New polystyrene (PS) foams with submicron pore sizes and open pore structure are introduced as potential cores for vacuum insulation panels (VIPs). Measurements of the thermal conductivity λ of the air-filled and evacuated PS foams, the influence of temperature T, opacifiers as well as gas pressure p on the thermal conductivity λ are presented. First results of the foam microstructures, as visualized by electron microscopy, confirm that pore sizes below 1 µm can be achieved. Thermal conductivity values of advanced samples in vacuum of about 7 mW/(m·K) were measured.

The thermal conductivity of spun glass fibers has been measured as a function of gas pressure and temperature at an external load of 0.1 MPa. At room temperature the thermal conductivity of the evacuated fibers was as low as 1.6• 10−3W/(m•K). An analysis of the heat transfer modes revealed that solid conduction contributes with 0.6 • 10−3 W/(m•K) and radiative conduction with 1.0 • 10−3 W/(m•K) to the thermal conductivity at room temperature.

We measured the total thermal conductivity λ of four resorcinol-formalde-hyde (RF-) aerogel tiles in a guarded hot plate apparatus and a hot-wire device. The temperature was varied between 20 and 80°C, the gas pressure (air) from 1000 mbar down to 1 • 10−4 mbar. All samples with bulk densities of ϱ = 158, 180, 205 and 236 kg/m 3 have been prepared using the same molar ratio of resorcinol to catalyst (R/C = 200). The measured thermal conductivities are between 5 and 8 • 10−3 Wm −l K −l in the evacuated state and in the range of 11 to 13 • 10−3 Wm −l K −1 in air at room temperature. The thermal conductivity data derived from the hot plate and the hot-wire device agree within 10−3 Wm −l K −l or 10 to 20 % of the absolute value, respectively. From the thermal conductivity measurements as a function of air pressure a typical pore size in the aerogels between 20 nm for ϱ = 236 kg/m 3 and 30 nm for ϱ = 158 kg/m 3 was derived. From additional infrared-optical transmission and reflection measurements the mass specific extinction e and the temperature dependent radiative conductivity could be calculated. The solid conductivity was separated by subtracting the infrared-optically derived radiative conductivity from the total conductivity of the evacuated samples. The solid thermal conductivity was found to increase by about 20 % in the temperature range from 20°C to 80°C. The total thermal conductivity in air as a function of the aerogel density shows a broad minimum. The optimal densitity for minimized thermal conductivity at room temperature was found to be about 180kg/m 3. To our knowledge the measured conductivities of the resorcinol-formaldehyde aerogels are within the lowest thermal conductivities ever measured for any solid body in air.

A method for manufacturing a vacuum insulation body (vacuum insulation panel; VIP) comprising the steps of: a) a vacuum-tight film (1) or slide connection is provided. b) A permeable to air but (on a powder-like filler 4) non-permeable sheet-like filter material (5) is provided. c) The sheet-like filter material (5) (with the vacuum-tight foil 1) or film joining edge connected so tightly that the connecting edge (6) between the sheet-like filter material (5) and the vacuum-tight film (1) or the film joining at least for the powder-like filler (4) is not permeable. d) The vacuum-tight film (1) or slide connection on the one hand and the sheet-like filter material (5) on the other hand are so arranged that can be filled in between a (with filler 4), closed to the outside receiving space (7) is obtained. e) The sheet-like filter material (5) is penetrated by a Einfullelements (8) of a filling device (9) for the powder-like filler material (4). f) At ambient pressure, ie in particular at normal atmospheric pressure, a desired amount of powder-like filler material (4) through the filling member (8) under a filling pressure (in the receiving space 7) is filled. g) removing the filling member (8) from the sheet-like filter material (5) After the filling of the receiving space (7) and the sheet-like filter material (5) is closed again at the affected site. located h) The combination of the vacuum-tight film (1) or sheet assembly and the sheet-like filter material (5) and the (in the receiving space 7) filler (4) is brought to a total relative to the ambient pressure in the process step f) lower pressure and thereby be the receiving space (7) and the therein powder-like filler material (4) through the sheet filter material (5) is vented therethrough. i) For further prolonged low pressure according to feature h) the vacuum-tight film (1) or foil connection is complete so tightly closed peripherally all round, that this joining edge (10) for air is not permeable, and so the receiving space (7) is hermetically sealed whole.

Aerogels are a unique class of materials possessing an open-cell structure with ultrafine cells/pores (<100nm), high surface area (400-1100 m2/g), and a solid matrix composed of interconnected particles, fibers, or platelets with characteristic dimensions of 10nm. Although monolithic aerogels are ideal candidates for many applications (e.g. transparent window insulation), current processing methods have limited their introduction into the commercial marketplace. Our research focuses on the formation of resorcinol-formaldehyde (RF) aerogel microspheres which offer an attractive alternative to monolith production. An inverse emulsion polymerization is used to produce these spherical gel particles which undergo solvent exchange followed by supercritical drying with carbon dioxide. This process yields aerogel microspheres (10-80µ diameter) which can be used as loosely packed powders, compression molded into near-net shapes using a polymer binder, or used as additives in conventional foaming operations to produce new aerogel composites with superior thermal properties. The emulsification procedure, thermal characterization, mechanical properties, and potential applications of RF aerogel microspheres will be discussed.

The pore size distributions of alumina and magnesia ceramics were determined by measuring the directional-hemispherical transmittance and reflectance. These values are highly sensitive to changes of the pore structure. The partially sintered alumina samples were measured at room temperature in a wavelength range from 0.5 to 6 μm. The equation of radiative transfer can be solved for absorbing and scattering media by a three-flux solution. With this three-flux solution the scattering coefficients were derived from the measured directional-hemispherical transmittance and reflectance. The scattering coefficients can also be calculated theoretically by the Mie theory, if the pore size distribution is known. Finally, the quantitative pore size distribution was determined by fitting the theoretical scattering coefficients to the experimental scattering coefficients. To check the correctness of the derived pore-size distribution, scanning electron microscopy (SEM) and atomic force microscopy (AFM) pictures of the alumina samples were taken. The pore-size distribution was then derived by counting the pores and determining the diameters D of the spherical pores. Both results agree well and show that the new procedure is a valuable tool to extract structural information during the final sintering state.

Because of the semitransparency of pBN in the infrared spectral region, the heat flux within this material does not only depend on its solid thermal conductivity, but also on its radiative properties. In order to characterise the heat transfer in pBN samples, the thermal and infrared optical properties were determined. From the measured spectral reflectance and transmittance of the samples, the radiative heat-transfer coefficient was derived. In addition, the thermal conductivity was determined via laser-flash and differential scanning calorimetry measurements. It was found that for temperatures above 600 K the radiative transport influenced the total heat-transfer coefficient significantly.

The thermal conductivity of pyrogenic silica powder boards mixed with a silicon carbide opacifier is measured as a function of gas pressure and of temperature. At room temperature and gas pressures around 1 to 5 mbar the thermal conductivity is about 0.004 W m(-1) K-1. At a mean temperature of 300 degreesC the evacuated panel has a thermal conductivity well below 0.010 W m(-1) K-1, because of the silicon carbide opacifier. Several square metres of vacuum panels have been encapsulated in laminated aluminium envelopes and tested as thermal insulations for building facades.

Computer simulations of switchable thermal insulation (STI) for solar heating of building facades have been performed. This technique uses a metal hydride to change the H-2 gas pressure within an evacuable panel and thus the thermal conductivity by about a factor of 50. Calculations of heat fluxes and temperatures have been performed in order to find the most suitable system arrangement and control strategy for the utilisation of solar thermal energy. Parameters of the dynamical simulation were the distance between the glass pane cover and the absorber surface, the panel - wall distance, and the dynamics of the switching process. The simulation shows that the annual heat gain can be as high as 140 kWh m(-2), with a variation of -30 kWh m(-2) upon change of the above parameters.

Measuring the pore size distribution in ceramics via preparation of polished sections and image analysis is a tedious task and other measuring methods for that purpose should be investigated. The measurement of light transmission gives a sensitive tool for the detection of changes in pore size distribution.Light transmission measurements are performed in situ during sintering of alumina samples at temperatures up to 1923 K. They are compared to shrinkage measurements by dilatometry. The temperature dependence of light transmission and the influence of absorption in alumina is discussed. Very pure alumina samples show no influence of absorption on the transmission at high temperatures. In less pure samples, however, increasing absorption with increasing temperature may strongly influence the transmission. The scattering and absorption coefficients could be calculated separately by numerical methods.

The thermal conductivity of powder fillings for load-bearing vacuum insulations is investigated. Different opacifiers have been tested in mixtures with perlite powder, precipitated silica, and fumed silica. Using temperature-dependent thermal conductivity measurements, the radiative thermal conductivity and the solid conductivity of the powder samples are separated. Additionally, the influence of the pressure load on the solid conductivity is studied. The thermal conductivities of silica powders with added opacifier powders (carbon black, magnetite, silicon carbide, titanium dioxide) can be as low as 0.003 W·m−1·K−1 if the powder boards are pressed with moderate loads. The use of microporous silica powders as filler materials allows internal gas pressures even beyond 10 hPa with only a moderate increase of the overall conductivity.

Light scattering by pore/particle interfaces causes diffuse light propagation in ceramics. The diffuse light transmission is highly sensitive to structural changes in the last sintering state. The transmission increases more than one order of magnitude between 93% and 99% of the theoretically possible density. By using diffuse transmission and reflection measurements, a quantitative analysis of the pore size distribution can also be made. The directional-hemispherical transmittance and reflectance of partially sintered Al2O3-samples were measured at room temperature in the wavelength range from 700 nm to 2500 nm. A three-flux solution of the equation of radiative transfer is shown to be an adequate tool to derive the extinction coefficients from the directional-hemispherical transmittances. The pore size distribution was determined by fitting theoretical light scattering of spherical pores, which was calculated by the Mie theory, to the experimental extinction data.

In order to optimize the infrared extinction of a SiC-powder in a silica powder matrix, Mie scattering calculations for spherical SiC-particles have been performed. A single oscillator-model was applied to calculate the optical constants of SiC. Taking into account the particle size distribution of a commercially available SiC-powder, its wavelength dependent extinction coefficient was calculated. The result is in very good agreement with the extinction spectrum of the powder derived by infrared optically measurements. Mie scattering theory also was used to find the optimum mean SiC-particle diameter of a mixture of 20% SiC-powder and 80% silica powder.

Measurements of the thermal conductivity of polyimide foams have been performed in the temperature range 173–323K for different gas pressures and different gas types (CO2 and Ar). The extinction of thermal radiation has been determined by hemispherical transmission and reflection measurements in the infrared. With these data, a quantitative model has been established which predicts the thermal conductivity of polyimide foams as a function of density, gas pressure and temperature. In addition the influence of low emissivity foils integrated into low density polyimide foams on the thermal conductivity has been calculated using a three-flux model of combined radiation and solid/gas conduction.

An evacuated thermal insulation panel has been developed consisting of glass panes as covers and a powder filling. Several powder materials and mixtures of powders have been testing regarding their thermal conductivity and the critical gas pressure for the onset of gas conductivity. With an opacified precipitated silica powder a thermal conductivity of less than 0.003 W/mK could be reached if evacuated below 0.1 mbar. A value of 0.004 W/mK has been measured at an internal gas pressure of 1 mbar. A crucial point of panel design is the rim seal which should provide a negligible gas permeation and a small thermal heat transfer coefficient. With very thin stainless steel foils these requirements could be met.

Thermal transport in low density silica aerogels was studied theoretically and experimentally over a wide range of optical thickness and ratio of radiative to conductive heat transfer. Measurements on the combined heat transfer were performed for aerogel densities between 5 and 220 kg m−3, for temperatures from 100 to 650 K, for internal gas pressures between 10−4 and 1000 hPa and two boundary emissivities of 0.04 and 0.77. A high precision numerical method for the calculation of the temperature profile and the total (combined) heat flux in these semi-transparent, non-scattering, non-grey media is presented.

Aerogels are a special class of open-cell foams with an ultrafine cell/pore size (<50 nm), high surface area (400-1100 M{sup 2}/g), and a solid matrix composed of interconnected colloidal-like particles or fibers with characteristic diameters of 10 nm. This paper examines the correlation between nanostructure and thermal conductivity in a series of resorcinol-formaldehyde (RF) aerogels prepared under different synthetic conditions.