Effect Of Rare-earth Oxide Additives Research Articles

Effect of rare-earth oxide additives on transparency and fluorescence of α-SiAlON ceramics

Recently, novel transparent and fluorescent materials are in demand for various optical applications such as lasers, scintillators, and solid-state lighting. α-SiAlON, which has excellent thermal and mechanical properties, also exhibits photoluminescence depending on the stabilized doped rare-earth ions. Its transparency and fluorescence depend on the rare-earth oxide added as a raw material, particularly in conventional powder processing. In this study, we fabricated α-SiAlON ceramics by adding various rare-earth oxides to elucidate their effects on the transparency and fluorescence of these ceramics. High-transparency α-SiAlON ceramics were fabricated by adding rare-earth oxides whose rare-earth ions have small ionic radii: Y2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, and Lu2O3. Because the fraction of α-SiAlON was high, the relative density was high, and the microstructure was composed of fine grains. In particular, α-SiAlON ceramics prepared by adding Ho2O3 showed lower light scattering than the other fabricated α-SiAlON ceramics because of the smaller α-SiAlON grains, resulting in higher in-line transmittance (48% at 600 nm). Furthermore, these transparent α-SiAlON ceramics exhibited fluorescence corresponding to the activated rare-earth ions: Ho3+, Er3+, Tm3+, and Yb3+ or Yb2+.

Effect of rare-earth oxide addition on luminescence properties of rare-earth silicon oxynitrides

Effect of rare-earth oxide addition on luminescence properties of rare-earth silicon oxynitrides

Effect of rare-earth oxide additives on the morphology of combustion synthesized rod-like $beta;-Si3N4 crystals

Effect of rare-earth oxide additives on the morphology of combustion synthesized rod-like $beta;-Si3N4 crystals

Effect of rare-earth oxide additives on the morphology of combustion synthesized rod-like β-Si 3N 4 crystals

This paper presents the results of synthesizing rod-like β-Si 3N 4 crystals by combustion synthesis (CS) with six rare-earth oxides (Y 2O 3, La 2O 3, CeO 2, Sm 2O 3, Gd 2O 3 and Yb 2O 3) as additives under high nitrogen pressure. The effect of rare-earth oxide additives on the final morphology of rod-like β-Si 3N 4 was investigated and the crystal growth mechanism was discussed in detail. The results reveal that the final morphology of combustion synthesized Si 3N 4 is strongly dependent on the viscosity of liquid formed by the rare-earth oxide and the SiO 2 on the Si powder surface. With the increasing of atomic number of the rare-earth elements, the final morphology is from elongated rod-like crystals to short columnar crystals.

The effect of rare-earth oxide addition on the hot-pressing of magnesium silicon nitride

Abstract The effect of rare-earth oxide addition (1–5 mass% of Ln 2 O 3 addition; Ln=Y, La, Nd, Sm, Gd, Dy, Er, and Yb) on the properties of hot-pressed (1550 °C, 90 min, 31 MPa) magnesium silicon nitride (MgSiN 2 ) compact (ceramic) has been investigated. The role of rare-earth oxide addition on the relative density was classified as follows: (i) positive effect (Y 2 O 3 , La 2 O 3 , and Yb 2 O 3 addition), (ii) no appreciable effect (Nd 2 O 3 and Er 2 O 3 addition), and (iii) negative effect (Sm 2 O 3 , Gd 2 O 3 , and Dy 2 O 3 addition). The grain sizes of the MgSiN 2 ceramics with rare-earth oxide addition were almost comparable to or slightly smaller than those of the pure MgSiN 2 ceramic. The average Vickers hardness of the MgSiN 2 ceramic with 1 mass% of Y 2 O 3 addition showed the highest value (21.5 GPa) amongst the MgSiN 2 ceramics with rare-earth oxide addition. The thermal conductivity of the MgSiN 2 ceramic had a maximum for the case of 1 mass% of Yb 2 O 3 addition (26.6 W·m −1 ·K −1 ) and was believed to be the highest value so far reported for MgSiN 2 ceramic. It was concluded that the relative density and Vickers hardness were best enhanced through the use of Y 2 O 3 addition, whereas the addition of Yb 2 O 3 was most suitable for enhancing the thermal conductivity.

Effect of rare-earth oxide addition on the thermal conductivity of sintered aluminium nitride

The densification of A1N ceramics and the improvement of its thermal conductivity are typically achieved by the addition of a small amount of oxides. The effects of oxide addition on the density and thermal conductivity of sintered A1N were investigated by Tsuge and co-workers [1, 2]. They found that the alkaliand rare-earth oxides (Re203) were useful additives for the fabrication of fully densified and highly thermally conductive A1N; Y203 is an especially good sintering additive. In the A1N sintering process, Y203 additive reacts with the surface oxide layer of A1N particles, forms the liquid phase of the Y A I O N system, causes the precipitation of yttrium-aluminium-oxide phases such as Y4A1209 (2Y203.A1203) in grain boundaries and lowers the oxygen content dissolved in A1N grains, and then the thermal conductivity of sintered A1N increases [2]. However, the effects of Re203 addition other than Y203 on the thermal conductivity of A1N have not been studied in depth. Recently A1N sintering with Y203 additive under reducing nitrogen gas atmosphere was reported to be a useful method to obtain sintered bodies with high thermal conductivity (>150 W m -a K -1) [3-7]. In this study the effects of Re203 addition on the thermal conductivity of A1N specimens sintered in reducing nitrogen atmosphere were investigated. A commercial A1N powder (Tokuyama Soda Co., Tokyo) with an average particle size of 0.6/xm and a specific surface area of 3.2 m 2 g-1 was used in this research. According to the manufacturer, this powder contains 1 wt % oxygen, 220 p.p.m, carbon and trace amounts of iron, calcium and silicon. In this work ND203, Sm203, Gd203, Dy203, Er203 and Yb20 3 powders (Hokko Chemicals Co., Tokyo) were used as the Re203 additives. I mol % of each of the rare-earth oxide powders as sintering aids were added, respectively, to the raw A1N powder. These powders were mixed in ethanol in a ball mill. After drying, the mixed powder was formed into pellets 14 mm in diameter and 8 mm high using a stainless steel die, and then cold isostatically pressed (CIPed) under 200 MPa pressure for 60 s. The CIPed pellets were placed in a graphite crucible, and then sintered using a graphite heater furnance at temperatures of 1773, 1873, 1973, 2073 and 2173 K for 1 and 3 h under 0.1 MPa nitrogen atmosphere. Furthermore, the CIPed samples were sintered in a graphite crucible with A1N packing powder in order to investigate the effect of the sintering atmosphere. The heating rate was 0.17 Ks Gd203 > Er203 > Yb203 >Nd203 >Sm203 addition. On the other hand, in sintering with packing powder, the thermal conductivity of A1N specimens with Re203 were about 95 W m -1K -1. The maximum thermal conductivity of A1N ceramics obtained in this work was 195 W m -1K -a for Dy203 addition. The results for the oxygen content of sintered A1N with the Re203 are shown in Fig. 2. The oxygen content of A1N specimens sintered without packing

Behavior of Urania–Rare‐Earth Oxides at High Temperatures

Uranium dioxide becomes hypostoichiometric when hated above 1600°C or in a reducing atmosphere. Upon cooling, free metallic uranium is rejected. The role and the effect of rare‐earth oxide additives on the stabilization of urania at high temperatures in a hydrogen environment are evaluated. A tentative phase diagram for the system uraniagadolinia is proposed.