Mechanical activation-assisted autoclave processing and sintering of HfB2-HfO2 ceramic powders

This study reports on the synthesis and consolidation of HfB₂-HfO₂ ceramic powders via mechanical activation-assisted autoclave processing followed by pressureless sintering (PS) or spark plasma sintering (SPS). HfCl₄, B₂O₃ and Mg starting powders were mechanically activated for 5 min to obtain homogeneously blended precursors with active particle surfaces. Autoclave synthesis was carried out at a relatively low temperature at 500 °C for 6 or 12 h. As-synthesized powders were purified from reaction by-products such as MgO and MgCl₂ by washing and acid leaching treatments. The characterization investigations of the as-synthesized and purified powders were performed by using an X-ray diffractometer (XRD), stereomicroscope (SM), scanning electron microscope (SEM) and particle size analyzer (PSA). The purified powders with an average particle size of about 190 nm comprised the HfB₂ phase with an amount of 79.6 wt% in addition to the HfO₂ phase and a very small amount of Mg₂Hf₅O₁₂ phase after mechanical activation for 5 min and autoclave processing for 12 h. They were consolidated at 1700 °C both by PS for 6 h and SPS for 15 min. The Mg₂Hf₅O₁₂ phase decomposed during sintering and bulk samples only had the HfB₂ and HfO₂ phases. The bulk properties of the sintered samples were characterized in terms of microstructure, density, microhardness and wear characteristics. The HfB₂-HfO₂ ceramics consolidated by PS exhibited poor densification rates. A considerable improvement was obtained in the relative density (~91%), microhardness (~16 GPa) and relative wear resistance (2.5) values of the HfB₂-HfO₂ ceramics consolidated by SPS.     

Effect of mechanical activation of coprecipitated precursor on synthesis of La2Zr2O7

A lanthanum zirconate (La₂Zr₂O₇, LZ) precursor has been prepared by coprecipitation of the relevant hydroxides from nitrate solution. The effect of the mechanical activation of the precursor on its thermal decomposition and LZ formation in the temperature range of 700–1100 °C has been investigated. After mechanical activation, the precursor releases volatile components (H₂O and CO₂) at lower temperatures. Mechanical activation accelerates the LZ crystallisation and results in the formation of phase-pure LZ without admixtures of unreacted zirconia and lanthana. The LZ powder prepared from the mechanically activated precursor is characterised by a larger BET surface area, in comparison to that synthesised from the as-prepared precursor under the same calcination conditions.     

Effect of sintering temperature on mechanical properties of magnesia partially stabilized zirconia refractory

The optimized sintering conditions for a 3.5 wt% magnesia partially stabilized zirconia (Mg-PSZ) refractory were proposed in our recent research. The influence of the sintering temperature on the development of phase composition, microstructure, densification, thermal expansion and mechanical strength was studied in detail by X-ray diffraction (XRD), scanning electron microscope (SEM), He-pycnometer, high temperature dilatometry and three-point bending test. The samples sintered at 1670 °C had the highest bend strength, the maximum densification, the lowest thermal expansion coefficient (CTE), a homogeneous microstructure and a linear change in thermal expansion.     

聚乙烯对油田加热集输工艺的适用性

为明确非金属复合管聚乙烯内衬在油田加热输送工艺的适用性,借助反应釜、扫描电镜研究4731B聚乙烯挂片在温度50 ℃、压力0.1、4、6MPa、采出原油与采出水介质中168 h内的渗透行为.研究发现,采出原油、采出水均可渗透进入聚乙烯使其溶胀、增重,采出原油引起的增重率大于采出水,最大为4.52％;聚乙烯表面产生裂纹,介...     

Influence of modified multi-walled carbon nanotubes on the mechanical behavior and toughening mechanism of an environmentally friendly granulated blast furnace slag-based geopolymer matrix

This study aimed to investigate the mechanical behavior of an environmentally friendly granulated blast furnace slag-based geopolymer matrix reinforced with modified multi-walled carbon nanotubes (MWCNTs). The modified MWCNTs were obtained using a modification method combining nitric acid and sulfuric acid and were then dispersed using sodium dodecylsulfate (SDS) as a dispersant. Two types and three concentrations of MWCNTs were mixed directly into the aqueous solution, sonicated, and then mechanically mixed with waste granulated blast furnace slag to form the geopolymer matrix. Raman and Fourier transform infrared (FT-IR) spectroscopy were used to evaluate the ordered structure and crystallization degree of the modified MWCNTs. Then, the dispersity of the modified MWCNTs was characterized using transmission electron microscopy (TEM). The compressive and bending strengths were measured to evaluate the mechanical behavior of specimens. Moreover, the polycondensation products, polycondensation degree, pore structure, and microscopic morphology of the geopolymer matrix were analyzed using X-ray diffraction (XRD), FT-IR spectroscopy, nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), and field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDS). The experimental results showed that the incorporation of 0.1% functionalized MWCNTs had an optimal influence on the fluidity and mechanical behavior. The slump diameters of geopolymers with 0.1% functionalized MWCNTs with and without SDS were increased by 16.3% and 23.5%, respectively, compared with the reference geopolymer matrix. For geopolymer matrix samples at a curing age of 28 d, the compressive strength of geopolymers with 0.1% functionalized MWCNTs with and without SDS were increased by 16.3% and 17.6%, respectively. For the bending strength, the corresponding increases were 17.6% and 18.7%, respectively. It was found that functionalized MWCNTs could increase the degree of polycondensation, leading to a more traditional amorphous N-A-S-H phase, a finer C–S–H phase, more Q⁴ (2Al) and Q⁴ (3Al), and lower porosity. In addition, the propagation of micro-cracks in the geopolymers was inhibited by the incorporation of functionalized MWCNTs.     

Bioceramic composites for orthopaedic applications: A comprehensive review of mechanical,biological, and microstructural properties

Bioceramics have been widely utilized for orthopaedic applications in which the biocompatibility and mechanical properties of the materials are vital characteristics to be considered for their clinical use. Till date, extensive studies have been devoted to developing a range of scientific ways for tailoring the microstructure of bioceramics in order to attain the trade-off of mechanical properties and biocompatibility of the final product. Owing to low reactivity, earlier stabilization and longer functional life of bioceramic, the developed implants are capable of replicating the mechanical behaviour of original bone. As the safety of the patient and its ultimate functionality are the ultimate goal of the selected implant material hence, the present literature survey investigates and brings forth the important aspects associated to the mechanical, biological and microstructural characteristics of bioceramics employed in orthopaedic applications. The review paper majorly focuses on effective utilization of various materials as an additive in bioceramics and processing techniques used for enhancement of properties, enabling the use of material in orthopaedic applications. The influence of various additives on the microstructure, mechanical properties and biological performance of developed bioceramics orthopaedic implants has been elaborately discussed. Furthermore, future prospects are proposed to promote further innovations in bioceramics research.     

Preceramic paper-derived Ti3Al(Si)C2-based composites obtained by spark plasma sintering

The paper describes the structure and properties of preceramic paper-derived Ti₃Al(Si)C₂-based composites fabricated by spark plasma sintering. The effect of sintering temperature and pressure on microstructure and mechanical properties of the composites was studied. The microstructure and phase composition were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. It was found that at 1150 °C the sintering of materials with the MAX-phase content above 84 vol% leads to nearly dense composites. The partial decomposition of the Ti₃Al(Si)C₂ phase becomes stronger with the temperature increase from 1150 to 1350 °C. In this case, composite materials with more than 20 vol% of TiC were obtained. The paper-derived Ti₃Al(Si)C₂-based composites with the flexural strength > 900 MPa and fracture toughness of >5 MPa m^1/2 were sintered at 1150 °C. The high values of flexural strength were attributed to fine microstructure and strengthening effect by secondary TiC and Al₂O₃ phases. The flexural strength and fracture toughness decrease with increase of the sintering temperature that is caused by phase composition and porosity of the composites. The hardness of composites increases from ~9.7 GPa (at 1150 °C) to ~11.2 GPa (at 1350 °C) due to higher content of TiC and Al₂O₃ phases.     

Effect of Nanoclay on the Mechanical,Thermal, and Water Absorption Properties of an UP-toughened Epoxy Network

Unsaturated polyester (UP)-toughened epoxy nanocomposites were prepared, and their effective mechanical and thermal properties were studied. Two types of organo-modified montmorillonite (OMMT) clays were used to prepare the nanocomposites. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis showed the formation of exfoliated silicate layers in the UP-toughened epoxy matrix. Mechanical tests revealed that nanocomposites (containing 1 wt% OMMT clay) showed an increase in tensile strength to 13.8%, flexural strength to 10%, and impact strength to 4% compared with an UP-toughened epoxy blend. The effect of different heating rates on the curing behavior of UP-toughened epoxy nanocomposites was investigated using non-isothermal differential scanning calorimetry. The data were interpreted using the Kissinger and Flynn–Wall–Ozawa models to find the curing reaction parameter. The water uptake behavior for nanocomposites increased with the addition of OMMTs. Scanning electron microscopy micrographs indicated morphological changes in the impact fractured samples of UP-toughened epoxy nanocomposites.     

Mechanical aspects of ceramic membrane materials

Interest in ceramic transport membrane materials has increased significantly leading also to questions with respect to mechanical reliability and robustness, hence, requiring knowledge of the mechanical properties. The current review focuses on the mechanical properties of such ceramics, emphasizing in particular relationships between mechanical properties, non-elastic effects, phase changes and materials’ stability. Room and elevated temperature application is considered with a main emphasis on elastic and creep deformation as well as fracture. Consideration is given to dense membranes as well as porous substrate materials for advanced asymmetric concepts. Properties are summarized for selected oxygen and proton conductors. Furthermore, mechanical properties of some selected porous ceramic and metallic substrate materials are given. In addition to the failure probability associated with the Weibull distribution of fracture stresses, creep rupture of dense materials and enhanced creep deformation of porous materials are aspects that need special consideration in the application of these materials in gas separation systems.     

Sintering,mechanical, electrical and oxidation properties of ceramic intermetallic TiC–Ti3Al composites obtained from nano-TiC particles

The paper discusses the development of a new material system for interconnect application in Solid Oxide Fuel Cells (SOFC) based on TiC–Ti₃Al. Nano-sized TiC powders utilized in this research were synthesized using carbon coated TiO₂ precursors from a patented process. The pressureless sintering of TiC–Ti₃Al in a vacuum was applied at temperatures between 1100 °C and 1500 °C and content of Ti₃Al was varied in the range of 10–40 wt%. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used for phase evaluation and sintering behavior. Relative density increased markedly with increasing sintering temperature because of grain growth and formation of the Ti₃AlC₂ secondary phase. Dense products (>95% TD) were prepared from nanosized TiC powders with 10 and 20 wt% Ti₃Al, but with about 8 to 10% porosity for 30 and 40 wt% Ti₃Al. The mechanical properties were determined from Vickers hardness and fracture toughness calculations. Vickers hardness decreased and fracture toughness increased with increasing Ti₃Al content. The electrical conductivity and oxidation behavior of TiC–Ti₃Al composites were investigated to evaluate the feasibility for SOFC interconnect application. The electrical conductivity measurements in the air at 800 °C for 100 h were made using the Kelvin 4-wire method.