Thermal Conductivity Of Glasses Research Articles

Thermal conductivity in modified sodium silicate glasses is governed by modal phase changes.

The thermal conductivity of glasses is well-known to be significantly harder to theoretically describe compared to crystalline materials. Because of this fact, the fundamental understanding of thermal conductivity in glasses remain extremely poor when moving beyond the case of simple glasses, e.g., glassy SiO2, and into so-called "modified" oxide glasses, that is, glasses where other oxides (e.g., alkali oxides) have been added to break up the network and alter, e.g., elastic and thermal properties. This lack of knowledge is apparent despite how modified glasses comprise the far majority of known glasses. In the present work, we study an archetypical series of sodium silicate [xNa2O-(100 - x)SiO2] glasses. Analyses of modal contributions reveal how increasing Na2O content induces increasing vibrational localization with a change of vibrations to be less ordered and a related general decrease in modal contributions to thermal conductivity. We find the vibrational phases (acoustic vs optical) of sodium vibrations to be relatively disordered compared to the network-forming silicon and oxygen species, explaining how increasing Na2O content decreases thermal conductivity. Our work sheds new light on the fundamentals of glassy heat transfer as well as the interplay between thermal conduction and modal characteristics in glasses.

Preliminary Investigation of Thermoelectric Electromotive Force Oscillation of NiCr/NiSi Thin Film Thermocouple in Dynamic Calibration.

In order to reveal the dynamic response characteristic of thin film thermocouples (TFTCs), the nichrome/nisil (NiCr/NiSi) TFTCs are prepared onto the glass substrate. With short pulse infrared laser system, NiCr/NiSi TFTCs are dynamically calibrated. The thermoelectric electromotive force (TEF) curves of NiCr/NiSi TFTCs are recorded by the memory hicorder system, which could reflect TEF signals with resolution ratio in nanosecond and microvolt, simultaneously. With increasing laser energy from 15.49 to 29.59 mJ, TEF curves display more and more violent oscillation, even negative value. The results show that the bounce of thermal energy happens between two interfaces of TFTCs because the thermal conductivity of glass and air is significantly lower than that of NiSi/NiCr TFTCs. The bounce of thermal energy results in the obvious decrease of nNiCr and nNiSi, as well as oscillation of TEF. For laser energy in 29.59 mJ, the bounce of thermal energy in NiCr film could result in nNiCr < nNiSi. Then, TEF value appears abnormal negative value. Based on the results, the complex thermal energy transport process in TFTCs dynamic calibration is revealed, which results in the oscillation of thermal energy and TEF signal.

An intelligent cooling material modified with carbon dots for evaporative cooling and UV absorption.

The emergence of cooling technology has brought about huge social benefits to society, but it is also accompanied by the serious problem of energy consumption. In countries close to the equator, intense solar radiation is accompanied by unbearable high temperatures and strong ultraviolet radiation. Therefore, we prepared a simple hydrogel with good evaporative cooling, which can work continuously and has good UV absorption, to solve the indoor cooling and UV radiation problems. Polyacrylamide (PAM) in the hydrogel provides a mechanically strong backbone, and polyethylene glycol (PEG) slows water loss and provides the hydrogel with the ability to reflect infrared light. Lithium bromide (LiBr) is a highly efficient water vapor absorbent, which can provide the hydrogel with water regeneration capability. Carbon dots (CDs) can provide excellent UV absorption for hydrogels, and CDs (4.28 kJ kg−1 K−1) have a higher specific heat capacity than water (4.20 kJ kg−1 K−1), which can store more heat for a better indoor cooling effect. The composite hydrogel has a good prospect of application in the windows of residential and high-rise buildings.

The influence of Gd2O3 on shielding, thermal and luminescence properties of WO3–Gd2O3–B2O3 glass for radiation shielding and detection material

The physical, structural, optical, shielding, thermal and luminescence properties of WO3-Gd2O3–B2O3 glasses were studied in this work. The effect of WO3 replacement by Gd2O3 on radiation shielding and radiation detection potential was evaluated. The glass density increases with increasing Gd2O3 concentration and the maximum value is 5.97 g/cm3. The FTIR and XRD result confirm that the trigonal BO3, tetrahedral BO4 and tungsten complex are the main chemical groups and coorperate into the amorphous structure of glass. The optical absorption spectra exhibit the absorbance of glasses in ultraviolet and visible light region. The shielding parameters of glasses, such as mass attenuation coefficient, effective atomic number, electron density and half value layer, were investigated theoretically and experimentally. They perform a small degradation of shielding property by increasing Gd2O3 content. There is no obvious dependence of Gd2O3 concentration on glass thermal conductivity and expansion. The strong photoluminescence of [WO6]6- group with 524 nm occurred under its charge transfer excitation and under the energy transfer from excited Gd3+ ion. In the radioluminescence, WGB glasses emitted the visible light with 562 nm based on the mixed emission from [WO6]6- group and oxygen vacancy. The glass possesses the X-ray detection efficiency around 18.65% of BGO crystal. The WO3–Gd2O3–B2O3 glass with 17.5 and 27.5 mol% of Gd2O3 is a promising γ-ray shielding material at room temperature and high temperature circumstance, respectively and one with 25 mol% of Gd2O3 owns the attractive potential for the X-ray radiation detection applications.

Hydrophobic in-situ SiO2-TiO2 composite aerogel for heavy oil thermal recovery: Synthesis and high temperature performance

Abstract In view of the global energy crisis, energy saving in high-temperature thermal production is urgent. The traditional rock wool and composite silicate board cannot meet the requirements of high efficiency thermal insulation for heavy oil recovery pipe due to their poor insulation performance, and the emerging SiO2 aerogel production has poor shielding ability to infrared thermal radiation, resulting in limited application at high temperature industry. In this study, a novel SiO2-TiO2 composite aerogel was synthesized by synchronous sol-gel technique instead of simply particle doping method, high temperature hydrophobic property was obtained by surface modification and pre-heat treatment. The structure characterization, thermal conductivity test, infrared radiation heat transfer calculation and energy saving simulation calculation of SiO2-TiO2 composite aerogel were carried out, and the thermal insulation performance evaluation of high temperature steam pipes application was obtained accordingly. Compared with glass fiber/SiO2 aerogel, the thermal conductivity of glass fiber/SiO2-TiO2 composite aerogel has achieved a 13.1% and 23.9% reduction in thermal conductivity at 300 °C and 400 °C, respectively. Energy saving simulation results showed that glass fiber/SiO2-TiO2 composite aerogel can save 31.94 wt% and 55.44 wt% of oil consumption annually comparing to the commonly used rock wool and composite silicate. At the same time, large hydrophobic angle (143.7°) and good stability are the guarantees for its long-term service under the complicated environment. To sum up, glass fiber reinforced SiO2-TiO2 composite aerogel can serve as super insulation to replace traditional insulation layer and pure SiO2 aerogel product in the field of ground steam pipes application.

Modelling analyses of the thermal property and heat transfer performance of a novel compositive PV vacuum glazing

This paper proposes an integrated photovoltaic vacuum glazing unit with an intermediate air cavity and a calibrated modelling approach to quantify its thermal properties and evaluate the heat transfer performance. Theoretical analyses of the heat transfer process are conducted with reasonable hypotheses and traceable boundary conditions. Three-dimensional heat transfer models are then established and cross-validated against previous publications. The detailed validation demonstrates the reliability of the developed complex models under different circumstances. Furthermore, four photovoltaic vacuum glazing configurations are compared in terms of the temperature distribution and overall heat transfer coefficient (i.e. U-value). Simulation results show that the photovoltaic vacuum double glazing can achieve the optimum performance among the four configurations based on simultaneous consideration of the PV module temperature and U-value. Sensitivity analyses of glazing design factors are also conducted for the U-value, which is found to be greatly reduced by decreasing the density and diameter of vacuum pillars as well as the glass thermal conductivity. A lowest U-value of 0.23 W/(m2·K) is achieved for the photovoltaic-vacuum double glazing and can be further improved with future design optimizations. This research can provide guidance to design improvement of PV vacuum glazing systems and promote their integration with building modelling tools.

Adhesion of freshwater columnar ice to material surfaces by crystallization from the melt

Abstract A new crystallization tower, based on the vertical draw, crystallization-from-the-melt technique of Czochralski, was designed, constructed, and validated for the growth of columnar ice on a range of material surfaces. In its current configuration, the crystallization tower can be used to grow crystalline laminates up to 75 mm thick on rectangular substrates that are up to 90 mm in diameter. Key to the success of this apparatus is the ability to independently control the temperature gradient between the substrate and liquid water reservoir as well as the speed of the linear stage used to regulate vertical motion. By imposing a slow draw rate with a small amount of undercooling, the ice laminates formed on the various surfaces showed close correspondence to the underlying rectangular shape of the substrates. With pre-seeding of the substrates, well-ordered polycrystalline ice with columnar microstructures was grown on aluminum and glass surfaces. Due to the rough, hydrophobic nature of Teflon, the microstructures were less ordered but still columnar. As a result of the low thermal conductivity of glass, larger undercooling was required to achieve growth on these surfaces as compared to aluminum. The crystallization tower can be used to grow ice directly on a variety of surfaces in a highly robust and automated fashion, which is of great utility to ice adhesion studies and investigations into the fundamental properties of ice.

Direct Growth of 5 in. Uniform Hexagonal Boron Nitride on Glass for High‐Performance Deep‐Ultraviolet Light‐Emitting Diodes

AbstractThe direct coating of 2D hexagonal boron nitride (h‐BN) on insulating solid glass will endow glass with advanced properties, thus offering killer applications of the new type hybrid of h‐BN glass. However, daunting challenges still remain regarding the direct growth methodology of h‐BN on glass. Herein, a catalyst‐free chemical vapor deposition route for the direct synthesis of 5 in. uniform h‐BN thin films on functional quartz and sapphire glass is developed. The optical transparency, surface wetting, and thermal conductivity of glass are readily tailored by varying the deposited h‐BN thicknesses from monolayer to over 20 layers. Encouragingly, the as‐obtained h‐BN/sapphire glass can serve as a stress‐releasing substrate for the van‐der‐Waals epitaxial growth of AlN functional layers, as well as a thermal conductive template for constructing high‐performance deep‐ultraviolet light‐emitting diodes. This work hereby provides a brand new direction for the application of h‐BN glass in next‐generation solid‐state lighting devices.

Multi-scale thermal modeling of glass interposer for mobile electronics application

Purpose – The functionality of personal mobile electronics continues to increase, in turn driving the demand for higher logic-to-memory bandwidth. However, the number of inputs/outputs supported by the current packaging technology is limited by the smallest achievable electrical line spacing, and the associated noise performance. Also, a growing trend in mobile systems is for the memory chips to be stacked to address the growing demand for memory bandwidth, which in turn gives rise to heat removal challenges. The glass interposer substrate is a promising packaging technology to address these emerging demands, because of its many advantages over the traditional organic substrate technology. However, glass has a fundamental limitation, namely low thermal conductivity (∼1 W/m K). The purpose of this paper is to quantify the thermal performance of glass interposer-based electronic packages by solving a multi-scale heat transfer problem for an interposer structure. Also, this paper studies the possible improvement in thermal performance by integrating a fluidic heat spreader or vapor chamber within the interposer. Design/methodology/approach – This paper illustrates the multi-scale modeling approach applied for different components of the interposer, including Through Package Vias (TPVs) and copper traces. For geometrically intricate and repeating structures, such as interconnects and TPVs, the unit cell effective thermal conductivity approach was used. For non-repeating patterns, such as copper traces in redistribution layer, CAD drawing-based thermal resistance network analysis was used. At the end, the thermal performance of vapor chamber integrated within a glass interposer was estimated by using an enhanced effective thermal conductivity, calculated from the published thermal resistance data, in conjunction with the analytical expression for thermal resistance for a given geometry of the vapor chamber. Findings – The limitations arising from the low thermal conductivity of glass can be addressed by using copper structures and vapor chamber technology. Originality/value – A few reports can be found on thermal performance of glass interposers. However thermal characteristics of glass interposer with advanced cooling technology have not been reported.

Characterization of thermal conductivity of SiO2–Al2O3–Y2O3 glasses

The thermal properties of SiO2–Al2O3–Y2O3 glasses were investigated within a temperature range of 25–800°C. This found that glass with a composition of 24Y2O3·21Al2O3·55SiO2 exhibits a thermal conductivity of 1.04W/mK at room temperature, and thermal conductivity increases with temperature due to an increase in the amount of bridging oxygen. The thermal conductivity of glasses with a composition of xY2O3·21Al2O3·(79-x)SiO2, on the other hand, decreased with an increase in either the Y2O3 content or Al2O3/SiO2 ratio. This decrease in thermal conductivity was analyzed with respect to the decrease in phonon mean free path resulting from the increased non-bridging oxygen content, which revealed 24Y2O3·21Al2O3·55SiO2 to have the maximum thermal conductivity of 1.7W/mK at 800°C. Glass systems incorporating yttria can therefore be considered suitable sintering additives for highly thermally conducting ceramics such as silicon nitride.

Study of thermal conductivity of glass with ZrO2-based thin films

Extraction-pyrolysis method is used for deposition of thin films of ZrO2 and ZrMgO3, ZrNiO3, ZrBaO3 onto glass substrates. The effect of thin films on coefficient of thermal conductivity of glass depending on the temperature is studied.

Home-built Apparatus for Measuring Thermal Conductivity of Glass and Polymer Materials

ABSTRACTAs a part of the IMI-NFG’s series of low-cost experiments in glass science [1,2] we have developed a simple home-built apparatus for measuring the thermal conductivity of glassy materials, from polymers to oxide glasses, in the range of 0.1 to 1.5 W/ °C. Our apparatus is inexpensive, relatively easy to construct and accurate enough for students to use for quantitative measurements of their own glass or polymer samples. Standard materials are used to demonstrate good correlation with literature values. We also measured the thermal conductivity of a silica filled epoxy and showed a linear increase with fill fraction to 20%. This simple, low-cost method can provide students and researchers with a much broader access to this important property.

Thermal Conductivity of Glasses Induced by Nuclear Quadrupole Interaction at Ultra Low Temperatures

It is investigated how nuclear degrees of freedom of tunneling system (TS) inherent in amorphous solids influence its acoustic properties. It was shown in our previous papers that below 10 mK nuclear quadrupole interaction breaks down the coherent tunneling. This phenomenon results in appearance of the quasi-gap in the distribution function for the tunneling amplitude splitting. The quasi-gap is responsible for the plateau in the temperature dependence of the real part of a dielectric permittivity or speed of sound. In this paper we are interested in ultrasonic absorption and thermal conductivity which are intimately connected. We demonstrate that there exists a temperature interval in a millikelvin region where the sound absorption behavior changes drastically from the behavior predicted by the standard tunneling model (STM). In particular, the sound absorption increases approximately by an order of magnitude. Since in the millikelvin region the heat transport is due to acoustic phonons, the thermal conductivity also should demonstrate a strong increase as compared to standard tunneling model. The application of a strong magnetic field is known to restore the coherent tunneling and the standard distribution for the tunneling splitting amplitude. Thus, one can expect that in a strong magnetic field the thermal conductivity should drop in the temperature interval where the coherent tunneling was initially destroyed.

Relation between Low-Temperature Thermal Conductivity and the Specific Heat of Cesium Borate Glasses

Low-temperature specific heat and thermal conductivity measurements have been performed on cesium borate glasses as a function of cesium oxide content. We have found experimental evidence of a concurrent growth of specific heat and thermal conductivity with increasing Cs(+) content. This finding shows the existence of an uncommon relationship between the peak in C(p)/T(3) and the plateau in thermal conductivity in glasses and represents the most intriguing result for these alkaline borate glasses. The role of local modes associated with heavy cations on the vibrational dynamics in oxide glasses has been considered. Furthermore, a possible correlation between low-temperature thermal properties and the structure on the nanometer length scale of these glasses is put forward.

Quadrupole effect on the heat conductivity of cold glasses

At very low temperatures, the tunneling theory for amorphous solids predicts a thermal conductivity κ ∝ T p , with p = 2 . We have studied the effect of the nuclear quadrupole moment on the thermal conductivity of glasses at very low temperatures. We developed a theory that couples the tunneling motion to the nuclear quadrupoles moment in order to evaluate the thermal conductivity. Our result suggests a cross over between two different regimes at the temperature close to the nuclear quadrupoles energy. Below this temperature we have shown that the thermal conductivity is larger than the standard tunneling result and therefore we have p < 2 . However, for temperatures higher than the nuclear quadrupoles energy, the result of standard tunneling model has been found.

Modeling high-temperature glass molding process by coupling heat transfer and viscous deformation analysis

Glass molding is as an effective approach to produce precision micro optical elements with complex shapes at high production efficiency. Since glass is deformed at a high temperature where the mechanical and optical properties depend strongly on temperature, modeling the heat transfer and high-temperature deformation behavior of glass is an important issue. In this paper, a two-step pressing process is proposed according to the non-linear thermal expansion characteristics of glass. Heat transfer phenomenon was modeled by considering the temperature dependence of specific heat and thermal conductivity of glass. Viscosity of glass near the softening point was measured by uniaxially pressing cylindrical glass preforms between a pair of flat molds using an ultraprecision glass molding machine. Based on the numerical models and experimentally measured glass property, thermo-mechanical finite element method simulation of temperature rise during heating and material flow during pressing was carried out. The minimum heating time and pressing load changes were successfully predicted.

Thermal conductivity in glasses with a phononic crystal like structure

We investigated the thermal conductivity of two glass samples with a phononic crystal like structure at temperatures below 100 mK. The samples consist of glass with holes on a triangular lattice. The diameters of the holes are 5µm and 25µm and the porosities are 62% and 45% respectively. The thermal transport in glasses at low temperatures is generally believed to be carried by phonons. The holes in the sample limit the mean free path for the thermal phonons and therefore reduce the heat transport. By measuring samples with restricted geometries it might be possible to observe heat transport channels which are not based on propagating thermal phonons. Such an additional heat transport channel should exist in glasses because of the existence of tunneling systems that interact with each other and therefore allow for an energy diffusion via resonant flip-flop processes. We present experimental data down to 20mK where the wavelength of the phonons becomes comparable to the lattice constant of the phononic crystal structure.

Thermal conductivity of mixed alkali silicate glasses at low temperature

Thermal conductivity of glass is one of the fundamental properties of it. However, that has not been studied enough. That of only less than 20 compositions has been measured below the room temperature. In this study, we measured the thermal conductivity of xNa2O·(100−x)SiO2 and (33−y)Na2O·yCs2O·67SiO2 glasses by a transient heating method in the temperature range from about 150K to room temperature. The conductivity of xNa2O·(100−x)SiO2 is found to decrease with the increase in alkali content. The dominant factor of this behavior is the decrease in phonon mean free path, which is due to the increase of non-bridge oxygen. Thermal conductivity of (33−y)Cs2O·yNa2O·67SiO2 is decreased with the increase in Cs2O/(Na2O+Cs2O) ratio. The dominant factor of this behavior is the decrease of sound velocity. However, composition dependence of the phonon mean free path also affects the thermal conductivity. Phonon mean free path of 33Cs2O·67SiO2 glass is longer than that of 33Na2O·67SiO2 glass, and should be related to the change in distribution of structural unit in glass. In addition, phonon mean free path of mixed alkali glasses are shorter than that of single alkali glasses.

The Role of Vibrations of Medium-Range Order Clusters in Thermal Conduction of Materials with a Disordered Structure

A microscopic model that provides a satisfactory explanation of the temperature dependence of the thermal conductivity coefficient for dielectric glasses in the temperature range above the plateau is proposed for the first time. According to this model, the transfer of thermal perturbations occurs through harmonic interaction of oscillators localized at medium-range order clusters with hinged bonds. It is demonstrated that the interaction coefficient of these clusters depends on the overlap integral of the spectral lines attributed to natural vibrations of the clusters, whereas the temperature behavior of the thermal conductivity coefficient is governed by the temperature evolution of the widths of the vibrational lines. With due regard for the results of investigations into the broadening of the vibrational lines, the temperature dependence of the thermal conductivity coefficient is calculated in the range 10–500 K. The calculated curve is in good agreement with the experimental data. The proposed model accounts for the low thermal conductivity of glasses in the temperature range under consideration.

Thermal Conductivity of a Glass: I. Measurement by the Glass–Metal Contact

The thermal (phonon) conductivity of glass has been measured by contacting the sample with a metal at a different uniform initial temperature. The subsequent temperature response in the metal is measured by a tiny thermocouple just underneath the (contact) surface. The coefficient of heat penetration λρcp follows directly from the fitted asymptotic temperature jump or drop for long times. Division by the separately measured heat capacity ρcp yields the thermal conductivity λ. The conductivity measurement reproducibility was σ = 3%. The standard deviation between validation measurements and round robin test results on Pyrex glass was σ = 5.8%, somewhat more than the accuracy σ = 5.2% of the round robin test results. The measurement method is insensible for slight imperfections of the thermal contact and infrared radiation diffusion (photon conductivity) in a hot glass. The method has been used with minor modifications for solid and molten samples at temperatures of 50–850°C and conductivities of 0.1–25 W/(m K). The thermal (phonon) conductivity of the investigated soda-lime silicate glasses increases slightly (∼27–30%) with temperature from ambient up to around the glass transition.