Combustion of coarse monodisperse titanium particles in air

Combustion of coarse monodisperse titanium particles in air

O. G. Glotov

Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Novosibirsk, Russia

1

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

2

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.

3

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

4

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

55

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

6

Specimen preparation

Inclusions: 69 % Ti, 31 % energetic binder

7

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

10

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

11

Parameters of b, e, z events12

Size and morphology evolution

30 6 TiTimD

13

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

15

star fir branch

for particles D > 300 micron

Sampling of the condensed combustion products

specimen

stainless steel tube 580 см

Petri dish

16

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

20

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 !