Fabrication and properties of La₂O₃-doped transparent yttria ceramics by hot-pressing sintering

Gan, Lin,Park, Young-Jo,Zhu, Lin-Lin,Go, Shin-Il,Kim, Haneul,Kim, Jin-Myung,Ko, Jae-Woong Elsevier 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.695 No.-

<P><B>Abstract</B></P> <P>In this work, highly transparent La<SUB>2</SUB>O<SUB>3</SUB>-doped yttria ceramics were fabricated by a hot-pressing method. The effects of the La<SUB>2</SUB>O<SUB>3</SUB> doping concentration (0–17 at.%) on the optical transmittance, microstructures, microhardness, and thermal conductivity levels of the transparent yttria were investigated in an effort to develop a user's choice guide pertaining to the optical, mechanical, and thermal properties. The optimal La<SUB>2</SUB>O<SUB>3</SUB> doping concentration for the optical transmittance was found to be 12 at.%, leading to in-line transmittance levels of 68.9% at 400 nm and 81.9% at 1100 nm (2 mm thick). The microhardness changed from 6.82 to 7.66 GPa and was found to be closely dependent on the grain sizes of the samples, which varied from 3.55 μm to 0.95 with changes in the La<SUB>2</SUB>O<SUB>3</SUB> doping concentration. The biaxial flexure strength of a hot-pressed sample with an average grain size of 1.46 μm exceeded that of a conventionally pressureless-sintered coarse-grained sample (grain size 40.82 μm) by 94.4%. The thermal conductivity showed a significant decrease from 16.40 to 5.71 W/mK with an increase in the La<SUB>2</SUB>O<SUB>3</SUB> doping concentration from 0 to 17 at.%. Potential applications of the transparent yttria ceramics with different compositions were suggested based on the combination of the optical, mechanical, and thermal properties.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Highly transparent La-doped yttria ceramics were prepared by hot pressing. </LI> <LI> Effects of La concentration on transmittance, microstructure were studied. </LI> <LI> Effects of La concentration on thermal conductivity were studied. </LI> <LI> Microhardness and biaxial flexure strength of the samples were studied. </LI> </UL> </P>

Optical and thermo-mechanical properties of fine-grained transparent yttria ceramics fabricated by hot-press sintering for infrared window applications

Gan, Lin,Park, Young-Jo,Zhu, Lin-Lin,Kim, Ha-Neul,Ko, Jae-Woong,Kim, Hai-Doo Elsevier 2018 Journal of the European Ceramic Society Vol.38 No.11

<P><B>Abstract</B></P> <P>In this work, highly transparent yttria ceramics Φ = 55 mm in size were fabricated by a hot-pressing method with 1 at.% ZrO<SUB>2</SUB> or 12 at.% La<SUB>2</SUB>O<SUB>3</SUB> as a sintering additive. For a 4-mm-thick specimen doped with ZrO<SUB>2</SUB>, the in-line transmittance reaches 71.1% at 400 nm and 80.9% at 1100 nm, and the transmittance of the La<SUB>2</SUB>O<SUB>3</SUB>-doped specimen is comparable to that of the ZrO<SUB>2</SUB>-doped specimen. By means of the relatively low sintering temperature of 1600 °C, the present samples exhibited very fine microstructures (<2 μm), giving rise to excellent mechanical strength levels (∼200 MPa). With regard to the 1 at.% ZrO<SUB>2</SUB>-doped specimen, the combination of high strength and high thermal conductivity (∼10 W/m K) substantially improved parameters related to the thermal shock resistance. The results of this study indicate that the hot-pressed transparent yttria ceramic doped with 1 at.% ZrO<SUB>2</SUB> is optically, mechanically, and thermally suitable for high-temperature IR window applications.</P>

Synthesis of Azole-containing Piperazine Derivatives and Evaluation of their Antibacterial, Antifungal and Cytotoxic Activities

Gan, Lin-Ling,Fang, Bo,Zhou, Cheng-He Korean Chemical Society 2010 Bulletin of the Korean Chemical Society Vol.31 No.12

A series of azole-containing piperazine derivatives have been designed and synthesized. The obtained compounds were investigated in vitro for their antibacterial, antifungal and cytotoxic activities. The preliminary results showed that most compounds exhibited moderate to significant antibacterial and antifungal activities in vitro. 1-(4-((4-chlorophenyl) (phenyl)methyl)piperazin-1-yl)-2-(1H-imidazol-1-yl)ethanone and 1-(4-((4-Chlorophenyl)(phenyl)methyl)piperazin-1-yl)-2-(2-phenyl-1H-imidazol-1-yl)ethanone gave remarkable and broad-spectrum antimicrobial efficacy against all tested strains with MIC values ranging from 3.1 to $25\;{\mu}g/mL$, and exhibited comparable activities to the standard drugs chloramphenicol and fluconazole in clinic. Moreover, 2-((4-((4-chlorophenyl)(phenyl)methyl)piperazin-1-yl)methyl)-1H-benzo[d]imidazole was found to be the most effective in vitro against the PC-3 cell line, reaching growth inhibition values (36.4, 60.1 and 76.5%) for each tested concentration: $25\;{\mu}g/mL$, $50\;{\mu}g/mL$ and $100\;{\mu}g/mL$ in dose-dependent manner. The results also showed that the azole ring had noticeable effect on their antimicrobial and cytotoxic activities, and imidazole and benzimidazole moiety were much more favourable to biological activity than 1,2,4-triazole.

Synthesis of Azole-containing Piperazine Derivatives and Evaluation of their Antibacterial, Antifungal and Cytotoxic Activities

Lin-Ling Gan,Bo Fang,Cheng-He Zhou 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.12

A series of azole-containing piperazine derivatives have been designed and synthesized. The obtained compounds were investigated in vitro for their antibacterial, antifungal and cytotoxic activities. The preliminary results showed that most compounds exhibited moderate to significant antibacterial and antifungal activities in vitro. 1-(4-((4-chlorophenyl) (phenyl)methyl)piperazin-1-yl)-2-(1H-imidazol-1-yl)ethanone and 1-(4-((4-Chlorophenyl)(phenyl)methyl)piperazin-1-yl)-2-(2-phenyl-1H-imidazol-1-yl)ethanone gave remarkable and broad-spectrum antimicrobial efficacy against all tested strains with MIC values ranging from 3.1 to 25 μg/mL, and exhibited comparable activities to the standard drugs chloramphenicol and fluconazole in clinic. Moreover, 2-((4-((4-chlorophenyl)(phenyl)methyl)piperazin-1-yl)methyl)-1H-benzo[d]imidazole was found to be the most effective in vitro against the PC-3 cell line, reaching growth inhibition values (36.4, 60.1 and 76.5%) for each tested concentration: 25 μM, 50 μΜ and 100 μM in dose-dependent manner. The results also showed that the azole ring had noticeable effect on their antimicrobial and cytotoxic activities, and imidazole and benzimidazole moiety were much more favourable to biological activity than 1,2,4-triazole.

Enhancement of the optical transmittance of hot-pressed transparent yttria ceramics by a multi-step sintering process

Gan, Lin,Park, Young-Jo,Zhu, Lin-Lin,Go, Shin-Il,Kim, Haneul,Kim, Jin-Myung,Ko, Jae-Woong Elsevier 2016 CERAMICS INTERNATIONAL Vol.42 No.12

<P><B>Abstract</B></P> <P>In this work, we report the enhancement of the optical transmittance of yttria ceramics via a ‘pre-sintering/hot-pressing/hot-isostatic pressing’ multi-step process. The in-line transmittance reaches 78.0% at 400nm and 83.2% at 1100nm with an average grain size of approximately 1µm. This sintering route is derived and upgraded from our previously reported one-step hot-pressing method for the fabrication of transparent yttria ceramics. Through the enhanced strength of the green body by pre-sintering, the formation of cracks and the breaking up of the as-hot-pressed samples can be effectively suppressed, leading to sound or crack-free but less transparent samples. After a post-HIPing treatment, the optical transmittance of the samples with a pre-sintering step was substantially improved to higher levels in the visible and the IR wavelengths compared to that of a sample which does not undergo pre-sintering. The corresponding mechanism was revealed by microstructural analyses.</P>

Weathering and Soil Formation in Responding to Changing Environment in an Alpine Region of the Qinghai-tibet Plateau

Gan-Lin Zhang,De-Cheng Li,Yu-Guo Zhao,Jin-Ling Yang,Feng Liu 한국토양비료학회 2014 한국토양비료학회 학술발표회 초록집 Vol.2014 No.6

Highly transparent Nd-doped yttria ceramics fabricated by hot pressing with ZrO₂ and La₂O₃ as sintering additives

Gan, Lin,Park, Young-Jo,Zhu, Lin-Lin,Kim, Ha-Neul,Ko, Jae-Woong,Lee, Jae-Wook Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.763 No.-

<P><B>Abstract</B></P> <P>Highly transparent Nd-doped yttria ceramics were fabricated by hot-pressing at 1600 °C with single addition and co-addition of ZrO<SUB>2</SUB> and La<SUB>2</SUB>O<SUB>3</SUB>. The binary additives were found to promote the densification of yttria more effectively than single addition, resulting in higher transmittance. The highest transmittance was obtained in the sample with 1 at.% ZrO<SUB>2</SUB> and 3 at.% La<SUB>2</SUB>O<SUB>3</SUB>, which reached 74.3% transparency at a wave length of 400 nm and 81.3% at 1100 nm. The optical absorption, luminescence, and fluorescence decay of this sample was investigated. The absorption cross-sections of the sample at 806 nm and 820 nm were 1.22 × 10<SUP>−20</SUP> and 1.31 × 10<SUP>−20</SUP> cm<SUP>2</SUP>, respectively. The strongest emission was measured at 1078 nm with a full-width at half-maximum of 5 nm with excitation at 808 nm and a fluorescence lifetime of 423 μs. Additionally, the microhardness of the all samples is ranging from 7.88 to 7.05 GPa with variation of the grain size from 0.85 to 1.81 μm, while the fracture toughness of the all samples is about 1 MPa m<SUP>1/2</SUP> and was found to be almost unchanged. These results have demonstrated that Nd-doped yttria ceramics for the application of laser gain media can be fabricated by hot-pressing.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Highly transparent Nd-doped yttria ceramics fabricated by hot-pressing. </LI> <LI> Effects of ZrO<SUB>2</SUB>-La<SUB>2</SUB>O<SUB>3</SUB> additives on the samples were studied. </LI> <LI> The optical and mechanical properties of the samples were studied. </LI> </UL> </P>

Fabrication of transparent MgAl₂O₄ from commercial nanopowders by hot-pressing without sintering additive

Zhu, Lin-Lin,Park, Young-Jo,Gan, Lin,Go, Shin-Il,Kim, Ha-Neul,Kim, Jin-Myung,Ko, Jae-Woong North-Holland 2018 Materials letters Vol.219 No.-

<P><B>Abstract</B></P> <P>Transparent magnesium aluminate spinel (MgAl<SUB>2</SUB>O<SUB>4</SUB>) ceramics were successfully fabricated for the first time using commercially available nanopowders without sintering additive by a single hot-press step process. This method does not involve all the complexity of powder, green body pre-treatment and post-treatment, which are commonly used in the fabricating process. Effects of holding time (3–12 h) at the sintering temperature 1500 °C on the transmittance, microstructure and Vickers microhardness are investigated. The highest transmittance is achieved for the sample hot pressed at 1500 °C for 12 h, which exhibits 80.2% at the wavelength of 1100 nm. These results may provide a guide for understanding the microstructural development of transparent spinel without sintering additive.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Pure MgAl<SUB>2</SUB>O<SUB>4</SUB> transparent ceramic was prepared by a single hot-press step. </LI> <LI> The transmittance of the sample at 1500 °C for 12 h reached 80.2% at 1100 nm. </LI> <LI> The Vickers microhardness decreases from 15.1 to 12.5 GPa with holding time from 3 to 12 h. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Fabrication of transparent Y₂O₃ ceramics with record-high thermal shock resistance

Zhu, Lin-Lin,Park, Young-Jo,Gan, Lin,Kim, Ha-Neul,Ko, Jae-Woong,Kim, Hai-Doo Elsevier 2018 Journal of the European Ceramic Society Vol.38 No.11

<P><B>Abstract</B></P> <P>Sintering-additive-free fine-grained highly transparent Y<SUB>2</SUB>O<SUB>3</SUB> ceramics featuring record-high thermal shock resistance were fabricated using commercial powders via vacuum pre-sintering (1375–1550 °C) followed by hot-isostatic pressing (1450 °C). The sample pre-sintered at 1450 °C provides the optimum microstructure for post HIPing, which resulted in a grain size of 0.64 μm. The transmittance, microhardness and fracture toughness of the thus HIPed sample are 80.8% at 1100 nm and 65.5% at 400 nm (1.2 mm thick), 8.0 ± 0.02 GPa and 1.00 ± 0.06 MPa m<SUP>1/2</SUP>, respectively. The thermal conductivity increases from 13.1 to 16.5 W/m/K with increasing vacuum pre-sinterin Proc. SPIE-Int. Soc. Opt g temperature from 1450 to 1550 °C. This hybrid sintering method realized high thermal conductivity and high strength simultaneously. Consequently, the thermal shock resistance of the HIPed specimen vacuum pre-sintered at 1450 °C in this work is the highest ever reported to the best of our knowledge, which makes the developed material a promising candidate for high-power laser host and IR dome.</P>

Fabrication and characterization of highly transparent Er:Y₂O₃ ceramics with ZrO₂ and La₂O₃ additives

Zhu, Lin-Lin,Park, Young-Jo,Gan, Lin,Go, Shin-Il,Kim, Ha-Neul,Kim, Jin-Myung,Ko, Jae-Woong Elsevier 2017 CERAMICS INTERNATIONAL Vol.43 No.16

<P><B>Abstract</B></P> <P>In this study, we report highly transparent Er:Y<SUB>2</SUB>O<SUB>3</SUB> ceramics (0–10at% Er) fabricated by a vacuum sintering method using compound sintering additives of ZrO<SUB>2</SUB> and La<SUB>2</SUB>O<SUB>3</SUB>. The transmittance, microstructure, thermal conductivity and mechanical properties of the Er:Y<SUB>2</SUB>O<SUB>3</SUB> ceramics were evaluated. The in-line transmittance of all of the Er:Y<SUB>2</SUB>O<SUB>3</SUB> ceramics (1.2mm thick) exceeds 83% at 1100nm and 81% at 600nm. With an increase in the Er doping concentration from 0 to 10at%, the average grain size, microhardness and fracture toughness remain nearly unchanged, while the thermal conductivity decreases slightly from 5.55 to 4.89W/mK. A nearly homogeneous doping level of the laser activator Er up to 10at% in macro-and nanoscale was measured along the radial direction from the center to the edge of a disk specimen, which is the prominent advantage of polycrystalline over single-crystal materials. Based on the finding of excellent optical and mechanical properties, the compound sintering additives of ZrO<SUB>2</SUB> and La<SUB>2</SUB>O<SUB>3</SUB> are demonstrated to be effective for the fabrication of transparent Y<SUB>2</SUB>O<SUB>3</SUB> ceramics. These results may provide a guideline for the application of transparent Er:Y<SUB>2</SUB>O<SUB>3</SUB> laser ceramics.</P>