Papers by Keyword: Zirconium Diboride

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Authors: Hai Long Wang, Shi Xun Zhang, De Liang Chen, Qian Fei Han, Hong Xia Lu, Hong Liang Xu, Chang An Wang, Rui Zhang
Abstract: ZrB2 powder has been prepared through carbothermal reduction boronization of zirconia/boron carbide/carbon mixtures heating assisted by microwave. The powder characteristics were investigated by X-ray diffraction (XRD), X-ray fluorescence (XRF), nitrogen absorption (BET model) and scanning electron microscope (SEM). The experiments indicated that excessive B4C is necessary and the carbothermic reaction reacts severely at a higher temperature and complete at 1600oC. The crystallite size has ranged from 50-100 nm, according to the calculated surface area. Highest purity of ZrB2 powder, which was synthesized at 1600oC, is 99.67 wt%. The surface area of ZrB2 powder synthesis at 1600oC is 18.33 m2/g. Vibration of temperature should affect the purity of ZrB2, as the sub reaction acted.
203
Authors: A.L. Chamberlain, W.G. Fahrenholtz, G.E. Hilmas, D.T. Ellerby
493
Authors: Shu Qi Guo
Abstract: In this study, oxidation behavior of ZrB2-MoSi2-SiC composite was investigated in the hot-pressed 5-20 vol% SiC-containing ZrB2-20 vol% MoSi2-based composites which were exposed to dry air between 1100°C and 1500°C up to 10 hours. The effects of SiC additive on the oxidation behavior were assessed. Experimental results showed that the weight gain due to oxidation exposure in air increased with increasing exposure temperature and exposure time. Parabolic oxidation behavior was observed for all the compositions composites. On the other hand, the weight gain decreased with increasing amount of SiC added. The addition of SiC improved the oxidation resistance of the composites, and the improvement was enhanced with increasing amount of SiC added. In addition, X-ray diffraction was used to identify major crystalline phases present in both the as-received and the post-oxidized composites. The oxidized sample surface was characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The microstructure of the post-oxidized composites consisted of two characteristic regions: oxidized reactive region and unreactive bulk material region. Furthermore, the oxidized reactive region divided into an outermost dense silica-rich scale layer and oxidized reactive mixture layer. The improvement of the oxidation resistance due to the addition of SiC is associated with the presence of the thicker dense outermost scale layer which inhibited inward diffusion of oxygen through it.
457
Authors: Guang Yi Ji, Hui Ming Ji, Xiu Ping Li
Abstract: Zirconium diboride nano-powders were synthesized by novel sol-gel technology using zirconium oxychloride, boric acid and sucrose as row materials. Different sol network modifiers, such as propylene oxide (PO) and citric acid (CA), were used to control the formation of zirconia precursor sol, respectively. PO could stabilize the sol by protonation and ring-opening reactions, and CA could form the sol network by chelation, then transformed to gel network. Gel was dried, ground, and exposed to carbonthermal reduction heat treatment (1500°C, 2h, flowing 95%argon mix with 5% hydrogen) to prepare ZrB2 nano-powders. In this study, effects of sol network modifiers on preparation procedure, powder characteristics were performed by using Infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The purity of ZrB2 will improve by increasing the molar ratio of B/Zr, the photomicrograph revealed nearly pure ZrB2 nano-powders with spherical shape of 50-200nm and well dispersed were obtained with a molar ratio of B/Zr of 3.0 at 1500°C for 2h using PO as chemical modifier.
139
Authors: Felipe Antunes Santos, Alfeu Saraiva Ramos, Claudinei dos Santos, Paulo Atsushi Suzuki, Durval Rodrigues Júnior
Abstract: The present study suggests the use of high energy ball milling to mix (to dope) the phase MgB2 with the AlB2 crystalline structure compound, ZrB2, with the same C32 hexagonal structure than MgB2, in different concentrations, enabling the maintenance of the crystalline phase structures practically unaffected and the efficient mixture with the dopant. The high energy ball milling was performed with different ball-to-powder ratios. The analysis of the transformation and formation of phases was accomplished by X-ray diffractometry (XRD), using the Rietveld method, and scanning electron microscopy. As the high energy ball milling reduced the crystallinity of the milled compounds, also reducing the size of the particles, the XRD analysis were influenced, and they could be used as comparative and control method of the milling. Aiming the recovery of crystallinity, homogenization and final phase formation, heat treatments were performed, enabling that crystalline phases, changed during milling, could be obtained again in the final product.
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Authors: Zhen Yu Yan, Shi Zhen Zhu, Qiang Xu, Ying Liu
Abstract: Due to extremely low oxygen transportation at elevated temperature, samarium zirconate (Sm2Zr2O7) with pyrochlore structure was introduced into ZrB2-based functional gradient composites as oxygen insulation. The elastic properties of composites with different phase ratio were investigated in this study. A series of nearly-fully dense ZrB2-based composites with different Sm2Zr2O7 content was consolidated by spark plasma sintering (SPS) technology. The microstructure and phase compositions were characterized by scanning electronic microscope (SEM) and X-ray diffraction respectively. The dynamic elastic properties were obtained by resonance method at room temperature. The results revealed that the addition of Sm2Zr2O7 can significantly improve its densification for the refractory diboride, which mainly caused by the high sintering activity of Sm2Zr2O7. Young’s modules of the series of composites obviously decreased with the increasing content of Sm2Zr2O7. The low Young’s modulus of Sm2Zr2O7 was the main reason. The Young’s modules of the series of composites were calculated theoretically. The experimental results matched the theoretical data well. A little deviation appeared due to the continuous structure of Sm2Zr2O7 in the composites.
474
Authors: Jie Guang Song, Fang Wang, Ming Han Xu, Shi Bin Li, Gang Chang Ji
Abstract: Zirconium diboride is widely applied because of some excellent performances. The results show the A1(OH)3-Y(OH)3/ZrB2 composite powders is prepared by a co-precipitation method, the shell-core structure A12O3-Y2O3/ZrB2 composite powders is prepared by sintering A1(OH)3-Y(OH)3/ZrB2 composite powders. The coating and density ZrB2-YAG-Al2O3 multi-phase ceramics is sintered at 1700°C, 20MPa for 4min by using Al2O3-Y2O3-80wt%ZrB2 composite powders, the oxidation weight is increased with increasing the oxidation temperature, however, the oxidation weight is decreased with increasing the YAG-Al2O3 content. ZrB2 reacted with O2 to form B2O3, and B2O3 is reacted with Al2O3 to form Al18B4O33, which is melted and coated on the surface of ceramics to form a protective layer for the oxidation resistance of ceramics at high temperature.
347
Authors: M. Amiriyan, W.J. Kelvin Chew, Ramesh Singh, R. Tolouei, M.A. Hassan, A. Hossain, I. Sopyan, S. Meenaloshini
Abstract: Over the last three decades, most of the efforts in mechanics of materials science have been focused to develop tougher and stronger ceramics via cost effective processing techniques. In the present work, 3 mol % Yttria-stabilized tetragonal zirconia (3Y-TZP) composites with 25 wt. % of ZrB2 was prepared by pressureless sintering method in argon atmosphere over the temperature range of 1350-1550°C for one hour holding time. The influences of zirconium diboride addition in the zirconia matrix, as well as the sintering temperature, on the densification, phase stability and electrical properties of sintered samples have been studied. The results revealed that electrical resistivity values is very low (high electrical conductivity) when 25 wt. % of ZrB2 is incorporated to pure 3Y-TZP.
228
Authors: Hai Tang Wu, Wei Gang Zhang
Abstract: ZrB2-SiC-BN ultrahigh-temperature ceramic (UHTC) was fabricated by hot-pressing at 1800°C under 23MPa pressure of argon. Compared to ZrB2-SiC, the flexural strength of ZrB2-SiC-BN composite material was enhanced by adding 30% BN, and the fracture toughness showed a slight decrease, while the hardness decreased sharply. The addition of 30% BN also noticeably improved the machinability of the composites. Furthermore, ablation resistance tests were carried out using an oxyacetylene torch under subsonic conditions. Results indicated that a coherent compact scale of zirconium silicate was formed, which acted as an effective barrier against the inward diffusion of oxygen.
2011
Authors: R. Mitra, Sunkari Upender, Manab Mallik, Subrata Chakraborty, Kalyan Kumar Ray
Abstract: A comparative study has been carried out on the mechanical properties at room temperature, thermal shock and ablation resistance as well as oxidation behaviour of ZrB2-20SiC, ZrB2-20SiC-5Si3N4 and ZrB2-20ZrC-20SiC-5Si3N4 (amounts represent volume percent) composites. Fracture toughness has been determined using either three-point bend tests on single edge notch bend specimens, or by indentation technique. Addition of Si3N4 as sintering aid leads to enhancement in flexural strength and fracture toughness in the composite without ZrC. The specimens were subjected to thermal shock by quenching from temperatures in the range of 800o- 1200oC to ice cold water, and to ablation by exposure to oxy-acetylene flame at 2200oC. The composite having ZrC as constituent, exhibits the highest resistance to damage due to thermal shock and ablation, while the ZrB2-SiC composite shows the least change in mass during ablation. On the other hand, thermogravimetric experiments from room temperature to 1300oC have shown that the presence of ZrC is detrimental for oxidation resistance. Hence, the constituents of the composites need to be selected on the basis of the nature of application. The results of this study show that the investigated ZrB2 based composites bear the potential for multiple use thermal protection of reentry type space vehicles.
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