Effect of silicon additions on the hot pressing of B4C

Hongkang Wei,Yu-Jun Zhang,Xiangyu Deng 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.5

In the present study, the effect of silicon additions on the hot pressing of boron carbide was investigated. B4C-based ceramic composites with the addition of silicon powder up to 12 wt.% were prepared by hot pressing at 1850 oC under a vacuum and 60 MPa pressure. The results show that addition of silicon powder affected the sintering behavior of B4C significantly. Silicon powder reacted with free-carbon originating in the B4C phase and formed a solid solution in the B4C structure. For the B4C-8 wt.%Si specimen, a high fracture toughness of 5.04 MPa·m1/2 and modest flexural strength of 354 MPa were obtained. It seems that the improvement in fracture toughness is attributed to the high relative density and the change of fracture mode by the formation of the SiC phase.

Experimental Study on the Seismic Mechanism of Full-scale Specimens of Superimposed Slab Shear Walls with Innovative Construction Details

Hongkang Zhao,Yaping Dai,Jun Yang,Youzhen Fang,Chengjie Mi,Lingchen Yang,Guojian Li 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.6

The seismic performance of precast reinforced concrete structures has long been a source ofconcern that impedes their use in seismic regions and high-rise buildings. To further optimizethe reinforcement configuration and enhance the seismic performance of the superimposedslab shear wall structures, this research proposed a superimposed slab shear wall withinnovative construction details. Five innovative superimposed slab shear walls and one cast-inplaceconcrete shear wall were designed and tested under low cycle lateral load. The effect ofaxial compression was considered during tests and analyses as well. In this paper, the seismicperformance, including failure mode, hysteretic behavior, load-bearing capacity, lateralstiffness degradation, energy dissipation, and seismic ductility was investigated and analyzed. The experimental results showed that five innovative superimposed slab shear walls and onecast-in-place concrete shear wall exhibited a similar failure mode of flexural-shear failure, anda large area of concrete was damaged and crushed at the shear wall corner. However, the areaof crushing concrete in the cast-in-place concrete shear wall was relatively small. And the areaof crushing concrete in the superimposed slab shear walls increased with the axial compressionratio. For the superimposed slab shear walls, the development of concrete cracks decreasedgradually with the enlargement in the axial compression ratio, while the length of the cracksincreased in this respect. The results indicated that innovative superimposed slab shear wallshad a higher strength capacity and lower lateral-resistant stiffness than the cast-in-placeconcrete shear wall. With the enlargement in the axial compression ratio, the peak strengthcapacity of the superimposed slab shear wall increased obviously, while it degraded rapidlyafter the peak load. It is suggested that the contribution of axial compression to the shear resistcapacity of the inclined section should not be considered in practical design. Meanwhile, theductility coefficients of the six specimens were larger than 2.2, which was in accordance withthe seismic requirements. This investigation could provide effective experimental data forfuture structural seismic performance evaluations and applications of precast superimposedslab shear wall structures.

Synthesis of boron carbide powder through gas-solid reaction method using nanoporous carbon as carbon source

Haozhan Lia,Hongkang Wei,Huijuan Qiu,Yukang Wanga,Chang-an Wang,Zhipeng Xie 한양대학교 청정에너지연구소 2023 Journal of Ceramic Processing Research Vol.24 No.1

Sub-micron boron carbide powders were synthesized through a gas-solid reaction process using ZIF-8-derived nanoporouscarbon and boron oxide as raw materials. The effects of calcination temperature and atmosphere, amount of boron oxide, andgas-solid reaction apparatus on phase composition and morphology of the synthesized boron carbide powders were studied. The results show that, even with sufficient boron oxide addition, it is not feasible to obtain boron carbide powder of high purityin argon environment. Although vacuum environment can significantly improve the purity of the synthesized boron carbidepowder, there are a large number of large particles of step morphology in the synthesized boron carbide powder. The improvedgas-solid reaction apparatus can effectively impede the formation of boron carbide particles of step morphology. Nearlyspherical submicron boron carbide particles with a median particle size of 480 nm and good particle size consistency couldbe synthesized at 1600 °C with 0.3 g nanoporous carbon and 10 g B2O3 under vacuum by using the improved apparatus

Analysis of the Wet-end Dynamics in Paper Mills

여영구,이성철,DongJunSeo,HongKang,JaeYongRyu 한국펄프.종이工學會 2003 펄프.종이기술 Vol.35 No.5

For the purpose of manufacturing water-resistant corrugated board boxes for agricultural products in the cold chain system, the effects of fiber types, wet strength agents and a moisture-proof chemical on the properties of the base papers were investigated first. PAE(polyamide amine epichlorohydrin) showed better performance than MF(melamine formalde-hyde) over broad stock pH ranges, which was prefered as wet strength agent for the paper grade. When short fibers(AOCC, KOCC) were mixed with long fiber(UKP) in certain ratios, some physical properties of the paper made with mixed fibers were similar to those of the paper made with UKP only. Paper containing AOCC showed the biggest increase in water resistance when PAE was added to the stock. Synergistic effects in moisture-proof and some mechanical properties of paper were appeared when PAR was added internally, together with the coating of a moisture proof chemical on the sheets.

Modeling of the Drying Process in Paper Plants

KiSeokHwang,여영구,이성철,DongjunSeo,HongKang 한국펄프.종이工學會 2003 펄프.종이기술 Vol.35 No.5

The newly developed system for measuring a contact angle on a sheet was examined to investigate reliability and reproducibility of the measured results. It was clearly confirmed that the automatic contact angle measuring system was much faster and more reliable way to determine the water resistance of a sheet, comparing with Cobb and Stockigt sizing tests. Cobb test showed less significant results with stringently sized sheets, and Stockigt test exhibited the big deviations by discrepancy of the recognition point of coloring according to different testers in spite of explicit test results. On the other hand, the contact angles measured by the automatic system were reproduced with less deviations, irrespectively of different testers. It was interesting to note that the contact angle might be able to used to predict Cobb and Stockigt sizing degree, based upon the high correlation coefficients of 0.95 and 0.97. Hereafter the automatic system will be upgraded to predict Cobb and stockigt sizing degree through the measurement of contact angle.

Modeling of Grade Change Operations in Paper Mills

DuSeokKo,여영구,JunSeokKo,SeongMunHa,JungWooLim,HongKang 한국펄프.종이工學會 2003 펄프.종이기술 Vol.35 No.5

Bright all-solution-processed CsPbBr3 perovskite light emitting diodes optimized by quaternary ammonium salt

Liu Ning,You Fangtian,Ji Chao,Gong Hongkang,Song Qi,Li Jiasen,Liang Chunjun,He Zhiqun 한국물리학회 2021 Current Applied Physics Vol.31 No.-

Perovskite light-emitting diodes (PeLEDs) prepared by the all-solution-process are gradually coming into view due to their low cost and flexible production process. However, the performance of CsPbBr3 device is limited by the high non-radiative recombination losses due to incomplete surface coverage and grain defects. Here a quaternary ammonium salt, tetrabutylammonium hexafluorophosphate (TBA-PF6) was simultaneously introduced into perovskite emission layers (CsPbBr3) and electron transport layer (TPBi (1,3,5-Tris(1-phenyl-1Hbenzimidazol- 2-yl) benzene) dissolved in ethyl acetate). As a result, the morphology and luminescence of CsPbBr3 films were improved, and the energy level of TPBi was more conducive to charge transport. Consequently, the maximum luminance and current efficiency of the modified green-emitting PeLEDs are improved. Furthermore, the optimized device had an operating life of more than 20 min at an initial luminance of 1230 cd/ m2. This work provides a simple and easy method to be scaled up for the development of low-cost all-solutionprocessed PeLEDs.