DK141331B - Process for modifying one or more properties of bodies of glass, vitrocrystalline, ceramic or mineral material. - Google Patents

Description

(tf) \ fiay di) PUBLICATION MANUAL 1 A-1 33 1 DENMARK c »mt.ci. = c os c 21/00 '(21) Application No 4828 / ¾ (22) Filed on 9 · B®P · 19¾ (23) Race day 9 · B®P · 19¾ (44) The assessment presented and

submitted to the public on the 25th of December

DIRECTORATE OF

PATENT AND TRADE MARKET (30) Priority gassed from dm

Sep 12 1968, 56873, LU 15 Aug. 1969 # 40892/69, GB

(71) GLAVERBEL MECANIVER, 166, Chaussee de la Hulpe, Watermael-Boitsfort, ΉΕ.

(72) Inventor: Emile Plumat, 279, Chaussee de Raneart, Gllly, BE: Francois Toussaint, Rue Terry Mouchon, 101, Lodellneart, BE.

(74) Plenipotentiary under consideration:

The engineering firm Lehmann & Ree.

(04) Process for modifying one or more properties of glass, vitrocrystalline, ceramic or mineral material.

The invention relates to a method for modifying one or more properties of bodies of glass, vitrocrystalline, ceramic or mineral material as a result of diffusion of at least one compound into the body from a medium in contact with CC

It is well known to bring substances to diffuse into glass bodies from a contact medium consisting of or containing a molten nitrate salt. In this way, various modifications can be obtained depending on the nature of the diffused substance and the conditions present in the treatment. By way of example, the diffusion can provide a change in the surface composition of the glass or an increase in its breaking strength.

These diffusion treatments are not easy to perform under industrial mass production conditions and achieve predictable and similar results. One of the difficulties is to ensure that the diffusion takes place sufficiently and predictably over a predetermined period of time. Sometimes the diffusion is delayed foreseeably after providing the conditions under which diffusion should take place, or the diffusion begins, after starting, to slow down or even stop, so that at the end of the stipulated period the required modification.

However, from the specification of Belgian Patent No. 712,091, it is known that these problems can be remedied by the addition of a regenerant and - possibly gaseous - auxiliary, such as e.g. CO 2 · The regenerant is present there as a separate, solid or liquid phase.

The object of the present invention is to provide a particularly advantageous method of the kind mentioned in the preamble of claim 11. This is achieved with the process according to the invention, characterized in that the medium consists of a molten nitrate or consists of molten salts, at least one of which is a molten nitrate and that the diffusion is carried out while the molten salt or salts are in contact with CC 2 in an amount of at least 0.1 liter / minute / m nitrate.

The use of the annoying regenerant is avoided, and in comparative experiments in which glass bodies of similar composition were treated, it was found that in cases where a medium in contact with CO 2 was used in the indicated amounts, diffusion began much faster than when the same medium was used under the same conditions, but in the absence of CC> 2.

Similar benefits were obtained from experiments with bodies of in vitro crystalline material. The reasons for the advantageous results of using CO 2 gas in the amounts indicated have not yet been fully established.

Possibly, the result is due to an influence of CC> 2 on the dissociation or dissociation and recombination reactions in the treatment medium, which increases the presence of O-ions, which in turn promotes the onset of diffusion.

Given the effect of CO 2, a certain modification of the treated body can be provided with the treatment medium at lower temperature, and this is advantageous, especially to avoid any unwanted deformation of the body.

The invention makes it possible to carry out a particular treatment e.g. a certain chemical cure during a treatment period that is substantially shorter than heretofore, with the result that chemically cured and otherwise treated articles can be made cheaper.

In carrying out the invention, it is not necessary that CO2 be present for the entire period of time during which one or more substances diffuse into the body from a contact medium. The benefit is obtained by complying with the above conditions only for an initial portion of the total period during which the diffusion takes place.

Of course, it is not necessary that the medium from which the diffusion takes place touch the whole body being treated. Such overall treatment may often be desirable, but in some cases it may be desirable to limit the treatment to only one or more parts of the body, e.g. in the case of a glass plate, to limit the treatment to the edge or edge portions of the plate to modify the appearance of or to reinforce only those parts.

The invention is of particular potential importance with regard to so-called chemical curing. It is known that glass can be reinforced by a chemical curing treatment, under which substance is caused to diffuse into the glass from a contacting medium while controlling the temperature during and after this diffusion so that the outer layer of the glass is brought into a pressure-pampering state or state. with increased tensile stress.

Chemical curing usually involves replacing ions in the glass with ions obtained from the touching treatment medium. It is e.g. it is possible to provide compressive stresses by replacing ions in the outer layer of the glass with ions which give these outer layers a less thermal expansion coefficient at a temperature sufficiently high and maintained for a sufficient period of time for stress equalization, and then allow the glass to cool. As another option, surface pressure stresses can be provided by replacing ions in the outer layer of the glass with larger ions, while the surface layer of the glass is at an elevated temperature, however, too low to allow substantial or at least not complete stress equalization during that time. at which this temperature is maintained, the glass being then cooled to normal temperature so that the induced voltages are "frozen". Furthermore, it is possible to provide surface pressure stresses by causing ions to penetrate the glass through a surface thereon from a contact medium under the influence of an electric field without a simultaneous equal movement of ions from the glass into the contact medium through this surface.

A chemical curing process can be applied not only to a glass body but also to a body of vitrocrystalline material. The curing treatment, applied to such a body, gives the best results when the phase of the vitrocrystalline material which is susceptible to the greater or greater degree of diffusion of substance from the contact medium is well distributed over the body surface. A chemical curing process can also be applied to a ceramic or rock body, provided that at the material surface sufficient ions are present, which are mobile at the treatment temperature, to allow the provision of surface pressure stresses or increase of surface stresses upon introduction or exchange of such ions. .

In the aforementioned chemical curing methods, the diffusion of substance into the body being treated is usually part of an ion exchange between the body and the contact medium. Particular importance is attached to processes according to the invention where the diffusion is part of an ion exchange phenomenon and especially to processes where this ion exchange is an exchange of alkali metal ions. However, it is to be understood that ion exchange is not essential to the invention. To give an example of an alternative type of method, it is possible to introduce ions into a body of glass, vitrocrystalline material, ceramics or rock from a contact medium without an associated movement of ions from the body into the medium by conducting the diffusion under the influence of an applied electric field which may be a continuous or pulsating unidirectional field or alternating field, and in a preferred embodiment of the invention, the diffusion of at least one substance into the body is carried out during at least part of the diffusion period during influence of an electric field.

The immediately preferred embodiments of the invention are embodiments in which potassium ions are introduced into the body from the contact medium in exchange with sodium ions under conditions such that curing of the body is carried out. In these processes, the treatment medium preferably comprises molten potassium nitrate.

The molten medium may constitute a bath in which the body to be treated, or a portion thereof, is immersed in the diffusion period.

As another option, at least one continuous or atomized stream of the medium can be applied to the body and caused to flow along the body.

There is an advantage of this method of contacting the body with the treatment medium, promoting the uniformity of treatment of the surface or surfaces wetted by the medium.

When a molten medium is used in the form of a treatment bath, the CO 2 gas can be bubbled through the bath. By appropriately injecting the gas, it can be ensured that even in a large-sized bath, the gas is distributed throughout the bath, and furthermore that, as the case may be, all dissociation and recombination products are distributed in the bath rather than being confined to site of their formation, and thus prevent or reduce any further influence. Thus, the diffusion initiation is promoted in a very favorable manner by bubbling CO 2 through the medium.

Preferably, the CO 2 gas is mixed with air. This mixture further increases the initial rate of diffusion, probably by further influencing the 0-ion content in the bath.

According to the invention, the amount of CO- brought into contact with 3 the molten salt or salts is at least 0.1 liter / minute / m nitrate (under standard conditions). If desired, the CO 2 gas can be used mixed with an inert gas such as nitrogen.

CO2, possibly in admixture with any other gas used in the process, may be introduced continuously or pulsed.

In the case where treatment is for example flowing over the body to be treated as discussed above, CO in admixture with any other gas used, is simultaneously blown against the surface or surfaces of the body so as to touch the medium flowing over this or these surfaces.

The invention will now be elucidated by means of a number of particular examples.

Example 1

A plate of ordinary baking soda lime was immersed in a bath o of molten potassium nitrate at a temperature of 470 ° C and immersed for a period of 20 hours. C0 ~ gas in an amount of 2.5 liters / minute / 3 Δ m of salt was bubbled through the bath throughout this time. Examination of the glass plate after its removal from the bath revealed that potassium ions emanating from the molten nitrate bath had replaced sodium ions in the glass at a depth of 30 microns from each of the plate's surfaces. This penetration was determined by a microprobe. As a result of the ion exchange, the glass plate had significantly higher breaking strength than before the treatment.

In a comparison experiment conducted on a similar glass plate under similar conditions except that no CO 2 was used, potassium ions could not be detected in the glass plate after its removal from the bath.

Example 2.

Plates of baking soda made of the following composition (by weight): SK> 2 68%

Na₂O 22.5%

CaO 9.5% 6 was chemically cured by spraying the plate with RbNO4 at 445 ° C, the Rubidi nitrate flowing continuously over the glass plate surfaces for 2 days. Examination of the plates showed that no rubidium ions were diffused into the glass. The room in which the treatment was carried out was then filled with CO 2 · The ambient atmosphere was made up of 100% CO 2 and was maintained by injecting CO 2 into the treatment room in an amount of 10 liters / minute / m 2 salt. The rubidium ions diffused into the glass and, after 30 hours of treatment, a significant increase in the breaking strength of the glass plates was already noticed.

Example 3

One of three portions of glass sheets made with the following composition (by weight):

SiO2 71% A1203 2%

Na20 13%

CaO 12% 3, measuring 1.60 m x 55 cm x 1 mm, was immersed in 8 m of a mixture comprising 99.8 wt% KNO 2 and 0.2 wt% I 2 CO 2 / with the temperature of the bath being 468 ° C. After 20 hours, the plates were removed from the bath. No ion exchange had taken place between the glass and the molten material in the bath.

In another experiment, another of the three batches of plates was immersed for 20 hours in a bath of the same composition but having a temperature of 485 °. Significant ion exchange occurred during this time, but the plates were deformed as a result of their exposure to the higher temperature.

In a third experiment, the third batch of plates was immersed for 20 hours in a bath of the same composition and temperature (468 ° C) as the one used in the first experiment, and CO 2 and air mixed were blown through the bath with a speed of 10 liters of CO2 and 40 liters of air per day. per minute m nitrate. The plates were removed from the bath after 20 hours and it was found that potassium ions had penetrated the plates at a depth of up to 30 microns from the plate surfaces, resulting in a significant increase in the breaking strength of the plates. The plates were free of deformation.

Example 4

A few of the batches of plates mentioned in the second part of Example 2 which had been enhanced by diffusion of rubidium ions into the glass in exchange for sodium ions were stored for 1 month in an ambient atmosphere at 20 ° C and then immersed in 20 minutes in a molten salt bath composed of 98% by weight NaNO3 and 2% by weight LiNO3 and at a temperature of 440Oq. No ion exchange between the plates and the molten medium occurred during this time. Some of the plates remained in the bath and then 3 CC> 2 was blown in an amount of 3 liters / minute / m salt. through the bath. After a period of 20 minutes, significant amounts of lithium and sodium ions were found in the glass in addition to the rubidium ions.

Example 5

A few of a portion of identical pieces of ceramic material made with the following composition (by weight): A1203 40%

Si02 55%

Na 2 O was immersed in a bath of pure potassium nitrate at 450 ° C and, during the immersion, the samples were exposed to a unidirectional electric field whose mean value between the electrodes was 50 V / cm, the electrodes being placed next to the samples. After a period of 10 hours, some of the pieces were removed from the bath to be examined and a mixture of CO 2 and air consisting of 30% by volume CO and 70% by volume of air in an amount of 2 liters mixture / minute / m salt is blown through the bath, which still contained the other pieces, preserving the electric field. Upon examination of the pieces taken, it was found that little or no ion exchange had occurred between the pieces and the molten salt during the 10 hour immersion period. The pieces left in the bath were removed after a further period of 1 hour and it was found that during this time potassium ions were diffused into the pieces at a depth of up to 70 microns. In another comparative experiment, the remaining pieces in the original portion were subjected to a similar sample in the presence of the above-mentioned mixture of CO 2 and air (30 vol% CO 2 and 70 vol% air), but an electric alternating field at a frequency of 16 , 6-10-3 Hz. In this case, the potassium ions penetrated into the test pieces to a depth of 25 microns on both sides.

Example 6

A piece of nepheline rock (Na ^ KAl ^ Si ^ O ^ g) was immersed in a bath of KNO. ^ Having a temperature of 470 ° C. No diffusion of ions into the rock occurred during a dipping period of 30 hours. In a comparison experiment on a similar piece of rock, under which the conditions were the same as before, with the only exception being a mixture of air and CO, in a volume ratio of 3: 1 and ^ 3 in an amount of 5 liters of mixture / minute / m of salt through the bath, a significant amount of potassium ions diffused into the rock in exchange for sodium ions during the 30-hour immersion period, with the result that the mechanical strength of the piece of rock increased.

8 141331

Example 7

Plates of vitrocrystalline material made of the following composition (by weight):

Si02 48%

Al203 32%

Na 2 O 10%

CaO 2%

TiO 2 8% was immersed in various potassium nitrate baths at 500 ° C. No diffusion of potassium ions into the plates occurred over a period of 5 hours. At the end of this time, CO2 in an amount of 0.5 liters / minute / m nitrate is bubbled through some of the baths.

In these baths, significant diffusion of potassium ions into the plates in exchange for sodium ions in the glass phase on the plate surfaces occurred during the following 5 hour period, whereas diffusion still did not occur in the other baths.