ICMCTF 2012! - CD-Lab Application Oriented Coating Development

distributions for several peaks to yield temperature values of 2.24 to 3.27
eV, and found them to be within reasonable estimates based on the
measured electrical energy delivered to each device.
More recently, we acquired streak spectrographs from Ni/Al laminates
encapsulated with vacuum-deposited parylene. This process insured that
any emission came only from the electrically Ni/Al laminates, and should
allow better quantification of temperature without the same level of
interference from residual gases. The encapsulation layer caused a much
slower 60 ns rise to peak emission intensity, compared to 8 ns for previous,
un-encapsulated tests. This rise time likely corresponded to a physical
acceleration of a portion of the encapsulation layer away from the substrate,
which we will measure and report in the final paper. We will also correlate
spectroscopic emission at early times with measured electrical input, and
gain insight into phase changes, mixing, and expected exothermic release
over these extremely short timescales. These studies are important for future
nanomanufacturing techniques, where it may be necessary to control spatial
thermal distributions much more precisely by careful control of the
timescales over which reactions take place.
10:20am TS3-1-8 Numerical simulations of self-propagating reactions
and analysis of reacted microstructures in Ru/Al multilayers, K. Woll
(k.woll@mx.uni-saarland.de), Functional Materials, Dept of Materials
Science and Engineering, Saarland University, Germany, I. Gunduz, C.
Rebholz, Dept. of Mechanical and Manufacturing Engineering, University
of Cyprus, Cyprus, F. Mücklich, Functional Materials, Dept of Materials
Science and Engineering, Saarland University, Germany
Energetic materials based on equiatomic Ru/Al multilayers have been
recently introduced by our group. The unusual combination of high
temperature as well as room temperature properties makes the equiatomic
Ru/Al system interesting as a new energetic material. So far, selfpropagating
reactions in Ru/Al multilayers have been studied with a focus
on the early stages of reaction. Parameters such as front velocity and
reaction temperature as well as the reaction mechanism have been
experimentally determined and compared to other systems. These results
clearly demonstrate that the Ru/Al system expands the reaction parameter
range of previously used systems in terms of velocity and temperature.
However, for a more detailed understanding of the reactions, numerical
simulation which focuses on the early reaction stages as well as
microstructural analysis to reveal the processes during later stages of
cooling was performed. Experimental studies were carried out to investigate
the effects of the interaction with surrounding air as a function of multilayer
period. For this, pyrometric measurements to follow the temperature
evolution during the reaction and cross sectional transmission electron
microscopy analysis of reacted foils were performed.
10:40am TS3-1-9 Fabrication, Characterization and Applications of
Novel Nanoheater Structures, Z. Gu (Zhiyong_Gu@uml.edu), Q. Cui, J.
Chen, J. Buckley, University of Massachusetts Lowell, US, T. Ando, D.
Erdeniz, Northeastern University, US, P. Wong, Tufts University, US, C.
Rebholz, A. Hadjiafxenti, I. Gunduz, C. Doumanidis, University of Cyprus,
Cyprus
Nanoheaters are reactive nanostructures that can generate localized heat
through controlled ignition. Besides the widely used nanofoil structure with
multiple alternative aluminum-nickel (Al-Ni) layers, various new
nanostructures have been fabricated in the last several years, including
consolidated compacts, bimetallic nanoparticles, and ball milled micro/nano
powders. In this presentation, we show that (1) Al-Ni compacts can be
fabricated by a novel ultrasonic powder consolidation (UPC) method, using
Al and Ni nanopowders as source materials; (2) Al-Ni bimetallic
nanoparticles have been synthesized by a galvanic replacement reaction
method using Al nanoparticle templates; (3) Al-Ni micro/nanopowders can
be prepared by a ball milling method using Al and Ni powders. The
structure and compositions of the nanoheater structures have been
characterized by electron microscopies (SEM and TEM), energy dispersive
x-ray spectroscopy (EDS), and x-ray diffraction (XRD). The ignition of
these nanoheater structures has been initiated by the electrical (ohmic)
method, microplasma (plasma arc discharge) method, etc. The reaction
characteristics of the nanoheater structures were investigated using high
speed optical and infrared imaging, and the thermal characteristics of the
samples were studied using differential scanning calorimetry (DSC). These
novel nanoheater structures have great potential to be used in micro-joining,
microelectronics assembly, and flexible electronics bonding.
Thursday Morning, April 26, 2012 82
11:00am TS3-1-10 Effect of Mechanical Activation on SHS and
Structure Formation in Nanostructured Geterogenious Reaction
Systems, N. Shkodich (n.f.shkodich@mail.ru), Vadchenko, Rogachev,
Sachkova, Institute of Structural Macrokinetics and Materials Science RAS,
Russia, Neder, Magerl, Institute of Crystallography and Structural Physics,
University of Erlangen-Nürnberg, Germany
One of the possibilities to produce nanostructured materials is the
combination of two non-equilibrium processing techniques, namely
mechanical activation (MA) and self-propagating high-temperature
synthesis (SHS). Mechanical activation provides the possibility of both
modificating the conditions of the chemical reaction run and changing the
thermal parameters of the synthesis (temperature, combustion velocity,
heating rate, and others) thus leading to the different structures and
properties of the final product.
Our investigation aimed at establishing the influence of MA on SHS. The
Ni─Al, Ti─BN and Ti─SiC─C systems were studied. Green mixtures were
prepared by dry mixing of the initial components in china crucibles at the
stoichiometric ratios corresponding to the following reactions : Ni+Al =
NiAl, 3Ti+2BN = 2TiN+TiB2 and 3Ti+SiC+C = Ti3SiC2.
Preliminary MA was preformed in a water cooled planetary ball mill (AGO-
2) type at room temperature under argon. The milling procedure was carried
out at the ball/mill ratio of 20: 1. The milling time varied from 0.20 s to 30
min.
The resultant mechanically activated particles were composed of layers of
the initial components alternating with each other at the nano level [1, 2]..
During mechanical activation of Ni+Al mixtures up to 7 min, specific
contact area between reagents Ni and Al increased approximately 15-20
times for each fraction.
Using high-resolution SEM and TEM methods for microstructural
investigation of Ni─Al activated samples, nanoscale structural components
were observed. Their average atomic weight was intermediate between the
Ni and Al. The main influence on the reactivity of heterogeneous systems
Ni ─ Al during milling is formation of nanoscale X-ray amorphous phases
and solid solutions.
Ignition temperature was measured for small amounts of activated mixtures
in the form of activated particles, pressed pellets, and rolled foil. The
dependences of the ignition temperature on the MA duration and the way of
the sample preparation were studied. It was found that after MA for 0 − 30
min the ignition temperature lowered by approximately 600°C for Ti─BN
and Ti─SiC─C systems; after MA for 0– 7 min it could be diminished by
300–400 °C for N─Al system.
For the determination of the internal microstructure, the particle size and
microstrains of mechanically activated powders 3Ti+2BN and 3Ti+SiC+C
and of the combustion products were analyzed by X-ray powder diffraction
on a Huber Guinier diffractometer at the Institute of Crystallography and
Structural Physics, in Erlangen, Germany.
Analysis showed that an increase in the MA duration of the 3Ti+2BN and
3Ti+SiC+C mixtures led to a decrease in the peak intensities and
broadening of the Ti peaks. With increasing activation time, the BN reflexes
in the 3Ti+2BN reaction mixtures were instantly broadened and in three
minutes their intensity became comparable to that of the background.
Similar behavior was also observed in case of graphite in the activated
3Ti+SiC+C mixtures. This evidences the destruction of the crystal structure
(amorphization) of boron nitride and graphite in the MA process [3].
The effect of milling time on the crystalline size and strain in the powder
mixtures and SHS products we determined from line broadening analysis of
the XRD peaks. The Rietveld full profile refinements were carried out with
the Fullprof Suite. As a result of up to 30 min MA, the average size of the
Ti crystallites was found to reduced down to 25 and 50 nm in the Ti + BN
and Ti─SiC─C systems, respectively. Mechanical activation was found to
affect the size of product crystallites. The value of the micro stains
increased with the MA duration.
Formation of nanocomposites at the stage of mechanical activation provides
proper conditions for synthesizing nanostructured SHS materials with a
complete inherence of the precursors’ structural morphology.
References
[1] N.F. Shkodich, N.A. Kochetov, A.S. Rogachev, D.Yu. Kovalev, N.V.
Sachkova, Izv. Vyssh. Uchebn. Zaved. Tsvetn. Metall., 5, (2006) 44-50.
[2] M.A. Korchagin, M.R. Sharafutdinov, N.F. Shkodich, B.P. Tolochko,
P.A. Tsygankov, I.Yu. Yagubova. Nuclear Instruments and Methods in
Physics Research A, 575, (2007) 149-151.
[3] Shkodich N. F, Rogachev A. S, Neder R. B., Magerl A., S.G.
Vadchenko, and O. Boyarchenko, High-Temperature Ceram. Mater.
Composites, 911 (2010) 881-887.
Acknowledgement