CC BY
27ISHS 2019 Moscow, Russia
SYNTHESIS OF METAL OXIDE RADICALS IN ROTATING REACTOR
WITH ALUMINOTHERMIC FLAME
G. I. Ksandopulo
Institute of Combustion Problems, Almaty, 050012 Kazakhstan
e-mail: ksand@inbox.ru
DOI: 10.24411/9999-0014A-2019-10071
Due to high heat resistance, inorganic radicals (HP) have the ability to influence on high-temperature chemical processes, for example modifying agents that affecting on crystallization kinetics of various metal melts, causing a change in their physical and mechanical properties. A similar effect can be expected in polymerization processes of inorganic and organic systems. Intervention in recombination chain of organic radicals during combustion of liquid fuels may allow HP to extinguish the combustion in near-wall layer of rocket thrust chamber; radical reactions is also important for the treatment of cancerous growth. A free valence of HP is predisposed to change, catalyze, activate, or inhibit various chemical processes, as well as to create nonstoichiometric compounds. The synthesis of solid-phase radicals is carried out in a cylindrical reactor is rotating around an outer axle, is filled with a mixture of powders based on metal oxide. During combustion of mixture there is formed a centrifugal - accelerated flow of clusters from recovered metal [1-3]. Overtaking the front of combustion wave when being impact into fresh layers of reaction mixture, this flow creates an attacking impulse, which accelerates and broadens the front of combustion wave. The reaction is carried out at temperatures of 2800-3500 K, and its time does not exceed 10-3 s. At the same time, an initiating energy is sufficiently large, both for formation of interatomic metallic bonds, and heteroatomic radical containing particles. An obvious requirement to conditions of radical synthesis is a high positive temperature gradient for heating of reaction mixture, as well as momentary cooling of the formed product. The forced effect of high-gradient heat at temperatures above 3000 K causes an appropriate degree of inequality in reaction medium, and its subsequent rapid cooling reduces the loss of free valence in acts of quadratic or other kind of death. Therefore, the achieving of maximum yield of radicals on concentration is a minimization of time interval between start and freezing of the reaction. In [1-4], there are presented fundamentals of self-propagating high-temperature synthesis (SHS) theory in oxide systems with mass transfer is caused by rotational forces effect on propagation of combustion wave. The aluminothermic reaction of SHS type is a source of the clusters:
MeO3 + 2Al = Me + Al2O3 + Q (I)
where MeO3 is metal oxide.
Synthesis products in two-layered systems stably contains inorganic radicals, in Table 1 there are presented results of X-ray diffraction analysis and EPR spectra for two types of attacked mixtures: y-AhO3 u B2O3 + Al. Synthesis was carried out by clusters of metals that generated by the reaction (I) in mixtures based on tungsten, molybdenum, copper, nickel, cobalt and titanium. In order to prevent uncontrolled explosive combustion regimes, the initial mixtures were diluted with an inert additive AhO3.
Due to the high thermal stability which was acquired during high-temperature synthesis, the synthesized metal oxide radicals can favorably influence to crystallization of metals structure and to improve the physicochemical properties of the alloys. Detailed studies of modifying abilities of the Al20B4O36 phase have been carried out. The signal magnitude is corresponding
to availability of free valence using EPR spectrum is proportional to the percentage of this chemical compound in probe. The silumin (brand AK12) (Si = 10.5% wt) has subjected to modification. The figure shows two images of cast structure of modified and unmodified silumin ingots. Their comparison shows that the introduction of modifier in the amount of 0.03% of the mass., leads to a radical change in the structure of the casting (Fig. 1).
Table 1. Investigation results of effectiveness of reaction mixture attack by clusters with different metals
Attacked reaction mixture
Element-attacked clusters
X-ray phase analysis of obtained _products_
Substance
Weight content, %
ESR spectrum of obtained product
Y-AI2O3
W
Mo
Ni
Co
CaAUOv
Al2,427 O3,64 Al2,66O4
W
66,8 18,4 11,7 3,2
Al2O3
Al7,7MO30SÍ3,3
Mo
73.4
21.5 5,1
Cu AI2O3 74,8
Al2,427 O3,64 11,3
Al2,66O4 8,3
Cu 1,6
SÍO2 1,5 Ca2,25(SÍ3O7,5(OH)1,5 1,3
)(H2O) 1,2 Cu2O
Al2O3
Al2,66O4
SÍO2 Ni
57,2 28,5 10,9 3,5
Al2O3
Al2,427O3,64 Al2,66O4
39.7 34,5
25.8
B2O3 + Al
W
Al2O3 Al20B4O36
Al
B(OH)3***
60,4 30,3 3,3 6,0
iSHS 2019
Moscow, Russia
Mo SiO2 47,9
B2Mo5Si 24,6
Mo 21,5
Al3Mo 5,9
Ti Al2O3 56,9
Na2B6O10 11,4
(TiN)0,88 7,2
AlN 5,2
AlTi3N 4,0
Na1,22AlnO17,11 6,7
TiN 5,1
Al 3,5
Cu Al2O3 29,6
SiO2 28,4
Al 17,1
Cu0 ,83Si0,17 13,4
Al2Cu 5,9
Al20B4O36 3,4
Cu 2,2
Fig. 1. Metallography of modified and non-modified silunim samples (line 150 |im).
The effect of this modifier cannot be explained by any of the accepted mechanisms. First of all, the syngony and crystal lattice parameters of modified corundum (trigonal: a = 0.467 nm) and aluminum borate (orthorhombic: a = 0.769 nm, b = 1.404 nm, c = 0.567 nm) do not correspond to those of the a-phase of aluminum (cubic: a = 0.404 nm) and P-phase silicon (cubic: a = 0.543 nm). Consequently, in this case the Dankov principle is not fulfilled (the principle of the structural-dimensional correspondence between the nucleation centers of crystallization and the crystallizing phase). The modifying effect cannot be explained by the action of boron, which could pass into the melt by the reaction B2O3 + 2Al ^ 2B + AhO3, since boron is not an independent modifier in the Al-Si dual system.
It should be noted that the maximum boron content in melt due to modifier does not exceed 0.012% by mass. At the same time, the content of boron in the crystallization process is in solid solution.
Thus, the hypothesis of the modifying ability of ceramics in the Al-B-O system, which has a strong disequilibrium associated with free valence, has received a direct experimental confirmation.
The study of properties of multiphase substances that obtained under extremely non-equilibrium conditions by combustion method under centrifugal acceleration impact, it shows that such materials can be successfully used in many areas: metallurgy, catalysis, magnetism, effects on chemical processes of chain nature, increase in the burning rate of powders in the
production of explosives substances and mixed fuels; et al. Extensive possibilities in order to synthesize new materials based on high energy chemistry and create processes where the Arrhenius barrier reaches 1 mJ or more. By placing successively attacked layers in the reactor and increasing the rotational frequency up to 10 thousand rpm, it is possible to replace the attacking heavy metal clusters by light metal clusters, to use the attacking layers based on rare-earth elements.
1 G.I. Ksandopulo, SHS in conditions of rotation: thermal and concentration combustion limits for oxide systems taken as an example, Int. J. Self-Propag. High-Temp. Synth., 2011, vol. 20, pp. 220-223.
2 G.I. Ksandopulo, Non-chain autoacceleration of SHS wave in conditions of rotation, Int. J. Self-Propag. High-Temp. Synth., 2015, vol. 24, pp. 8-13.
3 A. Baideldonova, G. Ksandopulo, L. Mukhina, Initiation of the adiabatic wave of combustion for obtaining the substances with the free valence, IOP Conf. Ser.: Mater. Sci. Eng., 2016, vol. 123.
4 G.I. Ksandopulo, A.N. Baideldinova, L.V. Mukhina, E.A. Ponamareva, Z.M. Azizov, Nanocarbon structures and other nontrivial substances in SHS products under centrifugal acceleration influence, Int. Symp. "Physics and chemistry of carbon materials and nanoengineering", Int. Conf. "Nanoenergetic materials and nanoenergy", Almaty, 2016, pp. 3-7.
