Banca de DEFESA: GABRIEL CLINT GONCALVES

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : GABRIEL CLINT GONCALVES
DATA : 10/06/2021
HORA: 14:00
LOCAL: modo remoto por videoconferência: meet.google.com/cju-eokf-uhp
TÍTULO:

Study of strengthening by chemical tempering of lanthanum oxide-containing aluminoborosilicate glasses

PÁGINAS: 97
GRANDE ÁREA: Engenharias
ÁREA: Engenharia de Materiais e Metalúrgica
SUBÁREA: Materiais Não-Metálicos
ESPECIALIDADE: Cerâmicos
RESUMO:

Aluminoborosilicate glasses with rare-earth oxides have been the object of study for applications in dental porcelains and in solid-state lasers due to high mechanical properties and high refractive index. The objective of this work was to verify the viability of ion-exchange toughening (chemical tempering) as an alternative to add value and further improve the mechanical properties of this type of glass. Compositions of the SiO₂­–B₂O₃–Al₂O₃–La₂O₃–TiO₂ and SiO₂–B₂O₃–Al₂O₃–La₂O₃–TiO₂–Na₂O systems were investigated in order to evaluate the need to include alkali metal oxide for the ion-exchange process. The sodium oxide content was varied by 0, 5 and 10 mol%. The glasses obtained by melting in an electric oven were chemically tempered by immersion and deposition of KNO3 paste at 650 ^oC and 700 ^oC at intervals of 30 minutes, 3 hours and 24 hours. The X-ray diffraction analysis (XRD) did not identify the presence of crystalline phases in any of the compositions, while the energy-dispersive spectroscopy (EDS) analysis detected phase segregation in the composition with 10% Na₂O, confirmed by Raman spectroscopy. The evaluation by differential scanning calorimetry (DSC) resulted in glass transition temperature (T_g) ranges of 724 and 694 ^oC for compositions with 0 and 5% Na₂O, respectively. T_g1 at 653 ^oC and T_g2 at 718 ^oC were found for 10% Na₂O. After tempering, there was no positive variation in Vickers hardness, remaining the same or less for all conditions analyzed. There was a growth of up to 47% in fracture toughness (K_Ic) in compositions with 5% and 10% Na₂O, jumping from 1.35 to 1.98 MPa.m^1/2 in the composition with the highest Na₂O content, according to the Indentation Fracture method (IF). The analysis of the surfaces by EDS detected K⁺ with intensity proportional to the time of exposure in the compositions with the addition of Na₂O, indicating the effectiveness of the ion exchange between sodium and potassium and its time dependence.

MEMBROS DA BANCA:
Presidente - Interno ao Programa - 1671394 - HUMBERTO NAOYUKI YOSHIMURA
Membro Titular - Examinador(a) Externo à Instituição - SONIA REGINA HOMEM DE MELLO CASTANHO - IPEN
Membro Titular - Examinador(a) Externo à Instituição - CATIA FREDERICCI - IPT-SP
Membro Suplente - Examinador(a) Interno ao Programa - 1676364 - JULIANA MARCHI
Membro Suplente - Examinador(a) Externo ao Programa - 1761015 - RENATA AYRES ROCHA