Na Chen

Microwave absorption properties of hollow microsphere/titania/M-type Ba ferrite nanocomposites

Low density composite powders of hollow microsphere/titania/M-type Ba ferrite were prepared using a two-step sol-gel technique. Their electromagnetic wave absorption properties were investigated in the 2–18GHz frequency range. Reflection loss less than −20dB was obtained between 7.5–9.4GHz for paraffin composites containing 25wt% titania over an absorber thickness of 2.0–3.0mm. A minimum reflection loss of −30.1dB was observed at 8.5GHz with a thickness of 2.4mm. The strong electromagnetic absorption properties are due to the introduction of a titania intermediate layer.

The Effect of Internal Stress on the Thermal Expansion Coefficient of Al/SiC p Composite

The effect of internal stress on the coefficient of thermal expansion (CTE) of the high volume fraction Al/SiCp composite was calculated and studied in a temperature range from 298 to 673 K. The results show that the CTE of composite rises slowly to a maximum value at about 530 K and then decreases with temperature because of the microstress induced by thermal mismatch between aluminum matrix and SiC particles. The macrostress in the composite changes the temperature at which the matrix begins to yield. The calculated CTE of the Al/SiCp composite is consistent with the experimental one before the temperature at which the matrix begins to yield. This temperature has been determined through theoretical calculation, which is well in accord with the experimental result.The effect of internal stress on the coefficient of thermal expansion (CTE) of the high volume fraction Al/SiCp composite was calculated and studied in a temperature range from 298 to 673 K. The results show that the CTE of composite rises slowly to a maximum value at about 530 K and then decreases with temperature because of the microstress induced by thermal mismatch between aluminum matrix and SiC particles. The macrostress in the composite changes the temperature at which the matrix begins to yield. The calculated CTE of the Al/SiCp composite is consistent with the experimental one before the temperature at which the matrix begins to yield. This temperature has been determined through theoretical calculation, which is well in accord with the experimental result.

Electromigration-driven motion of an elliptical inclusion

We present a rigorous analytical solution for electromigration-driven motion of an elliptical inclusion in an infinite two-dimensional conductor (here, an inclusion may imply a void). An elliptical inclusion will move at a velocity proportional to the applied electric field strength, inversely proportional to an equivalent inclusion size, and strongly affected by the shape parameter of the inclusion, but independent of rotation of the inclusion with respect to the direction of the applied electric field. For a given equivalent inclusion size, a circular inclusion will move at the lowest velocity, while a slitlike one moves quickly.