The properties of materials are the characteristics that each material has and how it behaves under heat, stress, oxygen, etc.
Each material will be more appropriate for a type of technical application thanks to its properties, for example, pots are made of stainless steel because it conducts heat well, is resistant and does not rust. However, the handles of the pots are made of plastic so that they do not conduct heat and we do not burn ourselves when holding the pot.
These properties tell us how the material will behave under stress.
It is the property of resisting scratching of the surface. Materials are hard if they do not scratch easily (steel) and are soft if they scratch easily (plaster or wood).
A hard material will scratch a softer material.
Another frequently performed hardness test involves pressing the tip of a small diamond pyramid into the material. the larger the imprint the diamond leaves, the softer the material will be.
It is the property of withstanding blows without breaking.
A material that withstands blows without breaking is called tough. A material that does not support blows will be brittle
A baseball bat made of wood will be very tough because it withstands blows well, but it will also be soft because it scratches easily.
A crystal glass will be fragile because it will break easily with blows, but it will also be hard because it does not scratch easily.
It is the property of recovering its original shape after being deformed by stress. The opposite of elasticity is plasticity.
Materials like latex or rubber are appreciated for being very elastic, but also wood or steel can be elastic in the case of ship masts or docks.
Plasticine is a good example of a plastic material because it permanently deforms under stress. Plastics also take their name from their ability to easily deform when hot.
- Mechanical strength
It is the ability to resist efforts without breaking. The more effort a material resists before breaking, the greater its mechanical resistance.
A small wooden strip of one square millimeter resists around 1.5 kilograms.
A nylon cable of one square millimeter resists 8 kilograms.
A steel cable of one square millimeter resists around 100 kilograms.
The mechanical resistance is measured in kg/mm2, that is to say, how many kilograms a cable of one square millimeter of this material supports before stretching permanently (elastic limit) or before breaking (breaking load).
Thermal and electrical properties¶
These two properties are related to each other. They describe how materials will behave in the face of heat and electricity.
- Thermal conductivity
It is the property of transporting heat easily.
Materials with high thermal conductivity will be used to make radiators, kitchen utensils, etc.
Materials with low thermal conductivity, also called insulators, will be used to insulate houses from the outside temperature or to make handles for frying pans, saucepans, etc.
Insulating materials like plastic or wood feel warm to the touch, while good conductive materials like steel feel cool to the touch.
- Thermal expansion
It is the property of a material to increase in size with temperature. It is a property that usually causes problems in structures such as buildings, train tracks, bridges, etc. The problem is solved by leaving holes every certain distance to allow the expansion of the materials in the summer heat without breaking or deforming.
The gaps created to avoid this problem are called expansion joints.
- Electric conductivity
It is the property of materials to allow the passage of electric current easily.
Metals are good conductors of electricity. Copper, aluminum, gold and steel are the most used to manufacture electrical conductors or contact surfaces.
Other very useful materials are semiconductors, because they can control electrical conductivity. All current electronic devices are manufactured with these materials.
Other physical properties¶
It is the amount of matter that contains a liter of material.
A material like lead has a high density because it weighs more than 11 kilograms for each liter.
A material like wood has a low density because it weighs approximately 1 kilogram for each liter.
With low-dense materials such as magnesium, lithium, aluminum, wood or plastics, lightweight products can be manufactured.
- Response to light
The materials can be transparent like glass and thanks to that windows can be made.
Other materials such as metals are shiny and reflect light, so they can be used to make mirrors or reflective surfaces.
Woods and leathers are highly prized for their superficial appearance.
These properties indicate how the material will behave during the manufacturing processes of objects and what operations can be performed.
It is the property of a material to withstand crushing without breaking. Malleable materials can be crushed between rolls to make thin sheets.
Aluminum is an example of a highly malleable material. Aluminum foil can be made by crushing between rollers.
Wood is not malleable because it breaks when you try to crush it. Thin sheets can be made with wood, but thanks to cutting, as in the case of a pencil sharpener, and not by crushing.
It is the property of a material to withstand stretching without breaking. Ductile materials can be drawn through small holes to make fine wires out of them.
Copper is an example of a very ductile material. Very fine wires can be made by drawing to make cables. Plastics are also very ductile when hot. For example hot glue gun tends to make very fine and long strings when removed after gluing.
Hot glass is another very ductile material. It can be easily stretched to make all kinds of objects.
It is the property of a material to melt with heat, becoming a liquid. This property is highly appreciated when manufacturing by moulding, introducing the molten material into a mold so that it takes the desired shape.
Plastics, metals and glass are examples of fusible materials that allow all kinds of shapes to be made very easily in a mold.
Fusible materials are also easily solderable, that is, they can be joined together by applying heat and pressure. This also facilitates manufacturing by being able to easily join parts together.
Non-fusible materials are wood, ceramics, thermosetting plastics such as bakelite, etc.
These properties define how the material behaves when faced with corrosive chemicals or with solar radiation.
It is the combination of oxygen with the materials, which produces its deterioration and breakage.
Many metals rust easily, especially iron, which is one of the most used metals. To prevent oxidation, iron is covered with paints, with other metals resistant to oxidation such as chrome (chrome plating) or tin (tin).
Plastics, glass, wood or ceramics are materials that resist oxidation very well.
- Resistance to acids and caustics
- Like oxygen, acids and caustic products such as bleach can damage materials, especially outdoors or near the sea. Plastics and glass are materials used to contain acids and caustics because they resist their effects very well.
- Resistance to radiation from the sun
Radiation from the sun, especially ultraviolet (UV) radiation, can break down certain materials and degrade them.
Many plastics that resist the rest of the chemical attacks very well resist the sun's radiation poorly and end up breaking and degrading outdoors.
These properties describe the impact of materials on the environment.
- Renewable materials
They are those materials that can be restored by natural processes at a faster rate than they are consumed. Non-renewable materials will run out sooner or later and we will no longer be able to use them.
For a material to be renewable it has to meet two conditions:
- Que el material provenga de una materia prima renovable o que se pueda reciclar sin pérdidas. Por ejemplo la madera, el algodón, el cristal o los metales.
- Que la materia prima se consuma de manera sostenible, es decir, a menor velocidad de la que se produce. Si talamos un bosque más rápido de lo que crecen los árboles, la madera de ese bosque se agotará y no será sostenible.
Examples of renewable materials:
All materials of animal and vegetable origin that are consumed at the same speed with which they are replenished. Wood, paper, cardboard, vegetable oil, leather, wool, silk, latex.
Materiales muy abundantes en el medio ambiente y que se reciclan sin pérdidas, como el hierro, el aluminio o el vidrio.
Examples of non-renewable materials:
Most of the plastics that come from oil and natural gas (which are limited resources).
Plastics can be recycled, but the process quickly degenerates them so that they can only be recycled a few times before being discarded.
There are some plastics that are made from renewable raw materials, but these are very few today.
- Toxic materials
A material is toxic if it is poisonous and produces negative effects on the health of living beings. Some materials have toxic components and others become toxic when discarded and decompose.
Finally, some materials do not contain toxins, but they generate a lot of pollution when they are manufactured, so they end up contaminating the environment.
Examples of toxic materials:
- Heavy metals such as lead, cadmium, mercury, chromium, etc. They are used to make fluorescent lights, electronic products, batteries or batteries.
- The plastics. Some emit toxic gases. Most are toxic when decomposed in the sun or when burned.
- Construction materials such as granite, which give off a radioactive gas called radon.
- Materials that release carcinogenic dust, such as asbestos, with which many construction materials are made. Today its manufacture and sale in the European Union is prohibited.
- Materials that consume a lot of energy to produce such as aluminum, steel, concrete are not toxic but emit CO2 (greenhouse gas) in their manufacture.
- A material may not be toxic but produce toxins during its manufacturing process. For example, the manufacture of paper with chlorine bleach or the manufacture of cloth with toxic dyes.
Examples of non-toxic materials:Glass, wood or non-heavy metals are not toxic.
- Recyclable materials
A recyclable material makes it possible to re-manufacture new products from waste products.
Products are discarded at the end of their useful life. In some cases, their materials can be reused to make new products, but most of the time they are discarded in mountains of garbage that end up negatively affecting the environment.
Glass and metals are highly recyclable because they do not lose their properties or degrade in the recycling process.
Plastics or paper are hardly recyclable because they break down very easily in the recycling process. Recycled products have lower quality than the originals.
- Biodegradable materials
A material is biodegradable if it breaks down in nature relatively easily and without producing toxic products.
Wood and its derivatives such as cardboard and paper are highly biodegradable.
Plastics are very little biodegradable.
Other ecological problems
Unsustainable extraction of renewable materials can deplete reserves and cause serious environmental problems. For example, the mass manufacturing of wind turbines can desertify areas of forest in the case of uncontrolled logging of balsa wood. The production of concrete is depleting many habitats by removing sand necessary for its manufacture.