Ferrocene-based Burning Rate Catalysts Research Articles

Molecular dynamic simulation on comprehensive performance of ferrocene-based burning rate catalysts in a solid propellent

To determine the compatibility and interaction between ferrocene (Fc) and other components in AP/HTPB/Fc-based BRCs propellant, molecular dynamics simulation (MD simulation) method was used to study the binding energy, cohesive energy density (CED), mean square displacement (MSD) and mechanical properties of mononuclear ferrocene (ethyl ferrocene, butyl ferrocene and octyl ferrocene), binuclear ferrocene (2,2-(ethyl ferrocene) propane, 2,2, -bis-(butylferrocene) propane and hydroxymethyl bis-ferrocenyl propane), ionic ferrocene (three ionic ferrocenes with ferrocene methyl dimethyl ammonium as cation, perchlorate, nitrate and picrate as anions respectively) and cyclic ferrocene (1- ferrocenyl methyl -2- ferrocenyl -3- methylbenzimidazolium, binuclear ferrocene bridged by bridged biphenylferrocene and dihydropyrazole).The binding energy results show that alkyl groups, polar groups (such as hydroxyl groups) and cyclic substituents can improve the interaction between Fc and AP/HTPB. Moreover, the electrostatic interaction between ionic ferrocene and AP is strong, but the van der Waals interaction between ionic ferrocene and HTPB is weak. The CED data show that the mixed models based on alkyl mononuclear ferrocene, catocene, cyclic ferrocene and ionic ferrocene all have high cohesive energy with good safety performance. The MSD results show that the order of anti-migration ability is cyclic ferrocene > binuclear alkyl ferrocene > mononuclear alkyl ferrocene > binuclear hydroxyl ferrocene > ionic ferrocene. Regarding to the value of mechanical parameters (K, G, E and K/G), the mixed model of AP/HTPB/ dihydropyrazole bridged binuclear ferrocene possess the best mechanical properties among the 12 models. Based on the comprehensive data, we conclude that dihydropyrazole bridged binuclear ferrocene is the most ideal ferrocene-based burning rate catalyst among 12 ferrocenes.

Encapsulation of ferrocenes in microporous ZIF-67 channels for boosting their anti-migration tendency and catalytic activity in ammonium perchlorate thermal decomposition

The enhancement of the anti-migration performance of ferrocene-based burning rate catalysts (BRCs) and their catalytic influence on ammonium perchlorate (AP) combustion in composite solid propellants through the confinement effect is acknowledged as an effective strategy. In this investigation, FcR@ZIF-67 nanocomposites were fabricated by introducing commercial ferrocenes (FcR = Cat, NBF, TBF, and NOF) into microporous ZIF-67 nanochannels. In the catalysis performance evaluations, the Cat@ZIF-67 exhibited prominent combustion catalytic efficiency on AP thermal decomposition by advancing the AP pyrolysis temperature peak by 111.4 °C and increasing its release heat by 2.3 times. Moreover, the anti-migration tests demonstrated that FcR@ZIF-67 composites remain predominantly immobile during prolonged storage at 50° C. The investigation results of in-situ solid FTIR, TG-FTIR-MS, and theoretical calculations for the AP thermal degeneration with Cat@ZIF-67 as a promoter, indicated that, in the oxygen-rich environment of AP, the thermal disintegration of Cat@ZIF-67 creates a Fe2O3-Co3O4 heterostructure that facilitated the generation of reactive oxygen species. This, in turn, accelerated the pyrolysis of AP and formed more thermodynamically stable gaseous products, advancing its exothermic degradation temperature and increasing its release heat. Based on these discoveries, a hypothetical catalytic mechanism for the thermal decomposition of AP is proposed.

One-step synthesis of ferrocenyl glycidyl ethers as combustion catalysts for the thermal decomposition of ammonium perchlorate

As an oxidant, the pyrolysis behavior of ammonium perchlorate is the key to the combustion of composite solid propellants. Seeking a suitable catalyst to promote AP decomposition has drawn much attention. Ferrocene-based compounds are often used as burning rate catalysts because of their excellent catalytic effect. However, ferrocene-based burning rate catalysts are prone to migration during storage of propellants. In this study, six ferrocenyl glycidyl ethers were designed and synthesized to improve the anti-migration properties, and the related spectra characterization techniques were adopted to confirm their molecular structures. Furthermore, their related properties and mechanisms were also studied. As a result, they showed good redox performance, positive promotion on AP decomposition, excellent combustion and mechanical performance. Meanwhile, they had a higher anti-migration behavior compared with catocene and ferrocene. This study demonstrates that ferrocenyl glycidyl ethers have great potential to be applied as multifunctional burning rate catalysts in composite solid propellants.

Enhanced anti-migration performance of carbon nanotubes confined ferrocenyl compounds and their synergistic catalytic activity on the thermal decomposition of ammonium perchlorate

To retard high-migration issues of the commercialized ferrocene-based burning rate catalysts (BRCs), six commercial ferrocenyl derivatives (FcR), including catocene, N, N-dimethylaminomethyl ferrocene, n-butylferrocene, tert-butylferrocene, n-octylferrocene and ferrocene, were filled into carbon nanotubes (CNTs) by ultrasonication. The CNTs incorporated ferrocene nanocomposites (FcR@CNTs) were characterized by TEM, SEM, BET, XPS, FTIR, Raman and XRD techniques, which indicated that the ferrocenes are successfully filled into the CNTs. The anti-migration and anti-volatility tests unveiled that the FcR@CNTs exhibit neglectable migration tendency after four weeks of aging at 50 °C and low volatility when tested at 70 °C for 24 h. The combustion catalytic results displayed that the FcR@CNTs nanocomposites play a vital role in promoting the thermal decomposition of ammonium perchlorate (AP), with the best one lowering the peak temperature of high-temperature decomposition stage (HTD) of AP by 114.2 °C and increasing its released heat by 160%. And it was found that the smaller the diameter of a CNT is, the lower the peak temperature of AP and the higher the released heat of AP. In addition, the decomposition mechanism of AP catalyzed by FcR@CNTs(L1) was studied by thermal decomposition kinetics, in-situ solid FTIR and TG-FTIR-MS methods. The results revealed that the nanocomposites can absorb more generated NH3 and HClO4 gases during AP decomposition with formation of superoxide anions (O2−), accelerating the oxidation of N2O to NO, and promoting the AP decomposition at lower temperature. Thus, a possible decomposition mechanism of AP catalyzed by FcR@CNTs is proposed.

Unanticipated ionic ferrocenyl compounds based on 5,5′-bis(1-hydroxytetrazole). Molecular structures, anti-migration and burning rate catalytic performances

Twenty-one ionic ferrocenyl ammonium (1–17) and 1,2,4-triazolium (18–21) compounds derived from 5,5′-bis(1-hydroxytetrazole) were synthesized and characterized by NMR, FT-IR, UV − Vis and elemental analysis, aiming at improving anti-migration ability of neutral ferrocene-based burning rate catalysts and reducing sensitivity of the ionic ferrocenyl compounds containing picrate anions. Six new compounds were additionally characterized by single-crystal X-ray diffraction. The characterization results showed that, by ion-exchange reactions, 1–10, 12, 15 and 17 are the anticipated compounds in their molecular structures, compounds 11, 13 and 16 were formed by C-N bond cleavage of the dinuclear ferrocenyl cation units and 18–21 were obtained by protonation of the divalent 5,5′-bis(1-hydroxytetrazolate) anion at one oxygen atom. Thermal gravimetry and anti-migration test indicated that the new compounds are highly thermally stable and show low volatility and low migration tendency. Cyclic voltammetry studies suggested that most of the novel salts are irreversible redox systems. The sensitivity tests towards impact revealed that compounds 1–17 are insensitive compounds. The catalytic tests implied that all compounds exhibit great effects on the thermal degradation of ammonium perchlorate and 1,3,5-trinitro-1,3,5-triazacyclohexane. Compounds 13–15 can be used as potential alternatives to catocene in the composite solid propellants.

Novel ferrocene-based 1,2,3-triazolyl compounds: Synthesis, anti-migration properties and catalytic effects on oxidizers during combustion

To tackle high-migratory and high-volatility problem of marketed neutral ferrocene-based burning rate catalysts, twenty-one ferrocene-based 1,2,3-triazolyl compounds (Fc-TAZs) were synthesized by click reaction and characterized completely by NMR, FT-IR, UV–Vis and elemental analysis. In addition, four compounds were structurally confirmed by single crystal X-ray diffraction. TG and DSC analysis showed that the new Fc-TAZs are of high thermal stability. Cyclic voltammetry investigations suggested that more than half of the Fc-TAZs are reversible redox systems. Anti-migration and anti-volatility tests revealed that all the Fc-TAZs display, on comparison with Catocene, extremely low volatility and migration tendency due to the appearance of polar oxygen and nitrogen atoms in their molecules. Catalytic activity tests of the novel Fc-TAZs towards the thermal decomposition of oxidizers, evaluated by TG and DSC techniques, indicated that all Fc-TAZs exert great effects on the thermal disintegration of AP and compounds 5, 7 and 11 can promote the thermal decomposition of HMX during combustion.

Synthesis of ethylene diamine-based ferrocene terminated dendrimers and their application as burning rate catalysts

Ferrocene-based derivatives are widely used as ferrocene-based burning rate catalysts (BRCs) for ammonium perchlorate (AP)-based propellant. However, in long storage, small ferrocene-based derivatives migrate to the surface of the propellant, which results in changes in the designed burning parameters and finally causes unstable combustion. To retard the migration of ferrocene-based BRCs in the propellant and to increase the combustion of the solid propellant, zero to third generation ethylene diamine-based ferrocene terminated dendrimers (0G, 1G, 2G and 3G) were synthesized. The synthesis of these dendrimers was confirmed by 1H NMR and FT-IR spectroscopy. The electrochemical behavior of 0G, 1G, 2G and 3G was investigated by cyclic voltammetry (CV) and the burning rate catalytic activity of 0G, 1G, 2G and 3G on thermal disintegration of AP was examined by thermogravimetry (TG) and differential thermogravimetry (DTG) techniques. Anti-migration studies show that 1G, 2G and 3G exhibit improved anti-migration behavior in the AP-based propellant.

Synthesis of ferrocene-based saccharides and their anti-migration and burning rate catalytic properties

In the search for ferrocene-based burning rate catalysts (BRCs) with good burning rate catalytic properties and low migration, we synthesized four ferrocene-based saccharides (S-Fcs).

Synthesis of ferrocenyl functionalized hyperbranched polyethylene and its application as low migration burning rate catalyst

Ferrocene based burning rate catalysts (BRCs) play an important role in the solid rocket propellants. However, the migration problem during curing and storage limits their application in the solid rocket propellants. To tackle this problem, the ferrocenyl functionalized hyperbranched polyethylene (HBPE-g-PFcEMA) with high molecular weight was synthesized as low migration BRCs. HBPE-g-PFcEMA was characterized by 1H NMR, FT-IR, GPC and XPS. The electrochemical properties of HBPE-g-PFcEMA were evaluated by cyclic voltammetry. TGA results revealed that the HBPE-g-PFcEMA was quite stable under 210 °C. The catalytic efficiency of HBPE-g-PFcEMA for thermal decomposition of ammonium perchlorate (AP) was evaluated by TGA method. When 17 wt% of HBPE-g-PFcEMA was added, the final decomposition temperature of AP was decreased dramatically from 417 °C to 339 °C and the maximum weight loss temperature of AP was decreased from 408 °C to 328 °C. The migration property of HBPE-g-PFcEMA was studied and compared with ferrocene. Ferrocene migrated out of the migration tube after 6 days storage while the HBPE-g-PFcEMA only showed little migration even after 31 days storage at 50 °C. Therefore, the HBPE-g-PFcEMA was a low migration BRC with high catalytic efficiency for thermal decomposition of AP, which might find its application in aerospace.

Low-migratory ionic ferrocene-based burning rate catalysts with high combustion catalytic efficiency

1-(Ferrocenylmethyl)alkylimidazolium-based ionic compounds with low-migration, high thermal stability and catalytic activity in the thermal degradation of ammonium perchlorate were synthesized and characterized.

Synthesis, characterization, migration studies and combustion catalytic performances of energetic ionic binuclear ferrocene compounds

The concept of energetic ionic compounds was introduced to retard migration problems encountered in ferrocene-based burning rate catalysts. Fourteen novel compounds, N,N′-bis[(ferrocenylmethyldimethyl)]-1,n-alkylenediammonium (alkylene chain length n = 3–6, 8–10) dinitrate and dipicrate, were synthesized and characterized by NMR, FT-IR, UV–vis spectroscopy, etc. Their thermal stability was determined by TG-DSC technique and found that most of them are thermally stable up to 160 °C. The cyclic voltammetry analysis revealed that the ionic compounds each shows a redox wave for ferrocenyl moiety and the non-conjugated alkylene spacers exert almost no influence on their redox properties. Migration tests showed that their migration tendency is much slower than that of extensively used 2,2-bis(ethylferrocenyl)propane (Catocene) and increases with the extention of alkylene chain length in the cations. Their catalytic performances for thermal decomposition of ammonium perchlorate (AP), 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and 1,2,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) were evaluated by DSC method. The ionic compounds presented highly combustion catalytic activity in thermal degradation of AP and RDX. The best catalytic activity in thermodecomposition of AP was obtained with N,N-bis(ferrocenylmethyldimethyl)1,3-propylene diammonium dinitrate, 1. The catalytic activity of 1 is better than that of Catocene and 1 could be used as an alternative to Catocene in hydroxyl-terminated polybutadiene/ammonium perchlorate (HTPB/AP) composite propellants.