Use of a carbonaceous coating for protecting a passive electric component from attack by ammonia and system comprising a passive electrical component, which is protected against attack by ammonia

Abstract

The invention relates to the use of a carbonaceous coating for protection of a passive electrical component from attack by ammonia, wherein the carbonaceous coating is a sol-gel coating or a plasma-polymeric coating. This coating comprises a particular carbon content.

Claims

1. A carbonaceous coating for a passive electrical component for protecting the passive electrical component from an attack by ammonia comprising: (i) a sol-gel layer which is producible or has been produced by a sol-gel method or (ii) a plasma-polymeric layer which is producible or has been produced by plasma-activated chemical vapor deposition; wherein each of (i) the sol-gel layer or (ii) the plasma polymeric layer has a surface facing away from the passive electrical component, and comprises a carbon content of 50 to 90 atom % at a depth of 80 nm below the surface and as measured by and based on a total number of atoms detected by XPS, or comprises an organometallic layer comprising a carbon content of 2 to 50 atom % at a depth of 80 nm below the surface and as measured by and based on the total number of atoms detected by XPS; wherein each of (i) the sol-gel layer or (ii) the plasma polymeric layer has at least one hydrolyzable group on the surface, the at least one hydrolyzable group being selected from the group consisting of ester, amide, urethane and urea groups, and (i) the sol-gel layer comprises a hydrolyzable carbon content of ≤15 atom % or (ii) the plasma-polymeric layer comprises a hydrolyzable carbon content of ≤10 atom %, wherein hydrolyzable carbon content is the portion of carbon within the at least one hydrolyzable group on the surface relative to the total carbon content on the surface as measured by XPS with C1s peak fitting.

2. The carbonaceous coating of claim 1, wherein the carbonaceous coating is an amorphous carbon coating or an organosilicon coating.

3. The carbonaceous coating of claim 1 further comprising an interlayer disposed between the passive electrical component and (i) the sol-gel layer or (ii) the plasma polymeric layer of the carbonaceous coating.

4. The carbonaceous coating of claim 3, wherein the interlayer comprises a ceramic layer.

5. The carbonaceous coating of claim 1, wherein a surface of the passive electrical component is selected from the group consisting of copper, aluminum, an alloy comprising copper, an alloy comprising aluminum, and a mixture of at least two of the aforementioned.

6. The carbonaceous coating of claim 1, wherein the passive electrical component is selected from the group consisting of a coil, a resistor, and a capacitor.

7. The carbonaceous coating of claim 1, wherein the carbonaceous coating comprises silicon.

8. The carbonaceous coating of claim 1 further comprising an interlayer disposed between the passive electrical component and (i) the sol-gel layer or (ii) the plasma polymeric layer of the carbonaceous coating; wherein the interlayer is selected from the group consisting of: an interlayer containing a crosslinked oil; an interlayer containing an uncrosslinked oil; an interlayer containing a crosslinked silicone oil; an interlayer containing an uncrosslinked silicone oil; an interlayer with a zone of crosslinked oil disposed between the interlayer and (i) the sol-gel layer or (ii) the plasma polymeric layer; an interlayer with a zone of crosslinked silicone oil disposed between the interlayer and (i) the sol-gel layer or (ii) the plasma polymeric layer; and a combination of at least two of the afore-mentioned.

9. The carbonaceous coating of claim 4, wherein the ceramic layer is selected from the group consisting of TiO.sub.2, SiO.sub.2, Al.sub.2O.sub.3, Ti.sub.xN.sub.y and BN.

10. The carbonaceous coating of claim 4, wherein the ceramic layer is an eloxal layer.

11. The carbonaceous coating of claim 1, wherein the carbonaceous coating has an elongation at break of ≥2.5%.

12. The carbonaceous coating of claim 1, wherein the carbonaceous coating has a hardness measurable by nanoindentation in a range of 2 GPa to 6 GPa.

13. The carbonaceous coating of claim 1, wherein the carbonaceous coating comprises (ii) the plasma-polymeric layer; wherein the carbonaceous coating further comprises an interlayer between the passive electrical component and ii) the plasma-polymeric layer; wherein carbonaceous coating has a silicon content of 5 atom % to 40 atom % based on a total number of carbon, silicon and oxygen atoms as measured by XPS at a depth of 80 nm below the surface.

14. The carbonaceous coating of claim 1, wherein the carbonaceous coating comprises (ii) the plasma-polymeric layer; wherein the carbonaceous coating further comprises an interlayer between the passive electrical component and ii) the plasma-polymeric layer; wherein the carbonaceous coating has an oxygen content of 30 atom % to 70 atom % based on a total number of carbon, silicon and oxygen atoms measured by XPS at a depth of 80 nm below the surface.

15. The carbonaceous coating of claim 1, wherein the carbonaceous coating has a thickness in a range of 100 nm to 100 am.

16. The carbonaceous coating of claim 1 further comprising an interlayer between the passive electrical component and (i) the sol-gel layer or (ii) the plasma polymeric layer of the carbonaceous coating; and wherein the interlayer and (i) the sol-gel layer or (ii) the plasma polymeric layer of the carbonaceous coating together have a dielectric strength measured according to DIN EN 60243-1 and DIN EN 60243-2 of ≥100 V measured up to a maximum current flow of 3 mA.

17. A system for contact with ammonia or ammoniacal media, comprising a passive electrical component having the carbonaceous coating as defined in claim 1 disposed in a region of the system intended for direct contact with ammonia or ammoniacal media.

18. The system as claimed in claim 17, wherein the system is a cooling apparatus or a plant for production, for processing, for use, for transport or for storage of ammonia or ammoniacal media.

19. A carbonaceous coating for a passive electrical component for protecting the passive electrical component from an attack by ammonia comprising: (i) a sol-gel layer which is producible or has been produced by a sol-gel method or (ii) a plasma-polymeric layer which is producible or has been produced by plasma-activated chemical vapor deposition; wherein each of (i) the sol-gel layer or (ii) the plasma polymeric layer has a surface facing away from the passive electrical component, and comprises a carbon content of 50 to 90 atom % at a depth of 80 nm below the surface and as measured by and based on a total number of atoms detected by XPS, or comprises an organometallic layer comprising a carbon content of 2 to 50 atom % at a depth of 80 nm below the surface and as measured by and based on the total number of atoms detected by XPS; and further comprising a ceramic interlayer disposed between the passive electrical component and (i) the sol-gel layer or (ii) the plasma polymeric layer of the carbonaceous coating; wherein the ceramic interlayer is selected from the group consisting of: a ceramic interlayer containing a crosslinked oil; a ceramic interlayer containing an uncrosslinked oil; a ceramic interlayer containing a crosslinked silicone oil; a ceramic interlayer containing an uncrosslinked silicone oil; a ceramic interlayer with a zone of crosslinked oil disposed between the ceramic interlayer and (i) the sol-gel layer or (ii) the plasma polymeric layer; a ceramic interlayer with a zone of crosslinked silicone oil disposed between the interlayer and (i) the sol-gel layer or (ii) the plasma polymeric layer; and a combination of at least two of the afore-mentioned.

20. The carbonaceous coating of claim 19, wherein: each of (i) the sol-gel layer or (ii) the plasma polymeric layer has at least one hydrolyzable group on the surface, the at least one hydrolyzable group being selected from the group consisting of ester, amide, urethane and urea groups, and (i) the sol-gel layer comprises a hydrolyzable carbon content of ≤15 atom % or (ii) the plasma-polymeric layer comprises a hydrolyzable carbon content of ≤10 atom %, wherein hydrolyzable carbon content is the portion of carbon within the at least one hydrolyzable group on the surface relative to the total carbon content on the surface as measured by XPS with C1s peak fitting.

21. The carbonaceous coating of claim 19, wherein the carbonaceous coating is an amorphous carbon coating or an organosilicon coating.

22. The carbonaceous coating of claim 19, wherein a surface of the passive electrical component is selected from the group consisting of copper, aluminum, an alloy comprising copper, an alloy comprising aluminum, and a mixture of at least two of the aforementioned.

23. The carbonaceous coating of claim 19, wherein the passive electrical component is selected from the group consisting of a coil, a resistor, and a capacitor.

24. The carbonaceous coating of claim 19, wherein the carbonaceous coating comprises silicon.

25. A system for contact with ammonia or ammoniacal media, comprising a passive electrical component having the carbonaceous coating as defined in claim 20 disposed in a region of the system intended for direct contact with ammonia or ammoniacal media.

26. The system as claimed in claim 25, wherein the system is a cooling apparatus or a plant for production, for processing, for use, for transport or for storage of ammonia or ammoniacal media.

27. The carbonaceous coating of claim 19, wherein the ceramic interlayer is selected from the group consisting of TiO.sub.2, SiO.sub.2, Al.sub.2O.sub.3, Ti.sub.xN.sub.y and BN.

28. The carbonaceous coating of claim 19, wherein the ceramic interlayer layer is an eloxal layer.

29. The carbonaceous coating of claim 19, wherein the carbonaceous coating has an elongation at break of ≥2.5%.

30. The carbonaceous coating of claim 19, wherein the carbonaceous coating has a hardness measurable by nanoindentation in a range of 2 GPa to 6 GPa.

31. The carbonaceous coating of claim 19, wherein the carbonaceous coating comprises (ii) the plasma-polymeric layer; wherein carbonaceous coating has a silicon content of 5 atom % to 40 atom % based on a total number of carbon, silicon and oxygen atoms as measured by XPS at a depth of 80 nm below the surface.

32. The carbonaceous coating of claim 19, wherein the carbonaceous coating comprises (ii) the plasma-polymeric layer; wherein the carbonaceous coating has an oxygen content of 30 atom % to 70 atom % based on a total number of carbon, silicon and oxygen atoms measured by XPS at a depth of 80 nm below the surface.

33. The carbonaceous coating of claim 19, wherein the carbonaceous coating has a thickness in a range of 100 nm to 100 μm.

34. The carbonaceous coating of claim 19, wherein the ceramic interlayer and (i) the sol-gel layer or (ii) the plasma polymeric layer of the carbonaceous coating together have a dielectric strength measured according to DIN EN 60243-1 and DIN EN 60243-2 of ≥100 V measured up to a maximum current flow of 3 mA.

Description

EXAMPLES

Measurement Examples

Measurement Example 1

(1) XPS Measurement Procedure at Layer Depth 80 nm

(2) A surface analysis by means of photoelectron spectroscopy (XPS) covered about the outermost 10 nm of a solid-state surface. In order to be able to analyze the chemical composition of the sample material at a depth of 80 nm by XPS, the surface is removed by ion beam bombardment. For this atomization process, argon ions having an energy of 3 keV are typically used. The time required to remove the uppermost 80 nm of a sample surface depends on the instrument-specific atomization rate. This is determined experimentally in each case by comparative measurements on corresponding reference samples. The typical pressure range for such sputtering processes is in the range from 1*10{circumflex over ( )}-5 to 1*10{circumflex over ( )}-6 mbar.

Measurement Example 2

(3) Testing of Electrical Insulation Properties:

(4) Partial Discharge Measurement Technique:

(5) .fwdarw.Nondestructive test method for determination of the electrical insulation effect of coatings (by way of example for the DWX-05 instrument, preferably on coil geometries or electric motors)

(6) Technique:

(7) The instrument used (DWX-05) is essentially a high-voltage source capable of generating a high-voltage pulse within a very short time (shorter than 1 msec—with a very large flank), or of “imprinting” it into the component. The component to be examined (preferably a coil or an engine part) is connected firstly to the voltage source and secondly to the measurement electronics. In addition, an RF antenna (including band filter) is connected to the instrument, which measures the occurrence of RF discharges (correlated to time) with the voltage pulse imprinted. It is important here that the antenna and the coil do not touch one another. The measurement is then effected from a preset voltage and is continually increased by a particular value (typically 5% of the last voltage tested) until TE discharge is detected or the required final voltage is attained. The measurement used is firstly the response of the system (the coil) itself (case A) and secondly the detection of RF discharges (case B) which are characteristic and are observed just before the occurrence of a flashover between two windings or to the tooth. The measurements are conducted at least three times for each voltage value and the final values are used to ascertain an average in order to obtain a statistically certain result. In the case of large variations in the final measurements, the sample should possibly be checked for homogeneity, or the measurement ascertained should be used only with restrictions.

(8) The variances allowed beforehand in the measurement signals from the target state thus effectively form the test criteria. Maximum possible voltage values in the present instrument are 5 kV.

(9) For this test method, the measurement signals are analyzed in two ways (optionally also both criteria simultaneously): 1. Comparing with a reference signal (recorded on an undamaged component or in a lower voltage range in which the insulation is definitely intact—assessment with reference to the curve profile)—deviations of more than +20% or −4% of the response signal detected from the scaled curve of the reference signal are regarded as “defective” insulation for the voltage value being tested in each case or a collapse in the response signal (resulting from a short circuit) Collectively case (A) 2. Measuring the RF discharge and comparing with the “base noise” of the RF signal—in the event of deviations or the occurrence of clear RF signals (correlated in time with the voltage profile of the signal imprinted), a partial discharge is detected and hence the coating is determined as being inadequate over and above this voltage value—it is additionally advisable to use the LaPlace 15/0 criterion in the automated evaluation. .fwdarw. Collectively case (B)

(10) Sample Requirements: Geometry in the form of a coil (metal substrate) Minimum inductivity requirement—currently at least 10 windings, instrument-specific value Full-area coating in constant quality of a component or of the individual components with respect to one another in a “batch check” Accessibility of the contacting and of the tooth (in the installed state) or regions on tooth and coil that can be contacted without coating. Mass production-capable testing for 100% of the components is possible by this test method

(11) Further information on this test method can be found in: Ein neues Verfahren zur automatischen Gewinnung der Teilentladungseinsetz- und Aussetzspannung an elektrischen Wicklungen nach IEC TS 60034-18-41 und IEC TS 61934 [A New Method of Automatically Obtaining the Partial Discharge Inception and Extinction Voltage of Electrical Windings According to IEC TS 60034-18-41 and IEC TS 61934]—from conference: Internationaler ETG-Kongress 2009—Symposium 3: Direktantriebe in Produktionsmaschinen und Industrieanlagen—Generatoren und Antriebe in regenerativen Kraftwerken [Direct Drives in Production Machines and Industrial Plants—Generators and Drives in Renewable Power Plants]/Symposium 4: Diagnostik elektrischer Betriebsmittel [Diagnostics of Electrical Equipment] Oct. 27, 2009-Oct. 28, 2009 at Düsseldorf, Germany.

Measurement Example 3

(12) Stress Test for Dielectric Strength

(13) Coils/samples were produced as in working example 1. An oven was heated to 300° C. and the coils were placed therein and stored therein for 500 h. After the aging, the samples were removed and cooled to room temperature within one hour. Thereafter, the samples were tested according to measurement example 2. A maximum drop in the dielectric strength by 15% was observed by comparison with the starting state prior to the aging.

Measurement Example 4

(14) Nanoindentation Measurement

(15) Nanoindentation is a testing technique by which the hardness of surface coatings can be ascertained by means of a fine diamond tip (triangular pyramids [geometry according to Berkovich], radius a few hundred nm). In this case, by contrast with the macroscopic determination of hardness (for example Vickers hardness), the measurement is not made on the remaining indentation trough that has been made by a normal force, and instead a penetration depth-dependent cross-sectional area of the nanoindenter has been assumed. This depth-dependent cross-sectional area is ascertained via a reference sample with known hardness (generally high-purity quartz glass).

(16) During the application of the normal force, nanoindentation uses sensitive steering electronics (capacitative plates) by which the penetration depth can be measured precisely as the normal force rises and falls again—quite differently to the conventional method.

(17) During the initial phase of load removal in situ, the standard force penetration depth curve indicates the stiffness of the sample. With the aid of the cross-sectional area of the nanoindenter which is known from the reference sample, the modulus of elasticity and hardness of the sample can thus be determined. The maximum testing force for the nanoindentation is generally below 15 mN.

(18) For measurement of the pure properties of the coating without any influence by the substrate, a rule of thumb of 10% of the layer thickness is used. Penetration curves that go below that include an influence by the substrate used. With rising penetration depths of more than 10% of the layer thickness, the measured values for modulus of elasticity and hardness successively approach those of the substrate. The described evaluation by this test method is named for Oliver & Pharr [Oliver].

(19) For simpler variation of the penetration depths at different loads, what is called the multiple loading and load relief method, the multiindentation method for short, is used. In this case, loads are applied and relieved on a fixed point in segments. The local load maxima are increased continuously. At the fixed point, it is thus possible to ascertain depth-dependent values of modulus of elasticity and hardness. In addition, for statistical purposes, various unaffected sites on the sample are likewise approached and tested in a measurement field. By comparison between single indentation and multiindentation methods, Schiffmann & Küster showed that there are only very small deviations between the values ascertained in the two methods [Schiffmann] For compensation, longer hold times are suggested for prevention of creep effects of the piezo scanner [Schiffmann].

(20) In the case of the measured samples of the working examples described in the text, measurement was made with 10 multiindentations per site with preferably a maximum of 5 mN, further preferably less than 2 mN, even further preferably less than 1 mN. The multiindentations have local force maxima that have then been reduced to 20% of the force. These load relief curves were evaluated in the form of a tangent from 98% to 40%.

(21) For statistics and homogeneity, 10 measurement points per sample were tested. The distance between the measurement points was 50 μm in order to avoid effects such as plastic deformations of the layer to be examined as a result of prior measurements, for example.

(22) The layer thicknesses of the samples that were used to determine the layer hardnesses were more than 1 μm in each case. To comply with the empirical formula for the penetration depth of max. 10% of the layer thickness, the load relief curves for the multi-indentations are admissible for the evaluation up to a maximum force of not more than 5 mN, further preferably less than 2 mN, even further preferably less than 1 mN. In the case of lower layer thicknesses, the corresponding maximum local force should be noted in order not to exceed the 10% rule.

(23) The maximum force for the penetration depth and the corresponding load relief curve is thus preferably not more than 5 mN, further preferably less than 2 mN; depending on the layer thickness of about 1000 nm it is even further preferably less than 1 mN.

Working Examples

Working Example 1

(24) Low-Pressure Plasma Coating Process

(25) The deposited plasma polymer layers based on an inorganic matrix structure (preferably silicon-based) have a comparatively high organic character which, by comparison with SiOx layers, results in a higher crack onset strain. The plasma layers are preferably deposited under reduced pressure at about 10.sup.−2 mbar with the aid of a high-frequency plasma discharge (PE-CVD). In this case, a silicon-containing working gas is fragmented. The resultant fragments precipitate on the substrate as a thin layer. In order to increase the density of the layer, an ion-assisted method is employed, meaning that the partly ionized fragments are fired into the growing layer under the influence of an electrical field. The use of this technology ensures the applicability of the coating to complex coil geometry.

(26) Low-Pressure Plasma Coating Process The plasma coating is conducted under reduced pressure with a reactor of size 360 L at about 10.sup.−2 mbar. An aluminum coil with 14 windings is extended to a length of 18 cm and placed onto two coupled sheets (200 mm×25 mm×1 mm). These sheets lie on an insulator plate (0.2 mm) which in turn lies on the actual plasma electrode. This construction prevents arcing that occurs during the plasma coating. The capacity of the coupled sheets is about 68 pF in each case. The frequency of the high frequency used of 13.56 MHz results in a resistance per coupled sheet of 171 ohms. At the start of the coating process, plasma activation with oxygen is conducted for 3 minutes. This step leads to an improvement in layer adhesion. In the second step, a primer layer is deposited. For this purpose, for oxygen, a flow rate of 5 sccm of hexamethyldisiloxane (HMDSO) is admitted into the reactor. The process time is 1 minute. The actual deposition process of the insulation coating is conducted at a HMDSO flow rate of 20 sccm. The process time is 2 hours. In order to hydrophilize the surface of the coated coil, it is subsequently possible to conduct a further plasma activation with oxygen. The plasma power and oxygen flow rate in all process steps are constant and are 45 W and 60 sccm respectively. The resulting layer had a composition (measured according to measurement example 1) of C: 32 atom %, O: 46 atom %, Si: 22 atom %. The nanoindentation hardness measured according to measurement example 4 was: 1.8 GPa±0.2 GPa The coated coil was locally characterized with regard to layer thickness and insulating effect (dielectric strength measured to DIN EN 60243-1 and DIN EN 60243-2). This resulted in the following values:

(27) TABLE-US-00001 TABLE 1 Area of winding Outer edge Inner edge (layer thickness about (layer thickness about (layer thickness about 4.5 μm) 7.0 μm) 11 μm) 470 V 610 V 640 V 470 V 540 V 720 V 450 V 620 V 670 V Ø 463.3 V Ø 590.0 V Ø 676.7 V

(28) Alternatively, the coating process by means of plasma can also be assisted by the application of what is called a BIAS voltage. Advantages here are the possibility of increasing the layer deposition rate and the possibility of generating a denser plasma polymer matrix.

Working Example 2

(29) Treatment Process of Anodization+LP Plasma Coating

(30) Al sheets/Al coils are wet-chemically cleaned, pickled and anodized in a sulfuric acid-based electrolyte for 5 to 60 minutes. The subsequent treatment of a hot compaction at 90° C. to 100° C. for 10 to 60 minutes is optional. The anodization layers thus produced on the aluminum coils have a layer thickness of 1 μm to 25 μm. Subsequent coating treatment by the scheme of working example 1.

Working Example 3

(31) Treatment Process of Anodization+Filling of the Pores of the Anodization Layer+LP Plasma Coating

(32) Al sheets are wet-chemically cleaned, pickled and anodized in a sulfuric acid-based electrolyte for 10 to 60 minutes. No hot compaction takes place. The sheets are subsequently aged in a US bath with HTA oil (5, 15, 30 min). There is a final heat treatment for crosslinking of the oil (7 d at RT or 30 min at 100° C.). Subsequent coating treatment by the scheme of working example 1.

(33) As a result, it is possible to increase dielectric strength by up to 20% compared to working example 2.

Working Example 4

(34) Aging of Coated Specimen Sheets in Ammonia Gas Atmosphere:

(35) The specimen sheets made of Al 99.5 that were coated in the experiments described above were installed into the pipe system in a cooling circuit at various angles of impact of the cooling gas. The coating consisted here either of a combination of eloxal (from working example 2) with a plasma polymer layer arranged thereon or of a plasma polymer layer (from working example 1 alone).

(36) As a comparison, the following were applied to the substrate from working examples 1 and 2:

(37) a) epoxy-based powder coating (3M Scotchcast 5555) according to manufacturer's description,

(38) b) an epoxy-isocyanate-based aircraft paint (Aerodur® Barrier Primer 37045, Akzo Nobel), likewise according to manufacturer's instructions,

(39) c) a fluoropolymer-based overcoat (Intersleek 1100SR from International Akzo Nobel) according to manufacturer's instructions, and

(40) d) a sol-gel coating to be used in accordance with the invention (Clearcoat U—Sil 120 GL, NTC-Nano Technology Coating GmbH), likewise according to manufacturer's instructions. The composition of the sol-gel layer according to measurement example 1 was determined as Si=7.6 atom %, o 0 32.2 atom %, C=56.6 atom % and N=3.6 atom %.

(41) The results are recorded in table 2.

(42) TABLE-US-00002 TABLE 2 Results of the aging of coated specimen sheets in ammonia gas atmosphere Insulation Theor. Layer Test Adhesion after test insulation Coating Ref. System thickness (14 d) result [V] [kV/mm] Powder (old) Epoxy ~50 μm x x up to 50 coating Aircraft Paint Epoxy- 100- x x paint isocyanate 130 μm Overcoat ✓ Fluoropolym. 80- ✓ ✓ >4000  40 100 μm Sol-gel Glass Polysiloxane- ~15-20 ✓ ✓ 530 ± 145 ~25 urethane μm (675 ± 430) resin Plasma Plasma Si.sub.xO.sub.yC.sub.z <5 μm ✓ ✓ 200 ± 40  PP~55 Eloxal + Ceramic Al.sub.2O.sub.3 + ~3 + 5 ✓ ✓ 350 ± 110 Eloxal~50 plasma Si.sub.xO.sub.yC.sub.z μm PP~55

(43) In table 2, “X” indicates failure of the coating.

(44) The installation state was parallel (parallel to the flow direction of the gas), at a 90° angle (perpendicular to flow direction) and at a 45° angle to the flow direction of the gas—in each case viewed from the sample normal. The flow rate of the ammonia gas here had typical values for such systems, here between 0.5 and 40 m/sec depending on the operation cycle.

(45) The samples were installed here in the normal part of an ammonia-driven cooling circuit. For this purpose, in each case three cycles of the typical working cycle in such a cooling system per day were run in the test arrangement. Cooling at −40° C. followed by thawing of the system at +80° C. in the ammonia (gas) atmosphere in alternation.

(46) In the studies, it was found that systems such as a powder coating that are characterized as stable were also found to be unstable under the conditions tested. Even the aircraft paint, which is approved for at least some of the temperature ranges in question, does not have sufficient durability. Both systems showed a virtually complete loss of adhesion after the test period. The overcoat used, as a fluoropolymer system, was found to be stable. However, in order to achieve comparable insulation effects to those possessed by the layers to be used in accordance with the invention, a distinctly greater layer thickness was necessary here (particularly by virtue of the application). This is disadvantageous especially in the field of coil applications since an important factor here is packing of maximum density for the component (fill factor). Furthermore, the PTFE constituents in fluoropolymers are generally stable to temperatures of briefly about 300° C.—thereafter, the systems (PTFE) begin to break down (possibly with formation of HF fractions) and hence lose their effect. In a cooling circuit, it is rare for such temperatures to be attained in the gas stream, but this is possible at the surface, for example, of a coil in use—and any weak point, no matter how small, can thus lead to failure of the component as soon as the insulating effect is lost. Furthermore, the organic constituents of such paint systems break down even at typically relatively low temperatures of above 200° C., which likewise results in degradation of the insulation properties.

(47) The coatings for use in accordance with the invention did not show any impairment at all as a result of the exposure. They have such good values that they are also of good suitability for replacing PTFE-containing layers in order to avoid their disadvantages.

(48) In addition, the conditions at the test site examined in the paint system were much harder than they would be for a compressor motor in a standard system.

(49) The mass and volume flow rates and temperatures and states of the ammonia are extremely different at the test site. A compressor motor is constantly subjected to a uniform temperature and to a vaporous or “gaseous” state of the coolant. For example, for a cold room at room temperature 2° C., the suction gas temperature in the compressor is fairly constant at −10° C. Liquid coolant or higher temperatures are not to be expected or to be strictly avoided.

(50) Of course, they would be smaller variations when the system is switched on and off, or after defrosting phases. However, the expansion valve of a refrigeration system exerts such rapid control that the actual suction gas temperature is adjusted within seconds. The compressor motor is cooled constantly with the suction gas volume flow.

(51) It can be concluded from this that the coatings for use in accordance with the invention have reserves of resistance for customary use. Against the background of this working example, it is preferable that the effects improved in accordance with the invention, in the case of doubt, occur under the conditions of the test experiment conducted in this example, i.e. more particularly under the conditions of a cycle from 80° C. to −40° C. three times per day in a direct gas stream at gas velocities of up to 40 m/s.

Working Example 5

(52) Determination of the Proportion of Hydrolyzable Groups on the Carbon

(53) 1. The determination procedure was analogous to the following literature reference: “Practical Surface Analysis”—Second Edition 1990, Volume 1 “Auger and X-ray Photoelectron Spectroscopy”, edited originally by D. Briggs and M. P. Seah, John Wiley & Sons, e.g. ISBN 0-471-92081-9—the following chapter therein: Appendix 3: Data Analysis in XPS and AES, A 3.7 The analysis of overlapping spectral features A 3.7.9 Curve synthesis and curve fitting, page 572 ff. In a departure from the procedure described, the area proportions were taken into account by a peak in the fit of the C—N components (if applicable by virtue of an N content in the coating) and the (C═O)—N or (C═O)—O components (hydrolyzable components). (kept the same relative to one another—1:1)

(54) 2. Results By the method described above, the plasma-polymeric coating from working example 1, the sol-gel coating from working example 4 and an aCH layer produced in a plasma-polymeric coating process were evaluated. This evaluation is illustrated in detail using the example of the sol-gel layer: According to the XPS measurement, at the surface of the sol-gel layer to be used in accordance with the invention, a concentration of 32.2 atom % of O, 3.6 atom % of N, 56.6 atom % of C and 7.6 atom % of Si is found. A fit or deconvolution (resolution) of the various species was conducted on the basis of the C1s peak (cf. FIG. 1). The peaks resolved are as follows:

(55) TABLE-US-00003 TABLE 3 Component peaks after deconvolution of the C1s peak Name Pos. FWHM % area C—C 285.0 1200 55.5 C—O 286.7 1200 19.4 (C═O)—N or (C═O)—O 289.4 1400 11.0 (hydrolyzable components) C═O 287.8 1189 3.1 C—N 285.8 1190 11.0 The proportion of hydrolyzable constituents is referred to as (C═O)—N or (C═O)—O or (see also FIG. 1). This shows that 11 atom % of the carbon atoms were present as a constituent of hydrolyzable groups for the sol-gel layer. Analogous measurements for the plasma-polymeric coating from working example 1 showed that 1.5 atom % of the carbon atoms are present in corresponding groups, whereas, for the plasma-polymeric aCH layer that was examined as the third example, 3 atom % of the carbon atoms were present in hydrolyzable groups. Without being bound to a theory, it seems to be the case that the layers having the carbon components present at the surface, owing to the small proportions of groups attackable by ammonia at the surface—but also by virtue of the backbone network present deeper into the coating—do not undergo any destruction and have good stability to ammoniacal media. In the case of the sol-gel coatings, even in the case of somewhat higher proportions of carbon in attackable groups at the surface, there appears to be sufficient resistance to ammoniacal media, as apparent from working example 4.