Tag Archives: gas

Pirani Gauge


The Pirani Gauge is used to measure low vacuum. In the system tungsten filaments are heated up by passing current through them. As gas molecules interact with the filament, heat is carried away and electrical resistance changes. Therefore if the measured current or voltage can be converted into pressure units.

Titanium Sublimation Pump

The titanium sublimation pump is a vacuum pump used as a part of vacuum systems in order to briefly improve the level of ‪#‎vacuum‬. The working principle is relatively simple. A pulsing current passes through a titanium filament, causing it to sublimate (goes directly from solid phase to gas phase). The fresh titanium chemically reacts with gas in the vacuum chamber, creating a solid product that deposits on the chamber walls. As the walls are also coated with highly reactive freshly deposited titanium, they may also chemically bind gas molecules that interact with them. Some gases may not chemically bind with titanium but can still be physically trapped under the titanium atoms on the chambers walls.

Ion Pump


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.

Diffusion Pump


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.

How to Generate Hydrogen by Splitting Water

Hydrogen is the most abundant substance in the universe. It fuels the starts that light the nightsky. Hydrogen will also power the future of mankind as it is already used as car fuel and within this century even in fusion reactors.

As most of you know, a water molecule consists of one oxygen atom and two hydrogen atoms. So in order to get hydrogen, it is needed to split the water molecule. This can be done for example electrochemically where an electrical potential is applied between electrodes in a salt water. For a home experiment one can simply put a 9 V battery into salt water and watch how hydrogen bubbles start to form at the cathode. At the same time oxygen is generated at the anode but since the anode on the battery is usually made of steel, it will quickly corrode as it reacts with chlorine and oxygen. This causes the salt water to go brown. So instead, you may want to use electrodes instead that are connected to an external power source. If a DC voltage is used then especially the anode needs to be made from a chemically inert conductive material such as platinum which doesnt oxidize. At this anode oxygen gas can be collected. At the same time hydrogen gas is generated at the cathode and can also be collected. If DC voltage is used then the electrode at cathodic potentials will not corrode very quickly as oxidation cannot occur. However hydrogen damage may eventually destroy the electrode.

Hydrogen damage occurs when the small atomic hydrogen generated at the cathode moves into pores and cracks inside the electrode and combines with other hydrogen atom to form molecular hydrogen. The molecular hydrogen however is too large to diffuse through metal and starts building up inside the sealed crack or pore and pressure increases until it splits the material.

In order to produce as much gas as possible, the surface area of electrodes needs to be increased. Make the electrodes rough, multilayered or highly porous for greater surface area.

If AC voltage is used to split water, then corrosion is suppressed and for some time even stainless steel can be used as both electrodes.


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