Manganese as Fuel in Slow‐Burning Pyrotechnic Time Delay Compositions

Manganese metal was evaluated as a fuel for slow‐burning delay compositions press‐filled in aluminium or compaction‐rolled in lead tubes. Oxides of antimony, bismuth, copper, manganese and vanadium were considered as oxidants. Measured burn rates for binary mixtures varied between 5 and 22 mm s⁻¹ but slower burning ternary and quaternary compositions were also found. The addition of fumed silica to the Mn/MnO₂ system had little effect on the propagation rate but a low level addition of hollow glass sphere significantly reduced the burn rate. Mn MnO₂ mixtures showed reliable burning over a wide stoichiometric range. In this system the fuel and the oxidant share a common metal. They combine to form the more stable intermediate oxide (MnO) releasing considerable quantities of heat in the process.     

The Effect of Additives on the Burning Rate of Silicon‐Calcium Sulfate Pyrotechnic Delay Compositions

The effect of fuel particle size as well as the influence of inert and reactive additives on the burning rate of the Si‐CaSO₄ composition was evaluated. The burning rate decreased with increase in fuel particle size, while the enthalpy remained constant. Addition of fuels to the base composition increased the burning rate, with an increase from 12.5 mm ⋅ s⁻¹ to 43 mm ⋅ s⁻¹ being recorded upon 10 wt‐% Al addition. Ternary mixtures of silicon, calcium sulfate, and an additional oxidizer generally decreased the burning rate, with the exception of bismuth trioxide, where it increased. The Si‐CaSO₄ formulation was found to be sensitive to the presence of inert material, addition of as little as 1 wt‐% fumed silica stifled combustion in the aluminum tubes.     

Mn+Sb2O3 Thermite/Intermetallic Delay Compositions

The binary Mn+Sb₂O₃ pyrotechnic composition was investigated for mining detonator time delay applications. EKVI thermodynamic modelling predicted two maxima in the adiabatic reaction temperature. The local maximum, at a manganese fuel content of ca. 36 wt‐%, corresponds to a pure thermite‐type redox reaction: 3 Mn+Sb₂O₃→3 MnO+2Sb. The overall maximum in the adiabatic reaction temperature (ca. 1640 K), at the fuel‐rich composition of 49 wt‐% Mn, is consistent with the reaction 5 Mn+Sb₂O₃→3 MnO+2 MnSb, i.e. a combination of the standard thermite with an additional exothermic intermetallic reaction. XRD analysis of combustion residues confirmed the formation of MnSb and Mn₂Sb for fuel‐rich compositions. Burn rates were measured using delay elements assembled into commercial detonators. The d₅₀ particle sizes were 23.4 and 0.92 μm for the Mn fuel and Sb₂O₃ oxidant powders, respectively. The delay elements comprised rolled lead tubes with a length of 44 mm and an outer diameter of 6.4 mm. The rolling action compacted the pyrotechnic compositions to 74 ± 2 % theoretical maximum density. The burning rate increased linearly from 4.2 to 9.4 mm s⁻¹ over the composition range 25–50 wt‐% Mn.     

Calcium Sulfate as a Possible Oxidant in “Green” Silicon‐based Pyrotechnic Time Delay Compositions

Chemical time delay detonators are used to control blasting operations in mines and quarries. Slow burning Si BaSO₄ pyrotechnic delay compositions are employed for long time delays. However, soluble barium compounds may pose environmental and health risks. Hence inexpensive anhydrous calcium sulfate was investigated as an alternative “green” oxidant. EKVI simulations indicated that stoichiometry corresponds to a composition that contains less than 30 wt‐% Si. However combustion was only supported in the range of 30–70 wt‐% Si. In this range the bomb calorimeter data and burn tests indicate that the reaction rate and energy output decrease with increasing silicon content. The measured burning rates in rigid aluminum elements ranged from 6.9 to 12.5 mm s⁻¹. The reaction product was a complex mixture that contained crystalline phases in addition to an amorphous calcium containing silicate phase. A reaction mechanism consistent with these observations is proposed.     

Measurement and Modelling of Pyrotechnic Time Delay Burning Rates: Method and Model Development

The burning rates of a slow reacting Mn+Sb₂O₃ and a fast reacting Si+Pb₃O₄ time delay composition, filled into lead tubes, were measured with an infrared camera, with two thermocouples and in the form of a fully assembled detonator. The infrared camera method returned values that were on average about 12 % lower than those recorded for the detonators. The temperature profiles measured for the slow burning elements were fully developed, whereas those obtained for the fast burning Si+Pb₃O₄ elements were not. A numerical model was developed to simulate the Mn+Sb₂O₃ system. Kinetic parameters were determined by least square fits to the recorded surface temperature profiles. The model made it possible to determine the effect of various property variations on the burning rate. The thermal conductivity of the delay composition was found to have the smallest impact and the heat of reaction the largest effect.     

Evaluation of Nano‐Co3O4 in HTPB‐Based Composite Propellant Formulations

Different propellant compositions were prepared by incorporating nano‐sized cobalt oxide from 0.25 % to 1 % in HTPB/AP/Al‐based composite propellant formulations with 86 % solid loading. The effects on viscosity build‐up, thermal, mechanical and ballistic properties were studied. The findings revealed that by increasing the percentage of nano‐Co₃O₄ in the composition, the end of mix viscosity, the modulus and the tensile strength increased, whereas the elongation decreased accordingly. The thermal property data envisaged a reduction in the decomposition temperature of ammonium perchlorate (AP) as well as formulations based on AP. The ballistic property data revealed an enhanced burning rate from 6.11 mm s⁻¹ (reference composition) to 8.99 mm s⁻¹ at 6.86 MPa and a marginal increase in pressure exponent from 0.35 (reference composition) to 0.42 with 1 % nano‐cobalt oxide.     

Development and Performance of the W/Sb2O3/KIO4/Lubricant Pyrotechnic Delay in the US Army Hand‐Held Signal

Gassy pyrotechnic delays composed of tungsten, antimony(III) oxide, potassium periodate, and various lubricants have been developed for use in the US Army hand‐held signal. The new compositions were developed to replace the current formulation, which contains potassium perchlorate and barium chromate, chemicals that are facing increasing scrutiny due to environmental regulation. The hand‐held signal delay housing was used to demonstrate the burning rate tunability of the new compositions. The addition of 1–5 % of waxy lubricants (stearic acid or calcium stearate) was found to have a profound effect on burning rate. The effect of tungsten content and the Sb₂O₃/KIO₄ ratio on burning rate was also probed. A wide range of inverse burning rates (2 to 15 s cm⁻¹) were demonstrated, which encompasses the 7 to 8.5 s cm⁻¹ range required by the hand‐held signal. The W/KIO₄ reaction produces I₂, which was observed by visible spectroscopy in the vapor above a sample of combustion residue.     

The effect of Sb2O3 on the properties of micro-arc oxidation coatings on magnesium alloys

Coatings incorporated with Sb₂O₃ were obtained on AZ31B magnesium alloy during micro-arc oxidation (MAO) by adding Sb₂O₃ (0, 2, 4, 6, 8 g/L) into the electrolyte. The voltage of MAO process, microstructure, element distribution, thickness, phase analysis, microhardness, adhesion, and corrosion behavior of the coatings were, respectively, investigated. The results showed that the addition of different concentrations of Sb₂O₃ caused the voltage variation, which resulted in the changes in microstructure, element distribution, and phase composition of coatings, and further led to the improvement of coatings properties. It was found that the addition of Sb₂O₃ could effectively decrease the breakdown voltage, and made the voltage of micro-arc oxidation stage change. Moreover, the presence of Sb₂O₃ influenced surface morphologies of the coatings. Additionally, with the increase in Sb₂O₃, the microhardness of coatings was 155.2, 199.78, 277.34, 267.53, and 127.93 HV, respectively; these were higher than substrate (68.5 HV). Moreover, the addition of Sb₂O₃ effectively improved adhesion. As the Sb₂O₃ increased, the corrosion rate was 2.19 × 10⁻⁴, 9.09 × 10⁻⁵, 4.10 × 10⁻⁵, 2.52 × 10⁻⁴, and 2.96 × 10⁻⁴ mm/a, respectively, and the corrosion resistance increased first and then decreased with the increase in Sb₂O₃. In sum, the optimal Sb₂O₃ concentration was 4 g/L.     

Preparation of oxygen gas barrier poly(ethylene terephthalate) films by deposition of silicon oxide films plasma‐polymerized from a mixture of tetramethoxysilane and oxygen

To prepare silicon oxide (SiOx)‐deposited poly(ethylene terephthalate) films with high oxygen gas barrier capability, SiOx deposition by plasma polymerization has been investigated from the viewpoint of chemical composition. Tetramethoxysilane (TMOS) is suitable as a starting material for the synthesis of the SiOx films. The SiOx deposition under self‐bias, where the etching action occurs around an electrode surface, is effective in eliminating carbonaceous compounds from the deposited SiOx films. There is no difference in the chemical composition between the SiOx films deposited under self‐bias and under no self‐bias. The SiOx films are composed of a main component of Si O Si networks and a minor component of carbonized carbons. The SiOx films deposited under no self‐bias from the TMOS/O₂ mixture show good oxygen gas barrier capability, but the SiOx films deposited under the self‐bias show poor capability. The minimum oxygen permeation rate for poly(ethylene terephthalate) films deposited SiOx film is 0.10 cm³ m⁻² day⁻¹ atm⁻¹, which corresponds to an oxygen permeability coefficient of 1.4 × 10⁻¹⁷ cm³‐cm cm⁻² s⁻¹ cm⁻¹ Hg for the SiOx film itself. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2091–2100, 1999     

(Sb2O3/Sb2O5)-doped SnO2–Co3O4–Cr2O3 varistors: The Sb2O4 in-situ formation and its influence over the electrical and microstructural properties

The present study aimed to systematically study the transitions and consequential effects of antimony oxide (Sb₂O₃ or Sb₂O₅) additions over the properties of a SnO₂-based varistor system. High energy ball-milling and conventional sintering were used to obtain the samples with the following molar composition: (98.95-X)% SnO₂ - 1% Co₃O₄ - 0.05% Cr₂O₃ - X% Sb₂O₃/Sb₂O₅ where X = 0, 0.05, 0.1, 0.2 and 0.4 mol%. The thermal analysis suggested the in-situ formation of Sb₂O₄ at ~450 °C from Sb₂O₃ or Sb₂O₅ during the sintering of mixed oxides. SEM, XRD, and electrical analysis revealed similar results by using Sb₂O₃ or Sb₂O₅; the addition of 0.05 mol% antimony oxide provides the foremost properties. The transition equations from Sb₂O₃ or Sb₂O₅ to Sb₂O₄ demonstrate equivalency in the amount of Sb₂O₄ formed. That fact, besides the results obtained, were used to discuss a reasonable route for Sb³⁺ and Sb⁵⁺ incorporation within the SnO₂ lattice.     

The Effect of Ambient Conditions on the Burning Rate of Gel Fuel Droplets

An experimental study was conducted to determine the dependence of the burning rate coefficient of gel fuel droplets on the pressure at different ambient oxygen nitrogen mixtures. Experiments were conducted using a pressure chamber, in which the droplet was suspended and the combustion process was video‐photographed by a high‐speed digital video camera. The tests were conducted at pressures between 0.1–4 MPa at different ambient oxygen nitrogen compositions (air, 40 % O₂ – 60 % N₂, and 60 % O₂ – 40 % N₂). The fuel was a compound of 95 % kerosene and 5 % gellant. At sub‐critical pressure conditions, the burning rate coefficient was found to increase with increasing ambient oxygen mass fraction. At supercritical conditions, no dependence of the burning rate coefficient on the ambient mixture was found. The results indicate that the burning rate coefficient depends on the oxygen partial pressure, at least at low pressures.     

Substituierte Alkinyle als axiale Liganden an häminähnlich gebundenem Eisen(III) - Einordnung in eine spektrochemische Serie

Substituted Alkinyles as Axial Ligands at Hemine Like Bound Iron(III) - Incorporation into a Spectrochemical Series . Substituted lithium alkynyles Li CC R (R = ^tBu, Ph, p-Cl C₆H₄, Me₃Si, ⁱPr₃Si, Ph₃Si) react with the hemine like macrocyclic iron(III) complex 6,13-di(ethoxycarbonyl)-5, 14-dimethyl-1, 4, 8, 11-tetraazatetradeca-4,6,12,14-tetraenato[2⁻]iron(III)-iodide (formula 2 ;) in tetrahydrofuran to form anionic low-spin di-adducts [fe(CC R)₂]⁻. The incorporation of the alkynyles into a spectrochemical series of the axial ligands (studied by the sharp equatorial-ligand-to-metal CT absorption band) results in the wavelength-sequence (nm): OH⁻ (≈︁ 510) « N₃⁻ (≈︁ 625) < ^tBu CC⁻ (664) < NH₃ (666) < Ph CC⁻ (692) < Ph NH₂ (695) < Me₃Si CC⁻ (698) < SCN⁻ (713) < Ph₃Si C  C⁻ (716) < CN⁻ (739) < 4-picoline (759) < pyridine (765) < nicotinamide (776) < methylnicotinat (788) < pyrazine (798) and points to a significant π-acceptor ability of the silyl substituents.     

Metal/Fluorocarbon Pyrolants: VI. Combustion Behaviour and Radiation Properties of Magnesium/Poly(Carbon Monofluoride) Pyrolant

The performance of poly(carbon monofluoride) (PMF) (synonym: graphite fluoride) (CF_x)_n, ( 1 ) as oxidizer in a fuel rich Mg based pyrolant (ξ(Mg)=0.45) is investigated. The radiance [W sr⁻¹] under both static and dynamic conditions, the spectral radiant exitance [W cm⁻² μm⁻¹], the linear burn rate [mm s⁻¹] and the mass consumption rate [g s⁻¹ cm⁻²] have been determined. Calculations for enthalpy of anaerobic and aerobic combustion [kJ g⁻¹] and for the equilibrium composition of the combustion products as well as combustion temperature are given. A mechanism for the reaction is discussed. The combustion product from Mg/(CF_x)_n surprisingly reveals the formation of single walled carbon nanotubes (SWCNT) and “carbon nano carpet rolls” (CNCR). For part V see Ref. [1].     

Combustion Characteristics of a Novel Grain‐Binding High Burning Rate Propellant

The novel grain‐binding high burning rate propellant (NGHP) is prepared via a solventless extrusion process of binder and spherical propellant grains. Compared with the traditional grain‐binding porous propellants, NGHP is compact and has no interior micropores. During the combustion of NGHP, there appear honeycomb‐like burning layers, which increase the burning surface and the burning rate of the propellant. The combustion of NGHP is a limited convective combustion process and apt to achieve stable state. The larger the difference between the burning rate of the binder and that of the spherical granular propellants exists, the higher burning rate NGHP has. The smaller the mass ratio of the binder to the spherical granular propellants is, the higher the burning rate of NGHP is. It shows that the addition of 3 wt.‐% composite catalyst (the mixture of lead/copper complex and copper/chrome oxides at a mass ratio of 1 : 1) into NGHP can enhance the burning rate from 48.78 mm⋅s⁻¹ in the absence of catalyst to 56.66 mm⋅s⁻¹ at P=9.81 MPa and decrease the pressure exponent from 0.686 to 0.576 in the pressure range from 9.81 to 19.62 MPa.     

One-step microwave-assisted synthesis of Sb2O3/reduced graphene oxide composites as advanced anode materials for sodium-ion batteries

Sb₂O₃/reduced graphene oxide (RGO) composites were prepared through a facile microwave-assisted reduction of graphite oxide in SbCl₃ precursor solution, and investigated as anode material for sodium-ion batteries (SIBs). The experimental results show that a maximum specific capacity of 503 mA h g⁻¹ is achieved after 50 galvanostatic charge/discharge cycles at a current density of 100 mA g⁻¹ by optimizing the RGO content in the composites and an excellent rate performance is also obtained due to the synergistic effect between Sb₂O₃ and RGO. The high capacity, superior rate capability and excellent cycling performance of Sb₂O₃/RGO composites demonstrate their excellent sodium-ion storage ability and show their great potential as electrode materials for SIBs.     

Development and Performance of Boron Carbide‐Based Smoke Compositions

Pyrotechnic smoke compositions for visual obscuration containing boron carbide, potassium nitrate, potassium chloride, and various lubricants are described. Only the waxy lubricants stearic acid and calcium stearate slowed the burning rate into a range suitable for end‐burning smoke grenades. For compositions pressed into steel cans, the addition of just 2 wt‐% calcium stearate was shown to reduce the burning rate from 0.50 cm s⁻¹ to 0.09 cm s⁻¹. In this system, potassium chloride serves as a diluent that reduces incandesence but also increases slag formation. Compositions containing potassium chloride in the 25–30 wt‐% range exhibited both acceptably low incandescense and slag formation upon burning, while also producing copious amounts of white smoke. These experimental compositions were loaded into full‐size grenade cans; field and smoke chamber testing revealed that they outperform the US Army’s in‐service M83 TA grenade both qualitatively and quantitatively. The photopic mass‐based figures of merit for experimental grenades KCl‐25, KCl‐30, and a production‐run M83 TA grenade were 2.51, 2.19, and 1.44 m² g⁻¹, respectively.     

Metal–Fluorocarbon Pyrolants: X. Influence of Ferric Oxide/Silicon Additive on Burn Rate and Radiometric Performance of Magnesium/Teflon/Viton® (MTV)

Both burn rate, u (mm s⁻¹) and mass consumption rate, (g s⁻¹ cm⁻²) of fuel rich magnesium/Teflon/Viton^® (MTV) (45/50/5) upon addition of silicon/ferric oxide for part of the PTFE decrease by 16 and 11%, respectively. However, the spectral efficiency E_β (J g⁻¹ sr⁻¹) increases by 24% in the 3–5 μm band.     

Study on high-temperature composite properties of fluorosilicone rubber with nano-Sb2O3

This article studied the influence of nano-Sb₂O₃ on the high-temperature composite performance of fluorosilicone rubber (FVMQ). FVMQ with 4% mass of nano-Sb₂O₃ content was prepared by mechanical blending method. The friction properties of FVMQ and Sb₂O₃/FVMQ composites at different temperatures were analyzed by means of three-dimensional profilometer and scanning electron microscopy. The results showed that nano-Sb₂O₃ can enhance the matrix strength of FVMQ, and this effect was obvious at high temperature. The elongation of Sb₂O₃/FVMQ composites was increased by 10.7% at 25°C. The tear strength of Sb₂O₃/FVMQ composites was increased by 53.1%. While the friction coefficient and the wear amount, respectively, were decreased by 20 and 48.53% at 200°C. Sb₂O₃/FVMQ composite showed excellent anti-wear, antifriction, anti-tear, and other characteristics in the high-temperature test. The enhancement of the cross-linking density of matrix caused by adding Sb₂O₃ into FVMQ can lead to the softening of rubber, and the type of wear changed from abrasive wear to adhesive wear. Thus, the composite showed good wear resistance.     

Y2O3–Al2O3–SiO2-based glass-ceramic fillers for the laser-supported joining of SiC

Four glass-ceramic filler compositions within the Y₂O₃–Al₂O₃–SiO₂ system were tested for their suitability in laser-supported joining of SiC materials. The compositions differed in terms of their primary crystallization behavior. Joint zone microstructures were investigated and joint tightness was determined using helium leak rate measurements after joining and subsequent annealing at 900 °C and 1050 °C.Yttria- and silica-rich compositions showed a partial crystallization of yttrium silicates during the short laser processing. Subsequent heat treatment effected further crystallization toward equilibrium conditions. Despite the strong change in the degree of crystallization no reduction of the tightness was observed for the best compositions; after 500 h annealing at 1050 °C tightness values of less than 10⁻⁸ mbar l s⁻¹ were measured. These results demonstrate the potential of the investigated filler system for high temperature stable hermetic sealing. At the same time the creation of homogeneously structured joints from glass-ceramic fillers using a laser-supported technology needs the understanding of the crystallization kinetics.     

CoAl2O4–mullite composites prepared by sol–gel processes

The formation of CoAl₂O₄–mullite composites from diphasic sol–gel precursors with 3:2 mullite composition doped with 1, 2 and 3 at.% Co²⁺ was studied by differential scanning calorimetry (DSC), X-ray diffraction and Rietveld structure refinement. The course of thermal reactions is dominated by the intermediate formation of two faint crystallized phases having different composition and activation energies. The former phase with smaller activation energy (822 kJ mol⁻¹) is attributed to cobalt-containing spinel structure and the latter with larger activation energy (about 1200 kJ mol⁻¹) to Al–Si spinel. With temperature increase Co-containing spinel transforms progressively in CoAl₂O₄, while Al–Si spinel forms mullite above 1100 °C. Mullite lattice parameters, Rietveld refinement data and the CoAl₂O₄/Co²⁺ ratio in annealed samples points out that the majority of cobalt is incorporated in CoAl₂O₄ and only about 0.6 at.% enters mullite structure or the glassy phase, or both.