Water-retention properties of porous ceramics prepared from mixtures of allophane and vermiculite for materials to counteract heat island effects

Kiyoshi Okada, Shunsuke Matsui, Toshihiro Isobe, Yoshikazu Kameshima, Akira Nakajima

Research output: Contribution to journalArticle

41 Citations (Scopus)

Abstract

Porous ceramics for anti-heat island effect were prepared from mixtures of allophane and vermiculite (VA samples). Allophane and vermiculite which had been ground for 0.5-2 h was mixed in various mass ratios, formed into pellets by uniaxial pressing at 40 MPa, and heated at 600-800 °C to form porous ceramics. The large thermal expansion of the vermiculite upon explosive dehydration of interlayer water causes cracking of the pellets with higher vermiculite contents. However, this can be controlled by grinding the vermiculite prior to heating. Grinding the vermiculite for ≥2 h suppresses its expansion, enabling pellet samples with high vermiculite contents to be prepared without cracking. The bulk densities of samples prepared at 800 °C from vermiculite ground for 2 h decrease from 1.72 to 0.94 with increasing allophane content. The pore size distribution in these samples shows a distinct peak at about 1 μm irrespective of the mixing ratio. The number of smaller pores (a) of the samples increases from 37 to 63% with increasing allophane content. This absorption rate is fast enough to absorb >90% of the Wa within 1 min for samples of 10 mm Ø × 5 mm3 size. By contrast, the release of the absorbed water is very slow, with 50% of the Wa retained for ≥30 h in the VA samples at a relative humidity of 55% at 20 °C; this is slower than in pure allophane and much slower than in a reference sample of foamed glass (about 4 h). All these properties make the VA samples useful as water-retaining materials to combat "heat island" effects.

Original languageEnglish
Pages (from-to)345-350
Number of pages6
JournalCeramics International
Volume34
Issue number2
DOIs
Publication statusPublished - Mar 2008
Externally publishedYes

Fingerprint

Thermal effects
Water
Dehydration
Pore size
Thermal expansion
Atmospheric humidity
Heating
Glass
vermiculite

Keywords

  • Allophane
  • Anti-heat island material
  • Porous property
  • Vermiculite
  • Water-holding property

ASJC Scopus subject areas

  • Ceramics and Composites

Cite this

Water-retention properties of porous ceramics prepared from mixtures of allophane and vermiculite for materials to counteract heat island effects. / Okada, Kiyoshi; Matsui, Shunsuke; Isobe, Toshihiro; Kameshima, Yoshikazu; Nakajima, Akira.

In: Ceramics International, Vol. 34, No. 2, 03.2008, p. 345-350.

Research output: Contribution to journalArticle

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