Plasma-assisted process of ceramization of polymer precursor on surface, surface comprising ceramic polymer

Abstract

The present invention lies in the fields of chemistry and materials engineering. More specifically, the present invention describes a process of heat treatment of polymeric precursors including as active phases particle charge or a mixture of active phases with inert phases called “fillers”. It is also described a surface including ceramic polymer obtained by said process. The volumetric positive variation resulting from the formation of new phases, which for their formation, incorporate atoms from the gaseous phase, contributes to a minor shrinkage of the composition during the heat treatment process. The process of the present invention allows obtaining the desired phases in smaller treatment times and lower temperatures, when compared to a thermal treatment process as conventional pyrolysis (PC) due to the presence of highly reactive species, as for example atomic nitrogen produced by the dissociation of nitrogen molecules in the plasma environment.

Claims

1. A ceramization process of a polymer precursor suspension containing at least one polymer precursor and at least one active filler or a mixture of the at least one active filler with at least one inert filler on at least one component surface, wherein the at least one inert filler is an agent added to stabilize distribution of the at least one active filler in the suspension, reducing sedimentation effects during the process, the process comprising the steps of: (a) preparation of the suspension comprising: said at least one polymer precursor; the at least one active filler; at least one solvent; and at least one dispersant; (b) application of said suspension on the at least one component surface, forming at least one suspension coated component surface; and (c) plasma-assisted pyrolysis heat treatment of the at least one suspension coated component surface in a medium that contains at least one reactive species from dissociation of molecules of at least one molecular species selected from the group consisting of hydrogen, nitrogen, hydrocarbons or combinations thereof, wherein the plasma-assisted pyrolysis heat treatment is DC plasma-assisted pyrolysis, and wherein the plasma-assisted pyrolysis heat treatment is performed at a pressure of about 1.33×10.sup.1 Pascal (0.1 Torr) to 1.33×10.sup.4 Pascal (100 Torr) and is carried out for 30 minutes to 300 minutes at a temperature of 800 to 1200° C.; and with the heat treatment by DC plasma-assisted pyrolysis, obtaining, from the at least one suspension coated component surface, a polymer derived crystalline ceramic from the at least one polymer precursor, wherein the polymer derived crystalline ceramic comprises a phase formed by reaction of the at least one active filler with the at least one reactive species.

2. The process according to claim 1, characterized by said at least one polymer precursor being an organometallic polymer.

3. The process according to claim 2, characterized by the organometallic polymer being selected from the group consisting of polyorganosilanes, polyorganocarbosilanes, polyorganosilylcarbodiimides, polyorganosilazanes, and combinations thereof.

4. The process according to claim 1, characterized by said active filler being selected from the group consisting of: Ti, Cr, V, Mo, B, MoSi.sub.2, Fe, Al, Nb, Hf, TiSi.sub.2, CrSi.sub.2, TiB.sub.2, Si, and B.sub.4C and/or said inert filler being selected from the group consisting of: Al.sub.2O.sub.3, SiC, BN, Si.sub.3N.sub.4, ZrO.sub.2, as well as combinations of the active fillers and the inert fillers in the same suspension.

5. The process according to claim 1, characterized by said at least one component surface being a metallic surface.

6. The process according to claim 1, characterized by the step (b) of applying said suspension on the at least one component surface being carried out by a technique selected from the group consisting of immersion, spray, spin coating, and casting tape.

7. The process according to claim 1, characterized by the plasma-assisted pyrolysis being carried out in a plasma reactor at a cathode or an anode.

8. The process according to claim 7, characterized by the plasma-assisted pyrolysis being carried out in a plasma reactor at the cathode.

9. The process according to claim 2, characterized by the organometallic polymer being selected from the group consisting of polycarbosilanes, polysilazanes, doped polysilazanes, polysilylcarbodiimides, polyborosilanes, and combinations thereof.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) In order to better define and clarify the content of the present patent application, the following figures are presented:

(2) FIG. 1 shows a graph of the characteristic curve of the current versus DDP of a glow discharge.

(3) FIG. 2 shows a scheme of the potential distribution between the electrodes in an abnormal glow discharge.

(4) FIG. 3 shows a scheme of interaction of the ions with the cathodic surface.

(5) FIG. 4 shows images of micrographs obtained by scanning electron microscopy (SEM), of TiSi.sub.2/HTTS samples (70/30 vol. %):

(6) (A) produced by the conventional pyrolysis process and

(7) (B) produced by an embodiment of the invention process of plasma-assisted pyrolysis (PAP-C), cathode configuration sample in the plasma reactor. Both samples were treated for 2 hours at 1150° C.

(8) FIG. 5 shows the images obtained by scanning electron microscopy (SEM), of the phase composition of samples TiSi.sub.2/HTTS (70/30 vol. %): A) produced by conventional pyrolysis process and B) produced by plasma-assisted pyrolysis process (PAP-C), sample in cathode configuration. Both samples were treated for 2 hours at 1150° C.

(9) FIG. 6 shows images of micrographs obtained by scanning electron microscopy (SEM), of TiSi.sub.2/HTTS samples (70/30 vol. %): A) produced by the conventional pyrolysis process and B) produced by plasma-assisted pyrolysis process (PAP) with the samples in the anode configuration in the plasma reactor. Both samples were treated for 2 hours at 1150° C.

DETAILED DESCRIPTION OF THE INVENTION

(10) The present invention provides a process and a product that solves the following technical problems/lead to the following benefits: a) increased conversion rate of active fillers mixed with polymer precursor, during the heat treatment step, generating nitrides and carbonitrides by reaction with atomic nitrogen generated in the plasma reactor environment and/or from the carbon present in the polymeric precursor. This provides the achievement of the desired phases in smaller treatment times and lower temperatures, when compared to a thermal treatment process as the conventional pyrolysis (CP).

(11) In an embodiment, it is used a plasma-assisted pyrolysis treatment (PAP). It can be understood as plasma-assisted pyrolysis (PAP) the pyrolysis heat treatment process performed in ionized gas (glow discharge) at a plasma reactor. By conventional pyrolysis, it is understood here the one performed in gaseous atmosphere in conventional ovens, i.e., in the absence of plasma.

(12) The atmosphere used in the plasma reactor consists of a gas stream, whose the chosen composition depends on the phases that it is wanted in the heat treatment process. For obtaining nitrides on ceramic composition layer, it is used a stream gas of N.sub.2+H.sub.2. As a result of electrical discharge between cathode and anode, the gas is ionized. The electrons present in the ionized gas are attracted to the anode, and along the way, they suffer inelastic collision with gas molecules, causing its dissociation. For example, electrons possessing high kinetic energy collide with nitrogen molecules (N.sub.2) causing the dissociation of part of nitrogen molecules, producing atomic nitrogen (reaction: N.sub.2+e.sup.−=e.sup.−+2N), which advantageously reacts with the metallic atoms of the active fillers. Similarly, atomic hydrogen is formed by the dissociation of H.sub.2 (reaction: e.sup.−+H.sub.2=e.sup.−+2H) when there is hydrogen in the gas mixture. The atomic hydrogen beneficially reacts with oxide films usually present on the surface of the fillers particles.

(13) The presence of atomic nitrogen present in the plasma environment, more reactive than the molecular nitrogen, allows the increasing of the conversion rate of metallic fillers in carbonitrides and nitrides. The volumetric positive variation resulting from the formation of new phases, which for their formation, incorporate atoms from the gaseous phase, contributes to a minor shrinkage of the composition during the heat treatment process. In addition, atoms from the gaseous atmosphere are also incorporated into the polymer precursor ceramization.

(14) The fillers can be of various natures (metallic, intermetallic and ceramic), and are generally added particles to the polymeric precursor for reducing the porosity and/or giving specific properties to the final material formed; in the case of fillers being of active type, they react with the atmosphere of pyrolysis and with the precursor forming new phases, being the fillers used: Ti, Cr, V, Mo, B, MoSi.sub.2, Fe, Al, Nb, Hf, TiSi.sub.2, CrSi.sub.2, TiB.sub.2, Si, Al, Al.sub.2O.sub.3, SiC, BN, Si.sub.3N.sub.4, ZrO.sub.2, B.sub.4C, or combinations thereof.

(15) The combination of polymeric precursor, active and inert charges and the variation of the atmosphere results in a greater variety of ceramics and composites materials, wherein some of them are not obtainable by other techniques.

(16) In an embodiment the ceramization process of surface polymer comprises the steps of:

(17) (a) preparation of a suspension comprising: at least one polymer precursor; at least one filler; at least one solvent; and at least one dispersant;

(18) (b) application of said suspension on at least a metallic component surface;

(19) (c) heat treatment of the suspension in a medium that contains at least one reactive species resulting from the dissociation of at least one molecule selected from the group consisting of hydrogen, nitrogen, hydrocarbons or combinations thereof.

(20) The process of heat treatment is by plasma-assisted pyrolysis. In one embodiment, the plasma-assisted pyrolysis is performed in a plasma reactor in a setting selected from the group consisting of cathode, anode or floating potential. In one embodiment, the plasma-assisted pyrolysis is performed in a plasma reactor at cathode configuration.

(21) In an embodiment of the process, said polymer precursor is selected from the group consisting of polysilanes, polysilsesquilazanes, polycarbosilanes, polysilazanes, doped polysilazanes, polysilylcarbodiimides, polyborosilanes, organometallic polymer comprising carbon, or combinations thereof.

(22) In an embodiment of the process, said organometallic polymer is selected from the group consisting of polyorganosilanes, polyorganocarbosilanes, polyorganosilylcarbodiimides, polysiloxanes, polyorganosilazane, or combinations thereof.

(23) In an embodiment of the process, the active filler is selected from the group consisting of Ti, Cr, V, Mo, B, MoSi.sub.2, Fe, Al, Nb, Hf, TiSi.sub.2, CrSi.sub.2, TiB.sub.2, Si, Al, B.sub.4C, or combinations thereof, and the inactive filler is selected from the group consisting of Al.sub.2O.sub.3, SiC, BN, Si.sub.3N.sub.4, ZrO.sub.2, or combinations thereof.

(24) In an embodiment of the process, the surface is a metallic surface.

(25) In an embodiment of the process, the step (b) of applying a suspension on at least one surface of a metallic component is carried out by a technique selected from the group consisting of immersion, spray, spin coating or casting tape.

(26) In an embodiment of the process, the step (c) of thermal treatment is carried out at a pressure of about 1.33×10.sup.1 Pascal (0.1 Torr) to 1.33×10.sup.4 Pascal (100 Torr), for 2 hours at a temperature of 1150° C. Step (c) may be carried out for 30 minutes to 300 minutes, at a temperature of 800 to 1200° C.

(27) In a second object, the present invention presents a ceramic composite coated component obtained by the above process in which the polymer precursor after ceramized is formed by at least one phase selected from the group consisting of SiCN, Si.sub.xN.sub.y (e.g. Si.sub.3N.sub.4), SiC, BCN, BN, TiCN, and SiCMN, where M is a transition metal.

(28) In one embodiment, the present invention presents said process of heat treatment comprising the following steps:

(29) (a) Preparing of the suspension containing the polymeric precursor, fillers, solvent and dispersants, under the conditions and quantities required for each system; said step includes the dispersion of fillers and homogenization of the suspension by mechanical magnetic agitation or ultrasonic and roller mills;

(30) (b) Applying the suspension, prepared in accordance with the procedure written in item (a), on the finished parts by immersion techniques, spray, spin coating or tape casting, wherein the choice of the technique to be used depends on the geometry of the finished piece to be covered; the part or component can be produced by the following manufacturing processes: powder metallurgy, casting, rolling, machining, extruding and forming;

(31) (c) Heat treating by plasma-assisted pyrolysis the polymeric suspension coated component comprising the fillers, where advantageously occurs the conversion of the ceramic polymer, as well as the conversion of particle fillers in nitrides and carbonitrides, by the reaction of these particles with the plasma reactive atmosphere, generated in the reactor during the pyrolysis heat treatment.

(32) In one embodiment, said suspension is applied, by immersion or spray techniques, on finished metallic components for granting resistance to deterioration and, in other applications, in finished components to provide corrosion protection. The components (parts) to be coated (coating substrates) are produced by different manufacturing processes of parts, such as powder metallurgy, casting, machining and forming. The precursor polymer containing active fillers particles is applied to the finished parts. After applying the coating they undergo a heat treatment called pyrolysis, in a hybrid plasma reactor. The hybrid plasma reactor is described in the document U.S. Pat. No. 7,718,919 B2.

(33) In the context of the patent application, “plasma” must be understood as a partially ionized gas, consisting of the same number of positive and negative charges (which keeps the system electrically neutral), and a different amount of atoms or non-ionized neutral molecules.

(34) In the context of the patent application, “ceramic” should be understood as a material comprising a three-dimensional crystalline grain network comprising at least a metal attached to carbon, nitrogen or oxygen atoms.

EXAMPLES—EMBODIMENTS

(35) The examples shown herein are intended only to illustrate some of the many ways to carry out the invention, without, however, limiting the scope of the same.

Example 1

(36) Production of PDCs with polymer precursor HTTS organo(silazanes) group, loaded with 70% by volume of TiSi.sub.2 (titanium disilicide) as active fillers provide ceramic materials of Ti—Si—CN system, that have remarkable mechanical properties by nature, with high values of hardness and wear resistance. FIG. 4 shows the difference in microstructure by micrographs obtained by scanning electron microscopy (SEM), and in residual porosity measured via picnometer of helium, after pyrolysis heat treatment carried out by 2 hours at 1150° C., where the FIG. 4A shows the result obtained by conventional pyrolysis of nitrogen gas flow (N.sub.2) while the FIG. 4B shows the result obtained on nitrogen plasma-assisted pyrolysis, with the samples in the cathode configuration of the reactor (PAP-C). The sample A has a porosity of 28% and the sample B presents a porosity of less than 2% in volume.

(37) FIG. 5 shows the phases formed by the reaction of TiSi.sub.2 particles (filler particles) with the atmosphere in the pyrolysis heat treatment. The expected result is the maximum of possible conversion of TiSi.sub.2 (Titanium disilicate) in TiCN (titanium carbonitrate). The phases were identified by x-ray diffraction, chemical composition analysis via EDS and scanning electron microscopy. In conventional pyrolysis, for 2 hours at 1150° C., the titanium carbonitride formed is limited to a thin layer on the surface of the particles of TiSi.sub.2 mixed to the polymer precursor (carbonitride layer thickness <1 μm); as to the plasma-assisted pyrolysis, with the samples connected to the cathode (cathode configuration), there was the reaction throughout the entire volume of TiSi.sub.2 particles.

Example 2

(38) FIG. 6 shows the difference in microstructure, by micrographs obtained by scanning electron microscopy (SEM), and in residual porosity, measured via helium pycnometer, after pyrolysis heat treatment carried out for 2 hours at 1150° C., where the FIG. 6A shows the result obtained by conventional pyrolysis in nitrogen gas flow (N.sub.2) while the FIG. 6B shows the result obtained on the nitrogen plasma-assisted pyrolysis, with the samples in the anode reactor configuration (PAP-A). The sample A has a porosity of 28% and the sample B presents a porosity of approximately 21% in volume.

(39) Examples 1 and 2 presented prove that the results obtained in plasma environment are superior to those obtained in conventional pyrolysis, especially when samples are connected with the cathode.

(40) The person skilled in art will understand the value of the knowledge presented herein and can reproduce the invention in the presented embodiments and in other variants, which are covered in the scope of the attached claims.