Glass forming region and bonding mechanism of low-melting V2O5–TeO2–Bi2O3 glass applied in vacuum glazing sealing

As a new kind of energy-saving glass, vacuum glazing has excellent thermal and sound insulation properties and is widely used in building, household appliances and solar photovoltaic. The edge sealing material, along with sealing method, is key to the fabrication of vacuum glazing. Low transition temperature (T_g) and good fluidity at sealing temperature (T_s) make low-melting glass of V₂O₅–TeO₂–Bi₂O₃ (VTB) system perfect to be the edge sealing material for vacuum glazing. The glass forming region of VTB ternary system was mapped for the first time in this work. Low-melting VTB glass of 40V₂O₅–50TeO₂–5Bi₂O₃–3ZnO–2Na₂O (wt%) was optimized to be the sealing material. Glass powder of this composition could be used to seal the edges of vacuum glazing at an extremely low temperature of 360°C. With the assistance of anodic-bonding method, the bonding strength of vacuum glazing was dramatically enhanced. Vacuum glazing fabricated under the optimized process parameters of 420°C, 600 V, and 60 min possesses a highest bonding strength of 4.31 MPa. Furthermore, anodic-bonding mechanism of low-melting VTB glass applied in vacuum glazing sealing has been thoroughly researched.     

High emissivity MoSi2–ZrO2–borosilicate glass multiphase coating with SiB6 addition for fibrous ZrO2 ceramic

To develop a high emissivity coating on the low thermal conductivity ZrO₂ ceramic insulation for reusable thermal protective system, the MoSi₂–ZrO₂–borosilicate glass multiphase coatings with SiB₆ addition were designed and prepared with slurry dipping and subsequent sintering method. The influence of SiB₆ content on the microstructure, radiative property and thermal shock behavior of the coatings has been investigated. The coating prepared with SiB₆ included the top dense glass layer, the surface porous coating layer and the interfacial transition layer, forming a gradient structure and exhibiting superior compatibility and adherence with the substrate. The emissivity of the coating with 3 wt% SiB₆ addition was up to 0.8 in the range of 0.3–2.5 μm and 0.85 in the range of 0.8–2.5 μm at room temperature, and the “V-shaped grooves” surface roughness morphology had a positive effect on the emissivity. The MZB-3S coating showed excellent thermal shock resistance with only 1.81% weight loss after 10 thermal cycles between 1773 K and room temperature, which was attributed to the synergistic effect of porous gradient structure, self-sealing property of oxidized SiB₆ and the match of thermal expansion coefficient between the coating and substrate. Thus, the high emissivity MoSi₂–ZrO₂–borosilicate glass coating with high temperature resistance presented a promising potential for application in thermal insulation materials.     

Improving Thermal Stability and Electrical Insulation of Gamma‐Irradiated Silicone Rubber Nanocomposites

Room temperature vulcanized silicone rubber (RTVSR) nanocomposites were prepared by mixing of surface‐modified montmorillonite nanoclay or nano fumed silica, or both of them with RTVSR to improve thermal stability, electrical insulation, and flame retardant. Their tensile strength, elongation, swelling, and solubility properties at different doses of gamma radiation were investigated to study the effect of gamma radiation on the properties of the nanocomposites. The thermal stability, flammability properties, and volume resistivity of the nanocomposites were also investigated. The nanocomposite which containing fumed silica has the best thermal, mechanical properties, electrical insulation and fire retardancy. The thermal characteristics, namely, T_onset, T_10%, T_comp, and T_max, of the nanocomposite sample containing fumed silica were 22, 23, 13, and 11 °C higher than those of the blank, respectively. The tensile strength (TS) increased when the radiation dose was increased up to 100 kGy, but elongation, swelling, and solubility decreased when the radiation dose was increased up to 150 kGy. It can be generally concluded that the nanocomposites containing fumed silica and irradiated to 100 kGy are characterized by having outstanding mechanical, thermal, fire retardant, and electrical insulation properties and hence, they may have wide industrial applications as good thermal and electrical insulating materials. J. VINYL ADDIT. TECHNOL., 26:354–361, 2020. © 2019 Society of Plastics Engineers     

Waste‐derived low‐cost mycelium composite construction materials with improved fire safety

Mycelial growth attracts academic and commercial interest because of its ability to upcycle agricultural and industrial wastes into economical and environmentally sustainable composite materials using a natural, low‐energy manufacturing process able to sequester carbon. This study aims to characterise the effect of varying ratios of high silica agricultural and industrial wastes on the flammability of mycelium composites, relative to typical synthetic construction materials. The results reveal that mycelium composites are safer than the traditional construction materials considered, producing much lower average and peak heat release rates and longer time to flashover. They also release significantly less smoke and CO₂, although CO production fluctuated. Rice hulls yielded significant char and silica ash which improved fire performance, but composites containing glass fines exhibited the best fire performance because of their significantly higher silica concentrations and low combustible material content. Higher concentrations of glass fines increased volume‐specific cost but reduced mass‐specific and density‐specific costs. The findings of this study show that mycelium composites are a very economical alternative to highly flammable petroleum‐derived and natural gas‐derived synthetic polymers and engineered woods for applications including insulation, furniture, and panelling.     

The dual effect of zirconia fiber on the insulation and mechanical performance of the fumed silica-based thermal insulation material

Inorganic fibers and opacifiers are indispensable for improving the strength and high temperature insulation performance of the fumed silica-based thermal insulation material. However, zirconia fiber enhances the strength of the fumed silica-based thermal insulation material and reduces the radiative heat transfer to replace the opacifier. The sample of fumed SiO₂/Al₂O₃ doped with 7% zirconia fiber (FZ7) has a lower density of 0.70 g/cm³ and a high porosity of 75.0%. In addition, the thermal conductivity of FZ7 at 800 °C is 0.077 W/(m·K), which is lower than the sample of fumed SiO₂/Al₂O₃ doped with 7% glass fiber (FG7) and 0.089 W/(m·K) at 800 °C. The effective extinction coefficient of the thermal insulation material containing zirconia fiber is larger than that of the glass fiber by Fourier transform infrared spectroscopy analysis and calculation, indicating that the zirconia fiber has a distinct absorption and scattering effect on infrared radiation to reduce the radiative heat transfer. Therefore, zirconia fiber enhances the strength and decreases the high temperature thermal conductivity of the composites with the dual effect on the insulation and mechanical performance of the fumed silica-based thermal insulation material.     

Polyacrylate/silica hybrids prepared by emulsifier-free emulsion polymerization and the sol–gel process

Polyacrylate/silica hybrids were prepared by emulsifier-free emulsion polymerization and the sol–gel process. The influence on the properties of polyacrylate/silica hybrids of the synthetic conditions, such as the dosage of polyvinyl alcohol, the ratio of the monomers, the dosage of tetraethoxysilane and the dosage of γ-methacryloxypropyltrimethoxysilane, was investigated. The hybrid material was characterized by Fourier transform infrared, differential scanning calorimeter, thermal gravimetric analyzer and dynamic light scattering. The results indicated that there were chemical bonds between SiO₂ and polyacrylate, that the thermal stability and the average diameter of polyacrylate emulsion particle increased with the incorporation of SiO₂, and that the glass transition temperature (T _g) of polyacrylate/SiO₂ was 8 °C higher compared with that of pure polyacrylate.     

Synthesis of zeolite beta using silica gel as a source of SiO2

The feasibility of synthesising pure zeolite beta in high yields using silica gel as the source of SiO₂ is demonstrated. The phase-purity and yield of beta is enhanced by using silica gels with high surface area. The influence of various synthesis parameters (Si/Al ratio, alkalinity, dilution level, concentration of the organic base, etc.) on the kinetics of synthesis as well as the quality and yield of the zeolite have been investigated. A correlation between XRD crystallinity of the samples with varying degrees of crystallinity and that estimated from framework IR spectroscopy, differential thermal analysis and adsorption of n-hexane is demonstrated. The dependence of the yield of zeolite beta on SiO₂/Al₂O₃ ratio of the gel is also reported. The results of the present study indicate the feasibility of a cheaper route for the manufacture of zeolite beta.     

高固含量聚硅酸钾基防火凝胶及其在复合防火玻璃中的应用

通过蒸发浓缩的方法制备了高固含量硅溶胶分散液,采用纳米粒度及Zeta电位分析仪研究了蒸发浓缩前后分散液中无机粒子粒径和Zeta电位的变化。进而,以高固含量硅溶胶分散液为原料,氢氧化钾溶液为固化剂,制备了高固含量聚硅酸钾基防火凝胶和复合防火玻璃,采用小型耐火试验炉、热重分析、扫描电子显微镜、红外光谱等测试手段,研究了复合防火玻璃的耐火性能及防火凝胶的热稳定性和耐火机理。结果表明:蒸发浓缩的方法对纳米粒子的粒径和分散稳定性几乎没有影响;分散液固含量的提高能够极大地提升复合防火玻璃的耐火隔热性,并一定程度上提升防火凝胶的热稳定性。     

Role of silica nanoparticle in multi‐component epoxy composites for electrical insulation with high thermal conductivity

Multicomponent epoxy micro/nano‐composites containing micro‐alumina, micro‐quartz, and nano‐silica were fabricated to develop electrical insulation materials with high thermal conductivity. Simply changing the ratio between the alumina and quartz microparticles caused a trade‐off relationship between the thermal conductivity and electrical insulation. Increasing the alumina content in the epoxy‐alumina/quartz micro‐composites enhanced the thermal conductivity but deteriorated the dielectric strength. An increase in the thermal conductivity without incurring a loss in the dielectric strength was achieved by incorporating silica nanoparticles in the epoxy micro‐composites. Adding silica nanoparticles to the epoxy micro‐composites was found to be more efficient in improving the thermal conductivity compared to increasing the alumina ratio, especially at low alumina/quartz ratios. This behavior corresponded to theoretical models. Therefore, we provide a useful insight, both practical and theoretical, into the more advanced optimization of designing multicomponent epoxy composites for electrical insulation with high thermal conductivity.     

Thermal stability and flame retardancy of polyester,cotton, and relative blend textile fabrics subjected to sol–gel treatments

Polyester (PET), cotton (COT), and two relative blend textile fabrics were treated by sol–gel processes. Tetraethoxysilane (TEOS) was used as inorganic precursor of silica phases; furthermore, different TEOS/H₂O ratios were examined to explore the effect of the presence of SiO₂ on the thermal and fire stability of the textile fabrics investigated. The distribution and dispersion of SiO₂ were observed by means of scanning electronic microscopy (SEM). SEM magnifications showed the formation of a continuous silica film located in the neighboring fibers; furthermore, in the case of PET, such a film incorporated silica particles with an average diameter ranging between 0.2 and 6 μm. The thermal and thermooxidative stabilities of the treated samples were investigated by thermogravimetric analysis: after the sol–gel treatment, the degradation mechanism was modified both in nitrogen and in air, and the improvement in the thermal stability was attributed to the presence of silica, which played a protective role in the degradation of the textile fabrics. Finally, we investigated the combustion behavior of the textile fabrics by cone calorimetry, measuring the time to ignition, the heat release rate, and the relative peak. The former was found to depend on the type of fabric; the latter generally evidenced a remarkable decrease for all of the treated samples, up to 35% compared to the neat counterparts. This indicated that the sol–gel treatments improved the flame retardancy of the PET/COT fabrics. This conclusion was also confirmed by limiting oxygen index tests, which evidenced burning kinetics changes in the presence of the silica coating. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A novel strategy for the construction of silk fibroin–SiO2 composite aerogel with enhanced mechanical property and thermal insulation performance

The practical application of silica aerogels is an enormous challenge due to the difficulties in improving both mechanical property and thermal insulation performance. In this work, silk fibroin was used as scaffold to improve the mechanical property and thermal insulation performance of silica aerogels. The ungelled SiO₂ precursor solution was impregnated into silk fibroin to prepare silk fibroin–SiO₂ composite aerogels via sol−gel method followed by freeze-drying. By virtue of the interfacial hydrogen-bonding interactions and chemical reactions between silk fibroin and silica nanoparticles, SiO₂ was well-dispersed in the silk fibroin aerogel and composite aerogels exhibited enhanced mechanical property. By increasing the loading of silk fibroin from 15 wt % to 21 wt %, the maximum compressive stress was enhanced from 0.266 to 0.508 MPa when the strain reached 50%. The thermal insulation performance of the composite aerogels was improved compared with pure silica aerogel, as evidenced that the thermal conductivity was decreased from 0.0668 to 0.0341 W∙m^‒1∙K^‒1. Moreover, the composite aerogels exhibited better hydrophobicity and fire retardancy compared to pure silica aerogel. Our work provides a novel approach to preparing silk fibroin–SiO₂ composite aerogels with enhanced mechanical property and thermal insulation performance, which has potential application as thermal insulation material.     

Preparation and properties of organosoluble polyimide/silica hybrid materials by sol–gel process

Organosoluble polyimide/silica hybrid materials were prepared using the sol–gel process. The organosoluble polyimide was based on pyromellitic anhydride (PMDA) and 4,4′‐diamino‐3,3′‐dimethyldiphenylmethane (MMDA). The silica particle size in the hybrid is increased from 100–200 nm for the hybrid containing 5 wt % silica to 1–2 µm for the hybrid containing 20 wt % silica. The strength and the toughness of the hybrids are improved simultaneously when the silica content is below 10 wt %. As the silica content is increased, the glass transition temperature (T_g) of the hybrids is increased slightly. The thermal stability of the hybrids is improved obviously and their coefficients of thermal expansion are reduced. The hybrids are soluble in strong polar aprotic organic solvents when the silica content is below 5 wt %. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2977–2984, 1999     

Natural rubber/ethylene propylene diene blends for high insulation iron crossarms

This research studied the composition and behavior of natural rubber (NR) and ethylene propylene diene monomer (EPDM) blends at various carbon black concentrations (0–30 phr) in terms of electrical resistivity, dielectric breakdown voltage testing, and physical properties. The blends having electrical properties suitable for application in high‐insulation iron crossarms were selected for investigation of compatibility and increased physical properties. The effect of the homogenizing agent concentration on improvement of compatibility of blends was studied by scanning electron microscopy, pulsed nuclear magnetic resonance spectroscopy, and rheology techniques. We also examined mechanical properties such as tensile strength, tear strength, elongation at break, and hardness. The NR/EPDM blends filled with a fixed concentration of silica were investigated for ozone resistance. A carbon black content as high as 10 phr is still suitable for the insulation coating material, which can withstand electrical voltage at 10 kVac. Addition of the homogenizing agent at 5 phr can improve the mechanical compatibility of blends, as evidenced by the positive deviation of shear viscosity of the rubber blend, that is, the calculated shear viscosity being higher than that of experimental data. Moreover, the pulsed NMR results indicated that the spin‐spin relaxation (T₂) of all three components of the rubber blend was compressed upon the addition of the homogenizing agent. The ratio of NR/EPDM in the blend to best resist the ozone gas is 80/20 with the addition of silica of 30 phr into the blend. Also, the NR/EPDM filled with silica had a decreased change in thermal and mechanical properties of blends after thermal aging. The synergistic effect of silica content and high NR content (80) in 20 phr EPDM could improve antioxidation by ozone in the absence of a normal antioxidant for natural rubber. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3401–3416, 2004     

Fire reactions of ceramic and polymer moulding composites

Abstract

Abstract

Low cost ceramic dough moulding compounds/composites (CDMC) are composed of inorganic metal silicates and chopped fibre reinforcements. This paper investigates the fire reactions of these materials under severe thermal and heat conditions. This research is targeted to potential applications in the replacement of glass fibre reinforced polymeric insulation materials such as phenolic composites as engine heat shields which experience high temperature and heat transmission. The materials developed can provide good properties, including heat insulation with high thermal stability for engine drafts, where traditional glass/phenolic composites were used and gave a very short life cycle. This work compares the thermal properties of the glass fibre reinforced phenolic composites and metal silicate composites produced under the same processing conditions. The results show that CDMC possesses significantly better thermal stability and heat resistance in comparison with phenolic moulding composite (phenolic dough moulding composites). The indication was that under the testing condition of heat flux of 75?kW?m^?2 intended for materials used for applications in marine, transport and possibly nuclear waste immobilisation, the integration of the CDMC was kept intact and survived as a high temperature insulation material.     

Moisture-Resistant and Mechanically Strong Polyimide-Polymethylsilsesquioxane Hybrid Aerogels with Tunable Microstructure

Moisture-resistant and mechanically strong polyimide (PI)-polymethylsilsesquioxane hybrid aerogels with doubly cross-linked structures are synthesized through sol–gel technology and supercritical CO₂ fluid drying. By using bis(trimethoxysilylpropyl) amine as a cross-linker, the end-capped polyamide acid derived from biphenyl-3,3′,4,4′-tetracarboxylic dianhydride and 4,4′-oxydianiline is cross-linked with a silica network using methyltrimethoxysilane as the silica source precursor. The resultant hybrid aerogels show low density (0.12–0.15 g cm⁻³), low thermal conductivity (0.032–0.049 W m⁻¹ K⁻¹), high hydrophobicity (125–140°) and good thermal stability (above 435 °C) with tunable microstructure. With the increase of silica sol volume, the microstructure of hybrid aerogels transforms from fibrous network to hierarchical microstructure. Aerogels with high content of silica sol exhibit good moisture resistance, high Young's modulus (Max. 19.6 MPa), and high specific modulus (Max. 131 kN m kg⁻¹), which are attributed to their unique hierarchical microstructure with a sheet skeleton. These hybrid aerogels are promising in the fields of thermal insulation, aerospace applications and so on.     

Synthesis of colloidal nanosilica from waste glass powder as a low cost precursor

Waste glass powder was used as a low cost precursor for production of colloidal nanosilica for the first time. The process includes production of wet silica gel and thermal peptization of the wet gel. Purification of the glass powder and wet gel production were initiated by acid washing. The obtained powder was reacted with sodium hydroxide to produce wet silica gel. Type of the applied acid was examined in one factor at a time route. Temperature of the alkaline step and concentrations of the applied acid and base were investigated using Taguchi design of experiments. After finding the best combination of the investigated factor levels in production of the wet gel, time of the stabilization in thermal peptization was studied. Characterizations of the wet gel and colloidal silica were performed by XRF, DLS, FESEM, TEM, FTIR and N₂ sorption evaluation. Accordingly pure and stable colloidal nanosilica (98.50%) with average particle size of 21.9?nm was produced from the glass powder successfully. Specific surface area of the dried porous optimum sample was 83.63?m²/g.     

Synthesis of silica aerogel thin sheets and evaluation of its thermal,electrical, and mechanical properties

Silica aerogels are excellent thermal and acoustic insulators because of interconnected open nanopores with more than 90% porosity and higher surface area. Silica aerogel is derived by sol-gel process and dried under super-critical, sub-critical or ambient pressure conditions. Thin silica aerogel sheets could be effective thermal insulators but high fragility hinders the wider applications. We have successfully developed a synthesis method for thin, flexible, and non-fragile aerogel sheets with excellent hydrophobicity, lower thermal conductivity, and non-combustible properties via ambient drying method. The silica aerogel sheets prepared compose of silica aerogel powder, fiber glass chopped strands, and solvent-based binder. Aerogel thin insulation sheets of thickness 164 μm were prepared by pressing through rollers using aerogel paste composed of aerogel powder, fiber glass strands, and binders. The thermal conductivity values obtained were between 0.02~0.63 W/mK at temperature 25~400°C, contact angle θ = 121‘_, weight loss 3.91% when heated up to 800°C in air, dielectric voltage breakdown 3.67 kV, dielectric strength 6.37 kV/mm and tensile strength of 2.65 N/mm². The overall thermal, electrical, and mechanical evaluation of aerogel thin insulation sheet showed they have higher potential to replace existing thick and bulky aerogel composites as thermal and electrical insulators in aviation, automobiles, electronics, and high power batteries.     

Nanofibers reinforced silica aerogel composites having flexibility and ultra-low thermal conductivity

For the sake of enhancing the performance of flexible silica aerogel in practical applications, flexible SiO₂/SnO₂ nanofibers (SSNF) reinforced flexible silica aerogel composites (abbreviated as SiO₂-SSNF) were successfully prepared. Firstly, the SiO₂/SnO₂ nanofibers with fine diameter (~320 nm) and excellent flexibility were prepared by electrospinning technology. Then the aerogel composites were synthesized by adding the flexible SSNF to the silica solution and through the sol-gel method and ethanol supercritical drying technology. The effects of different content of the nanofibers on thermal conductivity and Yong's modulus of SiO₂-SSNF aerogel composites were investigated. The SiO₂/SnO₂ nanofibers were randomly dispersed in the flexible silica aerogel and the great integrity of the material result in smaller linear shrinkage, better thermal protection, and mechanical properties compared with those pure SiO₂ aerogels. The final SiO₂-SSNF aerogel composites possess excellent thermal conductivity (0.025-0.029 W/(m∙K)) and higher Yong's modulus (70 kPa), which was twice than that of the pure silica aerogel. This prepared SiO₂-SSNF aerogel composites can be better used in thermal insulation due to its excellent flexible and thermal insulation property.     

CLAY SEWER PIPE MANUFACTURE.—IV. THE INFLUENCE OF DIFFERENT SALT GLAZING TEMPERATURES UPON THE COLOR AND GLOSS OF GLAZES OBTAINED ON CLAYS WITH VARYING SILICA,ALUMINA, AND IRON OXIDE CONTENTS1

Object .—A study was made of the effects of different salt glazing temperatures upon the color and brightness of salt glazes produced upon clays with varying silica, alumina, and iron oxide contents. Results .—In tests conducted in commercial kilns operating under normal conditions, it was found that increasing the salt glazing temperatures has a tendency to produce duller and darker glazes on clays containing iron oxide. The brightness of the glazes produced may be approximately represented by the following formula: -1.00×₁+ 0.376×₂ - (1.885 + 0.385(1.01253)^(T-1110))×₃= 100G ×₁, ×₂ and ×₃ represent the percentages of silica, alumina and iron oxide, respectively. T is the salt glazing temperature in °C. When G was greater than 0, the glazes were bright; when between -0.1337 and 0 they were semi matt; and when less than -0.1337 they were matt. The color obtained may be approximately represented by the following formula: 10.3x₁ - 2.65x₂+ (14.6 + 54.1 (1.0066)^(T-1110))x₃= 100°C When C was between 0 and 2, white to tan glazes were produced; when between 2 and 3.5, light brown glazes were obtained; when between 3.5 and 4.75, brown glazes were produced; when between 4.75 and 8.2, mahogany colors were obtained; and when above 8.2, dark brown to black glazes were produced. Clays containing a high iron oxide content should be salt glazed at low temperatures while clays containing a low iron oxide content should be glazed at high temperatures to produce the best glazes. Decreasing the iron oxide and alumina contents will improve the brightness of the salt glazes. High alumina clays will produce darker colors than high silica clays with the same percentage of iron oxide.     

Preparation of fumed silica compacts for thermal insulation using wet processing method

This paper describes the preparation of fumed silica compacts for thermal insulation, using wet processing method. A series of thermal insulation compacts based on fumed silica powder and glass fibers were prepared. The influence of the mass ratio about fumed silica and glass fibers on the fracture strength and thermal conductivity was investigated. The results showed that the fracture strength increased first and then decreased with the mass ratio increasing. The thermal conductivity decreased linearly with the mass ratio increasing. When the compact was pressed under 6 MPa with a mass ratio of 5:1, it exhibited excellent thermal insulation at room temperature with a thermal conductivity of 0.042W/mK. Moreover, the compact was hydrophobic, after being modified by KH‐570.