combustion of coarse monodisperse titanium particles in air o. g. glotov institute of chemical...
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Combustion of coarse monodisperse titanium particles in air
O. G. Glotov
Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Novosibirsk, Russia
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Content
Introduction \ Ti is unusual interesting object \ production of nanosized photocatalytic TiO2 particles in situ
Experiment \ creation of monodisperse burning titanium particles \ techniques: video record, quenching & sampling, SEM & EDS
Results \ evolution events \ motion law \ fragmentation \ condensed combustion products
Conclusions \ 300, 390 and 480 micron are identical \ heterogeneous reaction \ fir-branch fragmentation \ full metal consumption
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Refractory nonvolatile metal with с refractory oxide
Melting point: Ti 1939 K , TiO2 2130 К
Oxide density lower than metal density
Density: Ti 4.506 g/cm3, TiO2 4.250 g/cm3
Oxide protects metal against oxidation up to 500-550°С.
Then oxide dissolves in metal.
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Ti - interesting object for metal combustion theory
Ti
Engineering material
Metallic fuel
Ti considerably differ from Al, Mg, B
It is necessary to study the mechanism of Ti particles combustion in air
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To optimize the burning process for achieving highest completenessof metal combustion and high yield of smoke-like oxide with demanded parameters …
50 c
m
[Evgeny Shafirovich, Soon Kay Teoh, Arvind Varma. Combustion of levitated titanium particles in air / Combustion and Flame. 2008. V. 152, P. 262–271.]Sieves 20–25, 25–32, …, 90–106, 106–125 micron, electromagnetic levitation, laser ignition.
[I. E. Molodetsky, E. P. Vicenzi, E. L. Dreizin, C. K. Law. Phases of Titanium Combustion in Air // Combustion and Flame. 1998. V. 112, P. 522–532. ]Spark micro arc, ignited spheres 240 и 280 micron
[T. A. Andrzejak, E. Shafirovich, A. Varma. On the Mechanisms of Titanium Particle Reactions in O2/N2 and O2/Ar Atmospheres // Prop. Explos. Pyrotech. 2009, V. 34, P. 53–58.]Cylindrical sample 3.1253.125 mm. Laser heating. Thermocouple wires Pt/Rh 200 micron are welded to lateral surface.
Typical pyrotechnic
Tipowder
85 % mass < 50 micron
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Specimen, producing the burning monodisperse spherical Ti particles
Non-metalized composition-matrix with inserted inclusions made of metalized composition
Matrix ignites and ejects the particles
Inclusions transform into burning particles (agglomerate)
Number and size of the burning particles are predetermined by number and parameters of inclusions
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Specimen preparation
Inclusions: 69 % Ti, 31 % energetic binder
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Matrix:
27 % energetic binder,
50 % HMX,
23 % AP
8 Specimen preparation
9 Experiment
Catchpot filled with Ar1 – body2 – funnel3 – Petri dish
Specimen
D = 390 micron, L = 115 cm
Treatment of video records
Events
► Time moment
► Coordinate
► Velosity
Parameters of movement
► x(t)
► v(t)
Parameters of fragments’ scatter
► r
► vr
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Events:«b» (begin) – fragmentation starts«e» (end) – fragmentation is over«s» (stop) – forced quenching of a particle in the catchpot «z» (zero) – particle disappears \ vanishes«z» – “star” shape fragmentation
Events and scenarios
b
e z
Scenario bez
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Parameters of b, e, z events12
Size and morphology evolution
30 6 TiTimD
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Particles motion
x(t) v(t)
0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2 1,3
0
50
100
150
200
250
300
D=477 mcmV0=0,2 m/sCd=31/Re
x, c
m
time, s0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2
0
50
100
150
200
250
300
350
400
v,
cm
/s
time, s
V0=0,2 m/sCd=31/Re
ApproximationCd = A/Re A(D) = –7+0.126·D v0 = 139–0.202·D, v0 in cm/s, D in 300-480 micron
300 350 400 450 5000
10
20
30
40
50
60
70
80
A
D (мкм)
A(D) = -7.0 + 0.126D
Stokes classic Cd = 24/Re
A(D)
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A new shape of fragmentation – «fir branch»
Al
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star fir branch
for particles D > 300 micron
Sampling of the condensed combustion products
specimen
stainless steel tube 580 см
Petri dish
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Condensed combustion products
Numerical size distribution
10 20 30 400
1000
2000
3000
4000
5000
6000
N/N
mo
the
r
D, micron
log-normal approximationxc = 2.2 w = 0.33 A = 8746
R2 = 0.88 Data for 300-micronburning mother
particles
mother
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EDS data18
No shell-kernel structure
EDS
data
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EDS data set
TiO2.76 upon the average
1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0
TiOTi3O
4
Ti2O3
Ti3O5
Ti4O7
Ti8O15
TiO2
TiO3
TiO4
TiO5
O/Ti
lower oxide higher oxide
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Conclusions-121
The technique for creation the monodisperse burning Ti particles with size of hundred microns has been developed to investigate the Ti combustion mechanism
For the first time the evolution of particles of titanium with size of 300, 390 and 480 microns formed by merging a great number of small particles has been examined
Qualitative features of that size particles behavior are identical
Formation of a spherical particle occurs due to heterogeneous reaction and at an initial stage is accompanied by a bright luminescence
Motion of a burning particle can be described with use of drag coefficient exceeding classical Stokes’ coefficient (Cd 50/Re for 480-micron particles)
Prominent feature of the Ti particle evolution is fragmentation which in this specific case is performed with preservation of a mother particle (projection of splinters reminds a fir-tree branch). During fragmentation, there is an appreciable loss of weight and decrease in speed of a particle
After the combustion termination as a result of full metal consumption the residual particle consists of various oxides – from TiO to TiO5; its diameter is by 1.5-2 times less than initial one
22 Conclusions-2
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Thank you for attention !