We report a method for fabricating optical quality silica and silica-titania glasses by additive manufacturing, or 3D printing. Key to this success was the combination of sol-gel derived silica and silica-titania colloidal feedstocks, 3D direct ink writing (DIW) technology, and conventional glass thermal processing methods. Printable silica and silica-titania sol inks were prepared directly from molecular precursors by a simple one-pot method, which was optimized to yield viscous, shear-thinning colloidal suspensions with tuned rheology ideal for DIW. After printing, the parts were dried and sintered under optimized thermal conditions to ensure complete organic removal and uniform densification without crystallization.Characterizations of the 3D-printed pure silica and silica-titania glasses show that they are This article is protected by copyright. All rights reserved. 2 equivalent to commercial optical fused silica (Corning ® 7980) and silica-titania glasses (Corning ULE ® 7972). More specifically, they exhibit comparable chemical composition, SiO 2 network structure, refractive index, dispersion, optical transmission, and coefficient of thermal expansion. 3D printed silica and silica-titania glasses also exhibited comparable polished surface roughness and meet refractive index homogeneity standards within range of commercial optical grade glasses. This method establishes 3D printing as a viable tool to create optical glasses with compositional and geometric configurations that are inaccessible by conventional optical fabrication methods. † denotes value determined by LA-ICP-MS; a-SiO 2 used to represent amorphous SiO 2

molding have been demonstrated for fabricating complex glass structures. [11][12][13][14][15][16][17][18] However, there are limitations to these methods. In binder jetting, the sintered glasses can be fragile and appear opaque due to incomplete densification. Methods to print glass directly (e.g., fused deposition or filament feed) require high temperatures to melt the silica feedstock, resulting in filaments that are potentially vulnerable to thermal stresses and unable to completely merge into the desired structure, which may limit the printing speed and resolution of the printed parts. Soft replication molding cannot be used to produce gap-spanning features, and pseudo-3D objects (i.e., stacked assemblies of thin molded sheets) can only be formed by precisely aligning layers that must then be bonded during heat treatment. None of these methods have been shown to produce glasses that are simultaneously transparent, free form, and 3D with sub-millimeter features.We have developed a two-part process (forming and sintering) which uses direct ink writing (DIW) for the 3D printing of optically transparent glass structures with sub-millimeter features. DIW is a layer-by-layer assembly technique in which shear-thinning inks are extruded through a nozzle in a programmable pattern, upon which the inks rapidly solidify via gelation, evaporation, or temperature-induced phase change. [19] DIW has been used in a wide range of applications such as polymeric optical wave guides, complex scaffolds, 3D periodic graphene aerogels, and self-healing materials. [6,[20][21][22][23][24] Our process first relies on DIW printing of colloidal silica suspensions to form silica green bodies (porous, low density structures) of the desired shape. A key feature of this process is the ability to control yield stress and shear thinning to obtain ink properties best suited for specific applications of the printed glass. Second, the printed structures are dried and heated to temperatures below the melting point of silica to sinter the green body into a fully dense, amorphous, transparent solid structure (Figure 1). In contrast to direct 3D printing of molten glass, this two-step approach does not require high temperatures during printing and allows for higher resolution features, due to both the ability to extrude thinner filaments and the shrinkage that occurs during the densification stage.The critical challenges in formulating a suitable ink for formation of the silica green bodies toward glass structures are: i) the ink must possess the desired rheological behavior for printing and shape retention, and ii) the ink must be able to dry without cracking while still maintaining open porosity that Silica inks are developed, which may be 3D printed and thermally processed to produce optically transparent glass structures with sub-millimeter features in forms ranging from scaffolds to monoliths. The inks are composed of silica powder suspended in a liquid and are printed using direct ink writing. The printed structures are then dried and sintered ...

In light of COVID-19 in spring 2020, we developed a simple and versatile inquiry-based, laboratory-style active learning colorimetry experiment amenable to at-home quantitative analysis. In this experiment, students acquire an external calibration method using aqueous solutions of a self-selected chromophoric analyte from household products using a smartphone camera and RGB image analysis. We report typical student-obtained results for a 5point external calibration method using RGB image analysis and solutions prepared with green food colorant and blue food colorant. Solutions were prepared using common kitchen measuring tools, glass drinking cups served as sample cells or cuvettes, images were acquired with a smartphone camera, and image analyses were conducted using RGB analysis software. Results show analytical data can be readily obtained for both colorimetric and absorbance-based analyses. Experientially, results show that throughout method development students are challenged with various quantitative analysis learning objectives, including basic concepts about light−matter interactions, analytical solution preparation, chemical concentrations, unit analysis, significant figures, statistical analysis, and analytical figures of merit (i.e., method robustness, linearity, and sensitivity, etc.). Furthermore, by bringing chemistry into the home, students are challenged to be creative and access a wide range of problem-solving and critical thinking skills, some of which may not be exercised in traditional laboratory experiments and projects.

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Direct ink writing (DIW) three-dimensional (3D) printing provides a revolutionary approach to fabricating components with gradients in material properties. Herein, we report a method for generating colloidal germania feedstock and germania–silica inks for the production of optical quality germania–silica (GeO2–SiO2) glasses by DIW, making available a new material composition for the development of multimaterial and functionally graded optical quality glasses and ceramics by additive manufacturing. Colloidal germania and silica particles are prepared by a base-catalyzed sol–gel method and converted to printable shear-thinning suspensions with desired viscoelastic properties for DIW. The volatile solvents are then evaporated, and the green bodies are calcined and sintered to produce transparent, crack-free glasses. Chemical and structural evolution of GeO2–SiO2 glasses is confirmed by nuclear magnetic resonance, X-ray diffraction, and Raman spectroscopy. UV–vis transmission and optical homogeneity measurements reveal comparable performance of the 3D printed GeO2–SiO2 glasses to glasses produced using conventional approaches and improved performance over 3D printed TiO2–SiO2 inks. Moreover, because GeO2–SiO2 inks are compatible with DIW technology, they offer exciting options for forming new materials with patterned compositions such as gradients in the refractive index that cannot be achieved with conventional manufacturing approaches.