Synthesis, Processing, and Properties of Submicrometer‐Grained Highly Transparent Yttria Ceramics

Abstract

In this article, we report on the fabrication of 0.3-lm average grain-sized transparent yttria ceramics using a modified twostep sintering approach. This process yielded full densification of the yttria ceramics with a drastically reduced grain growth. These transparent yttria ceramics exhibited a transparency equivalent to that of single crystals in the near-infrared spectral region. The microhardness and fracture toughness of the 0.3-lm average grain-sized transparent yttria ceramics fabricated by a modified two-step sintering were found to exceed those of B300lm average grain-sized transparent yttria ceramics fabricated by conventional sintering by 25 and 70%, respectively.

Research Skills Enhancement in Future Mechanical Engineers

“…The ceramics part of the course should contribute to the following CDIO (Conceive-Design-Implement-Operate) skills number [2]:  1.2 (nuclear knowledge in engineering);  1.3 (advanced knowledge in engineering);  2.1 (thinking and resolution of engineering problems);  2.2 (experimentation and knowledge discovering);  2.4 (personal skills and attitudes);…”

“…One of the main concerns of the mechanical engineering professors of FEUP is the transmission of the best general competences CDIO (Conceive-DesignImplement-Operate) [2] and scientific knowledge, and also the development of skills that will be very helpful in the future active professional life.…”

Influence of La3+ ion in the yttria matrix in improving the microhardness of infrared transparent nano LaxY2-xO3 sintered via hybrid heating

“…But the hardness is at a moderate level compared to other window materials [3,8]. Even a  reduction in sintering temperature and soaking duration reduces the grain size to a great extent which improves the mechanical and transmittance properties [9].…”

“…Yttria is one of the most extensively studied and promising infrared transparent ceramics due to its excellent properties required for infrared transparent ceramics like isotropic body centred cubic structure which is stable even at 1800 ℃ [1], moderate refractive index and absence of birefringence [2], high thermal conductivity and low thermal expansion coefficient [3], high thermal shock resistance [4], high melting point [5], low emissivity in the mid infrared range at elevated temperatures [6], and high transparency in the visible and infrared range [7]. But the hardness is at a moderate level compared to other window materials [3,8].…”

“…Pellets were isostatically cold pressed at 200 MPa and sintered to 99.7% of the theoretical density at 1700 ℃ for a soaking duration of 4 h. The sintered pellets with an average grain size of 72 µm showed a transmittance of 73% at 580 nm after an annealing of 20 h at 1300 ℃ [12]. La 2 O 3 precursors, like La(OH) 3 and La 2 O 2 CO 3 , are effectively used to sinter the pellets at 1800 ℃ to improve the transmittance to 82.72% and 83.34% respectively at 4 µm [11]. Recently Gan et al [17] used hot pressing sintering to achieve a density of 99.9% in 12 at% La doped yttria ceramics which showed a transmittance of 68.9% at 400 nm and 81.9% at 1100 nm, whereas a pellet sintered without applying pressure achieved 99.8% of the theoretical density.…”