Patent Application
20200102432
The present invention relates to the field of materials technology, in particular materials resistant to high temperatures. The present invention therefore finds application in the various fields in which such materials are used, such as, for example, the aerospace, naval, automotive, railway and construction sectors in general or the electronics sector.
As is well known, a composite material is a material consisting of several simple materials aggregated by means of a specific production method. Said composite materials have a non-homogeneous structure and have the purpose to merge in the same material at least a pair of materials having different physico-chemical properties and different mechanical capacities. The components (ie the base materials) of a composite material, are at least one reinforcement and at least one matrix.
The reinforcement (or filler) is represented by a dispersed phase that has the function of ensuring rigidity and mechanical strength, supporting most of the working load.
Generally, the matrix consists of a homogeneous phase having the function to enclose the reinforcement, ensuring the cohesion of the composite material and homogenizing the dispersion of the particles or fibers reinforcement inside the composite, avoiding segregation phenomena.
In most cases the matrices are polymeric because they guarantee low density and therefore lightness of the final material. However, they have the defect of drastically lowering the mechanical performance as the temperature increases.
There are some international patent applications filed to describe a composite material resistant to high temperatures, such as the US patent US2016340586, entitled “Fire resistant material”.
It concerns a flame retardant composite material for which the materials used and the respective proportions are clearly indicated.
Although the above mentioned patent effectively solves the problem of resistance to high temperatures, it is not as efficient from the point of view of weight, thickness, mechanical performance of the material and production costs.
There does not seem to exist, in the state of the art, a composite material consisting of at least one reinforcement and at least a double matrix, one organic and one inorganic.
Therefore, the object of the present invention is to propose a new and innovative composite material, having high structural performances, a reduced thickness and weight.
A further object of the present invention, which is part of the same inventive concept, is to propose a new and innovative inorganic matrix, and the relative production method, for the above mentioned composite material.
Therefore, the technical problem posed and solved by the present invention is to provide a structural composite material which, in combination with high mechanical capacities, also associates a low weight and thickness, and a structural resistance to oxidation, characteristic of high temperature, for example over 700° C., environments.
This problem is solved by a method for obtaining an inorganic polymer-based matrix for a flame-resistant fibro-reinforced composite material, according to claim 1, from a matrix according to claims 5 and 9 and from a composite material, according to claim 13.
Preferred features of the present invention are detailed in the dependent claims.
The present invention provides some relevant advantages.
In particular, the characteristic mixture for obtaining the inorganic matrix, allows the possibility to use it in environments having high oxidative risk, for example at high temperature environments, preventing a structural deterioration.
Advantageously, the possibility to insert nanofillers having different nature within the above mentioned mixture, allows also to adjust a value of thermal conductivity of the inorganic matrix according to the required specific application.
A further advantage is that the production method of the matrix, according to the present invention, is quick and economical.
A still further advantage is that the composite material according to the present invention, having high mechanical capacities, has a contained weight and thickness and the thermal conductivity values can be adjusted according to the specific type of nanofiller used.
Other advantages, features and methods of use of the present invention will be clear from the following detailed description of some embodiments, presented by way of a non-limiting example.
The invention will be described below by at least one preferred embodiment for explanatory and non-limiting purposes with the support of the attached figures, wherein:
The present invention will now be illustrated purely by way of non-limiting example, or by restricting it, using the figures which illustrate some embodiments in relation to the present inventive concept.
The object of the present invention relates to the method for obtaining an inorganic matrix, to the inorganic matrix and to a composite comprising reinforcing fibers, a first inorganic matrix and a second organic matrix.
Advantageously, this composite, characterized by the combination of inorganic resins with organic resins, both nano-structured, is applied where there is a strong oxidation, characteristic of high temperature environments, typically over 700° C., as heat-resistant, fire-resistant material, or as a material to manufacture all those products having operating temperatures between −55° C. and 1200° C. and having a life cycle responding to the international aeronautical standards.
The composite material, object of the present invention, extends in a significant and extremely advantageous way the application field of the composite materials, without significantly increasing the costs and using the equipment typically used for the conventional composites, such as carbon molds having polymeric, or glass fiber, matrices made by aluminum alloy or steel.
Advantageously, said reinforcement consists of any fibrous material, for example basalt fiber, glass fiber—in particular, E, S or R glass—metal meshes, even more preferably carbon fiber.
Advantageously, said inorganic matrix comprises an alkaline polysialate, water-based, inorganic polymer. The matrix is advantageously nano-structured, in particular comprising nano-powders of beta silicon carbide, or hollow glass microspheres, or carbon nanotubes.
The primary role of said first inorganic matrix is to allow a resistance to very high temperatures due to its property to protect the fiber reinforcement against the oxidations typical of temperatures higher than 700° C.
Said first inorganic matrix is preferably a nano-composite polysialate matrix and is obtained by mixing an alkaline earth silicate component comprised in the group of cesium, sodium or, more preferably potassium, in a percentage by weight (% wt) between 40 wt % and 60 wt %, with an amorphous silica component and/or an aluminosilicate reactive powder.
The amorphous silica component may be thermal silica, fused silica or pyrogenic silica having an average particle size comprised between 0.01 μm and 15 μm.
The amorphous aluminosilicate component is in particular stoichiometrically controlled by an Al2O3×2SiO2 composition and a total amount lower than 6% of oxides other than SiO2 and Al2O3.
The main molar ratios of the polysialate resin thus obtained are comprised within the following ranges:
Moreover, the above mentioned alkaline polysialate matrix contains a charge having a nanometric size.
Preferably, the production method of the inorganic matrix according to the present invention comprises an ultrasonic mixing process of the charged mixture, so as to allow a homogeneity of the nanocaricles dispersion within the mixture.
Advantageously, as will be better described in the following, the nature of the specific nanocharge inserted in the mixture, determines a specific thermal conductivity value of the obtained inorganic matrix.
The addition of nanoparticles, in particular when homogeneously distributed, also improves the mechanical strength of the invention.
A first embodiment of the matrix according to the present invention comprises a nanometric powder, or nano particles, of silicon beta carbide having a dimension comprised between 50 nm and 950 nm and an average specific surface comprised between 10 m2/gr and 60 m2/gr, preferably between 40 m2/gr and 50 m2/gr.
Said nano powder is added, in an amount comprised between 0.5 wt % to 15 wt %, to the polysialate matrix, in order to form said first inorganic composite matrix.
Preferably, the percentage in weight of said nano silicon beta carbide particles is comprised between 1 wt % and 10 wt %. In particular, at a percentage of about 2.60 wt %, the matrix according to the first embodiment of the invention here described has a thermal conductivity value of about 0.9 W/mK at about 1200° C.
The matrix filled by silicon carbide beta nanoparticles is therefore characterized by a low thermal conductivity value.
A further embodiment of the matrix here described provides the use of hollow glass nanoparticles to be added to the mixture to allow a regulation of the porosity during the processing of the polymeric material.
A second embodiment of the inorganic matrix obtaining method according to the present invention, provides for the use of carbon nanotubes.
Preferably, the carbon nanotubes have an average diameter of 1 nm, an average length of 1.5 μm and an average specific surface comprised between 250 m2/gr and 500 m2/gr.
In the example here described, the percentage of said nanotubes is comprised between 0.1 wt % and 5 wt %.
In particular, at a percentage of about 0.50 wt %, the matrix according to the second embodiment of the invention here described has a thermal conductivity value of about 0.31 W/mK at about 1200° C.
The matrix filled by carbon nanotubes is therefore characterized by a high thermal conductivity value. This conductivity value increases according to the orientation degree of the nanotubes into the matrix.
In order to obtain the optimization of the ratio between specific weight and resistance, the composite material according to the present invention is also advantageously provided with a second organic matrix, which is also nano-structured.
Said second organic matrix, preferably phenolic, bismaleimidic, polysilazanate, epoxy or cyanate esters, advantageously provides the structural characteristics to the final composite material and regulates the porosity, in particular allows a reduction of the porosity of the material allowing an improvement of the reaction characteristics over liquids and gases.
The nano-structure of both matrices by means of beta silicon carbide nano-powders of hollow glass micro-spheres, is preferable and advantageous, since they perform the dual function of determining the porosity and contributing to the improvement of the material's life cycle, especially at very high temperatures, also improving the matrix-reinforcing fiber interface.
Preferably, the percentage of reinforcing fibers of the composite material according to the present invention is comprised between 54 wt % and 64 wt %.
Once the preliminary composite material (so-called pre-impregnated) has been obtained, i.e. consisting in the reinforcement and the first inorganic matrix, the following production steps are provided for obtaining the structural composite material according to the present invention:
(A) a first curing step, made in an autoclave or under a press with pressure values comprised between 1 bar and 10 bar, or at a normal atmospheric pressure, with temperatures comprised between 40° C. and 80° C.; said first curing phase may possibly take place in a vacuum;
(B) a second post-curing step, wherein the material is heating at temperatures comprised between 100° C. and 900° C.; the material resulting from this second post-curing step having a porosity comprised between 20% and 30%;
(C) a third impregnation step, carried out at controlled pressure value or by an immersion of the material resulting from the preceding second post-curing step in said second organic matrix;
(D) a fourth curing step in which the material is worked according to the known techniques based on of the specific resin constituting said second organic matrix; (E) a fifth post-curing step, wherein the material resulting from the preceding fourth curing step is heating at temperatures values comprised between 250° C. and 900° C. (for nanofillers comprising silicon beta carbide nanoparticles) or comprised between 400° C. and 900° C. (for nanofillers comprising carbon nanotubes), possibly in an inert gas atmosphere, for example nitrogen.
Advantageously, said third impregnation step, fourth curing step and fifth post-curing step can be repeated the desired number of times until the desired porosity, comprised between 2% and 30%, is obtained.
Preferably, the above mentioned steps are repeated at least twice.
In order to obtain final very low values of the porosity of the final material, until to a minimum value of 2%, said third impregnation step C, said fourth curing step D and said fifth step of post-curing, can be repeated cyclically.
Due to the materials used and to the obtaining method, the above mentioned structural composite material has characteristics that make it particularly suitable for the construction of structural components intended for environments with temperatures comprised between −55° C. and 1200° C. or any environment characterized by a strong oxidation.
In case of beta-silicon carbide nano-powders are used in the two matrices, both said first inorganic matrix and said second organic matrix, the percentage of said beta-silicon carbide nano-powders varies between 0.5% and 15% while their surface area varies between 10 m2/gr and 60 m2/gr.
The structural composite material according to the present invention advantageously has a density value comprised between 1.2 gr/cm3 and 1.4 gr/cm3, preferably 1.25 gr/cm3 and therefore a specific weight comprised between 1.20 g/cm3 and 1.35 gr/cm3.
In particular, the tensile strength of the composite material according to the present invention is advantageously comprised between 150 MPa and 250 MPa.
The firing resistance of the material thus obtained is one of the characteristics that make it particularly advantageous.
In fact, after being subjected to a fire event, it presents a strength substantially identical to the strength before exposure to the flame.
Moreover, it is advantageously resistant to the passing flame and does not emit fumes or vapors when exposed to fire.
The advantages offered by the present invention are evident considering the description above mentioned and will be even clearer in view of the attached figures, relating in particular to some embodiments of the invention according to the present invention.
With reference to
Said material consists of the reinforcing fiber impregnated with said first inorganic matrix constituted by polysialate with dispersion of beta silicon carbide nano-powders. Into this matrix said second organic matrix is added, inside which other beta silicon carbide nano-powders are dispersed.
The composite material thus obtained guarantees a very high number of cycles at temperatures up to 1200° C. and has the following structural characteristics:
With reference to
Said material consists of the reinforcing fiber impregnated with said first inorganic matrix consisting of polysialate with dispersion of hollow glass microspheres.
Said second organic matrix within which other hollow glass microspheres are dispersed, is added to the above mentioned first inorganic matrix.
The composite material thus obtained advantageously has very low values of thermal conductivity.
Its properties can be summarized in the following:
With reference to
Said material consists of the reinforcing fiber impregnated with said first inorganic matrix consisting of polysialate with dispersion of carbon nano-tubes.
The second organic matrix in which are dispersed other carbon nano-tubes, is added to this material.
The composite material thus obtained guarantees a very high number of cycles at temperatures up to 1200° C. and has the following structural characteristics:
In more general terms, to better define the scope of protection offered by the attached claims, the low thermal conductivity structural composite material, object of the present invention, is composed at least of:
In more general terms, to better define the scope of protection offered by the annexed claims, the structural composite material according to the described second embodiment, with a high thermal conductivity, consists of at least:
More in detail, regardless of which type of fiber is used, said reinforcing fiber must be present in a percentage by weight comprised between 54 wt % and 64 wt % of the composite material;
The material with which said first inorganic matrix is nano-structured provides a decrease of the material porosity, bringing it to a value comprised between 20% and 30%, and to obtain the desired thermal conductivity;
Advantageously, the conductivity degree of a laminar element made by the material according to the present invention is maximized by orientating the nanotubes along a thickness of the element, in particular by applying a magnetic field during the construction of the article. For example, an orientation of both the nanotubes present in the inorganic and in the organic matrix can be provided. In particular, the nanotubes can be oriented both during the realization phase of the pre-impregnated, and during the realization phase of the composite, or at viscosity values of the material (respectively of the first inorganic matrix and of the organic matrix) which allow this orientation through the application of a magnetic field.
In particular, at a complete orientation of the nanotubes along an axis identifying a thickness of the laminar element, the thermal conductivity of the invention can reach values over 80 W/mK, for example of 90 W/mK, in a temperature range comprised between 20° C. and 250° C.
Advantageously, the composite material thus obtained has a specific weight of 1.25 gr/cm3, a tensile strength value of 200 MPa and an elastic modulus of 36 GPa.
The mechanical and structural characteristics of the composite material according to the present invention, make it resistant to the passing flame, smoking-proof, vapor-proof and, above all, do not vary even if exposed to fire.
In particular, the composite material according to the present invention allows the realization of lamellar fire barrier elements characterized by a thickness of about 0.4 mm.
More in detail, for example, two skins of impregnated carbon fiber of 200 gr/m2 having percentages comprised between 54% and 64% by weight of reinforcing material, are sufficient to generate a thermal shield resistant to a flame with a temperature of 1.200° C. and a thermal flow up to 150 KW/m2.
The weight of the composite material having flame-retardant shield functions according to the present invention is extremely reduced, in particular it is equal to 500 gr/m2.
No material of the prior art allows, with such a reduced weight, the containment of a flame with a temperature of 1.200° C. and a thermal flow over 120 KW/m2. For example, titanium alloys are able to contain the flame with thicknesses of about 0.5 mm but have a weight of over 2000 gr/m2.
Even the ceramic matrix composites succeed in this purpose but they have weights of about 800 gr/m2 and therefore always higher than the invention according to the present invention. No material with such specific weight, has tensile strength characteristics of about 200 MPa and an elastic modulus of about 30 GPa.
In addition to the very high mechanical and structural performances, the material object of the present invention does not present high production costs, as the previously illustrated production process uses equipment commonly used for any composite material currently available on the market such as, for example: carbon molds having polymeric or glass fiber matrices or aluminum alloy or steel.
Advantageously, moreover, it will be possible to obtain components having complex shapes through a single piece, avoiding costly additional mechanical machining.
Finally, it is clear that modifications, additions or obvious variations may be made to the invention here described by a person skilled in the art, without thereby departing from the scope of protection provided by the attached claims.
The present invention has been described by way of illustration, but not of limitation, according to its preferred embodiments, but it is to be understood that variations and/or modifications may be made by persons skilled in the art without departing from the relative scope of protection, as defined by the attached claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102017000033960 | Mar 2017 | IT | national |
| 102017000033972 | Mar 2017 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IT2018/050054 | 3/28/2018 | WO | 00 |
