Bulk Equivalence Research Articles

Comparative study on the effect of chitosan, chitosan nanoparticles, and SiO2 loaded chitosan for the consolidation of the painted stone

The mural paintings are prone to deterioration due to surface powdering, cracking, and loss of painted layers, so coating the mural paintings with eco-friendly benign materials is urgent for consolidation and restoration purposes. Minimizing particle size to the nanoscale results in better properties compared to their bulk equivalents. This paper discussed the utilization of chitosan (Cs), chitosan nanoparticles (CsNPs), and silica-loaded chitosan (SiO2@CsNPs) to improve the consolidation of the painting surfaces on the facade of Neb-Maat-Ra's palace gate, which is a monument to King Ramesses IX (1125–1107 BC) in Egypt. Biopolymers are eco-friendly materials and considered an effective alternatives to synthetic coatings in the consolidation of cultural heritage. Cs has the potential to be a substitute for conserving well-painted paintings and stone, the presence of amino groups in chitosan's structure confers high biological activity and reactivity. CsNPs are more attractive compared to bulk chitosan, moreover, the incorporation of silica (SiO2) into CsNPs created good hydrophilic/hydrophobic balance and enhanced the mechanical scrub resistance. Digital Microscope, Scanning Electron Microscopy (SEM), Portable X-Ray Fluorescence Spectrometer (pXRF), (FTIR ATR), and Colorimetric measurements were used in performing the study. X-ray fluorescence was utilized to determine the compounds used in the facade of Neb-Maat-Ra's palace gate. Limestone served as the support, and hematite was used to create red pigment. The results showed that CsNPs and SiO2@CsNPs were superior to traditional Cs, however, the best result was observed for SiO2@CsNPs. Our study revealed the potential of CsNPs and SiO2@CsNPs in the protection of the facade of Neb-Maat-Ra, the son of King Ramesses.

Dynamical Systems Characterisation and Reduced Order Modelling of Thermoacoustics in a Lean Direct Injection (LDI) Hydrogen Combustor

Abstract In this study, the thermoacoustic instabilities of partially premixed hydrogen flames in a lean direct injection (LDI) multi-cluster combustor are characterised using dynamical systems theory. The combustor is operated at a range of bulk velocities (30 - 90 m/s) and equivalence ratios(0.2-0.6), and time-resolved pressure oscillations and integrated OH* chemiluminescence measurements were taken. The thermoacoustic system reveals a variety of dynamical states in pressure such as period-1 Limit Cycle Oscillation (LCO) with a single characteristic frequency, period-2 LCO with two characteristic frequencies, intermittent, quasi-periodic and chaotic states as either bulk velocity or equivalence ratio is varied. At a bulk velocity of 30 m/s, as the equivalence ratio is gradually decreased from 0.6 to 0.2, the dynamical behaviour follows a sequence from an intermittent state to a period-1 LCO, then to a quasi-periodic state, and eventually reaches a chaotic state. As the equivalence ratio is decreased for a bulk velocity of 60 m/s, the pressure oscillations evolve from a period-2 LCO to quasi-periodic state before flame blows off. The emergence of period-2 and quasi-periodic states indicates the presence of strong non-linear interactions among the cavity acoustic modes. The emergence of period-2 and quasi-periodic states indicates strong non-linear interactions among the cavity acoustic modes. These modes and their spatial behaviour are investigated using a Helmholtz solver, showing that hydrogen flames can excite a wide range of cavity acoustic modes

Dielectric breakdown and sub-wavelength patterning of monolayer hexagonal boron nitride using femtosecond pulses

Hexagonal boron nitride (hBN) has emerged as a promising two-dimensional (2D) material for many applications in electronics and photonics. Although its linear and nonlinear optical properties have been extensively studied, the interaction of hBN with high-intensity laser pulses, which is important for realizing high-harmonic generation, creating deterministic defects as quantum emitters, and resist-free patterning in this material, has not been investigated. Here we report the first systematic study of dielectric breakdown in chemical vapor deposition (CVD)-grown hBN monolayers induced by single femtosecond laser pulses. We report a breakdown fluence of 0.7 J cm−2, which is at least 7× higher than that of other monolayer 2D materials. A clean removal of hBN without leaving traces behind or causing lateral damage is demonstrated. The ablation features exhibit excellent fidelity with very small edge roughness, which we attribute to its ultrahigh fracture toughness due to its heterogeneous nature with three-fold symmetry. Moreover, even though defects are known to be abundant in CVD-grown hBN, we show experimentally and theoretically that its nonlinear optical breakdown is nearly intrinsic as defects only marginally lower the breakdown threshold. On top of this, we observe that hBN monolayers have a 4–5× lower breakdown threshold than their bulk equivalent. The last two observations can be understood if the carrier generation in monolayers is intrinsically enhanced due to its 2D nature. Finally, we demonstrate laser patterning of array of holes and lines in hBN with sub-wavelength feature sizes. Our work advances the fundamental knowledge of light-hBN interaction in the strong field regime and firmly establishes femtosecond lasers as novel and promising tools for resist-free patterning of hBN monolayers with high fidelity.

Effect of surface wettability on specific heat capacity of nano-confined liquid

Equilibrium Molecular Dynamics (EMD) simulations are carried out to investigate the effects of wall wettability and nanogap thickness (h) on the constant volume molar heat capacity (Cv) of liquid argon entrapped between two solid copper walls at a fixed temperature of 100 K. Lennard-Jones (LJ) potential is employed to model the interaction between atoms, with nanogap thickness (h) varying between 0.585 nm to 5.85 nm. To characterize interfacial surface wettability as hydrophobic or hydrophilic, the solid-liquid interaction potential has been altered, and its effect on molar heat capacity (Cv) has been evaluated. Simulation results reveal three key findings. As the surface becomes more hydrophobic (i) both maximum heat capacity (Cv,max), and critical nanogap thickness (hc) (nanogap thickness at which maximum heat capacity is obtained) decrease; (ii) the range of nanogap thickness where the heat capacity of nanoconfined liquid surpasses that of bulk liquid diminishes; (iii) the heat capacity of nanoconfined liquid tends to match its bulk equivalent. This anomalous behavior of heat capacity with changing wall wettability is explained by variation in both vibrational (mode of phonon transportation) and configurational (density oscillation near the wall, thermal boundary resistance, molecular mobility, etc.) contribution of nanoconfined liquid.

Rheological Properties of Ionically Crosslinked Viscoelastic 2D Films vs. Corresponding 3D Bulk Hydrogels.

Ionically crosslinked hydrogels containing metal coordination motifs have piqued the interest of researchers in recent decades due to their self-healing and adhesive properties. In particular, catechol-functionalized bulk hydrogels have received a lot of attention because of their bioinspired nature. By contrast, very little is known about thin viscoelastic membranes made using similar chelator-ion pair motifs. This shortcoming is surprising because the unique interfacial properties of these membranes, namely, their self-healing and adhesion, would be ideal for capsule shells, adhesives, or for drug delivery purposes. We recently demonstrated the feasibility to fabricate 10 nm thick viscoelastic membranes from catechol-functionalized surfactants that are ionically crosslinked at the liquid/liquid interface. However, it is unclear if the vast know-how existing on the influence of the chelator-ion pair on the mechanical properties of ionically crosslinked three-dimensional (3D) hydrogels can be translated to two-dimensional (2D) systems. To address this question, we compare the dynamic mechanical properties of ionically crosslinked pyrogallol functionalized hydrogels with those of viscoelastic membranes that are crosslinked using the same chelator-ion pairs. We demonstrate that the storage and loss moduli of viscoelastic membranes follow a trend similar to that of the hydrogels, with the membrane becoming stronger as the ion-chelator affinity increases. Yet, membranes relax significantly faster than bulk equivalents. These insights enable the targeted design of viscoelastic, adhesive, self-healing membranes possessing tunable mechanical properties. Such capsules can potentially be used, for example, in cosmetics, as granular inks, or with additional work that includes replacing the fluorinated block by a hydrocarbon-based one in drug delivery and food applications.

Toxicity evaluation of iron oxide nanoparticles to freshwater cyanobacteria Nostoc ellipsosporum.

The extensive usage of iron oxide nanoparticles (FeO NPs) in commercial and biomedical applications raises the risk of releasing their remains into the aquatic ecosystems and this could possibly cause cytotoxic effects on aquatic organisms. Thus, the toxicity assessment of FeO NPs on cyanobacteria, which are primary producers at the bottom of food chain in aquatic ecosystems, is essential to gain information about the potential ecotoxicological threat on aquatic biota. The present study investigated the cytotoxic effects of FeO NPs on Nostoc ellipsosporum using different concentrations (0, 10, 25, 50 and 100mg L-1) to track the time-dependent and dose-dependent effects and compared with its bulk equivalent. In addition, the impacts of FeO NPs and bulk counterpart on cyanobacterial cells were assessed under nitrogen as well as nitrogen-deficient conditions, because of ecological role of cyanobacteria in nitrogen fixation. The study revealed that the highest protein content was observed in the control in both types of BG-11 media compared to treatments of nano and bulk particles of Fe2O3. A 23% reduction in protein in nanoparticle treatment and a 14% reduction in bulk treatment at 100mg L-1 was observed in BG-11 medium. At same concentration, in BG-110 media, this decline was even more intense with 54% reduction in nanoparticle and a 26% reduction in bulk. Catalytic activity of catalase and superoxide dismutase was found to be linearly correlated with the dose concentration for nano and bulk form in BG-11 as well as BG-110 media. The increased levels of lactate dehydrogenase act as biomarker of the cytotoxicity brought on by nanoparticles. Optical, scanning electron, and transmission electron microscopy all demonstrated the cell entrapment, nanoparticle deposition on the cell surface, cell wall collapse and membrane degradation. A cause for concern is that nanoform was found to be more hazardous than bulk form.

Photocatalytic degradation and electrochemical energy storage properties of CuO/SnO2 nanocomposites via the wet-chemical method

Integrating semiconducting functional materials is a way to enlarge the photoexcitation, energy range, and charge separation, greatly elongating the photocatalytic efficiency to enhance the chemical and physical properties of the materials. This work depicts and investigates the impact of cuprous oxide (CuO) and tin dioxide (SnO2)-based catalysts with various CuO concentrations on photocatalytic and supercapacitor applications. Moreover, three distinct composites were made with varied ratios of CuO (5, 10, and 15% wt. Are designated as AT-1, AT-2, and AT-3) with SnO2 to get an optimized performance. The photocatalytic properties indicate that the CuO/SnO2 nanocomposite outperformed its bulk equivalents in photocatalysis using Methyl blue (MB) dye in a photoreactor. The results were monitored using a UV–visible spectrometer. The AT-1 ratio nanocomposite displayed 96% photocatalytic degradation compared to pure SnO2 and CuO. CV analysis reveals a pseudocapacitive charge storage mechanism from 0.0 to 0.7 V in a potential window in an aqueous medium. The capacitive performance was also investigated for all electrodes, and we observed that a high capacitance of 260/155 F/g at 1/10 A/g was attained for the AT-1 electrode compared to others, specifying good rate performance.

A Comprehensive Review of Nanomaterials: Types, Synthesis, Characterization, and Applications

Nanotechnology has infiltrated all sectors due to its unique and evident impacts, which give the scientific community numerous breakthroughs in the medical, agricultural, and other domains. Nanomaterials (NMs) have risen to prominence in technological breakthroughs due to their adjustable physical, chemical, and biological characteristics and superior performance over bulk equivalents. NMs are divided into many categories based on size, composition, capping agents, form, and origin. The capacity to forecast NMs' unique features raises the value of each categorization. As the manufacturing of NMs and industrial uses grow, so does their demand. The purpose of this review is to compare synthetic and naturally occurring nanoparticles and nanostructured materials to determine their nanoscale characteristics and to identify particular knowledge gaps related to the environmental application of nanoparticles and nanostructured materials. The paper review includes an overview of NMs' history and classifications and the many nanoparticles and nanostructured materials sources, both natural and manufactured. Furthermore, the many applications for nanoparticles and nanostructured materials.

Solid-State Preparation of Metal and Metal Oxides Nanostructures and Their Application in Environmental Remediation.

Nanomaterials have attracted much attention over the last decades due to their very different properties compared to those of bulk equivalents, such as a large surface-to-volume ratio, the size-dependent optical, physical, and magnetic properties. A number of solution fabrication methods have been developed for the synthesis of metal and metal oxides nanoparticles, but few solid-state methods have been reported. The application of nanostructured materials to electronic solid-state devices or to high-temperature technology requires, however, adequate solid-state methods for obtaining nanostructured materials. In this review, we discuss some of the main current methods of obtaining nanomaterials in solid state, and also we summarize the obtaining of nanomaterials using a new general method in solid state. This new solid-state method to prepare metals and metallic oxides nanostructures start with the preparation of the macromolecular complexes chitosan·Xn and PS-co-4-PVP·MXn as precursors (X = anion accompanying the cationic metal, n = is the subscript, which indicates the number of anions in the formula of the metal salt and PS-co-4-PVP = poly(styrene-co-4-vinylpyridine)). Then, the solid-state pyrolysis under air and at 800 °C affords nanoparticles of M°, MxOy depending on the nature of the metal. Metallic nanoparticles are obtained for noble metals such as Au, while the respective metal oxide is obtained for transition, representative, and lanthanide metals. Size and morphology depend on the nature of the polymer as well as on the spacing of the metals within the polymeric chain. Noticeably in the case of TiO2, anatase or rutile phases can be tuned by the nature of the Ti salts coordinated in the macromolecular polymer. A mechanism for the formation of nanoparticles is outlined on the basis of TG/DSC data. Some applications such as photocatalytic degradation of methylene by different metal oxides obtained by the presented solid-state method are also described. A brief review of the main solid-state methods to prepare nanoparticles is also outlined in the introduction. Some challenges to further development of these materials and methods are finally discussed.

Structure and magnetic state of hydrothermally prepared Mn-Zn ferrite nanoparticles

Magnetic behaviour of nanoparticles deviates from their bulk equivalents not only due to finite-size and surface effects but it may be also affected by occurrence of metastable states, such as non-equilibrium cation distribution. The chemical composition along with the specific cation distribution are decisive for magnetic properties of spinel ferrites, the nanoparticles of which can be easily tailored to exhibit peculiar properties suitable for various applications. The present study is devoted to hydrothermally prepared MnZn ferrite nanoparticles; namely to five samples with approximate composition Mn1−xZnxFe2O4, where x = 0.21–0.63, that were prepared by a surfactant-free hydrothermal procedure at a rather low temperature of 180 °C. XRD measurements evidenced the cubic spinel structure and a gradual decrease of the mean crystallite size from 14 to 10 nm with increasing zinc content, which was further confirmed by TEM analysis. 57Fe Mössbauer spectroscopy and temperature-variable magnetic measurements provided valuable insight into the blocking behaviour of particles on two dramatically different time scales and demonstrated that Néel relaxation can be enhanced by increasing the zinc content. Nanoparticles of the selected composition Mn0.62Zn0.41Fe1.97O4 were subjected to neutron diffraction study at 2 K to determine the ferrimagnetic order and in combination with Mössbauer spectroscopy to analyse the cation distribution. The non-zero occupancy of Zn2+ in octahedral sites evidenced a metastable distribution, and the supplemental DFT study revealed that the distribution of Mn2+ is non-equilibrium as well.

Experimental investigation on spark ignition of a staged partially premixed annular combustor

In this paper, the ignition transient process is experimentally investigated on a staged partially premixed annular combustor. This work focuses on the impact of bulk velocity and equivalence ratio on light-round speed and characteristic of flame propagation during light-round process. The set-up consists of two concentric transparent torus quartz walls and it is equipped with an air-curtain anti-pollution reflector above the combustor tilts at a 45° angle from the vertical, which allows visualization of the flame from both the side and the top of the combustor. High-speed images of the spontaneous flame emission with 5 kHz from the top view and 10 kHz from the side view are recorded. Image edge detection technology is used to analyze the flame front and leading point dynamics. Radial and azimuthal oscillations of the leading point trajectory indicate that there are the wrinkled turbulent flame fronts. The large span of flame fragment azimuthal propagation is due to swirling air in the combustor. It is found that the light-round process can be decomposed into three different distinct phases according to the light-round speed. The figures of light-round time and speed against equivalence ratio illustrate that bulk velocity and equivalence ratio play a positive role in light-round process under certain conditions (stochastic zone, linear descent zone). It is also confirmed that the ignition process is significantly impacted by the spray characteristics. The results presented in this paper bring new insights into the ignition of realistic gas turbine with centrally-staged combustor.

Experimental investigation on the flame propagation pattern of a staged partially premixed annular combustor

The transient ignition process of a staged partially premixed low-emission annular combustor was investigated experimentally in this paper. This study focused on the mechanism of injector-to-injector flame propagation. For various overall equivalence ratios and bulk velocities, a side visualization of the spreading flame captured by 10 kHz high-speed imaging technology during the light-round process illustrated that flame propagation from injector to injector presents three typical modes: spanwise-upstream, archlike-entrainment, and spanwise-entrainment, instead of following a purely azimuthal direction. The detailed processes of flame propagation with the various modes were analysed based on the flow field and spray patterns. Three schematic diagrams for the injector-to-injector flame propagation modes were established. The injector-to-injector flame propagation mode is dependent on the bulk velocity and equivalence ratio, which have a critical impact on the flow field and spray pattern as well as the subsequent flame morphology of the dome.

Experimental and Numerical Analysis of Gas Premix Turbulent Flames Stabilized in a Swirl Burner With Central Bluff Body

Abstract Lean premixed gas turbulent flames stabilized in the flow generated by an industrial swirl burner with a central bluff body are experimentally found to behave bistable. This bistable behavior, which can be triggered via a small change in some of the controlling parameters, for example, the bulk equivalence ratio, consists in a rather sudden transition of the flame from completely lifted to well attached to the bluff body. This has impact on combustion dynamics, emissions, and pressure losses. While several experimental investigations exist on this topic, numerical analysis is limited. This work is therefore also of numerical nature, with a twofold scope: (a) simulation and validation with experiments of the bistable flame behavior via computational fluid dynamics (CFD) in the form of large eddy simulation (LES) and (b) analysis of CFD results to shed light on the flame stabilization properties. LES results, in case of the lifted flame, show that the vortex core is sharply precessing at a given frequency. Phase averaging these results at the frequency of precession clearly indicates a counterintuitive and unexpected presence of reverse flow going all the way through the flame apex and the bluff body tip. The counterintuitive presence of a lifted flame is explained here in terms of the phase averaged data, which show that the flame apex is not placed at the center of the spinning reverse flow region. It is instead slightly shifted radially outward where the axial velocity recovers to low positive values of the order of the turbulent burning rate. A simple one-dimensional flame stabilization model is applied to explain this peculiar flame behavior. This model provides first an estimation of the flame radius of curvature in terms of axial velocity and turbulence quantities. This radius is therefore used to determine the total flux of reactants into the flame, given by an axial convection and radial diffusion contributions. Subsequently, the possibility of the flame positioned at the center of the vortex is excluded based on the balance between this flux and the turbulent burning rate. A clear explanation of the mechanism leading to the sudden flame jump has instead not been identified and only some hypotheses are provided.

Preharvest application of salicylic acid induces some resistant genes of sweet pepper against black mold disease

Pepper fruits are subjected to various postharvest diseases such as black mold caused by Alternaria alternata. The efficacy of exogenous applications of salicylic acid (SA) in bulk and nanoscale forms to control the black mold was studied. In vitro studies revealed that both SA bulk materials and SA nanoparticles (SANPs) at 1.4 mM significantly suppressed the growth of A. alternata, yet SANPs showed a higher suppressive effect compared to SA bulk equivalent. Examinations using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed hyphal and conidial deformations in addition to changes in cellular structure of A. alternata when treated with both forms of SA at 1.4 mM concentration. The preharvest spraying of SANPs at 1.4 mM displayed the highest significant suppression of disease severity under artificial inoculation and natural infection of pepper fruits. The efficiency of SA bulk materials and SANPs as elicitors to stimulate the innate immune responses in pepper plants were also investigated. The basic PR-1 gene (CaBPR1), beta-1, 3-glucanase (CaBGLU) and peroxidase (CaPO1) defense-related genes showed upregulation expression in leaves of pepper plants treated by both forms of SA. The expression of the three studied genes was affected by SA concentrations. Levels of expression of PR-1, β-1, 3-glucanase and peroxidase genes were the highest (8.8, 8.1 and 7.2 fold change, respectively) in pepper tissues treated with SANPs at 1.4 mM. This study contributes to our understanding of the potential use of SA nanoparticles as a safe strategy to inhibit the fungal infection.

Graphene to Advanced MoS2: A Review of Structure, Synthesis, and Optoelectronic Device Application

In contrast to zero-dimensional (0D), one-dimensional (1D), and even their bulk equivalents, in two-dimensional (2D) layered materials, charge carriers are confined across thickness and are empowered to move across the planes. The features of 2D structures, such as quantum confinement, high absorption coefficient, high surface-to-volume ratio, and tunable bandgap, make them an encouraging contestant in various fields such as electronics, energy storage, catalysis, etc. In this review, we provide a gentle introduction to the 2D family, then a brief description of transition metal dichalcogenides (TMDCs), mainly focusing on MoS2, followed by the crystal structure and synthesis of MoS2, and finally wet chemistry methods. Later on, applications of MoS2 in dye-sensitized, organic, and perovskite solar cells are discussed. MoS2 has impressive optoelectronic properties; due to the fact of its tunable work function, it can be used as a transport layer, buffer layer, and as an absorber layer in heterojunction solar cells. A power conversion efficiency (PCE) of 8.40% as an absorber and 13.3% as carrier transfer layer have been reported for MoS2-based organic and perovskite solar cells, respectively. Moreover, MoS2 is a potential replacement for the platinum counter electrode in dye-sensitized solar cells with a PCE of 7.50%. This review also highlights the incorporation of MoS2 in silicon-based heterostructures where graphene/MoS2/n-Si-based heterojunction solar cell devices exhibit a PCE of 11.1%.

An experimental examination of the role of turbulence on flame impingement heat transfer

Turbulence induced by actuators has been widely utilized as a effective means to enhance jet impingement heat transfer (JIHT). Flame impingement heat transfer (FIHT) has parital similarity to JIHT, and thus it is of interest to investigate the role of an actuator-induced turbulence to flame combustion as well as its FIHT. On a Bunsen burner that is incorporable with a ring-type turbulence actuator, a detailed experimental comparison of the flame appearance, reaction zone structure, thermal field and heat transfer of both laminar and turbulent flames under identical bulk flow conditions and equivalence ratios were conducted.Results show that the turbulent flame has a narrower stable-operation range than the laminar couterpart, and thus turbulence reduces the flame stability. A major difference between two flames exists at the reaction zone, which is identified to be a ‘brush’ structure in the turbulent case, instead of being a perfect cone in the laminar case. The flame brush changes the heat release behavior such that the temperature field of the turbulent flame shows lowered peak temperature while enlarged high-temperature zone. The changed heat release or temperature field reults in distinct local heat fluxes in the impinging flames at the stagnation region and near wall jet region. Consequently, the overall heat transfer rate of the turbulent flame becomes higher than the laminar flame. Accordingly, this study proposes that the actuator turbulence can be utilized as a useful technique to promote FIHT.

Experimental assessment of the lean blow-off in a fully premixed annular combustor

The behaviour of the flame in an annular combustor with multiple bluff-body injectors with swirl was investigated to provide insights into lean blow-off (LBO) mechanisms when flames interact. Two different configurations, with 12 and 18 burners, and various bulk velocities and equivalence ratios were tested. Flame shape and main features were studied by means of 5 kHz OH∗ chemiluminescence imaging and the stability limits were identified and compiled into stability regime diagrams. As the equivalence ratio of the mixture was reduced the individual flames would first exhibit a transition from a stable “W-shape” state to a stable “V-shape” state before becoming unstable close to extinction. In the 18-burner configuration LBO was characterised by random detachment and re-stabilisation of the flames over multiple burners across the chamber, until complete lift-off. In the 12-burner configuration the flame anchors on a few burners in azimuthally symmetric locations, making the overall flame less prone to global extinction. Finally, the stability curves were computed using a correlation based on the Damkhöler (Da) number and compared to single burner configurations. The beginning of the blow-off transient was found to be similar to the LBO condition for a single burner in the 12-burner setup, while the 18-burner configuration was less stable for all the conditions investigated. However, it was found that correlations based on single burner extinction data do not fully work for the extinction of interacting flames. The results provide insights into the blow-off of realistic gas turbine engines and can be used for validating models of such processes.

The Electrochemical and Mechanical Behavior of Bulk and Porous Superelastic Ti‒Zr-Based Alloys for Biomedical Applications.

Titanium alloys are well recognized as appropriate materials for biomedical implants. These devices are designed to operate in quite aggressive human body media, so it is important to study the corrosion and electrochemical behavior of the novel materials alongside the underlying chemical and structural features. In the present study, the prospective Ti‒Zr-based superelastic alloys (Ti-18Zr-14Nb, Ti-18Zr-15Nb, Ti-18Zr-13Nb-1Ta, atom %) were analyzed in terms of their phase composition, functional mechanical properties, the composition and structure of surface oxide films, and the corresponding corrosion and electrochemical behavior in Hanks’ simulated biological solution. The electrochemical parameters of the Ti-18Zr-14Nb material in bulk and foam states were also compared. The results show a significant difference in the functional performance of the studied materials, with different composition and structure states. In particular, the positive effect of the thermomechanical treatment regime, leading to the formation of a favorable microstructure on the corrosion resistance, has been revealed. In general, the Ti-18Zr-15Nb alloy exhibits the optimum combination of functional characteristics in Hanks’ solution, while the Ti-18Zr-13Nb-1Ta alloy shows the highest resistance to the corrosion environment. The Ti-18Zr-14Nb-based foam material exhibits slightly lower passivation kinetics as compared to its bulk equivalent.

Experimental study on the excitation of thermoacoustic instability of hydrogen-methane/air premixed flames under atmospheric and elevated pressure conditions

The current work examines the excitation of thermoacoustic instability of lean premixed hydrogen-methane/air low swirl flames under both atmospheric and elevated pressure conditions (up to 0.3 MPa). Under a given pressure condition, The tests were conducted at different bulk velocities (U), hydrogen proportions (ηH), and equivalence ratios (Ф). Results show that thermoacoustic instability can be excited by increasing one of these variables while keeping others the same. It was found that pressure elevation has a minor effect on the oscillation frequency. Moreover, it was demonstrated that the current instability is induced by large coherent structures. The effect of pressure elevation on the excitation of thermoacoustic instability is found to be Φ dependent. As indicators of the flame response to impinging vortices, the curvature and local flame surface area features were calculated with images captured with the planar laser-induced fluorescence of the OH radical (OH-PLIF) method. Results demonstrate a great similarity between the flame front evolution and the instability trend, implying that the effect of the chamber pressure on the instability trend can be indicated by the change in the flame front curvature and local flame surface area.

Impact of (nano)formulations on the distribution and wash-off of copper pesticides and fertilisers applied on citrus leaves

Environmental contextThere are great concerns around current wide usage of copper-based agrochemicals. We compare the fate of nano- and conventional forms of copper, in particular their resistance to wash-off by rain (rainfastness), following their application to citrus leaves. Results showing large differences between the formulations in the amount and forms of copper washed from the leaves provide essential information to optimise agrochemical efficacy while minimising the environmental impact. AbstractThis study compares the rainfastness of nine forms of Cu, including nano and conventional Cu-based fungicide formulations, as well as their salt or bulk equivalents. Rainfastness is the ability to resist wash-off; it is a key property for improving pesticide formulations and for assessing the potential transfer of pesticides to the soil. A new protocol was developed to characterise losses of Cu from treated leaves. It consisted of dipping the leaves in rainwater and then in an acid/ethanol mixture followed by size fractionation. The proportion of Cu lost by wash-off from citrus leaves ranged from <2% (Tribasic, nCuO or Cu(OH)2) up to 93% (CuSO4) of the initial amount of Cu applied. Intermediate Cu losses were observed for formulations with silica (nano)particles (9–14% of applied Cu), Kocide (22%), ChampDP (31%), and a formulation with graphene oxide (47%). Smaller particles generally resulted in less wash-off, possibly due to stronger attachment to the leaf surface, but other factors such as the particle shape and solubility also played an essential role. The retention of nCuO to the leaves was particularly high, and the exact mechanisms involved (e.g. foliar uptake) deserve further work. Most of the Cu was washed off in its ionic form (>74%). Two Cu formulations (one commercial formulation and the formulation with graphene oxide) also showed wash off in significant proportions of Cu (~17%) in the nano-sized fraction. This study provides essential information on the amounts and forms of Cu that may reach the soil after the application of Cu-based agrochemicals. The great diversity in behaviour across the range of formulations considered highlights the need for more systematic research to fully exploit the potential improvements of current agrochemicals through (nano)formulation technologies.