Scale Growth Rate Research Articles

Insight into the fretting corrosion behavior of 316L steel in liquid lead-bismuth eutectic at 500°C

Due to flow induced vibration caused by coolant circulation, fretting corrosion inevitably occurs between fuel cladding, heat exchanger tubes and their holders in Gen IV lead-bismuth eutectic (LBE) cooled nuclear reactors. In the current work, fretting corrosion behavior of 316 L steel in oxygen-saturated LBE at 500 °C has been investigated. It is shown that within the gross slip regime, the microstructure under fretting interface presents a stratified structure, composed of third body layer, oxide scales and plastic deformation layer. At the early stage of fretting corrosion, the dominant damage mechanism is fretting wear, showing that the thickness of third body layer is much larger than that of oxide scale. As fretting time increases, the dominant damage mechanism is gradually changed to LBE corrosion and fretting wear together, as the visible oxide scale is formed next to the third body layer. Moreover, the growth rate of oxide scales under fretting interface is accelerated by over an order of magnitude compared to that when 316 L steel exposed to LBE directly. In particular, after 60 h exposure, the thicknesses of oxide scale related to the worn and unworn regions are ∼4.5 μm and ∼0.2 μm, respectively. The occurrence of such phenomenon is thought to be ascribed to the severe plastic deformation under fretting contact interface, since the crystal defects served as perfectional nano-channels can promote the diffusivity of oxygen atoms. In addition, the acceleration diffusivities of oxygen atoms caused by the local high contact stress may also be responsible for this matter.

The effect of Re and Hf interaction on the oxidation performance in ReHf co-doped NiAl coating

Re-NiAl, Hf-NiAl and ReHf-NiAl coatings were fabricated and the interaction of Re and Hf was investigated. Re and Hf segregated together in ReHf-NiAl coating, and the co-precipitations phase in ReHf co-doped coating were verified as Hf5Re24 and Hf5Al3 after annealing. The formation of these precipitations further slowed down the growth rate of oxide scales. The dispersion and refinement of Hf by Re prevented the formation of spinel. The interaction mechanism of Re and Hf during annealing and oxidation process were discussed.

Toroidal Alfvén mode instability driven by plasma current in low-density Ohmic plasmas of the spherical tori

Due to intrinsically low magnetic fields, at low density the drift speed of the current-carrying electrons in spherical tokamaks can exceed fraction of the Alfvén speed sufficient for the excitation of the Alfvén gap modes. A particular case of the toroidal mode, observed during minor disruptions in Ohmic shots on SUNIST [Liu et al., Phys. Plasmas 23, 120706 (2016)], is considered in the present communication. Due to the negligible effect of the electron pressure gradient, the growth rate scales linearly with the drift speed, with slope inversely proportional to electron thermal velocity. In the absence of continuum damping, the threshold value of the drift speed for TAE excitation is independent of electron temperature.

Contribution of Sc doping to the growth and adhesion of alumina scale on AlCoCrFeNi high-entropy alloy

Equimolar AlCoCrFeNi high-entropy alloy (HEA) often experiences serious oxidation degradation despite its superior mechanical properties at elevated temperatures. Herein, we reveal that minor Sc addition can enhance the oxidation resistance of AlCoCrFeNi HEA at 1100 °C, and the microstructure and oxidation properties for (AlCoCrFeNi)100−xScx HEAs (Sc-0, Sc-0.1, Sc-0.5 and Sc-1) are evaluated. Except for the original A2 + B2 phases, the Laves phase is found with increasing Sc addition. Moderate Sc addition is beneficial for interface adhesion by lowering the driving force for scale spallation and enhancing the interface toughness, and excessive Sc addition, however, results in serious internal oxidation due to the generation of Sc2O3 stringers as the high diffusivity paths for inward O ions. It is also proved that enhancing the interface toughness is more beneficial to improve the oxidation resistance compared to reducing scale growth rate. Our results can offer guidance for designing advanced alloys with excellent oxidation resistance.

Generating periodic vortex pairs using flexible structures

In fluid dynamics, a planar starting flow through a narrow slit gives rise to a distinctive fluid mass in the form of counter-rotating vortex pairs, which do not undergo any propulsive detachment, known as ‘pinch-off’, from the tip-attached fluid layer. Our study envisions instigating the ‘pinch-off’ phenomenon in these vortex pairs using flexible plates as the slit edges to enhance momentum transport and self-propagation. In this study, considering a flow evolution model, we show that the growth rate of such ejected vortex pair scales as proportional to the square root of time. Using flexible plates to form the slit, we unearth a critical plate flexibility case with the Cauchy number, Ca=0.01, which induces a ‘pinch-off’ of the resultant vortex pair, a phenomenon absent in the case of rigid plates. We observe a train of vortex pairs generating one after the other, and the time period closely matches the plates’ oscillation period as the plates’ oscillation frequency locks-in with the shedding frequency of the vortex pairs. The streamwise speed of the leading vortex pair varies non-monotonically with Ca, showing an increase in the speed up to Ca≈0.04, and thereafter decreased speed due to upstream propagation of small-sized vortices. The new insights into inducing and controlling vortex pair behaviours pave the way for innovative applications in fluid transport and advanced flow manipulation techniques.

Distributed Medical Data Storage Mechanism Based on Proof of Retrievability and Vector Commitment for Metaverse Services.

The metaverse is a unified, persistent, and shared multi-user virtual environment with a fully immersive, hyper-temporal, and diverse interconnected network. When combined with healthcare, it can effectively improve medical services and has great potential for development in realizing medical training, enhanced teaching, and remote surgical treatment. The metaverse provides immersive services for users through massive and multimodal data, and its data scale and data growth rate are bound to show exponential growth. Blockchain-based distributed storage is a fundamental way to keep the metaverse running continuously; however, many blockchains, such as Ethereum and Filecoin, suffer from low transaction throughput and high latency, which seriously affect the efficiency of distributed storage services and make it difficult to apply them to the metaverse environment. To this end, this paper first proposes a network architecture for distributed storage systems based on proof of retrievability to address the problem of centralized decision making and single point of access in centralized storage. The secure data storage of the metaverse health system is ensured. Secondly, we designed two data transmission protocols through vector commitment and encoding functions to achieve the transfer of time cost from the critical path to storage nodes and improve the efficiency of data verification between nodes as well as the scalability of the metaverse health system. Finally, this paper also conducts security analysis and performance analysis of the proposed scheme, and the results show that our scheme is secure and efficient.

(Invited) Pt-Modified Aluminide Coatings for Ni-Base Single Crystal Superalloy

Single phase (Ni,Pt)Al coating has been widely employed as state-of-the-art bondcoat for protecting hot-sectional components in commercial aero engines, especially for the parts made of Ni-base single crystal (SX) superalloys. For high temperature protective coating serving on SX superalloy, two interfaces are vitally essential for acquiring reliably long service life: the interface growing thermally-grown oxide (TGO) and the interface connecting coating and substrate alloy. Normally, the excellent performance of PtAl coating derives from high Al content and the incorporation of Pt, which ensures formation of exclusively adherent oxide scale, α-Al2O3. To further improve the performance of Pt-modified aluminide coating, in present study reactive elements are introduced using co-electroplating method. Compared with singular doping, co-doping of Hf-Y demonstrated superior oxidation resistance. The oxide scale growth rate and spallation tendency of Hf-Y co-doped (Ni,Pt)Al coating were much smaller, as well as the surface rumpling extent. Besides, the grain size of Hf-Y co-doped (Ni,Pt)Al coating was finer than that of Hf- or Y- doped coatings in as-received state, indicating the capability of grain refinement. With the benefits of RE co-doping, the desirably thin/smooth TGO is thus accessible for Pt-modified aluminide coatings. The other issue is the element interdiffusion at high temperature, which would affect the mechanical property of SX superalloy. According to Fick′s law of diffusion, J Al = - D Al · δμ Al / δ x ,to reduce diffusion coefficient ( D Al ) or chemical potential ( δμ Al / δ x ) would both decrease the diffusion extent ( J Al ). Therefore, two strategies are employed: adding a diffusion barrier between coating and substrate, or designing a γʹ-PtAl coating. The performance of these modified aluminide coatings are evaluated in high temperature oxidation test. At last, doping behavior of some elements were explained by First-Principle Calculations.

The scaling of elemental stoichiometry and growth rate over the course of bamboo ontogeny.

Stoichiometric rules may explain the allometric scaling among biological traits and body size, a fundamental law of nature. However, testing the scaling of elemental stoichiometry and growth to size over the course of plant ontogeny is challenging. Here, we used a fast-growing bamboo species to examine how the concentrations and contents of carbon (C), nitrogen (N) and phosphorus (P), relative growth rate (G), and nutrient productivity scale with whole-plant mass (M) at the culm elongation and maturation stages. The whole-plant C content vs M and N content vs P content scaled isometrically, and the N or P content vs M scaled as a general 3/4 power function across both growth stages. The scaling exponents of G vs M and N (and P) productivity in newly grown mass vs M relationships across the whole growth stages decreased as a -1 power function. These findings reveal the previously undocumented generality of stoichiometric allometries over the course of plant ontogeny and provide new insights for understanding the origin of ubiquitous quarter-power scaling laws in the biosphere.

Growth Simulations of Urban Underground Space with Ecological Constraints Using a Patch-Based Cellular Automaton

The growth simulation of urban underground space (UUS) under the consideration of ecological constraints can effectively reveal the characteristics and trends of UUS changes, and provide a basis for planning the construction of sustainable and livable ecological cities. Therefore, this study considers urban ecological space as a constraint mechanism for UUS development and conducts a simulation study of the dynamic and complex UUS growth process, with a view toward guiding UUS planning under a long-term overall vision. In this study, a patch-based cellular automaton (CA) model is constructed to simulate the dynamic and complex growth process of UUS, subject to the ecological constraints generated by the agent-based land allocation optimization model. The spatial drivers of UUS growth simulation are determined based on the Random Forest (RF) algorithm. The results of the research case in Tianfu New District, Chengdu City, demonstrate that UUS expansion with ecological constraints exhibits sustainable characteristics. However, the growth rate of the UUS development scale is significantly lower when ecological constraints are present compared to when they are not. This study’s results contribute to urban management by finding a balance between UUS development and ecological space conservation, and providing theoretical support for rational UUS planning and decision making in the construction of low-carbon cities.

Improving functional properties of protective coatings obtained by electrophoretic deposition on steel interconnects for solid oxide cells by tuning particle size distribution

This paper analyses the effect of particle size distribution in the suspension on the quality of the resulting coating in the electrophoretic deposition of a protective coating on a steel interconnect for solid oxide cells (SOCs). Mn1.5Co1.5O4 commercial powder was subjected to grinding for 2, 4 and 18 h, and admixing it with the finest fraction was used to form thin layers on Crofer 22APU steel. The functional properties of the coatings, such as density and area-specific resistance (ASR) were evaluated over the respective temperature ranges. The resistivity of the coatings was measured in 60 and 1000 h tests. It was shown that the increase of the fine powder fractions yields a higher density layer, which contributes to slowing down the growth rate of the oxide scale and therefore can decrease ASR by 65%. The lowest resistivity was performed by the samples fabricated with the admixed powder. Post-test analysis by FIB/SEM/EDS did not reveal diffusion of chromium through the fabricated layers (after the 1000 h test), which is a key indicator of the reliability of the formed protective barrier.

Effect of Pre-Heat-Treatment on the Oxidation Resistance of MCrAlY Coatings: A Review

High-performance gas turbines and aircraft engines necessitate MCrAlY (M = Ni, Co, or Ni/Co) coatings with exceptional oxidation resistance. Pre-heat-treatment can enhance the performance of MCrAlY bond coatings in the following ways: First, it reduces the porosity of the bond coating and promotes the diffusion of elements within it. Second, pre-heat-treatment allows for the formation of a continuous, dense, and moderately thick layer of pure Al2O3 scale, which helps to delay the formation of mixed oxides. Lastly, proper pre-heat-treatment can increase the grain size of the Al2O3 scale, leading to a lower growth rate of the oxide scale. Additionally, this article proposes new directions for developing more reasonable and effective pre-heat-treatment methods, laying the foundation for the creation of thermal barrier coatings (TBCs) with greater durability and higher performance.

The dynamics of debris streams from tidal disruption events: exact solutions, critical stream density, and hydrogen recombination

ABSTRACT A star destroyed by a supermassive black hole (SMBH) in a tidal disruption event (TDE) is transformed into a filamentary structure known as a tidally disrupted stellar debris stream. We show that when ideal gas pressure dominates the thermodynamics of the stream, there is an exact solution to the hydrodynamics equations that describes the stream evolution and accounts for self-gravity, pressure, the dynamical expansion of the gas, and the transverse structure of the stream. We analyse the stability of this solution to cylindrically symmetric perturbations, and show that there is a critical stream density below which the stream is unstable and is not self-gravitating; this critical density is a factor of at least 40–50 smaller than the stream density in a TDE. Above this critical density the stream is overstable, self-gravity confines the stream, the oscillation period is exponentially long, and the growth rate of the overstability scales as t1/6. The power-law growth and small power-law index of the overstability implies that the stream is effectively stable to cylindrically symmetric perturbations. We also use this solution to analyse the effects of hydrogen recombination, and suggest that even though recombination substantially increases the gas entropy, it is likely incapable of completely destroying the influence of self-gravity. We also show that the transient produced by recombination is far less luminous than previous estimates.

Experimental study on the scale inhibition effect of the alternating electromagnetic field on CaCO3 fouling on the heat exchanger surface in different circulating cooling water conditions

Scaling on the heat exchanger surface resulted in large equipment cleaning, maintenance expenses and safety issues in the industrial production. To remove the heat exchanger scaling, research on the scale inhibition effect of the alternating electromagnetic field on CaCO3 fouling on the heat exchanger surface with the selected four Mg2+/Ca2+ molar ratios in circulating cooling water. Four indicators, namely, heat transfer resistance, scale inhibition rate, the growth rate of CaCO3, and conductivity were discussed extensively. The experimental results demonstrated that remarkable scale inhibition effect occurs, when the Mg2+/Ca2+ molar ratios is 0 and 1:1.2 with 46.80% and 39.28% of the scale inhibition rate, respectively. Compared with the control group, the heat transfer resistance was decreased, the adherent scale growth rate was slowed down, and the rising stage time was shortened in the experiment group. In addition, the decreased of conductivity in the experiment group indicated that the alternating electromagnetic field promoted the crystallization in the solution. XRD and SEM analysis demonstrated that the alternating electromagnetic field and Mg2+ could promote aragonite crystallization, reduce the polymerization degree, and decrease the crystal particle size of CaCO3. Affecting the crystallization process of adherent scale and promoting the homogeneous precipitation of non-adherent scale in solution is the key to the alternating electromagnetic field scale inhibition technology. This study could provide a guidance for the parameter selection in electromagnetic field scale inhibition technology of industry application.

Remote Sensing Study of the Impact of Social-Economic Development on The Scale of Land Use in The Shaki District

The study investigates the changes in both the quantity and quality of land use in the Shaki district resulting from the increased level of social and economic development. Remote sensing was used to analyze the projects implemented under the State program 'Social and Economic Development of Regions,' assessing their impact on land use. The projects were categorized as either 'changing' or 'replacing,' based on their degree of impact, scale, and transformations between areas. The study also examined the population distribution by altitude zones and settlement levels. The satellite images were decoded and the land use areas were divided into classes. The level of land use between 2001 and 2020 was analyzed using the support vector machine (SVM) method to calculate the scale, difference, and regional growth rate of individual areas. The changes that occurred were identified and explained. Additionally, the transitions between categories were studied, the main changing and expanding areas were identified, and the increasing and decreasing tendencies between classes were examined.

Enhancing oxide scale growth and adhesion via electrochemically regulating ion diffusion

Pre-oxidation is a common surface treatment approach to enhance the corrosion resistance of metals, which suffers from slow ion diffusion kinetics, bad oxide scale adhesion, and weak compactness. Herein, we propose an electrochemical oxidation approach in molten carbonate to improve the oxide scale growth and adhesion via electrochemically regulating ion diffusion in the formed oxide scale. An anodic polarization applied at the metal substrate enlarges the chemical potential gradient of oxygen and offers a favorable electric field across the metal/oxide interface to the oxide scale/molten salt interface, thereby speeding up the oxide scale growth rate in terms of increasing the diffusion rate of metal cations and oxygen ions through the oxide scale. At the same time, the oxide scale adhesion is remarkedly improved because the metal vacancies at the oxide/alloy interface are filled by the newly formed oxide. After being treated by electrochemical oxidation, the corrosion rate of the Ni-16Fe-4Mo alloys in molten Li2CO3-Na2CO3-K2CO3 decreased ten-fold. Overall, electrochemical oxidation enables the rapid formation of an adherent and corrosion-resistant oxide scale on the metal substrate, offering a general and effective way to fabricate corrosion-resistant films to survive in various aggressively corrosive media.

The importance of grain boundaries on the reactive elements effect in β-NiAlHf alloy

Cyclic oxidation of single crystalline and polycrystalline β-NiAlHf alloy was investigated at 1200 °C. The effect of grain boundary on the role of reactive elements was discussed. The results indicate that Hf effectively reduced the oxide scale growth rate and enhanced the scale adhesion in polycrystalline NiAl. But the single crystalline NiAlHf exhibits a higher oxide scale growth rate, severer internal oxidation and catastrophic scale spallation. The absence of the grain boundary leads to the negative effects of Hf.

Simultaneously improving mechanical properties and oxidation resistance of Ti-bearing high-entropy superalloys at intermediate temperature via silicon addition

Ti-bearing high-entropy superalloys (HESAs) often suffer from severe intergranular embrittlement and terrible oxidation degradation at intermediate temperatures. Here we showcase that minor Si addition can effectively mitigate the intergranular embrittlement and improve the oxidation resistance of the a (Ni2Co2FeCr)92Ti4Al4 HESA at 700 °C simultaneously. Experimental analysis revealed that the intergranular G phase induced by 2 at% Si addition can effectively suppress the inward diffusion of oxygen along grain boundaries at 700 °C, thus enhancing the tensile ductility of the alloy from ∼8.3% to ∼13.4%. Besides, the 2 at% Si addition facilitated the formation of a continuous Al2O3 layer during oxidation, contributing to a remarkable reduction in the growth rate of the oxide scale to a quarter of the Si-free HESA. Our results demonstrate that Si can be a favorable alloying element to design advanced HESAs with synergistically improved thermal-mechanical performance.

Superior oxidation resistance of the chemically complex but structurally simple Ti-Al-Ta-Ce-Si-La-B-nitride

Alloying (Ti,Al)N with Ta, CeSi2 or LaB6 is beneficial for both hardness and thermal stability. Here we show that their different mechanisms allow for a cumulative improvement when alloyed together, which is especially pronounced for the oxidation resistance. During isothermal oxidation treatments in ambient air at 900 °C (for up to 25 h), Ti0.44Al0.44Ta0.12N allows for a parabolic scale growth rate constant kp of 6.039 × 10-5 µm2/s. This is reduced to 2.074 × 10-5 and even 0.399 × 10-5 µm2/s when alloying with 2 mol% CeSi2 respectively CeSi2 + LaB6 (1 mol% each). The oxide scale growth kinetics for the latter can be even better described by a logarithmic or cubic law. In the as-deposited state the CeSi2 and CeSi2 + LaB6 alloyed (Ti,Al,Ta)N are single-phase fcc structured providing an indentation hardness of 32.6 ± 1.5 and 37.8 ± 1.5 GPa, combined with an indentation modulus of 496 ± 22 and 496 ± 14 GPa, respectively. After vacuum-annealing at 1000 °C, their hardness is still 33.0 ± 1.6 and 34.8 ± 1.1 GPa, and noticeable formation of hexagonal AlN and TaNx phases can only be detected by X-ray diffraction when annealed at temperatures above 1200 °C.Using CeSi2 and LaB6 instead of their elemental form is furthermore beneficial for the target production itself, as Ce and La are highly reactive.

Effects of Y addition on the pre-oxidation and corrosion behaviours of the alumina/niobium aluminide coatings on the surface of niobium core

Y-modified alumina/niobium aluminide coatings were prepared on the surface of the niobium substrate by pack cementation and subsequent pre-oxidation treatments. The pre-oxidation behaviour of the Y-modified and undoped alumina/niobium aluminide coatings in the air atmosphere at 1300 ℃ and their corrosion behaviour in the molten DZ4125L superalloy at 1500 ℃ were investigated in this study. It was demonstrated that the Y addition could reduce the growth rate of the oxide scale, suppress the localised oxidation failure and improve the molten superalloy corrosion-resistance of the alumina/niobium aluminide coatings. The mechanism of Y modification has also been revealed.

Evolutionary scaling of maximum growth rate with organism size

Data from nearly 1000 species reveal the upper bound to rates of biomass production achievable by natural selection across the Tree of Life. For heterotrophs, maximum growth rates scale positively with organism size in bacteria but negatively in eukaryotes, whereas for phototrophs, the scaling is negligible for cyanobacteria and weakly negative for eukaryotes. These results have significant implications for understanding the bioenergetic consequences of the transition from prokaryotes to eukaryotes, and of the expansion of some groups of the latter into multicellularity. The magnitudes of the scaling coefficients for eukaryotes are significantly lower than expected under any proposed physical-constraint model. Supported by genomic, bioenergetic, and population-genetic data and theory, an alternative hypothesis for the observed negative scaling in eukaryotes postulates that growth-diminishing mutations with small effects passively accumulate with increasing organism size as a consequence of associated increases in the power of random genetic drift. In contrast, conditional on the structural and functional features of ribosomes, natural selection has been able to promote bacteria with the fastest possible growth rates, implying minimal conflicts with both bioenergetic constraints and random genetic drift. If this extension of the drift-barrier hypothesis is correct, the interpretations of comparative studies of biological traits that have traditionally ignored differences in population-genetic environments will require revisiting.