DESCRIPTION

The present invention relates in general terms to a process for coating inserts for a die for food products, for example pasta, by means of atomic layer deposition (ALD) technique or by means of a liquid phase autocatalytic deposition technique. With the process it is possible to recondition the inserts for dies for food products, rather than replace them once they have reached the end of their working life, thus prolonging their duration and reducing the environmental impact. Prior art

The extrusion of pasta constitutes a crucial step in the production of the pasta itself since, by means of this operation, it is possible not only to determine the shape and thickness of the finished product, but also to provide the extruded product with distinctive characteristics in terms of its surface roughness. Usually the extrusion step is performed by means of the passage of the mixture through inserts which are typically made of brass or teflon or, less frequently, other materials such as steel or gold. The interaction between material and mixture determines the surface properties of the finished product: teflon allows a pasta with a particularly smooth external surface to be obtained; metals, on the other hand, provide the product with roughness. All the inserts are subject to wear over time, with a consequent increase in the die aperture and impossibility of producing a product with the required thickness and cooking time. In order to ensure the qualitative uniformity of the product, the worn inserts are typically disassembled, discarded and replaced with new inserts. The working life of an insert (measured in production hours) depends both on the material from which it is made and on the geometrical form of the die aperture. In metallic materials, wear is further accelerated by associated corrosion phenomena. In the art processes for the coating of inserts for dies used in the mechanical sector, for example by means of both liquid phase and vapor phase deposition of thin films and thick films, by means of physical techniques (PVD) or chemical techniques (CVD), are known. In this connection, the atomic layer deposition (ALD) technique is a particular form of chemical vapor deposition (CVD) in which, differently from the latter, the treated substrate is exposed to each reagent separately, and all the reactions involved are limited to the surface. In the conventional CVD technique, instead, the reagents are fed together into the reaction chamber and may react both in the gaseous phase and on the surface of the substrate, during aggregation and growth.

WO 201 1 /099868 describes a die for extruding metallic material, comprising plates with cavities provided with inserts, where the inserts are made of wear-resistant material consisting of steel provided with a coating obtained by means of the CVD technique.

WO 2010/024902 describes a die for forming a green ceramic body, provided with a wear-resistant coating consisting of an inorganic nitride or carbide and formed by means of CVD. US 6176153 relates to a disk-shaped die with a shaped opening for the extrusion of metallic material, provided with a metal oxide, nitride or carbide surface coating applied by means of CVD.

WO 2008151947 describes an extrusion die orifice for producing honeycomb ceramic bodies, comprising a base plate provided with a hard material coating (nitride, carbide, oxide, etc.) obtained by means of the CVD technique, electroplating, and the like.

US 2013/078328 Al discloses a pelletizing ring extrusion die, i.a. for food products, comprising a die body having a plurality of extension holes, wherein each hole comprises a surface with a low-friction coating deposited thereon. The low-friction coating comprises a metal, ceramic or composite and can be applied onto the surface of the extension holes by PVD and CVD methods.

US 2008/089970 Al discloses a cutter assembly for an extruder including an elongated extrusion member having an opened feed end. This cutter assembly is used for extruding shaped food pieces. A nidox coating can be applied to a bottom of the elongated extrusion member prior to the formation of the through hole, which forms the die. No mention is made of the technique by which such nidox coating is applied. US 2007/ 178198 Al discloses an apparatus for making variously shaped pastry shells, including an annular baking rim supported on a horizontal lower plate to define an upward-facing female die. The exterior surface of the baking ring can be coated with a non-stick, wear-resistant coating, e.g. PTFE or an oxide of aluminum, for ease of baking and cleanup. Nothing is said about the technique by which such coating is applied.

Although with the methods known in the art it is possible to obtain improvements in the extrusion of metallic or ceramic materials, there still exists the need to find an insert for a food die, suitable in particular for the extrusion of pasta, which has optimum wear-resistance and corrosion properties, and which may be used for example for the production of both long and short, rough or smooth pasta, overcoming the problems of the prior art. The present invention is able to minimize corrosion and increase the mechanical strength of the material, thus prolonging the working life of the insert and also allows reconditioning of the worn inserts by coating them using liquid phase or vapor phase deposition techniques, with undoubted advantages in terms of environmental sustainability: it is in fact not necessary to produce new inserts, nor dispose of the used inserts nor melt them down in order to recover the material, reducing considerably the amount of energy, material and emissions currently needed in order to restore the standard extrusion conditions.

Summary of the invention

According to a first aspect, the invention relates to a process for coating an insert for a die for food products, preferably for pasta, by means of surface deposition of one or more coating compositions, optionally alternated, comprising at least: a metal oxide, preferably selected from SiO2, ZrO2, A12O3 and ZnO, a metal nitride or a mixed oxide, by means of atomic layer deposition (ALD) technique or by means of a liquid phase autocatalytic deposition technique. In one embodiment, the invention relates to a process for coating an insert for a die for food products, preferably for pasta, by means of liquid phase autocatalytic chemical deposition of metal composites, by immersion in a bath containing metal ions, and phosphorus-containing compounds. In an alternative embodiment, the invention relates to a process for coating an insert for a die for food products, preferably for pasta, by means of the atomic layer deposition (ALD) technique, said process comprising the steps of: a) exposure of the surface of the insert to a suitable metal source within a reaction chamber of an ALD apparatus; b) evacuation treatment with inert gas; c) obtaining the insert coated with the corresponding metal nitride or oxide by exposing the surface of the insert obtained after step b) to a suitable oxygen or nitrogen source; d) evacuation treatment with inert gas.

In one embodiment, when the metal source is a source of silicon, in particular tris(tert-butoxy)silanol, prior to the step a) of exposure of the surface of the insert to a metal source within a reaction chamber of an ALD apparatus, the process of the present invention further comprises a step of exposing said surface of the insert to a source of aluminum ions (Al ³⁺ ) within the reaction chamber.

In this embodiment, there occurs a polymerization of the silicon atoms bonded to the aluminum atoms chemisorbed on the treated surface.

According to a further aspect the invention relates to an insert for a die for food products, preferably for pasta, obtained (or obtainable) with the present process.

In a preferred embodiment, said insert is made of brass and is coated with one or more coating compositions, optionally alternated, comprising at least one metal oxide preferably selected from S1O2, ZrO2, ZnO, or a mixed oxide, for example Ti-Zn oxide or a metal nitride.

By "mixed oxide" an oxide containing two or more metal cations is meant, such as the above-mentioned Ti-Zn oxide.

According to a further aspect, the invention relates to use of the ALD technique for coating an insert for a die for food products, more preferably for pasta. In a further aspect, the invention relates to the use of a liquid phase autocatalytic deposition technique for coating an insert for a die for food products, preferably for pasta.

Brief description of the drawings Figures la- lb show AFM images of an area equal to 10x10 μιη ² of a silicon substrate (Fig. la) having a thickness of 70 nm, coated with S1O2 (Fig. lb) by means of the ALD technique.

Figures 2a-2c show AFM images of a brass substrate (Fig. 2a) coated by means of the ALD technique with ZrO2 (Fig. 2b) and with S1O2 (Fig. 2c). Detailed description

By means of the present process it is possible to coat an insert for a die for food products, in particular for pasta, by using ALD techniques or by means of a liquid phase autocatalytic deposition technique.

In this connection, in a first embodiment, the process comprises coating an insert for a food extruder by means of a liquid phase autocatalytic deposition technique, by immersion of the insert to be coated in a bath containing metal ions, preferably Ni ²⁺ , and phosphorus-containing compounds, preferably hypophosphite. In this latter case, deposition occurs by means of reduction of the metal ions by the hypophosphite ions, the reaction mechanism resulting in co-deposition of phosphate ions from the associated solution and hydrogen evolution. Deposition takes place at preferred temperatures of between about 40- 100°C and at preferred deposition speeds of between 2-20 μιη/h. Deposition may optionally occur in the presence of solid particles of a suitable compound, obtaining in this way the co-deposition of said particles in the Ni-P matrix. Preferably, said particles are selected from: PTFE, silicon carbide and diamond.

In an alternative embodiment, the process according to the invention is performed by means of vapor phase deposition and comprises coating an insert for a food die by means of the ALD technique. In this case, the process is performed by means of exposure of said insert to a continuous flow of inert gas to which a metal source and then an oxygen or nitrogen (indicated below as oxygen/ nitrogen) source are suitably added. The continuous flow of inert gas may be for example nitrogen or argon and said metal and oxygen/ nitrogen source is added to said continuous flow, for example using electrovalves at exposure time intervals (pulsations) which vary from milliseconds to a few tens of seconds depending for example on the plant, the chamber and the experimental conditions chosen.

In other words, the invention relates to a process for coating an insert for a die for food products, preferably for pasta, by means of the atomic layer deposition (ALD) technique, said process comprising the steps of: a) chemisorption of molecules containing the metal by means of exposure of the surface of an insert for extruding a food product to a suitable metal source; b) evacuation (or washing) treatment with inert gas; c) formation of an atomic layer of the corresponding metal nitride or oxide by means of exposure of the coated surface obtained after step b) to a suitable oxygen or nitrogen source; and d) final washing or evacuation with inert gas.

As indicated above, at the end of the step d), the insert is again subjected to steps a)-d), using the same or also different metal source, for a number of cycles which varies depending on the thickness and the type of final coating composition which is to be obtained.

In this connection, the composition coating the surface of the insert according to the process of the invention comprises at least one metal nitride or oxide. Preferably, the present process by means of the ALD technique will comprise a first adsorption (or chemisorption) of the surface of the insert with metal atoms, due to the exposure to the chosen metal source, followed by the subsequent formation of the corresponding metal nitride or oxide, due to exposure to the oxygen or nitrogen source. In this embodiment, the process will comprise the use of a reactor for ALD deposition able to carry out a first pulsation of the metal source, followed by a time period of a few seconds of evacuation treatment of the chamber inside which the insert adsorbed with metal atoms is treated with inert gas in order to remove traces of metal source which have not been adsorbed or may be present inside the reaction chamber. Subsequently, the exposure of the treated surface to the oxygen or nitrogen source allows the formation of the corresponding metal nitride or oxide in the form of a coating atomic layer. The present process therefore comprises a further evacuation treatment in order to remove any oxygen/ nitrogen source residues, thus allowing steps a)-d) to be repeated, with the execution of different cycles for the deposition of successive atomic layers of coating composition. In one embodiment, the coating composition comprises one or more atomic layers of oxides or nitride which are alternated with each other. Preferably, in this connection, the coating composition comprises alternate layers of AI2O3 and ZnO.

Each cycle for the deposition of an atomic layer lasts about 20-30 seconds and is repeated so as to create a final thickness of the order of tens or hundreds of nanometers. With the present process for coating a die insert for food it is possible, in any case, to obtain a final coating by means of successive depositions of atomic layers of metal nitride or oxide, which are the same or different from each other, until the desired coating height is reached. Being atomic layers, a number of hours may be required in order to obtain a coating with heights of at least 10 ² nm, as for example indicated in the accompanying Table 1.

It should be noted that with the process of the invention it is possible to perform the coating using the ALD technique by means of the selective interaction between the free hydroxyls present on the surface of the insert and the metal source molecules. The free hydroxyls in fact determine the selectivity of the chemisorption reaction of the metal source molecules, which is therefore self-terminating. In other words, when the hydroxyl sites have been saturated by means of exposure to the metal source, the first chemisorption terminates and the substrate is subjected to the following step of evacuation and exposure to the oxygen/ nitrogen source as described above. Similarly, the chemisorption reaction of the oxygen or nitrogen atoms giving rise to the corresponding atomic coatings in the form of oxide or nitride is self-terminating, depending on the metal- containing molecules previously chemisorbed on the surface of the insert. The surface of the insert which is coated with the present process is preferably at least the extruding surface, for example the part of the insert which comes into direct contact with the pasta during the extrusion operation. In an equally preferred embodiment, coating is performed by means of exposure of the entire surface of the insert, namely both the extrusion surface and the remaining surface of the said insert.

The metal source is usually a metal, or preferably metallorganic, compound or even more preferably in the form of a liquid at atmospheric pressure and temperature, able to be adsorbed on the surface of the insert and combined with the oxygen and nitrogen source used in the subsequent exposure step. The metal source is suitably added to the continuous flow of inert gas for example by means of electrovalves for exposure times which may vary between 10 milliseconds and 60 seconds depending for example on the extent of the total surface area to be covered, the type of reactor, the process parameters such as the base pressure and temperature, and the mechanism of the reaction between the reagents involved.

"Metals" is understood in the present context as meaning both regular metals and semimetals, including silicon. In one embodiment, the metal source is preferably a coordination compound of silicon, zirconium, zinc or aluminum. Preferred silicon compounds are selected from silanes and silanols. Even more preferably, said metal source is at least one compound selected from: trimethyl aluminum (TMA), tetrakis dimethylamido zirconium (TDMAZ) and tris(tert- butoxy)silanol (TTBS) and diethylzinc (DEZ), TTBS and TDMAZ being particularly preferred. As will be understood, depending on the type of metal used, at the end of the present process an atomic coating containing the corresponding oxide or nitride will be obtained. By way of example, the use of TMA will result in the formation of a coating composition comprising Al ₂ O ₃ , while the use of TDMAZ and TTBS will result in the formation of a coating composition comprising respectively ZrO ₂ and, in accordance with a preferred embodiment, S1O2.

It should be noted that the silicon sources which can be used in the present process may be molecules able to provide optimum results by means of catalytic activation, by another metal (for example aluminum), of the surface to undergo exposure, and subsequent polymerization of the molecules on the catalytic center. In this connection, an example of a preferred silicon source is TTBS. In this connection, TTBS may be conveniently used after activation of the insert surface with a suitable aluminum source, subsequent exposure to the TTBS and polymerization of the TTBS molecules present inside the reaction chamber for the entire duration of the exposure time, by means of interaction with the chemisorbed aluminum. Therefore, according to an embodiment, the step of exposure to the metal source according to the present process may comprise a prior exposure to a suitable aluminum source, a subsequent exposure to the metal source, preferably TTBS, followed by polymerization of the TTBS molecules which are bonded to the aluminum atoms chemisorbed on the surface of the insert. A preferred source of aluminum is trimethyl aluminum (TMA).

Basically, the exposure of the insert to the aluminum source allows the aluminum atoms to be anchored to the surface of the insert by means of exchange of a metal binder with a hydroxyl group present on the surface of the insert to be coated. In this way, the metal source, preferably TTBS, will bind to the aluminum adsorbed on the surface of the insert, other metal source molecules may spread and react by means of a combined mechanism (see for example D. Hausmann et al, SCIENCE 2002, Vol. 298, pp 402) creating, by means of repetitive insertions, a siloxane polymer bound to the surface by means of the aluminum. The subsequent interconnection between the molecules of the siloxane polymer, by means of elimination of butanol molecules, is responsible for the self-terminating nature of the ALD reaction and the formation of the silica monolayer.

In the context of the present invention, the polymerization is particularly useful because, by means of a single cycle, it is possible to deposit a certain number of silica monolayers (also more than 30), each with a thickness of about 0.30-0.40 nm, obtaining, in a single cycle, very high thicknesses for an ALD deposition. At the end of deposition of each silica layer (i.e. at the end of each cycle), the insert is again exposed to the chosen aluminum source and subjected to the exposure and polymerization steps as described above, until a final coating having the required thickness is obtained. In this way it is possible to create an atomic coating of S1O2 using a silanol and water as metal and oxygen source, respectively, obtaining a rapid growth of the atomic layers of S1O2 which are deposited during each cycle and which will form the final coating.

In the case of silicon sources which do not require prior activation as described above, the process according to the invention comprises exposure of the substrate to a silicon source, such as a silane, followed by washing with inert gas and exposure to the oxygen source selected from: water, ozone and oxygen plasma.

In any case, the metal source is generally liquid and able to be poured out by means of the continuous flow of inert gas which acts, therefore, also as a transportation gas.

The person skilled in the art will recognize that the experimental times and conditions may be optimized depending on the type of reactors, reagents and substrates. For example, the speed of the gas, measured using a flowmeter, may vary between 5 and 100 seem (standard cubic centimeters) in the case of depositions in continuous flow mode and between 1 and 20 seem in exposure mode.

After the chemisorption of the metal atom source molecules, the following step of treatment with an inert gas (or evacuation) is useful in particular for removing from the chamber the metal source traces which are free and not fixed to the surface, achieving in this way a high degree of homogeneity of the surface coating. In general, as a result of the evacuation treatment according to the present process it is possible to avoid substantially the occurrence of gaseous phase reactions and consequent vapor phase deposition. The evacuation treatment with the gas lasts typically a few seconds, for example for an exposure time of between 5 and 60 seconds, depending on the reactor temperature.

Then, the insert is subjected to exposure to a suitable oxygen or nitrogen source, also followed by an evacuation treatment using inert gas. In this connection, the oxygen source is selected from: water, hydrogen peroxide, ozone and oxygen plasma, water being particularly preferred. Therefore, in one embodiment of the invention, preferred coating compositions will comprise silicon or zirconium oxides. As regards the nitrogen source, useful for the formation of a coating composition comprising the corresponding metal nitride, it is selected from: ammonia, amines, amides and nitrogen plasma. It should be noted that the process according to the invention may be performed cyclically using self-terminating reactions following the steps a)-d) indicated above, and alternated processes which comprise catalytic polymerization. In this way it is possible to perform the growth of atomic layers of metal nitrides or oxides, which are the same or different from each other depending typically on the metal source used, on the surface of the insert, repeating the process several times, namely increasing the number of cycles. Advantageously it is possible to control the height of the thickness of the coating composition which is formed on the surface of the insert, ensuring a high degree of homogeneity and excellent reproducibility of the results. The number of cycles is repeated until coating of the insert according to the present invention with a thickness preferably of between 50 nm and 600 nm, more preferably between 100 nm and 500 nm, is obtained.

Moreover, depending on the metal and oxygen/ nitrogen source precursors and the experimental conditions (for example the temperature) it is possible to obtain a coating having a different thickness and physical/ chemical and mechanical properties. In this way it is possible to further improve the friction and wear- resistance of the insert, allowing it to be used for longer periods of time, ensuring in any case an optimum reproducibility of the extruded food product. The composition coating the insert according to the present process may be analyzed for example in terms of structure, morphology and chemical composition by means of techniques known in the sector, such as X-ray reflectivity or (micro)diffraction, optical microscopy (OM), atomic-force microscopy (AFM) or ray fluorescence.

By way of example, the images shown in Figures la and lb, obtained by means of the AFM technique, show respectively the morphology of the substrate and the coating in the case where the substrate is formed by a monocrystalline Si wafer, with amplification of a selected area of 1.5x1.5 μπι ² . The average roughness calculated over an area of about 10x10 μιη ² is equal to about 2 nm for the coating of S1O2 and 2.5 nm for the uncoated substrate. The analysis shows moreover perfect coverage of the substrate and a good uniformity of the material deposited. It is evident also that the morphology of the coating is very different from the globular morphology of the substrate: the coating is in fact more smooth and more uniform than the uncoated substrate. Similar results were obtained considering a coating containing ZrO2.

AFM measurements were also carried out on brass (Fig. 2a-c), these showing a reduction in the surface roughness of the brass substrate as such (Fig. 2a) compared to the substrate coated both with ZrO2 (Fig. 2b) and with SiO ₂ , (Fig. 2c). It should be remembered that the process according to the invention is performed in temperature and pressure conditions such that gas phase reactions and/ or deposition of precursors in liquid form are substantially avoided. Therefore, in one embodiment, the temperatures of the system are higher than the vaporization temperatures of all the precursors used in the pressure conditions in which the process is performed, in particular of the metal and oxygen/ nitrogen source. In this connection, it was noted that it is particularly convenient to carry out the present process at a temperature of exposure to the metal and oxygen/ nitrogen sources higher than the vaporization temperature of the metal and oxygen/ nitrogen source chosen. Therefore, the temperatures for exposure of the insert according to the present process by means of ALD, i.e. the temperatures of the reaction chamber of the ALD apparatus, are preferably at least 40°C, so as to obtain convenient times for removal of the chosen metal or oxygen source. By using temperatures which are higher, but not close to the decomposition temperatures of the compounds used it is possible to avoid substantially collateral reactions which could occur for example inside the reaction chamber during the source exposure steps. Therefore, in one embodiment, the temperature of exposure to the oxygen/ nitrogen and metal sources is comprised between about 90°C and 300°C depending, for example, on the process and the mechanism considered. The concept of a temperature window for the ALD processes is known to the person skilled in the art (see for example T. Suntola, mater Sci Rep 1989, Vol. 4, pp. 261) and is used to define the temperature range within which the growth of the coating composition in the form of an atomic layer is linear in relation to the number of cycles. Advantageously, the process for coating the die insert for food products according to the present invention may be performed using apparatus and conditions which are known to the person skilled in the art, for example inside a reactor for ALD deposition at low pressure, preferably in the region of 0.1-5 Torr, or using a system such as the Savannah 100 system made by Ultratech Cambridge Nanotech Inc. Moreover, the present process may find a convenient application in the industrial sector since it may be used for coating inserts which are known in the art and therefore compatible with the common food extruders for pasta. The possibility of coating inserts using different metal oxides moreover ensures optimum versatility since it is possible to obtain extruded food products having, for example, a different roughness and different surface characteristics depending on the morphology of the coating layer applied.

A further substantial advantage of the present process is that, as a result of the present invention, the insert may be reconditioned, thus allowing it to be reused. The insert will therefore have a working life much longer than that of conventional uncoated inserts which, once they become worn and deteriorate to the point that they can no longer be used to optimum effect, are usually disposed of. The person skilled in the art will appreciate that the coated insert according to the present invention has an extremely long working life since it may be coated and reused whenever required, thus avoiding the need for disposal thereof.

With the present process it is possible to coat also inserts which have particularly complex forms ensuring, in any case, optimum results in terms for example of homogeneity of coating, wear resistance and stability over time.

According to an additional aspect the invention relates to a food die insert for pasta, which is coated with a coating composition comprising at least one metal oxide or nitride, preferably obtained (or obtainable) by means of the process according to the invention, as described and claimed here. The insert may be made of brass, or using copper alloys, steel or gold and may be optionally coated with teflon or made of teflon. Preferably, the insert is made of brass.

In any case, the composition will cover all or part of the insert, preferably at least the extruding surface of the insert, understood as being the surface which comes into direct contact with the pasta. Advantageously, owing to the ease of manufacture of the present coated insert, the present invention may be applied in the industrial sector using apparatuses known in the sector, for example designed for the ALD technique. As mentioned above, the insert is preferably coated by means of the ALD technique and even more preferably using a coating composition comprising S1O2. The present invention will now be described by the following experimental part without, however, limiting the scope thereof.

EXPERIMENTAL PART Example 1: inserts according to the invention, coated by means of the ALD vapor phase deposition technique using a coating composition comprising S1O2 or Zr02.

Inserts made of brass for extruding pasta, having a disk-like or parallelepiped shape, in both new and used condition, were considered. The metal source used was TTBS and TDMAZ, while the oxygen source was H2O and the Al source was TMA. Nitrogen with 99.999% purity was used as inert gas. Further conditions of the coating process are indicated in Table 1.

Table 1 : coated samples and deposition conditions

Deposition Coating Deposition

Coating temperature Samples thickness duration

(°C) (nm) (hours)

3 disk inserts

SiO ₂ 200 1 parallelepiped insert 100 2

1 new insert 1 worn insert

1 disk insert

1 parallelepiped insert

SiO2 200 500 7

1 new insert

1 worn insert

2 disk inserts

2 parallelepiped inserts

ZrO ₂ 200 100 8

1 new insert

1 worn insert

2 disk inserts

2 parallelepiped inserts

ZrO ₂ 200 500 35

1 new insert

1 worn insert

Using an ALD apparatus, type Savannah 100 (Ultratech Cambridge Nanotech Inc.), the insert was subjected to cycles of exposure to TTBS and TMA, or TDMAZ and water, at a temperature of about 200°C for a time period of between 2 and 35 hours. A final coating with a thickness of between about 100 nm and 500 nm comprising S1O2 and ZrO2 was therefore obtained, as indicated in the table.

Example la: inserts according to the invention, coated by means of liquid phase autocatalytic chemical deposition of Ni-P with added SiC. Inserts made of brass for extruding pasta, having a disk-like or parallelepiped shape, were considered. Deposition of a composite based on Ni-P containing silicon carbide particles with a thickness of 10 μηι was performed by means of autocatalytic deposition from baths at 60° C containing hypophosphite and Ni salts. Example 2: wettability tests based on contact angle of some coated inserts according to Example 1 and la.

The coated parallelepiped shaped inserts according to Example 1 and la with dimensions 10x24x4 mm and surface roughness not greater than 0.5 μπι were subjected to contact angle measurements for evaluation of the surface roughness.

The contact angle measured may provide an indication of the roughness of the pasta extruded with the coated insert. The roughness obtained with S1O2 is different from that obtained with ZrO2, while excellent stability and wear-resistance of the coating are maintained. The present process is therefore highly versatile since coatings with a high or also low wettability may be obtained, while maintaining in any case a high wear-resistance and working life. The following measurement parameters were kept constant for all the tests carried out:

- 10 measurements with droplets of double-distilled water (milliQ) for each sample by means of a tensiometer for sessile drop technique tests (CAM200, KSV). - Following deposition of the water droplet on the brass surface, the progression of the contact angle was monitored for a time period of 1 minute.

- Droplets with a volume of about 2 microL were deposited and, in order to ensure a balance between the evaporation times and the equilibrium times for spreading of the droplet, the contact angle was measured after 10 seconds.

- For fitting of the droplet profile an algorithm based on the Young-Laplace equation was used.

Table 2 shows the results obtained from the tests carried out. Each value corresponds to the average of 10 tests, including the mean standard deviation.

Table 2: results of the angle contact measurements carried out on the coated inserts according to Example 1 COATING/ THICKNESS CONTACT ANGLE (θ°)

Si0 ₂ - l OOnm <20

S1O2 - 500nm <20

Zr0 ₂ - lOOnm 84.8+ 1.4

Zr0 ₂ - 500nm 95.7±1.2

Bare brass, uncoated 84.7±1.4

Brass coated with Ni-P SiC 57.3 ± 2.0

The coating of S1O2 greatly increases the wettability of the brass sample, with the contact angle reaching a value of less than 20°.

The coating of Zr0 ₂ does not modify substantially the wettability of the sample compared to the bare brass. A silicon chip with low surface roughness (ideal substrate) with 100 nm of Zr0 ₂ coating was also sampled using the same ALD and tensiometer measurement conditions, in order to evaluate the contact angle of the coating alone. Zr0 ₂ produced a contact angle of 95.7 ± 1.2, a further indication of the fact that the Zr0 ₂ coating on the brass test-piece does not modify its wettability. The coating comprising Ni-P/ SiC reduces the wettability of the brass.

Example 3: wear tests by means of pin-on-disk testing of some coated inserts according to Example 1

The wear tests consist in assessing the behavior of a coating or a bulk material in predefined load and sliding wear conditions. The pin-on-disk configuration, in particular, involves the use of a test-piece (disk) on which a constant load (N) perpendicular to the surface of the sample is applied by means of a pin with known geometry (standard ASTM G99-04) . The sliding wear conditions are obtained by rotating the test-piece about its axis with a suitable angular speed for a given number of revolutions.

The results which can be obtained from this test are as follows:

- Coefficient of friction of test- piece/ counter-element in relation to the number of cycles, obtained by dividing the tangential force (Ft) provided by the instrument for the load applied; - Number of cycles at which breakage of the coating occurs

The following measurement parameters were kept constant for all the tests carried out:

- Counter-element: alumina ball (6 mm diameter); - Track radius: 6 mm;

- Sliding speed: 4 cm/s;

- Loads: 0.5 and IN;

- Distances: up to breakage of coatings, 1000 m for bare brass;

- Room temperature; - No lubricant.

Table 3 shows the results obtained from the pin-on-disk wear tests carried out on disk-shaped coated inserts according to Example 1 with a diameter of 30 mm and height of 3 mm.

Table 3: results of pin-on-disk wear tests

A comparison between coatings made of the same material and with different thicknesses shows that the coating with a thickness five times greater (500 nm as opposed to 100 nm) has a duration one order of magnitude greater than the other coating. This effect is more marked in coatings based on ZrO2. In the case where the thicknesses are the same and different covering materials are used, the coating which has the best properties is S1O2. In particular, the S1O2 coating with a thickness of 500 nm at the end of the test proved to be still intact and the brass substrate showed signs of failure. The composite coating Ni-P has a markedly higher duration since the thickness is two orders of magnitude greater than that of ALD coatings.