US2220411A - Refractory and method of making same - Google Patents

Description

mama Nov. 5,1940

um'rso STATES PATENT OFFICE 2,220,411 aaraacroar ANIS) Mn'rnon or MAKING corporation of Maine No Drawing. Application February 17, 1939,

Serial No. 250,928

Claims.

This application is a continuation in part of our copendlng applications Serial. No. 189,808, filed February 10, 1938 and Serial No. 246,156, filed'December 16, 1938. 5 Our invention relates to bonded refractories and especially to new methods of bonding refractories, and new refractory compositions.

The special refractories field is characterized not only by a group of special and usually ex- 1. pensive materials, but also by the mode of fabrication and manufacture indigenous to the particular refractory, none of which are normally applicable to themanufacture of other refractories. This special refractories field has develll oped because of certain unusual demands on refractories not satisfactorily fulfilled by refractories already in existence.

For example, some applications demand extremely high softening points; others, extreme resistance to thermal shock and to spalling; others, a minimal dimensional change through a wide range of temperatures; others, the possibility of direct fabrication to accurate and controlled sizes; others, certain special electrical properties; others, high heat conductivity; others, low heat conductivity; others, low specific gravity; others, high hot strength; others, high hot strength and low cold strength or vice versa, etc. plus any combination of the above properties besides a large number of special properties too numerous to mention.

One industry, which demands suitable refractories particularized to probably a greater extent than in any other, is the dental industry where the fabrication of investment for the casting of inlays and bridge work has become specialized to a very high degree. For example, an ideal refractoryi for the dental industry should have properties somewhat as follows: It should be 40 able to be cast from slip form of sumcient fluidity completely to fill all recesses and interstices of the mold, no matter how minute, without the formation of bubbles. It should remain in fluid form after mixing for at least 5 to 10 minutes without segregation or separation of the constituents. After remaining for from 5 to 10 min- .utes in fluid form, it should be capable of setting in the next 5 to 10 minutes to a hard, tough, strong piece with a controlled porosity factor as well as preferably undergoing setting expansion of approximately one half to one per cent. It should then be capable of being dried and fired with extreme rapidity. It should also be capable of completely controllablif'th'ermalexpansion properties, either temporary or permanent and above the size of the original mold in the temperature range from 1200 to 3000 F. or higher if necessary. so as .to compensate for the usual shrinkage on the cooling of cast alloys. It should not give off much gas at 1200 to 3000 F., 5 and it should have sufficient porosity to absorb any gases emitted by the casting metal. It should be strong when cast and weak when cold after use to permit easy removal of the cast. It should not react in any way chemically with the 10 'casting alloy. It should not dust. It should be a super-refractory. These properties are the major requirements of a refractory for dental use. There are several other characteristics, but they are of minorimportance. 15

Another use of refractories is for heavy duty at high temperatures. For this purpose zircon alone has the disadvantage that it is from 20% to 50% heavier than other refractories used in the high temperature field. Furthermore, the o very low thermal conductivity ofzircon is comparable to the best of thermal solid insulators. For many applications, strong tough refractory ware of good thermal conductivity is a desired condition. Such applications are for refractory g5 walls behind boiler tubes, such as used on ships where weight-saving and good thermal conductivity are required, for kiln furniture and kiln car bats, etc. A known refractory for this purpose consists of a mixture of zircon and silicon 3o carbide. Silicon cairbide has a heat conductivity approximately from 10 to 15 times that of zircon, and a specific gravity of 3.1 as against 4.6 for zircon. Hitherto the bonding agent employed in such refractories has been phosphoric 35 acid. However, in the manufacture of piecesof refractory were in which the length and breadth are very large in proportion to its thickness, the green strength during drying and preliminary firing is so low that handling pieces of any size is very difficult. Secondly, the finished fired strength is seldom greater than a modulus of rupture of 600-800 pounds per square inch. Thirdly, on firing above approximately 2800 F. the phosphate bond tends to be dissipated so that the 45 ware becomes weak and crumbly, thereby permanently losing its strength characteristics.

Another application of special refractories, as described and claimed in our copending application Serial No. 204,3'92,filed April 26, 1938, is 5 in the-high temperature insulation field. In this field, the insulating qualities of zircon or other insulating refractory are greatly increased by rendering the materials porous. This may be accomplished by incorporating in such refrac- 55- tories a pore-forming material such as coke, and

.',prepared when desired. Zircon refractories heretofore developed have been suitable only for ramming in damp, non-plastic forms in such shapes where ramming procedures are applicable. Their green strength is poor; no increase in strength is obtainable on long standing at room temperatures, and their plasticity is low. For these reasons, such zircon mixtures arenot suitable for slip casting or mold casting, or in methods of plastic mixes; hence the manufacture of intricate shapes, not amenable to ramming, cannot be made. Although the addition of organic bonds may be used to develop satisfactory green strength on ramming, these additions are, notwithstanding, of no avail when the mix is fluid enough to cast or pour.

We have discovered novel and improved methods, compositions, and bonding agents, which more or less completely fulfill the exacting demands for refractories, particularly in the dental industry. Furthermore by the use of these novel bonding agents and methods, we have found it possible adequately to bond practically any super-refractory materials which can be obtained in suitable grain sizes, or any desired combination of these refractory materials, with the exception of the highly basic magnesite or fused magnesia bodies.

Not only are these improved methods applicable to super-refractory materials, but also'to normal refractories, with the exception of magnesite and dolomite, that are capable of being obtained in suitable grain sizes, and to combinations of these normal refractories with eachother, or with the super-refractories. By -the use of these novel bonding agents and methods, we have found it conium silicate with the oxide or carbonate of the possible economically to prepare in a strong form the, highly porous light-weight type of refra'cto known as insulating firebrick.

These novel bonding agents comprise the following :f double silicates of zirconium and an element of the group consisting of lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc and aluminum; the hydrates of the group tour oxides T102, SnOa, Z102, 'rnoi; the zlrcona-tes of lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc and aluminum. These bonding agents may .be used either singly or in desired combination.

The double silicates may be prepared in. a variety of ways. For example, they may be prepared by thermally reacting finely divided zirnamed element: or by thermally reacting zirconium oxide and silica with the oxide or carbonate of the named-element; or by thermally reacting zirconium oxide with the silicate of the named element. A suitable setting agent involving aluminous material is a fired intimate mixture of clay and oxide, mixed mol forfmol, milled gfter firing at 2100 F. 'fo'r'"3 "hours, 'in which form it is suitable for use- The zirconates may be prepared by thermal reaction of zirconium oxide with theoxide or carbonate of the named element.

These bonding agents may be used alone, but

" jprermmy ii -combination with suitable amounts HaPOa because of the refractoriness of its thermal products, its ease in use, and also its relatively low corrosive activity in comparison with the other acids. A HSPO4 content up to 10% may be used, but we prefer to use between 3%-and 7%, since the lower the satisfactory H3PO4 content, the less is the danger of disintegration at high temperatures f the double silicates, calcium zirconium silicate is the most refractory and may be used up to a content of to 1% without serious decrease in refractoriness. The quantity. of the other double silicates, particularly those of the first group, should not exceed 3% if high refractoriness is desired. Combinations of calcium zirconium silicate and theother silicates provide the refractoriness of the calcium compound plus the greater reactivity of the more alkaline materials.

While up to 7% CaZrSiOs may be used to advantage, we prefer to use 4% or less when used alone, and 3% or less when used in combination with H3P04. When CaZrSiOs is used in com-; bination with the other double silicates, a satisfactory ratio is 8 parts of the double silicate of zirconium and calcium to 2 parts of the other double silicate (parts by weight). While up to 5% of such combinations may be used either with or without H4204, we prefer to use 3% or less when used alone, and 2% or le ss when used with HaPOi.

desirable properties from the standpoint of high green strength, it is desirable to use them. We also have found that mixtures of these two ,double silicates with calc um zirconium silicate produce to a large ex nt the high green strengths attainable with the use of the former, and without the cracking sometimes encountered.

In combination with H3PO4 no more than 1% to 3% of the above named oxides of the fourth group need be used, although up to ZrOi or Thm may be used to advantage. More than 3% TiOa or SnOz' causes undesired swelling.

' Any of the standard organic binders may be used to produce green strength; however, we have found that a 5% gelatine solution is the best for general usage, particularly. for zircon ware.

Refractory materials which can be bonded by means of the bonding agents of the present invention, comprise a wide variety of materials."

Amongst the most important of these is zircon. Others comprise, silicon carbide, refractory aluminum oxide, mullite, sillimanite, chromite; olivine, forsterite, quartz or other forms of refractory silica, refractory clay electrically fused zirconia, talc, feldspar, beryl, rutile, kaolin, spinel, kyanite, thorium oxide, thorite, ceria, an-

dalusite, baddeleyite, porcelain. This-list maybe further expanded by the use of either synthetic or natural mineralahncalcined, or in the raw state, or in the precalcined state. With silicon carbide we may use the so-called fire-sand which I is silicon carbide containingv some incompletely combined silica. The refractory. oxides include bauxite, raw or prec'alcined, gibbsite,

and corundum, or syntheticv fused aluminumpxide. Olivine is used raw oi calcined'sufllciently to form forsterite, Quartz is used in form of sand. crushed canister, or ascalcined quart:

which has been previously and suitably heated above 1470 C. so as to form cristobalite. The refractory clays include the various types of nonplastic fireclays, the flint clays, the kaoiins, etc. 5' These refractory materials may be used alone,

in combination with each other, or in combination with zircon, after transforming same into the proper physical state for casting. Amongst the most useful combinations is a mixture of zircon and silicon carbide. 7 By using these refractory materials in combination with the heretofore detscribed bonding agents, a casting refractory for practically every known application may be advantageously made,

with controlled working and setting times and,

also with practically any desired set of properties.

For example we have obtained for the dental industry, by continually varying a suitable mixture of zircon and quartz sands from pure zircon to pure quartz, permanent changes in dimensions varying all the way from 6.5% shrinkage to 3.5% expansion with any desired thermal expansion in the temperature range from 1200 F. to 3000 F.

normally required in dental refractories.

We have also found that the refractory combinations may be still further modified for special applications and for special properties by the addition of materials not properly considered refractory.

For example, the addition of a small amount of fluorspar produces high setting expansionand also contributes to a low temperature vitreous bond. Sodium-silico-fiuoride promotes high setting shrinkage and also contributes to low temperature vitreous bond. Lead compounds produce very low temperature vitreous'bonds and produce bodies having valuable electric insulating properties. Barium compounds add valuable 40 electrical resistivity and insulation properties. Various colored oxides may be added to produce desired body colors. Boron and magnesium compounds also contribute to the maintenance of high temperature electrical resistivity.

v The use of silicon carbide as a base enables us to produce an extremely highly refractory body with a high heat and electrical conductivity and a good resistance to thermal shock. It can be used in reducing atmospheres. Combinations of silicon carbide and zircon in cement form are also suitable as refractory coat for electrical heating elements. Refractory ware comprising a mixture of zircon and silicon carbide containing .the bonding agents of the present invention develops very high green and preliminary fire strength, and shows moduli of rupture between 1500 and 3000 pounds per square inch in the finished fired piece. Such ware also permits firing at much higher temperatures than 2800 F. without dissipation of strength characteristics of the bond. Finally, by use of these bonding agents in conjunction with HaPO4, ware of SiC plus zircon can be' cast, pressed, sprayed, or extruded, or dipped with the advantageous green strength developed at temperatures between 30 and 50 C.

sun further to decrease the weight or this high Fused alumina base bodies produce steady and even thermal expansion from room temperature to 1500' C. totalling 1.2 per cent. Spinel, sillimanlte, or kyanite bodies bonded by our improved methods have excellent electrical resistance at high temperatures. High kyanite addi- 5 tions produce rapid volume increases above 1100" C. Andalusite increases in volume above 1400" C. Natural baddeleyite shows rapid expansion at 2900 F. Forsterite, sillimanite, and mullite produce high temperature bodies with extreme l0 resistance to spelling as well as-high hot load strengths, etc.

The possible combinations of desirable properties which can be obtained with our bonding agents and procedures may be expanded to cover 15 practically every refractory application known in the casting field.

A description of the manner in which we practice our invention is as follows: The refractory grains suitable for the desired purpose are first 29 prepared in a physical state so that the aggregate is amenable to good casting procedure. For example, a mixture of equal parts by weight of minus 35 mesh grain size and minus 200 mesh grain size normally will afford a smoothly flowing 25 mix when incorporated in water. A refractory aggregate consisting entirely of minus 200 mesh material also produces good working properties resulting in a still finer grained product. Aggregates consisting wholly or in part of more 30 than 35 mesh coarseness usually cause a granular mixture which interferes with good application. To the properly sized refractory aggregate or mixture of various refractory aggregates is added about 6% by weight of phosphoric acid of 35 specific gravity 1.71; while 6% is satisfactory for most purposes, the phosphoric acid may be reduced as low as 2% or increased as high as 9% for particular applications. The acid and refractory grains are completely mixed, and then 49 passed through a 10 to 20 mesh screen to insure complete distribution of the acid throughout the refractory.

To partsby weight of this damp mixture is added between a and 10 parts by weight of the 45 bonding agents or proper mixtures of these bonding agents. While normally less than 3 parts of the bonding agent used does produce proper casting cold strength, more than 10 parts may be used if necessary or desired for particular 50 applications. The bonding agent is thoroughly mixed with the acid-refractory aggregate. To this mixture is then added sufllcient water to produce'an easily workable mixture. For a high density material consisting of zircon, the amount 55 of water necessary will vary between 8 and 12 cc. per 100 grams of the mix. For a. relatively low density material, such as quartz, clay, silicon carbide, etc., the amount of water necessary will vary between 10 and 15 cc. per 100 grams of 60 the mix. Tap water may usually be used directly as the water addition. However, we have found that time of set is normal when water has a high pH='7.5-8.5, due to dissolved lime compounds. and that the timeof set is appreciably increased when the tap water is neutral or on the acid side. The pH of neutral or acid waters may be suitably built up by proper treatment with lime. 70

The refractory-acid aggregate, bonding agent and water are thoroughly mixed until a smooth free-flowing slip is obtained and the fluid is then cast into place. The casting is allowed to stand quietly until sumciently hard for easy handling, 15

the molddemounted, and the piece dried and fired.

The speed and extent of the drying and firing operations depend on the size of the piece,

' the strength of the bond, the chemical and "physical nature of the base refractory. and to some extent the final application of the piece. For example, a refractory clay should be dried and fined slowly due to the shrinkage on drying and also changes in'crystal modification on the 1 increase in temperature. A zircon casting may be dried and fired with extreme rapidity because it does not-suffer from such defects. A mullite body is normally fired to 2400? to 2600 F. if its final application is high temperature service. A zircon body need be fired only to 1800 F., where its final application is resistance to low temperature fused phosphate corrosion, etc. To secure satisfactory hardness and strength in zircon ware containing H3P04, it should be fired to 1600- 1800 F., while such warewhich does not contain HaPO4 should be fired to at least 2400" E. to reach a satisfactory strength. The, great advantage in the H3PO4 addition is thatrlow temperature bonding is commercially inexpensive.

As to the amount and-type of mixture of these I bonding agents, several examples will clarify what potash, or lithia to the lime compound. These compoundsvalso increase the strength of 'vit reous bond. Use of the zinc, barium, magnesium compounds produces the set in 30 minutes to an hour, and the casting can be handled in 1% hours.- Here also, speed of setting may be still further increased by the addition of the alkali products 'to any of \these last three compounds. Normally about one part of alkali zirconium silicate may be added for every 2 to 3 parts of other corresponding compounds to produce the satisfactory set additions.

In general the thermal reaction products of zirconia and the oxidesv mentioned in respect to the bonding agent's (forming zirconates) will produce a faster and harder s'et than an equal amount of the corresponding zirconia, silica, and the oxide compound. For example, castings using magnesium zirconate can be made to set with extreme rapidity; an interval of 2 or 3 .minutes need elapse after casting before the casting' is quite hard, so that the piece can beremoved from mold and easily handled in approximately 10 minutes after casting. Here again '6") mixtures of zirconates and the double silicates as bonding agents show definite advantages.- For example, "magnesium zirconate alone remains relatively non-vitreous even on firing to quite high temperatures. ,f

This propertyis a decided advantage in dental refractory applications, since the refractory should be relatively weak even after exposure to high temperatures. Development of the vitre-.

ous. bond at high temperatures enhances the strength .and utility of the body for high temperature' servicewhich is accomplished by adding'tomagnesium zirconate small quantities of alkali or alkaline earth compounds of zirconia and silica. A vitreous bond is thereby developed at high temperatures which produces a strong temperature application. For example, a practicallyheat shockproof body of zircon is made by bonding with a mixture of 2 parts by weight magnesium zirconate and 1 part by'weight of sodium zirconium silicate or calcium zirconium silicate.

To form the light-weight, porous insulating refractories, the casting cement is prepared just as we have heretofore described except that just before casting, a definite volume of granular organic material, such as cork, coke, or wood, is added and well mixed in. The mixture is then cast, dried and fired; on firing the organic materials burn out leaving voids so as to produce a cellular'refractory body ofexcellent utility for thermal and sound insulation and also of very low specific gravity.

In the foregoing description relative to the properties required in the dental industry, a working time of several minutes was found to be necessary. We have found magnesium zirconate in combination with HaPO4 to be a very satisfactory bonding agent in every respect, ex-

cept one, for use in making dental refractories of practical utility. The chief drawback when used as we have described is the extremely rapid setting which does not allowtime for sufiicient workability.

We have found that this working time may be varied at will in a practical range simply by varying'the ratio of the weight of magnesium zirconate to the weight of acid used. For example,. 100 parts of a'base refractory of zircon containing 5 parts by weight of phosphoric acid will set in 1 to 3 minutes after complete mixture when-10 parts of magnesium zirconate are used. Increasing the acid concentration 'to 15 parts by weight without varying the other con.- stituents will increase the time of se); by several hours. We have found that smaller quantities of other added acids are more efilcient in this regard.

Such acids include the solid organic acids such as oxalic, tartaric, citric, etc., and theinorganic and organic strongly acid salts. Such inorganic and organic acid salts are sodium or potassium acid sulphate, sodium or potassium acid phosphates, ammonium acid sulphate or ammonium acid phosphate, the acid fluorides of sodium, potassium or ammonia. The organic acid salts are the acid salts of sodium, potassium or ammonium with oxalic, tartaric, citric acids, etc., for example, "sodium acid oxalate, etc. To a lesser extent, boric acid may be used.

From an industrial handling point of view,

theseaclds may also be considered more efllcacious than heavy concentrations of liquid phosphoric acid, due to. the diiiiculties involved in handling sludges highly concentrated in a liquid corrosive acid. Furthermore, the organic acids ,are eliminated easily in the firing cycle, and

can not complicate the possible utility of the finished body since no fired residue remains. In

the dental field, for example, a body containing 100 parts of was parts of H3PO4, 1o parts of magnesium zirconate, and 1 art of oxalic acid (-all parts by weight) may be worked in fluid form for 5 to 7 minutes after mixing, and will then set hard in '15 to 20 minutes after mixing, thereby eliminatingthe main disadvantage of magnesium zirconate for use in dental refractories. Magnesium zirconate also produces a setting expansion of of 1%, which is a desirable quality in dental refractories.

tough of excellent utility for-high While we have heretofore dealt chiefLv with gredients, parts by weight:

casting procedures, we do not limit ourselves to this type of application alone. Simply by reducing the amount of added water the cements may be applied by ramming or pressing.

. I To illustrate more in detail the methods of practicing our invention we will set forth several examples.

Example 1 The charge is made up of the following in-' gredients, parts by weight:

- Parts 35 mesh granular zircon 50 -200 mesh milled zircon 44 u HzPQ4 specific gravity 1.71 6 Oxalic a 1 Magnesium zirconate 10 Water 10 We mix the first four items thoroughly and 20 then add the magnesium zirconate, mix, add water, mix and cast. A super-refractory is then formed for dental work of low expansion when tired to 2200 F., and permanent shrinkage when above 2500 F.

Example 1 A The charge is made up of the following ingredients, parts by weight:

We then mix as in Example 1 and cast. Omission of oxalic acid produces a much more rapid set. A super-refractory is then formed i'or dental an and other work of high thermal expansion'when fired to 2800 F. 'and showing approximately 0.5% permanent expansion on firingto 2800 I".

. Example 1--Bv The charge is made up of the following in- Parts 35 mesh zircon sand 50 r 200 mesh milled quartz 44 H3Po4 specific gravity 1.71 6 oxalic acid 1 Magnesium zirconate 10 Water 11 We mix sameand cast as in Example 1 to pr '55 duce a super-refractory for dental and other work. Omission of the oxalic acid greatly speeds the set. This refractory shows high expansion up to at least 2800 Ft, undergoing a permanent expansion of 2.0% on short firing at 2800' F.

Example 1-c The charge is made up of the followingin gredients, parts by weight:

We mix same-and cast as-in Example 1 to produce a super-refractory for dental and other work. Omission oi the oxalic acid greatly speeds the set. This refractory shows very high expanu sion from 400 1''. to at least 2800' It, undergoing a permanent expansion of 3.5% on short firing t0 2800 F.

Example 2 Thecharge is made up of the following ingredients, parts by weight: 5

. Parts 35 mesh granular quartz 50 200 mesh milled quartz 44 H3PO4 specific gravity 1.71 6 m Bonding agent 10 Water 12 We mix and handle as in Example 1. The bonding agents consist of (a) the thermal reaction products of zirconia, silica and any oxide 15 of the group CaO, MgO, BaO, SrO, ZnO, A1203; (b) a 2:1 mixture of any of (a) with the thermal reaction product of zirconia and silica with L120, NazO, K; (c) the hydrates of titania, zirconla, thoria or tin. We dry and fire on schedule to 2 1800 F; where a porous non-vitreous body is desired, as in the dental casting industry. ,A tighter, more vitreous body with better high temperature properties is obtained by schedule firing to 2400 F.

Example 2-4 The charge is made up of the following ingredients, parts by weight:

Parts mesh granular quartz, 50 200 mesh milled quartz; 44 HaPO4t specific gravity 1.71 6 Bonding agent 0).- 5

Water 4 12 85 ()Bondin agent consists of the thermal reaction roduct of zircon silica and any oxide of 111.0, N330, We mix and handle as in Example 2 and then dry and re as stated in Example 2.

Example 2-3 40 The charge is made up oi the following ingredients, parts by weight:

Parts 35 mesh granular quartz 5'0 200'mesh milled quartz 44 45 H.1P04 specific gravity 1.71 6 Bonding agent 10 Water 12 silica and an oxide of the u L Na K.O M SrO, 'mo, n0, shoe v 1: and h hdle 'ee 3i Example 2 and then dry and fire as stated in Example 2.

Example 3 The charge is made up of the following in gredients, parts by weight:

Parts Refractory a gregate 0) --s5 mesh size Q Milled refractory material 200 mesh 44 H.1P04 8 1 Magnesium zirconate 10 Oxalic :aci 1 Water 4 8 t 5.5

()Ihcludes either aluminum oxide, silicon carbide,

rutile, fused zirconium dioxide, mullite, Iil ite, quartz, olivine, forsterlte, chromite, refracto clay, kaoliih beryl, spine], kyanite, thorium oxide, tho te, eeria, f dlpar, sndalusite, talc, baddeyleyite, porcelain, raw or mthetle, calcined or uncalcined, alone as stated or mixed with each 10 other or with zircon. (")A complete list is given in (F). We mix as in Example 1 and then cast, dry,- and fire to 1800 F. or to higher temperature predicatedby the use. vWhere the body doeenot have to withstand temperatures above 2400 1.1!;

p dients, parts by weight:

'10 iimitisused.

Erample 3-4 The charge is made up of the following ingredients, parts by weight:

15 Parts Refractory aggregate 35 mesh (same as ()in Example 3) u... 50 Refractory milled -200 mesh (sam as in Example 3) v 44 m HsP04 6 Bonding agent (see list in Example 2) 10 -WBter 8 to 15 We mix and handle as in and fire as in Example 3.

' zmm zc 3-3 The charge is made up of the following ingre- Example 1 and dry so Parts Refractory aggregate-35 mesh (same as in Example 3).. 50 Refractory milled -200 mesh (same as ("l in Example 3) 44 3| HaPO4 specific gravity 131-11 6 Bonding agent (see Exam le 2-A) e Water 8 to 12 We mix and handle as in Example 1 and dry 0 and fire as in Example 3.

Emmple' 3-0 The charge is made up of the following ingredients, parts by weight: 5 Parts Refractory aggregate -35 mesh (same as in Example 3) 50 Refractory milled 200 mesh (same as in Example 3) 44 m HaPO4 specific gravity 1.71 6 Bonding agent (see (i Example 2-3) 10 Water 8 to 12 We mix andhandle as in Example 1 and dry 5 and fire asinExarnple 3,. a a

Example3-'D The charge is made up of the following ingredients, parts by weight:

- Refractory aggregate 200 meshisee Examples 1, 1-A, 1--B, l--C and 3)- 94 11:104 specific gravity 1.71-.. 6 Bonding agent (see Examplesd, 2, 2-A, b a 2-3) -5 to 10 Oxalic acid (may omit if desired) 1 Water 12 to Example 4 The charge is made up ofthe following ingrefl dients,'parts by weight:

Refractory aggregate mesh (see 1, 1A, 1-B, 1-C and 3) -parts-, Refractory milled 200 mesh (see Example 1, 1A, 1B, 1-0 and 3)- parts. HaPOs specific gravity 1.71 do Bonding agent (see Example 1, 2, 2-A,

2-13) parts.... 5 Water do- 15 Oxalic acid (may omit if desired) "parts" -10+20 granular coke, .cork, or wood per 100 grams of above mix -430...

We mix all the ingredients except the cork as before, and then add cork and cast. We then dry and fire as in Example 3.

Example 4-4 a I The charge is made up of the following ingredients, parts by weight:

Refractory milled' #200 mesh (see Example 1, 1-A, 1B,'1C, 3)

, parts-.. 94 i5 Phosphoric acid -specific gravity 1.71 a parts-.. 10 Bonding agent (see Examples" 1, 2,

2-A, 2-3;) parts.... 5m 10 Oxalic acid (may omit if necessary) -parts 1.. Water d0 15 to 25 -10+20 granular coke, cork, or wood in 100 grams, of above mix cc- 100 We mix all the ingredients except the cork as a before, and then add cork and cast. We then dry and fire as in Example 3.

, Eztample 5 The following charge is made by intimately mixing, parts by weight:

mesh zircon sand ...z. 50 200 mesh milled zircon -1-.." 45

Milled calcium zirconium silicate (or Bazrsios, MgZrSiOs, SrZrSiQs, ZnZrSiOs, or mixtures of these) 5 Phosphoric acid Water 6 The thick slurry'is then poured into suitable molds and entrapped air isremoved by, unusual vibratory methods. At room temperatures, the

final set is obtained in about one hour, and the mold may then be stripped. The shape is then dried and fired to about 1000 C. in accordancewith approved refractory procedures. The final ware does not soften at 3000 F.

The above mix is made suitable for dipping, brushing or spraying by the addition of 2 or more parts of water. A

Although this example specifies 5 parts of milled setting agents, up to 20 parts of setting agent may be used in every case, except when ZnZrSlOs is used. Any increase of the amount of setting agent increases the green strength after I the set, decreases time of set and hardness of finished ware. As low as 2 parts of the setting agent can be used where prolonged time of set, rela tively. low green strength, etc., attendant on use- ,of smaller amounts of setting agent, are not important for the finished article. In the case of ZnZrBiOs, no more than 5 parts should be used. since larger quantities cause splitting of thick sectionson setting.

Example -A The mix comprises the following:

Parts 60 mesh zircon sand -i 50 200 mesh milled zircon 47 Sodium zirconium silicate (or lithium zirco- Example 5.

nium silicate or potassium zirconium sili- The mix is treated in the same manner as in The addition of two or more parts of water makes the mix amenable to spraying, dipping or brushing. Set is obtained in about one hour. Tlae finished refractory does not soften at 28 0 F. Although this Example 5A specifies 3 parts of milled setting agent, up to 10 parts can be used, rwulting in a pronounced decrease in time of set and decrease in refractory properties. The use of .more than 10 parts of the setting agent causes the piece to split on setting, particularly in thick sections.

I Example '5-B The mix comprises the following:

Parts 60 mesh zircon sand 50 200 mesh milled zircon; 45

Fired-equi-molecular mixture of clay and zirconium dioxide (or 5 parts zirconium spinel) 5 Phosphoric a 5 Water 6 This mix is treated in the same manner as in Example 5; the time of set is 1 hour, and the finished article is stable at 3000 F. The addition of 2 or more parts water makes the mix amenable to dipping, sprayingor brushing.

Although 5 parts of setting agent are specified, up to 20 parts canbe used; Anyincreasein the amount of the setting agent decreases the time of set with no marked decrease in refractory properties.

This mix is treated in the same manner as in Example 5; the time of set is 1% hours, and the finished article is stable at 3000 F. The addition Although 5 partsof setting agent are spec mesh pure zircon sand grams 1333. 3 up to 20 partscan be used. Any increase in the mesh Pure 7 amount of the setting agent decreases thetime mean carblde .of'set with no marked decrease in the refractory PhQsPhmTic acid of specm? i 3: 73 o qualities. An increase of ZrO: and Th0: increases the re ractoriness of the ware. 5% sell-tine solution p u 0 1 Either sodium zirconium silicate powder; Example or zirconium silicate pow- The mix comprises the following: der: or lithium zirconium silicate pow- M der; or barium zirconium silicate pow-H 60 mesh zircon. ..;:50 der or magnesium zirconium silicate I 200 mesh milled zircon powder; or zinc zirconium silicate powcalcium zirconium silicate 8 der; or strontium zirconium silicate Sodium zirconium silicate"-- 2 powder gra.ms Phosphoric acid '5 Or calcium zirconium silicate powder 100 grams..

of 2 parts of water makes the mix amenable to dipping, spraying or brushing.

The mix is treated in the same manner as in Example 5; the time of set is 30 minutes, and the finished article is stable at 3000' F. The addition of 2 or more parts of water makes the mix amenable to dipping, spraying or brushing.

Example 5E The mix comprises the following:

Parts mesh zircon 50 I -200 mesh milled zircon... 45 Calcium zirconium silicate 7 Zinc zirconium silicate 3 Phosphoric acid 5 Water 7 casting mix so as to form a mealy, partially dry.

mixture. The zirconium silicate as well as the double zirconium silicates referred to in these examples are definitely based on pure zirconium silicate of the following composition:

Percent Zirconium silicate (ZrSi04) 97 to 100 T102 .J -0 to 0.20 FezOz 0 to 0.05 NazO 0 to 0. 04 Rare earths, Ce, La, etc 0 to 0. 20 Free quartz 0.10 to 2.00

The zircon composition which we prefer to use in thisprocess and for use in making the double silicates specified therein has approximately the following compomtion:

Percent ZrSiO4 e 99. TiO: 0.030 F620: 0.010 NaaO 0.003 A120: 0. 020 CeO: 0. 030 10.20: 0. 005 P20: 0. 09 CrzO: 0. 001 CaO 0. 100 M 0. 002 CuO 0.001 8110: 0. 002 Boos 0. 001 with practically no trace of free quartz.

- Example 6 The following charge is made by intimately mixing the following ingredients:

' 'conium silicate powder -grams Or 8 parts of calcium zirconium silicate powder plus 2 parts of sodium zirconium silicate powder; or 2 parts of potassium zirconium silicate powder; or 2 parts of lithlumzirconium silicate powder; or 2 parts of barium zirconium silicate powder; or-2 parts of magnesium zirconium silicate powder; or 2 parts 01' zinc zirconium silicate powder; or 2 parts of strontium zirconium silicate powder grams" 100 Or T102 powder grams- Or ZlOz; or Thou-powder -grams- Up to 400- grams of ZrOa or Th0: may be used to advantage by adding 5 cc. of gelatine solution,

for each 200 gram addition above 100 grams.

The ratio of silicon" carbide to zircon may be varied from the above mix to Grams 35 mesh zircon 835 200 mesh zircon--. 415. 35 mesh silicon carbide 1250 The gelatine solution in this latter case is increased to'l50 cc. v

Where a close-grained, tight, low porosity body is desired, the mix is fabricated entirelyoi -200 mesh zircon and --200 mesh silicon carbide. For such a mix patterned after Example 6. we increase the amount of phosphoric acid to cc. and the amount of gelatine solution to cc. When equal weight mixtures ofzirconand silicon carbide are used in the200 mesh state, we increase the amount of phosphoric acid to 125 cc. and the amount of gelatine solution to cc.

The above ingredients are completely mixed, screened, pressed into the proper shape, which is then dried and fired in accordance with standard refractory procedureslto 1800 F.

. Example 6-4 For casting, dipping or spraying, the mix comprises: 35 mesh pure zircon sand grams 1.333. 3 200 mesh pure zircon sandgrams 666. 7 35 mesh silicon carbide -grams- 500.0 Phosphoric acid of specific gravity 1.71 g 3 5% vgelatine solution plus do--- Either sodium zirconium silicate powder; or potassium zirconium silicate powder, lithium zirconium silicate powder, magnesium zirconium silicate powder, barium zirconium silicate powder, stron-. tium zirconium silicate powder, zinc zir- 100 or calcium zirconium silicate powder ams" Or 8 parts of calcium zirconiumsilicate powder plus 2 parts of sodium zirconium silicate powder; or 2 parts of potassium zirconium silicate powder; or 2 parts of lithium zirconium silicate powder; or 2 parts of magnesium zirconium silicate powder; or 2 parts of barium zirconium silicate powder; or 2 parts of strontium zirconium silicate powder; or 2 partsoi zinc zirconium silicate powder.grams Where a close grained, tight, low porosity body is desired, the mix is. fabricated entirely 0! 200 mesh zircon and 200 mesnsiliconcarbide. For

" of phosphoric acid to 125 cc.

I Or 210: or ThOz-.. grams The above ingredients are completely mixed into a thick slurry. cast or sprayed into place,

standard refractory procedures.

Emmpleh-B The mix comprises the following ingredients:

35 mesh zircon sand "grams-.. 1066.6 --200 mesh zircon sand -grams 533.4 35 mesh silicon carbide -grams- 400.0 10 20 mesh petroleum coke -grams 500.0 Phosphoric acid of 1.71 sp. gr cc 85.0 5% gelatine solution cc 140.0

Plus Either sodium zirconium silicate powder;

or potassium zirconium silicate powder; or lithium zirconium silicate powder; or magnesium zirconium silicate powder; or strontium zirconium silicate powder; or'barium zirconium silicate powder; or. zinc zirconium silicate powderngramsm Or Calcium zirconium silicate powder .grams Or 8 parts of calcium zirconium silicate plus either, 2 parts or sodium zirconium silicate; or 2 parts of potassium zirconium silicate, 2 parts of lithium zirconium silicate, 2 parts of magnesium zirconium silicate, 2 parts of strontium zirconlum silicate, 2 parts of barium zirconium silicate, 2' parts of zinc zirconium 1 silicate grams Or T102 or SnO: -grams 50 Or ZrOa or-ThO2 grams 100 Up to 400 grams of ZrO: or Th0: may be used to advantage-by adding 5,cc. of gelatine solution for each 200 gram addition over 100 grams.

All the above ingredients, except the coke, are intimately-mixed, and the coke is folded in last. The ware is pressed, dried and fired in accordance with usual refractory procedures up to 1800 F. It produces a body weighing 50% less per unit volume than that derived in Example 6.

Example 6-0 The mix comprises the following ingredients:

Or a mixture of 8 parts of calcium zirconium silicate powder p1us'2 parts oisodlum zirconium silicate powder; or potassium zirconium silicate powder; or lithium zirconium silicate powder; or magnesium zirconium silicate powder;

' or zinczirconiumsilicate' powder; or v strontium zirconium silicate powder j or barium zirconium silicate powder grams- Or TiO: or'SnOa grams 50 Where a closs-grained, tight, low porosity body is desired, the mix is fabricated entirely of -200 mesh zircon and -200 mesh silicon carbide. For such a mix patterned after Example 6-0, we increase the amount of gelatine used to 280 cc. When the whole charge is mixed we press same into shape, dry, and fire according to standard refractory procedures up to 2400" F.

From the standpoint of utility and in further 10explanation of the above examples We present the following advantages: Quartz alone as added to other bodies adds a good measure of refractoriness, increases resistance to acid fluxes, adds hot strength at high temperatures, and enables a choice of any expansion value practically desired in the dental range particularly.

Zircon alone or added to other bodies produces super-refractoriness, increases resistance to acid fluxes, produces very dense bodies of high thermal shock resistance. It affords very low thermal expansions and low heat conductivity. Zircon refractories are also highly useful in appiications involving pronounced resistance to corrosion by alkali phosphate fused baths. The

corrosive nature of this type of fusion is such as to rapidly disintegrate the usual refractory bricks, such as flreciay, mullite, fused quartz, fused alumina, silicon carbide, magnesite, chromite, etc. Our zircon refractories have been found to withstand the action of such melts 10 to 100 times better than any other commercially known refractory of this type.

Of the other refractories, silicon carbide increases thermal resistance in reducing atmospheres, adds heat and electrical conductivity, re-

duces density, is super-refractory and shows excellent high temperature properties. Aluminum oxides afford steady and definite thermal expansions through a wide range of temperatures, adds poor thermal shock characteristics,

adds resistance to basic fluxes and is' super-refractory. The mullites, sillimanites, andalusite, kyanite, olivine, forsterite, etc. are super-refractories with excellent high temperature properties, show excellent resistance to glasses and glassy slags. Chromite is super-refractory,

neutral to slags, has poor thermal shock re sistance. Beryl, talc, spinei, and rutile, certain porceiains have excellent electrical properties,

poor super-refractory qualities with the exception of spinel. The magnesia minerals in general show good temperature characteristics of electrical resistivity. The feldspars, clays, and kaolin are well known with respect to properties and afford cheap sources of refractoriness.

Thorite, thoria, and ceria are super-refractories and possess good electrical properties. Zirconium dioxide is a neutral material, with a very high melting point. so By means of the above materials alone or in mixture each develops its particular set of properties to the extent that it is present, -and resuits in a collection of compositions which permits practically every known refractory appli- 65 cation to be covered. For example, combinations of zircon with rutile or rutiie alone, with magnesia containing materials, and bonded by the barium compounds, suitably shaped and fired produce an excellent set of electrical prop- 70 erties. Combinations of zircon and carborundum produce a body which is at once heatresistant and heat conducting. In other words each material develops the properties for which it is known when used alone or in combination with others by the use of the bonds we have heretofore described. This statement is true only when the bodies are fired or used considerably below the vitrification or combination point of any particular refractory combination. Above this temperature the refractory is modified by 5 the possible formation of eutectics. For example, mixtures of zircon and aluminum silicates soften and melt rapidly at approximately 3000 F. because of the formation of relatively low melting point eutectics. In the appended 10 claims, the term finely-divided refractory materials includes not only the materials of suit-' able grain size not more than 35 mesh coarseness but also the finely-milled materials of minus 200 mesh grain size as well as mixtures thereof 15 as set forth in the various examples.

We claim as our invention:

1. A composition suitable for forming refractory masses comprising a major proportion of a refractory material and a minor proportion of 0 a preformed zirconate of a metal taken from the group consisting of lithium, sodium, potassium, magnesium, calcium, barium, and strontium.

2. A composition suitable for forming refractory m'asses comprising a major proportion of a 2B refractory material, a minor proportion of a preformed zirconate of a metal taken from the group consisting of lithium, sodium, potassium. magnesium, calcium, barium, and strantium, and a minor proportion of an acid taken from 30 the group consisting of l'hPOs, HCI, H2804 and HNOa.

3. A composition suitable for forming refractory masses comprising a major proportion of a refractory material, a minor proportion of a 35 preformed vzirconate of a metal taken from the group consisting of lithium, sodium, potassium. magnesium, calcium, barium, and strontium, a lesser amount of a double=silicate of zirconium and a metal of said group, and a minor propor- 40 tion of an acid taken from the group consisting of HaPOi, HCI, H2504 and HNOa.

4. A composition suitable for forming refractory masses comprising a major proportion of a refractory material, a minor proportion of pre- 5 formed magnesium zirconate, and a minor proportion of an acid taken from the group consisting of HJPO4, HCl, H2804 and HNOa.

5. A composition suitable for forming refractory masses comprising a major proportion 50 of a refractory material, an organic acid, a minor proportion of preformed magnesium zirconate, and a minor proportion of an acid taken from the group consisting of HJPOA, HCl, H2804 and HNOa.

6-. A composition suitable for forming refractory masses comprising a major proportion of a refractory material, an organic acid salt,- a minor proportion of 9. performed magnesium zirconate, and a minor proportion of an acid taken from the group consisting of 1131904, HCl,

' H2804 and M03.

7. A composition suitable for forming refractory masses comprising a major proportion of a refractory material. an -inorganic acid salt. a minor proportion of a preformed magnesium zirconate, and a minor proportion of an acid taken .mm the group consisting bf HSPOG, HCl, E3804 and HNOs.

8. The method of making refractory materials which comprises mixing a major proportion of a refractory material with a minor pro- .portion of a preformed ziroonate of a metal taken from the group consisting of lithium, so- 1 and strontium, drying the mixture, and firing at an elevated temperature.

9. The method of making refractory materials which comprises mixing a major proportion of a refractory material with a minor proportion, of a preformed zirconate of a metal taken from the group consisting oi lithium, sodium, potassium, magnesium, calcium, barium, and strontium, and a minor proportion of an acid taken from the group consisting of H3P04,

H01, H2804, and HNOz, drying the mixture, and firing at an elevated temperature.

10.' The method of making refractory materials which comprises mixing a major proportion of a refractory material with a minor proportion of a preformed magnesium zirconate and a minor proportion of phosphoric acid, shaping the mass, drying, and firing at an elevated temperature.

CHARLES J. KIZNZE'. EUGENE WAINER.

v CERTIFICATE OF CORRECTION Patent No. 2,220,1111. November 5, 1914.0.

f cums J. mm, ET AL. a

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page i, first column, line-2.2, for 'fdetscribed" read "describedpage 6, second column, 1ine'52, for the word "unusual? read -usua1--; page 9, second column,

line 29, claim 2, for "strantium" read --str ontium-; and that the said Letters Patent should he read with this correction therein that the same may conform to the record of the case in the Patent Office. Signed and sealed this 17th day of December, A. 13. 191;,0.

* Henry Van Arsdale (Seal) Acting Commissioner of Patents.