Materials Processing Fundamentals: Nucleation, Crystallization, and Solidification
Sponsored by: TMS Extraction and Processing Division, TMS: Process Technology and Modeling Committee
Program Organizers: Jonghyun Lee, Iowa State University; Guillaume Lambotte, Boston Metal; Samuel Wagstaff, Oculatus Consulting; Antoine Allanore, Massachusetts Institute of Technology; Fiseha Tesfaye, Metso Metals Oy, Åbo Akademi University
Tuesday 2:00 PM
February 25, 2020
Room: 14A
Location: San Diego Convention Ctr
Session Chair: Fiseha Tesfaye, Åbo Akademi University; Jonghyun Lee, Iowa State University
2:00 PM Invited
Structural Study of a Levitated Salt Solution Using a Containerless Scattering Method: Geun Woo Lee1; 1Korea Research Institute of Standards and Science
We have developed a technique to study atomic and molecular structure of solutions using a combined device with electrostatic levitation and X-ray and Raman scattering. In this study, we levitate a salt solution and achieve extremely high supersaturation by evaporation. This gives a chance to reveal how the solution structure changes and affects phase selection. Here, we study NaCl solution structure and its hydration structure too. We find a dense region where shows chemical ordering, but still topologically disordering. This finding supports two-step nucleation phenomenon which has been predicted by computer simulation studies. We will demonstrate the evolution of solution structure.
2:30 PM
Multiple Crystallization Pathways on Highly Supersaturated Aqueous Solutions: Yong Chan Cho1; Geun Woo Lee1; Sooheyong Lee1; Yun-Hee Lee1; 1Korea Research Institute of Standards and Science
In supersaturated aqueous solutions, measurements of solution structure and its evolution can provide a key information for characteristic nucleation pathways. We present the structural evolution of dihydrogen phosphate (H2PO4) molecules in extremely supersaturated solutions (KH2PO4 (KDP) and NH4H2PO4 (ADP)) beyond metastable zone width limit. The combination of electrostatic levitation system, in-situ synchrotron X-ray diffraction and in-situ micro-Raman spectroscopy revealed molecular symmetry changes of H2PO4 in highly supersaturated KDP solution indicating the existence of clear solution-solution transition depending on the number of solvent (water) molecules. However, ADP solutions show with a well-developed medium range ordering which is different from those of KDP solution. Our result suggest that changes in short range and medium range order structures in solutions ultimately determines the route of nucleation and phase selection. This work can provide an important insight for understanding of various nucleation phenomena in molecule-level.
2:50 PM
Non-crystallographic Branching in Polymer Crystallization: a Molecular Picture of the Onset of Spherulite Formation: Tongtong Shen1; Chunyu Li1; Alejandro Strachan1; 1Purdue University
Crystallinity in polymers conveys enhanced mechanical strength, greater resistance to degradation and better barrier properties and polymers crystallizing from melt frequently adopt spherulitic forms. Despite significant efforts, the mechanism of their formation is still not clear, and this gap stems from lack of knowledge of molecular pictures during polymer crystallization. The objective of our study is to use large-scale molecular dynamics simulations to capture the process of non-crystallographic branching, responsible for spherulite formation, during polymer crystallization. We discovered that during early stage of growth, the thickening process of the parent lamella is predominant, causing significant deformation in its nearby regions. This deformation dramatically changes the molecular alignment in its vicinity and inducing nucleation with chain orientation similar to the primary grain. The predicted misalignment is in good agreement with experiments. We believe this process is the key source of static disorder formation, giving rise to further spherulitic growth.
3:10 PM
De-mineralization of a High Ash Coal in Acidic Salt Solution: Adeleke Abraham Adewale1; Lateef Jimoh1; Simeon Ibitoye1; 1Obafemi Awolowo University
In this research, the high ash and sulphur contents of Akunsa coal, Nigeria was successfully reduced. The ash and sulphur contents of the coal as received was determined to be 38 and 1.98%, respectively and were reduced by leaching the coal using sodium carbonate, nitric acid and sodium carbonate acidified in nitric acid at varying reagent concentrations, contact time and constant temperature of 90℃.The results obtained showed that the three leachant successfully reduced the ash and sulphur contents of the coal. However, nitric acid was found to be more potent in sulphur reduction than sodium carbonate, while sodium carbonate was more effective in ash reduction than nitric acid. It was further observed that the 1.5M sodium carbonate acidified in 1M nitric acid gave the highest leaching efficiency for the same pulp density as the ash was reduced by 76.8% to 8.8% and the sulphur reduced by 82.3% to 0.35%.
3:30 PM
Investigating Short-chain Alcohol Based Microemulsions as Viable Nanoparticle Synthesis Systems: Do Reverse Micelles Form in Ethanol/AOT/n-Heptane Systems?: Robyn E. Ridley1; Erick Alvarado1; Victor R. Vasquez2; Olivia Graeve1; 1University of California, San Diego; 2University of Nevada, Reno
Through a fundamental study on the effects of ethanol on the phase behavior of sodium bis(2-ethylhexyl) sulfosuccinate (AOT), particularly its ability to form reverse micelles in n-heptane, we consider the efficacy of ethanol/AOT/n-heptane systems for monodisperse nanoparticle synthesis. Using dynamic light scattering, molecular dynamics simulations, and 1H NMR spectroscopy, we investigate the aggregation behavior of AOT across a wide range of ethanol/AOT/n-heptane compositions. We identify mixed-solvent polarity as a driving factor for surfactant behavior in the system, and conclude reverse micelles do not form at any investigated compositions and likely cannot form in this system regardless of composition. However, other unique surfactant aggregate morphologies which offer new possibilities for nanoparticle shape control, including multilayered cylindrical structures and spherical AOT-in-ethanol structures, are found in this system. A preliminary phase diagram for the ethanol/AOT/n-heptane system is constructed from our results, proving useful in continued studies on system behaviors and synthesis potential.
3:50 PM Break
4:10 PM
Modified Gouy-Chapman-Stern Model of the Aqueous Na-AOT Reverse Micelle Sub-structure with the Addition of Salts: Robyn E. Ridley1; James P. Kelly2; Hoorshad Fathi-Kelly2; Victor R. Vasquez3; Olivia Graeve1; 1University of California, San Diego; 2Alfred University; 3University of Nevada, Reno
Aqueous Na-AOT reverse micelles used for nanoparticle synthesis processes have been shown to decrease in size with increased concentration and/or valency of additional salts until reaching a point of destabilization. Dynamic light scattering experiments and molecular dynamics simulations demonstrate a relationship between average reverse micelle size and the Debye screening length, and thus indicate that electrical double layer (EDL) theory for electrolytes near a charged surface is applicable to these systems. The reverse micelle internal substructure can be described by considering the surfactant layer as a charged surface and non-dissociated headgroup ions as a Stern layer. However, current models for EDL theory use assumptions of planar charged surfaces and infinite distance and thus cannot be directly applied to reverse micelles. As such, we modify the Gouy-Chapman-Stern model to account for curvature and confinement effects to analyze the behavior of reverse micelles with the addition of salts.
4:30 PM
Effects of Al Substitution for Zn on the Non-equilibrium Solidification Behavior of Zn−3Mg Alloys: Yeqing Wang1; Jianrong Gao1; Ashwin Shahani2; 1Northeastern University; 2University of Michigan
Zn-based alloys may find applications in medical industries because of good biocompatibility. It is of fundamental and technical interest to investigate their solidification behavior in casting. In this work, we investigated solidification paths of Zn-3Mg-2Al alloys using in situ X-ray diffraction technique and thermodynamic calculations. Results showed that compared to the binary Zn-3Mg alloys, the addition of 2% Al does not affect the solidification path. The Laves compound MgZn2 is the primary phase and its growth is followed by growth of a metastable MgZn2/Zn eutectic or stable Mg2Zn11/Zn eutectic. Competitive nucleation and growth of stable and metastable phases is discussed by calculations of their crystal/melt interfacial energy and interface growth kinetics. YWQ and JG acknowledge support by the National Natural Science Foundation of China (U1502272).
4:50 PM Cancelled
The Effect of Undercooling on the Nucleation and Growth of Large-size TiC of High Titanium Low Alloy Steel via In-situ Observation: Ji Cheng; Chen Tianci1; Zhu Miaoyong1; 1Northeastern University School of Metallurgy
The mechanism and kinetics of large-size TiC precipitation in high titanium alloy steel were investigated in-situ through a high-temperature laser-scanning confocal microscope, as well as thermodynamic calculations using Thermo-Calc. The size of austenite grains and TiC gradually decreases with the increase of undercooling. During the process of solidification, strong solute diffusion fields are formed through undercooling, which inhibited the nucleation of TiC, hence the second phase precipitation temperature is lower than the equilibrium precipitation temperature. Meanwhile, there is a critical cooling rate between 12 and 90 K/min that renders the capacity of γ formation equal to TiC. The nucleation location of TiC can be changed from grain boundary to grain interior by increasing undercooling. The growth pattern of TiC conforms to Avrami equation, at a higher undercooling, the time exponent is small and the relationship between growth length and time shows an approximate linear.