Combustion synthesis of tungsten, tantalum, and molybdenum nanopowders

Refractory metal nanopowders have recently been of interest as starting materials for preparation of heavy alloys with exceptionally good mechanical properties resulting from their structure homogeneity at a nanoscopic level. In the light of recently published papers, the combustion synthesis seems to be a promising technique for the large-scale production of metal nanopowders. In this method, the self-sustaining internal combustion of energetic composites is used to produce useful materials. The energy released in the combustion wave, propagating through a pressed sample of the green mixture, causes a rapid increase in temperature which in turns enables the processes and reactions with high activation barriers to proceed. Unbalanced conditions and high time and space variability of temperature in combustion wave are conducive to the creation of compounds and structures that are difficult to produce using other methods. Thanks to this combustion synthesis there is a source of simple and complex metal oxides, ceramic materials, metals and intermetallic compounds as well as various composites of the substances, both in powdery and compact forms. The product form and its microstructure depends on the synthesis conditions, especially on the size and morphology of substrate particles, reactants ratio, the initial density, the presence and concentration of additives, temperature and external pressure [1–6]. Metal powders are typically produced by reduction of relevant oxides. Aluminum, magnesium, zinc, calcium, zirconium, titanium, silicon, carbon and their mixtures or compounds are used as reducers [11]. If the combustion temperature is excessively high (above 2000°C) coarse metal powders are usually produced. The initially formed crystallites are irregular in shape, they melt on the surface and agglomerate giving even bigger particles. To overcome this problem, alkali metal halide is included as an additional reactant in the system. The additive melts in the combustion wave, reduces the combustion temperature, aids in transportation of the main reactant species, which positively affects the size and shape of combustion product particles. In addition, molten salt prevents grain growth by forming a protective layer around the particles. The current paper reviews recently published works (mainly by H.H. Nersisyan et al. [7, 12–23]) on molten salt assisted combustion synthesis (SACR ) of tungsten, tantalum and molybdenum nanopowders. A detailed description of the synthesis method including its specific features, the experimental procedure, combustion parameters and macro-kinetic aspects of chemical reactions in the combustion wave, and characterization of the metal nanopowders are presented

Catalytic effect of nano Fe₂O₃ on burning rate of aluminized PBAN/AP/HMX composite propellant

W artykule przedstawiono wyniki badań heterogenicznego paliwa rakietowego PBAN/NH₄ClO₄/HMX/Al zawierającego nano i mikrocząstki Fe₂O₃ lub ferrocen w roli katalizatora. Nanoproszek Fe₂O₃ był otrzymywany przez redukcję azotanu żelaza za pomocą alkoholu poliwinylowego w warunkach niskotemperaturowej syntezy spaleniowej. Zbadano morfologię i mikrostrukturę składników. Przeprowadzono obliczenia termodynamiczne i zmierzono prędkość spalania w bombie Crawforda. Stwierdzono, że katalityczny wpływ nanoproszku Fe₂O₃ na liniową prędkość spalania jest porównywalny z wpływem ferrocenu.In the present work, aluminized PBAN/AP/HMX composite propellants containing nanometer and micrometer sized Fe₂O₃ as well as ferrocene as catalysts were tested. Fe₂O₃ nanopowders were prepared by the sol-gel auto-combustion method using polyvinyl alcohol as a gelating agent (and fuel) and iron nitrate as an oxidizer and a precursor of iron oxide. The morphology and microstructure of the components and propellant samples were determined. Thermodynamic calculations were performed and burning rates were measured using the Crawford strand burning technique. It was stated that the catalytic effect of the F₂O₃ nanopowder on the burning rate is comparable with that of ferrocene

Optimization and scaling-up of 1,1-diamine-2,2-dinitroethene (FOX-7) synthesis

W niniejszej pracy dokonano optymalizacji procesu otrzymywania 1,1-diamino-2,2-dinitroetenu (FOX-7, DADNE ) w wyniku nitrowania jego bezpośredniego prekursora 2-metylopirymidyna-4,6-dionu (MPD). Zaproponowane modyfikacje obejmujące zarówno proces otrzymywania FOX-7 jak i MPD, pozwalają na prowadzenie szybszej i wydajniejszej oraz bezpieczniejszej syntezy tych związków. Dokonano pomiaru efektu cieplnego generowanego podczas procesu nitrowania MPD. Zmodyfikowane parametry procesu mogą być wykorzystane do otrzymywania FOX-7 w skali wielkolaboratoryjnej i półtechnicznej.In the paper, optimization of 1,1-diamine-2,2-dinitroethene (FOX-7) and its precursor, 2-methylpirymidyne-4,6-dion (MPD), syntheses are presented. The proposed modifications make it possible to synthesize both of the compounds in more efficient, faster, and safer processes. Heat effects of the MPD nitration were measured. The results obtained can be used to design equipment and to formulate procedure of FOX-7 production in a pilot scale process

Synthesis, structure and explosive properties of copper(II) chlorate(VII) coordination polymer with 4-amino-1,2,4-triazole bridging ligand

Otrzymano kompleksowy dichloran(VII) miedzi(II) z trzema cząsteczkami 4-amino-1,2,4-triazolu w roli ligandu mostkującego. Wykonano analizy składu pierwiastkowego, badania spektrofotometryczne w podczerwieni, analizy termiczne oraz badania wrażliwości i zdolności do detonacji pod wpływem bodźców termicznych. Stwierdzono, że otrzymany związek to koordynacyjny polimer, zbudowany z kationów miedzi powiązanych potrójnymi mostkami triazolowymi i otoczonych anionami chloranowymi(VII). Jest inicjującym materiałem wybuchowym o dużej odporności termicznej (do 250°C) i efektywności azydku ołowiu, ale jednocześnie charakteryzuje się znacznie mniejszą wrażliwością na tarcie (ok. 10 N).Copper(II) chlorate(VII) coordination polymer with 4-amino-1,2,4-triazole as bridging ligand was prepared and characterized by elemental analyses, IR spectra and TG/DTA analyses. Sensitivity and detonator tests were also preformed. The compound has a 1D chain structure in which Cu(II) ions are linked by triple triazole N1,N2 bridges. It is a detonat with performance close to that of lead azide, but at the same time it shows moderate sensitivity to thermal (explosively decomposes above 250°C) and mechanical stimuli (sensitivity to friction 10 N)

Investigation of the behaviour of steel and laminated fabric plates under blast load and fragment impact

An experimental investigation was undertaken in order to study the behaviour of laminated fabric and steel plates when subjected to impulsive load and fragment impact. Fully clamped rectangular plates were loaded by the blast wave generated due to explosion of TNT charges and by a steel fragment accelerated by the explosion products. The velocities of steel fragments and blast wave impulses were estimated experimentally and theoretically

Synthesis of tantalum nitride nanopowders in reactions of tantalum pentachloride with sodium azide

Otrzymano azotki tantalu w wyniku spontanicznych reakcji pentachlorku tantalu z azydkiem sodu w obecności chlorku sodu. Zbadano wpływ zawartości chlorku sodu w mieszaninie reakcyjnej na ciepło reakcji oraz skład i morfologię produktów. Wyniki badań XRD i SEM potwierdziły, że w warunkach syntezy powstaje amorficzny azotek tantalu i trzy fazy krystaliczne: heksagonalny i sześcienny TaN oraz trygonalny Ta₂N₀,₈₆. Wprowadzenie chlorku sodu do mieszaniny reakcyjnej zmienia skład fazowy produktów, obniża ciepło reakcji, zmniejsza wymiary krystalitów oraz ogranicza stopień ich aglomeracji.Tantalum nitride nanopowders have been synthesized by self-sustaining reactions of tantalum pentachoride with sodium azide in the presence of sodium chloride. The influence of NaCl contents in the reaction mixture on the reaction heat and composition of the reaction products was determined. Results of XRD analysis and SEM observations indicate that the purified reaction product is a mixture of amorphous TaN and three crystalline phases: hexagonal TaN cubic TaN and trigonal Ta₂N₀,₈₆. The presence of NaCl in the reaction mixture changes the reaction product phase composition, lowers the particle size and prevents their agglomeration

Combustion Synthesis of Titanium Carbonitrides

Titanium carbonitride (TiC0.5N0.5) micron powders were synthesized in reactions of titanium with zinc dicyanide: Zn(CN)2 + 4Ti → 4TiC0.5N0.5 + Zn. The reactions are sufficiently exothermic to propagate in the reactant mixture to form a self-sustaining, high-temperature synthesis (SHS). The final product was separated and the only byproduct (zinc) was removed by dissolution in dilute hydrochloric acid. The use of zinc dicyanide as the source of carbon and nitrogen causes the titanium carbonitride to contain only these elements in an atomic ratio of one. The reaction temperature can be easily reduced by the addition of zinc powder to the green mixture. Synthesis in the presence of zinc yields TiC0.5N0.5 powders consisting of round-shaped and unagglomerated particles