Title of Invention

A PROCESS FOR MAKING FERRITE POWDER

Abstract

ABSTRACT A process for making fcrrilc powder is disclosed wherein the raw materials are doped with one or more rare earths. Doping gives a fine grain structure in the product by countering the effect of silica in the raw materials, which tends to cause exaggerated grain growth. The process, thus, permits utilisation of low grade iron oxide ores containing even upto 6000 ppm silica unlike conventional processes. Doping also improves the magnetic properties of the product. Dopants investigated are Vanadium pentoxide(l), Bismuth trioxide(2), Tantalum trioxide(3), Titanium dioxide(4) and others and the mixtures thereof. (1) and (2) enhanced the saturation flux density while (2) and (4) favourably affected permeability and power loss characteristics respectively. A combination of the components (1) to (4) gave an allround improvement in the characteristics. Dopant dosages and proportions are discussed.

Full Text

I xms xnvention. relates to a process for making ferrite powder and more specifically to a process for making ferrite powder which can also utilise low-grade iron oxide ores having a high content of silica. The term ferrite refers to an iron-carbon compound which one encounters in the metallurgy of iron and steel and also to a group of ferrimagnetic materials whioh are widely used in the fields of eleotrioal and electronic engineering. In this specification, references to 'ferrite' are intended to refer to said group of magnetic materials(ferrimagnetic). Such ferrites are used as soft magnets and hard magnets in numerous applications in electrical and electronics engineering such as for example, memory cores, transformer oores particularly for high frequency applications, electric motors, permanent magnets in appliances and audio and video recording and playing equipment. Perrites are chemioal compounds whose constituents are oxides of one or more metallic elements of the transition group such as iron, manganese, cobalt5 nickel5 .q_opper, and zinc. Said-set of transition metal oxides oan be grouped into several combinations of the metallic ions and in each said combination the proportions of said metal ions oan be varied. It is interesting that several said combinations and variants thereof are, in fact, ferrite compounds possessing interesting and useful combi¬nations of magnetic properties. These ferrites are divided into four major classes based on their crystal structures which are. spinel, magnetoplumbite, garnet, and perovskite. The process of this invention is of particular relevance to said spinel ferrites but it must be mentioned that the process of the invention is easily and simply adapted in respect of other ferrites, by persons of ordinary skill in the art. Therefore, this specification mainly refers to spinel ferrites which are .©3F(&rred to briefly as spinels. Spinels have the general formula MeO.PeJO5_ wherein Me represents a divalent ion such as Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+ tf.\S combination of said divalent ions with an average valence of two. The magnetic oxide of iron (Pe_0.) has the structure FeOvFe5O- and is a naturally occuring spinel found in the form of the ore magnetite, the original 'lodestone' used in early navigation. In the field of application of magnets, the following are some of the important and/or critical properties thereofJ i. permeability, ii. saturation magnetisation, iii. hysterisis loss, iv. coercivity, and v. resistivity. Spinels have been developed possessing specific said properties or combinations thereof from the abovementioned list such as to suit particular applications. Two of the most widely used spinels are manganese-zinc (Mn-Zn) ferrite and nickel-zinc (Ni-Zn) ferrite. In the description and claims hereinbelow, the prior art process and the process of the invention are described in the context of manufacture of said Mn-Zn ferrite with some references to father ferrites. This is in the interests of coneiseaeBBS and is without limitation to the soope of the invention as the process of the invention is easily and simply adapted to the manufacture of Ni-Zn and other ferrites, spinel or otherwise. The basis for the prior art process for making ferrite is the chemical reaction between the oxides of the various metallic elements constituting the ferrite. Thus, for making Mn-Zn ferrite powder oxides of manganese, sine and iron ore are taken in their stoichiometric proportions and reacted at the appropriate temperature. A raw materials mixture of said metallic oxides is, therefore, made and subjected to the following essential processing stepsi- i. blending, i i• compact ing, iii. efL&eining, iv. grinding, and v. drying. Said steps define the prior art process for making ferrite powder. Said process comprises said essential steps and ma,y furthermore, comprise one or more useful, but optional 5 /Steps which is discussed hereinbelow. Said prior art / process has been adapted aftd modified by this invention to the include/ step of doping with rare earths resulting in the novel process of the invention for making ferrite powder. Several variants of said prior art process are feasible and are pr.otioed>in the art. Said variants arise. i. by adding of one or more useful but optional steps to said essential steps; ii by varying the nature of the raw materials mixture and/or the method of preparation thereof; and iii. by using different equipment, for carrying out said steps, from amongst a wide range of suitable equipment available in the art for each of said steps. These points are clarified further hereinbelow. An example of an optional step is sieving which may be introduced between the grinding and drying steps. She grinding is carried out in wate such as in a wet ball mill. She material f.aa a wet ball mill contains a lot of free water which can be removed by sieving(filtration), which decreases the load on the subsequent step, namely, drying. She simplest said raw materials mixture is that of the oxides of the relevant metals. Shese oxides are required to be of high ptmity and are therefore, often made by oxidation of the concerned metals. Alternatively, naturally ooouring oxides may be used provided they are of sufficiently high purity. For example, an iron oxide ore if used, must have a purity of 99.9# and the silica content not exceeding 150 ppm. In a further alternative, compounds of the relevant metals are taken and then decomposed to give said oxides. In this prooedure, chlorides, hydroxides, carbonates, nitrates or oxalates are taken and decomposed by roasting or other means to yield the required oxides. In a yet another alternative, said compounds of the relevant metals are taken together in the right proportions and decomposed as a mixture to directly yield said raw materials mixture of the oxides. There is 3 still further alternative prooedure under whioh said raw materials mixture oomprises said compounds taken in the right proportions and the deoomposition thereof is carried out within the caloining equipment used for the calcining step. In this arrangement, said decomposition takes place in-situ in the calcining equipment(kiln) where subsequently the ferrite formation reaction takes place. It will be observed therefore, that there are several alternatives for the starting materials for the formation of said raw materials mixture at well as different systems for the treatment thereof for obtaining said mixture of oxides. Thus said prior art process can be associated with a wide range of said starting materials and said systems. each combination thereof representing a variant of the prior art process. Some of the equipment available in the art for carrying out the steps of the prior art process are indicated below. i blending: wet ball mills, dry ball mills, V-blenders, conical blenders, fluid bed mixers and others, ii. compacting. roll flakers, briquetting machines and others, iii. calcining. stationery batch kilns, continuous tubular rotary kilns, tunnel kilns and others, iv. grinding: wet ball mills, attritors, edge runner mills and others, v. drying. rotary driers,'tray driers, fluid bed dryers and others. It is therefore possible to associate said prior art process with any of the different combinations of said equipment together with any of said alternatives and systems and further--more inolude one or more said optional steps giving a large number of said variants of the prior art prooess. This invention provides for the doping of said raw materials mixture with one or more rare earths during and/or prior to said blending step. This is novel. This invention has therefore adapted said prior art process by inclusion of said novel step of doping to give the novel process of the invention for the manufacture of ferrite powder. This invention has observed by experimentation that said doping of the raw materials mixture with rare earths has a very significant effect on the physical and magnetic properties of ferrites. Doping improves the grain structure of the ferrite formed giving a fine uniform grain structure. Further, said doping successfully counteracts the phenomenon of 'EGG-., that is,'exaggerated grain growth'• This phenomenon is observed when eilicaii content of the raw materials mixture is high, said high silica content causing the formation of relatively large grains in a fine grained matrix. Said ' EGKJ' phenomenon has a detrimental effect on the physical and magnetic properties of the ferrite. Still further, said doping heis the effect generally of enhancing the magnetic properties of the ferrite and selected dopants and combinations thereof have been determined by this invention such as to favourably influence said magnetic properties of the ferrite such. as permeability, powerloss and saturation flux density. The effects of doping are further elaborated hereinbelow. Iron oxides are often the major component of ferrites and therefore their availability and cost are important considerations in ferrite manufacture. Iron oxide of course, occurs in nature in the form of several oxide ores such as, for example, haematite, Pe.O_, which is, widely distributed in nature. The problem with haematite and other naturally occuring iron oxide ores is the impurities associated therewith, in particular, silica. The iron oxide used for ferrite manufacture must not have silica content exceeding 150 ppm. Naturally occuring iron oxides of such high pnrity are highly expensive. On the other hastd, iron oxide ores having silioa contents of 1000 ppm and above are abundant and very cheap. The f£ge of suoh cheap low grade iron ores in ferrite manufacture would be a great advantage provided the high silica oontent thereof could be managed, that is, the adverse effects thereof countered. The object of the invention was therefore to devise a process for making ferrite which would counter said adverse effects of silica and allow the use of a very cheap and widely available raw material, namely, iron oxides of silica contents of tOOO ppm and above. During the process experimental investigations, this invention has observed the further benefits of said rare earths doping namely• the finer and more uniformed grain struoture and better magnetic properties of the ferrite. This invention has devised a comprehensive set of doping systems efceh comprising one or more rare earths dopants suoh as to selectively pursue and, achieve one or more of the belowmentioned objectives and to have the desired combination of effects. i. improvement of the ferrite grain sturoture; ii. countering the effect of high silica in one or more components of said raw materials mixture} and iii. improve one or more desirable magnetic properties of the ferrite. Said novel doping step can be easily and simply adapted to any of said variants of the prior art process discussed hereinabove. Therefore, the scope of the invention extends to all said variants. Silica in iron oxide or other ferrite raw materials has the effect of causing formation of larger grains and the higher the said silioa content the greater is the tendency towards formation of said larger grains. The threshold for this effect is a silioa oontent of about 150 ppm below which said tendency is negligible. Beyond said threshold, said tendency increases very rapidly with increasing silica content. When sections of a ferrite sample in which iron has been used oxide containing over 1 50 ppm silica/are examined one observes relatively large grains embedded in a matrix of fine grains. That is, one finds this contrast of several relatively large grains distributed over a region of small and uniform grains. Said contrast phenomenon is referred to in the art as 'exaggerated grain growth' , 'BG-Gr' and is quantitatively specified by the ratio of the area of the seotion occupied by said relatively larger grains to the area occupied by said fine grains. Alternatively, the number of said larger grains in a seotion are oounted and the count per unit area provides a quantitative measurement of the effect of Bilica. Some measurements of said phenomenon are depicted in Fig. 1 of the accompanying drawings whioh is a plot of the number of exaggerated grains as a function of the amount of silica doping. This invention has addressed itself to said problem of EGG and the adverse effects thereof. The object of the invention was to minimise/eliminate said contrast and prevent degradation of said properties. This invention oonoeived the novel idea of doping the process materials during and/or prior to said blending step with the object of countering the effect of high silica. This invention has developed considerable know-how on the doping step having studied the effects of several dopants such as the range of rare earths with and without traces of platinum or palladium. This is novel. The traces of platinum and/ or palladium speed up the spinel formation reaction. This study has investigated said contrast phenomena upto silica levels of 1000 ppm in the iron oxide and has successfully developed said dopants and dopant combinations to counter silioa levels of about 6000 ppm in. iron oxide such as to restore said fine grain structure and avoid the degradation of the magnetic properties. Around a level of about 1000 ppm silica, said effect of silica on said grain structure, and ferrite proper-••ties stabilises and further increases in number of said relatively 5/arger grains are not observed even upto 6000 ppm silica. To summarise therefore, the development of the doping concept, the identification of individual dopants and combinations thereof, and the quantitative aspects of said doping in countering various silica levels and the added benefits of the dopants on said magnetic properties are all the novel innovations of this invention. Thus, this invention presents a ttovel process for the manufacture of ferrite powder which can utilise low grade iron oxide ores having high silioa contents even upto about 6000 ppm. The process of the invention, therefore, allows one to subs¬titute the high purity iron oxide raw material currently used by a far cheaper alternative, namely, low grade ores which are available widely and in abundanoe. In so far as the Indian ferrite industry is concerned the process of the invention offers the possibility of total import substitution as the entire requirement of high purity iron oxides of the Indian industry is currently met by high cost imports. The doping system of the invention also offers the prospect of a certain amount of process control over the magnetic properties of the ferrite being manufactured. that is, a doping combination oan be selected to selectively develop one or more of said properties. The art contains one more process for making ferrite which is referred to hereinbelow as the old process. Said old process does not have a compacting step but instead has a granulating. ste$. The processing steps in said old process are. blending, sieving, calcining, grinding. granulating and drying. Said old process can be carried out in the dry state or wet state. In the former, the blending and grinding steps are usually carried out in a dry ball mill whereas in the latter wet ball mills are used. She drying step is usually conducted in a spray drier and granulating is by a suitable binder such as polyethlene glyool or poly- vinyl alcohol. She calcining equipment oomprises a tubular rotary contiguous kiln. She old process is now not in wide use. However, it is also quite easily and simply adapted to include the novel doping step of the invention during and/or prior to said blending step. Said prior art process will now be described in further detail in the context of the manufacture of Mn-Zn ferrite the references to Mn-Zn ferrite being by way of example and not limiting to the scope of the process of the invention. The variant of the prior art process described hereinbelow and one which has been adapted in the specific embodiment described hereinbelow has the following features: i Raw materials mixture of oxides of the relevant mixture metallic elements (for the prior art process) (for the embodiw Bellary'iron oxide haematite on. of -merrt described silica content 0.3-0 .63$ plus oxides in detail of other metals. hereinbelow) ii optional step sieving between the grinding and included iii. blending iv. flaking v. calcining vi • grinding vii. drying drying steps fluid bed dryer Rotary roll flaker Tubular rotary continuous kiln wet ball mill fluid bed dryer She raw materials are mixed and ground to about 100-200 mesh. Shis powdered raw materials mixture is charged to a fluid bed mixer where the mixture is intimately mixed(homogenised)• The blended(homogenised) mixture is charged to a rotary tubular continuous kiln. For Mn-Zn ferrite the temperature in the reaction eone is controlled to aTsoHlt. 850#C. The reaotion temperature depends on the ferrite being manufacturedand $he range of temperatures in the reaction eone extends from about 800°C to about 1350°C. The atmosphere is controlled to the desired oxygen content in the various kiln eones where necessary but for Mn-Zn ferrite said control is not necessary. The calcined material discharging from said rotary kiln is charged into wet type batch ball mills. Water is charged to the mill to make up the water to solids ratio to the required value. For Mn-Zn ferrite about 400-500 litres of demineralised water are required per ton of solids oharge. The total amount of ch&rge. the proportions of water and solids therein, the volume and speed of the mill, the volume of the grinding media and residence time are controlled to give the desired particle siee quickly and efficiently. The particle size of the ground product depends on which ferrite is being manufactured and on the final application of the ferrite powder. The particle size of the ferrite powder has a significant effect on the subee--quent forming( pressing) operation', sinterability and on the shrin¬kage during sintering. Por Mn-Ze ferrite for use in small minia- -turised components the grinding is done down to about three mic--rons. The slurry from the ball mill is sieved to remove excess water and the wet solids are charged to a fluid bed dryer to yield the final product, dried ferrite powder. According to the invention, therefore, there iB provided a process for making ferrite powder comprising the blending of a mixture of the constituent raw material metallic oxides either in the pure form or as ores thereof, followed by the steps of compounding, cal -cining, grinding and drying thereof, wherein said mixture is dope with one or more rare earths with or without a trace of platinum the and/or palladium during and/or prior to/ said blending step, said process further having one or more optional steps such as sieving (filtration) between the grinding and drying steps. The process of the invention is particularly adapted for utili¬sation of cheap and widely available low grade iron oxide ores containing silica in excess of 1 50 ppm in place of "the high purity iron oxides which are compulsorily required by the prior art process. However, in the procees of the invention said high purity iron oxide ore may also be used. In suoh a case, doping will provide a finer and more uniform grain structure and better magnetic properties depending on the nature and amount of the dopant(s) used. Various systems of raw materials have been discussed hereinabove, as also some of the wide range of equipment available for carrying out the process steps of the invention. This opens up a large number of configurations of raw material systems and equipment and alternatives with which the process of the invention can be associated. The scope of the part invention extends to all said configurations one of which forms / of the embodimentsdescribed in detail hereinbelow. With regard to the doping step of the invention the scope thereof covers the whole range of rare earths and combi--nations thereof. Out of the several rare earths and combinations thereof investigated by this invention, the following were selected for extensive trials. vanadium pent oxide(V-05) , bismuth trioxide(Bi 0,), tantalum .r ioxide(la2a) and titanium dioxideCliOg) . Trials were conducted with traces of platinum and/or palladium added to the rare earths mentioned. V5O,. was found to be the most effective dopant and 500 ppm thereof very effectively countered silica levels of about 1000 ppm to 6000 ppm. Said dosage of V5Ou dopant restored the fine grain structure and no large grains were observed. Above a level of about 500 ppm, the effect of incremental doses of v2°c fell off. This invention further experimented with combinations of palladium added thereto. Studies were made with two-component dopant systems comprising vanadium pentoxide on the one hand and bismuth trioxide, tantalum trloxide or titanium dioxide on the other. The optimum proportion of said two compo- /be -nents was found tor about 1 .4» the quantum of dosage being determined by the level of silica in the iron oxide ore. lome of the experimental results of the investigation are ihown in Fig. 2 of the accompanying drawings which depicts rhe effect of V 0,. doping and combination doping on the number of exaggerated grainsCrelatively larger grains). This invention has observed that said dopants and dopant mixtures favourably affect such properties of the ferrite as bysterisis loss, permeability, resistive power loss caused by eddy ourrents>and flux density. Broadly, T-0- -Ti02 combination was found to reduce bysterisis loss as well as said resistive power loss. Doping with v 0 enhanced saturation flux density and a combination of bismuth and vanadium rare earths was found to enhance permeability. Thus the invention provides the process for manufacturing high permeability, high flux density, low power loss ferritee while utilising said low-grade iron oxide ores containing even around 6000 ppmiu of silica. This invention also provides the possibility of countering silica in other oxides of the raw materials mixture, that is other than iron oxide. This option can be used if said other oxides are available in lower grades and offer economic or production advantages. The process of the invention would be able to take care of high silica content in one or more components of said raw materials mixture. In order to provide a clearer understanding of the invention and without limitation to the scope of the invention, some embodimeniB thereof aare described in detail hereinbelow, by way of example• in reference to the manufacture of Mn-Zn ferriteo The raw materials preparation comprised mixing of high purity oxides of manganese and zinc with Bellary haematite iron oxide ore which had a silica oontent of about 0.3 to . The raw materials were mixed in the following proportions. MnO equivalent 0.36 weight fraction, ZnO equivalent 0.10 weight fraction 0 x3 equivalent: 0.54 weight fraction The raw material mixture was ground to aboutf 100-200 mesh size to make it ready for the first processing step of the process of the invention, namely, blending. Blending was carried out in a fluid bed blender(mixer) of Danish design. Batches of raw materials were charged into said blender and a dopant mixture comprising two components was added the in weight of the dopant mixture charged being/relation to the weight of iron oxide present in the batch. The dopant mixture in each of the embodiments contained a trace of palladium. The first component of the dopant mixture in each embodiment was V5Oc. The ratio of said first to said second component in each of the embodiments was 1.4. Said second component was one of following three rare earths! Ia2°3 » Tioo and Bi2°3. In the fourth embodiment said second component comprised a mixture containing equal amounts of said three rare earths. Said raw materials mixture with the added dopants was fluidised in said blender by means of air and the batch time was about ten minutes. The blended material was fed to a rotary roll flaker to achieve densification of the mass, the effect of which was to increase the speed and extent of conversion to the spinel during the calcination step. The flaked material was charged into a continuous tubular rotary kiln in which the reaction zone was maintained at a temperature of about 850°C for calcination. The calcined material was ground in a wet ball mill. About 400 to 500 litres of demineralised water were charged into the ball mill for every tonne of solids charge and the batch was ground down to about three microns size. The discharge of the ball mill was charged onto a sieve where the excess water was separated and drained. The solid material was charged into a fluid bed dryer where the fluidieation was carried out by hot air. The output from the dryer was the ferrite powder product ready for use or for packing and despatch. Samples of the ferrite powder were formed into toroids and sintered. Sections of the sintered product were examined to ascertain the grain structure. Both the grain structure of the samples and the magnetic properties thereof were compared with those of ferrite sample wherein said raw materials had not been doped. Given hereinabove is the procedure which was followed in case of all the four embodiments and in the case of the undoped sample. The difference between the embodiments was in the dopants charge. The details of the dopant charge in the various embodiments and the results observed are summarised hereinbelowl Embodiment I. The dopants charge was 350 ppm of V2O5 and 1400 ppm of of enhancing the saturation flu. density of the product. No large grains were observed. Embodiment III The dopants charge was 350 ppm of v205 and 1400 ppm of had the effect of giving a low power loss product. No large grains were observed. Embodiment III: The dopants charge was 350 ppm of V Or and 1400 ppm of enhancing the permeability of the product. No large grains were observed. Embodiment IV: The dopants charge was 350 ppm and 1400 ppm of a mixture of equal amounts of No large grains were observed. The ferrite product had a high flux density of 20,000 Gues, high permeability (p.) of 5 to 8 K and low power 1OSE, that is, at 10 KHz was 2 to 4.5 claim: 1. A process for making ferrite powder comprising the blending of a mixture of the constituent raw material metallic oxides either in the pure form or as ores thereof, followed by the steps of compounding, calcinning, grinding and drying thereof, wherein said mixture is doped with one or more rare earths with or without a trace of platinum and/or palladium during and/or prior to the said blending step said process further having one or more optional steps such as sieving (filtration) between the grinding and drying steps. 2. The process for making ferrite powder as claimed in the preceding claim 1 wherein said dopant in a mixture of two components with or without a trace of platinum and/or palladium, the first component and second rare earth compound of said mixture is being in the proportion 1:4, said first component comprising Vanadium Pentoxide (V205) and said second component being selected from Tantalum Oxide (Ta203), Titanium Dioxide (Ti02) and Bismuth Triodixe(Bi203). 3. The process for making ferrite powder as claimed in preceding claim 2 wherein said dopant comprises about 200 ppm to 800 ppm of said first and a proportionate amount of said second component, and is added in relation to the amount of the iron oxide in said raw materials mixture. 4. A process for making ferrite powder substantially as hereindescribed with reference to and as illustrated in the accompanying drawings.

Documents:

2780-mas-1998 abstract.pdf

2780-mas-1998 claims-duplicate.pdf

2780-mas-1998 claims.pdf

2780-mas-1998 correspondence-po.pdf

2780-mas-1998 description (complete)-duplicate.pdf

2780-mas-1998 description (complete).pdf

2780-mas-1998 drawings-duplicate.pdf

2780-mas-1998 drawings.pdf

2780-mas-1998 form-1.pdf

2780-mas-1998 form-19.pdf

2780-mas-1998 form-62.pdf