Amalgam (chemistry)

Mercury is a special metal. It can mix with other metals.

This mix is called an amalgam. An amalgam can be a liquid. It can also be a soft paste or a hard solid.

Many metals mix with mercury. Gold and silver mix with it easily. But iron does not mix with mercury.

People use amalgams for many jobs. One use is for filling teeth. This helps fix a tooth.

Mercury is also used in mining. It helps find tiny bits of gold in sand. It is a very useful tool.

An amalgam is a mix of mercury and another metal. This mix is called an alloy. Depending on how much mercury is used, it can be a liquid. It can also be a soft paste or a solid.

Many metals can form amalgams with mercury. Gold and silver mix with it very easily. Some metals, like iron, do not mix with mercury at all. Because of this, people used to carry mercury in iron flasks.

People use amalgams for many important jobs. Dentists use them to fill teeth. They mix mercury with metals like silver, tin, and zinc. The mix stays soft for a short time. This lets the dentist pack it into the tooth. Then, it turns into a hard compound.

Amalgams are also used in mining. Miners use mercury to find tiny bits of gold. They wash crushed rock over copper sheets coated in mercury. The fine gold sticks to the mercury to make an amalgam.

Mercury can be a harmful toxin. It must be handled with great care. Because it can pollute the air and water, many people use other ways to find gold today.

An amalgam is a special kind of alloy made by mixing mercury with another metal. Depending on how much mercury is used, the mixture can be a liquid, a soft paste, or a solid.

These alloys form through metallic bonding. This happens when electrostatic forces bind metal ions together into a crystal lattice structure. Many different metals can form amalgams with mercury. However, some metals like iron, platinum, tungsten, and tantalum are notable exceptions. Because mercury does not mix with iron, people once used iron flasks to carry it.

Making an amalgam is a fascinating thing that happens through chemical reactions. When metals touch mercury at room temperature, many will readily dissolve into it. This ability to dissolve, called solubility, actually increases as the temperature goes up. Some elements like indium, thallium, cadmium, and cesium dissolve very easily. The reaction that forms these amalgams is typically exothermic, which means it gives off heat. The final shape of the amalgam depends on the amount of mercury used. If there is a lot of mercury, it might stay liquid.

Humans have used amalgams for a very long time in many different ways. In China, people used amalgam gilding to coat silver as early as the third to first centuries BC. This was a way to make surfaces look like precious metal. In the 16th century, glassmakers on the island of Murano in Italy used tin amalgam. They created reflective mirror coatings by sliding glass over tin flooded with mercury. This method was the main way to make mirrors until around 1900.

Amalgams are also very important in the worlds of medicine and mining. Dentists use dental amalgams to fill cavities in teeth. These fillings are made by mixing mercury with metals like silver, copper, indium, tin, and zinc. The mixture stays soft for a short time so the dentist can pack it into the tooth. Then, it turns into a hard compound.

In mining, mercury helps people find tiny specks of gold. Miners wash crushed ore over copper sheets coated in mercury. The fine gold sticks to the mercury to form an amalgam.

Even though amalgams are useful, mercury is a harmful toxin that needs special care. Because it can cause pollution, many modern processes have changed. In the mining industry, mercury amalgamation has been replaced by other methods in developed nations. In dentistry, the EU prohibited using amalgam for children under 15 or for pregnant women in 2018. The FDA in the US also recommends against its use for certain high-risk groups. We must be careful because even small amounts of mercury can damage the environment.

An amalgam is a specific type of alloy created by combining mercury with another metal. These mixtures can exist in several different states, such as a liquid, a soft paste, or a solid. The physical state of the amalgam depends on the proportion of mercury used in the mixture. These alloys are held together through a process called metallic bonding. In this process, electrostatic attractive forces use conduction electrons to bind positively charged metal ions into a crystal lattice structure. While many metals can form amalgams, some notable exceptions exist. Metals such as iron, platinum, tungsten, and tantalum do not readily form these alloys with mercury.

The formation of an amalgam often occurs through a chemical reaction when metals contact mercury at room temperature. This process is typically exothermic, meaning the reaction releases heat. The ability of a metal to dissolve into mercury is known as solubility. This solubility generally increases as the temperature rises. Some elements, such as indium, thallium, cadmium, and cesium, are highly soluble in mercury. Conversely, heavier metals are generally less likely to form amalgams than lower mass metals. Because mercury does not dissolve iron, iron flasks were used historically to transport the liquid metal.

Different types of amalgams can be categorized by the metals involved. Alkali metal amalgams, such as those made with potassium, are very sensitive to air and water. These reactions are exothermic and can produce distinct chemical forms like KHg or KHg2. Sodium amalgam (NaHg2) is another specific type that features a unique structure. In this version, mercury atoms form hexagonal layers while sodium atoms form a linear chain. Sodium amalgam is produced as a byproduct of the mercury-cell chloralkali process. It serves as an important reducing agent in both organic and inorganic chemistry.

Post-transition metals also form various amalgams with unique properties. For example, tin amalgam was famously used to create reflective mirror coatings. During the 16th century, glassmakers on the island of Murano developed this by sliding glass over tin flooded with mercury. This specific coating consisted of 75% tin and 25% mercury. Aluminum can also form an amalgam, which is used as a reagent to reduce certain compounds. However, mercury can also cause serious corrosion in aluminum by destroying its protective oxide layer. Because of this risk, mercury is generally not allowed aboard aircraft near exposed aluminum parts.

Amalgams have a long history of use in human industry and art. Amalgam gilding was a common technique used to coat metal surfaces before the invention of electroplating. In China, this method was used to gild silver as early as the third to first centuries BC. While often less satisfactory than gold fire gilding, the technique is still practiced today at the Morimoto workshop in Kyoto, Japan. In the mining industry, mercury has been vital for extracting precious metals. The patio process, developed in Mexico in 1554, used amalgamation to process silver ores.

In gold mining, mercury is used to capture tiny particles of gold from sand or gravel. In placer mining, crushed ore is often washed over copper sheets coated in mercury. The fine gold particles stick to the mercury to form a heavy, dull gray solid mass. To recover the gold, the amalgam is heated in a distillation retort. This process evaporates the mercury, which can then be recovered by a condenser for reuse.

This method is effective for extracting "flour gold," which is too fine for other mechanical methods. However, the release of mercury vapors during this process can cause significant health issues.

Dental amalgams are another widely recognized application of these alloys. Dentists use mixtures of mercury with metals like silver, copper, indium, tin, and zinc to fill cavities. These materials are valued because they are inexpensive and easy to manipulate. The mixture remains soft for a short time, allowing it to be packed into irregular spaces before hardening.

While dental amalgams are generally considered safe, there are modern restrictions due to environmental concerns. In 2018, the EU prohibited dental amalgam for children under 15 and for pregnant or breastfeeding women. Similarly, the US FDA recommends against its use in certain high-risk groups to prevent mercury toxicity and pollution.