Materials and Their Degradation: The Scientific Explanation

Do you ever wonder why some of your shelves can withstand rain and sunlight longer than the others? The answer lies in the materials which fabricated into the shelves. Even though they look similar, each material has unique inner properties which make it degrade in its own mechanism. This article will discuss how the materials degrade and how to put the right material in the right job.

Corner shelves can be made of many materials such as wood, metals, stone, plastic, and glass. Some of them are not suitable for outdoor because the intolerance to sunlight. Some of them can’t be used in bathroom since they’ll protrude. Some of them will rust without a proper care. These phenomena could be¬†explained easily by inspecting the chemical and physical properties of the materials. It’s obvious that if degradation occur there must be some chemical reaction involved, at least some structure collapse in the molecular level.

Wood is a good example, any corner shelves made of wood could withstand sunlight without any significant changes. Since wood (and products from plant such as fabric) is structure of cellulose, which does not have any reaction with normal light. Cellulose can react with oxygen in the air at very high temperature, so wood can be burnt. The fact that there is structure of cellulose inside also explains why wood can permanently protrudes when soaked with water for a long time. It’s because cellulose is fiber, so there are some space between these fibers. When too much water penetrates into the space, the molecules of water push each fiber out from its neighbors and the wood is then bulged.

Bulging Process
Schematic drawing of bulging process

The process of water penetration requires some time and water normally evaporate before the wood protrudes. Thus, wooden shelves can be placed outdoor without problem, even in the rainy season. However, in high-moisture place such as bathroom water can’t vaporize fast enough. This is why wooden corner shelves are not recommend for the bathroom. Even though some well-protected wooden shelves can endure wetness, they’ll eventually protrude in the long term. Please be noted that this process will occur on engineered wood such as particle board much faster than solid wood.

 

Metallic shelves are usually stronger, more difficult to break, and have better tolerant to scratch than wooden shelves.  This is because metallic bonds between metal atoms are stronger than attraction among cellulose fiber. Since the atoms of the same element are alike, the structure gets only little change when the impact moves some atoms. Thus, metals tend to bend rather than break.

Metallic atom arrangement
atom arrangement of metal

Despite their strength, metals have some disadvantage. One of the bad things is that they can rust. The process of corrosion is complex and slightly different on each metal. Briefly, overall process can be explained by simple redox equation:

Rusting equation

This equation explains that metal atom is oxidized by oxygen into metal ion. After this, the ion will go through some others reaction to become insoluble metal oxide or metal hydroxide, which we call rust.

From the equation, we can explain why the presence of water quickens the process. We can also conclude that acids can speed up the reaction since they can remove the hydroxide ion, shift the equilibrium to the right.

Stainless steel can endure the process by protection layer of chromium oxide and nickel oxide on its surface. However, even the stainless stall can’t tolerate acids. So far, none metallic corner shelves should be used outdoor. Stainless steel shelves or well-coated ones could be placed in bathroom. For iron and brass corner shelves, keep them in dry room.

 

There are many types of plastic so their attributes are various. Some of them are very strong, beauty and expensive while some of them are just cheap material for corner shelves. I can’t list all of the types here, of course. However, all of them are consist of polymer that use carbon-carbon bond as backbone. Since the carbon bond is not strong as metallic bond, plastic shelves are usually not so good for impact.

Some types of plastic (such as polyethylene with proper additive) can endure sunlight for years. Even so, most plastic shelves aren’t made for intense sunlight. In UV radiation, some additives will become free radical and destroy the material. The same effect are also responsible for yellowish of old plastic .

 

Stone are also various. While granite gives high tolerant to everything, there aren’t any corner shelves made of granite because it’ll be very heavy. Marble corner shelves are exist, but they should be indoor only since acid rain will destroy them readily by simple chemical reaction:

Carbonate-acid reaction

Last but not least, glass is also popular material for corner shelves. Its hard but fragile properties come from the covalent bond between silicon and oxygen in its structure. Despite the fact that glass can break easily, it has high resistance to most of chemical. (In the laboratory, scientists use glassware to handle their chemical because its resistance.) Thus, glass shelves can be anywhere far form the baseball!