Synthesis and properties of alkali-activated iron ore tailings blended with metakaolin

In this study, synthesis, microstructural characteristics, mechanical properties, and environmental compatibility of alkali-activated binders derived from iron ore tailings (IOT)—with partial replacement with metakaolin (MK)—were investigated. The binders were produced with a NaOH solution, IOT, and MK. A thermal cure at 100°C was used and the MK was applied as a partial replacement of IOT in three proportions (10, 20, and 30 wt%). The IOT-based specimens presented an average of 98.0 and 18.0 MPa at 7 days age of curing for compressive and flexural strength, respectively. The mechanical properties of the alkali-activated binders with MK decreased as the substitution ratio increased. By the microstructural analysis, it was found a zeolite-type phase in alkali-activated IOT, while in the binders blended with MK, three new mineral phases were identified. Furthermore, Fourier transform infrared, quantitative X-ray diffraction, and environmental analysis suggest that the Fe species present in IOT acted in the alkali-activation reaction.     

Thermo-oxidative aging of acrylonitrile-butadiene rubber gaskets with real geometry used in plate heat exchangers

This study investigates the effects of aging on the physical and mechanical properties of commercially available acrylonitrile-butadiene rubber (NBR) gaskets while maintaining their original geometry. Thermo-oxidative cycles with 10 and 70 mm in length specimens were conducted from 80 to 170°C up to 180 days. The samples were analyzed employing compression set (CS), hardness, indentation modulus, cross-link density, total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and thermogravimetry. The results showed that longer specimens presented better resistance to thermo-oxidative aging. Indentation results indicated regular oxygen permeability into the entire samples up to 110°C, while at higher temperatures, limited diffusion oxidation (DLO) effects promoted non-uniform aging. Time–temperature superposition (TTS) and Arrhenius methods were applied to predict the specimens' lifetime using CS as a failure criterion. Activation energies for 10 and 70 mm samples were 68.74 and 43.63 kJ mol⁻¹, respectively. Thus, the 70 mm specimen's lifetime was greater than 10 mm. For temperatures below ≈38°C, the response to the thermo-oxidative aging is independent of specimen length. Therefore, in determining the lifetime of gaskets with complex geometry, longer specimens are recommended to provide more reliable results than those suggested by the standards.