Method for patinating zinc surfaces and system therefor

Abstract

The invention relates to a method for patinating zinc surfaces of a structural element, including the steps of: providing a structural element with a zinc surface in a housing; providing an atmosphere around the zinc surface, wherein said atmosphere comprises carbon based gas and humidity; and heating the zinc surface for at least one hour, to provide a patinated zinc surface. The heating of the zinc surface occurs by heating the atmosphere to a temperature of at least 50° C., the humidity is at least 70%, and the carbon-based gas concentration is at least 5% by volume. The invention also relates to a patinated evaporative condenser in a closed-circuit cooling tower The patinated evaporative condenser in a closed-circuit cooling tower is by the method according to the invention. A system for patinating zinc surfaces according to the invention is also disclosed.

Claims

1. A method for patinating zinc surfaces of a structural element, comprising: providing the structural element with a zinc surface in a housing; providing an atmosphere around the zinc surface, wherein said atmosphere comprises carbon based gas and humidity; and heating the zinc surface for at least one hour, to provide a patinated zinc surface; wherein the heating of the zinc surface occurs by heating the atmosphere to a temperature of at least 50° C. the humidity is at least 70%, and a carbon based gas concentration is at least 5% by volume.

2. The method of claim 1, wherein the carbon based gas is the group consisting of carbon dioxide, carbon monoxide, and mixtures thereof.

3. The method of claim 1, wherein the carbon based gas concentration is at least 10% by volume.

4. The method of claim 1, wherein the carbon based gas concentration is from 15% to 30% by volume.

5. The method of claim 1, wherein the heating occurs at a temperature of at least 60° C.

6. The method of claim 1, wherein the heating occurs at a temperature of at least 80° C.

7. The method of claim 1, wherein the humidity is at least 75%.

8. The method of claim 1, wherein the heating occurs for at least two hours.

9. The method of claim 1, further comprising the step of providing the structural element with the zinc surface to an object of the method prior to the step of providing the structural element with the zinc surface in the housing.

10. The method of claim 1, further comprising the step of providing zinc to the zinc surface prior to the step of providing the zinc surface in the housing.

11. The method of claim 1, further comprising the step of taking out the zinc surface of the housing after the heating the zinc surface step.

12. The method of claim 1, wherein the housing is a frame or container configured to contain the patinated zinc surface.

13. The method of claim 1, further comprising the step of analysing the patinated zinc surface.

14. The method of claim 1, further comprising the step of installing an evaporative condenser with the zinc surface in a closed circuit cooling tower.

15. A patinated evaporative condenser in a closed circuit cooling tower, wherein the patinated evaporative condenser comprises steel, zinc, and zinc carbonate, and wherein the patinated evaporative condenser is patinated by the method according to claim 1.

16. A system for patinating zinc surfaces, comprising: a housing; an ingress/egress to open the housing; an ingress for gas which is operatively coupled with the housing; an ingress for water vapour which is operatively coupled with the housing; and a heating element to heat the gas; wherein the system is configured to perform the method according to claim 1.

17. The system of claim 16, further comprising an egress which is operatively coupled with the housing.

18. The system of claim 16, wherein the heating element is switched on for at least two hours.

19. (canceled)

20. The system of claim 16, further comprising an evaporative condenser with the zinc surface in a closed circuit cooling tower within the housing.

21. (canceled)

22. The system of claim 16, wherein the heating element is switched on for at least four hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, in which:

[0077] FIG. 1 shows a schematic overview of the method according to the invention;

[0078] FIG. 2 shows a pipe comprising the different layers;

[0079] FIG. 3 shows a schematic system for patinating zinc surfaces of a structural element;

[0080] FIG. 4 shows a schematic system comprising the main electrical components of the system for patinating zinc surfaces of a structural element;

[0081] FIG. 5 shows pipes exposed to different carbon dioxide concentrations;

[0082] FIGS. 6A, 6B, 6C and 6D show IR spectra of analysed zinc patinated products;

[0083] FIG. 7 shows the results of the IR analysis of a zinc patinated product according to the invention; and

[0084] FIGS. 8A, 8B, 8C, and 8D show SEM-EDX analysis of the patination process at various stages.

DETAILED DESCRIPTION

[0085] Method 10 (FIG. 1) comprises the steps of providing zinc to the structural element with a surface 12, providing a structural element with a zinc surface in a housing 14, optionally the step of providing a structural element with a zinc surface to an object of the application can be applied, providing the housing with a carbon based gas and humidity 16, heating the zinc surface for at least one hour 18, wherein the heating occurs at a temperature of at least 50° C., the humidity is at least 70% and the carbon based gas concentration is at least 5% by volume. Furthermore, method 10 comprises the steps of taking out the zinc surface from the housing 20, preferably analysing the patinated surface 22 and even more preferably installing an evaporative condenser with a zinc surface in a closed circuit cooling tower 24.

[0086] It will be understood that the step of analysing the patinated surface 22 can also be performed before the step of taking out the zinc surface of the housing 20. Furthermore, it will be understood that combinations of the various steps are possible to. For example, the step of installing an evaporative condenser with a zinc surface in a closed circuit cooling tower 24 is optional.

[0087] Pipe 30 (FIG. 2), comprises inside 32 of steel pipe 34, zinc coating 36 and patina layer 38. Outside 40 of pipe 30 is covered with patina layer 38.

[0088] In a preferred embodiment all objects patinated and/or passivated by traditional methods can be patinated by the method according to the invention. For example, but not limited to, lampposts, post boxes, rain pipe, gutter, pipes, fences, concrete braiding, and the like.

[0089] In a preferred embodiment the method and/or system are also suitable for patinating a (metal) surface comprising another coating then zinc, for example, copper, bronze, lead, and the like.

[0090] System 50 (FIG. 3) is suitable for patinating zinc surfaces of structural element 52. System 50 comprises container 54 which is configured to have a substantially open configuration and a substantially closed configuration. In the substantially closed configuration, the container is configured to house structural element 52 comprising a zinc surface, such as an evaporative condenser with a zinc surface in a closed circuit cooling tower. The atmosphere in container 54 may be heated so that structural element 52 is also heated. Preferably, the atmosphere comprises a carbon-based gas and humidity, which may be continuously added to container 54. Container 54 further comprises analysing means 55, to analyse the patination layer.

[0091] Container 54 may further comprise entrance 56, wherein entrance 56 is configured to access inside 58 of container 54. Preferably the dimensions of entrance 56 have dimensions which are suitable to move structural element 52 from inside 58 of container 54 to the outside of container 54. Entrance 56 further comprises sealing means 60 to seal the entrance. Sealing means 60 are configured to seal the atmosphere inside 58 from the outside.

[0092] The container further comprises ingress 62 for allowing carbon-based gas to enter container 54. Tank 64 provides the carbon-based gas via conduit 66 to inside 58 of container 54. Heating element 68 may be operatively coupled to tank 64 and/or conduit 66 and/or ingress 62 to heat the carbon-based gas before it enters container 54.

[0093] System 50 further comprises tank 70, wherein tank 70 is configured to hold water vapour, or other forms thereof. Tank 70 is operatively coupled via conduit 72 and ingress 74 with inside 58 of container 54. The water vapour, or other form thereof, may be heated by heating element 76.

[0094] System 50 further comprises heating element 78 which may heat the atmosphere inside container 54.

[0095] System 50 optionally comprises gas egress 80, which is operatively connected to system gas exit 82, and water vapour egress 84 which is operatively connected to system water vapour exit 86.

[0096] System 90 (FIG. 4) shows a schematic overview of the main electrical components of a system for patinating a zinc surface, wherein container 92 comprises the zinc surface. The main electrical components of system 90 are operatively connected via conductors 94. Central processing unit 96 is configured for controlling the flow of water vapour and carbon-based gas into container 92. Central processing unit 96 may include a computing device.

[0097] System 90 further comprises tank 98 and 100 which are configured for storing either the carbon-based gas or water vapour or the like and are operatively coupled with container 92 via respectively conduit 102 or conduit 104. System 90 further comprises heating elements 106, 108 and 110 which are configured for heating the atmosphere within tank 98, tank 100 and container 92.

[0098] System 90 is provided with power via power supply 112, which is operatively coupled to heating elements 106, 108 and 110, central processing unit 96, and other electrical components of system 90.

[0099] System 90 further comprises sensors 114, 116, 118 and 120 which operatively coupled with central processing unit 96, to provide information about the patinating process within container 92 for controlling system 90. Sensors 114, 116, 118, 120 may comprise a sensor for determining the carbon-based gas within the atmosphere, determining the relative humidity, determining the temperature, determining the gas flow, and the like.

[0100] System 90 further comprises egress 122 and egress 124 which are part of container 92 and operatively couple gas exit 126 and water vapour exit 128 with container 92.

[0101] Conduit 102, conduit 104, gas exit 126, water vapour exit 128 comprises respectively valve 130, 132, 134, 136. Valve 130, 132, 134, 136 can close or open the respective conduit or exit. The valves are operatively coupled with central processing unit 96.

[0102] In an experiment performed with the method according to the invention, a steel surface which is zinc coated was patinated. The surface used was a zinc coated steel pipe comprising a diameter of 10 centimetre and a length of 10 centimetre. The surface was exposed to different carbon dioxide concentrations at a temperature between 53° C. and 57° C. for approximately three hours. The RH was determined every 30 minutes. The corrosion was determined by exposing the surface to a saturated oxygen solution of 150 mg Cl.sup.−/L for 24 hours. The results are shown in the Table 1, wherein CO.sub.2% is the carbon dioxide concentration, T is the temperature in degrees Celsius (° C.), RH is relative humidity, SD is the standard deviation of RH, and result is the overall results of the pipes exposed to corrosion.

TABLE-US-00001 TABLE 1 results of patination process with different carbon dioxide concentrations. Entry CO.sub.2 % T └° C.┘ RH └%┘ SD Result 1 atmosphere 56 65 15.7 white rust 2 1 57 67 13.9 Good 3 5 55 54 11.3 very good 4 10 54 50 7.0 very good 5 20 53 60 10.2 very good

[0103] Increasing the concentration of carbon dioxide shows good patination of the surface, and thus protection against corrosion. Concentrations in the range of 15% to 30% of carbon dioxide, and preferably above 20% of carbon dioxide were considered undesired as high concentrations of carbon dioxide are hazardous, and not cost effective.

[0104] It is shown that a concentration of at least 5% carbon dioxide provides the zinc coated metal surface with a very good patina layer. This will result in a longer lasting protection for corrosion.

[0105] In a further experiment performed with the method according to the invention, steel pipes were exposed to the conditions mentioned in table 1 (FIG. 5). Thus, control is the pipe exposed to a gas without any carbon dioxide, pipe one was exposed to a carbon dioxide concentration present in outside air, pipe two was exposed to a gas with a carbon dioxide concentration of about 1%, pipe three was exposed to a gas with a carbon dioxide concentration of about 5%, pipe four was exposed to a gas with a carbon dioxide concentration of about 10%, and pipe five was exposed to a gas with a carbon dioxide concentration of about 20%.

[0106] It becomes clear that a severe, efficient and effective patination layer is formed on the zinc coated surface of the pipes.

[0107] FIGS. 6A-D show IR spectra of analysed zinc patinated products. The IR spectra relate to the patinated zinc surface, wherein the surface it patinated over different times under the conditions of 20% CO.sub.2 gas at 60° C. The different times are 24 hours, 12 hours, 6 hours, and 3 hours, for respectively FIGS. 6A, 6B, 6C, and 6D. To prepare the samples, 10 to 100 μg of the patination layer was removed from the patinated surface using a binocular microscope under flat lighting. The obtained powder was grinded in a monocrystalline sapphire mini-mortar in the presence of cesium bromide. After hydrolic compression pellets of 5 mm in diameter were obtained.

[0108] The x axis of the spectra includes wavenumber (cm.sup.−1) and the y-axis includes the absorbance (A).

[0109] The pellets were analysed using an infrared absorption spectrometer, Fourier Perkin Elmer Frontier which was able to operate in the far infrared up to 200 cm.sup.−1. For each of the samples a global spectrum over 4000200 cm.sup.−1 was obtained. The pellets were then calcinated at 550° C. for about 30 minutes and reconstituted before analysis.

[0110] FIG. 6A shows the IR spectra of the collected patination layer before and after calcination. The IR spectrum before calcination, top line at 1500 cm.sup.−1, shows hexahydroxydicarbonate pentazinc (HCPZ) of medium crystallinity. The peaks at 1647, 1505, 1390, 1045, 957, 834, 739, 708, and 468 cm.sup.−1 relate to HCPZ. The peak at 3398 cm.sup.−1 is slightly shifted compared to the expected result (3420 cm.sup.−1). Therefore, this peak is more relevant to the hydration of the product than to the characterisation of OH of HCPZ. Furthermore, it becomes clear that there is a significant pollution (peaks at 2957, 2923, and 2852 cm.sup.−1). This pollution is related to the analysed product rather than to operational pollution. Therefore, the spectrum after calcination where only this pollution may be present (lower line at 1500 cm.sup.−1).

[0111] After calcination there is only one peak with shoulder related to HCPZ present at 425 cm.sup.−1. This peak relates to calcinated HCPZ in the form of zinc oxide. Due to the presence of small amounts of pollution the crystallisation of zinc oxide was disturbed and pollutions were incorporated within the crystal structure. The pollutions are silica and/or phosphate based molecules. The small peak at 1109 cm.sup.−1 relates to such pollution. The peaks at 3434 and 1634 cm.sup.−1 are related to water which was hydroscopically attracted by the sample.

[0112] It was found that the hydration factor is 0.81, the crystallinity factor is 3.51, and the stoichiometric ratio is 2.28 (FIG. 7).

[0113] FIG. 6B shows the IR spectra of the collected patination layer before and after calcination. The IR spectrum before calcination, top line at 1500 cm.sup.−1, shows HCPZ of medium crystallinity. The peaks at 1646, 1504, 1388, 1046, 960, 834, 738, 708, and 473 cm.sup.−1 relate to HCPZ. The peak at 3399 cm.sup.−1 is slightly shifted compared to the expected result (3420 cm.sup.−1). Therefore, this peak is more relevant to the hydration of the product than to the characterisation of OH of HCPZ. Furthermore, it becomes clear that there is a significant pollution (peaks at 2958, 2924, and 2854 cm.sup.−1). This pollution is related to the analysed product rather than to operational pollution. Therefore, the spectrum after calcination where only this pollution may be present (lower line at 1500 cm.sup.−1).

[0114] After calcination there is only one peak with shoulder related to HCPZ present at 427 cm.sup.−1. This peak relates to calcinated HCPZ in the form of zinc oxide. Due to the presence of small amounts of pollution the crystallisation of zinc oxide was disturbed and pollutions were incorporated within the crystal structure. The pollutions are silica and/or phosphate based molecules. The small peak at 1114 cm.sup.−1 relates to such pollution. The peaks at 3435 and 1643 cm.sup.−1 are related to water which was hydroscopically attracted by the sample.

[0115] It was found that the hydration factor is 0.87, the crystallinity factor is 3.55, and the stoichiometric ratio is 2.35 (FIG. 7).

[0116] FIG. 6C shows the IR spectra of the collected patination layer before and after calcination. The IR spectrum before calcination, top line at 1500 cm.sup.−1, shows HCPZ of medium crystallinity. The peaks at 1646, 1504, 1389, 1045, 960, 834, 737, 708, and 473 cm.sup.−1 relate to HCPZ. The peak at 3401 cm.sup.−1 is slightly shifted compared to the expected result (3420 cm.sup.−1). Therefore, this peak is more relevant to the hydration of the product than to the characterisation of OH of HCPZ. Furthermore, it becomes clear that there is a significant pollution (peaks at 2956, 2924, and 2854 cm.sup.−1). This pollution is related to the analysed product rather than to operational pollution. Therefore, the spectrum after calcination where only this pollution may be present (lower line at 1500 cm.sup.−1).

[0117] After calcination there is only one peak with shoulder related to HCPZ present at 425 cm.sup.−1. This peak relates to calcinated HCPZ in the form of zinc oxide. Due to the presence of small amounts of pollution the crystallisation of zinc oxide was disturbed and pollutions were incorporated within the crystal structure. The pollutions are silica and/or phosphate based molecules. The small peak at 1109 cm.sup.−1 relates to such pollution. The peak at 3437 cm.sup.−1 is related to water which was hydroscopically attracted by the sample.

[0118] It was found that the hydration factor is 0.92, the crystallinity factor is 3.35, and the stoichiometric ratio is 2.07 (FIG. 7).

[0119] FIG. 6D shows the IR spectra of the collected patination layer before and after calcination. The IR spectrum before calcination, top line at 1500 cm.sup.−1, shows HCPZ of medium crystallinity. The peaks at 1646, 1502, 1388, 1047, 960, 835, 706, and 469 cm.sup.−1 relate to HCPZ. The peak at 3400 cm.sup.−1 is slightly shifted compared to the expected result (3420 cm.sup.−1). Therefore, this peak is more relevant to the hydration of the product than to the characterisation of OH of HCPZ. Furthermore, it becomes clear that there is a significant pollution (peaks at 2958, 2923, and 2853 cm.sup.−1). This pollution is related to the analysed product rather than to operational pollution. Therefore, the spectrum after calcination where only this pollution may be present (lower line at 1500 cm.sup.−1).

[0120] After calcination there is only one peak with shoulder related to HCPZ present at 429 cm.sup.−1. This peak relates to calcinated HCPZ in the form of zinc oxide. Due to the presence of small amounts of pollution the crystallisation of zinc oxide was disturbed and pollutions were incorporated within the crystal structure. The pollutions are silica and/or phosphate based molecules. The broad peak at 1109 cm.sup.−1 relates to such pollution. The peaks at 3458 and 1629 cm.sup.−1 are related to water which was hydroscopically attracted by the sample.

[0121] It was found that the hydration factor is 1.05, the crystallinity factor is 3.74, and the stoichiometric ratio is 2.47 (FIG. 7).

[0122] FIG. 7 shows the results of the IR analysis (FIGS. 6A-6D) of a zinc patinated product according to the invention. The left set of four bars corresponds to the hydration, the middle set of four bars corresponds to the crystallinity, and the right set of four bars corresponds to the stoichiometric ratio. The left bar corresponds with a patination time of 24 hours, the second from the left bar corresponds with a patination time of 12 hours, the second from the right bar corresponds with a patination time of 6 hours, and the right bar corresponds with a patination time of 3 hours. It becomes clear that HCPZ provide effective and efficient protection, wherein the build up of the tight layers prevent further growth of the layer thickness and therefore an efficient and effective patinated surface is achieved.

[0123] Furthermore, it becomes clear that the crystallinity and stoichiometric ratio of the sample patinated for 6 hours is not in line with the expected results. This is due to a discontinuity of the patination time.

[0124] FIGS. 8A-8D show SEM-EDX analysis of the patination process at various stages according to the invention in relation to a conventional method.

[0125] FIG. 8A shows a fresh zinc surface without any treatment. The composition of the surface is about 79% Zn and about 21% O.

[0126] FIG. 8B shows a patination layer, wherein the zinc surface of FIG. 8A is treated with the method according to the invention for about 30 minutes. The composition of the surface is about 11% C, about 65% Zn, about 24% O, and traces of other elements such as Al, Pb, and Si.

[0127] FIG. 8C shows a patination layer, wherein the zinc surface of FIG. 8A is treated with the method according to the invention for about 7 hours. The composition of the surface is about 9% C, about 62% Zn, about 28% O, and traces of other elements such as Al and Pb.

[0128] FIG. 8D shows a patination layer, wherein the zinc surface of FIG. 8A is passivated with a conventional method by placing the zinc surface outside in Zelhem (Netherlands) for about six weeks between April and May. The composition of the surface is about 6% C, about 0.5% Zn, about 52% O, about 27% Ca, about 13% P, about 1.8% Mg, and traces of Si.

[0129] FIGS. 8A-8D show that a quick patination layer can be provided to a zinc surface. Furthermore, FIG. 8D comprises cracks in the passivation layer. The cracks are weak places and the metal can be oxidised quickly. The method according to the invention provides thin and hard patination layers without cracks (FIG. 8C). Therefore, the method according to the invention results in a more sustainable protection layer.

[0130] The experiments clearly shows the advantageous effects achieved with the method and system of the invention.

[0131] The present invention is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following claims, within the scope of which many modifications can be envisaged.