DIAMOND COATING – BASICS

DIAMOND PROPERTIES

The most  widely known property of diamond is doubtless  it’s incredible hardness of 10000  HV. Strongest known material, highest bulk modulus (1.2 x 1012 N/m2) Lowest compressibility (8.3 x 10-13 m2/ N). Highest known value of thermal conductivity at room temperature 2200 W/(m·K). Thermal expansion coefficient at room temperature (0.8 x 10-6 K) is comparable with that of invar (64FeNi). Broad optical transparency from the deep UV to the far IR region of the electromagnetic spectrum. Good electrical insulator (room temperature resistivity is ~1016 Ω cm). Diamond can be doped to change its resistivity over the range 10-106 Ω cm, so becoming a semiconductor with a wide bad gap of 5.4 eV. Very resistant to chemical corrosion (good electrode material).

REAL DIAMOND COATINGS (CVD)

NOT

DIAMOND LIKE COATINGS (DLC)

  • Nature created diamond with its unique physical properties, like the highest hardness.

  • Diamond single crystals created by  Heger Diamond show the same outstanding physical properties as natural diamond.

  • A crystalline diamond coating created by Heger Diamond consists of countless small single crystals forming a homogeneous coating onto the surface of the component. All these small diamond crystals offer the full potential of diamond.

TRIBOLOGICAL PROPERTIES

Diamond excels in a low coefficient of friction and extremely low wear, even under dry running conditions.

Heger Diamond offers the full potential of diamond as CVD  coating onto your mechanical seals and bearings. The main focus is the coating of mechanical seals made of silicon carbide.

Crystalline diamond is often confused with Diamond Like Carbon (DLC), however the physical properties are completely different. DLC has a hardness of 3500 HV our coating (real diamond) has 10000 HV. Furthermore the adhesion of DLC is weaker because of the lower coating temperature (250°C) which prevents a strong bond.

Diamond is deposited at temperatures of 800°C which results in a strong chemical bonding that is needed for high tribological loads.

The most extreme operating conditions for mechanical seals are dry running. If a conventional uncoated mechanical seal is used, the wear and friction increases very fast, the seal gets hot and the faces as well as the secondary sealing elements are destroyed. This results in leakage and in worst case in a complete breakdown of the sealing system.

If a diamond coated mechanical seal is used in same conditions the friction stays on a low level with almost no wear. With such diamond coated seals mixed lubrication and high abrasion by debris is possible. Because these advantages are achieved by a very thin coating only neither  the  design nor the concept have to be changed.

Abrasion

Besides the wear by tribological load it is the wear caused by abrasion that causes a lot of problems. Every application handling slurries;  mixing, pumping, conveying has to deal with this problem. Even in a lubricated tribosystem a third party i.e. sand or similar, can cause fatal damage to the sliding surfaces. Long time stability and almost no loss of surface material are the demands that are made.

Heger Crystalline Diamond :

  • the hardest known material

  • highly abrasion resistant

  • chemically inert in almost all environments

Thermal conductivity

Unlike most electrical insulators, diamond is a good conductor of heat because of the strong covalent bonding and low phonon scattering. Thermal conductivity of natural diamond was measured to be about 2200 W/(m·K), which is five times more than copper.

Mono-crystalline synthetic diamond enriched to 99.9% the isotope 12C has the highest thermal conductivity of any known solid at room temperature: 3320 W/(m·K) (7 -8 times copper {401 W/(m·K). Because diamond has such high thermal conductance it is already used in semiconductor manufacture to prevent silicon and other semiconducting materials from overheating. At lower temperatures conductivity becomes even better, and reaches 41000 W/(m·K) at 104 K (12C-enriched diamond).

Electrochemistry

Diamond coated electrodes made electric conductive by Boron doping show outstanding qualities and make some electro chemical processes possible at all .

In electrochemistry electrodes are widely used for synthesis and decomposition of various substances. The broader the electro-chemical window is, the more efficient is the electrode material. Platinum has a large electro-chemical window however it is very expensive. In comparison electrodes with crystalline diamond have a much broader electro-chemical window and none of the costs of platinum.

Heger Diamond can provide diamond electrodes on different substrates (Niobium, Titanium, Silicon) Because our different coating setup (horizontal and vertical) we are able to coat very different geometries (sheets, expanded metal, 3D structures). We can produce electrodes in almost any size.

Diamond electrodes for waste water Treatment

Due to their high oxygen evolution over-potential in aqueous solutions the production of strong oxidants is possible without the addition of any chemicals like in the Fenton process. Due to this, the waste water treatment is environmentally friendly and easily scalable by adjusting the required electric power only. Diamond electrodes have very good corrosion stability in aggressive medias.

The principle of electro-chemical waste water treatment

If standard waste water cleaning techniques are insufficient, oxidizing technologies are used. Such oxidation mineralizes the organic waste by agents like ozone and hydrogen peroxide which must be added to the waste water.

Diamond in comparison to other electrode materials has a very high over-potential for the electrolysis of water.  As a result, diamond can produce very strong oxidizing hydroxyl radicals (OH-Radicals) directly in water at a high current efficiency. The current density potential graph of diamond in comparison to platinum is shown above. Organic waste is reduced to CO2 and water.

Heger Diamond Electrolyzers can effectively clean and disinfect waste water from germs, dyes, cyanide’s, oils, hormone and other  organic waste (see picture below). Disinfection of drinking water with OH radicals and Ozone to kill viruses, legionella and bacteria is also possible.

Strong oxidizing agents like peroxo compounds can be synthesized on diamond electrodes.