US2759834A - Refractory and process for making same - Google Patents

Description

United States Patent M 2,759,834; I REFRACTORY ANDEPROEESSIFOR. Himansu Kurnar Mifl'a, Jamshedpur, Bihanlndir.

NoDrawing. Applicafin- April-22;-1953, Serial-Non 350,515;

1. Claim.. (Cl. 106.--59).

This invention relates to a process. for manufacturing a refractory material offthe neutral. andneutral-toybasic. type from a low grade, high silicious,, nonvrefractory chrome ore, and the article formed. thereby. There.- fractory produced by the method of'tliis inventionpossesses superior physical properties, e.- g.,,high.refractoriness-under-load and, high resistance. against, attack. of iron oxide. The present application. is. a-. continuation? in-part of co-pending application SerialNo. 74,8631 filedl February 5,1949 now abandoned;

In the past the production of'ahigli; grade refractory. material has been limited tothe use of chromeore characterized by a high pyrometric cone. equivalent. (fusion point), e. g.,. above cone 35 (above. 1785" C.'),-,,and. which did not contain more than silica.

Thus, Parmellee and Ally [Parmellee C. W. and Ally A. Some Properties of Chrome Spinelff'JI Akn. Ceram. Soc. (4) 213 (1932) quoting' McDowell state that for chromerbrick manufacture, S105 content of up to 5% in the chrome'oreais allowedyfrom' 5 to 9% is generally penalized and-above9% is rejected:

Litinsky [Litinsky L. Recent Development in the Production of Refractories Containing; Magnesia,'Iron &. Steel Industry p;. 498-: Sept. (1936)], states-a that for." chrome magnesite brick. the chrome: are employed; should? contain as muchrCrzOm and as little1-SiOz? asrposs-iblea U. S..Patent No:. 2,077,796 ofu'kpril;v 1937,. for'making: chrome-magnesitebrickgivesrthe silica contenttofrefractory gradechrome. ore used, as4i5%.

Schauer [Schauer T. Evaluation of: Chrome resfor. the Manufacture ofz Refractories? TonidsZtg. 63" (161). 701'702 I (62) 724-725 (i193f9.)] statesztoo much Si02zin:

chrome ore decreases refracto'rinessi.undenload;. ImevaL uating chrome ore fon the manufacture of -refractories he suggests that if the quotient forsthe: equation;

. PercentAliOs Percent MgO- Percent SiO is less. than 1.38, it indicatesrloweredi refractoriness;.andr resistance to temperature changes.

The use of low grade. chrome.ores:which,do?not;.conform to the aforesaid: specifications: has; also; been: attempted by first physically treating such: ores to: reduce; the silica content: to less. than; 10%; When: successful,

the beneficiation of such ores, e. g;, by physical: means;

'I hese' chrome ores-ihave.

Patented. Aug-,. 21, 1956 2:. always been avoided asva source of refractory'material for thisreason- It is; accordingly, an object of thi'sinventionto employ aalow grade non-refractory, highly silicious, hybrid chromeore for 'themanufa'cturei of a. superior grade -of" refractory, withoutf subjectingxthe raw material to. any process of beneficiation.

S0;farasithe'applicanttis aware; the type of chrome ore used: by him accordingto' the invention hasnotbeenusedz commercially. and therefore no published description, to the: knowledge: of applicant; hasappe'ared elsewhere.

Theexpression hybrid,"used'with reference to highly silicious low grade. chrome ore, has been used by the applicant in an' abbreviated sense to denote low: grade chrome" ore occurring in hybrid rocks, which latter have beerr. formed. by' the intrusion of ultra-basic rock into ferrugihous slialegivingiit a: foliatedi (Schistose) appear ance.. The; chromei ore= grains occur as disseminations invthis-vhybrid rock. The presence of high percentage of silica in the low grade chrome ore can be ascribed tct chrome ore: grains beings'intimatelys associated withshale and is therefore notcapableof being separated out withoutiexpensive mechanicaliprocessiirgrv The applicantlaims at using this highly silicious'. chrome; oreby employing chemical means.

Normally chrome: ore" in this region'o'ccurs mostlyas pockets or: veins: inultra-basic rocks: This: normal? chrome; ore" is; of; muchflhigher grade than the low; grade. chrome: orereferred to: abuve:

Therinvention, therefore; resides: in; a. process for'the. manufacture: of refractory material. fromx a low-grade: non-refractory; highly'silicious, hybrid: chrome ore and consists in; calcining such: orewith amorphous magnesiumi; oxides at. as temperature corresponding. to not: less; than: O'ntona cone 26. (1595? 6.); but preferablyito cone 31 (16.80? 6).); During? the: process',.th'e original structure: ofrthe: hybrid". chrome: ore; is completely altered: with the; formation. of spinels. and? forsterite. The spinelsi formed are. chrome: spinel; MgO:Crz.Os; magnesio fer rite-g. Mg0.:Fe20s;: aluminum. spinel; MgOzA'lzO'a. A sz a:result ofrthe process; all of: the;silica:.in theoriginal. ore:

isconverted:intonforsterite;. 2 'MgO SiOz.

Tibet finalr product is: therefore a. mixture. off the above: stated. various: spinels, forsterite. and excess magnesium oxide in the formiof the? crystalline-variety mineralogical-"- 13% known; as. periclase: All; the? formed minerals: viz. spinels; forsterite and periclase; have: hi gh melting: points? and hence, theend product made: according to: this in. vention .has ihigli refractoriness-under-load..

The: formation ofi the? crystalline: phases. of forsterite; and: spinels. can. take place onlyatzhighptemperaturesiand in an oxidising atmosphere; as: in' the absence 2 of oxygern. the. undesirable faya-litei (2-: FeQSiOa): available ins the: compositionzm'ay beiformed from" theferrous oxide. Fay alite tends to reduce the (P. C. E.) of the mass. This: can be. avoided? by. converting the ferrous oxide: ('EeG) tormagnesioferrite: M g0 FezOs.

Typicalt chemicalv analyses Ofi chrome: ones that": fall".

within the scope of'use according to this; invention, as.

welli as: theiit pyrorn'etritr cone equivalents (fusion. point) are given below:

(a) Chemical analysis (11) (iii) 0. 30 0. 20.. 6I00. 5. 2H 32. 58 27107 O. 30 2:44 1; 87

(b) Pyrometric cone equivalent (ORTON CONE) Cone 20 (1530 C.) to 23 (1580 C.); 14 (1400 C.) to 16 (1465 C.); less than cone 14 (1400 C.).

According to the well known definition, a material to be classed as refractory should not have a P. C. E. of less than Orton cone 23. The above stated materials are, therefore, non-refractory and this invention confines itself only to the use of such non-refractory, highly silicious, hybrid chrome ores.

Moreover, if the equation of Schauer referred to above is applied to the typical analyses herein stated, the quotients would be much less than 1.38. These types of chrome ore according to Schauer are not suitable for the manufacture of refractories and, as is well known, they have been regarded as unsuitable also by the trade.

The source of magnesium oxide may be the naturally occurring mineral magnesite (MgCOs) or brucite (Mg(OH)2). The amorphous variety as distinct from the crystalline variety periclase has been experimentally found to be more suited to promote the chemical reactions for the production of spinels and forsterite as described hereinafter in greater detail. The nascent i. e. freshly formed amorphous magnesium oxide formed during heating together of the chrome ore and magnesite or brucite is found to give best results.

A special feature of the process is that no beneficiation of the ore is necessary for the removal of silica and other compounds which are commonly regarded as deleterious for making high grade refractories. On the other hand, these ingredients viz. silica, and iron compounds are valuable for the intended purpose as they yield, according to the specification herein described, valuable compounds with high melting points. Every unit of weight of the raw material used in this process therefore, goes into the finished product with the exception of the loss due to the removal of the slight amount of volatiles present, and the loss inherent in processing a material.

Referring now to the process in detail, highly silicious chrome ore and magnesite are separately ground, the degree of fineness of the latter being preferably more than that of the former. This, however, is not absolutely necessary if each ingredient is initially in a fine state of subdivision as described below. The chrome ore should be crushed and ground to pass through a screen whose openings are not larger than 4 mesh, Tyler screen (4.699 mm.). The magnesite, similarly should be crushed and ground to pass through a screen whose openings are not larger than 20 mesh, Tyler screen (0.833 mm.).

Although it has been stated that magnesite should be ground to a finer degree than the ore, it is clear that if the ore is already ground to pass through a 20 mesh screen, it is not necessary to grind the magnesite to a degree finer than to pass through a 20 mesh screen.

The two ground materials are then intimately mixed, preferably in a countercurrent mixer and heated in a kiln to a temperature corresponding to above Orton cone 26 (1595 C.) and, preferably, to Orton cone 31 (1680 C.).

During the heating, chemical reactions take place in the solid state which break down the original structure of the ore and form new components (spinels and forsterite) with high melting points, as follows:

(a) SiOz of the ore combines with MgO to form forsterite according to the equation v 2MgQ+SiO2=2MgO :SiOz (forsterite) (b) and similarly Al203+MgO=MgOZAl203 (alumi- From the chemical equations given above, it is possible to readily determine the weights of MgO or (MgCOs) required for one part by weight of each of the ingredients, SiO2; A1203; FeO; and Cr2O3, present in the original ore. MgO by weight, required for one part by weight of each of the above is: 1.3; 0.4; 0.27; and 0.24 respectively.

It follows that for a chrome ore having a composition corresponding to sample analysis (II) above, the minimum requirement of MgO would be: (31.52 1.3)+ (8X04)+(18.43 0.27)+(32.58 O.24)=56.92 (or equivalent of 121.8 parts of MgCOs) i. e. 1 part of chrome ore would require 0.57 part of MgO or 1.21 parts of MgCOz.

In the above calculation, the percent of MgO available in the chrome ore has been neglected. As a matter of fact, addition of an excess MgO (or MgCOs) is preferable, since MgO is converted to periclase in the final product and thereby adds to the desirable physical properties of the final composition.

It has been found that when magnesite (MgCOa) is employed, best results are obtained when 50% more than the theoretically required amount of magnesite is used. Thus, instead of using 1.21 parts of MgCOs for every part of chrome ore, it is preferred to use 1.8 parts of MgCOs.

The proportion of required magnesite with respect to chrome ore is determined by the exact percentages of the various oxides present in the chrome ore. The permissible range is 1 part ore to 0.752.0 parts magnesite, the parts being by weight. If magnesium oxide is employed, then the proportion of chrome ore to magnesium oxide is 1 to 0.3751.0 by weight.

The MgCO referred to in the above calculations had the following approximate chemical analysis:

Silica F6203 CaO MgO The mass, after heating or calcining in a kiln, is crushed and sieved through different mesh sieves. Different proportions of sieved material are blended together without further crushing, mixed with an organic binder such as molasses or sulphite lye or lightly calcined magnesite and moulded into bricks or like shapes. These bricks may be used as such or after they have been fired in a kiln. For extreme severe conditions of service a second firing is preferred and this should be done at a temperature not less than Orton cone 18 (1490 C.) and preferably at Orton cone 30 (1650 C.)

According to a modification of the process, in order to lower the temperature of conversion to forsterite and spinels, fluxes such as boric acid and volatile salts such as ammonium sulphate or ammonium chloride may be added to the mixed mass prior to calcination, the fluxes being not less than 1.5 per cent but not more than 2 per cent of the total weight of the mass. The temperature of calcination of the mass with fluxes should not be less than Orton cone 20 (1530 C.). The boric acid, although aiding conversion, lowers the refractorinessunder-load value.

Tests on a few typical samples, compositions of which are given earlier in the specifications show that the final product has the following superior physical properties:

(I) Refractoriness-under-load.-A refractory made according to this process, when tested under a load of 2 kg./cm. did not deform at 1700 C. whereas most commercial grades of brick made from high grade chrome ore and magnesite, under the same load deformed at 1570 C. and completely collapsed at 1650 C.

(II) Resistance against attack of iron oxide-A 3" x 2" x 2" piece of refractory made according to this invention, when heated with a layer of 100 gram mill perature showed Bursting Expansion of 2%, as against 6 to 16% for commercial grades of brick made from high grade chrome ore and magnesite.

(III) A. S. T. M. load test at 1450 C.On subjecting bricks made by the process of the present invention to A. S. T. M. load test at 1450 C., it was found that the brick gave a contraction of 0.48% whereas commercial grades of brick failed by shearing diagonally at 1420 C.

Although the present invention has been shown and described in specific embodiments, nevertheless, various changes and modifications obvious to one skilled in the art are within the spirit, scope, and contemplation of the invention.

What is claimed is:

A novel refractory material having a high pyrometric cone equivalent and high refractoriness-under-load prepared by mixing together one part by weight of chrome ore containing about 20% to 43% by weight of SiOa,

about 5% to about 13% by weight of MgO, about 22% to -27% by Weight of FeO and A1203 combined, and about 27% to 34% by weight of CrzOs and characterized by a pyrometric cone equivalent below the temperature corresponding to Orton cone 23 and from about 0.375 to about 1.0 part by weight of amorphous magnesium oxide, both in a state of fine subdivision, the mixture being calcined at a temperature from about Orton cone 26 (1595 C.) to about Orton cone 31 (1680 C.) such that new compounds are formed.

References Cited in the file of this patent FOREIGN PATENTS 631,010 Germany 1936 435,448 Great Britain 1935 146,725 Australia 1949