Ceramics and plastics in everyday use
Everyone has already come across supposedly expensive ceramics in everyday life: Be it the Sunday dinnerware, the ceramic knife or the bathroom sink. If you compare these prices with those of everyday plastic objects – garden chairs, mugs or toilet seats – you will quickly get the impression that ceramic objects are always more expensive than those made of plastic. Is this justified and is it true at all? To get to the bottom of this question, we first need to take a closer look at the two groups of materials.
What makes ceramics so special?
Not all ceramics are the same, and in fact they are not only present in objects we encounter every day.
Because: the areas in which ceramics are used are manifold. As an example, we can consider the following areas in which ceramics are used:
- as building ceramics: e.g. bricks, roof tiles or clinkers
- as refractory ceramics: e.g. furnace linings
- or as technical ceramics for thread guides in the textile industry
In general, ceramics can shine with different positive properties. Technical ceramics in particular often have high hardness, high wear resistance and high corrosion resistance. In particular, the usually high melting temperatures of ceramics make them the material of choice in areas where temperatures can reach up to 1600 °C. Within the ceramic material group, however, opposing properties can also occur when comparing two materials: Silicon carbide, for example, can be used as a resistance heating element in industrial furnaces, while porcelain is used as an electrical insulator for high-voltage lines.
This is, of course, only a small overview of the material, but the (positive) properties can still be clearly seen.
What are plastics and what are they used for?
The word “plastic” in the vernacular usually refers to synthetic plastics, which can be described as artificially produced polymers (linking of smaller molecules).
Polymers can be found in a wide variety of applications and have become an indispensable part of everyday life – the PET bottle for transporting liquids or the housing of the computer mouse with which you probably clicked on this article.
This broad field of application is no coincidence. Plastics can be produced comparatively inexpensively from crude oil and can have a variety of properties depending on the type. There are rigid, flexible or elastic plastics – all with their own application niches.
What influences the price of the components?
1. the raw material price
First and foremost, the raw material of the material to be used in the respective component must be obtained. Raw materials for ceramics are usually extracted in open-pit or underground mining. Depending on the material, it must then be processed further. There are major differences here:
Clay – a mixture of various layered silicates – as used for tiles is probably one of the cheapest ceramic raw materials. This is partly because the material does not have to be “pure” and could, quite casually, be put “straight from the open pit into the kiln.” By contrast, the high-performance ceramic zirconium oxide, which is used for hip joint implants, for example, already costs a thousand times more, since the starting material (usually zirconium) still has to be processed after mining. Even more cost-intensive is, for example, yttrium-barium-copper oxide, which has to be synthesized at great expense, but is then superconducting at -181°C. In this case, the costs are even higher. Here, the costs again amount to about 100 times those of clay. The problem with all these raw materials: Only very few of them can be easily recycled after use.
As already mentioned at the beginning of this article, plastics are mostly obtained from one raw material: Crude oil. Due to the wide range of applications and the great demand for energy, crude oil is nowadays extracted in very large quantities and is comparatively cheap. The hydrocarbons contained in crude oil form the basis for the production of most polymers. In addition, some plastics can be easily recycled, as demonstrated by the return of deposits on beverage bottles.
Even if price differences exist for plastics, they do not vary as much as for ceramics. Even high-performance plastics such as PEEK are not more expensive by a factor of 1000 than conventional plastics such as PET or ABS.
2. The cost of sales
For the production of ceramic components, first and foremost a so-called green compact (ceramic mass brought into shape) must be produced. Green compacts can be produced by various processes such as pressing, extrusion or casting. 3D printing processes such as binder jetting or material extrusion also produce a green compact in a first step. With a few exceptions, this green compact must now undergo a firing process known as sintering. This part of the manufacturing process is comparatively expensive, as high temperatures (approx. 1600°C for aluminum oxide) have to be reached and kept.
While plastic components are also manufactured by pressing, extruding or casting, the sintering process is omitted with a few exceptions. Post-processing is usually not necessary.
As is so often the case, the initial question cannot be answered in a generalized way. Yes, in principle it is obvious: the raw material costs for ceramics are in the vast majority of cases higher than those of high-performance plastics, and the manufacturing costs are also usually higher – especially if the ceramic components are not mass-produced items such as bricks. When making the comparison, however, it is important to know which materials are being considered – and where they will be used. This is because it is important to note that the higher (purchase) costs of ceramics can be accompanied by considerable added value in some areas. Not only can the service life of a machine be extended by replacing plastic elements with ceramics – plastics will probably not be able to replace the porcelain insulator of the high-voltage line easily.