State Diffusion Method Research Articles

Transverse sections of multifilamentary Nb3Sn superconductor wires in TEM

New devices using fine multifilament superconducting wires are becoming more important, since these wires now have better thermal stability, lower losses and better current carrying capacity. The multifilament Nb3Sn superconductor wires reviewed in this report were made by the solid state diffusion method developed by Kaufman and Pickett. In this process, a niobium rod in a bronze jacket is extruded into an hexagonal shape, this rod is then cut into lengths, which are packed together in a bronze jacted and extruded again. This process is continued until the total reduction ratio for the niobium is a billion to one. At this point the wires are still ductile and can be fabricated into their final shape. The Nb2-bronze composite is then heat treated, and the tin from the bronze diffuses into the Nb, forming Nb3Sn. This heat treatment is important, since it controls both the amount of Nb3Sn formed and the grain size, which affects flux-pinning.

The frequency dependence of a.c. losses in type II superconductors

Abstract Energy losses occurring under the application of an alternating magnetic field were examined in type II superconductors representative of three different classes of material: (1) single-crystal niobium (elemental) in the Meissner state, (2) molybdenum-25 at.% rhenium (alloy) in fields both below and well above H C1, and (3) Nb3Sn (compound) principally in the mixed state. Losses were measured as a function of field amplitude and frequency in order to determine whether losses of other than hysteretic variety were present. The total loss per unit surface area per cycle associated with the superconductor was found to have the form W T(h 0, v) = W 0(h 0) + vF(h 0) where W 0(h 0) is identified as an hysteretic term, v is the frequency and h 0 the a.c. field amplitude. Only in the Mo-25 at.% Re alloy did the hysteretic term completely mask the frequency-dependent term. Hysteretic losses in the single-crystal niobium and two Nb3Sn specimens prepared by different solid state diffusion methods were strong...

The oxygen consumption of the pregnant uterus and fetus of macaca mulatta

Uterine and umbilical blood flows were estimated by the steady state diffusion method in eight pregnant rhesus monkeys with the fetus in utero near term under halothane and N 2O anesthesia. Blood was sampled from a maternal artery, two utero-ovarian veins, the umbilical vein and a fetal femoral artery. The mean uterine blood flow was 80 ml .min -1 and the mean uterine O 2 consumption 3.7ml STPD.min -1. The mean umbilical blood flow was 45 ml .min -1 and the mean fetal O 2 consumption 2.1ml STPD.min -1. During simultaneous determinations, the fetal O 2 consumption accounted for approximately 55% of that of the pregnant uterus and its contents. The maternal placental blood flow was estimated to be approximately 55 to 76% of the total uterine blood flow. The characteristics of the placenta for diffusional exchange of O 2 were calculated using several assumptions, and were found to be similar to those estimated for the human placenta.

New developments in silicon photovoltaic devices

The requirements which silicon photovoltaic devices have to meet in various applications are so widely different that it was necessary to develop three distinct types of devices:(1) A device which is operated in the forward biased condition, useful at moderately low to high light levels, known as a solar cell.(2) A device which is operated in the forward biased condition, useful at very low light levels, known as a low level cell.(3) A device operated in the reverse biased direction at low to high light levels, known as a photodiode.All three types are p-n junction devices, prepared by solid state diffusion methods, with each type designed to yield special characteristics. The spectral response, transient response, and temperature dependence of these devices are considered.