Number Density Of Clusters Research Articles

The evolution of precipitates in an Al–Zn–Mg alloy

The precipitation sequence in Al–Zn–Mg alloys has been subject to many revisions over the years as more structural details of the early-stage Guinier-Preston (GP) zones and precipitates have been uncovered. To further investigate this, a 7003 aluminium alloy naturally aged for one year was subjected to artificial ageing at 140 °C to investigate the evolution of early-stage precipitates. Scanning transmission electron microscopy was coupled with atom probe tomography and hardness measurements to characterise the precipitate structure and chemistry of the alloy at different stages in the heat treatment. The naturally aged condition contained a dense population of GPI zones, co-existing with a smaller distribution of η′ precipitates. After artificial ageing for 10 min, the hardness decreased from 121 HV to 88 HV. The number densities of clusters were similar in the two conditions, while the average size of the clusters had increased during the first 10 min of artificial ageing. The average Zn/Mg ratio of the clusters decreased from 2.0 to 1.7 and the clusters no longer exhibited the GPI zone atomic structure, indicating that the GPI zones had dissolved. Concurrently, the fraction of precipitates having η′ structure increased from 2% to 18%. During further ageing, the hardness increased again, reaching a peak after 5 h. In this condition, η′ was the dominant phase, co-existing with η1, η2 and T′ phases. Atomically resolved scanning transmission electron microscopy images in addition to precession electron diffraction patterns of the disputed T′ phase are presented and compared to literature.

Optical Breakdown on Clusters of Gas Nanobubbles in Water; Possible Applications in Laser Ophthalmology

Here we studied the regimes of optical breakdown in water, stimulated by nanosecond and picosecond laser pulses at a wavelength of 1064 nm. A distinctive feature of our theoretical model, confirmed in experiment, is that in our case the optical breakdown develops on heterogeneous centers-clusters of gas nanobubbles. To the best of our knowledge, this is the first study of the role of clusters of gas nanobubbles in the optical breakdown of liquids that are transparent to pump radiation. In the experiment described in this paper, it was found that when initially degassed water is saturated with dissolved air, the breakdown threshold decreases. A theoretical model describing this phenomenon is suggested. This model includes the development of an electron avalanche inside individual nanobubbles, followed by the stimulated optical coalescence of a nanobubble cluster. According to our estimates, this regime occurs at laser radiation intensities of about 106–107 W/cm2. It is important that at such low intensities the breakdown flash (the basic endpoint of optical breakdown) does not appear due to the deficit of input laser energy. We provide an experimental proof of the coalescence regime, stimulated by a laser pulse in nanosecond range. The experimental threshold of stimulated coalescence is in good agreement with the theoretical estimates. Since the stimulated optical coalescence mode occurs at very low laser intensities, its excitation does not result in mechanical side effects in eye tissues, i.e., a shock wave should not be excited. Note that shock wave always occurs during optical breakdown, which is traditionally excited at intensities of 1012 W/cm2. In our experiment, the generation of a shock wave at such pump intensities was also observed. Since, according to the estimates given in the article, the volume number density of nanobubble clusters in the intraocular fluid can reach 108 cm−3, the excitation of the stimulated optical coalescence mode of nanobubble clusters can be used in ophthalmic surgery, such as laser iridotomy.

Nucleation of cadherin clusters on cell-cell interfaces

Cadherins mediate cell-cell adhesion and help the cell determine its shape and function. Here we study collective cadherin organization and interactions within cell-cell contact areas, and find the cadherin density at which a ‘gas-liquid’ phase transition occurs, when cadherin monomers begin to aggregate into dense clusters. We use a 2D lattice model of a cell-cell contact area, and coarse-grain to the continuous number density of cadherin to map the model onto the Cahn-Hilliard coarsening theory. This predicts the density required for nucleation, the characteristic length scale of the process, and the number density of clusters. The analytical predictions of the model are in good agreement with experimental observations of cadherin clustering in epithelial tissues.

Hardening and ductility loss of RAFM steel CLF-1 irradiated with high-energy heavy ions

Irradiation induced hardening and ductility loss of a Chinese reduced-activation ferritic / martensitic steel CLF-1 is evaluated by utilizing the high-energy heavy ion irradiation and the subsequent miniature specimen test technique. Specimens were irradiated with high energy 14N6+ and 56Fe17+ ions supplied by a cyclotron to generate a quasi uniform atomic displacement damage plateau from surface to a depth about 25 μm. Three successively increasing damage levels (0.05, 0.1 and 0.2 dpa) were approached at a low temperature around 223 K. The small punch test at room temperature showed that the ductility loss can be observed at the lowest damage level and increases with the increasing damage level, similar to the variation trend of yield stress with irradiation dose. The TEM observation revealed that the average size and number density of irradiation-induced defect clusters also increased with displacement damage. Assuming that the hardening is caused by the self-interstitial-type dislocation loops, an estimation by combining the numerical calculation of the number density / mean diameter of dislocation loops with the dispersion barrier hardening model yields a similar dose dependence of the irradiation hardening.

PosgenPy: An Automated and Reproducible Approach to Assessing the Validity of Cluster Search Parameters in Atom Probe Tomography Datasets

Abstract One of the main capabilities of atom probe tomography (APT) is the ability to not only identify but also characterize early stages of precipitation at length scales that are not achievable by other techniques. One of the most popular methods to identify nanoscale clustering in APT data, based on the density-based spatial clustering of applications with noise (DBSCAN), is used extensively in many branches of research. However, it is common that not all of the steps leading to the selection of certain parameters used in the analysis are reported. Without knowing the rationale behind parameter selection, it may be difficult to compare cluster parameters obtained by different researchers. In this work, a simple open-source tool, PosgenPy, is used to justify cluster search parameter selection via providing a systematic sweep through parameter values with multiple randomizations to minimize a false-positive cluster ratio. The tool is applied to several different microstructures: a simulated material system and two experimental datasets from a low-alloy steel . The analyses show how values for the various parameters can be selected to ensure that the calculated cluster number density and cluster composition are accurate.

Directional-dependent precipitate microstructure and mechanical properties of tensile and compressive stress-assisted aged Mg-Zn alloys

Aging aided by external elastic stress is of scientific interest and practical importance in improving the precipitation hardening response of magnesium alloys. In this work, fiber textured Mg-6 wt.% Zn alloys were subjected to tensile and compressive stress-assisted aging (TSA and CSA, respectively), in which stress is applied along the extrusion direction. Results reveal that the precipitate microstructure, including shape, size, distribution and even internal defect structures exhibits a stress directional dependence. Aberration-corrected scanning transmission electron microscopy shows that a high number density of Zn solute clusters is produced upon CSA, and relatively fine β1’ precipitates are predominantly formed under TSA. First-principles calculations indicate that the stress direction-dependent solute diffusion ability is the leading cause of such directional-dependent precipitate characteristics. Furthermore, TSA generates a higher yield strength than that of stress-free aging (SFA), owing to the relatively high density of fine β1’ precipitates. Compared with SFA and TSA alloys, the CSA alloy contains massive Zn solute clusters and has higher yield strength and better ductility due to the strong cluster-dislocation interactions without the generation of local high stress concentration at the coherent interface. This work offers further insights into altering the precipitation behavior of Mg alloys by applying external stress field and provides possible solutions to achieve high strength-ductility synergy in Mg alloys.

Evidence of in-situ Cu clustering as a function of laser power during laser powder bed fusion of 17–4 PH stainless steel

The use of intrinsic heat treatments to control the microstructural evolution during additive manufacturing could eliminate the need for costly post-build processing. Using atom probe microscopy and cluster search algorithms, this study investigates the degree of Cu clustering and precipitation in 17–4 precipitate hardening (PH) stainless steel fabricated by laser powder bed fusion (LPBF). It was found that LPBF samples exhibit a greater than random degree of Cu clustering, irrespective of the laser power during fabrication. It is further shown that using a higher laser power (161.5 W rather than 127.5 W) led to a higher number density of Cu clusters, Cu precipitates, and higher hardness due to the greater heat input. The observations of Cu-rich clusters and precipitates within as-printed LPBF samples and its laser power dependence are novel and show potential for inducing desired strengthening phases directly during LPBF, mitigating the need for post-fabrication heat treatments.

Effect of cyclic ageing on the early-stage clustering in Al–Zn–Mg(-Cu) alloys

The cyclic application of mechanical stress to aluminum alloys at room temperature, referred to as cyclic ageing, continuously injects vacancies, enabling dynamic precipitation of a fine distribution of solute clusters. These are uniformly distributed throughout the bulk and are responsible for enhancing the mechanical properties to comparable values as T6 conditions obtained by conventional artificial aging. The atomic structure of the clusters in two Al–Zn–Mg (-Cu) alloys is studied using atomically resolved transmission electron microscopy, and their size, volume density and chemistry are investigated using atom probe tomography. It was found that cyclic ageing yields a high number density of solute clusters exhibiting structural similarities to the GPI zones commonly observed after low temperature ageing in such alloys. A subsequent 10-day natural ageing allows both cluster nucleation and further cluster growth, without altering their atomic structure. As compared to natural ageing, the strengthening caused by the solute clusters is accelerated during cyclic ageing, due to dynamic precipitation. The copper containing alloy also had higher amounts of Mg and Zn. Still, a slightly lower number density of smaller clusters with lower Zn/Mg ratio formed in this alloy, both after cyclic aging and after natural aging. The higher strength of this alloy is attributed to a higher strength contribution from each cluster.

AMICO galaxy clusters in KiDS-DR3: Cosmological constraints from counts and stacked weak lensing

Aims.We present a cosmological analysis of abundances and stacked weak lensing profiles of galaxy clusters, exploiting the AMICO KiDS-DR3 catalogue. The sample consists of 3652 galaxy clusters with intrinsic richnessλ* ≥ 20, over an effective area of 377 deg2, in the redshift rangez ∈ [0.1, 0.6].Methods.We quantified the purity and completeness of the sample through simulations. The statistical analysis has been performed by simultaneously modelling the co-moving number density of galaxy clusters and the scaling relation between the intrinsic richnesses and the cluster masses, assessed through stacked weak lensing profile modelling. The fluctuations of the matter background density, caused by super-survey modes, have been taken into account in the likelihood. Assuming a flat Λ cold dark matter (ΛCDM) model, we constrained Ωm,σ8,S8 ≡ σ8(Ωm/0.3)0.5, and the parameters of the mass-richness scaling relation.Results.We obtained Ωm = 0.24−0.04+0.03,σ8 = 0.86−0.07+0.07, andS8 = 0.78−0.04+0.04. The constraint onS8is consistent within 1σwith the results from WMAP and Planck. Furthermore, we got constraints on the cluster mass scaling relation in agreement with those obtained from a previous weak lensing only analysis.

On the influence of microstructure on the neutron irradiation response of HIPed SA508 steel for nuclear applications

The neutron irradiation response of a novel hot isostatically pressed SA508 Grade3 steel was studied, such to deduce any influence this unconventional RPV microstructure has on radiation response. In particular, the role of elevated ferrite fraction was investigated. Neutron irradiation was conducted at 155 ± 10°C to induce 0.1dpa of damage, this corresponded 2.53 ± 0.63 GPa hardening for the ferrite and 1.94 ± 0.57 GPa for the bainite as measured by nanoindentation. Atom probe tomography detected the presence of Mn-Ni-Si type clusters in both microconstituent phases. The ferrite microstructure showed a greater percentage of solute atoms available to form clusters than bainite, but it also contained a lower cluster volume fraction and number density compared to the bainite.

Nanoscale chemistry of Zircaloy-2 exposed to three and nine annual cycles of boiling water reactor operation — an atom probe tomography study

Atom probe tomography was used in this work to study the metal close to the metal/oxide interface in the zirconium alloy Zircaloy-2 exposed to three and nine annual cycles of operation in a commercial boiling water reactor. The two exposure times correspond to before and after the onset of acceleration in corrosion, hydrogen pickup, and growth.The alloying elements Sn, Fe, Cr, and Ni were observed to be redistributed after exposure. After both three and nine cycles, clusters containing Fe and Cr and typically of a spheroidal shape with an approximate diameter of 5 nm were observed to be located in layers presumed to be layers of <a>-loops. On average, the cluster number density was slightly higher after nine cycles, with larger and more Cr-rich clusters. However, there were large grain-to-grain variations, which were larger than the differences between the two exposure times. Ni was only occasionally observed in the clusters. Sn was observed to be slightly enriched in the Fe–Cr clusters, but the Sn concentration was higher between than inside the layers of clusters. After nine cycles, clusters of Sn were detected in regions that were depleted of Fe and Cr. Enrichment of Sn, Fe, and Ni at features that appeared to be <c>-component loops was observed after nine cycles, whereas no such features were observed after three cycles. Enrichment of Sn and Fe, and small amounts of Cr and Ni, was observed at grain boundaries after both exposure times. After three cycles, a partially dissolved second phase particle of Zr(Fe,Cr)2 type that contained about ten times more Cr than Fe was observed.

Strengthening magnesium by design: Integrating alloying and dynamic processing

Magnesium (Mg) has the lowest density of all structural metals and has excellent potential for wide use in structural applications. While pure Mg has inferior mechanical properties; the addition of further elements at various concentrations has produced alloys with enhanced mechanical performance and corrosion resistance. An important consequence of adding such elements is that the saturated Mg matrix can locally decompose to form solute clusters and intermetallic particles, often referred to as precipitates. Controlling the shape, number density, volume fraction, and spatial distribution of solute clusters and precipitates significantly impacts the alloy’s plastic response. Conversely, plastic deformation during thermomechanical processing can dramatically impact solute clustering and precipitation. In this paper, we first discuss how solute atoms, solute clusters, and precipitates can improve the mechanical properties of Mg alloys. We do so by primarily comparing three alloy systems: Mg–Al, Mg–Zn, and Mg–Y-based alloys. In the second part, we provide strategies for optimizing such microstructures by controlling nucleation and growth of solute clusters and precipitates during thermomechanical processing. Toward the end, we briefly highlight how one can enable inverse design of Mg alloys by a more robust Integrated Computational Materials Design (ICMD) approach.

Simulation of phase evolution in a Zr-based glass forming alloy during multiple laser remelting

Additive manufacturing by laser-based powder bed fusion is a promising technique for bulk metallic glass production. But, reheating by deposition of subsequent layers may cause local crystallisation of the alloy. To investigate the crystalline phase evolution during laser scanning of a Zr-based metallic glass-forming alloy, a simulation strategy based on the finite element method and the classical nucleation theory has been developed and compared with experimental results from multiple laser remelting of a single-track. Multiple laser remelting of a single-track demonstrates the crystallisation behaviour by the influence of thermal history in the reheated material. Scanning electron microscopy and transmission electron microscopy reveals the crystalline phase evolution in the heat affected zone after each laser scan. A trend can be observed where repeated remelting results in an increased crystalline volume fraction with larger crystals in the heat affected zone, both in simulation and experiment. A gradient of cluster number density and mean radius can also be predicted by the model, with good correlation to the experiments. Prediction of crystallisation, as presented in this work, can be a useful tool to aid the development of process parameters during additive manufacturing for bulk metallic glass formation.

Characterization of hardening behavior of carbon steels at low temperature irradiations

• Embrittlement factors of carbon steels irradiated at low temperature were fine dislocation loops and solute clusters of Mn-Si-Cu atoms. • Carbon steels and their weld metals containing high concentrations of Cu, Mn and Si had relatively high radiation hardening due to promotion of solute atom clustering. • Low temperature irradiation resulted in higher radiation hardening due to the higher number density of dislocation loops, despite the lower number density of solute clusters. • Low dose rate irradiation (electron irradiation) resulted in greater radiation hardening due to the higher number density of solute clusters than high dose rate irradiation (ion irradiation) did. Overpacks used for geological disposal of high-level radioactive waste will be irradiated by neutrons and γ rays with very low dose rate for a long time. A possible way to predict effects of such radiations is that microstructure changes under the expected irradiation conditions are estimated by both experiments and analytical modeling and then the changes in hardness and fracture toughness from the microstructure changes are estimated. In the present study, carbon steels, which are one of the candidate materials for overpacks, model alloys and a weld of carbon steel were irradiated with either Fe ions or electrons at 90 or 290 °C, and then the microstructure and hardness were investigated to gain an understanding about embrittlement factors of carbon steels and effects of both material composition and irradiation conditions (temperature, dose rate) on radiation-induced changes in microstructure and hardness. Formations of fine dislocation loops and solute clusters containing Mn, Si and Cu atoms were confirmed by microstructure analysis using transmission electron microscopy and atom probe tomography. Hardness increase was well correlated with the evolution of dislocation loops and solute clusters, indicating that these defects are embrittlement factors of carbon steels. Higher radiation hardening was confirmed for the materials containing a high density of Mn, Si and Cu, and the irradiation conditions of low temperature and low dose rate.

The role of silicon on solute clustering and embrittlement in highly neutron-irradiated pressurized water reactor surveillance test specimens

• The role of Si content on irradiation embrittlement was clarified. • Solute atom clusters of highly neutron-irradiated Japanese pressurized water reactor surveillance test specimens were analyzed by atom probe tomography. • The cluster radius and number density decreased and increased, respectively, with increasing Si content, resulting in a constant volume fraction of SCs. • Increase in Si reduces the degree of irradiation embrittlement. This is consistent with the results of our previous study based on Bayesian statistical analysis. Solute clusters (SCs) formed in pressurized water reactor surveillance test specimens neutron-irradiated to a fluence of 1 × 10 20 n/cm 2 were analyzed via atom probe tomography to understand the effect of silicon on solute clustering and irradiation embrittlement of reactor pressure vessel steels. In high-Cu bearing materials, Cu atoms were aggregated at the center of cluster surrounded by the Mn, Ni, and Si atoms like a core-shell structure. In low-Cu bearing materials, Mn, Ni, and Si atoms formed cluster and these solutes were not comprised core-shell structure in SCs. While the number of Cu atoms in clusters was decreased with decreasing nominal Cu content, the number of Si atoms had clearly increased. The cluster radius ( r ) and number density ( N d ) decreased and increased with increasing nominal Si content, respectively. The shift in the reference temperature for nil-ductility transition ( ΔRT NDT ) showed a good correlation with the square root of volume fraction ( V f ) multiplied by ( V f × r ) . The negative relation between the nominal Si content and ΔRT NDT indicated that increasing of nominal Si content reduces the degree of embrittlement.

Microstructural evidence for convection in high-silica granite

AbstractHigh-silica (&amp;gt;70 wt% SiO2) granites (HSGs) are critical carriers of tin, copper, and other melt-incompatible elements, yet much remains unknown about the mechanisms responsible for their formation. One of the key issues is the apparent lack of evidence for crystal-melt segregation (e.g., modal layering), without which little can be inferred about the dynamics (or lack thereof) of crystallizing HSGs. We examined the crystallographic orientation relationships of clustered quartz crystals from the 300-m-thick Bobbejaankop sill, Bushveld Complex, South Africa. We report an inward increase in the number density and size of quartz clusters toward the central horizon of the sill, coinciding with a significant increase in concentrations of tin, copper, and tungsten. The majority of crystal pairs within each cluster exhibit coincident-site lattice orientation relationships, representing low grain-boundary energy configurations. These clusters must have formed by synneusis in a magmatic environment where crystals could have moved freely, rotating into low-energy orientations on contact. We argue that this not only demonstrates that 100-m-scale crystal-poor and liquid-rich regions can be present in bodies of HSG, but also that such bodies can undergo long-lived convection during crystallization, driven by downwards movement of crystal-rich plumes at the roof, without significant crystal-melt segregation. This dynamic behavior provides a mechanism to homogenize major-element distribution across HSGs and to concentrate highly incompatible and economic elements into central mineralized horizons.

Characterization of in-situ ion irradiated Fe-21Cr-32Ni austenitic model alloy and alloy 800H at low doses

The microstructural evolution of ternary Fe-21Cr-32Ni (21Cr32Ni) model alloy and of alloy 800H was investigated with a series of in-situ ion irradiation experiments performed using the Intermediate Voltage Electron Microscope (IVEM)-Tandem Facility at Argonne National Laboratory (ANL). Samples were irradiated in-situ with 1 MeV Kr++ ions in the temperature range of 50K to 713K to doses up to 2 dpa. The size distribution of defect clusters, average defect cluster diameter, and defect cluster density were measured and compared. Results showed that the evolution of defects (i.e. the average defect cluster size and number density) in 21Cr32Ni model alloy and alloy 800H with dose were similar at irradiation temperatures up to 300K where they initially increased with dose up to 0.1 dpa after which no significant changes in defect size and density were observed with further irradiation. In addition, both alloys exhibited ordered defect structures along the <100> direction at relatively low temperatures, up to 300K, which remained stable throughout post-irradiation in-situ thermal annealing up to a temperature of 773K. During irradiation at 713K, small defect clusters were observed at low doses (<0.1 dpa) in both alloys. However, at this irradiation temperature, the clusters in 21Cr32Ni grew with a faster rate than those formed in alloy 800H, causing the microstructure in the former to be dominated by numerous large dislocation loops having both {111}- and {110}-type habit planes, and in the latter to be dominated by small defect clusters and small {111}-type dislocation loops. This may indicate that defect trapping by the solute atoms in alloy 800H at 713K can slow point defect migration to defect clusters and limit their growth.

The Supersonic Project: SIGOs, A Proposed Progenitor to Globular Clusters, and Their Connections to Gravitational-wave Anisotropies

Abstract Supersonically induced gas objects (SIGOs), are structures with little to no dark-matter component predicted to exist in regions of the universe with large relative velocities between baryons and dark matter at the time of recombination. They have been suggested to be the progenitors of present-day globular clusters. Using simulations, SIGOs have been studied on small scales (around 2 Mpc) where these relative velocities are coherent. However, it is challenging to study SIGOs using simulations on large scales due to the varying relative velocities at scales larger than a few Mpc. Here, we study SIGO abundances semi-analytically: using perturbation theory, we predict the number density of SIGOs analytically, and compare these results to small-box numerical simulations. We use the agreement between the numerical and analytic calculations to extrapolate the large-scale variation of SIGO abundances over different stream velocities. As a result, we predict similar large-scale variations of objects with high gas densities before reionization that could possibly be observed by JWST. If indeed SIGOs are progenitors of globular clusters, then we expect a similar variation of globular cluster abundances over large scales. Significantly, we find that the expected number density of SIGOs is consistent with observed globular cluster number densities. As a proof-of-concept, and because globular clusters were proposed to be natural formation sites for gravitational wave sources from binary black-hole mergers, we show that SIGOs should imprint an anisotropy on the gravitational wave signal on the sky, consistent with their distribution.

Effects of aging and irradiation on Fe-Ni-Al alloy

To explore the effects of aging and irradiation on the formation of solute clusters, Fe-2.8Ni-2.0Al (at.%) alloys after solid-solution treatment were aged at 500 ℃ for 16 h and 32 h and irradiated with Ar ions to the fluence of 4 × 1016 ions·cm−2 at 290 ℃, respectively. Transmission electron microscope and atom probe tomography were used to characterize the microstructure and solute atoms distribution. Results showed that B2-NiAl clusters were formed in aged alloys and the number density increased with time. The number density of clusters was 8.35 × 1022 m−3 after 32 h at 500 ℃ aging. However, high number density of dislocation loops and B2-FeNi clusters were found after irradiation at 290 ℃. The number density of clusters reached to 3.61 × 1023 m−3. The nucleation of B2-NiAl clusters under aging is driven by the phase transform free energy with the lower mixing enthalpy of Ni and Al atoms, while the formation of B2-FeNi clusters is due to the combination of the interaction between dislocation loops and Ni solutes with the enhanced diffusion rate of Ni atoms due to supersaturated vacancy.

Dust in brown dwarfs and extra-solar planets

Context. Modelling the formation of cloud condensation nuclei (CCNs) is key for predicting cloud properties in planet and brown dwarf atmospheres. The large diversity of exoplanets (rocky planets, mini-Neptunes, giant gas planets) requires a fundamental approach to cloud formation modelling in order to allow a full analysis of observational data contributing to exoplanet characterisation. Aims. We aim to understand the onset of cloud formation and study the formation of TiO2-CCNs. The formation of (TiO2)N clusters as precursors to extrasolar cloud formation is modelled by two different methods in order to understand their potential, identify underlying shortcomings, and to validate our methods. We propose potential spectral tracers for TiO2-CCN formation. Methods. We applied three-dimensional Monte Carlo (3D MC) simulations to model the collision-induced growth of TiO2-molecules to (TiO2)N-clusters in the free molecular flow regime of an atmospheric gas. We derived individual, time-dependent (TiO2)N cluster number densities. For T = 1000 K, the results are compared to a kinetic approach that utilises thermodynamic data for individual (TiO2)N clusters. Results. The (TiO2)N cluster size distribution is temperature dependent and evolves in time until a steady state is reached. For T = 1000 K, the 3D MC and the kinetic approach agree well regarding the cluster number densities for N = 1 … 10, the vivid onset of cluster formation, and the long transition into a steady state. Collision-induced growth and evaporation simulated using a 3D MC approach enables a faster onset of cluster growth through nucleation bursts. Different size distributions develop for monomer-cluster and for cluster-cluster growth, with the largest clusters appearing for cluster-cluster growth. Conclusions. The (TiO2)N cluster growth efficiency has a sweet-spot temperature at ≈1000 K at which CCN formation is triggered. The combination of local thermodynamic conditions and chemical processes therefore determines CCN formation efficiency. The onset of cloud formation may be observable through the (TiO2)4, (TiO2)5, and (TiO2)6 vibrational lines, which may be detectable with the Mid-Infrared Instrument on the James Webb Space Telescope or the Extremely Large Telescope’s mid-IR imager, but more complete line-list data are desirable.