Abstract: Refractory, as a high-temperature furnace lining, exerts a crucial role for energy saving in industry. The ceramic industry already have gained a better energy-saving and rapid firing by means of building lightweight kiln and kiln car with light insulating material. However, the furnaces, in which working lining contacts or even reacts with the molten metal, slag, raw materials or intermediate products, require a higher density so as to ensure better corrosion resistance and longer service life, and in consequence, often have large heat capacity, high energy consumption and low thermal efficiency. Working lining refractory used in high-temperature furnaces usually consists of aggregate and matrix (except casting refractories), and aggregate has a high density while the matrix is relatively loose and more vulnerable to slag attack. With the change of thermal physical properties, the metamorphic layer will be spalled, whether the aggregate is damaged or not. Thus properly lightweight aggregates should not significantly reduce the strength or anti-media erosion resistance of refractory. Lightweight refractories refer to a class of refractories with density between light and heavy refractories. In this kind of refractories, aggregates with higher porosity (especially closed porosity) substitute for dense aggregates. Under the premise of retaining high-temperature performance, the use of lightweight refractories with lower heat capacity and thermal conductivity can achieve the purpose of thermal insulation and energy saving. Therefore, lightweight aggregates have a dominant impact on the preparation process, microstructure and performance of lightweight refractory. In this paper, material systems, related properties and the preparation methods of lightweight refractory aggregate are summarized, including partial sintering method, sintering agent loss by pore-forming agent, in situ decomposition pore-forming technique, foaming method, nanoparticle-assisted sintering method, discharge plasma sintering method and so on. And then it reviews the application of lightweight aggregates, the related performance and the effectiveness in refractory castable, unburned carbon-containing refractories and fired shaped products. However, research has revealed the difficulty to obtain satisfactorily low apparent porosity and water absorption while pursuing reduction of aggregate’s thermal conductivity and bulk density in the preparation of lightweight aggregates, which has become an obstacle to the popularization of lightweight refractory. We also delineate a combinatorial method of carbo-thermal reduction, transporting oxidation, combined with reactive sintering method, which dispenses with the preparation of lightweight aggregates and is capable of producing corundum-spinel lightweight refractory with density gradient. Finally, the paper sketches out the future prospect for the research of lightweight refractory, from the perspectives of the fabrication of lightweight aggregate, as well as processing techniques, performance evaluation, standards and specifications of lightweight refractories.
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2018, Vol. 32 
