Silver is the most popular metal in the world. It has excellent ductility, high reflectivity (about 95%) and a grayish-white color with a beautiful shine. Dissolves only in concentrated sulfuric and nitric acids.

To increase the strength of a silver product, it is coated with a layer of rhodium. In this article you will learn what rhodium-plated silver is, as well as the rules for caring for products made from it.

What is rhodium plated silver? Differences from usual

First, let's figure out what rhodium-plated silver is. This is silver plated with rhodium. This metal is in the platinum group and is considered very durable. Rhodium itself is not used in the manufacture of jewelry, since it is several times more expensive than gold. But the physical properties of rhodium allow it to be used as a protective coating for silver.

The thickness of the rhodium coating on the product is less than the thickness of a human hair! (maximum thickness – 25 microns).

In addition to strength, rhodium adds more shine to a silver product, and a rhodium-plated product becomes indistinguishable from platinum products. Rhodium plated silver differs from ordinary silver in its bright shine and increased strength.

Silver is most often rhodium plated. Of all silver samples, this is the most durable. Rhodium plating allows you to achieve maximum strength for silver products.

Rhodium is also used with 750 carat white gold.

Rhodium coating eliminates allergic reactions that arise from skin contact with the product.

Rhodium is a very expensive metal. One gram of this metal costs from 2000 rubles. But jewelry is not made from rhodium because it is very fragile.

Silver plated with rhodium is carried out using the galvanic method, that is, the electrochemical deposition of rhodium onto the surface of the product.

Pros of rhodium plating:

Remarkable external characteristics of the product. Rhodium gives silver a bright shine that is sure to attract the attention of others.
Safety for humans. If you are allergic to silver, you can use rhodium plated jewelry and the allergy will not bother you.
Increased wear resistance of metal. Silver will be protected from various chemical and mechanical influences.

Disadvantages of rhodium plating:

Durability of the coating. Unfortunately, rhodium plating tends to wear off quickly during wear. The abrasions are especially noticeable in places of contact with the skin, as well as in places where the links are fastened.
When identifying the value of a product, a special examination is carried out. It is impossible to carry out such an examination without breaking the rhodium layer, so the coating will be damaged in any case.
High price for products.
Difficulty of restoration. Rhodium gives strength to silver, but if you manage to break the item, be prepared for the fact that restoration will be quite expensive. Rhodium does not tolerate soldering, and therefore the damaged coating will have to be removed and a completely new one applied.

One more thing to keep in mind is that some people may be incompatible with silver (not to be confused with an allergy). This may manifest itself in weakness, dizziness, nausea, or even inflammation of the earlobe.

You need to pay attention to your own well-being when choosing jewelry. If you feel unwell, or the symptoms described above appear, then in this case, no matter how beautiful the jewelry is, you should refuse it in favor of another metal.

Silver oxidation is used in jewelry making. This procedure uses a solution of potassium carbonate and potassium sulfide (1:1 ratio) diluted with water. As a result, a film is formed on the surface of the product. Oxidized silver, just like rhodinated silver, gains strength and does not darken, but rhodium plating allows you to achieve a better result.

Radiant or rhodium plated?

Rhodium plated silver bracelet

So, it has already been said above that rhodium-plated silver is silver coated with rhodium. Many people make the mistake of calling rhodium plated silver radiated. The word "radiated" comes from the name of the chemical element radium. This element is radioactive, therefore, it poses a danger to human health and cannot be used in jewelry.

Radium was discovered by the spouses Pierre and Marie Curie, and received the Nobel Prize for this. They found that there was less radioactivity in pure uranium than when the uranium was separated from uranium ore. Radium turned out to be a very expensive metal. At the beginning of the twentieth century, the price of radium was as follows: 1 gram of radium cost 200 kilograms of gold.

Despite its radioactivity, radium was used. Radon baths have been used for a long time to treat diseases of the musculoskeletal system and nervous system.

Radium is used for short-term irradiation of malignant tumors in the body. In the 20th century, radium was used in instrument making: in aviation and marine instruments and in special watches with illuminated dials. Glowing paints also contained radium.

There were no markings on devices containing radium, so a dosimeter had to be used. Radium is now being replaced by less radioactive isotopes (for example, tritium).

Therefore, radium has nothing to do with jewelry.

Most likely, this split is caused by a spelling error.

Because of this confusion, it has long been believed that rhodium-plated jewelry is hazardous to health. Now this opinion has no basis.

How to rhodium plated silver at home?

Anyone with at least basic knowledge of electrochemistry can carry out rhodium plating at home on their own.

Below are a few simple steps to carry out this procedure:

Carry out preliminary procedures. You will need to sand and polish the surface of the piece to create a perfectly smooth surface for application.
Rinse the jewelry thoroughly. This action is aimed at removing polishing residues and degreasing the surface of the product.
Place the jewelry in a bath with a special solution. This is necessary so that the solution spreads evenly over the entire surface of the product.
Pass an electric current through the solution. It will provoke a chemical reaction, during which rhodium will be released. It will lie on the product in a thin layer and completely cover it.

A little about the solution. You will need a special solution for dipping rhodium plating of jewelry, which is concentrated rhodium sulfate. This substance is sold in specialized jewelry stores.

You need to heat the solution to 40-50 degrees and then pass an electric current through it. The recommended voltage between the anode and cathode is 3.5-4 V. Such products are sold ready for use.

The duration of this procedure and the current intensity depend on the desired result. This value is individual in each case.

In workshops, the rhodium plating procedure can cost up to 1000 rubles. It all depends on the company’s pricing policy and the current cost of rhodium.

After rhodium plating, the product will look brighter and cleaner than before the procedure.

Rhodium plated silver: how to clean?

Unfortunately, rhodium plating does not prevent the product from turning black. ButRhodium plated products are very easy to clean. It will be enough to rinse them in warm water, wipe them with a clean soft cloth, and then slightly polish the products with a special cloth intended for jewelry.

If the jewelry contains precious or semi-precious stones, they should be washed with soapy water using a cotton pad or swab, and then wiped dry with a soft cloth. This way there will be no damage to either the stones or the setting.

Care must be taken to ensure that the product is dry after cleaning. Remaining moisture will negatively affect the coating.

Rhodium silver jewelry

Products made from rhodium-plated silver go well with various precious stones. In terms of price-quality ratio, these products are quite profitable. They are very popular among buyers. If you want to be admired, choose silver jewelry with amethysts, topaz, rubies, garnets, and turquoise. Jewelry made of rhodium-plated silver with amber looks very attractive.

Such products always look chic and attract the attention of others. Rhodium-plated jewelry with cubic zirconia is very similar to jewelry with diamonds, but costs several times less, and in appearance is in no way inferior to diamonds.

Of course, there is more jewelry for women than for men. These can be all kinds of rings, pendants, earrings, bracelets. But representatives of the stronger sex can also be pleased with a ring made of irradiated silver, as well as cufflinks as a gift.

Many jewelry workshops can offer you to make custom-made jewelry from rhodium-plated silver. Such a service cannot be called cheap, but you can become the owner of a unique piece of jewelry.

Products made from rhodium-plated silver cannot be distinguished from platinum. Even an experienced jeweler cannot do this visually.

Product care

It is easy to wash such jewelry. However, you must remember the nuances of caring for rhodium-plated jewelry.

These decorations require careful attention to yourself:

You need to choose your cleaning agent carefully. Rhodium can be damaged by harsh chemicals, so choose a mild cleaning agent.
The use of abrasive powders is also undesirable. Such substances can scratch the surface of the product, and it will lose much of its attractiveness.
You will be making a mistake if you use a silver cleaner on a rhodium plated item. Such products can be applied specifically to silver; for rhodium plating, you will have to choose a different substance.
It is necessary to minimize the contact of rhodium-plated silver with sweat. Under its influence, the coating may collapse. The same applies to swimming pool water. Chlorine will produce the same result. Therefore, it is better to remove the product before going to the gym or pool. Baths and saunas are also prohibited.
Contact with household chemicals will also not lead to anything good, so it is better to remove the decoration while washing dishes or cleaning.
It is better to wear rhodium-plated silver jewelry after using perfume or eau de toilette. Make sure the liquid is absorbed first and then put the product on.
Proper storage plays an important role in caring for rhodium-plated products. It is unacceptable to store such jewelry in a cardboard box. The sulfur contained in cardboard provokes the oxidation of silver and the loss of its attractive appearance. It is better to have a separate box for rhodium-plated silver jewelry. If you do not plan to wear such jewelry in the near future, then you need to store it in a piece of felt.
There is no need to allow contact between jewelry: do not put rings on one or adjacent fingers.
And, of course, to maintain a neat appearance, the owner is required to take careful care of the decoration, excluding mechanical influences.

If you comply with all the above conditions, then the earrings will last you up to 15 years, the rings from 1 to 3, and the chains will last about six months.

Rhodium is a precious metal that is part of the platinum group. It also includes platinum itself, palladium, ruthenium, iridium and osmium. Rhodium has a cool white luster. It is more resistant to corrosion than platinum. Rhodium is inferior to silver in its ability to reflect light, but this metal does not fade over time.

Everyone knows that precious metals cannot be cheap. And since rhodium also belongs to this category, the price per gram of the metal, which is also quite rare, is also quite high. Why then is it not used as a base metal for jewelry? The reason is the fragility of this metal. At the same time, it has amazing resistance to wear and mechanical damage, and compared to platinum it is much harder. And jewelers found an excellent use for it, offering the world rhodium-plated jewelry.

Why do you need rhodium plating?

Platinum and white gold are often coated with a layer of rhodium. This gives the products brightness and protects them from damage. It is worth noting that a separate metal called “white gold” does not exist in nature. White gold is an alloy of gold with a white metal - palladium, silver or nickel. The alloy turns out to have a yellowish tint, which somehow does not fit with the name. And the higher the sample of the material, the brighter the yellowness. Therefore, to give jewelry a beautiful color and shine, they are rhodium plated - rhodium plating is performed on jewelry. This procedure has a positive effect not only on the appearance of the product, but also on its durability. Rhodium coating performs a protective function, since this metal does not tarnish over time and does not lose its color. Rhodium is less prone to scratches than gold, and a product with such a coating may not deteriorate for a long time, even with daily wear. But this procedure is popular not only for white gold - rhodium-plated silver retains its shine much longer and does not turn black so quickly.

Pros and cons of rhodium plating

As we learn more and more about this expensive and rare metal, in the end, one cannot help but wonder whether rhodium is harmful to health or not? We hasten to reassure you: rhodium cannot cause any harm to your health. Including rhodium plating on costume jewelry or jewelry. Moreover, for those who want to wear items made of silver or gold, but are prone to allergies to these metals, rhodium can come to the rescue, because this metal is completely hypoallergenic. The disadvantages of rhodium plating include the fact that it is a temporary measure. Even rhodium can wear off over time, requiring repeated procedures. It is difficult to determine exactly how long the effect will last. This depends, first of all, on the thickness of the coating and on the frequency of wearing the product. When purchasing platinum, silver or gold jewelry, be sure to find out if it is rhodium plated. Although this can significantly increase the cost of the item, it is still more profitable to purchase it with a protective layer than to later restore tarnished jewelry.

Rhodium plated: all the pros and cons – rhodium plated

Rhodium plated. concept, advantages and disadvantages, all markings of rhodium-plated jewelry in Russia and abroad, what precious metals are plated with rhodium?

Rhodium is the most durable coating for jewelry

In the description of jewelry you can often find the following interpretations: “rhodium plated”, “rhodium-plated product”, “rhodium-plated silver”, “rhodium-plated white gold”, “gold plated with rhodium”, “the jewelry has undergone rhodium plating”, etc.

All these definitions say the same thing: that the decoration has a thin coating of precious metal – rhodium.

Rhodium is a platinum group metal, not inferior in value to gold, but in hardness it is much superior: the hardness of rhodium is more than 5 times higher than the hardness of gold. By the way, rhodium is twice as hard as platinum. And it is only inferior to steel (101 kgf/mm2 versus 123 kgf/mm2 - Brinell hardness).

It is this hardness that makes rhodium an indispensable material for all kinds of coatings. In addition, rhodium-plated jewelry acquires extraordinary shine and shine.

Thus, jewelry is plated with rhodium in practical(increased strength and wear resistance) and aesthetic purposes(giving shine).

Most often rhodium plated jewelry is made from white gold

in the photo is 18-karat white gold without rhodium plating (left) and with rhodium plating (right)

in the photo there is a ring made of silver in natural form and rhodium plated

In Russia and Ukraine, white gold 585, 750 or 375 is plated with rhodium. Abroad, white gold is rhodium-plated with a purity of 9 carats (375 purity), 10 carats (417 - inter-cork), 14 carats (ours 585) or 18 carats (750 purity gold). As for silver, rhodium plating is applied to silver items made in 925 standard.

Additionally, if you want to give new life to your old silver jewelry or experiment and turn a piece of jewelry (ring or earrings) from red gold into white, you can rhodium plate your jewelry at your local jewelry workshop.

To extend the service life, sometimes even base metals, the so-called brass-based jewelry alloys. - plated with rhodium. However, it will be more economical to coat the jewelry alloy with silver rather than with rhodium, which is why costume jewelry is often silver-plated. Thus, in jewelry, silver plating is a cheaper alternative to rhodium plating, but less durable.

About rhodium plating platinum read below.

Rhodium plating can be of various colors - white, pink and even the traditional yellow - the color of gold. The white rhodium plating definitely takes the cake.

Black rhodium is especially brilliant. Jewelry with black rhodium plating is truly exclusive.

Pure rhodium is not used in jewelry

No matter how beautiful this precious metal is, jewelry is not made from pure rhodium. First of all, due to the rarity of rhodium in nature. Explored global reserves of rhodium amount to only a few tons. Therefore, metal is used only in those areas where there is no worthy alternative to it.

And the physical characteristics of rhodium make it difficult for jewelers to work with this precious metal. Rhodium is a very hard, refractory metal. Melting point of rhodium almost 2 times higher than the melting point of gold.

Rhodium + platinum and palladium

Rhodium is also added as an alloying additive to platinum and palladium alloys, pursuing the same goal - to make the alloy even stronger and more durable.

Is platinum coated with rhodium? Excerpt from Resolution of the Russian Federation dated June 18, 1999 N 643 “On the procedure for testing and branding products made of precious metals”: “It is allowed to coat jewelry and other household products made from alloys of white gold, silver or platinum with a layer of rhodium, provided that these products are branded , as gold, silver or platinum, respectively." Therefore, theoretically, the use of rhodium as a coating for platinum products is possible, and there is a corresponding reason for this (this resolution). In practice, I have never encountered rhodium-plated platinum.

It should be noted that rhodium is absolutely hypoallergenic .

Rhodium plating markings

In English-language online jewelry stores, rhodium-plated items will be marked as follows:

rhodium plated white gold(9-18 Karat) – white gold of so many carats is plated with rhodium
rhodium silver jewelry– rhodium plated silver decoration
rhodium plated sterling silver– sterling silver with rhodium plated
black rhodium gold– gold plated with black rhodium

In its turn white gold unplated will indicate that white gold is not rhodium plated.

Rhodium plating price. Read more about rhodium plating on jewelry, the lifespan of rhodium, and the cost of refinishing rhodium plating.

10 facts about rhodium and rhodium plating. Use of rhodium in the jewelry industry. Rhodium - in pictures.

gold plated- gilding of jewelry abroad. How imported gold plating is marked, how long the gold plating lasts - find out all the details.

Metal rhodium. Rhodium plated

Rhodium is a precious metal that is part of the platinum group. It also includes platinum itself, palladium, ruthenium, iridium and osmium.

Rhodium has a cool white shine. It is more resistant to corrosion than platinum. Rhodium is inferior to silver in its ability to reflect light, but this metal does not fade over time.

Rhodium was discovered in 1803 by the English scientist William Wollaston. This specialist is known to us because he was the first to make small high-quality diamonds from large stones with defects, and was also able to isolate platinum from ore.

Rhodium prices

Everyone knows that precious metals cannot be cheap. And since rhodium also belongs to this category, the price per gram of the metal, which is also quite rare, is also quite high.

Until November 2008, the price of rhodium rose inexorably, reaching its shocking critical level of $10,100 per troy ounce. (about 31.5 grams). after which it collapsed to $900. As of April 8, 2015, the price of rhodium is $37.13 per gram, which, you see, is not cheap at all. Why then is it not used as a base metal for jewelry?

The reason is the fragility of this metal. At the same time, it has amazing resistance to wear and mechanical damage, and compared to platinum it is much harder. And jewelers found an excellent use for it, offering the world rhodium-plated jewelry.

Why do you need rhodium plating?

This procedure has a positive effect not only on the appearance of the product, but also on its durability. Rhodium coating performs a protective function, since this metal does not tarnish over time and does not lose its color. Rhodium is less prone to scratches than gold, and a product with such a coating may not deteriorate for a long time, even with daily wear. But this procedure is popular not only for white gold - rhodium-plated silver retains its shine much longer and does not turn black so quickly.

Pros and cons of rhodium plating

The disadvantages of rhodium plating include the fact that it is a temporary measure. Even rhodium can wear off over time, requiring repeated procedures. It is difficult to determine exactly how long the effect will last. This depends, first of all, on the thickness of the coating and on the frequency of wearing the product. (metal wears off from contact with other products and skin) .

When purchasing platinum, silver or gold jewelry, be sure to find out if it is rhodium plated. Although this can significantly increase the cost of the item, it is still more profitable to purchase it with a protective layer than to later restore tarnished jewelry.

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Svetlissa 06/22/2016

I bought a small batch of silver from Russian manufacturers and Turkish, it seems like it says rhodium plating. I searched the Internet and came across the fact that rhodium compounds are toxic and hazardous to health. On another site I found information that silver is not coated with pure rhodium. How can this be? Maybe Is it harmful? I understand that licenses, certificates, etc., but my conscience rejects these arguments of reason. And this batch of Turkish silver worries me too. How can I find out how pure it is, whether it’s technical silver?

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If you manage to dissolve rhodium in something, which is practically an impossible task in everyday life, then yes, a solution of rhodium in anything will be lethally toxic. The truth is that it is most likely not the rhodium itself that will send you to the next world, but the solvents.

Hundreds of millions of people wear rhodium-plated products. Allergies to rhodium are as rare as to gold, and toxicity is generally excluded. Rhodium, like gold, is a noble metal, which means that it is extremely difficult to force it to react chemically. And any toxic effect is primarily participation in a chemical reaction. If reactions are almost impossible, then there can be no talk of toxicity.

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MooZe 06/23/2016

I came across radioactive silver, or rather I was warned that it was brought from the Simipalatinsk test sites, and it is clearly phonite. I refused, I didn’t take the risk. The problem is that even the purity of silver will fade for a long time. It's quite possible that someone bought it

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It’s also almost difficult to imagine. The longest-lived radioisotope of silver, Ag110, has a half-life of only 250 days. Even if a piece of silver had been at the epicenter of the latest test, after a few years, not only a radiometer, not even a spectrometer, its radiation would no longer be detected. Ag110 is used for medical purposes; obtaining it is a very difficult process. There is no radioactive silver in nature.

Characteristics, pros and cons of rhodium plated silver

Silver is a unique metal whose properties allow it to be used not only in the jewelry industry, but also in the manufacture of parts for technical devices, as well as in medicine. Silver is characterized by softness and ductility, which makes the metal susceptible to deformation, which is why it is not used in its pure form. To enhance the strength of the metal, copper is added to it. But even this does not protect silver from deformation, since the jewelry industry uses alloys in which the proportion of silver exceeds 90%. Therefore, to protect silver from the effects of negative factors, it is coated with a layer of rhodium. In the subject literature and on electronic resources you can find phrases such as “radiated silver” and “rhodium-plated silver”.

Many people think that they are the same thing, but in fact they are not.

Rhodium plated silver

Rhodium plated silver is coated with a layer of rhodium, a rare metal belonging to the platinum group. Rhodium is several times more expensive than gold, so it is not used in jewelry production. At the same time, this metal is considered incredibly hard, which makes it suitable for making protective layers that cover jewelry. This procedure is called rhodium plating.

A layer of rhodium is applied not only to silver jewelry, but also to those made of 750-carat white gold. Rhodium plating not only protects jewelry from damage, but also gives it an exquisite shine. In addition, silver items with such a coating cannot be visually distinguished from platinum, the most expensive metal used in the jewelry industry. For rhodium plating, the galvanic method is used, and the procedure itself takes a few minutes.

Silver ring with rhodium-plated stone

Rhodium coating has a significant drawback: it wears off over time, especially for areas of jewelry that are constantly in contact with the skin. Rhodium plating also wears off at the points where the links are fastened. But this is not a reason to refuse exquisite jewelry, because the coating can be restored. To do this, just contact a master jeweler. Rhodium plating cannot be called a cheap service, since such coating consists of an expensive precious metal. For example, rhodium plating on a medium-thick ring will cost the client approximately $15.

Every owner of rhodium-plated jewelry should know that such silver requires special care and respect.

The rhodium layer can be destroyed under the influence of aggressive detergents - washing powder, dishwashing gel, etc. Therefore, during hand washing and dishwashing, rings and bracelets must be removed. Sprayed jewelry can also deteriorate when exposed to alcohol, so do not allow it to come into contact with alcohol-containing toners, lotions, etc.
Rhodium-plated products should not be treated with abrasive powders to clean surfaces, as solid particles will damage the coating.
Special chemical cleaners designed for caring for silver are not suitable for caring for items with a rhodium layer. These substances can be used to clean silver. but only if it does not have any coverage.
Rhodium plating deteriorates when exposed to sweat, so jewelry with this plating should be removed before going to the gym. The same rule applies to going to the pool, since water containing chlorine can cause the destruction of the rhodium layer.
How to clean silver with rhodium? In fact, the list of products that help clean such jewelry is limited. For example, you can prepare soapy water and thoroughly rinse jewelry that needs cleaning with it. After this, rinse the items with clean water and wipe gently with a soft cloth. The same technique is suitable for cleaning jewelry with precious stones.
Rhodium-plated jewelry should be stored correctly. A jewelry box is suitable for this purpose, but in no case a box made of cardboard. The thing is that cardboard may contain sulfur, and this substance provokes the oxidation of silver and the loss of its attractive appearance. If the product is not worn for a long time, it is recommended to store it in a piece of flannel.

The difference between pure silver and rhodium plated silver

Jewelry coated with a layer of rhodium, in addition to its advantages, also has disadvantages. For example, if a silver chain coated with such metal suddenly breaks, then after repairing it, the rhodium layer must be renewed, which will increase repair costs several times.

What is radium?

In many sources of information you can find such a phrase as “radiated silver”. Rhodium-plated metal is mistakenly called this, but such an error can be very misleading to the reader. If jewelry were coated with radium rather than rhodium, it would become deadly to its owner, and all because radium is a radioactive chemical element. For this reason, it cannot be used in any way in the jewelry industry, because the use of silver, which contains radium, would be fatal to humans.

Radium as a chemical element was discovered by the Curies, for which they received the Nobel Prize. It was found that radium is a decay product of uranium, so it can be found in small quantities in uranium ore. This metal is catastrophically scarce in nature. Thus, since the discovery of radium, scientists have extracted only one and a half kilograms of this metal.

Despite the danger of the chemical element, effective use was still found. For example, radon baths have been considered an effective method for treating diseases of the musculoskeletal system for several decades in a row. Radium was also used in technology; for example, in the last century, this metal was used to make luminous coatings that serve as backlight for watch dials and aircraft instruments. But due to radioactivity, radium was no longer used for this purpose.

The difference between rhodium-plated and radiated silver is colossal, since the latter option does not exist at all.

Rhodium (lat. Rhodium; designated by the symbol Rh) is an element of the side subgroup of the eighth group of the fifth period of the periodic system of chemical elements of D.I. Mendeleev, atomic number - 45. In appearance, compact rhodium is a beautiful silvery metal with a bluish tint.

Rhodium belongs to the noble metals of the platinum group. Compared to other metals in this group, it is brighter and harder - it becomes ductile only when heated.

The name of the element translated from ancient Greek means “rose”. It received this name due to the color of its typical compounds - they are red, like roses.

Rhodium is a very rare and trace element. Its average content in the earth's crust is 1 10-7% by weight. It does not have its own minerals. Contained in nickel and platinum ores in the form of a simple compound. It is also found in isomorphic admixtures of minerals of the iridium osmide group (up to 3.3%) and in copper-nickel ores. The rarest variety of osmic iridium is also known - native nevyanskite. It contains up to 11.3% rhodium. It is the richest mineral in rhodium.

Rhodium was discovered in England in 1803 by the remarkable scientist of his time, William Hyde Wollaston. While studying native South American platinum, he noticed a bright pinkish-red filtrate he obtained from a solution of native platinum in aqua regia. The solution acquired this color after the deposition of platinum and palladium. From this solution, Wollaston isolated a dark red powder, calcined it in an atmosphere of hydrogen and obtained a heavy white metal - rhodium.

Until the 20s of the last century, Russia purchased rhodium abroad. There were no specialist refiners in the country, the properties of rhodium and its “brothers” were poorly understood, and foreign companies kept secret the methods for extracting and purifying platinum group metals.

In 1918, the Institute for the Study of Platinum and Other Precious Metals was opened in our country. In the very first years, important research on the chemistry, refining and analysis of rhodium was carried out there. And in 1925, the first domestic rhodium was obtained from Ural platinum.

The credit for this belongs, first of all, to the outstanding chemist L.A. Chugaev and his students, later famous scientists I.I. Chernyaev, V.V. Lebedinsky and N.K. Pshenitsyn.

PHYSICAL PROPERTIES OF RHODIUM

In appearance, compact rhodium is a beautiful silvery metal with a bluish tint. It has a face-centered cubic lattice, unit cell parameter a = 0.3803 nm. Density at 20°C 12.41 g/cm3. Melting point 1963 °C, boiling point 3727 °C. Unlike gold and platinum, rhodium is difficult to machine. Therefore, it can be rolled or drawn into wire only at 800...900°C. Exhibits paramagnetic properties. The reflectivity of the rhodium surface is 80% for the visible part of the spectrum.

Other characteristics:
- heat of fusion - 21.8 kJ/mol;
- heat of evaporation - 494 kJ/mol;
- specific heat capacity - 0.244 J/(K mol);
- thermal conductivity - 150 W/(m K).

Rhodium occurs in nature as a stable isotope - 103Rh. Its longest-lived isotopes with half-lives are: 101Rh (3.3 years), 102Rh (207 days), 102mRh (2.9 years), 99Rh (16.1 days).

Compact rhodium is extremely resistant to any chemical attack. However, if you take an alloy of rhodium with zinc or cadmium and dissolve it in hydrochloric acid and then filter it, you will get a precipitate of finely divided rhodium that can explode in air.

CHEMICAL PROPERTIES OF RHODIUM

Rhodium is a noble metal; its chemical resistance in most corrosive environments is superior to platinum. Compact rhodium is not affected by either acids or alkalis. Only finely crushed rhodium slowly dissolves in hot aqua regia or concentrated sulfuric acid. Rhodium is also very resistant to the action of halogens: it reacts with chlorine, bromine and even fluorine only after prolonged heating. In this case, depending on the reaction temperature, halides of different compositions are obtained. In particular, mono-, di- and trivalent rhodium chlorides RhCl, RhCl2, RhCl3 are formed with chlorine. At high temperatures, rhodium slowly reacts with sulfur, turning into sulfides RhS, RhS2, Rh2S5.

Finely ground rhodium slowly oxidizes only at temperatures above 600°C:
4Rh + 3O2 = 2Rh2O3.
Rhodium exhibits a peculiar behavior when heated in air. At temperatures from 600 to 800 degrees, an oxide film - Rh2O3 - forms on its surface. When the temperature increases from 800 to 1000 degrees, the oxide film on the surface of rhodium again decomposes to metal.

When heated, rhodium slowly reacts with concentrated sulfuric acid:
2Rh + 6KHSO4 = 2K3Rh(SO4)3 + 3H2.

Rhodium hydroxide and oxide exhibit basic properties and react with acids to form Rh complexes:
Rh2O3 + 12HCl = 2H3RhCl6 + 3H2O;
Rh(OH)3 + 6HCl = H3RhCl6 + 3H2O.

In the presence of alkali metal chlorides, when it is possible to form 3– complexes, rhodium reacts with chlorine, for example:
2Rh + 6NaCl + Cl2 = 2Na3.

During sintering, it reacts with Na2O2 and BaO2 melts:
2Rh + 3BaO2 = Rh2O3 + 3BaO.

Rhodium exhibits the highest oxidation state +6 in the hexafluoride RhF6, which is formed by direct combustion of rhodium in fluorine. The connection is unstable. In the absence of water vapor, hexafluoride oxidizes free chlorine or NO:
2RhF6 + 3Cl2 = 2RhF3 + 6ClF.

Rhodium is easily alloyed with platinum, palladium, copper and other metals.

Rhodium compounds are quite rare in everyday life and their effects on the human body have not been fully studied. Despite this, they are highly toxic and carcinogenic substances. Rhodium salts can strongly stain human skin.

Rhodium deposits and mining

Less than 30 tons of rhodium are mined annually in the world. The main exporter of this metal is South Africa (approximately 80%). Industrial mining of rhodium is difficult because the metal occurs in ores mixed with other metals such as palladium, silver, platinum and gold.

Previously, the main deposits were located in Russia. Impressive reserves of native platinum were found in the Urals. But now they have already been developed. Today Mexico is the leader in rhodium reserves. It is followed by South Africa and Colombia. There is precious metal content in the US gold sands.

Obtaining rhodium

The technology for separating rhodium depends primarily on the type and composition of the processed raw materials. Let's consider the production of rhodium from native platinum.

From the mines, raw platinum goes to the refinery, where it is loaded into porcelain cauldrons and treated with aqua regia. The process occurs when heated during the day. As a result, rhodium goes into solution.

The solution is then treated with ammonium chloride to precipitate and separate the platinum. The remaining solution is evaporated: a precipitate is formed, which consists of several salts. It contains up to 6% rhodium. This precipitate is dissolved in water and the platinum is separated again in the same way. And the solution, in which rhodium, ruthenium and palladium remain, is sent for purification and separation as it accumulates.

Next, NaNO2 is precipitated with sodium nitrite and the precipitate of base metal hydroxides is separated from the solution; rhodium remains in solution in the form of Na3. After this, rhodium is isolated from the solution in the cold using NH4Cl; it leaves in the form of a poorly soluble complex (NH4)2Na. However, in this case, along with rhodium, iridium also precipitates; other platinum metals - ruthenium, palladium and platinum residues - remain in solution.

The precipitate is dissolved in dilute caustic soda and rhodium is again precipitated from this solution by the action of ammonia and NH4Cl - now in the form of another complex compound. The precipitate is separated and thoroughly washed with ammonium chloride solution.

The resulting cage is again loaded into a boiler with hydrochloric acid and heated for several hours. The reaction occurs:
2 + 6HCl > 2 +3NO2 + 3NO + 3H2O
with the formation of a new rhodium complex compound of bright yellow color. This is rhodium triamine trichloride. It is thoroughly washed with water and only after this the metallic rhodium is isolated.

The salt is loaded into the oven and calcined for several hours at 800...900°C. The complex compound decomposes and a powdery product of a mixture of rhodium with its oxides is formed. After cooling, the powder is thoroughly washed again with diluted aqua regia to remove the remaining small amount of base impurities, and then again loaded into the furnace and reduced to metal by calcining in an atmosphere of hydrogen.

APPLICATIONS OF RHODIUM

The price of rhodium is high not only because the element is precious, but also because there are more industries where it is needed than the metal itself. However, it is used only where there is no cheaper and more widespread alternative.

The lion's share of mined rhodium is consumed by the automotive industry. The excellent catalytic properties of the metal make it possible to produce exhaust gas neutralizers from its alloys.

An alloy of rhodium and platinum is a very effective catalyst in the production of nitric acid by oxidizing ammonia with air. It is in this area that rhodium as a catalyst metal has no analogues.

Rhodium in alloys with iridium and/or platinum is used in the production of thermocouples, which are used to effectively measure high temperatures up to 2200 degrees Celsius.

A major consumer of rhodium is the glass industry. An alloy of rhodium and platinum (usually 7% Rh) is used to make vessels for melting glass melt and producing the finest glass and quartz threads. Here rhodium is also practically irreplaceable.

The rhodium surface has a high reflectivity (80%) for the visible part of the spectrum. The reflectivity of rhodium is less than that of silver (95%), but its resistance to corrosive gases and high temperatures is much greater. Rhodium-plated surfaces do not fade even in a voltaic arc atmosphere. Therefore, reflectors of spotlights and technical mirrors of precision measuring instruments for various purposes are coated with rhodium.

Metallic rhodium is used for the production of mirrors subjected to strong heating (incandescence) for high-power laser systems (for example, hydrogen fluoride lasers), as well as for the production of diffraction gratings for devices for analyzing substances (spectrometers).

Made of precious metal and filters for LCD monitors. The need for them is growing every year. More and more rhodium is required for this industry.

Rhodium detectors are used in reactors to measure neutron flux.

There are precious minerals, the crystals of which grow under artificial conditions only on filters made of an alloy of platinum and rhodium.

Rhodium plating

Rhodium has a beautiful silvery-white hue for which it is highly prized in the jewelry industry. Its reflectivity is very high, the metal sparkles and shimmers, its shine is magnificent. Therefore, rhodium plating is becoming an increasingly popular procedure in jewelry workshops.

Rhodium plating is the application of a thin layer of rhodium (0.1 - 0.25 microns) to the surface of jewelry. The coating improves not only the appearance of metals, giving the surface a platinum shine, but also their chemical and mechanical properties. In addition, rhodium does not tarnish over time.

Advantages of rhodium birth:
- brilliant platinum color;
- resistance of the product to mechanical damage, scratches, etc.

Disadvantages of rhodium plating: - you cannot clean jewelry using abrasives, as the coating can be damaged;
- after each repair of the product, it will have to be re-plated with rhodium.

Rhodium plating does not last forever, but its service life depends on several factors, the main one being thickness. According to user experience, renewal of the rhodium layer on rings, earrings, and chains is required once every five years and less often, depending on the intensity of use of the product. In many cases, high-quality rhodium plating will decorate the metal for decades.

PRICE OF RHODIUM ON THE WORLD MARKET

Everyone knows that precious metals cannot be cheap. And since rhodium also belongs to this category, the price per gram of the metal, which is also quite rare, is also quite high.

Until November 2008, the price of rhodium rose inexorably, reaching a shocking critical level of $10,100 per troy ounce (about 31.5 grams), after which it collapsed to $900.

The graph shows the price of rhodium per troy ounce in US dollars over the past 10 years. As you can see, rhodium reached its maximum in 2008. This was rhodium’s finest hour: its price was 10 times higher than the price of gold. Since 2012, the price of the precious platinum group metal has stabilized somewhat.

The graph shows the price of rhodium per troy ounce in US dollars since May 2015.

Rhodium has a cool white shine. It is more resistant to corrosion than platinum. Rhodium is inferior to silver in its ability to reflect light, but this metal does not fade over time.

Rhodium prices

Everyone knows that precious metals cannot be cheap. And since rhodium also belongs to this category, the price per gram of the metal, which is also quite rare, is also quite high.

Until November 2008, the price of rhodium rose inexorably, reaching its shocking critical level of $10,100 per troy ounce. (about 31.5 grams), after which it collapsed to $900. As of April 8, 2015, the price of rhodium is $37.13 per gram, which, you see, is not cheap at all. Why then is it not used as a base metal for jewelry?

Why do you need rhodium plating?

Pros and cons of rhodium plating

Those who have nothing to do with precious metals and see them only in jewelry sometimes underestimate rhodium. One interesting fact can refute this opinion.

Once upon a time, at a rhodium processing factory, there was a unique mortar for grinding the precious metal. She looked ordinary, except that she weighed 30 kg. However, its price turned out to be commensurate with the cost... of the entire plant. And all because the material for the mortar was a very rare noble metal - rhodium.

What is rhodium?

In the periodic system D.I. Mendeleev, it is known as element 45, which in reality is one of the rarest precious metals on Earth.

Rhodium was discovered in 1803 by the famous English scientist William Hyde Wollaston. The researcher discovered a bright pink powder in a native platinum solution. After rolling in a hydrogen atmosphere, the reddish powder turned into a white heavy metal that looked like aluminum.

For its special shade it received the name ροδον, which translated from Greek means “rose”.

History of Rhodium

The amount of rhodium in platinum is measured in fractions of a percent, and for a long time the precious metal was practically unattainable.

In 1819-1824, the richest placers of so-called raw (that is, native) platinum were discovered in the Urals. A few years after this, its quantity was about two tons. For further processing, platinum was sent to St. Petersburg, and rhodium and other accompanying metals were discarded.

Only in the 40s of the 19th century, Kazan University professor K.K. Klaus became interested in the Ural deposits and found in them “no small amounts of rhodium, iridium, osmium and palladium.” At the same time, the scientist discovered a previously unknown platinum group metal - ruthenium.

Despite the fact that until the beginning of the 20th century, about 95% of the world's platinum reserves were mined in Russia, the use of the rare metals accompanying it was never found, and rhodium was sold abroad, one might say, for next to nothing.

In 1918, the Institute for the Study of Platinum and Other Precious Metals was opened in our country, where the most important studies of rhodium were carried out. And already in 1925, the rarest metal was first obtained in the USSR.

Until now, it, like other platinum group metals, is obtained from “raw” platinum or during the process of refining gold. However, even in our time, the properties of this incredibly rare element are not fully understood.

Why is rhodium valuable?

Its high melting point (1960 degrees) and resistance to external influences have made it popular in many industries, including chemicals, glass and jewelry.

The world's rhodium reserves amount to only a few tens of tons. Despite the fact that the cost of rhodium is several times higher than gold, the demand for it is increasing every year.

Compared to other platinum group metals, rhodium is brighter and harder - it only becomes ductile when heated.

Rhodium does not oxidize in air, it is not afraid of a humid environment, the influence of acids, sulfur, chlorine, fluorine and other aggressive environments. Due to its high strength, rhodium is more durable than other metals. Its reflectivity is about 80%. Of course, it is lower than that of silver, but the resistance to corrosion and temperature effects of rhodium is much higher.

That is why it is used as a protective and decorative coating for jewelry made of gold and silver.

Rhodium plating

Metal is applied to jewelry using an electrochemical reaction. Electroplating requires special attention, precise adherence to the technological process itself and preparation for it.

The product goes through several stages: ultrasonic washing, degreasing in alkali and sulfuric acid solutions, washing and treatment in a steam generator. At the final stage, the surface is treated with a special marker under the influence of electric current or completely dipped into a galvanic bath.

Rhodium is a metal with a white luster, so the coating looks especially advantageous on jewelry made of white gold and silver. In products made of red gold, with the help of a decorative coating, a combination of several shades of metal is achieved in one piece of jewelry without the use of soldering different alloys.

Traditionally, rhodium is used to cover the settings of jewelry stones (for example, diamonds or sapphires) to highlight the shine of jewelry inserts.

Black rhodium plating

Jewelers often use black rhodium plating, which gives the jewelry a slightly aged or, on the contrary, a fresh, modern look, and the stones against this “background” look brighter and more expressive. What determines the color of rhodium?

If you carefully read the composition on packages of rhodium of various shades, you will notice that they all differ in only one component - a solution of salts. The color of the future coating depends on it. Otherwise, rhodium of different colors is absolutely identical, which means it retains all the same properties as the light metal we are used to.

Caring for rhodium-plated products

First of all, you need to remember that rhodium plating is just a coating, a thin protective layer on the surface of the jewelry. Therefore, forget about powders, sandpaper and other abrasive substances, the use of which risks damaging the product.

If the rod is damaged, the best thing is to contact a specialist who will quickly restore the decorative coating. If this is not possible, use the same methods as for cleaning silver.