SHOCK-WAVE SYNTHESIS OF METAL SHOCK-WAVE SYNTHESIS OF METAL NANOPARTICLES FROM CARBOXYLATESNANOPARTICLES FROM CARBOXYLATES

B.P. TolochkoB.P. Tolochko11, V.M. Titov, V.M. Titov22, , A.P. ChernyshevA.P. Chernyshev1,31,3*, K.A. Ten*, K.A. Ten22, E.P. Pruuel, E.P. Pruuel22,, I.L. ZhoginI.L. Zhogin11, P.I. Zubkov, P.I. Zubkov22, N.Z. Lyakhov, N.Z. Lyakhov11, L.A. Lukiyanchikov, L.A. Lukiyanchikov22, M.A. , M.A.

SheromovSheromov44

11Institute of SolidInstitute of Solid State Chemistry and Mechanochemistry, Novosibirsk, State Chemistry and Mechanochemistry, Novosibirsk, 630128, Russia 630128, Russia 22Lavrentiev Institute of Hydrodynamics, Novosibirsk, Lavrentiev Institute of Hydrodynamics, Novosibirsk,

630090 Russia630090 Russia33Novosibirsk State Technical University, Novosibirsk, 630092 RussiaNovosibirsk State Technical University, Novosibirsk, 630092 Russia

44Budker Institute of Nuclear Physics, Novosibirsk, 630090 RussiaBudker Institute of Nuclear Physics, Novosibirsk, 630090 Russia* * chernysher@yahoo.comchernysher@yahoo.com

Dependence of TNT conductivity vs. time (schematic)

The sections ab and bc correspond to growing hot spots and ceasing chemical reaction, respectively.

0 1 2

1

2

3

4

5

0

Con

duct

ivity

, a.u

.

a

b

cd

Time, µs

~Here is a typical distance between “hot points”, χ is a mean temperature coefficient of conductivity. For trinitrotoluene χ is about 10–7 m2/s. At τ~100 ns equation we obtain using Michelson that approximately equals 10–7 m.

p

p

The particles as part of explosive

The particles as inclusions

Heat exchange

2p

eq ~

It is necessary to emphasize that the energy producing under detonation conditions into precursor particles less than in other region occupied by high explosives. The characteristic temperatures of such a particle less than one of environment due to the thermodynamic processes occurring are adiabatic. Really the time of temperature relaxation is estimated as

The calculations gives τ =10–3 s, that is ~103 times as large as the typical time of the reaction mixture formation ~ 10–6s. Therefore at first the particles of precursor are heated under shock compression (at first 0.2–0.5 mcs).

The temperature of precursor

DD

TCuaucududTC V

V

020

20 aubucD

The temperature T2 was found by the equation:

Where is the Hugoniot adiabat.

T2 is approximately equal to 2300 K for AgSt and 1800 K for ZnSt2 at pressure 34 GPa. It is supposed that /V=const.

Pressure

Hot spot

Calculations

0 2000 4000

2000

40004 103

300

T u( )

5 1030 u2000 4000

0

20

4040

2.009 10 3

P u( )

40001 u

0 2000 4000

2000

40004 103

300

T u( )

5 1030 u

AgSt

2000 40000

20

4040

1.883 10 3

P u( )

40001 u

T 3795( ) 1.789 103

ZnSt2

U, m/s

T, K

U, m/s

T, K

U, m/s

U, m/s

P, GPa

P, GPa

Thermodynamics under HP

p

po

dppTVTSTTHpTG ),()(,

i

ii pTVpTV ),(),(

•Kinetics restrictions on the rate of transformation under high pressureThe constant of the chemical reaction rate, r, depends on the pressure:

lnr = const – ΔV#·p/(RT), (3)here ΔV# = V# – Vi > 0, ΔV# - the molar volume of the activated complex, Vi –the sum of molar volumes of initial species.

Hence the precursor heating caused by work of compression is not enough for pyrolysis of carboxylates under super high pressure. More of heat is appeared when the matter of precursor fills pores and other defects under external pressure. As a result of that hot points are formed.

The temperature is much higher into hot spots.

Silver stearate shock wave compression

a) AgSt; b) T<2300 K, P<340 kbar; c) diamond block structure.

a) b) c)

Ag nanoparticles capsulated in amorphous carbon X-ray diffraction patterns of Ag and diamond

111 Ag

Diamond200 Ag

Diamond

50 Å

SAXS signal behavior from AgSt during detonation

Diffusivity at the initial stage of decomposition

Earlier it was shown by us that the typical size of silver particles near 70 Å. Log-normal size distribution takes place. The time of nanoparticles formation is equal to or more than 0.5 mcs. Let us evaluate the order of magnitude of diffusivity employing Einstein formulae. We have

D ~ < x2>/t ~10-10 m²/s. The value of D is near to the value of diffusivity of

liquid Dliq ~ 10–9 m²/s, while in solid state diffusivity equals ~ 10–12 m²/s at the temperature close to melting point. Thus diffusion properties of medium in which metal particles are formed is close to ones of the liquid state.

The initial stage of pyrolysis occurring through the anhydride

Decomposition of metal carboxylates

Decomposition of any metal carboxylate is difinded by strength of bond in molecular. The strengh of bond increase in the following row: М–О < R–COO < С–Н < С–Х (heteroatoms) < C–С.

The main type of these reactions is a primary decarboxylation with rupture of R – COO-bond and separation of carbon dioxide:

.

or.

e 2CORCOOR

RCOAgCOOAgR 2

ot

Molecular of carboxylate can decay via formation corresponding carboxylic acid:

COOHRCOORCOOAgR [H]Ag

Formation of nanodiamonds

CyHx→Cy(алмаз)+0.5xH2,

Diamonds are formed in the unloading wave by the free-radical mechanism in a media with diffusion properties close to those of a liquid state substance. Nanodiamonds begin to appear from free radicals (CH3, CH2, CH etc.) after 0.5 s of explosion. The catalytic role in the detonation synthesis is performed by atomic hydrogen.

Shock-wave impact on metal carboxylates leads to formation of the reaction mixture Metal – C – H – O. It was shown that in the course of these physicohemical processes, metal clusters undergo coalescence and diamond microparticles are formed (if the cathion has catalytic properties). The role of catalysts at detonation synthesis differs from their role in the HPHT process. At detonation synthesis, they are expected either to support sp3 hybridization or to accelerate formation of compounds to do that.

Diamond formation

It was found that after the shock-wave impact on AgSt induced the formation of the particles of diamond.The supposing reaction is following:Alkyls+other radicals→diamond+hydrogenThe diamond formation occurs beyond the Chapman-Jouguet plane.

Shock action on zinc stearate

A shock action on zinc stearate produced the formation of ultra dispersed ZnO.

Fig. 2. Zn(II) n-octadecanoate (C36H70O4Zn)

The boiling temperatures of silver, bismuth and zinc are equal to 2485 К, 1837 К and 1180 К respectively. Therefore it is not possible to obtain zinc nanoparticles from ZnSt2 because of their vaporization. The interaction between vapours of water and zinc leads to formation of ZnO.

The normalized distribution of metal particles by their sizes that sets in during the coalescence process is log-normal. The presence of CO and olefins leads to the growth of the amorphous carbon layer on the surface of metal clusters, which gradually lowers their catalytic activity down to zero and hinders further coalescence of metal nanoparticles.

Nanoparticles of alloys

explosion

explosion

Solid solution of M1St+M2St

M1St

M2StMetal nanoparticles

M1

M2

Alloy nanoparticles

Precursors

HE

HE

Bi+Pb

ConclusionConclusion It has been shown that the precursor “particles” under consideration differ It has been shown that the precursor “particles” under consideration differ from the rest explosive due to the higher content of carbon and presence from the rest explosive due to the higher content of carbon and presence of the metal catalyst in their chemical composition. It should be noted that of the metal catalyst in their chemical composition. It should be noted that energy released at detonation inside the precursor is lower than in the area energy released at detonation inside the precursor is lower than in the area free of stearates. Since the running processes are adiabatic, the typical free of stearates. Since the running processes are adiabatic, the typical temperature of a “particle” will be lower than the surrounding temperature. temperature of a “particle” will be lower than the surrounding temperature. The temperature equalization time scale is estimated to be ~10 The temperature equalization time scale is estimated to be ~10–3–3 s, which s, which is ~10is ~1033 times as large as the reaction time scale experimentally obtained. times as large as the reaction time scale experimentally obtained. Formation of metal nanoparticles in the reaction time scale requires high Formation of metal nanoparticles in the reaction time scale requires high density of the substance at high mobility of the metal-containing density of the substance at high mobility of the metal-containing compounds from which the nanoparticles form. High mobility in the dense compounds from which the nanoparticles form. High mobility in the dense substance (density of the explosive is about 1,6 kg/m³) is provided by high substance (density of the explosive is about 1,6 kg/m³) is provided by high temperature of the reaction mixture (T~1800÷2300 K). The model temperature of the reaction mixture (T~1800÷2300 K). The model suggested implies the metal clusters to grow by the diffusion mechanism, suggested implies the metal clusters to grow by the diffusion mechanism, i.e. the “building material” is delivered via diffusion. According to i.e. the “building material” is delivered via diffusion. According to computations, in this case diffusion properties of the medium where metal computations, in this case diffusion properties of the medium where metal particles form are close to those of a liquid state. The most important type particles form are close to those of a liquid state. The most important type of reactions at disintegration of carboxylates is the transfer of free radicals. of reactions at disintegration of carboxylates is the transfer of free radicals. Under detonation, temperature and pressure significantly exceed the Under detonation, temperature and pressure significantly exceed the analogous parameters in experiments on thermal destruction of metal analogous parameters in experiments on thermal destruction of metal carboxylates. The short time of the reaction mixture life is compensated by carboxylates. The short time of the reaction mixture life is compensated by high mobility and concentration of the reagents. The model implies that in high mobility and concentration of the reagents. The model implies that in the course of the physical-chemical processes metal clusters undergo the course of the physical-chemical processes metal clusters undergo coalescence and, if the cathion has catalytic properties, diamond micro-coalescence and, if the cathion has catalytic properties, diamond micro-particles form. Presence of CO and olefins leads to growth of the particles form. Presence of CO and olefins leads to growth of the amorphous carbon layer on the surface of metal clusters, which gradually amorphous carbon layer on the surface of metal clusters, which gradually lowers their catalytic activity down to zero and impedes further lowers their catalytic activity down to zero and impedes further coalescence of metal nanoparticles. coalescence of metal nanoparticles.

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