干冰在氧化石墨烯/白炭黑/天然橡胶复合材料湿法混炼中的应用研究

将干冰用于氧化石墨烯(GO)/白炭黑/天然胶乳(NRL)的混合乳液中,利用干冰气化产生的大量气泡破裂而形成的能量对填料聚集体的破碎作用,提高填料在NRL中的分散性,研究干冰用量对GO/白炭黑/天然橡胶(NR)复合材料性能的影响。结果表明:干冰用量较小时,随着干冰用量的增大,复合材料的Payne效应减弱,交联密度增大,物理性能提高,滚动阻力降低;干冰用量较大时,复合材料的Payne效应增强,交联密度减小,物理性能下降,滚动阻力提高;干冰用量为20份时,复合材料的物理性能最佳。     

纳米粘土/炭黑/天然橡胶复合材料动态性能的研究

以纳米粘土部分等量替代炭黑填充天然橡胶(NR),制备纳米粘土/炭黑/NR复合材料,研究纳米粘土用量对复合材料动态性能的影响。结果表明:当纳米粘土用量较小时,纳米粘土/炭黑/NR复合材料中填料分散性较好;与炭黑/NR复合材料相比,纳米粘土/炭黑/NR复合材料的滞后损失、动刚度和动静刚度比降低,当纳米粘土用量为2份时,复合材料的动态压缩生热和动静刚度比最低。     

白炭黑对累托石/天然橡胶纳米复合材料结构与性能的影响

采用乳液法制备累托石(REC)/天然橡胶(NR)纳米复合材料,研究白炭黑对REC/NR复合材料结构和性能的影响。结果表明:白炭黑粒子可以插入累托石片层形成网络结构。加入少量白炭黑后,REC/NR复合材料的物理性能变化不大。随着白炭黑用量的增大,复合材料的抗湿滑性能、抗切割性能和耐磨性能提高,压缩生热逐渐增大,当白炭黑用量为15份时,复合材料的耐磨性能最好;当白炭黑用量为20份时,复合材料的抗切割性能和抗湿滑性能较好。     

用作载重子午线轮胎胎面胶的炭黑填充粉末NR结构与性能研究

以天然胶乳和炭黑N234为原料,采用凝聚共沉法制备炭黑填充型粉末NR[P(NR/CB)],研究炭黑用量和不同配方对胶料硫化特性、物理性能、交联密度、微观结构、Payne效应及动态力学性能的影响,并与采用传统机械混炼法制备的炭黑/NR(CB/NR)进行对比.结果表明,与CB/NR硫化胶相比,P(NR/CB)硫化胶具有较高的拉伸强度、撕裂强度、回弹值和抗湿滑性能以及较低的滚动阻力,耐屈挠性能和耐磨性能大致相当,而动态压缩生热和压缩永久变形则降低了近50%.     

改性纳米二氧化硅的制备及其在溶聚丁苯橡胶/顺丁橡胶并用胶中的应用

用偶联剂KH570作修饰剂,采用液相原位表面修饰技术制备改性纳米二氧化硅,并考察其在溶聚丁苯橡胶(SSBR)/顺丁橡胶(BR)并用胶中的应用。结果表明:与未改性纳米二氧化硅相比,改性纳米二氧化硅在橡胶基体中的分散性较好,与橡胶的相容性提高,团聚减弱;改性纳米二氧化硅/SSBR/BR复合材料的物理性能和耐磨性能提高,Payne效应减弱;修饰量为50 mmol·kg~(-1)的改性纳米二氧化硅/SSBR/BR复合材料物理性能、耐热老化性能和耐磨性能最好。     

混炼方式对螺旋纳米碳纤维增强天然橡胶复合材料力学性能的影响

采用干法和湿法两种混炼工艺制备了螺旋纳米碳纤维(HCNFs)/炭黑(CB)/天然橡胶(NR)复合材料,通过扫描电镜、拉伸试验机和应变扫描仪分别对所制备复合材料的界面形貌、力学性能和Payne效应进行了测试分析,考察了混炼方式对复合材料宏观力学性能及Payne效应的影响。结果表明,与纯CB填料相比,在干湿两种混炼方式下,添加适量的HCNFs(1～6份)能提高HCNFs/CB/NR复合材料的300%定伸应力、扯断伸长率、拉伸强度和硬度。与干法混炼相比,湿法混炼能明显增强HCNFs/CB/NR复合材料的Payne效应,并提升在HCNFs高添加量(2～6份)条件下的拉伸强度和扯断伸长率,这主要源于湿法混炼能够有效改善HCNFs在橡胶基质中的分散性。     

炭黑/碳纳米管并用比对天然橡胶复合材料物理性能和导热性能的影响

研究炭黑(CB)/碳纳米管(CNTs)并用比对天然橡胶(NR)复合材料物理性能和导热性能的影响,结果表明:与CB/NR复合材料相比,CB/CNTs/NR复合材料的性能提高;当CB/CNTs并用比为28/7时,复合材料的物理性能最佳、储能模量最大、损耗因子峰值最小、热导率最高。透射电子显微镜分析表明:当CB/CNTs并用比为28/7时,CB与CNTs分散均匀,CNTs无弯曲团聚,良好桥接CB,构成有效的填料网络;当CNTs用量继续增大,CNTs和CB出现团聚现象。NR复合材料的性能与填料网络协同作用密切相关。     

粘土/天然橡胶纳米复合材料在矿用轮胎胎面胶中的应用

采用乳液聚合法制备粘土/天然橡胶(NR)纳米复合材料,并对其结构、性能及在矿用全钢载重子午线轮胎胎面胶中的应用进行研究。结果表明:粘土在NR基体中的分散性较好,粘土/NR纳米复合材料的Payne效应较强;与纯炭黑填充NR胶料相比,粘土/NR纳米复合材料的硬度、定伸应力和拉伸强度增大,耐磨性能下降,压缩生热升高,抗切割和抗屈挠裂纹性能提高;成品轮胎的耐久性能达到国家标准要求,抗崩花掉块性能明显提高。     

纳米凹凸棒土/炭黑复合填料对天然橡胶/丁苯橡胶/顺丁橡胶并用胶性能的影响

研究纳米凹凸棒土/炭黑N770/炭黑N330复合填料中纳米凹凸棒土/炭黑N770用量比对天然橡胶(NR)/丁苯橡胶(SBR)/顺丁橡胶(BR)并用胶性能的影响。结果表明:采用纳米凹凸棒土/炭黑N770/炭黑N330复合填料时,随着凹凸棒土用量增大,并用胶的F_L和F_(max)增大,硫化速度减慢,物理性能、耐磨性能和耐屈挠性能提高;纳米凹凸棒土/炭黑N770用量比为30/15时,并用胶的综合性能较优异。与添加其他无机填料(陶土、轻质碳酸钙和白炭黑)/炭黑复合填料的并用胶相比,添加纳米凹凸棒土/炭黑复合填料的并用胶拉伸强度和撕裂强度较高,耐屈挠性能较好,耐磨性能稍差。     

偶联剂Si69改性秸秆纳米纤维素对炭黑补强天然橡胶性能的影响

采用偶联剂Si69对棒状秸秆纳米纤维素(SNC)进行改性,得到改性棒状秸秆纳米纤维素(MSNC),研究MSNC对炭黑(CB)补强天然橡胶(NR)性能的影响。结果表明:MSNC与橡胶基体的相容性较好;与CB/SNC/NR复合材料相比,CB/MSNC/NR复合材料的交联密度较大,能在保持较好抗湿滑性能的同时降低滚动阻力,具有更强的交联网络和更多的受限橡胶分子,热稳定性更好;用量比为35/10/100的CB/MSNC/NR复合材料物理性能最佳。     

Phase diagram and properties of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 polycrystalline ceramics

yPb(In_1/2Nb_1/2)O₃-(1 − x − y)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (yPIN-(1 − x − y)PMN-xPT) polycrystalline ceramics with morphotropic phase boundary (MPB) compositions were synthesized using columbite precursor method. X-ray diffraction results indicated that the MPB of PIN-PMN-PT was located around PT = 0.33-0.36, confirmed by their respective dielectric, piezoelectric and electromechanical properties. The optimum properties were found for the MPB composition 0.36PIN-0.30PMN-0.34PT, with dielectric permittivity ?_r of 2970, piezoelectric coefficient d₃₃ of 450 pC/N, planar electromechanical coupling k_p of 49%, remanent polarization P_r of 31.6 μC/cm² and T_C of 245 °C. According to the results of dielectric and pyroelectric measurements, the Curie temperature T_C and rhombohedral to tetragonal phase transition temperature T_R-T were obtained, and the “flat” MPB for PIN-PMN-PT was achieved, indicating that the strongly curved MPB in PMN-PT system was improved by adding PIN component, offering the possibility to grow single crystals with high electromechanical properties and expanded temperature usage range (limited by T_R-T).     

Effects of Sb content on electrical properties of lead-free piezoelectric (K0.4425Na0.52Li0.0375) (Nb0.9625−xSbxTa0.0375)O3 ceramics

Lead-free (K_0.4425Na_0.52Li_0.0375) (Nb_0.9625−xSb_xTa_0.0375)O₃ piezoelectric ceramics were prepared by the conventional sintering method. The effects of the Sb content on the phase structure, microstructure, dielectric, piezoelectric, and ferroelectric properties of the (K_0.4425Na_0.52Li_0.0375) (Nb_0.9625−xSb_xTa_0.0375)O₃ ceramics were investigated. The much higher Pauling electronegativity of Sb compared with Nb makes the ceramics more covalent. By increasing x from 0.05 to 0.09, all samples exhibit a single perovskite structure with an orthorhombic phase over the whole compositional range, and the bands in the Raman scattering spectra shifted to lower frequency numbers. The grain growth of the ceramics was improved by substituting Sb⁵⁺ for Nb⁵⁺. Significantly, the (K_0.4425Na_0.52Li_0.0375) (Nb_0.8925Sb_0.07Ta_0.0375)O₃ ceramics show the peak values of the piezoelectric coefficient (d₃₃), electromechanical coupling coefficient (k_p), and dielectric constant (?), which are 304 pC/N, 48% and 1909, respectively, owing to the densest microstructure of typical bimodal grain size distributions. Besides, the underlying mechanism for variations of the electrical properties due to Sb⁵⁺ substitution was explained in this work.     

Electrical and photoluminescence properties of Sm3+ doped Na0.5La0.5Bi8-xSmxTi7O27 ceramics

In this study, Sm³⁺ doped Na_0.5La_0.5Bi_8-xSm_xTi₇O₂₇ (NBT-BITL-xSm, x = 0, 0.01, 0.015, 0.02, and 0.03) ceramics were synthesized via a conventional solid-state reaction process. The structural, electrical, and photoluminescence properties of NBT-BITL-xSm ceramics were systematically investigated. The crystal structure of NBT-BITL-xSm was refined using XRD Rietveld refinement and found to possess a single orthorhombic structure at room temperature. Raman spectroscopy revealed that Sm³⁺ ions preferred to substitute for Bi³⁺ located in the A-sites of pseudo-perovskite layers, inducing a slight decrease in orthorhombic distortion. Strong characteristic emission peaks of Sm³⁺ ions were observed in orange-red regions under a 407 nm laser source, and the sample with x = 0.015 achieved the optimal photoluminescent property. Dielectric measurements showed double anomaly permittivity peaks at the temperature of 589 and 600^°C (T_m and T_c, respectively). The complex impedance spectrum indicated that the electrical conductivities mainly originated from crystal grains at high temperature. The activation energy was calculated to be 1.37–1.44 eV from Arrhenius fitting results. After Sm³⁺ substitution, the activation energy for conductivity was increased as a result of reduced oxygen vacancies.     

(Fe1-xDyx)3C/C composites: structure,magnetism and electrocatalytic properties for hydrogen evolution reaction

The (Fe_1-xDy_x)₃C@C composites were produced by a simple sol-gel route. The structure, composition, morphology and magnetism of the composites are studied by many characterization methods, for example, X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy (SEM, TEM) as well as vibrating sample magnetometer (VSM). Analysis of the above results indicates that the (Fe_1-xDy_x)₃C is embedded in carbon nanotubes and carbon matrix and displays ferromagnetic properties. Moreover, this indicates that saturation magnetization (M_S) values of the composites tend to increase with the increase in Dy doping. More importantly, we investigates the electrochemical hydrogen production capacity of the (Fe_1-xDy_x)₃C@C composites.     

Electrical Properties of a Bismuth Layer-Structured Ba2Bi4Ti5O18 Single Crystal

Ba₂Bi₄Ti₅O₁₈ single crystals were grown, and their dielectric permittivity, conductivity, and ferroelectricity were investigated along the a -(or b -)axis and the c -axis separately. The dielectric permittivity at 1 MHz along the a -(or b -)axis was 2000 at the Curie temperature (360°C); this value was 8 times greater than that along the c -axis. The dc conductivity was greater along the a -(or b -)axis than that along the c -axis, by one order of magnitude. In regard to the ferroelectricity, the saturated remanent polarization was 120 mC/m² and the saturated coercive field was 3 MV/m along the a -(or b -)axis; values of 8.5 mC/m² and 0.81 MV/m, respectively, were observed along the c -axis. The Ba₂Bi₄Ti₅O₁₈ single crystals had large electrical anisotropies, which were due to the layered structure.     

Polarization-induced electro resistance and magneto resistance in La0.67Ca0.33MnO3/BaTiO3 composite film

La_0.67Ca_0.33MnO₃/BaTiO₃ composite films have been grown on Nb-doped SrTiO₃ substrates by the sol–gel method. The magnetic and ferroelectric properties in the composite films are investigated. A three-state memory is formed by applying a vertical electric field across the La_0.67Ca_0.33MnO₃/BaTiO₃ heterostructure, this behavior is attributed to the polarization-mediated resistive switching effect. In addition, the transport properties of La_0.67Ca_0.33MnO₃ thin film can be modulated by an external magnetic field, a 10.3 K shift of the metal insulator transition temperature is obtained with the change of applied magnetic field from 0 T to 6 T. Consequently, in La_0.67Ca_0.33MnO₃/BaTiO₃ heterostructure, the resistance behavior can be modulated by piezoelectric effect, ferroelectric polarization and magnetic field simultaneously.     

Enhanced dielectric and piezoelectric properties in Na0.5Bi4.5Ti4O15 ceramics with Pr-doping

The bismuth layer-structured Na_0.5Bi_4.5-xPr_xTi₄O₁₅ (x?=?0, 0.1, 0.2, 0.3, 0.4, and 0.5) (NBT-xPr³⁺) ceramics were fabricated using the traditional solid reaction process. The effect of different Pr³⁺ contents on dielectric, ferroelectric and piezoelectric properties of Na_0.5Bi_4.5Ti₄O₁₅ ceramics were investigated. The grain size of Pr³⁺-doping ceramics was found to be smaller than that of pure one, the maximum dielectric constant and Curie temperature T_c gradually decreased with increasing Pr³⁺ contents, and the dielectric loss decreased at high temperature by Pr³⁺-doping. Moreover, the activation energy (E_a), resistivity (Z’), remanent polarization (2P_r) and piezoelectric constant (d₃₃) increased by Pr³⁺-doping. The NBT-xPr³⁺ ceramics with x?=?0.3 achieved the optimal properties with the maximum dielectric constant of 1109.18, minimum loss of 0.00822 (250?kHz), E_a of 1.122?eV, Z’ of 7.9?kΩ?cm (725 ºC), d₃₃ of 18 pC/N, 2P_r of 12.04 μC/cm². The enhancement was due to the addition of Pr³⁺ which suppressed the decreasing of resistivity at high temperature and made it possible for NBT-xPr³⁺ ceramics to be poled in perpendicular direction, implying that it is a great improvement for Na_0.5Bi_4.5Ti₄O₁₅ ceramics in electrical properties.     

BiFeO3-PbZrO3-PbTiO3 ternary system for high Curie temperature piezoceramics

BiFeO₃-PbZrO₃-PbTiO₃ ternary solid solution system was investigated for the development of piezoelectric ceramics with high Curie temperatures. The search for the morphotropic phase boundary (MPB) compositions in this ternary system started from mixing two MPB compositions: 0.70BiFeO₃-0.30PbTiO₃ and 0.52PbZrO₃-0.48PbTiO₃. The content of PbTiO₃ was then further fine tuned in order to reach the appropriate volume fraction between the rhombohedral and tetragonal phases in the sintered ceramics. It was observed that the sintering temperature has a profound impact on the density, grain morphology, dielectric and ferroelectric properties of the ceramics. The composition that displays the best combined structure and properties was identified to be 0.648BiFeO₃-0.053PbZrO₃-0.299PbTiO₃, with a Curie temperature T_C of 560 °C, a remanent polarization P_r of 15.0 μC/cm², and a piezoelectric coefficient d₃₃ of 64 pC/N.     

Phase transition behavior and electrical properties of lead-free (1 − x)(0.98K0.5Na0.5NbO3–0.02LiTaO3)–x(0.96Bi0.5Na0.5TiO3–0.04BaTiO3) piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)(0.98K_0.5Na_0.5NbO₃–0.02LiTaO₃)–x(0.96Bi_0.5Na_0.5TiO₃–0.04BaTiO₃) (KNN–LT–BNT–BT) with x = 0–0.10 have been synthesized by a conventional sintering technique. All samples possess pure perovskite structure, showing room temperature symmetries of orthorhombic at x < 0.02, and tetragonal at 0.05 ≤ x ≤ 0.10. A coexistence of orthorhombic and tetragonal phases in the composition range of 0.02 ≤ x < 0.05 in this system is caused by the temperature of the polymorphic phase transition (PPT) decreasing to around room temperature but not the behavior of the morphotropic phase boundary (MPB). The samples near the coexistence region exhibit improved properties, which are as follows: piezoelectric constant d₃₃ = 155 pC/N, remnant polarization P_r = 24.2 μC/cm², and coercive electric field E_c = 2 kV/mm. The results indicate that although this kind of ceramics displays good properties, further study is needed to promote the stabilities of the ceramics in order to utilize them in varying temperature environments.     

Microwave Characteristics of A(B3+1/2B5+1/2)O3 Ceramics (A = Ba, Ca, Sr; B3+= La, Nd, Sm, Yb; B5+= Nb, Ta)

Dielectric properties of A(B³⁺_1/2B⁵⁺_1/2)O₃ (A = Ba, Ca, Sr; B³⁺= La, Nd, Sm, Yb; B⁵⁺= Nb, Ta) ceramics have been investigated at microwave frequencies. Sr(B³⁺_1/2B⁵⁺_1/2)O₃ and Ca(B³⁺_1/2B⁵⁺_1/2)O₃ ceramics have relative dielectric constants (ε _r ) above 20 and negative temperature coefficients of resonant frequency (T _f ). In the group of Ba(B³⁺_1/2B⁵⁺_1/2)O₃ ceramics, T _f changes from + 118 ppm/° to nearly zero according to the kinds of B-site ions. Among the ceramics investigated, Sr(Sm_1/2Ta_1/2)O₃ ceramics have the highest Q values at microwave frequencies. For Sr(Sm_1/2Ta_1/2)O₃ ceramics Q = 7000, ε _r = 27.7, and T _f =−62.5 ppm/° at 8.5 GHz. The microstructure of Sr(Sm_1/2Ta_1/2)O₃ ceramics is composed of a matrix of the ternary compound (Sr-Sm-Ta-O system) and secondary phase grains of the binary compound (Sm-Ta-O system).