USRE22997E - Porous refractory - Google Patents

Description

keiuueii May 4, 1948 UNITED- STATES PATENT OFFIC POROUS REFRACTORY Charles J. Kinzie, Youngstown,

and Eugene Wainer, Niagara Falls, N. Y., assignors to The Titanium Alloy Manufacturing Company, New

York, N. Y., a corporation of Maine No Drawing. Original No. 2,341,561, dated Febru ary 15, 1944, Serial No. Application for reissue rial No. 713,102

7 Claims.

This invention relates to the production of insulating refractories. More particularly, it relates to the production of porous insulating refractories, especially zircon refractories, bonded with suitable bonding agents. This application is a continuation in part of copending applications Serial No. 204,392, filed April 26, 1938, now abandoned, and Serial No. 256,928, filed February 17, 1939, now Patent No. 2,220,411.

"In'the past it has been known to construct porous-refractories by incorporatin with a refractory material a suitable quantity of organic pore-forming material, together with a liquid, to form -'a homogeneous mass, and then burning out the pore-forming material by firing at a. high temperature. Among the pore-forming materials that have been used are cork, sawdust, wood, etc. In the case of many of these refractory materials, the incorporation of such a pore-forming material has-been found to decrease the strength to such an extent as to render them commercially of low value. In order to increase the strength of refractory mat'erials, whether porous or non-porous, it"is also'known to incorporate bonding agents of various kinds. Among the bonding agents which have been used are phosphoric acid, certain double zirconium silicates, certain zirconates, and others. These may be considered as permanent bonding agents, that is, they serve to permanently bond the refractory although the bonding agent itself may in some cases be entirely removed. The

n green strength of the material, before firing, may f bein'creased by which is eliminated in d s not permanentl inanent bonding agents are in general less refracf tory,or produce in the course of firing materials which are less refractory, base material itself. As many of these highly refra'ct'ory materials, such 1 chief'utility from the fact "extremely high temperatures, it is thesmaller the quantity of bonding agent while $56111- attaining adding such materials as gelatin, the process of firing and bond the base. The perthan the refractory as zircon, derive their that they will withstand obvious that satisfactory strength, the better *"willbe the final result.

It is therefore an object of this invention to produce materials of high refractoriness, high h -porosity and high strength. It is another object Itofincrease the refractoriness of such materials um'ut harmfully affecting the porosity and strength without Other objects will appear hereinafter.

335,626, May 16, 1940.

November 29, 1946, Se-

These objects are accomplished by thoroughly mixing a refractory material, particularly a high temperature refractory material, with a bonding agent and asuitable quantity of liquid to a homogeneous consistency, then subsequently thoroughly mixing an organic pore-forming material with this mixture, shaping the mass, drying and firing at an elevated temperature. It has been found, in accordance with this invention, that the incorporation of the pore-forming material after the remaining ingredients of the mass have been thoroughly mixed with each other, produces greatly improved and unobvious results, as shown hereinafter.

For pore-forming material, there is used any granular organic solid of low or no ash content. Among such materials are cork,'wood and coke. Petroleum coke, whether calcined or uncalcined, is a particularly desirable material because of its controllably lowash content and relatively slow rate of burning, which is conducive to accurate control of the process, with the production of a highly uniform product. Coke also has the advantage that it is applicable to ramming and pressing procedures, while cork cannot be permanently pressed because of its elasticity, causing expansion when the pressure is released. In the case of cork, it is preferred to use a material having' arelatively slow burning rate, since cork with a fast burning" rate tends to eliminate volatile matter so rapidly as to create cracks and fissures during firing. The pore-forming material must be sized within definite limits so as to produce ware containing definite pore size. It must be of a size wholly and considerably coarser than the constituent grains of the refractory mix itself, since pore-forming material of a size in the same range" as the grainrefractory prevents grain to grain contact of the refractory in the green mix, with almost complete loss of bond on firing, whereas pore-forming material much coarser than the grains themselves allows grain to grain refractory contact resulting in well bonded final ware.- For example, where the refractory material is of particle size wholly-passing through an 80 mesh screen, pore-forming material no finer than 30 mesh should be used where the refractory' material is of a p'articlesize wholly passing through a 200 mesh screen, Dore-forming material no finer than mesh be used.

For refractory material zircon is preferably used because .of its high refractoriness. Other suitable high temperature refractories comprise silicon carbide, refractory aluminum oxide, mullite, sillimanite, chromite, olovine, forsterite,

quartz or other forms of refractory silica, refractory clays, electrically fused zirconia, talc, feldspar, beryl, rutile, kaolin, spinel, kyani-te, thorium oxide, thorite, ceria, andalusite, baddeleyite, porcelaln. This list may be further amended by: the use of either synthetic or natural minerals, uncalcined, or in the raw state, or in the precalcined state. With silicon carbide the so-called fire sand, which is silicon carbide containing some incompletely combined silica, may be used. The refractory aluminum oxides include bauxite, raw: or precalcined, gibbsite, and corundum, or-synthetic fused aluminum oxide. Olivine isused-ravk or'calcined sufiiciently to form forsterite. Quartz is used in the form of sand, ,gbBi fl'a as. calcined quartz which has. been previously and suitably heated above 1470 C. so as to ilorm cristobalite. The refractory clays include the various types of non-plastic fireclays, the flint clays, the kaolins, etc. These refractory materials may be used alone, in combination with each .other, or in combinationwith zircomaftertransforming same into the proper physical state for casting. Either milled or granular refractory material, or a mixture thereof; maybe used, although milled material or a mixture of milled and granular material is preferred.

For permanent bonding agent, a considerable variety of materials may be used: excellent bond for zircon ware is phosphoric acid; (H POl), which bonds even coarse zircon grains very tightly at low temperatures, and excellent porous'ware can be made by the use of phosphoricacid alone as a bond. However, the use of HgPGgalone as a. bond sufiers from the serious disadvantage in the high temperature range, sincePzQs becomesvola tile below 3000 F. and results in a pronounced permanent weakening of the structure unless the refractory is composed entirely of] finely milled material. Preferred bonding agents, either with zircon or with other refractory materials, are double silicates of zirconium and certain other metals, and certain zirconates, asdisclosed and claimed in Reissue Batent No. .1;2241 and copending applications Serial Nos. 25fi,9 2 8,n o,w Patent No. 2,220,411, and 329,524, now Patent No. 2,220,412, especially when, used in conjunction with phosphoric acid. Otherbondln' a ents that may be used are those, disclosed; and, claimedin copending application to Wainer andfiake, Serial No. 285,580, now Patent.No. 2 .26'I,772. To secure the best results, milled bondingaigentsarepreferred.

Any of the standard organic bindersmaybe used to produce green strength. It has been found that a 5% gelatin solution isthe'best forgeneral usage, particularly for zirconware.

The amounts of these various.,materials.. be varied within quitewide, limits, Thev amount of bonding agent should bekept aalowaspossible and still secure the desired: strength, both be:- cause the bonding agents useda'rel generally more expensive than the refractory base, such as. zircon, andbecause they are less. refractory than mate.- rials such as zircon. In, general, theQrefractory base should comprise a major portion -(i. e, at least, 50%) by weight of.the ntire massmriontothe addition of pore-formingimaterialr Whezrusing a combination of phosphoric acidandjhezirconates or double silicates of. zirconium another. metal, as disclosed, in Reissue,P,atent,No. 21,224 and copending applicationsserial Nos. 256.928,, now Patent No. 2,220,! 1.1, an(1,329 ?24, now, Batent. No. 2,220,412, as the bonding, egent-.,it,has.,been. found that lessthan 1.0. partaby w.eight. o$=.-H:RO(

and less than 15 parts by weight of zirconate or double silicate per 100 parts of refractory base is adequate for most purposes, although more'may be used if desired.

The phosphoric acid is ordinarily irsolutlon form, and this, togetherwith gelatin solution or] i other agent to secure green strength, and water,

if desired, comprises the liquid portion ofvzit'he mass. Sufiicient total liquid is employed to secure 5 the proper consistency, which may vary from a viscous slurry to a paste, depending upon f molding procedure to be used, such as ramming, pressing, molding or other desired method-of shaping. The presence of the gelatin solution in creases; theviscosity of a mass which would otherwise. be quite fluid.

All the above. ingredients (refractory base. bonding agent,- aqueous liquid, and green strength i,

bonding agent, if desired), except the pore- 013m ing material, are first thoroughly mixed together until a homogeneous mixture,.substantial1y out lumps, is formed. The porerf'orming, rial is then folded in" or mixed. withth'a, to a uniform consistency. The. amount. forming material depends upon the Gk. sired. In practice, it has been foundia porosity of to of total-'volumeis able andin. this case. the. pore-forming and other materials. removed. comprise from 70 to 75% of the volume ofjfih tire mass. The weight, of pore-formingfinatedot will of course depend upon its density; case of calcined coke with. a. zircon. approximately 3 parts by weight. ofzircontdlftd Zbparts by weight of, coke has, been founder a 18.

The mass is next, molded into... the, remnant; shape, allowed to dry, and isthe'n, rem

ing. In order to burn out the porer formingmatqe xam-m1.

' 1000 grams of' -'200.jmesh purifledizircomflm grams of mesh'purifiedgzirconesandt. 35' 87% H3PO4 solution (s er; 1.71). maize as 5%, gelatin solution,v are thoro gh ye ta gether to a homogeneousjconsistencxa of; 10+30 mesh ca1cined. .petroleu1n,. then mixed therewith until:- distriblitedl throughout the mass. The mass under pressure, dried andfired in standard refractoryprocedure in miebdioxidiu atmosphere to 1800 is. when, temperature: above 2800 F.. are usedthe PzQswillgslwlsjM till off so as to leave. the residual. mecmtidztig bondedin theform of a cellular brick mixv produces wareof 7.0 to. 15%;poros1tg 3 is suitable for the temperatureirangefiilfialgm 4000 F. It weighs approximately once-bait; of a similarly sized brick from.

isomitted.

Examine-2 2 treated as in Example 1,

- The table below shows the quantities EXAMPLES 3-19 In the following Examples 3-19, all them- ,gredients except the coke are thoroughly mixed together to a homogeneous consistency. The coke is then mixed therewith until evenly distributed throughout the mass. The mass is then shaped under pressure, dried and fired in accordance with standard refractory procedure in a good oxidizing atmosphere to 1800 F. (Examples 1-12, 18) or 2400" F. (Examples 13-47, 19) These mixes produce were of 70 to 75% porosity, and are suitable for the 2600 to 4000 F. range. and kinds of ingredients in the various examples.

600 grams calcined petroleum coke (size in mesh) 877 HQPOOJ solution (sp. gr. 1.71)

Other bonding agent (see below for kind) -200 mesh zircon 5% gelatin solution The other bonding agent in Examples 3, 4 and 13 may be milled sodium zirconium silicate, potassium zirconium silicate or lithium zirconium silicate; in Examples 5, 6 and 14 it is milled calcium zirconium silicate; in Examples 7, 8 and 15 it may be milled barium zirconium silicate, magnesium zirconium silicate, zinc zirconium silicate or a fired equimolecular mixture of clay and zirconia powder; in Examples 9, 10 and 16 it is a 4 to 1 milled mixture of calcium zirconium silicate, with either sodium zirconium silicate, potassium zirconium silicate, lithium zirconium silicate, zinc zirconium silicate, barium zirconium silicate or magnesium zirconium silicate; in Examplesll and 1'? it is milled T102 or SnOa; in Example 12 it is milled ZrOz or ThO2; in Examples 18 and 19 it may be the zirconate of either lithium, sodium, potassium, calcium, magnesium, zinc or barium.

EXAMPLE 20 50 parts of mesh refractory material (zircon, quartz, aluminum oxide, silicon carbide, rutile, fused zirconium dioxide, mullite, sillimanite, olivine, forsterite, chromite, refractory clay, kaolin, beryl, spinel, lryanite, thorium oxide, thorite, ceria, feldspar, andalusite, talc, baddeleyite, porcelain, raw or synthetic, calcined or uncalcined, or mixtures thereof), 44 parts of 200 mesh milled refractory material as above, 8 parts of 87% HBPO; solution (sp. gr. 1.71) 5 to 10 parts of calcium zirconium silicate or other bonding agent, 15 to 20 parts of water and 1 part of oxalic acid (which may be omitted if desired) are thoroughly mixed to a homogeneous consistency. 500 grams of this mass is then mixed with 500 cc. of 10+20 mesh granular coke, cork or wood. until the latter is evenly distributed throughout the mass. The mass is then shaped, dried and fired to 1800 to 2400 F., depending 6 upon the refractory used and the degree of reifractorin'ess desired.

EXAMPLE 21 ExArarLs 22 3000 grams of 200 mesh zircon, 90 grams of sodium zirconium silicate and 550 cc. of 5% gelatin solution were thoroughly mixed to a homogeneous consistency and screened through a 20 mesh screen. 2400' cc. of cork were then'mixed therewith until uniformly distributed throughout the mass with the formation of a smooth paste. The mass was then shaped into the form of a brick, dried and fired to 2500 F.

Refractory materials prepared in accordance with the present invention have been observed to exhibit strengths which were quite unexpected, as compared with similar refractory materials prepared by mixing all the ingredients at the same time, including the pore-forming material. This may be accounted for in part by the fact that the pore-forming material partially prevents intimate contact between the bonding'agent and the refractory base, if it is added before the refractory base and bonding agent are thoroughly intermingled. For comparative purposes, refractory bricks were constructed as follows, following the procedure of Example 22 as closely as ,possible except for the time at which the poreforming material wasadded.

with difficulty. The mass was rammed so as to secure approximately the same density as in Example 22. The mass was dried for the same period of time as in Example 22 and was then fired simultaneously and side by side in a furnace with the brick of Example 22 and for the same period of time.

The same procedure was followed as in A except that the ramming was omitted.

The brick of Example 22 and brick A were of approximately the same density, but were both about 1.6 times as dense as brick B. Certain strength tests were then applied to all three bricks. The cross-breaking and crushing tests used were the same or patterned after the recommended procedures of the A. S. T, M., except that, due to the small size of the testing equipment, a smaller test specimen was used throughout (for test procedures see 1939 Book of A. S. T. M. Standards, part II, Non-metallic materials-constructional, page 198).

The cross-breaking test equipment is provided with suitable bearings so that full contact is made with the specimen at all times. A specimen 4% inches long by 1 inch wide by 1 inch deep is used. The is positioned-on the bearingsv e a t y a pictured on page 200 or: therabovereierence. The load is. applied to the top knife edge by means of a lever'arm, and the load continually increased by pouring sand into a bucket held by the lever arm at a specified position on said arm.

The modulus. of rupture (cross-breaking strength) in pounds per square inch is reported as calculated, by the following formula:

where R=modulus of rupture in pounds per square inch W=total load in pounds at which specimen failed l'=distance between support in inches b=width of specimen in inches d=depth of specimen inlinches By means of the above test the modulus of ruptureof the three test. bricks are as follows: Example 2-2:,3120 pounds. per squareinch A=2250pounds per square inch 15:17 pounds per square inch The crushing strength was determined using the familiar recording Carver Laboratory hydraulic press.- A bearing'block was used for perfeet positioning of the-specimen as shown on page 199 of the above reference. Check runs were made on specimens varying in cross sectional area from 0.75 in. to 16 in Load was impressed at the rateof about 1000 pounds per minute, loading being stopped at first instance of failure.

The cold crushing strength in pounds per square inch was calculated-from the formula:

where S=cold crushing strength in pounds per square inch W=total load indicated by testing machine A=average of the gross areas of top andbottom ofthe specimen, in square inches, of the section of thespecimen perpendicular to the line of appllcation of the load. Y

By means of the above test the cold crushing strengths of the three bricks are:

Example 22:2170 pounds per square inch A=320 pounds persquare inch B=63=pounds per'square inch The invention and the advantages thereof havingbeen' described, it is understood that it is not intended to be limited, except as definedin the appended claims,

We claim: v

l. The method ofmaking a refractory structure of high porosity which comprises thoroughly mixing---a refractory base witha permanent bonding agent including a double-silicate of zirconium and a metal taken from the'group consisting of lithium, sodium, potassium, magnesium, calcium, bariumand'strontium'in the presence of an aqueous-liquid, subsequently adding to the batch a 2., The method" ofjmakin'g arefracto y structure of' ighporositi; which,compr ses ro shly mixins av refractory base with a permanentbondin a ent includin phosphoric. acidand a. double, s ili-.

atje of zirconium and a metal taken. from the.

r p consisting, of. lithium, sodium, potassium. magnesium. calcium, barium and strontium and a green strength bonding, agent in the presence of an aqueous. liquid, subsequently adding to the batcha. granular organic solid, shaping, the mass, drying, and firing at an, elevated temperature.

3; The method of makinga, refractory structure of high porosity which comprises thoroughly mixing zircon with a permanent bonding agent in the presence of an aqueous liquid, subsequently adding to the batch a granular organic-solid, shaping the mass, drying, and firing at an elevated temperature.

4.. Themethod of making a refractory structure of high porosity which comprises, thoroughly mixing zircon with a permanent bonding agent in the presence of an aqueousliquid, subsequently add ing to the batch a granular organic solid havin particle, sizes larger than the particle sizes of said zircon and said bonding agent, shaping the mass, drying and firing at an elevated temperature uptier-good oxidizing conditions.

5. The method of making a refractory structureofhigh.v porosity which comprises thoroughly mixing zircon with a permanent bonding agent, including a, double. silicate of zirconium and ametal taken from the group consisting of lithium, sodium, potassium, magnesium, calcium, barium and strontium inthe presence of an aqueous liquid, subsequently adding to the batcha granular organic solid, shaping the mass, drying and firing at an elevated temperature.

6. The method of making a refractorystructure of high porosity which comprises thoroughly-mixing zircon with a permanent bonding agent including phosphoric acid and adouble silicate of zirconium and a. metal takenfrom the group con-. sisting of lithium, sodium, potassium, magnesium, calcium, barium and strontium and. a green strength bonding agent in the presence of an aqueousv liquid, subsequently adding to the'batch a granular organic solid, shaping the: mass, drying and firing at an elevated temperature.

7. The method of making a refractory structure of highporosity which comprises thoroughly mixing zircon with apermanent bonding agent including phosphoric acid and a double silicateof zirconium and a metal taken from the group consisting of lithium, sodium, potassium, magnesium, calcium, barium and strontium and a green strength bonding agent in the presence of an aqueous liquid, subsequently adding to the batch a. granular organic solid having particle sizes larger than the particle sizes of said zircon: and said bonding agent,shaping the mass, drying and firing at an elevated temperature under. good oxidizing conditions.

' CHARLES J. KINZIE.

EUGENE WAINER.