Abstract
The invention relates to a method for producing a glass-ceramic composite object, and a glass-ceramic composite object produced from at least two starting elements. In the method, respective surfaces of at least two starting elements consisting of the precursor glass of the glass-ceramic material are pressed flat and directly against one another with the application of pressure, and at a temperature at which the ceramisation of the glass-ceramic material takes place they are joined so as to create a monolithic bond between the at least two starting elements.
Claims
1-14. (canceled)
15. A process for producing a glass-ceramic composite body having a coefficient of thermal expansion CTE in a range from 0 to 50 C. of not more than 00.110.sup.6/K, the method comprising: providing at least two starting elements consisting of a green glass of a glass-ceramic; arranging the at least two starting elements and contacting surfaces of the starting elements to be bonded; two-dimensionally pressing the surfaces of the at least two starting elements to be bonded to one another under the action of pressure; and creating a monolithic bond between the at least two starting elements by heating, under the action of pressure, the at least two starting elements pressed to one another to a temperature Tx at which ceramization of the green glass to the glass-ceramic takes place.
16. The process of claim 15, wherein the surfaces of the at least two starting elements to be bonded are provided with a flatness of less than 300 m and/or greater than 20 m.
17. The process of claim 15, further comprising the step of controlled geometric deformation of at least one of the at least two starting elements at a temperature between T.sub.g and T.sub.g+T.sub.s by sagging into a target shape.
18. The process of claim 15, further comprising the step of processing at least one of the at least two starting elements by water-jet cutting, CNC processing and/or sandblasting.
19. The process of claim 15, wherein at least one of the at least two starting elements has a surface interrupted by cavities and/or at least one of the at least two starting elements has a plate- or disk-shaped form.
20. The process of claim 15, wherein the pressure is generated by at least one added weight in a two-dimensional arrangement on or above at least one of the at least two starting elements and/or wherein the pressure is generated by a vacuum on the green glass structure.
21. The process of claim 15, wherein at least one of the at least two starting elements has a diameter and/or an edge length of at least 400 mm.
22. A monolithic composite body which has a coefficient of thermal expansion CTE in the range from 0 to 50 C. of not more than 00.110.sup.6/K, and which is produced by the process of claim 1.
23. The composite body of claim 22, having a diameter or an edge length of at least 400 mm.
24. The composite body of claim 22, wherein at least one of the at least two starting elements is a reinforcing element and/or at least one of the at least two starting elements is a functional element.
25. The composite body of claim 24, wherein mechanical stresses in a bonding region of the surface of the reinforcing element and the surface of the functional element are configured such that a stress of less than 20 nm/cm is measurable by stress birefringence measurement.
26. The composite body of claim 24, wherein at least one of the following is satisfied: an averaged density of the reinforcing element is less than 0.3 g/cm.sup.3; an averaged density of the composite body is less than 0.5 g/cm.sup.3; or a ratio V=H.Math.B/d.sup.2 is in a range from 100 to 2500, wherein H denotes a height of the reinforcing element, B denotes a width of the reinforcing element, and d denotes a thickness of inner walls of the reinforcing element.
27. The composite body of claim 22, wherein the surface of one of the at least two starting elements is cohesively bonded to the surface of at least one other one of the at least two starting elements such that crystallites have grown through a bonding surface formed by the two surfaces and penetrate both surfaces.
28. The composite body of claim 22, wherein the composite body is a lightweight mirror.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0071] The figures show:
[0072] FIGS. 1a-1c schematic diagrams of first and second functional elements having a reinforcing element (FIG. 1a), the process of the invention with a green glass structure (FIG. 1.b), and a composite body (FIG. 1c) of the invention in one variant of the invention.
[0073] FIG. 2 a process for producing a glass-ceramic composite body with the aid of an additional weight having a base area similar to the base area of the reinforcing element.
[0074] FIG. 3 a process for producing a glass-ceramic composite body with the aid of an additional weight having a base area similar to the base area of the reinforcing element with a thickened outer wall.
[0075] FIG. 4 a process for producing a glass-ceramic composite body with the aid of an additional weight having an increased base area compared to the base area of the reinforcing element with a thickened outer wall.
[0076] FIG. 5 a process for producing a glass-ceramic composite body with the aid of several partial additional weights above a reinforcing element with a thickened outer wall.
[0077] FIG. 6 an illustrative arrangement of partial additional weights.
[0078] FIG. 7 a schematic side view of a ceramized composite body.
[0079] FIGS. 8a-8b a schematic perspective diagram of a ceramized composite body in one variant (FIG. 8a) and a photograph of a ceramized composite body in a further variant (FIG. 8b).
[0080] FIG. 9. a scanning electron micrograph of the bonding region of a functional element to the reinforcing element;
[0081] FIG. 10 a schematic cross section of the bonding region of the reinforcing element to the functional element;
[0082] FIG. 11a a stress birefringence measurement profile of the composite body;
[0083] FIG. 11b a stress birefringence measurement diagram of the composite body;
[0084] FIG. 12 a stress birefringence measurement diagram of the bonding region of the reinforcing element to the functional element;
[0085] FIG. 13 a schematic diagram of the process of the invention comprising the optional step of sagging.
[0086] FIG. 14 a schematic diagram of a sagged composite body (bottom) compared to an unsagged composite body (top).
DETAILED DESCRIPTION OF THE INVENTION
[0087] FIGS. 2-6 show a process for producing a glass-ceramic composite body 1. It is possible here for a surface 4 of a first functional element 2 to be arranged, preferably in a flush arrangement, on a surface 6 of a reinforcing element 5. Ideally, the reinforcing element 5 has at least one, preferably more than one of the following features: at least one, preferably a multitude of cavities 10, openings 11 that penetrate the surface 6 or are open to the outside, inner walls 13, one or more outer walls 14, sides of the openings 12, a base area 20 of the reinforcing element 5.
[0088] The aim of the process is the ceramization and monolithic bonding of the ceramizable, vitreous elements provided and manufactured from green glass, especially the first functional element 2 and the reinforcing element 5. It is optionally possible to bond a second functional element 3 to the reinforcing element 5. FIGS. 2 to 6 also show an illustrative process setup. It is possible, as shown in these examples, to provide a reinforcing element 5 which is bonded in the course of the process to a first functional element 2 and/or a wide functional element 3, where the first functional element 3 preferably functions as mirror substrate and the second functional element 3 preferably functions as reverse side of a cover panel.
[0089] The reinforcing element 5 is generally disposed between the first functional element 2 and second functional element 3. The first functional element 2, in one variant of the invention, is disposed between an additional weight 30 and the reinforcing element 5, where the first functional element 2 is arranged in direct contact with the reinforcing element 5, and especially lies thereon. The surface 4 of the functional element 2 lies on the surface 6 of the reinforcing element here such that it makes contact with the openings 11 and hence also the cavities 10. The inner walls 13 are preferably arranged between the cavities 10, where the cavities ideally extend through the reinforcing element such that the cavities extend from one surface 6 to a surface opposite the surface 6, and especially break through at least one, preferably both surfaces. This means that the first functional element 2 is disposed on the inner walls 13 and/or on the outer walls 14 of the reinforcing element 5.
[0090] After the additional weight 30, the reinforcing element 5 and the first functional element 2 and/or second functional element 3 have been arranged, as shown in FIGS. 2 to 5, the ceramization operation can commence.
[0091] By virtue of the arrangement of the elements and of the additional weight, a directed pressure P acts by virtue of the weight of the additional weight on at least the first functional element 2 or second functional element 3, and especially also on the reinforcing element 5. The directed pressure P may then act, for example, at right angles to the surface 4 of an element 2, 3, 5, especially the first functional element 2 or second functional element 3, or parallel to a surface normal of the surface 4 of the first functional element 2 and/or second functional element 3. It is also possible here that this surface is curved.
[0092] The directed pressure P is higher than the pressure caused by the intrinsic weight of the functional element, and is preferably between 0.01 MPa and 0.1 MPa, more preferably about 0.02 MPa. By virtue of this pressure P within the above-specified temperature range, it is possible to precisely establish deformation of a functional element 2, 3 of preferably less than 0.6 mm, for example between 0.1 mm and 0.4 mm. This creates characteristic curvatures 15 (see FIG. 7) at the surface 4 of the functional element 2, 3, which in particular between the inner walls 13 and/or between the inner walls 13 and at least one outer wall 14 by virtue of the pressure P and softening of the vitreous material that takes place in the aforementioned temperature range.
[0093] FIG. 2 shows the process setup with the additional weight 30 disposed above or atop a functional element 2, 3. This additional element 30 exerts directed pressure that preferably acts uniformly on the functional element 2, 3. The functional element 2, 3 is disposed atop the reinforcing element, or on the inner walls 13 and outer walls 14. In the side view, the inner walls 13 and outer walls 14 are formed separately from one another by means of the continuous cavities 10, i.e. the cavities 10 lie between the inner walls 13 and outer walls 14. The outer walls 14, or a thickness of the outer walls 14, have an at least similar thickness to the inner walls 13, preferably even the same thickness.
[0094] A base area 20 of the reinforcing element 5 may correspond to a base area 21 of at least one functional element 2, 3. It is also possible here that a base area 31 of the additional weight 30 corresponds to the base area 20, 21 of the reinforcing element and especially of a functional element 2, 3. As a result, the effective pressure is distributed virtually uniformly.
[0095] Since stability in edge regions tends to decrease if anything, it is possible, as in FIGS. 2 to 5, to make the outer wall 14 of the reinforcing element 5 thicker than the inner walls 13; for example, the thickness of the outer walls 14 may be twice or three times the thickness of the inner walls 13. In order to cause the load or the pressure P to act more uniformly on the outer walls as well, the base area 31 of the additional weight 30 and/or the base area 21 of a functional element 2, 3 as shown in FIG. 3 may be greater than the base area 20 of the reinforcing element 5. This relates more particularly to a length, width and/or a diameter of the base areas 20, 21, 31.
[0096] FIGS. 5 and 13 show a similar setup to FIGS. 2 to 3, except that, rather than a single additional weight 30, there are several partial additional weights 32 arranged above or atop the functional element 2, 3. In this way, it is possible to distribute the pressure P more precisely over the regions where a monolithic bond of the functional element 2, 3 with the reinforcing element is created. For example, these may be exactly the regions on which a functional element 2, 3 lies atop an inner wall 13 and/or outer wall 14 of the reinforcing element. Regions above cavities 10 or openings 11 are under lower stress as a result. FIG. 6 shows, by way of example, one configuration form of partial additional weights 32. The partial additional weights 32 may accordingly be in the form of a ring and especially have different diameters, such that the partial additional weights 32 may be arranged one inside another, or partial additional weights 32 having a small diameter may be arranged within partial additional weights 32 having greater diameter. A defined distance A is preferably allowed between the partial additional weights.
[0097] FIGS. 7 and 8 show a glass-ceramic composite body 1 created in FIGS. 2 to 6 in a schematic diagram. FIG. 7 shows, in a diagram similar to FIGS. 1 to 5, how the composite body is constructed. A dotted line indicates where the interface of the functional element 2, 3 and the reinforcing element 5 ran before the ceramization. In fact, this interface is no longer detectable, and the elements are bonded homogeneously and monolithically to one another by virtue of the ceramization described in FIGS. 2 to 5, such that the composite body 1 is now in one-part form. The composite body has characteristic curves 15 at least between the inner walls 13 or between sides 12 of the cavities 10, but these may also be between the inner walls 13 and the outer walls 14.
[0098] FIG. 8 shows the composite body 1 in a perspective schematic diagram. The composite body has a first functional element 2 and a second functional element 3. The reinforcing element 5 is disposed between these functional elements 2, 3. The first functional element 2 and the second functional element 3 are arranged opposite one another here, such that, in particular, the surfaces 4 thereof are parallel to one another. Overall, the composite body 1 has a round, for example a circular, outline. The cavities 10 of the reinforcing element 5 extend through the reinforcing element 5 from the surface 4 of the first functional element 2 to that of the second functional element 3. The base area of the cavities 10 corresponds here to the base area of the former openings 11 prior to the ceramization, where the cavities 10 or the basic shape thereof have a honeycomb structure. By virtue of such a honeycomb structure, the walls 13, 14, especially the inner walls 13, may have a similar thickness and preferably also a uniform thickness.
[0099] The inner walls 13 and preferably the outer walls as well additionally have recesses 40, where the recesses 40 are formed such that the cavities 10, by means of the recesses 40, are directly or indirectly bonded fluidically to one another via the inner walls 13 and are connected to an outside environment. Additionally or alternatively, it is of course also possible that the second functional element 3 has recesses 40 via which the cavities 10 are fluidically connected directly to an outside environment. Particularly the working of the green glass body by water jet cutting for production of the cavities 10 makes it possible to establish low wall thicknesses of the inner walls 13. In this way, it is possible to produce a composite body having particularly low weight. Thus, in one embodiment, without restriction to the example shown, the averaged density of the reinforcing element is less than 0.3 g/cm.sup.3 or even less than 0.25 g/cm.sup.3. The averaged density is found from the ratio of the weight of the reinforcing element to the volume of the reinforcing element defined by the external measurements. In the example, the reinforcing element and the composite element alike have an outside dimension or shell in the form of a flat cylinder. The proportion by volume of the cavities of the reinforcing element, in a further embodiment and without restriction to the example shown in FIG. 8, is at least 85%. It is preferably the case for the composite body, which has a somewhat higher density because of the bulk functional elements, that the averaged density of the composite body is still lower than 0.5 g/cm.sup.3. The proportion by volume of the cavities is at least 80% by volume. It is apparent to the person skilled in the art that these embodiments having low density need not be restricted to waterjet-cut elements, since other structuring methods that enable correspondingly thin wall thicknesses of the wall elements may possibly also be used.
[0100] The inner walls 13, without restriction to the specific example shown, preferably have the shape of two-dimensional panel-shaped wall elements. For these wall elements, or inner walls 13, the parameter considered for the mechanical stability may be the ratio V=H.Math.B/d.sup.2 where H is the height, B the width and d the thickness of the inner wall 13. The height here is the dimension between the edges of the inner wall at the openings of the cavities. In the case of a reinforcing element having flat contact faces for the functional elements, the height H thus corresponds to the thickness of the reinforcing element. The width B is measured at right angles thereto and accordingly characterizes the distance between the bonds to adjacent inner walls 13. It is preferable that the ratio V is in a range from 100 to 2500.
[0101] FIG. 9 shows, in the upper part of the figure, a scanning electron micrograph of the connecting region of the functional element 2, 3, which is monolithically bonded to the reinforcing element 5. The image was taken with a NEON40 scanning electron microscope. As shown in FIG. 9, there is visually no apparent interface between two elements, which demonstrates the monolithic character of the bond. Measurement of the chemical composition along the bonding region confirms that the bond of the functional element 2, 3 to the reinforcing element 5 after ceramization or the ceramization method shown in FIGS. 1 to 5 is also chemically homogeneous and monolithic.
[0102] The corresponding measurement of the results thereof in the lower part of the diagram shown in FIG. 9 was measured along the path U-W shown as a line on the electron microscope image. The measurement path U-W preferably runs along a surface normal of the surface 4 of the functional element 2, 3 bonded to the reinforcing element 5 and parallel to the inner walls 13 and/or outer walls 14. It is clearly apparent that there are no significant chemical differences along the path U-W, or along the bonding region. This means that, during the ceramization process, the functional element 2, 3 has been bonded to the reinforcing element 5 such that any interface between these elements has completely disappeared.
[0103] FIG. 10 shows the bonding region in a schematic cross-sectional view. A functional element 2 is shown here atop, and especially bonded to, the reinforcing element 5. The two elements 2, 5 are cohesively bonded to one another such that crystallites 50 have grown through a bonding surface formed by the two surfaces. This means that the reinforcing element 5 and the functional element 2 are bonded by the crystallites, such that these elements or the material thereof has/have especially fused together or become intermeshed.
[0104] A similar statement can also be made after measurement of the internal stresses of the composite body 1. FIG. 11a is a measurement image of the internal stress distribution of the composite body 1, which has been created by the method of stress birefringence and especially using a high-precision polarimeter from llis. The measurement image (FIG. 11a) shows the structure and shape of the cavities 10 that are between the inner walls 13 of the composite body. The stress was measured on the inner walls 13. The result is the characteristic appearance that shows the outlines of the material regions of the composite body 1 in a front view. It will be apparent that the measurement was made through at least one functional element 2, 3 and the reinforcing element 5, or the glass-ceramic composite body 1 was surveyed in its entirety.
[0105] FIG. 11b shows a diagram of the measurement results from a measurement of stress birefringence along the path X-Y shown in FIG. 11a, i.e. a stress measurement at right angles to the connecting plane of the functional element and the reinforcing element. Along the path X-Y, 4 bonding regions were surveyed, which are represented by the respective maxima M of the values. The values that were detected between the inner walls 13, i.e. essentially in the region of the cavities 10, are shown between the maxima M. The values were normalized to the thickness of the composite element, given by the height of the inner walls 13 plus the thickness of the functional element(s). It is found that the measured stresses overall, and hence also in particular in the bonding regions of the functional element 2, 3 and the reinforcing element, are below 12 nm/cm, preferably below 10 nm/cm. In this example, the stress maxima are even only 9 nm/cm, expressed as the normative path difference. In addition, it can be stated that the measured stress birefringence, or the values of the measured stresses, are uniform in multiple bonding regions. Therefore, the measured stress maxima of at least two, preferably a multitude of, bonding regions of a functional element 2, 3 and of a reinforcing element are uniform within a measurement region of 3 nm/cm, preferably 2 nm/cm, more preferably 1 nm/cm. Such values show that, in the course of the process of the invention, stresses were introduced into the material or into the glass-ceramic composite body 1 that are preferably below the usual stresses.
[0106] FIG. 12 shows a diagram of the measurement results from a measurement of stress birefringence along a bonding region of the reinforcing element 5 with a functional element 2, 3, where the measurement zone runs parallel to the bonding plane or to the height of the inner walls 13 and at right angles to the surface 4 of the functional element 2. The measurement method is analogous to the measurement shown in FIG. 11b. The diagram shows a clear, but also very low, maximum M of the values between the reinforcing element 5 with a functional element 2, such that, in particular, a or the former interface of these elements prior to ceramization is apparent, or detectable, even after ceramization in a measurement of stress birefringence.
[0107] The stress birefringence values measured at this former interface, which is also at right angles to the measurement path U-W in FIG. 9, are in a similar range to the values shown in FIG. 11b. The maximum M of the measured stress at the bonding region is accordingly between 15 nm/cm and 10 nm/cm, expressed as the optical path difference. In a specific type of stress in the bonding region, in or after a measurement of stress birefringence, preferably directly adjoining the maximum, local minima I are also found, which ideally have a path difference below 10 nm, preferably below 8 nm, more preferably below 5 nm, especially with respect to the reinforcing element and/or at least one functional element. The path difference at the maximum M here is higher than in the reinforcing element and/or at least one functional element, and that in the minima I is smaller compared to the reinforcing element and/or at least one functional element.
LIST OF REFERENCE SYMBOLS
[0108] 1 glass-ceramic composite body [0109] 2 first functional element [0110] 3 second functional element [0111] 4 surface of the functional element [0112] 5 reinforcing element [0113] 6 surface of the reinforcing element [0114] 10 cavities [0115] 11 openings [0116] 12 sides of the openings [0117] 13 inner walls [0118] 14 outer wall [0119] 15 curves [0120] 15a curve maximum [0121] 16 base area of the curves [0122] 17 height of the curves [0123] 20 base area of the reinforcing element [0124] 21 base area of a functional element [0125] 30 additional weight [0126] 31 base area of the additional weight [0127] 32 partial additional weights [0128] 33 panel [0129] 34 sink shape [0130] 40 recesses [0131] 50 crystallites [0132] A distance between partial additional weights [0133] P pressure [0134] M maxima in the bonding regions [0135] I minima in the bonding regions [0136] V vacuum
