HAuCl4
Well-known member
Found this old paper online.
Anybody seen one of these machines up close?.
Anybody seen one of these machines up close?.
Zone Refining.
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Not likely to be found. It's generally done with an induction heating furnace. It's reputed to work well and can yield gold of high quality. Each successive pass through the molten stage should improve the quality of the gold, assuming additional passes are needed.
Harold
Harold
HAuCl4
Well-known member
In that paper, I found many interesting things:
The machine they describe melts in a vacuum, with no crucible, using electron bombardment, the list of contaminants have some substantial contaminants that I wasn't expecting to see, etc, etc.
All in all, very different from what I had imagined the method to be. (The metal refined and discussed in the paper was platinum). Maybe this is a for a specific application in the 70s, and more effective methods are in use?. I added all impurities and calculated the refined platinum to be just a little better than 9999 after 3 passes. I was expecting something like 6N or more. :shock:
The machine they describe melts in a vacuum, with no crucible, using electron bombardment, the list of contaminants have some substantial contaminants that I wasn't expecting to see, etc, etc.
All in all, very different from what I had imagined the method to be. (The metal refined and discussed in the paper was platinum). Maybe this is a for a specific application in the 70s, and more effective methods are in use?. I added all impurities and calculated the refined platinum to be just a little better than 9999 after 3 passes. I was expecting something like 6N or more. :shock:
HAuCl4
Well-known member
Zone Melting
a crystallophysical method of refining materials that consists in the movement of a narrow fusion zone along a long solid rod made of the material that is being refined. Nearly all industrially important metals, semiconductors, dielectrics, and inorganic and organic compounds— more than 120 substances—may undergo zone melting.
The first mention of the use of zone melting dates to 1927, when the method was used to purify iron. Zone melting became widely known in 1952 as a result of the works of W. Pfann (USA), who used it to produce germanium of high purity in a special container (container zone melting).
To perform container zone melting on a solid load placed in a container, a small melted region called a zone, which is shifted along the load, is created. In the process crystallization of the material takes place on one surface of the interface between the solid and liquid phases (the crystallization front), and the raw material is supplied at the other surface (the melting front). Container zone melting is used to refine a material that does not interact with the material of which the container is made. In 1953, P. Keck and M. Golei (USA) proposed a crucibleless method for zone melting of a vertical rod (the so-called floating zone method) for purifying semiconducting silicon. In this method, the fusion zone is restrained mainly by the forces of surface tension; therefore, crucibleless zone melting is widely used for refractory and active materials with sufficiently high surface tension and not very great density in liquid state (silicon, germanium, molybdenum, tungsten, platinum, palladium, rhenium, and niobium). Since 1955 zone melting has been widely used in laboratory and plant practice to produce pure materials with an impurity content of as little as 10−7-10−9 percent (so-called zone refining), for alloying and uniform distribution of the impurity throughout the ingot, and for growing single crystals, concentrating impurities in analytical practice, creating high-purity standards, and studying phase diagrams.
Zone refining is based on the fact that under conditions of equilibrium between the liquid and solid phases, the solubility of the impurities is different in the two phases. To produce pure metals the fusion zone is usually shifted through the ingot several times, or several shifting fusion zones are created simultaneously in the ingot, with sections of solid material between them. The rate of shifting of the fusion zone is usually 0.1-10.0 mm/min, and the number of passes is 10-15 or more. Refining is concluded when the maximum (final) distribution of the impurity, which cannot be changed by subsequent shifts of the zones, is attained.
The effectiveness of zone removal of impurities from a material depends on the distribution ratio of the impurity (the ratio of the concentration of the impurity in the solid phase to the concentration in the liquid phase), the number of passes and the rate of shifting of the zone, and the ratio of the length of the ingot to the length of the zone. Zone equalization consists in the introduction into the first zone of an alloying additive, which is uniformly distributed throughout the ingot upon repeated shifting of the zone. Alternate motion of the zone from the head to the tail of the ingot and back is sometimes used to achieve uniform distribution of the impurity throughout the ingot.
Zone melting may be used simultaneously with refining and to produce single crystals; a seed—the nucleus of a single crystal, oriented in a predetermined crystallographic direction—is used for this purpose. The first fusion zone is created at the interface of the seed with the rod that is to undergo zone melting, and part of the rod and part of the seed are fused. Thermal conditions that, upon solidification of the liquid metal, ensure controlled crystallization of the seed in the direction induced by the seed, are created at the interface of the seed and liquid metal phases. A special type is zone melting with a temperature gradient (a method of producing p-n transitions and producing phosphides and arsenides of gallium and indium). In this case a temperature and concentration difference is created between the boundaries of the liquid zone. Because of the different solubility of the components of the system at different temperatures, a shift of the zone in the direction of the temperature gradient takes place. The rate of shifting of the zone is usually 0.1-1.0 mm/hr, and the temperature difference may be as high as 80 deg/mm.
Various equipment is used for zone melting, depending on the function, conditions, and output of the process. Depending on the method of accomplishment, a distinction is made between container and crucibleless units, which in turn are divided into periodic, methodical, and continuous types according to the character of the process; into horizontal and vertical types according to the attitude of the melting material; into units with a moving ingot or heater according to the method by which the zone is shifted; into units that use resistance heaters (for materials with a melting point of up to 1500°C), induction heating (for melting substances with high electrical conductivity in a vacuum or inert gaseous medium), electron-beam heating (for in vacuo melting of materials with a high melting point), radiation heating (for materials with a low melting point), heating by thermal conductance and Joule heat according to the method of heating the zone; and according to the method used to mix the zone (convective, mechanical, or electromagnetic) and the composition of the atmosphere (vacuum or inert or shielding gas).
The equipment for container zone melting is a horizontal . pipe, within which a container with the load to be refined travels. The heaters are mounted outside the tube and heat either the load or the container. Zone-refined tin ingots weigh up to 60 kg; germanium ingots, 10 kg, and gallium arsenide ingots, 1 kg. Crucibleless zone melting is performed in a vertical tube in which the rod to be refined is mounted. The heater is located around the rod on the outside or within the pipe. The diameter of zone-refined silicon ingots may be 35-50 mm; of beryllium and iron ingots, 25 mm; and of vanadium ingots, 15 mm.
Container zone melting is developing in the direction of continuous zone melting units and processes (the zone-space, zone-transport, and electrodynamic methods), increased intensity of refining, reduced heterogeneity of the resultant crystals, and increased purity. The development of crucibleless zone melting is progressing toward an increase in the size of single crystals (a diameter of 55-65 mm), intensification of the refining process, and achievement of homogeneous distribution of impurities and structural flaws. The general trend in the development of zone melting is characterized by work on optimum conditions, the creation of more advanced equipment, the automation of the process, and the use of programming methods.
REFERENCES
Parr, N.Zonnaia ochistka i ee tekhnika. Moscow, 1963. (Translated from English.)
Zonnaia plavka, sb. Edited by V. N. Vigdorovich. Moscow, 1966.
Romanenko, V. N.Poluchenie odnorodnykh poluprovodnikovykh kristallov. Moscow, 1966.
Vigdorovich, V. N.Ochistka metallov i poluprovodnikov kristallizatsiei, Moscow, 1969.
Pfann, W. G.Zonnaia plavka. Moscow, 1960. (Translated from English.)
K. N. NEIMARK
a crystallophysical method of refining materials that consists in the movement of a narrow fusion zone along a long solid rod made of the material that is being refined. Nearly all industrially important metals, semiconductors, dielectrics, and inorganic and organic compounds— more than 120 substances—may undergo zone melting.
The first mention of the use of zone melting dates to 1927, when the method was used to purify iron. Zone melting became widely known in 1952 as a result of the works of W. Pfann (USA), who used it to produce germanium of high purity in a special container (container zone melting).
To perform container zone melting on a solid load placed in a container, a small melted region called a zone, which is shifted along the load, is created. In the process crystallization of the material takes place on one surface of the interface between the solid and liquid phases (the crystallization front), and the raw material is supplied at the other surface (the melting front). Container zone melting is used to refine a material that does not interact with the material of which the container is made. In 1953, P. Keck and M. Golei (USA) proposed a crucibleless method for zone melting of a vertical rod (the so-called floating zone method) for purifying semiconducting silicon. In this method, the fusion zone is restrained mainly by the forces of surface tension; therefore, crucibleless zone melting is widely used for refractory and active materials with sufficiently high surface tension and not very great density in liquid state (silicon, germanium, molybdenum, tungsten, platinum, palladium, rhenium, and niobium). Since 1955 zone melting has been widely used in laboratory and plant practice to produce pure materials with an impurity content of as little as 10−7-10−9 percent (so-called zone refining), for alloying and uniform distribution of the impurity throughout the ingot, and for growing single crystals, concentrating impurities in analytical practice, creating high-purity standards, and studying phase diagrams.
Zone refining is based on the fact that under conditions of equilibrium between the liquid and solid phases, the solubility of the impurities is different in the two phases. To produce pure metals the fusion zone is usually shifted through the ingot several times, or several shifting fusion zones are created simultaneously in the ingot, with sections of solid material between them. The rate of shifting of the fusion zone is usually 0.1-10.0 mm/min, and the number of passes is 10-15 or more. Refining is concluded when the maximum (final) distribution of the impurity, which cannot be changed by subsequent shifts of the zones, is attained.
The effectiveness of zone removal of impurities from a material depends on the distribution ratio of the impurity (the ratio of the concentration of the impurity in the solid phase to the concentration in the liquid phase), the number of passes and the rate of shifting of the zone, and the ratio of the length of the ingot to the length of the zone. Zone equalization consists in the introduction into the first zone of an alloying additive, which is uniformly distributed throughout the ingot upon repeated shifting of the zone. Alternate motion of the zone from the head to the tail of the ingot and back is sometimes used to achieve uniform distribution of the impurity throughout the ingot.
Zone melting may be used simultaneously with refining and to produce single crystals; a seed—the nucleus of a single crystal, oriented in a predetermined crystallographic direction—is used for this purpose. The first fusion zone is created at the interface of the seed with the rod that is to undergo zone melting, and part of the rod and part of the seed are fused. Thermal conditions that, upon solidification of the liquid metal, ensure controlled crystallization of the seed in the direction induced by the seed, are created at the interface of the seed and liquid metal phases. A special type is zone melting with a temperature gradient (a method of producing p-n transitions and producing phosphides and arsenides of gallium and indium). In this case a temperature and concentration difference is created between the boundaries of the liquid zone. Because of the different solubility of the components of the system at different temperatures, a shift of the zone in the direction of the temperature gradient takes place. The rate of shifting of the zone is usually 0.1-1.0 mm/hr, and the temperature difference may be as high as 80 deg/mm.
Various equipment is used for zone melting, depending on the function, conditions, and output of the process. Depending on the method of accomplishment, a distinction is made between container and crucibleless units, which in turn are divided into periodic, methodical, and continuous types according to the character of the process; into horizontal and vertical types according to the attitude of the melting material; into units with a moving ingot or heater according to the method by which the zone is shifted; into units that use resistance heaters (for materials with a melting point of up to 1500°C), induction heating (for melting substances with high electrical conductivity in a vacuum or inert gaseous medium), electron-beam heating (for in vacuo melting of materials with a high melting point), radiation heating (for materials with a low melting point), heating by thermal conductance and Joule heat according to the method of heating the zone; and according to the method used to mix the zone (convective, mechanical, or electromagnetic) and the composition of the atmosphere (vacuum or inert or shielding gas).
The equipment for container zone melting is a horizontal . pipe, within which a container with the load to be refined travels. The heaters are mounted outside the tube and heat either the load or the container. Zone-refined tin ingots weigh up to 60 kg; germanium ingots, 10 kg, and gallium arsenide ingots, 1 kg. Crucibleless zone melting is performed in a vertical tube in which the rod to be refined is mounted. The heater is located around the rod on the outside or within the pipe. The diameter of zone-refined silicon ingots may be 35-50 mm; of beryllium and iron ingots, 25 mm; and of vanadium ingots, 15 mm.
Container zone melting is developing in the direction of continuous zone melting units and processes (the zone-space, zone-transport, and electrodynamic methods), increased intensity of refining, reduced heterogeneity of the resultant crystals, and increased purity. The development of crucibleless zone melting is progressing toward an increase in the size of single crystals (a diameter of 55-65 mm), intensification of the refining process, and achievement of homogeneous distribution of impurities and structural flaws. The general trend in the development of zone melting is characterized by work on optimum conditions, the creation of more advanced equipment, the automation of the process, and the use of programming methods.
REFERENCES
Parr, N.Zonnaia ochistka i ee tekhnika. Moscow, 1963. (Translated from English.)
Zonnaia plavka, sb. Edited by V. N. Vigdorovich. Moscow, 1966.
Romanenko, V. N.Poluchenie odnorodnykh poluprovodnikovykh kristallov. Moscow, 1966.
Vigdorovich, V. N.Ochistka metallov i poluprovodnikov kristallizatsiei, Moscow, 1969.
Pfann, W. G.Zonnaia plavka. Moscow, 1960. (Translated from English.)
K. N. NEIMARK
HAuCl4
Well-known member
http://en.wikipedia.org/wiki/Czochralski_process
I imagine something like this can be done with gold, silver and other metals. May not be economical.
http://www.youtube.com/watch?v=6jv6n-cV7I0&feature=related
I imagine something like this can be done with gold, silver and other metals. May not be economical.
http://www.youtube.com/watch?v=6jv6n-cV7I0&feature=related
HAuCl4
Well-known member
While researching this zone refining process, and by totally unrelated coincidence I found that a compound called sodium aurate(III), NaAuO2, exists and it is soluble in excess of NaOH solutions.
The HAuCl4 first converts to insoluble Au(OH)3 along with AgCl which converts to AgOH, then it becomes soluble again in excess NaOH as NaAuO2, while AgOH converts to Ag2O and is left behind as a solid, that separates more easily than the persistent AgCl in acid solution.
Can gold be refined by iterative re-crystallization of NaAuO2?.
What a simple avenue to get rid of persistent traces of silver chloride!. 8)
The HAuCl4 first converts to insoluble Au(OH)3 along with AgCl which converts to AgOH, then it becomes soluble again in excess NaOH as NaAuO2, while AgOH converts to Ag2O and is left behind as a solid, that separates more easily than the persistent AgCl in acid solution.
Can gold be refined by iterative re-crystallization of NaAuO2?.
What a simple avenue to get rid of persistent traces of silver chloride!. 8)
HAuCl4
Well-known member
Lou said:
I tried this suggestion from Lou on a small scale with double distilled cation resined water and it worked like a charm with silver nitrate. A guy in a lab asked me if he could keep my sample (6 iterations). He had never seen a silver sample that was so clean and so closely matched the standard he had for the ICP. I traded the silver sample for 5 free ICP's...to be collected whenever... :lol:
Now I'm wondering if and what gold, platinum, palladium salts would be suitable to a similar physical/chemical re-crystallization iteration refining process. We already know that gold chloride isn't suitable. Any ideas guys?.
I posted in this thread to keep all my wacky ideas in the same place.
I got here Looking for info on Zone refining after Lou shared a patent on the subject:
I'm going to attempt to make a tool to refine and possibly alloy pgms. The machine itself isn't anything new: I'm going to make a traveling torch holder that's held above a fixed water-cooled hearth. A wire or rod on the hearth is slowly melted from one end to the other, moving the liquidus with the torch. The new thing would be process parameters: material: composition, size, shape; for the torch: electrode size, shape, current, polarity, speed, gas type, gas flow rate.
I've been using a high O2 to clean "dirty platinum" to about .99 -- still not clean enough to use. I intend to use the above process with a TIG torch to clean the .99 Pt. I expect anything not currently on the surface to migrate to the surface. If the Pt isn't clean enough when I start, I expect to have to clean & regrind the electrode when the arc starts wandering. Lou shared an article with me on zone melting. The travel speed was 2" per hour. I imagine that to be very slow, but I won't know until I try it. I think I'll have enough to do getting the TIG method dialed-in to keep me busy for a while.
I'm going to attempt to make a tool to refine and possibly alloy pgms. The machine itself isn't anything new: I'm going to make a traveling torch holder that's held above a fixed water-cooled hearth. A wire or rod on the hearth is slowly melted from one end to the other, moving the liquidus with the torch. The new thing would be process parameters: material: composition, size, shape; for the torch: electrode size, shape, current, polarity, speed, gas type, gas flow rate.
I've been using a high O2 to clean "dirty platinum" to about .99 -- still not clean enough to use. I intend to use the above process with a TIG torch to clean the .99 Pt. I expect anything not currently on the surface to migrate to the surface. If the Pt isn't clean enough when I start, I expect to have to clean & regrind the electrode when the arc starts wandering. Lou shared an article with me on zone melting. The travel speed was 2" per hour. I imagine that to be very slow, but I won't know until I try it. I think I'll have enough to do getting the TIG method dialed-in to keep me busy for a while.
