含端炔基聚碳硅氮烷的合成、耐热及陶瓷化性能

采用对苯二胺分别与甲基氢二氯硅烷(MeHSiCl2)或二甲基二氯硅烷(Me2SiCl2)胺解,以间氨基苯乙炔(APA)封端,制备含端炔基聚碳硅氮烷PCSN-A和PCSN-B。用FT-IR对其结构进行了表征,通过DSC研究了聚合物固化行为,采用TGA和XRD对其固化物的耐热性能和陶瓷化性能进行了研究。结果表明,PCSN-A由于结构内含有硅氢键(Si—H),Si—H键可参与固化,提高交联密度,其固化物具有优异于PCSN-B的耐热性能和陶瓷化性能,氮气下失重5%的温度(Td5)为564℃。氩气下1 450℃裂解的陶瓷化率为78.4%,得到β-SiC,α-SiC和α-Si3N4陶瓷,聚碳硅氮烷可用作耐高温树脂基体和陶瓷前驱体。

聚磷酸铵对人造石材抛磨废料/三元乙丙橡胶复合物陶瓷化性能的影响

人造石材在抛磨加工过程中会产生大量废料,废料直接填埋占用土地资源,容易造成环境污染。以人造石材抛磨废料为瓷化填料,制备可陶瓷化的人造石材抛磨废料/三元乙丙橡胶复合物,可实现固体废弃物资源再利用。研究聚磷酸铵(APP)用量对复合物力学性能、热稳定性及烧蚀所得陶瓷体的瓷化强度和微观结构的影响。结果表明,添加APP能提高陶瓷体的瓷化强度,当APP用量为80 phr时,冲击强度最高为0.44 kJ/m^(2),三点弯曲强度最高可达11 MPa。随APP用量增大,陶瓷体外观逐渐完整,表面凹坑减少,陶瓷体内部微观结构更为致密。

具有增强的自支撑和可陶瓷化性能的硅橡胶复合材料

为了优化硅橡胶复合材料的可陶瓷化性能和自支撑性能,南京工业大学研究团队将硅酸盐玻璃微粉和三聚磷酸钠(STPP)加入硅橡胶中,制备了具有优异自支撑性能和可陶瓷化性能的硅橡胶复合材料。研究发现,STPP的加入改善了复合材料在高温下的形状稳定性和自支撑性能。复合材料在850℃以上烧结的陶瓷残渣的弯曲强度大于5 MPa。X射线衍射和傅里叶变换红外光谱分析则表明,STPP的加入使陶瓷残渣的结晶含量提高了约25%,从而提高了可陶瓷化硅橡胶复合材料的自支撑性能。

新型锆硅复相陶瓷先驱体的制备及性能

将四-二乙氨基锆(TDEAZ)和乙炔基苯胺封端的聚碳硅氮烷(PCSN)进行液相共混,制备含有Zr、Si元素的新型复相陶瓷先驱体(ZPCSN),并通过FT-IR对其结构进行表征,利用DSC与TGA分别探讨其固化行为及耐热性能;并通过XRD与EDS研究ZPCSN的陶瓷先驱体、耐高温陶瓷。陶瓷化性能结果表明,ZPCSN结构中含有C≡C键,在固化过程中交联形成致密的三维网状结构,赋予ZPCSN优异的耐热性能;在1 600℃氩气氛围中,ZPCSN裂解形成Zr C/Zr N/Si C/Si3N4多元复相陶瓷,保留率为67.92%,这表明ZPCSN具有优异的陶瓷化性能。

新型含锆硅炔陶瓷材料的制备与性能

以甲基氢二氯硅烷(MeHSiCl2)、正丁基锂(n-BuLi)、三氯乙烯(HClC CCl2)与四氢铝锂(LiAlH4)为原料制备主链含H—Si—C≡C的硅炔聚合物(HS),将硅源与锆源(HG)进行共混,制备了一种新型复合陶瓷前驱体(GP)。采用傅里叶变换红外光谱(FT-IR)和核磁共振(NMR)对HS结构进行表征;利用FT-IR、差示扫描量热分析(DSC)与热失重分析(TGA)分别探讨GP固化行为及其耐热性能;通过X射线衍射(XRD)与激光显微拉曼光谱(Raman)等研究GP的陶瓷化性能。结果表明,GP具有优良的热稳定性能与陶瓷化性能,在1 600℃氩气气氛下保温3h可得到ZrC-ZrO2-SiC复相陶瓷,质量保留率达到75.64%。

助熔剂对可陶瓷化阻燃室温硫化硅橡胶泡沫性能的影响

为提升室温硫化硅橡胶泡沫的阻燃性能和耐火性能,本文以不同熔点玻璃粉和硼酸锌为助熔剂,云母粉为耐火填料,制备可陶瓷化阻燃室温硫化硅橡胶泡沫,并研究了不同无机填料种类和配比对硅橡胶泡沫微观形貌、热稳定性、阻燃性能和燃烧行为的影响及不同温度烧蚀下硅橡胶泡沫的陶瓷化行为。结果表明,玻璃粉的引入影响了硅橡胶泡沫的发泡过程,形成了孔径较大的泡沫结构,不利于硅橡胶泡沫阻燃性能、热稳定性、火安全性的提升,但在烧蚀实验中,其能够显著降低硅橡胶泡沫的陶瓷化温度;硼酸锌的引入能够显著提升硅橡胶泡沫的阻燃性能、高温区热稳定性和火安全性,并且硼酸锌与云母粉展现出较好的协同阻燃作用,硅橡胶泡沫的极限氧指数(LOI)最高达到33.2%,并通过垂直燃烧FV-0级,N_2气氛下热重分析测试中900℃时的残炭含量最高可达75.9%,硅橡胶泡沫的热释放和烟释放及烧蚀实验后的质量损失率均得到明显降低,同时,硼酸锌还有助于形成陶瓷状残炭。

Evolution of microstructure and mechanical properties in multi-layer 316L-TiC composite fabricated by selective laser melting additive manufacturing

In this study,the microstructure and mechanical properties of a multi-layered 316L-TiC composite material produced by selective laser melting(SLM)additive manufacturing process are investigated.Three different layers,consisting of 316L stainless steel,316L-5 wt%TiC and 316L-10 wt%TiC,were additively manufactured.The microstructure of these layers was characterized by optical microscopy(OM)and scanning electron microscopy(SEM).X-ray diffraction(XRD)was used for phase analysis,and the mechanical properties were evaluated by tensile and nanoindentation tests.The microstructural observations show epitaxial grain growth within the composite layers,with the elongated grains growing predominantly in the build direction.XRD analysis confirms the successful incorporation of the TiC particles into the 316L matrix,with no unwanted phases present.Nanoindentation results indicate a significant increase in the hardness and modulus of elasticity of the composite layers compared to pure 316L stainless steel,suggesting improved mechanical properties.Tensile tests show remarkable strength values for the 316L-TiC composite samples,which can be attributed to the embedded TiC particles.These results highlight the potential of SLM in the production of multi-layer metal-ceramic composites for applications that require high strength and ductility of metallic components in addition to the exceptional hardness of the ceramic particles.

Influence of pyrolysis temperature on structure and dielectric properties of polycarbosilane derived silicon carbide ceramic

β-SiC ceramic powders were obtained by pyrolyzing polycarbosilane in vacuum at 800-1200 °C. The β-SiC ceramic powders were characterized by TGA/DSC, XRD and Raman spectroscopy. The dielectric properties of β-SiC ceramic powders were investigated by measuring their complex permittivity by rectangle wave guide method in the frequency range of 8.2-18 GHz. The results show that both real part ε′ and imaginary part ε″ of complex permittivity increase with increasing pyrolysis temperature. The mechanism was proposed that order carbon formed at high temperature resulted in electron relaxation polarization and conductance loss, which contributes to the increase in complex permittivity.

Microstructure and mechanical properties of WC-Co,WC-Co-Cr_3C_2 and WC-Co-TaC cermets fabricated by spark plasma sintering

Spark plasma sintering was successfully used to produce WC-Co cermets with the addition of Cr3C2and TaC grain growth inhibitors. The spark plasma sintered compacts were investigated by scanning electron microscopy, X-ray diffraction analysis, density measurements, hardness tests, fracture toughness tests and elastic modulus tests. The results were comparedwithan inhibitor-free WC-Co cermet consolidated under the same process parameters. By using Cr3C2and TaC additives, it is possible to improve the hardness and fracture toughness of WC-Co cermets, but Cr3C2has better grain growth inhibition propertythan that of TaC. The best combination of hardness （HV30（2105±38）） and fracture toughness （（8.3±0.2）MPa·m^1/2） was obtained by the WC-5Co-2Cr3C2 cermet.

Eco-materials Research — Study on Preparation and Properties of Woodceramics

A new technique has been developed to prepare woodceramics with the raw material of wheat straws.The partial properties of woodceramics such as the remains of carbon, the density, the porosity, the bending strength, and resistivity are tested at the same time. Systematic analyses of the material properties, the forming mechanism, and the regularity of woodceramics are made. The effects of the formula of raw materials, the consistencies of phenol resin, and the temperature, on the technique and the properties of woodceramics are displayed. It is shown that wheat straws can be used to produce woodceramics with this technique. The presented work provides useful ideas for the study of the preparation of woodceramics.

Effect of annealing on microstructure and properties of Si_3N_4-AlN composite ceramics

Aiming at developing novel microwave-transparent ceramics with low dielectric loss, high thermal conductivity and high strength, Si3Na-AIN （30%, mass fraction） composite ceramics with La203 as sintering additive were prepared by hot-pressing at 1 800 ℃ and subsequently annealed at 1 450 ℃ and 1 850 ℃ for 2 h and 4 h, respectively. The materials were characterized by XRD and SEM. The effect of annealing process on the phase composition, sintering performance, microstructure, bending strength, dielectric loss and thermal conductivity of the materials was investigated. The results showed that both annealing at 1 850 ℃ and 1 450 ℃ promoted the phase transformation of α-Si3N4 to β-Si3N4. After annealing at 1 850 ℃, grain growth to a certain extent occurred in the materials. Especially, the elongated β-Si3N4 grains showed a slight increase in diameter from 0.2 μm to 0.6 μm approximately and a decrease in aspect ratio. As a result, as the annealing time increased to 4 h, the bending strength declined from 456 MPa to 390 MPa, whereas the dielectric loss decreased to 2.15× 10^-3 and the thermal conductivity increased to 16.3 W/（m.K） gradually. When annealed at 1 450 ℃, increasing the annealing time to 4 h significantly promoted the crystallization of glassy phase to La2Si6N803 phase in the materials, which led to the increase in bending strength to 619 MPa and thermal conductivity to 15.9 W/（m·K）, respectively, and simultaneously the decrease in dielectric loss to 1.53× 10^-3.

Influence of soaking time on nonlinear electrical behavior and dielectric properties of TiO_2-based varistor ceramics

The influence of soaking time on the nonlinear electrical behavior and dielectric properties of TiO2-based varistor ceramics was investigated. Based on single sintering process, six disk samples of （Sr, Bi, Si, Ta）-doped TiO2-based varistor ceramics were fabricated by sintering at 1 250 ℃ for 0.5-5.0 h. The samples were characterized by X-ray diffraction, voltage-current characteristics, energy spectra, metallographs, breakdown voltages, and apparent dielectric constant. It is found that the breakdown electrical field intensity at a current density of 10 mA/cma decreases from 5.5 to 4.1 V/mm first and then increases to 7.0 V/mm, the nonlinear coefficient increases from 2.39 to 2.62 first and then decreases to 2.42, and the apparent dielectric constant increases from 98 200 to 1l5 049 first and then decreases to 73 865 with the soaking time increasing from 0.5 to 5.0 h. These indicate that the optimal soaking time is 2.0-3.0 h considering both nonlinear electrical behavior and dielectric properties.

Dielectric properties and point defect behavior of antimony oxide doped Ti deficient barium strontium titanate ceramics

The microstructures and dielectric properties of Sb2O3-doped Ti deficient barium strontium titanate ceramics prepared by solid state method were investigated with non-stoichiometric level and Sb2O3content by SEM,XRD and LCR measure system.It is found that with the increase ofδ,(Ba0.75Sr0.25)Ti1-δO3-2δceramics transform from single phase solid solutions with typical cubic perovskite structure to multiphase compounds while(Ba0.75Sr0.25)Ti0.998O2.996ceramics remain to be single-phase with the increasing Sb2O3content.The distortion of the ABO3perovskite lattice caused by VTi″″and VO..induces the drop of Curie temperature and the rise of relative dielectric constant in(Ba0.75Sr0.25)Ti1-δO3-2δceramics with increasingδvalue.The orientation of VO??elastic dipoles results in the domain-wall pinning and thus the reduction of the dielectric loss.With increasing Sb2O3content,the relative dielectric constant,dielectric constant maximum and Curie temperature of(Ba0.75Sr0.25)Ti0.998O2.996ceramics decrease dramatically while the dielectric loss increases.

Influence of Yb_2O_3 doping on microstructural and electrical properties of ZnO-Bi_2O_3-based varistor ceramics

ZnO-Bi2O3-based varistor ceramics doped with Yb2O3 in the range from 0 to 0.4% （molar fraction） were obtained by a solid reaction route. The X-ray diffractometry （XRD） and scanning electron microscopy （SEM） were applied to characterize the phases and microstructure of the varistor ceramics, and a DC parameter instrument for varistor ceramics was applied to investigate their electrical properties and V-I characteristics. The XRD analysis of the samples shows that the ZnO phase, Bi2O3 phase, ZnTSbaOl2-type spinel phase and Zn2Bi3Sb3O14-type pyrochlore are present, and the Yb2O3 phases and Sb2O4 phases are found in varistor ceramics with increasing amounts of Yb2O3. The average size of ZnO grain firstly increases and then decreases with the increase of Yb2O3 content. The result also shows that the threshold voltage is between 656 V/nun and 1 232 V/mm, the nonlinear coefficient is in the range of 14.1-22.3, and the leakage current is between 0.60 μA and 19.6 μA. The 0.20% Yb2O3-added ZnO-Bi2O3-based varistor ceramics sintered at 900 ℃ have the best electrical characteristics.

Fabrication and Properties of 3Y-TZP/ZrO_2 / Al_2O_3 /MgO Ceramics

Studies on the sintering, microstructure, mechanical properties and low temperature degradation behavior of yttria stabilized-tetragonal zirconia polycrystal （3Y-TZP） were carried out. The results show that the addition of Al2O3 and MgO improve the sintering at low temperatures, and cause exaggerated grain growth and the transformation of tetragonaI-ZrO2 to monoclinic-ZrO2 with corresponding changes in the mechanical properties. The addition of the yttria-free monoclinic zirconia particles change the overall yttria distribution and induce an active transformation toughening mechanism. Furthermore, the dispersed yttria-free ZrO2 can inhibit the tetragonal zirconia transformation, which is beneficial to the improvement of the low temperature degradation behavior of 3Y- TZP ceramics.

Effects of various fillers on sintering, microstructures and properties of Ca-Ba-Al-B-Si-O glass/ceramic composites

Low-temperature sintering and properties of LTCC （low temperature co-fired ceramics） materials based on CaO-BaO-Al2O3-B2O3-SiO2 glass and various fillers such as Al2O3, silica glass, christobalite, AlN, ZrO2, MgO-SiO2, TiO2 were investigated. The results show that densification, crystallization, microstructures and dielectric properties of the composites are found to strongly depend on the type of filler. The densification process of glass/ceramic composites with various fillers is mainly from 600 ℃ to 925 ℃, and the initial compacting temperature of samples is 600 ℃. The initial rapid densification of samples starts at its glass softening temperature. LTCC compositions containing Al2O3, silica glass, AlN and MgO-SiO2 fillers start to have the crystallization peaks at 890, 903, 869 and 844 ℃, respectively. The crystallization peaks are believed as correlated to the crystallization of CaAl2SiO8, β-SiO2, Ca2Al2SiO7 and β-SiO2. The composite ceramic with Al2O3, silica glass and TiO2 ceramic have a better dense structure and better smooth fracture surface. Sample for Al2O3 has the lowest dielectric loss tanδ value of 0.00091, whereas the sample for MgO.SiO, has the highest dielectric loss tanδ value of 0.02576. The sample for TiO2 has the highest dielectric constant value of 14.46, whereas the sample for AIN has the lowest dielectric constant value of 4.61.

Effect of agarose content on microstructures and mechanical properties of porous silicon nitride ceramics produced by gelcasting

Porous Si3N4 self-reinforce ceramics were prepared by gelcasting using agarose solutions. By changing the agarose content in the slurries, the porous silicon nitride ceramics with different porosities, α→β-Si3N4 phase transformation, and mechanical properties were obtained. When the agarose content changed from 0.2% to 0.8% (w/w, based on powder), the porosities increased from 10.3% to 21.4%, while the fracture strength decreased from 455 to 316 MPa and the fracture toughness decreased from 6.6 to 5.5 MPa·m1/2. Many fibrous β-Si3N4 grains grown from the internal wall of the round pores is the typical microstructure of the gelcasting porous silicon nitride ceramic. Both elongated β-Si3N4 grains and suitable interfacial bonding strength contributes to high fracture toughness by favoring crack deflection and bridging. The growth mechanisms of fibrous grains resulted from the synergy of solution-diffusion-reprecipitation and vapor-liquid-solid (VLS).

Effect of TiO_2 content on the microwave dielectric properties of BaO-ZnO-TiO_2 ceramics

In this paper,the BaO-0.6ZnO-xTiO2 ceramics with x=2.5-2.8 have been prepared by the conventional solid-state ceramic route for the purpose of investigating the effect of TiO2 content on the microwave dielectric properties.The XRD results showed that the main crystal phase in the sintered ceramics was Ba4ZnTi11O27 and that the additional phases:Ba2ZnTi5O13 and BaZn2.03Ti3.93O10.89 were presented,depending on the TiO2 contents.The SEM photographs of the samples sintered at 1200℃ for 2 h showed a high compact microstructure.Because the phase composition of ceramics samples was changed with TiO2 content,the dielectric constant(εr),the quality factor values(Q×f) and the temperature coefficient of resonant frequency(τf) were first increased,continuously came up to a peak value,and then let up.It was lucky to find that the sample with composition BaO-0.6ZnO-2.7TiO2 had both the maximum dielectric constant εr=36.1 and the maximum Q×f value of 29320 GHz,and more importantly,it had an acceptable temperature coefficient of resonant frequency τf=10.45 ppm/℃.

Two-dimensional titanium carbide MXenes as efficient non-noble metal electrocatalysts for oxygen reduction reaction

MXenes, a new family of multifunctional two dimensional(2D) solid crystals integrating high electroconductivity and rich surface chemistries, are promising candidates for electrolysis, which, however, have rarely been reported. Herein, free-standing ultrathin 2D MXene nanosheets were successfully fabricated from bulky and rigid MAX phase ceramics by liquid exfoliation with HF etching(delamination) and TPAOH intercalation(disintegration).The high oxygen reduction reaction(ORR) performance has been obtained, due to the extremely small thickness of the asfabricated Ti3C2 around 0.5–2.0 nm, equivalent to the dimensions of single-layer or double-layer Ti3C2 nanosheets in thickness. The ORR performance of the obtained Ti3C2 MXene-based catalyst exhibits desirable activity and stability in alkaline media. This study demonstrates the potential of earth-abundant 2D MXenes for constructing high-performance and cost-effective electrocatalysts.

Microstructures and mechanical properties of SiBCNAl ceramics produced by mechanical alloying and subsequent hot pressing

Amorphous SiBCNAl powders were prepared via a mechanical alloying (MA) technique using crystalline silicon (Si), hexagonal boron nitride (h-BN), graphite (C), and aluminum (Al) as starting materials. SiBCNAl powders were consolidated by a hot pressing (HP) technique at 1800 °C under a pressure of 30 MPa in argon and nitrogen. The sintering atmosphere had a great influence on the microstructures and mechanical properties of the ceramics. The two ceramics had different phase compositions and fracture surface morphologies. For the ceramics sintered in argon, flexural strength, fracture toughness, elastic modulus and Vickers hardness were 421.90 MPa, 3.40 MPa·m1/2, 174.10 GPa, and 12.74 GPa, respectively. For the ceramics sintered in nitrogen, the mechanical properties increased, except for the Vickers hardness, and the values of the above properties were 526.80 MPa, 5.25 MPa·m1/2, 222.10 GPa, and 11.63 GPa, respectively.