Eutectic System

Frederick Guthrie, a British physicist and chemist, invented the word eutectic in 1884. A system is a homogeneous mixture of substances that melts or solidifies at a single temperature lower than each constituent's melting point. 

Eutectic meaning in simple words is a mixture of substances that melts and freezes at a particular temperature that is smaller than the melting points of the individual constituents or some other mixture of them. This temperature is defined as the eutectic temperature because it is the lowest potential melting temperature for involving component species at all mixing ratios. The eutectic temperature is seen as the eutectic point on a phase diagram.

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When a randomly selected liquid mixture of certain substances is cooled, a temperature is reached at which one part begins to detach in its solid state and continues to do so as the temperature is reduced further.

If this portion divides, the resulting liquid becomes increasingly rich in the other, until the liquid's structure approaches a point where all substances tend to disperse at the same time as an intimate mixture of solids.

This is the eutectic structure, and the eutectic temperature is the temperature at which it solidifies. Since one component's lattice melts at a lower temperature than the other's, non-eutectic mixture ratios would have different melting temperatures for their constituents. A non-eutectic aggregate, on the other hand, would solidify at various temperatures as it cooled until the whole mass was solid.

Eutectic Phase Transition

In the thermal equilibrium, this reaction is an invariant reaction. The transition in Gibbs free energy equals zero is another way of putting it. In concrete terms, this implies that the liquid and two solid solutions are in chemical equilibrium at the same time. There is also a thermal arrest during which the temperature of the device does not change for the remainder of the phase change. A eutectic reaction's solid macro-structure is determined by several factors, the most important of which is how the two solid solutions nucleate and expand. A lamellar structure is the most common, but other structures such as rod-like, globular, and acicular are also likely.

The eutectic solidification is defined as follows,

Liquid \[\xrightarrow[cooling]{\text{eutectic temperature}}\] α solid solution + β solid solution

  1. Two-phase solid

  2. Single-phase liquid

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What is Eutectic Mixture?

A eutectic mixture definition is defined as, a mixture of two or more components that, while not normally interacting to create a new chemical substance, inhibit the crystallisation phase of one another at certain ratios, resulting in a system with a lower melting point than any of the components.

The eutectic mixture may be produced between Active Pharmaceutical Ingredients (APIs), APIs and excipients, or excipients, allowing for a wide range of applications in the pharmaceutical industry. 

The following factors normally control the creation of eutectic mixtures: 

(a) The components must be miscible in the liquid state and often immiscible in solid-state.

(b) Close contact between eutectic forming materials is needed for contact-induced melting point depression.

(c) Chemical groups that can interact to form physical bonds, such as intermolecular hydrogen bonding, etc.

(d) Molecules that follow modified VantHoff's law.

Eutectic Mixture Example

In metallurgy and other areas, there are many examples of eutectic mixture or eutectoids.

These mixtures usually have beneficial properties that no other constituent material has.

  1. The eutectic point of an ethanol-water mixture is almost pure ethanol. The value indicates that distillation will achieve a full proof or purity of alcohol

  2. Minerals may create eutectic mixtures in igneous rocks, resulting in distinctive intergrowth textures such as those seen in granophyre.

  3. Soldering is mostly done with eutectic alloys. By mass, a standard formulation contains 63% tin and 37% lead.

  4. Corrosion tolerance and hardness are exceptional in eutectoid glassy metals.

  5. Printer with inkjet technology. Since the ink is a eutectic blend, it can be printed at a low temperature.

  6. Galinstan is a liquid metal alloy made up of gallium, indium, and tin that is used as a mercury substitute with low toxicity.

Eutectic Temperature

The eutectic temperature is the lowest possible melting temperature, for all mixture ratios of the constituent compounds in a eutectoid. The super-lattice will expel all of its components at this temperature, and the entire eutectic structure will dissolve into a jelly. In contrast, in a non-eutectic mixture, each part can solidify into a lattice at its particular temperature before the whole substance solidifies. Where a eutectoid is a stable mixture that occurs when two or more molten metals are cooled to a certain temperature. 

An example of eutectic temperature is,

Sodium chloride and water combine to form a eutectic mixture with a eutectic point of 21.2 °C and salt content of 23.3 per cent by mass.

When salt is applied on roads to aid snow removal or combined with ice to achieve low temperatures, the eutectic quality of salt and water is abused (for example, in traditional ice cream making).

Eutectic Composition

A eutectic is a melting composition of at least two elements, each of which melts and freezes in the same way. During the crystallisation process, a mixture of the components is created, resulting in the product behaving as a single unit. The materials freeze into a close-knit crystal mixture and melt at the same time, with no distinction (Lane, 1989). Eutectics are organic and/or inorganic chemical mixtures. As a result, eutectics may be rendered as organic–organic, inorganic–inorganic, or organic-inorganic blends.

FAQs (Frequently Asked Questions)

Q1. What is Non-Eutectic Composition?

Answer: Hypo-eutectic and hyper-eutectic compositions in eutectic structures are those that are not at the eutectic composition. Hypo-eutectic compositions have a lower percent composition of species and a higher composition of species than eutectic composition, whereas hyper-eutectic compositions have a higher composition of species and a lower composition of species than eutectic composition. When the temperature of a non-eutectic composition is reduced, one portion of the mixture can precipitate before the other. A pro-eutectoid phase of species will exist in a hyper-eutectic solution, while a pro-eutectic phase will exist in a hypo-eutectic solution.

Q2. What is the Eutectic Point?

Answer: The eutectic point is the lowest melting temperature for a mixture that occurs at a certain composition of components of several mixtures.

As an impure solid is heated, the part with the lower melting point causes microscopic melting in a pure field. In a phase diagram, the point at which the full number of allowable phases is in equilibrium. When you hit this stage, you must maintain a steady temperature before one of the phases vanishes. An invariant point is referred to as a eutectic.

Q3. Define Peritectic Point.

Answer: On a phase diagram, the point at which a previously precipitated phase reacts with the liquid to form a new solid phase.

The temperature must remain constant after this stage is reached before the reaction is completed. A peritectic is also an invariant point.