A Heater Without a Flame

How does a soldier hiding from the enemy heat his meal rations without lighting a fire and giving away his position? The army’s answer to that is the Flameless Reaction Heater (FRH). The heater contains finely powdered iron and magnesium metals, and table salt. To start the reaction, the soldier adds a small amount of water from his canteen, and the water quickly boils as the highly exothermic reaction occurs. This reaction involves lattice energy or the energy required to dissolve the solute (in this case the metals and salt). 

So how does this help us in our everyday goings on? Well, these could be great for camping trips. Much too often, a camping group gets careless with their fire and it spreads, and can destroy habitat and possibly cause death for the campers as well as others nearby. Using a flameless reaction heater gives the same amount of heat for cooking but doesn't include the potentially harmful side effects of embers and sparks. Of course, as a heat source for warming people, it doesn't do very well because it concentrates the heat in a very small area and doesn't allow much to escape into the air.

 A packet of an FRH.

It can also be used as an insert to a lunch bag, if maybe you want to bring some lasagna from last night and heat it up. You don’t want to burn down the lunchroom by using the 20-year old microwave that has a 50-50 chance of exploding in your face, so you whip out an FRH and some water from the water cooler, and voila! You have hot lasagna while your co-workers look on in envy, limp turkey sandwiches uneaten as they gaze longingly at your hot meal*.

*Note: the author has nothing against turkey sandwiches, and finds them to be quite enjoyable on occasion. Tuna fish, on the other hand… that’s a different story.



By: Brandon Oviedo

Kevlar

Kevlar is a synthetic (man-made) substance that is extremely strong. Kevlar is highly versatile, as it is incorporated into bulletproof jackets, bulletproof masks, army tanks, bullet heads, personal fighting armor, combat helmets, etc. Kevlar is 5 times stronger than steel, and under water it is 20 times stronger than steel. Kevlar's spider web-like weaving structure is responsible for its immense strength. 

A sheet of Kevlar. 

Kevlar integrated into a bulletproof vest. 

Kevlar is the commercial name for poly(p-phenylene terephtalamide). Kevlar is a polymer, meaning that it is made  from monomer chains. Each Kevlar segment or monomer contains 14 carbon atoms, 2 nitrogen atoms, 2 oxygen atoms, and 10 hydrogen atoms. The arrangement of polymer chains in Kevlar contributes to its flexibility, strength, and rigidity. Think of Kevlar as a grid of parallel molecules, similar to bendy straws that are stacked parallel to each other in their box. This orderly, untangled arrangement of molecules in Kevlar represents its crystalline structure. Kevlar is a polyaromatic amide. Aromatic refers to compounds with benzene rings (C6H6). Amides refer to a group of carbon, nitrogen, oxygen and hydrogen atoms.

Structure of Kevlar.

There is major hydrogen bonding that occurs in Kevlar. The hydrogen bonding that holds Kevlar's polymer chains occurs between polar amide groups on adjacent chains. In other words, there is a lot of hydrogen bonding between nitrogen and hydrogen atoms. Hydrogen bonding plays the most prominent role out of all the intermolecular forces in Kevlar.

Hydrogen bonding in Kevlar. 

A colored diagram of H-bonding in Kevlar. The individual polymer strands are held together by h-bonds that form between polar amide groups on adjacent chains.

In chemistry, kinetics describes the rate of a chemical reaction. Likewise, thermochemistry describes the energy associated with chemical reactions. In essence, it describes what is possible and what isn't. Thermochemistry focuses more on the amount of energy in the reactants/products and the overall energy change in the system. Back to Kevlar - remember, Kevlar is a man-made substance. Therefore, Kevlar had to be originally synthesized by someone. In fact, Kevlar was first synthesized in 1964 by Stephanie Kwolek at the Dupont laboratories in Wilmington, Delaware. There are 2 main steps in the synthesis of Kevlar. The first step is producing the basic plastic. This plastic is called poly-para-phenylene terephthalamide. The second step focuses on turning the product into strong-structured fibers. As mentioned before, Kevlar is synthesized from the monomers 1,4-phenyl-diamine (para-phenylenediamine) and terephthaloyl chloride. This produces a polymeric aromatic amide with alternating benzene rings and amide groups. Refer to the pictures below for a conceptual understanding of each step. When the amides are made, the polymer strands are aligned randomly. To make the actual material, the polymers are dissolved and spun, shaping the long polymer chains into the fiber. 

Synthesis of Kevlar. The reactants are the monomers 1,4-phenyl-diamine (para-phenylenediamine) and terephthaloyl chloride, respectively.

Some additional properties of Kevlar:

1. Kevlar is insoluble in water. 

2. Kevlar's molar mass is about 238.241 g/mol.

3. Hydrochloric acid (HCl) is a byproduct of the chemical reaction that makes Kevlar.

4. Kevlar is very heat resistant and decomposes above 675K or 402°C without melting.


By: Max Lauring

War Paint with a Twist

Every year, the explosions of over 16,000 IEDs (Improvised Explosive Devices) kill and wound US and NATO military service men and women deployed in Iraq and Afghanistan. The number of IEDs is from a count done in 2011, and that count is only expected to rise in this year and the next. As of 1 October 2012, more than 50 soldiers had been killed by shrapnel and IED explosions.

The problem with IEDs is that they are buried, and when riding in a bumping and shaking vehicle, they are almost impossible to detect. In recent months, soldiers have been getting training in the detection and defusing of the bombs. IEDs do not just create shrapnel, they also create a huge amount of heat—more than 1000 degrees Fahrenheit--when the explosives detonate.  This heat can do catastrophic damage to any exposed body parts, cook skin, and even set clothing on fire. Soldiers have received burns that can only be called gruesome, and for that reason, no further detail will be given.

Presented at a meeting of the American Chemical Society, a new paint has been designed to combat this problem. It would be applied to soldier’s faces, and would shield them from the extreme temperatures created in a bomb blast. The Army has used face paint before, but it has been made with hydrocarbom compounds, which burn easily and can amplify the effect of the massive temperature increase.  The Army also requires that the paint contain 35% DEET, another flammable substance that is used to keep bugs away.  The new paint, while still incorporating the DEET, uses less flammable silicon compounds, and uses a hydrogel around it. The hydrogel is made up of mostly water. An IED explosion’s heat lasts for around 2 seconds, but this new paint has been tested to last for up to 15 seconds. This is a big step forward in protecting our troops, and when combined with the D30 from below, many families won’t have to receive that dreaded visit from the two uniformed service members.                                      

Newly-developed face paint that shields soldiers' faces from high temperatures.

By: Jake Roth