The objective of this study is to investigate cocrystal solubility and dissolution behavior to elucidate the factors affecting these processes in various media. Six cocrystals with xanthines (theophylline (THP), caffeine (CAF) and theobromine (THB)) were prepared and characterized by powder X-ray diffraction and thermal methods. Two cocrystals (CAFCA I and THBSA) are new solids and their crystal structures were determined by single crystal X-ray diffraction. Cocrystal solubility behavior depended on the dissolving complex solubility and its dissociation behavior in solution. Two THP cocrystals - one with acetaminophen (ACE) and one with citric acid (CA) created different degrees of free THP supersaturation in solubility and dissolution studies. High transient THP supersaturation caused almost immediate THP hydrate crystallization from THPCAH and led to non-congruent solubility behavior. Such behavior was not observed with the ACETHP because free THP supersaturation was not sufficient to induce rapid crystallization but did so over longer equilibration times. Three salicylic acid (SA) cocrystals with xanthines (THP, CAF, and THB) were prepared; two (THPSA and CAFSA) had low aqueous solubility compared to their pure components and one (THBSA) had higher solubility. Both cocrystal components in these cocrystals produced higher solubility/dissolution rates in alkaline media due to ionization. Also, at higher pH, THB precipitated from THBSA solutions because of higher THB supersaturation under alkaline conditions. Caffeine (CAF) and theophylline (THP) both form cocrystals with citric acid (CA) which is a highly water-soluble cocrystal former. Both CAFCA Form I and II solubility and dissolution behavior were studied. THPCAH exhibited non-congruent dissolution because of rapid precipitation of THP hydrate on the dissolving cocrystal surface. CAFCA exhibited congruent dissolution because it did not produce sufficient supersaturation to precipitate CAF hydrate during dissolution. CA cocrystals also have the unusual behavior of high viscosities produced in the dissolution boundary layer due to CA’s high solubility. These viscosities alter diffusion coefficients which reduce dissolution rates from that expected based purely on solubility. To further understand cocrystal dissolution, a diffusion-convection-reaction (DCR) model was developed to predict cocrystal dissolution rates in various media. This model predicted concentration profiles of all species (complex, free components and reactive species) in the diffusion layer of a rotating disk intrinsic dissolution system. Predicted dissolution rates had varying degrees of agreement with experimental data depending on the cocrystal model and the medium into which the cocrystal dissolved.

<p>  </p> <p>Due to the difficulty in physically observing the phenomena inside the actual ladle furnace in the industry, to ascertain optimized methodology for high-grade steel production, an investigation was carried out using numerical modeling to simulate the behavior of alloying elements within the liquid steel bulk using ANSYS Fluent 2020 R1 (ANSYS Inc., Pittsburgh, PA, USA). The model solves the governing equations utilized in computing the trajectories of each particle in the discrete phase. Furthermore, a user defined (UDF) code maps the mass of each parcel based on the total amount of alloy injected. The code also defines the total time it takes for the shell formed around the added materials to melt or dissolve. The study consists of a two-step procedure: ladle stirring by argon inert gas injection and mixing study by injecting micro-alloying elements to capture the flow field, turbulence, and species transport occurring during the refining process. A generic dual plug ladle metallurgy furnace, dimensions, and data obtained from Nucor Steel is used to validate the CFD simulation results. Concise parametric studies consist of ladle geometry design adjustments, variations of argon gas flow rates, and different alloying elements. Though the efficiency of the LMF process is quantified using the mixing time, which decreases as initial gas flow rates increase, results from this study show that extremely high charging of ladles is optional in obtaining shorter mixing. Also, particles behave substantially differently when their densities are below or above that of steel, and their melting points and specific heat capacities influence the time it takes for them to melt or dissolve. The overall potential outcome for this study is to improve the mixing practices due to different optimal procedures required by some materials than others.</p>