Melting Point Of Silver Research Articles

Low-temperature ( T ⩽ 950°C) preparation of melt-textured YBa 2Cu 3O 7−δ superconductors

We report a new process to fabricate melt-textured YBa 2Cu 3O 7−δ superconductors. The highest heating temperature during the melt-textured growth process is 950°C, which is below the melting point of silver, thus making it possible to fabricate long wires for large-scale applications using silver and well-textured YBa 2Cu 3O 7−δ superconductor. We present microstructure data, as probed by SEM, that show the layered platelet structure. The superconducting critical current density is 100 times better than that of sintered bulk YBa 2Cu 3O 7−δ and comparable to the results obtained by the existing melt-texture growth technique.

Synthesis of melted YBa 2Cu 3O 7-x-0.325Ag superconductor contained in solid silver via synthesized precursor containing BaCuO 2.5

Concurrent synthesis and melt-processing of YBa 2Cu 3O 7- x -0.325Ag superconductor by thermo-mechanical processing of the silver-clad precursor containing 0.5Y 2O 3+2BaCuO 2.5+CuO+0.325Ag near the melting point of silver was studied. Melted orthorhombic YBa 2Cu 3O 7- x formed after 15 min at 950–965°C in air at 1.3 and 2.6 kPa. At 950–955°C the melted YBa 2 Cu 3O 7- x superconductor was contained by solid silver which melted at 960–965°C. The highest J c was 3600 (transport) and 1.2 x 10 5 A/ cm 2 (magnetization). On extending the heat-treatment from 15 to 30 min, orthorhombic YBa 2Cu 3O 7- x changed to tetragonal YBa 2Cu 3O 7- x . BaCuO 2.5 coexisted with YBa 2Cu 3O 7- x during its formation and presumably lead to orthorhombic YBa 2Cu 3O 7- x directly.

Silver substitution for Copper in Y1Ba2Cu307-y

Abstract A variety of samples with different amounts of silver substituted for copper in Y1Ba2(Cu1-xAgx)3O7-y were prepared and sintered at temperatures between 940°C and 1030°C. Samples with values of x up to 0.4 were superconducting above 77 K and the the room temperature resistivity was generally lower in samples sintered at or in excess of 980 C. The samples were analysed using x-ray diffraction and scanning electron microscopy. The results presented here show that silver remains largely isolated in intergranular cavities, resulting in improved connectivity and transport properties, despite the formation of impurity phases which emerge due to disturbances in the stoichiometry of the superconducting phase. Additionally, samples sintered at temperatures in excess of the melting point of silver exhibit enhanced grain growth, a denser morphology and more metallic behaviour in the normal state.

Solid silver particle production by spray pyrolysis

Solid, spherical, micron-sized silver metal particles were produced by spray pyrolysis from a silver nitrate solution. The effects of reaction temperature, carrier gas type, solution concentration, and aerosol droplet size on the characteristics of the resultant silver particles were examined. Pure, dense, unagglomerated particles were produced with an ultrasonic generator at and above 600° C using N 2 carrier gas, and at and above 900°C using air as the carrier gas. Solid particle formation at temperatures below the melting point of silver (962°C) was attributed to sufficiently long residence times (3.5–54 s) which allowed aerosol-phase densification of the porous silver particles resulting from reaction of the precursor.

Fabrication of highly aligned YBa2Cu3O7− δ- Ag melt-textured composites

Liquid phase processing techniques with slow cooling through the peritectic transformation have been utilized to fabricate bulk aligned 123-Ag composites. Coarse (∼30–40 μm) and fine (∼5–10 μm) particles of silver are distributed between and within the 123 grains. Although the processing temperatures employed are much higher than the melting point of silver, particles of silver are retained behind the advancing solid-liquid interface. The peritectic reaction occurs at the solid-liquid interface and the rate of the reaction is limited by diffusion between the two solid phases, hence the transformation invariably results in some unreacted phases. Ellipsoidal, Y 2BaCuO itx particles varying in size from 10–25 μm are trapped within the 123 phase. In addition, regions of CuO and BaCuO 2 are present in the sample as separate phases. Silver particles are also dispersed in these insulating regions of the microstructure. The 123-Ag composites have superior mechanical properties compared to melt-textured stoichiometric 123 samples. A detailed study describing the effects of processing on the microstructureof these aligned composites is reported.

Measurement of the Silver Point with a Simple, High-Precision Pyrometer

A pyrometer is described which is simple and easy to construct, yet fulfils the requirements of a standards laboratory which wishes to perform radiation thermometry to very high accuracy. A test of its performance is described in which it was used to measure the ratio of the spectral radiances at 650 nm of black bodies at the melting points of silver and gold. Taking the gold-point temperature to be 1064.43 °C, this measurement gave a result of (961.961 ± 0.017) °C (99% confidence level) as the value of the silver-point temperature.

A further simplified method for the separation of 111In from silver targets by thermochromatography

A simplified thermochromatographic process for the separation of 111In at normal pressure and temperatures lower than the melting point of silver from silver targets bombarded with α-particles, is described. The separation is performed in a quartz apparatus using mixed gas phases containing Ar, HCl and H 2O. Three quarters of the indium can be separated from the target block within 1 h at 1103 K. The electrophoresis using cellulose coated glass plates is recommended for the quality control of indium chloride solutions.

噴霧熱分解法による銀粒子の製造

Preparation of spherical silver particles was examined by using spray-pyrolysis technique from AgNO3 solution. The solvent was a mixture of H2O and C2H5OH (25-100 vol%). Although Ag particles were produced by pyrolysis above 650°C, the particles became solid and spheikir when the pyrolysis was done at temperatures higher than melting point of silver. The particle sizes were determined mainly by the degree of the splitting of atomized droplets during the heating process.

Electrochemical thermometry: A new approach to the determination of elevated temperatures on the thermodynamic scale

A high temperature, solid-electrolyte, oxygen-concentration cell is proposed as a means for determination of high fixed-point temperatures, such as the melting points of silver, gold and palladium, on the thermodynamic scale. An analysis of possible sources of errors in gold-point determinations indicates that the method is potentially comparable in accuracy to high temperature gas thermometry. Preliminary experiments gave results within a few degrees of the accepted values for the silver and gold points. It is believed that more refined measurements can be of considerable value as independent checks on important elevated fixed-point temperatures.

The Freezing Point of Silver

THE subject of high temperature thermometry has recently attracted considerable attention, and on account of the ease with which silver can be obtained in a pure state, coupled with its great thermal conductivity, the freezing point of this metal has been suggested as a standard temperature. We therefore wish to call attention to an error into which we believe M. le Chatelier has fallen with regard to this constant. In the Zeitschrift fur Physikalische Chemie, Band viii. p. 186, he says that the melting point of silver can be lowered by as much as 30° through the absorption of hydrogen; again, in the Comptes rendus for August 12, 1895, he states that the melting point of this metal is lowered by a reducing atmosphere. He therefore recommends that when the melting point of silver is used as a fixed point in calibrating pyrometers, the experiment should be performed in an oxidising atmosphere. This conclusion is contradicted by Prof. Calendar's experiments and by our own, for in the Phil. Mag., vol. xxxiii. p. 220, Callendar shows that the freezing point of silver is lowered and rendered irregular by an oxidising atmosphere; and our own results confirm this conclusion. But serious doubt having been raised on this point by so high an authority as M. le Chatelier, we have thought it right to make further experiments.

On the measurement of high temperatures

The author, after adverting to the many abortive endeavours of former experimentalists to obtain instruments for the accurate ad-measurement of high temperatures, and after suggesting doubts as to the confidence to which Wedgwood’s pyrometer is entitled, describes several attempts of his own to effect this very desirable object. In the course of his inquiries, a remarkable fact presented itself to his notice in the change which occurred in an index constructed on the compensation principle, and formed by two slips of metal, the one of silver and the other of gold, originally quite pure, and united without any alloy. In the course of a few years, although it had never been subjected to a heat above that of melting lead, the whole surface of the gold became converted into an alloy of silver, the impregnation extending gradually to a considerable depth in the gold, and destroying the sensibility of the instrument to changes of temperature. After trying various plans, he gave the preference to one founded on the following principles: namely, that the fusing points of the pure metals are fixed and determined; that those of the three noble metals, namely, silver, gold, and platina, comprehend a very extensive range of temperature; and that between these three fixed points in the scale, as many intermediate ones as may be required may be obtained by alloying the three metals together in different proportions. When such a series of alloys has been once prepared, the heat of any furnace may be expressed by the alloy of least fusibility which it is capable of melting. The determinations afforded by a pyrometer of this kind will, independently of their precision, have the advantage of being identifiable at all times and in all countries: the smallness of the apparatus is an additional recommendation, nothing more being necessary than a little cupel, containing in separate cells the requisite number of pyrometric alloys, each of the size of a pin’s head. The specimens melted in one experiment need only to be flattened under the hammer in order to be again ready for use. For the purpose of concisely registering the results, the author employs a simple decimal method of notation, which at once expresses the nature of the alloy, and its correspondence with the scale of temperature. Thus G. 23 P would denote an alloy of gold with 23 per cent. of platina. As the distance between the points of fusion of silver and of gold is not considerable, the author divides this distance on the scale into ten degrees; obtaining measures of each by a successive addition of 10 per cent. of gold to the silver, the fusion of which, when pure, marks the point of zero; while that of gold is reckoned at ten degrees. If minuter subdivisions were required for particular objects of research, these might easily be made, following always the decimal series. From the point of fusion of pure gold to that of pure platina, the author assumes 100 degrees, adding to the alloy which is to measure each in succession 1 per cent. of platina. Whether these hypothetical degrees represent equable increments of temperature is a question foreign to the purpose of this paper, and must be the subject of future investigation. The author then enters into a detailed account of the method he employed for insuring accuracy in the formation of the requisite series of alloys, and of various experiments undertaken to ascertain their fitness as measures of high temperatures. The determinations of the heats of the different furnaces adapted to particular objects, are given in a tabular form. The remaining portion of the paper contains the recital of the author’s attempts to determine by means of an apparatus connected with an air thermometer, the relation which the fusing point of pure silver bears to the ordinary thermometric scale. An extensive series of experiments, of which the results are given in a table, were made with this apparatus. From the data thus afforded, after making the necessary corrections, the author deduces the following results in degrees of Fahrenheit: viz. A full red heat 1200°; orange heat 1650°; melting point of silver (which had been estimated by Wedgewood at 4717°, and by Daniell at 2233°,) 1830°; of silver alloyed with one tenth gold 1920°. The paper is accompanied with drawings of the apparatus employed.