Glass-Ceramics

Glass-Ceramics are polycrystalline. They have two phases which are amorphous phase and crystall phase which can produce spontenous re-xtalisation process (which is do not wanted in glass manufacturing), (devitrification).  They can brazing at 700°C and also they have zero porosity, high strength, toughness, translucency or opacity, pigmentation, opalescence, low or even negative thermal expansion, high temperature stability, fluorescence, machinability, ferromagnetism, resorbability or high chemical durability, biocompatibility, bio-activity, ion conductivity, superconductivity, isolation capabilities, low dielectric constant and loss, high resistivity and break down voltage.

In manufacturing glass-ceramic, two phase follows: producing glass and adding nucleation agents during heat treatment to control the re-xtalisation process. Nucleation agents has wide variety systems like Li₂O x Al₂O₃ x nSiO₂-System (LAS-System),  MgO x Al₂O₃ x nSiO₂-System (MAS-System),  ZnO x Al₂O₃ x nSiO₂-System (ZAS-System),etc.[1]

Only specific glass composites suitable for precursors for glass-ceramics. As an example, ordinary window glasses can not crystalise. Glass-Ceramics structure occured by 50vol% to 95vol% crystalline commonly. One or more crystalline phases may form during heat treatment and as their composition is normally different from the precursor, these are named parent. These parents make better specialities to the material such as in LAS-systems, glass ceramics has thermal durability. [2]

References

[1] http://en.wikipedia.org/wiki/Glass-ceramic

[2] GLASS-CERAMICS: THEIR PRODUCTION FROM WASTES. A REVIEW (R. D. Rawlings, J. P. Wu, A. R. Boccaccini)

PAN Fibers (Polyacrylonitrile Fibers) Production Process

Carbon Fiber Production Process (PAN Based)

PAN Fibers (Polyacrylonitrile Fibers) 

              PAN Fibers started to producing in 1950s. It is a synthetic semi crystalline organic resin which has a structure that ( C₃H₃N ). PAN can not melt under normal conditions and this property gives to fiber flameproof characteristic. It is oxidized in air at 230°C and it is carbonized above 1000°C under normal conditions. 

             PAN is also a components repeat unit in some co-polymers (eg. SAN, ABS). Main reason of that is acrylinite which in PAN. Textile PAN is mixture of some co-polymers such as itaconic acid, acrylic acid, methyl acrylate, meth-acrylic acid and vinyl acetate. These acids which are in PAN structure effects reactivity of PAN. 

             PAN fibers can be made by wet, dry or melt-spinning process. Wet process is the most important process and commonly there are two solvents. These are DMF (Dimenthylformamide) and DMA (Dimethylacetamide). PAN Fibers contains at least 85% acrylonitrile.   

 

Stabilization of PAN Fibers

             PAN is needed stabilization process before carbonization because of it is a thermoplastic polymer. Stabilization process is also known as oxidation. It is an important process that determines cost of production and quality of product. Oxidation of PAN happens in approximately at 300°C with the shrinkage level control. PAN Fibers changes their color on this process.

             Best mechanical properties of stabilized PAN Fibers contain 10-14wt% Oxygen and has density of nearly 1.4g/cm³.   

Carbonization of PAN-Ox (Oxidated PAN)

             Carbonization of PAN is shorter process than oxidation. PANs temperature is changed rapidly to 3000°C. This process happens under N₂ atmosphere. This condition is safe for environment.

             In conclusion Oxidation and Carbonization are the most important parts of to determination of characteristic of PAN based carbon fibers.

 Graphitization of PAN fibers

             Carbonized PAN fibers structures are made similar to graphite and crystallography which include grain size and directions is arranged. Most important effect of graphitization is decreasing fibers strength but increasing density, thermal conductivity and Young's modulus.

             

                                  

CARBON FİBER

Carbon Fiber

What is Carbon Fiber 

                Carbon Fibers main components are basically Acrylic fiber, Tar and Nylon. Structure of carbon fiber is 4,5 times lighter than steel in spite of that is 3 times more stabilized.  

Production

               There are two types of carbon fiber production which are different from each other according to using tar or acrylic fiber(PAN). PAN based carbon fibers represents 94% of carbon fiber production in the world. 

PAN based carbon fibers

              There are four main phase of PAN based carbon fiber production which are oxidation, carbonization, surface improvement and coating.

Oxidation: Acrylic fibers temperature is increased up to 300°C in oxidation. Hydrogen which is in acrylic fiber is separated and oxygen is added during heating. This process brings in flameproof to the carbon fiber

Carbonization: In this process acrylic fibers temperature is increased up to 3000°C. In this case materials carbonization level increases to 100% and carbon fiber types be clear according to degree of temperature.

Surface treatment: Acrylic fibers are improved for stick better to resin in electrolytic environment.

Coating: Acrylic fibers are coated with resin and the process is completed.

Starin and Stress

Ductile materials and Brittle materials 

      Ductile
materials are characterized by their ability to yield at normal
temperatures. Brittle materials are
characterized by the fact that rupture occurs without any noticeable
prior change in the rate of elongation.



Yield Point

      The yield point, alternatively called the elastic limit, marks the end of elastic behavior and the beginning of plastic behavior.



Elasticity

      Elasticity is the tendency of solid materials to return to their original shape after being deformed



Plasticity

      Plasticity describes the deformation of a material undergoing non-reversible changes of shape in response to applied forces.

     

Refferences:
[1] http://en.wikipedia.org/wiki/Plasticity_%28physics%29
[2] http://en.wikipedia.org/wiki/Elasticity_%28physics%29
[3] http://global.britannica.com/EBchecked/topic/653244/yield-point
[4] http://en.wikipedia.org/wiki/Stress%E2%80%93strain_curve