Molten flux

Fluxes also contain agents that faciHtate appHcation, such as petroleum jeUy or alcohol. These bum or evaporate at elevated temperatures before the soldering temperature is attained, leaving behind a uniform coating of flux. Fluxes become molten before the joining process is reached. The molten flux flows or spreads to form a continuous coating over the surfaces to which they have been appHed. 

Contaminants in fuels, especially alkali-metal ions, vanadium, and sulfur compounds, tend to react in the combustion zone to form molten fluxes which dissolve the protective oxide film on stainless steels, allowing oxidation to proceed at a rapid rate. This problem is becoming more common as the high cost and short supply of natural gas and distillate fuel oils force increased usage of residual fuel oils and coal. 

Rb4Ge2Seg containing two MSe4 tetrahedra Hnked through Se-Se bonds (Fig. 14.11), were found to be isostructural to Gs4Ge2Seg, although this latter phase was prepared by a solvatothermal method versus our molten flux process [98]. 

This method emplosrs a molten flux which dissolves the material and re-deposits it upon a seleeted substrate. That is, the molten flux acts as a transport medium. The temperature of the flux can be varied to suit the material and to promote high solubility of the solute material in the molten solvent. One example is YIG", yttrium iron garnet, i.e.- Y3FesOi2 -This material is used in the Electronics Industry as single crystals for microwave generating devices. It can be grown via the molten flux method. 

A typical molten-flux apparatus is shown as 6.10.1. on the next paige. 

The material which is to form single crystals is dissolved in the molten flux to near saturation (Note that this requires prior knowledge regarding solubility of compound in molten flux). 

Pure aluminum is soft, light, and malleable. It is the most common metal in the Earth s crust (ca. 8 %). Small amounts of Cu or Mg additives make it hard and firm. The surface is passivated with an oxide layer. Produced by fused-salt molten flux electrolysis. Cannot be welded, but is nevertheless optimal for airplanes (in which case it is riveted), construction units (windows, frames), and utensils such as cans, foil, and tubes. Increasingly found in cars in order to minimize weight. Tiny holes are burnt into extremely thin aluminum films in data-storage units. It has no function in physiology, but Al ions in the bloodstream can be detrimental. 

Due to its high charge density and homogenous layer charge distribution synthetic fluorohectorite is one of the few available clays suitable for PCH formation. However, even this clay proved to have some disadvantages. Synthetic fluorohectorite is obtained from molten fluxes and is unstable with respect to calcination (partial defluorination) at 350 °C. 

Polished nickel or cobalt plates were mounted in cylindrical graphite forms (11 mm inner diameter), rapidly heated up to about 450 °C and then filled with a molten flux (-475 °C) consisting of the eutectic mixture 82 mass % ZnCl2 - 18 mass % NaCl. After 60 s holding the plates under the flux for cleaning their surfaces from possible contamination, the forms... 

Another ground, the court found, was that the process claims had been predicated upon an error. The claims called for having the electric current to be conducted by the molten flux, whereas properly speaking, the current was conducted in part, if not in its entirety, by the action of the electric arc. 

There are some comments to make here. First, the positions of the Sn, Pb, or Ba atoms in these phases is not known, so that for these compounds the model must be regarded as hypothetical. Secondly, it does not suit needle-shaped crystals, as the first layer laid down must already include the fault planes inherently contained within it. This point will be returned to later. Thus the alkali-metal intergrowth phases, which are needle shaped, do not fall into this class. This growth mechanism can also be applied to the barium ferrites, which are plate-like crystals that form from a molten flux, and it is possible that it could account for the sort of faulting noted in the amphibole chain minerals described on p. 135 et seq. 

A variety of properties of the flux must be controlled, including fusion characteristics (fusion temperature range and sintering characteristics), insulation characteristics, flow properties of the powder, viscosity of the molten flux, and non-metallic absorption ability. The viscosity influences the consumption rate of flux, heat transfer in the mold, and non-metallic dissolution rate, and has been the subject of published and unpublished work over the last ten years. 

A small amount, 2.5 to 3.0 g of representative gypsum specimen, was calcined for 1 h at 1000°C in a platinum crucible, and the loss on ignition was recorded. A portion of 1.0000 g of the calcined specimen was mixed with 6.000 g of dense lithium tetraborate (Spectroflux 100 , Johnson and Matthey Co.) and 0.3000 g of lithium fluoride. Approximately 3 mg of lithium bromide was added to the mixture as a release (nonsticking) agent. Fusions were carried out on a propane flame, using a Claisse fluxer (2] equipped with crucibles and molds made from 95% platinum-5% gold alloy. The volume of molten flux was adequate to fill the 32-mm diameter mold to a sufficient height and produce a disk approximately 4 mm thick. 

Growth of Single Crystals From a Molten Flux... 

The apparatus is simple and consists of a furnace whose temperature can be accurately controlled, a crucible to hold the molten flux, and a method of rotating the crucible to stir the flux containing the dissolved material. Single crystals can be induced to grow along the sides of the crucible by controlling the temperature and supercooling of the molten flux. 

Nonetheless, there is one area where molten flux growth has been very successful. That is epitaxial growth of a single crystal film on a substrate, such as that used for production of bubble memories. This is shown in the following, given as 4.2.58. on the next page. 

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