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RISS 인기검색어
- 검색키워드
- 저자 : van Riessen, A. (검색결과 6 건)
- 무료
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Impact of activator type on the immobilisation of lead in fly ash-based geopolymer
Lee, Sujeong,van Riessen, Arie,Chon, Chul-Min,Kang, Nam-Hee,Jou, Hyeong-Tae,Kim, Youn-Joong Elsevier 2016 Journal of hazardous materials Vol.305 No.-
<P><B>Abstract</B></P> <P>Immobilisation of heavy metals in geopolymers has attracted attention as a potential means of treating toxic wastes. Lead is known to be effectively immobilised in a geopolymer matrix, but detailed explanation for the mechanisms involved and the specific chemical form of lead are not fully understood. To reveal the effect of the activator types on the immobilisation of lead in geopolymers, 0.5 and 1.0wt% lead in the form of lead nitrate was mixed with fly ash and alkaline activators. Different alkaline activators (either combined sodium hydroxide and sodium silicate or sodium aluminate) were used to achieve the target Si:Al ratios 2.0 and 5.0 in geopolymers. Zeolite was formed in aluminate-activated geopolymers having a Si:Al ratio of 2.0, but the zeolite crystallization was suppressed as lead content increased. No specific crystalline phase of lead was detected by X-ray diffraction, electron diffraction or FT-IR spectrometry. In fact, double Cs corrected TEM analysis revealed that lead was evenly distributed with no evidence of formation of a specific lead compound. A sequential extraction procedure for fractionation of lead showed that lead did not exist as an exchangeable ion in geopolymers, regardless of activator type used. Aluminate activation is shown to be superior in the immobilisation of lead because about 99% of extracted lead existed in the oxidizing and residual fractions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The type of alkaline activator critically influences the lead immobilisation capability. </LI> <LI> Aluminate-activated geopolymers are more suitable for binding lead in the gel. </LI> <LI> When a greater amount of Al contributes to the localized negative charge the tight lead is more tightly bound. </LI> <LI> Lead disperses randomly forming no specific chemical compound with silicon. </LI> </UL> </P>
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Thermal analysis of geopolymer pastes synthesised from five fly ashes of variable composition
Rickard, William D.A.,Temuujin, Jadambaa,van Riessen, Arie Elsevier 2012 Journal of non-crystalline solids Vol.358 No.15
<P><B>Abstract</B></P><P>This paper presents a study on the thermal properties of a range of geopolymers in order to assess their suitability for high temperature applications such as thermal barriers, refractories and fire resistant structural members. Geopolymers were synthesised from five different fly ashes using sodium silicate and sodium aluminate solutions to achieve a set range of Si:Al compositional ratios. The thermo-physical, mechanical and microstructural properties of the geopolymers are presented and the effect of the source fly ash characteristics on the hardened product is discussed, as well as implications for high temperature applications. The amount and composition of the amorphous component (glass) of each of the fly ashes was determined by combining XRD and XRF results. It was found that the Si:Al ratio in the glass of the fly ashes strongly influenced the thermal performance of the geopolymers. Geopolymers synthesised from fly ashes with a high Si:Al (≥5) in the glass exhibited compressive strength gains and greater dimensional stability upon exposure to 1000°C, whereas geopolymers synthesised from fly ashes with low Si:Al (<2) in the glass exhibited strength losses and reduced dimensional stability upon high temperature exposure.</P> <P><B>Highlights</B></P><P>► Quantification of the crystalline and amorphous phases of five different fly ashes. ► Si:Al ratio in the glass of the fly ash influences the thermal performance. ► Compressive strength of geopolymers can increase by up to 5 fold after firing. ► Sodium aluminate activated geopolymers exhibit thermal stability up to 800°C. ► Sintering during thermal exposure improved inter-particle bonding.</P>
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Strategies to control the high temperature shrinkage of fly ash based geopolymers
Vickers, L.,Rickard, W.D.A.,van Riessen, A. Elsevier 2014 Thermochimica acta Vol.580 No.-
Strategies to control thermally induced shrinkage in fly ash based geopolymers are investigated. The use of low (<2) Si:Al ratios in the geopolymer provides superior thermal properties and the addition of fillers delivered additional improvements resulting in impressive thermal resistance. Two thermally stable inorganic fillers, α-alumina and wollastonite, were used because of their high melting points and relatively low thermal expansion. Shrinkage events at elevated temperatures revealed that samples containing filler exhibited 30-35% less volume shrinkage than the control at 1000<SUP>o</SUP>C. Initial compressive strength was moderate (~30MPa), but increased markedly when samples were fired in excess of 600<SUP>o</SUP>C (>100MPa). Wollastonite addition also improved the flexural strength of the samples which was attributed to its acicular shape imparting fibre-like qualities. Microstructural investigations showed that unfired samples predominantly consisted of spherical particles coated with reaction product. Firing to 1000<SUP>o</SUP>C converted the morphology to a more compact phase with increased pore size.
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Performance of fibre reinforced, low density metakaolin geopolymers under simulated fire conditions
Rickard, W.D.A.,Vickers, L.,van Riessen, A. Elsevier 2013 Applied clay science Vol.73 No.-
This paper presents a study on the thermal behaviour of metakaolin based geopolymers that have been foamed and fibre reinforced in order t1o assess their suitability for high temperature applications such as thermal barriers and fire resistant panels. An international standard fire curve (ISO 834, 1999) was used to simulate the heating conditions of a fire. Fire testing was conducted on 50mm thick panels with an exposure size of 200mmx200mm. Fire ratings of more than one hour were achieved for all samples.
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The effect of pre-treatment on the thermal performance of fly ash geopolymers
Rickard, W.D.A.,Borstel, C.D.,van Riessen, A. Elsevier 2013 Thermochimica acta Vol.573 No.-
This paper presents a study on the thermal behaviour of fly ash geopolymers that have been pre-treated prior to thermal exposure. Thermal and mechanical analysis was conducted on geopolymers that were leached in water and gradually dried and the results were compared to untreated samples. The aim of the pre-treatment was to remove the water and the excess alkali without damaging the structure prior to high temperature exposure. Fast dehydrating water is known to damage geopolymers by inducing cracks. Alkalis are known to be network modifiers and as such, where in excess, reduce the melting point of aluminosilicate glasses. It was found that the pre-treatment produced samples with negligible thermal expansion up to 700<SUP>o</SUP>C and less damage associated with dehydration which increased their post firing compressive strength. The pre-treated geopolymer panel had a marginally shorter fire rating than the as-cured sample though it exhibited greater resistance to cracking and slower post dehydration temperature increases.
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