This article explains the similarities between the process of making pancakes and the principles of foam glass, and explores how foam glass has a number of advantages as a building material, including thermal conductivity, water resistance, and durability. The pore structure of foam glass and the practical and environmental benefits of using recycled glass are also emphasized.
Sweet and fluffy pancakes are a brunch favorite for young and old alike. Their appeal lies in their simple ingredients and the process of making them. To make these pancakes, you”ll need white flour, sugar, melted butter, and a little baking powder. Add one beaten egg and mix well to form a thick, white batter. It’s important to get the right consistency because if the batter is too runny, the pancakes won’t rise properly. Also, the right ratio of flour to baking powder will ensure that the batter rises evenly and the texture of the pancakes remains soft and fluffy. Place this batter on low heat and flip it over when it starts to bubble on one side. The moment of bubbling is the most important, and if you miss it, the batter may burn and not rise.
The main ingredient in this baking powder is sodium bicarbonate (NaHCO3). The reaction of sodium bicarbonate with carbon dioxide occurs twice, once during the kneading process and again during the baking process. The carbon dioxide bubbles cause the dough to rise, resulting in fluffy, tender pancakes. If the pancakes don’t rise well, it’s because the batter is too thick, or the amount of baking powder is too low, and not enough carbon dioxide is generated. Conversely, if you add too much, the pancake will over-puff and collapse.
Foam Glass is the application of this baking technique to glass. Foam glass is a black glass that resembles a perforated sponge. The process of making foam glass is very similar to that of baking pancakes. First, you mix powdered glass with a little bit of manganese oxide (MnO2, Mn2O3, Mn3O4, etc.) and carbon powder. This pancake batter-like powder mixture is then placed in a device called a Heating Microscope and baked at a very high temperature. The temperature has to be raised to roughly the temperature at which glass powders can stick together, i.e., over 800°C. This causes the manganese oxide to decompose at high temperatures, a reaction that, from the manganese’s point of view, loses oxygen, so we use the opposite term of oxidation to describe it as reduction. The oxygen gas molecules that have left the manganese now find a new home: a carbon atom. The oxygen now forms a new covalent bond and recombines with the carbon to become a carbon dioxide gas molecule. This process of oxygen molecules becoming carbon dioxide is similar to how a small pancake puffs up after baking. A small glass of powder mixed with other ingredients will swell to about 1.5 times the cross-sectional area of a small glass, transforming it into a round piece of foam glass.
Foam glass can be used for roofs, exterior walls of buildings, and pipelines for transporting gases and liquids. One of the biggest advantages of foam glass is its low thermal conductivity. The pores inside the foam glass contain mainly carbon dioxide gas molecules, which have a lower thermal conductivity than other gas molecules such as air or carbon monoxide. The carbon dioxide gas trapped inside the foam glass prevents heat transfer from the outside. Foam glass is also pest-resistant, comparable to cement, and resistant to water penetration from the outside. In addition, foam glass has a low density and does not burn easily in the event of a fire, which is another important characteristic of foam glass as a building material.
Thinking back to pancakes, when we eat pancakes, we look for them to be fluffy, not burnt, not too dry, and just the right amount of moisture. Similarly, making foam glass requires the right proportions, the right temperature, and the right time, but what determines these right factors? The most representative factor is the ratio of closed to open pores. If you think about basalt, which is a very porous rock, the most visible pores are open to the outside world. We call these open pores. On the other hand, pores that are well contained within the foam glass are called closed pores. The ratio of these closed pores determines the thermal conductivity of the foam glass and its ability to resist water penetration: the more closed pores where carbon dioxide can be trapped, the less open pores where water and other sources of corrosion can enter. The problem with baking foam glass is that the higher the temperature, the more active the decomposition of manganese oxide, which increases the percentage of open pores. This is similar to how pancakes become overly fluffy when baked at too high a temperature. Also, when heated to a high temperature for a long time, the pores that are trapping gas enlarge and two pores merge into one large pore. This weakens the strength of the outer walls that support the pores, resulting in a less and less durable foam glass.
The quality of the foam glass also depends on the type of gas in the pores. Manganese oxide decomposes into manganese and oxygen gas. The oxygen gas then combines directly with the carbon powder to form carbon dioxide with a ratio of 2:1 oxygen to carbon. In some cases, the ratio is not quite right and it becomes carbon monoxide with a ratio of 1:1. However, carbon monoxide is twice as good at transferring heat as carbon dioxide, which increases the thermal conductivity of the foam glass. Therefore, a good foam glass should contain just the right amount of carbon powder to capture the maximum amount of carbon dioxide gas.
The glass powder used to make foam glass is recycled from glass that would otherwise be discarded. This includes LCDs used in computers, flat-screen TVs, and digital cameras, and CRT glass, which is classified as a hazardous material because it contains mercury. Currently, glass makes up 7-10% of all solid waste in the US and UK. Recycling this glass is important because it can cause great harm to the environment if landfilled or incinerated. In Europe, more than 75% of glass is recycled thanks to well-designed collection systems, and various recycling technologies are being developed. Building on these systems, foam glass is transforming otherwise unwanted glass waste into a high-value building material with very low-cost additives of carbon and manganese oxide. Foam glass is a practical, environmentally friendly technology with unlimited potential.
