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26EXPERIMENTAL STUDY OF THE EFFECT OF ATTACKING METAL PARTICLES ON MAGNESIUM, BORON, ALUMINUM, MOLYBDENUM OXIDES
A. N. Baideldinova", S. Tolendiuly", L. V. Mukhina*", and G. I. Ksandopulo"
aInstitute of Combustion Problems, Almaty, 050012 Kazakhstan *e-mail: milabrega@yandex.ru
DOI: 10.24411/9999-0014A-2019-10016
SHS in powder metal oxide systems carried out under rotating conditions allows to obtain a number of nontrivial substances with free valency. During transition of the combustion wave to a superadiabatic mode and "freezing" of high-temperature intermediate states of matter, nonequilibrium phases stable in time are formed.
1. The attacked layer based on magnesium oxide
In a two-layer system (CuO + Al) + MgO, defective aluminomagnesium spinel Mg0.388Al2.408O4 (38.5 % wt) was obtained which proved to be effective in catalytic processes. To increase the yield of this material, a four-layer system (CuO + Al)-MgO-(CuO + Al)-MgO was developed. In this system, the substance Mg0.388Al2.408O4 was obtained almost in pure form - 93.5% by weight.
The binding energy between magnesium and oxygen atoms in the MgO molecule has a high value of 570 kJ/mol. In order to break this bond between atoms and to allow magnesium interact with copper or aluminum in the four-layer system, the rotation speed was increased from 1500 to 2500 rpm, this corresponding to an increase in centrifugal acceleration at the boundary between the first attacker and the attacked layers from 377 to 1048 g. The increased energy potential of the reaction radically changed the picture of the process, resulting in formation of magnesium and copper aluminates (Mg2Ab and C^AU). Due to a successful combination of strength, plasticity, corrosion resistance, the both obtained phases are of interest for further study as modifying additives.
Spinel Al2MgO4 and copper oxide were formed under the action of the mixture based on copper oxide and aluminum attaking magnesium oxide in the presence of boron (CuO + Al) + (Mg + B). Aluminocobalt spinel Al0.27Coc.73(Al0.73Co1.27) and O4Al0.27Co0.73(Al0.73Co1.27)O4 which is also of interest, and noble spinel MgAhO4 of high purity (close to 100 %) were obtained under the action of cobalt clusters (Co3O4 + Al) + MgO on the layer of magnesium oxide.
2. The attacked layer based on boron oxide
Interesting results were obtained for four attacking systems - those of copper, molybdenum, tungsten and titanium.
2.1. The active layer generating copper clusters
The system (CuO + Al) - (B2O3 + Al) with a screen made of quartzite grains allowed to obtain a significant (13.4%) amount of non-equilibrium copper silicide Cu0.83Si0.17 and the compound Al20B4O36 in the amount of 3.4%. In the four-component system (CuO + Al)-(B2O3 + Al)-(CuO + Al)-(B2O3 + Al), a promising monovalent copper metaborate CuBO2 was obtained in the amount of 17.7%. Under other conditions, an intermetallic compound Cu9Al4 and a modifier Al20B4O36 were obtained in this system. According to EPR data, the products of each of the described systems contain substances with free valency.
2.2. The active layer generating molybdenum clusters
A two-layer system (MoO3 +Al)-(B2O3 + Al) made it possible to obtain compounds of boron with molybdenum M0B2 (0.4%), B2Mo5Si (24.6%), and the intermetallid AbMo (5.9%). In one
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of these samples, without the use of a quartzite filter, a foamed amorphous mass containing Mo3Si molybdenum silicide and cristobalite in small amounts was obtained.
In the system of pure boron oxide (MoO3 +Al)-B2O3, the substance AhoB4O36 was obtained in an amount of 3.8%, which is 0.4% more than in the copper-based system. The increase in the output of Al2oB4O36 in the course of transition from copper (density 8.94 g/cm3) to molybdenum (density 10.3 g/cm3) allows to suppose that when increasing the weight of clusters of the attacking metal, the output of the modifier will increase by a more significant amount. This assumption was confirmed by experiments on the attack of boron-containing layers by systems based on tungsten (density 19.3 g/cm3).
Table 1. Initial compositions, the arrangement of layers, phase composition and ESR spectra of the products of the systems (MeO +Al)-y-AhO3 for various metals._
Layers
X-ray phase analysis
EPR spectra
Formula
% mass
Co2O3 + Al Co2O3 + Al + 40% Al2O3
SiO2
y-AhO3
Al2O3
Al2.42?O3 .64 Al2.66O4
39.7 34.5
25.8
NiO + Al
NiO + Al + 35% Al2O3
NiO + Al
y-AhO3
Al2O3
Al2.66O4
SiO2 Ni
57.2 28.5 10.9 3.5
CuO + Al
CuO + Al + 40% Al2O3
y-AhO3
SiO2
Al2O3 74.8
Al2.427O3.64 11.3
5-AhO3 8.3
Cu 1.6
SiO2 1.5
Ca2.25(Si3O7.5(OH)l.5)(H2O) 1.3
Cu2O 1.2
MoO3 + Al MoO3 + Al + 30% Al2O3
MoO3 + Al + 40% Al2O3 MoO3 + Al y-AhO3
Al2O3
Al7.7Mo30Si3.3
Mo Al2O3
Al7.7Mo30Si3.3 MoO2 Mo SiO2
73.4
21.5 5.1 73.7
12.6 9.8 2.6 1.3
WO3 + Al
WO3 + Al + 40% AhO3 CaOWO3 + Al y-AhO3
CaAl4O7
Al2.427O3 .64 Al2.66O4
W
66.8 18.4 11.7
3.2
2.3. The attacking layer generating tungsten clusters
Two-layer systems (WO3 + Al)-(B2O3 + Al) have been developed to produce Al2oB4O36. The output of Al2oB4O36 was equal to 34%. Comparison of the results of experiments with attacking layers based on copper and molybdenum confirmed the fact that the density of the attacking metal plays a crucial role. To study the possibility of obtaining light metal borides, a
two-layer system (WO3 + Al)-(SiO2 + B2O3 +Al) was developed in which titanium boride was obtained.
3. The attacked layer based on aluminum oxide
To study the effect of metal clusters on the attacked layers of aluminum oxide being attacked y-AhO3 was used due its increased chemical activity with respect to a-AhO3. Table 1 shows EPR spectra of products of layer systems (MeO + Al)-y-AhO3. In all cases, there is a signal from free radicals between the third and fourth components of the Mn2+ standard.
The nonlinear dependence of the relative intensity of the free radical signal on the density of the attacking metal is presented in Table 2. According to EPR spectra, the heaviest metal-tungsten shows a significant advantage, as in the case of the attack of boron oxide layers (point 2).
Table 2. Metal density and the ratio of the height of the free valency peak to the height of the
standard peak._
Metal Density, g/cm3 The relative intensity of the peak
Co 890 018
Ni 8.90 2.16
Cu 8.94 0.23
Mo 10.30 2.07
W 19.30 4.42
4. The attacked layer based on molybdenum oxide
In a two-layer system (CuO + Al)-(MoO3 + Al), with the separation of the attacking and attacked layers by a filter of quartzite grains, a nontrivial substance Cu64O was obtained in a small amount (1% by weight). With an increase in the flow rate of copper clusters, in the product there is no molybdenum in the amount available for X-ray analysis. This means that the layer being attacked has been heated by the released energy to 1000-1260oC. As is known, in this temperature range there takes place sublimation of molybdenum trioxide, the process on which production of MoO3 from ash is based. This is also confirmed by the appearance in the product of a significant amount (38.2%) of mullite 3AhO3-2SiO2, the formation of which occurs in the temperature range of 1100-1200oC.
The removal of a quartzite filter from the initial layer system and a direct attack of the layer (MoO3 + Al) by copper clusters led to reduction of molybdenum from molybdenum trioxide. This indicates the fact that, firstly, the power of the flow was sufficient to initiate chemical reactions in the attacked layer. Secondly, the speed of the combustion wave front and the heating of the stoichiometric mixture of molybdenum oxide with aluminum exceeded the rate of trioxide sublimation, allowing it to react with the reducing agent. An important fact is also detection, using X-ray phase analysis, of cristobalite - a high-temperature phase of aluminum silicate, which is stable under equilibrium conditions in the temperature range from 1470°C to the melting point at 1728°C. The presence of cristobalite in the synthesis products indicates their rapid cooling and only a partial transition of the high-temperature phase to low-temperature one (mullite).
1 G.I. Ksandopulo, A.N. Baideldinova, The SHS process in the layered systems, SHS-composite materials: Multi-authored monograph, ed. by prof. Z.A. Mansurov, Almaty: Qazaq University, 2017, pp. 33-84.
2 G. Ksandopulo, A. Baideldinova, Y. Riabikin, L. Mukhina, E. Ponomareva, N. Vasilieva, Research of products of high temperature synthesis flowing in the rotation conditions, IOP Conf. Ser.: Mater. Sci. Eng., 2017, vol. 175, 012037.
