Titanium hydride(TiH_(2)), a promising high-energy additive, is doped into PTFE/Al to optimize the energy output structure of the reactive jet and strive for better aftereffect damage ability to the target. Six types ...Titanium hydride(TiH_(2)), a promising high-energy additive, is doped into PTFE/Al to optimize the energy output structure of the reactive jet and strive for better aftereffect damage ability to the target. Six types of PTFE/Al/TiH_(2) reactive liners with different TiH_(2) content are prepared by the molding and sintering method. The energy release characteristics of PTFE/Al/TiH_(2) reactive jet are tested by the transient explosion energy test, and are characterized from pressure and temperature. The reaction delay time,pressure history, and temperature history of the energy release process are obtained, then the actual value of released energy and reaction efficiency of the reactive jet are calculated. The results show that the peak pressure and temperature of the PTFE/Al/TiH_(2) jet initially increase and then decrease with increasing TiH_(2) content. When the TiH_(2) content is 10%, the actual value of released energy and reaction efficiency increased by 24% and 6.4%, respectively, compared to the PTFE/Al jet. The reaction duration of the reactive material is significantly prolonged as the TiH_(2) content increased from 0% to 30%. Finally,combined with the energy release behaviors of PAT material and the dynamic deformation process of liner, the enhancement mechanism of TiH_(2) on energy release of the reactive jet is expounded.展开更多
A ternary system of PTFE/Al/Bi_(2)O_(3)is constructed by incorporating PTFE-based reactive material and thermite for enhancing the energy release of the PTFE-based reactive material.The effects of Bi_(2)O_(3)in the PT...A ternary system of PTFE/Al/Bi_(2)O_(3)is constructed by incorporating PTFE-based reactive material and thermite for enhancing the energy release of the PTFE-based reactive material.The effects of Bi_(2)O_(3)in the PTFE/Al/Bi_(2)O_(3)on both mechanical properties and the energy release were investigated through various tests such as thermogravimetry-differential scanning calorimetry,adiabatic oxygen bomb test and split Hopkinson pressure bar test.The microstructure observed through scanning electron microscope and Xray diffraction results are used to analyze the ignition and reaction mechanism of PTFE/Al/Bi_(2)O_(3).The results indicate that the PTFE/Al/Bi_(2)O_(3)are capable of triggering the exothermic reaction of molten PTFE/Bi_(2)O_(3)and Al/Bi_(2)O_(3)over the PTFE/Al reactive materials,thereby promoting reactions.The excessive aluminum in the ternary system is beneficial for increasing energy release.The ignition of shock-induced chemical reactions in PTFE/Al/Bi_(2)O_(3)is closely related to the material fracture.The dominant mechanism for hot-spot generation under Split Hopkinson Pressure Bar test is the frictional temperature rise at the microcrack after failure.展开更多
To study the thermal decomposition of Al/Zr H_(2)/PTFE with different Al particle size as well as mechanical strength and impact sensitivity under medium and low strain rates,molding-vacuum sintering was adopted to pr...To study the thermal decomposition of Al/Zr H_(2)/PTFE with different Al particle size as well as mechanical strength and impact sensitivity under medium and low strain rates,molding-vacuum sintering was adopted to prepare four groups of power materials and cylindrical specimens with different Al particle size.The active decomposition temperature of Zr H_(2) was obtained by TG-DSC,and the quasi-static mechanics/reaction characteristics as well as the impact sensitivity of the specimen were studied respectively by quasi-static compression and drop-hammer test.The results show that the yield strength of the material decreased with the increase of the Al particle size,while the compressive strength,failure strain and toughness increased first and then decreased,which reached the maximum values of 116.61 MPa,191%,and 119.9 MJ/m respectively when the Al particle size is 12-14 mm because of particle size grading.The specimens with the highest strength and toughness formed circumferential open cracks and reacted partly when pressed.Those with developmental cracks formed inside did not react.It is considered that fracture of specimens first triggered initial reaction between Al and PTFE to release an amount of heat.Then ZrH_(2) was activated and decomposed,and participated in subsequent reaction to generate Zr C.The impact sensitivity of the specimens decreased with the increase of Al particle size.展开更多
Preparation of Zr2Al3C4-Al2O3 in situ composites was investigated by self-propagating high-temperature synthesis(SHS)involving both aluminothermic reduction of ZrO2 and chemical activation of PTFE(Teflon).The starting...Preparation of Zr2Al3C4-Al2O3 in situ composites was investigated by self-propagating high-temperature synthesis(SHS)involving both aluminothermic reduction of ZrO2 and chemical activation of PTFE(Teflon).The starting materials included ZrO2,Al,carbon black and PTFE.In addition to the conventional SHS method,the experiments were conducted by a chemical-oven SHS(COSHS)route to thermally assist the synthesis reaction.The threshold amount of 2%(mass fraction)PTFE was required to induce self-sustaining combustion.When the conventional SHS scheme was utilized,due to low combustion temperatures between 1152 and 1272°C and insufficient reaction time,the dominant carbide forming in the composite was ZrC instead of Zr2Al3C4.On the other hand,the COSHS technique increased the combustion temperature of the reactant compact to about 1576°C,lengthened the high-temperature duration for the reaction,and prevented Al vapor from escaping away.As a consequence,Zr2Al3C4-Al2O3 composites with a small amount of Zr3Al3C5 were obtained.The microstructure of the COSHS-derived product showed that plate-like Zr2Al3C4 grains were about 2μm in thickness and 10-30μm in length,and most of them were closely stacked into a laminated configuration.展开更多
In order to improve the wear resistance of elastic metallic-plastic thrust bearing pad, micro-assembling PTFE/Al2O3 multi-layer film was developed by alternating radio frequency（RF） magnetron sputtering PTFE and Al2...In order to improve the wear resistance of elastic metallic-plastic thrust bearing pad, micro-assembling PTFE/Al2O3 multi-layer film was developed by alternating radio frequency（RF） magnetron sputtering PTFE and Al2O3 targets. For enhancing the adhesion of the interfaces between PTFE and Al2O3 film, N+ implantation was employed. The structure, mechanical and micro-tribological properties were studied by XPS, X-ray photoelectron spectrometer and atomic force and friction force microscope （AFM/FFM）. The results show that the multi-layer consists of Al2O3 component and crystalline PTFE. The hardness of the multi-layer modified by ion implantation is less than that of Al2O3,but its toughness is greatly improved. The friction coefficient of PTFE/ Al2O3 multi-layer modified by ion implantation is much lower than that of Al2O3 film, and its resistance to wear is much greater than that of PTFE film. Therefore the wear resistance of elastic metallic-plastic thrust bearing pad is greatly improved.展开更多
Magnesium hydride(MgH2)was doped into PTFE/Al to improve the energy release characteristics of the material system and strive for better application in military engineering.Five types of PTFE/Al/MgH2 reactive material...Magnesium hydride(MgH2)was doped into PTFE/Al to improve the energy release characteristics of the material system and strive for better application in military engineering.Five types of PTFE/Al/MgH2 reactive materials with different MgH2 content were prepared by molding sintering method.The dynamic mechanical properties of the materials were studied by performing split-Hopkinson pressure bar(SHPB)tests and scanning electron microscope characterizations.The thermal behavior,reaction energy,reaction process and reaction mechanism were systematically investigated by conducting thermogravimetry-differential scanning calorimetry tests,oxygen bomb calorimeter measurements,Xray diffraction and SHPB tests.The results show that MgH2 particles less than 10%content contribute to heightening the dynamic mechanical properties of PTFE/Al system.The product Mg generated by decomposition of MgH2 can not only react with gas phase C2F4þbut also undergo a Grignard-type reaction with condensed PTFE.The reaction energy and ignition threshold of PTFE/Al/MgH2 reactive materials enhance monotonously as MgH2 content rose.With the increase of MgH2 content from 0%to 20%,the reaction time is prolonged as well as the reaction intensity is enhanced dramatically arising from the massive water vapour produced by the reaction between O2 and H2.The gaseous products generated can form a high pressure shortly after the reaction,which helps to elevate the damage effect of the PTFE/Al system.展开更多
Since the wear problems play a crucial role in the relatively moving systems, in this paper, the effect of counter-face roughness on the wear of extruded PTFE （polytetrafluoroethylene） which is a very common materia...Since the wear problems play a crucial role in the relatively moving systems, in this paper, the effect of counter-face roughness on the wear of extruded PTFE （polytetrafluoroethylene） which is a very common material for sliding bearing applications has been investigated to contribute related literature. PTFE is well-known for its exceptional tribological properties, and good toughness, and high thermal stability. It can also be used in dry sliding applications. PTFE is commonly used to reduce friction between relatively moving surfaces, lts wear rate can be reduced by adding micro or nano-sized fillers such as Al2O3, TiO2, SiO2, MoS2, Al, Pb, ZnO, Cu, ZrO2, Ni, CNF （carbon nano fiber）, carbon fiber, glass fiber, bronze, and graphite powder into the PTFE. In this study, an experimental research was carried out for filled and unfilled PTFE to compare their behaviors under different speeds and loads. Test materials were unfilled PTFE, PTFE ＋ wt. 5% Al2O3, PTFE ＋ wt. 15% Al2O3. Formation of transfer film was examined in dry sliding condition against stainless steel counter faces. All tribological tests were carried out in a commercially available tribo-tester sliding against AISI-416 C stainless steel. As a result of a series of systematic experiments, remarkable results have been obtained to make a distinctive comparison between unfilled and filled PTFE. The variation of friction coefficient with sliding distance during the tests has also been recorded. At the end of the tests, wear rate of related PTFE specimen was calculated based on measured data. Wear rate is found very high for unfilled PTFE, however, the lowest wear rate is recorded for PTFE ＋ wt. 15% Al2O3 as expected. The coefficient of friction remained approximately stable during the wear tests. Transfer films were inspected by observing the discs＇ surface with optical microscope.展开更多
基金National Natural Science Foundation of China (Grant No. 12002045)State Key Laboratory of Explosion Science and Technology,Beijing Institute of Technology (QNKT22-09) to provide fund for conducting experiments。
文摘Titanium hydride(TiH_(2)), a promising high-energy additive, is doped into PTFE/Al to optimize the energy output structure of the reactive jet and strive for better aftereffect damage ability to the target. Six types of PTFE/Al/TiH_(2) reactive liners with different TiH_(2) content are prepared by the molding and sintering method. The energy release characteristics of PTFE/Al/TiH_(2) reactive jet are tested by the transient explosion energy test, and are characterized from pressure and temperature. The reaction delay time,pressure history, and temperature history of the energy release process are obtained, then the actual value of released energy and reaction efficiency of the reactive jet are calculated. The results show that the peak pressure and temperature of the PTFE/Al/TiH_(2) jet initially increase and then decrease with increasing TiH_(2) content. When the TiH_(2) content is 10%, the actual value of released energy and reaction efficiency increased by 24% and 6.4%, respectively, compared to the PTFE/Al jet. The reaction duration of the reactive material is significantly prolonged as the TiH_(2) content increased from 0% to 30%. Finally,combined with the energy release behaviors of PAT material and the dynamic deformation process of liner, the enhancement mechanism of TiH_(2) on energy release of the reactive jet is expounded.
基金the National Natural Science Foundation of China (Grant No.12002045)State Key Laboratory of Explosion Science and Technology,Beijing Institute of Technology (Grant No.QNKT22-09)。
文摘A ternary system of PTFE/Al/Bi_(2)O_(3)is constructed by incorporating PTFE-based reactive material and thermite for enhancing the energy release of the PTFE-based reactive material.The effects of Bi_(2)O_(3)in the PTFE/Al/Bi_(2)O_(3)on both mechanical properties and the energy release were investigated through various tests such as thermogravimetry-differential scanning calorimetry,adiabatic oxygen bomb test and split Hopkinson pressure bar test.The microstructure observed through scanning electron microscope and Xray diffraction results are used to analyze the ignition and reaction mechanism of PTFE/Al/Bi_(2)O_(3).The results indicate that the PTFE/Al/Bi_(2)O_(3)are capable of triggering the exothermic reaction of molten PTFE/Bi_(2)O_(3)and Al/Bi_(2)O_(3)over the PTFE/Al reactive materials,thereby promoting reactions.The excessive aluminum in the ternary system is beneficial for increasing energy release.The ignition of shock-induced chemical reactions in PTFE/Al/Bi_(2)O_(3)is closely related to the material fracture.The dominant mechanism for hot-spot generation under Split Hopkinson Pressure Bar test is the frictional temperature rise at the microcrack after failure.
基金financial support from the National Natural Science Foundation of China(General Program.Grant No.51673213)the National Natural Science Foundation of China(Youth Science Foundation.Grant No.51803235)。
文摘To study the thermal decomposition of Al/Zr H_(2)/PTFE with different Al particle size as well as mechanical strength and impact sensitivity under medium and low strain rates,molding-vacuum sintering was adopted to prepare four groups of power materials and cylindrical specimens with different Al particle size.The active decomposition temperature of Zr H_(2) was obtained by TG-DSC,and the quasi-static mechanics/reaction characteristics as well as the impact sensitivity of the specimen were studied respectively by quasi-static compression and drop-hammer test.The results show that the yield strength of the material decreased with the increase of the Al particle size,while the compressive strength,failure strain and toughness increased first and then decreased,which reached the maximum values of 116.61 MPa,191%,and 119.9 MJ/m respectively when the Al particle size is 12-14 mm because of particle size grading.The specimens with the highest strength and toughness formed circumferential open cracks and reacted partly when pressed.Those with developmental cracks formed inside did not react.It is considered that fracture of specimens first triggered initial reaction between Al and PTFE to release an amount of heat.Then ZrH_(2) was activated and decomposed,and participated in subsequent reaction to generate Zr C.The impact sensitivity of the specimens decreased with the increase of Al particle size.
基金sponsored by the Ministry of Science and Technology of Taiwan,China,under the grant of MOST 105-2221-E-035-039-MY2
文摘Preparation of Zr2Al3C4-Al2O3 in situ composites was investigated by self-propagating high-temperature synthesis(SHS)involving both aluminothermic reduction of ZrO2 and chemical activation of PTFE(Teflon).The starting materials included ZrO2,Al,carbon black and PTFE.In addition to the conventional SHS method,the experiments were conducted by a chemical-oven SHS(COSHS)route to thermally assist the synthesis reaction.The threshold amount of 2%(mass fraction)PTFE was required to induce self-sustaining combustion.When the conventional SHS scheme was utilized,due to low combustion temperatures between 1152 and 1272°C and insufficient reaction time,the dominant carbide forming in the composite was ZrC instead of Zr2Al3C4.On the other hand,the COSHS technique increased the combustion temperature of the reactant compact to about 1576°C,lengthened the high-temperature duration for the reaction,and prevented Al vapor from escaping away.As a consequence,Zr2Al3C4-Al2O3 composites with a small amount of Zr3Al3C5 were obtained.The microstructure of the COSHS-derived product showed that plate-like Zr2Al3C4 grains were about 2μm in thickness and 10-30μm in length,and most of them were closely stacked into a laminated configuration.
文摘In order to improve the wear resistance of elastic metallic-plastic thrust bearing pad, micro-assembling PTFE/Al2O3 multi-layer film was developed by alternating radio frequency（RF） magnetron sputtering PTFE and Al2O3 targets. For enhancing the adhesion of the interfaces between PTFE and Al2O3 film, N+ implantation was employed. The structure, mechanical and micro-tribological properties were studied by XPS, X-ray photoelectron spectrometer and atomic force and friction force microscope （AFM/FFM）. The results show that the multi-layer consists of Al2O3 component and crystalline PTFE. The hardness of the multi-layer modified by ion implantation is less than that of Al2O3,but its toughness is greatly improved. The friction coefficient of PTFE/ Al2O3 multi-layer modified by ion implantation is much lower than that of Al2O3 film, and its resistance to wear is much greater than that of PTFE film. Therefore the wear resistance of elastic metallic-plastic thrust bearing pad is greatly improved.
基金support from the National Natural Science Foun-dation of China(General Program.Grant No.51673213)Na-tional Natural Science Foundation of China(Grant No.51803235)are gratefully acknowledged.
文摘Magnesium hydride(MgH2)was doped into PTFE/Al to improve the energy release characteristics of the material system and strive for better application in military engineering.Five types of PTFE/Al/MgH2 reactive materials with different MgH2 content were prepared by molding sintering method.The dynamic mechanical properties of the materials were studied by performing split-Hopkinson pressure bar(SHPB)tests and scanning electron microscope characterizations.The thermal behavior,reaction energy,reaction process and reaction mechanism were systematically investigated by conducting thermogravimetry-differential scanning calorimetry tests,oxygen bomb calorimeter measurements,Xray diffraction and SHPB tests.The results show that MgH2 particles less than 10%content contribute to heightening the dynamic mechanical properties of PTFE/Al system.The product Mg generated by decomposition of MgH2 can not only react with gas phase C2F4þbut also undergo a Grignard-type reaction with condensed PTFE.The reaction energy and ignition threshold of PTFE/Al/MgH2 reactive materials enhance monotonously as MgH2 content rose.With the increase of MgH2 content from 0%to 20%,the reaction time is prolonged as well as the reaction intensity is enhanced dramatically arising from the massive water vapour produced by the reaction between O2 and H2.The gaseous products generated can form a high pressure shortly after the reaction,which helps to elevate the damage effect of the PTFE/Al system.
文摘Since the wear problems play a crucial role in the relatively moving systems, in this paper, the effect of counter-face roughness on the wear of extruded PTFE （polytetrafluoroethylene） which is a very common material for sliding bearing applications has been investigated to contribute related literature. PTFE is well-known for its exceptional tribological properties, and good toughness, and high thermal stability. It can also be used in dry sliding applications. PTFE is commonly used to reduce friction between relatively moving surfaces, lts wear rate can be reduced by adding micro or nano-sized fillers such as Al2O3, TiO2, SiO2, MoS2, Al, Pb, ZnO, Cu, ZrO2, Ni, CNF （carbon nano fiber）, carbon fiber, glass fiber, bronze, and graphite powder into the PTFE. In this study, an experimental research was carried out for filled and unfilled PTFE to compare their behaviors under different speeds and loads. Test materials were unfilled PTFE, PTFE ＋ wt. 5% Al2O3, PTFE ＋ wt. 15% Al2O3. Formation of transfer film was examined in dry sliding condition against stainless steel counter faces. All tribological tests were carried out in a commercially available tribo-tester sliding against AISI-416 C stainless steel. As a result of a series of systematic experiments, remarkable results have been obtained to make a distinctive comparison between unfilled and filled PTFE. The variation of friction coefficient with sliding distance during the tests has also been recorded. At the end of the tests, wear rate of related PTFE specimen was calculated based on measured data. Wear rate is found very high for unfilled PTFE, however, the lowest wear rate is recorded for PTFE ＋ wt. 15% Al2O3 as expected. The coefficient of friction remained approximately stable during the wear tests. Transfer films were inspected by observing the discs＇ surface with optical microscope.
