Unveiling the Thermite Reaction

InfoThis is a summary of the following YouTube video:

People said this experiment was impossible, so I tried it

Veritasium

Oct 5, 2024

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Education

What is thermite?

  1. The video series explores a chemical reaction discovered over 125 years ago, known for releasing a significant amount of heat.
  2. Despite its intense heat, the reaction is not explosive, although it can cause explosions under certain conditions.
  3. The reactants involved in this reaction are highly stable and can endure extreme conditions, such as exposure to a blow torch, without reacting.
  4. Hollywood has utilized this reaction to simulate nuclear bomb effects due to its dramatic heat release.
  5. The reaction's most common application, unchanged for over a century, has been instrumental in facilitating global transportation.

Hans Goldschmidt and the first thermite reaction

  1. In the late 1800s, Karl and Hans Goldschmidt prepared to join their family business, a chemical factory producing dyes. They studied chemistry under Robert Bunsen, known for the Bunsen burner.
  2. After their father's death, Karl managed the company, and Hans joined him. Hans aimed to produce pure metals, essential for making vibrant dyes, which were rare and valuable at the time.
  3. Scheele's green, a toxic copper arsenite, was a dominant dye due to its unmatched color. The British Army's red coats used cochineal mixed with tin for a darker hue, highlighting the demand for pure metals.
  4. Purifying metals involved dissolving them in solutions, working with salts, and reducing them to metal, each step presenting challenges like contamination and separation difficulties.
  5. Hans Goldschmidt innovated by reacting metal oxides with aluminum, forming aluminum oxide and pure metal, a process now known as the aluminothermic or thermite reaction.
  6. The video documents a visit to Electro-Thermit in Germany, a company linked to Goldschmidt, where Hans' first successful reaction is replicated using copper instead of chrome.
  7. Thermite reactions release significant energy, with temperatures exceeding 2,000 degrees Celsius, due to strong aluminum-oxygen bonds. This energy melts the reaction products, making them intensely bright.

The reaction as it’s never been seen before

  1. The experiment aims to observe a thermite reaction inside a crucible by using thermally resistant glass as a window. This setup is unprecedented and challenges the belief that such observation is impossible due to the high temperatures involved.
  2. The glass used in the experiment is specially treated to withstand the molten metal's heat, although it will eventually melt. The goal is to have it melt slowly enough to contain the reaction for observation.
  3. The reaction involves iron thermite, a mixture of iron oxide and aluminum metal. The reaction starts at the igniter and spreads outward, resembling organic growth with a pulsing effect, which is a new observation for the researchers.
  4. The pulsing effect might be due to gas escaping or the need for the right ratio of reactants. The reaction proceeds in bursts, with pauses that might be caused by air pressure changes between the grains of reactants.
  5. Once the thermite has reacted, molten metal is ejected, and the liquid inside the crucible sloshes due to boiling materials. The boiling points of the metals involved are extremely high, contributing to this violent phase.
  6. The separation of pure metal from the reaction is achieved by exploiting the density difference between liquid iron and aluminum oxide. Iron, being denser, settles at the bottom, while aluminum oxide floats on top.
  7. The experiment demonstrates the transition from iron to aluminum oxide as the liquid pours out of the crucible, with iron resembling water in viscosity and aluminum oxide appearing more like warm honey.
  8. The process developed by Hans Goldschmidt in 1895 allows for the production of pure metals like chromium, copper, and iron. This method, initially intended for chemistry and dye production, has broader applications.

How thermite welding works

  1. Thermite was initially used for welding metal parts in remote locations where traditional welding equipment was impractical. It provided a strong and reliable weld, especially useful for shipping companies to repair broken shafts at sea.
  2. Thermite welding involves a chemical reaction that produces steel rather than pure iron by including carbon and other alloying elements in the thermite powder. Pure iron is not desirable due to its softness and susceptibility to corrosion.
  3. Most thermite produced today is steel thermite, which allows for mobile steel production wherever needed. This adaptability was particularly useful after the Cold War for destroying obsolete weapons like tank gun barrels.
  4. Thermite is used to destroy weapons by welding and rendering them useless. Once thermite is applied, the weapon cannot be reused, making it a quick, safe, and final method of destruction.
  5. A modern application of thermite is in data destruction. The heat generated by thermite can reach temperatures that demagnetize hard drives, making stored information unrecoverable.

I destroyed a laptop!

  1. The text begins with a demonstration of using thermite to destroy a laptop by generating heat for about 10 minutes. The thermite reaction is controlled to release energy slowly, ensuring the temperature is not excessively high, allowing for complete destruction of the laptop's data.
  2. The narrator discusses the effectiveness of Incogni, a service that helps remove personal data from data brokers, reducing spam calls. Incogni identifies data brokers holding personal information and sends legal requests to remove it, saving the user time and reducing unwanted calls.
  3. Thermite is not suitable as an explosive because its reactions involve solids and liquids, not gases, which are needed for explosive pressure. The controlled nature of thermite reactions allows for precise energy release, making it useful for applications like safely dismantling structures.
  4. An example of thermite's application is given with the removal of the Reichstag building's steel dome in 1957. Thermite charges melted the steel without causing damage to the rest of the building, showcasing its ability to be used in controlled demolitions.
  5. The text explains the importance of controlling the 'tap time' in thermite reactions, which is the duration before metal flows out of the crucible. Proper tap time ensures the metal separates from slag and maintains the desired temperature, affecting the steel's chemistry.
  6. Experiments are conducted to test control over the tap time and temperature of thermite reactions. By adjusting the thermite mixture, the reaction's timing and temperature can be precisely managed, demonstrating the versatility and precision of thermite in industrial applications.

How thermite is made

  1. Mill scale, a mixture of iron oxides, is a byproduct of hot rolling steel, where the surface oxidizes quickly due to heat and water, and is removed using water jets.
  2. The mill scale is dried to prevent any reaction with water, as thermite and water are incompatible, ensuring the mill scale remains dry for further processing.
  3. Iron oxide is separated into different sizes and compositions before being mixed with aluminum powder, both of which must be dry to control reactivity and achieve desired chemical qualities in steel.
  4. A 'portion' refers to a bag of thermite, which is individually bagged and stored in warehouses, with safety measures in place to handle the energy contained in thermite.
  5. A demonstration was set up to show the safety of handling thermite, where attempts to ignite a crucible of thermite with various ignition sources showed it is difficult to ignite without proper conditions.
  6. Despite heating thermite particles to glowing hot, they did not ignite, demonstrating the safety of handling thermite under controlled conditions.

Blow-torching thermite to show how reactive it is

  1. The demonstration begins with an attempt to ignite thermite using a blowtorch, highlighting the challenge of reaching the necessary temperature for ignition.
  2. Despite reaching temperatures of 500 to 700 degrees Celsius, the thermite does not ignite, demonstrating its stability under normal conditions.
  3. The stability of thermite is attributed to the aluminum powder, which is covered in a protective layer of aluminum oxide.
  4. This aluminum oxide layer acts as a barrier, preventing the thermite from reacting unless it is heated violently enough to break down the layer.
  5. The reaction requires a very high activation energy, which cannot be achieved with a lighter or propane torch, necessitating the use of barium hydroxide igniters.
  6. Barium hydroxide igniters, similar to those in sparklers, are used to generate enough heat to penetrate the aluminum oxide layer and initiate the reaction.
  7. Once the thermite reaction starts, it cannot be stopped, emphasizing the importance of controlled ignition.
  8. The video was filmed over five days in Germany, and future content will explore thermite's interaction with its environment and its application in welding railroad tracks.