Anodizing is an electrolytic passivation process which is used to increase the thickness of the natural oxide layer on the surface of metal parts. === Applications of Anodizing <ref>https://en.wikipedia.org/wiki/Anodizing</ref> ===* Anodizing It increases resistance to wear and corrosion and wear, and provides better adhesion for paint primers and glues than bare metal does.* Anodic films can also be used for a number of cosmetic effects, through either with of the following:** thick porous coatings that can absorb dyes or with ** thin transparent coatings that which add interference effects to reflected light.* Anodizing It is also used to prevent galling of threaded components.

=== Why Anodize? <ref name = "ref2">http://oatao.univ-toulouse.fr/2628/1/Mabru_2628.pdf</ref> ===[[File:AnodizedPlateAnodizedPanel.jpg|thumb| Black Anodized PlatePanel used in Pratham Satellite]][[File:UnAnodizedPanel.jpg|thumb|A Panel which isn't anodized]]Black inorganic anodized aluminium alloys are used for managing [[Passive Thermal Control| passive thermal control ]] on spacecraft and also for avoiding stray light in optical equipment. <br \>Due Thermal regulation of satellites happens primarily due to radiation, since convection is absent, thanks to the vacuum of space. Thus, thermal regulation of satellites is passively managed by radiative exchange between its external surfaces and the environment. Satellite satellite temperatures in a space environment are often passively controlled by choosing materials/surfaces having suitable thermal properties of suitable surfaces, i.e. having convenient solar absorptance (α) and emittance (ε). <br \>The Black coatings have the feature of black coatings is that their α/ε ratio is close very near to one, which allows passive thermal control more effective transferring of equipment by effectively transferring the heat via radiation. <br \>As mentioned in [http://oatao.univ-toulouse.fr/2628/1/Mabru_2628.pdf this paper], "Black anodic films (α > 0.93 ; ε > 0.90) including inorganic dyes are mainly used because of their low cost, their corrosive and wear resistances during storage, as well as the low risk of contaminating the spacecraft’s instruments, especially by outgassing. <br \>The anodic film is developed by electrochemical oxidation of the metal surface, without addition of any substances. From this point of view, the anodic film is not a coating, but a conversion interface tightly bound to the metallic substrate."

----In 2005, an alert from the European Space Agency (ESA) mentioned many cases of particle detachment from black anodic films, supported especially on 2XXX and 7XXX type aluminium alloys, after three thermal cycles. Such particle pollution is very hazardous for the lifetime of the satellite, potentially inducing the disturbance of any optical or mechanical mechanisms.

The anodizing process Anodizing is an electrochemical conversion of the metal surface process and does not involve the addition of external material. That is the reason why Therefore, anodic films are can be considered to be sufficiently adherent for the usual routine/normal applications. The coloured sealed films are studied from the mechanical point of view, before and after thermal cycling. This cycling simulates the space environment, potentially inducing internal stress, cracking and ultimately flaking of the coatings.----A 2005 alert from the European Space Agency (ESA) mentioned many cases of particle detachment from black anodic films, supported especially on 2XXX and 7XXX type aluminium alloys, after three thermal cycles. Such particle pollution is very dangerous for the lifetime of the satellite.<ref name = "ref2" />----

[[File:Cracking.png|thumb]]Due Owing to the difference of different thermal expansion coefficient between coefficients of the anodic film and the substrate, heating induces tensile stresses in the coating that are introduced by heating, which can lead to cracking if the fracture limit is reached.

[[File:Flaking.png|thumb]]The is a major risk for than cracking, when it comes to space applications is not simply the cracking of the surface layer but flaking, because the particles released could settle on cold parts, typically like mirrors, lenses or mechanisms.Then the Damage to satellite 's instruments would be damaged decreasing could result in decrease in the mission’s lifetime. In additionAlso, a high level of flaking could change the thermo-optical properties of the surface could change if the level of flaking is high, affecting thermal control.Flaking is generally observed on parts that had been thermally cycledundergone thermal cycling. The loss of adhesion is revealed , for example on pulling , when you pull off tapes used to fix thermocouples to the surface during thermal cyclesin the Thermo-vacuum test.<ref name = "ref2"/>

[[File:Crazing.png|thumb]]Anodized finishes will craze (crack) when When the aluminum aluminium substrate is deformed in any fashionway, the anodized finish will craze (crack). This happens because due to difference in elasticities: the base aluminum has a marginal small degree of elasticity, while but the anodized coating has virtually no negligible, or practically zero elasticity. When the part is bent, the base aluminum will deflect quite far to an extent without failing, but while the coating cracks immediately upon deflection. <ref>http://www.aacron.com/docs/Crazing%20Caused%20By%20Bending%20and%20Forming%20Operations.pdf</ref> 

In space, satellites are directly lighted by the sun and then pass into the shadow of Earth, causing thousands of thermal cycles during their lifetime(talking of Earth-orbiting satellites here). To simulate the space environment, the ESA Standard recommends performing 100 cycles between -100 and 100°C under vacuum which lasts for 5 minutes minimum and a have a slope of 10°C per minute. These conditions are defined for the general case and for all kinds of materials and equipment (from polymers to electronics).----If you are done reading this page, you can go back to [[Mechanical Subsystem]]