Method for treating vitreous materials by thermal poling

Abstract

The invention relates to a method for treating a silicate-type glass comprising alkali and alkaline-earth metal oxides or d.sup.10 or IIIA metal oxides, said method comprising at least the following steps: (a) incorporation of nitrogen into the surface of the glass; and (b) thermal poling treatment of the material obtained in (a), under a chemically inert controlled atmosphere. The invention also relates to the material produced by said method.

Claims

1. A method for treating a silicate-type glass comprising alkali and alkaline earth metal oxides or IIIA metal oxides, said method comprising: (a) incorporating nitrogen into a surface of the silicate-type glass whereby a material comprising nitrogen is obtained, and (b) thermal poling treatment of the material comprising nitrogen from (a) under a chemically inert controlled atmosphere, wherein the material comprising nitrogen is placed between an anode and a cathode without direct contact between the material comprising nitrogen and the anode.

2. The method according to claim 1, wherein (a) comprises a thermal treatment of the silicate-type glass at a temperature greater than or equal to 150° C. in a nitrogen-controlled atmosphere.

3. The method according to claim 2, wherein the temperature is 200° C. to 500° C. in (a).

4. The method according to claim 2, wherein in (a) the atmosphere comprises a gas selected from the group consisting of N.sub.2 and NH.sub.3.

5. The method according to claim 2, wherein in (a) the atmosphere comprises nitrogen N.sub.2, or a mixture of nitrogen and an inert gas selected from the group consisting of Ar and He.

6. The method according to claim 1, wherein in (b) the material comprising nitrogen is maintained at a temperature ranging from 150 to 500° C. and exposed to an electric field having a voltage of 0.1 to 10 kV.

7. The method according to claim 1, wherein in (b), the controlled atmosphere consists essentially of a gas selected from the group consisting of dry air, O.sub.2, N.sub.2, Ar, He, and a mixture of two or more of these gases.

8. The method according to claim 7, wherein in (b) the controlled atmosphere consists essentially of N.sub.2 nitrogen.

9. The method according to claim 6, wherein in (b) the material comprising nitrogen is maintained at a temperature of from 200 to 300° C.

10. The method according to claim 1, wherein the silicate-type glass has a mass composition of 0 to 40% Al.sub.2O.sub.3; 50 to 97% SiO.sub.2; 0 to 15% B.sub.2O.sub.3; 0 to 25% ZnO; 0% to 5% ZrO.sub.2; 0 to 10% TiO.sub.2; 0 to 40% Na.sub.2O; 0 to 40% Li.sub.2O; 0 to 40% K.sub.2O; 0 to 40% MgO; 0 to 50% CaO; 0 to 40% SrO; 0 to 40% BaO; 0 to 15% Ag.sub.2O; 0 to 15% Au.sub.2O.sub.3, Au.sub.2O; 0 to 15% Cu.sub.2O, and at least 95% by weight of the components, relative to the total mass of the glass, that are selected from the group consisting of Al.sub.2O.sub.3; SiO.sub.2; B.sub.2O.sub.3; ZnO; ZrO.sub.2; TiO.sub.2; Na.sub.2O; Li.sub.2O; K.sub.2O; MgO; CaO; SrO; BaO; Ag.sub.2O; Au.sub.2O.sub.3; Au.sub.2O; and Cu.sub.2O.

11. The method according to claim 1, wherein the silicate-type glass used is a glass of the composition, defined in % by mass, of from 60 to 74% of SiO.sub.2, 8.2 to 16.4% of Na.sub.2O, 3.2 to 7.40% CaO, 2.8 to 4.30% MgO, 0.3 to 1.20% Al.sub.2O.sub.3, 0.3 to 1.20% K.sub.2O and 0.1 to 0.30% SO.sub.3.

12. A method for improving durability of glazing of a silicate-type glass comprising alkali and alkaline earth metal oxides or IIIA metal oxides; or improving scratch resistance of a digital/tactile screen comprising alkali and alkaline earth metal oxides or IIIA metal oxides; or increasing resistance to abrasion of a mirror comprising alkali and alkaline earth metal oxides or IIIA metal oxides; said method comprising: (a) incorporating nitrogen into a surface of the silicate-type glass whereby a material comprising nitrogen is obtained, and (b) thermal poling treatment of the material comprising nitrogen from (a) under a chemically inert controlled atmosphere, wherein the material comprising nitrogen is placed between an anode and a cathode without direct contact between the material comprising nitrogen and the anode.

13. A method of manufacturing: a building glazing comprising a silicate-type glass comprising alkali and alkaline earth metal oxides or IIIA metal oxides; or a solar panel mirror comprising a silicate-type glass comprising alkali and alkaline earth metal oxides or IIIA metal oxides; or a screen for electronic devices comprising a silicate-type glass comprising alkali and alkaline earth metal oxides or IIIA metal oxides; or a fiberglass comprising a silicate: type glass comprising alkali and alkaline earth metal oxides or IIIA metal oxides; said method comprising: (a) incorporating nitrogen into a surface of the silicate-type glass whereby a material comprising nitrogen is obtained, and (b) thermal poling treatment of the material comprising nitrogen from (a) under a chemically inert controlled atmosphere, wherein the material comprising nitrogen is placed between an anode and a cathode without direct contact between the material comprising nitrogen and the anode.

Description

FIGURES

(1) FIG. 1 shows a schematic representation of a thermal poling assembly

(2) FIG. 2 shows a graph illustrating the second step of the method of the invention

(3) FIG. 3 shows a graphical representation of the evolution of Knoop hardness (ordinate) as a function of the load (abscissa in gram force gf) for a reference soda-lime glass (.square-solid.), a soda-lime glass annealed under N.sub.2 (•), a soda-lime glass poled thermally under N.sub.2 (.box-tangle-solidup.) and a soda-lime glass annealed under N.sub.2 and then thermally poled under N.sub.2 (.Math.).

(4) FIG. 4 shows the evolution of the Berkovich nano-indentation (ordinate in GPa) as a function of the load (abscissa in mN) for a reference soda-lime glass (.square-solid.), a soda-lime glass annealed under N.sub.2 (•), a soda-lime glass poled thermally under N.sub.2 (.box-tangle-solidup.) and a soda-lime glass annealed under N.sub.2 and then thermally poled under N.sub.2 (.Math.).

(5) FIGS. 5a and 5b show optical microscopy snapshot of surface states after climatic tests Snapshot of FIG. 5a:

(6) TABLE-US-00001 A1 B1 A2 B2 Snapshot of FIG. 5b:

(7) TABLE-US-00002 A3 B3 A4 B4 A1: reference glass, B2: reference glass after climatic treatment; A2: annealed reference glass under N.sub.2 then thermally poled under N.sub.2, B2: A2 glass after climatic treatment; A3: thermally poled reference glass under air, B3: A3 glass after climatic treatment; A4: reference glass thermally poled under N.sub.2, B4: A4 glass after climatic treatment.

(8) FIG. 6 shows the evolution of Knoop hardness (ordinate) as a function of the load (abscissa, in gf) of a soda-lime glass: reference glass thermally poled under N.sub.2 (.square-solid.); reference glass thermally poled under N.sub.2 then subjected to a climatic aging cycle (•)

(9) FIG. 7 shows the evolution of Knoop hardness (ordinate) as a function of the load (abscissa, in gf) of a soda-lime glass: annealed reference glass under N.sub.2 then thermally poled under N.sub.2 (.square-solid.); reference glass annealed under N.sub.2 then thermally poled under N.sub.2 after climatic tests (•).

EXPERIMENTAL PART

1—Materials and Methods

(10) 1—Materials Implemented:

(11) The glass which was used (reference soda-lime glass) is a glass available commercially from the company Menzel-Glaser. Its mass composition is as follows: 72.2% SiO.sub.2, 14.3% Na.sub.2O, 6.4% CaO, 4.3% MgO, 1.2% Al.sub.2O.sub.3, 1.2% K.sub.2O and 0.3% SO.sub.3, wherein the % is percentages by weight.

(12) A 1 mm thick sample (dimension of the order of 1 cm.sup.2) was used.

(13) 2—Equipment:

(14) The treatment was carried out in a chamber described below.

(15) The thermal poling assembly is divided into three parts: A hermetic enclosure allowing control of the atmosphere (primary vacuum, secondary, dry air, argon, nitrogen) A heating system by contact. The heating elements are inserted in an inconel chamber which also serves as a cathode. The temperature is controlled by a thermocouple located in the inconel chamber. A high voltage source from 0 to 15 kV. The anode and the cathode are located face to face. The cathode is connected to a Keithley® pico-ammeter. A guard electrode on the periphery of the cathode makes it possible to collect the surface currents and to measure the current through the sample by the pico-ammeter.

(16) 3—Methods of Evaluation of the Properties of the Material: Hardness evaluation: For nano-indentation, a Berkovich tip (NT600 nanoindenter MicroMaterials Limited) was used. For micro-indentation, a Knoop-type tip equipped with a LEICA VMHT AUTO® apparatus was used. Chemical analysis: A GD-Profiler 2 (HORIBA Jobin Yvon®) was used to perform the chemical analysis profiles. Evaluation of the transmittance: Cary 5000 Varian® UVNIS/NIR—XPS analysis: The XPS analyzes were carried out on a Thermo VG Scientific ESCALAB® 220 iXL spectrometer equipped with a A1 KcxX monochromatic source (1486.6 eV). The samples are placed in an ultra-vacuum chamber (UHV, 109 mbar) at room temperature. The collected data are formatted with a Gaussian-Lorentzian combination for modeling. AVANTAGE® software from Thermofisher Scientific is used to process the data. SHG: A micro-SHG coupling method was used to probe second harmonic generation. The device used is a Horiba HR800 confocal Ram/Jobin-Yvon® spectrometer with a laser source. The source used to measure the second harmonic signal is a pico-second EKSPLA® PL2200 laser emitting at a wavelength of 1064 nm.

(17) The microscope is equipped with a motorized stage (x, y, z) that allows 3D analysis with a spatial resolution of one micron. The poled incident beam is focused on the surface of the sample by a near-infrared lens (50× or 100×). The backscattered light is captured by the same lens and redirected to the analyzer. This analyzer is used to select the analysis poling. The beam thus poled is directed to a network and then to the CCD camera which makes it possible to select the second harmonic intensity. This method makes it possible to access the localization of the electric field within the material by identifying the zone presenting the second harmonic phenomenon (ref. V. Rodriguez, D. Talaga, F. Adamietz, J L Bruneel, M. Couzi, Chem Phys Lett, 2006, 431, 190).

(18) Climatic Aging Tests:

(19) Analyses were carried out in climatic chambers in order to simulate different atmospheres and in order to evaluate the chemical durability and to accelerate the aging of the coatings. The method used makes it possible to evaluate the behavior of the method in real conditions of external use.

(20) The climatic aging protocol is composed of the following phases: 1) A phase A of spraying on the glass a 1% saline solution of sodium chloride (pH 6.5 to 7.1) for a duration of 3 times 24 hours, wherein it falls on the samples at a rate of 2.0 to 4.0 ml/80 cm.sup.2/hour. 2) A phase B of increasing the temperature from 25° C. to 50° C. by increasing the % humidity in the chamber from 70 to 95% for a duration of 3 times 24 hours. 3) A thermal shock phase C of −15° C. to 50° C. with a duration of 24 hours.

(21) A complete cycle consists of the repetition of six cycles for a total duration of 6 weeks. A cycle lasts 7 days and is composed of the following sequence A-B-A-C-A-B-B.

II—Examples

(22) The treatment carried out involves two steps: the first step is a thermal treatment of the glass under a nitrogen atmosphere. The second step is a thermal poling treatment in a controlled chemically-inert atmosphere.

(23) 1—Step (a): Thermal Treatment Under Nitrogen Atmosphere

(24) The treatment was carried out in a mullite tube at a temperature of 400° C. under a controlled atmosphere under nitrogen (N.sub.2) for 24 hours. The treatment is carried out at a temperature close to the glass transition temperature of the soda-lime glass in order to render the surface of the glass reactive to the atmosphere of the enclosure. The treatments carried out at 300° C., 350° C. and 400° C. gave the same results. The ramps of rise and fall in temperature are of the order of 15° C./minute.

(25) The partially nitrided glass on the surface then undergoes thermal poling treatment.

(26) 2—Step (b): Thermal Poling Treatment Under a Nitrogen Atmosphere

(27) Thermal poling treatment is a controlled thermal treatment method, assisted by an electric field. The experiment is carried out in a closed enclosure under controlled atmosphere, under closed electrode, under argon or under N.sub.2. Failure to control this atmosphere (leakage, sealing problems, flow meters) may lead to undesirable chemical mechanisms that alter the mechanical properties of the glass.

(28) The thermal poling treatment was carried out by raising the temperature of the sample placed between two electrodes and the application of a potential difference as illustrated in FIG. 1: The glass sample 1 is placed between the anode 2 and the cathode 3, and the assembly is placed on a heating plate 4. The whole is placed in a closed chamber (not shown). The two electrodes are connected to a voltage generator 5.

(29) The temperature is gradually raised to the temperature of thermal poling in a range of 200 to 300° C. Once the temperature is reached, a voltage in a range of 1.0 to 3.0 kV is applied. The thermal poling treatment lasts 20 to 60 minutes. The temperature is then brought back to room temperature while the voltage is still maintained at the thermal bias voltage of the experiment. Once the system reaches room temperature, the voltage is lowered to 0V. The thermal poling processing is then completed.

(30) FIG. 2 graphically illustrates the second step of the method of the invention: the temperature (ordinate) is raised progressively (the time scale is represented schematically in the abscissa) to the desired threshold, then a voltage is applied, wherein this step is represented by the hatched area, finally the temperature is reduced to ambient and the voltage is reduced to 0V.

III—Characterization

(31) Evaluation of the hardness: We compared the evolution of the Berkovich nano-indentation as a function of the load for: Reference soda-lime glass (comparative). A glass obtained by application to the standard soda-lime glass of the treatment described above. Step (a): Thermal treatment under nitrogen (N.sub.2) (comparative). A glass obtained by application to the standard soda-lime glass of the treatment described above. Step (b): Thermal poling treatment under a nitrogen (N.sub.2) atmosphere (comparative). A glass obtained by application to the soda-lime glass reference treatments of steps (a) annealed under N.sub.2 and then (b) thermal poling under N.sub.2 (according to the invention).

(32) The results are illustrated in FIG. 4. For the glass of the invention, an increase in hardness of almost 40% in nanoindentation is observed for the low loads (1 and 2.5 mN).

(33) Evaluation of the Hardness—Micro Indentation Test:

(34) The evolution of the Knoop hardness as a function of the load was compared to: Reference soda-lime glass (comparative). A glass obtained by application to the standard soda-lime glass of the treatment described above. Step (a): Thermal treatment under nitrogen (N.sub.2) (comparative). A glass obtained by application to the standard soda-lime glass of the treatment described above. Step (b): Thermal poling treatment under a nitrogen (N.sub.2) atmosphere (comparative). A glass obtained by application to the reference soda-lime glass of the treatments of step (a), annealed under N.sub.2 and then step (b) thermal poling under N.sub.2 (according to the invention).

(35) The results are illustrated in FIG. 3. For the glass of the invention, the Knoop hardness is found to be much higher than that of the reference and comparative glasses. In particular for loads ranging from 1 to 25 gf or greater than 250 gf, there is a synergistic effect of the two treatments which was by no means predictable. Only one of these respective steps makes it possible to improve the hardness of the glass by a maximum of about 20% for 10 gf. Between 50 and 200 gf, the increase is less than 13%. It is less than 5% for a load of 200 gf to 300 gf. It is the synergy of the two steps carried out successively that allows a net improvement of the hardness of nearly 40% for a load of 10 gf. The synergy of the two steps allows an increase in the hardness of more than 15% for a load between 50 gf and 300 gf. Chemical analysis: The technique implemented, stripping coupling and spectroscopic analysis of the plasma shows a surface silica layer between 300 and 400 nm according to the experimental conditions of thermal poling. The migration of cations is observed (from several hundred nanometers for calcium and magnesium and up to several micrometers for sodium and potassium). Evaluation of transmittance: The results are described in Table 1 below. They are expressed as percent transmittance (T) before and after climate treatment (TC).

(36) TABLE-US-00003 Annealing + Reference Poling under poling under glass Air poling .sup.(1) N.sub.2 .sup.(2) N.sub.2 .sup.(3) T before TC (%) 91 78 92 92 T after TC (%) 86 71 91 91 Loss of T (%) 5.49 8.97 1.09 1.09 .sup.(1) Reference glass to which thermal poling treatment has been applied under air .sup.(2) Reference glass to which thermal poling treatment has been applied under a nitrogen atmosphere .sup.(3) Reference glass to which an annealing treatment was applied under a nitrogen atmosphere followed by a thermal poling treatment under a nitrogen atmosphere

(37) These analyses confirmed the preservation of the surface quality. The reference glass after climatic tests sees its transmittance greatly reduced (>5%). In the case of glass treated by thermal poling under nitrogen and in the method of the invention, the transmittance varies by 1%, which corresponds to the accuracy of the measurement. SHG: It has been found that a poled material is obtained. Climatic aging:

(38) FIGS. 5a and 5b illustrate the surface state of the glasses before (series a) and after (series b) aging in climatic chambers.

(39) Snapshots A1 and B1 illustrate the effect of thermal aging on untreated glass, i.e. a degradation of the optical qualities of the glass.

(40) Snapshots A3/B3 and A4/B4 validate the role of atmospheric control in maintaining the optical qualities of the glass surface.

(41) Snapshots A2 and B2 show the combined effect of annealing under N.sub.2 and thermal poling under N.sub.2 (according to the invention). It is found that the surface observed by optical microscopy remains unchanged. These snapshots explain the effect of the invention on the chemical durability after climate tests with respect to a soda-lime reference glass. The surface condition validates the method.

(42) The mechanical properties of the glasses having undergone the climatic aging treatment were then evaluated.

(43) The same micro-indentation tests (evolution of the Knoop hardness as a function of the load) were carried out following the climatic chamber tests. The results are illustrated in FIGS. 6 and 7. These tests make it possible to demonstrate the maintenance of the mechanical properties of hardness after climatic tests for the glasses which have undergone the treatment of the invention (FIG. 7). It can be seen that a poling treatment alone is not enough to keep such good hardness properties (FIG. 6).