Elsevier

Ceramics International

Volume 42, Issue 8, June 2016, Pages 10079-10084
Ceramics International

Sinterability, microstructure and compressive strength of porous glass-ceramics from metallurgical silicon slag and waste glass

https://doi.org/10.1016/j.ceramint.2016.03.113Get rights and content

Abstract

Porous glass-ceramics have been prepared by the direct sintering of powder mixtures of metallurgical silicon slag and waste glass. The thermal behavior of silicon slag was examined by differential thermal analysis and thermogravimetry to clarify the foaming mechanism of porous glass-ceramics. The mass loss of silicon slag below 700 °C was attributed to the oxidation of amorphous carbon from residual metallurgical coke in the silicon slag, and the mass gain above 800 °C to the passive oxidation of silicon carbide. The porosity of sintered glass-ceramics was characterized in terms of the apparent density and pore size. By simply adjusting the content of waste glass and sintering parameters (i.e. temperature, time and heating rate), the apparent density changed from 0.4 g/cm3 to 0.5 g/cm3, and the pore size from 0.7 mm to 1.4 mm. In addition to the existing crystalline phases in the silicon slag, the gehlenite phase appeared in the sintered glass-ceramics. The compressive strength of porous glass-ceramics firstly increased and then decreased with the sintering temperature, reaching a maximal value of 1.8 MPa at 750 °C. The mechanical strength was primarily influenced by the crystallinity of glass-ceramics and the interfaces between the crystalline phases and the glassy matrix. These sintered porous glass-ceramics exhibit superior properties such as light-weight, heat-insulation and sound-absorption, and could found their potential applications in the construction decoration.

Introduction

Metallurgical silicon slag is the by-product in the pyrometallurgical silicon industry. The annual production of metallurgical silicon nearly amounts to two million tons in China, thus the generation of silicon slag is about 200 kt annually. The main applications of metallurgical silicon slag involve the recycling of metallic silicon component, the deoxidizing agent in steelmaking, the production of non-ferrous alloys, the economical feed stocks of colloidal silica and organosilyl derivatives [1], [2], [3], [4].

Compared with huge amounts of metallurgical slag, e.g. steel and copper slags [5], [6], metallurgical silicon slag received little attention due to its relatively limited production, thus the related researches were scarcely reported. Besides the glassy phase and metallic silicon, metallurgical silicon slag generally contains carbon and silicon carbide, which are the common foaming agents at elevated temperatures. This enables the facile production of porous materials from silicon slag by the conventional sintering process without the addition of extraneous foaming agents [7], [8]. Similar to the application of steel slag [9], metallurgical silicon slag could be an ideal feedstock to produce light-weight porous glass-ceramics, which exhibit superior properties such as heat insulation, sound absorption and humidity control [10], [11], [12].

The objective of this study was to prepare the porous glass-ceramics from metallurgical silicon slag and waste glass without the addition of foaming agent. The thermal behavior of silicon slag was initially investigated to clarify the foaming mechanism in the sintering process. Then, the silicon slag was mixed with different amounts of waste glass, and directly sintered in the mold without the usual powder compaction. The sintering conditions were systematically studied to examine the sinterability and microstructure of porous glass-ceramics. The variation of mechanical strength of porous glass-ceramics was qualitatively interpreted in terms of the crystalline composition and microstructure.

Section snippets

Raw materials

The metallurgical silicon slag was obtained from Anyang Huaqiang Metallurgical Materials Co., Ltd. Henan, China. The slag lump was crushed into small pieces and ground with alumina balls in a planetary mill to obtain slag powder. The as-prepared powder was passed through a 200 mesh sieve. In the same way, waste glass powder was prepared from the exhausted fluorescent lamps, and passed through a 120 mesh sieve. The rectangular/cylindrical refractory molds were manually manufactured with ceramic

Characterization of silicon slag

The chemical composition of silicon slag was shown in Table 1. It contains not only the major constituents of silica and sodium oxide, but also minor constituents of calcia, alumina, magnesia and ferric oxide etc. As a comparison, waste glass contains comparable amount of network formers (SiO2 and Al2O3) and higher contents of network modifying oxides (CaO and MgO). Unfortunately, the XRF analysis merely presented the elemental composition in the oxide formulation, and could not determine the

Conclusions

Porous glass-ceramics have been prepared by the direct sintering of the powder mixtures of metallurgical silicon slag and waste glass. The foaming process was initiated by the internal constituents of carbon and silicon carbide in the silicon slag. The pore structure could be controlled by the content of waste glass and sintering parameters. The apparent density decreased with the increase of waste glass and heating rate, and the pore size increased with the content of waste glass, sintering

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (51404225) and the excellent youth project of National Natural Science Foundation of China (51422405).

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