CS218598B2 - Method of depositing the coating of the tin oxide of low specific resistance on the mineral base - Google Patents

Abstract

1. Method for depositing on glass substrate heated to a temperature of about 590 degrees C to 650 degrees C an adherent tin oxide coating having a resistivity of 5 x 10**-3 Ohm.cm or less, which comprises projecting on this substrate, under the form of laminar gas streams meeting in close proximity to a portion of said substrate's surface, a volatile tin compound and water vapor both diluted in separate own flows of carrier gas containing at least 30% of hydrogen (v/v) and which comprises displacing the substrate with regard to said streams so as to obtain said coating by formation of a homogeneous tin oxide deposit that takes place successively on progressively renewed and jointed areas of the substrate's surface.

Description

The invention pertains to a method of depositing a tin oxide coating of low specific resistance to mineral 'substrate such as glass, ceramics or other mineral substances, wherein the specific resistance is lower than 10 ^_2 ň.cm, wherein the surface of the substrate preliminarily heated at least 500 ° C reacts with the volatile tin compound and water vapor diluted in the carrier gas.

The use of tin oxide to induce the conductivity of a glass or ceramic substrate is known and has been the subject of numerous publications including: ZM Jarzebski and JP Marton: - "Physical Propenties of SnO ₂ Materials" by J. Electrochem. Soc. 1976, 199;

299c; 333c.

J. Kane Schw-eizer, W. Kern, "Chemical Vapor Deposition of Antimony-Doped Tin Oxide Films Formed from Dibutyl Tin Diacetate", J. Electrochem. Soc. 1976, 123, No. -2, -270; ------------------------------------------------ .. ...-........

H. Kim and H. A. Laitinen: "Composition and of Tin Oxide Films Prepared by Pynohydrolyitic Decomposition of Tin (IV) Compound", '- J. Amor. Ceramic. Soc. 58, 23 (1975). ·

It has already been described (Belgian patent specification 869 062) glass coated with a coating whose resistance (RD) is less than 50 ohms and has an increased IR reflectivity coefficient. This patent, however, does not indicate precisely how such glass is produced, and its content does not contribute to technical progress. Even so far, it has not been possible to produce conductive glass. which would have the necessary electrical - and - optical properties - and which, in addition, could withstand - at the same time - resist the curing and forming processes required for the manufacture of glass in the construction industry and for - automobile.

Known tin oxide coatings either have no conductivity or are not transparent, or are too brittle to withstand the mechanical - and thermal stresses - induced by the quenching and forming of the glass plates being treated;

A vapor deposition (CVD) technique has already been used to cover a substrate, such as a glass plate, with a tin oxide coating. From the article - H. Koch "Electrische Untersuchungen an Zmndioxydschichten" (Phys. State. 1963, vol. 3, pp. 1059 -a 55), the procedure -a · -the device for depositing a thin layer of SnO2 on a glass plate by SnCl reaction is particularly known. And H2O, which are diluted in the carrier gas in the presence of air in contact with each other with the top of the glass plate preheated to a temperature of the order of 200 to 400 ° C. The two reaction gases are ejected onto the glass by means of a nozzle with two coaxial nozzles from which the central nozzle receives dissolved SnO ₂ gas, while the external nozzle is supplied with a gaseous H ₂ O solution.

A method and apparatus very similar to the above has also been proposed, in particular in U.S. Pat

DOS no. 2,133,274, which in addition allow toho- -dotovat antimony SnO ₂ layer deposited on the substrate, -in the present case, also on a glass plate in order to reduce the specific electrical -odporu this layer. To this end, in particular, SbCl3 or SbC15 has been used in the form of a dilute in carrier gas, here in nitrogen introduced in the presence of SnCl2, and H2O on the substrate by means of a nozzle with three coaxial nozzles, each receiving one from the above compounds. Thus, the combination reaction occurs near the substrate and at a distance of the three nozzles. Here you can also - mention USA - pat. Nos. 3,850,679, 3,888,649 and British Pat. No. 1,507,996.

In addition, it is known to supply the reducing compound to the reaction. - the formation of tin oxide from the tin compound and water vapor improves - the conductivity of the layer formed - For example - Kuznetsov - - [Fizika Tverdovo Body, vol. 2, No. 1, 35-42 (1960)] describes the hydrolysis of SnCl 2 in an alcohol solution by spraying water and such a solution onto a surface at a temperature of 500 ° C, wherein the conductivity of the layer thus obtained [3 µm] is 10 ^_ 2 Ω ^_1 , which means a specific resistance of the order of 102 Q.cm. However, the transparency of the coating obtained under such conditions is not satisfactory.

The causes for which the addition of a reducing agent, which is likely to convert a portion of tetravalent tin into divalent tin, improve conductivity are not sufficiently clear, since it seemed likely that a metal Sn would be formed in which case the presence of the easily detectable as it would lead to a darkening of the transparent layer. On the other hand, it cannot be excluded that SnO could create, with the SnO resulting from the reduction, an excited 'molecule' electrically deficient [for example (Sn2 ^lv Oa) + +] »whose presence would improve conductivity by transmitting holes (hole conductivity).

Be that as it may be, it has been stated that when -se, as mentioned above, - uses CVD techniques for -reaction - the limit! SnCl 4, and H 2 O, do not provide the addition of alcohol as a reducing agent in a simple mixture of the SnCl 4 conductive layer, with properties noticeably improved, suggesting that premixing of the reagents is not aqueous. .....

In this context, it should be noted that the use of hydrogen in the SnO ₂ deposition by CVD is not known per se. In the journal Electrochemical Society 120 (5), 701-2, (1973), the deposition of SnO 2 layers on an oxygenated silicon substrate by CVD technique is described. The reactants consist of SnCl 4 and water vapor and the carrier gas is nitrogen. In this paper, it is suggested that the reaction was conducted in the additional presence of oxygen or hydrogen. However, according to the description of the experimental conditions given in this article, it is not possible to determine the relative amount of hydrogen used. It is likely that18598 was insignificant, since the cell does not indicate that the presence of hydrogen would lead to any increase in the conductivity of the layer.

S-nO ₂ . On the other hand, French Patent No. 1,207,231 (Philips) describes a process whereby CVD is deposited on a substrate of a metal oxide layer, and in particular SnO2, where Snúl ₄ reaches water vapor and possibly hydrogen, the hydrogen being used to produce the water needed. for the hydrolysis of tin (II) chloride by reaction with oxygen (e.g. air oxygen). However, the examples in this patent suggest that the percentage of hydrogen in the gas mixture used is relatively low (about 7.5%).

The essence of the process according to the invention is that the carrier gas contains at least 30 why hydrogen.

According to a preferred embodiment of the invention, hydrogen is formed by contact with the substrate by thermal decomposition of the hydro compound diluted in the carrier gas.

Suitably, the hydro-compound consists of methanol.

According to another embodiment of the invention, the hydrogen fluoride gas is supplied from the mixture with water in a ratio of 0.1 to 5 weight percent.

According to another embodiment of the invention, upon receiving the first tin oxide layer, the deposition operation is repeated at least once more.

The process of the invention has the advantage that it greatly reduces the high resistance of the conductive tin oxide layer and thus avoids the disadvantages of the prior art processes which provided tin oxide layers, whose specific resistance was often too high for many applications. Coatings having a specific resistance of not more than 10 ^_2 µm.cm and having thicknesses of approximately 1 to 3 µπι are now obtained by the method according to the invention, giving RD resistances in the range of 1 to 10 Ώ with a transparency of 60 to 95%. light with a reflectance of over 50% for infrared light.

The body obtained by the process according to the invention is characterized by the fact that it has the following properties for coating thicknesses of 1 to 3 μΐη: surface resistance RO = = 1-10-10, transparency> 70%, infrared reflectance> 50% ; further characterized by the fact that, preferably, said coating does not undergo appreciable changes when said body is subjected to curing and hot bending.

For curing, the body is heated to a temperature of about 700 ° C and then cooled in stages from 5 to 10 ° C / s. For bending, the body is heated up to the softening point and is preferably bent from the side where the coating is subjected to compression. In this operation, a radius of curvature of the order of 15 cm can be achieved without deteriorating the conductive coating. The specific resistance of the layer of Sn-O ₂ · object obtained according to the invention is of the order of at least 10 ^_2 iQ.cm.

Devices known in the art for coating mineral substrates - tin oxide - by vapor deposition (CVD) techniques can be used to carry out the method of the invention. As mentioned in the introduction, such apparatuses simultaneously introduce gas beams containing reaction substances (SnCl ₄ + + carrier gas and H ₂ O + carrier gas) onto a substrate heated to a suitable temperature (400-600 ° C). The process according to the invention is carried out in the same manner, using a mixture of hydrogen and an inert gas such as nitrogen as the carrier gas. This mixture preferably contains 30 to 80% by volume of hydrogen or more. However, practically pure hydrogen, for example up to 99.9% L, can be used in certain special cases

The tin compound used is preferably SnCl ₄ pure or dissolved in an inert solvent, but other volatile tin compounds, for example of the Sn (Alk) _{4 type} , where Alk denotes a lower alkyl radical, and tin in the -s compound, can also be used. -dibutyl-diacetyl.

Pro- carrying out the process according to the invention is preferably used in coating -equipment - with CVD, ^one described in British Pat. No. 2,044,137. Such a device makes it possible to effectively coat very high -speed -glass in the form of foils or sheets with an SnO ₂ layer -o extraordinary homogeneity which guarantees a body according to the invention performance at a very high level in terms of mechanical strength and electrical and optical properties of any kind.

Such a device makes it possible, for example, to coat a glass plate with a coating of tin oxide in the order of 0.5 to 3 µm, which at the same time has very good transparency, relatively low specific electrical resistance, remarkable glass adhesion and high mechanical resistance as well as high acid resistance.

A trial apparatus of this type, provided with a nozzle of 50 cm in length, in which the nozzle orifices had a width of 0.1, 0.1 and 0.2 mm, made it possible to process a glass plate having a width of 50 cm and a thickness of 4 mm. at 600 ° C and a drifting speed of 2 m / min. The distance separating the top side of the nozzle and the glass surface was 4 mm.

Containers having a capacity of 1 liter SnCl ₄ and 1 liter H ₂ O were used. The SnCl _{4 was} heated to a suitable temperature to supply the carrier gas N 2 / H 2 at a rate of 60 liters / hour. into the reservoir -for SnCi _; and 120 liters / hour. to a vaporizer and with a pump feed rate of 1 mol H ₂ O per hour, a feed rate of 2 mo was obtained ^; ly / h tin (II) chloride. In addition, the nozzle temperature was maintained at approximately 110 ° C by circulation of oil. .

The coating is a result of the reaction

SnCl ₄ + 2 H 2 O - SnO ₂ . + 4 HCl, which -stands -on the glass. At this point, it should be noted that, if it did not take special action, this reaction would proceed very violently with the formation of large amounts of stannous oxide SnO ₂ and hydrates of ty218598 pu SnO ₂ . nlLO at the outlet of the nozzle nozzles, which would present a risk of partial or complete clogging of the nozzles by depositing the same tin oxides on the glass in the form of a white veil and not in the form of the desired semiconductive transparent layer.

This danger has been eliminated · 'that a food additive by the reducing agent to the two gaseous flows S.nCl'4 steam and H ₂ 0 in the form of H ₂ contained in the carrier gas. In fact, hydrogen is a reducing gas for SnCl ₄ , a moderator of hydrolysis and, moreover, acts as a catalyst.

Under the above operating conditions, the reaction yield was about 70%. The glass was coated over its entire surface with a layer of SnO ₂ having a thickness of 0.5 to 2 microns, a transparency of 60 to 95% per sample and an average resistance of RD = 1 to 10, preferably 2 to 10 microns. 5 ohms for '1 to 2 micrometers' thickness.

In addition, it turned out that the layer of SnO ₂ . thus obtained had a particularly high hardness greater than that of the glass on which it was deposited. Its resistance was also very considerable, whether it was the · most intense · mechanical stresses, eg impact, or: the effects of acids. In particular, the glass may have been subjected to crowding, i.e. a curvature with a radius of curvature of 15 cm when heated to a temperature of between 600 and 700 ° C, without any damage to the S. nO ₂ coating. It was also possible to harden or harden under the conditions common to normal glass, i.e. to cool them gradually from a temperature of 700 ° C by a few ° C per minute.

In addition, it should be noted that a glass plate provided with a layer of SnO ₂ under the above conditions and measures can be cut with a diamond, either on the top or on the underside of the plate without spalling the layer.

For. use of the same equipment and under operating conditions not different from the above-mentioned speed of the plate, which was approximately 10 m / min, a SnO ₂ coating having a thickness of approximately 0.1 μη and an average specific resistance RD = 500 ,2 was obtained; almost 100% for visible radiation and mechanical properties practically equivalent to those of the coating obtained when moving the glass plate at a speed of 2 m / min.

The direct addition of H ₂ to alleviate the rapidity of the reaction of the SnCl ₄ and H ₂ O vapor is not the only possible measure. According to another embodiment of the invention, the carrier gas can be used exclusively with nitrogen and form the hydrogen necessary for the reduction from a volatile hydro-compatible solvent such as methanol CH 3 OH. In such a case, the action of the bubbler tank is reached and the methanol is carried in a controllable amount. valve itself only N ₂ · In this case, the carrier gas passing through the evaporator · also consisting of N _second

Due to the relatively high temperature at the outlet of the nozzles, methanol can decompose according to the reaction:

CH 3 OH -> 2 H 2 + CO.

It can also react with H2O according to the reaction:

CH 3 OH + H ₂ .0 -> 2 H 2 + CO ₂ .

In both cases, however, the hydrogen necessary to control the essential reaction mentioned above is generated in situ:

SnCl ₄ + 2 H ₂ O -> SnO ₂ + 4 HCl.

It should be noted that it has not been possible to determine which of the above CH 3 OH reactions is more advantageous. However, it was found that, under the operating conditions below, the introduction of methanol into the deposition of the SnO- ₂ layer was effective in controlling this process in the same manner as using nitrogen mixed with hydrogen as the carrier gas. However, if desired, mixtures of N ₂ / H ₂ can be used simultaneously to entrain water and HF and methanol diluted with N ₂ , and the respective amounts of diluents are controlled by valves.

In order to obtain a 20 cm wide glass plate covered with a transparent SnO ₂ coating in the presence of CH 3 OH, about 60 liters per hour of nitrogen are fed into both tanks, and these are regulated at the valve control. affixed · flow to the evaporator and is passed per hour · 60 l of N2, wherein the pump delivers two moles of H ₂ 0 per hour. Containers were brought to appropriate temperatures to keep the amount of reactant. was 1 mol per hour of SnCl ₄ and 0.5 mol per hour of CH 3 OH. The nozzle temperature maintained by the oil circulation was as before 110 ° C, while the glass plate was preheated to a temperature of approximately 600 ° C. The glass was carried at a speed of 2 m / min while maintaining a distance of 6 mm from the nozzle.

The SnO ₂ coating obtained was, as it turned out, practically identical in thickness, quality and mechanical electrical or physical properties to an analogous coating obtained without methanol, as described above.

It should be noted that the invention can be perfectly practiced without the use of HF gas. In this case, the coating has electrical properties and reflection in the infrared region analogous to those of coatings obtained in the presence of HF. However, it may happen that the coated glass has a somewhat less bright appearance and is less smooth than when. is worked in the presence of HF.

When working in the presence of this gas, HF can also be used directly in an aqueous solution in a vessel that serves to supply water vapor for the reaction. With respect to the proportion, 0.1 to 5% by weight of HF in water can be used. Glass,. Having a thickness of 4 mm, heated to about 600 ° C, was then coated with 0.9 n SnO 2 treated with HF at a rate of 2 m / min and at a distance of approximately 6 mm, from the nozzle. The carrier gas flow rates (N2 mixture, 40% - H2 60%) were 60 liters per hour for SnCl _Z1 and water vapor.

The SnO ₂ coating obtained according to the invention in the presence of HF is particularly perfect. In the above case, the specific resistance was RD = 4 Ω and the reflectance in the infrared region was of the order of 75%.

Besides, his; the visible light transparency was 90 - the surface was particularly smooth and - did not induce light scattering (no milky appearance) ·. The mechanical resistance properties were also very high. The glass thus coated with SnO2 treated with HF could undergo a heat treatment by cooling the same as that which traditionally is certain vehicle glasses, such as side windows of cars. It was also possible to heat-shrink such a plate (temperature approximately 650 degrees Celsius) and a radius of curvature of 15 cm without altering the properties of the HF-treated SniO2 coating.

In addition, the glass plate coated in the manner described could be machined in the usual manner (cutting, grinding, etc.) without damaging the coating.

Indeed, the HF-treated SnO ₂ layer had a hardness higher than that of the glass that supported it and could not be scratched; furthermore, its chemical resistance to acids and its impact resistance have proved particularly high. In addition, such glass resists perfectly curing in which it is cooled from a temperature of 700 ° C in stages at approximately 5 to 10 ° C per second.

It should also be noted that the HF-treated SnO ₃ layer deposited on the glass plate under the described conditions can be covered with silver or silver coating at 600 ° C, for example to form electrical contacts. Such a silver coating adheres very well to the surface of the SnO ₂ coating with a thickness of approximately 15 kg / cm ² .

Using the described apparatus, and under operating conditions other than those mentioned above, only - the driving speed of the plate which was indicated at approximately 10 m / min. - an HF-treated SnO ₂ coating having a thickness of approximately 100 дш, average -specific-resistance RD = —200 -Ω, transparency-approximately 100% for visible light, infrared reflectance 25 -% and mechanical properties identical to - properties obtained with SnO-2 coating also processed by HF at drift of the glass plate at a speed of 2 m / min.

The use of glass slabs of any size covered with a layer of SnO2) untreated or processed by HF can be very diverse according to their physical and especially electrical performance.

The glass plate according to the invention, coated with a layer of SnO ₂ , can, for example, be used to form insulating glass for windows or doors of residential rooms, vessels or non-floats, and because of its high transparency, visible light, emissivity and relatively high reflectivity for infrared radiation. In fact, such a plate has a sufficiently high aheric power (K = 2.3) to reduce the amount of thermal radiation that can pass through the plate in a fairly representative ratio. Advantageously, such glasses replace the conventional double glasses which, while maintaining the same dimensions, are more expensive and more fragile.

However, it is also possible to use glass coated with SnO‘2, treated or unprocessed, as a heated glass, for example, for rear view windows of vehicles. In addition, the glasses according to the invention are also advantageous with respect to other vehicle glasses, because, because of their excellent reflectivity in the infrared region, they contribute to improving the efficiency of the vehicle air conditioning.

It has also been observed that a glass plate carrying an SnO ₂ coating, when placed in an atmosphere of high humidity, does not cover an even layer of misting, but rather a large number of droplets that much less alter the visibility. through the coating itself and through the glass plate.

This feature is obviously particularly advantageous in the case of glass panes which are intended to form glass, in particular glass, of vehicles, and in particular the windscreens and rear windows of cars, buses, or trucks.

The glasses according to the invention can also be advantageously used in horticulture in the manufacture of glass panes or cold layers.

It should also be noted that the method according to the invention can be repeated on the substrate as desired. forms a coating composed of a plurality of successive layers, the composition of which may not be identical. Also, if desired, the untreated SnO2 layer can be covered with a second HF treated layer. In the same way, it is possible to form a coating of 10 consecutive layers, each having a thickness of 100 m, the electrical and optical properties of each layer not necessarily being identical.

It will be appreciated that the amount of reactant fed in depends on the thickness of each coating layer depending on the speed of the substrate. Under these conditions, the reaction stations can optionally be multiplied by placing two or more glazing devices side by side. In this way, the second layer is deposited on the first before the first layer has had time to cool - and so on - resulting in an overall coating that is extremely homogeneous.

Although in the foregoing description, embodiments of the apparatus in which the glass sheets to be coated with SnO _{2 were} mentioned were each placed at a distance from the nozzle corresponding to the distance separating the nozzle and the line

218590 side toe convergence - three nozzles of this nozzle - it should be noted that in practice it will be possible to reduce this distance somewhat in such a way that the mixture of reactants exiting the nozzles is formed on impact - on the glass and creates relatively intense local swirl which promotes the formation of this mixture.

Example 1

This example is for. - illustrating the differences that occur when SnO2 is deposited on a glass plate in the presence and absence of hydrogen.

The apparatus described above was used without using a methanol bubbler. Working conditions were as follows:

Reaction temperature: 590 ° C

Working pressure Ambient quantity delivered by the pump 10 moles

H ₃ O / h with 250-liter / h steam HF concentration in H2O 2/98 (v / v) carrier gas composition H2 / N2 40/60 (v / v) Evaporator temperature 140 ° C Gas flow in vessel (SnCbJ 370 1 / h vessel temperature 90 ° C SnCl4 flow rate 10 mol / h glass flow rate 1.2 m / min reaction gas suction rate 1500 -1 / ih carrier gas flow in evaporator 500 l / h.

A coating having the following properties was thus obtained: 0.6 µm thickness; resistance RD = = 20 Ω; transparency 80 ° / o.

Then, the H ₂ / N ₂ (carrier gas) mixture was replaced with - nitrogen only, and - under the same operating conditions, a coating with the following properties was obtained: thickness 0.7 µη; resistance RD = 1000 -Ω; 80 'transparency.

The above operating conditions correspond to approximately m-molar ratios of H2: 48 mol. %, H2O: 26 mol. % and SnCl _Z1 : 26 mol. ° / o; of -toho be thermodynamically calculated ratio of reactants and reaction -zplodin at equilibrium at 500 and 600 ^Q C and at ordinary pressure, and the following values were determined:

components (mol% i) with hydrogen without hydrogen * 500 ° C 600 [deg.] C 500 ° C 600 [deg.] C HCl 43.7 43.8 64.17 67.26 H ₂ 40.66 15.6 - - H ₂ O 15.6 21.9 9.91 8.37 SnClj (g) 13.1 0.0 0.0 0.0 SnCl ₂ (sec) 8.7 0.02 0.0 0.0 SnCl ₄ 0.06 0.0 41.45 41.17 SnO ₂ 0.0 40.6 16.1 16.8

* H2O 42 mol. %, SnO4 58 mol. % - (starting compound).

It is noteworthy that at the balance, the reaction carried out in the presence of H 2 does not give SnO 2 at all, and very little SnC-L 1. It is now understood that, under these working conditions (irreversible), there is a significant reduction of tin compounds to stannous compounds with a noticeable increase in the conductivity of the coatings.

Example 2

Applying a multi-layer coating.

A coating device comprising a battery of five 1 m nozzles arranged in parallel in a cascade, each practically identical to the above description, was used. The exhaust ducts were positioned in such a way that each nozzle was bounded by a discharge duct.

The nozzles were supplied with the reactants as described above, with the difference that the first four nozzles were supplied together in terms of H ₃ O, the last nozzle was supplied separately with HF / / H ₃ O solution at 5%. The central nozzles of all five nozzles were supplied together with S11Cl4.

It was processed under the following conditions:

Reaction temperature pressure

590 ° C ambient supply -water pump quantity (single for four first nozzles) 80 mol / h water supply pump + HF (fifth-nozzle) 20 mol / h composition H2O / HF 98/2 (mol / mol) ) carrier gas composition (common to five nozzles) H2 / N2 50/50 (v / v) total delivery of water carrier gas to the first four nozzles 7000 liters / h water carrier gas supply volume + HF 1? / h evaporator temperature 140 ° C supplying the carrier gas to the reservoir

3500 liters / h ° C mol / h m3 / h with SnCl 4.

• tank temperature -s S11Cl4 flow rate S11Cl4 total suction speed of glass movement m / min

A coating comprising five layers of 0.1 µm each was obtained, the last one being treated with fluorine.

The coating had the following properties: RD = = 20 Ώ; Infrared reflectivity 55%, transparency 85%.

Claims (6)

A method of depositing a tin oxide coating having a low specific resistance on a mineral substrate, such as glass, ceramic or other mineral material, wherein the specific resistance is less than 10 - ² - Q.cm, wherein on the substrate surface preheated to at least 500 ° C reacts with the volatile tin compound and water vapor diluted in the carrier gas, characterized in that the carrier gas contains at least 30% hydrogen. 2. The process of claim 1 wherein hydrogen is formed upon contact with the substrate by thermal decomposition of the hydro compound diluted in the carrier gas. 3. The method of items 1 and 2, wherein the hydro-compound consists of methanol. 4. The process of claim 1 wherein hydrogen fluoride gas is added to the carrier gas mixture with hydrogen. 5. A process according to claim 4, wherein the hydrogen fluoride gas is supplied in a mixture with water in a ratio of 0.1 to 5 weight percent. 6. The method of claim 1, wherein upon receiving the first tin oxide layer, the deposition operation is repeated at least once more.