Incipient Conditions Research Articles

Preparation and pipeline transport of CO2 as a hydrate slurry – Modelling and techno-economic analysis

CO2 transportation as a hydrate slurry is modelled in Aspen Plus, including the slurry preparation and the pipeline transport. Due to the lack of built-in models for the hydrate formation, mass and energy balances were developed and implemented using a User-block function. NRTL-RK global property method was used, given the accuracy in predicting the CO2 solubility in water under incipient hydrate formation conditions and the dissolution heat of CO2 in water. The conventional process of transporting CO2 in a supercritical state was also modelled to benchmark the hydrate-based technology. The hydrate-based process is safer than the conventional process as it requires lower operating pressures, but the estimated costs are higher due to the need for refrigeration and larger pipeline diameters for transportation. The addition of thermodynamic promoters, that moderate the hydrate formation conditions, the integration of cold streams with other processes, and valuing the water transported with CO2, will enhance the economic attractiveness of the hydrate-based process.

Exploring the hydrodynamics of dense beds of Geldart B and D gas-fluidized particles through the analysis of capacitance probe signals

The hydrodynamics of Geldart B and D solids dense fluidized beds, of spherical/irregular morphology, have been characterized using capacitance probes at ambient temperature and 500 °C. A statistical approach applied to the time series of local bed voidage reveals, at specific experimental conditions, a characteristic bimodal distribution in the emulsion phase voidage: a more expanded, high-voidage, phase can be distinguished from a low-voidage phase with values close to minimum fluidization condition. Quantitative and qualitative differences among tested materials can be associated to different particles morphology. Emulsion phase voidages for the tested samples collapse on the same characteristic value once normalized with the voidages at incipient fluidization condition. The Richardson-Zaki equation proves to effectively correlate also in the bubbling fluidization regime the voidage and gas superficial velocity in the emulsion phase. The influence of hydrodynamics of fluidized bed dense phase on mass transfer in the emulsion phase is clearly highlighted.

Diagnosing Incipient Faults for a Faster Adoption of Sustainable Aerospace Technologies

Next-generation aircraft require the development and integration of a deal of innovative green technologies to meet the ambitious sustainability goals set for aviation. Those transformational efforts are associated with a tremendous increase in the complexity of the onboard systems and their multiphysics-coupled behaviors and dynamics. A critical aspect relates to the identification of the coupled faults resulting from the integration of those green technologies, which introduce damage identifiability issues and demand new approaches for the efficient and accurate identification of non-nominal fault conditions. Model-based fault detection and identification (FDI) methodologies have been proven essential to identify onboard the damages affecting the systems from physical signal acquisitions, but existing methods are typically computationally expensive and fail to capture incipient coupled faults, which prevents their adoption and scaling with the increasing complexity of novel multiphysics systems. This work introduces a multifidelity framework to accelerate the identification of fault modes affecting complex systems. An original two-stage compression computes an optimally informative and highly reduced representation of the monitoring signals for the minimum demand of onboard resources. A multifidelity scheme for Bayesian inversion is developed to infer multidomain fault parameters from the compressed signals: variable cost and fidelity models are optimally queried for a major reduction of the overall computational expense. The framework is demonstrated and validated for aerospace electromechanical actuators affected by incipient multimodal faults. Remarkable accelerations of the FDI procedure are observed, and the exact identification of the incipient fault condition was achieved one order of magnitude faster than with standard algorithms.

Research on incipient and critical cavitation of a Francis turbine

Abstract Cavitation is an important performance index to evaluate the comprehensive performance of hydraulic turbine. Determination of the plant cavitation coefficient is one of the most important tasks in the design phase of a hydro-power station. In order to improve the design rationality of the cavitation coefficient, numerical simulations of a Francis turbine were carried out to study the cavitation evolution characteristics. A detailed comparative analysis were made to clarify the different cavitation coefficients and impacts on the Francis turbine. Discussions on plant cavitation coefficient selection of hydro-power plant were made form the perspective of cavitation influence on the unit. Based on these investigations, it can be concluded that a certain safety margin of incipient and critical cavitation coefficient were needed considering the rapid efficiency drop near the critical cavitation and serious pressure pulsation near the incipient cavitation condition. The ratio between the plant cavitation coefficient and critical cavitation of the studied Francis turbine were larger than the current standard in China, which means the good cavitation performance of the unit after it put into operation. This study can provide a reference for determining the cavitation coefficient more accurately and ensuring the operation safety of the unit.

Evolution and future prospects of hydropower sector in Nepal: A review

Nepal is one of the pioneers of hydropower development among Asian countries. The plethora of fast-flowing rivers provides immense potential for hydropower generation. However, Nepal still lacks a clear blueprint for the overall development and management of this sector. This paper aims to review the evolution of hydropower development, future prospects and roadblocks to hydropower development. With the growing energy demands projected to reach as high as 41,264.82 Gigawatt hours (GWh) in 2030 and 115,294.4 GWh in 2040 under different scenarios, this paper highlights the huge prospects the sector holds. It also proposes a focus on storage-type hydropower plants and concepts of energy banking to address the incipient condition of seasonal energy mismatch in the country, which has developed a condition of energy shortage during the winter and energy surplus during the monsoon. Moreover, projected changes in hydro-climatic extremes under the climate change scenarios is likely to affect water availability and subsequently the energy production in the majority of hydropower projects. Thus, this review can serve as a guideline to help understand the current scenario and make rational decisions and policies for the future management of the hydropower sector of the country.

Stability of boulders on cobble streambeds

The placement of boulders in streams enhances aquatic habitat by increasing the heterogeneity of flow conditions. Practical design must ensure the stability of individual boulders, requiring calculation of their incipient movement conditions. The stability of a boulder on a cobble bed is shown experimentally to depend on its size, the bed material size, the degree of embedment of the boulder, the slope of the bed and the flow velocity and depth. An equation is derived through a pivoting analysis for predicting the relationship between the critical ambient depth-averaged velocity and the critical flow depth; this, together with a resistance equation, can be used to predict the flow conditions for boulder stability. The equation is used to develop a simpler form for unsubmerged spherical boulders and cobbles. The stability equation is tested against the experimental data, using an experimentally determined drag coefficient relationship.

Optimal weight impulse extraction: New impulse extraction methodology for incipient gearbox condition monitoring

Gear faults in a transmission system generally cause impulse components in vibration signals, which is a crucial symbol for gearbox fault diagnosis. However, their related signals are often interfered or even submerged by the noisy meshing components (NMC) of gearboxes in degradation, which introduces challenges for incipient fault detection and condition monitoring. Commonly employed deconvolution-based methods attempt to design a filter to extract impulse components. However, these methods fail to address the interference issue of the NMC on deconvolution process. To overcome this limitation, this paper proposes an optimal weight impulse extraction (OWIE) methodology to suppress the NMC and highlight impulse component in vibration signal. Different from deconvolution-based methods, the proposed method locates impulses adaptively driven by waveform itself. A non-impulse part is suppressed through point-to-point removal, while impulse components are highlighted by subtracting a weighted signal from a raw signal. An iterative procedure is utilized to solve the optimal weight sequence by maximizing the kurtosis of an impulse signal. The effectiveness of the proposed OWIE is validated through a simulation case study and a run-to-failure experiment of gearboxes. Results demonstrate that the OWIE is sensitive to incipient faults and is suitable for the health condition monitoring of gearboxes.

Large-eddy simulation of elliptic hydrofoil tip vortex cavitation under incipient conditions

Large-eddy simulation (LES) is used to simulate flow over a three-dimensional elliptical hydrofoil at 12 degrees angle of attack and Reynolds numbers (Re) of 9×105 and 1.4×106 based on root chord length and freestream velocity. The simulations are performed at the cavitation number (σ) of 2.1 and are based on the experiments of Boulon et al. (1999), who studied the tip vortex cavitation behavior under the confinement of side and bottom walls. The present simulations correspond to their case where the confinement due to the bottom wall is negligible. The computational model of Brandao and Mahesh (2022) that treats vapor as a passive scalar in an incompressible liquid is extended to account for multiple groups of bubbles of different sizes, effectively making it a polydisperse model. This allows us to investigate the effects of water quality on inception. The simulations include two different freestream nuclei distributions that are taken from the water tunnel data of Khoo et al. (2020c). It was found that inception is strongly dependent on the amounts of nuclei in the freestream. When the flow is depleted of nuclei, inception is an intermittent event confined to a location very close to the hydrofoil tip. However, when the flow is rich in nuclei, a larger portion of the tip vortex cavitates, as well as part of the suction side very close to the leading edge of the hydrofoil. Probability density functions revealed that cavitation occurs in any region experiencing a pressure field lower than vapor pressure when the flow is rich in nuclei, while extremely low values of pressure (usually kPa of tension) are required to make a flow depleted of nuclei cavitate. The topology of a flow poor in nuclei was investigated and inception was found to occur in regions dominated by irrotational straining with high stretching rates. Lagrangian statistics showed that as Re is increased, nuclei have higher likelihood of experiencing very low pressure fields. However, the amount of time they are subject to very low pressures is also shorter with increasing Re.

A Neural Network-Based Flame Structure Feature Extraction Method for the Lean Blowout Recognition

A flame’s structural feature is a crucial parameter required to comprehensively understand the interaction between turbulence and flames. The generation and evolution processes of the structure feature have rarely been investigated in lean blowout (LBO) flame instability states. Hence, to understand the precursor features of the LBO flame, this work employed high-speed OH-PLIF measurements to acquire time-series LBO flame images and developed a novel feature extraction method based on a deep neural network to quantify the LBO features in real time. Meanwhile, we proposed a deep neural network segmentation method based on a tri-map called the Fire-MatteFormer, and conducted a statistical analysis on flame surface features, primarily holes. The statistical analysis results determined the relationship between the life cycle of holes (from generation to disappearance) and their area, perimeter, and total number. The trained Fire-MatteFormer model was found to represent a viable method for determining flame features in the detection of incipient LBO instability conditions. Overall, the model shows significant promise in ascertaining local flame structure features.

Incipient fault detection and condition assessment in DFIGs based on external leakage flux sensing and modified multiscale poincare plots analysis

Abstract Although doubly fed induction generators (DFIG) are widely used, difficulties in early fault detection and severity assessment for inter-turn short-circuit (ITSC) faults are highly prominent. In this manuscript, a novel incipient fault detection and state assessment method based on external leakage flux sensing and modified multiscale poincare plots (MMSPP) is proposed. An external leakage flux sensor is placed on the axial-end position of the generator to monitor the presence and evolution of ITSC faults. Multiscale poincare mapping is a novel nonlinear tool that is further developed and modified using the normal cumulative distribution function and multiscale computing methods to capture the behavior evolution and changes in the generator’s external leakage flux signals. The healthy indicator is based on the analysis of elliptical orbit features extracted from MMSPP, established by support vector data description with parameter optimization. The effectiveness of the proposed method was implemented and verified under an experimental environment on a 100 kW DFIG platform to detect incipient inter-turn short circuits (mainly considering the two-turn ITSC) and evaluate the performance degradation (three- to eight-turn ITSC) with 0%, 50%, and 100% different load conditions. The experimental results showed the viability of the approach and fault indicator for incipient fault detection and condition assessment of the wind generator’s low inter-turn insulation faults and for relative quantification of ITSC fault severity.

Vibro-Acoustic Responses and Pressure Signal Analysis for Early Surge Detection in a Turbocharger Compressor

Abstract High-speed centrifugal compressors may be exploited to pressurize fuel cell systems. Nonetheless, due to fuel cells significant interposed volumes, compressor behavior can lead to severe vibrations related to fluid-dynamic instabilities during part load operating conditions. In particular, surge strongly limits centrifugal compressors stable operating region when moving toward low mass flow rates due to a change in system working point. Therefore, compressor dynamic response must be adequately characterized for early surge detection. To this aim, a dedicated experimental activity was conducted on a vaneless diffuser turbocharger coupled to a solid oxide fuel cell emulator plant; compressor evolution toward surge was investigated. Several signal processing techniques were applied to pressure signals as well as vibro-acoustic responses to better predict compressor behavior and classify its status as stable or unstable. Cepstrum, cross-correlation, and wavelet transform have been identified as suitable techniques to define precursors able to early detect surge. By means of cross-correlation function, propagation phenomena in the ducts can be investigated to assess how they interact near compressor low-mass flowrate unstable conditions. Cepstrum provides a convenient way to determine pressure signal spectrum distortion in terms of further periodic components onset. These harmonic components are due to complex system responses generated by transient phenomena; indeed, cepstrum allows to identify hidden anomalous contributions in system response spectra which may arise in incipient surge conditions. Wavelet transform was performed on both structural and pressure response signals to observe their dominant energy contents temporal evolution; indeed, such spectral pattern time-dependent variation can detect the rise of unstable conditions. By exploiting all these techniques, a complete system identification is performed which allows a deeper investigation of the physical phenomena involved; moreover, a more complete set of surge precursors extracted from different probes' physical signals were defined. The results obtained provide original diagnostic insights for monitoring systems suited to perform early surge detection. Compressor instability prevention can extend its operating range, performance, and reliability to allow better integration with other plant components. Finally, cepstrum application for compressor instability identification can be regarded as a novel method in the fluid machinery field.

Shields Diagram and the Incipient Motion of Microplastic Particles.

Incipient motion conditions for 57 regular (spheres, cylinders, disks, square plates, cubes, square prisms, rectangular prisms, tetrahedrons, and fibers) and eight irregular microplastic particle groups, having various sizes and densities, are investigated in a circular flume. The present data set is combined with additional data from the literature and systematically analyzed. A new framework is developed for predicting incipient motion conditions for foreign particles, accounting for variations in static friction, hydraulic roughness, and hiding-exposure effects. Via this framework, incipient motion conditions for microplastic particles lying on a sediment bed are, for the first time, reconciled with the classical Shields diagram.

A new lower Turonian mosasaurid from the Western Interior Seaway and the antiquity of the unique basicranial circulation pattern in Plioplatecarpinae

We describe and name a new mosasaur taxon, Sarabosaurus dahli gen. et sp. nov., from the lower Turonian part of the Tropic Shale in Utah, USA. The holotype specimen preserves significant portions of the skull and axial postcranial skeleton. It was found in the upper part of the Watinoceras devonense Ammonite Zone, bounded by radioisotopic dates above and below, and is thus about 93.7 Ma, the oldest mosasaurid taxon known from the Western Interior Seaway. The new taxon possesses a vascular pattern of the basisphenoid heretofore only seen in late diverging plioplatecarpine mosasaurids. Reevaluation of the morphology of the basisphenoid of previously described Turonian mosasaurs using μCT techniques reveals the derived condition is also present in Yaguasaurus and the incipient condition in Tethysaurus and Russellosaurus. In these two taxa, the canals enter the basisphenoid, but do not pass into the basioccipital. Instead, they exit only high on the posterior wall of the sella turcica, in a position similar to the basilar artery of other lizards. This vascular pattern, both in its incipient and derived states, is unique among squamates and supports inclusion of the aforementioned taxa in a monophyletic Plioplatecarpinae, for which we provide an emended diagnosis. Phylogenetic analysis recovers Sarabosaurus dahli gen. et sp. nov. as the sister taxon to Yaguarasaurus and all other later diverging plioplatecarpines, with Russellosaurus and Tethysaurus as successive sister taxa. Tylosaurine mosasaurids retain the primitive condition of the basisphenoid vascularization pattern and implies a tylosaurine-plioplatecarpine divergence in the late Cenomanian or earliest Turonian.

From empirically to physically based early warning predictions of rainfall-induced landslides in silty volcanic soils: the Lattari Mountains case study

The work proposes a procedure to build an early warning predictive tool to assess the occurrence of rainfall-induced landslides in silty volcanic covers. The procedure combines both an empirically and a physically based tool used sequentially: the former is designed to be calibrated using older, highly sized and coarser rainfall data, and the latter to interpret recent and finer weather data. Both approaches need to be informed by a common experimental reference summarising the rainfall history, the rainfall point, defined as the couple made of antecedent 4-month rainfall cumulative value (C4m) and last-persistent event (CPLE). The empirical approach aims to identify if, in the (C4m–CPLE) plane, the rainfall point falls in a ‘safe’ or ‘potentially unsafe’ zone where the two distinct regions are built by interpreting rainfall data associated or not with landslide events. In the physically based approach, evaporation and runoff are estimated to refine the assessment of ‘effective’ rainfall points. The resulting transformed rainfall point (C′4 m, C′PLE) is turned into a prediction of the suction level at the mid-depth assumed as a ‘reference’ for the entire cover. Such value is compared with a suction threshold empirically defined. Suction levels prediction is developed by computing in the C′4 m–C′PLE plane the iso-suction lines generated by several rainfall scenarios. The accuracy of the developed procedure is comparable with state-of-the-art literature or operational approaches, properly identifying landslide case events and minimising the number of false alarms. Furthermore, it can inform the preparedness stages more effectively, explicitly accounting for the antecedent slope wetness stage and how it could be far from the incipient slope failure conditions. The developed procedure takes into account the effects of evaporation and antecedent rainfalls that, in dry periods, lead to very dry conditions in the subsoil, making even significant rainfall events inconsequential. Conversely, other procedures already operating in LEWS or highly considered literature background overestimate the effects of rainfalls during dry periods. The developed procedure delivers a simple but robust way to derive landslide thresholds based on the interpretation of past rainfall histories. At the same time, literature methods often require sophisticated approaches to retrieve thresholds.

Incipient detection of bearing fault using impulse feature enhanced weighted sparse representation

The bearing fault impact impulses induced by the contact between components with drawback, is difficult to be detected at sprouting stage due to the interference of background noise, harmonics, random shocks, etc. In this paper, an impulse feature enhanced weighted sparse representation (IFEWSR) algorithm is proposed to accurately detect the weak bearing fault impact feature from incipient stage condition monitoring (CM) signal. Firstly, a modified fault period estimation method is presented to improve the robustness and reduce the computational complexity of recently proposed algorithms. Secondly, a novel weighting strategy on wavelet coefficients, indicated by the period-assisted corelated kurtosis of envelope spectrum (CKSES), is presented to denote the contribution of subband signals for sparse representation calculation framework. In addition, the mean normalized energy-weight deviation (MNEWD) rule is proposed to evaluate the performance of the weighting algorithm on subband signals which is blank at present. Thirdly, a novel fault feature enhancement technique is developed to better capture the bearing fault feature information. The effectiveness and superiority of the proposed method are proved by simulation and experiments. Results show that the proposed IFEWSR method provides higher accuracy for incipient fault feature extraction and outperforms other state-of-the-art methods.

Characterization of transonic shock oscillations over the span of an OAT15A profile

The flow over a wing model with aspect ratio 2 and based on the supercritical airfoil (OAT15A) was experimentally investigated for a fixed Reynolds number (Re_textrm{c}) of 3times 10^{6} and numerous aerodynamic conditions. The angle of attack (AOA) and the Mach number (M_mathrm {infty }) were varied between 5^{circ } and 6.5^{circ }, and between 0.72 and 0.75, respectively. Here we focused on the dynamics of the shock front at incipient and developed buffet conditions, by employing background-oriented schlieren measurements on the wing’s upper surface. The spanwise variations of the shock front statistics and its frequency content were examined. The shock oscillations appeared to be the superposition of multiple fluid modes, of which the most dominant was the classic 2-D buffet, which induced uniform chordwise oscillations of the shock front. The hypothesis was formulated that the remaining modes are linked to physical phenomena reported in the literature, namely the side-wall boundary layer and the vortices detected in the mid-span separated flow.

Chalcolithic copper production and use in the western end of the Iberian Peninsula: The testimony of Castro de Chibanes (Portugal)

Recent archaeological excavations identified a prehistoric occupation at Castro de Chibanes (Setúbal Peninsula, Portugal) displaying ceramic crucibles and metal artefacts in stratigraphic levels assigned to 2500–1900 cal BC. Apart from basic tools such as flat axes and awls, the collection includes ceramic crucibles, with emphasis to an uncommon example with a pouring lip and four feet. The studied set was completed with metal prills and artefacts from neighbouring Chalcolithic settlements of Rotura and Pedrão. The studied collection was characterised by chemical and microstructural techniques (p-EDXRF, micro-PIXE, optical microscopy and SEM-EDS). Overall, the results point to a local production of copper with variable arsenic contents, agreeing with the composition of artefacts (Cu with 0.14 to 4.4 wt% As), whose post-casting manufacture included hammering and annealing (recrystallized grains and annealing twins), although with incipient conditions that prevented a full compositional homogenisation. These results were compared with the Chalcolithic metallurgy of southwestern Iberian Peninsula, allowing to integrate the Setúbal Peninsula region into a wider context of metal production and use during the 3rd millennium BC. Finally, a supposed Bell Beaker “tanged dagger” was found to be composed by a leaded bronze alloy with a worked microstructure exhibiting Cu-Fe sulphides with high Se contents. The contradiction between analytical features and ancient chronology led to a revision of the typology and chronology of this bronze, showing the importance of the integration of analytical and archaeological research.

Experimental investigation on the vibrational and fluid dynamics behaviour of a turbocharger compressor in the transition to surge operation

High-speed dynamic centrifugal compressors are widely used both in the modern internal combustion engine design and in advanced pressurized cycles and innovative plant layouts as fuel cell systems. Surge strongly limits the stable operating region of centrifugal compressors in low mass flow rate conditions especially during fast transients. Therefore, it is of great importance to investigate transient system dynamic response of compressor surge evolution and early detection of incipient compressor surge. A specific experimental investigation on compressor surge was carried out at the University of Genoa turbocharger test facility and results are presented and analysed in this paper. The activity consists of steady state and transient measurements used to characterize and identify compressor behaviour in correspondence of surge inception conditions. The frequency and time frequency data analysis have been applied on inflow pressure, anemometric and vibrational signals to identify their contents and so to be able to classify compressor operation as stable or unstable. Synchronous averages performed in the time domain have been identified as a suitable algorithmic tool to detect incipient surge conditions. Anemometric signal analysis allowed to identify intermitting phenomena in deep surge conditions may be related to the rise of a rotation stall condition. The obtained results provide original diagnostic and predictive methods to be integrated in a monitoring system capable of preventing surge and extending compressor operating range, performance and reliability to allow the integration with the other plant components.

Evolution process and mechanism of mid-channel bars composed of different bed materials in the Upper Jingjiang Reach after the Three Gorges Project operation

三峡及上游梯级水库群运用后,大坝下游江心洲以冲刷为主,直接影响分汊河段河势条件及航道边界的稳定性。本文采用卫星遥感影像、实测水沙及固定断面床沙级配等资料,分析上荆江枝江、沙市河段中不同河床组成江心洲的演变过程及其机理。结果表明:①三峡水库蓄水后(2003-2019年),沙市段沙质江心洲较枝江段卵石夹沙质江心洲萎缩更为显著,出露面积的减幅分别达31%和24%。②以关洲和金城洲分别代表卵石夹沙质和沙质江心洲,三峡工程运用后关洲洲头形态较为稳定,受无序采砂的影响其沙质组成的洲尾面积显著减小,而金城洲面积萎缩程度更大。③床沙组成对江心洲冲刷程度差异具有重要影响,关洲洲头较金城洲抗冲性更强,与其床沙在年内达到起动条件的数量更少、时长更短有关;建立了江心洲面积与水流冲刷强度及相对水深的定量关系,该关系能综合考虑水沙变化与床沙组成调整的影响,能更好地反演近期江心洲的面积变化特点。;After the operation of the Three Gorges cascade reservoirs (TGP), the mid-channel bars (MCBs) downstream of the dam were generally scoured and shrank, which directly affects the river regime in ana-branching reaches and the stability of the navigation channel boundaries. The morphological evolution processes and mechanisms of MCBs in the Zhijiang (ZJ) and Shashi (SS) sub-reaches of the Upper Jingjiang Reach were analyzed, using the remote sensing images, the hydrological data and the measured riverbed compositions. The results indicate that: (i) During the post-TGP period (2003-2019), the sandy MCBs in the SS subreach shrank more significantly than the one in the ZJ subreach. The total exposed area of the former decreased by 31%, while the latter decreased by 24%; (ii) Guanzhou (GZ) and Jinchengzhou (JCZ) were taken as the representative sandy-gravel and sandy MCBs, respectively. During the post-TGP period, the head zone of the GZ MCB was relatively stable, and the reduced area was mainly in the bar-tail zone due to the illegal sand mining, while the JCZ MCB had a more obvious erosion trend; (iii) The bed-material composition had an important influence on the erosion degree of MCBs. The GZ MCB had a stronger anti-erosion capacity than the JCZ MCB, which was related to the less amount and duration of bed material that can reach the incipient condition in a hydrological year. Moreover, different empirical relationships were developed between the exposed area of MCB, fluvial scour intensity, and relative water depth. It is found that comprehensive consideration of the effects of flow-sediment condition and bed-material composition adjustment can better explain the recent variations in the exposed areas of MCBs.

Comprehensive Model for the Synthesis of γ-Al2O3 Microsphere-Supported Bimetallic Iron- and Copper Oxide Materials.

The effects of incipient wetness impregnation synthesis conditions on the macro- and microscopic properties of bimetallic iron oxide/copper oxide@γ-Al2O3 microspheres were elucidated. The key steering factors for the macroscopic distribution of the metals throughout the support, and for the metal nanoparticle sizes, were the pH of the impregnation solution, the counterions present in the metal precursor, the amount of negatively charged groups on the alumina, the complexation of iron, the impregnation strategy (simultaneous or sequential) and, in the latter case, the order of impregnation. The interactions taking place during impregnation are identified as competitive adsorption of charged dissolved species (Fe/Cu cations, protons, and additional anions) in the impregnation solution. Adsorption can take place on either charged alumina sites or previously deposited metal (i.e., iron on iron, copper on copper, iron on copper, and copper on iron) and is affected by counterion shielding. Modeling of these interactions via simulation on an in-house-developed python code allowed quantification of the adsorption constants for each of the above-mentioned processes, where iron adsorbs much faster than copper on all surfaces, and adsorption of iron on both alumina surface groups and previously deposited copper contributes majorly to the final iron distribution. The findings in this work will allow for better prediction and control over bimetallic materials synthesized via the simple and scalable impregnation procedure.