β- Si 3 N 4 powders were shock compressed and quenched from 12 to 115 GPa. β-Si3N4 transforms to the spinel-type Si3N4 (c-Si3N4) by a fast reconstructive process at pressures above about 20 GPa. The yield of c-Si3N4 recovered from 50 GPa and about 2400 K reaches about 80% and the grain sizes are about 10–50 nm. It is proposed that the fast transformation to c-Si3N4 occurs by rearrangement of nitrogen stacking layers, which initiates partial breakup of the SiN4 tetrahedra and formation of SiN6 octahedra at high density. Because of the advantages of massive production and the nanometer characteristics of shock-synthesized c-Si3N4, it is possible to investigate the mechanical properties experimentally and to develop new industrial applications.

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For a long time, hexagonal diamond has been formed only by static and shock wave compression of well-crystallized graphites. Here, we demonstrate that cubic diamond loses its structure stability and transforms to hexagonal diamond in massive. This transformation has been completed in nanoseconds under a shock wave compression of cubic diamond, in which the shock pressure and temperature are only tens of giga pascal and hundreds of kelvin, thermodynamically being within the stability of cubic diamond. The formation of hexagonal diamond is interpreted as a direct transition (solid to solid) of cubic diamond by a kinetic mechanism due to the shear stress and enhanced temperature induced by the rapid shock wave compression.

Herein, magnetic wood was successfully prepared by in situ synthesizing Fe 3 O 4 in wood, through coprecipitation chemical interactions. A facile impregnation method, vacuum impregnation followed by pressure impregnation, was introduced to transport the adequate amount of ferric salt precursor and to further shorten the required production cycle. It was demonstrated that the obtained products exhibited outstanding microwave-absorbing properties. The best electromagnetic interference (EMI) absorbing properties could reach −64.26 dB at 14.36 GHz with the matching thickness of only 2.25 mm and broad absorbing bandwidth (| RL| > 10 dB) of 5.20 GHz covering 12.80−18.00 GHz. The subsequent thorough investigations proved that this good shielding property was due to the distinctive selfassembling morphology of Fe 3 O 4 formed in the inner surface of the lumen walls in wood, which permitted optimal impedance matching, the strongest dielectric loss, optimal magnetic loss, and an interconnected conductive network for electron hopping and migrating. This synthetic process for magnetic wood is quite facile, and the resulted EMI absorbing properties are tunable by the concentrations of the iron precursor solutions and the thickness values. This kind of synthetic magnetic wood can be potentially used as light-weight, flexible, and strong absorbing performance shielding materials for construction, furniture, decoration, and packing.