Metal is a term used that describes a number of different materials that are usually shiny, electrically and thermally conductive and above all, hard. Metals are extremely diverse. In fact, more than 75 percent of the 118 elements on the periodic table are made of metals.
So naturally, the question that poses itself to many is: “Which is the hardest metal on earth?” or “Which is the softest metal on earth?”
What is Mohs Scale?
The Mohs scale is used to measure the hardness of elements, which is graded using numbers from 1 to 10. It can be used to compare gemstones, metals and other materials, and evaluate their relative durability. To use an example, one of the hardest substances on earth, diamond, is rated 10 on the Mohs scale, while plastic and pencil lead, for instance, are on the other end of the scale, with a hardness grade of 1.
Hardest Metal on Earth
Tungsten: the hardest metal on Earth.
- Atomic number: 74
- Atomic symbol: W
- Atomic weight: 183.84
- Melting point: 6,192℉ (3,422℃)
- Boiling point: 10,030℉ (5,555℃)
Tungsten is the hardest metal on Earth. Also known as Wolfram, the rare chemical element exhibits a high density (19.25 g/cm3) as well as a high melting point. In its rare form, tungsten is hard to work with due to its brittleness which can be changed when turned pure. It has an ultimate strength of 1510 Megapascals. Tungsten is often utilized to create hard alloys, such as high speed steel to increase protection against abrasion as well as improve electrical conductivity. Its measure on Mohs scale is 7.5 and that of tungsten carbide is 8.5 – 9.
Sources of Tungsten
Most tungsten resources are found in China, South Korea, Bolivia, Great Britain, Russia and Portugal, as well as in California and Colorado. Though it is found in many places, 80 percent of the world’s supply is controlled by China, according to the BBC.
The element naturally occurs in the minerals scheelite, wolframite, huebnertie and ferberite. It is harvested from the minerals by reducing tungsten oxide with hydrogen or carbon.
Once it is sourced, tungsten is often mixed into alloys. The hardest alloys are shaped using diamonds. Diamonds are the only things harder than some tungsten alloys.
Uses of Tungsten
Tungsten is popularly used in the following areas:
- Tungsten was used extensively for the filaments of old-style incandescent light bulbs, but these have been phased out in many countries. This is because they are not very energy efficient; they produce much more heat than light.
- Tungsten has the highest melting point of all metals and is alloyed with other metals to strengthen them. Tungsten and its alloys are used in many high-temperature applications, such as arc-welding electrodes and heating elements in high-temperature furnaces.
- Tungsten carbide is immensely hard and is very important to the metal-working, mining and petroleum industries. It is made by mixing tungsten powder and carbon powder and heating to 2200°C. It makes excellent cutting and drilling tools, including a new ‘painless’ dental drill which spins at ultra-high speeds.
- Calcium and magnesium tungstates are widely used in fluorescent lighting.
Softest Metal on Earth
Cesium: the softest metal on Earth.
- Atomic number: 55
- Atomic symbol: Cs
- Atomic weight: 132.91
- Melting point: 82℉ (28℃)
- Boiling point: 1,240℉ (671℃)
Cesium is a rare, silver-white, shiny metal with brilliant blue spectral lines; the element’s name comes from “caesius,” a Latin word meaning “sky blue.” It is the softest metal, with a consistency of wax at room temperature. It would melt in your hands — if it didn’t explode first, as it is highly reactive to moisture.
Cesium is a naturally occurring element, although almost never on its own, according to the Jefferson Lab, with a presence in several minerals. It has a density of nearly twice that of water, and is very ductile.
Sources of Cesium
The world’s most significant and richest known source of caesium is the Tanco Mine at Bernic Lake in Manitoba, Canada, estimated to contain 350,000 metric tons of pollucite ore, representing more than two-thirds of the world’s reserve base.
Although the stoichiometric content of caesium in pollucite is 42.6%, pure pollucite samples from this deposit contain only about 34% caesium, while the average content is 24 wt%. Commercial pollucite contains more than 19% caesium.
The Bikita pegmatite deposit in Zimbabwe is mined for its petalite, but it also contains a significant amount of pollucite. Another notable source of pollucite is in the Karibib Desert, Namibia.
Uses of Cesium
Cesium is popularly used in the following areas:
- The most common use for caesium compounds is as a drilling fluid. They are also used to make special optical glass, as a catalyst promoter, in vacuum tubes and in radiation monitoring equipment.
- One of its most important uses is in the ‘caesium clock’ (atomic clock). These clocks are a vital part of the internet and mobile phone networks, as well as Global Positioning System (GPS) satellites. They give the standard measure of time: the electron resonance frequency of the caesium atom is 9,192,631,770 cycles per second. Some caesium clocks are accurate to 1 second in 15 million years.
- Caesium has no known biological role. Caesium compounds, such as caesium chloride, are low hazard.
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