WO2000048206A1

WO2000048206A1 - Materials and composites activable into a state of enhanced conductivity

Info

Publication number: WO2000048206A1
Application number: PCT/IL2000/000083
Authority: WO
Inventors: Michael Ram; Itzhak Azar; Avishai Qutlitzki; Meir Robert Reoven Drey; Joseph Gabbai; Eran Gabbai
Original assignee: Do-Coop Technologies Ltd.
Priority date: 1999-02-09
Filing date: 2000-02-09
Publication date: 2000-08-17
Also published as: JP2002536841A; EP1177564A1; AU2458100A; IL128432A0; CA2362254A1

Abstract

A novel material, which is artificially produced, solid, stable morphological mutant of chemically known mineral materials is provided. The material is capable of being activated by exposure to an electric field or physical pressure into a state in which it is capable of transmitting thermal and electric signals in an anisotropic fashion.

Description

Materials and composites activable into a state of enhanced conductivity

GENERAL DESCRIPTION OF THE INVENTION

The present invention relates to novel materials with unique properties, applicable in a variety of technologies and in which a layer that forms the boundary with a surrounding medium plays a significant role. The surrounding medium may be a fluid such as air or water, or a solid which forms a substrate for the material, and to which it is applied as a coating or which serves as matrix in which the material is ^"dispersed. The applications of the new material give rise to a variety of new technologies. Any system in which the new technology is applied, will be referred to herein as "Boundary Layer Technology System", and for short "BLTS", the novel materials of the invention will be referred to as "BLTS materials", and results from occurrences at the boundary layer will be referred to as "boundary layer effect(s)". The BLTS materials according to the invention are artificially produced, solid, stable morphological mutants of chemically known mineral materials, which known materials will be referred to herein as parent materials. The parent materials are normally essentially non-conductors, i.e. insulators of heat and electricity. On the other hand, the novel BLTS materials of the invention may be activated by exposure to an activating power into a state in which they are capable of transmitting thermal and electric signals in an anisotropic fashion.

In many cases, the anisotropic signal transmission will occur at a velocity exceeding the velocity of sound in the non-activated BLTS material, with only an infinitesimal attenuation, in accordance with the condition

where E stands for energy.

While for the purpose of characterization the signal transmitting properties can be established in an uncompounded BLTS material, in practice, the BLTS materials will preferably be used in composite form in which they have the required physical coherence and strength.

Accordingly, the invention further provides composites comprising a BLTS material and a substrate selected from the group of ceramic materials, glass, metals and synthetic materials. According to one embodiment, at least one face of a substrate body is fixedly coated with a BLTS material. By another embodiment, the BLTS material is dispersed in a substrate body. By yet another embodiment, the composite has a tiered structure with alternating BLTS material and substrate layers adequately bound to each other.

Typically, the activating power is an electric field (electric activation) or mechanical pressure exerted on a BLTS material composite in a selected direction (mechanical activation), or a mixture of both.

BLTS materials according to the invention are, as a rule, amorphous, and it is believed that they include chains of particles having each of which an ellipsoidal shape. Moreover, due to the collapse of the crystalline structure of the parent compound, the elemental composition (i.e. the relative proportions of the chemical elements from which the material is made) of the BLTS material is as a rule different from what it was in the parent compound.

The above reference to the heat and electricity conducting properties of the BLTS materials are singled out for characterizing purposes. It is, however, noted that in the activated state, the BLTS materials also have enhanced anisotropic conductivities of acoustic and electromagnetic waves, such as, for example, light and x-rays.

In the following, heat, electricity, sound and electromagnetic waves transmitted anisotropically by BLTS materials according to the invention will be referred to occasionally as "signals". For electric activation of a BLTS material, several modes are possible. Thus, for example, an electric field can be induced upon the BLTS material by producing a coat thereof or an electric conductor such as copper, and applying an electric potential differential to such coat. The nature of the electric field can be direct, alternating or a combination of both. The enhanced anisotropic conductivity of BLTS materials are best achieved by using field strengths of within the range of from about 2v/m and to about 1200v/m. The set-up is preferably such that the induced electric field lines are essentially in alignment with the desired direction of the anisotropic signal transmission.

For mechanical activation a solidified composite according to the invention of the kind in which the BLTS material is dispersed in a substrate body is subjected to mechanical pressure.

In the activated state, the BLTS material according to the invention is modified, whereby any boundary layer between the material and a surrounding medium assumes unique properties. Thus, by coating one face of a metal block, e.g. a copper block, with a BLTS material, and activating the latter in a manner specified, the resulting composite manifests an anisotropic signal conducting capacity. Where, for example, one face of a glass body is coated with a BLTS material according to the invention, and the material is activated in a manner specified, the normal, isotropic light transmission capacity of the composite turns anisotropic.

Coating of a substrate with a BLTS material according to the invention, can be effected by applying to a substrate the powderous BLTS material obtained from production, with the aid of a glue or binder. Alternatively, a ready-made composite in which a BLTS material is evenly dispersed in a matrix, may be glued to a substrate. The boundary layer effect of a BLTS material according to the invention, is also manifest in the modification of some mechanical properties of that layer. For example, if in a body coated with a BLTS material, the latter is activated and the body is pulled through water, the drag of the moving body is significantly reduced. By way of example, use can be made of this effect by significantly reducing the friction between a ship's hull and water, whereby significant amounts of fuel can be saved.

Likewise, if the body or parts thereof of a flying platform e.g. an aircraft, is coated with a BLTS material which is activated in a manner specified, icing is prevented and any ice formed prior to activation is removed.

The required energy, e.g. the strength of the electric field or the compression power required for the activation of a BLTS, material depends in a given case on the chemical nature of the material, on the intended use and on the desired degree of signal conductivity.

The fact that BLTS materials and composites according to the invention manifest their anisotropic signal conductivity properties only upon activation, opens a host of new technological applications. Thus, for example, by one application, a BLTS material or composite according to the invention, is used for the dissipation of heat from a local heat generating environment, by way of an anisotropic heat flow towards a desired heat sink such as the ambient environment, whereby overheating is prevented. A typical example for such a new technology is heat management in electronic systems such as power transistors, thyristors, CPUs and the like. In all such systems, the arrangement may, for example, be such, that the electric field associated with the BLTS material based heat withdrawal system is switched on each time the electronic system is switched on. Alternatively, a thermoelement may be provided which switches on the heat removal system according to the invention, whenever the temperature reaches a pre-determined upper value. This BLTS material based heat withdrawal system is markedly superior to known cooling systems which are bulky, cumbersome and less effective.

BLTS materials and composites according to the invention, may also be used as voltage-dependent resistors, also known in the art as varistors. For this application, the intensity of the electric field applied to the BLTS material, may be varied at constant temperature so that with the increase of the applied voltage, the electric conductivity of the varistor is changed.

Making a varistor from a BLTS material according to the invention has several advantages. For one, the volt versus ampere characteristics of BLTS based varistors have a steep slope with controllable values of the non-linearity index. Moreover, such varistors are superior to prior art varistors. According to the prior art, a varistor is manufactured by doping a resistor such as a ceramic body with metals such as bismuth, antimony, cobalt or chromium, which metals are incorporated in the resistor by sintering. However, some of these dopants may evaporate at the high sintering temperatures, leading to non-uniform properties of the resulting varistor.

Generally speaking, a BLTS material according to the invention is obtained from its parent compound by a sequence of thermal treatment operations. In the case of a BLTS material obtained from barium titanate (BaTi0₃), which is a preferred BLTS material according to the invention, these thermal steps include fusion of BaTi0₃ at a temperature above 840^°C to obtain a viscous melt, transferring the melt into a closed vessel in which a reduced pressure of about 0.5 atm. is maintained, passing the so-treated viscous material across an environment of microwave beams, e.g. of the order of 2.45 GHz, and finally quenching the material in cold water at a temperature of about 4°C.

The BLTS material obtained in this way from barium titanate is amorphous and, strictly speaking, can no longer be termed BaTiOs which latter describes a crystalline structure. Nevertheless, and for the sake of convenience only, such a material will be referred to hereinafter as barium titanate BLTS.

The above procedure is characterized, among others, by exposing the parent compound to thermal shocks. The procedure modalities of methods of making other BLTS materials according to the invention from different parent compounds, depend in each case on the nature of the parent compound, but essentially the production will include the exposure of the fused parent compound to a thermal shock.

The barium titanate BLTS obtained in the manner described above is converted into a composite, e.g. by spreading it together with a glue or binder in form of a relatively thin coat on at least one surface of a substrate of metal, ceramic, glass or a synthetic material.

Composites according to the invention, may also be prepared in form of matrices holding BLTS materials. Thus, for example, barium titanate BLTS may be worked up into a matrix type composite in a series of operations which include: i. producing an intimate mixture comprising at least 30% by weight of barium titanate BLTS, and a resin, such as polyurethane or an epoxy resin;

ii. heating the mixture to an elevated temperature being at least the softening temperature of the resin and then allowing it to cool gradually down to room temperature;

iii. applying at ambient temperature and by direct contact a direct electric voltage across the cooled mixture body in a first direction, and maintaining that voltage for a period of time, sufficient for the electric current to reach a saturation value, the magnitude of the applied voltage depending on the amount of the barium titanate BLTS material; in case of a few cubic centimeters, the applied voltage may be of the order of 600V, and the saturation value of the current will then be of the order of 5 amp;

iv. applying the same voltage across said body in a second direction normal to said first direction, and maintaining the voltage for a period of time sufficient for the electric current to reach a saturation value, which in case of a volume of several cubic centimeters, may be of about 200mA;

v. applying at ambient temperature, an alternating voltage of about 220V and 50Hz to two sides of the body resulting from the previous step and maintaining this voltage for a period of time sufficient for full solidification; and vi. compressing the resulting solid composition body so as to reduce its total volume by approximately 10% whereby the desired composite is obtained.

A composite obtained in this way can be used for various purposes such as, for example, for making a varistor or a heat dissipator .

In accordance with the present invention, there is further provided a signal transmitting system comprising a signal transmitting body made of a BLTS material composite, which signal transmitting body has signal input and output terminals, the system further comprising means for exposing said signal transmitting body to an electric field.

If desired, the above signal transmitting system may comprise control means for switching on and off said means for exposing said signal transmitting body to an electric field, according to requirements. For example, where the signal transmitting system according to the invention serves for the withdrawal of heat from a heat generating operating device, said control means may be associated with control means for switching said operating device on and off. In the alternative, a thermoelement may be provided for switching on the electric field whenever the temperature in the device reaches a predetermined value and switching off the electric field when the temperature drops below said predetermined value.

According to one embodiment of a signal transmitting system according to the invention, the said signal transmitting body is a barium titanate BLTS composite.

By selection of the BLTS material component of the signal transmitting composite body and by designing a desired switching scheme, one can control the attenuation and modalities of the passing signals.

BRIEF DESCRIPTION OF THE DRAWINGS

The presented invention will now be described, by way of example only, with reference to the annexed drawings, in which: Fig. 1 is a flow diagram of a method of making a BLTS material according to the present invention;

Fig. 2 is a schematic illustration of a heat transfer system constructed and operative in accordance with one embodiment of the invention;

Fig. 3 is a schematic illustration of a heat transfer set-up showing the thermal management characteristics of the BLTS composition; Fig. 4 is a cross-section of a non-linear resistor according to the present invention, constructed and operative in accordance with one embodiment of the invention;

Fig. 5 shows the current-voltage characteristic at room temperature, in the direction of maximal conductivity for a BLTS composition according to the invention;

Fig. 6 shows the temperature dependence of the dielectric permittivity at different frequencies of the applied electric field of the electrically activated BLTS composition according to the invention;

Fig. 7 shows the temperature dependence of the tangent of the dielectric losses at different frequencies of the applied electric field of the electrically activated BLTS composition according to the invention;

Fig. 8 shows schematically a vessel for the production of a BLTS material composite in form of an elongated cylindrical body, capable of pressure activation;

Fig. 9 shows schematically an experiment which demonstrates the drag reduction of an activated BLTS composite body in water;

Fig. 10 shows a typical image of the surface of a BLTS material dried on mica substrate when the distance between the particles is significantly greater than their average size; Fig. 11 shows a typical image having size of 220 nm of the surface of a BLTS material dried on mica substrate when the particles are relatively close to each other; and

Fig. 12 shows a typical image having size of 1 μm of the surface of a BLTS material dried on mica substrate when the particles are relatively close to each other.

DETAILED DESCRIPTION OF A SPECIFIC EMBODIMENT

In the following detailed disclosure the invention will be described with reference to barium titanate BLTS which is a preferred embodiment of a BLTS material.

Example 1

In this Example, a method is described for making barium titanate BLTS according to the invention.

Fig. 1 shows schematically an assembly for use in a method of making barium titanate BLTS from BaTi0₃ in accordance with the teachings of the present invention. As shown, the method comprises the following production steps:

(a) commercial BaTi0₃ powder, milled if desired, is placed in a hopper 1 from where it is fed in a controlled fashion and under pressure P into an oven 2 maintained at a temperature above

840°C, whereby the powder is converted into a viscous mass; (b) during heating the pressure inside oven 2 exceeds 100 kg/inch , and by the action of this pressure the said viscous mass is ejected through an opening at the bottom of oven 2 into a pipe 3 in which a reduced pressure of about 0.5 atm is maintained, and a stream of the viscous mass moves downward inside pipe 3 by force of gravitation;

(c) the viscous mass emerging from pipe 3 is passed across an electromagnetic microwave magnetron 4, whose interior is maintained under atmospheric pressure and which operates at the frequency range of 1 GHz to 18 GHz.

(d) the material outflowing from the magnetron drops into a vat 5 holding a body of cold water 6 kept at a temperature selected from the range of -4 °C to 9°C, whereby the viscous material is quenched and disintegrates into particulate form; (e) the particulate material so obtained stratifies according to particle size and a desired fraction or desired fractions is or are recovered in a manner known per se (not shown), e.g. by centrifugation or filtration followed by drying, and in this way BLTS barium titanate is obtained.

Preferably, the working frequency of the microwave magnetron in step (c) is about 2.45 GHz and the temperature of cold water 6 in step (d) has a value of about 3.98±0.05 °C.

The barium titanate powder used as starting material for the purposes of the present invention may be of commercial or technical grade, but it should not contain any impurities that might have a significant adverse effect on the resulting barium titanate BLTS particles. The barium titanate BLTS material produced as described above is amorphous, and is thus a morphological mutant of the chemically known crystalline parent compound BaTi0₃. Samples made of this material were studied by using commercial

Scanning Probe Microscope. In such tests a drop of the material in water solution was placed on the cleaved mica surface and air-dried.

Fig. 10 illustrates a typical image of one of such samples. As one can see, patches of thin layers of the studied materials present particles, which are mostly round in the lateral plane. An analyzes of the distribution of the size of the particles shown in the picture reveals that for the total number of 320 particles the average diameter of the 270 smallest particles is 10 nm. Further, the average diameter of the next larger 40 particles, is 30 nm, and the average diameter of the 10 largest particles is 60 nm. All the particles are aspherical having their height to be much smaller than their diameter. For the example illustrated above in Fig. 10, the average height of the particles is 0.7 nm (for the group of the smallest particles), 2 nm (for the medium sized particles), and 4 nm (for the largest particles).

It was found that when the distance between the particles is significantly greater than their average size, the particles are arranged homogeneously on the surface. In contrast, as the density of the particles increases, the particles show an affinity to assemble into linear chains. Fig. 11 and Fig. 12 demonstrate this phenomenon on the images having sizes of 220 nm and 1 μm, respectively. The barium titanate BLTS obtained as described above, can be used for fabricating composites which, when electrically activated show enhanced and anisotropic thermal and electric conductive properties. Such a fabrication is described in the following Example 2. Example 2

A composite according to the invention, comprising barium titanate BLTS dispersed in a resinous matrix is prepared as follows:

(i) a mixture is prepared containing at least 30 % by wt. of the barium titanate BLTS obtained in accordance with Example 1, the balance being a polyurethane or epoxy resin;

(ii) the above mixture is heated while mixing to a temperature sufficient to obtain a viscous mass, whereby the BLTS particles are uniformly dispersed in the viscous resin. The mixture is allowed to cool down to ambient temperature, whereby a composition body is obtained comprised of a resin matrix with BLTS particles evenly dispersed therein;

(iii) a direct electric voltage of around 600 V or even higher is applied across the said body in a first direction and is maintained for a period of about 1 hour, until the measured electric current reaches its saturation value of about 5 amp;

(iv) the same voltage is then applied across the body in a second direction normal to said first direction, and is maintained for a period of about 1 hour, until the measured electric current reaches its saturation value of around 200 mA;

(v) an alternating voltage of 220 V and 50 Hz is applied to any two opposite sides of the body at ambient temperature and is maintained for a period of time sufficient for the body to fully solidify;

(vi) the resulting solid body is compressed in all directions so as to reduce its total volume by at least 10 %, whereby the desired composite is obtained. Fig. 2 shows schematically the use of the BLTS composition of Example 2 for the purpose of thermal management, which is one specific example of the implementation of the general concept of signal transfer according to the invention. Specifically, there is shown here a system for heat transfer which includes at least one layer of a BLTS composite 7 sandwiched between a heat transfer surface of an electronic device 8 and a heat transfer surface of a cooling radiator 9 serving as heat sink. Layer 7 of a BLTS composite is connected by wires 10 to an electric power source 11. A switch 12, which may, for example, be any kind of electronic switch, and which, is fitted into wires 10. When switch 12 is switched on an electric field forms across the BLTS composite layer 7, whereby the composite is activated. In the activated state, the composite 7 has an enhanced thermal conductivity, whereby heat is removed from the electronic device 8 to radiator 9, from where it is dissipated to the surrounding atmosphere. If desired, switch 12 may include data storage software permitting real time coordination of the activation of layer 7 with the changes in temperature in the region to be thermally stabilized.

Fig. 3 is a schematic illustration of a set-up for testing the thermal management characteristics of a BLTS composite according to the invention. As shown, the set-up includes a copper bock 15, which is coupled to a first electric power supply 16 via a heat generating resistor 17 having a desired resistance and hence heat generating capacity, such as, for example, 5 or 10W.

A tested BLTS composite 18, sandwiched between a heat transfer surface of said copper block 15 and a heat transfer surface of a radiator 19 designed to maintain the ambient temperature Ti and thus act as a thermostat.

A second electric power source 20 is connected to the BLTS composite 18 via a switch 21 designed to switch on and off the electric power supply from source 20 to the BLTS composite 18 by any desired protocol or real time response to the temperature of copper block 15. In the switched on state an electric field is generated across the BLTS material composite body 18 whereby the latter is activated. A device 22 serves for measuring the temperature T₂ of the copper block 15.

The temperature T₂ of the copper block was first measured when the sample tested was the BLTS composite of Example 2, and again when the sample tested was a known heat insulator. Results of the tests are summarized in the following Table:

Table

Heat power Ti ^υC T₂ ^υC T₂ ^υC [Watts] For BLTS For insulator

5 19 47 67

10 20 49 100

As can be seen from the table, due to the enhanced thermal conductivity of the electrically activated BLTS composite 18, the value of the temperature T₂ is significantly lower for the BLTS composite than it is in the case of a known heat insulator.

Another example of implementation of the basic concept of the present invention is the use of a BLTS composite for producing voltage-dependent resistors. As shown in Fig. 4, a resistor body 25 made of a BLTS composite is sandwiched between the two cap electrodes 26 with soldered connecting wires 27. Resistor 25 is under the influence of the electric field formed between the two cap electrodes 26 and at the same time serves for passing electric current between the electrodes across a given resistance. The said given resistance changes with the applied voltage, in consequence the change of degree of activation of the BLTS material components of the resistor 25.

Example 3 The electrical properties of the BLTS composite fabricated by the method of Example 2 were evaluated.

Current versus voltage characteristics of the nonlinear resistor made of the BLTS composition of Example 2 were performed on a block sample of size 15x30x10 mm, the set-up being as in Fig. 4. A DC voltage ranging from 2V to 24V was applied, and the corresponding current was measured. The accuracy of the measurements was better than 2%. Fig. 5 shows the current- versus-voltage behavior at 20 C of the said resistor and as can be seen, the S-type curve displays a strong nonlinear behavior. Depending on the particular application of the resistor, the non-linearity characteristics of the curve can be varied within wide limits by choice of the concentration of the BLTS particles and judicious selection of the procedure of composite fabrication.

The complex dielectric permittivity ε*(ω) = ε' - iε" (where ε' is the dielectric permittivity, ε" is the dielectric losses and i = - ϊ), were measured by means of an HP 8510C vector network analyzer in the broad frequency range of 1Hz - 1MHz and a temperature range of -40 C - 150°C. The applied electric field for activation of the BLTS composition was 12V. The maximum error for the dielectric permittivity, ε', and tangent losses, tan δ =ε"/ε', measurements was estimated as being less than 2%. Fig. 6 shows the temperature dependence of the dielectric permittivity on the temperature at different frequencies of the applied electric field of the electrically activated BLTS composite of Example 2. As one can see, the composite shows a temperature behavior of the dielectric permittivity which is typical for solids. Fig. 7 shows the temperature dependence of the tangent of the dielectric losses of that BLTS composite at different frequencies of the applied electric field. The maximum of dielectric losses, appeared within the temperature interval of the measurement, corresponds to the relaxation process related to the dynamics of the molecules and dipole active groups in the material. As one can see, the peak of the relaxation process has a typical temperature behavior, i.e. it shifts towards high temperatures when the frequency increases.

Example 4

The barium titanate BLTS obtained as described in Example 1 can also be used for fabricating composites in which activation of the BLTS component occurs by the application of mechanical pressure to the material instead of an electric field. The composite thus obtained also shows enhanced anistropic thermal properties. Such a fabrication is now described with reference to Fig. 8.

A thick walled cylindrical vessel 30 is used, e.g. of ceramic material, having a wall 31 enclosing an elongated cylindrical chamber 32.

(i) A mixture is prepared at room temperature containing at least 80% by wt. of the barium titanate BLTS obtained in accordance with Example 1, the balance being an epoxy glue;

(ii) the above mixture is heated with continued mixing to a temperature about 60°C-70°C, whereby the BLTS particles are uniformly dispersed in the glue; (iϋ) the mixture is placed into the elongated cylindrical chamber 32 of vessel 30 (Fig. 8) and pressure is applied at the open end of chamber 32, and the pressure is gradually increased and maintained until the volume of the mixture is - l o -

determined by the length of the mixture body inside chamber 32, is reduced by about 10%; (iv) the resulting compressed body, while still inside chamber 32 is subjected to a rotating magnetic field of around 500 Gauss 5 and a frequency of around 200 Hz, with the magnetic field lines extending diametrically across vessel 30, for a period of about 20 minutes; (v) the resulting semi solid body is allowed to cool down to ambient temperature and is maintained at this temperature for 10 a period of time sufficient for the body to fully solidify, whereby a composite body is obtained comprised of a glue with BLTS particles dispersed therein; (vi) the resulting barium titanate BLTS is extracted from vessel 30 and is ready for use.

15 The enhanced thermal conductivity properties of the composite of

Example 4 were tested by sandwiching the elongated cylindrical composite body obtained above between a heat source of 4W and a thermostat maintaining the temperature Ti at 20°C. The inner and outer radii of the cylindrical body were respectively 3 mm and 6 mm and the height was

20 25 mm. For activation of the material a pressure of 100 kg/cm was applied at the two end faces of a sample of the cylindrical composite body. The temperature T₂ at the end close to the heat source was measured, a first time when the sample chosen was said pressurized BLTS composite cylindrical body and then again when it was a copper block of the same geometry and

25 size. It was found that T₂ had the values of 70°C and 95°C for, respectively, the BLTS composite and for the copper block, i.e. the heat conductivity of the pressure activated BLTS composite body was superior to that of copper. Example 5

Many possible applications of the BLTS material composite are based on a boundary layer effect by which the friction coefficient between an activated BLTS material composite and water is reduced. In this way the hydraulic drag of a body moving in water may be significantly reduced.

An experimental set-up for the illustration of this phenomenon is presented in Figs. 9a-c. As shown, the experimental set-up includes a tank 35 with inlet 36 and outlet 37 and holding a body of water 38.

A pendulum 39 having a swinging body 40 is suspended above tank 35 so that body 40 is immersed in the body of water 38. Body 40 is a BLTS material composite and is associated with means (not shown) for applying at will an activating electric potential thereto.

Fig. 9a shows a state of rest in which body of water 38 is stagnant. In this state pendulum 39 is in its normal rest position. In the state of Fig. 9b water flows across tank 35 and the body of water 38 is thus in a dynamic state of flow. Due to the friction between the flowing water and swinging body 40, pendulum 39 is deflected into a state of dynamic equilibrium in which the pendulum forms an angle α with the vertical rest position of Fig. 9a. In the state of Fig. 9c the water flow is maintained at exactly the same intensity as in Fig. 9b. However the BLTS material in the swinging body 40 is now activated whereby the friction coefficient with water is reduced and a state of equilibrium is established in which the pendulum 39 is deflected from the vertical rest position of Fig. 9a by an angle β smaller than angle α in Fig. 9b.

The reduction of the friction coefficient of an activated BLTS composite in accordance with the teachings of the present invention may be utilized for the reduction of the drag of marine vessels. To this end the hull or part thereof of a marine vessel is plated with a BLTS material composite and means are provided for the electric activation thereof. The BLTS plating is activated at will whenever the vessel moves, and in this way significant amounts of fuel can be saved.

Example 6

In accordance with the invention BLTS materials can be prepared which in the activated state have hydrophobic properties by which water and ice are rejected from a surface of an activated BLTS material composite whereby icing is prevented. The ice rejecting properties of such a composite were demonstrated in the following experiments:

In a first experiment a graphite pipe 2 inch in diameter and 20 inch long, was wrapped in a polyurethane film and placed vertically in a cold chamber maintained at -10°C. Water was sprayed into the chamber in form of fine droplets, whereupon a layer of ice built up rapidly on the polyurethane film surface. The adhering ice could not be pried off mechanically without some of the polyurethane film adhering to the ice, even at a temperature only slightly below 0°C.

In a second experiment, an identical pipe was prepared with a film of the barium titanate BLTS material spattered on the pipe surface. When water was sprayed under identical conditions, a similar layer of ice built up on the BLTS film surface. A voltage difference of 6V was applied in order to activate the BLTS film. As a result, the ice detached spontaneously and left a clean and intact surface.

The same test was repeated at -20°C with identical results. The ice rejecting properties of an activated BLTS composite may be utilized for the prevention of ice formation on the surface of bodies, e.g. of flying objects such as aircrafts, helicopters, balloons, unmanned air vehicles (UAVs), etc. To this end, surfaces of an object which are susceptible to being iced, e.g. the fuselage and wings of an aircraft, are coated with a BLTS material composite and means are provided for its activation upon the formation of icing conditions.

As it should be understood by a man of the art, the invention is not confined to the precise details of the foregoing examples and variations may be made thereto. For instance, a BLTS material may also be obtained from PZT (PbZrTiOe), ZIRCONIA (Zr0₃), or BASED ALUMIBA (A1₂0₃) minerals.

Other variations are possible within the scope of present invention as defined in the appended claims.

Claims

CLAIMS:

1. A novel, artificially produced, solid, stable moφhological mutant of chemically known mineral material (parent materials), which novel material is capable of being activated by exposure to an activating power into a state in which it is capable of transmitting thermal and electric signals in an anisotropic fashion.

2. A novel material according to claim 1, wherein the transmission of signals occurs at a velocity exceeding the velocity of sound in the non-activated novel material and with only an infinitesimal attenuation, in accordance with the condition t^i ~ i^out ' )

where E stands for energy.

3. A novel material according to claim 1 or 2, wherein the anisotropic transmission of thermal and electric signals occurs upon exposure to an electric field.

4. A novel material according to claim 1 or 2, wherein the anisotropic transmission of thermal and electric signals occurs under physical pressure in a selected direction.

5. A novel material according to Claim 1, obtained from the parent material barium titanate.

6. A novel material according to Claim 1, obtained from the parent material PZT (PbZrTi0₆).

7. A novel material according to Claim 1, obtained from the parent material ZIRCONIA (Zr0₃).

8. A novel material according to Claim 1, obtained from the parent material BASED ALUMINA (A1₂0₃).

9. A composite including a novel material according to Claim 1 or 2, in combination with a substrate material.

10. A composite according to Claim 9, wherein said substrate material is a member selected from the group of ceramic materials, glass, metals and synthetic materials.

11. A composite according to Claim 9 or 10, wherein said novel material is applied as a fixed coat to at least one face of a substrate body.

12. A composite according to Claim 9 or 10, having a tiered structure with alternating BLTS material and substrate layers, adequately bound to each other.

13. A composite according to Claim 9 or 10, wherein said novel material is dispersed within a body of said substrate.

14. A composite according to any one of Claims 9 to 13, wherein said novel material is obtained from barium titanate.

15. A method of making a novel material according to any one of Claims 1 to 8, comprising subjecting a parent material to a thermal shock treatment.

16. A method according to Claim 15, also comprising subjecting the parent material to irradiation by electromagnetic radiation.

17. A method according to Claim 12, wherein said electromagnetic radiation are microwaves in the GHz region.

18. A method according to any one of Claims 15 to 17 for making the material of claim 5, comprising fusing BaTi0₃ at a temperature above 840^°C to obtain a viscous melt, transferring the melt into a closed vessel in which a reduced pressure of about 0.5 atm. is maintained, passing the so-treated viscous material across an environment of microwave radiation of the order of 2 GHz, and quenching the material in cold water at a temperature of about 4°C.

19. A method of making a composite according to claim 13 and 14, comprising: (i) providing producing an intimate mixture comprising at least 30% by weight of barium titanate BLTS, and a resin;

(ii) heating the mixture to an elevated temperature being at least the softening temperature of the resin and then allowing it to cool gradually down to room temperature;

(iii) applying at ambient temperature and by direct contact a direct electric voltage across the cooled mixture body in a first direction, and maintaining that voltage for a period of time, sufficient for the electric current to reach a saturation value; (iv) applying the same voltage across said body in a second direction normal to said first direction, and maintaining the voltage for a period of time sufficient for the electric current to reach a saturation value;

(v) applying to the two sides of the resulting body at ambient temperature an alternating voltage and maintaining it for a period of time sufficient for full solidification; and

(vi) compressing the resulting solid composition body so as to reduce its total volume by approximately 10%, whereby the desired composite is obtained.

20. A signal transmitting system comprising a signal transmitting body made of a BLTS composite as defined in any one of Claims 9 to 14, which signal transmitting body has signal input and output terminals, the system further comprising means for exposing said signal transmitting body to an electric field.

21. A signal transmitting system comprising a signal transmitting body made of a BLTS composite as defined in any one of Claims 9 to 14, which signal transmitting body has signal input and output terminals, the system further comprising means for subjecting said signal transmitting body to pressure.

22. A signal transmitting system according to Claim 20 or 21, used for heat removal from a heat generating system. 5

23. A signal transmitting system according to Claim 22, wherein said heat generating system is an electronic device.

24. A method of reducing the drag of a marine vessel, comprising providing on such vessel or parts thereof a plating of a BLTS material composite as defined in any one of Claims 9 to 14 and electrically activating l o said plating at will when the vessel moves.

25. A marine vessel having a plating of a BLTS material composite as defined in any one of Claims 9 to 14, in association with means for electrically activating said plating at will when the vessel moves.

26. A method of preventing ice formation on a body, comprising providing 15 on such body or parts thereof a coating of a BLTS material composite as defined in any one of Claims 9 to 14 and activating said coating at will upon the formation of icing conditions.

27. A method according to Claim 26 applied to a flying object.

28. A flying object having a plating of a BLTS material composite as 20 defined in any one of Claims 9 to 14, in association with means for electrically activating said plating at will upon the formation of icing conditions.