Studies on W–Re Mixed-Matrix Cathodes

The performance of tungsten-rhenium (W-Re) mixed-matrix cathodes of varying compositions was studied. The work function, when the tungsten percentage is 50 plusmn 25%, is close to that of a Re-coated cathode. The I-V characteristics show an emission anomaly. It was found that the patch fields are not the main reason; rather, it is the field enhancement which is responsible for this anomaly. The emission microscopic results show that the work function distribution does not greatly differ from that of a B-Type cathode. Auger electron spectroscopy, in conjunction with scanning electron microscope studies, supports the presence of a thick active layer. The cathodes exhibited decay and heating effects with pulsed-current emission. The nonmetallic behavior is attributed to the presence of an appreciable amount of unreduced BaO. Poisoning studies show that the resistance to oxygen poisoning is better than that of a conventional B-Type cathode. A chemical technique was developed to prepare a finely divided powder of W-Re sigma-phase alloy. The cathodes made out of this alloy powder showed better emission and uniformity compared to those of simply mixed cathodes.