Effect of silane modification on CNTs/silica composites fabricated by a non-firing process to enhance interfacial property and dispersibility

Carbon nanotube/ceramic composites have been in the spotlight thanks to their excellent properties. Sintering is the vital part of ceramics fabrication in terms of reliability, however sintering the carbon nanotube (CNT) based ceramic composites is a challenging task. In this study, interfacial bonding of silane functionalized CNT with silica ceramic is investigated by a non-firing sintering process. CNTs are first treated by a mixed acid with the aid of a silane 3-aminopropyl triethoxysilane (APTES), which improves the chemical bonding and dispersibility of CNT in ceramic bodies. The extent of APTES chemical functionalization and mechanical property of CNT/silica ceramic composites are characterized using Raman spectrometer, FT-IR analysis, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and three-point bending strength measurement. Results show that composites are successfully prepared without sintering with stable CNT-silica interface, superior dispersibility, and good mechanical properties.     

回归模型的建立——回归分析在陶瓷多元系中的应用

以确定普通陶瓷坯体的烧结温度与化学组成之间的定量关系为研究目标，结合基本的工艺原理探讨如何建立适宜的回归模型，从而合理的应用多元回归分析得出正确的回归方程。     

A novel technique for the preparation of fine ceramic oxides

In this paper, we put forward a novel and simple chemical route for the preparation of fine ceramic oxides i.e. ferrites using triethylammonium carbonate as the precipitating agent. The particles were studied and characterized by X-ray diffraction and scanning electron microscopy. The emphasis is on the superiority of this technique over other chemical and conventional routes.     

Characteristics of wheat dust flame with the influence of ceramic foam

A vertical dust combustion pipeline with high-speed photography, micro-thermocouple and pressure sensor was built to investigate the influence of ceramic foam on the wheat dust explosion flame. Ceramic foams with different parameters were adopted in this paper, and compared with metal mesh. The chemical structures of dust explosion residue were characterized by X-ray photoelectron spectroscopy. Results indicate that the wheat dust flame propagation and structure were significantly destroyed by ceramic foam. With the decreasing aperture or increasing layer, the blocking effect of ceramic foam was aggravated on the dust flame. The flame cannot pass through the ceramic foam with 20 PPI and 3 layers. On the upper end of ceramic foam, the flame temperature is positively proportional to the aperture but inversely proportional to the layers. With the PPI and layers of ceramic foam increases, the combustion pressure firstly increases and then decreases when the dust combustion intensity is strong. Ceramic foam shows the incentive effect to some extent on the combustion pressure, but the continuous inhibition effect is found for the metal mesh.     

Microarc oxidation coating formed on SiCw/AZ91 magnesium matrix composite and its corrosion resistance

A ceramic coating was synthesized on the surface of SiCw/AZ91 magnesium matrix composite by means of microarc oxidation (MAO) technique. Scanning electron microscope (SEM) was employed to characterize the surface morphology and cross-section microstructure of the coating. The phase structure and the chemical composition of the ceramic coating were analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the coating was evaluated by immersion test and electrochemical method. The results showed that the corrosion rate of the coated SiCw/AZ91 composite was decreased greatly compared with that of the bare composite because of the protective microarc oxidation coating.     

Effect of the Oxidation Time on Properties of Ceramic Coatings Produced on Ti-6Al-4V by Micro-Arc Oxidation

Ceramic coatings were prepared on Ti-6AI-4V alloy using ac micro-arc oxidation (MAO) in silicate-hypophosphate solution. Growth regularity and formation mechanism of ceramic coatings were discussed. It was found that during the first stage the growth rate of coatings toward the external surface was larger than that toward substrate and then the coating began to grow mainly towards Ti alloy. When the total coating thickness reaches a certain value, it would no longer increase. In addition, the variations of the composition and microstructure of ceramic coatings according to the depositing time were also investigated with X-ray diffraction (XRD) and scanning electron microscope (SEM). The amount of rutile TiO2 gradually increased, whereas the amounts of the anatase TiO2 and amorphous phases first increased and then decreased slightly.     

X-CT无损测试技术用于陶瓷涂层三维重构和孔隙率计算

陶瓷涂层对海工环境中的钢筋有着较好的保护作用。在碳钢表面喷涂磷酸盐陶瓷涂层, 采用XRD和XRF对陶瓷涂层的物相组成进行分析。结果表明: 实验用陶瓷的主要晶相成分为P₂O₅与SiO₂。采用SEM对陶瓷的表面和截面形貌进行观察, 发现陶瓷涂层内存在微裂纹, 涂层的厚度约为349 μm。采用X-CT测试可以得到陶瓷内部结构的高清图像, 并利用Matlab和Mimics软件对高清图像进行三维重构。此外通过阈值分割技术, 将CT图像内的孔与基体灰度值区分开来, 并计算得到陶瓷涂层的孔隙率为14%, 并采用压汞测试技术对测试结果进行验证。研究认为X-CT无损测试是一种建立陶瓷涂层内可视化孔结构分析的有效工具。     

Orthophosphates of langbeinite structure for immobilization of alkali metal cations of salt wastes from pyrochemical processes

Mixtures of alkali metal chlorides used as electrolytes in pyrochemical processes for nuclear fuel production and spent nuclear fuel reprocessing were subjected to conversion into orthophosphate ceramic materials based on langbeinite mineral. The results of the solid-state synthesis of the phosphates are described. The phase and chemical composition, chemical stability, and heat resistance of the orthophosphates were studied by X-ray phase analysis, X-ray spectrum microanalysis, emission spectrum analysis, and scanning electron microscopy. Quantitative incorporation of alkali metal cations, including Cs, into such materials was proved. The use of a binder (89% Bi₂O₃ + 11% NaF mixture) considerably increases the density of the ceramic prepared and substantially enhances its chemical stability.     

Microstructures and Composition of Ceramic Coatings on Aluminum Produced by Micro-Arc Oxidation

Microstructures and phase composition of the ceramic coatings formed on pure aluminum by heteropolar pulsed current ceramic synthesizing system for different periods were investigated by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). Results show that the amount of the discharge channels in the ceramic coating sminish while the aperture largen in the micro-arc oxidation process, and the surface of the ceramic coatingmelted and solidified in the process.XRD studies of ceramic coatings deposited for different time show that these coatings consist mainly of α-Al2 O3, γ-Al2 O3 , θ-Al2 O3 and a little amorphous phase, and phase composition of compact and porous ceramic coatings don' t have much difference but have a little change of the content of α-Al2 O3 and amorphous phase.     

Microstructural characteristics,porosity and strength development in ceramic-laterized concrete

Interfacial bonding between constituent materials and pore sizes in a concrete matrix are major contributors to enhancing the strength of concrete. In a bid to examine how this phenomenon affects a laterized concrete, this study explored the relationship between the morphological changes, porosity, phase change, compressive, and split tensile strength development in a ceramic-laterized concrete. Varying proportions of ceramic aggregates, sorted from construction and demolition wastes, and lateritic soil were used as substitutes for natural aggregates. Strength properties of the concrete specimens were evaluated after 7, 14, 28 and 91 days curing, but morphological features, using secondary electron mode, were examined only at 7 and 28 days on cured specimens, using Scanning electron microscope (SEM). From all the mixes, selected samples with higher 28 day crushing strength, and the reference mix, were further characterized with more advanced analysis techniques, using the mercury intrusion porosimetry (MIP), thermogravimetric analysis (TGA), X-ray Diffractometer, and SEM (backscatter electron mode-for assessment of the interfacial transition properties between aggregates and paste).The reference mix yielded higher mechanical properties than the concrete containing secondary aggregates, this was traced to be as a result of higher peaks of hydration minerals of the concrete, coupled with its low tortuosity and compactness. However, a laterized concrete mix containing both 90% of ceramic fine and 10% of laterite as fine aggregate provided the optimal strength out of all the modified mixes. Although, the strength reduction was about 9% when compared with the reference case, however, this reduction in strength is acceptable, and does not compromise the use of these alternative aggregates in structural concrete.     

化学气相沉积陶瓷复膜抗腐蚀试验研究

油气田开发过程中的井下腐蚀严重,由于腐蚀失效引起的损失极大地增加了油气田开发的成本。金属陶瓷具有很好的抗腐蚀性能,因此选择化学气相沉积(CVD)陶瓷复膜技术对井下工具进行表面处理以提高其抗腐蚀性能。选择油气田井下工具常用的钢作为实验对象,采用CVD法生成陶瓷复膜,通过抗应力腐蚀试验和电化学试验分析陶瓷复膜抗腐蚀性能,同时利用扫描电镜进一步分析陶瓷复膜抗腐蚀机理。实验结果表明:通过CVD陶瓷复膜的35CrMo具有很好的抗硫化氢腐蚀的能力。     

Investigation on the structural and photoluminescent properties of chromium-doped ceramics cordierite

This work presents the investigation about the structural and optical properties of a doped-chromium system containing cordierite (Mg₂Al₄Si₅O₁₈) as main phase. The sample composition and the structural data were obtained from X-ray diffraction (XRD) measurements and the results were analyzed by Rietveld method. Photoluminescence (PL) spectra under several excitation wavelengths and photoluminescence excitation (PLE) measurements were performed. The obtained results from PL and PLE experiments are evidences that Cr³⁺ occupies octahedral sites in this ceramic system. By correlating the optical results, the crystal field parameter (Dq) and Racah interelectronic repulsion parameters (B and C) were calculated and discussed according to the Tanabe-Sugano (TS) theory for d³ transition metals in octahedral sites.     

静态铝热自蔓延高温合成陶瓷层耐蚀性的研究

对比研究了静态铝热ＳＨＳ陶瓷涂层在不同组成，不同冷却保温条件和腐蚀阶段的耐蚀性，试验得出，腐蚀在第一阶段最为严重以后趋于平缓稳定，添加ＳｉＯ２和保温缓冷的涂层可减少孔隙，改善组织分布，从而提高耐蚀性。     

Mikrostrukturelle und oberflächenanalytische Charakterisierung keramischer Verstärkungskomponenten

Microstructural characteristics of different as-received SiC-whiskers, continuous polymer-derived as well as CVD processed SiC-based fibers and C-fibers were evaluated in an interdisciplinary approach including X-ray diffraction, scanning electron microscopy, analytical transmission electron microscopy and surface analytical methods (AES, XPS). It was found necessary to compare the chemical information collected from small volumes of the micro-structure to analytical data from bulk composition in order to receive a coherent picture of the complex impurity distribution in ceramic toughening components. This is particularly true for SiC-whiskers where both structural homogeneity and chemical purity are strongly related to growth conditions. SiC-based fibers were established as polyphase, non-stoichiometric components too. Their toughening potential in all ceramic composites is partly sacrificed because of excessive SiC grain growth under high-temperature processing conditions which results in a significant strength reduction.     

Machining and surface finishing of brittle solids

Ceramic materials are finished primarily by abrasive machining processes such as grinding, lapping, and polishing. In grinding, the abrasives typically are bonded in a grinding wheel and brought into contact with the ceramic surface at relatively high sliding speeds. In lapping and polishing, the ceramic is pressed against a polishing block with the abrasives suspended in between them in the form of a slurry. The material removal process here resembles three-body wear. In all these processes, the mechanical action of the abrasive can be thought of as the repeated application of relatively sharp sliding indenters to the ceramic surface. Under these conditions, a small number of mechanisms dominate the material removal process. These are brittle fracture due to crack systems oriented both parallel (lateral) and perpendicular (radial/median) to the free surface, ductile cutting with the formation of thin ribbon-like chips, and chemically assisted wear in the presence of a reactant that is enhanced by the mechanical action (tribochemical reaction). The relative role of each of these mechanisms in a particular finishing process can be related to the load applied to an abrasive particle, the sliding speed of the particle, and the presence of a chemical reactant. These wear mechanisms also cause damage to the near ceramic surface in the form of microcracking, residual stress, plastic deformation, and surface roughness which together determine the strength and performance of the finished component. A complete understanding of the wear mechanisms leading to material removal would allow for the design of efficient machining processes for producing ceramic surfaces of high quality. The research was supported in part by the National Science Foundation through grants MSS 9057082, Jorn Larsen-Basse, Program Director and DDM 9057916, Bruce Kramer, Program Director.     

Hydroxyapatite/gelatin/gellan sponges as nanocomposite scaffolds for bone reconstruction

The aim of this work was the morphological, physicochemical, mechanical and biological characterization of a new composite system, based on gelatin, gellan and hydroxyapatite, and mimicking the composition of natural bone. Porous scaffolds were prepared by freeze–drying technique, under three different conditions of freezing. The morphological analysis showed a homogeneous porosity, with well interconnected pores, for the sample which underwent a more rapid freezing. The elastic modulus of the same sample was close to that of the natural bone. The presence of interactions among the components was demonstrated through the physicochemical investigation. In addition, the infrared chemical imaging analysis pointed out the similarity among the composite scaffold and the natural bone, in terms of chemical composition, homogeneity, molecular interactions and structural conformation. Preliminary biological characterization showed a good adhesion and proliferation of human mesenchymal stem cells.     

Chemical composition and corrosion resistance of passive chromate films formed on stainless steels 316 L and 1.4301

The chemical composition and corrosion behavior of the natural and formed by chemical treatment in chromium-containing solution passive films on 316 L and 1.4301 stainless steel surfaces have been investigated by means of X-ray photoelectron spectroscopy and electrochemical in situ method of anodic polarization curves. It have been established that the oxide films formed by the chemical treatment have different chemical composition (Cr-enriched), color and reduced corrosion resistance compared to the natural passive films on both steels. The results have shown that the lower part of the oxide layer represents a uniform modified passive film and the upper one is a porous Cr³⁺-enriched film with an island-like structure. The latter permits a direct contact of the solution with the modified passive film which controls the corrosion resistance by the dissolution of the Fe³⁺ oxides present in the lower thinner layer.     

Electromagnetic wave absorption potential of SiC-based ceramic woven fabrics in the GHz range

This article investigates the electromagnetic wave-absorbing properties of SiC-based ceramic woven fabrics. The electrical conductivity of ceramic woven fabrics was modified by heat treatment in air, resulting in oxidation, and the electromagnetic wave absorption potential of single- and double-layer ceramic woven fabrics were determined in the 17–40 GHz frequency range using the free-space method. The absorption potentials of ceramic woven fabrics of different chemical composition and weave were correlated with their material properties through X-ray diffraction, scanning electron microscopy, and electrical resistance measurement. The effect of the different arrangements of fabrics in multilayer forms, and how oxidation affects the electromagnetic wave absorption potential of the fabrics are discussed. Various double-layer combinations of SiC-based woven fabrics revealed promising potentials for both reduced reflection and transmission, resulting in ~90% absorption in the GHz range, which makes them powerful candidate materials for electromagnetic wave absorption applications.     

Microstructure and tribological properties of alumina ceramic with laser-dispersed tungsten additions

The surface of slightly porous, commercially available alumina ceramic was laser-modified with tungsten and/or zirconia additions. The thickness of the resulting multiphase surface layers ranged from 300–800 m depending on the chemical composition and the parameters of the laser process used. Microstructure and worn surfaces were analysed by scanning electron microscopy and energy- dispersive X-ray spectroscopy. Mechanical properties were characterized by using Vickers hardness and nanoindentor testing. Tribological tests were carried out on the surface-modified ceramics using a ball-on-block tribometer. All tests were conducted in unlubricated oscillating sliding contact against balls of alumina in laboratory air at room temperature, relative humidities varying between 3% and 80%, and in distilled water. The multiphase surface layers showed a total volume fraction of second phases up to 40 vol% embedded in the alumina matrix, whereas the average size of the alumina grains was substantially reduced compared with the substrate ceramic. Tungsten dispersoids were distributed homogenously in the ceramic matrix and eutectic Al2O3–ZrO2 phase occurred along the boundaries of the alumina crystallites. Mechanical and tribological properties varied as a function of the microstructure of the laser-modified ceramics, i.e. type and volume fraction of the second phases, and both friction and wear were substantially reduced compared with the commercially available monolithic alumina ceramic used for reference. Friction coefficient and amount of linear wear of the ceramics decreased with increasing relative humidity of the surrounding air. © 1998 Kluwer Academic Publishers     

Effect of Fe ions on the thermal and optical properties of the ceramic coating grown in-situ on AZ31 Mg Alloy

This research investigates the effect of Fe₂(SO₄)₃ on the thermal and optical properties of the ceramic coatings formed on AZ31 Mg alloy. The different ceramic coatings were obtained by plasma electrolytic oxidation (PEO) in electrolytes that contain varied concentrations of Fe₂(SO₄)₃. The microstructure, element distribution, composition as well as the thermal and optical properties of the coatings were studied with scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), UV–VIS–NIR spectrophotometer and infrared reflectometer. The results show that all of the coatings prepared were mainly composed with MgO, with trace-amount of Fe₃O₄ presents and Fe seems entered into the MgO crystal structure. With the increasing of the concentration of Fe₂(SO₄)₃, the solar absorptance and infrared emittance increased initially but then remain stable. We found that at the concentrations 8 g L⁻¹, the coating has the highest solar absorptance (0.94) and infrared emittance (0.83). Our results show that coatings formed with this method could be useful as a thermal control coating in a variety of applications, such as in the spacecraft.