Luis Felipe Verdeja González

EchoTech: A Water Management System

One of the worlds major problems is the scarcity of water, due mainly to the unmeasured water consumption and the waste of this vital element. This paper describes a modular water management system, which helps not only in monitoring consumption but also in finding water leaks and water pollution

Total Insolubility and Solubility in Alloys

The solubility between two metals is analyzed as a function of the affinity between them and the possibility of forming, during solidification, intermetallic, eutectic, or total solid solutions, exemplified with different phase diagrams of alloys of these types. Interstitial solid solutions are presented in a graphic fashion, analyzing interatomic spacing, coordination index, and deformation of crystalline lattices. The shape of the cooling curves used to sketch phase diagrams is presented and the lever rule to calculate the fraction of phases present in an alloy is explained through examples. Also, partition coefficient which is a linear approximation to estimate amounts of liquid and solid during solidification can result in heterogeneities of the forming crystals.

Nonequilibrium Solidification and Chemical Heterogeneities

The partition coefficient is used as a mathematical tool to analyze chemical heterogeneities to produce concentration curves of cooling phenomena, which can be used to understand solidification of liquid metals (Scheil equation) contained in molds with different heat transport capacity, resulting in segregation of the normal, inverse, and gravity types. The relationship between undercooling and columnar structure is presented with steel ingots as examples. Furthermore, segregation produced by gas, crystal forming, or cracks is described. The effect of microsegregation (microshrinkages) and its possible elimination by homogenization heat treatments is examined. The effect of nonequilibrium conditions on phase reactions such as eutectic and peritectic ones, is indicated using an Al-Cu alloy to distinguish zones with considerable chemical segregation during dendrite growth, which can also be observed in Al-Mg or Cu-Sn systems where this type of equilibrium can result in partition coefficient modification.

Phase Transformation Kinetics

The mechanisms of solidification during cooling of a metal from an atomic point of view are analyzed using the liquid-solid surface free energy and wetting angles for different solid and liquid materials. The process for homogeneous nucleation and critical nucleus size calculations are explained from a thermodynamic (free energies) point of view as a function of undercooling and nucleation rate final amount of nucleus forming crystals are presented. A comparison between homogeneous and heterogeneous processes is described and the resulting microstructures including formation of dendrites due to growth in preferential directions is explained, while its relation to temperature, time, and transformation curves is shown (Johnson-Mehl-Avrami model). Also continuous cooling curves are obtained. Furthermore, unidirectional nuclei growth is also presented considering different heat removal mechanisms and examples of dendritic structures depending on the thermal characteristics of the mold, are presented.

Solidification of Metals

The characteristics of metallic atoms are explained together with their behavior from the gaseous to the solid states, from a thermodynamic point of view. Crystalline systems and calculations related to packaging, volume change, and lattice during solidification are analyzed. The phenomenon of solidification of a metal is explained using thermodynamics of bonding during cooling and its resulting crystalline structure and grain microstructure are presented in a general fashion. Finally, the stiffness of the atomic bond is analyzed as a function of temperature and the relationship between melting point, heat treatments, and deformation temperatures are explained.

Solid-State Transformations in the Fe-C System

Equilibrium transformations in the Fe-C system are analyzed using the metastable phase diagram for these two elements through the crystallographic structure of cementite, austenite, and ferrite. Microstructures are used to illustrate the transformation of austenite into ferrite from a kinetic point of view for steels with different carbon compositions. The Fe-Fe 3 C diagram is analyzed in detail distinguishing between hypereutectoid and hypoeutectoid steels, as well as hypoeutectic and hypereutectic white castings. Different methods to estimate the strength of ferritic-pearlitic steels (including Pickering formula) are used. The effect in eutectic composition and temperature of different alloying elements distinguishing them as either alpha or gamma-stabilizing nature is shown, as well as precipitate-forming elements.