Method of strengthening by coating bodies made of vitreous or partly vitreous material

PUBLISHING WRITING No. 337 659 mtci C 03 c 17 / 02Kl. 32 b 17/02

SWEDEN

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PATENTS AND REGISTRATION OFFICE

Patent Application. No 5711/68 Filed on 26 IV 1968 Validity Day on 26 IV 1968

Ans. generally available on 28 X 1968

Ans. laid out and the pamphlet published 16 viii 1971

Priority requested from 27 IV 1967 (Luxembourg, 53 54θ) and 4 III 1968 (United Kingdom, 10 459)

GLAVEEBEL, WATERMÄEL-BOITSFORT, BELGIUM

Inventor E Plumat, Gilly and R van Laethem, Loverval

Ombud PU Brain

Ways to increase the strength of objects of glass or glass ceramic material

The invention relates to a method of increasing the strength of articles made of glassy or partially glassy material, e.g. glass ceramic material and articles treated in such manner.

D_en The mechanical strength of objects made of normally cooled glass or material comprising a certain proportion of a glass phase or phases, such as glass ceramic or glass crystalline material, is adversely affected by the presence of microscopic surface cracks or scratches. Such faults act as a voltage booster when the surface that is incorrectly exposed is subjected to tensile stresses. The microcracks can also propagate spontaneously. This explains why the tensile strength of an ordinary glass sheet is twenty times lower than its compressive strength.

It is well known that the tensile strength of glass can be improved by curing it by heat. The temperature conditions prevailing in such treatment tend to deform certain objects and heat cure is therefore not always a satisfactory solution to the problem.

Dupl. kl. 52 bs17 / 22

Special glass, which have considerable hardness and resistance to scratching and / or which can be glazed in heat to increase their surface hardness, are also known. The composition of such glasses makes them expensive.

According to the present invention, the strength of an article made of glass or partially glassy material is increased, e.g. glass ceramic material by flashing onto a portion of the article to form a glassy coating which adheres to the article and which differs in chemical composition from the article, so that a solid state phase conversion can be achieved in the coating, whereby the solid state phase conversion is induced by one or more physical treatments, so that one or more new vitreous phases are formed during or during and after the phase transformation and that the phase conversion in the solid state makes the coating at least as hard as the object by the presence of the new vitreous phase (s).

It has been found that if a piece of glass provided with surface scratches according to this method is provided with a coating (which can be quite thin) that covers the scratched surface or surfaces, the coated glass can stand up to considerably higher tensile strengths than the uncoated glass. Due to the phase conversion in situ, the coating acts to some extent to prevent the propagation of the cracks, but the reason for this phenomenon is not properly understood.

The invention is particularly intended although not exclusively for use in the reinforcement of glass objects, e.g. flat or curved glass sheets or continuous glass strips (including drawn glass and mirror glass) and bottles, bottles, insulators, mugs and other glassware. The increase in the strength of a glass band or glass sheet usually involves coating at least one or each of the main surfaces of the sheet or tape, if not the edges thereof. However, depending on the nature of the coating composition, advantages can sometimes be gained by coating only the edges or only the edges and adjacent edge areas of the main surfaces of the sheet or tape. The application of the coating composition to the edges of a glass sheet and subsequent treatment of the coating in accordance with the invention is particularly favorable.

The invention can be applied with particular advantage to increase the strength of articles made of glass of ordinary composition, e.g. glass made from readily available inexpensive ingredients, e.g. quartz, soda, lime and feldspar, as such glasses have remarkably good optical, acoustic and thermal properties and, for many purposes, require an improvement only in their mechanical properties. Embodiments of the invention which are of particular importance in which an article of such an inexpensive glass is coated with a more readily crystallizable glass or crystallization or recrystallization are provided in situ in the coating.

If the coating applied to the article is amorphous, this has certain advantages in that such an amorphous coating can easily be applied as a film with a uniform surface and thickness.

According to certain embodiments of the invention, the coating composition is selected and applied so as to form a glassy film in which solid phase transformation, e.g. Separation between glass and crystalline phases can be achieved by heat treatment. Glassy film coatings adhere particularly well to glassy and therefore glassy surfaces. In addition, compact glass films can have a considerable thickness say on the order of 1 mm.

As will be exemplified below, it is possible to coat an article with a glassy film, whereby at least one crystalline phase can then be readily separated by suitable heat treatment. Such a crystalline phase or phases can form a relatively fine network on the surface of the coated glass or glass crystalline material and thus guarantee that if this material is loaded to break it is broken into very small fragments which are not sharp and cut. However, some vitreous films exhibit phase separation when subjected to appropriate heat treatment in the sense that one or more new vitreous stains appear. A coating which exhibits various glassy phases and which has undergone phase conversion, in situ, in this way can also prevent glass from breaking into sharp pieces or fragments.

It has been found that various glass compositions, which have not hitherto been assumed to fall within the category of separating glass, are in reality sensitive to the development of phase separation by suitable heat treatment. Examples of such glasses will be given below.

In other embodiments of the invention, the coating composition is selected and applied to form a crystalline coating in which solid phase conversion can be achieved by heat treatment.

As will be exemplified later, coatings containing one or more crystalline phases may be formed in which one or more new crystalline phases may be formed by heat treatment. Phase conversion may involve interdiffusion or interference of various crystalline phases, which promote homogeneity of the coating. It has been found that in such crystalline coatings, mineral compounds with advantageous mechanical or optical or chemical properties, e.g.

4 · spinels are easily and quickly formed. Glass phases can also be caused to appear in some crystalline coating films. Generally, heat treatments to perform and effect this kind of phase conversion involve heating the coating to melt temperature and then cooling it relatively quickly. This process is of course only applicable if the phase conversion occurs at a temperature lower than the deformation point of the coated glassy or partially glassy material.

To achieve specific optical effects, e.g. increased light reflection, it is advantageous to provide a coating which in its final transformed state comprises glassy phases with a high refractive index, e.g. phases included bl. a. a lead oxide, bismuth or titanium.

The method according to the invention has the additional advantage that the final material can have higher surface hardness as well as improved tensile strength. It is obvious that this property is important in that it makes it possible to manufacture a material with a high degree of surface hardness using a glass substrate without special components, e.g. a single glass with a hardness according to Moh's hardness scale of 7 or less. The coating which provides the desired surface hardness may comprise hard constituents which have a melting temperature which is too high to be used in the manufacture of glass for drawing or otherwise formed into shaped articles, but which can be used to form a thin film through one or the other. another of the technical procedures described below. In order to achieve a high degree of surface hardness, it is useful to form a coating comprising at least one crystalline phase composed of quartz (SiO 2), zircon (ZrSiO 2), beryl (A 2 Be 2 Si 2 g), topaz (AlgSiO 2 (F.0H)₂, ZrBg, TiN, TaC, ZrC, corundum (Al₂0 ^), B₂C, TiC, SiC or A1B. A glass article exhibiting such a crystalline coating is not expensive and may exhibit a surface hardness greater than the hardness of the corresponding mineral crystal. The hardness of topaz according to Moh's hardness scale is 8, while a film formed of wide topaz crystals on glass exhibits a hardness of 8.5 applied to a glass with a hardness of 6.5 according to the same hardness scale.

Improved surface hardness can be achieved not only by coatings which are completely crystalline, but also by coatings which in their final state include both a crystalline phase or phases and a glass phase or phases. The glass phase can go in one with the glass material in the substrate.

For example, If one or more crystalline powders, such as quartz or corundum, are showered on a glass substrate heated to softening temperature, the crystalline phase will be mechanically integrated into the glass surface and diffusion often occurs between the lattice of the crystals and the glass phase.

It is to be understood that the coating where the phase conversion occurs does not necessarily need to be continuous. Thus, small areas of a glassy coated surface may be exposed. In addition, the phase conversion may extend slightly into the surface of the substrate and the adhesion of the coating thereby improved.

The coating may, of course, contain hard crystals formed during the phase conversion either from any other crystalline phase or phases or by degassing of a glass phase or phases. The latter method is favorable for the formation of a hard thin film of uniform thickness.

An article coated by a method according to the invention may be subjected to a curing treatment, e.g. in a manner similar to thermosetting glass, if the object is able to withstand this treatment without being deformed. Alternatively, pressure surface stresses can be induced or increased by diffusing ions into the coating from a touching medium in a similar manner known to chemically cure glass processes.

The solid state phase conversion in the coating can in most cases be achieved or initiated by heat treatment. The term solid phase conversion is not intended to exclude conversions where the constituents undergoing conversion pass through an intermediate molten or flowable state. In some cases, a suitable heat treatment may in fact involve heating the coating formed initially to bring it, at least partially melted, followed by cooling to a temperature range favorable for a solid phase or phases to appear distinct in its physical structure and / or any composition from any phase contained in the original glassy, ​​crystalline or glass crystalline coating. In any case, however, a solid state transformation is accomplished by converting a material forming or forming part of a solid coating onto the substrate to form a phase or phases of different structure and / or composition from that previously formed in the solid state. coating.

The use of the term heat treatment does not include only treatments where an increase in the temperature of the coating occurs to effect the phase conversion. Ingredients for forming an initial layer may e.g. applied in a molten state and if the ingredients are selected appropriately, the only subsequent necessary heat is 337659^rthe treatment a control of the cooling so that the coating is cooled according to a scheme suitable to ensure that after or during solidification of the coating, a solid phase conversion takes place within the coating, this conversion occurring either during the cooling or after a period of time which may be short or long. Depending on the composition of the coating, the phase conversion can take from a few seconds to several days.

Significant advantages lie in applying the coating composition to a glass or partially vitreous object while at elevated temperature during a molding process, e.g. a drawing process in the manufacture of disc glass. In particular, there is a considerable economy in heat consumption compared to processes where the object is allowed to cool and then reheated before the application of the coating. The coating of glass during the drawing to sheets is an important application of the invention. In such a drawing process, the continuously drawn glass strip is cut into slices as it leaves the drawing machine. The coating composition may be applied to the drawing chamber, e.g. slightly above the glass meniscus. The coating components may e.g. is composed of salts, applied in finely divided or evaporated form, or powder of high melting point, applied by sprinkling and may form on one or each surface of the glass a film which is fixed to or integrated with the glass. If the phase conversion that occurs in the coating or coatings gives the coating or coatings a hardness which makes cutting difficult, this is not necessarily a disadvantage, since in some cases the phase conversion does not normally occur or is complete until after &lt;hn time when cutting has already taken place. in the manufacture of glass sheets. In cases where the phase conversion normally occurs faster, it can be delayed.

The application of a coating composition to the glassy or partially glassy substrate, while being at a temperature above its softening point, ensures that the coating is well bonded to the substrate. In some cases, volatile materials will be released, such as HgO, H₂In the form of microscopic bubbles, which also suggest a phase conversion. Such bubbles can form active centers that promote solid phase transformation.

If a coating composition is applied in a molten state to a cooled glass surface, the applied composition has a tendency to improve such a surface by a kind of polishing action, so that this process also has its advantages.

A variety of coating methods can be used to apply a coating composition in carrying out the method of the invention. The choice of approach must of course take into account the nature of the composition constituents in any given case.

As an example, the coating substances can be atomized or brought into steam state in contact with the substrate, e.g. by evaporation of coating substances in vacuo. By these different methods thick or very thin amorphous layers of uniform thickness can be formed. Various components can be atomized simultaneously or in succession with an amount and a speed that can be controlled during deposition. Alternatively, coating may be by immersion of the vitreous or partially vitreous article. This method allows relatively thick coatings to be formed on a glass, which has a lower melting temperature than the material in the substrate. By way of example, the substrate or one of its surfaces to be coated can be immersed in molten salts to form a crystalline coating layer or a coating of relatively soft glass.

Different coating procedures can be used to apply different ingredients in a given coating, either simultaneously or in succession. Thus, one component may be applied by evaporation in vacuo, and another component may be applied by immersion or sputtering. In real samples, ordinary glass coatings were formed by atomizing SiO and CaSiO4 followed by immersion in a suspension of AgCl + NaOH and then by a heat treatment to induce phase separation. It was found that when a heat treatment was carried out at low temperature, the final coating exhibited photographic properties. The phase transformation consisted mainly of the appearance of a new crystalline phase. When the heat treatment was carried out at a high temperature, the final coating exhibited phototropic properties, ie. it became reversibly less translucent to light when exposed to light of increasing intensity, the original translucency recovered automatically at decreasing intensity in the irradiating light. Phase conversion that occurs as a result of the heat treatment at the higher temperature resulted mainly in the appearance of a new glass phase.

In several cases, phase conversion can be promoted by including a dopant in the coating composition. The effect of such agents may be to reduce the time for phase conversion to occur or to induce phase conversion in glass, which would normally for theoretical reasons be considered incapable of separation. As dopants, the oxides of the following elements may be specifically mentioned: Ti, Mn, Cu, Co, Cd, Ni, Al, Zr,

Rb, Fe, Mg, Be, V, rare earth metals and precious metals, the choice being made in a given case such that the yalence on the cation of the dopant differs from the cation of the new phases, the formation of which is to be promoted. Said dopants may be combined with other compounds in complex phases in the coating film or they may form a particular phase. A coating formed by Si0₂, Al₂0 ^ oeh Na₂0 in which phase separations usually occur after 10 hours at 800 ° C, e.g. separated in the same phases after 1 hour at 700 ° C of 2 wt% TiO₂ is included in the film, but the final coating then contains a phase composed almost entirely of Ti0₂ in the form of rutile. Phase conversion in a coating can also be promoted by exposing the coating film to sound waves or ultrasonic waves at a frequency higher than 10,000 periods / second and even over 10 million periods / second. This treatment can be combined with any other treatment, e.g. heat treatment. It has been found that in this way the initial separation of phases, either glassy or crystalline, can be greatly accelerated. In this process, unusual crystallographic phases are sometimes obtained, as is the case with zinc, cadmium and their oxides. Preferably, the waves are generated by electrostrictive or piezoelectric methods, or by barium titanate generators, but especially at very high frequencies by magnetostriction, by superimposing a continuous magnetic field and a high frequency magnetic field Vibrating at the specific frequency, e.g. that of a steel plate arranged parallel to the surface of the glass plate or other substrate supporting the coating film or even performing oscillations at the specific frequency of the film itself. Electrical effects ranging from 50 to 3,000 watts / m have been used. The phase separation rate is multiplied by 10 ...... 1,000 depending on the power used.

The coating film formed in accordance with the invention may exhibit either as a result of the heat treatment or for any other reason a coefficient of thermal expansion which differs from the corresponding coefficient of the glassy or partially glassy substrate. If the coating has an expansion coefficient that is higher than the substrate, the method of the invention may exert the additional beneficial effect of generating or increasing the compressive stresses in the surface of the coated substrate. However, it is permissible for the coating to have a lower coefficient of thermal expansion than the substrate, because the effect of the coating in preventing or reducing the risk of propagating surface cracks in the substrate may consider the reduction in compressive stresses in the substrate surface or the elimination of tensile stresses therein. nevertheless improved.

Various embodiments of the invention will now be described in conjunction with the accompanying drawings, in which: Figure 1 is a sectional elevational view of a portion of a Pittsburgh process for drawing glass; Figure 2 a section along line II-II of Figure .

and Fig. 3 is a phase separation curve.

Example I

Figures 1 and 2 show a glass oven 1 comprising a bottom 2, a side wall 3 and a vault provided with a front part 4 and a middle part 5 · The surface level of the glass is denoted by 6. A strip of glass 8 is drawn from the molten mass in the drawing chamber 14. The meniscus 7 to the drawn glass band 8 is stabilized by a drawbar 9 arranged centrally with respect to two L-shaped blocks 1.0. Tilted walls 11 connect the tops of the blocks 10 to a tower portion 12 which in itself occupies tensile roll pairs, of which only one 13 is shown. The pull rollers pull the belt 8-up through the barrel portion. The cooled glass leaves the tower part in the top and is cut into slices.

Two main coolers 15 are arranged opposite the glass band 8 in the drawing chamber, near the meniscus. Gas burner tubes 16 with gas discharge nozzles 17 are disposed along the inner surfaces of the coolers 15 and leave a series of flames 18. Higher up in the drawing chamber 14 are two auxiliary coolers 19 supported at one end of conduits 20 for supply of coolant. The auxiliary coolers 19 are also equipped with a gas supply line 21 formed with openings 22 for leaving flames 22 '.

A hopper 30 can be fed with one or several very finely divided powders from distributors (not shown). This funnel is formed by an inclined wall 31 which touches a rotating distribution cylinder 32, the surface of which 33 is sand-coated and by an inclined wall 34 of adjustable height, whose lower end 3? is arranged at a small distance from the surface of the cylinder 32. The bottom end of the funnel 30 communicates with an inclined jib 36 extending through the wall 11, the lower end 37 of this jam being disposed near the glass band 8. The lower end of the jam, which is subjected to the high temperatures, is surrounded by a sleeve. 38 through which water is circulated through openings 34 and 40. Electric vibrator elements 41 are attached to the lower part of the jam 36.

Powder feeding equipment identical to the parts bearing reference numerals 30-41 are symmetrically arranged on the other side of the drawing chamber to feed the powder to the other side of the glass band, but this equipment has been omitted from the drawing.

Powdered material is fed in precisely dosed amounts to the funnel 30 so that it is filled to a level slightly higher than the bottom of the inclined wall 34. The cylinder 32 rotates clockwise as shown by the arrow and feeds the powder into the baffle 36. The powder is discharged as a fine shower on the surface of the glass band 8 above the meniscus 7.

Glass made of a kit with the following weight composition:

<td>Si0₂</td><td> 70%</td>

<td>Na₂0</td><td> 12%</td>

<td>CaO</td><td> 10%</td>

<td>MgO</td><td> 3%</td>

<td>Fairy₂0₃</td><td>track</td>

<td>ai₂O₃</td><td> 5%</td>

1 and 2. The temperature of the glass in the meniscus 7 was 920 ° C. A strip drawn from such a glass exhibited, in a cooled state, a surface hardness of about 6.6 according to Mohs' scale.

The funnel 30 (and the second funnel, not shown) was fed with a powdered special glass (dimensions between 10 and 50 microns), obtained by melting a batch of the following composition at 1,000 ° C followed by refining, abrupt cooling and crushing:

ZnO: 60%

B₂0₃ : 20%

Si0₂ : 10%

Ρ₂θ_? ·' 6%

A1₂O₃ : 2%

Na₂0 : 2%

The powder leaving the jam 36 and the jam on the other side of the drawing chamber formed adhesive coatings 42 on the glass band 8 when the glass in the contact area was still soft. The applied powder was formed into a glassy coating film in the drying section, where the temperature in the upper part was 80 ° C. The coated glass could easily be cut even after storage for one hour at ambient temperature. However, a solid state transformation had already begun in coatings after that time and, depending on this, it was found that the glass was completely split along the cutting line.

The phase conversion continued during storage and after 100 hours at ambient temperature the coatings included a glass phase of zinc borate and another glass phase of aluminum phosphorus silicate. The coating film 42 on each side of the deflected glass had a thickness of a few fractions of a millimeter. The bending strength of the glass was increased tenfold due to the coatings.

A treatment was carried out identical to that just described except for 1 wt% industrial TiO₂ (grain size &lt;20 microns), the above powdered glass was added to the hopper.

The coating layers were given the same heat treatment, ie. cooling from 92 ° C to 80 ° C in the barrel portion 12. The cooled coated glass could still be easily cut, but phase conversion in the coating layers was completed within 10 hours. This shortening of time can possibly be attributed to the titanium ions having a valence of 4 ·, which differs from the aluminum cations (+ 3) and the zinc cations (+ 2). In addition, the glass phases formed in the coatings of this comparative sample contained a practically pure crystalline phase of Ti₂. When the coated glass was bent into rupture after the phase transformation was completed, it was split into very small non-cutting pieces.

A further treatment was then carried out identical to that just described except that 5% by weight alumina (grain size less than 30 microns) was added to the powdered glass in the funnel 30 except the addition of 1% by weight titanium dioxide.

The resulting coated glass had similar properties to that obtained in the previous treatment, but the surface hardness was greater. The hardness reached 8.5, within 10 hours according to Moh's hardness scale. This can be attributed to the appearance of a crystalline phase rich in corundum in the coating layers. After the treatment, it was found that the coating layers were very difficult to scratch or scratch.

Example II

Glass ceramic discs were made from a kit with the following weight composition:

<td>Si0₂</td><td>5o%</td>

<td>algo +</td><td> 25%</td>

<td>Li₂0</td><td>co</td>

<td>Ti0₂</td><td> 4-%</td>

<td>CaO</td><td> 7%</td>

<td>^p2°5</td><td> 6%</td>

by melting, refining, shaping and heat treatment for 80 hours at 700 ° C. The glass ceramic material was crystalline in the panels themselves and opaque, but contained at least in the surface areas of the panels about 25% glass phase. The material was brittle and had a tensile strength of 11 kg / mm².

First 10% by weight of AgCl was deposited and then at the same time $ 20

SiO, $ 50 CaSiOg, $ 20 AlgO4 calculated in weight percent on the disks by evaporation in vacuum and in darkness. The discs were then heated to another

600 ° C in the dark for 20 hours. Phase transformation took place in the deposited coating layers, with the result that the coatings comprised three phases:

aluminum silicate, calcium aluminate and silver chloride. The discs had o photographic properties and their tensile strength was 100 kg / mm.

Example III

Bottles and electrical insulators of borosilicate glass formed of a kit with the following weight composition:

<td>Si0₂</td><td> 60$</td>

<td>Na₂0</td><td> 12$</td>

<td>CaO</td><td> 10$</td>

<td>MgO</td><td> 6$</td>

<td>^B2°3</td><td> 6$</td>

<td>^p2°5</td><td> 1$</td>

<td>al₂0g</td><td> 5$</td>

is evaporated in vacuo with a coating of 60 $ Si0₂, $ 10 Al₂0g, 10 $ CaO, 5 $ MgO, 5 $ Ti0₂, $ 10 Na₂0 (weight percent), the coatings having a thickness of 0.1 micron.

The vials were then irradiated with X-rays to initiate nucleation in them and then heated for 1 hour at 500 ° C during which time the vials were intermittently exposed to ultrasound pulses at a frequency of 50,000 periods / second for intervals of 5 seconds. Glass crystals appeared in the coatings, i.a. rutile, titanite, wollastonite, diopside, enstatite, albite, in a glass phase. The impact and vibrational strength of the bottles doubled throughout the treatment and at breakage, the objects were split into small, essentially non-cutting fragments.

Example IV

Fig. 3 shows a curve for a phase splitting glass, made of 5 $ P₂° 5 θ⁰*¹ 95$ ^{of one} mixture of SiO₂ and MeO, where Me is a cation such as e.g. barium. The relative proportions of Si0₂ and MeO are deposited on the abscissa and temperature of the ordinate. the liquidity curve 51 is also shown and a horizontal line 52 indicates the end of the liquidity area and the beginning of the solid state. In the liquidity curve there is an immersion 53) which is believed to be attributable to a separation zone 54-. A glass was made with a composition whose representative ordinance cuts the reduction 53. Upon cooling, it was found that in reality a separation or phase splitting zone 54 · existed below and above the horizontal line 52. A glass of the same composition was used to form a film on a glass substrate and then cooled so that phase separation occurred. The result was that the substrate was reinforced and could withstand tensile stress, which would otherwise have caused surface cracks to propagate eggs in the substrate.

The diagram serves to suggest the way in which other ice sets, whose pairing properties have not yet been realized, can be examined.

Example V

A glass of ordinary composition in the form of a 1 mx 1 mx 0.003 m slab having a surface hardness of 6.2 according to Mohs hardness scale is coated at 80 ° C by depositing the following oxides at a time of evaporation in vacuo in the molar proportions below:

Fairy₂0^ 0,5

MgO 1

Mn0₂ 1

Ti0₂ 5

AlpO, 5

CaO 3

The thickness of the coating was about 0.02 microns. The coating was exposed to radiant heat to gradually increase its temperature up to 1000 ° C while the plate lay on a flat surface. After cooling, abundant crystallization became evident, the / crystalline phases comprising ilmenite and anatase, which were present in an amorphous phase of potassium aluminate. The coated glass which now exhibited a surface hardness of 6.5 according to Mohs' scale could be easily cut. The coated surface was then irradiated with x-rays for 24 hours at 800 ° C. Upon cooling the glass, it was found that the previously formed phases had been transformed, with the appearance of rutile, corundum, pyrolusite, potassium aluminate, hematite and some ilmenite, which were finely distributed and covered. The surface hardness was then 8.2 according to Mohs' scale.