CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No.

62/322,864 filed April 15, 2016 the entire disclosure of which is hereby incorporated by reference herein.

TECHNICAL FIELD

[0002] The present disclosure relates to materials that could seamlessly transition from opaque to transparent or translucent, such as engineered advance-ceramics transitioning to glass to create a single structure. The opaque materials are advanced ceramics (specifically the two presented here are: geopolymer ceramic and/or glass-foam ceramic). These advanced ceramics can be directly and seamlessly bonded to a translucent or transparent dense glass without the use of an intermediate adhesive or use of a frame. That is, an opaque advanced ceramic structure can include an integrated transparent glass window, as the two can be bonded directly and seamlessly and without any frames, mechanical joints, connective tissue or adhesives such as caulking or epoxy. Such advanced ceramic-glass structure can be prepared by sintering a geopolymer or a glass-foam with a transparent or translucent glass to form a single component in which the interface is visually abrupt or in which the interface is a graded composition with the desired gradient properties from one material to the other.

BACKGROUND

[0003] Airtight and watertight seams or interfaces between two disparate materials are desirable when constructing a variety of structures for applications in architecture, building construction, industrial design, aerospace and in the arts, etc.

[0004] Each field has different reasons for airtight and watertight seams or interfaces between disparate materials. For example, in architectural applications there is a desire to eliminate frames around non-operable windows to avoid a thermal bridge; there is also a desire to create functionally graded materials, structures, and building components (i.e. to have greater strength, density, added thermal, acoustical insulation where needed and avoid waste); for building construction there is a desire for such materials while simplifying the wasteful and imprecise conventions and to promote an impermeable seal; and in industrial design such materials are desired where precision and reliability of a seal between materials are required such as in a range of products from biomedical devices, implants, or prosthetics at a variety of scales to everyday products.

[0005] Current solutions for installing a window in a building typically use a metal frame to mechanically fasten glass inside a masonry wall, requiring an array of smaller or compound joints to deal with a number of functional requirements to create the necessary thermal, fluid, vapor, and acoustical barriers and insulating layers, each introducing added complexity, involving numerous building trades, and added costs of materials and labor.

[0006] Great efforts have gone into developing multi-pane thermo-acoustic window assemblies to create framed airtight chambers with a vacuum or gas infill to improve thermal and acoustic capacity. These systems require an array of complex components that may snap together or require other types of mechanical joints. To prevent penetration/passage of wind and rain complex window structures are designed composed of inner and outer windows, as well as multiple frames (for example an outer frame forming the opening and a window frame attached to the glass) and multiple casings that need to be joined. They need to accommodate draining spaces and valves, devices to block wind and rain to penetrate and to flow backward into the assembly. See, e.g., U.S. patent publication number 6209269 Bl, U.S. patent publication number 7637058 B2, etc.

[0007] In addition, the inner frame should be installed inside the outer frame in the field, requiring precision of the fit between the frames, added labor and cost in the production, installation, and any future services and repairs due to the deterioration of parts/components- which can also greatly affect environmental performance.

[0008] In addition, work involving joining glass and ceramic or making composites has been disclosed. For example U.S. Patent Nos. 2,149,133 A (to Leculr) and 2,227,770 (to Ungewiss) describe joining glass to porous ceramic materials using a weld or fusing glass onto ceramic. U.S. Patent No 6,532,769 Bl (to Meinhardt et al.) discloses a glass-ceramic compound and method to join or seal ceramic components together or to metal components which are useful for joining electrochemical cells; U.S. Patent No 7,695,560 (to Macedo) discloses a lower density composite concrete made up of cementitious materials (including cement, sand and fly ash) and foam glass aggregate which is lighter than traditional concrete but mostly can be used as structural support including support panels and flooring or where low density concrete is needed such as high rise buildings. U.S. Patent No 8,999,869 (to Goedeke) discloses a low temperature process to provide glass-ceramic joining but more specifically used for fuel or electrolysis cells.

[0009] However, there is a continuing need to make possible airtight and watertight interfaces between materials and components without compromising the functional requirements that they satisfy (e.g. structural or thermal functional requirements).

SUMMARY OF THE DISCLOSURE

[0010] Advantages of the present disclosure are materials that seamlessly transition from opaque to translucent or transparent, such as functionally graded materials. Such materials are useful as monocoque architectural components (like wall panels) or building fragments with integrated non-operable windows. Such seamless materials are also useful in equipment, vessels, and systems, where high strength and lightweight are needed for example in the inner non-load- bearing skin of structures used in extreme conditions, air/space crafts, and water vessels, among other.

[0011] These and other advantages are satisfied, at least in part, by materials that seamlessly transitions from an opaque material to a transparent material. Such materials can comprise an advanced ceramic derived from a geopolymer or similar alkali activated binders, seamlessly bound to a glass. Other of such materials can comprise a glass-foam seamlessly bound to a dense glass. Geopolymer to glass foam is also contemplated in the present disclosure. Advantageously, glass foam can act as additional insulation if sandwiched inside layers of geopolymer derived ceramic.

[0012] In practicing aspects of the present disclosure, the geopolymer is produced from metakaolin, a derivative thereof, or fly ash. .The geopolymer can be adjusted to have a coefficient of thermal expansion that matches a coefficient of thermal expansion of the dense glass. The glass can be transparent or translucent. The transition from the opaque material to the transparent material can be abrupt or graded.

[0013] Another aspect of the present disclosure includes processes of producing materials that seamlessly transitions from a composite opaque material to a translucent or transparent material. Such processes include contacting a geopolymer composite of glass or glass powder or foam and heating the composite to form a gradual transition of the opaque material to the transparent material to produce, after the sintering, a sintered functionally graded material, with varying degrees of compressive strength, thermal insulation and optical properties.

[0014] Another such process includes heating to sinter an assembly of a composite, e.g., glass powder and foaming agents to glass along a gradient to form a glass-foam seamlessly bound to a dense glass. In some embodiments thereof, prior to sintering the glass powder, foaming agents and glass chips are composed to form a gradual transition of the opaque layer to the transparent layer to produce, after the sintering, a sintered functionally graded material.

[0015] Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent similar elements throughout and wherein:

[0017] Figure 1 is a picture of an advanced ceramic (derived from geopolymer) to glass structures in which a metakaolin-based geopolymer ceramic is directly and seamlessly bonded to a translucent glass in accordance with an embodiment of the present disclosure.

[0018] Figure 2 is a plot of an XRD analysis of a starting metakaolin (MK) and GP fired at 850°C. The data confirm that firing the GP at 850°C leads to an amorphous phase compatibile with glass.

[0019] Figures 3 A and 3B are SEM images showing a seamless transition from a dense glass (on top) layer to a metakaoline-based geopolymer ceramic of a functionally graded material prepared according to an embodiment of the present disclosure. Although the geopolymer can be porous if set at room temperature, in this example it has transformed into a sintered ceramic body with closed porosity because it was heated to above 600 °C. [0020] Figure 4 schematically illustrates a strategy for forming a graded transition from transparent glass (bottom) to an opaque glass-foam (top) structure. Such a material can be formed by firing an assembly of glass chips on the bottom to create a transparent glass layer, then glass chips mixed with glass powder to create a translucent layer, then glass powder to create an opaque layer, and then on the very top a mixture of glass powder and foaming agent that will result in an opaque, glass-foam layer after firing.

[0021] Figure 5 is an SEM image of gradient structure of a porous glass-foam (far left) to a dense glass (far right) prepared according to an embodiment of the present invention.

[0022] Figure 6A and 6B are pictures of a glass-foam to glass structure in which the glass-foam is seamlessly transitioned to a transparent glass in accordance with another embodiment of the present disclosure.

[0023] Figure 7 illustrates a process for forming a graded material transiting from transparent glass (top) to an opaque composition of Fly Ash based geopolymer (bottom), and a 21 -layer column of functionally graded material

[0024] Figure 8 shows a 5-layer column of functionally graded material made of iron- free glass powder, geopolymer and glass chips, (the glass chip layer was exposed to the air (top layer)).

[0025] Figure 9 shows a 6-layer column of functionally graded material made of soda- lime glass and geopolymer and the glass chip layer exposed to the air (top layer).

[0026] Figure 10 shows a 5-layer column of functionally graded material made of soda- lime glass and geopolymer and the glass chip layer exposed to the air (top layer).

DETAILED DESCRIPTION OF THE DISCLOSURE

[0027] The present disclosure relates to two or more materials that seamlessly transition from opaque to transparent or translucent. The opaque materials can be an advanced ceramic derived from a (Metakaoline, slag, or Fly Ash)-based geopolymer or from glass-foam or a composite thereof. The transparent or translucent material is glass. Advantageously, the opaque material can be bonded to the translucent or transparent glass without the use of an intermediate adhesive or use of a frame. That is, a ceramic to glass structure can be bonded directly and seamlessly and without any mechanical joints, connective tissue or adhesives such as caulking or epoxy. Such materials can be prepared to form a visually abrupt joint or a graded composition with the desired rate of growth from one material to the other. For example, to form a functionally graded material, the ingredients can be organized/composed to result in a gradual transition (for example in a linear sequence) to produce a functionally graded material (as in Figure 7 and 8).

[0028] The functionally graded materials and seamless joint between disparate materials of the present disclosure can eliminate a vast number of static joints (mechanical and chemical) in a building without undermining functional requirements. The functionally graded materials of the present disclosure permit seamless and direct transition from opaque to glass structures in a wall, where skylight is placed on a roof, and the simplification of details between wall and roof condition. Such joints reduce heat loss and thermal-bridge around windows and overall through the building envelope. Such materials and joints can also be advantageously included in equipment, vessels, and systems, where high strength and light weight are needed; also building in harsh weather where impermeability between and through surface materials are required and allow for a more sustainable practice in production processes and in building performance (i.e.: less embodied and operational energy). The use of this technology will also facilitate streamlining production and use of geopolymer composites in the building industry, where multiple advantages of geopolymer cement over "Portland Cement" are most obvious.

[0029] Advantageously, the ceramic to glass materials of the present disclosure can have a flexural strength of no less than about 21MPa, an approximate compression strength of no less than about SOMPa, an elastic modulus of no less than about 17 GPa, or any combination or subcombination thereof. Our experiments show that the strength at the interface between the geopolymer derived ceramic to glass or glass-foam to dense glass is strong. When failure of the material occurs, it does not occur at the interface of the opaque to glass transition.

[0030] The opaque to transparent or translucent materials of the present disclosure make possible an airtight and watertight transition between the two disparate materials. Such joints are useful in creating structures for harsh conditions (terrestrial shelters as well as outer-space habitats, aerospace engineering, the arts, industrial design, and particularly architecture, permitting novel construction details, spatial conditions, surface conditions, and insulation against sound, water, moisture, gases, or air.

[0031] In an aspect of the present disclosure, a ceramic to glass structure comprises a ceramic derived from a geopolymer. G copolymers (GP) are cementitious materials that can replace Portland cement with many advantages. GP concrete has higher compressive strength than regular concrete, faster curing times, and no significant shrinkage. It is not as permeable as regular concrete, resists freezing, is fire resistant and more stable even in high temperatures of 1200°C (2200F), is chemical resistant, is less brittle, and is not likely to corrode. Useful geopolymer for the present disclosure include inorganic aluminosilicates such as poly(sialate- disiloxo) type Additional geopolymers as disclosed by Davidovits et al., Geoploymer Tooling Material, SAMPLE 1991, 36(2), 1939-1949, can also be employed. Also an alkali-activated binder (AAB) material can be used as the opaque material in the present disclosure. Such materials form through a chemical reaction between the high alkaline solution (mostly sodium silicate solution) and aluminosilicate source powders such as slag and fly ash. The resultant product of AAB is similar to geopolymer. Different AABs have been exemplified in the Examples including alkali activated fly ash (AAF), alkali-activated slag (AAS) or binary of fly ash and slag (AAFS). Alkali activators include solutions of Li, Na or K hydroxides and Li, Na or K silicates.

[0032] Any glass can be used in the ceramic-glass joints of the present disclosure including translucent or transparent glass panels typically use for building materials, for example silica-soda-lime, alumino-silicate or borosilicate glasses. Typically the glass is made of silicon dioxide and other oxides (Na, K, Ca, Li, B, Al) and has a coefficient of thermal expansion of between about 4 and 10 ppm, and has a density of between 2.2 and 2.6 g/cm ³ .

[0033] In an aspect of the present disclosure, the coefficient of thermal expansion (CTE) of the geopolymer or similar material is adjusted to match the CTE of the particular glass used to form the ceramic-glass joint. Matching the CTE of the ceramic and glass advantageously reduces or eliminates stress and cracking at the interface. The CTE of the geopolymer can be adjusted by adjusting the alkali (e.g., potassium) content of the geopolymer as well as by the addition of suitable additives in particulate form.

[0034] The ceramic derived from geopolymer can be seamlessly interfaced with dense glass, e.g. translucent or transparent glass, creating both structural and optical continuity. For example, the ceramic to glass structure can be prepared by placing a translucent or transparent glass in contact with a geopolymer in monolithic or powder form and heating to form the ceramic to glass structure. The geopolymer component can be employed in an as-produced form (material synthesized at room temperature or < 100°C), or after firing it at a temperature higher than 400°C, or as a mixture of fired and unfiled geopolymer. This process converts the geopolymer to a ceramic material, improving its mechanical-physical properties. G copolymers of the present disclosure can be cost effective and safe to make and also an excellent substitution for Portland Cement, which not only has significant drawback associated with its production, but its strength is significantly decreased in case of fire.

[0035] The ceramic to glass structures of the present disclosure makes possible an airtight and watertight transition between the two disparate materials by bonding them at temperatures higher than 600°C (in our experiments 850°C to allow glass to soften effectively) making possible an integrated glass window, exhibiting multiple optical characteristics across a single plane.

[0036] For example, geopolymers fired at T> 600°C have low thermal conductivity and are lightweight due to their closed porosity. Further, both dense and porous geopolymers can be obtained at room temperature and successively transformed to ceramic materials after firing. Geopolymers present low thermal conductivity and are lightweight due to their high closed porosity. Glass-ceramics (ceramics made through the controlled crystallization of a glass) can also serve as the ceramic in this application.

[0037] In addition, ceramic derived geopolymers are refractory and can be used where there is a need for insulation in proximity to high heat such as fireplaces, in replacement for asbestos, concrete and bricks. The seamless bonding of such materials is useful in equipment, vessels, and systems, where high strength and lightweight are needed for example in the inner non-load-bearing skin of structures used in extreme conditions, air/space crafts, and water vessels. In the construction industry, panels or monocoque components made of geopolymers can be sandwiched and bonded between thin layers of glass for added stiffness and strength, to serve as cladding in addition to their inherent insulating value.

[0038] An additional advantage to an aspect of the present disclosure is the use of environmentally friendly materials (such as recycled glass,) and process (bonding GP to glass.)

[0039] Another aspect of the present disclosure includes an opaque to transparent structure prepared as a glass-foam to dense glass structure. The glass-foam component can be seamlessly interfaced with the dense glass, e.g. translucent or transparent glass, creating both structural and optical continuity. For example, a transition from an opaque glass-foam to transparent glass layer can be formed by a compositional gradient of glass chips which are progressively mixed with fine glass powder. Figure 4 illustrates such a compositional gradient and the result of firing such a composition. Alternatively, a transition from an opaque glass- foam to transparent glass layer can be formed by kiln forming techniques, where a mixture of glass powder and foaming agent is placed adjacent to a piece of soda-lime window glass and fired at 850 °C.

[0040] In an embodiment of the present disclosure, a glass-foam seamlessly bound to a dense glass can be prepared by heating/firing an assembly of glass foaming agents and glass along a gradient. For example, heating/firing an assembly including: (i) a mixture of glass powder and foaming agent to form an opaque layer, (ii) an optional composition of glass chips mixed with glass powder to form an optional translucent layer, and (ii) glass chips to form a transparent layer, can form the glass-foam to a dense glass structure wherein the glass-foam is directly and seamlessly bound to the dense glass.

[0041] By processes disclosed herein, two or more disparate materials can be united, achieving seamless and/or sequential growth from one to the other. In particular, sintering or casting transparent glass with an advanced ceramic derived from geopolymer can be used to make the ceramic to glass structures. In addition, the coefficient of thermal expansion of the geopolymer can adjusted to match the coefficient of thermal expansion of the particular glass used in forming the ceramic-glass joint to develop a strong interface.

EXAMPLES

[0042] The following examples are intended to further illustrate certain preferred embodiments of the invention and are not limiting in nature. Those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific substances and procedures described herein.

[0043] Examples of GP bound directly to glass

[0044] Production of GP: Starting materials for the production of GPs were Metapor®

(provided by Poraver) and the potassium silicate ASIL6® (12.7 wt K20, 26.5 wt% Si02, 60.8 wt H2O) (provided by PQ Corporation). Metapor®, an industrially available metakaolin, was used by calcining the metakaolin in an interval comprised between 800 and 850°C and then mixed with foam glass powders of Poraver®. Although this example employed Metapor® and Poraver®, other metakaolins and sodium potassium silicates could be used with appropriate adjustments to prepare the GPs.

[0045] Starting materials were dissolved by lithium metaborate fusion and run on a

Perkin-Elmer Optima 5300 ICP (inductively coupled plasma emission spectrometer), rock standards were used to calibrate the results. The chemical analysis is reported in Table 1.

* Oxide composition of the dehydrated GP was calculated from the chemical composition of the MK and Ksil.

[0046] Preliminary investigations were performed to obtain GPs having the same coefficient of thermal expansion (CTE) as soda lime glass after firing at 850°C. Control of the CTE was obtained by preparing GPs pastes with a fixed amount of metakaolin (MK) and mixing different alkali activating solutions of potassium silicate (KSil). The percentage of alkalis in an amorphous aluminosilicate matrix was used to tailor the CTE, with the understanding that by increasing the potassium (i.e. alkali) content the CTE increases.

[0047] To produce the GP pastes, the activating solution was stirred with a hand mixer and the metakaolin powders were slowly added for 15 minutes to form a homogeneous paste. The pastes were then poured in plastic containers and cured in closed boxes to prevent moisture evaporation. After curing, chips of soda lime glass (SLG) were placed on top of the cured pastes and fired at 850°C for 60 min applying a 10°C/min heating rate to ceramize the geopolymer in contact with the molten glass.

[0048] Samples were cooled at 5°C/min and annealed at 570°C for 60 min, then the temperature was decreased at l°C/min to room temperature. The fired samples were first examined using a stereomicroscope until a composition exhibiting no cracks was found. Successively the CTE was controlled using a dilatometer, verifying a good match between the two materials with no cracks formation as determined by scanning electron microscopy (SEM FEI Nova NanoSEM 630 FESEM). [0049] After the preliminary experiments an optimal composition was found to be 100 g of KSil with 112.5 g of MK which was prepared by placing the Sil in a container with about 5 wt.% of water with stirring to decrease the viscosity of the solution, successively 112.5 g of MK were slowly added forming a homogeneous paste.

[0050] To investigate the mechanical properties of the interface between glass and the ceramized GPs, the GP was dehydrated at 200°C for 60 ruin and then ground to particles below 200 μιη. The preliminary dehydration of the powders limits the shrinkage and associated development of cracks after firing. Suitable temperatures for the dehydration range from 100 to 300°C, and dehydration times of lh or more are suitable. Heating and cooling rates can be selected in a wide range of values, as they do not affect significantly the dehydration process. Particles could be ground to other sizes as well (e.g. 10 micron to 1 mm), depending on the specific characteristics that are desired in the final component and application (e.g. density, total porosity, pore morphology of fired GP). The powders were placed in a ceramic mold (5x5 cm ² ) and hand pressed in contact with a soda lime glass slab and fired at the desired temperature (the desired firing temperature is in the range 600 to 900°C, depending on the type of glass employed). Heating rates of 2 to 10°C/min can be applied, and firing times can range from 0.5 to a few hours. By this process, a ceramic derived from the GP component was seamlessly and directly bound to the glass creating both a structurally and optically continuous ceramic-glass joint. See Figure 1.

[0051] The integration and mechanical properties of the ceramic-glass structure was then investigated. In this regard, Four-point bending tests (40 mm outer span and 20 mm inner span) were performed using an Instron 5866 (Instron, Dan vers, MA) on 10 specimens with dimensions of 3 x 6 x 50 mm ³ . In order to remove surface flaws, all samples were carefully polished to a 6 um finish before testing, using abrasive papers and diamond paste. The edges of the bars were beveled using fine abrasive papers and diamond paste. The cross-head speed was 1 mm/min until fracture.

[0052] The geopolymers and derived ceramics were also tested. For example, the geoploymer powders were subjected to simultaneous DSC-TGA (SDT Q600, TA Instruments, New Castle, DE) on alumina crucibles at 10°C/min in 100 ml/min air flow. The morphological features of sintered samples were characterized by scanning electron microscopy. The crystalline phase assemblage was investigated on powdered samples by X-ray diffraction (Bruker D8 Advance, Karlsruhe, Germany), employing Cu a radiation (0.15418 nm), with data being collected in the range 2Θ = 10-60 (in 0.05° steps, with a 3 s counting time). Water absorption, WAB, and apparent density, were determined according to the UNI EN ISO 10545-3 standard protocol. The bulk density, was obtained by considering the mass to volume ratio for 5

selected samples. The density of the solid, or true density, was evaluated by means of helium gas pycnometry (Micromeritics AccuPyc 1330, Norcross, GA), on powders sieved below 63 um. The three density values (pa, pb and pt) were used to compute the amounts of open and closed porosity.

[0053] Table 2 summarizes the mechanical properties of the fired GP samples (100% geopolymer) and GP to glass samples (GP joined to glass). Firing the GP forms a lightweight ceramic, showing a total porosity of 42.6% that was present mostly as closed cells as demonstrated by the very low water absorption (0.7%). Furthermore, the bending and compressive strengths were evaluated to be about 21 MPa and 50 MPa, respectively.

[0054] Table 2 Characterization data for samples being flexural strength, compression strength, elastic modulus, bulk density, p _a apparent density, pt true density, relative density, compression strength, OP open porosity, CP closed porosity, and TP total porosity. GP=sample made only of fired GP powder; GP-SG=sample made of fired GP powder joined to glass.

[0055] It was further observed that the ceramic-glass joint samples cracked always in the ceramic layer and never at the ceramic-glass interface, thus confirming a maximal integration between the two layers.

[0056] Figure 2 is a plot of an XRD analysis showing quartz, metakaolin and limited unidentified trace crystal phases present in the starting metakaolin. The broad band of the XRD pattern of the GP fired at 850°C suggests the formation of an amorphous ceramic. Comparing the XRD results shows how firing GP to 850 °C results in formation of more amorphous phases shown by broad peak or background hump in Figure 2; however the XRD results of initial MK reveal the existence of more crystalline peaks as Quartz or Metakaolin.

[0057] SEM images, as shown in Figures 3A and 3B, demonstrate a seamless transition from a dense glass layer to a porous ceramic derived from the GP for the prepared ceramic to glass structures. The control of the CTE provided a good match between glass and ceramic derived GP which is evidenced by a total absence of micro cracks at the interface.

[0058] While the foregoing examples employed Metapor® and Poraver® to prepare geopolymers, the geopolymer can be obtained with different metakaolins and/or different combinations of alkali silicates in order to match the CTE of soda lime glass. Moreover different types of glass can be used in alterative to soda lime glass.

[0059] Example of glass-foam to dense glass structure

[0060] A transition between a dense, transparent glass to a glass-foam can be made according to the present disclosure in multiple ways, i.e. casting a composition with a gradient of glass chips, glass powder and foaming agents to create an interface between glass and GF using different thickness of glass, as well as by kiln forming techniques, where a mixture of glass powder and foaming agent is placed adjacent to a piece of soda-lime window glass and fired at 850 °C.

[0061] For example, a transition from a transparent glass layer to an opaque glass-foam suitable for applications in architecture can be formed by a compositional gradient of glass chips which are progressively mixed with fine glass powder. Figure 4 illustrates such a compositional gradient and the result of firing such a composition. For example, when firing at 850°C the glass chips form a transparent layer, whereas the glass powders act as an opacifier. The structural gradient is realized mixing the glass powder with a progressively increased amount of foaming agent. During firing the glass will sinter and bloat as an effect of the thermal decomposition of the foaming agent.

[0062] Glass-foams were manufactured by pouring, in a mold, a mixture of glass powder with 1-2 wt.% of silicon carbide (SiC), a typical foaming agent. Heating the mixture until 850°C caused the glass to soften with viscous flow sintering and SiC oxidation. The reaction products of SiC with environmental oxygen are Si0 ₂ and CO/C0 ₂ gases that bloated the glass during sintering. As a result of firing, a grey pumice like foam was obtained. [0063] The interface between glass and GF for structures prepared in this experiment was studied through Scanning Electron Microscopy (SEM), no cracks were observed and a maximal match between the two layers was obtained. As provided in Figure 5, an SEM image shows a progressive transition from glass-foam (on the left) to translucent glass (in the middle) and finally to dense transparent glass (on the far right).

[0064] In an alternative process of forming a glass to glass-foam structure, a mixture of glass powder and foaming agent is placed adjacent to a piece of soda-lime window glass and fired at 850 °C. Figure 6A and 6B show pictures of such a structure. As shown in the figures, a sharp transition from glass-foam to dense glass can be obtained by firing a glass slab in contact with a mixture of glass powder mixed with foaming agent.

[0065] Example of functionally graded material using alkali activated binder materials

[0066] Alkali activated binder materials can be used in place of or in addition to geopolymers. For example, the solid materials (precursor) used to make alkali activated binder (AAB) in this study were: a class F fly ash (FA) meeting ASTM C618-15 requirements which is provided by Headwaters Resources in PA, and a grade 100 ground granulated blast furnace slag (GGBFS) meeting ASTM C989M-12. Error! Reference source not found.3 below presents the chemical compositions of FA and GGBFS before activating them with an alkaline solution.

[0067] Three AAB mixtures were designed (Table 4). The mixtures were labeled as:

AAS (representing an alkali activated Slag), AAF (representing an alkali activated Fly ash), AAFS (representing a hybrid binder of 80%(vol) Fly ash and 20%(vol) Slag). To prepare the activator solutions, a commercially available aqueous sodium silicate was mixed at different proportions with sodium hydroxide (NaOH) solution. The commercial aqueous sodium silicate consisted of 18.4% mass Na20, 28.4% Si02, and 53.2% H20, and had pH = 13.7 and specific gravity of 1.60 at 20°C.

[0068] The alkali activated binder materials can be used in place of geopolymers to make functionally graded structures according to the present disclosure.

[0069] Example of functionally graded material

[0070] The schematic diagram in Figure 7 illustrates a process for forming a graded material transiting from transparent glass (top) to an opaque composition of Fly Ash based geopolymer (bottom). The sample for this experiment measured 2 inches by 1 inch by 16 inches and included 21 layers: Staring from the top 100% glass, the ratio of glass drops about 5% in each successive layer (so 95% glass and 5% GP in the second from top layer) down to 5% glass and 95% GP on the very bottom. As such the structural strength on the bottom is higher and the top layer which in this specimen is translucent could be 100% transparent if the firing schedule was adjusted.

[0071] Figures 8, 9 and 10 illustrate how the composition of glass (iron-free glass powder vs. soda-lime glass powder), exposure conditions (which layer is at the very top) and the gradual change of material can affect the final product of functionally-graded materials. Figure 8 shows a 5-layer column of functionally graded material made of iron-free glass powder, geopolymer and glass chips, (the glass chip layer was exposed to the air (top layer)). Figure 9 shows a 6- layer column of functionally graded material made of soda-lime glass and geopolymer and the glass chip layer exposed to the air (top layer). Figure 10 shows a 5-layer column of functionally graded material made of soda-lime glass and geopolymer and the glass chip layer exposed to the air (top layer).

[0072] Example of matching geopolymer and glass coefficient of thermal expansion

[0073] Geopolymer and glass powder together were fused together by being fired and heated up at very high temperatures (up to 850 °C). In order to achieve good bonding between the initial materials at such a high temperature, their coefficients of thermal expansion (CTE) should be close and similar to each other. Previous studies showed that the properties of geopolymer is highly dependent on the properties of alkaline solution (for sodium silicate solution, it includes pH, n-modulus and water content of activating solution). In order to adjust CTE of geopolymer to be close enough to the glass, different solutions have been designed for making geopolymer and CTE of them were measured and compared with CTE of soda-lime glass. In general, the results indicate that CTE of soda-lime glass and geopolymers are close to each other and there is a slight difference between them. The best match has been observed for the geopolymer which is made of the sodium-silicate solution of n=1.60 and pH=13.7 (i.e., 111=0.2, r=1.65).

[0074] While the claimed invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one of ordinary skill in the art that various changes and modifications can be made to the claimed invention without departing from the spirit and scope thereof. Thus, for example, those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific substances and procedures described herein. Such equivalents are considered to be within the scope of this invention, and are covered by the following claims.