The malleability is a physical property of matter which is characterized by allowing bodies or objects being deformed by action of a force without cracking in the process. This action can be a hammer blow, a detonation, the pressure of a hydraulic press or a roller; by any means that flatten the material into a sheet
Then, malleability is observed in daily life in a notorious way but at the same time unnoticed. For example, aluminum foil represents the malleable nature of this metal, since with it extremely thin and deformable sheets are manufactured by our own hands.
Therefore, a cursory method of recognizing the malleability of a material is to observe whether sheets, plates, sheets or veneers have been made of it; the thinner they are, it is natural to think that the more malleable they are.
Another possible definition for this property would be the ability of a material to be mechanically reduced to a 2D body, without cracking or fracturing. Therefore, we speak of a plastic behavior, which is usually studied in metals and alloys, as well as in certain polymeric materials.
How to determine the malleability? Hammer and buttons
The malleability of a material can be determined qualitatively using a hammer and, if necessary, a torch. Starting from spheres of different metals, alloys or polymeric materials (silicones, plasticines, etc.), they are subjected to hammer impacts until they are sufficiently softened in the form of a sheet or a button.
Material that is easier to soften without cracks or cracks in the sphere will be more malleable at room temperature. If when we hit the metal sphere it releases small fragments from the sides, it is said that its structure does not resist pressure and that it is incapable of deforming.
There are materials that are not too malleable at room temperature. The experiment is repeated by heating the spheres with the torch on a base that resists high temperatures. It will be found that there are metals or alloys that now become more malleable; phenomenon widely exploited in the metallurgical industry.
The thinner these buttons are, and the fewer fractures they show hot, the more malleable they will be. If the pressure exerted by the hammer could be quantified, we would have absolute values of the malleability of such metals obtained thanks to this experiment and without resorting to other equipment.
Relationship with hardness and temperature
From the previous section it was seen that, in general, the higher the temperature of the material, its malleability will be equally higher. It is for this reason that metals are heated red hot so that they can be deformed into rolls, plates or sheets.
Also, the malleability is usually inversely proportional to the hardness: higher hardness implies less malleability.
For example, imagine that one of the spheres is diamond. No matter how much you heat it with the blowtorch, at the first blow of the hammer your crystals will fracture, making it impossible by this method to make a diamond button. Hard materials are also characterized by being brittle, which is the opposite of toughness or resistance.
Thus, the spheres that crack at the slightest blows of the hammer are harder, more brittle, and less malleable.
Role of the metallic bond
For a body to be malleable, especially metallic, its atoms must be able to efficiently rearrange themselves in response to pressure.
Ionic compounds, like covalent crystals, present interactions that prevent them from reestablishing after pressure or impact; dislocations or lens defects become larger and fractures eventually appear. This is not the case with all metals and polymers.
In the case of metals, malleability is due to the uniqueness of their metallic bond. Its atoms are held together by a sea of electrons that travels through the crystals to their limits, where they cannot jump from one crystal to another.
The more crystalline grains they find, the harder (resistant to being scratched by another surface) the metal will be and, therefore, the less malleable.
The atoms within a metallic crystal are arranged in rows and columns, capable of sliding together thanks to the mobility of their electrons and depending on the orientation of the pressure (on which axis it acts). However, a row of atoms cannot slide from one crystal to another; that is, its edges or grain boundaries play against such deformation.
Effect of temperature and alloying
From the atomic perspective, the increase in temperature favors the union between the crystalline grains and, therefore, the sliding of the atoms under pressure. That is why temperature increases the malleability of metals.
Similarly, it happens when metals are alloyed, as the new metallic atoms lower the grain boundaries, bringing the crystals closer to each other and allowing better internal displacements.
Examples of malleable materials
Not all materials observed in 2D are necessarily malleable, since they have been cut or manufactured in such a way that they acquire said shapes or geometries. It is because the malleability tends to focus mostly on metals, and to a lesser degree, on polymers. Some examples of malleable metals, materials, or mixtures are:
-Mud (before cooking)
Other metals, such as titanium, require high temperatures to become malleable. Also, lead and magnesium are examples of non-malleable metals, as are scandium and osmium.
Note that glass, clay ornaments, and wood are malleable materials; However, both glass and clay go through stages where they are malleable and can be given 2D figures (windows, tables, rulers, etc.).
With regard to metals, a good observation to determine how relatively malleable they are, is to find out if with them and their alloys coins can be made; as with the brass, bronze and silver coins.
Serway & Jewett. (2009). Physics: for science and engineering with Modern Physics . Volume 2. (Seventh edition). Cengage Learning.
Terence Bell. (December 16, 2018). What Is Malleability in Metal? Recovered from: thebalance.com