Topic:

Glossary: H

Here you are going to find explications of important terms in plasma technology:

I,J

P,Q

X,Y,Z

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hard-coat layers: Hard-coat layers that are but a few micrometers thick are often applied as wear protection on highly loaded parts like e.g. tools, bathroom fittings, glasses frames, cutting-tools etc. Popular because of their high hardness are nitrides, borides or carbides.
high-frequency generator: High frequencies in electronics and communications engineering mean high frequencies of electric current or electric and/or magnetic fields between 10.000 Hz und 1.000.000 Hz (10 kHz-1 MHz). Frequencies below these values are normally called mid-frequencies. Because of their wide range, high-frequency technology is mainly applied in the areas of mobile telephone systems, radio and television engineering, radar, and by satellites. High frequency is often abbreviated to HF or RF (radio frequency).
Hexamethyldisiloxan (HMDSO): Hexamethyldisiloxane (HMDSO, (CH3)3SiOSi(CH3)3) is a molecule that is often applied as precursor (intermediate product, liquid reactant) for CVD, PACVD, or atmospheric pressure plasma for the deposition of SiOx layers. The non-toxic substance is fragmented in the plasma and its atomic components are transported towards the surface. HMDSO has a boiling point of 101Ê¡C and a melting point of -59°C. Its density is 0,764Êg/mLÊat 20Ê¡C.
high-grade steel: Aseptic iron-base alloy with more than 18% Cr and 8% Ni, less than 0.5% C.
high-purity surfaces: Under strictly controlled surrounding conditions, high-purity layers can be disposed and cleaned afterwards. The cleansing process is material-bound. Carbon compounds can be removed from a metal surface e.g. by oxygen plasma. The thus generated high-purity surfaces are needed in the sciences mainly.
High-tension discharge: see „high-voltage discharge“
High-voltage discharge: High voltages are commonly called voltages of more than 1000V (=1kV). By means of these high voltages, strong electrical fields can be generated in which charged particles can be produced and accelerated.
hydrogen: Diatomic gas (H2) that is applied as process gas in plasma. Weak sputtering effect because of the low mass, but good results in removing reducible surface layers, e.g. surface oxides on metals. Hydrogen plasmas have a very high enthalpy and are therefore hard to fire. Under atmospheric conditions, backing gas (nitrogen-hydrogen mixtures) is applied in order to deoxidise copper.
hydrogen plasma: Plasma that is generated with the aid of hydrogen gas.
hydrophilic: „Hydrophilic“ can be translated from Greek as „loving water“ and is a technical term in chemistry that describes substances which mix with water, respectively solid bodies whose surfaces are readily wetted by water. Hydrophilic substances are often lipophobic at the same time, thus they mix only poorly with grease or oil.
Hydrophilic surfaces are often covered with an invisible water film. Contact angles describe the angle between a surface and the water skin of a drop. Surfaces with a contact angle of less than 90° are called hydrophilic. A simple and good method to test if a surface is hydrophilic or hydrophobic are test inks ( - see „test inks“). Via test inks, one can measure the surface tension and thus make a statement about the material being hydrophilic or hydrophobic. A hydrophilic surface can have a surface tension of e.g. 72 mN/m or more. Most metals are hydrophilic. Other hydrophilic substances are salts (ion compounds) or polar substances that are soluble in the polar water.
The opposite of hydrophilicity is hydrophobicity. Molecules that are both hydrophobic and hydrophilic are called amphiphilic. In most of the cases, one part of the molecule is hydrophobic and another part hydrophilic. Cleaning active substances, like e.g. tensides or fatty acids, have these properties. Therewith they dissolve hydrophobic dirt in water.
hydrophilicity: see „hydrophilic“
hydrophobic: „Hydrophobic“ can be translated from Greek as „water repellent“ and is a technical term in chemistry that describes substances which don‘t mix with water, respectively solid bodies whose surfaces don‘t get wetted by water. This can be observed for example through water drops rolling off the surfaces. Nonpolar and uncharged substances such as grease, wax, alcohol with long alkyls - thus except for methanol and ethyl alcohol - alkanes, alkenes, methane etc. are hydrophobic. When dissolving materials like methane in water, entropically unfavourable clathrate structures are formed. That‘s the reason why such substance‘s solubility in water is only poor. Hydrophobic substances are almost always lipophilic as well, that means they dissolve readily in grease and oil.
Contact angles describe the angle between a surface and the water skin of a drop. Surfaces with a contact angle of less than 90° are called hydrophilic. A simple and good method to test if a surface is hydrophilic or hydrophobic are test inks ( - see „test inks“). Via test inks, one can measure the surface tension and thus make a statement about the material being hydrophilic or hydrophobic. A hydrophobic surface can have a surface tension of e.g. 30 mN/m or less. On such surfaces (e.g. teflon) water rolls off very well. An extreme example for a hydrophobic surface is the surface of lotus leaves and blooms. They consist of a rough hill-structure in the area of a few micrometers, and besides it has a hydrophobic surface. Because of this peculiarity, lotus has contact angles of more than 160° such that water drops on it are almost perfectly round. Dirt particles lying on the surface can thus be washed away easily by moving water drops. The lotus effect is applied in the textile industry for dirt-repellent layers.
The opposite of hydrophobicity is hydrophilicity. Molecules that are both hydrophobic and hydrophilic are called amphiphilic. In most of the cases, one part of the molecule is hydrophobic and another part hydrophilic. Cleaning active substances, like e.g. tensides or fatty acids, have these properties. Therewith they dissolve hydrophobic dirt in water.
Catheters are small tubes or hoses of diverse gauge, made from plastics, latex, silicone, metal, or glass; with the help of catheters, hollow organs or cavities can be probed, emptied, filled, or rinsed.
hydrophobicity: see „hydrophobic“