Identification, evolution and transformation of silicon compounds in a heat treated biomass to high temperatures

Name: Enrique Ronald Yapuchura Ocaris
Type: PhD thesis
Publication date: 04/02/2019
Advisor:

Namesort ascending Role
Francisco Guilherme Emmerich Advisor *

Examining board:

Namesort ascending Role
Wanderlã Luis Scopel Internal Examiner *
Thiago Eduardo Pedreira Bueno Internal Examiner *
Miguel Ângelo Schettino Junior Internal Examiner *
José Domingos Ardisson External Examiner *
Francisco Guilherme Emmerich Advisor *
Cleocir José Dalmaschio External Examiner *

Summary: Scanning electron microscopy (SEM) coupled with X-ray dispersive energy (EDS) spectroscopy, Raman spectroscopy and X-ray diffraction (XRD) were successfully used to observe the location and morphology of silica (SiO2) phytoliths in carbonaceous materials derived from biomass and its transformation into silicon carbide (SiC) and SiO2 particles at high heat treatment temperatures (HTT). The analyzes were conducted on carbonaceous materials (chars) derived from the endocarp of babassu coconut (ECB), which naturally contains 1.6 wt.% of silica in its mineral matter. It was observed that ECB chars with HTT between 500 and 1200 °C have globular echinate morphotype SiO2 phytoliths with sizes between 12 and 16 μm; these phytoliths are mainly concentrated around the surface of the char submillimetric fibers present in the endocarp of babassu coconut and also in the general carbonaceous matrix of the material. Phytoliths are not found within the submillimetric char fibers. At the HTT of 1200 °C the phytoliths begin to rounded, and above 1300 °C HTT, most of the phytoliths decompose, part of the silicon reacts with carbon forming nanocrystalline β-SiC (crystallite size ~ 35 nm). Another part generates numerous (tens to hundreds) amorphous or nanostructured SiO2 micro- and sub-microparticles (with sizes predominantly below 2 μm) are observed at sites previously occupied by phytoliths. Few rounded phytoliths survive at 1400 °C HTT, but disappear in higher HTTs (1600-2000 °C). It is likely that the ensembles of SiO2 micro- and submicroparticles observed at many sites correspond to the remaining inner remaining part of the original phytoliths whose most external SiO2 structures (at and near the surface) decompose and participate in the carbothermic reaction for the formation of SiC. In addition, this study is complemented with the Raman spectroscopy characterization of the carbonaceous structure of the ECB heat treated samples, reporting characteristic parameters of the Raman D and G bands of carbonaceous materials.

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