What metal is harder than platinum?
Is Platinum the Hardest Metal?
“Platinum Is the Hardest Metal” and Other Common Misconceptions about the Hardness of Precious Metals
Lots of people assume that platinum is the hardest precious metal. But they are wrong! Although platinum is about two times harder than gold, it is still a relatively soft metal that can be shaped fairly easily. Perhaps the misconception that platinum is very hard has arisen because people confuse tarnish-resistance with hardness. Platinum is extremely tarnish-resistant, yes. But is it also especially hard? No. The fact that it resists tarnishing explains why it can be plated onto silver (which tarnishes easily) to create jewelry that retains its bright surface sheen. But that has nothing to do with hardness.
How Does Platinum’s Hardness Compare to Other Substances?
Fortunately, there is a standard measure of hardness. It’s called the Moh’s Scale of Hardness. It is used to rate the hardness of a variety of substances and elements, not only metals. The softest materials it rates are assigned a rating of 1; the hardest earn a rating of 10.
The softest stuff rated on the Moh’s Scale is talc, a mineral you can crumble easily, using only your fingers. It is assigned a rating of only 1. The hardest substance on the Moh’s scale is the diamond, which rates a ranking of 10.
So, where do different metals rank on the Moh’s Scale? Here’s a list . . .
- Gold, silver, zinc and aluminum rank at only between 2.5 and 3
- Platinum ranks at 3.5
- Iron and nickel rank at 4
- Titanium and rhodium rank at 6
And What about Lead?
Lead, which is known to be among the softest of all metals, rates only 1.5 on the Moh’s Scale. And as you know, lead is doggone soft. You can actually make a mark on it using only your fingernail.
Are There Standard Measures of Corrosion Resistance?
That is a logical question to ask. Unfortunately, it is difficult to answer, for a very simple reason . . .
Metals and other substances corrode differently, depending on what they are exposed to
Stainless and other steels, for example, barely oxidize at all when they are exposed to air. But when they are exposed to other substances like some acids, they can corrode much more quickly. So as much as we would like to summarize the corrosion resistance of different metals for you, we cannot; it is far simpler to rate hardness.
One common example? That beautiful new stainless steel kitchen appliance you bought last year, which is now covered with spots and ugly marks. “It is supposed to be stainless steel,” you complain, “how can it get stained?”
It got stained because it was exposed not only to air (which would cause no damage) but to some kind of cleaner or other product that contained a chemical that did the damage.
Do You Have Questions? We Have Answers!
Do you have gold, platinum, palladium, rhodium, or silver scrap? If you do, how can you process it and make money?
Fortunately, that question is not difficult to answer. Call our precious metal recycling consultants at 800-426-2344 and tell us what is on your mind.
The metals and their alloys
The mechanical properties of the six platinum metals differ greatly. Platinum and palladium are rather soft and very ductile; these metals and most of their alloys can be worked hot or cold. Rhodium is initially worked hot, but cold-working can be done later with rather frequent annealing. Iridium can be worked hot, as can ruthenium, but with difficulty; neither metal can be cold-worked appreciably.
Osmium is the hardest of the group and has the highest melting point, but its ready oxidation is a limitation. Iridium is the most corrosion-resistant of the platinum metals, while rhodium is valued for retaining its properties at high temperatures.
Structural applications
Since pure annealed platinum is extremely soft, it is susceptible to scratching and marring. In order to improve hardness, it is alloyed with a variety of other elements. Platinum jewelry is very popular in Japan, where it is called hakkin, or “white gold.” Alloys for jewelry castings include 90-percent-platinum–10-percent-palladium, which is readily worked and brazed. Adding ruthenium to platinum-palladium alloys increases their hardness while maintaining their oxidation resistance. Alloys of platinum-palladium-copper are used in wrought products, since these alloys are harder than platinum-palladium alloys yet less costly.
Crucibles used for single-crystal production in the semiconductor industry require both corrosion resistance and stability at high temperature. For this application, platinum, platinum-rhodium, and iridium are the best suited. Platinum-rhodium alloys are employed in the production of thermocouples that are capable of measuring temperatures as high as 1,800 °C (3,270 °F). Palladium is used in both the pure and alloyed states for a variety of electrical applications (accounting for 50 percent of consumption) and for dental alloys (30 percent of consumption). Rhodium, ruthenium, and osmium are used rarely in the pure state but rather as alloying elements for the other platinum-group metals.
Catalysts
Approximately 42 percent of all platinum produced in the Western world is employed as a catalyst. Of this, 90 percent is applied to automotive exhaust systems, where refractory pellets or honeycomb structures coated with platinum (as well as palladium and rhodium) promote the conversion of unburned hydrocarbons, carbon monoxide, and nitrogen oxides into water, carbon dioxide, and nitrogen.
An alloy of platinum and 10 percent rhodium, formed into a gauze and operating at bright red heat, serves as the catalyst in the reaction between ammonia and air to produce nitrogen oxides and ultimately nitric acid. By feeding in some methane along with the ammonia mixture, hydrocyanic acid can be produced. In petroleum refining, platinum is distributed onto the surface of aluminum oxide pellets and placed into reactor vessels. There it catalyzes the reforming of long-chain naphtha molecules into branched-chain isoparaffins, which are desirable in the blending of high-octane gasoline.
Electroplating
All the platinum metals can be electroplated. Palladium is the easiest to process, and the plated metal is much harder than the wrought metal. The hardness of electrodeposited ruthenium makes it suitable for instruments where a low-pressure rubbing contact is required.
Rhodium is the most commonly electroplated of the platinum metals because of the hardness and lustre of the electrodeposit. Although the cost of rhodium is greater than that of platinum, its lower density allows the use of a lesser weight of metal to obtain a deposit of comparable thickness.
Chemical compounds
Organometallic complexes of platinum-group metals, such as alkylplatinum complexes, are employed as catalysts in olefin polymerization, the production of polypropylene and polyethylene, and the oxidation of ethylene to acetaldehyde.
Platinum salts are finding increasing use in cancer chemotherapy as drugs marketed under the generic names carboplatin and cisplatin. Ruthenium oxide-coated electrodes are employed in the production of chlorine and sodium chlorate. Rhodium sulfate and rhodium phosphate are the compounds preferred for rhodium electroplating baths.
What metal is harder than platinum?
The first rule for the Ladies Wedding Band is to choose the same carat of gold (or grade of Platinum or Palladium) as your engagement ring. This way the metals will match in both colour and hardness; the hardness is an important factor as putting a harder metal against your engagement ring may cause increased wear which can result in expensive repair work.
Gold
Gold comes in several colours the norm being Yellow Gold, White Gold or Rose Gold but other colours are possible, purple, green and blue.
Most people refer to Gold as 9, 14, 18 or 22 carat, however, this is an old terminology when pure or fine gold was 24 carat which is a proportion or in other words gold was calculated on a basis of 24 parts (for example 18 carat is 18 parts gold and 6 parts other metals) the metals or alloys added to gold will dictate the colour.
In 1976 this was revised and all new hallmarks are stamped parts of 1,000, 18 carat no longer has 18 stamped in it but 750 (example 750 means 75% gold and 25% other metals) which is the same proportions as before but more accurate.
Other metals are added to gold to change the colour or to improve the malleability or hardness of the metal. As an example some brass alloys are mixed with the pure Gold to create Yellow Gold. Grade one 18ct White Gold is achieved by adding 25% Palladium, Rose (red) 18ct gold will have 20% copper and 5% Silver added, the unusual (like purple) can be achieved by adding a percentage of aluminium and blue by adding iron, these however are very rarely used as they are difficult to work with.
Palladium
Palladium is part of the Platinum group of metals and when the ore (rock) is dug up it contains 6 metals in the Platinum family that have to be refined and separated. They are Platinum, Palladium, Rhodium, Ruthenium, Iridium and Osmium.
Palladium has all the characteristics of Platinum, hypoallergenic (950 Palladium contains no nickel) is a pure white metal and does not need plating (coating) to keep its colour, harder than Gold (hardness is measured by what is called Mohs scale of mineral hardness) 1 being the softest and 10 (Diamond) being the hardest. Gold is 2.5 to 3.5 dependent on the alloys mixed and Palladium and Platinum are 4 to 4.5. Palladium is approximately 25% lighter than Platinum which accounts for some of the price difference along with the rarity and the fact that city trading in Palladium is not so prevalent as in Platinum.
Our Palladium is 950 (95%) with 5% Ruthenium mix making it a grade 1 metal (not to be confused with a palladium and silver mix). A perfect choice for jewellery with the Platinum look without the price tag.
Platinum
Platinum along with Palladium is the hardest of the precious metals, resistant to wear, never tarnishes and is not likely to cause an allergic reaction. (It also has magnetic properties which are said to be beneficial to joints).
The density of Platinum makes it heavier than Palladium, along with the scarcity of the metal, forms part of the reasons why Platinum has become the most popular metal in recent years and demand continues to increase. There is a slight colour difference between Platinum and Palladium which means if you have a Platinum engagement ring you should stick to the same to create that perfect look.
Silver
Sterling Silver is 92.5% pure silver, Silver is the softest of all the precious metals to bring the hardness up we add 7.5% of copper, it scores 2.5 on the Mohs hardness scale.
