Dense spinel ceramic samples were prepared in present study via hot-press technique with and without the addition of sintering additive (LiF). Maximum sintering temperature was in the range of 1550-1600 °C and the applied load was 40 MPa. Two different temperatures of the first dwell were tested: 1100 °C and 1220 °C. Commercially available spinel powder (S25CRX) was used in present study. Density criteria were determined by the Archimedes method. Determined porosity was in the range of 0-0.97 %. SEM characterization revealed an inhomogeneous microstructure in the case of samples with the first dwell at 1220 °C. Moreover, secondary phases were identified inside the residual porosity (LiF and/or MgF2). Without the addition of LiF, the produced sample was opaque. Transparency of samples was achieved after the temperature of the first dwell was lowered (1100 °C). The maximum measured in-line transmittance was in the range of 48-67 % (for the wavelength range of 380-790 nm). On the basis of literature, a novel mechanism of the creation of oxygen vacancies during the densification with the addition of LiF was suggested.
In questo studio sono stati prodotti campioni di spinello densi mediante pressatura a caldo con e senza aggiunta di additivi di sinterizzazione (LiF), utilizzando temperature massime di sinterizzazione nell'intervallo 1550-1600 °C e applicando un carico di 40 MPa. In particolare, è stato analizzato l'effetto della temperatura della permanenza intermedia sperimentando due diverse temperature: 1100 °C e 1220 °C durante il ciclo termico. E' stata utilizzata una polvere di spinello commerciale (S25CRX). La densità è stata determinata col metodo di Archimede. La porosità dei campioni è risultata nel range 0-0,97 %. La caratterizzazione SEM ha rivelato una microstruttura disomogenea nel caso dei campioni con permanenza intermedia a 1220 °C. Inoltre, all'interno della porosità residua sono state identificate fasi secondarie (LiF e/o MgF2). Il campione prodotto senza l'aggiunta di LiF è opaco. Campioni trasparenti sono stati ottenuti abbassando la temperatura della prima permanenza (1100 °C). La trasmittanza misurata è nel range 48-67 % (per lunghezze d'onda di 380-790 nm). Sulla base de i risultati riportati in letteratura, è stato suggerito un nuovo meccanismo di creazione di vacanze di ossigeno durante la densificazione dello spinello con l'aggiunta di LiF.
Ceramici densi di spinello: preparazione tramite pressatura a caldo e caratterizzazione
Jan Hostasa;Andreana Piancastelli;Daniele Dalle Fabbriche
2017
Abstract
Dense spinel ceramic samples were prepared in present study via hot-press technique with and without the addition of sintering additive (LiF). Maximum sintering temperature was in the range of 1550-1600 °C and the applied load was 40 MPa. Two different temperatures of the first dwell were tested: 1100 °C and 1220 °C. Commercially available spinel powder (S25CRX) was used in present study. Density criteria were determined by the Archimedes method. Determined porosity was in the range of 0-0.97 %. SEM characterization revealed an inhomogeneous microstructure in the case of samples with the first dwell at 1220 °C. Moreover, secondary phases were identified inside the residual porosity (LiF and/or MgF2). Without the addition of LiF, the produced sample was opaque. Transparency of samples was achieved after the temperature of the first dwell was lowered (1100 °C). The maximum measured in-line transmittance was in the range of 48-67 % (for the wavelength range of 380-790 nm). On the basis of literature, a novel mechanism of the creation of oxygen vacancies during the densification with the addition of LiF was suggested.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.