Porous SiC using polycarbosilane/camphene solutions: Roles of freeze casting parameters

In order to control the pore characteristics and macroscopical performance of porous ceramics, roles of the freeze casting parameters are the key points. Herein, aligned dendritic porous SiC was fabricated by freeze casting of PCS-camphene solutions with different solid loading, freeze front velocity, temperature gradient, and freezing temperature. Influence of these parameters on the microstructure and compressive strength of porous SiC was investigated. With increasing the PCS content, freeze temperature, freeze front velocity or temperature gradient, degree of undercooling of the camphene was increased, resulting in the formation of smaller pore size, decreased porosity and increased compressive strength. Compared to variables of freeze temperature and temperature gradient, increased freeze front velocity was more efficiency in improving the compressive strength of porous SiC, owing to the formation of smaller pore size and longer secondary dendritic crystals. Promising micron-sized porous SiC with high porosity (79.93 vol%) and satisfactory strength (15.84 MPa) was achieved for 10% PCS-camphene solution under optimized freezing conditions.     

Low thermal conductivity in porous SiC–SiO2–Al2O3–TiO2 ceramics induced by multiphase thermal resistance

The introduction of multiple heterogeneous interfaces in a ceramic is an efficient way to increase its thermal resistance. Novel porous SiC–SiO₂–Al₂O₃–TiO₂ (SSAT) ceramics were fabricated to achieve multiple heterogeneous interfaces by sintering equal volumes of SiC, SiO₂, Al₂O₃, and TiO₂ compacted powders with polysiloxane as a bonding phase and carbon as a template at 600 °C in air. The porosity could be controlled between 66% and 74% by adjusting the amounts of polysiloxane and the carbon template. The lowest thermal conductivity (0.059 W/(m·K) at 74% porosity) obtained in this study is an order of magnitude lower than those (0.2–1.3 W/(m·K)) of porous monolithic SiC, SiO₂, Al₂O₃, and TiO₂ ceramics at an equivalent porosity. The typical specific compressive strength value of the porous SSAT ceramics at 74% porosity was 3.2 MPa cm³/g.     

Crushing behavior of alumina inclusions with different porosity during hot compression

Alumina inclusions in commercial as-cast 2.25Cr1Mo0.25V aluminum deoxidized steel exhibited a feature of porous structure. In order to investigate the crushing characteristics of alumina inclusion during hot working, a series of alumina blocks with different porosity whose properties are similar to the alumina inclusions in ingots were prepared using spark plasma sintering. The crushing behavior of alumina blocks during hot compression with quasi-static load was studied. A prediction model of compressive strength of alumina inclusions considering apparent porosity was established on basis of hyperbolic sine Arrhenius equation. A novel crushing mode diagram for alumina inclusions characterized by Z parameter was proposed. The crushing mechanism of alumina inclusions under different deformation parameters was clarified by fracture characteristics. The results showed that the hot compression process of alumina presented a typical brittle fracture, the compressive strength was more sensitive to deformation conditions at lower apparent porosity as compared with the conditions of higher apparent porosity. With the increase of Z, the crushing mode of alumina inclusions gradually changed from intergranular fracture to transgranular fracture.     

Fabrication of Al2O3–ZrO2 ceramics with high porosity and strength

This study describes the synthesis of ceramics, in which a micrometre-sized Al₂O₃–ZrO₂ nanopowder was used as an oxide base for the hardening of the materials. To a suspension of this mixed metal oxide, the pore-forming crystallisation additives camphor and carbamide were added to produce ceramics with thin permeable pores. Camphor crystallised in the oxide suspension in the form of single pentagonal stars and сarbamide crystallised in the form of thin elongated needles. The use of the different crystallisation additives allowed the formation of ceramics after sintering that have both permeable and complex pore morphologies, where anisotropic properties were observed using carbamide as an additive but not when camphor was used. The total porosity of the resulting ceramics was 51.3%, with a compressive strength in the range of 17.3–92.3 MPa.     

龙门山前侏罗系沙溪庙组致密砂岩储层叠前地震预测

龙门山前侏罗系沙溪庙组致密砂岩横向变化快、非均质性强、孔隙结构复杂，储层与围岩阻抗差异小，岩石物理规律不清，且地震叠前道集资料品质差、测井横波资料匮乏，优质储层预测困难。针对以上问题，通过叠前反褶积、阿尔法滤波、剔除拟合振幅补偿优化处理了叠前CRP道集，采用改进的Xu-White模型预测了横波，并通过贝叶斯稀疏脉冲反演获得了叠前弹性参数VP/VS，预测了砂体边界，最后在砂体边界控制下，利用蒙特卡罗—贝叶斯分类方法反演了孔隙度，预测了致密砂岩有利储层发育区。研究表明：贝叶斯稀疏脉冲反演简化了稀疏脉冲反演过程，求解更稳定，砂岩边界控制下的孔隙度反演排除了泥岩影响，提高了孔隙度预测精度，该技术在龙门山前侏罗系沙溪庙组致密砂岩有利储层预测中取得了较好的效果，具有一定的推广应用价值。     

Petrographic and petrophysical characterization of some Paleozoic rocks,Um Bogma area,Southwest Sinai,Egypt

Sixty-two samples were collected from the five formations at Um Bogma area, (Southwest Sinai, Egypt). Nine samples were collected from Sarabit El Khedim Formation, ten samples were collected from Abu Hamata Formation, eighteen samples were collected from Adedia Formation, eight samples were collected from Um Bogma Formation and eighteen samples were collected from Abu Thora Formation.The Paleozoic rocks at Um Bogma area, consist mainly of sandstones, siltstones, shales, limestone and dolostones, which are unconformably overlie igneous and metamorphic rocks (granite, diorite and gneiss) of Precambrian age.The petrographic studies were applied to identify different rock units, different facies and its diagenetic history and to reveal its effect on the storage capacity properties. Different types of porosity (oversized, intergranular, fracture and vuggy porosities) have been identified based on the petrographic investigation of the studied thin sections.The Paleozoic sandstone rock samples are characterized by porosity average about 19% for Facies 1 (quartz wack) and about 18%for Facies 2 (quartz arenite) and permeability average 420?mD for Facies 1 (quartz wack) and 690?mD for Facies 2 (quartz arenite), so these rocks can be considered as good reservoir rocks. The Paleozoic carbonate rock samples (Facies 3) are characterized by poor porosity (less than 7%) and very low permeability (less than 0.5?mD), which caused by matrix and diagenetic processes and refer to bad reservoir rocks.Porosity can be linked to the two derived electrical properties (formation resistivity factor and electrical tortuosity) of the studied Paleozoic rocks at Um Bogma area. The electrical tortuosity has significant effects on both permeability and formation resistivity factor. The permeability decreases with increasing electrical tortuosity and the relation between both of them is inverse relationship with good coefficient of correlation. The permeability decreases with increasing electrical tortuosity and the relations between both of them are inverse relationships with high coefficient of correlation. The formation resistivity factor increases with increasing electrical tortuosity and the relations between both of them are positive relationships with a fair to very high coefficient of correlation.     

Microwave and conventional treatment of low-cement high-alumina castables with different water-to-cement ratio; Part II. Dehydration

Modern refractory castables contain between 3.5 and 5?wt.-% water that is necessary for sufficient flow during emplacement and for the formation of hydrate phases, necessary for the green strength of the material. Prior to the high temperature use of this material, it must be dried very carefully to avoid explosive spalling.This paper will demonstrate that beside conventional drying of pre-shaped materials in resistance furnaces microwave radiation is an energy saving and rapid method to remove pore water as well as hydrate bond water from the castable. In comparison to resistance furnaces, the use of microwave radiation does not affect the castable properties as there are mechanical strength (MOR, CCS), open porosity and pore size distribution. This study proved microwave radiation as valuable alternative with a series of tabular alumina based low cement castables (LLC) in which the water-to-cement-ratio (wcr = 0.64, 0.75, 0.82 and 1.13) was systematically altered by changing the cement concentration at constant mixing water concentration of 4.5%.     

Application of grits waste as a renewable carbonate material in manufacturing wall tiles

This work focuses on the reuse of grits waste, from cellulose industry, as a raw material to replace traditional carbonate material in ceramic wall tiles. Wall tile formulations bearing up to 15?wt% of the grits waste were prepared for replacement of calcareous. The tile manufacturing route consisted of dry powder granulation, uniaxial pressing, and firing at temperatures ranging from 1100?°C to 1180?°C by using a fast-firing cycle. The wall tile specimens were tested to determine their physical and mechanical properties (linear shrinkage, water absorption, apparent porosity, apparent density, breaking strength, and flexural strength). The firing behavior, phase transformations, and microstructure were evaluated by dilatometry, XRD, and SEM. The results showed that the fired wall tile specimens are composed of anorthite and quartz, as major mineral phases, and mullite as a minor phase. It was found that the grits waste had a positive influence on the properties and microstructure of the wall tile specimens. The results also revealed that the grits waste from cellulose industry could be used as a total replacement of traditional calcareous material in wall tile formulations.     

Synthesis and electrochemical performance of three-dimensional ordered hierarchically porous Li4Ti5O12 for high performance lithium ion Batteries

In this work, a three-dimensional ordered hierarchically porous (3DOHP) Li₄Ti₅O₁₂ that possesses inner-particle mesopores resulting from a soft template method and a three-dimensional ordered macroporous (3DOM) Li₄Ti₅O₁₂ using polystyrene spheres as a hard template have been synthesized. Both 3DOM Li₄Ti₅O₁₂ and 3DOHP Li₄Ti₅O₁₂ have ordered macropores and interconnected skeletons with a regular periodicity revealed by SEM and TEM observations. The specific surface area of 3DOHP Li₄Ti₅O₁₂ is up to 135 m² g^?1 which is much higher compared with that of 3DOM Li₄Ti₅O₁₂ because of the existence of inner-particle mesopores. Attributed to the higher surface area and smaller crystal grain size, more excellent cycle performance and rate capability are obtained for 3DOHP Li₄Ti₅O₁₂ compared to 3DOM Li₄Ti₅O₁₂. In addition, the hierarchically porous structure of 3DOHP Li₄Ti₅O₁₂ can meet rapid insertion and deinsertion of lithium ion even at extremely high rate. It is apparent that 3DOHP Li₄Ti₅O₁₂ has a lower total resistance and faster Li⁺ diffusion coefficient compared to 3DOM Li₄Ti₅O₁₂ according to electrochemical impendence spectroscopy analysis.     

Capillary effects on flax fibers – Modification and characterization of the wetting dynamics

Introducing bio-based composites has now become an opportunity of development for industry. Accordingly, Liquid Composite Moulding (LCM) processes are increasingly used for manufacturing those composites, mainly in the transportation industry, since they are considered as effective and low cost routes to manufacture bio-based composites fitting high quality requirements, even for parts with complex shape. However observations of a large amount of voids in bio-based composites call for an improved understanding of the local wetting phenomena that occur during impregnation of the natural reinforcements. The purpose of the present work is to study the influence of flax fiber surface chemistry on the local wetting dynamics. Flax reinforcements were submitted to a thermal treatment to modify the chemical composition of fiber surface. In order to analyze the fiber’s wetting behavior, some methods for measuring apparent static contact angles and surface energy were firstly validated on solids of defined geometry, and subsequently applied to untreated and treated flax fibers. The Owens–Wendt’s approach was used to determine both components of apparent surface energy, indicating polar and dispersive interactions in materials. Subsequently dynamic tests were carried out on both types of chopped flax fibers in order to evaluate apparent advancing dynamic contact angles. Considerations about morphological effects have also been included. Finally bio-based composite plates reinforced with untreated and treated flax quasi-UD were simultaneously fabricated by LCM process, and observation of the porosities highlighted some benefits of using treated flax fibers.