Fabrication of mullite-bonded porous silicon carbide ceramics by in situ reaction bonding

An in situ reaction bonding technique was developed to fabricate mullite-bonded porous silicon carbide (SiC) ceramics in air from SiC and α-Al₂O₃, using graphite as the pore-former. Graphite is burned out to produce pores and the surface of SiC is oxidized to SiO₂ at high temperature. With further increasing the temperature, the amorphous SiO₂ converts into cristobalite and reacts with α-Al₂O₃ to form mullite (3Al₂O₃·2SiO₂). SiC particles are bonded by the mullite and oxidation-derived SiO₂ to obtain porous SiC ceramics. The reaction bonding behavior, open porosity, pore size distribution and mechanical strength of porous SiC ceramics were investigated as a function of the sintering temperature, forming pressure and graphite content. In addition, the phase composition and microstructure were also studied.     

Ordered mesoporous carbon preparation by the in situ radical polymerization of acrylamide and its application for resorcinol removal

In this study, acrylamide (AM) was, for the first time, successfully used to synthesize ordered mesoporous carbon (OMC) through in situ polymerization inside SBA‐15 (Santa Barbara Amorphous type material) as a hard template. A straightforward and environmentally friendly method was proposed and verified with an emphasis on the precursor modification for the preparation of OMC. The influences of the structure and the amount of SBA‐15 on the OMC structure and adsorption capacity were evaluated. To improve the adsorption capacity and yield, the following three approaches were tried: (1) the use of concentrated sulfuric acid (H₂SO₄) to fix carbon and nitrogen, (2) the use of a crosslinking agent, and (3) the addition of melamine as a possible nitrogen source. The adsorption capacities for resorcinol were evaluated, and they showed an improvement of 37% in comparison with that of the commercially available granular activated carbon (27 mg/g). Well‐OMC materials were obtained with higher yields with H₂SO₄ and crosslinking agent compared with those obtained for the pure AM precursor. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43426.     

Novel two-step sintering and in situ bonding method for fabrication of ZrP2O7 ceramics

Sintering performance at high temperatures is a serious issue for tetravalent metal pyrophosphate MP₂O₇ ceramics (M = Ti, Zr, Hf, Ge, Sn, etc.). Herein, we investigated the influence of high synthesis temperatures and amounts of ZrP₂O₇ precursors on the properties of ZrP₂O₇ ceramics. A ZrP₂O₇ powder was first synthesised via a solid-state reaction; this powder was used in the fabrication of the ZrP₂O₇ ceramic using a combination of two-step sintering and in situ bonding using MgO as the sintering aid. The phase composition and microstructure of the ZrP₂O₇ powder as well as the ZrP₂O₇ ceramic were studied by X-ray diffraction and scanning electron microscopy. The physical properties and room-temperature thermal conductivity of the ZrP₂O₇ ceramic were investigated. The ceramic exhibited high thermal stability at 1350 °C. This study indicates that the mechanical properties of the ZrP₂O₇ ceramic can be enhanced while maintaining their low thermal conductivity by sintering it at 1300 °C with the addition of an appropriate amount of the ZrP₂O₇ precursors to the ZrP₂O₇ powder.     

Electrical,thermal, and mechanical properties of porous silicon carbide ceramics with a boron carbide additive

The effects of the boron carbide (B₄C) content and sintering atmosphere on the electrical, thermal, and mechanical properties of porous silicon carbide (SiC) ceramics were investigated in the porosity range of 58.3%–70.3%. The electrical resistivities of the nitrogen-sintered porous SiC ceramics (∼10^–1 Ω·cm) were two orders of magnitude lower than those of argon-sintered porous SiC ceramics (∼10¹ Ω·cm). Both the thermal conductivities (3.3–19.8 W·m^–1·K^–1) and flexural strengths (8.1–32.9 MPa) of the argon- and nitrogen-sintered porous SiC ceramics increased as the B₄C content increased, owing to the decreased porosity and increased necking area between SiC grains. The electrical resistivity of the porous SiC ceramics was primarily controlled by the sintering atmosphere owing to the N-doping from the nitrogen atmosphere, and secondarily by the B₄C content, owing to the B-doping from the B₄C. In contrast, the thermal conductivity and flexural strength were dependent on both the porosity and necking area, as influenced by both the sintering atmosphere and B₄C content. These results suggest that it is possible to decouple the electrical resistivity from the thermal conductivity by judicious selection of the B₄C content and sintering atmosphere.     

Enhancing performance of optical sensor through the introduction of polystyrene and porous structures

Simple and promising approaches for developing high‐performance Fe³⁺ sensors were proposed. Polyvinyl chloride (PVC) membrane containing pyrene as a fluorescent indicator was prepared via solvent‐cast method. Upon immersion into 1.0 mM Fe³⁺ solution, the fluorescence emission of the membrane decreased with the ratio of fluorescence intensities before and after (F₀/F) immersion of 1.25. The sensitivity enhancement was achieved through the introduction of polystyrene (PS) onto PVC and the introduction of porous structures. Polyvinyl chloride‐graft‐polystyrene copolymers (PVC‐g‐PS) were synthesized via Atom Transfer Radical Polymerization using PVC as macroinitiator. The grafting percentages of PS on PVC calculated from Nuclear Magnetic Resonance Spectroscopy were 17 and 41. The membrane prepared from low molecular weight copolymer showed higher sensing ability than that from PVC with the F₀/F value of 1.39. The increase in PS chain length did not significantly affect the fluorescence quenching. A Stern–Volmer quenching relationship was found with K_sv of 3.96 × 10² M^?1. The effect of porous structures on fluorescence quenching was studied by introducing Triton X‐100 as a porogen to PVC/pyrene solution. Attenuated total reflection Fourier transform infrared spectroscopy and Scanning Electron Microscopy analyses confirmed a complete removal of Triton X‐100 after 3 days of immersion in water. The porous membrane demonstrated an enhanced sensing performance with the F₀/F value of 1.46. PVC‐g‐PS/pyrene membrane exhibited highly sensitive and selective responses toward Fe³⁺ over Cu²⁺, Mg²⁺, Co²⁺, Zn²⁺, Ni²⁺, and Ag⁺. In addition, a good reversibility after five cycles of quenching and regeneration was obtained. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41759.     

Rheology,morphology, and mechanical properties of HMSPP/POE blends and its alternate layered foam

In this article, the multilayered foaming sheet with alternate layered structure was successfully prepared through multilayer co‐extrusion. The high melt strength polypropylene (HMSPP)/poly (ethylene‐co‐octene) (POE) blend and POE were designed as foaming layers and film layers, respectively. POE was added into HMSPP to reduce the crystalline degree and improve the processing performance. The rheological results indicated that the addition of POE had a little effect on relaxation process and the strain hardening behavior of HMSPP when the POE content was lower than 50%. The results of the foam morphology showed that the cell size and its distribution of the multilayered foaming sheet with alternate layers were better than that with single layer. In addition, the cell size reduced and the cell density increased with increasing the number of layers from 4 to 32. The mechanical properties of the multilayered foaming sheet with alternate layers also could be improved through assembling of foaming layers and film layers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41339.     

A facile,green, versatile protocol to prepare polypropylene‐g‐poly(methyl methacrylate) copolymer by water‐solid phase suspension grafting polymerization using the surface of reactor granule technology polypropylene granules as reaction loci

A facile and environment friendly process, called water‐solid phase suspension grafting polymerization, was developed to prepare polypropylene‐g‐poly(methyl methacrylate) (PP‐g‐PMMA) copolymer with a submicrometer microdomain. In this approach, graft polymerization was elaborately regulated to occur within micropores of polypropylene particles prepared by reactor granule technology. FTIR spectra of the samples after extraction demonstrated that PMMA was successfully grafted onto the PP. The results showed grafting percentage (GP) of PMMA increased with the increasing monomer ratios to PP and that could reach 13.6%. Whereas the grafting efficiency decreased as the monomer ratio increased. The addition of second monomer styrene improved GP up to 24.5%. Differential Scanning Calorimetry tests showed that the grafting of PMMA have a slight effect on the melting point and the relative crystallinity of PP. TEM micrographs demonstrated PMMA domains distributed in PP matrix with sizes ranging from about 100 to 300 nm. In addition, Shear viscosity increased with the growing GP indicated by rheological measurement. The preliminary evaluation showed PP‐g‐PMMA was effective in improving the compatibility of PP/acrylonitrile‐styrene‐acrylate blends. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Morphologies and properties of polycarbonate/polyethylene in situ microfibrillar composites prepared through multistage stretching extrusion

The sheets of polycarbonate (PC)/polyethylene (PE) in situ microfibrillar composites are successfully prepared directly through multistage stretching extrusion with an assembly of laminating‐multiplying elements (LMEs) instead of the secondary processing. The morphological development of the PC dispersed phase in PE matrix with increasing the number of LMEs during multistage stretching extrusion investigated by scanning electron microscope shows that core‐skin structure of the microfibrillar PC/PE composites during multistage stretching extrusion with 4 LMEs is weakened, and the diameter of the PC microfibrils is relatively more uniform, indicating that the shear field in LMEs greatly affects the morphology of PC dispersed phase in PE matrix. The tensile, crystalline, melting, orientation and rheological behavior of the PC/PE microfibrillar composites are also investigated. The results show that the PC microfibrils are helpful to increase complex viscosity and yield stress of the PE/PC composites. In addition, it is found that the glass transition temperature of PC in PE matrix reduced with increasing the number of LMEs during dynamic rheological testing. It is coincided with the results of DSC analysis of the PC/PE composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40108.     

High performance synthetic paper used for color printing based on ultrahigh molecular weight polyethylene/SiO2 by using TIPS method

The production of traditional cellulose paper not only consumes lots of timber, but also brings about some environmental issues. Therefore, it is being increasingly replaced by synthetic paper. In this study, ultrahigh molecular weight polyethylene (UHMWPE)/SiO₂ synthetic paper with high application performance was prepared by the thermally induced phase separation method using mineral oil as diluent. The corresponding properties of synthetic paper, including surface morphology, overall porosity, tensile strength, thermal stability, acid and alkali resistance, whiteness, and inkjet print effect were investigated respectively. The results show that the overall porosity of UHMWPE/SiO₂ synthetic paper is above 45%, and the tensile strength exceeds 4.3 MPa. UHMWPE/SiO₂ synthetic paper also presents light weight, as well as good resistance to heat, acid and alkali. Meanwhile, the average whiteness of the samples is up to 91.8%. The sample K‐50, which contains 31.5 wt % SiO₂, takes on the best print performance caused by its dense surface and higher SiO₂ content. It is indicated that UHMWPE/SiO₂ synthetic paper has good market prospects in the color printing. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41529.     

Fabrication and analysis of polymer microstructures through ion microprobe techniques

In this work, we explored the capabilities of energetic focused beams of light ions for the fabrication and analysis of microstructures produced on commercial polyethylene terephthalate (PET) foils. To that end, single lines and multi‐structure patterns were drawn directly on the foils using Proton Beam Writing (PBW) techniques followed by chemical etching. The characterization of the microstructures was carried out with on‐axis Scanning Transmission Ion Microscopy (STIM) employing H⁺¹, He⁺², and Li⁺³ ions in the MeV range. Scanning Electron Microscopy (SEM) was employed as well. The results show that a polymer like PET can be patterned trough a proper combination of irradiation parameters and etching times. However, aspect ratios obtained in this way are quite poor. Moreover, STIM images obtained from different regions of the ion energy spectra reveal patterns and cavities seen neither by conventional STIM, where the whole energy spectrum is used, nor by SEM. Moreover, striking differences are observed when different ions are used for STIM analysis. The results suggest that heavier ions provide additional information of the structures under analysis when compared with usual STIM employing protons. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43253.     

Compressive and thermal characterization of syntactic foams containing hollow silicon carbide particles with porous shell

Silicon carbide hollow particle (SiC_HS) reinforced vinyl ester matrix syntactic foams are prepared and characterized for compressive properties and coefficient of thermal expansion (CTE). Two types of SiC_HS were utilized in 60 vol % to prepare syntactic foams. These SiC_HS had ratio of inner to outer radius of 0.91 and 0.84 for the thin and thick walled particles. The specific compressive strength values were 33.4 and 38.8 kPa/kg/m³ and the specific compressive modulus values were 0.8 MPa/kg/m³ and 0.6 MPa/kg/m³ for the thin and thick walled SiC_HS‐filled syntactic foams, respectively. The shell of the hollow particles contained microporous voids, and the porosity was estimated as 16.6% and 24.8% in the walls of the thin and thick walled particles, respectively. The shell porosity adversely affected the specific compressive strength and the modulus of the syntactic foam. However, the SiC_HS‐filled syntactic foams exhibited low CTE values (26.7 and 15.9 × 10^?6/°C). These CTE values were 65.1% and 79.3% lower than the CTE of the neat resin. Such properties can be useful for applications where syntactic foams are exposed to high temperatures and dimensional stability is important. A theoretical model is used to estimate the porosity level in the SiC shells and estimate the effective mechanical properties of the porous SiC material that forms the particle shell. Such analysis can help in using the models as predictive tools to estimate the mechanical properties of syntactic foams. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40689.     

Preparation and properties of porous polytetrafluoroethylene hollow fiber membrane through mechanical operations

Porous polytetrafluoroethylene (PTFE) hollow fiber membranes were prepared from fine powder through a series of mechanical operations including paste extrusion, heat treatment, stretching and sintering. In contrast to conventional process, the heat treatment used in this study was performed at 200°C to 330°C (near the melting point) on the PTFE nascent hollow fiber (precursor of membrane). The results showed that the introduction of heat treatment step effectively improved the mechanical properties of precursors, the ultimate stress and strain increased observably with heat treatment temperature, which was beneficial to subsequently stretching precursors to make them porous. Furthermore, the morphological changes and improvement of membrane properties caused by stretching operation were investigated for porous PTFE hollow fiber membrane having finer pore size and higher porosity. The porous microstructure of nodes interconnected by fibrils varied depending on the stretching conditions, such as the stretching temperature, rate, and ratio. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42696.     

Preparation of a hydrophobically enhanced antifouling isotactic polypropylene/silicone dioxide flat‐sheet membrane via thermally induced phase separation for vacuum membrane distillation

Isotactic polypropylene (iPP) hydrophobic flat‐sheet membranes were fabricated for use in vacuum membrane distillation (VMD) through a thermally induced phase‐separation process with dispersing hydrophobically modified SiO₂ nanoparticles in the casting solution to achieve a higher hydrophobicity and to sustain a stable flux in VMD. The contact angle (CA) measurements indicated that the incorporation of nano‐SiO₂ into a casting solution mixture containing 20 wt % iPP had a 20.9% higher CA relative to that of SiO₂‐free membranes. The addition of nano‐SiO₂ also induced morphological changes in the membrane structure, including changes in the pore size distribution, porosity, and suppression of macrovoids. The pore size distribution of the iPP–SiO₂ membranes became narrower compared with that of the SiO₂‐free membranes, and the porosity also improved from 35.45 to 59.75% with SiO₂ addition. The average pore size and maximum pore size of the iPP–SiO₂ membranes both decreased. The ability of the membranes to concentrate an astragalus aqueous solution (a type of traditional Chinese medicine) with VMD was investigated. The surface hydrophobicity and antifouling performance of the iPP–SiO₂ membranes improved with nano‐SiO₂ addition to the membrane casting solution. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42615.     

The role of two different internal donors (phthalate and 1,3‐diether) on the formation of surface structure in MgCl2‐supported Ziegler–Natta catalysts and their catalytic performance of propylene polymerization

The role of two different internal donors [a phthalate (diisobutylphthalate) and a 1,3‐diether (2,2‐diisobutyl‐1,3‐dimethoxypropane)] on the formation of surface structure in MgCl₂‐supported Ziegler–Natta catalysts and their catalytic performance of propylene polymerization was investigated by comparing and correlating the catalyst structures and the polymerization characteristics. In the catalyst formation, the 1,3‐diether had better affinity for the MgCl₂ surface than the phthalate and the 1,3‐diether generated the (110) surface more than the (104) surface while the phthalate generated both the (110) and (104) surfaces of MgCl₂. With both donors introduced, the (110) and (104) surfaces were generated simultaneously, although the (110) surface was dominant due to the higher affinity via the 1,3‐diether. In addition, it seemed probable that the active sites formed on the (110) plane showed isospecific characteristics in the presence of a donor while those formed on the (104) plane could be isospecific regardless of a donor. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40536.     

Recycling of waste red mud for fabrication of SiC/mullite composite porous ceramics

SiC/mullite composite porous ceramics were fabricated from recycled solid red mud (RM) waste. The porous ceramics were formed using a graphite pore forming agent, RM, Al(OH)₃ and SiC in the presence of catalysts. The influence of firing temperature and the pore-forming agent content on the mechanical performance, porosity and the microstructure of the porous SiC ceramics were investigated. Optimal preparation condition were determined by some testing. The results indicated that the flexural strength of specimens increased as a function of firing temperature and a reduction in graphite content, which concomitantly decreased porosity. The ceramic prepared under optimal conditions having 15?wt% graphite and sintered at 1350?°C, demonstrated excellent performance. Under optimal preparation conditions the flexural strength and porosity of the ceramic were 49.4?MPa and 31.4%, respectively. Scanning electron microscopy observation result showed that rod-shape mullite grains endowed the samples with high flexural strength and porosity. X-ray diffraction analysis indicated that the main crystallization phases of the porous ceramics were 6H-SiC, mullite, cristobalite and alumina. This work demonstrates that RM can be sucessfully reused as a new raw material for SiC/mullite composite porous ceramics.     

Fabrication of carbon-coated boron carbide particle and its role in the reaction bonding of boron carbide by silicon infiltration

To tackle the dissolution problem of boron carbide particles in silicon infiltration process, carbon-coated boron carbide particles were fabricated for the preparation of the reaction-bonded boron carbide composites. The carbon coating can effectively protect the boron carbide from reacting with liquid Si and their dissolution, thus maintaining the irregular shape of boron carbide particles and preventing the growth of boron carbide particles and reaction formed SiC regions. Furthermore, the nano-SiC particles, originated from the reaction of the carbon coating and the infiltrated Si, uniformly coated on the surfaces of boron carbide particles, thus forming a ceramic skeleton of the nano-SiC particles-coated and -bonded boron carbide particles. The Vickers hardness, flexural strength and fracture toughness of the composites can be increased by 26 %, 45 %, and 37 % respectively, by using carbon-coated boron carbide particles as raw materials.     

Fabrication by photoinitiated polymerization and characterization of millimeter‐size poly(divinyl benzene) hollow foam shells

In this study, millimeter‐size compound droplets were prepared easily by a one‐step microfluidic method. We varied the diameter and wall thickness of the shells over a wide range by setting the flow rate. Poly(divinyl benzene) (PDVB) shells with a 3–4.8 mm diameter were fabricated through photopolymerization and supercritical drying. The gel point of photopolymerization was monitored by a rotational rheometer. Moreover, the influence of the oil‐soluble photoinitiator phenyl bis(2,4,6‐trimethyl benzoyl) phosphine oxide (BAPO) on the properties of the foam shell were investigated by transmission electron microscopy, scanning electron microscopy, and nitrogen sorption measurements. Significant differences in the mechanical properties and porous features were obtained for different BAPO concentrations. The surface areas of the foam shells decreased, and the densities of the foam shells increased with increasing BAPO concentration. In addition, the nonconcentricity and out‐of‐roundness values were mainly less than 7 and 3%, respectively, for most of the shells. The results indicate that the PDVB hollow foam shells are a promising inertial fusion energy target. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41625.     

Extrusion of highly porous silicon nitride ceramics with bimodal pore structure and improved gas permeability

Highly porous Si₃N₄ ceramics with bimodal pore structure were prepared by the extrusion processing with petroleum coke of 30 μm as pore‐maker. The microstructure, mechanical strength, and gas permeability were investigated. The microstructure with petroleum coke contained not only numerous fine pores by interlocking the high aspect ratio β‐Si₃N₄ grains, but also some large pores of 15‐25 μm left by the burnout of petroleum coke. The resultant samples obtained an improved gas permeability of 1.2 × 10^?12 m², which is approximately two times that of samples without petroleum coke addition. Furthermore, the mechanical strength is still superior even at a porosity of 67% in comparison with the other porous ceramics used in the current diesel particulate filter.     

Epoxy shape‐memory polymer reinforced by thermally reduced graphite oxide: Influence of processing techniques

In this article, epoxy shape‐memory polymer (ESMP) reinforced with 1 wt % thermally reduced graphite oxide (TrGO) was fabricated by solution blending and three‐roll mill (TRM) mixing, respectively. Both blending techniques allowed a uniform TrGO dispersion in ESMP matrix, and the TRM mixing lead to an exfoliation of the TrGO worms. Compared with pristine ESMP, the TrGO/ESMP composites showed 36.4–41.1% increase in Young's modulus and 38.1–44.1% improvement in tensile strength. The TrGO/ESMP composite fabricated by TRM mixing had a T_5% (the temperature where the material lost 5% of its initial weight) 16.4°C higher than pure ESMP. Compared with pure ESMP, a significant improvement of recovery force by 84.4% and 311.1% was obtained by TrGO/ESMP composite fabricated by solution blending and TRM mixing, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42502.     

Sintering and characterization of in situ formed porous cordierite ceramics with nano boehmite additions

In this study, we investigated the effect of sintering temperature and nano boehmite additions on the phase composition, densification, and mechanical properties of porous cordierite ceramics. Ceramic samples were sintered at temperatures ranging from 1200 to 1400°C. Carbon powder was used as a pore forming agent to improve the porosity of the ceramic structure. Nano boehmite and carbon additions significantly enhanced ceramic porosity and average pore size in sintered samples. The bulk density and apparent porosity of the sintered samples were found to be 0.96–1.53 g/cm³ and 42.3%–65.6%, respectively. Sintered samples had cold crushing strengths of 1.5–14.3 MPa. The microstructure obtained by scanning electron microscopy was used to measure average pore size in sintered samples and was found to be 41.93 µm for stoichiometric composition (SC), 67.72 µm for SC and nano boehmite, and 102.98 µm for SC, nano boehmite, and carbon. The microstructure of the sintered samples revealed that the crystallinity of the in situ formed phases increased with the increase in nano boehmite additions.