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| [[File:Float-zone crystal growth process svg.svg|right|thumb|Liquid moves from left to right during melting in the float-zone crystal growth process]]
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| [[File:Si-crystal floatingzone.jpg|thumb|upright=.8|Silicon crystal in the beginning of the growth process]]
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| [[File:Si-crystal floatingzone growing.jpg|thumb|upright=.8|Growing silicon crystal]]
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| [[File:Tantalum single crystal and 1cm3 cube.jpg|thumb|A high-purity (99.999% = [[Nines (purity)|5N]]) [[tantalum]] single crystal, made by the floating zone process (cylindrical object in the center)]]
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| '''Zone melting''' (or '''zone refining''' or '''floating zone process''') is a group of similar methods of purifying crystals, in which a narrow region of a crystal is molten, and this molten zone is moved along the crystal (in practice, the crystal is pulled through the heater). The molten region melts impure solid at its forward edge and leaves a wake of purer material solidified behind it as it moves through the ingot. The impurities concentrate in the melt, and are moved to one end of the ingot. Zone refining was developed by [[William Gardner Pfann]] in [[Bell Labs]] as a method to prepare high purity materials for manufacturing [[transistor]]s. Its early use was on [[germanium]] for this purpose, but it can be extended to virtually any [[Solution|solute]]-[[solvent]] system having an appreciable concentration difference between solid and liquid phases at equilibrium.<ref>[http://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_6/advanced/t6_1_3.html Float Zone Crystal Growth]</ref> This process is also known as the float zone process, particularly in semiconductor materials processing.
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| ==Process details==
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| The principle is that the segregation coefficient ''k'' (the ratio of an impurity in the solid phase to that in the liquid phase) is usually less than one. Therefore, at the solid/liquid boundary, the impurity atoms will diffuse to the liquid region. Thus, by passing a crystal [[boule (crystal)|boule]] through a thin section of furnace very slowly, such that only a small region of the boule is molten at any time, the impurities will be segregated at the end of the crystal. Because of the lack of impurities in the leftover regions which solidify, the boule can grow as a perfect single crystal if a [[seed crystal]] is placed at the base to initiate a chosen direction of crystal growth. When high purity is required, such as in semiconductor industry, the impure end of the boule is cut off, and the refining is repeated.
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| In zone refining, solutes are segregated at one end of the ingot in order to purify the remainder, or to concentrate the impurities. In '''zone leveling''', the objective is to distribute solute evenly throughout the purified material, which may be sought in the form of a single [[crystal]]. For example, in the preparation of a transistor or [[diode]] [[semiconductor]], an ingot of germanium is first purified by zone refining. Then a small amount of [[antimony]] is placed in the molten zone, which is passed through the pure germanium. With the proper choice of rate of heating and other variables, the antimony can be spread evenly through the germanium. This technique is also used for the preparation of [[silicon]] for use in [[computer chip]]s.
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| ===Heaters===
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| A variety of heaters can be used for zone melting, with their most important characteristic being the ability to form short molten zones that move slowly and uniformly through the ingot. [[Induction coil]]s, ring-wound [[resistance heater]]s, or gas flames are common methods. Another method is to pass an [[electric current]] directly through the ingot while it is in a [[magnetic field]], with the resulting [[magnetomotive force]] carefully set to be just equal to the weight in order to hold the liquid suspended. Zone melting can be done as a [[Batch production|batch process]], or it can be done continuously, with fresh impure material being continually added at one end and purer material being removed from the other, with impure zone melt being removed at whatever rate is dictated by the impurity of the feed stock.
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| ''Indirect-heating floating zone'' methods use an induction-heated tungsten ring to heat the ingot radiatively, and are useful when the ingot is of a high-resistivity semiconductor on which classical induction heating is ineffective.
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| ===Mathematical expression of impurity concentration===
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| When the liquid zone moves by a distance <math>dx</math>, the number of impurities in the liquid change. Impurities are incorporated in the melting liquid and freezing solid.<ref>James D. Plummer, Michael D. Deal, and Peter B. Griffin, Silicon VLSI Technology, Prentice Hall, 2000, p. 129</ref>
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| :<math>k_O</math>: Segregation coefficient
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| :<math>L</math>: Zone length
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| :<math>C_O</math>: Initial uniform impurity concentration of the rod
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| :<math>C_L</math>: Concentration of impurities in the liquid
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| :<math>I</math>: Number of impurities in the liquid
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| :<math>I_O</math>: Number of impurities in zone when first formed at bottom
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| The number of impurities in the liquid changes in accordance with the expression below during the movement <math>dx</math> of the molten zone
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| :<math>dI = (C_O - k_O C_L) \, dx\;</math>
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| :<math>C_L = I/L\;</math>
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| :<math>\int_0^x dx = \int_{I_O}^I \frac{dI}{C_O - \frac{k_O I}{L}}</math>
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| :<math>I_O = C_O L\;</math>
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| :<math>C_S = k_O I / L\;</math>
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| :<math>C_S (x) = C_O \left ( 1 - (1 - k_O) e^{- \frac{k_O x}{L} } \right )</math>
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| ==Applications==
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| ===Solar cells===
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| In [[solar cells]] float zone processing is particularly useful because the single crystal silicon grown has desirable properties. The bulk charge [[carrier lifetime]] in [[float-zone silicon]] is the highest among various manufacturing processes. Float-zone carrier lifetimes are around 1000 microseconds compared to 20-200 microseconds with [[Czochralski process]], and 1–30 microseconds with cast [[multi-crystalline silicon]]. A longer bulk lifetime increases the efficiency of [[solar cells]] significantly.
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| ==Related processes==
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| ===Zone remelting===
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| Another related process is '''zone remelting''', in which two solutes are distributed through a pure metal. This is important in the manufacture of semiconductors, where two solutes of opposite conductivity type are used. For example, in germanium, pentavalent elements of [[group V]] such as [[antimony]] and [[arsenic]] produce negative (n-type) conduction and the trivalent elements of [[Boron group|group III]] such as [[aluminum]] and [[boron]] produce positive (p-type) conduction. By melting a portion of such an ingot and slowly refreezing it, solutes in the molten region become distributed to form the desired n-p and p-n junctions.
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| ==See also==
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| * [[Fractional freezing]]
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| * [[Freeze distillation]]
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| * [[Laser-heated pedestal growth]]
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| * [[Wafer (electronics)]]
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| * [[Verneuil process]]
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| ==References==
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| {{Reflist}}
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| * William G. Pfann (1966) ''Zone Melting'', 2nd edition, [[John Wiley & Sons]].
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| * Hermann Schildknecht (1966) ''Zone Melting'', Verlag Chemie.
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| * Georg Müller (1988) ''Crystal growth from the melt'' Springer-Verlag, Science 138 pages ISBN 3-540-18603-4, ISBN 978-3-540-18603-8
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| {{DEFAULTSORT:Zone Melting}}
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| [[Category:Industrial processes]]
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| [[Category:Semiconductor growth]]
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| [[Category:Chemical processes]]
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| [[Category:Crystals]]
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What is the number one external hemorrhoid treatment? So, this really is not an simple question since different folks have different conditions. However, in this short article, you'll learn certain techniques to help healing a hemorrhoid.
Later I did find out he had hemorrhoidectomy surgery. At the time I wondered if surgery was the number one prolapsed hemorrhoids treatment for him. I didn't learn anything regarding hemorrhoids back then.
Another treatment for hemorrhoids will be to use witch hazel. It's been shown to succeed at helping decrease swelling and helps with healing hemorrhoids which are bleeding. If your piles are very swollen, this usually undoubtedly assist we today.
Then there is a high tech method of removing a hemorrhoid. Laser is regarded as the latest tool which has been use inside order to receive rid of your hemorrhoid. This is usually applied with those internal plus outside hemorrhoids depending on the severity of the issue.
Witch Hazel when selected as an ingredient in hemorrhoid treatments has an virtually magical impact. If you empty a little bottle of Witch Hazel into your toilet tissue box, the tissue might absorb it. This makes a pretty soothing replace for coarser toilet tissue and is fantastic for gentle cleansing of the delicate region as well as reducing pain and itching.
Step 2 - Keep away from Strenuous Working Out. We know functioning out for numerous folks is a duty. However strenuous exercises like cycling plus weight lifting could result extra strain found on the muscles. Yoga, swimming and aerobics are first-rate methods to receive in a first-rate exercise when hemorrhoids are inside need of a break.
When this bath is performed, you may then wish To take several ice (wrapped up inside a cloth) plus apply it to a anal region. This causes a decrease inside the amount of blood that is flowing to the area; additionally ice will have a numbing effect offering you a little more relief from pain.