Structure Characterization and Optimization of Process Parameters on Compressive Properties of Glass-Based Foam Composites A.A. Francis, and M.K. Abdel Rahman Central Metallurgical Research and Development Institute-CMRDI, department of advanced materials, Cairo-Egypt; adel_francis@hotmail.com (for correspondence) Published online 24 August 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ep.11842 The influence of process parameters, including tempera- ture, reaction time, and amount of foaming agent (SiC), on compressive property and porosity of glass-based foam compo- sites was studied by Box-Behnken experimental design. The interaction between the process parameters and their statistical significance on porosity and compressive strength was assessed through ANOVA. The glass-based foams, prepared from silicate wastes, were characterized by XRD, SEM, DSC, and compres- sive tests. Processing temperature was considered as the most significant factor. The two crystalline phases resulting from the heat treatment at 900–1000˚C have been identified as Ca 2 M- g 0.75 Al 0.25 Si 1.75 O 7 and CaSiO 3 . Two quadratic equations, cor- relating the compressive strength and porosity with the three process parameters, were developed whose R 2 values are 0.9977 and 0.935, respectively. The optimal process parameter settings to achieve an adequate porosity (56.6%) and high compressive strength (11.7 MPa) were determined. The glass- based products exhibited typical behavior of brittle foams. The stress-displacement curve implies that the failure mode is mainly due to damage accumulation process. Box-Behnken experimental design offers a cost effective option in the mass production of a wide range of glass-based foam products with promising engineering applications. V C 2013 American Institute of Chemical Engineers Environ Prog, 33: 800–807, 2014 Keywords: glass-based foam composites, Box-Behnken design (BBD), recycling, industrial wastes, optimization INTRODUCTION In developing countries and countries with economies in transition, management of waste often emerges as a problem that endangers human health and the environment. Although it may first appear to be national issue, the scope and magni- tude of waste problems are growing steadily as rapid techno- logical development, population density and standards of living rise. Therefore, in order to reduce environmental load- ing and effectively use natural resources, recycling of industrial wastes is needed to ensure better human health and safety. This article is devoted to the development of glass-ceramic foams, based on blast furnace slag by adding glass cullet and pore-forming agent, upon firing for structural and thermal applications. It is also concerned with the physical and mechanical property of the sintered materials within the tem- perature range 900–1000˚C. Blast furnace slag (BFS) is a byproduct of the steel and iron industries. It contains mainly inorganic constituents such as silica, calcium oxide, alumina, and magnesium oxide, in decreasing amounts as the main constituents, together with minor constituents such as MnO, Fe 2 O 3 and Al 2 O 3 . Due to the low iron content, it can be safely used in the production of cement and the preparation of mate- rials such as glass-ceramics [1–3], ceramic tiles, and bricks. In recent years, the production of foams has attracted sig- nificant attention, due to the wide range of engineering applications (e.g., molten metal filters, catalyst supports, acoustic insulators, porous burners, and biomedical devices). Foam glass is an interesting and feasible option for recycling waste glasses [4, 5]. However, to the authors’ knowledge, the statistical design of experiments has not been applied to optimize the foaming process and identify the major influ- encing parameters for producing glass-ceramic foams from a mixture of silicate wastes. Considerable work has been done regarding the recycling and management of cathode ray tube (CRT) wastes. Ling et al. [6] assessed the feasibility of utiliz- ing CRT glass as a substitute for natural aggregates in cement mortar. Other authors [7] focused on the re-use of lead- containing glass in the manufacturing of clay bricks and roof tiles. From an environmental point of view, it is believed that open-loop recycling and closed-loop recycling are two major ways for recycling CRT glass [8]. Some investigation has been carried out to evaluate the application of end-of-life CRT glass as the main component for porcelain stoneware tiles [9]; X-ray radiation-shielding applications [10]; and ceramic glazes [11]. It has been shown that high strength foam glass– ceramic products with interesting properties for heat insula- tion, sound absorption or shock wave absorbing material applications can be obtained from waste cathode ray tube [12]. An open-loop recycling method has been conducted by Mear et al. [13] to produce foam glasses from cathode ray tubes incorporated with TiN or SiC as foaming agents in addition to a stabilizing oxide. The effects of factors such as temperature, reaction time and reducing agent content on the microstructure of foam glasses from waste funnel glasses have also been investigated [14]. Fernandes and his co- authors [15] reported the preparation of high compressive strength foams using sheet glass wastes in combination with fly ash and carbonate as foaming agent. Few studies applied the sintering route for different types of silicate wastes, V C 2013 American Institute of Chemical Engineers Environmental Progress & Sustainable Energy (Vol.33, No.3) DOI 10.1002/ep 800 October 2014