Conferences, Lectures, & Seminars
Events for October
-
Separating Gases with Ionic Liquids
Thu, Oct 08, 2009 @ 12:45 PM
Mork Family Department of Chemical Engineering and Materials Science
Conferences, Lectures, & Seminars
Lyman Handy Colloquium SeriesPresentsJoan F. BrenneckeUniversity of Notre DameAbstract: Ionic liquids (ILs) are non-volatile organic salts that have low melting points, frequently below room temperature. Typical compounds are comprised of a quaternary ammonium, quaternary phosphonium, imidazolium or pyridinium cation with a wide variety of common anions. Since they cannot evaporate and cause air pollution, they are being vigorously investigated as promising alternatives to volatile organic solvents. Here we report on their use as absorption solvents for gas separations. Many important gas separations are highly energy intensive, especially those involving cryogenic distillation or desorption of chemically-complexed gases. We show that many ILs show good selectivity for CO2 and SO2 over gases such as N2, O2 and H2. We measure pure and mixed gas solubilities using gravimetric microbalances, as well as any of a variety of volumetric systems, with and without gas sampling. We show that some gas separations, especially when the partial pressure of the target gas is relatively high, can be achieved by physical absorption into ionic liquids.Engineering ionic liquids for gas separations involving gases with low partial pressures may be best achieved by including functional groups on the ionic liquid that can chemically react with the target gas. We show results of CO2 uptake as a function of pressure and temperature for a variety of ionic liquids, containing primary and secondary amine functionality on either the cation or the anion. Using FTIR we are able to differentiate between physically dissolved CO2 and CO2 that has reacted with the amine moiety. We show how the capacity and the enthalpy for the reaction can be tailored by the inclusion of additional functionality in the ionic liquid. The physical solubility of N2 and O2 in these same ILs remains low so that the selectivity for CO2 removal is extremely high. Preliminary process design calculations indicate that the functionalized ionic liquids require significantly less energy for CO2 capture from post-combustion flue gas than the commercially available aqueous amine technology.
Location: John Stauffer Science Lecture Hall (SLH) - 100
Audiences: Everyone Is Invited
Contact: Petra Pearce Sapir
-
SIZE MATTERS: Mechanical properties of materials at nano-scale
Thu, Oct 22, 2009 @ 12:45 PM
Mork Family Department of Chemical Engineering and Materials Science
Conferences, Lectures, & Seminars
Distinguished Lecture SeriesPresentsJulia GreerCaltechAbstract:While "super-sizing" seems to be the driving force of our food industry, the direction of materials research has been quite the opposite: the dimensions of most technological devices are getting ever smaller. These advances in nanotechnology have a tremendous impact on parts of the economy as diverse as information, energy, health, agriculture, security, and transportation. Some of the examples include data storage at densities greater than one terabit per square inch, high-efficiency solid-state engines, single-cell diagnostics of complex diseases (e.g. cancer), and the development of ultra light yet super-strong materials for vehicles, with the component sizes comprising these technological devices reduced to the sub-micron scale. The functionality of these devices directly depends on their structural integrity and mechanical stability, driving the necessity to understand and to predict mechanical properties of materials at reduced dimensions. Yield and fracture strengths, for example, have been found to deviate from classical mechanics laws and therefore can no longer be inferred from the bulk response or from the literature. Unfortunately, the few existing experimental techniques for assessing mechanical properties at that scale are insufficient, not easily accessible, and are generally limited to thin films. In order to design reliable devices, a fundamental understanding of mechanical properties as a function of feature size is desperately needed; with the key remaining question whether materials really are stronger when the instrumental artifacts are removed, and if so then why and how. A key focus in Professor J.R.Greer's research is the development of innovative experimental approaches to assess mechanical properties of materials whose dimensions have been reduced to nano-scale not only vertically but also laterally. One such approach involves the fabrication of nanopillars with different initial microstructures (single crystalline, nano-crystalline, amorphous, etc.) ranging in diameter from 100 nm to 800nm by using Focused Ion Beam (FIB) and micro-fabrication approaches. Their strengths in uniaxial compression and tension are subsequently measured in a one-of-a kind in-situ mechanical deformation instrument developed in the Greer lab. This instrument is called SEMentor, as it is comprised of the Scanning Electron Microscope (SEM) and Nanoindenter, which allow for precise control of displacement and loading rates, as well as for simultaneous video capture. Some representative images of various nano-sized mechanical testing specimen are shown in Figure 1. In this seminar we will discuss the differences observed between mechanical behavior in two fundamental types of crystals: face-centered cubic (fcc) and body-centered cubic (bcc), as well as of nano-crystalline Nickel and amorphous metallic glasses with nano-scale dimensions. In a striking deviation from classical mechanics, we observe a SMALLER IS STRONGER phenomenon in single crystals manifested by the significant (~50x) increase in strength of as material size is reduced to 100nm. To the contrary, nano-crystalline materials tend to exhibit the opposite trend: SMALLER is SOFTER. Finally, metallic glasses, whose Achilles; heel has always been the occurrence of catastrophic failure at very small strains, exhibit non-trivial ductility when reduced to nano-scale. Furhtermore, unlike in bulk where plasticity commences in a smooth fashion, all of these materials exhibit numerous discrete strain bursts during plastic deformation. These remarkable differences in the mechanical response of nano-scale solids subjected to uniaxial compression and tension challenge the applicability of conventional plasticity models at the nano-scale. We postulate that they arise from the effects of free surfaces, leading to the significant differences in dislocation behavior for the case of crystals, grain-boundary activity for the case of nano-crystalline solids, and shear transformation zones in metallic glasses. and serve as the fundamental reason for the observed differences in their plastic deformation. These mechanisms and their effect on the evolved microstructure and the overall mechanical properties will be discussed.
Location: John Stauffer Science Lecture Hall (SLH) - 100
Audiences: Everyone Is Invited
Contact: Petra Pearce Sapir