Heterogeneous Nucleation Research Articles

Microstructural behavior of mortars containing thermo-activated crushed demolition residue (TCDR)

The construction industry has been constantly expanding and is, consequently responsible for a high consumption volume of natural raw materials and for generating large amounts of waste. In detriment of this scenario, this research proposes the reuse of Construction and Demolition Waste (CDW), especially that from plaster for making mortars. The residue was thermo-activated at 650 °C for a period of 2h, a heating rate of 10 °C/min, it was crushed in a jaw crusher and passed through an ABNT N° 16 sieve. The mortars were prepared with a (cement:sand) ratio of 1:6 by mass, the sand was partially replaced by the residue in proportions of 0, 10, 20 and 30%, using Ordinary Portland Cement (OPC). Tests were carried out on consistency index, mass density, incorporated air content, isothermal calorimetry, water retention, mass density in the hardened state, flexural strength, compressive strength, water absorption and void index, in addition to testing techniques characterization, such as laser granulometry, pozzolanic activity using the Modified Chapelle method and Lúxan method, X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) as well as Mercury Intrusion Porosimetry (MIP). It was possible to observe that the residue has amorphous phases, through XRD and heterogeneous nucleation of smaller particles, proven by the calorimetry test, contributing to the increase in mechanical strength. The results indicate that the mixture with 30% replacement achieved a greater increase in mechanical strength, lower absorption rates and consequently, a reduction in the distribution of pore sizes.

Excellent combination of strength and ductility in austenitic lightweight steel achieved by warm rolling process

In this study, warm rolling was applied to Fe–28Mn–11Al–1C–5Ni (wt.%) austenitic lightweight steel, which realized the higher dislocation density and finer dislocation-cell structures, achieving a better mechanical properties with ∼2.0 GPa of yield strength and ∼6.8 % of total elongation than cold rolling in the same conditions. In the subsequent partial recrystallization condition, the numerous dislocations and substructures existed in warm rolled steel provide more heterogeneous nucleation sites for grain refinement, resulting in the ultrafine-sized austenite and B2 with the size of 0.36 μm and 0.24 μm, respectively. Combined with grain refinement strengthening, solid solution strengthening, precipitation strengthening, and dislocation strengthening in the unrecrystallized austenite, the present steel shows an ultimate tensile strength of 1734 MPa, a uniform elongation of 21.7 % and a specific tensile strength of 267 MPa g−1 cm3. Such an excellent combination of strength and ductility induced by simple warm rolling and annealing is much better than previously reported for lightweight steels.

Improvement in microstructure and mechanical properties of wire arc additively manufactured 7075 aluminum alloy via adjusting TiC particle addition

7075 aluminum alloys with varying TiC particle additions were fabricated by simultaneously depositing a standard 7075 wire and a TiC treated wire at different wire feed speed ratios. The effects of TiC content on the microstructure and mechanical properties of 7075 alloy were investigated. Results indicated that the addition of TiC particles can effectively refine the grain structure through heterogeneous nucleation, and the grain refinement effect was enhanced with increasing TiC particle content in the range of 0–0.70 wt%. Moreover, TiC particles can restrain the continuous distribution of second phase at grain boundaries. TiC particles tended to cluster at grain boundaries as its content exceeded 0.48 wt%, which adversely affected their beneficial effect on the improvement of mechanical properties. At an optimal TiC content of 0.48 wt%, the tensile strength and elongation in the horizontal direction exhibited remarkable enhancements of 27.2% and 319%, respectively, compared to those without the addition TIC particle.

A biodegradable ZnFe2O4/PLLA electrospun fibers based longitudinal mode piezoelectric membrane for health monitoring

Recently, multifunctional sensors based on piezoelectric active film fabricated with environmental friendly materials is a nascent field which can address the growing concern of electronic waste. Nevertheless, frequently utilized poly(vinylidene fluoride) (PVDF) and poly(L-lactic acid) (PLLA) encounter challenges of limited biocompatibility and weak piezoelectricity with low shear piezoelectric coefficient (d14), respectively. Accordingly, a biodegradable piezoelectric sensor comprising of PLLA nanofiber blended with ZnFe2O4 nanoparticles was developed in this work. The ZnFe2O4 nanoparticles served as heterogeneous nucleation center leading to improved piezoelectric coefficient and output than pure PLLA due to more consistent orientation of CO dipoles. The ZnFe2O4/PLLA film exhibited significant performance improvement featured with 1.7-fold higher longitudinal piezoelectric coefficient (d33 ∼ 6.5 ± 0.3 pm/V), nearly 250 % boosting on the output voltage. The ZnFe2O4/PLLA piezoelectric sensor induced high sensitivity (2–10 N:0.55 V/N; 10–32 N:0.29 V/N) and excellent mechanical stability for 27,000 cycles. The results of the soil burial experiment demonstrate that the film can degrade by over 75 % within 90 days, confirming its excellent biodegradability. Moreover, the ZnFe2O4/PLLA nanofibers based piezoelectric sensor could serve as effective detection evidenced by different output signals of head motion, pulse and artery beating demonstrating its feasible application for health monitoring. Considering the characteristics of straightforward fabrication and readily accessible sustainable materials, the ZnFe2O4/PLLA sensor provides an appealing eco-friendly solution for self-powered flexible personal devices disregarding the need to dispose of electronic waste.

Revealing the heterogeneous nucleation mechanism of Mg17Al12 on impurity Mg2Si particles in commercial AZ31 alloy

Silicon (Si) is an inevitable impurity element in the AZ31 alloy. In this study, the Si impurity was detected mainly as fine Mg2Si particles dispersed widely within the central region of the Mg17Al12 phase. During the solidification process, the Mg2Si particle precipitates at about 565 °C, before the Mg17Al12 phase of 186 °C, potentially acting as the heterogeneous nucleation core for the Mg17Al12 phase. The orientation relationship between Mg2Si and Mg17Al12 was investigated using the edge-to-edge matching model (E2EM) calculations, which showed a misfit of only 0.1 %. This low misfit suggests that Mg2Si can serve as a heterogeneous nucleation site for Mg17Al12. The surface and interface structures of Mg2Si (220) and Mg17Al12 (332) were constructed, and then investigated through the first-principles calculation. The theoretical results indicate that Mg and Al are easily adsorbed on the surface of Mg2Si, with Al showing higher adsorption energy than Mg. Furthermore, the interface between Mg2Si and Mg17Al12 exhibits favorable thermodynamic stability. Combined with experiments and theoretical calculations, it is confirmed that the Mg2Si particles, formed due to the Si impurity, provide effective heterogeneous nucleation sites for the Mg17Al12 phase.

Silk sericin-coated polyamide thin-film composite membranes to simultaneously improve anti-scaling properties, long-term storage, and waste-to-resource recovery

A polyamide thin-film composite (PA-TFC) membrane, which is one of the widely used for desalination and water softening processes, features a lot of carboxyl groups inevitably formed by hydrolysis of unreacted acyl chlorides after interfacial polymerization. However, since carboxyl groups interact with multivalent cations and thereby cause membrane scaling, it is desirable to reduce the density of carboxyl groups on the membrane surface. In this regard, silk sericin (SS) can be an excellent alternative to modifying the surface characteristics to mitigate scaling because it has various hydrophilic amino acids with a much lower density of carboxyl groups per unit mass. Given the properties, we prepared anti-scaling TFC membranes by coating SS on the PA active layer. According to the result, the SS-PA-TFC (16.4% decrease) significantly reduced the flux decline to half of the PA-TFC (36.7% decrease) during the 48-h scaling test under the condition for heterogeneous gypsum crystal nucleation. More importantly, the comparison of operation duration until cleaning obviously revealed the anti-scaling properties of the SS-PA-TFC, which was evidenced by about 7.5 times longer duration than the PA-TFC. Furthermore, the cyclic scaling test in 19 mM CaSO4 showed that the SS-PA-TFC (3.6%) could decrease the irreversible fouling to about one-fifth of the PA-TFC (15.9%). This outstanding anti-scaling performance of the SS-PA-TFC stemmed from the less negatively charged (‐40.8 and ‐28.1 mV for the PA-TFC and SS-PA-TFC, respectively) and much more hydrophilic surface (52.2° and 18.2° for the contact angles of the PA-TFC and SS-PA-TFC, respectively). Suprisingly, the above-mentioned anti-scaling properties of the SS-PA-TFC membrane were achieved without the trade-off between water flux and salt rejection thanks to a very thin SS coating layer (ca. 16 nm). Apart from the anti-scaling properties, SS coating also improved long-term storage and waste-to-resource recovery.

Microstructure and mechanical property improvement of concurrent wire-powder feeding laser melting deposition Ti-6Al-4V via TiC addition

Wire-feed laser metal deposition (LMD-W) offers a high deposition rate and low cost, making it an effective solution for reducing costs and enhancing efficiency in manufacturing large-scale titanium aerospace components. Currently, the material used for LMD-W is typically a single alloy wire, which limits the flexibility and functionality of manufacturing composite materials. This work employed a novel concurrent wire-powder feeding laser metal deposition (LMD-WP) process to manufacture TiC/Ti-6Al-4V composite. In the LMD-WP method, Ti-6Al-4V wire was fed laterally, while TiC particles were delivered coaxially. Only 1.0 wt% TiC particles were added to prevent excessive TiC, which could cause stress concentration and increase crack sensitivity. The microstructure and mechanical properties of Ti-6Al-4V alloy and TiC/Ti-6Al-4V composite were investigated. The results indicate that with coaxial TiC particle addition, the α-Ti in TiC/Ti-6Al-4V is noticeably refined. Additionally, in situ TiC acts as heterogeneous nucleation sites, restricting α-Ti growth and reducing its aspect ratio. Furthermore, TiC particles weakened the α-Ti texture in the (0001) and (11–20) directions. Moreover, adding TiC particles significantly enhanced tensile strength, with the yield strength reaching 950 MPa and the ultimate tensile strength reaching 1048 MPa. Compared to Ti-6Al-4V alloy fabricated by LMD-W, this represents an increase of 11.25% and 10.72%, respectively. The improvement in tensile properties is principally ascribed to grain boundary strengthening, Orowan strengthening and dislocation density strengthening. This work introduces an innovative approach and abundant data for the additive manufacturing of TiC/Ti-6Al-4V composite with high efficiency and low cost.

Effect of N on microstructure, nucleation mechanism and mechanical performance of (Ti, Nb) C particles in Fe-based composite coating via plasma spray welding

Compared with the coating of Ti-Nb-C system, the coating of Ti-Nb-C-N system shows better mechanical properties, especially wear resistance. Therefore, this investigation was focus on the in-situ (Ti, Nb) C reinforced Fe-based composite coatings (D1 composite coatings) and in-situ (Ti, Nb) (C, N) reinforced Fe-based composite coatings (D2 composite coatings) which were created on high strength steel via plasma spray welding (PSW) technology in the environment with nitrogen and without nitrogen, respectively. The two coatings were compared to explore nucleation mechanism of nitrogen on (Ti, Nb) C particles, grain size, particle morphology and the influence on the mechanical performance of coatings. The findings showed that the changes in the typical microstructure morphology and the shape of the reinforced particles of the two coatings were not obvious. However, the heterogeneous nucleation sites of (Ti, Nb) C were provided by introducing nitrogen. In addition, the introduction of nitrogen could refine the grains of D1 composite coatings. As a result, the average grain size of D1 composite coatings decreased by an order of magnitude, and the crystal orientation of the grains in the composite coatings showed better isotropy. The average microhardness of D2 composite coatings was 967.52 HV1, which was 1.5 times of the average microhardness of D1 composite coatings. The wear loss of D2 composite coatings was 0.4 mg, which was only half of that of D1 composite coatings (0.8 mg).

Understanding condensation halo growth on superhydrophobic surfaces: Insights from a vapor diffusive model

Anti-icing technologies are vital across various sectors, from transportation to energy systems. In this study, we investigate the formation of condensation halos during the process of condensation–freezing on superhydrophobic surfaces. Experimental tests were conducted on metallic nanostructured superhydrophobic surfaces, where droplet icing was induced and observed under controlled conditions. The formation of condensation halos, characterized by the sudden appearance and subsequent vanishing of microdroplets around the freezing droplets, was captured and analyzed. A vapor diffusive model coupled with heterogeneous nucleation theory was developed to understand and quantify the growth of condensation halos. The model considers vapor diffusion around the icing droplet and the critical vapor pressure required for nucleation. Experimental observations and theoretical predictions demonstrated a strong dependence of condensation halo size on the icing droplet radius. The study sheds light on the mechanisms underlying condensation halo formation and provides insights into the intricate interplay between droplet size, surface properties, and environmental conditions in condensation–freezing phenomena, offering valuable perspectives for the development of effective anti-icing strategies.

Understanding heterogeneous nucleation and predicting grain size in wire and arc additive manufacturing of steels with inoculation

Understanding heterogeneous nucleation and predicting grain size in wire and arc additive manufacturing of steels with inoculation

Atomic-scale heterointerfacial engineering of multilayered structures in Fe-Cr-based alloys revealed through LRLM model and its modified model

Two Fe-Cr-based alloy foils, denoted as Y2 and MY1 samples, were prepared, as well as transmission electron microscope (TEM) was used to investigate the atomic matching and orientation relationships (ORs) across the interfaces in these samples. From the analyses of the interfaces, the ORs and atomic matching modes between adjacent phases are revealed. Furthermore, the reconstructed multilayer models for each interface have been established on the basis of the ORs, and it is found that the formation of stable interfaces is conductive to the nucleated phases nucleating on the surfaces of the substrates. As for the OR verification, parallel ORs are verified effective through long-range lattice matching (LRLM) model, while non-parallel OR is verified through modified LRLM model. Finally, the sequential atomic heterogeneous nucleation behaviors of TiN and δ-Fe originated from Mg- /Y-bearing oxides have been reconstructed.

The role of symmetric tilt grain boundaries on the precipitation of hydrides in zirconium: A molecular dynamics study

Zirconium (Zr) alloys are widely used as structural materials in the core of nuclear reactors. However, the absorption of hydrogen by these alloys during the reactor operation may lead to the precipitation of hydrides. Such hydrides have considerable effects on the microstructure and mechanical properties of the alloys, thus significantly impacting their overall performance. In this work, we investigate the behavior of hydrogen in the presence of symmetric tilt grain boundaries in Zr using molecular dynamics simulations. To systematically explore the conditions for the formation of hydrides, we consider hydrogen concentration levels of up to 50 at.%. We find that hydrogen concentrations of 30 at.% or lower are below the threshold for the precipitation of hydrides, while fcc coordinated hydrides precipitate at 50 at.%, which is very close to the solubility limit of hydrogen in Zr at 800 K. We find that the grain boundaries (GBs) play a pivotal role in the behavior of hydrogen, as well as the formation of hydrides in Zr systems. In most cases, large amounts of hydrogen are found to accumulate at GBs. However, both homogeneous and heterogeneous nucleation are observed during the formation of hydrides at the grain interiors and GBs, respectively. Nonetheless, in some cases the GB inhibit the formation of hydrides.

Microstructure evolution and property regulation of CoCrNiNbx laser cladding coatings

The influence of different Nb on the microstructure evolution, properties of the CoCrNi laser cladding coatings was investigated. With the increase of Nb addition, the eutectic structures showed a transition from planar crystals to cellular crystals to dendritic crystals. Besides, the eutectic lamellae gradually became dense. A large amount of Ni3Nb-HCP structure precipitates were precipitated in the coatings with excessive Nb. The introduction of Nb brought about an increase in heterogeneous nucleation cores, which in turn significantly refined the grain size in the secondary remelting zone of the cladding coating. As the Nb content increased, the hardness of coatings gradually increased, but both wear resistance and corrosion resistance showed a trend of first increasing and then decreasing.

In Situ Visual Observation of Surface Energy-Controlled Heterogeneous Nucleation of Metal Nanocrystals.

Electrochemical growth of metal nanocrystals is pivotal for material synthesis, processing, and resource recovery. Understanding the heterogeneous interface between electrolyte and electrode is crucial for nanocrystal nucleation, but the influence of this interaction is still poorly understood. This study employs advanced in situ measurements to investigate the heterogeneous nucleation of metals on solid surfaces. By observing the copper nanocrystal electrodeposition, an interphase interaction-induced nucleation mechanism highly dependent on substrate surface energy is uncovered. It shows that a high-energy (HE) electrode tended to form a polycrystalline structure, while a low-energy (LE) electrode induced a monocrystalline structure. Raman and electrochemical characterizations confirmed that HE interface enhances the interphase interaction, reducing the nucleation barrier for the sturdy nanostructures. This leads to a 30.92-52.21% reduction in the crystal layer thickness and a 19.18-31.78% increase in the charge transfer capability, promoting the formation of a uniform and compact film. The structural compactness of the early nucleated crystals enhances the deposit stability for long-duration electrodeposition. This research not only inspires comprehension of physicochemical processes correlated with heterogeneous nucleation, but also paves a new avenue for high-quality synthesis and efficient recovery of metallic nanomaterials.

Pore-Scale Study on the Effect of SO2 on Hydrate-Based CO2 Sequestration in a High-Pressure Microfluidic Chip

Summary To mitigate the effects of greenhouse gases, the sequestration of greenhouse gases such as carbon dioxide (CO2) in seafloor sediments in the form of hydrates has become a safe and efficient method. If sulfur dioxide (SO2), one of the flue gas impurities, is also sequestered, the cost of CO2 purification and sequestration can be effectively reduced. However, there is a lack of in-situ observation of how SO2 affects the nucleation and growth process of CO2 hydrates. In this study, a visual microfluidic chip combined with in-situ Raman spectroscopy was used for the first time to investigate the impact mechanism of SO2 on the nucleation and growth kinetics of CO2 hydrates in porous media. The results indicate that SO2 could promote the nucleation and growth of CO2 hydrate in the following aspects: First, the diffusion of SO2 in solution induces spontaneous convection of the solution in the pores, which could promote the nucleation of mixed hydrates. After nucleation, dissolved SO2 acts as a “seed” for hydrate formation, and the pore solution is covered with hydrate microcrystals, providing heterogeneous nucleation sites for hydrate growth in solution. During the growth stage, SO2 could induce the preferential growth of mixed hydrates within the solution and enhance the growth rate of hydrates, acting as a promoter of hydrate formation. As CO2-SO2 mixed hydrates preferentially grow in solution and grow denser, it could quickly cement the pores, which could significantly improve the stability of the reservoir and form a strong hydrate barrier in the reservoir. These findings have important theoretical value and guiding significance for the synchronous sequestration of CO2-SO2 by hydrates.

Optimizing the microstructure and enhancing the mechanical prsoperties of hypereutectic Al–Si alloys by Mg addition

The impact of Mg on the solidification structure of hypereutectic Al–Si alloys with different Si contents (15 wt% and 18 wt%) was investigated. 3%Mg was added to Al–15Si alloy to modify the phases in the solidification structure for the improvement of mechanical properties, and T6 heat treatment was used to optimize the microstructure and precipitate strengthening phase. The solidification structure was observed by OM and TEM respectively, and the precipitation behavior of each phase was detected through DSC. The results show that the addition of Mg decreased the undercooling of the alloy melt, thus suppressing the precipitation of primary Si phase. Nanoscale β” precipitates were precipitated in the matrix after T6 heat treatment. This resulted in an increase of 54% and 165% in the UTS and EL of the alloy, reaching 252 MP and 15.1%, respectively. Primary Si crystals were present in two forms in Al–18Si–8Mg alloy: spinel twin and non-twin, while Mg2Si always maintained the faceted crystals during the growing process, where only (100) and (111) crystal planes were observed. XRD, SEM and EBSD have been used to prove that Mg2Si crystals with different morphologies could become the heterogeneous nuclei of two types of primary Si crystals. The process of nucleation and growth of primary Si with Mg2Si as the heterogeneous nuclei was experimentally analyzed and theoretically predicted.

Improving the fatigue life of laser powder bed fusion Scalmalloy® by friction stir processing

A major concern about parts produced by laser powder bed fusion (L-PBF) are intrinsic defects or porosities that are difficult to overcome by simply optimizing the process parameters. As these defects and porosities play a crucial role in the mechanical behaviour, especially in fatigue, additive manufactured parts are often subjected to thermo-mechanical post-treatments. To this end, this work proves Friction Stir Processing (FSP) to be an effective post-treatment to drastically reduce the porosity level. FSP leads to an improvement of 60 % of the technical fatigue strength and by two orders of magnitude of the fatigue life of L-PBF Scalmalloy® specimens. The fatigue performances obtained on FSPed and heat-treated specimens are equivalent or even better than the best fatigue life reported in the literature, whatever their L-PBF conditions and post-treatments, while avoiding Hot Isostatic Pressing. However, FSP reduces the beneficial effect of the conventional strengthening heat-treatment applied to L-PBF Scalmalloy®, lowering the high tensile strength for which the alloy is normally reputed. Advanced characterisation by X-ray microtomography and Transmission Electron Microscopy allows us to reach a better understanding of the involved phenomena: drastic reduction of the biggest defects and heterogeneous nucleation of Sc- and Zr-rich precipitates on grain boundaries and dislocations.

Using MXene as a Chemically Induced Initiator to Construct High‐Performance Cathodes for Aqueous Zinc‐Ion Batteries

AbstractMXene usually exhibits weak pseudo‐capacitance behavior in aqueous zinc‐ion batteries, which cannot provide sufficient reversible capacity, resulting in the decline of overall capacity when used as the cathode materials. Taking inspiration from polymer electrolyte engineering, we have conceptualized an in situ induced growth strategy based on MXene materials. Herein, 5.25 % MXene was introduced into the nucleation and growth process of vanadium oxide (HVO), providing the heterogeneous nucleation site and serving as an initiator to regulate the morphology and structural of vanadium oxide (T‐HVO). The resulted materials can significantly improve the capacity and rate performance of zinc‐ion batteries. The growth mechanism of T‐HVO was demonstrated by both characterizations and DFT simulations, and the improved performance was systematically investigated through a series of in situ experiments related to dynamic analysis steps. Finally, the evaluation and comparison of various defect introduction strategies revealed the efficient, safety, and high production output characteristics of the in situ induced growth strategy. This work proposes the concept of in situ induced growth strategy and discloses the induced chemical mechanism of MXene materials, which will aid the understanding, development, and application of cathode in aqueous zinc‐ion batteries.

The impact of template effect at different temperatures on homocrystallization-to-stereocomplexation transformation in Poly(L-lactide)/Poly(d-lactide) racemic blends

Stereocomplexation, formed between enantiomeric poly(L-lactide) (PLLA) and poly(d-lactide) (PDLA), is 50 °C higher than the melting point of PLLA (or PDLA) homocrystallites (HCs). In a certain temperature range, stereocomplexation can induce homocrystallization-to-stereocomplexation (HC-to-SC) transformation through template effect. In this work, a series of temperature programs designed through differential scanning calorimetry (DSC) were used to study the impact of template effect at different temperatures (TH-S) on HC-to-SC transformation in PLLA/PDLA racemic blends. It was found that HCs can be efficiently converted to stereocomplex crystallites (SCs) through template effect when TH-S was 210 °C. When TH-S was 220 °C, SCs with large lamellar crystal thickness were obtained, which had a higher melting point, about 10 °C higher than the conventional SCs. At a TH-S of 230 °C, the melt-crystallization peaks of HCs and SCs were clearly observed during the DSC cooling process because PLLA/PDLA helical pairs were still retained in the PLLA/PDLA melt. The results demonstrated that the residual PLLA/PDLA helical pairs can accelerate remarkably the crystallization rate of SCs and generated new SCs due to template effect, and the new SCs significantly accelerated the crystallization rate of HCs resulted from the heterogeneous nucleation effect. Non-isothermal crystallization behavior of PLLA/PDLA racemic blends at different cooling rates was also studied. The results indicate that the lower cooling rate promotes SCs formation more strongly than the promotion effect on HCs.

Vapor bubble nucleation in flowing liquids

In this work, a stochastic diffuse interface model coupled with the Navier–Stokes equations has been exploited to numerically investigate vapor nucleation in a non-equilibrium system (a flowing liquid). Both homogeneous and heterogeneous nucleation is addressed and the influence of macroscopic flows on nucleation observables is discussed. The extended mesoscale simulations allow us to infer the spatial distributions of the nucleated bubbles via Voronoi tessellation analysis and to represent the nucleation phenomenon as a stochastic Random Poisson Point process. The findings open the way to design multiscale fluid simulations experiencing phase change.