Nucleation Characteristics Research Articles

Rockburst characteristics in syncline regions and microseismic precursors based on energy density clouds

Cases of rockbursts were investigated to analyze the influence of syncline structures on rockbursts. In a syncline structure in Xing’an Coal Mine, the relationship between the activity of mining-induced tremors and a violent rockburst was studied from temporal and spatial distribution graphs of tremors and pictures of energy density clouds. The results indicated that the temporal and spatial distributions of tremors before the rockburst intuitively illustrate areas in which tremors were concentrated; however, the tremors showed more complex spatial distribution characteristics, and it was difficult to identify the evolutionary trends in tremors over time. Energy density clouds exhibited obvious nucleation characteristics, and presented an obvious extension around the nucleus until a rockburst or strong tremor happened around the edges thereof. High-stress regions formed due to the syncline structure can be identified by applying seismic velocity tomography. According to the distribution of wave velocity, large-diameter hole drilling and deep-hole blasting were implemented in targeted areas. The activity of tremors induced by the follow-up mining confirmed the effectiveness of these stress relief measures.

Formation of spherical-shaped GaN and InN quantum dots on curved SiN/Si surface

This paper reports the formation of GaN and InN quantum dots (QDs) with symmetric spherical shapes, grown on SiN/Si(111). Spherical QDs are grown by modulating initial growth behavior via gallium and indium droplets functioning as nucleation sites for QDs. Field-emission scanning electron microscope (FE-SEM) images show that GaN and InN QDs are formed on curved SiN/Si(111) instead of on a flat surface similar to balls on a latex mattress. This is considerably different from the structural properties of In(Ga)As QDs grown on GaAs or InP. In addition, considering the shape of the other III–V semiconductor QDs, the QDs in this study are very close to the ideal shape of zero-dimensional nanostructures. Transmission-electron microscope images show the formation of symmetric GaN and InN QDs with a round shape, agreeing well with the FE-SEM results. Compared to other III–V semiconductor QDs, the unique structural properties of Si-based GaN and InN QDs are strongly related to the modulation in the initial nucleation characteristics due to the presence of droplets, the degree of lattice mismatch between GaN or InN and SiN/Si(111), and the melt-back etching phenomenon.

Homogeneous and Heterogeneous Crystal Nucleation in Glass of the Li2O–SiO2 System

The results of studying the kinetics of homogeneous (spontaneous) and heterogeneous (catalyzed) crystal nucleation in silicate glass is presented for glasses in the Li2O–SiO2 system. Nucleation is catalyzed via the photosensitive mechanism by adding poorly soluble impurities, shifting the glass composition towards the higher content of one of the components (autocatalysis), and by passing steam through the glass melt. The fundamental characteristics of crystal nucleation are obtained. The composition ranges with the maximum and minimum steady-state crystal nucleation rates are identified.

The Effect of Power, Pulse Rate and Treatment Time of Sonication on the Nucleation and Growth of α‐Lactose Monohydrate (α‐LM) Single Crystals from Aqueous Solution

AbstractIn the present study, different kinds of ultrasound variables such as power (P‐75W to 225W), pulse rate (Pr‐10s to 60s) and treatment time (T‐04 min and T‐08 min) are employed on the crystallization of α‐ lactose monohydrate (α‐LM) from aqueous solution. The applied energy density of sonication in aqueous solution shows a profound effect on the nucleation and growth characteristics of α‐LM as regards the principal benefits such as reduction of induction period and supersaturation levels required for nucleation, decrease in crystal size with narrow crystal size distribution (CSD) and increase in nucleation rate than uninsonated solution, but have no effect on crystal morphology. Ultrasound promotes only α‐LM nucleation and no nucleation of either both α and β‐L is observed in all the 36 experiments carried out. The form of grown crystals is confirmed by powder X‐ray diffraction (PXRD) and their thermal behaviour is studied by differential scanning calorimetry (DSC) analyses. The purity of the grown crystals is determined using automatic digital polarimeter.

Enhanced nucleation and growth of HfO2 thin films grown by atomic layer deposition on graphene

Nucleation and growth characteristics of HfO2 thin films on graphene are investigated using atomic layer deposition (ALD). Substantial delay (∼70 ALD cycles) in the nucleation of HfO2 films is observed during HfO2 ALD on graphene, which causes large leakage current in Au/HfO2/graphene capacitors at low HfO2 ALD cycles (<200). The nucleation delay in HfO2 ALD decreases significantly to ∼10 ALD cycles with graphene surface treatment using trimethylaluminum (TMA) and H2O. Graphene surface treatment is performed in an ALD chamber prior to the deposition of HfO2 film using TMA and H2O at 150 °C (same as the HfO2 ALD process temperature). With the improvement in the nucleation of the HfO2 films, the leakage current decreases significantly by a factor of 102–105 (at 1 V) than that without surface treatment for a given number of HfO2 ALD cycles. A higher dielectric constant of HfO2 film is achieved using the surface treatment (k ∼14.5) than that without the surface treatment (k ∼5.6). The resistance of graphene increases substantially (ΔR/R0 ∼24%) after the growth of HfO2 films by ALD without surface treatment, indicating degradation of graphene properties. However, the electrical resistance of graphene changes negligibly (ΔR/R0 ∼0.5%) after the growth of HfO2 films with surface treatment, implying a conservation of the carrier mobility of graphene. This indicates the importance of surface treatment on graphene for HfO2 film growth by ALD. Therefore, the graphene surface treatment using TMA and H2O thus enables an achievement of enhanced nucleation and electrical properties of HfO2 films without degrading the mobility of graphene, thus providing promising opportunities in graphene electronics.

Effects of interatomic potential on precipitation sequences of medium Al concentration in Ni&lt;sub&gt;75&lt;/sub&gt;Al&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;V&lt;sub&gt;25-&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; alloys

The study of material properties show that there is a large space and time span from the electronic level, atomic level, to molecules, clusters, mesoscopic to macroscopic continuous medium. Different levels are dealt with by using different research methods. The interatomic potential function method is an important intermediary bridging from atomic level to cluster and mesoscopic physics research. Therefore, it is not only for a research field of condensed matter physics, but also for an interdisciplinary research. The interatomic potential, as the basis of all computer simulations at an atomic level, directly affects the accuracy of simulation results. That is to say, it is a greatly significant to study the interatomic potential at the atomic level. This article is based on the inversion algorithm and microscopic phase field, and the influence of medium Al concentration and temperature on the precipitation process of Ni&lt;sub&gt;75&lt;/sub&gt;Al&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;V&lt;sub&gt;25-&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; alloy are studied. At the same concentration, the first nearest neighbor interatomic potential of L1&lt;sub&gt;2&lt;/sub&gt; and DO&lt;sub&gt;22&lt;/sub&gt; phase increase linearly with increasing temperature, which is proportional to each other. However, the first nearest neighbor interatomic potential for L1&lt;sub&gt;2&lt;/sub&gt; (DO&lt;sub&gt;22&lt;/sub&gt;) phase increases (decreases) with the increase of Al atom concentration at a constant temperature. When the temperature is 1046.5 K and the concentration of Al is 0.06, the interatomic potential of L1&lt;sub&gt;2&lt;/sub&gt; phase is consistent with the first principles calculation by Chen, indicating the reliability of the inversion algorithm. At the same time, the inverse interatomic potentials are taken into consideration in the microscopic phase field simulation to investigate the relationship between the precipitation sequence of the medium Al alloy and the interaction potential between atoms. That is to say, when the first neighbor interatomic potential of L1&lt;sub&gt;2&lt;/sub&gt; is greater than (less than DO&lt;sub&gt;22&lt;/sub&gt;) L1&lt;sub&gt;2&lt;/sub&gt; (DO&lt;sub&gt;22&lt;/sub&gt;) precipitated preferentially. The first nearest neighbor interatomic potential for L1&lt;sub&gt;2&lt;/sub&gt; and DO&lt;sub&gt;22&lt;/sub&gt; are equal, both of which are precipitated at the same time. In particular, when the concentration of Al atoms is equal to 0.0589, it is found that L1&lt;sub&gt;2&lt;/sub&gt; and DO&lt;sub&gt;22&lt;/sub&gt; are simultaneously precipitated. The precipitation mechanism of the alloy with medium Al concentration is a hybrid mechanism with both non-classical nucleation and instability decomposition characteristics. Since the precipitation mechanism of the medium-concentrated alloy is a hybrid mechanism with both non-classical nucleation and spinodal decomposition, the microscopic phase field method is used to invert the interatomic potential, which increases the reliability of the precipitation sequence of medium the Al alloy.

Preparation of bilayer graphene utilizing CuO as nucleation sites by CVD method

Graphene is an attractive 2D material for optoelectronics applications. However, due to the spontaneous nucleation characteristics of graphene growth on the metal substrates using chemical vapor deposition method, the polycrystalline graphene exhibited many crystal defects, leading to poor crystal quality. Properly controlling the density of nucleation sites is an important and necessary mean to increase the quality of graphene material. In this work, a new method to synthesize high-quality graphene on Cu substrate was reported by utilizing the CuO nanoparticles as nucleation sites. It was found that when annealing the copper substrate at 300 °C for 30 min with Ar:O2 flow ratio of 64:1, the copper substrate showed the lowest roughness and the density of CuO nucleation sites after hydrogen etching (H2 21 sccm at 1035 °C). Bilayer graphene with diagonal length of ~ 3 µm was successfully prepared centering on the CuO nucleation sites. This work supplied a new clue for high quality and monocrystalline graphene preparation.

Characterization of Nonequilibrium Condensation of Supercritical Carbon Dioxide in a de Laval Nozzle

Carbon capture and storage could significantly reduce carbon dioxide (CO2) emissions. One of the major limitations of this technology is the energy penalty for the compression of CO2 to supercritical conditions. To reduce the power requirements, supercritical carbon dioxide compressors must operate near saturation where phase change effects are important. Nonequilibrium condensation can occur at the leading edge of the compressor, causing performance and stability issues. The characterization of the fluid at these conditions is vital to enable advanced compressor designs at enhanced efficiency levels but the analysis is challenging due to the lack of data on metastable fluid properties. In this paper, we assess the behavior and nucleation characteristics of high-pressure subcooled CO2 during the expansion in a de Laval nozzle. The assessment is conducted with numerical calculations and corroborated by experimental measurements. The Wilson line is determined via optical measurements in the range of 41–82 bar. The state of the metastable fluid is characterized through pressure and density measurements, with the latter obtained in a first-of-its-kind laser interferometry setup. The inlet conditions of the nozzle are moved close to the critical point to allow for reduced margins to condensation. The analysis suggests that direct extrapolation using the Span and Wagner equation of state (S–W EOS) model yields results within 2% of the experimental data. The results are applied to define inlet conditions for a supercritical carbon dioxide compressor. Full-scale compressor experiments demonstrate that the reduced inlet temperature can decrease the shaft power input by 16%.

Experimental investigation of variability in bubble departure characteristics between nucleation sites in subcooled boiling flow

Experiments have been conducted in a vertical square channel for investigation of wall nucleation characteristics in subcooled boiling flow. Bubble departures from multiple sites are measured simultaneously for nine conditions. Existing bubble departure diameter models are benchmarked and are shown to be satisfactory in predicting condition-average bubble departure diameter. However, significant variations are observed in the bubble departure frequency across different nucleation sites of a given condition largely due to intermittent periods of inactivity. A benchmark of the existing bubble departure frequency models shows that the models are generally applicable to an ‘active’ frequency but cannot account for the impact of these periods of inactivity. This finding highlights an important issue in the current modeling and understanding of the gas-phase boundary condition. This periodic inactivity, if not incorporated into the wall nucleation modeling, will result in a large overprediction of bubbles generated at the wall. A physical justification for this inactivity is discussed based on the modeling of the active nucleation site density.

Electrodeposition of Nickel on Titanium in Aqueous Acidic Electrolytes

Nickel may be produced in acidic chloride-sulfate based electrolytes. Nickel is initially deposited on stainless steel or titanium cathodes to produce starting sheets while chlorine gas is evolved on DSA anodes. Stress in the nickel deposit may cause bending of the cathode sheet. In addition, irregular growth such as dendrite formation may occur. In extreme cases, short-circuiting of electrodes will happen. Fundamental electrochemical studies of the initial stages of the electrodeposition process may give valuable information for obtaining smooth nickel deposits. Electrochemical experiments of nickel deposition were carried out on titanium substrates using cyclic voltammetry and potential step, and examined with SEM imaging. The measurements were performed at different deposition potentials and times to get an overall picture of the nucleation and growth of nickel on titanium substrates. Further deposition studies have been performed using in situ AFM to study the whole process from single nickel nuclei to a cohesive layer, and determine the nucleation mode and characteristics. The effects of electrolyte composition and pH will be presented. The pre-treatment of the substrate is important for the nucleation and properties of the nickel deposit. The figure illustrates the different nucleation overpotential for a smooth and rough titanium substrate. Figure 1

Experimental investigations on nucleation, bubble growth, and micro-explosion characteristics during the combustion of ethanol/Jet A-1 fuel droplets

The combustion characteristics of ethanol/Jet A-1 fuel droplets having three different proportions of ethanol (10%, 30%, and 50% by vol.) are investigated in the present study. The large volatility differential between ethanol and Jet A-1 and the nominal immiscibility of the fuels seem to result in combustion characteristics that are rather different from our previous work on butanol/Jet A-1 droplets (miscible blends). Abrupt explosion was facilitated in fuel droplets comprising lower proportions of ethanol (10%), possibly due to insufficient nucleation sites inside the droplet and the partially unmixed fuel mixture. For the fuel droplets containing higher proportions of ethanol (30% and 50%), micro-explosion occurred through homogeneous nucleation, leading to the ejection of secondary droplets and subsequent significant reduction in the overall droplet lifetime. The rate of bubble growth is nearly similar in all the blends of ethanol; however, the evolution of ethanol vapor bubble is significantly faster than that of a vapor bubble in the blends of butanol. The probability of disruptive behavior is considerably higher in ethanol/Jet A-1 blends than that of butanol/Jet A-1 blends. The Sauter mean diameter of the secondary droplets produced from micro-explosion is larger for blends with a higher proportion of ethanol. Both abrupt explosion and micro-explosion create a large-scale distortion of the flame, which surrounds the parent droplet. The secondary droplets generated from abrupt explosion undergo rapid evaporation whereas the secondary droplets from micro-explosion carry their individual flame and evaporate slowly. The growth of vapor bubble was also witnessed in the secondary droplets, which leads to the further breakup of the droplet (puffing/micro-explosion).

Nucleation modeling of the Antarctic stratospheric CN layer and derivation of sulfuric acid profiles

Abstract. Recent analysis of long-term balloon-borne measurements of Antarctic stratospheric condensation nuclei (CN) between July and October showed the formation of a volatile CN layer at 21–27 km altitude in a background of existing particles. We use the nucleation model SAWNUC to simulate these CN in subsiding air parcels and study their nucleation and coagulation characteristics. Our simulations confirm recent analysis that the development of the CN layer can be explained with neutral sulfuric acid–water nucleation and we show that outside the CN layer the measured CN concentrations are well reproduced just considering coagulation and the subsidence of the air parcels. While ion-induced nucleation is expected as the dominating formation process at higher temperatures, it does not play a significant role during the CN layer formation as the charged clusters recombine too fast. Further, we derive sulfuric acid concentrations for the CN layer formation. Our concentrations are about 1 order of magnitude higher than previously presented concentrations as our simulations consider that nucleated clusters have to grow to CN size and can coagulate with preexisting particles. Finally, we calculate threshold sulfuric acid profiles that show which concentration of sulfuric acid is necessary for nucleation and growth to observable size. These threshold profiles should represent upper limits of the actual sulfuric acid outside the CN layer. According to our profiles, sulfuric acid concentrations seem to be below midlatitude average during Antarctic winter but above midlatitude average for the CN layer formation.

Thin uniform nickel seed layer formation and its impact on Ni-Cu contact adhesion for c-Si solar cell applications

Abstract Poor contact adhesion is one of the major concerns in the low cost Ni-Cu front contact metallization for c-Si solar cells. It reduces the mechanical as well as electrical reliability of the solar cell. Thermal annealing of the Ni seed layer is generally considered as crucial step for contact adhesion and cell performance, however the deposition of Ni seed layer itself requires proper investigation. The objective of this work is to improve the contact adhesion by improving Ni seed layer characteristics. This has been achieved through detailed process optimization of electroless Ni deposition using Palladium (Pd) activation method and subsequent annealing. After optimizing the Pd activation process with respect to its nucleation and growth characteristics, a very thin (∼20 nm) conformal seed layer deposition has been obtained with excellent uniformity across textured solar cell substrate. In addition, no interfacial void formation is observed after seed layer annealing, even at 600 °C. This has resulted in significantly improved contact adhesion of 23 MPa.

Domain nucleation behavior in ferroelectric films with thin and ultrathin top electrodes versus insulating top layers

The effect of varying the thickness of Pt top electrodes made by the electron beam induced deposition technique on the domain nucleation characteristics of Pb(Zr,Ti)O3 films has been investigated by piezoresponse force microscopy. The advantage of this experimental setup is that the nucleation position can be precisely controlled allowing comparison between two capacitor structures with different top electrode thicknesses and negating the role of defect-induced polarization switching scenarios. In the ultrathin limit (<5nm), the coercive biases of polarization switching change substantially relative to thicker electrodes, from −4.6 to −2.6V and from +3.5 to 5.5V respectively, which we link to a work function size effect. The evolution of the piezoresponse and coercive biases as a function of hysteresis loop cycling is presented and contrasted with that obtained on the bare film surface with no top electrode. To provide a counterpoint to the observed effects with top electrodes, we have demonstrated the variation in switching due to a top silicon oxide insulating layer. This work has revealed a method which could be used to control nucleation bias in ferroelectric thin film systems.

Effect of Sulfide Precursor Selection on the Nucleation, Growth, and Elemental Composition of Cu2ZnSnS4 Nanocrystals

A means to synthesize large quantities of Cu2ZnSnS4 (CZTS) nanocrystals (NCs) is necessary for large-scale production of solution-processed CZTS solar cells. We embarked on a pioneering attempt to investigate and understand the conditions necessary to synthesize CZTS NCs in a novel formamide solvent system using an easily scalable heat-up method and focused on the effect of sulfide precursor selection (thioacetamide vs thiourea). Unlike previous reports, which studied metallic and binary compounds, the compound (CZTS) we investigated comprises more than one metallic element. This difference in composition made possible the observation that sulfide precursor selection strongly alters the elemental composition of the NCs, a vital consideration for multinary compounds of which their performance is strongly dependent on their elemental composition. We found also that sulfide precursor choice influences the nucleation and growth characteristics of the NCs but not the phase of the final product or the phase tra...

Understanding the isothermal growth kinetics of cdse quantum dots through microfluidic reactor assisted combinatorial synthesis

With the use of a microfluidic-assisted combinatorial reactor, the synthesis of CdSe quantum dots was optimized by varying one parameter at a time, and the isothermal growth kinetics of CdSe quantum dots using various models was analyzed. To understand precisely the nucleation and growth characteristics of CdSe quantum dots (QDs), we synthesized the CdSe QDs using various experimental conditions. Different model equations, like acceleratory growth-time curves, sigmoidal growth-time curves or Johnson-Mehl-Avrami-Kolmogorov (JMAK), acceleratory growthtime curves based on diffusion, geometric model growth-time curves, and nth order growth-time curves were fitted. Among all growth models, the JMAK model with \(\alpha = 1 - {e^{ - {{(kt)}^n}}}\), and n = 1 was the best fitting model with the MATLAB interactive curve-fitting procedure were used. Errors associated with the best-fitting model and statistics for the goodness of fit were analyzed. Most of the models were not as good as the other than the proposed model. The errors associated with the proposed model were minimal, and the growth kinetics and other associated statistical factors are very similar, for all the variables investigated. The minimal error associated with the reproducibility and the similar data for growth kinetics for all studied parameters indicated that microfluidic-assisted combinatorial synthesis can be used in the industrial production of QDs. By using the proposed model to obtain an understanding of growth of QDs, their size and properties can be managed and simulated.

Bacterial Ice Nucleation in Monodisperse D2O and H2O-in-Oil Emulsions.

Ice nucleation is of fundamental significance in many areas, including atmospheric science, food technology, and cryobiology. In this study, we investigated the ice-nucleation characteristics of picoliter-sized drops consisting of different D2O and H2O mixtures with and without the ice-nucleating bacteria Pseudomonas syringae. We also studied the effects of commonly used cryoprotectants such as ethylene glycol, propylene glycol, and trehalose on the nucleation characteristics of D2O and H2O mixtures. The results show that the median freezing temperature of the suspension containing 1 mg/mL of a lyophilized preparation of P. syringae is as high as -4.6 °C for 100% D2O, compared to -8.9 °C for 100% H2O. As the D2O concentration increases every 25% (v/v), the profile of the ice-nucleation kinetics of D2O + H2O mixtures containing 1 mg/mL Snomax shifts by about 1 °C, suggesting an ideal mixing behavior of D2O and H2O. Furthermore, all of the cryoprotectants investigated in this study are found to depress the freezing phenomenon. Both the homogeneous and heterogeneous freezing temperatures of these aqueous solutions depend on the water activity and are independent of the nature of the solute. These findings enrich our fundamental knowledge of D2O-related ice nucleation and suggest that the combination of D2O and ice-nucleating agents could be a potential self-ice-nucleating formulation. The implications of self-nucleation include a higher, precisely controlled ice seeding temperature for slow freezing that would significantly improve the viability of many ice-assisted cryopreservation protocols.

Key thermodynamic characteristics of nucleation on charged and neutral cores of molecular sizes in terms of the gradient density functional theory

The gradient density functional theory and the Carnahan–Starling model formulated for describing the contribution of hard spheres have been used to calculate the profiles of condensate density in small critical droplets formed via homogeneous nucleation, as well as in stable and critical droplets formed via heterogeneous nucleation on solid charged and neutral condensation cores of molecular sizes. The calculations performed for water and argon at different values of condensate chemical potential have yielded the heights of the activation barriers for homoand heterogeneous nucleation as functions of vapor supersaturation at preset system temperatures. The interaction of condensate molecules with a solid core has been described by the resultant potential of molecular attractive forces. In the case of a charged core, the long-range Coulomb potential of electric forces has additionally been taken into account. Dielectric permittivities have been calculated as known functions of the local density of the fluid and temperature. The radius of the equimolecular droplet surface has been chosen as a variable describing the droplet size. Dependences of the chemical potential of condensate molecules in a droplet on its size have been plotted for water and argon with allowance for the action of capillary, electrostatic, and molecular forces. It has been shown that the role of the molecular force potential in heterogeneous nucleation increases with the size of condensation cores.

Precursor dependent nucleation and growth of ruthenium films during chemical vapor deposition

Nucleation and film growth characteristics are reported during chemical vapor deposition of Ru on SiO2 using triruthenium dodecacarbonyl [Ru3(CO)12] and ruthenium bis(di-t-butylacetamidinate) dicarbonyl [Ru(tBu-Me-amd)2(CO)2]. Films grown from Ru3(CO)12 follow the three dimensional (3D) Volmer–Weber growth mode. In contrast, films grown from Ru(tBu-Me-amd)2(CO)2 follow the pseudo-layer-by-layer growth mode with two dimensional wetting layer islands forming before 3D particle growth is observed on the islands. A relationship between free isolated hydroxyl [(Si-OH)i] group density and Ru nucleation density is found for Ru3(CO)12 and is associated with (Si-OH)i acting as the reaction sites for activation of Ru3(CO)12 and in turn generating an adjustable adatom concentration. Carbon monoxide and ammonia addition to the gas phase during film growth from Ru(tBu-Me-amd)2(CO)2 lead to smoother films by inducing surface reconstructions during the 3D phase of pseudo-layer-by-layer growth; these gases also lead to films with lower resistivity and lower crystalline character.

Nucleation and growth characteristics of graphite spheroids in bainite during graphitization annealing of a medium carbon steel

The evolution of microstructure in bainite during graphitization annealing at 680°C of Jominy-quenched bars of an Al-Si bearing medium carbon (0.4C wt%) steel has been studied and compared with that in martensite by using light, scanning and transmission electron microscopy. The results show that the graphitization process in bainite is different from that in martensite in many aspects such as the initial carbon state, the behavior of cementite, the nucleation-growth feature and kinetics of formation of graphite spheroids during graphitization annealing, and the shape, size and distribution of these graphite spheroids. The fact that the graphitization in bainite can produce more homogeneous graphite spheroids with more spherical shape and finer size in a shorter annealing time without the help of preexisting coring particles implies that bainite should be a better starting structure than martensite for making graphitic steel.