Gypsum-based Silica Gel Humidity-controlling Composite Materials:Preparation,Characterization,and Performance

Gypsum was used as substrate,and silica gel was mixed into substrate at a certain mass ratio to prepare humidity-controlling composites;moreover,the moisture absorption and desorption properties of gypsum-based composites were compared with adding different silica gel particle size and proportion.The morphological characteristics,the isothermal equilibrium moisture content curve,moisture absorption and desorption rate,moisture absorption and desorption stability,and humidity-conditioning performance were tested and analyzed.The experimental results show that,compared with pure-gypsum,the surface structure of the gypsum-based composites is relatively loose,the quantity,density and aperture of the pores in the structure increase.The absorption and desorption capacity increase along with the increase of silica gel particle size and silica gel proportion.When 3 mm silica gel particle size is added with a mass ratio of 40%,the maximum equilibrium moisture content of humidity-controlling composites is 0.161 g/g at 98% relative humidity(RH),3.22 times that of pure-gypsum.The moisture absorption and desorption rates are increased,the equilibrium moisture absorption and desorption rates are 2.68 times and 1.61 times that of pure-gypsum at 58.5% RH,respectively.The gypsum-based composites have a good stability,which has better timely response to dynamic humidity changes and can effectively regulate indoor humidity under natural conditions.

Effect of Hybridization on the Mechanical Properties of Pineapple Leaf Fiber/Kenaf Phenolic Hybrid Composites

In this study,pineapple leaf fiber(PALF),kenaf fiber(KF)and PALF/KF/phenolic(PF)composites were fabricated and their mechanical properties were investigated.The mechanical properties(tensile,flexural and impact)of the PALF/KF/PF hybrid composites were investigated and compared with PALF/KF composites.The 3P7K exhibited enhanced tensile strength(46.96 MPa)and modulus(6.84 GPa),flexural strength(84.21 MPa)and modulus(5.81 GPa),and impact strength(5.39 kJ/m2)when compared with the PALF/PF and KF/PF composites.Scanning electron microscopy(SEM)was used to observe the fracture surfaces of the tensile testing samples.The microstructure of the 7P3K hybrid composite showed good interfacial bonding and the addition of KF improved the interfacial strength.It has been concluded that the 3P7K ratio allowed obtaining materials with better mechanical properties(tensile,flexural and impact strengths)than PALF/PF and KF/PF composites.The results obtained in this study will be used for further comparative study of untreated hybrid composites with treated hybrid composites.

Fluxing Agents on Ceramification of Composites of MgO-Al2O3-SiO2/Boron Phenolic Resin

Fluxing agents of zinc borate, antimony oxide, galss frit A and glass frit B, with different melting or softening point temperatures, were added into MgO-Al_2O_3-SiO_2/boron phenol formaldehyde resin（MAS/BPF） composites to lower the formation temperature of eutectic liquid phase and promote the ceramification of ceramifiable composites. The effects of fluxing agents on the thermogravimetric properties, phase evolution, and microstructure evolution of MAS/BPF composites were characterized by TG-DSC, XRD and SEM analyses. The results reveal that the addition of a fluxing agent highly reduces the decomposition rate of MAS/BPF composites. Fluxing agents lower the formation temperatures of liquid phases of ceramifiable MAS/BPF composites obviously, and then promote the ceramification and densification process. The final residues of composites are ceramic surrounded by large amount of glass phases.

Ceramification of Composites of MgO-Al_(2)O_(3)-SiO_(2)/Boron Phenolic Resin with Different Calcine Time

The ceramifiable polymer composite of MgO-Al_(2)O_(3)-SiO_(2)/boron phenolic resin(MAS/BPF)with 40wt%of inorganic fillers was calcined at 1200℃for different time to promote ceramification of ceramifiable composite and improve heat resistance.The effects of different calcine time on the macroscopical morphology,mass loss,phase evolution,microstructure and chemical bond evolution of MAS/BPF composites were characterized by XRD,XPS,and SEM analyses.The experimental results reveal that the increase of calcine time result in the fewer holes,relatively denser and smoother top layer of MAS/BPF composites and protect the interior from deeper decomposition.The final residues of composites are amorphous carbon and C-O-Si-Al-Mg ceramic.And MAS/BPF composites show excellent mass stability,low shrinkage and self-supporting features after 2 h holding compared with BPF composites without 40wt%of inorganic fillers.

Property of three-dimensional silica composites

Silica fibers-reinforced, fused silica composites were fabricated with repeated vacuum-assisted liquid-phase infiltration. The mechanical properties, thermal properties, and ablative properties of the samples were evaluated. The effect of the silica fiber content and treatment temperature on the flexural strength of the three-dimensional SiO2 （3-D SiO2） composites also was investigated. The SiO2 composites show good mechanical properties and excellent ablative performance. The flexural strength increases with an increase in silica fiber content, and decreases with an increase in treatment temperature. When the volume fraction of the silica fiber is 50vo1% and the treatment temperature is 700℃ the flexural strength of the composites reaches a maximum value of 78 MPa. By adding cyclohexanone surfactant, the infiltration property can be largely improved, resulting in the density of SiO2 composites increasing up to 1.65 g/cm^3. The fracture surfaces of the flexural specimens observed using SEM, show that the pseudoplasticity and the toughening mechanisms of the composites are caused by absorption of a lot of energy by interface debonding and fiber pulling out.

Effect of electropolymer sizing of carbon fiber on mechanical properties of phenolic resin composites

Carbon fiber/phenolic resin composites were reinforced by the carbon fiber sized with the polymer films of phenol, m-phenylenediamine or acrylic acid, which was electropolymerized by cyclic voltammetry or chronopotentiometry. The contact angles of the sized carbon fibers with deionized water and diiodomethane were measured by the wicking method based on the modified Washburn equation, to show the effects of the different electropolymer film on the surface free energy of the carbon fiber after sizing by the electropolymerization. Compared with the unsized carbon fiber, which has 85.6°of contact angle of water, 52.2°of contact angle of diiodomethane, and 33.1 mJ/m2 of surface free energy with 29.3 mJ/m2 of dispersive components (γL) and 3.8 mJ/m2 of polar components (γsp), respectively. It is found that the electropolymer sized carbon fiber tends to reduce the surface energy due to the decrease of dispersiveγL with the increase of the polymer film on the surface of the carbon fiber that plays an important role in improving the mechanical properties of carbon/phenolic resin composites. Compared with the phenolic resin composites reinforced by the unsized carbon fiber, the impact, flexural and interlaminar shear strength of the phenolic resin composites were improved by 44 %, 68% and 87% when reinforced with the carbon fiber sized by the electropolymer of m-phenylenediamine, 66%, 100%, and 112% by the electropolymer of phenol, and 20%, 80 %, 100% by the electropolymer of acrylic acid. The results indicate the skills of electropolymerization may provide a feasible method for the sizing of carbon fiber in a composite system, so as to improve the interfacial performance between the reinforce materials and the matrix and to increase the mechanical properties of the composites.

Effects of precoating and calcination on microstructure of 3D silica fiber reinforced silicon nitride based composites

Three-dimensional silica fiber reinforced silicon nitride based composites were fabricated by preceramic polymer infiltration and pyrolysis method using perhydropolysilazane as a precursor. The effects of precoating and high temperature calcination on the microstructures of the composites were investigated by scanning electron microscopy. For the composite without a precoating, the fracture surface is plain, and the fiber/matrix interfaces become very unclear after calcination at 1 600 ℃ due to intense interfacial reactions. The composite with a precoating shows tough fracture surface with distinct fiber pull-outs, and the fiber/matrix interfaces are still clear after calcination at 1 600 ℃. It is the appropriate precoating process that contributes to the good interfacial microstructures for the composite.

Processing and performance of 2D fused-silica fiber reinforced porous Si_3N_4 matrix composites

Two-dimension （2D） fused-silica fiber reinforced porous silicon nitride matrix composites were fabricated using slurry impregnation and cyclic infiltration with colloidal silica sol. The microstructure and fracture surface were characterized by SEM, the mechanical behavior was investigated by three-point bending test, and the dielectric constant was also measured by impedance analysis. The microstructure showed that the fiber and the matrix had a physical bonding, forming a clearance interface. The mechanical behavior suggested that the porous matrix acted as crack deflection, and the fracture surface had a lot of fiber pull-out. However, the interlaminar shear strength was not so good. The dielectric constant of the composites at room temperature was about 2.8-3.1. The relatively low dielectric constant and non-catastrophic failure indicated the potential application in the radome materials field. 2008 University of Science and Technology Beijing. All rights reserved.

Mechanical Properties of Phenolic-Resin Composites Reinforced with CF/BF Interlayer Hybrid Fibers

Phenolic-resin composites reinforced with carbon fiber（CF） and basalt fiber（BF） interlayer hybrid fibers plain fabric were fabricated.The tensile strength,compressive strength and interlaminar shear strength of the prepared composites were studied.The results indicated that hybrid fibers reinforced composites possessed the advantages of both CF and BF.When resin content was 35% by volume fraction,the comprehensive mechanical performance of BF/CF reinforced phenolic resin composites reached the optimal values with the warp and weft direction tensile strength,compressive strength and interlayer shear strength being 252 MPa and 487 MPa,105 MPa and 129 MPa,21 MPa and 20 MPa,respectively.The scanning electron microscope（SEM） observations showed that the BF/CF hybrid fibers reinforced composites had better interfacial adhesion.

Corrigendum to“Effect of organo-modified montmorillonite nanoclay on mechanical,thermal and ablation behavior of carbon fiber/phenolic resin composites”[Defence Technol 17(3)(June 2021)812e820]

Due to editing errors,the ordinate and unit of Fig.5(a)in the article were incorrect.The correct ordinate of Fig.5(a)should be Flexural strength(MPa).In the published article<Effect of organo-modified montmorillonite nanoclay on mechanical,thermal and ablation behavior of carbon fiber/phenolic resin composites>.

The Impact Compression Behaviors of Silica Nanoparticles—Epoxy Composites

The compressive properties of epoxy with different silica nanoparticles (SiO2 nanoparticles) contents at quasi-static and high strain rates loading were investigated via experiment. This article evaluates the compressive failure behaviors and modes at different SiO2 nanoparticles contents and different strain rates. The results indicated that the stress strain curves were sensitive to strain rate, and the compressive failure stress of composites with various SiO2 nanoparticles contents increased with the strain rates, and it increased along with SiO2 nanoparticles contents and then declined. The compressive failure stress and the compressive failure modes of the composites were apparently different from the change of SiO2 nanoparticles contents.

Titania-Silica Composites: A Review on the Photocatalytic Activity and Synthesis Methods

The photocatalyic activity of titania is a very promising mechanism that has many possible applications like purification of air and water [1]-[4]. To make it even more attractive, titania can be combined with silica to increase the photocatalytic efficiency and durability of the photocatalytic material, while lowering the production costs [1]. In this article, relevant literature is reviewed to obtain an overview about the chemistry and physics behind some of the different parameters that lead to cost-effective photocatalytic titania-silica composites. The first part of this review deals with the mechanisms involved in the photocatalytic activity, then the chemistry behind certain methods for the synthesis of the titania-silica composites is discussed, and in the last and third part of this review, the influence of silica supports on titania is discussed. These three sections represent three different fields of research that are combined in this review to obtain better insights on the photocatalytic titania-silica composites. While many research subjects in these fields have been well known for some time now, some subjects are only more recently resolved and some subjects are still under discussion (e.g. the cause for the increased hydrophilic surface of titania after illumination). This article aims to review the most important literature to give an overview of the current situation of the fundamentals of photocatalysis and synthesis of the cost-effective photocatalyic composites. It is found that the most cost-effective photocatalytic titania-silica composites are the ones that have a thin anatase layer coated on silica with a large specific surface area, and are prepared with the precipitation or sol-gel methods.

Evolution of Physical and Chemical Properties of Phenolic Resin-Based Carbon/Carbon Composites Reinforced with Short Discrete Fibers during Pyrolysis

In the present work, novolac phenolic resin-based composites reinforced with short discrete carbon fibers were pyrolized at different temperatures from 400℃ to 900℃. Their physical and chemical properties were studied, linterfacial bonding between the matrix and carbon fiber and its influence on mechanical properties of analyzed composites were analyzed. Experimental results demonstrated strengthening of interfacial bonding with increase of pyrolysis temperature. Evolution of failure behavior was observed.

The Influence of Carbon Nanotubes and Nano-Silica Fume on Enhancing the Damping and Mechanical Properties of Cement-Based Materials

This paper conducted experimental studies on the damping and mechanical properties of carbon nanotube-nanosilica-cement composite materials with different carbon nanotube contents. The damping and mechanical properties enhancement mechanisms were analyzed and compared through the porosity structure test, XRD analysis, and scanning electron microscope observation. The results show that the introduction of nanosilica significantly improves the dispersion of carbon nanotubes in the cement matrix. At the same time, the addition of nanosilica not only effectively reduces the critical pore size and average pore size of the cement composite material, but also exhibits good synergistic effects with carbon nanotubes, which can significantly optimize the pore structure. Finally, a rationalization suggestion for the co-doping of nanosilica and carbon nanotubes was given to achieve a significant increase in the flexural strength, compressive strength and loss factor of cement-based materials.

Evaluation of Sawdust and Rice Husks as Fillers for Phenolic Resin Based Wood-Polymer Composites

We produced Wood-Polymer Composites (WPCs) with phenolic resin (PR) filled with saw dust (SD) and rice husks (RH) in a PR:fillerratio of 60:40 wt.%. RH and SD were grinded and sieved into particles μm. The aim of this research work was to evaluate sawdust and rice husks as fillers for sustainable phenolic resin based WPCs. Therefore, we investigated the thermal stability of PR/RH and PR/SD WPCs then we studied and compared the tensile, flexural properties of PR/SD and PR/RH WPCs samples, as well as their dimensional stability after water absorption test. Furthermore, through ultraviolet light exposure, we evaluated the effects of photo-oxidation on the water stability and mechanical properties of PR/RH and PR/SD WPCs samples compared to unexposed ones. PR filled with SD presented better mechanical properties compared to PR/RH WPCs samples. However, PR/RH WPCs showed good mechanical properties, and better thermal resistance and better water repulsion capabilities compared to PR/SD WPCs samples. Although, long time UV exposure ended up lowering considerably the mechanical properties and water resistance of PR/SD and PR/RH WPCs, both RH and SD offer great added value as fillers for PR based WPCs;SD having better interactions with PR matrix compared to RH.

Controlled Release of Diclofenac Sodium from Silica-Chitosan Composites

The release profiles of acidic form of diclofenac sodium adsorbed on mesoporous silicas (Silochrom and two samples of spherical silicas) were compared with the dissolution characteristics of the pure drug. Desorption of diclofenac sodium from impregnated silicas with various surface liophilicity and composites of silica with chitosan have been studied using rotating basket method in phosphate buffer, pH 6.8. Sedimentations of sodium diclofenac via adsorption and impregnation from alcohol solution on fumed silica and modified silicas with grafted aminopropyl and trimethylsilyl groups were carried out. Polymer-containing composites have been prepared by capsulation of silica particles with impregnated diclofenac sodium by protonated and deprotonated forms of chitosan. Effect of the silica surface nature on the active substance release rate was ascertained. Significant prolongation of diclofenac sodium release was detected in the case of application of hydrophobic silica as a carrier and protonated chitosan as a polymeric shell.

The Development and Characterization of Zirconia-Silica Sand Nanoparticles Composites

The present study aims to develop zirconia-Silica sand nanoparticles composites through powder processing route and to study the physical properties, mechanical properties and microstructure of the composites. Zirconia based silica sand nanoparticles composite with 5, 10, 15 and 20 wt.% were developed through powder processing technique and sintered at 1500 ℃ for two hours. A decreasing trend of green density however an improvement in sintered density was observed. Also the addition of silica sand nanoparticles with 20 wt.% increased the hardness up to 12.45 GPa and microstructures indicated the diffusion mechanism of silica sand nanoparticles into pore sites of the composites.

Photocatalytic Degradation of Phenol over MWCNTs-TiO2 Composite Catalysts with Different Diameters

Titania-based composite catalysts were prepared through a sol-gel route employing multi-walled carbon nanotubes with different diameters. The materials were characterized using thermogravimetric analysis, nitrogen adsorption-desorption isotherm, powder X-ray diffraction, scanning electron microscopy, and diffuse reflectance UV-Vis absorption spectra. The application of the catalysts to photocatalytic degradation of phenol was tested under UV-Vis irradiation. A synergetic effect on phenol removal was observed in case of composite catalysts, which was evaluated in terms of apparent rate constant, total organic carbon removal and photonic efficiency.

Micromechanical interlocking-inspired dendritic porous silicabased multimodal resin composites for the tooth restoration

Porous silica particles have shown great potential application as reinforcing fillers in the field of dentistry due to their ability to construct the micromechanical interlocking effect at filler-matrix interface.However,how to accurately regulate the pore structure,especially the pore size,to increase the degree of the micromechanical interlocking and the performance of materials remains a challenge.Herein,we have proposed a facile self-assembly process to synthesize dendritic porous silica with tunable pore sizes(DPS-x)by adjusting the chain-length of the alcohols in the microemulsion.The mechanism of nucleation-growth is further put forward.The results indicate that the pore size of DPS-x indeed affects the mechanical property of composites,where the DPSpen particles with intermediate pore size are chosen as the optimal reinforcing fillers.The bimodal and multimodal filler formulations are further established to address the loading limitation of unimodal DPS-pen(46 wt.%).In virtue of the closepacked structure of identical spheres,the particle sizes of secondary silica embedded into the maximally loaded bimodal D3S7 composite(DPS-pen:Si430=30:70,w/w)are theoretically calculated without trials.Among all formulations,the developed multimodal D3S7+Si178+Si90 filler exhibits superior mechanical properties,the lowest shrinkage,and high polymerization conversion for dental composites,along with satisfied waster sorption and solubility,and good biocompatibility in vitro and in vivo,which are comparable to commercial composite Z350 XT(3M,USA).These DPS-x particles and their multimodal fillers can also be applied to other polymer-based biomaterials.

Removal of Microcystin-LR in lake water sample by hydrophilic mesoporous silica composites under high-throughput MALDI-TOF MS detection platform

Microcystins(MCs),a family of cyclic heptapeptide cyanotoxins,exists in aquatic environment where cyanobacterial bloom happens,which will accumulate in aquatic organisms and transfer through the food chain to higher trophic levels,posing a health risk to both animals and human bodies.Among various MCs,Microcystin-LR(MC-LR)is worthiest studied for its strong toxicity,ubiquity and widespread.Here in this work,iminodiacetic acid(IDA)decorated magnetic mesoporous silica(mSiO_(2))nanocomposites(Fe_(3)O_(4)@mSiO_(2)-IDA)were facilely synthesized which possessed the merits of large surface area(188.21 m^(2)/g),accessible porosity(2.66 nm),excellent hydrophilicity and rapid responsiveness to magnetic field.Then the composites were successfully employed to the removal process of Microcystin-LR in real water samples followed by Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry(MALDI-TOF MS)analysis,achieving the removal efficiency above 92.5%even after ten recycles of the composites.It provided a potential method for removing MC-LR in aqueous environment with high effectiveness,lower costs and less secondary contamination.