Preparation of humidity-controlling porous ceramics from volcanic ash and waste glass Dinh-Hieu Vu a,b, * , Kuen-Sheng Wang a , Bui Xuan Nam b , Bui Hoang Bac c , Tien-Chun Chu a a Graduate Institute of Environmental Engineering, National Central University, No.300, Jhongda Rd., Jhongli, Taoyuan 32001, Taiwan b Faculty of Mining, Hanoi University of Mining and Geology, Tu Liem, Hanoi, Viet Nam c Faculty of Geology, Hanoi University of Mining and Geology, Tu Liem, Hanoi, Viet Nam Received 14 January 2011; received in revised form 26 April 2011; accepted 28 April 2011 Available online 5 May 2011 Abstract This work investigated the preparation of a humidity-controlling porous ceramic via sintering of a mixture of volcanic ash soil and waste glass at 800–815 8C for 5–10 min. The final products were analyzed to identify the porous and mechanical properties, the moisture adsorption–desorption performance characteristics, and the adsorbed moisture amount. The most superior ceramic product, manufactured by mixing 30% weathered volcanic ash and 70% waste glass, was sintered at 800 8C for 5 min. The porous properties included a BET surface area of 163.73  12 m 2 /g, porosity of 52.08  2.1%, and a pore size of approximately 9 nm in diameter. The total amount of water adsorbed by the superior ceramic product was 0.047 cm 3 /g. In addition, the mechanical characteristics, including a bulk density of 1.34  0.2 g/cm 3 , 2.61  0.1% shrinkage, 4.64  0.3% ignition loss, and 6.58  0.4 MPa bending strength, are consistent with those of commercial porous ceramics. The leaching concentration of heavy metals in the final products were all well below the TCLP regulation limits. Thus, the most superior products meet the standards for commercial porous ceramics. # 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: Volcanic ash; Waste glass; Sintering; Mesoporous ceramic 1. Introduction In residential construction technology, humidity and ventilation control are essential, and they must be considered during construction to prevent the building walls from retaining moisture and growing mold [1]. To control the environmental humidity in houses, various solutions have been employed, such as the use of air-conditioning or pressed organic materials in the walls [2–4]. However, these solutions have disadvan- tages; the use of air-conditioning for long periods of time is costly while the organic material used in the walls is flammable, weak, and non-durable. In some cases, inorganic compounds, such as calcium chloride, silica-gel, and clay-sand, have also been used as wall materials for [5–7], but these materials exhibit poor water adsorption-desorption ability, and are potentially harmful to human health [8]. Therefore, the development of a low-cost, energy-efficient and safe ceramic that incorporates inorganic materials for humidity control is desirable. Certain porous materials, such as diatomaceous earth, sepiolite, silica gel, zeolite, and alumina gel, possess pore properties that are able to carry out capillary condensation. Recently, these materials have been recently used to control humidity and reduce energy consumption [9–14]. These mesoporous materials usually have a high specific surface area, significant porosity, and an appropriate pore structure, which enhance their ability to control the humidity in the environment. The relationship between the porous structure of a material and the capillary condensation mechanism is illustrated by the Kelvin equation: ln P P 0   ¼ 2g V L RT 1 r c where, P/P 0 is the relative pressure of vapor in equilibrium with a meniscus having a radius of curvature r c , g and V L are the www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 37 (2011) 2845–2853 * Corresponding author at: Postal address: Graduate Institute of Environmen- tal Engineering, National Central University, No. 300, Jhongda Rd., Jhongli, Taoyuan 32001, Taiwan. Tel.: +886 3 422 7151x34666; fax: +886 3 422 1602. E-mail address: vudinhhieu@gmail.com (D.-H. Vu). 0272-8842/$36.00 # 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2011.04.118