Research PaperPreparation and encapsulation performance of Al2O3-SiO2-B2O3 glass-ceramic for high temperature thermal storage
Introduction
Thermal energy storage is widely considered to be a practical and effective method to integrate renewable energies into the production, which has been attracted particular interest and significance in the thermal applications such as heating, hot water, cooling and air-conditioning [1], [2], [3], [4]. Recently thermal energy storage materials mainly include sensible, latent heat and thermal chemical energy storage. The latent heat is generally much higher than sensible heat, further smaller storage volume and the temperature variation during operation is restrained because the phase change occurs at nearly constant temperature. Therefore the latent heat has been widely used in the industrial applications such as waste heat recover, manufacturing, construction materials, mining and metallurgical industry [5], [6].
In the high temperature thermal storage fields, molten salts had been attracted more attentions than molten metal and alloys [7], [8], [9], due to low cost, good stability, relatively low vapor pressure and high thermal capacity especially [10], [11]. However, the severe corrosion during solid-liquid phase change progress limited the application. In order to fix this problem, many methods are proposed [12], [13], [14]. Wäckelgård et al. [15] developed one new cermet (ceramic-metal) composite coating in a solar concentrating system for combined heat and power operating between 250 and 350 °C. Ma et al. [16] prepared a typical Fe-encapsulation material/Cu-core structure by an aerodynamic levitation method. A new type of PCMs based micro capsules containing an n-eicosane core and ZrO2 encapsulation material with the dual-functional characteristics of latent-heat storage/release and photo luminescence was designed and synthesized by Zhang et al. [17].
Although the metal or alloys as encapsulation materials have good heat transfer performance, thermal reliability, etc. [18], [19], which are easy to be oxidized once the temperature exceed 800 °C, therefore it limits the application [20], [21]. The glass-ceramic of Al2O3-B2O3-SiO2 have been attracted considered interests and presented a good prospects in the fields of electronics, information, mechanical and chemical engineering [22], [23] due to its low thermal expansion coefficient, long chemical durability, good corrosion resistance, high temperature resistance and dense structure [24], [25]. Therefore it can be as encapsulation material applied in thermal storage fields. Recently the glass-ceramic used in thermal storage rarely reported. In this paper, B2O3-Al2O3-SiO2 glass-ceramic was fabricated and characterized, and the phase composition, morphology, porosity ratio, density, thermal conductivity and thermal stability were investigated.
Section snippets
Experiment
Commercially available pure powders of Al2O3 (purity ⩾99.0%), SiO2 (purity ⩾99.0%) and B2O3 (purity ⩾99.0%) were supplied by China national medicine holding reagent co., Ltd. The binary phase diagram of Al2O3 and SiO2 were showed in Fig. 1. The liquid phase appears at the lowest temperature with the Al2O3 is about 10 wt.% in the Al2O3-SiO2 system, therefore the Al2O3/SiO2 mass ratio was fixed at 10%. The B2O3 was introduced in the Al2O3-SiO2 system in order to decrease the melting temperature,
XRD analysis
Fig. 2 showed the XRD diffraction patterns of samples with different conditions. The main chemical compositions were SiO2, Al4B2O9 and H3BO3. Fig. 2(a) showed the XRD diffraction patterns of different samples were heated for 3 h at 900 °C, and Fig. 2(b) showed the samples were heated at 700 °C, 800 °C, 900 °C and 950 °C with B2O3 content was 50%, respectively.
The possible reactions of Al4B2O9 and H3BO3 were:
Morphology analysis
Morphologies of B2O3-Al2O3-SiO2 glass-ceramic were
Conclusions
In this paper, Al2O3-SiO2-B2O3 glass-ceramic was prepared and investigated as encapsulation material for high temperature thermal storage industry. Several conclusions were summarized as follow: The main chemical compositions are SiO2, Al4B2O9 and H3BO3. The glass-ceramic performances good chemical stability, meanwhile it showed a good thermal stability from 300 °C to 900 °C. The porosity of this glass-ceramic nearly reached to 1.0% above the temperature of 900 °C, thermal conductivity are between
Acknowledgements
This work was supported by the Science and Technology Support Program of Hubei Province (Grant Nos. 2014BAA134 and 2015BAA107).
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