Solid-State Reactions in Model Oxide Systems

AbstractThe kinetics of thin-film solid-state reactions have been investigated in two model spinel forming oxide systems, NiO/Al2O3 and MgO/Fe2O3. In the NiO/Al2O3 system, thin-films of epitactic NiO were reacted with (0001), , and orientated Al2O3 (corundum). The kinetics of the spinel forming reaction for this system were found to be linear-parabolic in nature. Additionally, it was found that the kinetics of the spinel-forming reaction varied by nearly two orders of magnitude between the fastest and slowest diffusion couples. The substrate determines the orientation of the overlayers and thereby the structure of the phase boundaries. In the MgO/Fe-oxide system, thin films of epitactic Fe oxide were reacted with {001} MgO. The kinetics of this spinel forming reaction were parabolic in nature, indicative of diffusion control. In contrast to the N1O/Al2O3 system, the movement of phase boundaries are not the step controlling the reaction rate, but rather the diffusion of one of the cations across the reaction layer. In comparing the reaction rates for the two systems the activation energy for the formation of the spinel product in the MgO/Fe-oxide system was found to be almost a factor of 4 lower in comparison to the NiO/Al2O3 system.

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Kinetics of Triplet Sublevel Selective Photochemical Reactions in the Solid State

Zeitschrift für Naturforschung A ◽

10.1515/zna-1981-0709 ◽

1981 ◽

Vol 36 (7) ◽

pp. 743-750

Author(s):

Manfred Gehrtz ◽

Christoph Bräuchle ◽

Jürgen Voitländer

Keyword(s):

Solid State ◽

Reaction Rates ◽

Photochemical Reactions ◽

Solid State Reactions ◽

Physical Activation ◽

Zero Field ◽

Excited Triplet ◽

The Individual ◽

Activation Rates ◽

Kinetics Of

Abstract A detailed description of the overall kinetics of photochemical reactions has to deal with photo-physical activation and de-activation rates as well as with true photochemical rates. Based on the hypothesis that for photoreactions involving the lowest excited triplet state the chemical reaction rates of the individual triplet zero-field levels have different values, a method is presented for the evaluation of these rates from bulk measurements under steady state illumination conditions. The complications arising from the detection of solid state reactions are discussed, and a simple solution is given, illustrated by a numerical example.

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Solid State Interfacial Reactions Between Tic Thin Films and Ti3AI Substrates

MRS Proceedings ◽

10.1557/proc-398-275 ◽

1995 ◽

Vol 398 ◽

Cited By ~ 1

Author(s):

Weimin Si ◽

Michael Dudley ◽

Pengxing Li ◽

Renjie Wu

Keyword(s):

Thin Films ◽

Solid State ◽

Ion Beam ◽

Depth Profiling ◽

Solid State Reactions ◽

Reaction Products ◽

Ion Beam Sputtering ◽

Thermodynamical Equilibrium ◽

Beam Sputtering ◽

Kinetics Of

ABSTRACTThe products and kinetics of solid state reactions between TiC and Ti3Al have been investigated using X-ray diffractometry (XRD) and Auger electron spectroscopy (AES) with Ar ion beam sputtering. Diffusion couples were prepared by sputtering TiC thin films onto polished Ti3AI substrates, and then isothermally annealed in vacuum in the temperature range of 800 to 1000°C for 0.25 to 2.25 hours. The thickness of the interfacial reaction layer was obtained from AES elemental concentration depth profiling, while the reaction products were identified from XRD spectra. In the TiC/Ti3Al system, the reaction product was primarily P(Ti3AlC) phase. The growth-rate of the reaction product was fitted to a parabolic growth law (dZ/dt = k1/Z) and the activation energy of the rate constant was about 36.16 kcal/mole. The reaction mechanism will be discussed on the basis of thermodynamical equilibrium in Ti-Al-C ternary system.

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TEM studies of solid-state reactions in sputter-deposited Nb/Al multilayer thin films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100167561 ◽

1996 ◽

Vol 54 ◽

pp. 1020-1021

Author(s):

F. Ma ◽

S. Vivekanand ◽

K. Barmak ◽

C. Michaelsen

Keyword(s):

Thin Films ◽

Solid State ◽

Stoichiometric Composition ◽

Analytical Electron Microscopy ◽

Grain Structure ◽

Solid State Reactions ◽

Multilayer Thin Films ◽

X Ray Diffraction ◽

X Ray ◽

Sputter Deposited

Solid state reactions in sputter-deposited Nb/Al multilayer thin films have been studied by transmission and analytical electron microscopy (TEM/AEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The Nb/Al multilayer thin films for TEM studies were sputter-deposited on (1102)sapphire substrates. The periodicity of the films is in the range 10-500 nm. The overall composition of the films are 1/3, 2/1, and 3/1 Nb/Al, corresponding to the stoichiometric composition of the three intermetallic phases in this system.Figure 1 is a TEM micrograph of an as-deposited film with periodicity A = dA1 + dNb = 72 nm, where d's are layer thicknesses. The polycrystalline nature of the Al and Nb layers with their columnar grain structure is evident in the figure. Both Nb and Al layers exhibit crystallographic texture, with the electron diffraction pattern for this film showing stronger diffraction spots in the direction normal to the multilayer. The X-ray diffraction patterns of all films are dominated by the Al(l 11) and Nb(l 10) peaks and show a merging of these two peaks with decreasing periodicity.

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Electric-Field Effects on Reactions Between Oxides

MRS Proceedings ◽

10.1557/proc-481-303 ◽

1997 ◽

Vol 481 ◽

Author(s):

Matthew T. Johnson ◽

Shelley R. Gilliss ◽

C. Barry Carter

Keyword(s):

Solid State ◽

Electric Field ◽

Elevated Temperatures ◽

Ionic Current ◽

Reaction Rates ◽

Solid State Reactions ◽

Interfacial Stability ◽

Electric Field Effects ◽

Thin Film Diffusion ◽

Microscopy Techniques

ABSTRACTThin films of In2O3 and Fe2O3 have been deposited on (001) MgO using pulsed-laser deposition (PLD). These thin-film diffusion couples were then reacted in an applied electric field at elevated temperatures. In this type of solid-state reaction, both the reaction rate and the interfacial stability are affected by the transport properties of the reacting ions. The electric field provides a very large external driving force that influences the diffusion of the cations in the constitutive layers. This induced ionic current causes changes in the reaction rates, interfacial stability and distribution of the phases. Through the use of electron microscopy techniques the reaction kinetics and interface morphology have been investigated in these spinel-forming systems, to gain a better understanding of the influence of an electric field on solid-state reactions.

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