Silica, otherwise known as Silicon Dioxide, is a covalently structured molecule consisting of one oxygen and two silicon atoms. The chemical structure of silica gel, a granular solid, is formed when numerous hydroxides (-OH) attach themselves to the silicon atoms of the silicon dioxide molecules, resulting in a large covalently bonded
Figure 1 – Silicon Dioxide Molecule lattice. In 1918, Walter A Patrick, a chemistry professor patented the designed synthesis route for creating silica gel(Silica Gel, Unknown, 2015). Patrick disclosed this process to be infusing sodium silicate with sulphuric acid in an acidic aqueous solution, which would dry and form a solid silica xerogel. The chemical properties of this substance allow for numerous applications in society today, however a multitude of positive and negative economic, social and environmental impacts have arisen as a result.
Moisture, along with condensation, can instigate a catalysed decomposition process in a multitude of everyday products, leading to mould and spoilage (Silica Gel, Unknown, 2015). Therefore, the highly porous silica gel proves to be a pragmatic solution due to its conveniency. Silica Gel, which was first known in the 1640’s, contains adsorbent properties allowing it to retain 40% of its weight in moisture, controlling local humidity and therefore classifies as a desiccant. (Silica Gel FAQs, Unknown, 2014) These properties allow for a wide variety of applications, therefore making the substance incredibly valued in society. Silica gel is an economical, simple and reliable solution for many situations, and can be applied wherever moisture can cause damage and degradation. To name a few applications of this substance, it can preserve foods, maintain the functionality of packaged electronics, eradicate rust/corrosion on metals, and avert the growth of fungus and mould on clothing, leather and paintings.
The silica gel market will see a compound annual growth rate (CAGR) of 6.21% from 2016 until 2020 due to increasing demand from large global consumers such as China who are continuously driving the market. China accounted for 30% of total silica gel consumption worldwide, while also surmounting other consumers in terms of production(Global Silica Gel Market 2016-2020: Growing Demand for Silica Gel in China – Research and Markets, Unknown, 2016). This is a result for the widespread application of silica gel as desiccant in packaging/electronics and shipping sectors. The key manufacturers of silica gel, such as BASF, Clariant and Evonik will ultimately contribute to their nation’s gross output, aggrandising their nation’s overall economy.
The application of silica gel throughout history has had a variety of social implications. First founded in 1640, silica gel was exploited in gas mask canisters during WWI (Dessicants at War!, Mr Green, 2011), as defence from chemical warfare. During this war, Nikolay Zelinsky, a Russian scientist, devised gas masks which employed activated carbon alternatively to silica gel. However, this concept was not implemented until after WWII, where asbestos was utilised instead. After society discovered that asbestos prompted severe illness, Zelinsky’s gas mask was combined with aerosol filters to form the modern gas mask. During WWII, the substance was utilised to; eradicate moisture from penicillin, prevent moisture destruction to military equipment, produce high octane gasoline through fluid catalytic cracking(Silica Gel, Unknown, 2015) and finally was used as a catalyst for the manufacture of butadiene (C4H6) from ethanol (C2H6O) for the synthetic rubber program.
Silica Gel packets are printed with the words “do not eat” for numerous reasons. Cobalt Chloride is used to indicate moisture in many silica gel packets(What happens if you DO eat silica gel?, Annie, 2011), and has the potential to cause cancer if ingested, while also being toxic for reproduction. Since the substance comes in the form of small beads, swallowing can lead to choking. The desiccant properties of silica gel will come into play when exposed to moisture in the mouth and other parts of the body, leading to irritation and finally vomiting/nausea.
The disposal of silica gel can have various effects on the environment. Although standard silica gel in itself is chemically unreactive and non hazardous, the substance can adsorb toxins from hazardous waste resulting in an imminent threat to the surrounding environment. Silica gel containing Cobalt Chloride (CoCl₂) was labelled as hazardous waste by the Environmental Protection Agency since it could“could pose a greater hazard than standard silica gel as cobalt can leach into runoff or groundwater and poison aquatic life” (Cobalt Indicating Silica Gel Health and Safety Update, Unknown, 2005). The contamination of silica gel in soil and water is prohibited in the European Union due to manufacturer reports stating that cobalt chloride is carcinogenic and toxic to laboratory animals (Cobalt Indicating Silica Gel Health and Safety Update, Unknown, 2005).
Silica Gel, although reliable and simple to use, is vastly outperformed by various other desiccants which prove to be overlying alternatives considering environmental and economical impacts. Bentonite Clay is a solid clay formed through the drying of calcium bentonite, and possesses an attraction towards water molecules (H2O), making it desirable for adsorbing moisture on its vast surface area. Although bentonite clay has a lower adsorption rate than silica gel, it is significantly more inexpensive, non-hazardous to the environment, consumes less energy during production, and is chemically inert.
Relative Humidity (RH) also plays a role in the effectiveness and practicality of a desiccant. Molecular sieves are an increasingly demanded alternative to silica gel and can adsorb more moisture at lower RH’s. This is shown in figure 2, where the molecular sieve follows a steep inline at lower RH percentages. “Where a very low relative humidity is required, molecular sieves are often the most economic desiccant because of their high adsorption capacity at low relative humidity.’(How Do Silica Gel and Molecular Sieves Compare with Varying Relative Humidity?, Unknown, 2015). An example of the practicality of this desiccant would be on airliners, where the internal RH is often under 10%, with airliners being a key mode of transport for packaging. Molecular sieves are not just extremely adsorbent, but resistant to increasing temperatures as they will not displace moisture as easily as silica gel or bentonite clay.
Figure 2 –
Conclusively, silica gel possesses a major role economically and socially, however has negative implications on bodily health and the environment. It has had various applications throughout history due to its chemical properties, making it incredibly valued in society. It is reliable, simple and effective, however can be outclassed by new technologies which can be more practical depending on the criteria of the consumer. Therefore, silica gel is a substance that will continually be used for an abundance of functions in the future, and with an increasing demand on the global markets, silica gel will be so-ever present in our daily lives.