• On Stainless Steel
• During the stone age, metals were extremely rare save for some deposits of copper and gold which were hard to find.
• Without gold, copper and iron, Stone Age peoples used mainly wood, flint, and bone.
• Wood, flint, and bone break easily. Metals, on the other hand can be hammered into shape because of their fluidity and malleability. They also harden when hit. “The first people to discover these properties ten thousand years ago had found a material that was almost as hard as a rock but behaved like a plastic and was almost infinitely reusable.”
• A razor gets blunt because of the many collisions with hair that force crystals to “rearrange themselves into a different shape, making and breaking bonds and creating tiny dents in the smooth razor edge”.
• Dislocations, tiny defects (“atomic disruption”) in the crystalline structure, allow metals to change shape without breaking. “Heating metals allows the dislocations to move about and reorganize themselves with one of the outcomes being that it makes metals softer.”
• Material: stainless steel
• Discovery/Chemistry: Harry Brearley was investigating different metal alloys to find improved hardness for gun barrels, mostly by trial and error trying different metals. In one mixture, he happened to use the correct proportion of carbon and chromium, creating a special alloy crystal wherein the C and Cr atoms were both inserted inside the iron crystals. The addition of chromium did not make the resulting alloy harder but it did make it impervious to rusting or formation of iron(III) oxide. Instead, impervious chromium oxides were formed that produced an invisible, impenetrable layer that protected the iron atoms from oxidation.
• Uses: It was used for making sinks that are “indomitable and gleaming” and unreactive toward many household refuse they come in contact with (fats, acids, bleach, etc.). Brearley was able to fashion tasteless cutlery from this alloy because the iron atoms are not in contact with and therefore cannot react with saliva.
• Quality: “indomitable” is the adjective used by the author for this metal.
• Cultural significance: Its shiny and non-corrosive surface makes it very useful in architecture and art, as in Anish Kapoor’s Cloud Gate in Chicago that “reflects back to us our feeling of modernity, of being clinical, and of having conquered grime, and the dirt and messiness of life”.
[USE THIS IN CHEMISTRY 1B IN DISCUSSION OF ALLOYS]
CHAPTER 2: TRUSTED
• On Paper
• “A tree’s core strength derives from a microscopically small fiber called cellulose, which is bound together by an organic glue called lignin.”
• Material: PAPER
• Discovery/Invention: Said to be one of the four great inventions of the Chinese.
• Chemistry/Uses:
o Writing/Printing Paper is derived from trees primarily composed of cellulose fibers glued together by an organic glue lignin. In the processing, wood is delignified by heating very small wood chips at very high temperatures which break the lignin bonds and leave behind a tangled mess of cellulose fibers in water called wood pulp. Laying the fibers flat to dry turns the wood pulp into paper. Making the paper white, smooth, and shiny requires bleaching and the addition of fine white powder of calcium carbonate. Another coating has to be applied to prevent ink from soaking into the cellulose fiber giving the appearance of ink bleeding. The yellowing of paper is prevented by making non-acid paper that is not coated with aluminum sulfate which makes the paper acidic causing the cellulose to react with the hydrogen ions which causes the yellowing. Yellowing can also be caused by residual lignin which reacts with oxygen producing chromophores which turn paper yellow (e.g. newspaper).
o Photographic paper is a white piece of paper coated with a fine gel containing silver chloride and silver bromide. Exposure to light causes the silver ions to get reduced to blackis/greyish silver metal crystals. The amount of light exposure (captured by the camera) of the silver ions creates the dark and light shading. If the film is removed from the camera and flooded with light, the image would completely turn black as all the silver ions will react.
o Books: The invention of paper (sad to be one of four by the Chinese) more than 2000 years ago inherited from stone, clay, and wood the important role of recording and transferring information after transition from oral history. It did not see its full potential in this role however until the invention of the codex or the book. The thinness and flexibility of paper lend well to binding into rigid a stack (like a “reformed block of wood”) protected by hard covers, creating a “fortress for words for thousands of years”.
o Wrapping paper: The material ability of paper to form creases that can be folded around an object and upon the creation of a weak point (initial tear) can be torn easily makes it a good candidate for concealing objects and, perhaps, turning them into gifs. “Paper’s mechanical properties lend themselves to folding and bending. The cellulose fibers of which it is made can be partially snapped in the area of maximum bend, allowing a permanent crease to form, while sufficient fibers remain intact for the material not to crack and fall apart.”
o Receipts (one type) are (thermal) paper impregnated with a leuco dye and acid that react upon exposure to heat causing the dye to change to a color visible against the white paper.
o Paper Bags: The strength of a fancy shopping paper bag (the one used to hold expensive store-bought clothes) is due to synthetic adhesives. Although the lignin is gone, hydrogen bonds between cellulose fibers give the paper some strength. However, upon getting wet, the hydrogen bonds break and the fibers come loose. A paper bag has greater energy usage compared to that of a plastic bag which makes them an “indulgence” according to the author.
o The look of paper and feel of paper can be controlled chemically and mechanically. Stiffness can be controlled by adding “sizings”, fine powder additives like kaolin and calcium carbonate, that reduce the papers ability to absorb moisture, allowing ink to dry on the surface, and controlling the whiteness. This composite matrix of powders and the binders that bond them to the cellulose (concrete is an example of a composite matrix) allows control of the paper’s stiffness, strength, and weight. E.g. glossy magazine paper has to be stiff but thin and light.
o Card paper (such as those used as train or plane tickets): Need to be thick and thus becomes stiff.
o Money: Its sophisticated design functions to protect money from forgeries.
o 1) It is made of cellulose from cotton and not wood which makes it stronger, durable against tearing after getting wet, and gives it a crisper sound. Being made from cotton cellulose also makes it difficult to counterfeit with wood-based paper. Paper made from wood cellulose contains starch that turn black upon contact with an iodine pen; paper made from cotton cellulose does not contain starch and so no mark appears upon contact with iodine pen. [USE IN 30A]
o 2) Using different densities of cotton creates a “watermark” in the form of a pattern or a picture that can be seen by shining light through the paper.
o Electronic paper: This type of paper used in some flat screen e-books makes of actual ink called the Janus ink (Janus being the Roman god of transition) to create text or images. Janus ink is composed of dye particles that have a white side and black side of opposite electrical charges. Applying a specific distribution of electrical charges across the paper causes the particles to be either white up or black up which, in aggregate, form the intended image or text. Because the particles have to rotate upon any change, it is a bit slower and not as fast as the liquid crystal display in an ipad, for instance.
o Newspaper: see cultural significance below
o Love letter: see cultural significance below
• Quality: TRUSTED. See chemistry above.
• Cultural significance:
o Yellowing paper and the smell of old paper create “sensual impressions…(that) allow you to enter the past much more readily, providing a portal to the world”.
o Photographs provided “a way for identification to be standardized and verified and, in this sense, has been accepted as the final arbiter of what we look and, by extension, who we actually are”. Photographs provide a “material history” that contributes to our collective history and documentation.
o Wrapping with paper “ritualizes the act of giving and receiving, turning that object into a gift”. “The unwrapping of a present is akin to the act of birth; a new life for the object begins.”
o “A long line of famous scientists and engineers throughout history claimed the back of the envelope as an important theater of ideas.” Enrico Fermi popularized this practice and formalized it as “an order of magnitude calculation”. “This way of looking at the world prizes above all not exact answers but answers that are easily understandable and say something fundamental about the world using only the information available on a bus.”
o “The look and feel of paper turn out to be of the utmost importance and the secret to why it is so useful as a material. It can be transformed from rustic to official, from retro to glamorous, simply by changing the surface layer. Controlling these aesthetic considerations is vital to the economic fortunes of commercial publications.”
o Money represents the “most sophisticated piece of paper” invented “which they need to be because they are a literal, material manifestation of the trust we all have in the whole economic system”.
o “There is something about a printed photograph or newspaper headline that makes the event it describes more real than in any other form of news reporting. Perhaps this is because there is an undeniable reality to the newspaper itself: it is a real material object. That authenticity rubs off on the news. It can be pointed to, underlined, cut out, pinned on notice boards, stuck in a scrap-book, or archived in libraries. The news becomes an artifact, frozen in time; the event may be long gone, but it lives on as an indisputable fact because of its material presence—even if it is untrue.”
• Question for 1A: Do a back-of-the-envelope calculation to estimate the number of atoms in the earth using the following assumptions: Assume an atom occupies a cube of side 10-10 m. The circumference of the earth at the equator is about 40,000 km. (A calculation the author did literally on an envelope featured in this chapter.)
CHAPTER 3: FUNDAMENTAL
• On concrete
• Chemistry: Concrete is composed of powdered rock that contains some calcium carbonate and silicates. Upon heating to a temperature of 1450 Celsius, the mixture starts to fall apart and form calcium silicates. Correct proportions of aluminum and iron rich rock impurities are needed to turn it into concrete. Once cooled down, the resulting ashy mixture is called cement. When water is added to cement, it starts to form a gel that hardens into a matrix composed of crystal-like calcium silicate hydrate fibrils. As the fibrils grow in the presence of water, they expand and mesh together trapping more and more of the water until it changes from a gel-like consistency back to hard rock. Adding too much water will result in residual water (unreacted with calcium silicates) weakening the concrete. Too little water leaves unreacted cement which also weakens the structure of the concrete. “Although concrete reacts with water to harden to a reasonable strength within 24 hours, the process by which this artificial rock develops its internal architecture and so its full strength takes years.”
• Reinforced concrete was discovered by Parisian gardener, Joseph Monier. He was trying to construct plant pots that were not made of terra cotta or fired clay due to its weakness. He tried concrete but it was still weak. To strengthen it, he embedded loops of steel inside the concrete. As his luck would have it, the concrete calcium silicate fibrils bonded both the rocks and the metals. The strength and endurance of reinforced concrete also have to thank very similar coefficient of expansions between concrete and metal.
• A type of self-healing concrete is being developed that makes use of embedded alkaliphilic bacteria (B. pasteurii) that has the ability to excrete calcite. B. pasteurii bacteria are hardy and can remain dormant encased inside rock for decades. They are embedded along with starch in the concrete within the calcium silicate fibrils. When a crack develops in the fibrils, water can percolate into the steel causing rusting. With embedded bacteria, the bacteria themselves are also released, feed on the starch, grow and replicate, and produce calcite ( a form of calcium carbonate) that can then bond and seal the crack. “Research now shows that cracked concrete that has been prepared in this way can recover 90 percent of its strength thanks to these bacteria.”
• Self-cleaning concrete also exists. Microscopic crystals of titanium oxide layered on the surface. Upon absorption of UV rays, they produce free radical ions that break down organic dirt. (Titanium oxide is also known to reduce the level of nitrogen oxides in the air like a catalytic converter.)
• Discovery and Cultural significance:
• The invention of concrete by the Romans allowed them to build the infrastructures requisite for empire building: ports, aqueducts, bridges, the dome of the Pantheon in Rome that still exists today.
• “Concrete is by a long way the cheapest building material in the world.”
• "Concrete is literally the foundation of our whole society: it is the basis of our cities, our roads, our bridges, our power stations.”
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