| 1. |
- Ablikim, M., et al.
(författare)
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Branching fraction measurement of J/ψ→KSKL and search for J/ψ→KSKS
- 2017
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 96:11
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Tidskriftsartikel (refereegranskat)abstract
- Using a sample of 1.31 x 10(9) J/Psi events collected with the BESIII detector at the BEPCII collider, we study the decays of J/Psi -> KSKL and KSKS. The branching fraction of J/Psi -> KSKL is determined to be B(J/Psi -> KSKL) = (1.93 +/- 0.01 (stat) +/- 0.05 (syst)) x 10(-4), which significantly improves on previous measurements. No clear signal is observed for the J/Psi -> KSKS process, and the upper limit at the 95% confidence level for its branching fraction is determined to be B(J/Psi -> KSKS) < 1.4 x 10(-8), which improves on the previous searches by 2 orders in magnitude and reaches the order of the Einstein-Podolsky-Rosen expectation.
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| 2. |
- Bartek, A., et al.
(författare)
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Fabrication of silicon nitride/oxynitride by reaction bonding and post sintering
- 1992
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Ingår i: 4th International Symposium on Ceramic Materials and Components for Engines. - London : Elsevier. - 1851667768 ; , s. 625-632
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Konferensbidrag (refereegranskat)abstract
- Reaction bonding and post sintering of silicon nitride/oxynitride was investigated as a route to fabricate a material with good oxidation resistance and good high temperature strength. Silicon powders, mixed with 0, 2, 4, 8 and 16 wt% silica, were CIPed at 150 MPa and nitrided using the nitrogen demand principle. Four different nitriding gas compositions were used, consisting of different amounts of hydrogen, argon and helium mixed with nitrogen. Post sintering at atmospheric pressure and by HIP at 160 MPa were investigated to densify the materials. Samples were characterised by XRD, SEM and Hg-porosimetry in both the nitrided and sintered state
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| 3. |
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| 4. |
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| 5. |
- Lei, B.Q., et al.
(författare)
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Mechanisms and kinetics of nitridation in silicon powder compacts
- 1995
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Ingår i: Ceramic materials and components for engines. - : World Scientific Publishing Co Pte Ltd. - 9810219059 ; , s. 189-193
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Konferensbidrag (refereegranskat)abstract
- Due to the strongly exothermic nature of silicon nitridation, a clear understanding of the nitridation process and an effective control regime, especially when the nitridation involves a rather large mass of silicon are of commercial interest. The nitridation process was investigated by reacting "large masses" of silicon powder compacts (about 1.5 kg) in a nitriding atmosphere in which some auxiliary gases such as Ar or He were added. Because of the exothermic heat, the reaction kinetics were found to be influenced by the amount of silicon in the nitridation cycle. The effect of the additional gases (Ar and He) is enhanced as the mass of silicon loaded in the furnace increases. The kinetics and the corresponding mechanisms of the whole nitridation cycle are discussed and a mechanism for the second reaction maximum is proposed. 22 refs.
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| 6. |
- Lei, B.Q., et al.
(författare)
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Optimization of the silicon nitridation process
- 1992
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Ingår i: 4th International Symposium on Ceramic Materials and Components for Engines. - London : Elsevier. - 1851667768 ; , s. 633-640
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Konferensbidrag (refereegranskat)abstract
- By investigating the nitridation processes using a large mass of silicon under different atmospheres, it was found that the nature of heat conduction and mass transport were influenced by the size of the silicon powder compact and/or the number of compacts. Two main reaction maxima were observed and both accelerating as well as retarding influences on the reaction rate could be identified. The extent and starting temperature of the first reaction maximum was found to be greatly influenced by gas composition. Also investigated was the influence of different nitridation atmospheres (N2+Ar, N2+H2, N2+H2+Ar and N2+He) on microstructure of large silicon powder compacts. A homogeneous and complete reaction could be achieved by tailoring the gas composition
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| 7. |
- Li, W.B., et al.
(författare)
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A kinetic model for reaction bonding process of silicon powder compact
- 1997
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Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 17:9, s. 1119-1129
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Tidskriftsartikel (refereegranskat)abstract
- In order to obtain detailed information about the kinetics and the reaction nature of a complex reaction process like reaction bonding of silicon nitride, mathematical modelling of the process is necessary. The previous quantitative models for this process have been based only on the mechanism that the nitrogen diffuses through the solid silicon nitride without taking into account the multiple reaction mechanisms. In the present study, a comprehensive kinetic model, which is based on analysis of the multiple mechanisms in a silicon powder compact reacting with nitrogen gas and forming silicon nitride, is constructed for a solid-gas reaction bonding process with specific application to the reaction-bonding of silicon nitride. The model will incorporate the rate equation for each mechanism into a constitutive equation from which more complete information of process kinetics can be predicted. The results predicted by the present model have been compared with previous experimental results and satisfactory agreement obtained
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| 8. |
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| 9. |
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| 10. |
- Li, Wen Bin, et al.
(författare)
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Stresses developed in reaction-bonded ceramics
- 1995
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Ingår i: Ceramic materials and components for engines. - : World Scientific Publishing Co Pte Ltd. - 9810219059 ; , s. 465-468
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Konferensbidrag (refereegranskat)abstract
- For a number of reaction-bonded ceramics, the reaction starts from the surface of the particles, forming a shell of products surrounding a reactant core. The reaction is continued by inward growth of the shell by means of diffusion of the reactant elements from the particle surface to the interface between the shell and core and vice versa. Since there exists a volumetric change due to the reaction, the products forming at the shell/core interface will be severely constrained. Strain and stress fields are then built up within the particles. A physical and mathematic model to calculate the strain and stress during and after the reaction bonding process is constructed. The preliminary results of estimation of stresses within the particles and their possible effect on reaction kinetics are presented and briefly discussed
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