Browsing by Author "Luz, Ana Paula"
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Item Catalytic graphitization of novolac resin for refractory applications(Ceramics International, Elsevier, 2018-03) Talabi, Segun Isaac; Luz, Ana Paula; Lucas, Alessandra de Almeida; Pagliosa, Carlos; Pandolfelli, Victor CarlosThis study investigated how to induce graphite generation from the carbonization process of novolac resins using conditions that can be adopted for carbon-containing refractories (CCRs) production. The effect of boron oxide or boric acid (graphitizing agents), cross-linking additive (hexamethylenetetramine) and some processing parameters (mixing technique, vacuum degassing, heating rate and thermal treatments) on carbon graphitization from a commercial novolac resin were evaluated. The X-ray diffraction (XRD) technique was selected to measure the graphitization level and crystal parameters of the prepared samples. Based on the attained results, adding graphitizing agents prior to the pyrolysis of resin resulted in carbon crystallization. The best graphitization level was obtained when the mixtures containing 6 wt% B2O3 or 10 wt% H3BO3 were fired up to 1000 °C for 5 h using a heating rate of 3 °C/min. Although the reproducibility of the obtained results was ascertained, heterogeneous graphitization could be observed based on the XRD profiles, as well as some discrepancies in the calculated graphitization level values. This phenomenon was attributed to the additives susceptibility to agglomeration, preferential graphitization starting from lower binding energy sites and heat treatment temperature, among others.Item Graphitization of Lignin-Phenol-Formaldehyde Resins(Materials Research, Scielo, 2020) Talabi, Segun Isaac; Luz, Ana Paula; Pandolfelli, Victor Carlos; Lima, Vitor Hugo; Lucas, Alessandra de AlmeidaEnvironmental friendliness and cost demand the development of lignin-modified phenolic (LPF) resins for application as a binder for carbon-containing refractories (CCRs) production. Moreover, the in-situ graphitization of such resins can produce crystalline carbon, which is an essential component of CCRs. Consequently, this study investigated LPF resins graphitization using ferrocene, boron oxide and boric acid. The modified resins were synthesized using thermally treated kraft lignin based on 1.5 formaldehyde to phenol molar ratio and with up to 30 wt.% lignin as phenol replacement. The resins chemical composition and the structural organization and oxidation resistance of carbons derived from the plain resins and those containing the graphitizing additives were determined. The results showed that ferrocene and the boron compounds could induce graphitic carbon generation when carbonizing LPF resins at 1500 °C for 5 hours. The best graphitization level (73%) was achieved when 10 wt.% boric acid was added to the resin produced with 20 wt.% lignin. Regarding the formulations containing ferrocene, the highest amount of graphitic carbon (48%) was generated when 5 wt.% of this additive was added to the resin synthesized with 10 wt.% lignin. The carbons derived from the formulations containing boron oxide presented the best oxidation resistance.Item Structural evolution during the catalytic graphitization of a thermosetting refractory binder and oxidation resistance of the derived carbons(Materials Chemistry and Physics, Elsevier, 2018-06) Talabi, Segun Isaac; Luz, Ana Paula; Pandolfelli, Victor Carlos; Lucas, Alessandra de AlmeidaCarbon-containing refractories' (CCRs) thermomechanical properties depend on the presence of carbonaceous phase with a structure and features similar to those of graphite. Based on this, boron oxide and boric acid were used to induce graphite generation during the pyrolysis of novolac resin (binder for CCRs) to provide an additional source of crystalline carbons. In this study, the structural evolution leading to crystallization of the derived carbons was studied via Fourier Transform Infrared (FTIR) spectroscopy. The results showed that the carbons graphitization was as a result of the formation and cleavage of the Bsingle bondOsingle bondC bond during heat treatment. The lower binding energy of this bond compared to plain Csingle bondC bond permits carbon atoms rotation and restructuring necessary for graphite generation during the pyrolysis operation. Furthermore, the research investigated the oxidation resistance of the derived carbon samples with the aid of thermogravimetric (TGA) and differential scanning calorimetry (DSC) equipment. The influence of different mixing routes at the preparation stage and hexamethylenetetramine (HMTA) addition to the resin formulations on the carbons' oxidation resistance was also examined. The analysis provides insight on the parameters that control the oxidizing behavior of the different samples obtained based on these variations. Several factors including graphitization, composition and atoms bond strength were observed to influence their performance when the carbons were exposed to the non-reducing environment at high temperatures up to 1000 °C.Item Synthesis and graphitization of resole resins by ferrocene(Progress in Natural Science: Materials International, Elsevier, 2019-02) Talabi, Sgun Isaac; Luz, Ana Paula; Pandolfelli, Victor Carlos; Bernardes, J. S.; Lucas, Alessandra de AlmeidaCommercial (Rs) and laboratory synthesized resoles (LSRs) containing 3–5 wt% ferrocene have been used to study the development of thermosetting resin compositions as binder materials for carbon-containing refractories (CCRs) production. The LSRs were developed based on formaldehyde to phenol 1.5 mol.% (1.5Rs) and 2.0 mol.% (2Rs). Microstructure and oxidation resistance of carbons derived from plain and modified resins have been compared. Chemical structure of the resins was studied using Fourier Transform InfraRed-Attenuated Total Reflection (FTIR-ATR) spectroscopy. X-ray Photoelectron spectroscopy was used to examine chemical changes during heat treatment of the modified products. Flow behavior of plain and formulated resins has been measured under isothermal condition. Rheology measurement results show that the selected amount of ferrocene did not affect the resin near-Newtonian fluid behavior and processability during refractory production. X-ray diffraction (XRD) analysis and transmission Electron Microscope (TEM) were used to characterize the derived carbon samples after thermal treatment of the resins. The results demonstrate that ferrocene is an excellent additive for crystallizing resoles carbon. The presence of fringes in TEM images indicates the graphitized carbon microstructure. The carbon reactivity in an oxidizing environment was also determined via thermogravimetric analyzer (TGA). Several factors, such as bond strength and atoms arrangement, have been found to control the carbonized modified-resin oxidation resistance.