Combustion Tests Research Articles

Optimization of intumescent flame retardant system based on ammonium polyphosphate, double pentaerythritol, and zinc borate for thermoplastic polyurethane composite

AbstractThe widespread industrial applications of thermoplastic polyurethane (TPU) are partially limited by its flammability. The design of high‐performance intumescent flame retardants (IFR) is of great significance for enhancing flame retardant (FR) performance of TPU. In this work, an IFR system consisting of ammonium polyphosphate (APP), double pentaerythritol (DPER), and zinc borate (ZB) is proposed. The optimized experimental parameters with 15 wt.% additive amount of FR, APP‐DPER weight ratio of 2.28:1 and 15.56 wt.% ZB content are regulated based on Box–Behnken design‐response surface methodology (BBD‐RSM) to obtain TPU/FR composite with superior limiting oxygen index value of 30.2%. Noticeably, the design efficiency of TPU/FR composite is significantly improved by utilizing BBD‐RSM. Results of vertical burning test show that the optimized TPU/FR composite passes UL 94 V‐0 rating and peak heat release rate is dramatically reduced from 1355.88 (neat TPU) to 201.01 KW/m2 through cone calorimeter test. In addition, scanning electron microscopy accompanied with Raman spectroscopy are conducted to characterize the morphology and composition of residual char for further exploring the FR mechanism of IFR system in TPU. The as‐prepared TPU/FR composite has provided new potential application in engineering fields.

Synthesis of PMM and Synergistic Flame Retardant Effect with Ammonium polyphosphate

A novel flame retardant poly {[(2-Methyl-acrylic acid 2-(dimethoxyphosphoryloxy)-ethyl ester]-co-[2-Methyl-acrylic acid 2-(trimethoxysiloxy)-ethyl ester]} (PMM) containing dimethoxyphosphoryloxy and trimethoxysiloxy groups in side chains was synthesized. The structure of PMM was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (1H NMR), and the thermal performance of PMM was characterized by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The effect of PMM on polypropylene’s flame retardancy and thermal behaviors was investigated by limited oxygen index (LOI), vertical burning test (UL-94), and TG tests. The experimental results indicate that the addition of PMM helps to improve the flame retardancy and thermal stability of PP. When the addition of PMM and APP in PC was 15% and 20%, the LOI value of PC reached 28.4%, and the UL-94 test rating reached V-0 level. The charred structure observed by scanning electron microscopy (SEM) indicated that the char surface for PP/APP/PMM system holds an intumescent char structure compared to neat PP, and the synergy exists in the composites. The PMM slightly decreased the tensile property in terms of strength but increased the elongation at break for PP composites.

The Tensile, Thermal and Flame-Retardant Properties of Polyetherimide and Polyetherketoneketone Processed via Fused Filament Fabrication.

Polymer materials are increasingly widely used in high-fire-risk applications, such as aviation interior components. This study aimed to compare the tensile, thermal, and flame-retardant properties of test samples made from ultra-performance materials, polyetherimide (PEI) and polyetherketoneketone (PEKK), using the fused filament fabrication process (FFF). The tensile tests were performed for these materials at different raster angles (0, 45, and 90°). The thermomechanical tests were done in the axial, perpendicular, and through-thickness directions to the extruded filaments. The impact of printing parameters on the flame retardancy of 3D-printed samples was investigated in vertical burn tests with varying specimen thicknesses and printing directions. Experimentally, it was testified that PEKK had better isotropic behaviour than PEI for mechanical performance, thermal expansion, and fire-resistant properties, which are essential in fabricating intricately shaped products.

Investigation of a conveyor belt fire in an underground coal mine: Experimental studies and CFD analysis

Coal produced in underground mines is transported to the surface by means of conveyor belts throughout long roadways. The combustion of belts puts a large number of employees at great risk. Underground collieries differ from other underground mines -due to the combustible nature of the product. The most prevalent cause of belt fires in underground coal mine is spontaneous combustion due to oxidation of the coal, which also enables the conveyor belt to burn over time. In 2014, a belt fire in an underground coal mine in Manisa-Soma, Turkey caused 301 fatalities. A study has been conducted on this accident for approximately 3 years, consisting of combustion tests in a purpose-built research gallery, comparison of the test results with mine records of the accident, and CFD modelling of the mine environment. The intensity of the fire was sufficient to redirect the air flow underground, causin large amounts of toxic gases to fill almost the entire mine in approximately 15 minutes. It is recommended that CFD analysis be used in planning emergency action strategies in underground mines.

A biphosphophenanthrene structure intumescent flame retardant with superior smoke suppression performance for epoxy resin

The intrinsic flammability and high smoke production are two major defects that epoxy resin (EP) must overcome during the practical application. However, few current studies have acknowledged in both fire resistance and smoke suppression performance, which is vitally interrelated with quality of char layers. Herein, a P/S-containing compounds (PODSE) was prepared via esterification and then supplemented with ammonium polyphosphate (APP) to develop an intumescent flame retardant for heightening the strength of char. With 20 wt% PODSE/APP, the peak of smoke produce rate (pSPR) and total smoke production (TSP) of EP3 reduced by 88.1 % and 87.0 %, respectively, indicative of superior smoke suppression performance. It attained a limited oxygen index (LOI) value of 40.0 % with V-0 rating during vertical burning test (UL-94) and the char residues at 700 °C increased from 15.8 % to 29.9 % compared with pure EP. More importantly, in order to figure out the reason for such highly-improved performance, the residual chars after cone calorimeter (CC) test were comprehensively investigated. The result showed that the internal chars of the samples modified by PODSE/APP exhibited honeycomb-like structure instead of irregular network structure of the one modified with single PODSE, endowing the char layers with higher expanded ratio and strength, which responded to excellent insulation effect. This finding provided theoretical and experimental basis for further exploration of P/S synergistic intumescent flame retardant.

Development of a UiO-66 Based Waterborne Flame-Retardant Coating for PC/ABS Material.

The flame-retardancy of polymeric materials has garnered great interest. Most of the flame retardants used in copolymers are functionalized additives, which can deteriorate the intrinsic properties of these materials. As a new type of flame retardant, functionalized metal-organic frameworks (MOFs) can be used in surface coatings of polymers. To reduce the flammability, a mixture of phytic acid, multi-wall carbon nanotubes, zirconium-based MOFs, and UiO-66 was coated on a PC/ABS substrate. The structure of the UiO-66-based flame retardant was established by FT-IR, XRD, XPS, and SEM. The flammable properties of coated PC/ABS materials were assessed by LOI, a vertical combustion test, TGA, CCT, and Raman spectroscopy. The presence of a UiO-66-based coating on the PC/ABS surface resulted in a good flame-retardant performance. Heat release and smoke generation were significantly reduced. Importantly, the structure and mechanical properties of PC/ABS were less impacted by the presence of the flame-retardant coating. Hence, this work presents a new strategy for the development of high-performance PC/ABC materials with both excellent flame-retardancy and good mechanical properties.

Synthesis of DOPO Derivatives for the Fabrication of Flame Retardant Epoxy Composites

Four flame retardant DOPO derivatives were succesfully synthesized by Pudovik reaction, including 6,6'-(([1,1'-biphenyl]-4,4'-diylbis(azanediyl))bis (thiophen-2-ylmethylene))bis(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) 5a, 6,6'-(((sulfonylbis(4,1-phenylene))bis(azanediyl)) bis(thiophen-2-ylmethylene))bis(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) 5b, 6,6'-((1,4-phenylenebis(azanediyl))bis(furan-2ylmethylene))bis(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) 5c and 6,6'-((oxybis(4,1-phenylene))bis(1-(thiophen-2-yl)ethane-2,1-diyl))bis(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) 5d. Among them, flame retardants 5a and 5d were synthesized for the first time. DOPO derivatives were combined with functionalized ammonium polyphosphate using polyethyleneimine (PEI-APP) as flame retardant systems for epoxy composites. The combination of compound 5a and PEI-APP gave the materials with the best flame retardancy. 6wt% of PEI-APP/6% of 5a promoted the composite material to V-0 rating in UL-94 vertical burning test and the limiting oxygen index reached 28.9%. The impact of flame retardants towards the mechanical and physical properties of epoxy resin was also evaluated. The combination of 5a with PEI-APP showed the least decrease in mechanical strength of epoxy composite.

Bio-based epoxy vitrimer with inherent excellent flame retardance and recyclability via molecular design

The development of biobased fire-safe thermosets with recyclability heralds the switch for a transition towards a circular economy. In this framework, we introduced a novel high-performance bio-epoxy vitrimer (named GVD), which was fabricated by forming a crosslinking network between bio-epoxy glycerol triglycidyl ether (Gte), varying amounts of reactive flame-retardant agent 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) (0–7 wt%) and a vanillin-based hardener (VA) with imine bonds. For instance, the epoxy vitrimer GVD5, featuring a DOPO content of 5 wt%, achieved a V-0 rating in the vertical burning test (UL-94) and obtained a limiting oxygen index (LOI) value of 31 %, surpassing the performance of pristine epoxy. Furthermore, the peak heat release rate and total heat release of GVD5 were reduced by 38.2 % and 26.3 %, respectively, compared to pristine epoxy. The GVD vitrimers further demonstrated exceptional reprocessability and recyclability, attributed to the presence of dynamic imine bonds within the topological crosslinking network. Remarkably, the epoxy vitrimers maintained the mechanical properties of the parent epoxy. Therefore, this work provides a facile strategy for fabricating high-performance and multi-functional bio-epoxy thermosets.

Self-extinguishable, intumescent poly(urethane-triazole)s as halogen-free flame retardant materials via bulk polymerization of azide-alkynes

In the present study, an unexplored class of non-halogenated self-extinguishable and intumescent phosphorous-based poly(urethane-triazole)s (P-PUTs) were achieved through the bulk polymerization of azide-alkynes notably in absence of catalyst. A series of azide-functionalized urethane monomers (tetra azides) were synthesized by the reaction of 1,3-diazido-propan-2-ol with commonly used, but three structurally different diisocyanates, viz, aliphatic, alicyclic, and aromatic. Concurrently, a dialkyne, phenyl di-prop-2-ynyl phosphonate was synthesized and co-polymerized with these urethane tetrazides through bulk polymerization at 80 °C. The curing kinetics of the polymerization was monitored by differential scanning calorimetry (DSC) under non-isothermal conditions with different heating ramps. Thermal behaviour, elemental and morphological properties of the synthesized P-PUTs were comprehensively investigated employing thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDX), respectively. The flame retardant properties of P-PUTs were assessed by UL–94 vertical burning test, limiting oxygen index (LOI) and lab-scale flammability test. All the P-PUT compositions were found to self-extinguish immediately after the removal of flame with a V-0 rating of UL-94 V, the LOI value (vol%) are 26.3 %, 28.2 % and 29.0 % for H2P-PUT, I2P-PUT and T2P-PUT, respectively and the corresponding char yields were 26.03 wt%, 25.76 wt% and 39.58 wt% along with significant intumescence. This apart, the films with a transparency of 96.5 %, 96.7 % and 94.3 % in the visible wavelength for H2P-PUT, I2P-PUT and T2P-PUT, respectively, can possibly make these P-PUTs materials attractive as fire retardant top coats on wood substrates.

Enhancement of fire safety in epoxy resin composites through incorporation of microencapsulated diatomite

AbstractDiatomite (DIA) particles are commonly employed as flame‐retardant additives for polymers, yet their intrinsic inefficiency requires substantial quantities for optimal efficacy. To address this issue, we proposed a novel approach involving the microencapsulation of DIA with polyethylene glycol phosphate (PEGP) to enhance the flame retardancy of epoxy resin (EP). Characterization of the prepared DIA@PEGP utilized scanning electron microscopy with energy‐dispersive x‐ray spectrometry and Fourier transform infrared spectroscopy. The resulting EP composite, DIA@PEGP‐4/EP, achieved a limiting oxygen index of 33.2% and achieved a V‐0 level in vertical combustion tests. Compared to EP, DIA@PEGP‐4/EP demonstrated significantly improved fire performance, with 38.6%, 47.8%, 25.0%, 41.3%, and 60.4% reduction in peak heat release rate, total heat release, peak smoke production rate, total smoke production, and CO yield. Furthermore, the highest FPI value of 0.080 m2·s/kW for DIA@PEGP‐1/EP and the lowest FGI value of 8.734 kW/m2·s for DIA@PEGP‐4/EP, indicate that the incorporation of DIA@PEGP into EP enhances its fire safety. The flame retardancy mechanism of DIA@PEGP‐4 involves the formation of a phosphorus‐containing aromatic carbon layer during EP char formation, capturing radicals in the gas phase during combustion.

Elaboration of Thermally Performing Polyurethane Foams, Based on Biopolyols, with Thermal Insulating Applications.

In this work, biobased rigid polyurethane foams (PUFs) were developed with the aim of achieving thermal and fireproofing properties that can compete with those of the commercially available products. First, the synthesis of a biopolyol from a wood residue by means of a scaled-up process with suitable yield and reaction conditions was carried out. This biopolyol was able to substitute completely the synthetic polyols that are typically employed within a polyurethane formulation. Different formulations were developed to assess the effect of two flame retardants, namely, polyhedral oligomeric silsesquioxane (POSS) and amino polyphosphate (APP), in terms of their thermal properties and degradation and their fireproofing mechanism. The structure and the thermal degradation of the different formulations was evaluated via Fourier Transformed Infrared Spectroscopy (FTIR) and thermogravimetric analysis (TGA). Likewise, the performance of the different PUF formulations was studied and compared to that of an industrial PUF. From these results, it can be highlighted that the addition of the flame retardants into the formulation showed an improvement in the results of the UL-94 vertical burning test and the LOI. Moreover, the fireproofing performance of the biobased formulations was comparable to that of the industrial one. In addition to that, it can be remarked that the biobased formulations displayed an excellent performance as thermal insulators (0.02371-0.02149 W·m-1·K-1), which was even slightly higher than that of the industrial one.

Synthesis of MXene-Based functional coatings on rigid polyurethane foam surfaces: A comparative study of layer-by-layer self-assembly and hydrothermal methods

A flame retardant for rigid polyurethane (RPUF) was designed and synthesized to expand the application field of RPUF. The flame retardants, namely MXene/PEI/PA-L and MXene/PEI/PA-H, were synthesized using phytic acid (PA), polyethyleneimine (PEI), and MXene through layer-by-layer (LBL) self-assembly method and hydrothermal method, respectively. In terms of mechanical performance, MXene/PEI/PA-L imparted brittleness to RPUF while MXene/PEI/PA-H enhanced its toughness, enabling RPUF to adapt to diverse application scenarios. The flame retardant properties were evaluated via vertical combustion test, cone calorimetry test, and thermogravimetric test, and the gas phase flame retardant mechanism was analyzed by TG-FTIR. MXene/PEI/PA constituted a N-P-Ti synergistic flame retardant system. During combustion, MXene/PEI/PA formed a layered dense carbon layer to cut off the external oxygen transport channel and absorbed many oxygen-containing free radicals. MXene/PEI/PA-L demonstrated efficient smoke suppression capability, while MXene/PEI/PA-H showed superior thermal insulation performance. The ignition time (TTI) of the composite foam reached 47 s, the total smoke release (TSR) value decreased by 92 %, and the flame retardant grade reached 5VA. Coated RPUF had excellent flame retardant ability.

Numerical Evaluation of Sodium Droplet Swarm Combustion and Its Modeling Optimization

Because of its superior thermal-hydraulic qualities, liquid sodium has been applied to a variety of industries, including energy storage, solar energy, sodium-cooled fast reactors, and aerospace. However, fires brought on by sodium leaks at high pressure can have major thermodynamic repercussions and put employees and equipment in use at risk directly or indirectly. As a result, a realistic and accurate forecast of the combustion behavior of sodium droplet swarm can offer technical backing for the use of liquid sodium in engineering as well as a way of sodium fire prevention and control. Spray dynamics (droplet settling, droplet particle size distribution, etc.), combustion kinetics (premixed combustion, gas phase combustion, etc.), sodium aerosol diffusion, and other specialized phenomena all contribute to the complex process of sodium droplet swarm combustion. The NACOM code created by Brookhaven National Laboratory for sodium droplet swarm combustion is utilized in this paper as a framework. The code is first validated using the benchmark of the sodium droplet swarm combustion tests carried out by prestigious institutions. The validation results demonstrate that the code’s drag model, droplet combustion model, and heat transfer model are to blame for the significantly overestimated thermodynamic effects of sodium droplet swarm combustion. NACOM is subsequently developed twice for the authors’ previously developed vapor-liquid two-layer-structure drag model, chemical kinetic combustion model, and suitable heat transfer coefficient. It is then thoroughly assessed for the separate-effects tests and integral-effects test. The evaluation results demonstrate that the optimized drag model accelerates the settling of sodium droplets due to the consideration of the sodium-vapor drag reduction effect, reducing the thermodynamic effects of liquid sodium combustion; the optimized premixed combustion model can accurately predict the low-temperature sodium droplet swarm combustion conditions, resolving the issue of serious misvaluation of the original version of NACOM. The associated research findings can serve as valuable resources and tools for deeper comprehension of the combustion effects and mechanisms of sodium droplet swarm under various operating settings (such as leakage rate and oxygen concentration).

An efficient combustion concept for low calorific gases

The main features of low calorific gases as those from biomass gasification processes, landfills, mines and sewage sludge are well known. They can be expressed as low calorific values, high water content, corrosive actions and composition changes. Due to these characteristics there are up to date no combustion systems available which are capable to utilise such gases efficiently. The ordinary combustion concepts frequently do not guarantee sufficient flame stability. The high emissions of harmful substances as CO and NOx are another problem. Because of mentioned difficulties it is necessary and also a challenge to develop an efficient and flexible combustion system which can handle these problems. Through several matching steps of numerical and experimental investigations Gaswärme-Institut e. V. Essen (GWI) developed a progressive combustion system based on the concept of continuous air staging (COSTAIR). Burner tests at a small scale thermal load of 30 kW proved a stable combustion and low NOx and CO emissions for different qualities of low calorific gases. The best design of a small scale burner was transferred to larger thermal loads by applying of scale-up criteria. Already achieved experimental results at 200 kWth confirmed the efficient performance and the high potential of the burner for use of low calorific gases.

Preparation and characterization of ethylene‐propylene‐diene monomer rubber/metal hydroxide composites by electron beam irradiation

AbstractEthylene‐propylene‐diene monomer (EPDM) rubber has widespread uses in various applications due to its ozone and oxidation stability, weatherability, electrical insulation, and elasticity. However, its further use is limited by low flame retardancy and low thermal stability. This study incorporated metal hydroxide flame retardant to enhance flame retardancy and electron beam cross‐linking to simultaneously enhance mechanical properties, thermal stability, and flame retardancy. The utilization of electron beam irradiation resulted in an increase in gel content and a decrease in swelling ratio with increasing absorbed doses, indicating the successful formation of cross‐linked network structures. The hot‐set elongation was significantly reduced to 0.6%–0.8%, while the decomposition temperature increased with increasing absorbed doses, indicating improved thermal stability. The results from limiting oxygen index measurements and burning tests demonstrate that the flame retardancy of EPDM was improved by the combined effect of metal hydroxide flame retardant and electron beam cross‐linking.Highlights EPDM/metal hydroxide composites were prepared via electron beam irradiation. Metal hydroxide flame retardants were incorporated to enhance flame retardancy. EBI simultaneously enhanced mechanical property and thermal stability.

Valorization of kapok fiber by phosphorylation with a reactive phosphorus‐ and nitrogen‐containing flame retardant for enhanced fire safety

AbstractKapok fiber (KF) with a naturally hollow structure has found an increasing application in filling and composite materials, most of which have a demand of flame retardancy. To realize this high‐value utilization, KF was phosphorylated by a reactive phosphorus‐ and nitrogen‐containing flame retardant for enhanced fire safety. The flame retardant was first synthesized by the reaction of urea and diethylene triamine pentakis (methyl phosphonic acid) (a commercially available scale inhibitor) with low cost, and then, applied in the phosphorylation of KF in the presence of dicyandiamide. In thermogravimetric analysis, phosphorylated KF showed 38.1% residue weight in nitrogen and 10.2% residue weight in air at 700°C, whereas the residue weight of KF was 8.4% in nitrogen and 1.5% in air. In microcalorimetric analysis, the heat release capacity and total heat release of phosphorylated KF displayed a reduction of 81% and 55%, respectively. In vertical combustion test, phosphorylated KF was difficult to ignite and had no afterburning or smoldering. The tests indicated that phosphorylated KF had excellent charring properties, low heat release, and good flame retardancy. This work suggests a promising strategy of enhancing the flame retardancy of KF and increasing its applicability in filling and composite materials.

The Effect of Different Diluents and Curing Agents on the Performance of Epoxy Resin-Based Intumescent Flame-Retardant Coatings.

The epoxy resin-based (ESB) intumescent flame-retardant coatings were modified with 1,4-butanediol diglycidyl ether (14BDDE) and butyl glycidyl ether (BGE) as diluents and T403 and 4,4'-diaminodiphenylmethane (DDM) as curing agents, respectively. The effects of different diluents and curing agents on the flame-retardant and mechanical properties, as well as the composition evolution of the coatings, were investigated by using large-plate combustion, the limiting oxygen index (LOI), vertical combustion, a cone calorimeter, X-ray diffraction, FTIR analysis, a N2 adsorption and desorption test, a scanning electron microscope (SEM), a tensile strength test, and a viscosity test. The results showed that the addition of 14BBDE and T403 promoted the oxidation of B4C and the formation of boron-containing glass or ceramics, increased the residual mass of char, densified the surface char layer, and increased the specific surface area of porous residual char. When their dosage was 30%, ESB-1T-3 coating exhibited the most excellent flame-retardant properties. During the 2 h large-plate combustion test, the backside temperature was only 138.72 °C, without any melting pits. In addition, the peak heat release rate (PHRR), total heat release rate (THR), total smoke production (TSP), and peak smoke production (PSPR) were reduced by 13.15%, 13.9%, 5.48%, and 17.45%, respectively, compared to the blank ESB coating. The LOI value reached 33.4%, and the vertical combustion grade was V-0. In addition, the tensile strength of the ESB-1T-3 sample was increased by 10.94% compared to ESB. In contrast, the addition of BGE and DDM promoted the combustion of the coating, affected the ceramic process of the coating, seriously affected the formation of borosilicate glass, and exhibited poor flame retardancy. The backside temperature reached 190.93 °C after 2 h combustion. A unified rule is that as the amount of diluent and curing agent increases, the flame retardancy improves while the mechanical properties decrease. This work provides data support for the preparation and process optimization of resin-based coatings.

A comparative study between the use of nanoparticles of magnesium oxide and zinc oxide as coating for polymeric surfaces a flame retardant and corrosion resistance

This study deals with the preparation of magnesium oxide nanoparticles (MgO NPs) and zinc oxide nanoparticles (ZnO NPs) by the co-precipitation method. The prepared metal oxide was characterized by X-ray diffraction analysis, scanning electron microscope, transmission electron microscope, element analysis examination, and UV–Visible and IR spectroscopies. The results of these tests showed the nano size, uniform distribution, and purity of the prepared powders. They proved the appearance of cubic and hexagonal phases of MgO NPs and ZnO NPs, respectively. These NPs have 4.2 eV and 3.12 eV energy gap values, respectively. The preparation of a coating consisting of MgO NPs and ZnO NPs involves combining them separately with epoxy in ratios of 3 %, 6 %, and 9 %. This mixture is then used to cover the polymeric surface using the immersion method. The nanocomposites have been examined before and after applying a coating via different techniques including X-ray diffraction analysis, infrared spectrum, atomic force microscopy, combustion test, thermal gravimetric decomposition, thermal conductivity, corrosion rate, hardness, and tensile strength. According to the results, it is found that the immersion coating method gives good dispersion of the NPs within the polymer matrix. Moreover. When comparing the use of MgO NPs and ZnO NPs, it is found that the use MgO NPs has given better results for flame retardancy, thermal gravimetric analysis and reduction of corrosion compared to the use of ZnO NPs, which has given better mechanical properties and thermal conductivity than MgO.

Energetic characteristics of highly reactive Si nanoparticles prepared by magnesiothermic reduction of mesoporous SiO2

In this study, highly reactive silicon nanoparticles (h-Si) were successfully prepared by an improved magnesiothermic reduction process with ∼ 100 nm mesoporous silica nanoparticles as templates. The prepared h-Si have an average particle size of 18 nm, an active content of 85 %, and a specific surface area of 69.2 m2/g. Meanwhile, the preparation process is simple, green (avoiding the use of HF), and shows a great improvement in the inhibition of side reactions. The energetic characteristics of h-Si were compared with those of commercially available silicon nanoparticles (c-Si) by using ultrasonically mixed KClO4 as the oxidizer. Thermal analysis indicates that h-Si/KClO4 has an advanced reaction onset temperature, increased heat release, and lower reaction activation energy. In constant-volume combustion tests, h-Si/KClO4 shows excellent ignition and combustion characteristics in the fuel-rich state. In addition, electrostatic discharge sensitivity tests indicate that the minimum ignition energy of stoichiometric h-Si/KClO4 exceeds 100 mJ, which is much more insensitive than that of n-Al/KClO4 (∼2 mJ). Overall, h-Si show enhanced reactivity and have attractive advantages in applications where suitable combustion properties and low electrostatic sensitivity are required.

Perfluorotetradecanoic acid-directed precipitation of P(VDF-HFP) around nano-Al for the improved ignition and combustion characteristics

In this study, the self-assembly method is used to modify Al nanoparticles (Al NPs) with perfluorotetradecanoic acid (PFTD) to obtain Al@PFTD. Based on the C–F…F–C interaction and the hydrogen bond between –CF and –CH, the adsorbed PFTD is used to direct the precipitation of P(VDF-HFP) around modified Al NPs to obtain Al@PFTD@P(VDF-HFP) composite energetic materials. Scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy are used to characterize the prepared samples, which prove a successful preparation process. The prepared Al@PFTD@P(VDF-HFP) is compared with physically mixed Al/P(VDF-HFP) counterparts by thermal analysis, electric ignition and constant-volume combustion tests. Thermal analysis results show that the reaction onset temperature of Al@PFTD@P(VDF-HFP) is 20 °C lower while its heat release is 135% higher. Electric ignition and constant-volume combustion tests show that the ignition delay, combustion time and pressurization rate are 50% shorter, 50% shorter and 40% faster, respectively. The improved energetic performance is mainly due to PFTD-directed precipitation of P(VDF-HFP) around Al NPs. Moreover, the fluorine-containing PFTD also contributes positively to energy density and reactivity through the pre-ignition reaction.