Glass ceramic composites

Abstract

A method for joining glass ceramic surfaces to each other and/or other types of surfaces using a silicate liquid is disclosed. The products are suitable for use as, e.g. mirror blanks or microlithography stages, at low temperatures. Component pieces are polished then joined at low temperature using a silicate-containing joining liquid. Assembly is then performed in such a way that the joining liquid forms an interface between each component. After a period of low or slightly elevated temperature curing, rigid joints are formed throughout and the composite is dimensionally, vibrationally, and temperature stable and can withstand tensile stresses >4000 psi. The room-temperature cured composite can be heat treated using a slow, systematic temperature increase to dehydrate the joints. A sealing coating may optionally be provided to prevent excess dried joining liquid from flaking off the formed joint.

We claim:  
     
         1 . A low-temperature process for the fabrication of lightweight composite glass ceramic structures, comprising: 
 providing a plurality of glass ceramic components, said glass ceramic components each being polished to form at least one joining surface on each component,    providing a silicate-containing joining liquid to at least one of the joining surfaces,    bringing the joining surfaces of the plurality of glass components together to form a joint,    allowing the joint to cure for a period of time of at least 20 hours at a temperature of at least 20 degrees C., whereby a cured joint is formed between said plurality of glass components, and    dehydrating the cured joint gradually by raising the temperature slowly and maintaining an elevated temperature below the glass transition temperature of the glass ceramic for at least 20 hours.    
     
     
         2 . A method as claimed in  claim 1 , wherein the step of dehydrating comprises gradually raising the temperature at a rate which allows dehydration of the joint without imparting damage to the joint from accelerated H 2 O evaporation.  
     
     
         3 . A process as claimed in  claim 1 , wherein the glass ceramic components are Zerodur® components.  
     
     
         4 . A process as claimed in  claim 1 , wherein the glass ceramic components include a low expansion material prepared by partially ceramizing a lithium alumino silicate glass.  
     
     
         5 . A process as claimed in  claim 1 , wherein the glass ceramic components include a material selected from the group consisting of Nexcera, Clearceram, VO2, Astrositall and Sitall.  
     
     
         6 . A process as claimed in  claim 1 , wherein the silicate containing liquid is a lithium silicate containing liquid or a sodium silicate containing liquid.  
     
     
         7 . A process as claimed in  claim 1 , wherein the silicate containing liquid is an alkali silicate, alkaline earth silicate, mixed alkali silicate, mixed alkaline earth silicate, or mixed alkali/alkaline earth silicate liquid.  
     
     
         8 . A process as claimed in  claim 2 , wherein the step of gradually raising the temperature comprises increasing the temperature at a rate less than or equal to 3 degrees K/hour.  
     
     
         9 . A process as claimed in  claim 8 , wherein the temperature is periodically stabilized and held.  
     
     
         10 . A process as claimed in  claim 9 , wherein the temperature is stabilized at intervals of from 5 to 20 degrees C. and held for at least 10 hours.  
     
     
         11 . A process as claimed in  claim 10 , wherein the temperature is stabilized at intervals of about 10 degrees C. and held for about 20 hours.  
     
     
         12 . A process as claimed in  claim 1 , wherein the components include at least one component with a hollowed out light-weighted portion.  
     
     
         13 . A process as claimed in  claim 1 , wherein the components comprise segments of a light-weighted core.  
     
     
         14 . A process as claimed in  claim 1 , wherein the components include a mirror blank.  
     
     
         15 . A process as claimed in  claim 1 , wherein the period of time is at least one hour.  
     
     
         16 . A process as claimed in  claim 1 , wherein the period of time is at least one day.  
     
     
         17 . A process as claimed in  claim 1 , wherein the period of time is at least one week.  
     
     
         18 . A process as claimed in  claim 1 , wherein the step of providing the silicate containing liquid comprises applying the silicate containing liquid in an amount of at least 0.01 microliter/cm 2 .  
     
     
         19 . A process as claimed in  claim 2 , wherein the temperature is from 60 to 600 degrees C.  
     
     
         20 . A process as claimed in  claim 19 , wherein the temperature is below 120 degrees C.  
     
     
         21 . A glass ceramic composite, comprising: 
 a plurality of glass ceramic components, said components being rigidly connected by a silicate-containing layer formed by curing a silicate-containing liquid between the glass ceramic components at a temperature of at least 20 degrees C. for at least 20 hours.    
     
     
         22 . A glass ceramic composite as claimed in  claim 21 , wherein the cured silicate-containing layer is dehydrated at a temperature at or below 600 degrees C.  
     
     
         23 . A glass ceramic composite as claimed in  claim 22 , wherein the cured silicate-containing layer is dehydrated at a temperature at or below 120 degrees C.  
     
     
         24 . A glass ceramic composite as claimed in  claim 21 , wherein the plurality of glass ceramic components comprise Zerodur components.  
     
     
         25 . A glass ceramic composite as claimed in  claim 21  wherein the plurality of glass ceramic components include a glass ceramic material prepared by partially ceramizing a lithium alumino silicate glass.  
     
     
         26 . A glass ceramic composite as claimed in  claim 20 , wherein the plurality of glass ceramic components include a material selected from the group consisting of Nexcera, Clearceram, VO2, Astrositall and Sitall.  
     
     
         27 . A glass ceramic composite as claimed in  claim 21 , wherein at least one of the glass ceramic components contains a hollowed out space.  
     
     
         28 . A glass ceramic composite as claimed in  claim 21 , wherein at least one of the components comprises a mirror blank.  
     
     
         29 . A glass ceramic composite as claimed in  claim 21 , wherein the light weighted section is prepared by assembling separate segments of glass ceramic.  
     
     
         30 . A glass ceramic composite as claimed in  claim 16 , wherein the rigid connection can withstand tensile stresses during usage of at least 750 psi.  
     
     
         31 . A mirror blank suitable for use in space or flight applications comprising a plurality of glass ceramic components joined by a silicate-containing liquid and cured at a temperature of at least 20 degrees C.  
     
     
         32 . A mirror blank as claimed in  claim 31 , wherein the mirror blank is formed from a face plate, a back plate, and at least one supporting element.  
     
     
         33 . A mirror blank as claimed in  claim 32 , wherein there are a plurality of supporting elements.  
     
     
         34 . A mirror blank as claimed in  claim 33 , wherein the plurality of supporting elements comprise crossed vertical walls, said vertical walls being provided with slots to form a lattice.  
     
     
         35 . A mirror blank as claimed in  claim 34 , wherein each lattice opening forms a cell, and the cell is provided with a ventilation hole or is open to the surrounding environment.  
     
     
         36 . A composite glass ceramic structure suitable for use as a microlithography stage comprising a plurality of glass ceramic components joined by a silicate-containing liquid and cured at a temperature of at least 20 degrees C.  
     
     
         37 . A method of joining lightweight composite glass ceramic surfaces comprising applying to at least one of said surfaces a silicate-containing solution and curing for an extended period at a slightly elevated temperature above room temperature.  
     
     
         38 . A method as claimed in  claim 37 , wherein the temperature is from 30 to 50 degrees C., and the extended period is at least 20 hours.  
     
     
         39 . A glass ceramic composite as claimed in  claim 21 , wherein said silicate-containing layer comprises, in weight %, 
 H 2 O 50-99.9    SiO 2  0.01-40    Al 2 O 3  0-10    Li 2 O 0-20    Na 2 O 0-20    K 2 O 0-25    MgO 0-10    CaO 0-10    BaO 0-10    SrO 0-10.    
     
     
         40 . A light weight glass-ceramic mirror blank, comprising: 
 a face plate which is circular in shape,    a back plate which corresponds in shape and size to the face plate,    a plurality of support elements located between said face and back plates, said plurality of supporting elements forming a latticework    said latticework and face plate and back plate defining a plurality of cells,    said cells each being provided with a ventilation aperture or being open to the environment,    said face plate, plurality of supporting elements, and back plate being joined by a silicate-containing liquid in a plurality of joining steps to form a plurality of joints, and at each step, the joint cured at a temperature of at least 20 degrees C. for a period of at least 20 hours.    
     
     
         41 . A mirror blank as claimed in  claim 1 , wherein the joint is further dehydrated at a temperature of from 30 to 50 degrees C. for at least 20 hours.  
     
     
         42 . An optical or electrooptical device comprising a composite of  claim 21 .  
     
     
         43 . A device of  claim 42  which is an etalon.  
     
     
         44 . A vacuum chamber comprising a composite of  claim 21 .  
     
     
         45 . A composite of  claim 21  which has a low coefficient of expansion.  
     
     
         46 . A low-temperature process for the fabrication of a lightweight composite glass ceramic structure, comprising: 
 providing at least two surfaces at least one of which is a glass ceramic, and the other of which is a glass-ceramic or another material having a surface group which reacts with a silicate joining liquid to form a stable bond, said surfaces each being polished to form joining surfaces on each,    providing a silicate-containing joining liquid to at least one of the joining surfaces,    bringing the joining surfaces together to form a joint,    allowing the joint to cure for a period of time of at least 20 hours at a temperature of at least 20 degrees C., whereby a cured joint is formed between said surfaces, and    dehydrating the cured joint gradually by raising the temperature slowly and maintaining for at least 20 hours an elevated temperature below the lowest temperature at which one of the joined components is adversely affected.    
     
     
         47 . A process of  claim 46  wherein at least one of the surfaces is SiO 2 , quartz, Al 2 O 3 , multi component silicate glass, BK-7, ULE, antimony silicate glass, a low expansion metallic alloy, optionally coated with a thin layer of SiO 2 , germanium glass, tellurium glass or borosilicate glass.  
     
     
         48 . A process of  claim 46  where at least one of the surfaces is a glass and said elevated temperature is below the lowest glass transition temperature of said joined surfaces.  
     
     
         49 . A process as claimed in  claim 46 , wherein the glass ceramic component is a Zerodur® component.  
     
     
         50 . A glass ceramic composite, comprising: 
 at least two surfaces at least one of which is a glass ceramic and the other of which is a glass-ceramic or another material having a surface group which reacts with a silicate joining liquid to form a stable bond, said surfaces being rigidly connected by a silicate-containing layer formed by curing a silicate-containing liquid between the glass ceramic surface and said other surface at a temperature of at least 20 degrees C. for at least 20 hours.    
     
     
         51 . A glass ceramic composite as claimed in  claim 21 , wherein the glass ceramic surface comprises Zerodur®.  
     
     
         52 . A glass ceramic composite of  claim 21  wherein said other surface is SiO 2 , quartz, Al 2 O 3 , multi component silicate glass, BK-7, ULE, antimony silicate glass, a low expansion metallic alloy, optionally coated with a thin layer of SiO 2 , germanium glass, tellurium glass or borosilicate glass.  
     
     
         53 . A process of  claim 46  wherein said joining liquid comprises ground or fritted silica-containing glass-ceramic or glass.