Submicron SiO2 Powder: Characterization and Effects on Properties of Cement-Free Iron Ditch Castables

Submicron materials are those with particle size diameters between 0.1 and 1 μm. Submicron SiO2 generally refers to SiO2 powder with a D90 < 1 μm (D90 refers to the particle size distribution exhibited by the sample and corresponds, in this case, to 90% of the particles not exceeding a diameter of 1 μm). In this study, a new type of cement-free iron ditch castable was prepared using dense corundum and silicon carbide as the primary raw materials with submicron SiO2 powder as the binder. The effects of submicron SiO2 powder content on the bulk density, apparent porosity, linear rate of change, compressive strength, and bending strength were investigated. The mechanism of action of the submicron SiO2 powder was also investigated by analyzing its microstructure and particle size distribution. The results revealed that (1) the submicron SiO2 powder can be used as the sole bonding agent in the preparation of cement-free iron ditch castables; (2) in comparison to traditional castables, the cement-free castable developed in this study demonstrated strong service performance and high-temperature bending strength.

Leaf application of silicon in young cacao plants subjected to water deficit

The objective of this work was to evaluate the physiological and anatomical traits of plants of a cacao (Theobroma cacao) clone in response to water deficit after leaf application of silicon. A randomized complete block design was used, with four replicates, in a 2x3 factorial arrangement of two water regimes (irrigated or nonirrigated) and three silicon concentrations (0.0, 1.5, and 3.0 mg mL-1) applied in wettable SiO2 powder. The plants were evaluated 20 days after the irrigation regimes were applied. The use of SiO2 increased the stability of cell membranes and the photochemical efficiency of the plants under water deficit. The 1.5 mg mL-1 concentration of SiO2 increased photosynthetic rate, water use efficiency, and carboxylation efficiency, besides mitigating the effect of oxidative stress. Stomatal density was reduced in nonirrigated plants under the highest concentration of Si. The 1.5 mg mL-1 concentration of Si is considered optimal for the photosynthetic metabolism of young cacao plants under soil water limitation.