Damage tolerant oxide/oxide fiber laminate composites

Oxide-fiber/oxide-matrix composites were developed using non-infiltrated woven fiber layers between matrix-infiltrated fiber layers in order to achieve damage tolerant behavior. A fiber interface coating was not used. This technique enables damage tolerance in materials with strong fiber-matrix bonding and under oxidizing conditions. Fabrication of composites was carried out through a slurry infiltration technique. Slurries for fiber (Nextel™ 720, 3M) infiltration were prepared using a submicron α-Al₂O₃ powder coated with an amorphous SiO₂-layer through a sol–gel process. Hot-pressing was used to densify and bond the laminate layers together, followed by pressureless heat-treatment to allow mullite to form. Room temperature three-point bending tests were performed on as-received samples and on samples which underwent long-term annealing at high temperatures (1200–1300°C) in air. Subsequent examination revealed that due to the lack of a fiber interface coating, matrix-infiltrated fiber layers behaved in a quasi-monolithic manner with little or no crack deflection. Layers of non-infiltrated fibers, however, provided damage tolerance by deflecting cracks in the plane of the laminate and by serving as a mechanical bond between matrix-infiltrated layers. The laminate composites demonstrate reasonable room-temperature fracture strength both in the as-received state (88 MPa) and after exposure to 1300°C air for 200 h (72 MPa) along with extensive fracture deflection through the layers of non-infiltrated fiber. Composite properties, specifically fracture strength and damage tolerance, can be tailored by varying lay-up and processing parameters such as fiber-matrix ratio and type of fiber weave.     

Evaluation of novel interphases for oxide/oxide ceramic matrix composites

Abstract

Stoichiometric MXO₄ type compounds, where M represents a rare earth or yttrium ion and X a pentavalent cation, have been prepared using mixed oxide and liquid precursor methods. Their stability in relation to Al₂O₃, mullite, and yttrium–aluminium garnet (YAG) has been determined by examining interfaces exposed in reaction couples after heating to 1400°C. Complex oxides of the phosphate and vanadate type are shown to possess the desired chemical stability with some of the candidate oxides and can be considered as suitable interphase materials. Close control over composition and homogeneity is shown to be important in determining their performance as potential interphases due to the possible formation of a liquid phase which can react readily with the oxide matrix or fibre. Selected MXO₄ compounds have also been successfully deposited on to oxide substrates and woven oxide fibres using liquid precursors and RF magnetron sputtering techniques, yielding controlled and uniform fibre coatings.     

丁腈橡胶/功能化氧化石墨烯复合材料的研究

用硅烷偶联剂KH590对氧化石墨烯进行功能化改性,得到的功能化氧化石墨烯再通过乳液共混和机械共混等工艺制备了丁腈橡胶/功能化氧化石墨烯复合材料。表征分析了功能化氧化石墨烯的结构和表面形态,研究了丁腈橡胶/功能化氧化石墨烯复合材料的机械性能。结果显示,与氧化石墨烯相比,功能化氧化石墨烯的亲水性和表面形态均发生了较大变化,其与丁腈橡胶形成的复合材料与丁腈橡胶/氧化石墨烯复合材料相比,拉伸强度提高的幅度更大且断裂伸长率降低的幅度更小。     

Preparation and characterization of graphite oxide/polypyrrole composites

Graphite oxide (GO)/polypyrrole (PPy) composites (GPs) and 1,5-naphthalene disulfonic acid (1,5-NDA) doped GPs (1,5-NGPs) have been successfully synthesized via in situ polymerization of pyrrole on GO. The conductivity of 1,5-NGPs is as high as 7 S/cm, seven orders of magnitude higher than that of pristine GO. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results show PPy “dressed” on the surface of GO layers, while Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses confirm the interaction between GO and PPy. The results of thermogravimetric analysis (TGA) and heat treatment at 1000 °C show that the “dressed” PPy on the surface of GO layers in GPs and 1,5-NGPs has effectively prevented the deflagration of GO.     

Isothermal crystallization of polyethylene oxide/silver nanoplate composites

This research was accomplished to investigate the kinetics of isothermal crystallization of polyethylene oxide (PEO)/silver nanoplate composites. It was obtained that the spherulites increased in size and numbers with time for the composites with various particle loadings. Additionally, the spherulite growth rate of composites decreased with an increase in the crystallization temperature and increased with the addition of nanoplates. The spherulite growth rate was further analyzed by the theory developed by Lauritzen and Hoffman. The product of the lateral surface free energy (σ) and the end surface free energy (σ_e) decreased with an increase in the content of nanoplates. We proposed the possible crystallization mechanisms of these PEO/nanoplate composites according to the change of σ and σ_e with the presence of nanoplates. A controlled experiment showed a minor change in PEO crystallization with the presence of a surfactant C₁₆TAB. This implied that the unique size and shape of nanoplates plays a key role on hindering the primary nucleation of PEO and increasing the spherulite growth rate. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Crystallization behavior of polyethylene oxide/para-nitroaniline microdispersed composites

The crystallization behavior of polyethylene oxide (PEO) containing microdispersed nonlinear optical chromophores such as para-nitroaniline (PNA) has been investigated with respect to composition and different methods of film preparation techniques viz. solvent casting, melt casting, and powder molding. Large variations in the intensities of major reflections, 012 and 101, from PNA crystallites were observed depending on the composition as well as the method of preparation. The morphology of the samples examined under cross-polarizing conditions revealed highly birefringent crystallites dispersed in the spherulitic morphology of the PEO matrix in contrast to weakly birefringent crystals of the additive by itself. At high concentrations exceeding 45 wt % the PNA crystals act as substrates for the growth of polymer crystals. These results have been explained on the basis of intermolecular interaction as well as good lattice match between the crystalizing components, leading to preferential growth of the crystals along a certain direction. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1127–1137, 1997     

Electrochemical inspection of polypyrrole/chitosan/zinc oxide hybrid composites

Polymer nanocomposite composed of polypyrrole, chitosan, and zinc oxide nanoparticles has been synthesized and it has been evaluated for various electrochemical aspects of the current electrochemical industry. The polypyrrole (PPy) was synthesized by the chemical oxidative polymerization reaction by employing ammonium persulfate as oxidizing agent. Composites of polypyrrole/chitosan (PPy/Chy) and polypyrrole/chitosan/ZnO (PCZ) composites were synthesized by the solution blending method. Detailed structural, morphological, thermal characterization of PPy, PPy/Chy, and PCZ were performed to characterize the specific features of the systems. The composites exhibit better thermal stability and high surface area and the addition of ZnO nanoparticle increase the crystallinity of the composite. Electrochemical characterization of the ITO electrodes modified with PPy, PPy/Chy, and PCZ were performed using cyclic voltammetry, electrochemical impedance spectroscopy, and amperometry techniques. The present study highlights the role of a bio-compatible material with high surface area and conductive constituent for designing of various high performing electronic noninvasive sensors, biosensors, and so forth.     

Flash sintering of alumina/reduced graphene oxide composites

The flash sintering behavior of Al₂O₃/reduced graphene oxide (rGO) composites was investigated. rGO was used as a composite component and a conductive additive. Under the electric fields of 250–400 V cm⁻¹, the flash event occurred at extremely low temperatures of 236–249 °C. The current density limit played a significant role in the degree of densification. A larger current density resulted in a higher density of the sample. However, current densities larger than 33.33 A cm⁻² resulted in broken samples because of the localization of high current density coupled with the formation of hot spots. Flash sintering at a furnace temperature of 800 °C, electric field of 300 V cm⁻¹ and current density limit of 33.33 A cm⁻² produced nearly completely dense Al₂O₃/rGO composites. In addition to the current limit, the furnace temperature is also a key parameter that controls the degree of densification to achieve “safe” flash sintering.     

New liquid processing of oxide/oxide 3D wowen ceramic matrix composites

In this work, a novel process named Flexible Injection Process (FIP) was developed to manufacture near-net shape oxide/oxide composites reinforced with 3D interlock fibers. This process uses a flexible membrane to apply pressure to promote transverse impregnation of the fibrous reinforcement by a slurry charged with sub-micron ceramic particles. Due to the through-thickness filtration and compaction, FIP process is much faster than typical in-plane impregnation and results in composites with lower residual porosity than those produced by traditional processes. In this study, a mathematical modeling of the impregnation in FIP was developed and compared to experimental infiltration experiments. Furthermore, ceramic matrix composites (CMCs) produced by FIP were compared to composites manufactured via an established RTM-like process. The two molding processes were compared to determine if the different flow behaviors have an impact on material densification, porosity formation, mechanical properties, and manufacturing time. CMCs produced by both methods resulted in similar microstructures, as determined by mercury intrusion porosimetry, even if FIP composites were marginally less porous. Finally, a comparison of mechanical properties resulting from the two manufacturing methods has shown a similar behavior. Thus, the main advantages of FIP molding were identified to be the shorter cycle time and the robustness of the impregnation compared to RTM-like processes.     

Damage modeling of oxide/oxide ceramic matrix composites under cyclic loading conditions

Ceramic matrix composites exhibit optimal high temperature property and complex nonlinear behaviors including irreversible deformations and stiffness degradation under different mechanical loading conditions. In the present work, the damage evolution of the material under multi-axial loads considering effects of loading-unloading cyclic was studied and a novel continuum damage constitutive model was proposed. The material degradation was decomposed into monotonic damages and cyclic damages. The anisotropic hardening behavior of the material was considered by taking orientation dependence into account. Compared to the experimental results, the constitutive model could accurately predict the stress-strain response and stiffness degradations of the oxide/oxide ceramic matrix composites for monotonic loading and cyclic loading.     

Investigation of long-term thermal aging-induced damage in oxide/oxide ceramic matrix composites

Long-term thermal aging is a typical factor affecting the thermo-mechanical fatigue life for hot-end components in the gas turbine. The present work focuses on the development of thermal aging-induced damage in 2-D woven oxide/oxide ceramic matrix composites from micro-mechanism and macroscopic mechanical performance. The porosity evolution and mechanical performance after long-term thermal aging were characterized through mercury intrusion measurements and uniaxial compressive tests, respectively. The results show that the decrease of micro-porosity directly reflects the irreversible evolution of material microstructure in the thermal aging process, and the decrease of compressive strength after aging is the macroscopic reflection of the microstructure variation. The porosity increment of matrix was thus used to characterize the thermal aging-induced damage, establishing a unique analysis model between the increment of micro-porosity under thermal aging and the corresponding degradation of material compressive strength. The experimental results are in good agreement with the established model.     

Erosion characteristics of N720/alumina oxide/oxide ceramic matrix composites in a combustion environment

The erosion behavior of N720/Alumina oxide/oxide composite was investigated under a combustion environment to better represent particle ingestion of a jet engine. The effect of particle velocity, particle size, temperature and impingement angle were investigated. In addition, room temperature studies were also conducted for comparison. Eroded sites were investigated using optical and scanning electron microscopy to understand the extent of erosion and erosion mechanisms. The results indicate that erosion rate increased with an increase in particle velocity and particle size. Also, erosion rate increased from room temperature to 815 °C and then decreased from 815 °C to 1200 °C. Brittle fracture is the predominant mode under normal impacts and as the impact angle is decreased increased ploughing/wear is evident.     

氧化石墨烯/天然橡胶复合材料的制备与性能

采用己内酰胺（CPL）改性氧化石墨烯（GO）（CPL-GO）,与天然橡胶（NR）复合后通过熔融共混法制备了CPL-GO/NR复合材料。考察了CPL-GO用量对CPL-GO/NR复合材料物理机械性能、界面相互作用和气体阻隔性能的影响。结果表明,CPL改性GO后,X射线衍射层间距增加,片层堆砌更为松散,CPL-GO与水接触角增至91.2°。当CPL-GO的质量分数为2.0%时,CPL-GO/NR复合材料的拉伸强度为26.1 MPa,较纯NR提高了50.9%。随着CPL-GO用量的增加,复合材料的储能模量增加,损耗因子的峰值减小,表明GO经CPL表面改性后与NR复合,增强了两相界面间的相互作用,从而提高了复合材料抵抗变形的能力。在40 ℃下,当CPL-GO的质量分数为3.0%时,CPL-GO/NR复合材料的气体渗透系数较纯NR下降了57.1%。     

一步水热法合成铜改性的介孔γ-Al_2O_3及其吸附脱硫性能研究

采用一步水热合成法,以Al(NO3)3为铝源,P123为模板剂,Na OH、Na2CO3和K2CO3分别为沉淀剂,Cu(NO3)2为铜源,制备出负载铜的金属有序介孔γ-Al2O3,并运用N2吸附-脱附和XRD等技术对其结构进行表征,同时探讨了铜改性的介孔γ-Al2O3对模型燃油中的噻吩的吸附性能。结果表明,这3种沉淀剂都能制备出比表面积大(>226 m2/g),孔径分布中心为3.3 nm,孔体积为0.27⁰.35 cm3/g的负载铜的介孔γ-Al2O3,且样品都保持了较好的介孔结构。样品对模型燃油中噻吩的吸附脱硫性能表明,用Na OH作为沉淀剂且负载铜的介孔γ-Al2O3样品对噻吩的吸附性能较好,原因在于此样品具有较大的比表面积且铜在此样品中的分散性较好。     

ZnO/石墨烯复合材料的制备及性能研究

本文将采用溶胶-凝胶法制备纳米ZnO和通过Hummers法制备的石墨烯进行简单的一步超声复合,得到ZnO/石墨烯复合材料。利用XRD、TEM以及紫外可见分光光度计对所制备的ZnO和石墨烯样品进行测试表征,并以亚甲基蓝的降解效率来评价ZnO/石墨烯复合材料的光催化活性能。研究表明:ZnO/石墨烯的光催活性较纯氧化锌提高了4倍有余,当石墨烯质量比为15%时,ZnO/石墨烯的光催化活性最强。     

Multifunctional polyimide/graphene oxide composites via in situ polymerization

In this article, we detail an effective way to improve electrical, thermal, and gas barrier properties using a simple processing method for polymer composites. Graphene oxide (GO) prepared with graphite using a modified Hummers method was used as a nanofiller for r‐GO/PI composites by in situ polymerization. PI composites with different loadings of GO were prepared by the thermal imidization of polyamic acid (PAA)/GO. This method greatly improved the electrical properties of the r‐GO/PI composites compared with pure PI due to the electrical percolation networks of reduced graphene oxide within the films. The conductivity of r‐GO/PI composites (30:70 w/w) equaled 1.1 × 10¹ S m^?1, roughly 10¹⁴ times that of pure PI and the oxygen transmission rate (OTR, 30:70 w/w) was reduced by about 93%. The Young's modulus of the r‐GO/PI composite film containing 30 wt % GO increased to 4.2 GPa, which was an approximate improvement of 282% compared with pure PI film. The corresponding strength and the elongation at break decreased to 70.0 MPa and 2.2%, respectively. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40177.     

Piezoelectric and mechanical properties of hydroxyapatite/titanium oxide composites

Hydroxyapatite (HAp) is the most common bioactive ceramic used to replace hard tissue in the body. Because of its low resistance and fragile nature, more attention is being given to composites based on HAp such as HAp/TiO₂ composites. This study aims at reporting the synthesis of HAp/TiO₂ composites (hereafter named HT composite) by sol-gel and co-precipitation methods assisted by ultrasonic radiation. The structural characterization was carried out by X-ray Diffraction (XRD) and Scanning Transmission X-ray Microscopy (STXM) techniques using synchrotron radiation, which allowed a mixture of phases to be identified separately in the two materials once the composite was formed. A Rietveld refinement for XRD data determined the phase percentage and structural parameters obtained for each material. In addition, crystallite size using the modified Scherrer equation was determined. A piezoelectric character of the two materials was confirmed by Piezoresponse Force Microscopy (PFM) to determine the piezoelectric coefficient (d_eff). Finally, PinPoint-AFM force curves confirmed an increase in the Young's modulus value for the HT composite.     

Photoelectrochemical and electrochromic properties of polyimide/graphene oxide composites

A series of novel multicolored near-infrared electrochromic polyimide (PI)-based composites with graphene oxide (GO) were prepared by using in situ polymerization. The prepared PI/GO composites are readily soluble in many organic solvents, and display outstanding thermal resistance, stably electrochromic characteristics, high coloration efficiency, short switching time, and anodic electrochromic behavior. Scanning electron microscope and transmission electron microscopy showed a good and uniform dispersion of the GO sheets in the PI matrix. The surface of the composites contains hydrophilic functional groups such as C–O and CO, which have been characterized by X-ray photoelectron spectroscopy. The typical, stable photoelectrical response showed that there was electron transfer in the interior of composites film under illumination, and the electrochemical impedance spectra result was consistent with the photoelectrical response. The different content of GO played a pivotal role in the electron transfer and regulated the conductivity of the composites. The work functions were obtained by KPFM measurements, and the work function is increasing with the contents increasing of GO in the composites. The properties prove that the composite is multipurpose material which will cater for photoelectric conversion and electrochromic application.     

氧化锌晶须/聚丙烯复合材料性能的研究

制备了四针状氧化锌晶须(T—ZnOw)／聚丙烯复合材料,研究了不同偶联剂处理的T—ZnOw及其用量对复合材料力学性能的影响,并对偶联机理做了初步探讨。研究结果表明,当添加T-ZnOw质量分数为20％时,复合材料的力学性能最好;与处理前相比,处理后的T—ZnOw复合材料的拉伸强度和冲击强度有不同程度的提高;不同偶联剂处理的T—ZnOw对复合材料力学性能的影响不同。