Effects of ZrO₂-La₂O₃ co-addition on the microstructural and optical properties of transparent Y₂O₃ ceramics

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.11

<P><B>Abstract</B></P> <P>Commercial Y<SUB>2</SUB>O<SUB>3</SUB> powder was used to fabricate Y<SUB>2</SUB>O<SUB>3</SUB> ceramics sintered at 1600°C and 1800°C with concurrent addition of ZrO<SUB>2</SUB> and La<SUB>2</SUB>O<SUB>3</SUB> as sintering aids. One group with different contents of La<SUB>2</SUB>O<SUB>3</SUB> (0–10mol%) with a fixed amount of 1mol% ZrO<SUB>2</SUB> and another group with various contents of ZrO<SUB>2</SUB> (0–7mol%) with a fixed amount of 10mol% La<SUB>2</SUB>O<SUB>3</SUB> were compared to investigate the effects of co-doping on the microstructural and optical properties of Y<SUB>2</SUB>O<SUB>3</SUB> ceramics. At low sintering temperature of 1600°C, the sample single doped with 10mol% La<SUB>2</SUB>O<SUB>3</SUB> exhibits much denser microstructure with a few small intragranular pores while the samples with ZrO<SUB>2</SUB> and La<SUB>2</SUB>O<SUB>3</SUB> co-doping features a lot of large intergranular pores leading to lower density. When the sintering temperature increases to 1800°C, samples using composite sintering aids exhibit finer microstructures and better optical properties than those of both ZrO<SUB>2</SUB> and La<SUB>2</SUB>O<SUB>3</SUB> single-doped samples. It was proved that the grain growth suppression caused by ZrO<SUB>2</SUB> overwhelms the acceleration by La<SUB>2</SUB>O<SUB>3</SUB>. Meanwhile, 1mol% ZrO<SUB>2</SUB> acts as a very important inflection point with regard to the influence of additive concentration on the transmittance, pore structure and grain size. The highest in-line transmittance of Y<SUB>2</SUB>O<SUB>3</SUB> ceramic (1.2mm in thickness) with 3mol% of ZrO<SUB>2</SUB> and 10mol% of La<SUB>2</SUB>O<SUB>3</SUB> sintered at 1800°C for 16h is 81.9% at a wavelength of 1100nm, with an average grain size of 11.2µm.</P>

Enhancement of the thermal shock resistance of transparent Y₂O₃ ceramics by reducing the content of sintering additive

Zhu, Lin-Lin,Park, Young-Jo,Gan, Lin,Kim, Ha-Neul,Ko, Jae-Woong,Lee, Jae-Wook,Kim, Hai-Doo Elsevier 2018 Ceramics international Vol.44 No.14

<P><B>Abstract</B></P> <P>It is known that 1.0 at.% is the lowest amount of ZrO<SUB>2</SUB> which can be used for the sintering of well-balanced Y<SUB>2</SUB>O<SUB>3</SUB> ceramics to ensure both transparency and strength. In this work, a highly transparent Y<SUB>2</SUB>O<SUB>3</SUB> ceramic material doped with a reduced amount of ZrO<SUB>2</SUB> (0.5 at.%) was fabricated by means of a hot-press sintering method at a temperature as low as 1600°C using commercial powders. The in-line transmittance of the 0.5 at.% ZrO<SUB>2</SUB>-doped Y<SUB>2</SUB>O<SUB>3</SUB> sample (2 mm thick) is 80.8% at 1100 nm and 72.2% at 400 nm with an average grain size of 1.06 μm. By reducing the ZrO<SUB>2</SUB> content from 1.0 to 0.5 at.%, the thermal conductivity is increased by 18.2% with only a slight decline in the strength and the band gap becomes broader. Consequently, the Hasselman mild-thermal-shock figure of merit of the developed specimen increases by 13.0% overall. These results indicate that this Y<SUB>2</SUB>O<SUB>3</SUB> ceramic has potential for use as a laser host or an infrared window material used on Mach-speed applications.</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 and characterization of highly transparent Y₂O₃ ceramics by hybrid sintering: A combination of hot pressing and a subsequent HIP treatment

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.9

<P><B>Abstract</B></P> <P>We succeeded in the optimization of highly transparent Y<SUB>2</SUB>O<SUB>3</SUB> ceramics with a submicrometer grain size approximately 0.6 μm by hot pressing (1300–1550 °C) and a subsequent HIP (1450 °C) treatment using commercial Y<SUB>2</SUB>O<SUB>3</SUB> powders as starting powders and ZrO<SUB>2</SUB> as a sintering additive. The optimum microstructure for the HIP treatment was prepared by hot pressing at a temperature as low as 1400 °C for 3 h with a relative density of 99.3%. The thus HIP-treated specimen showed the best transmittance (2 mm thick) ever reported of 83.4% and 78.3% at 1100 and 400 nm, respectively. Specifically, the transmittance using this hybrid sintering method improved substantially in the visible range compared to that of the counterpart using hot pressing only. A simulation of the transmittance based on the Beer-Lambert law and Mie scattering theory has proved that this improvement is mainly due to the elimination of nanopores below 15 nm in size.</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>

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>

Behavior of Circular RC Columns with Two Layers of Spirals

Lin-Zhu Sun,Dong-Yan Wu,Jun-Liang Zhao,Fang Yang,Wei Li 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.3

RC columns with two layers of hoops is a new kind of column recently proposed. The concrete of the column is under three different degrees of confinement, namely unconfined concrete cover, singly-confined concrete between the two layers of hoops and doubly-confined concrete inside the inner layer of hoops. The strength and ductility of the column can be greatly enhanced due to better confinement. In this study, the behaviour of circular RC columns confined using two layers of spirals were investigated through axial compression test on scaled-down column models. The responses and failure modes of the columns were examined. The average stress-strain curves of the singly-confined and doubly-confined concrete were derived, taking advantage of the concept of average effective confinement pressure. The performance of a stress-strain model previously proposed for square RC columns with two layers of hoops was also investigated.

Few-shot link prediction with meta-learning for temporal knowledge graphs

Zhu Lin,Xing Yizong,Bai Luyi,Chen Xiwen 한국CDE학회 2023 Journal of computational design and engineering Vol.10 No.2

With the deepening of the research on knowledge graph embedding, temporal knowledge graphs (TKGs), which are dynamic changes over time, have gradually gained the attention of researchers. Although some TKG-embedding models have been proposed, they did not perform well for certain relationships with insufficient samples, since they all require tremendous training samples. Thus, few-shot link prediction tasks, namely predicting new relation-specific quadruples by observing only a few samples, are still very challenging. In this paper, a method named meta-reasoning for TKGs (MetaRT) is proposed to solve this universal but challenging problem. MetaRT works by extracting the meta-information of a specific relation and updating it quickly, so that the model can learn the most critical information in TKG swiftly and independently. In the meantime, temporal information can be managed well by a TKG learner. Finally, through a large number of experiments, it shows that MetaRT outperforms other existing TKG-embedding models on the problem of few-shot learning.

Risk Assessment of Financial Market under the Restriction of Market Incentive Mechanism

Lin Zhu 보안공학연구지원센터 2016 International Journal of u- and e- Service, Scienc Vol.9 No.11

In order to solve the problems of fuzzy expression and invalid inter-agent trust during the process of adopting traditional negotiation mode to describe the enterprise and the enterprise supply chain, a global negotiation model based on Norm and trust evaluation is proposed in this paper. Specifically, Norm semantic tool is adopted to describe enterprise information, and such parameters as fitness and trust degree of the negotiation model are evaluated through the “commitment” based trust evaluation method. Meanwhile, the improved genetic algorithm is adopted for the task solution of the negotiation issues involving in enterprise environment, and the improved contract net protocol is adopted for the task solution of the negotiation issues involving in enterprise business. Finally, the example for a certain production enterprise supply chain is adopted for the detailed design of the negotiation model. The experiment proves that the model can realize the global task solution of the negotiation issues involving in both enterprise environment and business, and the solution efficiency thereof is improved more or less.

DeNOx performance and characteristic study for transition metals doped iron based catalysts

Lin Zhu,Zhaoping Zhong,Han Yang,Chunhua Wang,LixiaWang 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.4

Novel, environmentally-benign catalysts for selective catalytic reduction of NOx were prepared by citric method through introducing transition metal elements (Ce, Cu and Co) into iron oxide. The physical-chemical properties of different catalysts were investigated by the characterization technologies like N2-physisorption, XRD, NH3/NOTPD and H2-TPR. The results indicated that the introduction of transition metal elements increased the specific surface area and adsorption ability for reactants (NH3 and NOx). The redox capacity for the doped catalysts was improved at the same time. These characteristics all contributed to the improvement of catalytic performance. The CoFeOx catalyst exhibited the widest temperature window for SCR reaction, and the CeFeOx catalyst showed the most obvious decline of NOx conversion with the elevation of temperature above 250 oC. Water vapor inhibited the SCR activity at low temperatures and relieved the decline of NOx conversion at higher temperatures. Meanwhile, the formation of N2O was inhibited. The pretreatment of SO2 leaded to the sulfation of the active species for different catalysts. The decline of redox capacity and the reduction of active nitrate adsorbed species accounted for the serious loss of SCR activity at low temperatures. The abundant surface acid sites brought by the sulfation process might be the main reason for good SCR activity in the medium temperature range.