molecules
Article The Study of HEMs Based on the Mechanically Activated Intermetallic Al12Mg17 Powder
Sergei Sokolov * , Alexander Vorozhtsov, Vladimir Arkhipov and Ilya Zhukov Laboratory of Metallurgy Nanotechnologies, National Research Tomsk State University, Lenin Avenue, 36, 634050 Tomsk, Russia; [email protected] (A.V.); [email protected] (V.A.); [email protected] (I.Z.) * Correspondence: [email protected]; Tel.: +7-923-406-77-01
Academic Editor: Svatopluk Zeman Received: 30 May 2020; Accepted: 19 July 2020; Published: 5 August 2020 Abstract: In this work, Al–Mg intermetallic powders were characterized and obtained by melting, casting into a steel chill and subsequent mechanical activation in a planetary mill. The method for producing Al12Mg17 intermetallic powder is presented. The dispersity, morphology, chemical composition, and phase composition of the obtained powder materials were investigated. Certain thermodynamic properties of high-energy materials containing the Al-Mg powder after mechanical activation of various durations were investigated. The addition of the Al-Mg powders to the high-energy composition (synthetic rubber SKDM-80 + ammonium perchlorate AP + boron B) can significantly increase the burning rate by approximately 47% and the combustion heat by approximately 23% compared with the high-energy compositions without the Al-Mg powder. The addition of the Al12Mg17 powder obtained after 6 h of mechanical activation provides an increase in the burning rate by 8% (2.5 0.1 mm/s for the mechanically activated Al Mg powder and ± 12 17 2.3 0.1 mm/s for the commercially available powder) and an increase in the combustion heat by 3% ± (7.4 0.2 MJ/kg for the mechanically activated Al-Mg powder and 7.1 0.2 MJ/kg for the commercially ± ± available powder). The possibility of using the Al-Mg intermetallic powders as the main component of pyrotechnic and special compositions is shown.
Keywords: alloys; mechanical activation; propellants; aluminum; magnesium; magnalium; metals combustion; high-energy materials; ignition; reactive materials
1. Introduction Improving the energy characteristics of high-energy materials (HEMs), improving traditional components, and searching for new components is a relevant objective for many fields of science and technology. High-energy metal powders began to be intensively studied as fuels for burning systems when Russian scientists Kondratyuk and Tsander suggested using high-energy metals (Al, Be, B, Mg, Zr, Ti, etc.) as energy additives for propellants [1]. Metal powders with a high enthalpy of combustion are of great interest as reactive materials in the compositions of propellants, explosives, pyrotechnics, etc [2]. Fine metal powders that are part of high-energy systems are mainly used as components to control the burning rate and reduce ignition delays [3–5]. Aluminum powder is the most affordable, widely studied, and effective additive in various high-energy compositions [4,6,7]. Despite the extensive use of aluminum as a metal fuel, there are certain disadvantages. The major disadvantage is the formation of an oxide film on the surface of aluminum particles, which prevents the rapid flow of chemical reactions and forms agglomerates before ignition [8]. To reduce agglomeration, aluminum particles must be optimized for rapid ignition. There are various methods to solve this problem: the use of nanosized aluminum powder [9]; the use of metallic and polymer coatings [10,11]; the use of other additives [12,13]; and the replacement of pure aluminum powder with powders of intermetallic alloys [14–17]. Despite the attractive properties of
Molecules 2020, 25, 3561; doi:10.3390/molecules25163561 www.mdpi.com/journal/molecules Molecules 2020, 25, 3561 2 of 14 nanosized aluminum powder, it can reduce the specific impulses of propellants, lead to poor rheology and loss of quality during aging [18], since it can contain 10–25 wt % of aluminum oxide [7]. Metallic and polymer coatings result in decreased agglomeration sizes in comparison to pure Al, but they are still about five times larger than the initial particle size. Additives (such as nickel) require large amounts to reduce agglomeration, but higher molecular weight products can significantly reduce performance. Al-based alloys allow a more efficient use of the base material and expand its scope. Various metals are used to change characteristics. The addition of alloying materials (Mg, Zr, Ti, etc.) in aluminum leads to an increase in the combustion heat and burning rate and a reduction in the ignition delay compared with pure aluminum powder. Al-based intermetallic alloys (Al-Mg, Al–Zr, Al–Ti, etc.) are of great interest as metal fuel in various energy compositions [2–20]. In particular, Al-Mg alloys have long been studied as reactive materials and as replacements for pure metal powders [14–17,21,22]. The use of Mg powders in compositions of high-energy materials has several advantages. Compositions with magnesium powder ignite at a lower temperature than with aluminum powder and can be used to ignite compositions with a high ignition temperature [23]. One of the promising, simple, and inexpensive methods of obtaining metal powders with increased reactivity is mechanical activation in a planetary mill. The first studies in this field began in the 19th century [24]. Using the mechanical method, there is the milling of the material in a solid or liquid state without changing the chemical composition. During the milling, powders are affected by the high energies, multiple impacts, abrasion, crushing, and shearing actions of milling bodies on the walls of the ball mill container and the material. The high strain rate related to these collisions results in a combination of fracture, ductility, atomic mixing, and a partial reaction between the components of the material [25]. Using this method, it is possible to obtain mechanically activated powders with improved physics and chemical properties, which are very difficult or impossible to obtain by other methods [26,27]. There are studies reporting the effect of mechanical activation on the thermal-physical properties of metal powders [27,28]. Despite the considerable interest in investigating the effect of the mechanical activation of eutectic alloys on the combustion parameters of high-energy materials, quantitative data on their combustion temperature, burning rate, oxidation degree, and other important properties remain limited. In particular, there are no studies on the effect of the duration and mode of mechanical activation on the combustion parameters of the Al-Mg system as a part of high-energy additives. Thus, the purpose of this work is to experimentally study the structure, dispersity, oxidation degree, burning rate, and combustion heat of the Al-Mg powder materials in the high-energy compositions, depending on the duration of mechanical activation in a planetary mill.
2. Materials and Methods
2.1. Preparation of Al-Mg Material First, 99% pure Al-Mg alloy was obtained from commercial-purity aluminum ingot (99 wt % Al, 0.9 wt % Si, 0.04 wt % Mg and other impurities) and commercial-purity magnesium ingot (99.95 wt % Mg, 0.01 wt % Al, 0.01 wt % Mn, and other impurities). The alloy was fabricated by casting in a clay-graphite crucible. The fusion of aluminum and magnesium was carried out in argon. Aluminum ingot was loaded into the crucible and placed in a furnace. When the temperature reached 730 ◦C, Al melt was removed from the furnace, and magnesium ingot was added into the aluminum melt in small parts in a mass ratio of Al:Mg—1:1. The magnesium ingots were shaped cubes and parallelepipeds, and the approximate mass of individual fragments was 100–150 g. For homogeneous distribution of the components in the melt, mixing was carried out using the device with a rotation speed of 1500 rpm [29]. Mechanical mixing was carried out until the magnesium ingot was completely dissolved in the aluminum melt. The resulting alloy was poured into a steel chill at a temperature of 670 ◦C. Molecules 2020, 25, 3561 3 of 14
2.2. Mechanical Activation Molecules 2020, 25, x FOR PEER REVIEW 3 of 15 The obtain alloy was crushed using a jaw crusher. The obtain Al-Mg flakes were mechanically milled in a2.2. planetary Mechanical mill Activation (Figure 1), the main element of which is the ball mill container. The lid of the container hasThe two obtain taps. alloy One was of themcrushed is using used a tojaw evacuate crusher. The the obtain working Al-Mg space, flakes were and mechanically the second is used to pump inertmilled gas (argon).in a planetary Steel mill balls (Figure with 1), athe diameter main element of 8.7 of mmwhich were is the usedball mill as container. grinding The bodies. lid of The mass the container has two taps. One of them is used to evacuate the working space, and the second is used ratio of grindingto pump bodiesinert gas to (argon). powder Steel mixture balls with was a diamet 2:1.er The of 8.7 mechanical mm were used activation as grinding was bodies. conducted The for 6 h in an argonmass atmosphere ratio of grinding with bodies a rotation to powder frequency mixture was of 12 2:1. rpm. The mechanical activation was conducted for 6 h in an argon atmosphere with a rotation frequency of 12 rpm.
Figure 1. Schematic diagram of the planetary mill. Figure 1. Schematic diagram of the planetary mill. 2.3. Particle Size, Chemical Analysis, Morphology, and Phase Composition 2.3. Particle Size, Chemical Analysis, Morphology, and Phase Composition The average particle size of the mechanically activated powder mixtures was measured using The averagean ANALYSETTE particle 22 size MicroTec of the plus mechanically apparatus (Fritsch activated GmbH, Dresde powdern, Germany) mixtures based was on the measured laser using an ANALYSETTEdiffraction 22method MicroTec in the range plus 0.08–2000 apparatus µm (Fritschand the Fraunhofer GmbH, Dresden,theory. The Germany)dispersion was based carried on the laser out in a liquid medium (distilled water). The chemical analysis of the intermetallic Al-Mg powders diffraction method in the range 0.08–2000 µm and the Fraunhofer theory. The dispersion was carried was performed using an XRF-1800 wavelength-dispersive spectrometer. When calibrating the XRF- out in a liquid1800, mediuma curve was (distilled constructed water). showing The the chemicalrelationship analysis between ofthe the element intermetallic content in the Al-Mg standard powders was performedsample using and an its XRF-1800 measured intensity wavelength-dispersive (calibration curve); then, spectrometer. the element content When in calibrating the studied sample the XRF-1800, a curve waswas constructed found. The showing microstructure the relationship of the powders between was determined the element using content a Vega3 in Tescan the standard (TESCAN sample and ORSAY HOLDING, Brno, Czech Republic). To determine the amount of oxygen in the powder, a its measured intensity (calibration curve); then, the element content in the studied sample was found. LECO ONH (LECO Corporation, Michigan, USA) analyzer was used. X-ray diffraction analysis of The microstructurethe powders of was the performed powders using was a determined Shimadzu XRD using 6000 a diffra Vega3ctometer Tescan with (TESCAN CuKα radiation. ORSAY The HOLDING, Brno, Czechphase Republic). composition To was determine determined theusing amount the POWDER of oxygen CELL 2.4 in program the powder, and PDF a LECO4+ (Powder ONH (LECO Corporation,Diffraction St. Joseph, File) database. MI, USA) analyzer was used. X-ray diffraction analysis of the powders was α performed2.4. using Calorimetric a Shimadzu Studies XRD 6000 diffractometer with CuK radiation. The phase composition was determined using the POWDER CELL 2.4 program and PDF 4+ (Powder Diffraction File) database. Calorimetric studies of the mechanically activated powder mixtures were performed using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) on a Mettler Toledo 2.4. Calorimetric Studies thermal analyzer with a TGA/SDTA 851 module (Mettler-Toledo, LLC, Columbus, OH, USA) in Al2O3 Calorimetriccrucible in studiesthe temperature of the range mechanically of 25–1200 °C activated(heat rate 10 powderK/min) in an mixtures O2/Ar atmosphere. were performed using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) on a Mettler Toledo thermal analyzer with a TGA/SDTA 851 module (Mettler-Toledo, LLC, Columbus, OH, USA) in Al2O3 crucible in the temperature range of 25–1200 ◦C (heat rate 10 K/min) in an O2/Ar atmosphere.
2.5. Process to Obtain Samples of HEMs The basic composition of the samples contained the following: bidispersed ammonium perchlorate (AP) with a dispersion of 160–315 µm and less than 50 µm in a ratio of 60/40 as an oxidizing agent; Molecules 2020, 25, 3561 4 of 14 divinyl rubber based on butadiene rubber, which was plasticized with transformer oil in a ratio of 20/80 (SKDM-80) as a combustible binder; and amorphous black boron powder (B-99) as an energy additive. The amorphous boron was selected due to its high combustion heat (Qboron = 58 KJ/g). In traditional high-energy materials, aluminum powder is used as an energy additive with a lower combustion heat (QAl = 31 KJ/g). The Al12Mg17 powder additive was selected to increase the combustion completeness of boron. Aluminum powder has a high combustion temperature, and magnesium is a highly flammable component. The content of components in the studied samples (Table1) was selected from the condition of ensuring the same value of the excess coefficient of the oxidizer (α = 0.5), where BC—Basic composition; BC(0)—Basic composition with the addition of Al-Mg without mechanical activation (t = 0); BC(2)—Basic composition with the addition of Al-Mg with mechanical activation (t = 2 h); BC(6)—Basic composition with the addition of Al-Mg with mechanical activation (t = 6 h).
Table 1. The components of high-energy compositions.
Components of HEMs, wt % Code AP Boron SKDM-80 Commercially-Available Al-Mg Al-Mg 2 h Al-Mg 6 h BC 74 15 11 - - - BC(0) 70.5 14.3 10.5 4.7 - - BC(2) 70.5 14.3 10.5 - 4.7 - BC(6) 70.5 14.3 10.5 - - 4.7
From the obtained mixtures, the samples with a diameter of 10 mm and a height of 30–40 mm were pressed. The obtaining of the studied samples consisted of sequential mixing of the components (ammonium perchlorate, Al-Mg powders, and processing aids) with a polymer combustible binder. To obtain high-quality samples, the oxidizer charge was divided into several parts. For homogeneous distribution of the components, each charge was mixed for 10–15 min. In this work, the Al-Mg powder, because of its high exothermicity, was used as a catalytic additive that is capable of increasing the energy parameters of boron in the high-energy compositions and also significantly increasing their burning rate. Experimental studies to determine the combustion heat and burning rate, as well as the calculation of the combustion heat, were carried out according to the approved methods presented in [30,31].
2.6. Study of the Combustion Heat and Burning Rate of HEMs The combustion heat was measured using a calorimetric apparatus, the main part of which is a bomb calorimeter. To obtain results with high accuracy, important requirements are imposed on the bomb calorimeter described in [32]. Critical requirements are that it is gastight and has mechanical strength under high pressure. The container of the calorimetric apparatus was filled with 3 L of distilled water, and a bomb calorimeter was immersed in it. For a uniform and quick distribution of water temperature throughout the calorimetric apparatus, a propeller was placed next to the bomb calorimeter. The propeller provided rotation at a speed of 400–500 rpm. The water temperature was measured using a Beckman metastatic thermometer, which allows high-precision measurements. After performing all the above steps, the samples of HEMs were ignited, and the temperature of water in the container of the calorimetric apparatus was measured. Three experiments were performed for each composition. The burning rate of the studied samples was measured in the air atmosphere under a pressure of 0.1 MPa. The initial temperature of the samples is the ambient temperature (22 ◦C). The samples with a diameter of 10 mm and a height of 30 mm were armored with a linoleum solution in acetone. The samples were ignited by the local heating of the upper surface with a molybdenum spiral. Burning time was fixed by a stopwatch. The process was observed visually and also with a NIKON D600 camera and a Yukon thermal imager, UX 70P (Yukon Advanced Optics Worldwide, UAB, Lithuania). Molecules 2020, 25, 3561 5 of 14
Molecules 2020, 25, x FOR PEER REVIEW 5 of 15 3.Molecules Results 2020 and, 25, Discussion x FOR PEER REVIEW 5 of 15 3. Results and Discussion 3.1.3. Results Particle and Size, Discussion Chemical Analysis, Morphology, and Phase Composition 3.1. Particle Size, Chemical Analysis, Morphology, and Phase Composition 3.1.The Particle particle Size, sizeChemical distribution Analysis, forMorphology, the Al-Mg and powder Phase Composition after mechanical activation in the planetary mill isThe shown particle in Figure size distribution2. The particle for the size Al-Mg distribution powder after substantially mechanical depends activation on in the the durationplanetary of The particle size distribution for the Al-Mg powder after mechanical activation in the planetary mechanicalmill is shown activation. in Figure With 2. The an increase particle insize the distribution duration of substantially mechanical depends activation, on thethe particleduration size of of mill is shown in Figure 2. The particle size distribution substantially depends on the duration of themechanical Al-Mg powder activation. decreases. With an The increase obtained in the Al-Mg durati powderon of mechanical (after 6 h activation, of mechanical the particle activation) size of was mechanical activation. With an increase in the duration of mechanical activation, the particle size of comparedthe Al-Mg with powder commercially decreases. availableThe obtained Al-Mg Al-Mg powder. powder It was(after found 6 h of thatmechanical the average activation) particle was size the Al-Mg powder decreases. The obtained Al-Mg powder (after 6 h of mechanical activation) was comparedµ with commercially available Al-Mg powder.µ It was found that the average particle size is iscompared 49 m for with the obtainedcommercially Al-Mg available powder Al-Mg and powder. 50 m for It was the commerciallyfound that the availableaverage particle Al-Mg size powder, is 49 µm for the obtained Al-Mg powder and 50 µm for the commercially available Al-Mg powder, respectively49 µm for the (Figure obtained3), where Al-Mg D m,1powderand Dandm,2 —modal50 µm for particle the commercially diameter. available Al-Mg powder, respectively (Figure 3), where Dm,1 and Dm,2—modal particle diameter. respectively (Figure 3), where Dm,1 and Dm,2—modal particle diameter.
Figure 2. Particle size distribution for the Al-Mg powder. FigureFigure 2. ParticleParticle size size distributi distributionon for for the the Al-Mg Al-Mg powder. powder.
Figure 3. Particle size distribution for the Al-Mg powder and the commercially available Al-Mg powder. FigureFigure 3. 3.Particle Particle size distribution for for the the Al-Mg Al-Mg powder powder and and the the commercially commercially available available Al-Mg Al-Mg powder. powder. Molecules 2020, 25, 3561 6 of 14 Molecules 2020, 25, x FOR PEER REVIEW 6 of 15
The dependence of the averageaverage particleparticle sizesize <
Figure 4. 4. DependenceDependence of the of average the average particle particle size of sizethe Al-Mg of the powder Al-Mg on powder the duration on the of duration mechanical of mechanicalactivation. activation.
Al-Mg powders (after mechanical activation) have a bimodal particle size distribution (2 maxima Dm,1 andand D Dm,2m,2 areare observed observed in in Figure 22;; Figure Figure3). 3). The The mass mass median median diameter diameter (d (d4343)) forfor the unimodal distribution function of the commercially available powder and the bimodal distributiondistribution function of the mechanicallymechanically activatedactivated powder powder are are approximately approximatel they the same same (the (the diff erencedifference is approximately is approximately 1 µm). 1 However,µm). However, the bimodal the bimodal distribution distribution function function (the presence (the presence of two fractions) of two fractions) can significantly can significantly affect the characteristicsaffect the characteristics of the studied of the processes. studied processes. X-ray fluorescencefluorescence analysis of the obtained Al-MgAl-Mg alloy is shown in Table2 2.. TheThe Al-MgAl-Mg alloyalloy obtained byby castingcasting has has an an almost almost equilibrium equilibrium content content of the of main the componentsmain components with minimum with minimum oxygen content.oxygen content. Quantitative Quantitative analysis analysis of the oxygen of the contentoxygen in content the Al-Mg in the alloy Al-Mg and alloy the mechanically and the mechanically activated Al-Mgactivated powder Al-Mg was powder performed. was perfor It wasmed. found It was that found the that oxygen the oxygen content content in the Al-Mgin the Al-Mg alloy before alloy mechanicalbefore mechanical activation activation is approximately is approximately 0.003 wt 0. %,003 while wt %, the while oxygen the contentoxygen incontent the Al-Mg in the powder Al-Mg afterpowder mechanical after mechanical activation activation does not does exceed not 0.1 exceed wt %. 0.1 wt %.
Table 2. Results of X-ray fluorescence fluorescence analysis of the Al-Mg alloy.
Result,Result, at. % at. % ElementElement Al-MgAl-Mg Alloy Alloy Commercially–Available Commercially–Available Al-Mg Al-Mg Alloy Alloy Al 50.4121 44.4907 AlMg 48.6949 50.4121 51.8649 44.4907 MgSi 0.5359 48.6949 0.0473 51.8649 SiFe 0.2229 0.5359 0.0275 0.0473 FeCr 0.0595 0.2229 0.0284 0.0275 CrTi 0.0250 0.0595 - 0.0284 TiC 0.0249 0.0250 - - CZn 0.0094 0.0249 0.0052 - ZnNi 0.0076 0.0094 0.0111 0.0052 NiGa 0.0076 0.0076 0.0075 0.0111 GaO 0.0001 0.0076 3.5126 0.0075 OCu - 0.0001 0.0040 3.5126 CuMo - - 0.0007 0.0040 MoNb - - 0.0001 0.0007 Nb - 0.0001 Aluminum powder is known to have a dense oxide film on the surface. The oxide film of the intermetallic Al12Mg17 powder is not as dense as that of aluminum powder. This is due to the protective propertiesAluminum of oxide powder films. The is known possibility to have of the a format denseion oxide of such film a on film the is surface.determined The by oxide the condition film of the of intermetalliccontinuity formulated Al12Mg17 bypowder Pilling is and not Bedwor as denseth as (Pilling-Bedworth that of aluminum coefficient powder. This(PBC)) is due[33]. to the protective 𝑂𝑥𝑖𝑑𝑒 𝑣𝑜𝑙𝑢𝑚𝑒 𝑃𝐵𝐶 = (1) 𝑀𝑒𝑡𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 Molecules 2020, 25, 3561 7 of 14
properties of oxide films. The possibility of the formation of such a film is determined by the condition of continuity formulated by Pilling and Bedworth (Pilling-Bedworth coefficient (PBC)) [33].
Oxide volume Molecules 2020, 25, x FOR PEER REVIEW PBC = 7 of (1)15 metal Metal volume AccordingAccording to thethe conditioncondition of of continuity, continuity, the the molecular molecular volume volume of the of oxidethe oxide formed formed from from the metal the metaland oxygen and oxygen should should be greater be greater than the than molecular the molecu volumelar volume of the metal of the used metal to formused theto form oxide the molecule. oxide molecule.Otherwise, Otherwise, the oxide filmthe oxide is not film enough is not to enough cover the to entirecover metalthe entire with metal a continuous with a continuous layer. As a layer. result, Asthe a oxide result, film the is looseoxide and film porous. is loose If PBCand >porous1, the. film If PBC forms > under1, thecompression film forms conditions;under compression therefore, conditions;the film is continuoustherefore, the and film may is continuous have protective and ma properties.y have protective If PBC < properti1, the filmes. inIf PBC the process< 1, the offilm its ingrowth the process sustains of its tension, growth which sustains contributes tension, towhich its destruction contributes and to its cracking. destruction In this and case, cracking. the film In is this not case,continuous the film (e.g., is not the continuous oxide film of(e.g., magnesium). the oxide fi Thelm eofff ectmagnesium). of magnesium Theon effect the oxideof magnesium film is enhanced, on the oxidesince film the magnesiumis enhanced, content since the in themagnesium film is always content many in the times film higher is always than many the magnesium times higher content than thein themagnesium particle [ 34content]. If the in magnesiumthe particle [34]. content If the is greatermagnesium than content 1% in the is greater alloy, the than oxide 1% filmin the consists alloy, theentirely oxide of film magnesium consists oxideentirely MgO of magnesium [34]. The PBC ox coeideffi MgOcient [34]. for some The PBC metal coefficient oxides isshown for some in Tablemetal3. oxides is shown in Table 3. Table 3. Pilling-Bedworth coefficient (PBC) for some metals. Table 3. Pilling-Bedworth coefficient (PBC) for some metals. Metal Si Ti Zr Al Mg Ca Li Metal Si Ti Zr Al Mg Ca Li PBC 2.04 1.73 1.45 1.45 0.81 0.64 0.58 PBC 2.04 1.73 1.45 1.45 0.81 0.64 0.58
TheThe SEM SEM images images of of the the Al-Mg Al-Mg powder powder after after 6 6 h h of of mechanical mechanical activation activation are are shown shown in in Figure Figure 5.5. FigureFigure 55a,ba,b are identical, but they have didifferentfferent magnifications magnifications (Figure (Figure 55aa magnificationmagnification isis equalequal × × 509,509, and and Figure Figure 55bb magnificationmagnification is equalequal × 10200).10200). In In particular, particular, Figure Figure 5a5a shows a wide range of × powderpowder particle particle sizes, sizes, and and Figure Figure 55bb shows in moremore detail the complex shape and structure of the particles.particles. The The powder powder has has separate separate particles particles of of irregular irregular shape, shape, which which is is typical typical for for materials materials after after mechanicalmechanical activation. activation.
(a) (b)
Figure 5. SEM-images (Det. SE+BSE) of the AlMg powder after 6 h of mechanical activation at magnifications 509 (a) and 10200 (b). × × The XRD pattern of the mechanically activated Al-Mg powder is shown in Figure6. It was found that peaks in the XRD pattern corresponds to the Al12Mg17 phase. According to the Al-Mg state diagram, the Al12Mg17 phase is formed at the same percentage (Al 50%/Mg 50%) of each component in the alloy, which is confirmed by the results of chemical analysis (Table2). It should also be noted that Molecules 2020, 25, x FOR PEER REVIEW 8 of 15
Figure 5. SEM-images (Det. SE+BSE) of the AlMg powder after 6 h of mechanical activation at magnifications × 509 (a) and × 10200 (b).
The XRD pattern of the mechanically activated Al-Mg powder is shown in Figure 6. It was found thatMolecules peaks2020 in, 25 the, 3561 XRD pattern corresponds to the Al12Mg17 phase. According to the Al-Mg state8 of 14 diagram, the Al12Mg17 phase is formed at the same percentage (Al 50%/Mg 50%) of each component in the alloy, which is confirmed by the results of chemical analysis (Table 2). It should also be noted the XRD patterns of the mechanically activated Al-Mg powder and commercially available Al-Mg that the XRD patterns of the mechanically activated Al-Mg powder and commercially available Al- powder are completely identical. Mg powder are completely identical.
FigureFigure 6. 6. XRDXRD pattern pattern of of the the Al-Mg Al-Mg powder powder after after 6 6h h of of mechanical mechanical activation activation..
3.2.3.2. Calorimetric Calorimetric Studies Studies TheThe results results of of thermogravimetric thermogravimetric analysis analysis (TGA) (TGA) and and differential differential scanning scanning calorimetry calorimetry (DSC) (DSC) of of thethe Al-Mg Al-Mg powder powder after after 2, 2, 4, 4, and and 6 6 h h of of mechanical mechanical activation activation are are shown shown in in Figure Figure 7.7. As As can can be be seen seen fromfrom TGTG/DSC/DSC curves,curves, the the Al-Mg Al-Mg powder powder after after 2 h of 2 mechanical h of mechanical activation activation does not showdoes endothermic not show endothermicmelting. The melting. Al-Mg powders The Al-Mg after 4powders h and 6 hafter of mechanical 4 h and 6 activation h of mechanical show endothermic activation melting, show endothermicwhich corresponds melting, to which the melting corresponds point of to 450 the◦ meltinC andg is point consistent of 450 with °C and the is Al-Mg consistent state diagramwith the Al- [35]. Mg stateThe diagram oxidation [35]. degree of the powder obtained after 2 h of mechanical activation is 70.65% at two exothermic peaks at temperatures around 600 ◦C and 820 ◦C. The oxidation degree of the powder obtained after 4 h of mechanical activation is 77.31% at four exothermic peaks at temperatures around 520 ◦C and 710 ◦C. The oxidation degree of the powder obtained after 6 h of mechanical activation is 74.4% at exothermic peaks at temperatures around 520 ◦C and 690 ◦C. The oxidation degree of the powders obtained after 4 and 6 h of mechanical activation is close to the theoretical value for the case of complete oxidation (77.4%), which indicates the formation of Al2O3 and MgO [16]. According to the results of thermal analysis, with an increase in the time of mechanical activation, the exothermic peak shifts to the zone of lower temperatures, and mechanical activation for more than 4 h does not significantly affect the position of peaks on the TG/DSC curves of the studied materials. The summarized results of the obtained experimental data of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) are presented in Table4, as well as the results of mass changes depending on the mechanical activation duration are shown in Figure8.
Table 4. Summary of the results of TG/DSC analysis.
2 h 4 h 6 h
Endothermic peak, ◦C - 460.4 459.7 Endothermic peak area, J/g - 313.5 261.3 − − Exothermic peak 1, ◦C 600 520 520 Exothermic peak 2, ◦C 820 710 690 Exothermic peak area 1, J/g 5790 8723 7801 Exothermic peak area 2, J/g 9200 4118 2440 Mass change (600 ◦C), wt % 16 35 34 Mass change (800 ◦C), wt % 30 62 60 Mass change (1000 ◦C), wt % 66 76 74 Residual mass (1182.3 ◦C), wt % 70.65 77.31 74.74 Molecules 2020, 25, x FOR PEER REVIEW 9 of 15 Molecules 2020, 25, 3561 9 of 14
(a)
(b)
(c)
FigureFigure 7.7. TG/DSCTG/DSC curves curves of ofthe theAl-Mg Al-Mg powder powder obtained obtained after 2 after h (a), 2 4 h h ((ab),) and 4 h 6 ( bh) (c and) of mechanical 6 h (c) of mechanicalactivation. activation.
The oxidation degree of the powder obtained after 2 h of mechanical activation is 70.65% at two exothermic peaks at temperatures around 600 °C and 820 °C. The oxidation degree of the powder obtained after 4 h of mechanical activation is 77.31% at four exothermic peaks at temperatures around Molecules 2020, 25, x FOR PEER REVIEW 11 of 15
Table 4. Summary of the results of TG/DSC analysis.
2 h 4 h 6 h Endothermic peak, °C - 460.4 459.7 Endothermic peak area, J/g - −313.5 −261.3 Exothermic peak 1, °C 600 520 520 Exothermic peak 2, °C 820 710 690 Exothermic peak area 1, J/g 5790 8723 7801 Exothermic peak area 2, J/g 9200 4118 2440 Mass change (600 °C), wt % 16 35 34 Mass change (800 °C), wt % 30 62 60 Molecules 2020, 25, 3561 Mass change (1000 °C), wt % 66 76 74 10 of 14 Residual mass (1182.3 °C), wt % 70.65 77.31 74.74
FigureFigure 8. 8. DependenceDependence of of mass mass change change on on the the mechanical mechanical activation activation duration duration at at different different temperatures temperatures
(1—(1—T T=600= 600 °C,◦C, 2—T=800 2—T = 800 °C,◦ 3—T=1000C, 3—T = 1000°C). ◦C).
3.3.3.3. Combustion Combustion Heat Heat and and Burning Burning Rate Rate TheThe combustion combustion heat was determined for thethe samplessamples whosewhose compositionscompositions areare shown shown in in Table Table1. 1.As As can can be be seen seen from from Figure Figure9, 9, the the addition addition of of the the mechanically mechanically activated activated Al-MgAl-Mg powderpowder toto thethe compositioncomposition of of HEMs HEMs leads leads to to an an increase increase in in th thee combustion combustion heat heat by by approximately approximately 23% 23% compared compared withwith thethe compositioncomposition without without the the mechanically mechanically activated activated Al-Mg Al-Mg powder. powder. It was It found was thatfound the that addition the additionof the mechanically of the mechanically activated Al-Mgactivated powder Al-Mg to powder the composition to the composition BC (basic composition), BC (basic composition), regardless of regardlessthe duration of the of mechanical duration of activationmechanical and activation dispersion and of dispersion the powder, of the does powder, not aff ectdoes the not combustion affect the combustionheat. Comparison heat. Comparison of the studied of Al-Mgthe studied powder Al-Mg after powder 6 h of mechanical after 6 h of activation mechanical and activation commercially and available Al-Mg powder showed that the difference in the combustion heat is 3% (7.4 0.2 MJ/kg for commercially available Al-Mg powder showed that the difference in the combustion ±heat is 3% (7.4 the mechanically activated Al-Mg powder and 7.1 0.2 MJ/kg for the commercially available powder). ± 0.2 MJ/kg for the mechanically activated Al-Mg ±powder and 7.1 ± 0.2 MJ/kg for the commercially availableFrom experimental powder). data,From it experi was foundmental that data, the combustionit was found heat that of the the compositions combustion of heat HEMs of doesthe compositionsnot depend on of the HEMs method does of not obtaining depend powderson the meth andod is of the obtaining same for powders all compositions and is the containing same for theall compositionsAl-Mg powders. containing As can be the seen Al-Mg from powders. Table2 and As Figure can 9be, duringseen from mechanical Table 2 activation, and Figure there 9, during are no mechanicalchanges in activation, the chemical there composition are no changes of the in material,the chemical which composition would contribute of the material, to an increase which would in the combustion heat. contributeMolecules 2020 to, 25an, x increase FOR PEER in REVIEW the combustion heat. 12 of 15
FigureFigure 9.9. Combustion heat of the HEM compositions.compositions.
TheThe resultsresults ofof thethe burningburning raterate ofof thethe preparedprepared compositionscompositions of HEMs (Table1 1)) in in the the air air at at normalnormal pressurepressure (Figure(Figure 1010)) werewere obtained.obtained. TheThe samplesample containingcontaining onlyonly amorphousamorphous boronboron powderpowder (composition(composition BC)BC) hashas thethe lowestlowest burningburning rate,rate, whilewhile whenwhen thethe Al-MgAl-Mg powderpowder waswas addedadded toto thethe composition, the burning rate of the composition increases by approximately 47%. At the same time, the Al-Mg powder obtained after 6 h of mechanical activation gives the largest increase in the burning rate. Comparison of the studied Al-Mg powder obtained after 6 h of mechanical activation and the commercially available Al-Mg powder showed that the difference in the burning rate is 8% (2.5 ± 0.1 mm/s for the Al-Mg powder obtained after 6 h of mechanical activation and 2.3 ± 0.1 mm/s for the commercially available powder).
Figure 10. Burning rate of the HEM compositions.
The difference in the combustion modes is probably explained the difference in the structure of the Al-Mg powder particles and the formation of bimodal particle size distribution. The difference in the structure as well as formation of bimodal distribution are explained by the difference in the method for obtaining the Al-Mg powders. The commercially available Al-Mg powder was obtained by spraying inert gas in a sealed chamber. The studied Al-Mg powder was obtained by mechanical activation in the planetary mill, and the phase composition of the studied Al-Mg powder is dominated by the Al12Mg17 phase. The mechanically activated Al12Mg17 powder has increased reactivity and is easier to react due to structural yielding and the formation linear crystal defects: dislocations and point defects (ionic and atomic vacancies, interstitial ions) [36]. The summary results of the obtained experimental data are presented in Table 5, where Q— combustion heat; U—burning rate; ΔQ and ΔU—difference in the combustion heat and burning rate of the compositions with Al-Mg alloy from the base composition.
Molecules 2020, 25, x FOR PEER REVIEW 12 of 15
Figure 9. Combustion heat of the HEM compositions.
MoleculesThe2020 results, 25, 3561 of the burning rate of the prepared compositions of HEMs (Table 1) in the11 air of 14at normal pressure (Figure 10) were obtained. The sample containing only amorphous boron powder (composition BC) has the lowest burning rate, while when the Al-Mg powder was added to the composition, the burning rate of the composition increases by approximately 47%. At the same composition, the burning rate of the composition increases by approximately 47%. At the same time, time, the Al-Mg powder obtained after 6 h of mechanical activation gives the largest increase in the the Al-Mg powder obtained after 6 h of mechanical activation gives the largest increase in the burning burning rate. Comparison of the studied Al-Mg powder obtained after 6 h of mechanical activation rate. Comparison of the studied Al-Mg powder obtained after 6 h of mechanical activation and the and the commercially available Al-Mg powder showed that the difference in the burning rate is 8% commercially available Al-Mg powder showed that the difference in the burning rate is 8% (2.5 ± 0.1 (2.5 0.1 mm/s for the Al-Mg powder obtained after 6 h of mechanical activation and 2.3 0.1 mm/s mm/s± for the Al-Mg powder obtained after 6 h of mechanical activation and 2.3 ± 0.1 mm/s± for the for the commercially available powder). commercially available powder).
Figure 10. Burning rate of the HEM compositions.
The didifferencefference in the combustion modes is probably explained the difference difference in the structure of the Al-Mg powder powder particles particles and and the the formation formation of of bimo bimodaldal particle particle size size distribu distribution.tion. The The difference difference in inthe the structure structure as aswell well as as formation formation of of bimodal bimodal distribution distribution are are explained explained by by the the difference difference in the method for obtaining the Al-Mg powders.powders. The commerciallycommercially available Al-Mg powder was obtained by spraying inert gas in aa sealedsealed chamber.chamber. The studiedstudied Al-MgAl-Mg powderpowder was obtainedobtained by mechanicalmechanical activation inin the the planetary planetary mill, mill, and and the phasethe phase composition composition of the studiedof the Al-Mgstudied powder Al-Mg is dominatedpowder is bydominated the Al12 Mgby17 thephase. Al12Mg The17 mechanicallyphase. The mechanically activated Al12 activatedMg17 powder Al12Mg has17 increasedpowder reactivityhas increased and isreactivity easier to and react is dueeasier to structuralto react due yielding to structural and the yielding formation and linear the formation crystal defects: linear dislocations crystal defects: and pointdislocations defects and (ionic point and defects atomic (ionic vacancies, and at interstitialomic vacancies, ions) [ 36interstitial]. ions) [36]. The summary summary results results of the of obtained the obtained experiment experimentalal data are data presented are presented in Table 5, in where Table Q—5, wherecombustion Q—combustion heat; U—burning heat; U—burning rate; ΔQ and rate; ΔU—difference∆Q and ∆U—di in thefference combustion in the heat combustion and burning heat andrate burningof the compositions rate of the compositions with Al-Mg alloy with from Al-Mg the alloy base from composition. the base composition.
Table 5. Summary of the results of combustion heat and burning rate. BC: Basic composition; BC(0): Basic composition with the addition of Al-Mg without mechanical activation (t = 0); BC(2): Basic composition with the addition of Al-Mg with mechanical activation (t = 2 h); BC(6): Basic composition with the addition of Al-Mg with mechanical activation (t = 6 h).
Code d43, µm Dm,1, µm Dm,2, µm Q, MJ/kg ∆Q, % U, mm/s ∆U, % BC - - - 6.0 0.2 - 1.7 0.08 - ± ± BC(0) 50 54 - 7.1 0.2 19 2.3 0.08 36 ± ± BC(2) 196 322 80 7.3 0.2 22 2.2 0.08 27 ± ± BC(6) 49 58 18 7.4 0.2 23 2.5 0.08 47 ± ±
4. Conclusions The Al-Mg powder, in view of its high exothermicity, was used as the catalytic additive that is capable of increasing the energy parameters of boron in the high-energy compositions and also significantly increasing their burning rate. The addition of the mechanically activated Al12Mg17 powder to the composition (SKDM-80 + ammonium perchlorate + amorphous boron) leads to an increase in the burning rate and the combustion Molecules 2020, 25, 3561 12 of 14 heat by approximately 47% and 24%, respectively. The greatest increase in the burning rate is achieved when using Al12Mg17 powder obtained after 6 h of mechanical activation in the planetary mill. Comparison of the burning rate and the combustion heat of the Al-Mg powders obtained by various methods showed that the addition of the studied Al12Mg17 powder obtained after 6 h of mechanical activation provides an increase in the burning rate by 8% (2.5 0.1 mm/s for the mechanically activated ± Al Mg powder and 2.3 0.1 mm/s for the commercially available powder) and the combustion heat 12 17 ± by 3% (7.4 0.2 MJ/kg for the mechanically activated Al Mg powder and 7.1 0.2 MJ/kg for the ± 12 17 ± commercially available powder). It was found that the addition of the Al-Mg powder in the compositions of HEMs, regardless of the method of obtaining and dispersion of the powders, does not affect a significant change in heat release. The phase composition of the commercially available Al-Mg powder and intermetallic powder obtained by the alloying and subsequent mechanical activation in the planetary mill are represented by the fragile intermetallic Al12Mg17 phase, which according to the state diagram of the Al-Mg system corresponds to the eutectic region. It was found that the increase in the duration of mechanical activation of the Al-Mg powder from 2 to 3 h leads to a significant decrease in particle size from 196 to 64 µm, and the morphology of the Al-Mg powder consists of individual particles of irregular shape, which is typical for powders after mechanical milling. It should be noted that Al-Mg powders (after mechanical activation) have a bimodal particle size distribution. The mass median diameter (d43) for the unimodal distribution function of the commercially available powder and the bimodal distribution function of the mechanically activated powder are approximately the same (the difference is 1 µm). It was found that with an increase in the duration of mechanical activation in the planetary mill, the exothermic peak of the Al12Mg17 powder on the DSC curve shifts to the zone of lower temperatures, and mechanical activation for more than 4 h does not significantly affect the position of peaks on the TG/DSC curves of the studied materials.
Author Contributions: Writing—original draft, S.S.; funding acquisition, I.Z.; supervision, A.V.; writing—review and editing, V.A. and I.Z. All authors have read and agreed to the published version of the manuscript. Funding: This research was supported by Ministry of Science and Higher Education of the Russian Federation, project No 0721-2020-0028. Acknowledgments: This research was supported by Ministry of Science and Higher Education of the Russian Federation, project No 0721-2020-0028. Conflicts of Interest: The authors declare no conflict of interest.
References
1. Tsander, F.A. Flights to other planets: (Theory of interplanetary travels). In Pioneers of Rocket Technology: Kibalchich. Tsiolkovsky. Tsander. Kondratyuk; Selected works; Nauka Pablishers: Moscow, USSR, 1964; pp. 277–359. 2. Dreizin, E.L. Metal-based reactive nanomaterials. Prog. Energy Combust. Sci. 2009, 35, 141–167. [CrossRef] 3. Young, G.; Wang, H.; Zachariah, M. Application of Nano-Aluminum/Nitrocellulose Mesoparticles in Composite Solid Rocket Propellants. Propellants Explos. Pyrotech. 2015, 40, 413–418. [CrossRef] 4. De Luca, L.T.; Galfetti, L.; Saverini, F.; Meda, L.; Marra, G.; Vorozhtsov, A.B.; Sedoi, V.S.; Babuk, V.A. Burning of Nano-Aluminized Composite Rocket Propellants. Combust Explos. Shock Waves 2005, 41, 80–94. [CrossRef] 5. Yankovskiy, S.; Korotkikh, A.; Arkhipov, V. The effect of dispersity of aluminum powder on ignition and specific impulse of thrust HEMs. MATEC Web Conf. 2014, 3, 191–192. 6. Pang, W.; De Luca, L.; Huixang, X.; Xuezhong, F.; Fengqu, Z.; Fangli, L.; Wuxi, X.; Yonghong, L. Effects of nano-metric aluminum powder on the properties of composite solid propellants. Int. J. Energetic Mater. Chem. Propul. 2015, 14, 265–282. [CrossRef] 7. Jayaraman, K.; Anand, K.; Chakravarthy, S.; Sarathi, R. Effect of nano-aluminium in plateau-burning and catalyzed composite solid propellant combustion. Combust. Flame 2009, 156, 1662–1673. [CrossRef] Molecules 2020, 25, 3561 13 of 14
8. Gany, A.; Caveny, L. Agglomeration and ignition mechanism of aluminum particles in solid propellants. Symp. (Int.) Combust. 1979, 17, 1453–1461. [CrossRef] 9. Jayaraman, K.; Anand, K.; Bhatt, D.; Chakravarthy,S.; Sarathi, R. Production, characterization, and combustion of nanoaluminum in composite solid propellants. J. Propul. Power. 2009, 25, 471–481. [CrossRef] 10. Yavor, Y.; Gany, A. Effect of nickel coating on aluminum combustion and agglomeration in solid propellants. In Proceedings of the 44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Hartford, CT, USA, 21–23 July 2008; p. 5255. 11. Yagodnikov, D.; Andreev, E.; Vorob’ev, V.; Glotov, O. Ignition, combustion, and agglomeration of encapsulated aluminum particles in a composite solid propellant. I. Theoretical study of the ignition and combustion of aluminum with fluorine-containing coatings. Combust. Explos. Shock Waves 2006, 42, 534–542. [CrossRef] 12. Reese, D.; Groven, L.; Son, S.; Mukasyan, A. Intermetallic compounds as fuels for composite rocket propellants. In Proceedings of the 47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, San Diego, CA, USA, 31 July–3 August 2011; p. 5865. 13. Sippel, T.; Son, S.; Groven, L.; Zhang, S.; Dreizin, E.L. Exploring mechanisms for agglomerate reduction in composite solid propellants with polyethylene inclusion modified aluminum. Combust. Flame 2015, 162, 846–854. [CrossRef] 14. Shoshin, Y.L.; Mudryy, R.S.; Dreizin, E.L. Preparation and characterization of energetic Al-Mg mechanical alloy powders. Combust. Flame 2002, 128, 259–269. [CrossRef] 15. Shoshin, Y.L.; Trunov, M.A.; Zhu, X.; Schoenitz, M.; Dreizin, E.L. Ignition of aluminum-rich Al–Ti mechanical alloys in air. Combust. Flame 2006, 144, 688–697. [CrossRef] 16. Belal, H.; Han, C.W.; Gunduz, I.E.; Ortalan, V.; Son, S. Ignition and combustion behavior of mechanically activated Al-Mg particles in composite solid propellants. Combust. Flame 2018, 194, 410–418. [CrossRef] 17. Aly, Y.; Dreizin, E.L. Ignition and combustion of Al-Mg alloy powders prepared by different techniques. Combust. Flame 2015, 162, 1440–1447. [CrossRef] 18. Cerri, S.; Bohn, M.; Menke, K.; Galfetti, L. Aging of HTPB/Al/AP rocket propellant formulations investigated by DMA measurements. Propellants Explos. Pyrotech. 2013, 38, 190–198. [CrossRef] 19. Brill, T.B.; Ren, W.; Yang, V. Solid Propellant Chemistry, Combustion, and Motor Interior Ballistics; American Institute of Aeronautics and Astronautics: Reston, VA, USA, 2000; pp. 749–776. 20. Meda, L.; Marra, G.; Galfetti, L.; Severini, F.; De Luca, L. Nano-Aluminum as Energetic Material for Rocket Mater. Sci. Eng. C 2007, 27, 1393–1396. [CrossRef] 21. Chen, R.H.; Suryanarayana, C.; Chaos, M. Combustion Characteristics of Mechanically Alloyed Ultrafine-Grained Al-Mg Powders. Adv. Eng. Mater. 2006, 8, 563–567. [CrossRef] 22. Aly, Y.; Schoenitz, M.; Dreizin, E.L. Ignition and combustion of mechanically alloyed Al-Mg powders with customized particle sizes. Combust. Flame 2013, 160, 835–842. [CrossRef] 23. Gopienko, V.G.; Petrovich, S.Y.; Cherepanov, V.P. Metal Powders of Aluminum, Magnesium, Titanium and Silicon. Consumer Properties and Applications, Kor. RAS prof. AI Rudskogo; Publishing House Polytechnic University: St. Petersburg, Russia, 2012. 24. Takacs, L. The historical development of mechanochemistry. Chem. Soc. Rev. 2013, 42, 7649–7659. [CrossRef] 25. Suryanarayana, C. Mechanical alloying and milling. Prog. Mater. Sci. 2001, 46, 1–184. [CrossRef] 26. Matveev, A.; Zhukov, I.; Ziatdinov, M.; Zhukov, A. Planetary Milling and Self-Propagating High-Temperature Synthesis of Al-TiB2 Composites. Materials 2020, 13, 1050. [CrossRef][PubMed] 27. Seplyarsky, B.S.; Kochetov, N.A.; Kochetkov, R.A. Influence of mechanical activation on the combustion rate of pressed samples and bulk density samples from a mixture of Ni–Al. Chem. Sustain. Dev. 2012, 20, 377–383. 28. Tsapalo, L.I.; Naiborodenko, Y.S.; Kasatskiy, N.G.; Arkatova, L.A. Influence of mechanical activation on
high-temperature synthesis of Fe3Al and its catalytic properties during carbon dioxide conversion of natural gas. Chem. Sustain. Dev. 2012, 20, 377–383. 29. Vorozhtsov, S.; Minkov, L.; Dammer, V.; Khrustalyov, A.; Zhukov, I.; Promakhov, V.; Khmeleva, M. Ex situ introduction and distribution of nonmetallic particles in aluminum melt: Modeling and experiment. JOM 2017, 69, 2653–2657. [CrossRef] 30. Dubkova, Y.; Zhukov, A. The analysis of combustion heat of the metallized solid fuel compositions. MATEC Web Conf. 2017, 92, 1068. [CrossRef] 31. Dubkova, Y.; Zhukov, A.; Zhukov, I.; Promakhov, V. Experimental study of the boron-containing mixtures burning rate. MATEC Web Conf. 2017, 110, 1022. [CrossRef] Molecules 2020, 25, 3561 14 of 14
32. Monakhov, V.T. Methods for Studying the Flammability of Substances; AmerindPublishingCo.: NewDelhi, India, 1985; p. 436. 33. Xu, C.; Gao, W. Pilling-Bedworth ratio for oxidation of alloys. Mater. Res. Innov. 2000, 3, 231–235. [CrossRef] 34. Breiter, A.L.; Kashporov, L.; Mal’tsev, V.; Pokhil, P.; Popov, E.; Pepekin, V.; Stasenko, A. Combustion of individual aluminum-magnesium alloy particles in the flame of an oxidizer-fuel mixture. Combust. Explos. Shock Waves. 1971, 7, 186–190. [CrossRef] 35. Murray, J.L. Phase Diagrams of Binary Magnesium Alloys; ASM International Metals Park: Ohio, OH, USA, 1988; pp. 17–34. 36. Boldyrev, V.V.; Avvakumov, E.G. Fundamentals of Mechanical Activation, Mechanosynthesis and Mechanochemical Technologies; Pb. SB RAS: Novosibirsk, Russia, 2009; pp. 15–26.
© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).