Galvanizing or galvanization is the electrochemical process by which one metal can be covered with another.[1] It is called galvanization because this process was developed from the work of Luigi Galvani, who discovered in his experiments that if a metal is brought into contact with a severed leg of a frog, it contracts as if it were alive; He later realized that each metal presented a different degree of reaction in the frog's leg, which implies that each metal has a different electrical charge.
Later he ordered the metals according to their charge and discovered that one metal can be coated with another, always depositing a metal with a higher charge on another with a lower charge, and taking advantage of this quality of his discovery, galvanizing, electroplating, and then electroplating were later developed.
Utility
The function of galvanizing is to protect the surface of the metal on which the process is carried out.
The most common galvanizing consists of depositing a layer of zinc (Zn) on iron (Fe); since, since zinc is more oxidizable, less noble than iron and generates a stable oxide, it protects iron from oxidation when exposed to oxygen in the air.
It is generally used in pipes for the conduction of water whose temperature does not exceed 60 °C since then the polarity of the zinc is reversed with respect to the steel of the tube and it corrodes instead of being protected by the zinc.
To avoid corrosion in general, it is essential to avoid contact between dissimilar materials, with different oxidation potential, which can cause galvanic corrosion problems due to their combination.
It may happen that either of both materials is suitable for potential galvanizing with other materials and yet their combination is inappropriate, causing corrosion, due to the different oxidation potential mentioned.
One of the most frequently made errors is the use of copper pipes combined with galvanized steel pipes (see standards UNE 12502.3, UNE 112076, UNE 112081). If the copper pipe, which is a more noble material, is located upstream of the galvanized pipe, the copper ions, which necessarily exist in the water or the copper particles that can be dragged by erosion or from any other source, will be cemented on the zinc of the galvanized pipe downstream and this will oxidize by forming a local Cu/Zn bimetallic stack at the points where the copper ions have been deposited as metallic copper on the galvanized pipe.[2] From that point onwards This will accelerate the corrosion of the galvanized coating at all these points. Once the zinc has disappeared from the coating, the battery will be Cu/Fe and will continue to corrode until the steel tube is punctured.[3] As the galvanizing is previously installed, this failure goes unnoticed and is usually attributed to the end of its service life or even to the poor quality of the galvanizing. The cause, however, has been the poor quality of the design: the installation of the copper pipe upstream, which is what has caused corrosion of the galvanizing downstream.
hot dip galvanized
Introduction
Galvanizing or galvanization is the electrochemical process by which one metal can be covered with another.[1] It is called galvanization because this process was developed from the work of Luigi Galvani, who discovered in his experiments that if a metal is brought into contact with a severed leg of a frog, it contracts as if it were alive; He later realized that each metal presented a different degree of reaction in the frog's leg, which implies that each metal has a different electrical charge.
Later he ordered the metals according to their charge and discovered that one metal can be coated with another, always depositing a metal with a higher charge on another with a lower charge, and taking advantage of this quality of his discovery, galvanizing, electroplating, and then electroplating were later developed.
Utility
The function of galvanizing is to protect the surface of the metal on which the process is carried out.
The most common galvanizing consists of depositing a layer of zinc (Zn) on iron (Fe); since, since zinc is more oxidizable, less noble than iron and generates a stable oxide, it protects iron from oxidation when exposed to oxygen in the air.
It is generally used in pipes for the conduction of water whose temperature does not exceed 60 °C since then the polarity of the zinc is reversed with respect to the steel of the tube and it corrodes instead of being protected by the zinc.
To avoid corrosion in general, it is essential to avoid contact between dissimilar materials, with different oxidation potential, which can cause galvanic corrosion problems due to their combination.
It may happen that either of both materials is suitable for potential galvanizing with other materials and yet their combination is inappropriate, causing corrosion, due to the different oxidation potential mentioned.
One of the most frequently made errors is the use of copper pipes combined with galvanized steel pipes (see standards UNE 12502.3, UNE 112076, UNE 112081). If the copper pipe, which is a more noble material, is located upstream of the galvanized pipe, the copper ions, which necessarily exist in the water or the copper particles that can be dragged by erosion or from any other source, will be cemented on the zinc of the galvanized pipe downstream and this will oxidize by forming a local Cu/Zn bimetallic stack at the points where the copper ions have been deposited as metallic copper on the galvanized pipe.[2] From that point onwards This will accelerate the corrosion of the galvanized coating at all these points. Once the zinc has disappeared from the coating, the battery will be Cu/Fe and will continue to corrode until the steel tube is punctured.[3] As the galvanizing is previously installed, this failure goes unnoticed and is usually attributed to the end of its service life or even to the poor quality of the galvanizing. The cause, however, has been the poor quality of the design: the installation of the copper pipe upstream, which is what has caused corrosion of the galvanizing downstream.
On the contrary, in the event that the copper pipes are installed at the end of the network, that is, downstream of the galvanized pipe, this problem does not exist as long as it is guaranteed that there is no return water that, after passing through the copper, passes through the galvanized pipe. If this risk exists, an anti-return system must be installed. In any case, it is necessary to place an insulating sleeve between the galvanized steel of the general installation and the final copper pipe to avoid galvanized/copper contact. This solution, however, is ineffective in the previous case, general copper pipe and final branches of galvanized steel. Even if corrosion is eliminated at the point of contact between both materials, which is the only thing the sleeve does, corrosion will not be prevented. This will occur due to the copper ions carried by the water, or the copper particles, which will produce pitting on the entire downstream galvanizing installation, as explained.
Other widely used galvanizing processes are those that refer to decorative pieces. These pieces are coated for mainly decorative purposes, buckles, buttons, keychains, stationery and countless products are plated in copper, nickel, silver, gold, bronze, chrome, tin, etc. In the case of jewelry, gold plating is used (generally 18 to 21 carats). Jewelry is also coated in rarer metals such as platinum and rhodium.
In intaglio or manual intaglio engraving, a resource was usually used that allowed longer print runs to be obtained, preventing premature wear of the engraved copper printing plates, galvanically covering them with a thin film of iron.
Process
Contenido
Existen varios procesos para recubrir de zinc el acero. Los principales son:.
hot dip galvanization
Galvanizing is a procedure for coating finished iron/steel parts by immersion in a crucible of molten zinc at 450°C.
Its main objective is to prevent oxidation and corrosion that humidity and environmental contamination can cause on iron. This activity represents approximately 50% of zinc consumption in the world and for more than 150 years it has been established as the most reliable and economical procedure for protecting iron against corrosion.
This process is not just about depositing a few micrometers "Micrometer (unit of length)") of zinc on the surface of the steel. The zinc coating is chemically bonded to the steel base because there is a diffusion metallurgical chemical reaction between the zinc and iron or steel at 450°C. When the steel is removed from the bath, several superficial layers of zinc-iron alloy have formed in which the zinc has solidified. These different layers of alloy are harder than the base steel and have an increasing zinc content as they approach the surface of the coating. The treatment must comply with the ISO 1461 standard (Galvanized coatings on iron and steel).
Galvanized iron or steel is mainly used in construction (metallic "Armor (construction)" trusses, protective fences, electro-welded gratings, etc.). Other uses are: street furniture (lighting, signage, barriers); "Catenary (railway)" catenary carriers and various signaling means used in swimming pools or at sea (particularly aggressive humid environment and/or containing chlorine), in wastewater treatment plants or in buildings for livestock breeding (acidic environment).
electrolytic galvanized
The following elements are used in electrolytic galvanizing processes:
On the contrary, in the event that the copper pipes are installed at the end of the network, that is, downstream of the galvanized pipe, this problem does not exist as long as it is guaranteed that there is no return water that, after passing through the copper, passes through the galvanized pipe. If this risk exists, an anti-return system must be installed. In any case, it is necessary to place an insulating sleeve between the galvanized steel of the general installation and the final copper pipe to avoid galvanized/copper contact. This solution, however, is ineffective in the previous case, general copper pipe and final branches of galvanized steel. Even if corrosion is eliminated at the point of contact between both materials, which is the only thing the sleeve does, corrosion will not be prevented. This will occur due to the copper ions carried by the water, or the copper particles, which will produce pitting on the entire downstream galvanizing installation, as explained.
Other widely used galvanizing processes are those that refer to decorative pieces. These pieces are coated for mainly decorative purposes, buckles, buttons, keychains, stationery and countless products are plated in copper, nickel, silver, gold, bronze, chrome, tin, etc. In the case of jewelry, gold plating is used (generally 18 to 21 carats). Jewelry is also coated in rarer metals such as platinum and rhodium.
In intaglio or manual intaglio engraving, a resource was usually used that allowed longer print runs to be obtained, preventing premature wear of the engraved copper printing plates, galvanically covering them with a thin film of iron.
Process
Contenido
Existen varios procesos para recubrir de zinc el acero. Los principales son:.
hot dip galvanization
Galvanizing is a procedure for coating finished iron/steel parts by immersion in a crucible of molten zinc at 450°C.
Its main objective is to prevent oxidation and corrosion that humidity and environmental contamination can cause on iron. This activity represents approximately 50% of zinc consumption in the world and for more than 150 years it has been established as the most reliable and economical procedure for protecting iron against corrosion.
This process is not just about depositing a few micrometers "Micrometer (unit of length)") of zinc on the surface of the steel. The zinc coating is chemically bonded to the steel base because there is a diffusion metallurgical chemical reaction between the zinc and iron or steel at 450°C. When the steel is removed from the bath, several superficial layers of zinc-iron alloy have formed in which the zinc has solidified. These different layers of alloy are harder than the base steel and have an increasing zinc content as they approach the surface of the coating. The treatment must comply with the ISO 1461 standard (Galvanized coatings on iron and steel).
Galvanized iron or steel is mainly used in construction (metallic "Armor (construction)" trusses, protective fences, electro-welded gratings, etc.). Other uses are: street furniture (lighting, signage, barriers); "Catenary (railway)" catenary carriers and various signaling means used in swimming pools or at sea (particularly aggressive humid environment and/or containing chlorine), in wastewater treatment plants or in buildings for livestock breeding (acidic environment).
electrolytic galvanized
The following elements are used in electrolytic galvanizing processes: