T. K. Kundu

Atomistic simulation of the surface structure of wollastonite

Abstract Atomistic simulation techniques have been used to calculate the surface structure and stability of wollastonite crystal. Seven predominant surfaces have been modelled and their calculated surface energy corresponds well with their morphological domination. The surface energy, hydration energy and reaction energy values indicate wollastonite surfaces stabilized to great extent by adsorbing water in dissociated form. The Ca 2+ replacement from the first few layers of the surface is found to be energetically more favourable, elucidating high dissolution phenomena of wollastonite mineral.

Atomistic simulation of the surface structure of wollastonite and adsorption phenomena relevant to flotation

Abstract Atomistic simulation techniques have been used to calculate the surface structure and stability of wollastonite crystal and its adsorption behaviour in the presence of molecular and dissociated water, and two widely used collector head group molecules of methanoic acid and methylamine. Seven predominant surfaces have been modelled and their calculated surface energies correspond well with their preferred morphological domination. Surfaces are identified having fourfold and threefold coordination of surface silicon. Threefold surface silicon are stabilized by addition of hydroxyl ion on them and proton on surface oxygen. Stable surfaces thus obtained are subjected to surface Ca 2+ replacement by 2H + by transforming 2O 2− to 2OH − . Surface energy and reaction energy values indicate wollastonite surface stabilized to a great extent by adsorbing water in dissociated form. The Ca 2+ replacement from the first few layers of the surface is energetically more favourable in acidic condition. Three Miller indexed surfaces terminating with fully coordinated silicon were reconstructed to make the surface free of lone oxygen, and these surface cuts were chosen to carry out simulation work for adsorption of molecules. A comparison of surface energies revealed that all the surfaces become stabilized in the presence of added molecules but the presence of methylamine decreases surface energy to lowest values. Adsorption of dissociated water is preferred by {100} and {102} surfaces, while {001} surface adsorbs methylamine strongly as the results show highly negative adsorption energies. In terms of pure molecule adsorption, the preferred adsorption sequence for all the surfaces is methylamine>methanoic acid>water. For {100} and {102} predominant surfaces, the difference in adsorption energy values is not much and we conclude that the collectors having long-chain hydrophobic alkyl chain, the two head group molecules considered, cannot render enough hydrophobicity due to inadequate adsorption on wollastonite. Thus the presence of activators/modifiers in actual wollastonite flotation practice is substantiated.

Pentagonal dodecahedron methane hydrate cage and methanol system — An ab initio study

AbstractDensity functional theory based studies have been performed to elucidate the role of methanol as an methane hydrate inhibitor. A methane hydrate pentagonal dodecahedron cage’s geometry optimization, natural bond orbital (NBO) analysis, Mullikan charge determination, electrostatic potential evaluation and vibrational frequency calculation with and without the presence of methanol using WB97XD/6-31+ +G(d,p) have been carried out. Calculated geometrical parameters and interaction energies indicate that methanol destabilizes pentagonal dodecahedron methane hydrate cage (1CH4@512) with and without the presence of sodium ion. NBO analysis and red shift of vibrational frequency reveal that hydrogen bond formation between methanol and water molecules of 1CH4@512 cage is favourable subsequently after breaking its original hydrogen bonded network. Graphical AbstractA theoretical study of methane hydrate pentagonal dodecahedron cage (1CH4@512) with and without the presence of methanol and sodium ion using WB97XD/6-31++G(d,p) have been performed. Calculated geometrical parameters and interaction energies indicate that methanol distorts 1CH4@512 cage with and without the presence of sodium ion.

Stability Analysis and Frontier Orbital Study of Different Glycol and Water Complex

A detailed theoretical study of hydrogen-bond formation in different polyethylene glycol + water complex and dipropylene glycol + water have been performed by Hartree Fock (HF) method, second-order Moller-Plesset perturbation theory (MP2), and density functional theory (DFT) using 6-31++G(d,p) basis set. B3LYP DFT-D, WB97XD, M06, and M06-2X functionals have been used to describe highly dispersive hydrogen-bond formation appropriately. Geometrical parameters, interaction energies, deformation energies, deviation of potential energy curves of hydrogen bonded O–H from that of free O–H, frontier orbitals, and charge transfer have been studied to analyze stability and nature of hydrogen bond formation of various glycol and water complexes. It is found that WB97XD is best among all the applied DFT functionals to describe hydrogen bond interaction, and intermolecular hydrogen bonds have higher covalent character and accordingly higher strength when glycol acts as proton donor for glycol + 1 water complex system.

Theoretical Study of Hydrogen Bond Formation in Trimethylene Glycol-Water Complex

A detailed quantum chemical calculation based study of hydrogen bond formation in trimethylene glycol- (TMG-) water complex has been performed by Hatree-Fock (HF) method, second-order Moller-Plesset perturbation theory (MP2), density functional theory (DFT), and density functional theory with dispersion function (DFT-D) using 6-31

DFT-based inhibitor and promoter selection criteria for pentagonal dodecahedron methane hydrate cage

AbstractDensity functional theory (DFT)-based simulations have been performed to provide electronic structure property correlation based reasoning for conceptualizing the effect of encapsulated methane molecule on the formation of methane hydrate cages, the role of methanol and ethylene glycol as inhibitor and the role of tetra-hydro-furan (THF) and cyclopentane as promoter of methane hydrate. Geometry optimization of 512 cage, 51262 cage and 51264 cage with and without encapsulated methane and the cluster of 512 cage with ethylene glycol, methanol, cyclopentane have been performed by density functional theory using ωB97X-D/6-31+ +G(d,p) method. Methane hydrate formation inhibition by methanol and ethylene glycol as well as methane hydrate stabilization by cyclopentane and tetrahydrofuran are critically analysed based on the interaction energy, free energy change, dipole moment and infrared frequency calculation. Calculation of free energy change for formation of methane hydrate with/without reagents at various temperature and pressure using optimized structure is reported here. It is observed that hydrogen bond between water molecules of clathrate 512 cages become stronger in the presence of cyclopentane and tetrahydrofuran but weaker/broken in the presence of ethylene glycol and methanol. Simulated results correspond well with experimental findings and can be useful for designing new inhibitor and promoter molecules for gas hydrate formation. Graphical AbstractDFT studies have been performed to show the effect of some inhibitor and promoter molecules on pentagonal dodecahedron methane hydrate cage (1CH4@512) structures and electronic properties. It illustrates scientifically the role of promoter (e.g., cyclopentane) and inhibitor (e.g., methanol) on stability and formation possibility of (1CH4@512).

Drain Rate and Liquid Level Simulation in Blast Furnace Hearth Using Plant Data

Proper understanding and control of drainage of hot metal and slag from hearth are essential for a stable and efficient blast furnace operation. Various operational problems like irregular casting intervals, damage to lining, low blast intake, furnace pressurization, and so forth are normally encountered when liquid levels in the hearth exceed a critical limit where hearth coke and deadman start to float. Estimation of drain rate and liquid level in hearth needs to be simulated based on the operating parameters available as carrying out any direct measurement is extremely difficult due to the hostile conditions. Here, a mathematical model has been developed to simulate real-time liquid level and drainage behavior of the furnace hearth. Based on the computed drainage rate, production rate, and mass balance, the model is able to predict occurrence of slag-out time and cast close time which are in good agreement with the plant data.

Design of Methane Hydrate Inhibitor Molecule Using Density Functional Theory

A strategy for designing methane hydrate inhibitor molecule has been established depending upon geometrical parameters, interaction energy, highest occupied molecular orbital (HOMO)—lowest unoccupied molecular orbital (LUMO) structures and energies, natural bond orbital analysis, potential energy curve, Mullikan charge, IR intensity and red shift. One methane hydrate inhibitor molecule namely 2,2′-oxydipropane-1, 3-diol has been designed based on the established design strategy. Theoretical study of effectiveness of the designed inhibitor molecule has been performed for methane hydrate pentagonal dodecahedron cage (1CH4@512) using WB97XD/6-31++G(d,p). Calculated geometrical parameters, interaction energies and HOMO–LUMO study indicate that reduction of the strength of hydrogen bonded network of 1CH4@512 cage is more by designed inhibitor 2,2′-oxydipropane-1,3-diol compared to conventional thermodynamic inhibitor (methanol) and consequently 2,2′-oxydipropane-1,3-diol can be more effective methane hydrate inhibitor than methanol.

Effect of Strain on the Physical Properties of Lanthanum Nickelate

Lanthanum nickelate (LaNiO3) is a promising material for stable fuel-cell electrode, optoelectronic and magneto-electronic devices. Density functional theory (DFT) based calculations were carried out to investigate the effect of strain on the physical properties of the correlated metal LaNiO3. Electronic structure, optical conductivity and temperature variation of resistivity have been studied in detail using GGA+U approach. It has been observed that LaNiO3 under strain is more metallic compared to the unstrained system. However LaNiO3 under compressive strain is found to be more metallic than that under tensile strain. Electron localization function calculation revealed that LaNiO3 under tensile strain has more covalent bonding than that under compressive strain, which results in an increase in resistivity for the system under tensile strain. The theoretical understanding of the alternation of physical properties of the system, caused by misfit strain may help in the application of the system in different device purposes using strain engineering.

Cellular Automata Modeling of Decarburization of Metal Droplets in Basic Oxygen Steelmaking

In steelmaking, a supersonic jet is blown over the bath to refine the hot metal to produce steel. The refining process primarily consists of removal of impurities from the hot metal to a permissible level. The impact of oxygen jet on the surface of the hot metal bath results in ejection of droplets, which mix with slag and form emulsion. The formed emulsion plays an important role in refining reactions kinetics and understanding of this process is required todevelopimproved process control model for the steel industry. In this paper, cellular automata technique has been explored to simulate decarburization in emulsion caused by interfacial reactions between the metal droplets and slag. In the course of the work, a framework has also been developed to quantify the contribution of carbon monoxide, generated by decarburization, in bloating of metal droplets and formation of halo around the droplets. The model has incorporated diffusion and decarburization reaction based on probabilities to study the evolution of the system. Simulations with varying parameters have been performed and decarburization trends obtained are comparable with the experimentally determined data reported in literatures.