the agglomeration rate of nanoparticles increases significantly, resulting in a decrease in the absorbance of the suspension. The high-voltage non-uniform electric field generated by the active Cu rod electrode can effectively inhibit the agglomeration of TiO2 nanoparticles. However, the suppression effect of an external electric field is not necessarily the higher the voltage, the better. Different nanomaterials have different critical voltages. The high-voltage electric field of 1 kV has the best inhibitory effect on the agglomeration and deposition of TiO2 nanoparticles. An in-depth analysis of the mechanisms of the movement and agglomeration of TiO2 particles in suspension under high-voltage electric field excitation was conducted. The result shows that the agglomeration and sedimentation of particles in suspension depend on the Zeta potential of the nano particles. The higher the absolute value, the more stable the dispersion system is.

Enhanced Oxygen Evolution Reaction in Alkaline Water Electrolysis Using Bimetallic NiFe Metal-Organic Frameworks Integrated with Carbon Nanotubes

Hydrogen is considered a very clean and highly available renewable energy resource for the future. Water electrolysis (WE) is a conspicuous promising technology to produce hydrogen on a large scale, without generating carbon dioxide. In this study, we prepared bimetallic NiFe-based metal–organic frameworks (MOFs) integrated with CNTs (NiFe–BTC@CNTs) as highly efficient electrocatalysts for the oxygen evolution reaction (OER) in alkaline water electrolysis. Combining NiFe MOFs and CNTs significantly enhanced the electrochemical performance and structural integrity of the catalyst. The NiFe–BTC@CNT (30 wt.% CNTs) demonstrates a significant low overpotential of 230 mV at 10 mA·cm⁻2, superior catalytic activity with a Tafel slope of 36 mV·dec⁻1, and excellent stability under both constant and dynamic operating conditions. These unique characteristics are attributed to the high surface area and abundant active sites provided by the bimetallic MOF structure, combined with the exceptional electrical conductivity and mechanical strength of CNTs. Furthermore, the integration of CNTs improves the dispersion while preventing the agglomeration of MOF particles, ensuring a more uniform and accessible active surface area. This research highlights the potential of the NiFe–BTC@CNT catalysts as high-performance durable electrocatalysts for sustainable hydrogen production, offering a significant advance in the development of advanced materials for energy conversion and storage applications.

Deep insight into the effect of smithsonite particle size on surface heterogeneity and adsorption behavior: A case of fatty acid system

The studies for microfine mineral flotation have focused on the two main directions of increasing the apparent mineral particle size and reducing the bubble size, while little research has been reported on the special surface properties and adsorption mechanisms of mineral particles of different sizes. In this study, sodium oleate was chosen as a typical surfactant. The mechanism of the effect of smithsonite particle size on the heterogeneity and adsorption behavior of the mineral surface was explored in depth. Through microflotation experiments, BET area tests, Washburn contact angle tests, particle agglomeration tests, adsorption tests and inorganic carbon analysis, it was pointed out that the smaller the size of the particles, the greater the surface wettability, and the smaller the density and thickness of adsorbed oleate on the surface. The difficulty of encapsulating the mineral surface with a hydrophobic layer of oleate hydrocarbon chains, as well as suboptimal particle aggregation sizes, are key reasons for the poor flotation behavior of fine smithsonite. Furthermore, the inhomogeneity of active sites and charge distribution of surface components of smithsonite with different sizes was revealed from a microscopic point of view by DRIFT spectroscopic analysis, XPS analysis and zeta potential measurements. As the particle size of smithsonite decreases, the positive charge density on the surface is higher and the hydration tendency is more intense, hindering the adsorption of oleate. This work is expected to guide the full particle size recovery of minerals in the flotation from a novel microscopic point of view.

High-Temperature Behavior of Pd/MgO Catalysts Prepared via Various Sol–Gel Approaches

A series of Pd/MgO catalysts based on nanocrystalline MgO were prepared via different sol–gel approaches. In the first two cases, palladium was introduced during the gel preparation, followed by drying it in supercritical or ambient conditions. In the third case, aerogel-prepared MgO was impregnated with an ethanol solution of Pd(NO3)2. The prepared catalysts differ in particle size and oxidation state of palladium. The catalytic performance and thermal stability of the samples were examined in a model reaction of CO oxidation at prompt thermal aging conditions. The as-prepared and aged materials were characterized by low-temperature nitrogen adsorption, UV-vis spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and ethane hydrogenolysis testing reaction. The highest initial activity (T50 = 103 °C) was demonstrated by the impregnated sample, containing Pd0 particles of 3 nm in size. The lowest T50 value (215 °C) after aging at 1000 °C was demonstrated by the impregnated Pd/MgO-WI sample. The high-temperature behavior of the catalysts was found to be affected by the initial oxidation state and dispersion of Pd. Two deactivation mechanisms, such as the agglomeration of Pd particles and migration of small Pd species into the bulk of the MgO support with the formation of Pd-MgO solid solutions, were discussed.

Study on Engineering Properties and Mechanism of Loess Muck Grouting Materials

Shield tunneling generates a massive amount of muck, and achieving the on-site reuse of muck is an urgent need in the field of shield tunneling. This study, based on a section of the Xianyang diversion tunnel in a loess stratum, aims to optimize the mix ratios of loess muck grouting materials to meet specific performance requirements. Laboratory tests were conducted to analyze the effects of the bentonite content and water–solid ratio on the properties of grout. The engineering properties, cost, and environmental impact of the optimized loess muck grouting materials were compared with those of traditional grouting materials. Additionally, XRD, SEM, and CT were employed to investigate the solidification mechanism of loess muck grouting materials. The results show that the bleeding rate, setting time, fluidity, and consistency of loess muck grouting materials decreased with increasing bentonite content, while these properties increased as the water–solid ratio rose. The compressive strength reached 0.26 MPa and 1.05 MPa at 3 d and 28 d, respectively. Compared to traditional grouting materials, the economic cost and carbon emissions of loess muck grouting materials were reduced by 49.46% and 37.17%, respectively. As the curing time increased, gel filling and particle agglomeration reduced the number of pores. The dense microstructure is the primary factor for the improvement of strength.

Core‐Shell Structured CoP@C Cubes as a Superior Anode for High‐Rate and Stable Sodium Storage

AbstractTransition metal phosphides have emerged as a class of promising anode materials of sodium‐ion batteries owing to their excellent sodium storage capacity. However, the limited electronic conductivity and significant volume expansion have impeded their further advancement. In this work, we propose a rational design of cube‐like CoP @C composites with unique core‐shell structure via in situ phosphating and subsequent carbon coating processes. The uniform carbon coating serves as a physical buffering layer that effectively mitigates volume changes during charge/discharge processes, and prevents particle agglomeration and fragmentation, thereby enhancing the structural stability of electrode. Moreover, the nitrogen‐rich carbon layer not only provides additional active sites for sodium ion adsorption but also improves the electrode conductivity and accelerates charge transport dynamics. Consequently, the as‐synthesized CoP@C exhibits a remarkable capacity retention rate of 94.8 % after 100 cycles at 0.1 A g−1 and achieves a high reversible capacity of 146.7 mAh g−1 even under a high current density of 4.0 A g−1.

Studies on Dry Sliding Wear Mechanisms of Al7075/Si3N4 Composites

Abstract In this investigation, Al7075 aluminum alloy reinforced with Si3N4 particles (3, 6, 9, and 12 wt%) was used as reinforcements to manufacture composites through a stir-casting approach. The microstructural characteristics have shown significant grain refinement owing to the presence of Si3N4 particle distribution during the solidification. SEM micrographs confirm the uniform distribution of Si3N4 particles with considerably fewer particle agglomerations throughout the matrix alloy. The reinforcement particle cluster formation is relatively increased for increasing the Si3N4 content. The SEM and EDS analyses showed good integrity at the matrix–refinement interface with no interfacial compound formation. The mechanical properties, such as hardness (up to 118 BHN), tensile strength (up to 281 MPa), and yield strength (up to 178 MPa), were enhanced by 30.69% and 20.27%, respectively. The wear-rate and coefficient of friction of the composites were evaluated with increasing percentages of Si3N4 content. The average wear-rate of the composites is 0.019, 0.0085, 0.0075, and 0.0065 mm3/m, respectively, for the increased Si3N4 ceramic particulate content from 3 to 12 wt%, while the average COF of the composites is 0.45, 0.37, 0.32 and 0.28 respectively. With the addition of Si3N4 particulate content, the wear resistance performance of the composites at 30 N has shown up to 46% enhancement and increased from 0.0052 to 0.0103 mm3/m with the increasing sliding velocity from 1.5 to 3.5 m/s for varying Si3N4 particulate content from 3 to 12 wt%, while reducing the COF up to 65%, and from 0.43 to 0.27. Different wear mechanisms are characterized by identifying the typical features of wear on the SEM micrographs of the worn surfaces. The dominant wear mechanisms of the composites are typically observed as abrasion, oxidation, delamination and melt wear. The mechanism and behavior of composites under dry sliding conditions are analyzed through the construction of wear maps. The windows of wear mechanisms and progression in terms of load and sliding velocity for the composites with various wt% of Si3N4 content were identified, analyzed, and presented.

Prediction of Transport and Deposition of Porous Particles in the Respiratory System Using Eulerian-Lagrangian Approach.

Deep lung delivery is crucial for respiratory disease treatment. Although nano and submicron particles exhibited a good deposition efficiency in deep regions of the lung, powder nonuniformity and particle agglomeration reduce their efficiency. Inhalation of porous particles (PPs) can overcome the mentioned challenges due to their larger size and low-density. The present study numerically investigates the deposition and penetration efficiency of orally inhaled PPs. A revised drag coefficient was implemented for PP transport. A realistic mouth-throat to the fifth generation of the lung was reconstructed from CT-scan images. A dilute suspension of uniformly distributed particles was considered at three inhalation flow rates (15, 30, and 45 L/min). Governing equations of the flow field and particle transport are solved using an Eulerian-Lagrangian approach. The results demonstrate that inhaling PPs significantly reduces the total and regional deposition of particles. There was also a critical porosity value under moderate and high inhalation flow rates for large PPs. Below this critical value, PP deposition efficiency substantially decreases. Additionally, it was also found that under low inhalation flow rates, the impact of porosity value is negligible. Almost 95% of the PPs penetrate the lower branches. These findings provide particle engineers and pharmaceutics with profound insight into developing novel inhalation techniques and drug delivery methods for deep lung delivery.

Electrochemical performance of cobalt-doped NiO thin films synthesized by spray pyrolysis

ABSTRACT In this work, various cobalt-doped NiO thin films have been synthesized via the spray pyrolysis. The cobalt-doped NiO thin films show a cubic phase with preferred orientation along the (111) plane. The scanning electron microscopy images of the cobalt-doped NiO thin films show interconnected flakes with small agglomerated particles. The optical bandgap decreases from 3.30 eV for the undoped NiO thin film to 2.90 eV for 20 mol% cobalt doping, with an increase in cobalt doping concentration in NiO. The electrochemical activities have been tested in 2M KOH electrolyte with cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. The highest specific capacitance observed for the 10 mol% cobalt-doped NiO thin film electrode is 760 Fg−1 at a scan rate of 5 mVs−1. The 10 mol% cobalt-doped NiO thin film electrode shows 92% retention in capacitance after 1000 cycles and a low charge transfer resistance of 10 Ωcm2.

Effect of MoS2 particle size on tribological and vibration reduction properties of thermoplastic polyurethane

The incorporation of lubricating filler can improve the self-lubricating properties of polymers and mitigate friction-induced vibration under harsh conditions. However, filler performances significantly vary depending on its size. In this study, molybdenum bisulfide (MoS2) particles of various sizes were utilized as lubricating additives to reinforce thermoplastic polyurethane (TPU). The results showed that an appropriate decrease in the particle size of MoS2 facilitated more efficient stress transfer from the polymer to the particle due to strengthened interfacial interaction, resulting in improved mechanical properties of the reinforced TPU composites. Additionally, the adsorption property of the MoS2 particle improved, extending the duration of the MoS2 tribo-film. These beneficial phenomena endow TPU composites with excellent tribological and frictional vibration reduction properties, with the 500 nm MoS2 presenting the best reinforcing effect. However, further reduction in particle size caused particle agglomeration, which adversely affected the mechanical and self-lubricating properties of the composite and eventually reduced the frictional vibration reduction properties. The findings obtained herein provide a valuable reference for developing a novel polymer with excellent friction and vibration reduction properties.

Study on foaming behavior of block copolymer/inorganic particles co‐construction of toughened epoxy resin foams

AbstractLow toughness and brittleness limit its application range of thermosetting epoxy resin (EP) based foams. In current research, inorganic particles are commonly utilized as heterogeneous nucleating agents to enhance foaming quality and EP toughness. However, the increasing inorganic particle content usually leads to particle agglomeration, which negatively impacts foaming quality and reduces EP performance. Block copolymers, which appear as liquid to effectively mitigate agglomeration, are employed as toughening materials for EP. In this study, a small number of modified calcium silicate particles (MCS) were used as anchor points to induce the distribution of block copolymers (P‐F68) to improve EP toughness and effectively enhance cell nucleation, thus, EP/MCS/P‐F68 foams performance was improved. The research results showed that EP foams obtained excellent cell structure and very small foam density (0.256 g/cm3) at the P‐F68 content of 10 wt%. The continuous increase of P‐F68 content would lead to the thickening of cell wall and the increase of cell size. Simultaneously, the core‐shell structure formed by P‐F68 in EP effectively enhanced the toughness of EP foams and mitigated its brittleness, offering crucial theoretical guidance for toughening and regulating the cell structure of EP foams.

Nanostructural evolution by applying various fuels in combustion design of CuZnAl mixed-oxides over HZSM-5 used in one-step production of CH3–O–CH3

The influence of different fuels (urea, ethylene glycol and citric acid) in combustion-based design of nano-structured CuO–ZnO–Al2O3/HZSM-5 catalyst was investigated. The catalytic performance were evaluated in a single step production of dimethyl ether form syngas. The X-ray diffraction, Field emission scanning electron microscopy, Transmission electron microscopy, Energy-dispersive x-ray, Temperature Programmed Reduction-H2, N2 Adsorption and Desorption isotherms and Fourier-transform infrared spectroscopy techniques were used to characterize physico-chemical properties of prepared nanocatalysts. The X-ray diffraction results clarified that application of citric acid increased relative crystallinity of Cu and Zn oxides existed in catalyst structure. The Fourier-transform infrared spectroscopy results demonstrated that the zeolite structure was not destroyed after CuO–ZnO–Al2O3/HZSM-5 introduction. The Field emission scanning electron microscopy and Transmission electron microscopy images illustrated that the nanocatalyst synthesized with citric acid has the highest porosity and less population of particle agglomerations. The highest amount of surface area was obtained when citric acid was used as fuel. According to Temperature Programmed Reduction-H2 profiles, the reducibility of nanocatalyst synthesized with citric acid is higher than other samples. The activity of the fabricated nanocatalysts for syngas to Dimethyl ether process were tested at temperature and pressure range of 225–300 °C and 10–40 bar, respectively. Using citric acid as fuel led to achieve greater amount carbon monoxide conversion and Dimethyl ether yield. Furthermore, stability test represented that the activity of this nanocatalyst remained quite stable during 1060 min.

Influence of ultrasonic assistance on the microstructure and friction properties of laser cladded Ni60/WC composite coatings

The effects of different ultrasonic vibration powers on the distribution, phase structure, friction and wear properties of WC reinforced particles in laser melted Ni60/WC composite coatings are investigated. The effects of ultrasonic vibration on the microstructure, elemental distribution, crystal orientation, friction and wear properties of the fused coatings are analyzed. The experimental results show that the deposition of WC particles in the lower and middle parts of the coating is significantly improved after the introduction of ultrasonic vibration during the fusion cladding process. In particular, at 600 W ultrasonic power, not only the distribution uniformity of tungsten carbide particles in the coating is optimal, but also the composite coating shows better wear resistance. However, too much ultrasonic power increases the possibility of particle agglomeration. In addition, although the phase pattern of the coating does not change after ultrasonic vibration, the width of the columnar crystalline region of the coating is reduced, and the coating is covered by a homogeneous lamellar nanoscale eutectic structure with the phase compositions of the γ-(Fe, Ni) and M23C6 phases. The ultrasonic vibration improves elemental segregation of the coating, reduces the large number of precipitated phases in the coating, weakens the grain growth orientation, and relieves the local stress concentration in the coating. In addition, the mechanism of the influence of WC particles on the microstructure evolution and wear resistance of the composite coatings is discussed.

Tailoring efficient manganese bromide-based scintillator films with ethyl acetate assistance

Metal halide scintillators serve as a compelling substitute for traditional scintillators in X-ray detection and imaging due to their low-temperature fabrication process, high light yield and mechanical flexibility. Nevertheless, the spatial resolution and photoluminescence quantum yield (PLQY) of these films are hindered by the agglomeration and uneven distribution of metal halides crystal particles during the fabrication process. We introduce a modified fabrication approach for metal halide scintillator films involving an additional step of ethyl acetate (EA) treatment, resulting in the preparation of a smooth EA-treated (Ph4P)2MnBr4/Polydimethylsiloxane film. The carbonyl groups within EA interact with elements of the (Ph4P)2MnBr4 microcrystals powder, ensuring uniform dispersion and preventing agglomeration. The EA-treated composite film demonstrates a remarkable PLQY of approximately 95% and an impressive spatial resolution of 14 lp/mm, with enhanced stability under harsh environments. These characteristics ensure its suitability as a high-performance X-ray imaging scintillator.&#xD.

Impact of Carbonization Temperature on the Structure and Li Deposition Behavior of 3D Dual Metal Carbon Fibers

Li deposition within lithiophilic–lithiophobic metal carbon fibers is influenced by several structural factors, including electrical conductivity, surface‐bound functional groups, particle size and distribution of the lithiophilic–lithiophobic components, which are significantly affected by the carbonization temperature. To gain a deeper understanding of how these different parameters affect the Li deposition behavior, a detailed analysis of Ag and Cu containing carbon fibers at carbonization temperatures from 500 to 1000 °C is performed. At lower carbonization temperatures, the fibers exhibit an unordered carbon structure with a high concentration of heteroatoms and a lithiophilic–lithiophobic gradient. However, the high electrical resistance at these temperatures impedes Li‐ion interaction with the fibers, leading to the formation of mossy and dead Li. In contrast, higher carbonization temperatures result in the removal of heteroatoms and a more ordered carbon structure. The agglomeration of Cu and Ag particles at these temperatures disrupts the lithiophilic–lithiophobic gradient, causing concentrated Li deposition on top of the fibers. A threshold temperature of 700 °C has been identified for achieving homogeneous Li deposition. At this temperature, the lithiophilic–lithiophobic gradient still exists, and the more ordered carbon structure enhances Li‐ion interaction with the fibers, resulting in stable Li deposition for over 1100 h.

Enhancing activated sludge dewatering performance: Impact of alum dosage on dehydration characteristics and microstructure

Sludge flocs encapsulate a significant amount of bound water, resulting in poor dewatering efficiency. To address this issue, the addition of alum (KAl(SO4)2·12H2O) has emerged as an effective strategy for enhancing sludge dewatering performance. This research specifically investigates the effects of various alum dosages on the dewatering characteristics of sludge. The introduction of alum alters internal temperature, pH levels, and intracellular osmotic pressure, which facilitates the release of trapped water within the flocs. Additionally, alum accelerates sludge sedimentation and promotes the agglomeration of smaller particles into larger ones, further improving dewatering efficiency. However, determining the optimal alum dosage for sludge conditioning is essential, as excessive amounts can lead to a decrease in dewatering performance.

The Application of Ultrasound Pre-Treatment in Low-Temperature Synthesis of Zinc Oxide Nanorods

Zinc oxide, due to its unique physicochemical properties, including dual piezoelectric and semiconductive ones, demonstrates a high application potential in various fields, with a particular focus on nanotechnology. Among ZnO nanoforms, nanorods are gaining particular interest. Due to their ability to efficiently transport charge carriers and photoelectric properties, they demonstrate significant potential in energy storage and conversion, as well as photovoltaics. They can be prepared via various methods; however, most of them require large energy inputs, long reaction times, or high-cost equipment. Hence, new methods of ZnO nanorod fabrication are currently being sought out. In this paper, an ultrasound-supported synthesis of ZnO nanorods with zinc acetate as a zinc precursor has been described. The fabrication of nanorods included the treatment of the precursor solution with ultrasounds, wherein various sonication times were employed to verify the impact of the sonication process on the effectiveness of ZnO nanorod synthesis and the sizes of the obtained nanostructures. The morphology of the obtained ZnO nanorods was imaged via a scanning electron microscope (SEM) analysis, while the particle size distribution within the precursor suspensions was determined by means of dynamic light scattering (DLS). Additionally, the dynamic viscosity of precursor suspensions was also verified. It was demonstrated that ultrasounds positively affect ZnO nanorod synthesis, yielding longer nanostructures through even reactant distribution. Longer nanorods were obtained as a result of short sonication (1–3 min), wherein prolonged treatment with ultrasounds (4–5 min) resulted in obtaining shorter nanorods. Importantly, the application of ultrasounds increased particle homogeneity within the precursor suspension by disintegrating particle agglomerates. Moreover, it was demonstrated that ultrasonic treatment reduces the dynamic viscosity of precursor suspension, facilitating faster particle diffusion and promoting a more uniform growth of longer ZnO nanorods. Hence, it can be concluded that ultrasounds constitute a promising solution in obtaining homogeneous ZnO nanorods, which is in line with the principles of green chemistry.

Structure and properties of powders obtained by electrodispersion of pure Nickel metal waste in distilled water

Purpose. Investigation of the composition, structure and properties of powder materials obtained by electrodispersion of nickel waste of the PNK-0T1 brand in an oxygen-containing medium – distilled water.Methods. To determine the composition, structure and properties of powder materials, samples of powders obtained from waste nickel grade PNK-0T1 were studied. The powder material was obtained by electroerosive dispersion in distilled water. Microanalysis of powder particles was carried out using a scanning electron microscope, an analysis of the size distribution of powder particles was obtained using a particle size analyzer, an X-ray spectral microanalysis of powder particles was carried out using an energy-dispersive X-ray analyzer embedded in a scanning electron microscope, an analysis of the phase composition of powder particles was carried out using X-ray diffraction on the diffractometer.Results. During the study, it was revealed that the shape of the particles obtained from nickel powders is spherical and elliptical, and agglomerates of smaller particles are also noted on the increase. Oxygen and nickel are present in the composition of powder materials. The phases of pure nickel and nickel oxide NiO are marked in the phase composition. From the analysis of the granulometric histogram, it follows that the particle size spread varies in the range of 0.26...18.62 microns, the average volume diameter of the particles was 5.2 microns.Conclusion. The obtained research results can be used to develop a new heavy pseudo-alloy using metal waste from expensive raw materials by the method of electroerosive dispersion, followed by improvement and optimization of the composition and structure of the alloy.

Effects of acoustic shock waves on the structural and optical properties of cadmium borate

Cadmium borate (CdB₂O₄), an inorganic compound combining transition metals and non-metals, has a broad range of optical applications. In this study, CdB₂O₄ was subjected to acoustic transient pressure using a semi-automatic Reddy tube, with shock pulses applied at counts of 100, 200, 300, and 400 at a Mach number of 1.5, corresponding to a transient pressure of 0.59 MPa and a temperature of 520 K. Control and shock-treated samples were analyzed using XRD, Raman, FTIR, SEM, UV-DRS, and photoluminescence spectroscopy to investigate shock wave effects. The XRD analysis revealed peak disappearance, the formation of new peaks, increased crystallinity, and instability in crystallite size. Raman spectroscopy showed peak disappearance, shifts, and broadening of lattice modes. SEM indicated increased particle size and agglomeration under shock conditions, consistent with changes in crystallinity. UV-DRS analysis shows a slight change in their band gap. Photoluminescence exhibited fluctuating trends in luminescent properties after the shock treatment. The findings reveal that CdB₂O₄'s structural and optical properties are sensitive to acoustic pressure, suggesting its potential for tailored optical behavior in specific applications. These results enhance our understanding of how acoustic pressure affects CdB₂O₄ and open new possibilities for optimizing its use in high-pressure applications.

Kinetics, catalyst design, and hydrodynamic analysis in Fischer–Tropsch synthesis: Fixed Bed vs Fluidized Bed Reactors

While fixed beds maximize contacting between the fluid and solid phase, commercial processes operate with fluidized beds for highly exothermic reactions, like Fischer–Tropsch (FT), to maximize heat transfer thereby minimizing catalyst sintering and deactivtion. However, conversion is lower due to gulf-streaming and poorer gas-solids contacting. In experimental reactors (<10mm) gulf-streaming is negligible and gas-solids contacting is excellent as bubbles are small. Here, we measure CO conversion over 3 FT catalysts—Fe/Ce/SiO2-K, Cu, Fe/Zr/SiO2-K, Cu, Fe/Catalox-K, Cu—across the same reactor operating in the fluidized bed and fixed bed regime. Flow rates were increased up to a maximum of 5 times the minimum fluidization velocity (Umf). The reactor operated at 2MPa, with a H2/CO molar ratio of 2, and 275°C≤T≤325°C. The average CO conversion was higher in the fixed bed but temperature control was more difficult, which could account for some of the differences. The highest ▪ selectivity (80% to 84%) was with the Fe/Catalox-K, Cu at 275°C, 2 to 4×Umf, in the fixed bed reactor. A first order reaction model characterized CO conversion well (R2>0.91) for the Fe-Catalox and Fe-Zr catalysts with activation energies >70kJmol−1. Conversion was essentially independent of temperature for the Fe-Ce composition in both the fixed bed and fluidized bed. BET surface area decreased 22% to 52% after the reaction. XRD analysis after the reaction revealed a 4% to 10% decrease in crystallinity, along with the presence of various Fe carbide compounds. Post-reaction SEM-EDS images indicated particle agglomeration and carbon deposition on the catalyst surface. Despite these morphological changes, the impact on CO conversion seemed minimal. Residence time distribution tests confirmed that gas was essentially in plug flow for both the fixed bed and fluidized bed configurations.