Silica Insulation Research Articles

A replacement of traditional insulation refractory brick by a waste‐derived lightweight refractory castable

AbstractLightweight insulation refractories are essential for high‐temperature performance to reduce energy consumption. This study investigates a new insulation material, that is, solid waste rice husk ash (RHA) derived lightweight refractory castable, replacing traditional insulation refractory brick. The RHA is generated after the burning of rice husk as biomass fuel. The RHA is used as an aggregate and alkali‐extracted silica sol from RHA as a binder to fabricate the insulation castable. The nanosilica containing (~30 wt%) sol is employed to synthesize the refractory castable by varying the sol amount (2.5‐12.5 wt% silica from sol). The castable specimens are cast by a vibro‐caster and fired at 900‐1200°C in a muffle furnace. The physic‐mechanical and thermal conductivity (κ) of the castable is investigated. At 1100°C with 10 wt% dry sol retaining sample shows an excellent apparent porosity (~65%), low bulk density (~ 0.8 g/cm3), and κ (0.136 W/m k) with sustainable compressive strength (6 MPa). The acquired results are a good match with the literature (other wastes‐derived insulation materials) and industrial (silica insulation brick) obtained data. These promising outcomes may inspire the refractory industries for using RHA as an aggregate and RHA extracted sol as a binder for making insulation castable.

Loss-Separation Study on Silica-insulated Gas-atomized Fe-Si-Al Soft Magnetic Composites

Fe-Si-Al soft magnetic composites were composed of gas-atomized Fe-9.6wt.%Si-5.4wt.%Al alloy powders insulated with silica nanoparticles. The influence of silica insulation content on the core’s magnetic properties was studied. It was found that increasing the silica mass ratio deteriorated the effective permeability and core loss in the frequency range of 40-120 kHz, while improved the quality factor at 100 kHz and DC-bias performance. The effective demagnetizing field reflected by density and the core’s volume resistivity may cause the variations of these magnetic parameters. Loss separation fitting was performed using the Bertotti formula, indicating that silica insulation increased the hysteresis loss and reduced the eddy-current loss. The hysteresis loss took over at the frequency lower than 120 kHz in this work. With increasing the frequency, the eddy-current loss grew more quickly than the hysteresis loss. Therefore, different methods should be adopted to reduce the core loss according to the core’s application frequency.

Microstructure and Thermal Insulation Property of Silica Composite Aerogel.

Tetraethyl orthosilicate was selected as a matrix of heat insulating materials among three silanes, and an anti-infrared radiation fiber was chosen as a reinforcement for silica aerogel insulation composite. The silica aerogel was combined well and evenly distributed in the anti-infrared radiation fiber. The heat insulation effect was improved with the increase in thickness of the aerogel insulation material, as determined by the self-made aerospace insulation material insulation performance test equipment. The 15 mm and 30 mm thick thermal insulation material heated at 250 °C for 3 h, the temperatures at the cold surface were about 80 °C and 60 °C, respectively, and the temperatures at 150 mm above the cold surface were less than 60 °C and 50 °C, respectively. The silica aerogel composites with various thicknesses showed good thermal insulation stability. The silica insulation composite with a thickness of 15 mm exhibited good heat insulation performance, meets the thermal insulation requirements of general equipment compartments under low-temperature and long-term environmental conditions. The thermal conductivity of prepared silica aerogel composite was 0.0191 W·m−1·k−1 at room temperature and 0.0489 W·m−1·k−1 at 500 °C.

A highly tunable and angle-insensitive plasmon resonances based on graphene ring-circle arrays

In our work, we propose a highly tunable and angle-insensitive plasmon resonances based on graphene ring-circle arrays. This was done by putting a layer of silica insulation material on the bottom layer of graphene ring-circle. Through simulation using finite difference time domain method (FDTD), it is found that a high sensitivity and low sensing medium refractive index nmed can be achieved. By changing the doping level ng and the Fermi level EF, we can find the graphene ring-circle arrays sensor has a good tunability. In addition, the simulation results indicate that the sensor of the graphene ring-circle has a good angle polarization tolerance and remarkable tunable performance. Therefore, the introduction of graphene ring-circle into sensor can strengthen the absorption of biological molecules and effectively detect the sensing range. Thus, it can be easily used to detect possible refractive index changes in gases, liquids and mixed solutions by the graphene ring-circle sensor. There will be more wide application prospects in the fields of biosensing, detection and imaging.

Energy and economic analysis of Vacuum Insulation Panels (VIPs) used in non-domestic buildings

The potential savings in space heating energy from the installation of Fumed Silica (FS) and Glass Fibre (GF) Vacuum Insulation Panels (VIPs) were compared to conventional expanded polystyrene (EPS) insulation for three different non-domestic buildings situated in London (UK). A discounted payback period analysis was used to determine the time taken for the capital cost of installing the insulation to be recovered. VIP materials were ranked using cost and density indexes. The methodology of the Payback analysis carried out considered the time dependency of VIP thermal performance, fuel prices and rental income from buildings. These calculations show that VIP insulation reduced the annual space heating energy demand and carbon dioxide (CO2) emissions by approximately 10.2%, 41.3% and 26.7% for a six storey office building, a two floor retail unit building and a four storey office building respectively. FS VIPs had the shortest payback period among the insulation materials studied, ranging from 2.5years to 17years, depending upon the rental income of the building. For GF VIPs the calculated payback period was considerably longer and in the case of the typical 4 storey office building studied its cost could not be recovered over the life time of the building. For EPS insulation the calculated payback period was longer than its useful life time for all three buildings. FS VIPs were found to be economically viable for installation onto non-domestic buildings in high rental value locations assuming a lifespan of up to 60years.

Effects of Powder Additives on Thermal Shrinkage of Nanoporous Silica Insulation

Effects of Powder Additives on Thermal Shrinkage of Nanoporous Silica Insulation

Effects of Powder Additives on Thermal Shrinkage of Nanoporous Silica Insulation

In this study, four powder additives were introduced as high-temperature shrinkage inhibitors to make high performance nanoporous silica insulation. The introduction of fumed alumina could greatly improve the thermal stability of the composites at higher temperatures, and the maximum service temperature could be increased to about 1000°C. When 5% fumed alumina was added, the volume shrinkage decreased from 18.49% to 3.47%. Moreover, better results could be achieved with the increase in mass ratio. In addition, fumed titania also improved the thermal stability of the composites to some extent, while boron carbide and boron nitride led to poor performance

An Analysis of the Energy Performance and Economic Efficiency of the Practical use of Low Carbon Fumed Silica Insulation Panel Using Recycled Resources

Based on the increase of the global interest in climate change, various political and technological efforts are being made in Korea in order to reduce carbon dioxide emissions, considered to be one of the main causes of greenhouse gas effects. Low energy and low carbon technologies with high reusability that enhance the performance of architectural materials have been developed in the architectural construction field [1]. This study has developed an FS insulation panel using recycled resources, and has verified the enhancement of economic efficiency, reduction of carbon dioxide emissions, and enhanced energy performance of the developed insulating panel. The results of the analysis have confirmed a 1.2t reduction of carbon dioxide emissions and a 7.3% increase in energy performance in comparison to standard insulators based on the existing legislative standards. Furthermore, cost effectiveness was also seen as the cost increased by 72% with a 10 year return period.

High Performance of Fumed Silica Insulation Board for Green Building

The linear shrinkage and flexural strength of fumed silica insulation board were investigated for high performance. Different opacifiers and mass ratios have been tested in mixtures with pyropyllite, ZrSiO4, SiC and TiO2. Depending on the refractive index of opacifier, linear shrinkage was different. The higher refractive index of opacifier lead to the lower linear shrinkage of board. Additionally, the influence of the heat treatment was studied. The surface of board was hardened by heat, so flexural strength was increased as increasing the temperature of heat treatment. The thermal conductivity of fumed silica insulation board was lower than 0.022 W/mK.

Effect of Composition on Thermal Conductivity of Silica Insulation Media

Nano-sized fumed silica-based insulation media were prepared by adding TiO2 powders and ceramic fibers as opacifiers and structural integrity improvers, respectively. The high temperature thermal conductivities of the fumed silica-based insulation media were investigated using different types of TiO2 opacifier and by varying its content. The opacifying effects of nanostructured TiO2 powders produced by homogeneous precipitation process at low temperatures (HPPLT) were compared with those of commercial TiO2 powder. The nanostructured HPPLT TiO2 powder with a mean particle size of 1.8 microm was more effective to reduce radiative heat transfer than the commercial one with a similar mean particle size. The insulation samples with the HPPLT TiO2 powder showed about 46% lower thermal conductivity at temperatures of about 820 degrees C than those with the commercial one. This interesting result might be due to the more effective radiation scattering efficiency of the nanostructured HPPLT TiO2 powder which has better gap filling and coating capability in nano-sized composite compacts.

Metal-Oxide-Semiconductor Capacitors Fabricated by Layer-by-Layer Nanoassembly and Microfabrication

Metal oxide semiconductor (MOS) capacitors were fabricated by electrostatic layer-by-layer self-assembly (LbL-SA) combined with a modified lift-off technique. The MOS capacitors were built on both n-type and p-type silicon substrates. The numbers of silicon dioxide (SiO2) nanoparticle layers were varied to characterize the electrical performance of MOS capacitors. Unlike the conventional process, LbL-SA allows us to deposit the thin films for a semiconductor device with a lower temperature, lower cost, and shorter processing time. The stability of the silica insulation layers was also investigated. Atomic force microscopy (AFM) served to monitor the film quality of the self-assembled thin films.

808 断熱材の新しい有効熱伝導率推定方法の提案(G06-2 熱物性・加工,G06 熱工学)

Concerning thermal insulation of alumina silica, an empirical equation, which relates the bulk density ρ, the absolute temperature T, and the thermal conductivity of the gas λ_a to the effective thermal conductivity λ, is proposed. The effective thermal conductivity has already been shown to be composed of conduction through the solid and the gas, and further thermal radiation thorough the insulation material. In our previous study, although we have proposed the empirical equation for alumina silica insulation, the accuracy of estimation was not good at the temperature below 600℃. In this study, a more accurate empirical equation is proposed by modifying the thermal conductivity of the gas. The newly proposed empirical equation is determined using thermal conductivities measured under vacuum conditions. The values predicted by using the proposed empirical equation are shown to agree well with the measured results.

Water Adsorption and Desorption Kinetics on Silica Insulation

Silica is an important component of thermal insulation used in aerospace transport vehicles. Although normally hydrophilic and requiring rewaterproofing after flight, silica insulation has been reported to become hydrophobic on heating and cooling in a vacuum and, therefore, potentially hydrophobic after reentry. To understand and model these processes, the rates of desorption and adsorption of water on silica were studied by thermogravimetry, Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy. Silica powders with a high surface area were heatedin vacuoin the temperature range 200–1000°C, infrared absorbance spectra were obtained at various temperatures, and surface structure was examined by X-ray photoelectron spectroscopy. A kinetic sorption model was developed based on a Langmuir rate expression. Activation energies for adsorption and desorption were determined by fitting the experimental results numerically. The study found adsorption of water on the heat-treated silica occurs within seconds, implying hydrophobicity is lost rapidly after the heat-treated silica is exposed to water.

Analysis and control of electrical insulation leakage in platinum resistance thermometers up to 1064 °C

Electrical insulation resistance measurements and standing dc voltage measurements have been made on fifteen standard platinum resistance thermometers in the range 631 °C to 1064 °C. A model for the insulation leakage resistance in the thermometer-furnace system is proposed that takes into account ground leakage loops and the dc insulation battery effect. A study of the properties of the insulation battery has led to a more complete understanding of the insulation leakage process, particularly in the commonly used silica insulation. It has been discovered that both the dc and ac insulation resistance of silica-insulated thermometers can be increased by orders of magnitude by applying a dc bias voltage of about +6, 4 V between the thermometer leads and ground. This bias voltage dependence has led, in turn, to an explanation for a severe ground effect reported elsewhere that caused the insulation resistance to deteriorate for days at a time. By applying a +6, 4 V bias to the thermometer leads, it has been demonstrated for a 25 Ω thermometer that the dc and ac leakage temperature error at 962 °C can be reduced from over 90 m°C to about 0,1 m°C, and that the dc error can be reduced to about 0,1 m°C over the range 631 °C to 1064 °C. It is shown that this bias voltage technique can readily be applied to a dc commercial thermometer bridge, and can be used to estimate the leakage temperature error during a normal temperature measurement.

Effect of core insulation on the quality of the extrudate in canned extrusions of γ-titanium aluminide

Non-isothermal forward extrusions of cast γ-TiAl (Ti-49.5Al-2.5Nb-1.1Mn, at%) were performed with billet temperatures of 1050, 1150, and 1225°C and a die and container temperature of 260°C. The billets were canned using 304 stainless steel tubing. Finite-element analysis indicates that rapid heat loss occurs from the canned billet to the die during the extrusion process. The temperature gradient in the billet produces non-uniform microstructure. A technique was developed to insulate the billet with layers of 0.050 inch (1.27 mm) thick silica fabric. The use of an insulator reduces billet heat loss during its transfer from furnace to press and during the extrusion process. Differences in microstructure and mechanical properties of the extrusions performed with and without the silica insulation were investigated and compared.

Screened mercury-electrode clamps for dielectric measurements

Mercury-electrode clamps with guard ring are described for the accurate determination of the dielectric constant and power factor of insulating materials in the form of disks about 5 cm. in diameter. The electrodes are made of mild steel and fused silica insulation is used. The apparatus is suitable for measurements at frequencies up to 1 Mc./sec. as well as for D.C. insulation measurements.

Some Notes on the Tilted Gold Leaf Electrometer, with Suggestions as to the Manipulation of Gold Leaf Suspensions, Suitable Insulators for Electrometer Work, &c

A new model of the C. T. R. Wilson tilted electrometer is described and its mode of use and method of adjustment are gone into. The instrument is provided with an adjustable charged plate, fused silica insulation, a microscope mounted on the same stand as the electroscope case, and has a number of other conveniences. The depth of the case is such as to permit the use of a high power objective. The electrometer has a small electrostatic capacity, and owes its high sensitiveness to its ability to work in a condition near instability. An appendix deals with the manipulation of gold leaf suspensions, and reviews the various insulators which are at present available for refined electrometer work.