Claims:WE CLAIM:

1. Iron powder having metallic iron content of about 99% and having ratio of apparent density to particle true density in range of about 0.08 to 0.11.

2. The iron powder as claimed in claim 1, wherein the iron powder has particle true density ranging from about 7.7 g/cc to 7.85 g/cc; apparent density ranging from about 0.65 g/cc to 0.85 g/cc; tap density ranging from about 0.8 g/cc to 1 g/cc; and surface area ranging from about 2 m2/g to 9 m2/g.

3. The iron powder as claimed in claim 1, wherein the iron powder has porosity ranging from about 75% to 85%.

4. The iron powder as claimed in claim 1, wherein the iron powder has average particle size ranging from about 15 microns to 40 microns.

5. The iron powder as claimed in claim 1, wherein iron powder comprises:
10% of size fraction less than 3 micron;
50 % of size fraction less than 10 micron; and
90 % of size fraction less than 50 micron, when iron oxide is reduced in the temperature range of 400°C to 500°C.

6. The iron powder as claimed in claim 1, wherein iron powder comprises:
10% of size fraction less than 5 micron;
50 % of size fraction less than 15 micron; and
90 % of size fraction less than 65 micron when iron oxide is reduced in the temperature range of 500°C to 600°C;

7. The iron powder as claimed in claim 1, wherein iron powder comprises:
10% of size fraction less than 15 micron;
50 % of size fraction less than 45 micron; and
90 % of size fraction less than 75 micron when iron oxide is reduced in the temperature range of 600°C to 700°C.

8. The iron powder as claimed in claim 1, wherein iron powder comprises:
10% of size fraction less than 20 micron;
50 % of size fraction less than 50 micron; and
90 % of size fraction less than 105 micron when iron oxide is reduced in the temperature range of 700°C to 800°C.

9. A process for producing iron powder, comprising steps of:
heating iron oxide at a temperature ranging from about 400°C to 800°C, followed by reducing the heated iron oxide in static bed condition to obtain reduced iron;
cooling the reduced iron; and
pulverizing the cooled iron to obtain iron powder.

10. The process as claimed in claim 9, comprises a step of screening the iron oxide having particle size lesser than 150 microns before subjecting to heating, wherein the screening is carried out using a mesh.

11. The process as claimed in claim 9, wherein the heating is carried under inert atmosphere in presence of nitrogen or argon or a combination thereof.

12. The process as claimed in claim 9, wherein the reduction is carried out under reducing atmosphere in presence of hydrogen for a period ranging from about 120 minutes to 240 minutes and wherein the reduction is carried out at a temperature ranging from about 400°C to 800°C

13. The process as claimed in claim 9, wherein the reducing is carried out under reducing atmosphere for a period ranging from about 120 minutes to 300 minutes by supplying cracked Ammonia gas and wherein the reduction is carried out at a temperature ranging from about 400°C to 800°C.

14. The process as claimed in claim 9, wherein the reduced iron is cooled to a temperature ranging from about 20°C to 40°C under inert atmosphere in presence of nitrogen or argon or a combination thereof.

15. The process as claimed in claim 9, wherein the pulverising is carried out to obtain the iron powder having average particle size ranging from about 15 microns to 40 microns.

16. The process as claimed in claim 9, wherein purity of iron in the iron powder is about 99%.

17. The process as claimed in claim 9, wherein pyrophoric tendency of iron powder is arrested by maintaining the temperature of reduction above 600°C.

18. The process as claimed in claim 9, wherein pyrophoric tendency of iron powder is arrested due to inter particle sintering of individual iron powder particles.

19. The process as claimed in claim 9, wherein the iron powder has surface area ranging from about 2 m2/g to 9 m2/g, the iron powder has apparent density to particle true density ratio lesser than 0.11, the iron powder has particle true density ranging from about 7.7 g/cc to 7.85 g/cc, apparent density ranging from about 0.65 g/cc to 0.85 g/cc, tap density ranging from about 0.8 g/cc to 1 g/cc, the iron powder has porosity ranging from about 75% to 85%.

Dated this 02nd day of November, 2017

Durgesh Mukharya
IN/PA-1541
Of K&S Partners
Agent for the Applicant
To:
The Controller of Patents,
The Patent Office, at: Kolkata , Description:TECHNICAL FIELD
The present disclosure relates a field of metallurgy in general. The disclosure describes an iron powder with high purity and high surface area. The disclosure also relates to a process of preparing said iron powder with high purity and high surface area.

BACKGROUND OF THE DISCLOSURE
Manufacturing of iron powder through various raw materials and reducing agents is not new to the world, more interest is laid on the synthesis of potential iron powder with advanced physical and chemical properties. Iron powders with high purity and high surface area finds its application in porous electrodes, water treatment, food agriculture, catalyst, electromagnetic and metal fuel applications.

However, the iron powder known in the art is either produced through fluidized bed reduction which is very complex process or at high reduction temperatures which increases the cost of production and cost of the final product. The known processes also employ ferrous salts which results in residual impurities in the iron powder. Thus, there appears to be a need to overcome the limitation or disadvantages observed in the iron powder and the process of preparing the same. The present disclosure aims at overcoming such limitations and the disadvantages.

SUMMARY OF THE DISCLOSURE
Accordingly, the present disclosure relates to an iron powder having purity of iron at least 99% or about 99.5 % and having ratio of apparent density to particle true density ranging from about 0.08 to 0.11

In an embodiment, the present disclosure relates to an iron powder having particle true density ranging from about 7.7 g/cc to 7.85 g/cc; apparent density ranging from about 0.65 g/cc to 0.85 g/cc; tap density ranging from about 0.8 g/cc to 1 g/cc; and surface area ranging from about 2 m2/g to 9 m2/g.

The present disclosure also relates to a process of preparing the iron powder, comprising steps of:
heating iron oxide at a temperature ranging from about 400°C to 800°C, followed by reducing the heated iron oxide in static bed condition to obtain reduced iron;
cooling the reduced iron; and
pulverizing the cooled iron to obtain iron powder.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
In order that the disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present disclosure where:

FIGURE 1 illustrates the X-ray powder diffraction (XRD) analysis data of the iron powder.

FIGURE 2 illustrates the scanning electron microscope (SEM) analysis data of the iron powder.

FIGURE 3 illustrates the SEM analysis data of the iron powder at reduction temperatures 450°C, 550°C, 650°C and 750°C, respectively.

DETAILED DESCRIPTION
The present disclosure relates to iron powder.

The present disclosure relates particularly to iron powder having surface area ranging from about 2m2/g to 9m2/g.

In an embodiment, the iron powder has surface area of about 2 m2/g, about 2.5 m2/g, about 3 m2/g, about 3.5 m2/g, about 4 m2/g, about 4.5 m2/g, about 5 m2/g, about 5.5 m2/g, about 6 m2/g, about 6.5 m2/g, about 7 m2/g, about 7.5 m2/g, about 8 m2/g, about 8.5 m2/g or about 9 m2/g.

In an embodiment, the iron powder has iron having purity of at least 99%.

In another embodiment, the iron powder has iron having purity of about 99.1%, about 99.2%, about 99.3%, about 99.4% or about 99.5%.

In an embodiment, the iron powder comprises iron content of at least 99%.

In an embodiment, the iron powder comprises iron content of about 99.1%, about 99.2%, about 99.3%, about 99.4% or about 99.5%.

In an embodiment, the iron powder comprises iron ranging from about 99 % to 99.5%, carbon at about 0.1%, sulphur at about 0.02%, oxygen at about 0.1% to 0.5%, phosphorus at about 0.05%, manganese at about 0.2%, calcium at about 0.04% and magnesium, cadmium, lead, argon, and mercury at about 0.01%.

In an embodiment, the iron powder has true density ranging from about 7.77g/cc to 7.85g/cc.
In another embodiment, the iron powder has true density of about 7.77g/cc, about 7.78 g/cc, about 7.79 g/cc, about 7.80 g/cc, about 7.81 g/cc, about 7.82 g/cc, about 7.83 g/cc, about 7.84 g/cc or about 7.85 g/cc.

In an embodiment, the iron powder has apparent density ranging from about 0.65g/cc to 0.85 g/cc.

In another embodiment, the iron powder has apparent density of about 0.65 g/cc, about 0.66 g/cc, about 0.67 g/cc, about 0.68 g/cc, about 0.69 g/cc. about 0.70 g/cc, about 0.71 g/cc, about 0.72 g/cc, about 0.73 g/cc, about 0.74 g/cc, about 0.75 g/cc, about 0.76 g/cc, about 0.77 g/cc, about 0.78 g/cc, about 0.79 g/cc, about 0.80 g/cc, about 0.81 g/cc, about 0.82 g/cc, about 0.83 g/cc, about 0.84 g/cc or about 0.85 g/cc.

In an embodiment, ratio of apparent density to true density of the iron powder is ranging from about 0.08 to 0.11.

In an embodiment, the iron powder has tap density ranging from about 0.8g/cc to 1 g/cc.

In another embodiment, the iron powder has tap density of about 0.82 g/cc, about 0.84 g/cc, about 0.86 g/cc, about 0.88 g/cc, about 0.90 g/cc, about 0.92 g/cc, about 0.94 g/cc, about 0.96 g/cc, about 0.98 g/cc or about 1.0 g/cc.

In an embodiment, the iron powder has porosity ranging from about 75% to 85%.

In another embodiment, the iron powder has porosity of about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84% or about 85%.

In an embodiment, the iron powder has average particle size ranging from about 15microns to 40microns.

In another embodiment, the iron powder has average particle size of about 15 microns, about 17 microns, about 19 microns, about 21 microns, about 23 microns, about 25 microns, about 27 microns, about 29 microns, about 31 microns, about 32 microns, about 33 microns, about 34 microns, about 35 microns, about 36 microns, about 37 microns¸ about 38 microns, about 39 microns or about 40 microns.

The present disclosure further relates to a process of preparing the iron powder described above, wherein the process is less complex when compared to the processes known in the art to produce iron powder. The said process produces iron powder with enhanced surface area and enhanced purity.

In another embodiment, the process is simple yet highly efficient process to produce iron powder with enhanced surface area and enhanced purity and special physical properties. Also, the process is economical as it uses reduced temperatures for heating the raw material and reduced temperatures for reduction.

In an embodiment, iron powder with enhanced surface area and enhanced purity having special physical and chemical properties is produced from industrial by-product material including but is not limiting to iron oxide obtained from spray roasting of acid pickle liquor.

In an embodiment, the iron oxide includes but is not limited to ferrous oxide, ferric oxide and ferric oxy-hydroxides.

In an embodiment, the process of producing the iron powder comprises steps of-
heating iron oxide, followed by reducing the heated iron oxide in static bed condition to obtain reduced iron;
cooling the reduced iron; and
pulverising the cooled iron to obtain the iron powder.

In an embodiment, the iron oxide prior to heating is subjected to screening to select those iron oxides having particle size less than 150 micron using 150 micron sieve.

In an embodiment, the iron oxide is heated to a temperature ranging from about 400°C to 800°C.

In another embodiment, the iron oxide is heated to a temperature of about 400°C, about 450°C, about 500°C, about 550°C, about 600°C, about 650°C, about 700°C, about 750°C or about 800°C.

In an embodiment, the iron oxide is heated under inert atmosphere in presence of nitrogen or argon or a combination thereof.

In an embodiment, during the said process, when the iron oxide reaches a temperature ranging from about 400°C to 800°C, the iron oxide is subjected to reduction under reducing atmosphere in presence of hydrogen for a period ranging from about 120 minutes to 240 minutes.

In an embodiment, the heated iron oxide is subjected to reduction under reducing atmosphere in presence of hydrogen for a period of about 120 minutes, about 140 minutes, about 160 minutes, about 180 minutes, about 200 minutes, about 220 minutes, or about 240 minutes.

In an embodiment, the reduction of the iron oxide under reducing atmosphere is carried out at a temperature ranging from about 400°C to 800°C.

In an embodiment, the reduction of the iron oxide is carried out using reducing agent selected from a group comprising hydrogen and cracked ammonia or a combination thereof.

In another embodiment, the reduction of the iron oxide under reducing atmosphere is carried out at a temperature of about 400°C, about 450°C, about 500°C, about 550°C, about 600°C, about 650°C, about 700°C, about 750°C or about 800°C, under reducing atmosphere in presence of hydrogen.

In an embodiment, in the above described process when the iron oxide is heated and reduced in presence of hydrogen at a temperature ranging from about 400°C to 600°C, it causes pyrophoricity of the iron powders. However, heating and reduction in presence of hydrogen at a temperature ranging from about 600°C to 800 0C arrests pyrophoric tendency of iron powders due to inter particle sintering of individual iron powders particles leading to lower surface area, reveals that any reduction temperatures beyond 600 0C would arrest the pyrophoricity of iron powders.

In an embodiment, the reduced iron oxide is cooled to a temperature ranging from about 20°C to 40°C, under inert atmosphere in presence of nitrogen or argon or a combination thereof.

In another embodiment, the reduced iron oxide is cooled to a temperature of about 20°C, about 25°C, about 30°C, about 35°C or about 40°C, under inert atmosphere in presence of nitrogen or argon or a combination thereof.

In an embodiment, upon cooling, the cooled iron is subjected to pulverising to obtain iron powder having average particle size ranging from about 15microns to 40microns.

In another embodiment, the pulverising is carried out to obtain iron powder having average particle size of about 15 microns, about 17 microns, about 19 microns, about 21 microns, about 23 microns, about 25 microns, about 27 microns, about 29 microns, about 31 microns, about 32 microns, about 33 microns, about 34 microns, about 35 microns, about 36 microns, about 37 microns¸ about 38 microns, about 39 microns or about 40 microns.

In an embodiment, the iron powder obtained upon reducing iron oxide at a temperature ranging from about 400°C to 500°C comprises 10% of the fraction at a particle size less than 3 micron, 50% of the fraction at a particle size less than 10 micron and 90% of the fraction at a particle size less than 50 micron, cumulatively.

In an embodiment, the iron powder obtained upon reducing iron oxide at a temperature ranging from about 500°C to 600°C comprises 10% of the fraction at a particle size less than 5 micron, 50% of the fraction at a particle size less than 15 micron and 90% of the fraction at a particle size less than 65 micron, cumulatively.

In an embodiment, the iron powder obtained upon reducing iron oxide at a temperature ranging from about 600°C to 700°C comprises 10% of the fraction at a particle size less than 15 micron, 50% of the fraction at a particle size less than 45 micron and 90% of the fraction at a particle size less than 75 micron, cumulatively.

In an embodiment, the iron powder obtained upon reducing iron oxide at a temperature ranging from about 700°C to 800°C comprises 10% of the fraction at a particle size less than 20 micron, 50% of the fraction at a particle size less than 50 micron and 90% of the fraction at a particle size less than 105 micron, cumulatively.

In an embodiment, the iron powder obtained by the process described above has surface area ranging from about 2m2/g to 9m2/g.

In another embodiment, the iron powder obtained by the process described above has surface area of about 2 m2/g, about 2.5 m2/g, about 3 m2/g, about 3.5 m2/g, about 4 m2/g, about 4.5 m2/g, about 5 m2/g, about 5.5 m2/g, about 6 m2/g, about 6.5 m2/g, about 7 m2/g, about 7.5 m2/g, about 8 m2/g, about 8.5 m2/g or about 9 m2/g.

In an embodiment, the iron powder has surface area ranging from about 2 m2/g to 3 m2/g when the iron oxide is reduced at a temperature ranging from about 700°C to 800°C.

In another embodiment, the iron powder has surface area ranging from about 3 m2/g to 5 m2/g when the iron oxide is reduced at a temperature ranging from about 600°C to 700°C.

In another embodiment, the iron powder has surface area ranging from about 5 m2/g to 8 m2/g when the iron oxide is reduced at a temperature ranging from about 500°C to 600°C.

In another embodiment, the iron powder has surface area ranging from about 8 m2/g to 9 m2/g when the iron oxide is reduced at a temperature ranging from about 400°C to 500°C.

In an embodiment, the iron powder obtained by the process described above has purity of iron at least 99%.

In another embodiment, the iron powder obtained by the process described above has purity of iron of about 99.1%, about 99.2%, about 99.3%, about 99.4% or about 99.5%.

In an embodiment, the iron powder obtained by the process described above has iron content of at least 99%.

In another embodiment, the iron powder obtained by the process described above has iron content of about 99.1%, about 99.2%, about 99.3%, about 99.4% or about 99.5%.

In an embodiment, the iron powder obtained by the process described above comprises iron at about 99% to 99.5%, carbon at about 0.1%, sulphur at about 0.02%, oxygen at about 0.1% to 0.5%, phosphorus at about 0.05%, manganese at about 0.2%, calcium at about 0.04% and magnesium, cadmium, lead, argon and mercury at about 0.01%.

In an embodiment, the iron powder obtained by the process described above has true density ranging from about 7.77g/cc to 7.85g/cc.

In another embodiment, the iron powder obtained by the process described above has true density of about 7.77g/cc, about 7.78 g/cc, about 7.79 g/cc, about 7.80 g/cc, about 7.81 g/cc, about 7.82 g/cc, about 7.83 g/cc, about 7.84 g/cc or about 7.85 g/cc.

In an embodiment, the iron powder obtained by the process described above has apparent density ranging from about 0.65g/cc to 0.85 g/cc.

In another embodiment, the iron powder obtained by the process described above has apparent density of about 0.65 g/cc, about 0.66 g/cc, about 0.67 g/cc, about 0.68 g/cc, about 0.69 g/cc. about 0.70 g/cc, about 0.71 g/cc, about 0.72 g/cc, about 0.73 g/cc, about 0.74 g/cc, about 0.75 g/cc, about 0.76 g/cc, about 0.77 g/cc, about 0.78 g/cc, about 0.79 g/cc, about 0.80 g/cc, about 0.81 g/cc, about 0.82 g/cc, about 0.83 g/cc, about 0.84 g/cc or about 0.85 g/cc.

In an embodiment, the iron powder obtained by the process described above has ratio of apparent density to true density is ranging from about 0.08 to 0.11.

In an embodiment, the iron powder obtained by the process described above has tap density ranging from about 0.8g/cc to 1 g/cc.

In another embodiment, the iron powder obtained by the process described above has tap density of about 0.82 g/cc, about 0.84 g/cc, about 0.86 g/cc, about 0.88 g/cc, about 0.90 g/cc, about 0.92 g/cc, about 0.94 g/cc, about 0.96 g/cc, about 0.98 g/cc or about 1.0 g/cc.

In an embodiment, the iron powder obtained by the process described above has porosity ranging from about 75% to 85%.

In another embodiment, the iron powder obtained by the process described above has porosity of about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84% or about 85%.

In an embodiment, the iron powder obtained by the process described above has average particle size ranging from about 15microns to 40microns.

In another embodiment, the iron powder obtained by the process described above has average particle size of about 15 microns, about 17 microns, about 19 microns, about 21 microns, about 23 microns, about 25 microns, about 27 microns, about 29 microns, about 31 microns, about 32 microns, about 33 microns, about 34 microns, about 35 microns, about 36 microns, about 37 microns¸ about 38 microns, about 39 microns or about 40 microns.

Additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon the description provided. The embodiments provide various features and advantageous details thereof in the description. Descriptions of well-known/conventional methods and techniques are omitted so as to not unnecessarily obscure the embodiments. The examples provided herein are intended merely to facilitate an understanding of ways in which the embodiments provided may be practiced and to further enable those of skill in the art to practice the embodiments provided. Accordingly, the following examples should not be construed as limiting the scope of the embodiments.

EXAMPLES

EXAMPLE 1: Preparation of Iron Powder at reducing temperature of about 450°C
Iron oxide with chemical composition as described in Table 1 below and having particle size 0.5- 150 micron is taken as raw material.
About 100 g iron oxide is filled in semi cylindrical ceramic boats and height of the iron oxide powder bed in the boat is maintained at less than 25mm in static bed condition. Iron oxide is heated to a temperature of about 450°C under inert atmosphere in a furnace. After the temperature of about 450°C is achieved the furnace ambience is switched to reducing atmosphere by supplying hydrogen for a period of about 240 minutes. The reduced iron is cooled to a temperature ranging from about 20°C to 40°C under inert atmosphere. The cooled iron is ground to less than 150 micron size to obtain iron powder. The chemical composition of the obtained iron powder is described in Table 2 below.
The iron powder was subjected to X-ray powder diffraction (XRD) and scanning electron microscope (SEM). The figures 1 and 2 illustrate the XRD analysis data and SEM analysis data, respectively.
The SEM analysis data illustrates that the micron range particle size of the iron powder is formed due to the inter particle bonding of numerous nano range particles resulting in large surface area and high internal porosity.
XRD analysis of the iron powder sample is performed to depict the purity of the iron powder formed. XRD pictograph of the iron powder showcases three strong peaks in the 2? range of 44.5 to 45.6, 64.5 to 65.6 and 82 to 83, which reveals the significant presence of pure iron. Presence of no other peaks in the entire XRD graph reveals the purity of the iron formed with no traceable impurities.
The iron powder obtained has true density of about 7.8 g/cc and has surface area of about 8.095m2/g.

Composition
(%) Fe2O3 MgO CaO SiO2 Al2O3 MnO P Cu V Cl
Iron Oxide
Powder 99.79 0.003 0.03 0.022 0.05 0.07 0.008 0 0.0009 0.07

Table 1: Chemical composition of iron oxide

Composition
(%) Fe (met) O2 C S P Mg Mn Ca Others
Iron Powder 99.5 0.1 0.05 0.01 0.05 0.01 0.2 0.07 ~ 0.001

Table 2: Chemical composition of iron powder.

Example 2: Preparation of Iron powder at reducing temperature of about 550°C
Experimental procedure and conditions are similar to as mentioned in Example 1. However, the iron oxide is heated and reduced at a temperature of about 550°C.
The iron powder obtained has surface area of about 6.66m2/g and having true density of about 7.8 g/cc.

Example 3: Preparation of Iron powder at reducing temperature of about 650°C
Experimental procedure and conditions are similar to as mentioned in Example 1. However, the iron oxide is heated and reduced at a temperature of about 650°C.
The iron powder obtained has surface area of about 4.13m2/g and having true density of about 7.83g/cc.

Example 4: Preparation of Iron powder at reducing temperature of about 750°C
Experimental procedure and conditions are similar to as mentioned in Example 1. However, the iron oxide is heated and reduced at a temperature of about 750°C.
The iron powder obtained has surface area of about 2.03m2/g and having true density of about 7.83 g/cc.

Figure 3 illustrates the SEM analysis data of the iron powder upon reduction at temperatures 450°C, 550°C, 650°C and 750°C, respectively.

Additional embodiments and features of the present disclosure is apparent to one of ordinary skill in art based on the description provided herein. The embodiments herein provide various features and advantageous details thereof in the description. Descriptions of well-known/conventional methods and techniques are omitted so as to not unnecessarily obscure the embodiments herein. The foregoing description of the specific embodiments fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results. Any discussion of documents, acts, materials, devices, articles and the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application. While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made to the embodiments without departing from the principles of the disclosure. These and other modifications in the nature of the disclosure or the embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.