Nickel-cobalt alloy. Purpose of the coating and electrolytes for application.

Purpose of nickel-cobalt alloy coating

The nickel-cobalt alloy has a shiny silver-gray color. It is used:

• The main thing is as hard magnetic coatings for recording information in memory elements or recording sound. Simply put, the coating is a carrier of information;
• As protection against external magnetic fields;
• In the manufacture of magnetic circuits;
• In the manufacture of matrices for casting and pressing plastic products.

The process of electrolytic deposition of nickel-cobalt alloy has not been fully studied, but has received significant industrial application.

Nickel-cobalt electroplating designation: N-Co

Distribution of paramagnets and diamagnets in the periodic table of Mendeleev elements

The magnetic properties of simple substances change periodically with increasing atomic number of the element.

Substances that are not attracted to magnets (diamagnets) are located mainly in short periods - 1, 2, 3. Which metals are not magnetic? These are lithium and beryllium, and sodium, magnesium and aluminum are already classified as paramagnetic.

Substances that are attracted to magnets (paramagnets) are located mainly in the long periods of the Mendeleev periodic system - 4, 5, 6, 7.

However, the last 8 elements in each long period are also diamagnetic.

In addition, three elements are distinguished - carbon, oxygen and tin, the magnetic properties of which are different for different allotropic modifications.

Electrolytes and coating deposition modes

The potentials of nickel and cobalt in solutions differ slightly from each other, so precipitation of the alloy is not particularly problematic.

The composition of the alloy and deposition modes greatly influence the value of the so-called coercive force. The maximum value of this value is achieved when the nickel content in the alloy is 30%.

Coating deposition is possible from chloride, sulfate, sulfate-chloride, sulfamate and fluoroborate electrolytes.

Table 1 - Influence of the electrolyte on the magnitude of the coercive force

The composition of the electrolyte directly affects the composition of the resulting alloy. With a ratio of Ni2+ and Co2+ of 1:1, the nickel content in the alloy will be 5%. By increasing the nickel content to 5:1, its content will increase to 40%.

Table 2 - Example of optimal sulfuric acid electrolyte and modes of deposition of nickel-cobalt alloy

When depositing an alloy, it is worth considering that the anodes must be powered individually. If you want to get an alloy with 40% nickel, then you need to pass 40% of the total current only through the nickel anodes. The electrochemical equivalents of nickel and cobalt are close.

Side subgroup of the 8th group

(or, according to modern nomenclature, groups 8, 9 and 10)

groups 9 and 10 do not exhibit oxidation states 9 and 10, and the same oxidation states are most stable. As a result, the similarity of elements horizontally becomes greater than vertically. Therefore, it is more convenient to consider the Fe-Co-Ni triad together, and then consider the 6 remaining elements, united under the name “platinum metals”. Note that in the textbook by F. Cotton and J. Wilkinson, this principle is maintained throughout: the d-elements of the fourth period are considered first, and then all the others.

Nickel-iron alloy plating

The coating is used as a soft magnetic coating (coercive force less than 1000 A/m). Used as magnetic protection against external fields and in magnetic video recording heads.

The composition of the electrolyte also plays a decisive role. To obtain a coating with the required minimum coercive force, a nickel content in the alloy is required - 80%.

To obtain the coating, it is recommended to use sulfamate and fluoroborate electrolytes. In them, coatings are deposited with low internal stresses, which is especially important when depositing thick alloys. Fluorocarbon electrolyte is highly stable.

Paramagnets and ferromagnets

Let's consider the option when each atom of a substance has its own magnetic field. These fields are multidirectional and compensate each other. If you place a magnet next to such a substance, the fields will be oriented in one direction. The substance will have a magnetic field, a positive and a negative pole. Then the substance will be attracted to the magnet and can itself become magnetized, that is, it will attract other metal objects. For example, you can magnetize steel clips at home. Each one will have a negative and a positive pole, and you can even hang a whole chain of paper clips on a magnet. Such substances are called paramagnetic.

Ferromagnets are a small group of substances that are attracted to magnets and are easily magnetized even in a weak field.

Application of Invar alloy

Its low temperature coefficient of expansion allows it to be used for the production of:

• parts of control and measuring instruments;
• tapes and wires for geodetic work;
• laser supporting structures;
• parts of clock mechanisms, chronometer pendulums;
• rolled products: hot-rolled rod and sheet, cold-rolled strip, seamless pipes, forged rods.

To increase strength, cold plastic deformation of an iron-nickel alloy is performed, and then low-temperature heat treatment is performed. For greater resistance to corrosion under normal atmospheric conditions, its surface is polished and a protective layer is applied if the product is intended for use in aggressive environments. The anti-corrosion properties of Invar will also increase by adding about 12% chromium to its composition, while it retains constant elasticity when heated to 100 degrees.

Cobalt metallurgy

The discovery of metal cobalt occurred in the thirties of the 18th century. thanks to the Swedish chemist Georg Brandt. Despite this, the then-discovered element was used in the form of compounds long before George discovered it. In ancient Egypt and China they used it to paint glass blue. In the centuries following the discovery of cobalt, it was still used in the form of chemical compounds and nothing more. However, in the 20th century, the role of cobalt metal was firmly established in technology and the metallurgy industry. This happened after the creation of alloys from cobalt and steel, which differed significantly in quality.

By the 30s of the 20th century, the amount of cobalt produced began to increase in capitalist countries. During the period from 1939 to 1956, about 150 thousand tons were produced in the world (not counting Russia). cobalt

This surge in production is explained by the fact that cobalt, in its unique and useful properties, exceeded the technical requirements for metals and was well combined with innovations in technology of that time.

In its properties, cobalt is somewhat similar to nickel. It combines well with many other metals and can create a valuable industrial alloy with them. The most abundant deposits of copper-cobalt ores are located mainly in Central Africa, as well as silver-cobalt ores in North Africa.

The USA and southern Canada also have small deposits of nickel ores, as well as valuable types of man-made mineral and chemical resources from which cobalt can be extracted. In many European countries, cobalt is mined by processing technogenic mineral and chemical resources.

In the USA, the entire cobalt industry is controlled by one company, which is why there is a catastrophic shortage of it for the country’s needs and the state has to import it from other countries. At a certain point in time, imports of this element into the United States exceeded its own production by 3 times. Mainly imported from Africa, Canada, England, Germany and Norway. Almost all mined cobalt is supplied from Africa to the market of countries that seek to raise their capital.

Cobalt is an expensive metal, which limits the possibilities of its use. It is several times more expensive than nickel. It is most often used together with iron, chromium, tungsten and molybdenum, resulting in very durable and valuable alloys. Therefore, it is widely used in the tool industry, where tool strength is most important. Permanent magnets made of cobalt have a high magnetic induction. And the alloy of platinum and cobalt has the highest magnetic energy.

Cobalt increases the heat resistance of heat-resistant steels: they become more heat-resistant compared to an alloy of nickel and chromium. Thus, cobalt is an essential component of many heat-resistant alloys. Cobalt is also used in the field of drilling, for the manufacture of special drilling tools. And non-metallic cobalt compounds are used in paints, catalysts and primers. Even in nuclear energy, cobalt is used.

Magnetic alloys

These alloys are widely used in electrical engineering. They are used to make permanent magnets, transformer cores, electrical measuring instruments, and electromagnets. People have long known that iron has magnetic properties and as a result it has many uses.

Much later it was discovered that the same property is inherent in nickel and some other metals. Products made from a magnetic alloy of iron and nickel also have the ability to retain their own magnetic field when the external one is no longer present. Moreover, this personal field is again capable of influencing other magnetic bodies.

A little history

Invar is an alloy of iron and nickel, which contains 36% alloying additive. It was first discovered in France in 1896 by physicist Charles Guillaume. At this time, he was working on the search for inexpensive metal for standards of mass and length measures, which were made from a very expensive platinum-iridium alloy. Thanks to this discovery, the scientist received the Nobel Prize in physics in 1920.

The word "invar" in Latin means unchanging. This means that the coefficient of thermal expansion of an iron-nickel alloy remains constant over a wide temperature range - from -80 to 100 degrees Celsius. This alloy has several other names: nilvar, vakodyl, nilo-alloy, radiometal. Invar is a trademark of Imphy Alloys Inc., which is owned by the steel company Arcelor Mittal.

Kovar alloy

The mixture consists of metals with excellent mechanical properties. They are easy to process and can be easily rolled, drawn, forged and stamped. An alloy of cobalt, nickel and iron is otherwise called kovar. A well-chosen combination of chemical elements provides the material with excellent characteristics. This alloy has good thermal conductivity, a high coefficient of electrical resistivity and linear expansion rates close to zero over a wide temperature range. The only drawback is low corrosion resistance in damp environments, so protective coatings made of silver are often used. Kovar is widely used in industry for the production of:

• pipes, tapes and wires;
• capacitors;
• equipment housings in instrument making;
• parts in radio electronics;
• housings in the electrovacuum industry.

The content of expensive cobalt and nickel in the alloy increases the cost of the material, but good characteristics and long-term operation cover the initial investment.

Nickel ore processing technology

The technology for processing nickel ores is complex and multi-stage. Sometimes some of the raw materials have to be returned to previous stages of the process. To a large extent, it is determined by the percentage of the desired mineral in the feedstock.

So:

• nickel-rich ores (over 1% of the composition) are immediately sent for smelting;
• the poorer - ordinary people - are enriched;
• silicate ferruginous ores undergo hydrometallurgical processing;
• silicate magnesium ores are used for pyrometallurgical processing;
• There are also complex combined schemes with which oxidized and mixed ores are processed.

To nickel

In order to obtain nickel from ore, the initial raw material goes through a number of processing stages:

• First of all, the ore is cleaned of moisture and rottenness. To do this, it is crushed, then dried and sintered in ovens.
• The fluxes and gypsum obtained as a result of the first stage are diluted with coke and the entire resulting mass is melted into matte (an intermediate metallurgical product).
• As a result of smelting, matte and slag are formed. The slag is sent to the dump. And the matte is blown in a convector.
• After this, white nickel matte and again slag are obtained, part of which is again sent for smelting, and the other part is used to produce carbon monoxide.
• The white mass, containing a significant amount of nickel, is again crushed and ground, and then sent for firing.
• Nickel oxide is reduced using charcoal.
• The final stage in obtaining the desired chemical element Ni is electrolytic refining.

Nickel

To cobalt

To obtain cobalt from nickel ores, they are first dissolved with sulfuric acid, ammonia or water. Pyrometallurgical processes are sometimes used.

Cobalt hydroxides are then obtained using chlorine compounds or cobalt is isolated at cathodes using electrolysis using electrolysis. To obtain high-purity metal, the solution is first thoroughly cleaned of impurities: copper, iron, lead and nickel.

Deposits in Russia and the world

More than 400 deposits produce nickel ores around the world. The largest domestic deposits are located in the following areas:

• Taimyr district - Oktyabrskoye and Talnakhskoye.
• Murmansk region - Zhdanovskoye.
• Chelyabinsk region - Sakharinskoe.
• Ural - Serovskoe.
• Orenburg region - Buruktalskoe.

Smaller ones are present in Karelia, the Voronezh region, on the territory of the Republic of Tyva, in the Amur region and the Kamchatka Territory.

There are significant deposits abroad:

• in Canada, Cuba, South Africa,
• in Ukraine, Albania and Greece,
• in Indonesia, the Philippines, Australia and New Caledonia.

List of locations of the largest cobalt deposits by country of the world:

• Bou Azzer, Morocco.
• Qinghai, China.
• Ramu, Papua New Guinea.
• Voisey's Bay Mine, Sudbury Area Mine, Nunavik Mine, Canada.
• AdlayCagdianaoTandawaProject, Philippines.
• Flounder, Mount Keith, Marrin, Australia.
• Moa region, Cuba.
• Altai Republic, Russia.
• Katanga Province, Congo.
• Insizwa, South Africa.

general information

Copper (cuprum) is a metal that has a golden-reddish color and is characterized by high thermal and electrical conductivity. Another distinctive quality of the element is its high ductility. Nuggets are found less and less often in nature; they are most often mined from ore.

When determining the authenticity and purity of a sample, you can turn to an expert, but determining a chemical element in a laboratory is quite expensive. Therefore, you need to focus on several home methods.