This invention relates to a method and an apparatus for use in the manufacture of carbon coated nanoparticles.

Carbon coated nanoparticles may be manufactured in relatively small quantities using a range of techniques. Such nanoparticles are thought to have a wide range of uses. By way of example, it is thought that the incorporation of carbon coated nanospheres, or particles of generally spherical shape, into a number of lubricants would be beneficial. However, whilst the methods used in the manufacture of such nanoparticles are unsuitable for use in their mass production, commercial production of lubricants containing the nanoparticles, or other commercial use of the nanoparticles cannot be undertaken. It is an object of the invention to provide a method and apparatus for use in the production of carbon coated nanoparticles which may allow mass production thereof.

According to a first aspect of the invention there is provided a method for use in the production of carbon coated nanoparticles comprising the steps of:

providing nanoparticles within a rotary furnace; and

introducing a carbon source into the rotary furnace, whilst the furnace is rotating and is at a temperature within the range of 700-800°C for a period of time in the range of 10- 40 minutes. By way of example, the temperature may be held at approximately 775°C for approximately 40 minutes. The carbon source may comprise, for example, 20vol% styrene with 80vol% acetone, delivered to the rotary furnace at a rate within the range of 1.2-2.4 ml/h. A carrier gas, for example in the form of Argon, may be used to carry the carbon source into the rotary furnace.

It has been found that the use of a rotary furnace in the production of carbon coated nanoparticles is advantageous in that agglomeration of the particles is reduced and the formation of a complete, substantially uniform thickness carbon coating on the nanoparticles is enhanced.

The nanoparticles may comprise, for example, inorganic fullerene-like (IF) WS ₂ nanoparticles. Alternatively, IF-MoS ₂ nanoparticles, or other nanomaterials such as Si0 ₂ , SiC or Al ₂ 0 ₃ ceramic nanoparticles may be used. Other nanoparticles may be used without departing from the scope of the invention. By way of example, the invention also relates to the carbon coating of nanoparticles of Ti0 ₂ , Al ₂ 0 ₃ with diameters in the range of 20-200nm. The techniques used in coating such particles are substantially as outlined hereinbefore. Conveniently, the nanoparticles are produced within the rotary furnace.

For example, the step of providing the nanoparticles within the rotary furnace may comprise the steps of:

supplying a precursor and a sulphur containing gas to the rotary furnace;

heating the precursor and sulphur containing gas to a temperature within the range of 800-900°C, whilst the furnace is rotating; and maintaining the precursor and sulphur containing gas at this elevated temperature for a period of time of at least 20 minutes, whilst continuing to rotate the furnace, to produce the nanoparticles within the rotary furnace. The precursor may comprise, for example, W0 ₃ or Mo0 ₃ to produce IF-WS ₂ or IF-MoS ₂ nanoparticles.

The production of nanoparticles within a rotary furnace is advantageous in that agglomeration of the particles is reduced.

By producing nanoparticles within a rotary furnace, and subsequently forming a carbon coating on the nanoparticles whilst they are located within the rotary furnace, mass production of carbon coated nanoparticles may be achieved. The mass production may take the form of a batch process. Alternatively, by introduction of the carbon source at an appropriate point in the furnace, a continuous manufacturing process may be attained.

According to another aspect of the invention there is provided an apparatus for use in the manufacture of carbon coated nanoparticles comprising a rotary furnace, and inlet means whereby a carbon source can be introduced into the rotary furnace.

Conveniently, the rotary furnace is used to manufacture nanoparticles to which a carbon coating is subsequently applied. Means for introducing a, for example, W0 ₃ precursor and a sulphur containing gas to the rotary furnace are also conveniently provided to attain this. The rotary furnace conveniently comprises a reaction tube supported so as to be rotatable about its axis, at least part of the quartz tube being located within a heater means. The reaction tube may include at least one baffle operable to promote mixing of the materials located within the tube as the tube rotates. The reaction tube may take the form of a quartz tube. However, other materials may be used. Indeed, a stronger material such as stainless steel may be preferred.

The invention further relates to carbon coated nanoparticles manufactured according to the method outlined hereinbefore and/or using the apparatus outlined hereinbefore.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic view of a rotary furnace for use in an embodiment of the invention;

Figure 2 is a diagrammatic representation of a gas supply to the rotary furnace of Figure 1 ; Figure 3 is a diagrammatic view illustrating part of the rotary furnace; and

Figure 4 is a high resolution transmission electron microscope image of a particle manufactured using the method and apparatus of an embodiment of the invention. Referring firstly to Figure 1 , a rotary furnace 10 for use in the manufacture or production of carbon coated nanoparticles is illustrated. The rotary furnace 10 comprises a reaction tube 12 within which the carbon coated nanoparticles are produced, in use. The reaction tube 12 is supported by a support device 14 including a first series of rollers 16 arranged to support one end of the tube 12 and a second series of rollers 18 arranged to support the opposite end of the tube 12. The first series of rollers 16 are motor driven, the second series of rollers 18 being idler rollers which are free to rotate. It will be appreciated that by operation of the motor driven rollers 16, the tube 12 is driven for rotation about its axis.

In this embodiment, the reaction tube 12 takes the form of a quartz tube. However, it will be appreciated that other materials may be used. For example, stronger materials such as stainless steel may be preferred.

The quartz tube 12 extends through a gas, electric or otherwise fired heater 20 operable to heat the tube 12 and the contents thereof. The furnace, in this embodiment, is capable of raising the tube 12, and the contents thereof, to a temperature in the region of 1200°C. However, in use when performing the method of the invention, this temperature is not attained.

A gas inlet arrangement 22 is connected at one end of the quartz tube 12 and is operable to supply various gases and particles carried by gases thereto. A suitable rotary seal 24 is provided to avoid the escape of gas between the rotating, in use, quartz tube 12 and the inlet arrangement 22.

A similar rotary seal 26 is provided at the opposite end of the quartz tube 12, providing a seal between the tube 12 and an outlet filter 28.

As shown in Figure 2, the gas inlet arrangement 22 is operable to control the supply of materials to the quartz tube 12. The inlet arrangement 22 comprises a purge gas source 30 connected, via a purge gas valve 32, to a supply pipe 34 connected, in turn, to the tube 12 via the rotary seal 24. The purge gas is conveniently Argon, but other gases could be used for this purpose, if desired. The arrangement 22 further comprises a sulphur containing gas source 36 connected, via a control valve 38, to the supply pipe 34. The sulphur containing gas conveniently comprises H ₂ S.

In addition, the arrangement 22 further comprises a precursor inlet arrangement 40 whereby precursor materials can be supplied to the supply pipe 34. In this arrangement, the precursors are W0 ₃ precursors. However, this need not always be the case and will depend upon the nanoparticles to be produced. The arrangement 40 conveniently comprises a feed or carrier gas line 42 into which W0 ₃ precursors can be introduced by a suitable piston arrangement 44 or other suitable feed device, the W0 ₃ precursors being carried by the feed gas into the supply pipe 34. The feed gas may comprise Argon.

To allow the introduction of a carbon containing material, the arrangement 22 further comprises a carbon containing material source 46 operable to inject the carbon containing material, for example 20vol% stryrene with 80vol% acetone, into a feed gas stream in a line 48 connected to the supply pipe 34.

In the example illustrated, the tube 12 is of length approximately 2m, the central 1 m of which is heated, the tube 12 being of outer diameter 40mm and inner diameter 36mm. It will be appreciated that the invention is not restricted to this specific arrangement, and that other size tubes may be used without departing from the scope of the invention. In order to promote relative movement of the materials located within the tube 12 in use, the tube 12 is preferably provided with internal baffles. As shown in Figure 3, the internal baffles conveniently comprise relatively small diameter quartz cylinders 12a secured to the inner surface of the tube 12 and extending longitudinally thereof. By way of example, the cylinders 12a may be of 5mm diameter. As shown, two diametrically opposed cylinders 12a may be provided. However, fewer, or more, cylinders may be provided within the scope of the invention. It is thought that the provision of baffles within the tube 12 encourages movement of the powders located within the tube 12, in use, helping to separate the particles and so reduce agglomeration. Tests have shown that the provision of the baffles can result in a significant increase in the production of nanoparticles. As an alternative to the use of baffles, the interior of the tube could be roughened to promote mixing of the particles upon rotation of the tube 12.

In use, initially the furnace is operated to cause rotation of the quartz tube 12 whilst the temperature thereof is raised to, for example 550°C. During this time, the valve 32 is open, but the other valves are closed, so that Argon is supplied to the tube 12, purging the air therefrom. After around 30 minutes, it is assumed that the Argon will have replaced all of the air from the tube 12. At this time, the purge gas is switched off by operation of the valve 32, the valve 38 is operated to commence the supply of the sulphur containing gas to the quartz tube 12, and the furnace temperature is raised to around 800-900°C. Subsequently, the arrangement 40 is operated to supply W0 ₃ precursors to the tube 12.

The furnace continues to rotate, and the temperature is maintained in the 800-900°C range for a duration of approximately 20-40 minutes, during which time the chemical reaction W0 ₃ + H ₂ S→ WS ₂ + H ₂ 0 occurs. The duration during which the temperature is held in this range will depend upon the amount of the W0 ₃ precursor supplied to the tube 12. Once this reaction is complete, no sulphur will be present in the gas reaching the filter.

After the temperature has been held at the desired level for the appropriate length of time for the reaction to be completed, the furnace temperature is allowed to fall, during which time the valve 38 is closed to terminate the supply of sulphur containing gas, and the valve 32 is opened to allow flushing of the tube 12 with the purge gas.

It has been found that by using this methodology, IF-WS ₂ nanoparticles are formed.

Having formed the IF-WS ₂ nanoparticles within the rotary furnace, a carbon coating is applied thereto by continuing to rotate the furnace, raising the temperature therein to a temperature within the range of 700-800°C and operating the carbon material containing source 46 to supply carbon containing material to the tube 12. It is envisaged that the carbon containing material will be delivered at a rate falling within the range of 1.2-2.4 ml/h for a period of 10-40 minutes. By way of example, the furnace may be held at a temperature of 775°C for 40 minutes with the carbon containing material be delivered at a rate of 2.4 ml/h. However, this is merely one example, and other arrangements are possible without departing from the invention. The carbon containing material is conveniently carried into the tube 12 by a stream of a carrier gas such as Argon, for example supplied to the tube 12 at a rate of 100ml/min. Such a technique results in the deposition of a carbon layer to the outer surfaces of the nanoparticles. The continued rotation of the furnace during this operation assists in ensuring that the nanoparticles are completely and substantially uniformly coated. The thickness of the carbon coating can be controlled by appropriate control over the rate of supply of the carbon containing material to the tube 12 and the duration over which the material is supplied. After deposition of the carbon coating, the furnace is allowed to cool whilst the tube 12 continues to rotate and the materials are subsequently removed therefrom. Figure 4 is a high resolution transmission electron microscope image of a particle 50 manufactured using the method and apparatus, and clearly shows the nanoparticle 50 as being of hollow, multilayered IF-WS ₂ form, of approximately 50nm diameter. The outer surface of the particle 50 is provided with a carbon material coating 52 of thickness in the region of 2-3nm. The method and apparatus outlined hereinbefore allow the production of a relatively large quantity of carbon coated nanoparticles in a relatively simple and convenient manner.

Whilst the arrangement described hereinbefore relates to the production of carbon coated IF-WS ₂ nanoparticles, produced using W0 ₃ precursors, the invention is not restricted in this regard. By way of example, carbon coated IF-MoS ₂ nanoparticles, or other nanomaterials such as Si0 ₂ , SiC, Ti0 ₂ or Al ₂ 0 ₃ ceramic nanoparticles may be produced in accordance with the invention Using the method outlined hereinbefore, the apparatus has been used to provide a nanoscale thin layer of carbon coating on other nano-particles including, for example, Ti0 ₂ and Al ₂ 0 ₃ with diameters in the range of 20-200nm. The parameters of the method may require slight adjustment, but the method works successfully provided the particles have a high enough melting point and do not easily react with carbon at temperatures less than about 1000°C. For a Ti0 ₂ particle, it has been found that the carbon coating can form up to about 14wt% of the original Ti0 ₂ particle, for a particle of size in the region of 20nm diameter. The carbon coated nanoparticles produced using the method and apparatus outlined hereinbefore are suitable for use in a wide range of applications. For example, they are thought to be of significant benefit when used as an additive to lubricants, enhancing the temperature range over which the lubricants can be used. By way of example, it is thought that the operating temperature range of a lubricant may be increased y around 70°C through the use of carbon coated nanoparticles therein. However, this is just one of many applications in which they may be used. Whilst the method outlined hereinbefore is of a batch process, it will be appreciated that the method could be modified to form a continuous manufacturing process by appropriate modification of the apparatus to ensure that the particles are carried through the furnace and by arranging for the introduction of the carbon containing material part way along the furnace.

A wide range of modifications and alterations may be made to the arrangement described hereinbefore without departing from the scope of the invention.