Sol Content Research Articles

Effect of alumina sol on the preparation of magnesia‐alumina spinel foam ceramics by foaming‐sol method

AbstractIn this work, magnesia‐alumina spinel foam ceramics were prepared by foaming‐sol method using magnesia alumina spinel as raw material, anionic surfactant potassium oleate (PO) as foaming agent, and alumina sol as curing agent. The curing mechanism and the effect of alumina sol content on the stability of foam slurry and the properties of foam ceramics were investigated. In the foam slurry, the alumina sol can react with PO, so magnesia‐alumina spinel can be fixed in the foam structure through the gel network to improve the stability of the foam slurry. The gelation process reduces the viscosity of the foam slurry. The pores of magnesia‐alumina spinel foam ceramics sintered at 1500°C are mostly closed pores and the average pore was 29.7–42.1 µm. With the increase of alumina sol content, the bulk density of magnesia‐alumina spinel foam ceramics increased from 1.3 to 1.9 g/cm3, the cold compressive strength from 8.8 to 22.7 MPa, and the thermal conductivity from .417 to .806 W·m−1·K−1(350°C).

Mechanical Properties and Degradation Rate of Poly(Sorbitol Adipate-Co-Dioladipate) Copolymers Obtained with a Catalyst-Free Melt Polycondensation Method.

A new family of polyester-based copolymers-poly(sorbitol adipate-co-ethylene glycol adipate) (PSAEG), poly(sorbitol adipate-co-1,4 butane diol adipate) (PSABD), and poly (sorbitol adipate-co-1,6 hexane diol adipate) (PSAHD)-was obtained with a catalyst-free melt polycondensation procedure using the multifunctional non-toxic monomer sorbitol, adipic acid, and diol, which are acceptable to the human metabolism. Synthesized polyesters were characterized by FTIR and 1H NMR spectroscopy. The molecular weight and thermal properties of the polymers were determined by MALDI mass spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis. The degradation rate was investigated, at 37 °C, in 0.1M NaOH (pH 13) and in phosphate-buffered solution (PBS) at pH 7.4. It was found that the polymers degraded faster in NaOH (i.e., in a day) compared to their degradation in PBS, which was much slower (in a week). The highest degradation rate was noticed for the PSAEG sample in both media, whereas PSAHD was the most stable polymer at pH 7.4 and 13. A reduced hydrophilicity of the polymers with diol length was indicated by low swelling percentage and sol content in water and DMSO. Mechanical studies prove that all the polymers are elastomers whose flexibility increases with diol length, shown by the increase in percentage of elongation at break and the decrease in tensile stress and Young's modulus. These biodegradable copolymers with adaptable physicochemical characteristics might be useful for a broad variety of biological applications by merely varying the length of the diol.

Comparative study of the effect of cross‐linking degree on chitosan hydrogels synthesized with low and medium molecular weight chitosan

AbstractChitosan (CS) is often used in hydrogels due to its natural origin, sustainability, non‐toxicity, and biodegradability. However, the physicochemical properties of CS hydrogels generated via physical cross‐linking are relatively poor. CS hydrogels were prepared by cross‐linking with glutaraldehyde (GA) at different ratios ranging from 1% to 10% (w/w), using two different molecular weight CS. The swelling degree of hydrogels was investigated at pH 2.0, 5.6, and 7.4. The structure, morphology, and thermal characteristics of hydrogels were examined using Fourier transform infrared, scanning electron microscopy, differential scanning calorimetry, and thermogravimetric analysis, respectively. Compression tests were conducted using Zwick/Roell universal testing equipment following ASTM D695. In vitro degradation studies were performed in enzyme and enzyme‐free mediums at pH 7.4. The study demonstrated that low molecular weight CS (L‐CS) hydrogels have a lower sol content and higher swelling values than medium molecular weight CS (M‐CS) hydrogels. Both L‐CS and M‐CS hydrogels cross‐linked with 1% GA showed maximum swelling degrees at pH 2.0. Thermal analysis concluded that M‐CS hydrogels have higher thermal stability than L‐CS hydrogels. It was also found that the M‐CS hydrogels have higher compressive moduli. The degradation experiments in both enzyme and enzyme‐free media showed that L‐CS hydrogels have higher degradation rates.Highlights Chemically cross‐linked hydrogels synthesized using low and medium molecular weight chitosan. The mechanical and physical properties of medium and low molecular weight chitosan hydrogels were compared. Degradation experiments were performed in both enzyme and enzyme‐free media. Swelling values decreased noticeably with the increasing molecular weight. Low molecular weight chitosan improved the biodegradability of hydrogels.

Properties of epoxy resin matrix composites improved by silica sol‐activated hollow ceramic microspheres

AbstractSilica sol can activate the surface of hollow ceramic microspheres and improve the properties of composite materials by improving the interface between the microspheres and the epoxy resin. The group changes on the surface of microspheres were measured using infrared spectroscopy. The microspheres were observed with a scanning electron microscope. The density, water absorption, and mechanical properties of the materials were tested using scales and mechanical testing machines. The results showed that SiO2 and silane molecules were introduced on the surface of the microspheres after treatments. As the silica sol content increased, the slurry viscosity increased by 34.5%, the composite density increased by 5.8%, and the water absorption decreased by 35.8%. When the silica sol content was 25%, the flexural strength and compressive strength of the composites were 73.49 and 116.27 MPa, respectively, which were 37.8% and 23.6% higher than those of the untreated composites, and the mechanical properties became clearly improved. High mechanical properties enable the materials to be used in deeper ocean areas.Highlights Nanoparticles are introduced onto the surface of hollow microspheres. The activated microspheres can bind better to the silane coupling agent. Silane coupling agent assisted by silica sol improved interfacial bonding. Surface activation of microspheres improves the properties of composites.

Recycling waste tire rubber through an innovative water-medium ionizing radiation treatment: Enhancing compatibility and mechanical performance

In this research, we solved the compatibility problems of rubber mixtures containing waste ground tire rubber (GTR) with an innovative and environmentally friendly, water-based ionizing radiation treatment, meaning that the GTR is under water. Our hypothesis was that the strong oxidizing agents that appear during the radiolysis of water can activate the surface of the GTR, resulting in reactive functional groups containing oxygen, which can help establish a better interaction between the matrix and the GTR. We treated the GTR using different absorbed doses and examined the changes in the GTR using Soxhlet-extraction and cross-link density measurements. The surface of GTR was characterized by Fourier-transform infrared spectroscopy. Then we prepared GTR-containing natural rubber-based mixtures in an internal mixer, using two different mixing techniques. The mixtures were vulcanized in a hydraulic press, and the mechanical and morphological properties were investigated. As a result of the radiation treatment, cross-link density decreased slightly, while sol content did not change significantly. The FTIR spectra indicated that oxygen-containing groups appeared on the surface of the treated GTR. In the case of one-step vulcanizates, tensile strength increased by 11% and tear strength by 40%, while elongation at break remained high. For the two-step mixtures, tensile strength improved by 25%, tear strength by 35%, while elongation at break was over 400%. An irradiation dose of 20 kGy produced the best result, which is sustainable in mass production.

Changes in crosslinking structure of thermo‐oxidative aging chloroprene rubber and its effect on strain‐induced crystallization

AbstractChloroprene rubber (CR) is frequently quoted as an example of strain‐induced crystallizing elastomer. Many researchers have focused on studying the aging mechanism and mechanical properties of aged CR, little has been done on the effect of crosslinking structure on strain‐induced crystallization (SIC). The present paper related systematic investigations combining the changes of crosslinking structure and its influence on SIC. It was firstly investigated based on FTIR, crosslinking density test and GPC. The results showed that the molecular chains were oxidized in the early stage of aging, but the crosslinking reaction still dominated. At the same time, sol content and polydispersity decreased. In the later stage of aging, CR was oxidized, resulted in severe molecular chains fracture and an increase in the free sol content and polydispersity. The impact of aging on SIC under tensile condition was further investigated by the tensile tests. An obvious stress‐hardening was found for unaged CR, but not in aged CR. The crystallinity and microcrystalline region orientation tests showed that oxidation, crosslinking by double bonds and dechlorination during aging were not conducive to the orientation of molecular chains during stretching. It is the aging process that has an adverse effect on the SIC of CR.

Preparation and ablation resistance of carbon fiber with yttrium silicate coating

AbstractIn order to solve the shortcoming of fiber oxidation in a high‐temperature environment and improve the antiablative performance, yttrium silicate is coated on the carbon fibers’ surface by the sol‐gel process. In the present work, investigations of the ablation resistance of carbon fiber composites with yttrium silicate coatings (YS‐CFs) prepared by different sol contents and sintering temperatures are reported. The results show that YS‐CFs exhibit excellent ablation resistance in the oxyacetylene test with a heat flow of 1.5 MW/m2. The surface coating of carbon fiber is composed of a mixture of cristobalite, yttrium monosilicate, and yttrium disilicate. The best ceramic coating could be obtained by dipping 20% silica sol and 14% yttrium sol in turn and sintering at 1300°C. In this case, the linear and mass ablation rates reach the minimum values of .667 μm/s and 2.975 mg/s, respectively. YS‐CFs could be used as reinforcements for thermal protection materials in high‐temperature environments.

Fabrication of carbon fiber reinforced aluminum matrix composites by inorganic binders

Infiltration is an important issue for unidirectional carbon fiber-reinforced aluminum matrix (CF/Al) composites. In the present study, aluminum dihydrogen phosphate (ADP) and silica sol were used to prepare CF preforms, then CF/Al composites were prepared by simulated horizontal continuous casting. The results showed that silica sol significantly affects the curing process of ADP. When the content of silica sol is 50 % and heated at 500 °C, the product transformed from Al(PO3)3 (cubic system) to an amorphous phase with good thermostability. The mixture binder can fully fill the gaps between CFs, leading to a dense CF preform. The obtained CF/Al composite has a good bonding interface between Al and CFs, without pores or crack defects, and thus shows an obvious enhancement in tensile strength of 64.9 MPa, which is 34.6 % improved compared with that of CPAl. The CF/Al composites also maintained a good electrical conductivity of 56.9 % IACS, similar to that of CPAl.

Three dimensional hybrid microcrystalline graphite-silica sol stabilized stearic acid as composite phase change material for thermal energy storage

Solid-liquid phase change material (PCM) is widely investigated, however it's low thermal conductivity and leakage issue hinder its large-scale commercial application. Numerous researchers have taken different approaches to enhance its thermal property, and have verified the optimized performance of the newly developed series of PCMs through experimental data and simulation results. In this report we developed a form-stable composite with the three-dimensional (3D) hybrid structure matrix to tackle this issue. Microcrystalline graphite (MG) was used as the structure material, and silica sol was used as a binder and porous skeleton to design and prepare the microcrystalline graphite-silica sol matrix in a 3D hybrid structure. Stearic acid (SA) was introduced to the 3D hybrid matrix to form composite PCM. The effects of the mass ratio between MG and silica sol on the pore structure of the 3D hybrid matrix were investigated systematically. With increasing the mass content of silica sol in the hybrid matrix, the loading capacity increases followed by decreasing, with a maximum loading of stearic acid as high as 49.94 % observed. The composite PCM could achieve the highest melting/cooling latent heat of 95.76 J g−1/96.04 J g−1 and higher thermal conductivity by 90.9 % than pure SA. The thermal infrared image indicated that the optimized composite had a better transient temperature response than pure SA. The leakage test proved that the 3D hybrid matrix stabilizes SA well, exhibiting excellent shape stability during phase change. These results demonstrated that the composition of MG/silica gel is an effective strategy, giving enhanced energy storage characteristics, including thermal stability, energy storage capacity, and thermal reliability.

Insights into the calcination temperature and loading amount of the catalyst support (TiO2) in the fibrous ceramic-based catalytic filter element prepared by microwave drying

The fibrous ceramic-based catalytic filter element (CFE) is a promising multifunctional material capable of simultaneously removing dust and NOx from hot gases. In this study, various calcination temperatures and titanium sols with different solid contents were used to prepare CFEs based on microwave drying, and their influences on the catalytic performance were experimentally investigated. The results showed that both the calcination temperature and the solid content of the titanium sol had important impacts on the catalytic activity. As the calcination temperature increased, the particle size, crystallite size, and average pore diameter of the loaded catalyst support (TiO2) increased, while the specific surface area decreased, ultimately resulting in a decline in the catalytic activity. However, a suitable calcination temperature ranging from 300 to 400 °C was required to achieve a good combination between the catalyst and the fibrous ceramic and a relatively uniform mesoporous structure. Furthermore, the increase in the solid content gave rise to a corresponding increase in the TiO2 loading amount, which increased the pressure drop and reaction surface area of the CFE. Excessive vanadium content caused by insufficient catalyst support induced side reactions of NH3 oxidation under high-temperature conditions, thereby reducing catalytic activity. Therefore, the preferred calcination temperature and solid content were set at approximately 300–400 °C and 8 wt%, respectively. The final prepared CFE demonstrated superior catalytic performance and adaptable gas velocity properties.

Effects of Sulfur Sources on Ruminal S Bioavailability, Fermentation Activity and Microbial Populations Measured In Vitro

The aim of this study was to better understand the ruminal solubility, bioavailability, effect on fermentation and microbiota of different sulfur (S) forms. In vitro fermentations with rumen fluid were conducted for 70hrs. Hay was incubated solely (CON), or with 0.5%DM of S, as: elemental sulfur (ES), Na2SO4 (NaS), (NH4)2SO4 (NHS) and MgSO4 (MgS). Fermentation was assessed by gas production (TGP) and dry-matter degradability (dDM%). Solubility and bioavailability were estimated by S concentration of the supernatant (SOL) and of bacteria (BACT). Microbial community was assessed by amplification of the 16SrRNA gene. NHS decreased (p<0.05), ES and NaS didn’t affect, while MgS increased (p<0.01) TGP. MgS increased (p<0.001), whilst ES, NaS and NHS showed no effect on dDM%. Sulfate sources increased (p<0.001), while ES did not affect the S content of SOL. S content of BACT suggests that sulfates have a high bioavailability, while ES is poorly assimilated by bacteria. Some variations of the microbial community were observed, including a lower abundance of methanogens with all S sources and a higher abundance of Desulfovibrio with MgS. These findings suggest that ES has limited solubility, whereas sulfates, particularly MgS, exhibit a high level of solubility in the rumen, resulting in a more effective utilization by bacteria.

An Investigation into Electrodeposited Co−Ni−TiO2 Films with Improved Mechanical and Corrosion Properties

This investigation proposes the use of sol-enhanced electrodeposition to create a range of Co−Ni−TiO2 films. The addition of TiO2 sol controls the nucleation process and the properties of the composite films by generating TiO2 nanoparticles in situ in the electrodeposition process. The transmission electron microscopy (TEM) and zeta potential analyses revealed a relatively homogenous distribution with particle size in the range below 100 nm for the TiO2 nanoparticles produced. Microstructure, phase composition, hardness, friction, and corrosion resistance of Co−Ni−TiO2 films were thoroughly investigated in relation to TiO2 sol concentration. The results show that the addition of a limited content of TiO2 sol upgraded Co−Ni films by producing a Co−Ni−TiO2 film with a high dispersion of TiO2 nanoparticles. On the other hand, too much TiO2 sol could cause agglomeration and hinder the metal deposition process, resulting in surface pores and the deterioration of film performance.

Enhancement of Wood Coating Properties by Adding Silica Sol to UV-Curable Waterborne Acrylics

In recent years, with the development of the coating industry and the increasing awareness of environmental protection, the modification of waterborne wood coatings has become the focus of research. Generally, the system composed of silica sol modification and UV curing can make up for the defects of poor mechanical properties, low hardness, and slow curing speeds of waterborne wood coatings. Herein, we used silica sol-reinforced UV-curable waterborne acrylic wood coatings and tested the related physical properties of the coatings. FT-IR analysis showed that the Si-O-Si bond appeared, indicating that the silica sol was successfully grafted onto the waterborne acrylic molecular chain. The results showed that the mechanical properties of the UV-curable waterborne acrylic wood coating film reached their optimum when the content of silica sol was 1 wt%, the number of UV lamps was 3, and the drying time was 20 min. The corresponding values for wear resistance, hardness, adhesion, and impact strength were 0.106 g (high level), grade 3, and 90 kg·cm, respectively. However, when the content of silica sol is greater than 1 wt%, the related physical properties of the coatings will decrease. The results showed that the gloss of the coating decreased with increasing silica sol content. When the silica sol content was 2 wt%–6 wt%, the coating showed a matte gloss. This present work shows that the modification process is simple, controlled, inexpensive, and meets the demand for UV-curable waterborne acrylic wood coatings in daily life.

Efficient construction of tubular mullite fiber membrane filter with high gas permeance for gas/solid filtration

Ceramic filter membranes exhibit great potential in industrial hot gas filtration. However, it was limited by its low gas permeance due to the low porosity and high transfer resistance. In this work, novel filter-pressing method was employed to fabricate fibrous ceramic fiber membrane tubes (FCFMTs) by using mullite fibers, glass fibers and silica sol. The silica sol and glass fibers were used as composite sintering aids to enhance the mechanical strength at a relatively lower sintering temperature. In addition, the freeze drying method was investigated in detail to guarantee the uniformity of silica sol in the matrix of the FCFMTs. It was demonstrated when the addition content of the silica sol and glass fibers were 40 vol% and 30 wt%, respectively, the sintering temperature was 1200 °C, the FCFMTs obtained a mean pore size of 35 μm and gas permeance of 787 m3m-2h-1KPa−1, respectively. The fly ash particles recycled from the electrical plant were employed as model dust in the dust-laden gas. The resulting FCFMTs also exhibited high particle rejection behavior towards dust-laden gas with rejection rate of above 99.9 %. The pressure drop and the outlet dust concentration were below 2 kPa and 0.1 mgm−3, respectively after three filtration-cleaning cycles. This work provides an important reference for high-performance ceramic filter for the cleaning or filtration of dust-laden gas.

Recycling waste nitrile rubber (NBR) and improving mechanical properties of Re-vulcanized rubber by an efficient chemo-mechanical devulcanization

Waste rubbers are environmental pollutants that could not be easily recycled. Devulcanization (i.e. as a reverse process of rubber vulcanization) is considered as a promising method for recycling of rubber wastes. In this study, a simple and effective chemo-mechanical devulcanization for waste nitrile rubber (WNBR) was introduced and compared to the mechanical, thermo-chemo-mechanical and radio-chemo-mechanical methods. The mechanical stress was applied to crumbed waste rubbers using a two roll mill in presence of different chemical agents (i.e. N-cyclohexyl-2- benzothiazole sulfonamide (CBS), tetra methyl thiuram disulfide (TMTD), diphenyl disulfide (DPDS), VitaX and a mixture of VitaX and DPDS). The sheet formation time on two roll mill, crosslink density (CLD) and sol/gel contents of waste rubber powders were measured before and after devulcanization. The devulcanized rubbers were characterized using TGA, DSC and GPC analysis. Finally, the properties of devulcanized nitrile rubber (i.e. the tensile, hardness and curing properties) were evaluated and compared to pristine NBR. It was found that VitaX is the most efficient chemical agent among the chemical agents. It caused 43, 87 and 98% decrement in the sheet formation time of chemo-mechanically, thermo-chemo-mechanically and radio-chemo-mechanically devulcanized samples compared to the mechanically devulcanized NBR, respectively. The samples also showed 24, 33 and 100% increment in the sol content, devulcanization percent and tensile strength compared to the mechanically devulcanized NBR, respectively.

Radiation softening and hardening of PDMS in combined neutron and γ rays

We report on the irradiation of a modified silica-filled room temperature vulcanized (RTV) PDMS. The irradiation experiments were conducted in air with combined neutron (approx. 6·1012 n·cm−2·s−1 at energies 1 meV to 1 MeV with an approximated maximum of 3% tail towards higher energy neutrons from 1 MeV up to 100 MeV) and γ rays (739–28,900 Gy at energies 0.01 MeV to 50 MeV) in the NAA position in the Swiss Spallation Neutron Source SINQ. Softening of the gel prevailed for the shorter exposures, hardening for the longer exposures within the explored range of exposure time (1.5 to 47 min). The material changes were sensed using dynamic mechanical analysis (DMA), analysis of the swelling in good solvents (o-, m-, p- xylene), Raman and FTIR spectroscopy, and water contact angle measurement. While the irradiation of PDMS influenced the swelling in the xylenes, melting temperature and elastic modulus, it did not discernibly influence the Raman and FTIR spectra, sol content, and water contact angle. Irradiation can be used as a post treatment of PDMS items enabling the optimization of elastic modulus and swelling characteristics.

Effects of sol contents and sintering temperatures on SiO2 coated needled carbon fibre felt composites

ABSTRACT Carbon fibre has excellent mechanical properties at high temperatures but weak oxidation resistance. The paper prepared the anti-oxidative silica coating on the surface of needled carbon fibre felt by the sol–gel method and discussed the effects of sol content and sintering temperature on the coatings’ performance. The phase composition, density, thermal conductivity and thermal stability of derived composites were characterised, and the structure and morphology of SiO2 coatings were also analysed by scanning electron microscopy. The results indicated that a uniform and complete coating could be formed on the fibre surface when the sol content exceeds 20%. Ceramic particles sintered below 1200°C were amorphous silica, while those sintered at 1350°C were cristobalite. Compared with other processes, 20% silica sol content or sintering at 1350°C could provide better antioxidant protection. The new coating process is significant for retarding fibre oxidation in a high-temperature environment.

Tailor-made microstructures lead to high-performance robust PEO membrane for CO2 capture via green fabrication technique

Emerging excessive greenhouse gas emissions pose great threats to the ecosystem, which thus requires efficient CO2 capture to mitigate the disastrous issue. In this report, large molecular size bisphenol A ethoxylate diacrylate (BPA) was employed to crosslink poly (ethylene glycol) methyl ether acrylate (PEGMEA) via the green and rapid UV polymerization strategy. The microstructure of such-prepared membrane could be conveniently tailored by tuning the ratio of the two prepolymers, aiming at obtaining the optimized microstructures with suitable mesh size and PEO sol content, which was approved by a novel low-field nuclear magnetic resonance technique. The optimum membrane overcomes the trade-off challenge: dense microstructures lower the gas permeability while loose microstructures lower high-pressure-resistance capacity, realizing a high CO2 permeability of 1711 Barrer and 100-h long-term running stability under 15 atm. The proposed membrane fabrication approach, hence, opens a novel gate for developing high-performance robust membranes for CO2 capture.

Compositions for Limestone Restoration

Information about the lime composition used for the restoration of limestone is given. To develop a repair composition, a polysilicate solution was used. It has been established that polysilicate solutions contain a monomer, oligomer and polymeric varieties of silica. It was found by the molybdate method that the content of the polymeric form of silica γ-SiO2 in the polysilicate solution is 15–19.93%, depending on the content of the silica sol. This composition of the polysilicate solution contributes to the manifestation of the high reactivity of silica. The technology for carrying out restoration work involves the application of a primer layer - liquid glass, followed by the application of a calcium chloride solution. After 20-30 minutes after applying the primer, it is possible to apply the repair composition with a spatula. It is shown that the use of a polysilicate solution in the formulation of a lime composition helps to increase the water resistance, adhesion strength of the composition to the base, and accelerates curing.

Efficient thermo-oxidative reclamation of green tire rubber and silanized-silica/rubber interface characterization

A stepwise separation of reclaimed silanized silica (r-SS) from waste green tire rubbers was achieved using a thermo-oxidative reclamation process, and the interfacial interaction between silanized silica and rubber was quantified. The exfoliation of the residual and bound rubber from the r-SS surfaces under different temperatures ranging from 150 to 230 ℃ was investigated, with or without the addition of vegetable oil. The particle size of r-SS decreased from hundreds of micron-meters to nanometers with the increase of reclamation degree, i.e., the degree of devulcanization of vulcanized rubber, as quantified by the sol content, and the thickness of the bound rubber layer decreased to 4–6 nm at 230 ℃. This work provides a feasible solution for recycling of waste green tires, and also promote the understanding of the interfacial interactions between silanized silica and rubber by thermo-oxidative reclamation.