All posts by Captain Corrosion

Ion Pump

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The ion pump is a high vacuum pump that is based on ionizing the gas. When the gas that enters the ‪#‎ionpump‬ it always has some ions in it and those are pulled towards the titanium cathode. These ions are then trapped between the titanium atoms and they may also chemically react with titanium forming solid titanium nitride or titanium oxide, depending on the gas. In addition electrons and titanium atoms are emitted from the cathode when bombarded by the ionized gas molecules. These electrons are then accelerated towards the steel anode as the potential between the anode and cathode is thousands of volts. A magnetic field caused by the magnets makes the electrons move spirally so they spend more time in the open and more likely hit gas molecules to ionize them. The generated gas ions move again towards the cathode and kick out even more electrons and titanium atoms. Some of the kicked out titanium atoms also deposit on the anode and in this process bury gas molecules under them. The pump may work for several years if used in high vacuum environment and if the amount of pumped gas is not large. At some point however the cathodes need to be replaced.

Turbomolecular Pump

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Turbomolecular pump ( ‪#‎TMP‬ ) is a popular high vacuum pump, that is widely used in many vacuum systems (electron microscopes for example) as it is clean, fast and efficient for maintaining high vacuum over a long period of time. Inside the pump there are rotor blades that rotate with a speed up to 90 000 rotations per minute and stator blades that are stationary. If a gas molecule enters the pump then it is hit by the rotor blades that are tilted at a certain angle. The kinetic energy from the blade is transfered to the gas molecule and causes it to move down and hit a stator blade that is also tilted at a certain angle, causing the molecule to „bounce“ down, where it meets the next rotor blade. Eventually the gas molecules reach the bottom of the turbomolecular pump where they are removed with a backing pump (prevacuum pump). The turbomolecular pump usually also needs a pre-vacuum before it can work efficiently and this can be done with a pre-vacuum pump (for example a scroll compressor pump). Once the pressure is low enough, the ‪#‎turbomolecularpump‬ starts working and the rotation speed of the rotor blades is gradually increased.

Diffusion Pump

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The diffusion pump is an oil-based vacuum pump, that is used for obtaining different levels of vacuum – even high vacuum of 10 powered -9 Pascal. In this system the oil is boiled by a heating with a heater. Next, the jets of vaporized oil grab the gas molecules in the chamber and transport them to the colder chambers walls where oil condensates and moves down. At this stage the captured gas molecules are released and removed from the system with a pre-vacuum pump. The ‪#‎diffusionpump‬ has very high pumping speeds and it can even be used for the pumping of corrosive gases. The downside however, is the possibility of contaminating the vacuum system with oil and therefore oil traps are highly recommended.

Uniform Corrosion

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Uniform corrosion (general corrosion) is discussed in this short educational video.

Corrosion is one of the greatest problems of mankind as materials degrade due to the environment, leading to an annual corrosion cost of billions of euros. Since there are so many materials in the world there are also many forms of corrosion. One of the most common forms is the uniform corrosion, also known as general corrosion. The first sign of this type of corrosion is the dulling of the freshly polished surfaces – if corrosion is ignored then it keeps progressing and eventually the material no longer serves its purpose. So how to prevent this type of corrosion? The first most obvious thing is to use materials that are more corrosion resistant. However, often we dont have better materials with a reasonable price and then we need to apply protective coatings.

Corrosion Allowance

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One of the most widely used methods to counter  the degradation of a materials mechanical properties to due to corrosion is to use more material. If the speed of uniform corrosion is known (mm per year), then it is possible to calculate the required thickness of the material, so that it can serve its purpose during its expected lifetime. The Steel Bridge in Portland (USA) is just one example where this method is used. Protective coatings are also often applied in order to slow down the corrosion of the construction material even more.

Penetration of Nuclear Gamma Radiation

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Nuclear radiation is emitted from a material when the nucleus of an unstable atom loses energy by emitting ionizing radiation. The emitted radiation consists of gamma rays, alpha particles (He2+), beta particles (high energy electrons or positrons) and conversion electrons. From these components gamma rays are most dangerous for humans as they can easily penetrate the skin and cause severe damage to internal organs. Although gamma radiation is often an unwanted byproduct when producing nuclear power, it also has found use in medicine and food industry. In medicine gamma radiation is used for cancer treatment as it kills the cancer cells. In food industry the radiation is used to sterilize food as it kills bacteria and leaves the food unharmed. Gamma radiation can easily penetrate different materials and this makes radiation protection difficult. The penetration depends on the atomic number and therefore heavy metals such as Pb (lead) are used for shielding. In this experiment we use a geiger counter to measure the radiation emitted from a cobalt-60 isotobe and see how well we can block the radiation by using different materials such as wood, aluminum, steel, tungsten, pork cutlets and led casing.

Auger Effect

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The Auger electron is generated during an excited atoms relaxation process, where excess energy is transfered to an outer shell electron, which leaves the atom and becomes the Auger electron. The energy of this electron depends on the binding energies of the participating electrons and is unique to the element where it occurs. As the Auger electrons energy is very low, it can escape the material from only near the surface (few nanometers). This means that this signal is highly surface sensitive and can be used to obtain information from only the surface, not from the bulk material as it is common with other material characterization methods.

Characteristic X-Ray Radiation

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Characteristic X-Rays are generated when excited sample atoms undergo a relaxation process. For that the atoms need to be excited first and this can be done with high energy electromagnetic radiation (in XRF) or accelerated particles such as electrons (in SEM). The primary beam kicks out an inner shell electron and a vacant spot is left behind. As this state is unstable, a higher shell electron will soon move into this vacant spot and during this process energy is emitted in the form of X-Rays. This emitted radiation has a specific energy which depends on the binding energies of the two electrons that participated in this process. If this emitted ( characteristic ) x-ray radiation is detected then the composition of the material can be measured.

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