External Tin Research Articles

Investigations Towards Ultra-Low Cost Nb3Sn SRF Cavity Fabrication Via Melt Casted Bronze Route Processing

A novel approach to fabricating Nb3Sn SRF cavities and other RF components using an ultra-low-cost melt casting fabrication process has been investigated. This simple, low cost melt casting technique has the potential to be used to fabricate nearly any superconducting Nb3Sn structure using either the Bronze Route (BR), Internal Tin (IT), External Tin (ET) processes as well as normal conducting pure copper (Cu) cavities. Most of the heat treated samples that were examined using SEM/EDX seemed to show a reasonable correlation of Tc onset and transition width (ΔTc) of the ingots initial/starting Sn content to the desired stoichiometric Nb3Sn phase, where the lower starting Sn content coupons resulted in lower Tc's with broader transition widths and the higher starting Sn coupons resulted in higher Tc's with narrower ΔTc's. The best samples had Tc onsets ∼17–18 K and ΔTc's < 2 K. Two samples were further tested for RF surface resistance (Rs) and Quality Factor (Q) at JLAB. These RF measurements were performed at 7.4 GHz using a calorimetric technique and showed two transitions, one at ∼8 K and another at ∼14 K; values of Rs were at least two orders of magnitude higher than similar high quality Nb3Sn films directly deposited substrates by JLAB and with another superconducting transition close to the superconducting transition temperature of niobium. Substantial improvements in the processing variables ranging from higher quality of the initial ingots with higher Sn content, to better electro-polishing and reaction heat treatment regimens will be necessary to realize improved RF performance metrics.

Chemical and morphological characterization of commercial tinplate for food packaging

The structure of tinplate is usually described as a sequence of layers involving an external tin layer (passivated by a chromate conversion coating), an intermediate FeSn2 layer, and the steel substrate. This structure description applies well to tinplate produced in the past by hot dipping but not necessarily to modern materials fabricated through tin electrodeposition and subsequent heat treatment. In this work, the chemical composition and the structure of 5 commercial tinplate materials have been investigated using Auger electron spectroscopy, scanning electron microscopy, 3D white light interferometry, and electrochemical chrono‐potentiometry. The study revealed that the intermediate layer consists indeed in a wide interface where tin, steel, and the FeSn2 alloy coexist. Moreover, the thickness of the Sn film varied locally significantly. A new tinplate structure was proposed in order to reliably appraise corrosion relevant features.

TiC, TiN과 TiC/TiN 코팅의 트라이볼로지 특성

CA 이온도금기술에 의한 TiC와 TiN 그리고 TiC/TiN 코팅재를 비교하기 위하여 트라이볼로지 물성을 연구하였다. 실험은 Falex journal V block 시스템을 이용한 터보시험기에서 수행하였다. 코팅재의 마찰과 마모특성은 작용된 하중과 미끄럼 속도에 의하여 다양하게 결정되었다. TiC와 TiN 그리고 TiC/TiN 코팅재는 표면에서 트라이볼로지 특성이 현저하게 증가하였다. 단층코팅에서는 TiC보다 TiN이 좋은 결과를 얻었다. 그러나, TiC/TiN의 다층코팅은 다른 어떤 단층코팅보다 좋은 성능을 보였다. 다층코팅의 성능이 향상된 핵심요소는 TiN층 외부와 강 사이에서 부착이 증가하게된 TiC의 역할 때문이다. The tribological properties of TiC, TiN and TiC/TiN coatings on steels prepared by the cathodic-arc (CA) ion plating technique were investigated. Experiments were carried out on a tribo-test machine using a Falex journal V block system. The friction and wear characteristics of the coatings were determined by varying the applied load and sliding speed. The TiC, TiN and TiC/TiN coatings markedly increased the tribological characteristics of the surface. As far as a single layer coating was concerned, TiN goes better results than TiC. However, the TiC/TiN multilayer coating performed better than either single layer coating. The major factor in the improved performance of the multilayer coating was the role of TiC in improving the adhesion between the external TiN layer and the substrate steel.

Boride coatings obtained by pack cementation deposited on powder metallurgy and wrought Ti and Ti–6Al–4V

Wear resistance of Ti alloys needs to be improved, and an effective way to achieve this is through surface treatment. Boronizing is a surface treatment in which boron diffuses into the surface of Ti leading to the formation of hard and wear-resistant Ti borides. Boronizing of wrought and/or cast Ti alloys by pack cementation has been studied, while similar coatings on Ti alloys produced by powder metallurgy (PM) have not been reported. Also critical process parameters for boronizing Ti alloys, such as pack cementation powder composition and the process temperature have not been systematically studied and analysed. The present work reports on the surface modification of PM Ti and PM Ti–6Al–4V by boronizing, and presents some important thermodynamic aspects of the process comparing it with similar coatings applied to wrought Ti–6Al–4V. The coatings were characterised using scanning electron microscopy and X-ray diffraction. For both Ti and Ti–6Al–4V alloys the use of amorphous B as a B element supplier in the boriding powder pack led to the formation of a uniform external boride layer, while the use of B4C as a B element supplier in the pack and under the same boronizing conditions, led to the formation of an external TiN layer and an internal layer containing B. The thermodynamic calculations performed proved successful in determining the appropriate conditions for boride coating deposition and estimating the phases likely to be formed. Finally the effect of surface roughness on the coating quality is discussed.

Effect of cutting speed on the performance of coated and uncoated cutting tools in turning nodular cast iron

This paper presents the results of an experimental investigation on the effect of cutting speed in turning nodular cast iron with coated and uncoated cutting tools. Three different carbide cutting tools were used, namely TiCN + TiC + TiCN + Al 2O 3 + TiN-coated carbide tools with multilayer coating of 7.5 and 10.5 μm thickness and uncoated WC/Co tool. Turning experiments were carried out at four different cutting speeds, which were 125, 150, 175 and 200 m/min. Feed rate ( f) and depth of cut ( a p) were kept fixed at 0.25 mm/rev and 1.5, respectively, throughout the experiments. Tool performance was evaluated with respect to tool wear, surface finish produced and cutting forces generated during turning. Uncoated WC/Co tool was the worst performing tool with respect to tool wear and was the worst with respect to surface finish. If tool wear, surface finish and cutting force results are considered together, among the three tools studied, 10.5 μm thick multilayer TiCN + TiC + TiCN + Al 2O 3 + TiN-coated carbide tool with external TiN layer is the most suitable one for turning nodular cast iron, especially at high cutting speeds.

Synthesis and spectroscopic studies of diorganotin derivatives with tolfenamic acid. Crystal and molecular structure of the first complex of tolfenamic acid, 1,2:3,4-di-μ 2-2-[(3-chloro-2-methylphenyl)amino]-benzoato- O, O-1,3-bis-2-[(3-chloro-2-methylphenyl)amino]benzoato- O-1,2,4:2,3,4-di-μ 3-oxo-tetrakis[di- n-butyltin(IV)

The complexes [Me 2LSnOSnLMe 2] 2 ( 1) [Bu 2LSnOSnLBu 2] 2 ( 2) and Bu 2SnL 2.H 2O ( 3), where HL is 2-[bis(3-chloro-2-methylphenyl)amino]benzoic acid (tolfenamic acid), have been prepared and characterized structurally by means of 19Sn Mössbauer, vibrational and 1H- and 13C-NMR spectroscopies. The crystal structure of complex 2 has been determined by X-ray crystallography. Three distannoxane rings are present to the dimeric tetraorganodistannoxanes of planar ladder arrangement with distorted trigonal-bipyramidal geometry about the five-coordinated tin centers. The structure, which has twofold symmetry, features a central Sn 2O 2 unit with two additional tin atoms linked at O. Pairs of tin atoms are bridged by bidentate carboxylate ligands and the external tin atoms have their coordination geometry completed by a monodentate carboxylate ligand. The tin atom geometries are similar and are based on a trigonal bipyramidal arrangement. Significant π→π stacking, C–H–π interactions and intrarmolecular hydrogen bonds stabilize this structure. The polar imino hydrogen atom on N(1) and N(2) participate in a bifurcate intramolecular hydrogen bond. In this case complex 2 is self-assembled via C–H–π and π→π stacking interactions. Tin-119 Mössbauer, vibrational and NMR data are discussed in terms of the crystal structure and the proposed structures for 1 and 3. From the variable-temperature Mössbauer effect, the Debye temperatures for 1– 3 were determined.

Crystal and molecular structure of 1,2:3,4-di-μ 2-[2,6-dichlorophenyl)amino]benzeneacetato-O,O-l,3-bis[(2,6-dichlorophenyl)amino]-benzeneacetato-O-1,2,4:2,3,4-di-μ 3-oxo-tetrakis[di-n-butyltin(IV)]: {[nBu2Sn(O2CCH2C6H4N(H)C6H3Cl2)]2O}2

Abstract The crystal and molecular structure of 1,2:3,4-di-μ 2-[(2,6-dichlorophenyl)amino]bezeneacetato-O,O-1,3-bis-[(2,6-dichlorophenyl)amino]benzeneacetato-O-1,2,4:2,3,4-di-μ 3-oxo-tetrakis[di-n-butyltin(IV)], {[nBu2Sn(O2CCH2C6H4N(H)C6H3Cl2)]2O}2, C88H112Cl8N4O10Sn4, has been determined at room temperature. The colorless crystals are monoclinic, space group C2/c with unit cell dimensions a = 31.447(2) Å, b = 11.27(4) Å, c = 29.423(4) Å, β = 114.479(6)°, Z = 4 and D x = 1.501 Mg m−3. The structure was solved by direct methods and refined by a full-matrix least-squares procedure to final R = 0.044 using 5742 reflections. The tetranuclear structure, which has 2-fold symmetry, features a central Sn2O2 unit with two additional tin atoms linked at O. Pairs of tin atoms are bridged by bidentate carboxylate ligands and the external tin atoms have their coordination geometry completed by a monodentate carboxylate ligand. The tin atom geometries are similar and are based on a trigonal bipyramidal arrangement.

実用Ｎｂ３Ｓｎ超電導線材の構成と臨界電流のひずみ依存性

An investigation was made on the strain dependence of critical cuurent Ic for three kinds of practical Nb3Sn superconducting wires which are in the course of development, with an emphasis on the correlation with wire constitution.In the internal tin diffusion processed wires with a single tin core at the center, the reversible strain limit, εirrev was small and the strain sensitivity of Ic was high. This is ascribed to the strain concentration induced by Kirkendall voids observed in the center of fracture surface.Internal reinforcement using SUS 405 steel increased both εm, the strain corresponding to peak Ic, and the strain sensitivity, and decreased the εirrev in addition to a marked increase of flow stress. In the light of both the serration in the stress-strain relation and fracture surface morphology, the degradation of strain characteristics are attributable to the strain concentration in Nb3Sn layer associated with localized deformation of the steel at low temperatures.In the external tin diffusion in situ processed wires, both Nb3Sn layer formed in the periphery and the unreacted core in the center of the wire controlled the strain characteristics. The smaller the core size was, the larger the critical current density and the smaller the εm or εirrev. Inhomogeneity of tin diffusion in the cross section as well as in the longitudinal direction resulted in deviation of the core and tin balling, respectively. They deteriorated the strain characteristics of the wire significantly.Improvements of the strain characteristics in these wires through proper constitution and heat treatment were briefly discussed.

Tin supply and microstructure development during reaction of an external tin process Nb3sn multifilamentary composite

The class of “high tin” multifilamentary Nb3Sn superconducting composites depends on the diffusion of tin from a high tin reservoir to the niobium filaments where the superconducting A15 phase grows by solid state reaction. In particular, external tin composites are fully fabricated as niobium filaments in a copper matrix and the wire is subsequently coated with tin prior to reaction. In the work reported a detailed study is made of tin diffusion and microstructure development during the reaction of a 1369 filament external tin composite wire consisting of 37 × 37 bundled filaments of 3.5 μm diameter. During the initial low-temperature anneal stage the formation and evolution of copper-tin intermetallic phases is followed. High-temperature reaction anneals were then carried out at 755 and 588° C. The rapid conversion of e-phase to α-Cu is accompanied by diffusion of tin towards the centre of the composite and the growth of Nb3Sn A15 phase layers on the niobium filaments. The variation of tin composition and layer thickness is reported for different stages of reaction. In addition, the average composition of the A15 layer is measured as a function of the radial position of the filament, and the tin concentration gradient is measured within the A15 layer for the outermost filaments of the composite. The results show clearly the very strong dependence of the A15 layer growth rate on the tin concentration in the matrix. As a result, for an isothermal anneal at 755° C the layer growth is highy non-uniform across the composite. Furthermore it can be seen that additional inhomogeneity of the layer composition arises as a consequence of the bundled geometry of the composite. An important practical observation is that when the layer thickness approaches the filament radius the A15 compound is still far from stoichiometry particularly for filaments near the centre of the composite. The results overall emphasize the need for a detailed understanding of tin supply and compound growth before optimum heat-treatment procedures can be prescribed for a particular external tin design. A comparison of anneals at 755 and 588° C indicates that the relative rates of tin diffusion and A15 layer growth changes strongly with temperature; this suggests that a combination of anneals at different temperatures might be necessary for the optimization of the superconducting properties of high tin composites.

Analysis of the tin diffusion step in Nb3Sn-Cu superconducting wire produced by the external tin process

Assuming volume diffusion is dominant, an analysis has been presented which allows one to analytically describe the three stages of the solid-state diffusion process for adding Sn in the external tin method for preparing Nb3Sn/Cu superconducting material. It is shown that one obtains a maximum intermetallic compound layer thickness in stage III which then decreases to zero thickness. Important practical questions in utilizing this process are the times required to complete stages I and II of the process, and this analysis predicts that the times required to complete stage I are on the order of days while stage II is completed in a matter of hours. The roles of grain-boundary diffusion and sample geometry are discussed and it is concluded that the analysis may be regarded as an upper bound for determining the times required to complete stages I and II of the solid state Sn diffusion process.

Void formation in Nb3Sn-Cu superconducting wire produced by the external tin process

The tin (Sn) diffusion step for producing Nb3Sn-Cu superconducting wire by the external Sn process was modeled in experiments where either pure Sn or a Cu-Sn alloy was plated on sheets of either pure Cu or a Cu-Sn bronze. Each stage of the three-stage solid-state diffusion process was evaluated and it was found that rows of voids are produced in stage I of the process. These voids coarsen in stages II and III and in the worst case they are observed to coalesce and cause complete spalling away of the Sn-rich diffusion layers. Methods for minimizing void formation and possible causes of the void formation are discussed.

Fabrication and performance of in-situ processed Nb&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;Sn tape and multistrand wire

A tape conductor and a multistrand wire, each of which has two different types, have been fabricated in long lengths. Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn filaments of one type of the tape conductor are twisted. A pancake magnet (46 mm inner and 80 mm outer winding diameter) has been made of those tape conductors and tested in backup field of 7.5 Tesla. The tests have revealed that the twist improves stability of the tape conductor. Total magnetic field of 9.8 T was achieved using the tape with twisted Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn filaments for windings of end pancake modules. Both types of the tape were made by external tin diffusion method and have critical current capacities of 240 Amp at 10 Tesla. The multistrand wires were manufactured by tin cored internal diffusion method. One type containes single tin core, the other type seven tin cores. The single and seven tin-cored wires have been successfully drawn to diameters of 0.62 and 1.26 mm respectively. Critical current densites of those wires were found to be <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(1.4 \sim 2.0) \times 10^{4}</tex> Amp/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 11 Tesla.

Submicron multifilamentary high performance Nb3Sn produced by powder metallurgy processing of large powders

Powder metallurgy processed submicron multifilamentary Nb3Sn superconducting wires were fabricated starting with 250–500-μm-diam powders. A multiple strand bundling procedure was used to simulate large scale production with actual areal reductions greater than 106 to achieve submicron fibers. Both external tin and tin core processing were successful. Typical Cu-36 wt.% Nb-Sn materials gave overall critical current densities of 8×104 A/cm2 at 12 T, 3×104 A/cm2 at 14 T, and 6×103 A/cm2 at 16 T. These results demonstrate that particle size and billet size can be scaled from earlier laboratory scale to large scale fabrication to produce high performance materials.