All posts by angela02pd2014

Meeting Steel

I was watching the Discovery Channel the other day and came across a show about steel.  Living in today’s technologically advanced era often leads me into thinking that cars, boats, bridges, pots and pans are very ordinary, but I’ve never realized just how ubiquitous steel is (or the fact that steel isn’t an element).  I was so intrigued by steel that day that I actually sat for over an hour to watch the show.  So how is steel made and why is it used so widely?  Curious, I decided to learn more about steelmaking and hope to provide some insight into this ‘ordinary’ material.

Steel is essentially an alloy of iron, the second most abundant metal on Earth (Iron Fact-ite, n.d.), and 0.5 to 1.5 percent concentration of carbon (Brain & Lamb, 2000).  It is used widely for its strength, durability, affordability, flexibility, and recyclability.  What got me interested was also the connection between its manufacturing process and redox reactions, which is what we are currently learning about in IB Chemistry.

The two visuals below sum up steelmaking in a nutshell.

To make steel, coal is first converted to coke, or pure carbon, as a source of energy for the blast furnace, where iron ore is turned into molten iron and limestone is added.  Inside the blast furnace, carbon and carbon monoxide act as reducing agents in reducing iron (III) oxide, the ore, into iron.  Because carbon is above iron on the reactivity series, carbon, being more reactive, is oxidized and iron is reduced, as seen below. (Brown, n.d.)

Fe2O3(s) + 3CO(g) à 2Fe(l/s) + 3CO2(g)

Fe2O3(s) + 3C(g) à 2Fe(l/s) + 3CO(g) (Brown, n.d.)

At the same time, limestone (CaCO3) is used to remove impurities, such as silica, in the iron ore.

CaCO3 + SiO2 à CaSiO3 + CO2 (Brown, n.d.)

In the next stage, the molten iron is mixed with recycled steel and alloys based on the customers’ needs.  This then enters either a basic oxygen furnace, where 70 percent iron is mixed with 30 percent recycled steel, or an electric arc furnace, where 70 to 100 percent recycled steel is used (Making Steel, n.d.).  The molten steel produced is then sent to a slab caster to be casted into solid steel slabs, which is later reheated to ensure that the slabs were all at the same temperature before being rolled into strips.  The steel slabs then go to the roughing mill and finishing mill, which reduces the slabs’ thickness and rolls them into strips, and become hot rolled products.  Then hydrochloric acid (HCl) is applied to remove surface scales before the steel strips are cooled, and now they are ready for sale for construction, automotive, appliances, and manufacturing. (Steel Builds a Better World, n.d.)

I found steel’s manufacturing process rather interesting, but what was more also interesting was the fact that steel is 100 percent recyclable and can be “recycled infinitely without ever affecting its strength or durability” (Steel Builds a Better World, n.d.).  As someone who cares about environmental health, I was very happy to know about this.  In fact, manufacturing using recycled metals not only reduces greenhouse gas emissions but also saves up to 56 percent the energy used to make steel from iron ore.  Moreover, it is also beneficial to the economy in that in 2008 alone, the “scrap recycling industry generated $86 billion and supported 85,000 jobs” (West, n.d.).

On the other hand, however, iron and steel manufacturing also raises environmental concerns.  The iron and steel industry release air pollutants, such as sulphur dioxide, nitrogen dioxide and carbon monoxide, and particulates, such as soot and dust, into the air.  Moreover, steel works also releases large volumes of wastewater, which, if retained in unsealed ponds, may contaminate other local water ecosystems.  Additionally, the consumption of 21.1 gigajoules per tonne of energy (used by US scrap-based plants in 1988) also brings up the issue of energy conservation. (Spiegel, n.d.)

I realized that it is important to consider both merits and shortcomings before reaching conclusions.  As much as steel is useful and recyclable, its manufacturing also harms our environment.  This research was an eye opener for me as I found a real-life application, steelmaking, for what we’re learning in class!

Bibliography

Brain, M., & Lamb, R. (2000, April 1). How Iron and Steel Work. HowStuffWorks. Retrieved October 9, 2013, from science.howstuffworks.com/iron4.htm

Brown, D. (n.d.). The Extraction of Iron.Doc Brown. Retrieved October 9, 2013, from http://www.docbrown.info/page04/Mextracta.htm

Iron Fact-ite. (n.d.). Planet Earth. Retrieved October 9, 2013, from www.gsa.org.au/resources/factites/factitesIron.pdf

Making Steel: How It’s Made. (n.d.).SteelWorks. Retrieved October 9, 2013, from www.steel.org/en/Making%20Steel/How%20Its%20Made.aspx

Spiegel, J. (n.d.). Environmental and Public Health Issues. International Labour Organization. Retrieved October 9, 2013, from http://www.ilo.org/oshenc/part-xi/iron-and-steel/item/593-environmental-and-public-health-issues

Steel Builds a Better World. (n.d.).Dofasco. Retrieved October 9, 2013, from www.dofasco.ca/HOW_STEEL_IS_MADE/html/Steel.pdf

The Chemistry of Steelmaking. (n.d.).School Science. Retrieved October 9, 2013, from resources.schoolscience.co.uk/Corus/14-16/steel/msch1pg1.html

West, L. (n.d.). Metal Recycling – Benefits of Metal Recycling – Why Recycle Metal?.Environmental Issues – News and Information about the Environment. Retrieved October 9, 2013, from http://environment.about.com/od/recycling/a/metal-recycling.htm

Pictures

Steel Finishing Flowline. (n.d.). Steel Works. Retrieved October 9, 2013, from www.steel.org/Making%20Steel/How%20Its%20Made/Steelmaking%20Finishing%20Flowline.aspx

Steelmaking Flowline. (n.d.). Steel Works. Retrieved October 9, 2013, from www.steel.org/Making%20Steel/How%20Its%20Made/Steelmaking%20Flowlines.aspx

Teeth Nightmare: Cavities

Tooth
Figure 1: Tooth structure (Gordon, n.d.)

I must admit that I have a lot of teeth cavities. Needless to say, going to the dentist has been – and still is – a nightmare for me. Perhaps my tendency of getting tooth cavity is inherent (Fotek, 2012), or perhaps it is simply due to my lack of care when I brush my teeth. Either way, I am curious about how cavities actually form, so I’ve decided to explore tooth decay in hope of finding a way to keep my teeth healthy.

Simply put, cavity – also known as dental caries (Gordon, n.d.) – is a teeth infection that is related to bacteria and causes the decay of the tooth enamel. The enamel is the outermost layer of the teeth and the hardest and most mineralized substance in the body (Gordon, n.d.) (see figure 1). However, despite its hardness, the enamel can be damaged when interacting with bacteria and food, typically the carbohydrates. While the mouth has many different types of bacteria, only few, such as Streptococcus mutans, Lactobacillus casei, and acidophilus, are associated with cavities (Gordon, n.d.). These bacteria stick to the surface of the teeth and form a sticky film called dental plaque (National Maternal & Child Oral Health Resource Center, n.d.). When carbohydrate-containing food is consumed, these bacteria eat the carbohydrates and release acids, attacking the teeth enamel, usually within 20 minutes of eating (Briseno, n.d.). Normally, the pH in the mouth is about 6.2 to 7.0, but it drops after eating. When the pH reaches 5.2 or below, the acid begins to dissolve the enamel (Gordon, n.d.). Continuous acid attacks result in cavities, which, if not treated, can extend into the living pulp tissues (see figure 1), where the bacterial infection can spread to other parts of the face and body (National Maternal & Child Oral Health Resource Center, n.d.).

Here, acid’s reaction with the tooth links into our study in IB Chemistry of acid’s corrosive property. The enamel, or calcium-deficient carbonated hydroxyapatite (, is composed of mineral, protein, lipid, and water that form a crystal lattice (Lussi, 2006). The hydrogen ions, released by the acid in the mouth’s aqueous environment, react with carbonate and phosphate ions in the enamel, causing the mineral ions to be etched away and hence demineralizing the tooth, as illustrated below (Lussi, 2006):

Ca10xNax(PO4)6y(CO3)z(OH)2uFu + 3H+ →  (10-x)Ca2+ + xNa+ + (6-y)(HPO42) + z(HCO3) + H2O + uF

(note: Ca10xNax(PO4)6y(CO3)z(OH)2uFu + 3H+ is the enamel)

As a result, the enamel surface is reduced and softened (British Dental Association, 2004), which can cause toothaches (Fotek, 2012). Fortunately though, our body has a way of combating tooth decay. Through minerals in the saliva that act as buffers, our body is able to remineralize and repair the damaged enamel automatically (British Dental Association, 2004). Similarly, the fluoride in toothpastes also has the same effect (British Dental Association, 2004).

Essentially, the culprit for teeth decay is the acid and not the sugar. In fact, acid can also erode the teeth when consumed directly. Acidic drinks, such as soft drinks and lemon juice, double the damage to the teeth, because these drinks are high in both acid and sugar. Interestingly, yogurt is low in pH yet it doesn’t have erosive potential due to its high content in calcium and phosphate (Lussi, 2006). Therefore, the erosive potential of acidic drinks depends on a variety of factors, including their pH, mineral content, type of acid, and adhesion to the teeth (Lussi, 2006).

After knowing acid’s pernicious effects to the teeth, I can now understand why dentists ask us to brush our teeth regularly. As mundane as it may sound, brushing the teeth is the easiest way we can maintain our dental health. In addition, fluoride toothpaste should also be used, because study has shown that regular brushing by itself doesn’t prevent teeth decay while brushing with fluoride toothpaste does (British Dental Association, 2004). As a general rule of thumb, eating starch-based food with acidic drinks should be minimalized if not avoided.

In my research, I also came across physical factors that cause tooth wear, but I’ve decided not to go further as my focus was on teeth decay. However, for further exploration, an interesting area to go into could be gum diseases, because they are also caused by plaque buildup but involve studies of the bones and tissues that support the teeth (National Institute of Dental and Craniofacial Research, 2012).

You may ask, after reading all this, so what – what’s the big deal with dental awareness? Many of us take our teeth for granted, and perhaps don’t realize just how crucial a role they play. Without a set of healthy teeth, we will not be able to enjoy the scrumptious dishes we consume everyday. In short, our teeth are a fundamental if not indispensable link to our dietary health. It is, therefore, important to understand the nature of tooth decay to help us prevent it. Hopefully, after the short reading from above, you’ll think twice before you eat sugar-rich food and soft drinks the next time.

Bibliography

Briseno, T. (n.d.). What wears down tooth enamel, and how can you prevent it?.Discovery Fit & Health. Retrieved March 2, 2013, from health.howstuffworks.com/wellness/oral-care/problems/what-wears-down-tooth-enamel1.htm

Fotek, P. (2012, February 22). Toothaches. Medline Plus. Retrieved March 2, 2013, from www.nlm.nih.gov/medlineplus/ency/article/003067.htm

Gordon, J. (n.d.). Cavities and Fillings 101. Discovery Fit & Health. Retrieved March 2, 2013, from http://health.howstuffworks.com/wellness/oral-care/problems/cavity1.htm

Lussi, A. (2006). Dental Erosion. Basel: Karger.

Periodontal (Gum) Disease: Causes, Symptoms, and Treatments. (2012, August). National Institute of Dental and Craniofacial Research. Retrieved March 2, 2013, from http://www.nidcr.nih.gov/OralHealth/Topics/GumDiseases/PeriodontalGumDisease.htm

Tools. (2004). British Dental Association. Retrieved March 2, 2013, from www.3dmouth.org/1/1_2.cfm

Tooth Decay. (n.d.). British Dental Association. Retrieved March 2, 2013, from www.3dmouth.org/2/2_3.cfm

What is Tooth Decay. (n.d.). National Maternal & Child Oral Health Resource Center. Retrieved March 2, 2013, from www.mchoralhealth.org/OpenWide/media/flash/decay_flash.htm

Image

Gordon, J. (n.d.). Cavities and Fillings 101. Discovery Fit & Health. Retrieved March 2, 2013, from http://health.howstuffworks.com/wellness/oral-care/problems/cavity1.htm

Lussi, A. (2006). Dental Erosion. Basel: Karger.