Unless otherwise stated, in this specification, all compositions are given on a percentage by weight basis.

According to one aspect of the invention, there is provided a combustible product which includes an admixture of a first exothermic composition and a second, different, exothermic composition, the first exothermic composition including a metal and a metal oxide capable of reacting exothermically with each other, with the metal being in stoichiometric excess, and the second exothermic composition including a metal and a metal oxide capable of reacting exothermically with each other.

The metal may be in stoichiometric excess by a factor of at least about 9, preferably between about 20 and about 90, e. g. about 35,, in the first exothermic composition.

The second exothermic composition may have an ignition temperature which is lower than an ignition temperature of the first exothermic composition.

According to another aspect of the invention, there is provided a combustible product which includes an admixture of a first exothermic composition and a second, different, exothermic composition, the first exothermic composition including a metal and a metal oxide capable of reacting exothermically with each other, and the second exothermic composition including a metal and a metal oxide capable of reacting exothermically with each other, one of the first exothermic composition and the second exothermic composition having a lower ignition temperature than the other of the second exothermic composition and the first exothermic composition.

The exothermic composition with the lower ignition temperature may have a higher calorific value than the other exothermic composition. For the first exothermic composition and the second exothermic composition as Hereinafter described, it is typically the second exothermic composition which has the lower ignition temperature.

The ignition temperature of the exothermic composition with the lower ignition temperature may be less than about 1200 °C, preferably less than about 1000 °C, e. g. between about 800 °C and about 1000 °C.

Typically, the first exothermic composition and the second exothermic composition are in particulate form with the metals and metal oxides, as powders or flakes, being closely bound in the particles. Thus, typically, the first exothermic composition and the second exothermic composition are in granulated or prilled form, with the granules or prills preferably being water-resistant and of homogenous composition.

The first exothermic composition and/or the second exothermic composition may include a binder. The inventors are aware of many suitable binders, e. g. polyalkylene carbonates, resins, starch-based aqueous binders, sodium silicate, and the like. One example of a particularly suitable binder is a phenolic resin.

The metal may in principle be any metal from the periodic table of elements or alloys of such metals capable of thermitic reactions with metal oxides. Typically, for both the first exothermic composition and the second exothermic composition, the metal is selected from the group consisting of aluminium, aluminium alloy, magnesium, magnesium/aluminium alloy, and two or more of these, without a requirement that the metal must be the same for the first exothermic composition and the second exothermic composition, although they may be the same.

The metal oxide may in principle be any oxide of a meta ! of the periodic table of elements capable of thermitic reactions with metals or metal alloys. Typically, for both the first exothermic composition and the second exothermic composition, the metal oxide is selected from the group consisting of Fe203, Fe304, MnO3, Mu02, and two or more of these, without a requirement that the metal oxide must be the same for the first exothermic composition and the second exothermic composition, although they may be the same.

The combustible product may be in the form of a solid body, the solid body being characterised in that it retains its shape during combustion. By"solid"is meant that the body is firm and stable in shape. The body may thus be hollow, if desired.

Preferably, the solid body is porous. Advantageously, porous bodies have improved heat transfer rates when used as a heat source compared to non-porous bodies.

At least one of the first exothermic composition and the second exothermic composition may thus include a shape-retaining agent to enable the combustible product to retain its body shape during combustion. Examples of suitable shape- retaining agents are aluminium oxide and silicon oxide, the aluminium oxide thus not necessarily being included as a metal oxide for taking part in the exothermic reaction, but rather as a shape-retaining agent and to provide heat insulation properties. The aluminium oxide may also act as a catalyst in the exothermic reaction when the first exothermic composition and/or the second exothermic composition includes aluminium as the metal. Typically, it is the first exothermic composition which includes the shape- retaining agent.

When the first exothermic composition includes one or more shape-retaining agents, the shape-retaining agent or agents may form between about 10 % and about 40 %, preferably between about 15 % and about 25 %, of the first exothermic composition.

In one embodiment of the invention, the first exothermic composition includes between about 5 % and about 20 % aluminium oxide and between about 10 % and about 20 % silicon oxide, both as shape-retaining agents.

The first exothermic composition and/or the second exothermic composition may include an accelerant and/or ignition temperature modifier. Examples of suitable accelerants/ignition temperature modifiers are metal salts (e. g. sodium nitrate), strong oxidizer salts (e. g. KMn04 and KC104), coal dust, easily ignitable metals (e. g. magnesium), redox mixtures (e. g. silicon red lead/lead oxides), organic or inorganic oxidising or reducing agents (e. g. sulphur and teflon), and sodium aluminium fluoride.

When the first exothermic composition includes an accelerant, it may be present in a range between about 5 % and about 30 %.

When the second exothermic composition includes an accelerant, it may be present in a range between about 1 % and about 50 %. In one embodiment of the invention, the second exothermic composition includes aluminium and iron oxide as metal and metal oxide, and sodium nitrate as an accelerant, the sodium nitrate being in a concentration of about 28 % of the combined mass of aluminium and iron oxide present in the second exothermic composition.

The metal of the first exothermic composition capable of reacting exothermically with the metal oxide may be present in the first exothermic composition in a range with a lower limit of about 50 %, or lower at about 45 %, or even as low as about 15 %. An upper limit of the range may be about 75 %, or higher at about 80 %, or even as high as about 90 %.

The metal oxide of the first exothermic composition capable of reacting exothermically with the metal may be present in the first exothermic composition in a range with a lower limit of about 2 %, or lower at about 1.5 %, or even as low as about 1 %. An upper limit of the range may be about 5 %, or higher at about 8 %, or even as high as about 85 %.

The metal of the second exothermic composition capable of reacting exothermically with the metal oxide may be present in the second exothermic composition in a range with a lower limit of about 35 % or lower at about 30 %, or even as low as about 25 %. An upper limit of the range may be about 70 %, or even higher at about 85 %, or even as high as about 90 %.

The metal oxide of the second exothermic composition capable of reacting exothermically with the metal may be present in the second exothermic composition in a range with a lower limit of about 20 %, or lower at about 15 %, or even as low as about 10 %. An upper limit of the range may be about 75 %, or higher at about 85 %, or even as high as about 95 %.

The combustible product may include the first exothermic composition and the second exothermic composition in a mass ratio falling in a range with a lower limit of about 1: 0.16. The lower limit may be as low as about 1: 0.05, or even as low as about 1: 0.02. An upper limit of the range may be about 1: 0.5, or higher at about 1: 0.6, or even as high as about 1: 0.8. In one embodiment of the invention, with the metal being aluminium in both the first exothermic composition and the second exothermic t 1 composition, and the metal oxide being iron oxide in both the first exothermic composition and the second exothermic composition, the combustible product includes the first exothermic composition and the second exothermic composition in a mass ratio of about 1: 0.25.

The combustible product may burn in air at a temperature of between about 1500 °C and about 3500 °C, typically between about 2000 °C and about 3000 °C, e. g. between about 2800 °C and about 3000 °C.

According to a further aspect of the invention, there is provided a combustible product which comprises a solid body which includes an admixture of a first exothermic composition and a second exothermic composition, the first exothermic composition including a metal and a metal oxide capable of reacting exothermically with each other, and the second exothermic composition including a metal and a metal oxide capable of reacting exothermically with each other, the solid body being characterised in that it retains its shape during combustion.

The first exothermic composition and the second exothermic composition may be as hereinbefore described.

Thus, in particular, the metal of the first exothermic composition may be in stoichiometric excess by a factor of at least about 9, in the first exothermic composition; one of the first exothermic composition and the second exothermic composition may have a lower ignition temperature than the other of the second exothermic composition and the first exothermic composition; the exothermic composition with the lower ignition temperature may have a higher calorific value than the other exothermic composition; the ignition temperature of the exothermic composition with the lower ignition temperature may be less than about 1200 °C; the first exothermic composition and the second exothermic composition may be in granulated or prilled form, with the granules or prills being water-resistant and of homogenous composition; for both the first exothermic composition and the second exothermic composition, the metal may be selected from the group consisting of aluminium, aluminium alloy, magnesium, magnesium/aluminium alloy, and two or more of these, without a requirement that the metal must be the same for the first exothermic composition and the second exothermic composition, and, for both the first exothermic composition and the second exothermic composition, the metal oxide may be selected from the group consisting of Fe203, Fe304, MnO3, Mg02, and two or more of these, without a requirement that the metal oxide must be the same for the first exothermic composition and the second exothermic composition; the solid body may be porous; at least one of the first exothermic composition and the second exothermic composition may include a shape-retaining ! agent to enable the combustible product to retain its body shape during combustion; the first exothermic composition may include one or more shape-retaining agents, the shape-retaining agent or agents forming between about 10 % and about 40 % by weight of the first exothermic composition; the first exothermic composition and/or the second exothermic composition may include an accelerant and/or ignition temperature modifier; the metal of the first exothermic composition capable of reacting exothermically with the metal oxide may be present in the first exothermic composition in a range with a lower limit of about 15 % and an upper limit of about 90 %, and the metal oxide of the first exothermic composition capable of reacting exothermically with the metal may be present in the first exothermic composition in a range with a lower limit of about 1 % and an upper limit of about 85 %; the metal of the second exothermic composition capable of reacting exothermically with the metal oxide may be present in the second exothermic composition in a range with a lower limit of about 25 % and an upper limit of about 90 %, and the metal oxide of the second exothermic composition capable of reacting exothermically with the metal may be present in the second exothermic composition in a range with a lower limit of about 10 % and ! ar) upper limit of about 95 %; the first exothermic composition and the second exothermic composition may be in a mass ratio falling in a range with a lower limit of about 1: 0.02 and an upper limit of about 1: 0.8 ; and the combustible product may burn in air at a temperature of between about 1500 °C and about 3500 °C.

According to yet another aspect of the invention, there is provided process for producing a combustible product, the process including forming an admixture which includes a first exothermic composition and a second, different, exothermic composition, the first exothermic composition including a metal and a metal oxide capable of reacting exothermically with each other, with the metal being in stoichiometric excess, and the second exothermic composition including a metal and a metal oxide capable of reacting exothermically with each other.

According to yet a further aspect of the invention, there is provided a process for producing a combustible product, the process including forming an admixture which includes a first exothermic composition and a second exothermic composition, the first exothermic composition including a metal and a metal oxide capable of reacting exothermically with each other, and the second exothermic composition including a metal and a metal oxide capable of reacting exothermically with each other, one of the first exothermic composition and the second exothermic composition having a lower ignition temperature than the other of the second exothermic composition and the first exothermic composition.

The process may include forming a solid body from the admixture.

Forming a solid body from the admixture may include mixing the admixture or the first exothermic composition and the second exothermic composition with a resin to form a moulable composition, moulding the moulable composition, and curing the resin to provide a solid body of a desired shape. The so-called"cold box moulding process"may be used for this, with conventional cold box resins being suitable.

Instead, forming a solid body from the admixture may include mixing the admixture or the first exothermic composition and the second exothermic composition with an aqueous binder to form a moulable composition, moulding the moulable composition, and drying the moulable composition to provide a solid body of a desired shape.

In another embodiment of the invention, forming a solid body from the admixture includes compressing the admixture with or without a resin or a binder into a solid body of a desired shape, followed by a curing process, if required.

Preferably, the solid body is porous.

Preferably, the resin is a water-resistant resin. Instead, or in addition, the granules or prills of the first and/or the second exothermic composition may be coated with one or more water resistant coatings.

The method may include adjusting the pH of the resin.

The resin or binder may be present in a concentration of between about 1 % and about 15 %, typically between about 2 % and about 10 %, of the weight of the solid body.

The first exothermic composition and the second exothermic composition may be as hereinbefore described, and the combustible product may be as hereinbefore described.

Thus, in particular, the metal may be in stoichiometric excess by a factor of at least about 9, in the first exothermic composition; the second exothermic composition may have an ignition temperature which is lower than an ignition temperature of the first exothermic composition; the first exothermic composition and the second exothermic composition may be in particulate form with the metals and metal oxides being closely bound in the particles ; for both the first exothermic composition and the second exothermic composition, the metal may be selected from the group consisting of aluminium, aluminium alloy, magnesium, magnesium/aluminium alloy, and two or more of these, without a requirement that the metal must be the same for the first exothermic composition and the second exothermic composition, and, for both the first exothermic composition and the second exothermic composition, the meta ! oxide may be selected <BR> <BR> <BR> from the group consisting of Fe203, Fe304, MnO3, Mg02, and two or more of these,<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> without a requirement that the metal oxide must be the same for the first exothermic composition and the second exothermic composition; and the first exothermic composition and the second exothermic composition may be admixed in a ratio falling in a range with a lower limit of about 1: 0.02 and an upper limit of about 1: 0.8.

The invention extends to the use of a combustible product which includes at least one exothermic composition comprising a metal and a metal oxide capable of reacting exothermically with each other and which is in the form of a solid body that retains its shape during combustion, as a heat source, the metal and metal oxide forming at least about 20 % by mass of the combustible product.

The metal and metal oxide may form at least about 30 %, preferably at least about 40 %, more preferably at least about 50 % by mass of the combustible product.

The combustible product may be as hereinbefore described.

The combustible product may be in brick form, and may be used to ignite fuel in an oven. In one particular embodiment of the invention, the combustible product is used to ignite coal in a clay brick manufacturing oven.

The combustible product may be ignited using an ignition sachet or an ignition pellet, which may comprise, or which may consist of, the second exothermic composition.

The invention will now be described in more detail, by way of example.

EXAMPLE An exothermic combustible product in accordance with the invention was prepared, based on aluminium and iron oxide being the metal and metal oxide in both the first exothermic composition and the second exothermic composition. The first exothermic composition had the following composition and characteristics: Aluminium (Samex 2) 52. 5 % Aluminium Oxide 17. 5 % Silicon (IV) Oxide 1. 8 % Sodium Nitrate 6. 0 % Iron Oxide (Fe203) 1. 8 % Resin Binder 20. 4 % Sizing-1.5 mm + 0. 300 mm Free flowing apparent density 1.25 g/cm3 The second exothermic composition had the following composition and characteristics: Aluminium (Samex 1) 39. 5 % Iron Oxide (Fe203) 21. 32 % Sodium Nitrate 26.18 % Resin binder 13. 00 % Sizing -1.5 + 0.300 mm Free flowing apparent density 1.25 g/cm3 The aluminium used for the first exothermic composition was in the form of aluminium flakes, which is sold under the trade name Samex 2 and available from Metlite Alloys (Gauteng) (Pty) Ltd of 18 Ampere Road, Labore, Brakpan, 1540, South Africa. The aluminium used in the second exothermic composition was also in the form of aluminium flakes, as sold under the trade name Samex 1 and also available from Metlite Alloys (Gauteng) (Pty) Ltd. The Samex aluminium was obtained from raw, waste aluminium such as waste aluminium dross, slag, shavings and foil, which was milled. Both of the Samex 1 and Samex 2 aluminium products are typically prepared in accordance with the method disclosed in the specification of South African Patent No.

92/6995, which is incorporated in its entirety herein by way of reference. The aluminium oxide in the first exothermic composition comes from the Samex 2 aluminium product, which includes aluminium oxide.

The iron oxide used is typically obtained from iron oxide fines recovered from the tailings from mining processes of ore bodies or from other production processes.

Before processing into the first and second exothermic compositions, the iron oxide (Fe203) was in powdery form.

The first exothermic composition and the second exothermic composition were used in granulated form. The granulation process as disclosed in the specification of South African Patent Application No. 2000/6014 was used to granulate the raw materials.

The exothermic combustible product was then formed into a brick consisting of 80 % of the first, granulated exothermic composition and 20 % of the second, granulated exothermic composition. The brick was formed by admixing the first exothermic composition and the second exothermic composition and a phenolic resin, feeding the admixture into a mould, and curing the phenolic resin by gassing the admixture with tri-ethylamine gas. As will be appreciated, this so-called"cold box" forming process can be used to provide solid bodies of any desired shape. The cold box forming process is disclosed in more detail in the specification of South African Patent Application No. 2001/9541, which is incorporated herein by way of reference. It is to be noted that manufacturing of the solid body was also successful using mechanical compression techniques.

The resultant brick-shaped exothermic combustible product was porous. The brick-shaped product had a length of 200 mm, a width of 75 mm and a height of 50 mm.

A 25 mm diameter hole, with a depth of 40 mm, was moulded into the brick-shaped body.

It was determined that the brick-shaped combustible product had an ignition temperature of about 1200 °C and that it burnt in air at a temperature of about 3000 °C, once ignited. Due to the insulating properties of the brick, temperatures of 2600 °C to 2800 °C were sustained for approximately 30 minutes after combustion.

In order to ignite the product, an igniter pellet or an ignition sachet can be used. Advantageously, the igniter pellet, or the contents of the ignition sachet can be manufactured from the prilled or granulated second exothermic composition, or can consist of the prilled or granulated second exothermic composition. Furthermore, the igniter pellet can be formed using the same cold box forming process as described above, such that it fits snugly into the moulded aperture in the brick-shaped solid body.

A range of raw materials is available and suitable for the sachet of the ignition sachet, such as linen, paper and synthetic materials. The igniter pellets and the ignition sachets can be ignited using an igniter cord, a sparkler or the like.

During the combustion of the brick-shaped combustible product, the product retains its shape and thus, once the combustion process has been completed, a brick- shaped residue is left behind. Advantageously, in contrast to prior art combustible products of which the applicants are aware, the exothermic combustible product of the invention does not produce a visible slag residue. Instead, any slag which may be formed as a result of the exothermic reaction taking place between the metals and metal oxides, is retained inside the three-dimensional structure of the solid product.

When aluminium is used as the metal in the combustible product, corundum is formed during the combustion process, assisting in retaining the shape of the solid body during and after combustion.

As will be appreciated, there are many applications for a combustible product in accordance with the invention, particularly when in a solid form, and particularly as a source of heat. Examples of such applications are incineration, the melting of scrap metal, illegal firearms, metal junk, etc., particularly on site, to provide compact blocks of metal which can be safely and affordably transported, in ignition/initiation processes for demilitarisation of time-expired ammunition, unexploded i ordinance and landmine clearance operations, in pyrotechnics and in continuous processes where a substrate mixture is fed and burned in an oven, with the combustible product supplying the heat necessary for the processing once ignited by the oven.

One particular application of the combustible product is for use as a heat source to ignite coal used in clay brick manufacturing processes. The combustible product, in brick form, can easily be used and stacked in kilns or ovens used to manufacture clay bricks. The combustible product can replace the expensive, resistance heating oven plates and other conventional methods currently used to ignite the coal. Typically, about five ignition points are used in the ovens.

Advantageously, the combusted bricks can be recovered from the ovens and recycled to obtain metals and metal alloys which can be reused in a process to manufacture the combustible product of the invention. Similarly, any reject product can be easily recycled by milling the product.

The combustible product of the invention, as exemplified, advantageously uses waste material, such as aluminium dross, as raw material. The product has a high calorific value and a low ignition temperature and retains its shape during and after combustion. This last feature makes it easy to remove the combusted product from kilns, ovens, and the like and facilitates recycling of the combusted product.