WO2007129088A1

WO2007129088A1 - Carbon nanotube enhanced magnets

Info

Publication number: WO2007129088A1
Application number: PCT/GB2007/001685
Authority: WO
Inventors: Martin Pick
Original assignee: Q-Flo Limited
Priority date: 2006-05-10
Filing date: 2007-05-08
Publication date: 2007-11-15
Also published as: GB0609194D0

Abstract

The present invention relates to the addition of carbonaceous material, advantageously in the form of carbon nanotubes, filled or otherwise and/or carbon nanotube fibres to magnetic substances such that the intrinsic magnetism of the magnetic substances is enhanced. The mixture so produced can, if required be fixed through the addition of suitable fixing mediums such as epoxy resin. The resulting fixed, nanotube enhanced, permanent magnets are suitable for use in applications beyond the scope of non-enhanced permanent magnets.

Description

Carbon nanotube enhanced magnets.

During the latter part of the twentieth century the discovery of carbon Qo Buckminster Fullerenes [H. W. Kroto, J.R. Heath, S.C. O'Brien, R.F. Curl and R.E. Smally, (Nature 318, 162 1985)] and carbon nanotubes [S. Ijima Nature 354, 56 1991] have led research groups worldwide to work on the production and properties of these remarkable materials. The Buckminster Fullerene is a Cδo allotrope of carbon that forms itself into a closed geodesic structure based on CO hexagons. It was named after the famous architect Buckminster Fuller who designed dome like buildings based on a hexagonal/pentagonal structural form. This is shown in his design, commissioned in 1953 by the Ford Motor Company, for the Union Tank Car Company dome, Baton Rouge, Louisiana. Carbon nanotubes and nanofibres similarly contain Ce hexagon structures but unlike Buckminster Fullerenes are tube-like and can be produced as hollow cored, singlewalled nanotubes [SWNT], hollow cored multiwalled nanotubes [MWNT] and nanofibres that do not posses a hollow core.

All nanotubes lend themselves for use in electronic and magnetic technologies, the singlewalled and multiwalled variants particularly so. It is in the domain of electronic, magnetic technology that this invention exists.

The growth of nanotubes and nanofibres in a gas phase reactor was demonstrated by Zhu et al [Science 296 884 (2002)]. The group reported the formation of twenty centimetre long single-wall nanotubes via the pyrolysis of hexane, ferrocene and thiophene. Only isolated strands were produced. It was the work of a team at Cambridge University Department of Materials Science and Metallurgy that produced high volumes of singlewall, multiwall nanotubes together with nanotube fibre. The department has also been successful in producing vertically aligned carbon nanotubes on quartz substrates, these nanotubes are of high quality and can be produced in quantity. Use can be made of such nanotubes in the described invention.

The production of the aforementioned nanotubes makes use of a high temperature reaction vessel. One such example is a vertical glass tube, typically 150 mm in diameter and 1 metre long. A surrounding vertical furnace heats the top of the tube, the reaction zone, to a temperature exampled by 1050-1200 degrees C. A temperature gradient is maintained along the vertical axis of the tube with the base, the extraction zone, being at a temperature exampled by 500 degrees C. The dimensions of the reaction vessel are for example only, diameter and length will be determined by requirement, e.g. for laboratory use or industrial application, vessel diameters from 10 mm to >1 metre are acceptable as are vessel lengths >10 metres. The temperature of the hot, reaction zone can vary as can the temperature of the cooler extraction zone, temperature gradients included in the range 2000 degrees C to 50 degrees C would be acceptable. When in use a feedstock of a carbon carrying component, exampled by ethanol, a catalytic component or precursor exampled by ferrocene and a promoter exampled by thiophene is injected at the top of the reaction vessel into a carrier gas, exampled by hydrogen flowing from top to bottom of the reaction vessel at a rate exampled by 400 to 800 ml/min, flow rates can vary from <25 ml/min to >1500 ml/min. Use can be made of such nanotubes in the described invention. The inclusion of ferrocene as a ferric precursor or catalyst initiates the formation of individual nanotubes. Although Fe is the chosen element for the purposes of the described invention there are other suitable candidates that will allow nanotube growth, usually a transition metal that has an incomplete penultimate electron shell and exhibits more than one valency allowing it to form complexes. Metals from this group of elements are therefore ideal as catalysts and are exampled by group VlB chromium, molybdenum and tungsten. Group Vl I lB transition metals can also be used e.g. iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum and manganese. Mixtures of the aforementioned metals can also be used. Metals from the lanthanide and actinide series are also suitable. Preferred metals for the described invention are Fe, Ni, Co, Mo or mixtures thereof. A promoter, which for the purposes of the described invention is exampled by thiophene, is added to the ethanol, ferrocene solution; its addition adds sulphur to the reaction process. Use can be made of such nanotubes in the described invention.

Many processes can be used to enhance the electrical and/or magnetic properties of nanotubes. One such example is the production of carbon nanotubes with iron inside the tube as described by Charanjeet Sigh, MiIo S.P. Shaffer, Krzysztof K.K. Koziol, Ian A. Kinloch, Alan H. Windle [Chemical Physics Letters372 (2003) 860-865] and T. Mϋhl et al. [Journal of Applied Physics Vol. 93 Number 10]. Use can be made of such nanotubes in the described invention.

It was shown that magnetism can be induced into nanotubes through contact with other magnetic substances [O. Cespedes, M.S. Ferreira, S. Dsenvito, M. Kociak, J.M.D. Coey, (Contact induced magnetism in carbon nanotubes, Journal of Physics, Condens. Letter 16, 2004, L155-L161)]. The described invention develops this effect to affect and/or effectively modify the magnetic coercivity of permanent magnets such as those produced from magnetic powders exampled by but not restricted to Strontium Ferrite and Neodymium Iron Boron. Magnetic powders are widely used in industrial applications.

Magnets can be magnetically hard or soft, hi the case of a hard magnetic substance once magnetized a significant magnetic field strength is required to reverse the polarity of the magnetism. This is referred to as the coercivity of the magnet and the required force as the coercive force iH_c. Coercivity is measured in units of Oersteds (Oe). LQ permanent magnets a high value is usually but not always desirable. This invention provides a method to modify the coercivity of composite magnets at the macro and micro scale both for hard and soft magnets, some permanent some not. Soft magnets are particularly useful when used in shielding systems where protection is required from electro magnetic fields.

The hard magnetic properties of Ferro magnets derive from magnetocrystalline anisotropy, which is the propensity for the magnetic spins to align in a preferred direction, determined by the crystal structure of the material. To maximise the coercivity and hence energy product of a hard ferrite magnet, the ferrite particles should be no larger than a single magnetic domain (typically 1 micron size or less). Excessive sintering of fine powders therefore can lead to a degradation of the coercivity through grain growth. However, a moderate level of heat treatment can lead to coercivity enhancements, for example from 1600 Oe to 3440 Oe in the case of BaFe₁₂Oi₉ heated for one hour in temperatures of up to 1200 °C. hi the work undertaken strontium ferrite and neodymium iron boron are offered as exemplars of hard magnetic substances which can be obtained in particulate or powder form.

The inventors of the described invention have shown that the incorporation of carbonaceous materials and in particular carbon nanotubes with magnetic powder influences the coercivity of the powder in its untreated state. This influence can lead to an increase or decrease in coercivity. The effect is present whether the nanotubes used are filled with magnetic substances or not. It is the provision of permanent magnets whose magnetism is modified by carbonaceous material, preferably carbon nanotubes and the methods of achieving this that is the core of the described invention.

According to the described invention there is provided a mixture of carbonaceous material as exampled by carbon nanotubes and magnetic substances such that the intrinsic magnetism of the magnetic substances, exampled by strontium ferrite and neodymium iron boron, is modified. The mixture showing the modification can be made permanent by combining it with a fixing medium as exampled by epoxy resin. The resulting composite matrix is exampled by a bisphenol-A resin (Araldite 556, Huntsman), a hardener (XB 3473 obtained from Vantico Ltd) and a 5wt%/95wt% mixture of carbon nanotubes and magnetic powder respectively. Other fixing mediums and binders exampled by resins, thermoplastic polymeric binders, polymers such as nylon, foams, gels and synthetic thermoplastic rubbers can also be used. The quoted percentages for nanotubes, magnetic powders and fixing medium can be varied according to need. The carbon nanotubes used to modify the magnetic properties of magnetic substances can be single walled nanotubes, multiwall nanotubes, both filled and non filled, nanofϊbres and/or a mixture of each.

In one embodiment of the described invention the mixture of carbonaceous materials, exampled by graphite powder, carbon nanotubes and magnetic powder, is prepared by adding both materials to ethanol and ultrasonicating preferably for a time exceeding twenty minutes. The resultant sample is left in a fume cupboard to dry, overnight in this preferred example of process. Scanning electron micrographs [JEOL JSM -6340 electron microscope by FEG] of various percentage dispersions of nanotubes and magnetic powders show variations in the uniformity of dispersion. For the quoted materials and the method of mixing the 5wt%/95wt% ratio of nanotubes to magnetic powder was chosen. As the described method of mixing is for example only it is understood that other methods of mixing may give the required effect for other ratios of carbonaceous and magnetic substances. The above method of mixing as described in the above example can also be applied to substances such as Samarium, Gadolinium/Germanium, Samarium Iron Nitrogen and naturally occurring magnetic substances. The intrinsic magnetic properties of these substances will be affected according to the phase distribution and/or phase separation of the final mixture. The following two descriptions of mixing process are given as examples only.

1. Point two five grammes (0.25 g) of graphite powder was purchased from Sigma- Aldrich and placed in a beaker containing 100 ml of acetone. Ferrite powder 90.25 grammes) was then added to the acetone. Ultrasonic power was then applied to the beaker using an ultrasonic bath to disperse the magnetic and graphite powders in the acetone. The acetone was then evaporated to leave the mixed powders.

2. Carbon nanotubes were grown from silica substrates by the pyrolysis of ferrocene and toluene, as described in:

"Production of aligned carbon nanotubes by the CVD injection method. "

Singh C, Shaffer M, Kinloch I and Windle A, Physical B-Condensed Matter 323 (1-4): 339-3402002.

The nanotubes were removed from the growth substrate and 0.1 g of them were added to 5 g of epoxy resin, of Ferrite powder (0.1 grammes) was then added to the resin and a shear mixer was used to distribute the nanotubes and powder throughout the resin. The epoxy resin was then cured by the addition of the hardener and heat treatment in a vacuum oven, as described by the polymer's manufacturer.

Dispersion of the nanotubes can be achieved by number of methods known by skilled in the art such as chemical functionalisation (e.g. use of acid groups, treatment by sodium hydroxide ethanol solution) and surfactants.

Alternatively, the carbonaceous material can be grown directly off the magnetic particles to improve the intimate mixing between the nanotubes and the particles. These nanotube/magnetic particle hybrids can then either be used exclusively or mixed with additional nanotubes and/or magnetic particles. Preferably, the nanotubes will be grown from the magnetic particles by the catalytic vapour process, in which a nanosized catalyst is used to crack a hydrocarbon gas. hi one embodiment, the surfaces of the magnetic particles are suitable roughened by electrochemical etching or physical milling to provide a rough surface which can act as the catalysts. Alternatively, the particle may be coated with a catalyst using techniques known by those skilled in the art. For example, the surface can be coated by nanosized transitional metal particles, such as cobalt, nickel and iron. Alternatively, the surface can be coated with precursors such as salts (e.g. nitrates) which then are suitably treated to form active catalysts (e.g. reduced and/or heated). The stability, activity and selectivity of the catalyst can also be improved by its use in combination with a passivating layer such as TiN, silica or MgO, which is directly coated onto the particles or via precursor such as a magnesium salt which is then oxidized. This layer may be coated onto the magnetic particle prior to the introduction of the catalyst or with the catalyst.

Once prepared with an active catalyst surface the catalysts are reacted in a hydrocarbon gas (e.g. methane, toluene, acetylene,). Diluent carrier gases and other gases maybe used combined with this feedstock, with examples including argon, nitrogen, ammonia, and hydrogen. These gases may have an active role in the nanotube growth such as etching away unwanted carbon. The reaction occurs at temperatures of 400 to 1800 deg C, more preferable 500 to 1200 deg C. If a plasma- CVD reactor is used then the substrate temperature at which the particles are at is from room temperature up to 1200 deg C, more preferably up to 600 deg C.

In another embodiment, the catalyst is deposited onto the particles in-situ during the reaction. For example, the reaction feedstock can contain ferrocene which breaks down to form iron particles which then absorb on the surface of the magnetic particles.

The catalyst coated particles maybe reacted by various reactor configurations, including fluidised bed reactor, fixed bed reactor and continuous reactor where the particles are dropped through a vertical furnace. In addition a plasma may be applied to enhance the nanotube growth and/or nanotube alignment.

Substances which are considered 'Soft' as opposed to 'Hard' in magnetic terms as exampled by manganese zinc can also have their magnetic and electro magnetic properties affected when mixed with carbonaceous material again exampled by graphite powder and carbon nanotubes. As has been already been mentioned these substances when fixed by suitable binders are well suited for use in electro-magnetic field shielding systems.

Carbon black, carbon fibre, single wall nanotubes, multi wall nanotubes, carbon cloth, both woven and non woven are further examples of carbonaceous materials that can be used to enhance the properties of permanent magnets.

For example only the mixture of nanotubes and magnetic powder so produced can be fixed by the addition of epoxy resin or through the use of any of the aforementioned fixers or binders.

In another embodiment, the nanotubes may be added to the resin and then introduced to the magnetic powder during the fixing process.

As exampled by a combination of 95% ferrite powder with 5% multi walled carbon nanotubes (by weight) it was observed that there is a clear link between the degree of homogeneity within the mixture and its coercivity.

High coercivity occurs when there is intimate mixing of carbon nanotubes and ferrite powder. The resultant coercivity is significantly greater than that exhibited by the ferrite powder alone. For the purposes of this description carbon nanotubes and ferrite powder are examples of carbonaceous material and magnetic substances respectively.

For the purposes of clarity mixing is also referred to as phase distribution and/or phase separation.

Coercivity is moderate, similar to that of magnetic powder alone, in samples where phase separation is more apparent, clusters of magnetic powder are formed and there are fewer carbon nanotubes. Low coercivity, significantly less than magnetic powder alone, was exhibited by a phase distribution where the concentration of carbon nanotubes is low.

Final coercivity of the carbonaceous material, magnetic powder mixture is dependant on its degree of homogeneity. The degree of homogeneity can be used to affect the coercivity of untreated magnetic powder. Carbonaceous material is exampled by carbon nanotubes and magnetic powder by strontium ferrite.

As a further example the resultant carbon nanotube, magnetic powder mixture showed coercivity values greater than 2000 Oe which was higher than the as-received sample of ferrite of 1300 Oe. A mixture of 1% carbon nanotubes and 99% neodymium iron boron exhibited a coercivity of 2000-4000 Oe which is considerably in excess of the as-received powder.

The described invention allows the magnetic hardness of magnetic substances to be modified by the addition of carbonaceous material. The modification to the magnetic properties of magnetic substances can be made permanent by incorporating the mixture into a matrix in a manner familiar to those skilled in the art. With care in the choice of appropriate binders and due consideration of the percentages of carbonaceous materials and magnetic substances it is also possible to provide permanent magnets which are optically transparent. Similarly permanent magnets which are transparent to electro magnetic fields can be produced.

In addition to improving the magnetic properties, the addition of nanotubes to the magnetic powders improves the mechanical and electrical properties of the powder and their subsequent composites. The mechanical properties are important since the final magnetic components are used applications where they can encounter high stresses, for example in motor parts which rotate at speeds up to 100,000 revolutions per minute. The components also encounter other extreme service life conditions such as high temperature, high pressure and corrosive environments. The service life of these components is typically limited by the mechanical properties of the magnet, and any improvement in fracture stress, hardness and fatigue life of the component is beneficial.

The invention will further be described with reference to the following scanning electron micrographs [SEMs] and graphs.

Fig. 1. Is an SEM of nanotubes and magnetic powder. The distribution is considered uniform.

The scale bare as shown is 10 microns.

Fig. 2 Is an SEM of nanotubes and magnetic powder. The distribution is considered uniform.

The scale bar as shown is 1 micron. Fig. 3. Is an SEM of nanotubes and magnetic powder. The distribution is considered non-uniform.

The scale bar as shown is 10 microns.

Fig. 4. Is an SEM of nanotubes and magnetic powder. The distribution is considered non-uniform.

The scale bar as shown is 1 micron.

Fig. 5. Is an SEM of nanotubes and magnetic powder. The distribution is considered non-uniform .

The scale bar as shown is 1 micron.

Fig. 6 . Is an SEM showing the distribution of graphite and magnetic powder.

The scale bar as shown is 10 microns.

Fig. 7. Is an SEM showing he distribution of neodymium iron boron powder and carbon nanotubes.

The scale bar is shown as 10 micron.

Fig. 8. Is a graph showing the coercivity of mixtures of magnetic powders and carbon nanotubes when mixed at different ratios. Inset is a graph of the coercivities at low mixture ratios.

Fig. 9. Is a graph of the coercivity of magnetic powder when mixed with graphite powder at various ratios.

With reference to Fig 1.

Indicated at 1 are carbon nanotubes and at 5 particles of strontium ferrite. The mixture ratio is 5% carbon nanotubes to 95% strontium ferrite weight for weight. It can be seen that there is even distribution of nanotubes and magnetic powder. The scale bar as shown is 1 μm

With reference to Fig. 2.

Indicated at 1 are carbon nanotubes and at 5 particles of strontium ferrite. The mixture ratio is 5% carbon nanotubes to 95% strontium ferrite weight for weight. It can be seen again that there is a uniform distribution of nanotubes and magnetic powder. The scanning microscope scale bar as shown is 10 μm. With reference to Fig. 3.

Indicated at 1 are carbon nanotubes and at 5 strontium ferrite particles. With a ratio of 75wt% carbon nanotubes and 25wt% strontium ferrite there is uneven distribution.

The scale bar as shown is 10 micron.

With reference to Fig. 4.

Indicated at 1 are carbon nanotubes and at 5 strontium ferrite particles mixed in a ratio of 75wt% carbon nanotubes and 25wt% strontium ferrite. The predominance of the strontium ferrite particles in this sample shows the non-uniform distribution of particles when viewed against Fig 3. which is an SEM of the same sample.

The scale bar as shown is 1 micron.

With reference to Fig. 5.

Indicated at 1 are carbon nanotubes and at 5 strontium ferrite particles. The ratio of mixing is 0.1 wt% carbon nanotubes and 99.9wt% strontium ferrite particles. Once again it can be seen that there is non-uniform distribution of strontium ferrite and nanotubes for this sample.

The scale bar as shown is I micron.

With reference to Fig. 6.

Indicated at 5 are particles of strontium ferrite and at 7 areas of graphite powder. It can be seen there is no uniformity of distribution of the ingredients.

The scale bar as shown is 10 micron.

With reference to Fig. 7.

Indicated at 1 are carbon nanotubes and at 9 particle of neodymium iron boron.

The scale bar as shown is 10 micron With reference to Fig. 8.

The graph of the percentage mixtures of carbon nanotubes and strontium ferrite illustrates the interaction of the ingredients as indicated by increased coercivity. Indicated at 15 are the results of coercivity for the 5wt% of carbon nanotubes and 95wt% of strontium ferrite powder. It can be seen that at 2600 Oersteds the hardness of the as-received strontium powder has been considerably increased. The highest figures are those obtained from the samples showing the most uniform distribution of carbon nanotubes and strontium powder. Inset at 8a is an expanded portion of the graph which covers the mixture ratio from 0wt% to 5wt% for carbon nanotubes.

With reference to Fig. 9.

The graph shows that the percentage distribution of graphite powder to magnetic powder, in this case strontium ferrite affects the coercivity of the mixture. A strong interaction is shown at 23.

Claims

We claim.

1. The modification of the magnetic properties of finely divided magnetic substances through the addition of carbonaceous material.

2. As claimed in claim 1 where the magnetic substance is ferromagnetic.

3. As claimed in claim 1 where the magnetic substance is paramagnetic.

4. As claimed in claim 1 where the magnetic substance is diamagnetic.

5. As claimed in claim 1 where the magnetic substance is predominantly strontium ferrite.

6. As claimed in claim 1 where the magnetic substance is predominately neodymium iron boron.

7. As claimed in claims 1 to 6 where carbon nanotubes are present.

8. As claimed in claims 1 to 6 where graphite powder is present.

9. As claimed in claims 1 to 6 where carbon nanofibres are present.

10. As claimed in claims 1 to 6 where carbon black is present

11. As claimed in claims 1 to 6 where graphite powder and carbon nanotubes are present.

12. As claimed in claims 1 to 6 where graphite powder and carbon nanofibres are present.

13. As claimed in claims 1 to 12 where the carbonaceous material and magnetic powder are mixed through dispersion in a common medium.

14. As claimed in claims 1 to 12 where the carbonaceous material and the magnetic powders are mixed through shearing the dry powders.

15. As claimed in claims 1 to 12 where the carbonaceous material and the magnetic powders are mixed through ball milling.

16. As claimed in claims 1 to 7 and 9 where the carbonaceous material is grown directly onto the magnetic powder.

17. As claimed in claims 13 to 15 where the mixture is homogeneous throughout.

18. As claimed in claims 13 to 15 where the mixture is inhomogeneous.

19. As claimed in claim 18 where the mixing gives rise to localised variation in properties.

20. As claimed in claim 19 where the localised variations are magnetic.

21. As claimed in claim 19 where the localised variations are mechanical.

22. As claimed in claim 19 where the localised variations are electrical.

23. As claimed in claim 19 where the localised variations are thermal.

24. As claimed in claims 1 to 15 and 17 to 23 where the mixture of carbonaceous material and magnetic substances is made permanent.

25. As claimed in claim 16 where the grown carbonaceous material and the magnetic substances is made permanent.

26. As claimed in claims 24 and 25 where the physical shape is predetermined.

27. As claimed in claims 24 and 25 where the mechanical properties are made permanent.

28. As claimed in claims 24 and 25 where the electro-magnetic properties are made permanent.

29. As claimed in claim 24 where the mixture is made permanent by bonding.

30. As claimed in claim 24 where the finely divided material is coalesced.

31. As claimed in claim 24 wherein the mixture of carbonaceous materials and magnetic substances is made permanent by its incorporation in a matrix or other media.

32. As claimed in claim 24 wherein the mixture of carbonaceous materials and magnetic substances is made permanent with an epoxy composite.

33. As claimed in claim 24 wherein the mixture of carbonaceous material and magnetic substances is made permanent with a thermoplastic polymeric binder.

34. As claimed in claim 24 wherein the mixture of carbonaceous material and magnetic substances is made permanent with a thermoplastic binder.

35. As claimed in claim 24 wherein the mixture of carbonaceous material and magnetic substances is made permanent with synthetic thermoplastic rubber.

36. As claimed in claim 24 wherein the mixture of carbonaceous materials and magnetic substances is made permanent with foam.

37. As claimed in claim 24 wherein the mixture of carbonaceous materials and magnetic substances is made permanent with a gel.

38. As claimed in claim 24 where the mixture of carbonaceous material and magnetic substances is made permanent by mixing with a binder and pressing.

39. As claimed in claim 38 where temperature control is applied during pressing.

40. As claimed in claim 24 where the mixture of carbonaceous material and magnetic substances is made permanent by mixing with a polymeric binder prior to extrusion and forming of a final component.

41. As claimed in claims 24 to 40 where a permanent magnet is produced.

42. As claimed in claim 41 where a permanent structure is produced which can interact with electro magnetic radiation.

43. As claimed in claim 24 where the mixture of carbonaceous material and magnetic substances is made permanent by adding thermoplastic polymeric material prior to injection or compression moulding.

44. As claimed in claim 25 where a permanent structure is produced by adding a thermoplastic polymeric material prior to injection or compression moulding.

45. As claimed in claim 41 a permanent magnet such that its magnetic hardness, as measured in Oersteds is greater than that of a permanent magnet composed solely of magnetic substances.

46. As claimed in claim 41 a permanent magnet such that its hardness as measured in Oesteds is less than that of a permanent magnet composed solely of magnetic substances.

47. As claimed in claim 41 a permanent magnet such that its hardness as measured in Oersteds is unchanged from that of a permanent magnet composed solely of magnetic substances.

48. As claimed in claim 41 a permanent magnet containing carbon nanotubes and magnetic substances.

49. As claimed in claim 41 a permanent magnet containing carbonaceous material not in nanotube and nanofibre form, carbon nanotubes and magnetic substances.

50. As claimed in claim 48 a permanent magnet containing single walled nanotubes.

51. As claimed in claim 48 a permanent magnet containing multiwalled nanotubes.

52. As claimed in claim 41 a permanent magnet containing carbon nanotube fibre.

53. As claimed in claim 48 a permanent magnet wherein the carbon nanotubes are composed of single walled nanotubes, multiwalled nanotubes and nanotube fibre either together, singly in pair form or in any in other combination.

54. As claimed in claim 25 a permanent structure containing carbon nanotubes and magnetic substances.

55. As claimed in claim 25 a permanent structure containing carbonaceous material carbon nanotubes and magnetic substances.

56. As claimed in claim 54 a permanent structure containing single walled carbon nanotubes.

57. As claimed in claim 54 a permanent structure containing multiwalled carbon nanotubes.

58. As claimed in claim 25 a permanent structure containing carbon nanotube fibre.

59. As claimed in claim 54 a permanent structure wherein the carbon nanotubes are composed of single walled nanotubes, multiwalled nanotubes and nanotube fibre either together, singly in pair form or in any other combination.

60. A permanent magnet as claimed in claims 48 to 51 and 53 wherein the carbon nanotubes are filled with magnetic substances.

61. A permanent structure as claimed in claims 54 to 57 and claim 59 wherein the carbon nanotubes are filled with magnetic substances.

62. A permanent magnet as claimed in claims 48 to 51 and 53 wherein the carbon nanotubes are a mixture of non-filled nanotubes and those filled with magnetic substances.

63. A permanent structure as claimed in claims 54 to 57 and claim 59 wherein the carbon nanotubes are a mixture of non-filled nanotubes and those filled with magnetic substances.

64. A permanent magnet as claimed in claim 41 wherein its magnetic coercivity is hard as measured in Oersteds.

65. A permanent magnet as claimed in claim 41 where its thermal conductivity is modified.

66. A permanent magnet as claimed in claim 41 where its electrical conductivity is modified.

67. A permanent structure as claimed in claims 4 land 42 where the concentration of the carbonaceous material is varied locally to produce localised modification to its electro magnetic radiation absorbance properties.

68. A permanent magnet as claimed in claim 41 where the concentration of carbonaceous material is varied locally to produce a localised modification of its thermal conductivity.

69. A permanent magnet as claimed in claim 41 where the concentration of carbonaceous material is varied locally to produce a localised modification of its electrical conductivity.

70. A permanent magnet as claimed in claims 41 where it is transparent to electro magnetic radiation.

71. A permanent magnet as claimed in claim 41 where it is optically transparent.

72. A permanent magnet as claimed in claim 42 where it is transparent to electro magnetic radiation.

73 A permanent magnet as claimed in claim 42 where it is optically transparent.

74. As claimed in claims 41 and 42a permanent magnet as a component in mechanical systems.

75. As claimed in claim 73 a permanent magnetic component which increases the life of the mechanical system.

76. As claimed in claims 41 and 42 a permanent magnet as a component of electrical systems.

77. As claimed in claim 72 a permanent magnet as a component of an electric motor.

78. As claimed in claim 73 a permanent magnet which increases the life of an electric motor.

79. As claimed in claims 41 and 42 a permanent magnet as for use in extreme environments.