Glassy carbon as a novel mould material for replicative forming of precision glass optics.
Biplab Kumar Paul and Dipayan Sanyal*
Non-oxide Ceramics and Composite Division, CSIR-Central Glass & Ceramic Research Institute 196, Raja S. C. Mullick Road, Kolkata 700032.
Carbon - Science and Technology 10/4 (2018) 58 - 66.
© Applied Science Innovations Private Limited, India.
Full Text (OPEN ACCESS): CST-318.pdf
Schematic flowchart for aspherical glass lens fabrication using glassy carbon mould. Indications: Tungsten carbide master mould (1); PDMS replication (2); Phenolic mixture (3); Cured resin after carbonization process (4) and Glass precursor (5).
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Raman spectra of glassy carbon.
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Keywords: Phenolic resin, glassy carbon, mould, XRD, FESEM, RS, XPS
Abstract: Replicative forming of precision glass optics has been fast emerging as a rapid, net
shape process chain for mobile camera lenses, CD/DVD pickup lenses, microscope objectives,
night vision lenses, Fresnel lenses and so on. The process involves moulding a glass gob at high
temperatures exceeding the glass transition temperature using a predefined loading and thermal
cycle. Typically, the mould material is required to have high strength, low thermal expansion,
chemical inertness and anti-adhesion properties, especially at high temperatures. Traditional
mould materials, such as, invar or tungsten carbide are difficult to machine which adversely
affects the cost of the entire process. In the present work, glassy carbon mould has been
developed using p-tolune sulfonic acid (PTSA) cured phenolic resin by a process of
carbonization where the composition ratio of phenolic resin and PTSA solution was standardised
accompanied by the pyrolysing conditions. Detailed characterisation of the phase evolution,
surface compositions, morphology and mechanical parameters of the glassy carbon has been
conducted by X-Ray diffraction (XRD) technique, Raman Spectral (RS) analysis, X-ray
Photoelectron Spectroscopy (XPS), Field Emission Scanning Electron microscope (FESEM),
Energy Dispersive Spectroscopy (EDX) and Nanomechanical testing which reveal an optimal
combination of properties of the glassy carbon that makes it an attractive low cost mould
material for replicative forming process chain of glass optics fabrication.
