Composite solid propellants(CSPs) have widely been used as main energy source for propelling the rockets in both space and military applications. Internal ballistic parameters of rockets like characteristic exhaust ve...Composite solid propellants(CSPs) have widely been used as main energy source for propelling the rockets in both space and military applications. Internal ballistic parameters of rockets like characteristic exhaust velocity, specific impulse, thrust, burning rate etc., are measured to assess and control the performance of rocket motors. The burn rate of solid propellants has been considered as most vital parameter for design of solid rocket motors to meet specific mission requirements. The burning rate of solid propellants can be tailored by using different constituents, extent of oxidizer loading and its particle size and more commonly by incorporating suitable combustion catalysts. Various metal oxides(MOs),complexes, metal powders and metal alloys have shown positive catalytic behaviour during the combustion of CSPs. These are usually solid-state catalysts that play multiple roles in combustion of CSPs such as reduction in activation energy, enhancement of rate of reaction, modification of sequences in reaction-phase, influence on condensed-phase combustion and participation in combustion process in gas-phase reactions. The application of nanoscale catalysts in CSPs has increased considerably in recent past due to their superior catalytic properties as compared to their bulk-sized counterparts. A large surface-to-volume ratio and quantum size effect of nanocatalysts are considered to be plausible reasons for improving the combustion characteristics of propellants. Several efforts have been made to produce nanoscale combustion catalysts for advanced propellant formulations to improve their energetics. The work done so far is largely scattered. In this review, an effort has been made to introduce various combustion catalysts having at least a metallic entity. Recent developments of nanoscale combustion catalysts with their specific merits are discussed. The combustion chemistry of a typical CSP is briefly discussed for providing a better understanding on role of combustion catalysts in burning rate enhancement. Available information on different types of combustion nanocatalysts is also presented with critical comments.展开更多
Nano-catalysts containing copper–cobalt oxides(Cu–Co–O) have been synthesized by the citric acid(CA) complexing method. Copper(II) nitrate and Cobalt(II) nitrate were employed in different molar ratios as the start...Nano-catalysts containing copper–cobalt oxides(Cu–Co–O) have been synthesized by the citric acid(CA) complexing method. Copper(II) nitrate and Cobalt(II) nitrate were employed in different molar ratios as the starting reactants to prepare three types of nano-catalysts. Well crystalline nano-catalysts were produced after a period of 3 hours by the calcination of CA–Cu–Co–O precursors at 550 °C. The phase morphologies and crystal composition of synthesized nano-catalysts were examined using Scanning Electron Microscope(SEM), Energy Dispersive Spectroscopy(EDS) and Fourier Transform Infrared Spectroscopy(FTIR) methods. The particle size of nano-catalysts was observed in the range of 90 nm–200 nm. The prepared nano-catalysts were used to formulate propellant samples of various compositions which showed high reactivity toward the combustion of HTPB/AP-based composite solid propellants. The catalytic effects on the decomposition of propellant samples were found to be significant at higher temperatures. The combustion characteristics of composite solid propellants were significantly improved by the incorporation of nano-catalysts. Out of the three catalysts studied in the present work, Cu Co-I was found to be the better catalyst in regard to thermal decomposition and burning nature of composite solid propellants. The improved performance of composite solid propellant can be attributed to the high crystallinity, low agglomeration and lowering the decomposition temperature of oxidizer by the addition of Cu Co-I nano-catalyst.展开更多
The chemical electrolytes are widely used in electrochemical machining(ECM)and have a significant effect on both the material removal rate(MRR)and the surface finish(Ra)of the workpiece.The process parameters of ECM,s...The chemical electrolytes are widely used in electrochemical machining(ECM)and have a significant effect on both the material removal rate(MRR)and the surface finish(Ra)of the workpiece.The process parameters of ECM,such as current density,electrolyte composition,and feed rate,are vital for optimizing machining performance.Research has indicated that high current density can create localized non-conductive passivating films,which impede metal dissolution.In this study,the aqueous solution of sodium nitrate(NaNO_(3))combined with gold nanoparticles(AuNPs)has been used as a novel electrolyte to evaluate the machining performance of the 20MnCr5 steel alloy.The inclusion of AuNPs in the NaNO_(3) solution enhanced local surface effects and promoted low-valence metal dissolution.The results demonstrated that the MRR and average surface roughness of the 20MnCr5 workpiece improved by 19.6%and 35.5%,respectively,when AuNPs were utilized compared to the alone NaNO_(3) electrolytic system.The experimental results also showed that the MRR increased within the current density range of 5.5 A/cm^(2) to 15.8 A/cm^(2),but declined in the range of 15.8 A/cm^(2) to 32.5 A/cm^(2).This decrease in the MRR at higher current densities can be attributed to the formation of non-conductive metal oxide passive layers.The oxygen evolution reaction(OER)was observed with the NaNO_(3) electrolyte at higher current densities,resulting in the formation of numerous micropores on the surface of the workpiece.In contrast,when the electrolyte was combined with AuNPs,these micropores ruptured quickly,creating new sites for the re-dissolution of metal ions.The microstructural changes on the machining surfaces under different operating conditions were analyzed using field emission scanning electron microscopy(FESEM),and the results are presented.Possible surface reactions,such as the formation of metal oxides and the release of oxygen gas,are discussed based on energy-dispersive X-ray(EDX)analysis and cyclic voltammetry(CV)studies.展开更多
文摘Composite solid propellants(CSPs) have widely been used as main energy source for propelling the rockets in both space and military applications. Internal ballistic parameters of rockets like characteristic exhaust velocity, specific impulse, thrust, burning rate etc., are measured to assess and control the performance of rocket motors. The burn rate of solid propellants has been considered as most vital parameter for design of solid rocket motors to meet specific mission requirements. The burning rate of solid propellants can be tailored by using different constituents, extent of oxidizer loading and its particle size and more commonly by incorporating suitable combustion catalysts. Various metal oxides(MOs),complexes, metal powders and metal alloys have shown positive catalytic behaviour during the combustion of CSPs. These are usually solid-state catalysts that play multiple roles in combustion of CSPs such as reduction in activation energy, enhancement of rate of reaction, modification of sequences in reaction-phase, influence on condensed-phase combustion and participation in combustion process in gas-phase reactions. The application of nanoscale catalysts in CSPs has increased considerably in recent past due to their superior catalytic properties as compared to their bulk-sized counterparts. A large surface-to-volume ratio and quantum size effect of nanocatalysts are considered to be plausible reasons for improving the combustion characteristics of propellants. Several efforts have been made to produce nanoscale combustion catalysts for advanced propellant formulations to improve their energetics. The work done so far is largely scattered. In this review, an effort has been made to introduce various combustion catalysts having at least a metallic entity. Recent developments of nanoscale combustion catalysts with their specific merits are discussed. The combustion chemistry of a typical CSP is briefly discussed for providing a better understanding on role of combustion catalysts in burning rate enhancement. Available information on different types of combustion nanocatalysts is also presented with critical comments.
文摘Nano-catalysts containing copper–cobalt oxides(Cu–Co–O) have been synthesized by the citric acid(CA) complexing method. Copper(II) nitrate and Cobalt(II) nitrate were employed in different molar ratios as the starting reactants to prepare three types of nano-catalysts. Well crystalline nano-catalysts were produced after a period of 3 hours by the calcination of CA–Cu–Co–O precursors at 550 °C. The phase morphologies and crystal composition of synthesized nano-catalysts were examined using Scanning Electron Microscope(SEM), Energy Dispersive Spectroscopy(EDS) and Fourier Transform Infrared Spectroscopy(FTIR) methods. The particle size of nano-catalysts was observed in the range of 90 nm–200 nm. The prepared nano-catalysts were used to formulate propellant samples of various compositions which showed high reactivity toward the combustion of HTPB/AP-based composite solid propellants. The catalytic effects on the decomposition of propellant samples were found to be significant at higher temperatures. The combustion characteristics of composite solid propellants were significantly improved by the incorporation of nano-catalysts. Out of the three catalysts studied in the present work, Cu Co-I was found to be the better catalyst in regard to thermal decomposition and burning nature of composite solid propellants. The improved performance of composite solid propellant can be attributed to the high crystallinity, low agglomeration and lowering the decomposition temperature of oxidizer by the addition of Cu Co-I nano-catalyst.
文摘The chemical electrolytes are widely used in electrochemical machining(ECM)and have a significant effect on both the material removal rate(MRR)and the surface finish(Ra)of the workpiece.The process parameters of ECM,such as current density,electrolyte composition,and feed rate,are vital for optimizing machining performance.Research has indicated that high current density can create localized non-conductive passivating films,which impede metal dissolution.In this study,the aqueous solution of sodium nitrate(NaNO_(3))combined with gold nanoparticles(AuNPs)has been used as a novel electrolyte to evaluate the machining performance of the 20MnCr5 steel alloy.The inclusion of AuNPs in the NaNO_(3) solution enhanced local surface effects and promoted low-valence metal dissolution.The results demonstrated that the MRR and average surface roughness of the 20MnCr5 workpiece improved by 19.6%and 35.5%,respectively,when AuNPs were utilized compared to the alone NaNO_(3) electrolytic system.The experimental results also showed that the MRR increased within the current density range of 5.5 A/cm^(2) to 15.8 A/cm^(2),but declined in the range of 15.8 A/cm^(2) to 32.5 A/cm^(2).This decrease in the MRR at higher current densities can be attributed to the formation of non-conductive metal oxide passive layers.The oxygen evolution reaction(OER)was observed with the NaNO_(3) electrolyte at higher current densities,resulting in the formation of numerous micropores on the surface of the workpiece.In contrast,when the electrolyte was combined with AuNPs,these micropores ruptured quickly,creating new sites for the re-dissolution of metal ions.The microstructural changes on the machining surfaces under different operating conditions were analyzed using field emission scanning electron microscopy(FESEM),and the results are presented.Possible surface reactions,such as the formation of metal oxides and the release of oxygen gas,are discussed based on energy-dispersive X-ray(EDX)analysis and cyclic voltammetry(CV)studies.
