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Li Y.,Wuhan University of Science and Technology | Wang Q.,Wuhan University of Science and Technology | Fan H.,Wuhan Research Institute of Metallurgical Construction | Sang S.,Wuhan University of Science and Technology | Zhao L.,Wuhan University of Science and Technology
Ceramics International | Year: 2014

Silicon carbide whiskers have been synthesized by using reactive graphite as a template. Natural graphite flake was firstly activated using chemical oxidation and thermal oxidation methods. After that, the reactive graphite sources were mixed with silicon powder and heated in the coke bed at 1200 and 1400 C. The structural evolution of graphite and morphologies of SiC whiskers were studied with the aids of XRD, SEM, TEM and EDS techniques. The results showed that natural graphite flake can be activated into reactive graphite such as oxidized graphite and expanded graphite with much more defects using thermal and chemical oxidation methods. The expanded graphite with a great deal of defects has higher reactivity than natural graphite flake and oxidized graphite and accelerates the formation of long and thick SiC whiskers. It is proposed that the vapor-solid mechanism is predominant for the growth of β-SiC whiskers in this system. During heating-up, Si or SiO vapors meet with the activated carbon atoms on graphite substrate to form SiC nucleus. Then these vapors continually deposit on the SiC nucleus following the SiC whiskers which grow along the 〈111〉 direction. © 2013 Elsevier Ltd and Techna Group S.r.l.


Fan H.,Wuhan Research Institute of Metallurgical Construction | Fan H.,Wuhan University of Science and Technology | Li Y.,Wuhan University of Science and Technology | Huang Y.,China First Metallurgical Group Co. | And 2 more authors.
Materials Science and Engineering A | Year: 2012

Silicon, microsilica and their combination were used as additive in carbon containing refractories, respectively. The effects of such additive on microstructures and mechanical properties of Al 2O 3-ZrO 2-C refractories were investigated. The results show that in refractories of this kind, silicon is responsible for the formation of SiC whiskers; microsilica mainly dominates the formation of mullite; while their combination (silicon plus microsilica) brings high partial pressure of SiO(g) and leads to the co-existence of finer SiC whiskers and needle-like mullite. The various microstructures unquestionably cause differences in mechanical properties of Al 2O 3-ZrO 2-C refractories. The use of silicon mainly results in an enhanced mechanical strength, while the addition of microsilica primarily triggers the improvement in toughness. When the combination of silicon and microsilica is used as additive, excellent strength and toughness can be obtained simultaneously in Al 2O 3-ZrO 2-C refractories, which is mainly attributed to the synergistic effects of SiC whiskers formed from silicon additive and needle-like mullite formed from microsilica additive. © 2012 Elsevier B.V.


Wu S.,University of Science and Technology Beijing | Zhang J.,University of Science and Technology Beijing | Ren W.,Wuhan Research Institute of Metallurgical Construction | Li Z.,University of Science and Technology Beijing
Materials Science and Technology Conference and Exhibition 2010, MS and T'10 | Year: 2010

Center and centerline segregation are serious problems for steel internal quality. There are few mathematic models to explain its formation mechanism. This paper is the one to use the cellular automation-finite element model (CA-FE) to simulate temperature field, flow field and solute field through coupling heat, flow and solute transport equations under the real cooling condition during the continuous casting process. In order to verify the simulation results, composition analysis is conducted using the samples planed along the thickness direction of the slabs. The result of centerline segregation simulated was extremely similar to that detected in the slabs. The flow induced by natural convection was strong at first and it could bring the surplus solute at the interface to the central part of the liquid phase; and at the near end of the solidification, due to the block of mushy region, the velocity of natural convection was so small that it couldn't bring the solute to the center and thus centerline segregation was diminished remarkably. Copyright © 2010 MS&T'10®.


Wu S.,University of Science and Technology Beijing | Zhang J.,University of Science and Technology Beijing | Ren W.,Wuhan Research Institute of Metallurgical Construction | Li Z.,University of Science and Technology Beijing
Materials Science and Technology Conference and Exhibition 2010, MS and T'10 | Year: 2010

This paper simulated the solidification structure of 60Si2Mn Spring Steel by using the cellular automation-finite element model (CA-FE) under the real cooling condition during the continuous casting processes, and the results were compared with the actual solidification structure which was obtained through lab experiment. Effect of casting steel superheat degree, secondary cooling intensity and casting speed on caster solidification structure are investigated. The result shows that there is no well-developed columnar grain and the equiaxed grain ratio exceeds 80% or more when the steel superheat degree is 10°C. The columnar grain clearly developed, and the equiaxed grain ratio was significantly reduced to 45% and 34% respectively when the superheat temperature is raised to 20°C and 30°C. The equiaxed grain ratio was only 23%, and the columnar grain is very thick when the superheat temperature is raised to 50°C. The equiaxed grain area can be significantly expanded when decreasing the pouring steel superheat degree or increasing the cooling intensity of secondary cooling zone. The columnar grain slightly developed when the casting speed increases under the same superheat degree. Copyright © 2010 MS&T'10®.


Zeng J.,Wuhan Research Institute of Metallurgical Construction | Zeng J.,Wuhan University of Science and Technology | Xu J.,Wuhan University of Science and Technology
Key Engineering Materials | Year: 2012

Gravimetric and coulometry are recognized as primary method in actual measurement, so their accuracy can be appraised by their precision. The precision of measurements of ZrO 2+HfO 2 by mass balance of difference and gravimetric by precipitation mandelic acid was compared. It shows that the precision of mass balance of difference (0.022%) is better. There is no significant difference between the two averages. So the accuracy of mass balance of difference is higher as its precision is better. © (2012) Trans Tech Publications.

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