Preparation and hierarchical porous structure of biomorphic woodceramics from sugarcane bagasse

Biomorphic woodceramics with controllable pore structure were prepared from sugarcane bagasse impregnated with epoxy resin followed by sintering at different temperatures. The phase composition, chemical composition, morphology and pore texture of the products were characterized by XRD, FTIR, SEM, mercury porosimetry and N₂ adsorption. The biomorphic woodceramics are typical non-graphitizable carbon and display a hierarchical porous structure from micrometer (0.6–21 μm) to nanometer scale (3.1–9.3 nm). The woodceramics retain the tubular structures of sugarcane bagasse before calcination at 1100 °C. Furthermore, an increase in the sintering temperature results in the decrease of BET surface area, average pore diameter and pore volume in the mesopore scale. This work provides a simple, economical, and environmentally friendly method for the production of hierarchical porous woodceramics. The final products have their potential applications as adsorbents, catalyst supports and filters.     

Synthesis of biomorphic SiC fabric ceramic from pre-processed ramie fibres

Biomorphic SiC fabric ceramic was synthesised by in situ reactive molten silicon infiltration process using artificial ramie fibres’ template, phenolic resin, and silicon. The phase compositions, microstructure, and physical characteristics of the biomorphic fabric ceramic were characterised and tested. The results show that the final ceramic retains the ramie fabric structure, and presents duplex microstructure including biomorphic SiC fibres and network SiC ceramic around the biomorphic fibres. This biomorphic SiC fabric ceramic is constituted by 95.8% of SiC, has a low density of 1.02?g?cm^?3 and a high porosity of 63.7%, and shows low linear shrinkages and better electrical resistivity along the fibre axis. The uniform and fine SiC particles with the size of ～4?µm indicate that the reaction–formation mechanism is the dissolution of carbon and the precipitation of SiC, without a second precipitation.     

活性污泥对管式多孔α-Al_2O_3陶瓷膜支撑体性能影响的初步研究

以剩余活性污泥作为支撑体的成孔剂,采用滚压成型及熔膜芯法制备管状多孔α-Al2O3陶瓷膜支撑体,研究了粘结剂羧甲基纤维素(CMC)和活性污泥的加入量对氧化铝陶瓷膜支撑体品质的影响。结果表明,随着成孔剂和粘结剂的增多,支撑体孔隙率和渗透通量呈增大趋势,孔隙率最大可达43.07%,纯水通量在0.4~1.0 MPa压力下变化范围为12 786.67~37 617.84 L/(m2·h·MPa)。     

活性污泥对管式多孔α-Al_2O_3陶瓷膜支撑体性能影响的初步研究

以剩余活性污泥作为支撑体的成孔剂,采用滚压成型及熔膜芯法制备管状多孔α-Al2O3陶瓷膜支撑体,研究了粘结剂羧甲基纤维素（CMC）和活性污泥的加入量对氧化铝陶瓷膜支撑体品质的影响。结果表明,随着成孔剂和粘结剂的增多,支撑体孔隙率和渗透通量呈增大趋势,孔隙率最大可达43.07%,纯水通量在0.4~1.0 MPa压力下变化范围为12 786.67~37 617.84 L/（m2·h·MPa）。     

Three‐dimensional pore structure and ion conductivity of porous ceramic diaphragms

The ion conductivity of two series of porous ceramic diaphragms impregnated with caustic potash was investigated by electrochemical impedance spectroscopy. To understand the impact of the pore structure on ion conductivity, the three‐dimensional (3‐D) pore geometry of the diaphragms was characterized with synchrotron x‐ray absorption tomography. Ion migration was calculated based on an extended pore structure model, which includes the electrolyte conductivity and geometric pore parameters, for example, tortuosity (τ) and constriction factor (β), but no fitting parameters. The calculated ion conductivities are in agreement with the data obtained from electrochemical measurements on the diaphragms. The geometric tortuosity was found to be nearly independent of porosity. Pore path constrictions diminish with increasing porosity. The lower constrictivity provides more pore space that can effectively be used for mass transport. Direct measurements from tomographs of tortuosity and constrictivity opens new possibilities to study pore structures and transport properties of porous materials.     

Preparation and characterization of pure SiC filters with an asymmetric structure

In this work, SiC filters with an asymmetric structure were successfully constructed, consisting of solid-state-sintered SiC (S–SiC) supports and in-situ synthesized SiC membranes. The S–SiC supports were prepared by a pressureless sintering technique. Following the preparation of the supports, SiC membranes ~30 μm in thickness were formed in-situ on their surfaces through a dip-coating process combined with carbothermal reduction. Using X-ray diffraction, only the peaks of the SiC phase were detected for both the S–SiC supports and the SiC membranes, indicating the high purity of the asymmetric SiC filters. The distribution of the pore throat size in the SiC membranes was narrow with an average value of ~130 nm, suggesting a high filtration precision. The flexural strengths of the S–SiC supports at room temperature and 1000 °C were 123.6 ± 18.1 MPa and 114.0 ± 4.5 MPa, respectively, enabling the asymmetric SiC filters to withstand high temperatures and high pressures during service. Moreover, asymmetric SiC filters presented excellent acid and alkali corrosion resistance, indicating their great potential for applications in corrosive environments.     

Velocity of elastic waves in porous ceramic materials: influence of pore structure

Abstract

A review has been undertaken of recently published data on ultrasonic velocity-porosity for a variety of porous ceramic materials, including information on pore structure. These experimental data have been compared with data calculated using a spheroidal pore model incorporating information on pore volume fraction, shape, and orientation. Good agreement is obtained between experimental and calculated values, especially when fractional porosity is less than about 0·25, even when a single 'effective' pore shape is employed in the calculation. The agreement improves if a different pore shape for each porosity level (point by point analysis) is used. The predictive ability of the spheroidal pore model is thus demonstrated.     

Characterization and oxidation properties of biomorphic porous carbon with SiC gradient coating prepared by PIP method

A biomorphic porous carbon coated with SiC (SiC/BPC) was prepared by controlled carbonizing native pine under Ar atmosphere and then processed with precursor infiltration-pyrolysis (PIP) of organosilane. Microstructure and component of SiC/BPC were analyzed by FT-IR, XRD, SEM and EDS (attached with line scanning program). The non-isothermal oxidation properties and mechanism of SiC/BPC were studied by TGA. The kinetic parameters were calculated through model-free kinetics methods. Experimental results showed that SiC/BPC had a topologically uniform interconnected porous network microstructure; the obtained gradient SiC coating on BPC surface was amorphous and combined well with the carbon surface, which can improve the oxidation resistance of BPC clearly. The non-isothermal oxidation reaction of SiC/BPC exhibited a partial self-accelerating characteristic. The oxidation process was complicated, firstly it was controlled by gas diffusion in coating, then controlled by chemical reaction, and at last it was controlled by gas diffusion and chemical reaction together, the corresponding effective activation energy was calculated also.     

Preparation of a novel BN/SiC composite porous structure

A kind of BN/SiC open cell ceramic foams were fabricated from complex co-polymeric precursors of polycarbosilane and tris(methylamino)borane [B(NHCH₃)₃] using a high pressure pyrolysis foaming technique. The as-fabricated foams exhibit cell sizes ranging from 1 to 5 mm with bulk densities varying from 0.44 to 0.73 g/cm³, depending on the proportion of the starting materials. Studies on microstructure and properties of the porous material shown that addition of BN into SiC can improve dramatically its oxidation resistance during 800–1100 °C and compression strength which was generally about a 5–10 times higher than that of a pure SiC foam.     

Preparation of biomorphic porous zinc oxide by wood template method

This paper presents an effective method to fabricate highly porous zinc oxide (ZnO) derived from different wood templates, where the microstructure features of wood template were well reproduced in the final product. Biomorphic ZnO was fabricated via the sol–gel method by the infiltration of the precursor sol into the wood template and the sintering of wood template at high temperature under air atmosphere. Many characterization methods such as x-ray diffraction (XRD), scanning electron microscopy (SEM) and pore size analyzer detection were used to investigate the crystalline phase and microstructure of the product as well as the pore size of biomorphic ZnO. In our work, highly porous ZnO derived from different wood templates had been prepared. The relevant results revealed that the specie of wood template and sintering temperature played vital roles in the pore size, specific surface area and pore volume of the product.     

Preparation and stereolithography of SiC ceramic precursor with high photosensitivity and ceramic yield

Stereolithography of ceramic precursors is a valuable additive manufacturing technology for complex ceramic parts. In this study, a new SiC ceramic precursor—liquid hyperbranched polycarbosilane (LHBPCS) grafting acrylate group was synthesized by chlorinating some Si–H groups of LHBPCS with Cl₂ followed by reacting with hydroxyethyl acrylate. The reaction processes and structures of intermediate reactant and target product were confirmed by FT-IR and ¹H NMR. According to photolithography experiment and hardness test under UV light, the synthesized LHBPCS had high photo-curing activity. Thermogravimetric analysis indicated it also possessed high ceramic yield (the ceramic yield at 1000 °C was 74.4%). After shaping with stereolithography, defect-free green bodies could be got. When heated to 1000 °C, the transparent yellow green bodies transformed into black SiC rich ceramic parts and 18.3–25.1% linear shrinkage associated with the precursor-to-ceramic conversion was observed. Because the shrinkage in the pyrolysis stage was nearly isotropic and the shrinkage was lower than other reported data, no obvious deformation or crack was found in the pyrolyzed parts.     

Preparation and characterisation of HA/TCP biphasic porous ceramic scaffolds with pore-oriented structure

Porous hydroxyapatite/tricalcium phosphate (HA/TCP) ceramic scaffolds with a uniform unidirectional pore structure were successfully fabricated by an ice-templating method by using Ca-deficient HA whiskers and phosphate bioglass. HA whiskers showed good dispersibility in the slurry and favoured the formation of interconnected pores in the scaffolds. Addition of bioglass powders enhanced the material sintering process and the phase transformation of Ca-deficient HA to β-TCP. Calcium-phosphate-based scaffolds with a composition from HA to an HA/β-TCP complex could be obtained by controlling the freezing moulding system and slurry composition. The fabricated scaffolds had a porosity of 75–85%, compressive strength of 0.5–1.0 MPa, and a pore size range of 130–200 µm.     

Synthesis and hierarchical pore structure of biomorphic manganese oxide derived from woods

Biomorphic manganese oxides on two different wood templates (fir and paulownia) were fabricated by infiltration with nitrate and subsequently calcination. X-ray diffraction (XRD) test and microscopy observation (FESEM and TEM) were employed to characterize the phase and structure of biomorphic manganese oxides. The pore structure of the resulting products was studied through mercury intrusion and nitrogen adsorption measurement. Infrared (IR) adsorption properties were investigated by Fourier Transmission Infrared (FTIR). The final oxide products contain hierarchical pore structure from μm to nm scale, and also show unique pore size and distribution with hierarchy on nanoscale derived from the specific wood template, the changeable connectivity of nanoscale pore channel controlled by calcinations temperature. The rise of temperature leads to diminishing of average pore diameter and volume but more uniform pore size distribution and higher degree of pore connectivity. The overall collapse in IR adsorption spectra of biomorphic manganese oxides with the rise of calcination temperature is related to the effect of nanoscale pore structure especially the increasing of pore connectivity.     

Preparation and characterization of novel porous metal/ceramic catalytic membrane materials

In order to obtain improved separation or catalytic activity, we propose a method to modify the surface of porous ceramic membranes by modifying the surface of sol particles. The key technical difficulty of this method is how to get appropriate ligands which can make metal ions adsorb on sol particles in the appropriate pH range in which the sol maintains its dynamic stability. Pd/γ-A1₂O₃ catalytic membrane materials with mesopore and a narrow pore size distribution were prepared by this method. Other kinds of metal/ceramic catalytic membrane materials such as Ni/γ-Al₂O₃, Pt/γ-Al₂O₃ can also be obtained by the same method.     

Control of pore structure during freeze casting of porous SiC ceramics by different freezing modes

The frozen moulds, including homogeneous, unidirectional and bidirectional freezing, were designed using materials with different thermal conductivities, and the temperature variations of the moulds and samples during the freezing process were simulated by finite element analysis. Highly porous SiC ceramics with significant differences in pore structure were fabricated by using the SiC/water slurries prepared via uniform or oriented freeze casting with various freezing modes, and porosity and compressive strength of the as-fabricated ceramics were investigated. The results showed that the pore structure of ceramics prepared by homogeneous freezing was relatively intricate and inconsistent, and had a higher compressive strength. In contrast, the pore structure of ceramics fabricated using bidirectional freezing mode was more ordered and higher porosity was observed. Moreover, porous ceramics prepared by unidirectional freezing mode exhibited a typical gradient structure with increased pore size from tens of micrometers in the bottom to hundreds of micrometers in the top.     

高活性木炭的制备与孔结构表征

介绍了二步炭化法制备高活性木炭工艺。研究了保温时间和温度对活性木炭吸附性能的影响,并通过ESEM和HRTEM等对其孔结构进行表征。结果表明:二步炭化法可很好地提高木炭的性能,可制得孔径主要集中在0.6～2.0nm的活性木炭;随着保温时间延长,活性木炭的比表面积、孔容积均增大。在较佳实验条件下,所制高活性木炭的比表面积、总孔容积和微孔容积分别为1288.4m2/g、0.784mL/g、0.407mL/g。     

Optimized vacuum/pressure sol impregnation processing of wood for the synthesis of porous,biomorphic SiC ceramics

Pine (Pinus silvestris) wood with shaped sample dimensions of 20 mm × 20 mm × 5 mm (axial) was selected as the raw material. Samples were dried and, for a half of the samples, resin extraction from the sample was applied. SiO₂ sol was prepared, and samples were impregnated under different vacuum/pressure conditions. Relative impregnation efficiency was calculated for impregnated samples and varied from 95 up to 105% of the theoretical value for different samples and impregnation conditions. Impregnation and drying procedures were repeated up to three times to increase the SiO₂ amount introduced in the sample. Impregnated samples were pyrolyzed at 500 °C under oxygen free atmosphere with the subsequent high temperature treatment at 1600 °C in an Ar atmosphere. Biomorphic SiC ceramics and its precursors were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). An experimental result shows that the optimized vacuum/pressure impregnation technique is highly effective for the introduction of SiO₂ in the wood.     

Improved mechanical strength and thermal resistance of porous SiC ceramics with gradient pore sizes

Thermal insulation applications of porous SiC ceramics require low thermal conductivity and high mechanical strength. However, low thermal conductivity and high mechanical strength possess a trade-off relationship, because improving the mechanical strength requires decreasing the porosity, which increases the thermal conductivity. In this study, we established a new strategy for improving both the mechanical strengths and thermal resistances of porous SiC ceramics with micron-sized pores by applying a double-layer coating with successively decreasing pore sizes (submicron- and nano-sized pores). This resulted in a unique gradient pore structure. The double-layer coating increased the flexural strengths and decreased the thermal conductivities of the porous SiC ceramics by 24–70 % and 29–49 % depending on the porosity (48–62 %), improving both their mechanical strengths and thermal resistances. This strategy may be applicable to other porous ceramics for thermal insulation applications.     

Fabrication and characterization of cordierite-bonded porous SiC ceramics

A reaction bonding technique was used for the preparation of cordierite-bonded porous SiC ceramics in air from α-SiC, α-Al₂O₃ and MgO, using graphite as the pore-forming agent. Graphite was burned out to produce pores and the surface of SiC was oxidized to SiO₂ at high temperature. With further increasing the temperature, SiO₂ reacted with α-Al₂O₃ and MgO to form cordierite. SiC particles were bonded by the cordierite and oxidation-derived SiO₂. The reaction bonding characteristics, phase composition, open porosity, pore size distribution and mechanical strength as well as microstructure of porous SiC ceramics were investigated. The pore size and porosity were strongly dependent, respectively, on graphite particle size and volume fraction. The porous SiC ceramics sintered at 1350 °C for 2 h exhibited excellent combination properties, the flexural strength of 26.0 MPa was achieved at an open porosity of 44.51%.     

Preparation and characterization of Beta/MCM-41composite zeolite with a stepwise-distributed pore structure

A Beta/MCM-41 composite zeolite with a stepwise-distributed pore structure was prepared with a silica-alumina source originated from alkaline treatment of zeolite Beta. The material was characterized by various techniques. The results indicated that this composite possesses a mesopore system of MCM-41 and the microporous structure of Beta zeolite. Hydrothermal stability and acidity was improved over MCM-41 due to the introduction of Beta building units into the mesopore walls. The composite was used as the support of a Pd-Pt catalyst for the hydrogenation of naphthalene in the presence and absence of 4, 6-dimethyldibenzothiophene. It was demonstrated that the catalyst has an enhanced activity and sulfur tolerance during naphthalene hydrogenation.