Wide Ribbons Research Articles

The variation of power loss and domain wall spacing with applied stress in wide amorphous ribbon material

The power loss of wide, 1.3 cm, ribbons of commercially produced Metglas 2826 (Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</inf> Ni <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</inf> P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</inf> B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> ) have been measured under sinusoidal flux conditions. These measurements have been performed on samples in the as-cast unpolished, annealed unpolished, as-cast polished and annealed polished condition over a frequency range from 20 to 1000 Hz at flux densities up to 0.75 T. The variation of power loss with tensile stress applied in the direction of the ribbon length over the range 0 to 25 MPa (0 to 3600 psi) has been determined. The variation of domain configuration with tensile stress for the annealed polished samples has been observed by the Kerr magneto-optic effect technique. The static hysteresis loss of the ribbons has been reduced by the application of the tensile stress but at higher frequencies the stressed samples exhibit a higher power loss. The total power loss has been divided into the major constituent losses and the high excess eddy current loss is attributed to the observed high domain wall spacing to thickness ratio. The effect of polishing the ribbons in order to observe the domains is to introduce a complex stress which increases the power loss. The power loss of the annealed samples has not been reduced by the application of the tensile stress.

High speed EFG of wide silicon ribbon

A system for high speed EFG of silicon ribbon is described which is capable of growing ribbon up to 7.5 cm in width and 7.5 cm/min in speed. A technique for achieving constant width growth has been developed through the utilization of temperature gradients along the ribbon width to stabilize and control the ribbon edge. Problems which have to be solved with respect to maintaining growth stability and eliminating buckling of the ribbon at higher growth speeds are examined in detail.

Growth of 10 cm wide silicon ribbon

The temperature distribution in the die, a most important parameter in ribbon crystal growth, is measured by a new, simplified method. The distribution determined by the new method corresponds fairly well with that measured using a thermocouple. The dependence of the temperature distribution in the die on the flow rate of Ar gas is investigated. Ribbon crystals, 10 cm in width, are grown from metallurgical and semiconductor grade silicon using a rectangular heater and controlled Ar gas flow rate. Precipitates in the ribbon are studied by infrared microscopy, and their number and form are shown to depend on the growth speed.

Problems in Growth of 4-Inch Wide Silicon Ribbon Crystals

Ribbon crystals with 4-inch width are grown using a specially designed rectangular heater. Wide ribbons crack spontaneously during crystal growth or handling. Thermal stress in crystals is calculated using the observed temperature distribution in crystals. It is clarified that larger maximum shear stress is concentrated around the center of the crystal in wider ribbons. Local thermal stress leads to residual stress, which is the main reason for spontaneous cracks in these ribbons.

Planar and cylindrical jet streaming of water and of molten Fe40Ni40B20 alloy

The nature of liquid streaming instabilities is an important consideration in many processes. In chill-block melt spinning of glassy metallic alloys, for example, molten alloy is expelled from a pressurized crucible in order to form a jet which is impinged and chilled against a rapidly moving substrate surface, thereby continuously casting ribbon or tape. The geometry of wide glassy alloy ribbons made by using a melt ejection crucible with a slit-shaped orifice is partially controlled by the tendency for the planar melt jet to undergo capillary inversion. The current investigation describes experiments in which the inversion lengths of planar water and molten Fe40Ni40B20 alloy streams were studied. The results show agreement with values obtained by using a theoretical model based on an inviscid isothermal liquid. Also, measurement of cylindrical jet break-up length has been conducted for both water and for molten Fe40Ni40B20 alloy. Results in both instances show agreement with a theoretically derived expression applying to an inviscid isothermal liquid if an experimentally measured stream perturbation factor is determined for each liquid. Therefore, it is shown that modeling of both planar and cylindrical molten alloy jet behavior is possible by either theoretical calculation based on an inviscid isothermal liquid or by water streaming experiments if differences in liquid density, surface tension, and stream perturbation factor are considered.

Manufacture of amorphous alloy ribbons

Amorphous alloys are prepared in continuous ribbon form by rapid quenching directly from the melt. In particular, the process of chill block melt-spinning involves the continuous impingement of molten alloy against a rapidly moving substrate surface. Principles of chill block melt-spinning are presented with regard to the formation of continuous, rapidly-quenched amorphous alloy ribbon. The effects of numerous process variables on sample geometry and physical properties are examined through experimental results obtained by the author and by other researchers. Principles of narrow ribbon manufacture are extended to describe means of fabricating wide ribbon. Manufacturing problems unique to extended runs and potential solutions are cited. Effects of process parameters on magnetic and physical properties of as-cast samples are discussed.

Response of type II superconductors to magnetic fields varying in intensity and direction: model of nonrotating vortices; infinite slab geometry

The evolution of the longitudinal and transverse components of the magnetic induction in a long and wide ribbon of a type II superconductor subjected to a magnetic field directed along the plane of...

Evaluation of Temperature Distribution of Melt in Silicon Ribbon Growth

An improved Edge-defined Film-fed Growth apparatus is used to grow wider silicon ribbon crystals. A rectangular graphite heater with a shape similar to the die top structure is used in order to increase the length of uniform temperature. A thermal radiation modifier prevents the growth of crystals with non-uniform thickness. The lateral temperature distribution at the die is quantitatively analyzed from the thickness of the grown crystal. The appropriate temperature distribution for growing wide ribbons is determined. As a result, growth of an 8.4 cm wide ribbon is achieved. The dependence of the crystal thickness and width on the growth rate and system temperature is also investigated.

Wide silicon ribbon crystals

An improved edge-defined film-fed growth (EFG) apparatus is used for the growth of wide silicon ribbon crystals. This apparatus utilizes a specially designed heater and a thermal radiation modifier, which facilitate an appropriate temperature profile at the die top where crystals grow. A ribbon crystal as wide as 84 mm is obtained.

Arrangement of subunits in assembled histone H4 fibers.

The structure of assembled histone H4 fibers has been studied by analysis of electronmicrographs, including optical diffraction. An individual fiber has the appearance of an 80-A wide ribbon, twisted at intervals of about 330 A. Thicker fibers which have been observed seem to be bundles of ribbons. In diffraction patterns from both kinds of fiber, layer lines at axial spacings of about 1/55 A-1, 1/37 A-1, and 1/27 A-1 were most consistently observed. The possible arrangements of molecules within the twisted ribbons have been deduced and are found to be fairly closely related. The ribbons appear to consist of two parallel, unstaggered rows of repeating units, which are probably H4 dimers. The similarity between the observed layer line spacings of the H4 fibers and the spacings of the maxima in x-ray diffraction patterns from whole chromatin suggests that the H4 fibers have a structure related to that of chromatin. Since homogeneous preparations of histones H2A, H2B, and H3, or any mixture of these four histones, can form similar structures, it seems likely that the basic organization of chromatin is determined by a fibrous histone core around which the DNA is wrapped.

Epitaxial silicon solar cells on “ribbon” substrates

The ability to grow Si in ribbon form offers the potential for greatly reducing the cost of solar cells compared with the present technology that is based on cutting large-cross-section ingots with the accompanying material waste. In the recent past, the edge- defined-growth (EFG) process technology has received much attention, and progress was made in growing 1-in.-wide ribbons of significant length. However, this material is polycrystalline over most of its length. In addition, the possible inclusion of the die materials (carbon) and associated contaminants leads to difficulties in controlling the minority-carrier lifetine in the ribbon. Thus, because of lattice defects (e.g., dislocations, grain boundaries, andcontaminants), problems are anticipated in obtaining a high yield of efficient solar cells by direct diffusion into such ribbon material produced with the present technology. This paper reports on a study of means of generally improving the quality of solar cell devices obtained by using thin epitaxial layers deposited on such material. The program encompasses analytical studies aimed at relating the defects to device performance, and the fabrication of solar cells on a comparative basis (diffusio versus epitaxial growth on crystals of similar quality) to establish the improvement which is obtained. Indeed, the program described in this report demonstrated substantially improved performance with ≈50-μm-thick epitaxial layers compared with those made by direct diffusion. The difference in performance was analyzed in detail to yield significant new insight into the factors controlling the solar cell efficiency when such devices are fabricated in large- grained polycrystalline silicon ribbon.

Sur la parametrisation des courbes de variation thermique des susceptibilites diamagnetiques des carbones pregraphitiques

Electronic properties of pregraphitic carbons are usually studied using a free electron gas and a free charge carrier mass models (this mass decreases if the cristallite diameter increases). The two dimensional gas model[1] yields an analytic formula (1) which parametrizes experimental magnetic susceptibility of carbons with the help of two numerical parameters T 0 and K 0 . However, since diamagnetic susceptibility increases with crystallite sizes in the range of 30 Å to 200 Å, the electronic levels cannot yet be assumed to form an energy continuum (band). A recent calculation of magnetic susceptibility [5] shows that London theory [6] is well adapted to explain this diamagnetism. In this paper, each carbon is described by graphitic ribbons without interlayer interactions, but forming a Grand Canonical Ensemble. In such a way the diamagnetic formulas related to the π electrons are expressed in (4) and (5). The numerical results of Ref. [5] show that the negative χ d term is proportional to the width ribbon L , and is almost independant of temperature. The positive χ p term is due to a splitting of the degenerated levels. These properties lead to the following simplified model: in the vicinity of the energy gap δE , the energy levels are assumed to be equidistant when no magnetic field is applied and every term a i is assumed to be equal to a unit quantity a (Fig. 1). In the case where the graphitic ribbon width L is in the range of 30 Å to 100 Å and the temperature T in the range (100°K, 1000°K), χ p term may be reduced to the expression (6). These conditions lead to the expression (8) which is analogous to (1) providing that T 0 is replaced by δ E 2k . The numerical results of Ref. [5] show that e 2 a and 1 δE are roughly proportional to L . Therefore the magnetic susceptibility may be expressed in the form (7) where α 1 , α 2 and α 3 are parameters. The χ ' term represents the σ electron dimagnetism neglected in the London theory. The magnitude of this term is taken to be −0.3 × 10 −6 emu cgs. A value α 2 = 0.68 is obtained from Ref. [5]. The best agreement with the experimental results shown on Fig. 2 gives: α 1 = −0.056 × 10 −6 emu cgs α 3 = −3.5 × 10 4 . When each carbon is characterized by the parameter L , the experimental points are fitted well by the formula (8) (curves in full lines on Fig. 2). It can be seen that the L values are analogous to the experimental crystallite diameter L a . When the size of these samples is greater than 100 Å the agreement with experiments deteriorates (Fig. 6b) because of the interactions between graphitic planes which involve non linear variations between χ d , e 2 a and 1 δE with respect to L . The analogy between the expression (8) and (1) obtained respectively with continuum and discrete levels can be related to the analogy of magnetic susceptibility curves as the number of aromatic rings increases until the graphite is reached.

Superconducting Magnet Models for Isabelle

The development program for the superconducting magnets of the Intersecting Storage Accelerators is described. The dipole magnet design is of the cos ? type and employs wide ribbon conductor. Magnetic measurements are compared with calculations which include the effects of conductor magnetization and iron saturation. Calculations of the harmonics due to the magnet ends will also be presented along with estimates of the effect of the shape of the outer boundary of the iron shield on the field and the degree of interaction between the magnets in the two rings. The conductor is a metal-filled braid woven from 186 wires each containing 400 filaments. A precision molding technique has been developed which assures accurate placement of the turns and could be used for semi-mass production. The iron cores are laminated and assembled in a special way to eliminate the axial differential expansion between the coil and the core. Correction coils for the 3? and 5? terms are built into the bore tubes. These coils are necessary to correct the small (10-3) harmonics produced by conductor magnetization at low field and iron saturation at high fields.

Vapor-Deposited Nb3Sn Ribbons

The electromagnetic performance of high-field type-II superconductors is significantly affected by structural factors such as crystal size, crystal orientation, or crystal strain. Because the vapor-deposition process for depositing single-phase, polycrystalline, stoichiometric Nb3Sn on a heated moving substrate permits control of these structural parameters, this technique is used for the deposition of continuously monitored layers of Nb3Sn on long lengths of ribbon substrate. The thickness of teh Nb3Sn layer is controlled and can be readily varied to meet specific magnet requirements. For small-bore, high-field, layer-wound magnets, a family of commerical 0.090-in.-wide ribbons has been developed. For larger-bore magnets, in which ``pancake''-type construction is desirable, a commercial line of ½-in.-wide ribbons is currently being offered. Custom-size ribbons have been made as narrow as 0.025 in. and niobium stannide has been deposited on wires as thin as 0.005 in. in diameter. This paper describes these different ribbons and discusses their electromagnetic performance. Normalized curves have been developed for calculation of short-sample critical currents as a function of volume of niobium stannide. For instance. from 20 to 95 kG, normalized critical current In (i.e., the ratio of critical current at any desired field to the critical current at 100 kG) can be expressed as follows: In=Ic/I100 kG=exp(−0.0152H+1.597). From 95 to 140 kG, the following approximate expression can be used: In=Ic/I100 kG=exp(−0.02581H+2.592),where Ic is the critical current at the desired magnetic field, I100 kG is the critical current at 100 kG, and H is the magnetic field in kG. The current density of the Nb3Sn layer in the various types of vapor-deposited ribbon remains essentially constant. When a constant current density at 100 kG is used for the various Nb3Sn layer thicknesses, the Nb3Sn thickness and the ribbon width can be incorporated into the expression for critical current from 20 kG to 95 kG as follows: Ic=(W/0.090)37.4×104(t−7.5×10−5)exp(−0.0152H+1.597). From 95 kG to 140 kG, the following expression applies: Ic=(W/0.090)37.4×104(t−7.5×10−5)exp(−0.02581H+2.592),where W is the ribbon width in inches and t is the Nb3Sn layer thickness in inches. These data are discussed in detail. The critical currents obtained in actual magnets are often lower than the short-sample performance. In many magnet applications, it is economically desirable to obtain the highest possible current density. To achieve these goals, it may be necessary to compromise the amount of normalized metal parallel to the superconductor. Specific examples of optimization of magnet current density as a function of silver plating and cooper cladding of the superconductor ribbon are described.

Superconducting Magnet Materials

Superconducting Magnet Materials

Electron Microscopy of Dislocations and Other Defects in Sapphire and in Silicon Carbide, Thinned by Sputtering

AbstractIon bombardment has been employed as a means of thinning crystals of silicon carbide and sapphire for subsequent investigation with transmission electron microscopy. The procedures employed are described. In sapphire, small specks were found, and these were attributed to clustering at room temperature of defects introduced by the bombardment with ∼ 2 keV argon ions used during thinning. Upon heating to 800 °C, extensive networks of dislocations were formed, and the motion of these dislocations could be followed. Gas bubbles were present after annealing for an hour at 900 °C or above. No dissociation of the dislocations in sapphire was observed, but the Burgers vectors were along the a directions as anticipated. In silicon carbide, wide ribbons of stacking fault were found on the basal planes, and the stacking fault energy was estimated to be 4 erg cm−2 within an order of magnitude.

The observation of dislocations in thin single crystal films of gold prepared by evaporation

Abstract An evaporation technique has been developed to allow thin (approx. 200 Å thick) detached single crystal films of gold to be prepared. These films are very coherent and uniform in thickness. Dislocation lines are observed in these films with a density of 1010-1011/cm2 The dielocations may be observed to move inside the electron microscope. A prominent feature of the movement is the occurrence of wide ribbons of stacking fault due to the splitting of a dislocation in to two partial dislocations. Cross-slip is observed also. Annealing of the films has produced some regular arrays of dislocations, including hexagonal networks and arrays at low angle boundaries. Small loops are also found in some of the films and are interpreted as dislocation loops resulting from the collapse of discs of vacancies.

On the current induced in a conducting ribbon by a current filament parallel to it

It has been shown that, if a plane wave is incident normally on a flat conducting ribbon, both components of induced current density differ little from what would obtain if the width of the ribbon was infinite, save very near the edges. The density very near the edges was evaluated for ribbons whose total width was 2?/? or 4?/? it emerged that the distribution of density was very nearly the same in each case and did not differ significantly from the distribution at the edge of a very wide ribbon, which is known from another solution. In other words, the distribution very near an edge is sensibly independent of the width of the ribbon. An example of great practical interest is the current induced in a flat reflecting sheet by a current filament parallel to it, or?speaking generally?when the incident wave has a cylindrical, in contrast to a plane, front. The exact solution for this case is known in principle but is impracticable to evaluate numerically. However, the solution can be evaluated when the ribbon is very wide indeed and the cylindrical wave starts from a line in the vicinity of the single bounding edge. Experience indicates that it seems reasonable to suppose that the ?edge effect? for this limiting case will not differ significantly from the effect at both edges when the cylindrical source is situated on the normal to a ribbon of finite width. The distribution of induced current has been evaluated when the cylindrical source is (a) distant ?? from a half-plane and 0.592? from its bounding edge, (b) distant 0.96? from a half-plane and 0.555? from its bounding edge, (c) distant ?? from a half-plane and 0.99? from its bounding edge. In each case the disturbance of density is found to be concentrated in a width of about 0.1? from the bounding edge. Then follows a Section which shows that the net electric force at the foot of the perpendicular from a filament distant ?? from a plane is almost zero when the induced currents which are more distant than 0.99? from this point are ignored. And that the small residue of force is sensibly equilibrated by the force which arises from the effect of two bounding edges, as estimated from the edge effect which obtains in a corresponding half-plane. The Section is intended to show that the calculable edge effects appropriate to a half-plane provide a very close solution for a ribbon of finite width. Then it is shown that the diffraction pattern for a filament in the presence of an infinite conducting plane depends dominantly on the currents which are induced in the width, say, ?? from the foot of the perpendicular. Curves from which the diffraction pattern can readily be deduced are given for a filament distant from a plane and due to the currents induced in the central strips of various widths; they are intended to be of practical use as an aid to design. The modifications to these patterns which would result from the estimated ?edge effects? which must occur when the reflector has a finite width, in contrast to the pattern accruing from the current induced in a finite width of an infinite plane, are considered and found to be insignificant. Accordingly, it is suggested that the diffraction pattern for a filament and a reflector of finite width can be estimated very closely by crediting the reflector with the currents which would be induced in the same width of an infinite plane. It is held that this has established a principle of considerable use in practice. Although an aerial and a flat reflector is not a case of much practical concern, at least it is one which can now be worked out simply and with considerable accuracy; it appears that there is little to be gained from making the reflector wider than 3/2?. The principle developed in the paper must be capable of wide extension, and it should be possible to extend it to apply to cylindrical and to parabolic reflectors. It is hoped to do this in due course.