Conventionally, gradients in material compositions are introduced either (1) axially, by fusing together multiple layers containing uniform composition, or (2) radially, by diffusing species (typically small, fast diffusing ions) into or out of rod-shaped silica sol-gels or solids at elevated temperatures. Unfortunately, diffusion-based gradients are limited to symmetric, parabolic profiles and have maximum achievable diameters (in the case of gradient refractive index lenses) of ~20 mm, with most commercial versions being <2 mm in diameter. Introduction of larger, slower diffusing species proves challenging.
LLNL technology uses Direct Ink Writing (DIW) additive manufacturing to introduce the composition gradient into an amorphous, low density form (LDF), which is then heat treated to transparency as a whole structure, thus reducing edge effects.
LLNL researchers have developed a method for fabricating active or passive optical glass components, non-optical glass components, and/or glass sensors with custom material composition profiles in 1-, 2-, or 3-dimensions. In this method, DIW additive manufacturing technique is used to print filaments of a rheologically-tuned ink--containing a glass forming species--into a loosely bound, amorphous, low density form (LDF), analogous to a green body in ceramics. DIW inks of different compositions may be blended inline at the print nozzle to achieve the desired material composition at the desired location within the LDF. Once the LDF (e.g. monolith, film, or freeform) has been completely formed, the part is dried to remove residual organics and heat treated to form a transparent glass. The resultant glass part retains the compositional variation that was imparted during printing, and it can be further processed to achieve the desired surface figure, surface flatness, or surface quality via grinding and polishing.
Livermore’s DIW-printed invention enables:
- The formation of optical or non-optical glass with custom composition profiles that are not achievable by conventional glass processing techniques.
- The introduction of species that cannot be introduced easily by diffusion methods.
- The creation of glass optics containing custom patterned material properties that are far larger than those achievable by diffusion methods.
LLNL DIW printing technique can be used to make active or passive optical glass components (e.g. lenses, corrector plates, windows, screens, collectors, waveguides, mirror blanks, sensors, etc.) with specialized compositions and material properties for both commercial or government applications. This technique can be used to introduce ions, molecules, or particles in arbitrary (i.e. custom) locations within the glass components (monoliths, films, or free forms) to achieve spatially varying material properties within the glass, including: absorptivity, transmission, refractive index, dispersion, scatter, electrical conductivity, thermal conductivity, thermal expansion, gain coefficient, glass transition temperature (Tg), melting point, photoemission, fluorescence, chemical reactivity (e.g. etch rate) and density/porosity.
LLNL has filed a patent application for its Direct Ink Writing Printed Gradient Composition Glass method that has been reduced to practice.
Additional references for technology background and context of this invention:
- Silica glass with tailored refractive index profile using direct-ink-write additive manufacturing(abstract LLNL-ABS-706878 and presentation LLNL-PRES-731470))
- 3D Printed Transparent Glass (D. T. Nguyen, et al., Adv. Mater. 2017, 29, 1701181.) DOI: 10.1002/adma.201701181
- A method for preparing optical glass components with custom-tailored composition profiles(LLNL-ABS-685161)
- Optical Materials and Components by Additive Manufacturing: Gradient index (GRIN) glass (poster LLNL-POST-709144)
- Rheological Characterization of Colloidal Silica Suspensions for 3D Printing of Optical Glass Monoliths (presentation LLNL-PRES-723093)
- Novel sol-gel derived SiO2-TiO2 particle systems for direct ink writing compositionally tailored GRIN glasses (presentation LLNL-PRES-728230)