Liquid metal
The term liquid metal is used to designate metals in the liquid state, as well as the product of metal powder epoxy resin - dispersions (for example, conductive adhesives or the like. Thermal compound used).
Metals liquid at room temperature
Only one metallic element is liquid at room temperature (20 ° C), mercury with a melting point of −38.83 ° C. Sometimes francium (estimated: 27 ° C), cesium (28.44 ° C) and gallium (29.76 ° C melting temperature) are counted among the elementary liquid metals.
But there are also metallic alloys that are liquid at room temperature:
- Alloys of alkali metals such as NaK , an alloy of sodium with potassium .
- Alloys containing gallium, such as galinstan made from gallium, indium, and tin .
- Alloys that contain mercury, such as the eutectic mercury- thallium alloy with 8.5% thallium, which melts at −58 ° C.
Liquid metals are used, for example, in liquid thermometers , as electrodes , coolants, or thermal pastes .
Gallium and its alloys can be used with restrictions in an open atmosphere. In the solid state, gallium forms a passivating oxide layer similar to aluminum. In the liquid state, however, this layer breaks open, so that the gallium oxidizes over time. The other two groups are not suitable for use in an open atmosphere:
- Alkali metals corrode extremely quickly in air; at higher temperatures or in connection with water there is even a risk of explosion.
- Mercury evaporates at room temperature and is highly toxic. The use of mercury in the free atmosphere is therefore prohibited in the EU and in many other countries or linked to strict requirements.
Alloys with low melting point
In technology, all metals are referred to as liquid metal that are in the liquid state when they are used. These are mainly metals with melting points below 350 ° C. For example, liquid tin is used in the manufacture of window glass , on which the glass melt flows and hardens (see float glass ). Liquid sodium is used as a coolant in reactors or high-performance engines.
The low-melting metal alloys are mostly eutectic alloys made of various elements that already have a rather low melting point, including bismuth alloys in particular :
| alloy | Melting point | eutectic | Bismuth | lead | tin | Indium | cadmium | Thallium |
|---|---|---|---|---|---|---|---|---|
| Roses metal | approx. 94 ° C | No | 50% | 25% | 25% | - | - | - |
| Cerrosafe | approx. 74 ° C | No | 42.5% | 37.7% | 11.3% | - | 8.5% | - |
| Wood's metal | 70 ° C | Yes | 50% | 26.7% | 13.3% | - | 10% | - |
| Field's metal | 62 ° C | Yes | 32.5% | - | 16.5% | 51% | - | - |
| Cerrolow 136 | 58 ° C | Yes | 49% | 18% | 12% | 21% | - | - |
| Cerrolow 117 | 47.2 ° C | Yes | 44.7% | 22.6% | 8.3% | 19.1% | 5.3% | - |
| Bi-Pb-Sn-Cd-In-Tl | 41.5 ° C | Yes | 40.3% | 22.2% | 10.7% | 17.7% | 8.1% | 1.1% |
Dispersions
There are numerous products on the market which are called liquid metal (Petec liquid metal, Loctite 3450, Conrad liquid metal, etc.). Mostly these are metal or ceramic dispersions in epoxy resin, which after hardening have metal-like material properties and are used for gluing or repairing metal objects. Thermally conductive pastes such as B. Arctic Silver are sometimes referred to as liquid metals.
There are products on the market that are also known as liquid metal. This is usually a metal powder embedded in a polymer, which is processed like an oil or a paste and, under certain conditions, simulates metallic properties (strength).
In addition, there are alloys such as Reflex S01, Gunsmoke, bronze, brass and, in prepared mixtures, the standard metals such as aluminum, iron, copper and tin, which can be applied by cold spraying or painting. The metal particles are mixed in the cold state with a polyester and hardener and can then be painted for approx. 60 minutes. Painting systems such as in the automotive sector or industrial painting systems can be used for this. The applied layer is approx. 180 µm. Thicker layers are also possible. When the surface is reduced by approx. 25 µm by grinding, it is mainly the paint mist that is removed. This results in a surface that contains approx. 95% metals. The entire matrix has approx. 85–90% metal. The surfaces have almost all the properties of solid metals. However, they are electrically non-conductive. The surfaces can be treated further (matt, satin, high-gloss, patinated in green, black, rust).
Metallic glasses
The translation of the company name Liquidmetal Technologies sometimes causes confusion in German-speaking countries as well . Products produced by Liquid Metal alloys form metallic glasses include, but are not liquid at room temperature (possibly amorphous) and have melting points of several hundred degrees Celsius. Glasses are often viewed as frozen liquids in physics , but are not liquids in common parlance. In popular scientific articles in particular about the very modern and exotic material class of metallic glasses, liquid metal is often used, but this is usually due to linguistic misunderstandings and a lack of specialist knowledge.