Characterization of porous silicon nitride/silicon oxynitride composite ceramics produced by sol infiltration

Porous silicon nitride/silicon oxynitride composite ceramics were fabricated by silica sol infiltration of aqueous gelcasting prefabricated Si3N4 green compact. Silica was introduced by infiltration to increase the green density of specimens, so suitable properties with low shrinkage of ceramics were achieved during sintering at low temperature. Si2N2O was formed through reaction between Si3N4 and silica sol at a temperature above 1550 degrees C. Si3N4/Si2N2O composite ceramics with a low linear shrinkage of 1.3-5.7%, a superior strength of 95-180 MPa and a moderate dielectric constant of 4.0-5.0 (at 21-39 GHz) were obtained by varying infiltration cycle and sintering temperature. (C) 2010 Published by Elsevier B.V.

Critical Biot's number for Determination of the Sensitivity of Spherical Ceramics to Thermal Shock

A critical Biot number, which determines both the sensitivity of spherical ceramics to quenching and the durations of the temperature-wave propagation and the thermal stresses in the ceramics subjected to thermal shock, is theoretically obtained. The results prove that once the Biot number of a ceramic sphere is greater than the critical number, its thermal shock failure will be such a rapid process that the failure only occurs in the initial regime of heat conduction, whereas the thermal shock failure of the ceramic sphere is uncertain in the course of heat conduction. The presented results provide a guide to the selection of the ceramics applied in the thermostructural engineering with thermal shock.

Enhanced Thermal Shock Resistance of Ceramics through Biomimetically Inspired Nanofins

We propose here a new method to make ceramics insensitive to thermal shock up to their melting temperature. In this method the surface of ceramics was biomimetically roughened into nanofinned surface that creates a thin air layer enveloping the surface of the ceramics during quenching. This air layer increases the heat transfer resistance of the surface of the ceramics by about 10 000 times so that the strong thermal gradient and stresses produced by the steep temperature difference in thermal shock did not occur both on the actual surface and in the interior of the ceramics. This method effectively extends the applications of existing ceramics in the extreme thermal environments.

Solving MIN UR problem by triangle evolution algorithm with archiving and niche techniques

In this paper, as an extension of minimum unsatisfied linear relations problem (MIN ULR), the minimum unsatisfied relations (MIN UR) problem is investigated. A triangle evolution algorithm with archiving and niche techniques is proposed for MIN UR problem. Different with algorithms in literature, it solves MIN problem directly, rather than transforming it into many sub-problems. The proposed algorithm is also applicable for the special case of MIN UR, in which it involves some mandatory relations. Numerical results show that the algorithm is effective for MIN UR problem and it outperforms Sadegh's algorithm in sense of the resulted minimum inconsistency number, even though the test problems are linear.

Investigation of ion-atom collision dynamics through imaging techniques

The principle and technique details of recoil ion momentum imaging are discussed and summarized. The recoil ion momentum spectroscopy built at the Institute of Modern Physics (Lanzhou) is presented. The first results obtained at the setup are analyzed. For 30 keV He2+ on He collision, it is found that the capture of single electron occurs dominantly into the first excited states, and the related scattering angle results show that the ground state capture occurs at large impact parameters, while the capture into excited states occurs at small impact parameters. The results manifest the collision dynamics for the sub-femto-second process can be studied through the techniques uniquely. Finally, the future possibilities of applications of the recoil ion momentum spectroscopy in other fields are outlined.