Pubblicazioni su rivista 2012
Alkali-bonded SiC based foams. Medri V, Ruffini A. Journal of the European Ceramic Society (2012), Vol. 32: pp.1907-1913.
Abstract: Silicon carbide (SiC) foams were developed by using a low temperature process such as chemical consolidation that is suitable to replace the sintering step. An alkali aluminosilicates binder, also known as geopolymer, was used. It was prepared from metakaolin, as aluminosilicatic raw powder, and KOH/K2SiO3 aqueous solution. The foaming agent was the metallic silicon present as impurity in SiC powders. Different grades of SiC were used as the main component (90 wt%) of the foams and the micro and macrostructures varied with the morphologies of the SiC raw powders. The surface of SiC grains participates to the geopolymeric process because of the dissolution of the silica layer into the alkaline solution. SiC foams were tested and characterized under oxidative atmospheres up to 1200 °C.
Bulk composition and microstructure dependence of effective thermal conductivity of porous inorganic polymer cements. Kamseu E, Nait-Ali B, Bignozzi MC, Leonelli C, Rossignol S, Smith DS. Journal of the European Ceramic Society (2012), Vol. 32: pp. 1593-1603.
Abstract: Experimental results and theoretical models are used to assess the effective thermal conductivity of porous inorganic polymer cements, often indicated as geopolymers, with porosity between 30 and 70 vol.%. It is shown that the bulk chemical composition affects the microstructure (grains size, pores size, spatial arrangement of pores, homogeneity, micro cracks, bleeding channels) with consequently the heat flow behaviour through the porous matrix. In particular, introduction of controlled fine pores in a homogeneous matrix of inorganic polymer cements results in an increase of pore volume and improvement of the thermal insulation. The variation of the effective thermal conductivity with the total porosity was found to be consistent with analytical models described by Maxwell–Eucken and Landauer.
Insulating behaviour of Metakaolin-based Geopolymer Materials assess with Heat Flux Meter and Laser Flash Techniques. Kamseu E, Ceron B, Tobias H, Leonelli C, Bignozzi MC, Muscio A, Libbra A. Journal of Thermal Analysis and Calorimetry (2012), Vol. 108(3): pp. 1189-1199.
Abstract: Thermo physical behavior of metakaolin-based geopolymer materials was investigated. Five compositions of geopolymers were prepared with Si/Al from 1.23 to 2.42 using mix of sodium and potassium hydroxide (* 7.5 M) as well as sodium silicate as activator. The products obtained were characterized after complete curing to constant weight at room temperature. The thermal diffusivity (2.5–4.5 9 10-7 m2 /s) and thermal conductivity (0.30–0.59 W/m K) were compared to that of existing insulating structural materials. The correlation between the thermal conductivity and parameters as porosity, pore size distribution, matrix strengthening, and microstructure was complex to define. However, the structure of the geopolymer matrix, typical porous amorphous network force conduction heat flux to travel through very tortuous routes consisting of a multiple of neighboring polysialate particles.
Mechanical and biological characterization of geopolymers for potential application as biomaterials. Catauro M, Bollino F, Kansal I,Kamseu E, Lancellotti I, Leonelli C. AZojomo - Journal of Materials Online (2012). DOI : 10.2240
Abstract: In this study two different geopolymer compositions have been investigated and characterized as potential biomaterials. The geopolymers are mainly composed of metakaolin, with some silica additions so that to reach molar ratio SiO2/Al2O3 = 2.10, plus additions of NaOH and sodium silicate in different percentages as activator and ligand, respectively. The work presents exhaustive microstructural characterization (FT-IR, SEM/EDS, XRD) and bioactivity studies on pressed powders of the two geopolymers. The materials were composed of amorphous aluminosilicates and a limited amount of zeolitic phases, found on the top surface. The compressive strength was higher than 65 MPa and flexural strength around 20 MPa after 20 days of curing at room temperature. In order to study their bioactivity, samples were soaked in a simulated body fluid (SBF) for 3 weeks to verify the ability to form a surface hydroxyapatite layer observable with SEM/EDS analysis.
The influence of process parameters on in situ inorganic foaming of alkali-bonded SiC based foams. Medri V, Ruffini A. Ceramics International (2012), Vol. 38(4): pp. 3351-3359
Abstract: Silicon carbide (SiC) foams were developed with a low temperature process by using an inorganic alkali aluminosilicates binder, also known as geopolymer. The foaming agent was the metallic silicon present as impurity in the SiC powder. Si0 in the alkaline solution led to gas evolution that induced the foaming of the slurries. The binder was a geopolymeric resin with atomic ratio Si/Al=2 and potassium as alkaline cation, classified as (K)poly(silalate-siloxo). The geopolymeric resin was prepared using metakaolin as aluminosilicatic raw powder, while the alkali aqueous solution was KOH/K2SiO3. Metakaolin in alkaline conditions dissolved and re-precipitated to form geopolymeric nano-particulates that acted as a glue to stick together SiC particles (90 wt%). Process parameters such as water addition, mixing time and curing temperature were correlated to the foam structure. The formation of prolate pores induced anisotropy in the compressive strength. The foams were studied by dilatometric analysis in inert and oxidative atmospheres up to 1200°C.