One commonly used strategy to enhance polymers specific properties such as the resistance to partial discharges erosion is the incorporation into the polymeric matrix of inorganic micro or nanoparticles. This study fo...One commonly used strategy to enhance polymers specific properties such as the resistance to partial discharges erosion is the incorporation into the polymeric matrix of inorganic micro or nanoparticles. This study focused on the dielectric properties of Low-Density Polyethylene (LDPE) filled with nano-sized Magnesium Oxide (MgO) particles compounded by thermo-mechanical process and one of the purposes was to establish appropriate processing parameters in order to reach the desired dielectric properties. LDPE was used as a matrix and was reinforced by MgO particles having a nominal average size of 30 nm. The MgO nanoparticles were treated with a silane coupling agent (3-Glycidyloxypropyl Trimethoxysilane). The samples were initially prepared in a melt-mixing chamber with a MgO content of 1% wt. These pre-mixed samples were further treated by the means of thermo-mechanical mixing in a conical co-rotating twin-screw extruder in order to improve the dispersion and distribution of the MgO particles. In this report, both lifetime under a PD activity and AC dielectric strength of pure and nano-filled LDPE samples have been measured and compared. Nano-filled LDPE samples were found to exhibit an improve lifetime, without any detrimental impact on their short-term dielectric strength. This suggests that nano-filled LDPE may be for electric applications for which the dielectric materials may be exposed to partial discharge activities. This is significant result for the use of MgO-reinforced PE as an insulating material for HV cables since the resistance to PD is closely related to treeing resistance which is the main electrical degradation mechanism that leads to failure for shielded extruded power cables.展开更多
为提升钛酸铋钠(NBT)基无铅陶瓷电容材料的储能性能,以A位掺杂方式向0.65[Na_(0.5)Bi_(0.5)TiO_(3)]-0.35Sr_(0.7)Bi_(0.2)TiO_(3)中引入MgO,并采用固相烧结法制备了不同摩尔含量(x=0.01~0.06)的0.65[(Na1-x,Mgx)0.5Bi_(0.5)TiO_(3)]-0....为提升钛酸铋钠(NBT)基无铅陶瓷电容材料的储能性能,以A位掺杂方式向0.65[Na_(0.5)Bi_(0.5)TiO_(3)]-0.35Sr_(0.7)Bi_(0.2)TiO_(3)中引入MgO,并采用固相烧结法制备了不同摩尔含量(x=0.01~0.06)的0.65[(Na1-x,Mgx)0.5Bi_(0.5)TiO_(3)]-0.35Sr_(0.7)Bi_(0.2)TiO_(3)(NBT-SBT)陶瓷样品。通过SEM观察和XRD表征,发现随着Mg^(2+)含量的增加,NBT-SBT陶瓷的晶粒尺寸呈先减小后增大的变化,在Mg^(2+)掺入量(x)为0.025时,陶瓷晶粒尺寸最小。介电温谱和电滞回线测试表明该陶瓷为典型的铁电弛豫体,具有较高的介电常数(εr)和电极化强度(Pmax)。在100 k V/cm电场下,(Na0.94,Mg0.06)BT-SBT的可释放能量密度Wrec高达1.65 J/cm^(3),储能效率η为75%,综合性能优于同类NBT基陶瓷样品。结果表明,MgO掺杂的(Na1-x,Mgx)BT-SBT陶瓷具有优异的储能密度和效率,可为电子电力设备等领域的高功率储能电容器件的研究提供参考。展开更多
研究了不同掺量MgO膨胀剂在自然养护、标准养护、限制养护和高温养护条件下对混凝土力学性能的影响,结果表明:随着MgO膨胀剂掺量增大,各养护条件下,混凝土抗压强度均逐渐降低;不同养护条件对混凝土强度影响明显,高温养护下强度发展最快...研究了不同掺量MgO膨胀剂在自然养护、标准养护、限制养护和高温养护条件下对混凝土力学性能的影响,结果表明:随着MgO膨胀剂掺量增大,各养护条件下,混凝土抗压强度均逐渐降低;不同养护条件对混凝土强度影响明显,高温养护下强度发展最快,自然养护下,强度发展最慢;对于C30混凝土,掺20 kg MgO膨胀剂对混凝土强度无明显负面影响;掺MgO膨胀剂混凝土长龄期抗压强度无倒缩现象。展开更多
In Mg-Ca alloys the grain refining mechanism,in particular regarding the role of nucleant substrates,remains the object of debates.Although native MgO is being recognised as a nucleating substrate accounting for grain...In Mg-Ca alloys the grain refining mechanism,in particular regarding the role of nucleant substrates,remains the object of debates.Although native MgO is being recognised as a nucleating substrate accounting for grain refinement of Mg alloys,the possible interactions of MgO with alloying elements that may alter the nucleation potency have not been elucidated yet.Herein,we design casting experiments of Mg-xCa alloys varied qualitatively in number density of native MgO,which are then comprehensively studied by advanced electron microscopy.The results show that grain refinement is enhanced as the particle number density of MgO increases.The native MgO particles are modified by interfacial layers due to the co-segregation of Ca and N solute atoms at the MgO/Mg interface.Using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy,we reveal the nature of these Ca/N interfacial layers at the atomic scale.Irrespective of the crystallographic termination of MgO,Ca and N co-segregate at the MgO/Mg interface and occupy Mg and O sites,respectively,forming an interfacial structure of a few atomic layers.The interfacial structure is slightly expanded,less ordered and defective compared to the MgO matrix due to compositional deviations,whereby the MgO substrate is altered as a poorer template to nucleate Mg solid.Upon solidification in a TP-1 mould,the impotent MgO particles account for the grain refining mechanism,where they are suggested to participate into nucleation and grain initiation processes in an explosive manner.This work not only reveals the atomic engineering of a substrate through interfacial segregation but also demonstrates the effectiveness of a strategy whereby native MgO particles can be harnessed for grain refinement in Mg-Ca alloys.展开更多
文摘One commonly used strategy to enhance polymers specific properties such as the resistance to partial discharges erosion is the incorporation into the polymeric matrix of inorganic micro or nanoparticles. This study focused on the dielectric properties of Low-Density Polyethylene (LDPE) filled with nano-sized Magnesium Oxide (MgO) particles compounded by thermo-mechanical process and one of the purposes was to establish appropriate processing parameters in order to reach the desired dielectric properties. LDPE was used as a matrix and was reinforced by MgO particles having a nominal average size of 30 nm. The MgO nanoparticles were treated with a silane coupling agent (3-Glycidyloxypropyl Trimethoxysilane). The samples were initially prepared in a melt-mixing chamber with a MgO content of 1% wt. These pre-mixed samples were further treated by the means of thermo-mechanical mixing in a conical co-rotating twin-screw extruder in order to improve the dispersion and distribution of the MgO particles. In this report, both lifetime under a PD activity and AC dielectric strength of pure and nano-filled LDPE samples have been measured and compared. Nano-filled LDPE samples were found to exhibit an improve lifetime, without any detrimental impact on their short-term dielectric strength. This suggests that nano-filled LDPE may be for electric applications for which the dielectric materials may be exposed to partial discharge activities. This is significant result for the use of MgO-reinforced PE as an insulating material for HV cables since the resistance to PD is closely related to treeing resistance which is the main electrical degradation mechanism that leads to failure for shielded extruded power cables.
基金supported by the National Natural Science Foundation of China (No.52004044)the Natural Science Foundation of Chongqing,China (No.CSTB2022NSCQ-MSX0801)+3 种基金the Foundation of Chongqing University of Science and Technology,China (No.ckrc2022030)the Graduate Research Innovation Project of Chongqing University of Science and Technology,China (No.YKJCX2220214)the Science and Technology Innovation Training Program of Chongqing University of Science and Technology,China (No.2022046)the College Students’Innovation and Entrepreneurship Training Program of Chongqing University of Science and Technology,China (No.2022007).
文摘为提升钛酸铋钠(NBT)基无铅陶瓷电容材料的储能性能,以A位掺杂方式向0.65[Na_(0.5)Bi_(0.5)TiO_(3)]-0.35Sr_(0.7)Bi_(0.2)TiO_(3)中引入MgO,并采用固相烧结法制备了不同摩尔含量(x=0.01~0.06)的0.65[(Na1-x,Mgx)0.5Bi_(0.5)TiO_(3)]-0.35Sr_(0.7)Bi_(0.2)TiO_(3)(NBT-SBT)陶瓷样品。通过SEM观察和XRD表征,发现随着Mg^(2+)含量的增加,NBT-SBT陶瓷的晶粒尺寸呈先减小后增大的变化,在Mg^(2+)掺入量(x)为0.025时,陶瓷晶粒尺寸最小。介电温谱和电滞回线测试表明该陶瓷为典型的铁电弛豫体,具有较高的介电常数(εr)和电极化强度(Pmax)。在100 k V/cm电场下,(Na0.94,Mg0.06)BT-SBT的可释放能量密度Wrec高达1.65 J/cm^(3),储能效率η为75%,综合性能优于同类NBT基陶瓷样品。结果表明,MgO掺杂的(Na1-x,Mgx)BT-SBT陶瓷具有优异的储能密度和效率,可为电子电力设备等领域的高功率储能电容器件的研究提供参考。
文摘研究了不同掺量MgO膨胀剂在自然养护、标准养护、限制养护和高温养护条件下对混凝土力学性能的影响,结果表明:随着MgO膨胀剂掺量增大,各养护条件下,混凝土抗压强度均逐渐降低;不同养护条件对混凝土强度影响明显,高温养护下强度发展最快,自然养护下,强度发展最慢;对于C30混凝土,掺20 kg MgO膨胀剂对混凝土强度无明显负面影响;掺MgO膨胀剂混凝土长龄期抗压强度无倒缩现象。
基金financial support under grant number EP/N007638/1supported by EPSRC under grant number EP/W021080/1
文摘In Mg-Ca alloys the grain refining mechanism,in particular regarding the role of nucleant substrates,remains the object of debates.Although native MgO is being recognised as a nucleating substrate accounting for grain refinement of Mg alloys,the possible interactions of MgO with alloying elements that may alter the nucleation potency have not been elucidated yet.Herein,we design casting experiments of Mg-xCa alloys varied qualitatively in number density of native MgO,which are then comprehensively studied by advanced electron microscopy.The results show that grain refinement is enhanced as the particle number density of MgO increases.The native MgO particles are modified by interfacial layers due to the co-segregation of Ca and N solute atoms at the MgO/Mg interface.Using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy,we reveal the nature of these Ca/N interfacial layers at the atomic scale.Irrespective of the crystallographic termination of MgO,Ca and N co-segregate at the MgO/Mg interface and occupy Mg and O sites,respectively,forming an interfacial structure of a few atomic layers.The interfacial structure is slightly expanded,less ordered and defective compared to the MgO matrix due to compositional deviations,whereby the MgO substrate is altered as a poorer template to nucleate Mg solid.Upon solidification in a TP-1 mould,the impotent MgO particles account for the grain refining mechanism,where they are suggested to participate into nucleation and grain initiation processes in an explosive manner.This work not only reveals the atomic engineering of a substrate through interfacial segregation but also demonstrates the effectiveness of a strategy whereby native MgO particles can be harnessed for grain refinement in Mg-Ca alloys.