تحضيراكسيد الحديد الاحمر الصناعى المستخدم للبويات والدهانات

Fe2O3 (Iron Oxide, Ferric Oxide)

Family Colorant

Ferrosic Oxide

(Sources: Iron Oxide, Stained Clays, many others)

-Iron compounds are the most common coloring agent in ceramics.

On one hand, they are nuisance impurities where they stain an otherwise white clay or glaze or where they muddy an otherwise bright color.

At the same time, iron exhibits so many personalities with different kiln atmospheres, temperatures, and firing cycles and with different glaze chemistries that it is among the most exciting of all materials.

-Chemically, iron is amphoteric like alumina. Fe2O3 generally behaves as a refractory antiflux material in a glaze melt, combining with alkalis.

Oxidation iron-red glazes, for example, can have very low alumina contents yet do not run off ware because the iron acts like alumina to stabilize and stiffen the melt. However these glazes likely will have somewhat reduced durability.

-In glazes low in flux it can behave as an alkali, combining with silica.

-Fe2O3 is very affected by a reducing atmosphere where it can act as a flux in both bodies and glazes at high temperatures.

Its fluxing action in reduction is quite remarkable and can be demonstrated using a line blend in a clear glaze. Higher amounts of iron exhibit dramatically increased fluidity (see FeO for more info).

-Fe2O3 is the most natural state of iron oxide where it is combined with the maximum amount of oxygen.

In oxidation firing it remains in this form to typically produce amber to yellow up to 4% in glazes (especially with lead and calcia), tans around 6% and browns in greater amounts.

In the 20% range, matteness is typical. However, once it reduces to FeO and immediately begins fluxing and forming a glass, it is difficult to reoxidize.

Since the breakdown of carbon or sulfur compounds in body and glaze so easily reduces iron, a slow and very thoroughly oxidizing atmosphere is critical through the 700-900C range to assure that all the iron remains in its antiflux oxidized form.

-Most glazes will dissolve more iron in the melt than they can incorporate in the cooled glass. Thus extra iron precipitates out during cooling to form crystals.

This behavior is true both in oxidation and reduction. For example, a typical mid-temperature fluid oxidation glaze of 8-10% iron will freeze black with fine yellow crystals.

Lower temperature glaze with their high flux content can dissolve more iron (i.e. aventurine).

-Zinc can produce unpleasant colors with iron.

-Titanium and rutile modify iron and can give some striking variegated effects.

For example, a popular middle temperature pottery glaze employs 4% tin, iron, and rutile in a clear base to give a highly variegated gloss brown. Another popular cone 6 glaze uses 85% Albany slip, 11% lithium, and 4% tin to produce an attractive gloss brown with striations and flow lines similar to classic lead glaze effects.

-While many iron-stained clays are reddish in color, high iron clays can also be blackish, grey, brown and deep brown, pinkish, greenish and yellowish or maroon.

Some can be quite light in color yet fire to a brown or red color. 6-7% iron is considered a high-iron clay, but some stained clay-like materials can have 20% or more iron. A typical ivory colored oxidation firing body has 1-2% iron oxide.

-Low temperature earthenwares can exhibit a wide range of iron red colors, depending on the firing temperature.

Typically, low fired materials burn to a light orange. As temperature is increased this darkens to light red, then dark red, and finally to brown.

The transition from red to brown is often very sudden, occurring across a narrow temperature range.

Thus the working temperature should be sufficiently above or below this range to avoid radical color changes associated with kiln variations.

-Fe3O4 is an intermediate form of iron which is brown in color and exhibits intermediate properties.

Fe3O4 can either be a mix of FeO and Fe2O3 resulting from an incomplete conversion from one type to the other, or it can be a completely different mineral form of iron known as magnetic iron oxide from the ore magnetite.

The latter is a hard crystalline material of use in producing specking in bodies and glazes.

-Generally additions of iron oxide to a glaze will reduce crazing (if supplied in adequate amounts; beyond 1 or 2 percent).

METHOD FOR PRODUCING FERRIC OXIDE PARTICLES

the manufacture of ferric oxide sols.

Especially, a process for making ferric oxide sols in which the particles comprising the sols are discrete and uniform in size and shape.

In one specific aspect, the preparation of acicular, or fibrous, particles of ferric oxide less than one micron in length via sol formation.

In another aspect, the preparation of uniform size, elongated spherical particles of ferric oxide from 50 my to 150 mg in length via sol formation.

Magnetic sound recorder tapes and many other electronic devices use a ferromagnetic material, usually magnetic iron oxide, impregnated, coated, or imprinted in the case of magnetic inks, on a non-magnetic base such as paper or tape.

The most satisfactory form for either 'y-FC O or Fe O magnetic iron oxide is small, acicular particles.

This size and shape is characteristic of the magnetic iron oxides possessing the best magnetic properties and also allows a more continuous and more uniform covering of the base.

Other uses for ferric oxide include pigments for rubber, paints, paper, linoleum, and ceramics.

The high-grade powder obtained from ferric oxide sols is used as a polishing agent for glass, precious metals, and diamonds.

As Well, it is used in the manufacture of magnetic materials such as ferrites and garnets.

ferric oxide sol preparation in which a solution of a ferric salt is added slowly to boiling water.

Most of these investigators chose to Work in very dilute solutions l% E5 0 which have minimal commercial interest.

It has been found that the particles formed by the prior art are not dense, discrete particles uniform in shape and size; in fact, the converse is true.

It is an object of this invention to prepare ferric oxide sols in which the particles are small, discrete, and uniform in size and shape.

It is a further object of this invention to provide a method of making small, acicular ferric oxide particles suitable for use in electronic devices described above after a hase transformation to 'y-Fe O or reduction to Fe O or Fe.

the discovery that discrete, dense particles, uniform in size and shape can be prepared at concentrations of 1% Fe O and greater by refluxing a solution of ferric chloride and a buffering agent.

Solutions of ferric salts tend to hydrolyze even in the cold to give hydrous ferric oxide and the corresponding strong acid, in accordance with the following reaction:

On aging, the hydrous ferric oxide loses water and crystallizes as ct-Fe O hematite.

Both aging and hydrolysis are accelerated by increased temperature. Therefore higher temperatures are needed for particle densification.

But the concomitant effect of the temperature on the hydrolysis rate creates problems in controlling the rate of nucleation and particle growth, which is an essential factor in the preparation of good sol particles.

Since the rate of hydrolysis of ferric salts cannot be controlled in boiling (or hot) water (i.e., it proceeds briskly of its own accord without the addition of hydroxyl ions, removal of anions, or any of the other techniques used in the preparation of sols such as thoria and silica sols) control is obtained through slow addition of a cold solution of a ferric salt to boiling water.

While not wishing to be bound by theoretical explanation, itis believed that the strong acid released in the hydrolysis reaction is harmful to good particle formation; therefore, the inclusion of an acid neutralizing buffering agent such as ammonium acetate to control the acidity of the solution is beneficial to good particle formation. The following overall reaction is believed to take place:

The procedure is follows:

A solution of a ferric salt is prepared.

The Fe O content of the solution can vary considerably from 0.1% Fe O up to the saturation point; concentrations of less than 1% Fe O however, are inconveniently dilute.

This solution is mixed with a solution of ammonium acetate.

The mole ratio of NH Ac/Fe should not exceed 3/1. This mixed solution is added slowly, dropwise, to a quantity of boiling water under reflux.

The ferric salt-ammonium acetate solution is kept at room temperature during addition to the boiling water.

The Fe O content of the suspension when addition is complete can be varied but probably should not exceed about 10% Fe O When the addition is complete the suspension is refluxed an additional period of time.

This additional refluxing is not absolutely necessary but is beneficial to the particles. During addition and subsequent refluxing the suspension is stirred.

The suspension is then allowed to cool to room temperature.

At this point the particles are heavily flocculated by the electrolyte and settle rapidly. After removal of the electrolyte, principally ammonium salt, the particles can be easily dispersed into a sol.

Removal of the electrolyte can be accomplished by many methods:

(1)

decanting the supernatant liquor after the particles have settled and replacing it with distilled water,

(2)

centrifuging and redispersing in distilled Water and

(3)

by passing the sol from the first method through a mixed ion-exchange resin bed.

The volume of water in which the particles are redispersed may be varied in accordance with the Fe O content desired in the final sol.

The acetic acid can be recovered by conventional methods.

The following discussion pertains to the B3 0 particles after electrolyte removal.

As long as the particles remain wet after they have been removed from suspension by centrifuging or other means, they are discrete and can be readily redispersed.

If the particles are dried at room temperature a very fine-size powder results. A portion of the particles in this powder are loosely aggregated.

This loose aggregation can be broken up by conventional techniques such as grinding after which the original discrete particles are obtained.

The particles produced by the above method are somewhat elongated spheroids in the Ill/L size range.

They are composed of much smaller particles bound together.

Acicular, or fibrous particles are produced by the same general procedure as that described above with the exception that dropwise addition of the ferric salt-ammonium acetate solution to boiling Water is avoided; rather, all of the solutions are rapidly mixed.

In this case, the Fe O content of the final mixture should not exceed about 15%, and generally about 2% Fe O is satisfactory.

The armmonium acetate/Fe mole ratio should be about 3/1 or sli htly less. The solution is refluxed with stirring for a from 2 to 24 hours.

Refluxing past 2 hours is not absolutely necessary but it improves the discreteness of the particles and tends to increase their length.

The particles produced by this invention are rod-like, averaging about 0.1 micron in length and 0.01 micron in width. Standard X-ray diffraction techniques identify the material as (3-Fe O -H O.

The following two examples illustrate the procedure for producing acicular, fibrous particles, using the method described above.

The iron oxide compounds produced by the process of this invention are well known articles of commerce.

They are used not only for pigmenting paints and lacquers, but also in rubber, plastic, paper, cement, emulsions, plaster and in cosmetics.

They are used in the production of catalysts, magnetic and electronic components and in polishing compounds.

For these purposes, control of particle size, and color is required, particularly for pigment applications where reproducible hiding power, tinctorial strength and color tone are essential.

The process yields yellow and red ferric oxides of big quality and purity in uniform particle size of excellent color and color strength.

The process of this invention allows the production of ferric oxide and ferric oxide hydrates at a higher production rate and thus, more economically than heretofore possible.

The oxidation and precipitation processes of this invention are conducted in the presence of a starting slurry of a hydrated ferric oxide present in minor amounts.

If a yellow ferric oxide hydrate slurry is employed, a yellow oxide will be produced analyzing 86.5 to 88.5% F6203.

If a red oxide slurryis used, a red oxide analyzing 96 to 99% Fe O will be formed.

Both the red and yellow oxides produced by the process of this invention have excellent color shades and are of fine uniform particle size in the range of about 0.25 to 5 mircons.

When the process of this invention is of short duration, such as for 2 or 3 days, a light shade of the red or yellow oxide is produced.

Longer processing yields progressively deeper shades such as dark orange and purple colors of the larger particle size oxide hydrates.

the oxidation of a ferrous salt solution by means of anhydrous ammonia and a free-oxygen containing gas. In US.

, a method for the production of yellow iron oxides is disclosed which comprises the alkaline precipitation of hydrated iron oxide produced by the oxidation of ferrous salts by air in the presence of a seed slurry of hydrated ferric oxide.

The preparation of a red iron oxide is disclosed in US.

oxidizing iron with air in the presence of a ferrous salt solution and a red hydrated ferric oxide seed slurry.

The process of this invention contemplates the production of ferric oxide by oxidation of a ferrous salt solution and the oxidation of metallic iron, in the presence of a minor amount of a slurry of hydrated ferric oxide, by the action of air and ammonia.

The process of this invention offers important advantages over the above-mentioned prior art in that I have obtained an unobvious and unpredictable increase in yield which would not be apparent in considering the combination of yields from a process employing the oxidation of ferrous salts in the presence of a seed slurry of hydrated ferric oxide, by the action of oxygen and anhydrous ammonia, and a process employing the oxidation of metallic iron by heating and oxidizing an aqueous ferrous salt solution in the presence of metallic iron

The process makes possible greatly increased yields from plant production facilities.

For example, tests in five commercial yellow oxide production tanks, each in excess of 10,000 gallons capacity, using the process of this invention, averaged 42.5% greater yield over five tanks operating under the same conditions using the metallic iron oxidation process. Of this greater product yield, 12% was due to the stoichiometric yield from the oxidation of the ferrous salt by air and ammonia as measured by the salt and ammonia consumed.

The balance of the increased yield, 30.5%, was due to the unexpected potentiating effect of the ammonia on the oxidation of iron.

Another advantage is a greater tank slurry fluidity or mobility for any given solid concentration which improves mixing and circulation of tank liquids and thereby improves the production rate and lowers processing costs.

Moreover, since shade development is faster by the process of this invention, the processing time to reach a given commercial shade is reduced by up to 50%, making possible more finished tank batches in a given time than possible With former commercial processes.

Still another advantage of this invention is the preparation of products of increased purity over the processes due in part to the less acidic conditions of the tank and also to the use of proportionately less metallic iron.

The metallic iron of the commercial processes is usually scrap iron, a commodity which fluctuates in quality and which can adversely affect the purity of the oxide made there-from.

Another very important advantage of this invention lies in the ammonia neutralization aspect wherein the iron salt concentration in the final tank slurry is lowered, thereby lowering the processing cost and decreasing the pollution hazard of process effiuent.

While the above advantages of this invention apply to both yellow and red oxide production, in the latter case, it is observed that the overall increase in productivity is proportional to the amount of ammonia used.

This invention has demonstrated a 21 to 30% greater rate of production of red oxide compared to the oxidation process when scrap iron is used alone under the same conditions.

A specific embodiment of the process of this invention as it relates to the production of yellow ferric oxide comprises adding a minor amount of a yellow ferric oxide seed slurry prepared by any method and preferably prepared by precipitating ferrous hydroxide from an aqueous ferrous salt solution with alkali and oxidizing said ferrous hydroxide with air.

the art that a greater concentration produces a lighter colored product and a. lesser concentration produces a darker product.

An intermediate range is one wherein the concentration of seed is in the range of about 0.1 to 0.3 pound per gallon based on the total reaction mixture volume.

To the seed slurry is added an aqueous ferrous salt solution.

The ferrous salt can be any water-soluble ferrous salt such as ferrous chloride, ferrous sulfate or ferrous acetate. Ferrous sulfate, copperas, is preferred because of its low cost and availability.

A range of from about 0.5 to 1.0 pound per gallon based on the total operating volume is preferred onthe basis of process control and economy.

While other concentrations are effective, less than the preferred range decreases the reaction rate and more than the preferred range is uneconomical since unreacted ferrous salt is obtained in the processing effluent.

To the mixture of ferrous salt solution and seed slurry is added scrap iron. The amount of scrap iron is also not critical.

However, we have found a range of about 2 to 6 tons for a processing tank of 12,000 gallons operating volume to be an economical range.

The tank slurry temperature is adjusted to from about 150 to 200 F. and preferably about 175 F.

by any heating means.

In usual practice, steam coils in the tank are used. Air and ammonia gas are introduced through separate sparge rings in the tank at such a rate as to maintain the acidity of the reaction mixture at a pH of from about 3 to 4.5 and preferably at about pH 4.0.

The pH of the process slurry may be adjusted higher by decreasing the volume of air or by increasing the amount of ammonia.

While air is the most convenient gas to use, pure oxygen, oxygen-enriched air and other oxygen-containing gases may be used efiectively in the process of this invention.

The ammonia of this invention is preferably in the form of ammonia gas.

However, ammonia in aqueous solution or anhydrous liquid ammonia may also be effectively used.

As the process is continued, the yield is monitored by analysis of the tank slurry.

Additional scrap iron and ferrous salt are added to maintain production and to prevent raw ma terials becoming exhausted.

The process is shut down when the desired shade of oxide is obtained. A medium red oxide shade is obtained by using a red oxide seed slurry by the process of this invention in about 100 hours.

The product is collected by the usual rotary vacuum filtration, washing and conveyor drying.

Other methods for collecting, filtering and drying are well known to those skilled in the art.

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