Cure characteristics of hydroxyl terminated polybutadiene (HTPB) prepolymer with avariety of blocked toluene diisocyanate (TDI) in the presence of triethylamine (TEA) andchloroacetic acid catalyst are reported. Phenol...Cure characteristics of hydroxyl terminated polybutadiene (HTPB) prepolymer with avariety of blocked toluene diisocyanate (TDI) in the presence of triethylamine (TEA) andchloroacetic acid catalyst are reported. Phenol, thiophenol, p-chloropheno1, p-nitrophenol,p-cresol, resorcinol, naphthols, caprolactam and butylated-hydroxytoluene were used as blockingagents. Viscosity measurements have been carried out using a mixture of HTPB and blocked TDIin cyclohexanone in the presence of the catalysts at 50℃ and 60℃ using Haake rotational vis-cometer. Viscosity measurements have also been carried out with 50% solids such as ammonium sulphate along with HTPB and TDI adduct.展开更多
The oxygen evolution reaction(OER)is the bottleneck in the overall photocatalytic splitting of water.The active sites(terminal titanium or bridging oxygen)and active species(molecular or dissociative water)of the init...The oxygen evolution reaction(OER)is the bottleneck in the overall photocatalytic splitting of water.The active sites(terminal titanium or bridging oxygen)and active species(molecular or dissociative water)of the initial step of the photocatalyzed OER on the prototypical photocatalyst TiO_(2),remain debatable.Herein,the photocatalytic chemistry of monolayer water on oxygen-pretreated TiO_(2)(110)(o-TiO_(2)(110))and reduced TiO_(2)(110)(r-TiO_(2)(110))surfaces initiated by 400 nm light illumination was investigated by time-dependent two-photon photoemission spectroscopy(TD-2PPE).The photoinduced reduction of the H_(2)O/o-TiO_(2)(110)interface rather than the H2O/r-TiO_(2)(110)interface was detected by TD-2PPE.The difference in 2PPE originated from the presence of the terminal hydroxyl anions(OHt^(-))on H_(2)O/o-TiO_(2)(110),as identified by X-ray photoelectron spectroscopy and temperature-programmed desorption.Therefore,the evolution of the electronic structure of H_(2)O/o-TiO_(2)(110)was attributed to the photocatalyzed oxidation of the terminal hydroxyl anions,which most likely formed gaseous·OH radicals,reducing the interface.This work suggested that the oxidation of hydroxyl anions on top of the terminal titanium ions on TiO_(2),which were excluded previously in solution,need to be considered in the mechanistic studies of the photocatalyzed OER.展开更多
Lipase from Candida sp.99-125 catalyzed ring-opening polymerization of e-caprolactone in the presence of 6-mercapto-1-hexanol was presented as a new metal-free approach for direct synthesis of welldefined thiol-termin...Lipase from Candida sp.99-125 catalyzed ring-opening polymerization of e-caprolactone in the presence of 6-mercapto-1-hexanol was presented as a new metal-free approach for direct synthesis of welldefined thiol-terminated poly（e-caprolactone）.Remarkably,high chemoselectivity of lipase from Candida sp.99-125 toward hydroxyl and thiol was exhibited and quantitative thiol fidelity over 90% was achieved.The tedious protecting/deprotecting steps for thiol and metal residue were avoided.The polymerizations with around 70% monomer conversion were conducted in bulk and toluene at relative low temperature of 40 ℃.Number–average molecular weight of resulted polymers ranged from 3000 to4700 Da by changing the feed ratio between monomer and initiator.The structures of obtained thiolterminated poly（e-caprolactone） were demonstrated by combining NMR and SEC analyses.展开更多
Different GAP-based CSRP samples with different binder contents were prepared and compared with that of conventional HTPB propellant.The crosslinker mixture of trimethylol propane(TMP)and butane diol(BD)was used in th...Different GAP-based CSRP samples with different binder contents were prepared and compared with that of conventional HTPB propellant.The crosslinker mixture of trimethylol propane(TMP)and butane diol(BD)was used in the GAP matrix beside the addition of dibutyltin dilaurate(DBTDL)to ensure cross-linking and curing completion of the prepared CSRP.The viscosity and hardness of all prepared formulations were monitored continuously during the curing process.The mechanical characteristics of cured samples were tested.The burning rate at operating pressure and specific impulse were measured,while the theoretical specific impulse(I sp)was calculated by ICT code and compared with the measured results.According to the results,DOA was found to be a suitable plasticizer for GAP when using in propellant.The mechanical properties of CSRP with 25%GAP can produce the optimum mechanical behavior,which is close to that of HTPB-based CSRP.The optimum GAP-based formulation is one candidate to replace the traditional HTPB-based CSRP with high burning rate for some applications.展开更多
Solid fuel ramjets (SFRJ) are known for their operational simplicity and high specific impulse. The performance of the SFRJ propulsion system is directly tied to the energy density and combustion behavior of the fuel....Solid fuel ramjets (SFRJ) are known for their operational simplicity and high specific impulse. The performance of the SFRJ propulsion system is directly tied to the energy density and combustion behavior of the fuel. A typical solid fuel used in a ramjet application is a collection of metal particles suspended in a polymeric binder. Boron is the ubiquitous candidate when considering metal additives for fuels due to an impressive 122.5 kJ/cm3 energy density. However, boron requires long residence times in combustors due to its high melting and boiling points. Magnesium appears to be a natural complement to boron;while possessing a lower energy density (42.1 kJ/cm3), it burns with a high flame temperature and readily reacts in combustion with a low melting point. In this study, several HTPB–boron–magnesium fuels are studied on a small scale to evaluate performance for ramjet application. Holography experiments are conducted, as well as laser ignition tests, to study particle behavior just above the fuel surface. Small, center-perforated fuel grains are examined in a direct-connect SFRJ test stand configuration to measure ignition temperatures and performance parameters. Combustion efficiency of the HTPB–boron–magnesium fuel is found to significantly increase for one of the fuels studied.展开更多
文摘Cure characteristics of hydroxyl terminated polybutadiene (HTPB) prepolymer with avariety of blocked toluene diisocyanate (TDI) in the presence of triethylamine (TEA) andchloroacetic acid catalyst are reported. Phenol, thiophenol, p-chloropheno1, p-nitrophenol,p-cresol, resorcinol, naphthols, caprolactam and butylated-hydroxytoluene were used as blockingagents. Viscosity measurements have been carried out using a mixture of HTPB and blocked TDIin cyclohexanone in the presence of the catalysts at 50℃ and 60℃ using Haake rotational vis-cometer. Viscosity measurements have also been carried out with 50% solids such as ammonium sulphate along with HTPB and TDI adduct.
基金supported by the National Key Research and Development Program of China(No.2021YFA1500601)the National Natural Science Foundation of China(Nos.22322306 and 22288201)+3 种基金the Chinese Academy of Sciences(Nos.YSBR007,XDB0970000)the Key Research Project of Shaanxi Provincial Science and Technology Department(No.2023-YBNY-158)the Xi’an Science and Technology Project(No.22NYYF016)the 111 Project。
文摘The oxygen evolution reaction(OER)is the bottleneck in the overall photocatalytic splitting of water.The active sites(terminal titanium or bridging oxygen)and active species(molecular or dissociative water)of the initial step of the photocatalyzed OER on the prototypical photocatalyst TiO_(2),remain debatable.Herein,the photocatalytic chemistry of monolayer water on oxygen-pretreated TiO_(2)(110)(o-TiO_(2)(110))and reduced TiO_(2)(110)(r-TiO_(2)(110))surfaces initiated by 400 nm light illumination was investigated by time-dependent two-photon photoemission spectroscopy(TD-2PPE).The photoinduced reduction of the H_(2)O/o-TiO_(2)(110)interface rather than the H2O/r-TiO_(2)(110)interface was detected by TD-2PPE.The difference in 2PPE originated from the presence of the terminal hydroxyl anions(OHt^(-))on H_(2)O/o-TiO_(2)(110),as identified by X-ray photoelectron spectroscopy and temperature-programmed desorption.Therefore,the evolution of the electronic structure of H_(2)O/o-TiO_(2)(110)was attributed to the photocatalyzed oxidation of the terminal hydroxyl anions,which most likely formed gaseous·OH radicals,reducing the interface.This work suggested that the oxidation of hydroxyl anions on top of the terminal titanium ions on TiO_(2),which were excluded previously in solution,need to be considered in the mechanistic studies of the photocatalyzed OER.
基金supported by a grant from the National Basic Research Program of China (Nos.2012CB725204 and 2011CB710803)the National High Technology Research and Development Program of China (No.2014AA021201)+1 种基金Natural Science Foundation of China (No.81302632)the Priority Academic Program Development of Jiangsu Higher Education Institutions and China Postdoctoral Science Foundation (No.2014M551574)
文摘Lipase from Candida sp.99-125 catalyzed ring-opening polymerization of e-caprolactone in the presence of 6-mercapto-1-hexanol was presented as a new metal-free approach for direct synthesis of welldefined thiol-terminated poly（e-caprolactone）.Remarkably,high chemoselectivity of lipase from Candida sp.99-125 toward hydroxyl and thiol was exhibited and quantitative thiol fidelity over 90% was achieved.The tedious protecting/deprotecting steps for thiol and metal residue were avoided.The polymerizations with around 70% monomer conversion were conducted in bulk and toluene at relative low temperature of 40 ℃.Number–average molecular weight of resulted polymers ranged from 3000 to4700 Da by changing the feed ratio between monomer and initiator.The structures of obtained thiolterminated poly（e-caprolactone） were demonstrated by combining NMR and SEC analyses.
文摘Different GAP-based CSRP samples with different binder contents were prepared and compared with that of conventional HTPB propellant.The crosslinker mixture of trimethylol propane(TMP)and butane diol(BD)was used in the GAP matrix beside the addition of dibutyltin dilaurate(DBTDL)to ensure cross-linking and curing completion of the prepared CSRP.The viscosity and hardness of all prepared formulations were monitored continuously during the curing process.The mechanical characteristics of cured samples were tested.The burning rate at operating pressure and specific impulse were measured,while the theoretical specific impulse(I sp)was calculated by ICT code and compared with the measured results.According to the results,DOA was found to be a suitable plasticizer for GAP when using in propellant.The mechanical properties of CSRP with 25%GAP can produce the optimum mechanical behavior,which is close to that of HTPB-based CSRP.The optimum GAP-based formulation is one candidate to replace the traditional HTPB-based CSRP with high burning rate for some applications.
基金The authors wish to thank Cliff Bedford and ONR Code 35 for funding under contract number N0001416WX01613.Additionally,the authors thank the NAVAIR ILIR program,managed at by the N-STAR program(Naval Research–Science and Technology for America's Readiness)administered by Lee Cambrea.
文摘Solid fuel ramjets (SFRJ) are known for their operational simplicity and high specific impulse. The performance of the SFRJ propulsion system is directly tied to the energy density and combustion behavior of the fuel. A typical solid fuel used in a ramjet application is a collection of metal particles suspended in a polymeric binder. Boron is the ubiquitous candidate when considering metal additives for fuels due to an impressive 122.5 kJ/cm3 energy density. However, boron requires long residence times in combustors due to its high melting and boiling points. Magnesium appears to be a natural complement to boron;while possessing a lower energy density (42.1 kJ/cm3), it burns with a high flame temperature and readily reacts in combustion with a low melting point. In this study, several HTPB–boron–magnesium fuels are studied on a small scale to evaluate performance for ramjet application. Holography experiments are conducted, as well as laser ignition tests, to study particle behavior just above the fuel surface. Small, center-perforated fuel grains are examined in a direct-connect SFRJ test stand configuration to measure ignition temperatures and performance parameters. Combustion efficiency of the HTPB–boron–magnesium fuel is found to significantly increase for one of the fuels studied.
