PROCESS FOR PROVIDING A CORROSION RESISTANT COATED GLASS SUBSTRATE

Abstract

A corrosion-resistant coated glass substrate suitable for use in a humid environment and a process for producing same, the process comprising providing a soda lime silica glass substrate, providing a liquid coating composition comprising a polysilazane at a concentration of between 0.5% and 80% by weight, contacting one or both surfaces of the glass substrate directly with the coating composition, and curing the coating composition thereby forming a corrosion-resistant coated glass substrate having a silica layer on one or both sides of the glass substrate with a thickness of from 12 nm to 300 nm.

Claims

1. A process for producing a corrosion-resistant coated glass substrate suitable for use in a humid environment, the process comprising: i) providing a soda lime silica glass substrate; ii) providing a liquid coating composition comprising a polysilazane at a concentration of between 0.5% and 80% by weight; iii) contacting one or both surfaces of the glass substrate directly with the coating composition; and iv) curing the coating composition thereby forming a corrosion-resistant coated glass substrate having a silica layer on one or both sides of the glass substrate with a thickness of from 12 nm to 300 nm.

2. A process according to claim 1 wherein the silica layer or each silica layer comprises 95% or more silica in the form of SiO.sub.2, more preferably the silica layer or each silica layer comprises 97% or more silica in the form of SiO.sub.2.

3. A process according to claim 1 wherein the silica layer or each silica layer comprises 98% or more silica in the form of SiO.sub.2.

4. A process according to claim 1 wherein the silica layer or each silica layer comprises a continuous film.

5. A process according to claim 1 wherein the silica layer or each silica layer comprises a non-porous film.

6. A process according to claim 1, wherein the corrosion-resistant coated glass substrate exhibits a haze increase of 24% or below after 50 days at 98% relative humidity and 60° C.

7. A process according to claim 1, wherein the silica layer, or each silica layer has a thickness of: 15 nm or higher; preferably 20 nm or higher; more preferably 25 nm or higher; and most preferably 75 nm or higher.

8. A process according to claim 1, wherein the silica layer or each silica layer has a thickness: 280 nm or lower; more preferably 260 nm or lower.

9. A process according to claim, wherein the silica layer or each silica layer has a thickness in the range: 15 nm to 300; preferably 20 nm to 300 nm; more preferably 20 nm to 280 nm; and most preferably 20 nm to 250 nm.

10. A process according to claim 1 wherein the silica layer or each silica layer has a refractive index in the range 1.42 to 1.55.

11. A process according to claim 1, wherein the silica layer or each silica layer comprises nitrogen in an amount of 5% or less, more preferably the silica layer or each silica layer comprises nitrogen in an amount of 3% or less.

12. A process according to claim 1, wherein the silica layer or each silica layer comprises nitrogen in an amount of 2% or less.

13. A process according to claim 1, wherein the silica layer is deposited directly on each surface of the glass substrate.

14. A process as claimed in claim 13, wherein the silica layer deposited directly on each surface of the glass substrate comprises a thickness of 20 nm to 200 nm.

15. A process according to claim 1, wherein the glass substrate is toughened glass.

16. A process according to claim 1, wherein the silica layer or each silica layer is/are the only coating on the glass substrate.

17. A process according to claim 1, wherein the silica layer or each silica layer is/are undoped.

18. A process according to claim 1, wherein the silica layer on one or each surface of the glass substrate comprises 97% or more silica in the form of SiO.sub.2; and wherein the silica layer on one or each surface of the glass substrate has a thickness of 75 nm or higher and a thickness of less than 144 nm.

19. A process according to claim 1 wherein the coating composition is cured using a predetermined curing temperature and/or ultraviolet radiation.

20. A process according to claim 1, wherein the liquid coating composition comprises a solvent, preferably an aprotic solvent, more preferably dialkyl ether.

21. A process according to claim 1, wherein the polysilazane is a compound of formula [R.sup.1R.sup.2Si—NR].sub.n, wherein one of R.sup.1, R.sup.2, and R.sup.3 are each independently selected from H or C.sub.1 to C.sub.4 alkyl, and n is an integer.

22. A process as claimed in claim 21, wherein the polysilazane comprises perhydropolysilazane.

23. A process according to claim 1, wherein the or both surfaces of the glass substrate is/are contacted directly with the coating composition by a method selected from: dip coating, spin coating, roller coating, spray coating, air atomisation spraying, ultrasonic spraying, and/or slot-die coating.

24. A process as claimed in claim 23, further comprising cleaning one or both surfaces of the glass substrate before depositing the coating composition.

25. A process as claimed in claim 24, wherein cleaning the glass substrate surfaces comprises treatment with one or more of: abrasion with ceria; washing with alkaline aqueous solution; washing with deionised water rinse; and/or plasma treatment.

26. A process according to claim 19, wherein the predetermined curing temperature is a temperature of 130° C. or higher, preferably a temperature in the range 130° C. to 650° C. or 150° C. to 550° C., and more preferably a temperature in the range 250° C. to 520° C.

27. A process according to claim 19, wherein the ultraviolet radiation used to cure the coating composition applied directly to one or both surfaces of the glass substrate comprises UV C radiation.

28. A process according to claim 1, wherein the polysilazane is at a concentration in the range 0.5% to 20% by weight in the coating composition, preferably in the range 0.5% to 10% by weight, more preferably in the range 1% to 5% by weight.

29. A process for producing a corrosion-resistant coated glass substrate suitable for use in a humid environment, the process comprising: i) providing a soda lime silica glass substrate; ii) providing a liquid coating composition comprising a polysilazane at a concentration of between 0.5% and 80% by weight; iii) contacting one or both surfaces of the glass substrate directly with the coating composition; and iv) curing the coating composition thereby forming a corrosion-resistant coated glass substrate having a silica layer on one or both sides of the glass substrate, wherein v) the silica layer on one or each surface of the glass substrate comprises 97% or more silica in the form of SiO.sub.2; and wherein vi) the silica layer on one or each surface of the glass substrate comprises a fully-densified, continuous, non-porous film.

30. A process for producing a corrosion-resistant coated glass substrate suitable for use in a humid environment, the process comprising: i) providing a soda lime silica glass substrate; ii) providing a liquid coating composition comprising a polysilazane at a concentration of between 0.5% and 80% by weight; iii) contacting one or both surfaces of the glass substrate directly with the coating composition; and iv) curing the coating composition thereby forming a corrosion-resistant coated glass substrate having a silica layer on one or both sides of the glass substrate, wherein v) the silica layer on one or each surface of the glass substrate comprises 97% or more silica in the form of SiO.sub.2; and wherein vi) the silica layer on one or each surface of the glass substrate comprises a fully-densified, continuous, non-porous film, and vii) the silica layer on one or each surface of the glass substrate has a thickness of 75 nm or higher and a thickness of less than 144 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0114] The present invention will now be described by way of example only, and with reference to, the accompanying drawings, in which:

[0115] FIG. 1 shows a photograph of five samples, four coated samples and one uncoated sample after treatment for 50 days in a humidity cabinet at 98% humidity and 60° C.

[0116] FIG. 2 shows a photograph of the same five samples as in FIG. 1 (denoted as letters (a) to (e)) after 8 days in the humidity cabinet at 98% humidity.

[0117] FIG. 3 is a scanning electron micrograph of Example 1 from FIG. 1 taken at 80° sample tilt.

[0118] FIG. 4 is a scanning electron micrograph of Example 4 from FIG. 1 taken at 90° sample tilt.

[0119] FIG. 5 is a line chart showing the residual elemental nitrogen content in perhydropolysilazane (PHPS) derived silica coatings after heat treatment at various temperatures for 1 hour.

[0120] FIG. 6 is a line chart showing the residual elemental nitrogen content in perhydropolysilazane (PHPS) derived silica coatings after heat treatment at 500° C. for various periods of time.

DETAILED DESCRIPTION OF THE DRAWINGS

[0121] The present invention will now be described by way of example only, with reference to, the following non-limiting examples.

EXAMPLES

Preparation of Silica Layers.

[0122] Silica layers were deposited onto a soda lime glass substrate using diluted or undiluted 20% by weight stock solution in dibutyl ether (DBE) of perhydropolysilazane (PHPS) (available from Merck). During coating operations the stock solution was diluted with DBE at dilution ratios ranging from 1:1 to 1:12.

[0123] The substrate surface was cleaned prior to coating using combinations of ceria scrub, 2% potassium hydroxide (KOH) wash, deionised water rinse and air dry. Plasma treatment was also undertaken as required to remove remaining organic contaminants from the surface to reduce the contact angle of the substrate before coating to less than or equal to 5°.

[0124] In the following examples the coating solution was applied to the substrate surface by spin coating (other liquid coating methods may alternatively be used) and cured using elevated temperature.

[0125] Spin coating is a procedure used to deposit uniform thin films (that is, films in the range 10 nm to 10 μm) to flat substrates. Usually a small amount of coating material is applied on the centre of the substrate, which is either spinning at low speed or not spinning at all. The substrate is then rotated at high speed in order to spread the coating material by centrifugal force. A machine used for spin coating is called a spin coater, or simply spinner.

[0126] Rotation is continued while the fluid spins off the edges of the substrate, until the desired thickness of the film is achieved. The applied solvent is usually volatile, and simultaneously evaporates as rotation continues. Therefore, the higher the angular speed of spinning, the thinner the film. The thickness of the film also depends on the viscosity and concentration of the solution and the solvent.

[0127] As an alternative or as an addition to curing at elevated temperature, ultraviolet radiation (for example short wavelength UV C using a mercury or iron discharge lamp) may be used to cure the coatings to give a silica layer.

[0128] Volumes of 2 ml of polysilazane solution of pre-determined concentration were applied directly to the cleaned surface of a glass substrate. The substrate was ‘spun-up’ at an acceleration of 1000 rpm/s to 2000 rpm. The substrates were subsequently heated for 1 hour at relatively low, medium or high temperature (1 hour heat up, 1 hour hold, and around 8 hours cool down).

[0129] Examples 1 to 5 were deposited using perhydropolysilazane (PHPS) as the silica precursor as indicated in Table 1.

TABLE-US-00001 TABLE 1 PHPS Coating Solution ISO ISO Concentration Thickness Cure 9050 9050 Water (% PHPS in (nm) Temperature Tvis Haze Rvis Contact Example DBE) (SEM) (° C.) (%) (%) (%) Angle (°) Glass — — 0 89.8 0.14 — 26.3 substrate only 1 8 103 500 89.7 0.35 7.6 39.8 2 15 181 500 89.4 0.45 8.4 39.8 3 9 112 300 90.3 0.25 7.6 94.4 4 11 150 300 89.5 0.17 8.1 88.2 5 9 111 150 89.7 0.32 8.2 88.2 ‘Tvis’ is visible light transmission and ‘Rvis’ is visible light reflectance

Characterisation of Examples

[0130] The silica coated substrates examples were tested for optical properties (according to ISO 9050) water contact angle (50 μl deionized water droplet) and resistance to humidity-induced corrosion.

[0131] Scanning electron microscopy (SEM) was also performed using a Philips XL30 FEG operating in plan and cross-section mode at varying instrument magnification and tilt angle (80° and 90°) in order to assess the thickness of the silica coatings.

[0132] That is, the examples were imaged using scanning electron microscopy (SEM) and images of the specimens were captured at varying instrument magnifications using both 80° and 90° specimen tilt. Specimens were taken from the sample, mounted onto aluminium stubs in cross-section and ultrasonically cleaned in methanol for 10 seconds. The cleaned specimens were coated with a thin layer of platinum (providing a uniform conductive surface) prior to examination using the SEM. The images of the specimens from the Examples showed amorphous dense, non-porous and continuous coating layers with a very smooth surface, that is, a Sa value of less than 2 nm over a 5 μm×5 μm area measured by Atomic Force Microscopy, where Sa is a measure of the roughness of an area of a surface. Measurements taken from the SEM 90° tilt images were used to determine average coating thickness.

[0133] The optical properties of the samples were determined and are indicated in Table 1 above. The refractive index of the silica layers was determined by computer modelling and found to be from 1.46 to 1.52. That is, optical modelling was performed using: i) the transmission and reflection spectra data measured using a Perkin Elmer Lambda spectrometer; and ii) the coating thickness data from the SEM measurements; which were then processed using CODE software available from W. Theiss Hard and Software (http://www.mtheiss.com).

[0134] The refractive index (at 550 nm) for a test coating of silica was modelled by using a 2% PHPS solution, 1000 rpm, 10 seconds spin-time with curing at 200° C. for 2 hours, to deposit a clear silica PHPS coating on a test substrate of glass having a 49 nm thick TiO.sub.x coating to ensure good optical contrast. Optical modelling was found to provide a good fit to 49.8 nm thick silica coating of refractive index 1.518.

[0135] The results of the optical measurements, water contact angle, and coating thickness from SEM are as indicated in Table 1 for Examples 1 to 5 deposited after 2 hours curing time, together with comparative results for an uncoated float glass substrate.

[0136] It can be seen from the results in Table 1 that the examples of silica coatings deposited from PHPS/DBE solutions exhibit high optical transmission and colour neutrality, as required by coated glass substrates used in for example shower enclosures. Furthermore, by varying the PHPS:DBE ratio, a range of silica coating thicknesses can be obtained. This allows the silica coating to be ‘fine-tuned’ to meet end user requirements.

Humidity Induced Corrosion Testing

[0137] FIG. 1 shows a photograph of five samples, four coated samples and one uncoated sample, after treatment for 50 days in a humidity cabinet at 98% humidity and 60° C.

[0138] The samples are:

[0139] (a) Example 1;

[0140] (b) uncoated toughened float glass; and

[0141] three commercially available treatments marketed for protecting glass surfaces, each coated according to the manufacturers' instructions on the same type of glass substrate as for Example 1. The three commercially available treatments are:

[0142] (c) BalcoNano (trade mark);

[0143] (d) Ritec Clearshield (trade mark); and

[0144] (e) Liquid Glass (trade mark).

[0145] The four coated samples (Example 1 and the three commercial coated glass samples, BalcoNano (trade mark), Ritec Clearshield (trade mark), and Liquid Glass (trade mark) and the toughened uncoated float glass sample were placed in a humidity cabinet at around 98% humidity and 60° C. for 50 days. Photographs of the samples are shown in FIG. 1. It can be seen from FIG. 1 that Example 1 is much less corroded than the other samples.

[0146] Photographs of the four coated samples and the toughened uncoated float glass after 8 days in the humidity cabinet at around 98% humidity are shown in FIG. 2. The top 5 samples were removed from the cabinet and wiped with a wet cloth then returned after 3 days. The samples were wiped again prior to recording the image depicted in FIG. 2. Again, it can be seen from FIG. 2 that Example 1 is much less corroded than the other samples.

[0147] The haze of the samples before and after humidity testing for 50 days was measured using a haze meter (BYK Gardner Haze-Gard Plus, in compliance with ASTM D 1003 haze measurement standard incorporated herein by reference). The results are indicated below in Table 2.

TABLE-US-00002 TABLE 2 Average haze Haze range Average haze before after after weathering weathering weathering (%) Sample (%) (%) (*estimate) a Example 1 2.51-4.37  3.5   0.3 c BalcoNano ™ 62.7-72.2 69.5 <1* commercial wipe on treatment b Toughened Float Glass 57.1-80.0 73.1   0.14 (untreated) d Ritec Clearshield ™ 78.7-83.1 80.6 <1* commercial treatment e Liquid Glass N/A N/A N/A

[0148] The results of Table 2 show that Example 1 exhibited a lower haze after weathering (3.5%) compared to the other samples (all with a haze value greater than 69%). That is, the haze values recorded for Example 1 are very different to the haze values recorded for the other samples. Haze is a good indicator of the degree of weathering (the higher the value the worse the result). A haze value of 3.5% for Example 1 after accelerated weathering, indicates that Example 1 is able to offer excellent performance in for example a shower enclosure. Haze levels greater than 69% are not acceptable, as any shower screen formed therefrom would exhibit limited transparency and would not be aesthetically pleasing to the end user.

[0149] FIG. 3 is a scanning electron micrograph of Example 1 from FIG. 1 taken at 80° sample tilt. It can be seen from FIG. 3 that there is a dense smooth silica layer deposited on the glass surface denoted by (1)

[0150] FIG. 4 is also a scanning electron micrograph of Example 4 at 90° sample tilt also showing a dense smooth silica layer, again denoted by (1).

[0151] It can be seen also from FIGS. 3 and 4 that the silica layer is continuous, without defects and without pinholes. This is required in order to prevent moisture ingress into the silica coating and also, subsequent moisture ingress to the interface formed between the silica layer and the glass surface. If the latter were to occur, then it is likely that moisture could and would attack the silica layer from both sides. In addition, moisture attack at the silica/glass interface could also cause delamination and coating failure in a humid environment such as a shower enclosure.

Hardness of Coatings

[0152] The hardness of the silica layers in Examples 1 to 5 were tested using the pencil hardness test. The pencil hardness test, also referred to as the Wolff-Wilborn test, uses the varying hardness values of graphite pencils to evaluate a coating's hardness. An Elcometer 501 Pencil Hardness Tester was used to ensure that the cylindrical pencil lead is maintained at a constant angle of 45° and exerts a force of 7.5N (1.68 lbF). The pencil lead, prepared beforehand using a special sharpener and abrasive paper, was inserted into the Elcometer 501 hardness tester and pushed over the smooth, flat coated surface. The lowest hardness value of the pencil which marks the coating determines the coating's hardness rating.

[0153] The hardness of the coatings was very high at 7H to 9H+ before a mark was found on the samples. Hardness was found to generally increase with curing temperature and length of cure.

Additional Examples Prepared for a Range of Silica Coating Thicknesses Derived from Polysilazane (PHPS)

[0154] A further set of examples were prepared with a variety of silica coatings thicknesses prepared by spin coating to cover the thickness range 23 nm to 144 nm followed by curing. These coatings were prepared using polysilazane (PHPS) and dibutylether solutions. The spin coating conditions are provided in Table 3.

TABLE-US-00003 TABLE 3 Spin coating conditions PHPS:DBE dispensed volume Around 2 ml Spin speed 2000 rpm Acceleration 1000 rpm/sec. Curing Conditions 1 hour at 500° C. (around 1 hour heat up, 1 hour hold at required temperature and around 8 hour cool down Dilution range of the PHPS:DBE 1:12.2-1:0.795 solutions required to cover the silica coating thickness range

[0155] Durability tests were performed on the coated glass substrates to assess the coatings according to Architectural (EN1096) and Automotive (TSR 7503G) glass standards, incorporated herein by reference. The results of the durability tests are presented in Tables 4, 5 and 6.

[0156] Durability performance was characterised by:

[0157] (i) The change in visible transmission, ΔTvis, (measured according to EN410 incorporated herein by reference) following each durability test compared to an untested reference sample.

[0158] (ii) The change in water contact angle following each durability test compared to an untested reference sample.

[0159] (iii) The change in haze (light scatter) following abrasion testing (after 20 cycles using a felt pad attached to a 500 g weight) compared to an untested reference sample. The durability testing confirmed the acceptable performance of the coated substrates and hence the coatings for use in for example a shower enclosure.

TABLE-US-00004 TABLE 4 Durability test results investigating changes in light transmission over a range of test conditions Anti- Salt Silica Acid Freeze Alkali Spray En. Thickness Reference Test Test Test (% Cycle Kerosene Sample (nm) (% T vis) (% Tvis) ΔTvis (% T vis) ΔTvis (% Tvis) ΔTvis Tvis) ΔTvis (% Tvis) ΔTvis (% Tvis) ΔTvis 1 23 89.3 89.3 0 89.3 0 89.4 0.1 86.1 −3.2 89.4 0.1 89.4 0.1 2 47 89.53 89.8 0.27 89.3 −0.23 89.7 0.17 86.1 −3.43 89.8 0.27 89.9 0.37 3 93 90.2 90.2 0 89.9 −0.3 90 −0.2 89.9 −0.3 90 −0.2 90.2 0 4 144 89.11 89.3 0.19 89.3 0.19 89.3 0.19 85.1 −4.01 89.6 0.49 89.6 0.49

[0160] The acid test involved exposing a silica coated substrate (100/50 mm) to 0.1N sulphuric acid (H.sub.2SO.sub.4) for a period of 2 hours.

[0161] The alkali test involved exposing a silica coated substrate (100/50 mm) to 0.001N sodium hydroxide (NaOH) for a period of 2 hours.

[0162] The anti-freeze test involves

[0163] The salt water spray test involved exposing a silica coated substrate (100/100 mm) to salt water for 21 days.

[0164] The Environmental cycle test (En Cycle) involved exposing a silica coated substrate (100/100 mm) to changes in temperature ranging from 80 degrees C. to minus 40 degrees C. for 21 days.

[0165] The Kerosene test involved exposing a silica coated substrate (100/50 nm) to Kerosene for a period of 2 hours.

[0166] It can be seen from Table 4 that whilst all the samples changed properties following the durability tests, the magnitude of the change (ΔT vis) for the coated samples is considered to be an acceptable level of performance for same for use in a shower enclosure. That is, the tests indicate that the silica coating of the present invention is robust enough to survive an end use application in for example a shower or bathroom environment.

TABLE-US-00005 TABLE 5 Durability test results investigating changes in contact angle over a range of test conditions Reference Anti- Silica Contact Acid Freeze Alkali Salt En. Thickness Angle Test Test Test Spray Cycle Kerosene Sample (nm) (CA °) (°) ΔCA (°) ΔCA (°) ΔCA (°) ΔCA (°) ΔCA (°) ΔCA 1 23 18.50 38.46 19.96 34.77 16.27 37.83 19.34 28.66 −9.80 23.08 11.69 31.58 13.08 2 47 49.31 48.54 −0.77 52.95 3.64 25.21 −24.10 30.88 −17.66 30.26 −22.69 46.89 −2.42 3 93 41.46 39.51 −1.95 61.48 20.02 34.34 −7.11 22.74 −16.76 66.11 4.63 45.35 3.89 4 144 46.81 41.38 −5.42 27.78 −19.03 45.88 −0.93 27.86 −13.52 56.96 29.18 51.36 4.55
It can be seen in Table 5 that the contact angle of the silica coating surface in each of the samples changes following durability testing (change in contact angle, ΔCA). This change indicates that the silica coating has changed following each durability test. In common with the optical assessment reported in Table 4, the magnitude of the change (ΔCA) is considered an acceptable level of performance for use in a shower enclosure. The tests indicate that the silica coating is robust enough to survive end use in a shower. That is, the above tests also indicate that the silica coating of the present invention is robust enough to survive an end use application in for example a shower or bathroom environment.

TABLE-US-00006 TABLE 6 Durability test results (Haze change) Silica Thickness Average Haze Average Haze ΔHaze Sample (nm) Before Test (%) After Test (%) (%) 1  23 3.22 3.51 0.29 2  47 3.27 3.49 0.22 3  93 3.16 3.37 0.21 4 144 3.24 3.74 0.5

[0167] It can be seen from Table 6 that all samples exhibit only a small change in haze (ΔHaze (%)) after durability testing compared to before testing. Haze is a good indicator of the degree of weathering (with high haze values and high delta haze values before and after testing indicating poor results). In Table 6 all of the examples show acceptable haze and acceptable ΔHaze performance, and therefore, all of the samples may be used in a shower enclosure. That is, the above haze results confirm that the silica coating of the present invention are robust enough to survive an end use application in for example a shower or bathroom environment.

Determination of Levels of Nitrogen and Silica in the Perhydropolysilazane Coatings.

[0168] Silica coatings on glass were prepared by spin coating from a perhydropolysilazane (PHPS) precursor and were exposed to a range of heat treatments. Following each heat treatment the coatings were analysed using X-ray Photoelectron Spectroscopy (XPS) to measure the residual nitrogen content in the coatings. The elemental nitrogen content for each heat treatment condition is listed in Table 7 below.

TABLE-US-00007 TABLE 7 Heat Heat Treatment Treatment Nitrogen Temperature Time Content (degrees C.) (minutes) (%) Room Temp  60 17.4 200  60 21.2 400  60  7.0 500  10 10.8 500  20 10.2 500  40  2.2 500  60  1.2 500 1080  0 600  60  0.0

[0169] FIG. 5 is a line chart showing the residual elemental nitrogen content in perhydropolysilazane (PHPS) derived silica coatings after heat treatment at various temperatures; all heat treatments are for 1 hour. It can be seen that the required level of 0% nitrogen is achieved for a heat treatment of 500° C. for 1080 minutes, or 600° C. for 60 minutes. A nitrogen level of 1.2%, achieved after 500° C. for 60 minutes is considered to be an excellent result.

[0170] FIG. 6 is a line chart showing the residual elemental nitrogen content in perhydropolysilazane (PHPS) derived silica coatings after heat treatment at 500 degrees C. for various periods of time.

[0171] From the above results it is apparent that dense non-porous and continuous silica layers deposited from a polysilazane in the form of perhydropolysilazane were, surprisingly, found to protect previously uncoated glass surfaces from humidity induced corrosion.

[0172] The coatings were deposited from perhydropolysilazane (PHPS, a polysilazane that transforms to form a layer of SiO.sub.2 upon heat treatment with the loss of at least ammonia). Following deposition, the SiO.sub.2 coatings was cured at low (150° C.), medium (300° C.) or high (500° C.) temperature.

[0173] The dense silica layers prepared and tested in accordance with the present invention offer corrosion protection functionality when placed in a humid environment and thereby prevent glass staining. The coated glass substrates prepared in accordance with the present invention are therefore suitable for use in applications in for example shower and bathroom environments. In addition, the coated glass substrates prepared in accordance with the present invention, also increase the warehouse life of the glass when stored prior to sputter cutting, etc., as the glass prepared according to the invention demonstrate improved resistance to humidity at around 98% and 60° C.