Ion beam treatment method for producing superhydrophilic glass materials
10570060 · 2020-02-25
Assignee
Inventors
Cpc classification
C03C3/087
CHEMISTRY; METALLURGY
International classification
C03C3/087
CHEMISTRY; METALLURGY
Abstract
Process for treatment by an ion beam of a glass material where: the acceleration voltage of the ions is between 5 kV and 1000 kV; the temperature of the glass material is less than or equal to the glass transition temperature; the dose of nitrogen (N) or oxygen (O) ions per unit of surface area is chosen within a range of between 10.sup.12 ions/cm.sup.2 and 10.sup.18 ions/cm.sup.2 so as to reduce the contact angle of a drop of water below 20; a prior pretreatment is carried out with argon (Ar), krypton (Kr) or xenon (Xe) ions in order to strengthen the durability of the superhydrophilic treatment. Superhydrophilic glass materials of long duration are thus advantageously obtained.
Claims
1. A process for surface treating a virgin soda-lime glass, consisting of: subjecting the virgin soda-lime glass to a pretreatment ion bombardment prior to a treatment ion bombardment to obtain a pretreated soda-lime glass, wherein: the pretreatment ion bombardment is with a pretreatment ion beam, ions of the pretreatment ion beam being ions of elements selected from the group consisting of argon (Ar), xenon (Xe), and krypton (Kr), an acceleration voltage of the ions in the pretreatment ion beam is greater than or equal to 5 kV and less than or equal to 1000 kV; a temperature of the virgin soda-lime glass during the pretreatment ion bombardment is less than or equal to the glass transition temperature of the virgin soda-lime glass; and a dose of ions delivered to the soda-lime glass during the pretreatment ion bombardment as measured in ions per unit of surface area is within a range of between 10.sup.12 ions/cm.sup.2 and 10.sup.18 ions/cm.sup.2; and subjecting the pretreated soda-lime glass to the treatment ion bombardment with a treatment ion beam to obtain a treated soda-lime glass, ions of the treatment ion beam being ions of elements selected from the group consisting of nitrogen (N) and oxygen (O), wherein: an acceleration voltage, AV, of the ions in the treatment ion beam is greater than or equal to 5 kV and less than or equal to 1000 kV, a temperature of the pre-treated soda-lime glass during the treatment ion bombardment is less than or equal to the glass transition temperature of the virgin soda-lime glass, the treatment ion bombardment delivers to the pre-treated soda-lime glass a dose of ions as measured in ions per unit of surface area within a range of between 510.sup.15 ions/cm.sup.2 and 10.sup.18 ions/cm.sup.2 the treatment ions are produced by electron cyclotron thereby producing multicharged ions, and the process for surface treating the virgin soda-lime glass increases hydrophilic properties of the virgin soda-lime glass thereby reducing a contact angle of water drops on the treated soda-lime glass by at least about 40 as compared to the virgin soda-lime glass to obtain a superhydrophilic surface having a resultant contact angle of water drops of less than 20.
2. The process as claimed in claim 1, wherein the ions of the pretreatment ion beam are argon (Ar) ions, and the dose range for the argon (Ar) ions is between 510.sup.16 and 510.sup.17 ions per cm.sup.2.
3. The process as claimed in claim 1, wherein the ions of the pretreatment ion beam are krypton (Kr) ions, and the dose range for the krypton (Kr) ions is between 10.sup.16 and 10.sup.17 ions per cm.sup.2.
4. The process as claimed in claim 1, wherein the ions of the pretreatment ion beam are xenon (Xe) ions, and the dose range for the xenon (Xe) ions is between 510.sup.15 and 510.sup.16 ions per cm.sup.2.
5. The process as claimed in claim 1, wherein the ions of the treatment ion beam are nitrogen ions, and the dose of ions per unit of surface area and the acceleration voltage of the ions are determined so that the surface atomic concentration of nitrogen is greater than or equal to an atomic concentration threshold of 0.1%.
6. The process as claimed in claim 1, wherein the ions of the treatment ion beam are nitrogen (N), the acceleration voltage AV is greater than or equal to 10 kV and the dose of ions per unit of surface area is greater than or equal to a value resulting from an empirical equation DNmin=(AV/20).sup.2, where the resulting value represents the minimum dose of nitrogen atoms DNmin expressed in 10.sup.16 ions/cm.sup.2 and the acceleration voltage AV is measured in kV and input into the empirical equation as a unitless value.
7. The process as claimed in claim 1, wherein the ions of the treatment ion beam are oxygen (O), the acceleration voltage AV is greater than or equal to 10 kV and the dose of ions per unit of surface area is greater than or equal to a value resulting from an empirical equation DOmin=10.Math.(AV/20).sup.1.5, where the resulting value represents the minimum dose of oxygen atoms DOmin expressed in 10.sup.16 ions/cm.sup.2 and the acceleration voltage AV is measured in kV and input into the empirical equation as a unitless value.
8. The process as claimed in claim 1, wherein the glass material is movable with respect to the ion beam at a rate, R.sub.FP, of between 0.1 mm/s and 1000 mm/s.
9. The process as claimed in claim 8, wherein the same region of the glass material is moved under the ion beam according to a plurality, N, of passes at the rate R.sub.FP.
10. The use of the process as claimed in claim 1 in order to treat a bulk glass part selected from the group consisting of a motor vehicle windshield, a spectacle lens, a lens of an optical device, a mirror, a window of a building, an optical fiber, and a glass syringe body.
11. The process as claimed in claim 1, wherein the ions of the treatment ion beam are oxygen ions, and the dose of ions per unit of surface area and the acceleration voltage of the ions are determined so that the surface atomic concentration of oxygen is greater than or equal to an atomic concentration threshold of 2.5%.
12. The process as claimed in claim 1, wherein the acceleration voltage, AV, of the ions in the treatment ion beam is greater than or equal to 5 kV and less than or equal to 200 kV.
13. The process as claimed in claim 1, wherein the acceleration voltage, AV, of the ions in the treatment ion beam is greater than or equal to 10 kV and less than or equal to 100 kV.
14. The process as claimed in claim 1, wherein the dose of ions as measured in ions per unit of surface area is in a range of between 10.sup.16 ions/cm.sup.2 and 10.sup.18 ions/cm.sup.2.
15. The process as claimed in claim 1, wherein the dose of ions as measured in ions per unit of surface area is in a range of 510.sup.15 ions/cm.sup.2 and 10.sup.17 ions/cm.sup.2.
16. A process for rendering a soda-lime glass superhydrophilic, comprising: subjecting the soda-lime glass to a pretreatment ion bombardment prior to a treatment ion bombardment to obtain a pretreated soda-lime glass, wherein: the pretreatment ion bombardment is with a pretreatment ion beam, ions of the pretreatment ion beam being ions of elements selected from the group consisting of argon (Ar), xenon (Xe), and krypton (Kr) to obtain a pretreated glass material an acceleration voltage of the ions in the pretreatment ion beam is greater than or equal to 5 kV and less than or equal to 1000 kV; a temperature of the soda-lime glass during the pretreatment ion bombardment is less than or equal to the glass transition temperature of the soda-lime glass; and a dose of ions delivered to the soda-lime glass during the pretreatment ion bombardment as measured in ions per unit of surface area is within a range of between 10.sup.12 ions/cm.sup.2 and 10.sup.18 ions/cm.sup.2; and subjecting the pretreated soda-lime glass to the treatment ion bombardment with a treatment ion beam to obtain a treated soda-lime glass, ions of the treatment ion beam being ions of elements selected from the group consisting of nitrogen (N) and oxygen (O), wherein: an acceleration voltage, AV, of the ions in the treatment ion beam is greater than or equal to 5 kV and less than or equal to 1000 kV, a temperature of the pretreated soda-lime glass during the treatment ion bombardment is less than or equal to the glass transition temperature of the soda-lime glass, the treatment ion bombardment delivers to the pretreated soda-lime glass a dose of ions as measured in ions per unit of surface area within a range of between 510.sup.15 ions/cm.sup.2 and 10.sup.18 ions/cm.sup.2, and after the treatment ion bombardment, the treated soda-lime glass has a contact angle of water drops of less than 20 and a minimum detachment angle of water drops that is at least about 35 lower than a minimum detachment angle of water drops of the soda-lime glass prior to the pretreatment ion bombardment and the treatment ion bombardment.
Description
BRIEF DESCRIPTION OF THE DRAWING FIGURES
(1)
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(3)
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(5)
DETAILED DESCRIPTION
(6) The choice of the ions and of the conditions of bombardment of these ions according to the invention makes it possible to advantageously obtain an increase in the hydrophilicity of the glass material which is expressed by a reduction in the contact angle and an increase in the surface energy of the glass material treated. These properties are very important in reducing the formation of mist on a motor vehicle windshield, spectacle lenses, lenses or mirrors of optical devices, or structural glasses. Antifogging property denotes the behavior and the quality of a glass material in slowing down, reducing or preventing the formation of a condensate of moisture in the mist form.
(7) Surprisingly, the inventors have been able to find that the ranges chosen according to the invention for acceleration voltage and dose of ions per unit of surface area make it possible to select experimental conditions where the strengthening of hydrophilic properties toward a superhydrophilicity (characterized by a contact angle of a drop of water of less than 20, indeed even of less than 10) associated with antifogging properties is possible by virtue of an ion bombardment.
(8) This superhydrophilicity put at the service of antifogging properties can also prove to be highly advantageous for increasing the surface energy of an optical cladding of an optical fiber, for thus improving the adhesion of the protective cladding (made of polymer) which surrounds the optical cladding.
(9) It is also possible to look for hydrophilic, indeed even superhydrophilic, properties in order to promote the sliding of an elastomer piston in the body of a glass syringe.
(10) In addition, they have been able to find that the process according to the invention can be carried out under cold conditions, in particular at ambient temperature, and that it is advisable for the temperature of the glass material to remain less than or equal to the transition value of the glass material during the implementation of the process. It is thus possible to advantageously prevent the glass material from undergoing, in its body, a crystallographic modification harmful to its mechanical properties.
(11) The choice of the dose of ions per unit of surface area within the dose range according to the invention can result from a prior calibration stage where a sample consisting of the glass material envisaged is bombarded with one of the ions from N or O. The bombarding of this glass material can be carried out in various regions of the material with a plurality of doses of ions, within the range according to the invention, and the regions treated are observed so as to choose an appropriate dose as a function of the contact angle of a drop of water with the glass material or also the minimum detachment angle of this same drop obtained by inclining the sample with respect to a horizontal plane. Beyond this minimum detachment angle, the drop of water slides and is incorporated on its journey with the other droplets, entraining and removing with it the condensate of moisture constituting the mist.
(12) The treated regions can thus be observed by simple observation techniques, such as a photograph of the drop taken in the plane of the glass material placed on a table, or also the recording of the angle of inclination from which the drop moves over the glass material.
(13) Without wishing to be committed to any one scientific theory, it may be thought that this phenomenon can be explained by the nature of the chemical bonds created by the incident ion in the glass material. The incident ion recombines with the silicon preferably in the form of silicon oxide or silicon nitride, forming highly polarized bonds favorable to the increase in the surface energy, hence an increase in the initial polar nature. Surprisingly, the inventors have been able to find that the surface of the material then assumes a polar, in other words hydrophilic, nature which can be intensified according to the dose and the implantation energy to the point of becoming superhydrophilic (contact angle of a drop of water of less than 20, indeed even of less than 10).
(14) Apart from the strengthening of the superhydrophilic properties associated with the antifogging properties independent of the light exposure conditions, the process of the invention makes it possible to harden the surface of the glass material over a thickness of the order of a micron. The process of the invention thus exhibits the advantage of increasing the resistance of the surfaces to the mechanical stresses of the environment.
(15) According to different alternative embodiments: the glass material is not subjected to any prior ion bombardment treatment; the glass material is pretreated with noble ions, such as Ar, Kr or Xe. This pretreatment has the effect, by a preferred atomic sputtering mechanism, of depleting the implantation region, of approximately 200 nm in thickness, in alkali metal ions, such as sodium (Na), thus creating a depletion region. This depletion region has the characteristic of being less reactive with regard to leaching processes.
(16) According to the latter embodiment, the soda-lime glass material is treated beforehand with heavy noble ions belonging to the list of the elements consisting of argon (Ar), krypton (Kr) and xenon (Xe). This prior treatment has the role of creating a sodium (Na) depletion region favorable to reducing the phenomenon of leaching of the glass. This is because it should be remembered that an oxide glass generally exhibits a good resistance to corrosion. Nevertheless, the process of weathering the glass can be modified by subjecting the latter to baths of different pH values. In the case of an acidic leaching solution, a mechanism of ion (alkali metal ion/hydrogen species) exchange then takes place between the glass and the bath. There is thus formed, at the surface of the glass, a thin weathering film consisting of the dealkalinized layer. This layer is characterized by a lower refractive index than that of the underlying healthy glass. The decrease in the index is related, on the one hand, to the departure of alkali metal ions from the glass but also to the appearance of pores. These volumes correspond to the cavities left in the matrix by the departure of these ions. The leaching phenomenon is expressed by a bleaching of the glass. A reduction in the presence of sodium at the surface is expressed by a reduction in the appearance of pores.
(17) The inventors have carried out corrosion tests by microgravimetric weighing (difference in weight before and after immersion) of virgin and treated samples of soda-lime glass by immersing them in a hydrochloric acid (HCl) solution with a pH=1, at ambient temperature (20 C.). according to different immersion times. The samples were treated according to two doses, 10.sup.16 and 10.sup.17 ions/cm.sup.2, with a beam of multicharged argon (Ar.sup.+) ions Ar.sup.+, Ar.sup.2+, Ar.sup.3+, Ar.sup.4+, Ar.sup.5+, the respective intensities of which are 2, 1.29, 0.6, 0.22 and 0.11 mA. These multicharged ions were extracted with a voltage of 40 kV (kilovolts). The surface stoichiometric composition of the glass in silicon (Si), oxygen (O) and sodium (Na), before and after treatment and before immersion in hydrochloric acid (HCl) was analyzed by XPS (X-ray Photoelectron Spectroscopy). These results are recorded in table a. Before each weighing, the samples immersed in hydrochloric acid (HCl) were washed with distilled water and then dried.
(18) TABLE-US-00001 TABLE a virgin 10.sup.16 Ar ions/cm.sup.2 10.sup.17 Ar ions/cm.sup.2 O 45.22% 47.11 49.36% Si 17.12% 18.32 25.09% Na 6.13% 3.69 0.92%
(19) The results obtained by XPS demonstrate, under the effect of the treatment by ion bombardment with argon (Ar), the surface depletion in sodium (Na), the concentration of which changes from 6.13% to 3.69% and then to 0.92%.
(20) The inventors have recorded, in table b, for the same virgin glass and glass treated according to two doses 10.sup.16 and 10.sup.17 (Ar ions/cm.sup.2) and on just one side, the weights of the samples, expressed in grams, according to different durations of immersion in the HCl solution, expressed in days. The microbalance has an accuracy of 100 micrograms.
(21) TABLE-US-00002 TABLE b Duration of immersion 0 days 1 day 4 days virgin 3.7069 3.7068 3.7067 10.sup.16 (Ar ions/cm.sup.2) 3.8812 3.8812 3.8811 10.sup.17 (Ar ions/cm.sup.2) 3.9523 3.9523 3.9523
(22) On the basis of these results, it is apparent that the rate of corrosion corresponding to the loss in weight is lower for the treated glass than the virgin glass. There thus indeed exists a correlation between the depletion in sodium (Na) and the increase in the resistance to corrosion.
(23) The inventors have attempted to extrapolate these experimental results to heavy ions of any type, such as krypton (Kr) and xenon (Xe). In order to approximately evaluate the progression and the trends in the depletion in alkali metals (sodium), the form and the extent of this depletion region, the inventors have developed a semiempirical model based both on the mean degree of sputtering by weight of a soda-lime glass, measured experimentally by loss in weight (microgravimetric weighings carried out before and after bombardment of a sample), and on experimental data relating to the degrees of sputtering associated with the different atomic species participating in the composition of the glass as a function of the type of ion, of their energy and of the dose received (data compiled in the work Stopping and Range Ions in Matter (SRIM) by James Ziegler). In this model, the inventors have incorporated the fact that the atoms sputtered out of the glass all originate from the region of travel of the incident ion in the glass and that, when stationary sputtering conditions are achieved (sputtered thickness greater than the thickness of travel of the ion), the experimental degrees of sputtering associated with each of the atomic components participating in the composition of the glass are encountered. By virtue of this model, the inventors have been able to demonstrate that, before reaching stationary sputtering conditions, a depletion region gradually becomes apparent where a mechanism of soda-lime depletion (preferred expulsion by sputtering of the sodium ions) competes, the effects of which are gradually erased by an overall sputtering by weight of the glass. When stationary conditions are achieved, the concentration profile for alkali metal ions stabilizes to give concentrations lower than the initial concentrations.
(24) By using this semiempirical model and by taking as basis a mean initial stoichiometric composition of the soda-lime glass given in table c, the inventors have obtained, for this soda-lime glass bombarded with Ar or Xe heavy ions according to three different energies (20, 40 and 60 keV) and for different doses, the following estimated results:
(25) TABLE-US-00003 TABLE c Initial stoichiometric composition of the soda-lime glass (in %) O 60 Si 25 Na 10 Ca 3 Mg 1 Al 1 Total 100
(26) TABLE-US-00004 TABLE d Estimated stoichiometric composition of Na (sodium) After bombardment After bombardment Dose with Ar with Xe (ions/cm.sup.2) 20 keV 40 keV 60 keV 20 keV 40 keV 60 keV 0 10% 10.sup.16 9.6% 9.72% 9.8% 8% 8.8% 8.8% 2 .Math. 10.sup.16 9.3% 9.4% 9.8% 3% 6.5% 7% 5 .Math. 10.sup.16 7% 8% 8.8% ~0 ~0 0 10.sup.17 ~0% 5.5% 7.2% ~0 ~0 ~0 2 .Math. 10.sup.17 ~0% ~0 1% ~0 ~0 ~0 10.sup.18 ~0% ~0 ~0 ~0 ~0 ~0
(27) From this semiempirical model, it emerges overall from table d that, for energies of between 10 and 100 keV, the possibility ought to exist of obtaining a significant depletion in sodium (Na) ions, and thus a strengthening of the resistance to leaching, by choosing a dose located: preferably between 5.10.sup.16 and 5.10.sup.17 ions/cm.sup.2 for a bombardment with argon (Ar), preferably between 5.10.sup.15 and 5.10.sup.16 ions/cm.sup.2 for a bombardment with xenon (Xe), by extrapolation, a range of between 10.sup.16 and 10.sup.17 ions/cm.sup.2 will be given for krypton (Kr).
(28) The inventors have extrapolated this semiempirical model for real beams of multicharged ions by combining the effects obtained for multienergy argon Ar.sup.+ ions. For a beam of ions composed of multicharged Ar.sup.+, Ar.sup.2+, Ar.sup.3+, Ar.sup.4+ and Ar.sup.5+ ions, the respective intensities of which are 2, 1.29, 0.6, 0.22 and 0.11 mA, extracted with a voltage of 35 kV (kilovolts) and the respective energies of which are 35, 70, 105, 140 and 175 keV (kiloelectron-Volt). The inventors have been able to estimate the concentrations of alkali metal ions Na according to two implantation doses 1.710.sup.16 and 1.710.sup.17 ions/cm.sup.2.
(29)
(30) Strengthening the resistance to leaching of the glass by prior treatment with heavy ions can only promote an increase in the durability of the superhydrophilicity obtained by treatment with nitrogen (N) or oxygen (O) ions. In order to make possible the creation of a superhydrophilic layer of very long duration, the inventors thus recommend this pretreatment by bombardment with Ar, Kr or Xe heavy ions within the ranges of doses indicated above, for the purpose of reducing the reactivity the surface to any leaching process.
(31) According to various embodiments of the treatment process of the invention for enhancing the hydrophilic properties of a glass material, which can be combined with one another: the dose of ions per unit of surface area is between 10.sup.15 ions/cm.sup.2 and 10.sup.18 ions/cm.sup.2; according to one embodiment, the dose of ions per unit of surface area is between 10.sup.15 ions/cm.sup.2 and 10.sup.17 ions/cm.sup.2; according to one embodiment, the dose of ions per unit of surface area is between 5.10.sup.15 ions/cm.sup.2 and 10.sup.18 ions/cm.sup.2; the acceleration voltage of the ions is between 5 kV and 200 kV; according to one embodiment, the acceleration voltage of the ions is between 10 kV and 100 kV; the acceleration voltage of the ions is between 10 kV and 50 kV; the acceleration voltage of the ions is between 20 kV and 40 kV; the dose of ions per unit of surface area and the acceleration voltage of the ions are determined so that the surface atomic concentration is greater than or equal to an atomic concentration threshold of 0.1% for nitrogen and an atomic concentration threshold of 2.5% for oxygen; the ions of the ion beam are nitrogen (N), the acceleration voltage AV is greater than or equal to 10 kV and the dose of ions per unit of surface area is greater than or equal to a value DNmin=(AV/20).sup.2, where DNmin is expressed in 10.sup.16 ions/cm.sup.2 and the acceleration voltage AV is expressed in kV, or else the ions of the ion beam are oxygen (O), the acceleration voltage AV is greater than or equal to 10 kV and the dose of ions per unit of surface area is greater than or equal to a value DOmin=10.Math.(AV/20).sup.1.5, where DOmin is expressed in 10.sup.16 ions/cm.sup.2 and the acceleration voltage AV is expressed in kV; the ions are produced by an electron cyclotron resonance (ECR) source which produces multicharged ions and has the advantage of being compact and sparing in energy; the glass material is chosen from the list of the soda-lime glasses.
(32) According to one embodiment, the dose of ions per unit of surface area is between 10.sup.15 ions/cm.sup.2 and 10.sup.17 ions/cm.sup.2 and the acceleration voltage of the ions is between 10 kV and 50 kV, for example between 20 kV and 40 kV.
(33) According to one embodiment, the hydrophilic treatment process of the invention comprises a preliminary stage where the dose of ions per unit of surface area and the acceleration voltage of the ions are determined according to the following stages: a. an acceleration voltage of the ions between 10 kV and 100 kV is chosen; b. a dose of ions per unit of surface area of between 10.sup.15 ions/cm.sup.2 and 10.sup.17 ions/cm.sup.2 is chosen; c. a treatment according to the invention is carried out under the conditions chosen; d. the contact angle of a drop of water on the glass material thus treated is measured; e. the measured contact angle is compared with a desired value for contact angle; f. if the measured contact angle is greater than the desired value for contact angle, a treatment according to the invention is again carried out with a dose of ions per unit of surface area double that previously used; g. stages c to f are repeated until determining the dose of ions per unit of surface area and the acceleration voltage of the ions in order to obtain a measured contact angle less than or equal to the desired value for contact angle.
(34) According to one embodiment, the desired value for contact angle is less than or equal to 20, for example equal to 20 or equal to 15 or equal to 10.
(35) Other distinguishing features and advantages of the present invention will emerge in the description below of nonlimiting implementational examples.
(36) According to implementational examples of the present invention, soda-lime glass material samples have formed the subject of studies, with nitrogen ions for some samples and with oxygen ions for other samples. These ions were emitted by an ECR source. The family of the soda-lime glasses combines glasses based on silica SiO.sub.2, on calcium and on sodium generally introduced in the manufacture in the form of CaO and Na.sub.2O. These glasses are the most widespread; they are used for the manufacture of bottles and glazings and represent of the order of 90% of glass production.
(37) The beam of nitrogen ions with an intensity of 1 mA comprises N.sup.+, N.sup.2+ and N.sup.3+ ions; the extraction and acceleration voltage is 20 kV; the N.sup.+ energy is 20 keV, the N.sup.2+ energy is 40 keV and the N.sup.3+ energy is 60 keV.
(38) The beam of oxygen ions with an intensity of 1 mA comprises O.sup.+, O.sup.2+ and O.sup.3+ ions; the extraction and acceleration voltage is 20 kV; the O.sup.+ energy is 20 keV, the O.sup.2+ energy is 40 keV and the O.sup.3+ energy is 60 keV.
(39) The sample to be treated moves with respect to the beam with a rate of movement of 120 mm/s with a side advance at each return of 4 mm (10% of the diameter of the beam, which measures 40 mm). The treatment is carried out in several parts in order to achieve the necessary dose.
(40) The hydrophilicity of the surface can be evaluated by depositing a drop of water on the surface.
(41) Tests were carried out by depositing drops of water on the surfaces treated by the process of the invention for doses corresponding to 10.sup.15, 10.sup.16 and 10.sup.17 ions/cm.sup.2 with an acceleration voltage of 20 kV. The values of the contact angles of the drops of water deposited on the glass material treated respectively with nitrogen ions and oxygen ions according to the process of the invention with different doses are given in tables 1 and 2.
(42) Tests were also carried out by depositing drops of water on the surfaces treated by the process of the invention with nitrogen ions for doses corresponding to 10.sup.15, 10.sup.16 and 10.sup.17 ions/cm.sup.2 with an acceleration voltage of 35 kV and are given in the second part of table 1.
(43) TABLE-US-00005 TABLE 1 Nitrogen Glass 10.sup.15 ions/cm.sup.2 10.sup.16 ions/cm.sup.2 10.sup.17 ions/cm.sup.2 Virgin at 20 kV at 20 kV at 20 kV Contact 62 34 9 to 12 5 angle () Glass 10.sup.15 ions/cm.sup.2 10.sup.16 ions/cm.sup.2 10.sup.17 ions/cm.sup.2 virgin to 35 kV to 35 kV to 35 kV Contact 62 61 56 40 angle ()
(44) TABLE-US-00006 TABLE 2 Oxygen Glass 10.sup.15 ions/cm.sup.2 10.sup.16 ions/cm.sup.2 10.sup.17 ions/cm.sup.2 virgin at 20 kV at 20 kV at 20 kV Contact angle 62 43 29 10 ()
(45) It is found that hydrophilic properties are obtained with nitrogen or oxygen from 10.sup.15 ions/cm.sup.2 for an acceleration voltage of 20 kV. It is found that hydrophilic properties are obtained with nitrogen from 10.sup.17 ions/cm.sup.2 for an acceleration voltage of 35 kV. The contact angle decreases with the dose. For the same dose, nitrogen is more effective than oxygen in creating superhydrophilic properties (contact angle less than 20, in particular less than 10). For an acceleration voltage of 20 kV, and for nitrogen, superhydrophilic properties are clearly observed from a dose of approximately 10.sup.16 ions/cm.sup.2; for oxygen with the same acceleration voltage, it is necessary to achieve a dose approximately ten times greater of 10.sup.17 ions/cm.sup.2. Thus, for a soda-lime glass material, there is a change from a hydrophilic behavior to a superhydrophilic behavior which is associated in particular with antifogging properties.
(46) The inventors thus demonstrate that there exists a range of possible doses for achieving a superhydrophilic nature. The minimum dose obtained by this study is 10.sup.16 ions/cm.sup.2 for nitrogen and 10.sup.17 ions/cm.sup.2 for oxygen and for an acceleration voltage of 20 kV. The inventors estimate that, overall, the dose range for achieving noticeable hydrophilic properties (contact angle of a drop of water less than or equal to 20) is approximately between 510.sup.15 ions/cm.sup.2 and 10.sup.18 ions/cm.sup.2 for an acceleration voltage of 20 kV.
(47) Furthermore, the inventors have been able to find that, for a greater acceleration voltage equal to 35 kV, the doses required in order to obtain the superhydrophilic properties (contact angle of a drop of water less than 10) are greater, approximately three times greater, than that required for a voltage of 20 kV, both for nitrogen and for oxygen. For nitrogen, the dose is approximately 310.sup.16 ions/cm.sup.2 and, for oxygen, the dose is approximately 2.510.sup.17 ions/cm.sup.2.
(48) For a voltage of 20 kV, the respective doses of 10.sup.16 nitrogen ions/cm.sup.2 and 10.sup.17 oxygen ions/cm.sup.2 correspond, after calculation, to a surface atomic concentration of implanted ions of approximately 0.1% for nitrogen and 2.5% for oxygen.
(49) For a voltage of 35 kV, the respective doses of 310.sup.16 nitrogen ions/cm.sup.2 and 310.sup.17 oxygen ions/cm.sup.2 correspond, after calculation, to a surface atomic concentration (at the furthest surface) of implanted ions of approximately 0.1% for nitrogen and 2.5% for oxygen for a voltage.
(50) On the basis of these experimental results, the inventors have estimated, by calculation, that the surface atomic concentration has to exceed an atomic concentration threshold of approximately 0.1% for nitrogen and 2.5% for oxygen in order to obtain a superhydrophilicity effect. On the basis of this threshold atomic concentration from which these superhydrophilic properties appear, the inventors have been able to calculate, by extrapolation, for a given acceleration voltage, the minimum dose required in order to obtain these superhydrophilic properties. These results are recorded in the table below for nitrogen and oxygen:
(51) For nitrogen, the following results are obtained by extrapolation:
(52) TABLE-US-00007 Acceleration voltage (kV) 10 20 30 40 50 Minimum dose required 0.15 1 2 3.6 8.8 (10.sup.16 ions/cm.sup.2)
(53) For an acceleration voltage greater than 10 kV, it is possible to extract, from this table, the empirical formula connecting the minimum dose of nitrogen ions DNmin, expressed in 10.sup.16 ions/cm.sup.2, to the acceleration voltage AV, expressed in kV:
DNmin=(AV/20).sup.2.
(54) For oxygen, the following results are obtained by extrapolation:
(55) TABLE-US-00008 Acceleration voltage (kV) 10 20 30 40 50 Minimum dose required 2.25 10 17 28 41 (10.sup.16 ions/cm.sup.2)
(56) For an acceleration voltage greater than 10 kV, it is possible to extract, from this table, the formula connecting the minimum dose of oxygen ions DOmin expressed in 10.sup.16 ions/cm.sup.2, to the acceleration voltage AV, expressed in kV:
DOmin=10.Math.(AV/20).sup.1.5
(57) The ability of a surface to discharge water, thus mist, can be evaluated by measuring the detachment angle (B) of the drop on the surface.
(58) The results are combined in tables 3 and 4 respectively for nitrogen and oxygen with ion beams, the characteristics of which are those indicated above.
(59) TABLE-US-00009 TABLE 3 Estimated doses (10.sup.16 N ions/cm.sup.2) Minimum detachment angle () 0 55 0.1 33 1 25 10 15
(60) TABLE-US-00010 TABLE 4 Estimated doses (10.sup.16 O ions/cm.sup.2) Minimum detachment angle () 0 55 0.1 48 1 32 10 20
(61) It is found that the samples treated according to the process of the invention exhibit detachment angles lower by 40 than the detachment angle of the virgin sample for nitrogen and by 35 for oxygen. This means that the force necessary in order to cause the drop of water to slide is lower. This sliding force Fs corresponds to the weight W of the drop projected onto the sliding plane: Fs=Wsin(A). On applying this rule, it is estimated that the sliding force of the drop for the virgin sample is equal to W.Math.sin(55) and, for a dose of 10.sup.17 ions/cm.sup.2, is equal to W.Math.sin(15), i.e. a decrease in the adhesion of the drop to the treated glass material by a factor of 70%.
(62) According to different embodiments of the process according to the present invention, which can be combined with one another: the glass material is movable with respect to the ion beam at a rate, R.sub.FP, of between 0.1 mm/s and 1000 mm/s. It is thus possible to move the sample in order to treat regions for which the size is greater than that of the beam. The rate of forward progression R.sub.FP can be unchanging or variable. According to one embodiment, the glass material moves and the ion beam is stationary. According to another embodiment, the ion beam scans the glass material. It is also possible for the glass material to move when the ion beam is movable. According to one embodiment, the same region of the glass material is moved under the ion beam according to a plurality, N, of passes at the rate R.sub.FP. It is thus possible to treat the same region of the glass material with a dose of ions corresponding to the sum of the doses of ions received by this region on conclusion of the N passes. It should also be noted that, if the size of the glass material allows it, the treatment stage can be static and result from one or more flashes of ions.
(63) The superhydrophilic surfaces treated according to the process of the invention thus exhibit a threefold advantage: Of inhibiting the formation of mist independently of the brightness conditions, over a long period of time. Of bringing about better spreading of the droplets, which merge to give a film of water which evaporates more rapidly. Of more rapidly discharging the droplets located on slightly inclined planes.