Tag Archives: materjaliteadus

How to Renew Tarnished Silver

June 12, 2014Uncategorizedcoin, corrosion, electrochemistry, hõbe, hõbeda poleerimine, jewelery, korrosioon, materials science, materjaliteadus, polish, renew, renew silver, renew tarnished silver, silver, silver polishing, silverware, tableware, tarnish, tarnished silverCaptain Corrosion

Silver, a valuable metal, has been used long time in making coins, tableware and jewelery. The metal surface however becomes tarnished within a few years and this is caused by corrosion as silver reacts with the surrounding environment.

The surfaces can be easily renewed with stuff available at home – all you need is water, aluminum foil, salt and soda.

Follow these steps to do it yourself:

1. Mix salt and soda into water

2. Wrap the silver price into aluminum foil

3. Put the wrapped silver piece into the solution and wait a few minutes

For a greater effect you might want to boil the water solution as chemical reactions occur faster at higher temperatures.

Why this simple technique works? Silver is usually tarnished as it forms silver sulfide. In order to remove sulfur from the silver, it is needed to put it into contact with a more active metal such as aluminum. The solution there provides with a path for sulfur to move from silver to aluminum.

How Anodizing Works

June 12, 2014Uncategorizedaluminum, anodeerimine, anodizing, corrosion, corrosion protection, electrochemistry, engineering, materials science, materjaliteadus, titaniumCaptain Corrosion

Anodizing is an electrochemical process where a thicker oxide layer is grown on the material. This is useful for improving an objects corrosion and wear resistance, manufacture nanoporous templates or give the material a decorative appearance. Not all materials can be anodized however as their oxides are not dense and hard but the technique has been widely used on aluminum, titanium, zinc, magnesium and their alloys.

The anodizing system consists of a power source, anodizing bath, electrolyte and anodizable material. The bath is usually made from a chemically resistant conductive material such as stainless steel and serves as a cathode. The anodizable material serves as an anode and is placed inside the anodizing bath with the electrolyte. Both the anode and the cathode need to be connected to the power source. The grown oxide layers properties depend on the material, used electrolyte, temperature and electrical parameters used for anodizing.

In order to produce a uniform oxide layer, the substrates are also treated before the process. The main problem is usually organic contamination of the surface, which prevents growth of the oxide layer. This is removed with organic solvents such as acetone. Often the thin native oxide layer is also removed via etching before the anodizing.

How an X-Ray Tube Works

June 12, 2014Uncategorizedbremsstrahlung, characteristic x-rays, engineering, materials science, materjaliteadus, radiation, röntgentoru, security, spectroscopy, tomography, x-ray, x-ray diffraction, x-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, x-ray radiation, x-ray tube, XPS, XRD, XRFCaptain Corrosion

X-ray tubes are widely used for generating X-ray radiation. This radiation has a shorter wavelength than visible light and can easily penetrate through different materials. It can be used in different applications such as materials characterization (XRF, XPS, XRD etc), medicine (x-ray tomography) or security in airports.

The radiation is generated with the help of accelerated electrons. These electrons are first generated on a tungsten cathode via thermoionic emission. Then these electrons are accelerated towards the anode due to a high electric potential between the anode and the cathode. When the electrons interact with the anode, x-rays are emitted. The radiation consists of two components – characteristic x-rays and bremsstrahlung. Characteristic x-rays are generated during the relaxation process of excited anode atoms. This radiation has a specific energy. Bremsstrahlung with a broad range of energy however is emitted from the primary electrons when they slow down or change trajectory during interaction with the anode.

The generated x-rays leave the tube through a beryllium window. This material is used as it has a low atomic number and doesnt absorb much of the emitted radiation.

There are also other types of x-ray tubes, such as the twin anode x-ray tube and the rotating anode x-ray tube.

In the case of twin-anode system, the anodes are made from different materials and only one of them is bombarded with electrons at the same time. This allows fast and easy switching between two excitation energies. The other anode will also serve as a backup if one should fail.

Using a rotating anode allows the heat to distribute on a larger surface area and therefore it is possible to get x-rays with much higher energies and intensities.