Search

In this study the surface segregation of In from a dilute Cu(In) alloy to the surface was investigated. The Cu(In) alloy was prepared by diffusion doping. A thin layer of In was deposited onto the backside of a polycrystalline Cu crystal. The In layer was covered with a thin Cu layer to prevent the In from melting and evaporating from the Cu crystal. The Cu crystal was annealed in an Ar gas atmosphere. During annealing the temperature was increased stepwise from 150 to 900 to prevent the In layer from melting. Finally the Cu crystal was annealed at 900 for 456 hours. As a result, the polycrystalline Cu crystal was successfully doped with an In concentration of 0.059 at%. Using Auger electron spectroscopy (AES) coupled with an Ar+ ion gun (for sur- face sputter cleaning) and a programmed crystal heater inside the ultra high vacuum (UHV) chamber, the segregation profiles where recorded by monitoring the surface condition of In and S on the Cu crystal during linear heating and constant temperatures heating. The constant temperature segregation measurements were performed in the tem- perature range 460 to 580 . The segregation profiles showed that both In and S segregates from the Cu crystal. In segregates to the surface at a much higher rate than S. In reached a maximum surface coverage of 25 % for the temperatures 460 ,490 and 520 and 16 % for temperatures 550 and 580. Both the In and S segregation profiles were fitted with semi-infinite solution of Fick’s equation and the segregation parameters (Q and D0) were obtained for In as Q = 191.9 kJ.mol−1, D0 = 1.1 × 10−5 m2.s−1 and for S as Q = 201.1 kJ.mol−1, D0 = 4.4 × 10−2 m2.s−1. The linear temperature measurements were carried out from the temperature range 100 to 800 at heating rates of 0.025; 0.05; 0.1 and 0.2.s−1. All seg- regation profiles showed In segregation to the surface that reached a surface maxi- mum coverage of 23−25 %. The segregation of In was accompanied by a slow seg- regating S that replaced the In co

Summary: The local buckling failure mechanism and subsequent debond propagation in sandwich columns and panels with composite face sheets containing a face-to-core debond is experimentally, analytically, and numerically analyzed. The experimental investigation is based on a comprehensive test program to examine local buckling failure and fracture toughness of sandwich specimens consisting of glass/epoxy face sheets over various density PVC foams and a balsa wood core. Elastic foundation and finite element models are developed for prediction of the local buckling load of sandwich columns and panels containing an implanted debond at the face/core interface. Nonlinear finite element analysis was conducted to investigate debond propagation in the post-buckling region. Overall, model predictions were in agreement with experimental results. The buckling load was found to decrease with reduced face sheet stiffness, reduced core modulus, and increased debond length. Sandwich panels with circular debonds were more resistant to local buckling than those with square debonds of the same characteristic size. Circular debonds of 50 mm diameter and square debonds of 45 mm side length established the threshold for local buckling failure. Nonlinear finite element analysis of debonded sandwich columns and panels showed that the major crack displacement is opening (mode I). The tendency of the crack tip to first open and then close after buckling of the face sheet is believed to be due to the formation of an eccentric load path at the onset of buckling. The fracture mechanics analysis of debonded sandwich panels showed that the energy release rate is much higher in the direction perpendicular to the applied load than along the loading direction, and exceeds the measured toughness value in the transverse direction. This explains the experimental observation that a debond embedded in a sandwich panel tends to propagate in the transverse direction., College of Engineering and Computer Science, Collection: FAU Electronic Theses and Dissertations Collection, Thesis (Ph.D.)--Florida Atlantic University, 2005.

Summary: Debond failures in structural sandwich may lead to severe reductions in load-bearing capability of the structure because of impartial transfer of shear and tensile forces between facing and core due to the lack of interfacial bonding. Analysis of interfacial bonding in sandwich specimens subjected to transverse tensile and shear forces is presented. Stress intensity factors computed based on the near-tip displacement field are related to experimental crack growth observation on the sandwich beams with aluminum skins on a wide range of PVC foam cores. Experimentally it was found that the crack tends to grow at the interface between the bondline and core as opposed to skin/bondline interface. In shear dominated fields, a pre-existing flow tended to deflect into the core rather than grow along the interface. The tendency for kinking and the direction of the kink is examined experimentally and analyzed using the finite element method., College of Engineering and Computer Science, Collection: FAU Electronic Theses and Dissertations Collection, Thesis (M.S.E.)--Florida Atlantic University, 1993.

Summary: The planar, dinuclear, tridentate ligands, 1,3,5,7-tetrakis(2-pyridylimino)benzodipyrrole (TAII) and 1,3,5,7-tetrakis(4,6-dimethyl-2-pyridylimino)benzodipyrrole (DiMeTAII) were synthesized and characterized as were all intermediates characterized by both infrared and 1H-NMR spectra. Evidence is presented for the formation of Mo4(OAc)6-(DiMeTAII) (I), the dinuclear analog of Mo2(OAc)3-BAII using UV/Vis to show the delta--->delta* transition typical of the quadruple bond and for the determination of percent molybdenum which is consistent with the proposed structure. A review of recent studies into the field of quadruply bonded metal containing polymers will be discussed along with application of compound (I) in this field., Charles E. Schmidt College of Science, Degree granted: Thesis (M.S.)--Florida Atlantic University, 1993., Collection: FAU Electronic Theses and Dissertations Collection

Summary: The complexes MoX4(Multiimine)2, where X = Cl, Br, I and Multiimine = dimethyl-bipyridine, bipyridine, phenanthroline, bipyrazine, bipyridazine and bipyrimidine, have been prepared. The product complexes apparently contain non-bridged quadruple molybdenum-molybdenum bonds. Each molybdenum is coordinated to a bidentate diimine and two halogen atoms. An electronic absorption study reveals an important trend that the intensity of the delta-->delta* transition increases with decreasing energy. This shows the energy of this band is determined by mixing of this transition with a metal-to-ligand charge transfer transition. An EEC type mechanism is proposed for the redox behavior of these compounds on the basis of an electrochemical study and some consistent results are obtained by correlating the oxidation potentials with the delta-->delta* transition energies. Also, fairly good correlations of both the delta-->delta* transition energies and the oxidation potentials with pk(a) of L are obtained., Thesis (M.S.)--Florida Atlantic University, 1991.