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 TiO 2 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, TiO К Oxide density lower than metal density Density: Ti g/cm 3, TiO g/cm 3 Oxide protects metal against oxidation up to °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 completeness of metal combustion and high yield of smoke-like oxide with demanded parameters … 50 cm

[Evgeny Shafirovich, Soon Kay Teoh, Arvind Varma. Combustion of levitated titanium particles in air / Combustion and Flame 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 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   mm. Laser heating. Thermocouple wires Pt/Rh  200 micron are welded to lateral surface. Typical pyrotechnic Ti powder 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 Ar 1 – body 2 – funnel 3 – 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 ► v r 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 ez Scenario bez 1

Parameters of b, e, z events 1212

Size and morphology evolution 1313

Particles motion x(t)v(t) Approximation Cd = A/Re A(D) = – ·D v 0 = 139–0.202·D, v 0 in cm/s, D in micron A(D) 1414

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  5  80 см Petri dish 16

Condensed combustion products Numerical size distribution Data for 300-micron burning mother particles mother 17

EDS data 18

 No shell-kernel structure EDS data 19

EDS data set TiO 2.76 upon the average 20

Conclusions 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 (C d  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 TiO 5 ; its diameter is by times less than initial one 2 Conclusions-2

2323 Thank you for attention !