Unlike crystalline solids, there is no strict order in the arrangement of particles in an amorphous solid.
Although amorphous solids are capable of maintaining their shape, they do not have a crystal lattice. A certain pattern is observed only for molecules and atoms located in the vicinity. This order is called close order . It is not repeated in all directions and is not stored in long distances, like crystalline bodies.
Examples of amorphous bodies are glass, amber, artificial resins, wax, paraffin, plasticine, etc.
Features of amorphous bodies
Atoms in amorphous bodies vibrate around randomly located points. Therefore, the structure of these bodies resembles the structure of liquids. But the particles in them are less mobile. The time they oscillate around the equilibrium position is longer than in liquids. Jumps of atoms to another position also occur much less frequently.
How do crystalline solids behave when heated? They begin to melt at a certain melting point. And for some time they are simultaneously in a solid and liquid state, until the entire substance melts.
Amorphous solids do not have a specific melting point . When heated, they do not melt, but gradually soften.
Place a piece of plasticine near the heating device. After some time it will become soft. This does not happen instantly, but over a certain period of time.
Since the properties of amorphous bodies are similar to the properties of liquids, they are considered as supercooled liquids with very high viscosity (frozen liquids). Under normal conditions they cannot flow. But when heated, jumps of atoms in them occur more often, viscosity decreases, and amorphous bodies gradually soften. The higher the temperature, the lower the viscosity, and gradually the amorphous body becomes liquid.
Ordinary glass is a solid amorphous body. It is obtained by melting silicon oxide, soda and lime. By heating the mixture to 1400 o C, a liquid glassy mass is obtained. When cooling liquid glass does not solidify like crystalline bodies, but remains a liquid, the viscosity of which increases and the fluidity decreases. Under normal conditions, it appears to us as a solid body. But in fact it is a liquid that has enormous viscosity and fluidity, so low that it can barely be distinguished by the most ultrasensitive instruments.
The amorphous state of a substance is unstable. Over time, it gradually turns from an amorphous state into a crystalline state. This process occurs in different substances with at different speeds. We see candy canes becoming covered in sugar crystals. This does not take very much time.
And for crystals to form in ordinary glass, a lot of time must pass. During crystallization, glass loses its strength, transparency, becomes cloudy, and becomes brittle.
Isotropy of amorphous bodies
In crystalline solids physical properties vary in different directions. But in amorphous bodies they are the same in all directions. This phenomenon is called isotropy .
An amorphous body conducts electricity and heat equally in all directions and refracts light equally. Sound also travels equally in amorphous bodies in all directions.
Properties amorphous substances used in modern technologies. Special Interest cause metal alloys that do not have crystal structure and belong to amorphous solids. They are called metal glasses . Their physical, mechanical, electrical and other properties differ from those of ordinary metals for the better.
Thus, in medicine they use amorphous alloys whose strength exceeds that of titanium. They are used to make screws or plates that connect broken bones. Unlike titanium fasteners, this material gradually disintegrates and is replaced over time by bone material.
High-strength alloys are used in the manufacture of metal-cutting tools, fittings, springs, and mechanism parts.
An amorphous alloy with high magnetic permeability has been developed in Japan. By using it in transformer cores instead of textured transformer steel sheets, it is possible to reduce losses by eddy currents 20 times.
Amorphous metals have unique properties. They are called the material of the future.
Solids are divided into amorphous and crystalline, depending on their molecular structure and physical properties.
Unlike crystals, molecules and atoms of amorphous solids do not form a lattice, and the distance between them fluctuates within a certain range possible distances. In other words, in crystals, atoms or molecules are mutually arranged in such a way that the formed structure can be repeated throughout the entire volume of the body, which is called long-range order. In the case of amorphous bodies, the structure of molecules is preserved only relative to each one such molecule, a pattern is observed in the distribution of only neighboring molecules - short-range order. A good example presented below.
Amorphous bodies include glass and other substances in a glassy state, rosin, resins, amber, sealing wax, bitumen, wax, and organic matter: rubber, leather, cellulose, polyethylene, etc.
Properties of amorphous bodies
The structural features of amorphous solids give them individual properties:
- Weakly expressed fluidity is one of the most known properties such bodies. An example would be glass drips, which for a long time stands in the window frame.
- Amorphous solids do not have a specific melting point, since the transition to a liquid state during heating occurs gradually, through softening of the body. For this reason, the so-called softening temperature range is applied to such bodies.
- Due to their structure, such bodies are isotropic, that is, their physical properties do not depend on the choice of direction.
- Substance in amorphous state has more internal energy, than in crystalline. For this reason, amorphous bodies are able to independently transform into a crystalline state. This phenomenon can be observed as a result of glass becoming cloudy over time.
Glassy state
There are liquids in nature that are practically impossible to transform into a crystalline state by cooling, since the complexity of the molecules of these substances does not allow them to form a regular structure. crystal lattice. Such liquids include molecules of some organic polymers.
However, with the help of deep and rapid cooling, almost any substance can transform into a glassy state. This is an amorphous state that does not have a clear crystal lattice, but can partially crystallize on the scale of small clusters. This condition a substance is metastable, that is, it persists under certain required thermodynamic conditions.
Using cooling technology at a certain speed, the substance will not have time to crystallize and will be converted into glass. That is, the higher the cooling rate of the material, the less likely it is to crystallize. For example, to produce metal glasses, a cooling rate of 100,000 - 1,000,000 Kelvin per second will be required.
In nature, the substance exists in a glassy state and arises from liquid volcanic magma, which, interacting with cold water or air, cools quickly. IN in this case the substance is called volcanic glass. You can also observe glass formed as a result of the melting of a falling meteorite interacting with the atmosphere - meteorite glass or moldavite.
Having a certain melting point is important sign crystalline substances. It is by this feature that they can be easily distinguished from amorphous bodies, which are also classified as solids. These include, in particular, glass, very viscous resins, and plastics.
Amorphous substances (unlike crystalline ones) do not have a specific melting point - they do not melt, but soften. When heated, a piece of glass, for example, first becomes soft from hard, it can easily be bent or stretched; with more high temperature the piece begins to change its shape under the influence of its own gravity. As it heats up, the thick viscous mass takes the shape of the vessel in which it lies. This mass is first thick, like honey, then like sour cream, and finally becomes almost the same low-viscosity liquid as water. However, it is impossible to indicate a certain temperature of transition of a solid into a liquid here, since it does not exist.
The reasons for this lie in the fundamental difference in the structure of amorphous bodies from the structure of crystalline ones. Atoms in amorphous bodies are arranged randomly. Amorphous bodies according to their structure there are no liquids. LS6 in solid glass the atoms are arranged randomly. This means that increasing the temperature of glass only increases the range of vibrations of its molecules, giving them gradually greater and greater more freedom movement. Therefore, the glass softens gradually and does not exhibit a sharp “solid-liquid” transition, characteristic of the transition from the arrangement of molecules in in strict order to the disorderly.
Heat of Melting
The heat of fusion is the amount of heat that must be imparted to a substance when constant pressure And constant temperature, equal temperature melting to completely convert it from solid crystalline state into liquid.
The heat of fusion is equal to the amount of heat that is released when a substance crystallizes from a liquid state.
During melting, all the heat supplied to a substance goes to increase the potential energy of its molecules. Kinetic energy does not change, since melting occurs at a constant temperature.
Experientially studying melting various substances of the same mass, you can see that to turn them into liquid it takes different quantities warmth. For example, in order to melt one kilogram of ice, you need to expend 332 J of energy, and in order to melt 1 kg of lead - 25 kJ.
A physical quantity showing how much heat must be imparted to a crystalline body weighing 1 kg in order to completely convert it into liquid state, is called the specific heat of fusion.
Specific heat of fusion is measured in joules per kilogram (J/kg) and is denoted by the Greek letter X (lambda).
The specific heat of crystallization is equal to the specific heat of fusion, since during crystallization the same amount of heat is released as is absorbed during melting. So, for example, when water weighing 1 kg freezes, the same 332 J of energy are released that are needed to convert the same mass of ice into water.
To find the amount of heat required to melt a crystalline body of arbitrary mass, or the heat of fusion, it is necessary specific heat melting of this body multiplied by its mass:
The amount of heat released by the body is considered negative. Therefore, when calculating the amount of heat released during the crystallization of a substance of mass m, one should use the same formula, but with a minus sign.
Unlike crystalline solids, there is no strict order in the arrangement of particles in an amorphous solid.
Although amorphous solids are capable of maintaining their shape, they do not have a crystal lattice. A certain pattern is observed only for molecules and atoms located in the vicinity. This order is called close order . It is not repeated in all directions and does not persist over long distances, as in crystalline bodies.
Examples of amorphous bodies are glass, amber, artificial resins, wax, paraffin, plasticine, etc.
Features of amorphous bodies
Atoms in amorphous bodies vibrate around randomly located points. Therefore, the structure of these bodies resembles the structure of liquids. But the particles in them are less mobile. The time they oscillate around the equilibrium position is longer than in liquids. Jumps of atoms to another position also occur much less frequently.
How do crystalline solids behave when heated? They begin to melt at a certain melting point. And for some time they are simultaneously in a solid and liquid state, until the entire substance melts.
Amorphous solids do not have a specific melting point . When heated, they do not melt, but gradually soften.
Place a piece of plasticine near the heating device. After some time it will become soft. This does not happen instantly, but over a certain period of time.
Since the properties of amorphous bodies are similar to the properties of liquids, they are considered as supercooled liquids with very high viscosity (frozen liquids). Under normal conditions they cannot flow. But when heated, jumps of atoms in them occur more often, viscosity decreases, and amorphous bodies gradually soften. The higher the temperature, the lower the viscosity, and gradually the amorphous body becomes liquid.
Ordinary glass is a solid amorphous body. It is obtained by melting silicon oxide, soda and lime. By heating the mixture to 1400 o C, a liquid glassy mass is obtained. When cooled, liquid glass does not solidify like crystalline bodies, but remains a liquid, the viscosity of which increases and the fluidity decreases. Under normal conditions, it appears to us as a solid body. But in fact it is a liquid that has enormous viscosity and fluidity, so small that it can barely be distinguished by the most ultrasensitive instruments.
The amorphous state of a substance is unstable. Over time, it gradually turns from an amorphous state into a crystalline state. This process occurs at different rates in different substances. We see candy canes becoming covered in sugar crystals. This does not take very much time.
And for crystals to form in ordinary glass, a lot of time must pass. During crystallization, glass loses its strength, transparency, becomes cloudy, and becomes brittle.
Isotropy of amorphous bodies
In crystalline solids, physical properties vary in different directions. But in amorphous bodies they are the same in all directions. This phenomenon is called isotropy .
An amorphous body conducts electricity and heat equally in all directions and refracts light equally. Sound also travels equally in amorphous bodies in all directions.
The properties of amorphous substances are used in modern technologies. Of particular interest are metal alloys that do not have a crystalline structure and belong to amorphous solids. They are called metal glasses . Their physical, mechanical, electrical and other properties differ from those of ordinary metals for the better.
Thus, in medicine they use amorphous alloys whose strength exceeds that of titanium. They are used to make screws or plates that connect broken bones. Unlike titanium fasteners, this material gradually disintegrates and is replaced over time by bone material.
High-strength alloys are used in the manufacture of metal-cutting tools, fittings, springs, and mechanism parts.
An amorphous alloy with high magnetic permeability has been developed in Japan. By using it in transformer cores instead of textured transformer steel sheets, eddy current losses can be reduced by 20 times.
Amorphous metals have unique properties. They are called the material of the future.
A solid is a state of aggregation of a substance, characterized by constancy of shape and the nature of the movement of atoms, which perform small vibrations around equilibrium positions.
Crystalline bodies. A solid body under normal conditions is difficult to compress or stretch. To give solids the desired shape or volume in plants and factories they are processed at special machines: turning, planing, grinding.
In the absence external influences a solid body retains its shape and volume.
This is explained by the fact that the attraction between atoms (or molecules) is greater than that of liquids (and especially gases). It is sufficient to keep the atoms near their equilibrium positions.
The molecules or atoms of most solids, such as ice, salt, diamond, metals, are located in in a certain order. Such solids are called crystalline. Although the particles of these bodies are in motion, these movements represent oscillations around certain points (equilibrium positions). The particles cannot move far from these points, so the solid retains its shape and volume.
In addition, unlike liquids, the equilibrium points of atoms or ions of a solid, being connected, are located at the vertices of the regular spatial lattice, which is called crystalline.
The equilibrium positions relative to which thermal vibrations of particles occur are called nodes of the crystal lattice.
Monocrystal is a solid body whose particles form a single crystal lattice (single crystal).
Anisotropy of single crystals. One of the main properties of single crystals, in which they differ from liquids and gases, is the anisotropy of their physical properties. Anisotropy refers to the dependence of physical properties on direction in a crystal. Anisotropic are mechanical properties(for example, it is known that mica is easy to exfoliate in one direction and very difficult in a perpendicular direction), electrical properties(the electrical conductivity of many crystals depends on the direction), optical properties (the phenomenon birefringence, and dichroism - absorption anisotropy; for example, a single crystal of tourmaline is “colored” in different colors- green and brown, depending on which side you look at it from).
A polycrystal is a solid consisting of randomly oriented single crystals. Most of the solids we deal with in everyday life are polycrystalline - salt, sugar, various metal products. The random orientation of the fused microcrystals of which they are composed leads to the disappearance of the anisotropy of properties.
Amorphous bodies. In addition to crystalline bodies, amorphous bodies are also classified as solids. Amorphous means “shapeless” in Greek.
Amorphous bodies are solid bodies that are characterized by a disordered arrangement of particles in space.
In these bodies, molecules (or atoms) vibrate around randomly located points and, like liquid molecules, have certain time settled life. But, unlike liquids, this time is very long.
Amorphous bodies include glass, amber, various other resins, and plastics. Although at room temperature these bodies retain their shape, but as the temperature rises they gradually soften and begin to flow like liquids: amorphous bodies do not have a certain melting temperature.
In this they differ from crystalline bodies, which, with increasing temperature, do not gradually, but abruptly, transform into a liquid state (at a very specific temperature - the melting point).
All amorphous bodies are isotropic, that is, they have the same physical properties in different directions. When impacted, they behave like solid bodies - they split, and if exposed for a very long time, they flow.
Currently, there are many substances in an amorphous state obtained artificially, for example, amorphous and glassy semiconductors, magnetic materials and even metals.
