The Efficiency of the Centrifuge is Force Action on the Propagation Mechanism of SHS-Wave

Adiabatic wave (AW) is generated by the effect of two forces, namely centrifugal and Coriolis forces, caused on the reaction of the self-propagating high-temperature synthesis (SHS). The synthesis occurs in the aluminothermic oxide system placed inside the heat insulated cylindrical reactor rotating around a vertical axis. Actually there take place two processes during the SH synthesis: 1. separation of the reaction products, in particular aluminum (corundum) oxide concentrated on a quartz wall of the reactor and forming a tube; 2. formation of a coherent flow of liquid metal particles accelerating in the reactor axis direction according to its rotation speed and co-ordinates of Rх particle in the reactor. The size of the cluster representing particles practically does not change from the very moment of their generation as a result of the reaction due to their motion coherency. Considering the motion speed particles get inside a fresh combustible mixture deeper and deeper and, thus, initiate ignition of the accumulating reaction mixture. This provides growth of the heat release rate and transition of the process to the adiabatic mode. Metal clusters bearing kinetic energy and heat energy of the reaction (T = 2.8-3.5 thousand K) actually have a high energy potential that can increase according to growth of the rotation speed and longitudinal size of the reactor. So, if any highly endothermic reaction mixture takes place within a reactor co-ordinate with exponential growth of the moving clusters energy this reaction can be initiated and consequently will give start to numerous research capabilities. A real possibility of such rare and new materials synthesis technology is illustrated using as an example a reaction of the boron and aluminum oxides attacked by 92 m/s speed moving tungsten clusters with formation of a product from the intermediate boron and aluminum oxides and also tungsten and aluminum borides. The results of the synthesized oxide material study using a radio spectrometer has been presented and presence of free valency in it has been identified. Production of free valency materials is of interest in terms of their mixture with nanomaterilas and their compaction at ultrahigh pressure with the purpose to receive new materials with original mechanical, electric, photo-electric, and other properties. The references given below contain data on this technology studied previously.


Introduction
Earlier [1] using the metal particles generating oxide systems as an example, МО 3 +2Аl → M+Al 2 O 3 +Q (1) We studied factors contributing to the SHS-wave stability in the conditions of the centrifugal force effect.This study allowed for identification of the front propagation features in the cylindrical insulated reactor rotating around a vertical axis [2][3][4][5][6].
There are two forces that affect the liquid metal particles formed in reaction (1) with m mass: 1) Centrifugal force F Н directed along R х radiusvector 2) Coriolis force F H directed perpendicular to R х radius-vector R х -is a co-ordinate and a radius-vector of the SHS wave propagating in the radial direction; n -is a number of revolutions per minute; U -is the reactor axis motion speed in the plane direction; Х, У -are axes of the rectangular coordinates system.
One of the features observed during rotation of the reactor (Fig. 1) is separation of liquid and solid phases of the reaction products [2][3] as a result of interaction between specified forces and a hydrodynamic resistance force generated by them.Accelerated movement of the particles along the reactor axis is caused by continuous increment of their R x rotation radius in the course of the reaction front propagation (Fig. 1).Thus, due to F Н force effect, growth of the particles emerging in the combustion wave front is limited, since their movement becomes coherent.Performed study [4] proves that in the quiescence state the primary size of the metal drops in the reaction similar to (1) is equal to 10 -6 m.Actually movement of such particles in the quiescence state speed does not depend on the gravitational forces.
Another feature of such SHS-process with fixed rotation frequency is that particles of the reaction metal product emerging at certain critical value R x develop centrifugal speed Wy that exceeds velocity of U f (U k > U f ) front thermal propagation.Considering fixed R x and n values, Tables 1 and 2 illustrate mechanics of the reacting system rotation process during reaction (1) regarding tungsten and iron.For instance, one can see that U k velocity developed by the tungsten particles along the radius-vector with R x values = 0.1; 0.25 and 0.3 m, correspondingly, at n = 3000 min -1 reaches 30 ÷ 90 ms -1 .
The SHS-wave propagation rate in the quiescence state U f equals only (0.01 ÷ 0.05) ms -1 .A typical reaction time in a δ = 0.002 m wide front is τ = δ/UP = (0.1 -0.04) sec.The contact time of the metal particles running through the front is τ = δ/U = 6.6•10 -5 sec ÷ 2.2•10 -5 sec.Supposedly, in the rotation conditions hot metal particles (T = 3•103) with over critical 1 speed, continuously get through the front forming ahead a suspended layer i.e. a zone that is spontaneously ignited by the oncoming front heat conductivity.Growth of R х radius-vector leads to increase in the F Н centrifugal force and size of the self-ignition zone.
1 flow velocity at which a layer resistance becomes equal to its mass.

Table 1
Kinetic energy and enthalpy dependence on the tungsten particle radius and the reactor radius-vector   The SHS-wave autoacceleration degenerated based on such mechanism actually is a source of the adiabatic wave (AW) and a cause of its thermal instability.It is evident from Tables 1, 2 and Figs.2-4, and also data [1] that particles kinetic energy exponentially grows with increase in the R x value.
The purpose of this study is to identify properties of the resulting high energy potential E C sufficient for initiation of highly endothermic chemical processes since there is a possibility to reach a supersonic AW velocity by variation of n and R x values.

Energy (AW) and Its Kinetic Ability
At critical R x point of the SHS-wave transition to AW and further at R x > R k when its chemical and kinetic potential is highest, a flow of the attacking particles can be directed arranged so as to initiate highly endothermic reactions.Thus, having combined two different and consistent reaction mixtures within a uniform rotating reactor we have managed to create a new reactor (Fig. 2) able to generate both a sonic and supersonic waves.Calculations have revealed that attacked reaction mixtures in the consecutive phase reactions can consist of two and more various reaction layers.
In a simplified one-phase version of the reactor, the first part is "attacking" similar to reaction (1) for AW generation; whilst the second part is "attacked" with highly endothermic reaction mixture.Using Tables 1-2 and Figures 3-4 one can estimate a total number of N particles with a certain radius r•10 -3 m.As an ideal version, we can assume that all particles have the same radius, therefore all tungsten reduced in the first part of the reactor in the amount of 0.045 kg at point R x = 0.3 m will transform to N = 558 particles each with energy E k ~ 0.72 J, its total value being 446 J. Further assuming that an attacked layer thickness is equal to 0.02 m and a particle velocity taken from Table 1.2 is equal to U = 94.4 ms -1 , the attacking particle contact time in such layer is τ ≈ 0.02/94.4≈ 2•10 -4 sec.Consequently, capacity of the flow falling onto the attacked layer is Р = 446/2•10 -4 = 2•10 6 W.
Considering that both micro-and macro particles dispersed by the centrifugal force, apart from the translational energy, have a high temperature reaching 2500-3500 K, one can expect to overcome the activation reaction barrier within the attacked layer as a В-О bond rupture approximately equal to 770 KJ/mol [6] even at R x = 1•10 -3 m.Energy of a chemical bond rupture in the inorganic materials with oxygen does not exceed 1000 KJ/mol in known examples.Therefore performed assessment shows that a total energy of the attacking tungsten particles significantly surpasses this value and, hence, this supposed process is possible.Thus this technology presented as a new project has a considerable chance to increase its capacity with increase of n and R x values and therefore numerous metals can be used as attacking particles.

Random Examples and Certain Range Sections Covered by AW Technology
Below given are certain idealized trends that are currently being studied [9][10] or can be studied as an attacking reagent, e.g. using tungsten particles as one of the extensive attacking particle examples row with favorably high density.The tungsten particles spectrum within the cluster is rather represented narrow since F H growth starting from R x = R k reduces the coalescence event number.As indicated above, the authors [4] believe that the М * cluster size at the generation moment is equal to 10 -5 -10 -6 m.
Presence of larger particles in the flow is caused only at the start of SHS-process when the highest М * cluster growth rate is possible due to small F H value.
In the absence of details of the macrokinetic mechanism between a liquid cluster and attacked re-agent we can judge only based on the actual reaction products.E.g. transformation of a boron oxide and aluminum powder reaction mixture will start from activation of boron oxide: and thus will initiate numerous aluminum interaction channels: In turn, emerging aluminum and boron oxides start interacting with each other and resulting in the spinel-like structures and thus reactions of oxygen redistribution between aluminum and boron with formation of various intermediate oxides become possible.Free valencies arising at boron and aluminum atoms can enter layered annular structures.Studies [9][10] demonstrate that formation of WB 2 and AlB as an extreme case is possible as well.An important feature of this complex interaction of three metals in these experiments is absence of attacking metal oxides in the attacked layer, this fact being probably attributed to insufficient particles energy in selected conditions of the experiment.Figure 5 illustrates data on the EPR sample in reactions (5)(6)(7)(8) testifying to occurrence of the free valency in Al α O β B γ system.The X-ray phase analysis data are also provided in [9][10].Synthesis of the Eurasian Chemico-Technological Journal 16 (2014) 35-39 bimetallic oxides of sulphides, carbides, nitrides, and other metal oxides (MO) with the perspective to produce free valency materials seems highly promising as there is a chance for numerous combinations with nanomaterials.
MgO + Zr * → Mg * -O -Zr * (8) Considering the above mentioned experimental observation that the attacking metal has been absent in the oxidation products, noteworthy that realization of reaction (8) needs more severe conditions to activate the attacking metal, for instance, up to the sound speed or even more.
Apart from that there is a real possibility to use an attacking metal cluster, e.g. with Fe, V (or other elements) so as to initiate a focused polymerization of any monomer with the formation of the electrophysical characteristics gradiency.
Reactions ( 4) -( 9) and a number of similar reactions are extremely useful for production of original materials that are fit for 20-50 thousand atmosphere pressurized «joint» of their mixtures with nanometals as well as other free valency materials.Therefore considered research trend is of potential practical interest in the search for new ways of synthesis of the materials with original mechanical, thermal, photo-electric, and electrophysical properties.