Critical experiments were performed on Al and MoO3 thermites. The diameter and alumina shell thickness of the Al nanoparticles were varied, and flame propagation velocities were measured. The results strongly support the melt-dispersion mechanism and contradict the diffusion oxidation mechanism. The parameters that control the oxidation rate and flame velocity are justified and directions for the synthesis of Al nanoparticles (which are opposite to the current directions based on diffusion oxidation) are suggested. An equation for the flame velocity versus Al nanoparticle geometrical parameters, thermomechanical properties, and synthesis parameters is formulated.

1.
B. S.
Bockmon
,
M. L.
Pantoya
,
S. F.
Son
,
B. W.
Asay
, and
J. T.
Mang
,
J. Appl. Phys.
98
,
064903
(
2005
).
2.
K. B.
Plantier
,
M. L.
Pantoya
, and
A. E.
Gash
,
Combust. Flame
140
,
299
(
2005
).
3.
J.
Granier
and
M. L.
Pantoya
,
Combust. Flame
138
,
373
(
2004
).
4.
K.
Park
,
D.
Lee
,
A.
Rai
,
D.
Mukherjee
, and
M.
Zachariah
,
J. Phys. Chem. B
109
,
7290
(
2005
).
5.
A.
Rai
,
K.
Park
,
L.
Zhou
, and
M.
Zachariah
,
Combust. Theory Modell.
10
,
843
(
2006
).
7.
M. A.
Trunov
,
M.
Schoenitz
,
X.
Zhu
, and
E. L.
Dreizin
,
Combust. Flame
140
,
310
(
2005
).
8.
V. I.
Levitas
,
B. W.
Asay
,
S. F.
Son
, and
M. L.
Pantoya
,
Appl. Phys. Lett.
89
,
071909
(
2006
).
9.
V. I.
Levitas
,
B. W.
Asay
,
S. F.
Son
, and
M. L.
Pantoya
,
J. Appl. Phys.
101
,
083524
(
2007
).
10.
Current trends are to substitute the oxide shell with metals such as gold, nickel, and silver [
T. J.
Foley
,
C. E.
Johnson
, and
K. T.
Higa
,
Chem. Mater.
16
,
4086
(
2005
)]
or C13F27COOH [
R. J.
Jouet
,
J. R.
Carney
,
R. H.
Granholm
,
H. W.
Sandusky
, and
A. D.
Warren
,
Mater. Sci. Technol.
22
,
422
(
2006
)] to reduce the dead weight and initial barrier for diffusion. This is useful for some applications but not for those where the goal is to increase the reaction and flame velocity, because the strength of such shells is significantly lower compared to alumina and MDM cannot operate. Indeed, even bare Al nanoparticles with D=20nm require more than 1s for complete oxidation at T=900°C (Ref. 4).
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