Processing of CaLa₂S₄ infrared transparent ceramics: A comparative study of HP and FAST/SPS techniques

Abstract

The densification of CaLa 2 S 4 (CLS) powders prepared by combustion method was investigated by the use of Field-Assisted Sintering Technique (FAST) and Hot Pressing (HP). CLS powders were sintered using FAST at 1000°C at different pressures and heating rates and sintered by HP under 120 MPa from 800°C to 1100°C for 6 hours with a heating rate of 10°C/min. Comparison of both techniques was further realized by use of the same conditions of pressure, dwell time, and heating rate. Complementary techniques (XRD, SEM-EDS, density measurements, FTIR spectroscopy) were employed to correlate the sintering processes/parameters to the microstructural/compositional developments and optical transmission of the ceramics. Both sintering techniques produce ceramics with submicrometer grain size and relative density of about 99%.Nevertheless, HP is more suitable to densify CLS ceramics without fragmentation and also reach higher transmission than FAST. Transmission of 40%-45% was measured out of a possible maximum of 69% based on the Fresnel losses in the 8-14 μm window when HP is applied at 1000°C for 6 hours under 120 MPa. In both techniques, ceramics undergo reduction issues that originate from graphitic sintering atmosphere.

Crystallization of glass materials into transparent optical ceramics

“…However, the current literature provides little data on transparent non-oxide ceramics obtained through the glass crystallization route. The transparent non-oxide ceramics reported to date have been prepared only through the conventional powder processing approach, such as for ZnS [33,45], ZnSe [34], CaLa 2 S 4 [46], and others. One reason for this limitation is the lack of flexibility in the glass-forming process to enable fabrication of non-oxide transparent ceramics through glass crystallization.…”

Fabrication and optical properties of transparent fine-grained Zn1.1Ga1.8Ge0.1O4 and Ni2+ (or Cr3+)-doped Zn1.1Ga1.8Ge0.1O4 spinel ceramics

“…Transparent polycrystalline ceramics are promising optical materials for laser media [1,2], infrared domes [3,4], electro-optic devices [5,6], high refractive index lenses [7,8], scintillators [9,10], white light-emitting diodes [11,12], or transparent armors [13,14]. Compared to glasses, ceramics have stronger mechanical properties, greater thermal conductivity and excellent energy lasing effects due to their high crystallinity.…”

“…J o u r n a l P r e -p r o o f KNbTeO 6 [22], CaF 2 [23], CaLa 2 S 4 [3] and others. The reason for this lies in the inherent optical isotropy of cubic materials, while polycrystalline ceramics with lower symmetries exhibit optical anisotropy (i.e.…”

First La2O2S infrared transparent ceramics

“…Young's modulus (GPa) FLIR® CVD ZnS (Vitron) [62] CVD 178.3 74 Clear® CVD ZnS (Vitron) [62] CVD + HIP 148.3 88 ZnS-ISCR [63] Hot Pressing 310 85.9 ZnSe (APC) [64] CVD 112 67.2 CaF 2 [65,66] Single crystal 170 110 CaLa 2 S 4 -ISCR [67,68] Hot Pressing 570 95.8…”