TN 295 No. 8878 ^^^H ] r ■ ■:r ^WWWMBWWBIII^'- i^r.cfi'' **'\ '■-. *^<* 'oV' -V • .0^ ,^ .,.o, % '" ^^^ V*.. V v^ .» ^°-v.. /..i^-.% C5 'o . . < /V o V ^°'-<^. <* aO ^ "■' .■?>^ ^n .4;* »:r(\^^V^ t^ .^ »V o •4- ^ %,. '""" ^°-n^. \- o V "' -^ '^^^'' •'^^„./ /^_^/A-= ^^..f ,0 1'^^ '<*_. ^0^ ^,^^ ^ \ ^*^ . 01 . , -^ -^^0^ l-J'" . o > .^^ . •^ ^■^ / ,«> A ■*■" , ^°-^<^, ^^ .or..-, ^o .V V A ^. C"^ ♦ ■0- 4^. ^ ^^ A^ '^^ • • • \C) ^ " ,0 .•* o.^' 0^ - ' • "^^ ^^ ^£ ^ <*> **''-. '•. '> s V ,0 ,0 > V ;* <^ ■S\ ^"^^ .^.:^%% ^'* \- J" ► .^■^ IC ^^^^ Bureau of Mines Information Circular/1982 Chemically Bonded Refractories— A Review of the State of the Art *>@i UNITED STATES DEPARTMENT OF THE INTERIOR ^Ws.S^>i Information Circular 8878 Chemically Bonded Refractories— A Review of the State of the Art By Rustu S. Kalyoncu UNITED STATES DEPARTMENT OF THE INTERIOR James G. Watt, Secretary BUREAU OF MINES Robert C. Norton. Director As the Nation's principal conservation agency, the Department of the Interior ^\ has responsibility for most of our nationally owned public lands and natural resources. This includes fostering the wisest use of our land and water re- sources, protecting our fish and wildlife, preserving the environmental and cultural values of our national parks and historical places, and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to assure that their development is in the best interests of all our people. The Department also has a major re- sponsibility for American Indian reservation communities and for people who live in Island Territories under U.S. administration. ,4 This publication has been cataloged as follows Kalyoncu, R. S Chemically bonded refractories— a review of the state of the art. (Bureau of Mines information circular ; 8878) Includes index. Supt. of Docs, no.: I 28.27:8878. 1. Refractory materials. I. Title. 11. Series: Information cir- | cular (United States. Bureau of Mines) ; 3878. -TN355-.U4-[TN677.5] 622s [666'.72] 81-607575 AACR2 For sale by the superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page Abstract 1 Introduction 2 Chemical bonding 2 Phosphate bond 3 Phosphate bonding agents 3 Fundamental studies 4 Properties of phosphate-bonded materials 6 Silicate bond 9 Alkali silicates 9 Ethyl silicate 10 Oxychlor ide , oxysulf ate and oxynltrate bonds 11 Conclusions and recommendations 13 Bibliography 15 ILLUSTRATIONS 1. Compressive strength of magnesite body as a function of average degree of poljrmerizatlon of (NaP03)n 4 2. Effect of heat treatment on phase constitution of aluminum phosphate binder 8 TABLE 1 . Oxide reactions with phosphoric acid 5 CHEMICALLY BONDED REFRACTOR lES-A REVIEW OF THE STATE OF THE ART By Rustu S. Kalyoncu ' ABSTRACT A major goal of the Bureau of Mines is to conserve the Nation's mineral resources by developing improved performance materials. In sup- port of this mission, a survey of the state of the art of chemically bonded refractories has been made, covering the scientific literature, government reports, and patents. This review includes research and development results for phosphate, silicate, oxychloride, oxysulfate, and other bonding agents used in refractories manufacture. A significant finding of the review was that references on bonding mechanisms, bond formation kinetics, and other important process param- eters and conditions were few and universally vague. As a result, rec- ommendations are made to expand research efforts to investigate the kinetics and mechanisms of reactions in chemically bonded refractories. ^Ceramic engineer, Tuscaloosa Research Center, Bureau of ^4ines, Tuscaloosa, Ala. INTRODUCTION Improved ceramic materials are in constant demand for processes involving severe chemical, corrosive, and thermal environments , especially at high pres- sures. During the past decade, demand for higher quality ceramic materials has significantly increased. This is true, for example, in the steel industry where oxygen steelmaking has increased produc- tion rates and operating temperatures, thereby compounding the demand for basic refractories that can withstand higher temperatures for use in furnace linings, ladles, stacks, checkers, etc. Since the steel industry constitutes 65 percent of the refractory consimiption, efforts to meet industry's demands for high- quality refractories have increased accordingly. The development of chemically bonded refractories represents an impor- tant accomplishment in the advancement of the technology. Chemically bonded brick, also referred to as unfired brick, is formed with the aid of selected additives that set up at room tempera- ture and provide structural integrity, eliminating the need for high-temperature sintering. Chemically bonded refractories offer significant energy savings by eliminating the need for high-temperature processing. In addition, the many methods for modi- fying the chemical bond offer a large number of opportunities for developing new compositions to withstand a variety of severe environments encountered in many industrial processes. However, it should be recognized that chemically bonded refractories using calcium alumi- nate, sodium metasilicate, MgSO^ (mag- nesiian sulfate), MgCl2 (magnesium chlo- ride) , H2SO4 (sulfuric acid) , phosphoric acid, and alkali phosphates as bonding agents have been available for many years. This report presents a review of literature on the present state of the art of chemically bonded refractories and identifies areas requiring research and development to fulfill the need for improved ceramic materials. This work supports the Bureau of Mines' mission to conserve the Nation's mineral resources and reduce imports of critical materials by developing improved performance mate- rials and using more abundant domestic mineral resources. CHEMICAL BONDING Reference to a chemically bonded refractory made as early as 1905 (25) 2 and claimed that a valuable refractory lining could be made by "mixing such sub- stances as magnesite, chromite, etc. with sodium silicate and calcium chloride." Unfired refractory brick was mentioned by MacCallum (55-56) and chemically bonded brick by Youngman ( 103 ) . Progress in the chemically bonded refractories in the United States began in the 1930' s, with R. P. Heuer dominating the patent litera- ture. Heuer received a number of patents (34, 36-40) on bonding refractory mate- rials with sulfates, sodium silicate, sulfite lye, and small additions of clay ^ ■^Underlined numbers in parentheses refer to items in the bibliography at the end of this report. or bentonite. In 1941, Heuer patented a chemically bonded brick (38) that was molded in steel cases. Two U-shaped steel sheets were placed in the top and bottom of the press mold so that, after forming, the brick was encased in steel on four sides. The expansion due to oxi- dation of the steel casing helped to off- set shrinkage at high temperatures. Since the 1950' s, refractory research has made significant advances with the establishment of more modern laboratory facilities and the participa- tion of scientists from other disci- plines, such as physics, chemistry, and materials sciences. These scientists have brought new schools of thought to the experimentation and interpretation of research results. Phosphate-bonded high-Al203 (alu- mina) refractories are being used in such areas .as iron-transport cars, soaking pit slag lines, and steel ladles. Various monolithic refractory linings with chemi- cal bonding, including hydraulically cast materials, are being evaluated for use in coal conversion process vessels. PHOSPHATE BOND Recognition of bonding properties of phosphoric acids and various phosphates is not new. Numerous processes for using phosphate materials as bonding agents in refractories have been known for many years. Because they possess high fusion temperatures, phosphate bonds have always been of special interest in the field of chemically bonded refractories and have been studied extensively. Phosphate Bonding Agents The first significant review article on phosphate-bonded refractories appeared in 1950 (46); in it, three methods of developing chemical bonds were described: (1) reaction of siliceous coii5)ounds with phosphoric acids, (2) metal oxide-phosphoric acid reactions, and (3) reaction of acid phosphates with the refractory grains. The reaction of siliceous compounds with phosphoric acid results in a hard white or translucent product (depending on the exact silicate composition) , char- acterized by a lack of crystallinity. Various auxiliary materials are usually added to alter the properties of the chemical bond, but the basic setting mechanism consists of formation of a Si0 2 (silica) gel. However, this low-melting frit is not a very effective bond for high-temperature applications. A number of patents have been issued for refractories bonded with phosphoric acid. One such patent describes a ZrSi0 4 (zircon) refractory with an alkaline, alkaline earth, or magnesium zirco- nium silicate, using HCl, H2SO4, citric, or phosphoric acid as the bonding agent (48) . Phosphoric acid gave the best results, presumably because of its greater reactivity with the silicate com- ponents and the higher viscosity of its melts. Other silicates, such as those of Al, Cr, and Mg, react with phosphoric acid to form a chemical bond at about 200° C (J_0). Phosphoric acid forms bonds through reactions with the cationic as well as silicate groups. For example, ZrSiO^ appears to form zirconium phosphate as well as silicon phosphates, and may form double phosphate salts of silicon and zirconium as well (64) . Aluminum, chro- mium, and magnesium oxides are also known to react with phosphoric acid at 200° C to form chemically bonded materials. These metal-phosphate reaction products have been found to be refractory and stable (thermally, chemically, etc.). Instead of the oxides, the halides of ^fe, Sn, Th, Ca, Ba, Al , Zr, or Ti may be used with phosphoric acid to form a chemically bonded refractory (65). Aluminum hydrate may be used with refractory clay, filler, and phosphoric acid to form a bond that becomes permanent when heated to 100° to 300° C. A third method of using phosphates in refractory chemical bond formation is by the direct addition of monobasic or dibasic phosphates. Either alkaline earth acid phosphates or ammonium acid phosphates with aluminous materials may be used in place of phosphoric acids. In fact, since the reaction with phosphoric acid is very rapid, the use of phosphates of alkaline and alkaline earth metals is preferred. Even more preferable is the use of various organic derivatives such as hydrazine, hydroxylamine, aniline, methylamine, or ethylamine acid phos- phates (101). Acid phosphates may also be formed by mixing triphosphate with an acid to form monophosphate or diphos- phate. This process may be used with alkaline earth phosphates, such as cal- cium, which are less costly than other materials (50). It should also be noted that phos- phate bonding agents have been used for other types of applications. Sodivnn polyphosphate (Na4P20-7-NagP40 , 3) , an inorganic colloid, is used to disperse TiOj for casting because it improves green strength ( 100 ) . alkali silicate binders to be improved by additions. A simimary tions with phosphoric reaction products is table 1. The strength of is also reported alkali phosphate of oxide reac- acid and their presented in The use of alkali metaphosphates as chemical bonding agents in refractory mortars has been studied by Herold and Burst (33). Sodium hexametaphosphate (NagPgOjg), forms rubberlike polymers and yields high-strength mortars with fire- clay aggregates. These binders are com- monly used in high-Al203 refractory mor- tars and ramming mix. Effects of average degree of poly- merization (n) of vitreous sodium poly- phosphates [(NaP03)n] have also been investigated (73) . Maximum strength was attained on samples cured at 800° C, with an average degree of polymerization of 24, as depicted in figure 1. Strength was higher when 4.3 weight-percent phos- phate was added as an aqueous solution than when 5 weight-percent was added as a finely divided powder. 150 130 110 £.li.U r^ 'v B 200 1 \ 180 ■ 1 \ 160 ■ J V 140 - ^ ^^ 120 1 1 , 20 (24) 40 60 AVERAGE DEGREE OF POLYMERIZATION, n FIGURE 1. - Compressive strength of magnesite bodyaSQ function of average degree of polymerization of (NaP03)n. A, HaPOj added in pov^der form; B, NaPOs added as water solution. (73) Fundamental Studies Published literature describing fun- damental studies of chemical bonding in refractories is almost nonexistent. How- ever, there have been several attempts to explain the kinetic processes (9, 47). Attempts to better understand bonding mechanisms, chemical kinetics of bond formation, and the conditions governing these processes have been very limited. A clear understanding of these fundamen- tal parameters has not been achieved. The proprietary nature of the refractories technology discourages pub- lication, for fear of losing the com- petitive advantage. A large volume of patent literature exists on the subject (50-51, 55, 6]_, 63-65), but emphasis is on the mechanics of refrac- tory preparation rather than the science of chemical bonding or the fundamental processes. TABLE 1. - Oxide reactions with phosphoric acid Oxide Time of setting, hours 1/30 1/30 NS NS 1/30 NS 12 NS NS 3 1/2 1/20 3 NR NS NS NR NS NR 1/60 NS NR 24 NR NR 72 1/60 1/60 1/6 1/30 NR NR NR 12 NR 18 48 NR 1/6 NR Temp, rise of 0.5 cm^, ° C Modulus of rupture, psl Product reported in chemical literature Other data and observations BeO Be(6H)2 MgO Mg(0H)2 , MgO calcined at 1,280° C. CaO calcined at 1,100° C. CaO calcined at 1,100° C; liquid con- tained 9.6 pet CaO. SrO calcined at 1,400° C; liquid con- tained 9 pet SrO. BaO calcined at 1,400° C; liquid con- tained 9 pet BaO. CuO < CdO ZnO calcined at 1,100° C. SnO SnOj HgO Hg20 NiO PbO Pb02 Pb304 B2O3 Al^Oj Al203'xH20 CO2O3 Cr203'xH20 ^^203 ^6304 La203 La203 calcined at 1,400° C. 1^203 Si02 H2Si03 Ti02 Ti(OH)^ Zr02 ZrCOH)^ Th0 2 from Th(N0 3)4 at 300° C. Ce02 V2O5 Cr03*xH20; M0O3; W0 3'XH20. ND Not determined. NR No reaction. NS Not set. 15 18 30 ND 25 ND 24 6 15 27 3 23 24 7 38 5 1 2 36 36 18 30 2 5 2 30 750 570 ND ND 500 ND 520 ND 570 700 850 100 ND ND ND ND ND ND ND ND ND 1,260 ND ND ND 300 ND 400 ND ND ND ND 200 ND 250 ND ND 180 ND Be(H2P04)2; Be(H2P04)2-BeHP04 do MgHPO^; Mg(H2P04)2 do do Ca(H2P04)2"xH20. do None. .do. CuHP04-H20. Cd(H2P04)2. SnHPO^ None Hg3(P04)2.. Hg3P04 None Pb3(P04)2.. None Pb(H2P04)4 H2BO3 None Al(H2P04)j. None. .do. FeH3(P04)j-2-l/2H20; Fe(H2P04)3. None La2(HP04)j do Y2(HP04)3. None do. .. do TiOHPO^ None Zr(HP04)2 Th(HP04)2-H20. None V0 2H2P04'4-1/2H20. Normal reaction. Do. Violent reaction. Do. X-ray pattern shows MgO and weak lines for Mg(H2P04)2. Violent reaction. X-ray diffraction shows crys- talline pattern. Violent reaction. Do. Normal reaction. X-ray pattern shows absence of crystalline Cd3(P04)2. X-ray pattern shows absence of crystalline Zn3(P04)2, 0.0, 2, 4H2O. None. Do. X-ray pattern shows Hgj(P04)2. X-ray pattern shows Hg3P0^. None. X-ray pattern shows Pb3(P04)2. None. Cracked on setting; X-ray pattern shows crystalline product containing Pb3(P04)2; Pb02 absent. None. Do. X-ray pattern shows amorphous product. None. Do. Tacky product. None. Violent reaction. None. Shrinkage cracking. None. Do. Do. Do. Do. Do. Tacky product. None. Do. Do. Source: Reference 47. Properties of Phosphate-Bonded Materials With the proper selection of the bonding material and aggregates, phosphate-bonded materials do not exhibit reduced strength on heating. They remain highly refractory and possess good abra- sion and slag resistance after heating. Alumina-phosphoric acid ramming composi- tions are particularly resistant to Fe203 slags at temperatures up to 1,350 C (62) . Cement-free phosphate-bonded cast- ables vary in their properties depending on the type and amount of bonding agent and the type and grading of the aggre- gate used. It is reported that tabular Al203-based castables show a reduction in hot strength above 800° C. This decrease becomes even more severe for castables containing MgO as a setting agent. This type of castable, however, is widely used in chemical plants because of its chemi- cal durability. Silicon carbide (SIC) is added to phosphate-bonded high-Al20 3 products to increase their hot strength. This increase is thought to be due to formation of Si02 phosphates in the presence of SiC. Erosion resistance of AI2O3 cast- ables has been improved through the use of phosphate bonding (27). The use of phosphoric acid is claimed to result in much higher strengths than the use of metal phosphates such as aluminum phos- phate. Phosphoric acid is the preferred binder for attaining maximum bond strength, and the hygroscopic tendencies of these compositions can be eliminated by curing at 650° F. High bond strength, dimensional stability, and resistance to erosion are retained to temperatures of 3,400° F in these compounds, and resist- ance to erosion is improved by about an order of magnitude over the existing commercial erosion-resistant castables. Stiffening and subsequent loss of work- ability observed in phosphate-bonded high-Al203 refractories (53) is believed to be caused by the precipitation of insoluble aluminous orthophosphates form- ing as a result of the reaction of acid salts with Al203-bearing materials in the mix. The use of inhibited phosphoric acid as the bonding agent (53-54) pre- vents this loss of workability. The AI2O3-H3PO4 reaction is reported to have the following sequence: AI2O3 + 6H3PO4 > 2A1(H2P04)3 + 3H2O; A1(H2P04)3 < -^ AlP04»xH20 + 2H3PO4; 257° C 2A1(H2P04)3 > Al2(H2P 207)3 + 3H2O; 500° C Al2(H2P 207)3 > [A1(P03)3]^ + 3/2XH2O. (1) (2) (3) (4) The orthophosphate A1(H2P04)3 is water soluble and, as the bonding phase, is sticky and very viscous. It is a pre- cursor to Al2(H2P207)3 and A1(P03)3 in the cured refractory. Prevention of softening requires stopping or slowing down the reaction described in equation 2. This is accom- plished in one of two ways: The AI2O3 surfaces are coated with a nonreactive substance that prevents H3PO4 from react- ing with the AI2O3, which keeps the pH low with excess H3PO4 and shifts equation 2 to the left to retain soluble acid phosphate; or a sequestering agent is used to hold the aluminum in solution to prevent AIPO4 precipitation. The volume stability is measured either by creep under load or by reheat- change at high temperatures and is an important performance criterion in many refractory applications. The volume stability of burned and unburned phosphate-bonded high-Al203 brick was determined by Baab and Blackwood (2). The authors concluded that phosphate-bonded high-Al203 refractories had poor high-temperature volume stabil- ity, compared with conventionally made brick, with corresponding AI2O2 contents. Figure 2 summarizes the phase con- versions in an aluminum phosphate binder with a molar ratio of P2'-'5 (phosphorus pentoxide) to AI2O3 of approximately 2.3 (49). The diagram provides a general reference for the various phases that may be produced and the approximate tempera- ture ranges over which phase transforma- tions or conversions take place. As shown, extensive physicochemical changes can take place upon heating the aluminum phosphate phase. It is generally agreed that the hydrated aluminum phosphate phase, AlH-j(P04 )2 '3112 0, is the major phase producing chemical bonding. Upon further heat treatment, this phase is eventually converted to AlPO^ (berlinite and cristobalite forms) and A1(H2P04)3. Orthophosphate with SiO, AIPO4 is isostructural '2 ^—' ^^ ) ^'^<1 shows similar inversions to the alpha and beta forms of quartz, tridymite, and cristobalite. The compound A1(H2P04)3 is a highly hygro- scopic phase (78), which is converted to an amorphous phase above 570° F. Dehy- dration processes are completed between 925° and 1,470° F. A glassy metaphos- phate phase appears above 2,000° F, decomposing to AlPO^ , with evaporation of 4 is reported to be stable before decompos- ^205 P2O5. The AlPO up to at least 3,200° F 2O3 vapors. Hot gunning materials with phosphate binders for use in the maintenance of basic oxygen furnaces (BOF) are commer- cially available (104 ). Operator- controlled variables, such as moisture content and distance from the lance to the wall, contribute significantly to the performance of these phosphate-bonded gunning mixtures. Aggregates from reclaimed BOF brick containing carbon demonstrate improved adherence between the gunned material and wall, compared with conventional aggregates. Comparison of the amount of bonding agent with strength data shows that as the quantity of bonding agent increases, the cold strength increases (54). However, hot modulus of rupture (MOR) decreases with increasing quantity of bonding agent after an optimum 2.25 percent, for com- mercially available sequestered phosphate binders in basic compositions. The short-chain phosphates give the highest hot MOR. However, it should be noted that the moisture content and chain length also play very important roles in the mechanical stability of the cement. Short-chain glassy phosphates (n=7 sequestered phosphate) give optimum results at moisture levels of 3 percent, and bond levels of 2.05 percent. Phosphate-bonded gunning mixtures (guncretes) are widely used for hot repairs of Si02 structures in coke ovens at temperatures above 600° C, with very favorable results (94). Zirconia (Zr02) refractories with phosphate bonding agents are receiving increasing use because of their high refractoriness and low thermal conductiv- ity (J^)» Small additions of metallic powders, such as nickel, further increase the strength and thermal shock resistance of these compositions. Rate of heating in the early stages of the curing process is a significant factor in the develop- ment of final density (porosity) and mechanical strength. Low-shrinkage ramming compositions of high-Al203 bodies have been prepared from coarse-grained chamotte, clay, co- rundum, and phosphoric acid (96). Mull- ite (3Al203*2Si02) formation by the reaction of corundum with free Si02 is thought to account for the lack of sig- nificant shrinkage in these systems dur- ing service. Curing of these coiqaosi- tions at temperatures above 400° C reduces the hydration tendency of the AIPO4 aluminum phosphate bond. Hydrated alumina (Al203*3H20) reacts with H3PO4 without heat to form variscite (A1P04*2H20) and a mixture of amorphous products. The AI2O3 phosphate bond pro- duced by direct incorporation of Al203*3H20 into the refractory body, fol- lowed by flaked lime, was found to be much stronger than those produced with AI2O3 phosphate prepared separately. starting mixture (Pn.; AL03 = 2.3) (Predominant phase) I 210°-290° F J AIH3(P04)2 • H2O I 300°-390° F AI(H,POJ 4/3 AIPO4 (Berlinite) AIPO4 (Cristobalite) >1,470'' F I AIPO4 (Tridymite) 1,870° F AI(H,P0J3 480*'-570° F I Amorphous phase I 600° -750° F r 1 AIH3P30,o AKPOa)^ 925°-1,470° F i AI(P03)3 1,470°-1,830° F AI(P03)3 Al^iH '0,h >750° F AUP.O,) 1,800°-2,190° F AIPO4 (Cristobalite) 2,000°-2,370° F Metaphosphate glass I 2,370°-2,730° F AIPO4 P2O5 + (Cristobalite) I >3,200° F f "^ 1 AI2O3 P2O5I FIGURE 2. - Effect of heat treatment on phase constitution of aluminum phosphate binder. (49) Phosphate-bonded basic refractories have been manufactured from fired MgC03 (magnesite) with high strength and good spalling resistance (95). These compositions have been used as ramming mixtures for high temperature furnaces up to 1,500° C. MgO + 2H3P04- ■Mg(H2P04)2 + HjO. (5) Forsterite refractories with magnesium phosphate bonds have shown increased strength at temperatures between 500° and 700° C, and no signs of diminishing strength to 900° C ( 105 ). Refractories made with about 5 percent bonding agent exhibited the highest compressive strengths. Increasing the chemical bond- ing agent beyond 5 percent decreased the strength because of a "washing out" of the excess bonding agent, which did not react with the refractory matrix. Refractory brick produced from dense briquettes without chemical bonding agents have lower strengths than do por- ous briquettes containing 5 percent bond- ing phase. This phenomenon is explained by potential displacement of the bonding phase to grain boundaries without pene- tration through the grains to form an effective chemical bond. SILICATE BOND Sodium silicate and ethyl silicate [(.€2^^)/^ SiO^] are the most common sili- cate binders used in refractory applica- tions. Sodium silicate binders have been studied and used most extensively in refractories and foundry applications. Alkali Silicates Alkali silicate binders, especially sodium silicates, have been used in the formulation of protective coatings for refractory linings (49) , refractory ce- ramic foams ( 87 , 105 ) , waterproof cement (45), metal casting molds (42), refrac- tory castables (41), and ramming mixtures (30). Refractory compositions in which alkali silicates have been used as chemi- cal binders include high AI2O3 (^tL* 22l^ ' AI2O3 silicates (16-17, 92), mullite (90) , magnesium ( 30 , 81) , and several nonoxide refractory materials (31). Water glass (sodium metasilicate) has been used as a refractory binder for blast furnace slags ( 6_) , sand-clay mix- tures (7), and other metallurgical slags (28). Patent literature indicates that alkali metal silicates have been employed as refractory binders, usually with several other additives such as strength- ening agents, components to provide hydration resistance, and plasticizers (89-90, 92 , 97-99). Boric oxide (B2O3) or B203-producing compounds such as Na2B407 (sodium borate) or similar inor- ganic salts are commonly used with alkali silicate bonding agents. The main func- tion of B2O3 is to prevent hydration and extend the shelf life of the binder (99). Alkali silicates have been used in refractory mixtures containing mullite whiskers and powder (88-89) , AI2O3 whis- kers and powder ( 92 ) , magnesium grains (90) , AI2O3 cements (86), clay concrete (75), and various other AI2O3 silicates ( "69 , 75-76, 80). It is also reported that Na2SiFg (sodium f luosilicate) is used frequently with water glass in cast- able refractory compositions ( 61 , 67). The addition of metal powders such as Fe , Cr, and Ni increases strength at high temperatures (57). Silicate bonding agents have also been employed with phosphate bonding agents in castable formulations (68). Refractory castable compositions, for example, have been formulated containing sodium silicate, sodium carbonate, and AI2O3 phosphates (5J^, ^, 23)« The use 10 of silicate and phosphate bonding agents together has been the exception rather than the rule. The use of gypsum (CaS04'2H20) in refractory compositions containing lime, calcium silicates, and dolomitic lime with water glass greatly retards the hydration of CaO and MgO in the calcium silicate solutions (5^). The addition of 3 to 5 percent gypsum in such composi- tions increased the strength by 33 percent. However, gypsum contents above 7 percent reduced the strength of the calcium silicate refractories sharply. Water glass has been most success- fully used as a bonding agent in foundry applications (43). The chemical bonding agents used in steel foundry molds include furane binders (such as urea for- maldehyde or phenol formaldehyde solu- tions to which furfuryl alcohol has been added) with 5 to 20 percent P2O5 by weight of the furane binder (18). Ethyl Silicate Ethyl silicate-bonded refractories are prepared from a slurry of refractory grains with ethyl silicate, containing amine additives. The slurry is made as dry as possible and poured, tamped, or pressed into a vibrated mold. When the slurry has gelled, the article is stripped from the mold and the volatiles are removed by air drying and baking the pressed block to 200° C. The use of ethyl silicate as a binder in refractory components is also discussed in the refractories literature (19-20, 22-24, 29, 22.-60> ^' 102 ). The relatively good performance of nozzles of mullite and Zr02 with calcined AI2O3 com- positions in sliding gate systems has been attributed to the use of ethyl sili- cate bonding agents (81). The ability of ethyl silicate-bonded refractories to withstand the combined effects of severe thermal shock and chemical corrosion is closely related to the fine texture of the AI2O3 matrix in the refractory. Ethyl silicate binders are especially appropriate for the forma- tion of multilayered refractory molds in the lost-wax process (59). Multi- layered molds have been prepared using refractory grog or powdered fused quartz fillers and ethyl silicate binders. However, the hydrolysis and conden- sation of ethyl silicate can affect the quality of the refractory products fabricated. Other organic silicate binders have also been prepared by reacting sodium silicate with ethyl silicate. The time of setting for the organic silicate formed by this reaction at room tempera- ture is about 90 to 100 minutes, enabling the product to be formed before setting occurs. Compressive strengths as high as 400 kg/cm2 have been obtained using these organic silicate binders (60). When ethyl silicate is used as a refractory binder, it is usually pre- pared by the direct reaction of sili- con tetrachloride and ethyl alcohol. If the alcohol is anhydrous, the prod- uct is an orthosilicate (tetraethoxy si- lane) , with HCl gas being produced as a byproduct: SiCl4 + 4EfOH- •Si(OEt). + 4HC1. (6) However, if industrial ethyl alcohol, which almost always contains some water, is used, the product obtained, called technical ethyl silicate, is a mixture of the orthosilicate (tetraethoxysilane) and polysilicates (ethoxypolysiloxanes) , because the water present in the alcohol causes some hydrolysis and polymerization (21). When used by itself, ethyl silicate has no bonding ability and, therefore, it is necessary to treat ethyl silicate with water to form a gel from the resulting ethyl silicate hydrolysate, which is the actual bonding agent. Alka- line hydrolysis procedures are in general preferred when ethyl silicate is used in the manufacture of refractories. How- everj acid hydrolysis procedures are usu- ally preferred in foundry processing. The vjater for the hydrolysis of ethyl 11 silicate can be provided by a Si0 2 aqua- sol, and in this way a hydrolysate with a high Si0 2 content can be prepared (2_2) . By using strongly basic amines with the ethyl silicate, intricate refractory shapes can be cast to close tolerances (85) . A few examples are electric fur- nace element carriers, crucibles, and glass feeder ware, such as plungers and orifice rings (86). Most refractory materials are suitable for use with mix- tures of ethyl silicate and highly basic amines (amine-modif led ethyl silicate) . Included among the frequently used cast- able refractory materials are AI2O3 and AI2O3 silicates such as sillimanite and mullite (87^), Zr02, ZrSi04, and SiC. Finished products with these compositions have high dimensional accuracy and excel- lent surface finish, as well as good resistance to thermal shock. OXYCHLORIDE, OXYSULFATE, AND OXYNITRATE BONDS Magnesium oxychloride cement is the product obtained when MgO and solution of MgCl2 react together, Magnesite is cal- cined so as to give a lightly burned reactive product which is ground and mixed as required with a strong solution (about 20 percent anhydrous salt) of MgCl2. Combination of MgO and MgCl 2 takes place with the evolution of heat resulting in the formation of magnesium oxychloride (3MgO«MgCl2*nH20) (68). Tlie aged oxychloride cement appears to be composed of varying-sized particles of Mg(0H)2 (magnesium hydroxide) from which radiate a large number of fine needlelike crystals of oxychloride, which bond the material together. Addition of MgCl2 solution to MgO powders provides appreciable strength through the formation of cementitious phases at the grain boundaries. The dis- sociation of the bond phase occurs over a wide range of elevated temperatures, with loss of water at lower temperatures and loss of HCl at higher temperatures, leav- ing only MgO as the residual phase (14) . The system MgO-MgCl2-H20 has been the subject of numerous investigations since the discovery of the hydraulic properties of MgO and MgCl2 mixtures in water during the 1800' s. The compounds 5Mg(0H)2 •MgCl2*nH20 and 3Mg(0H) 2*MgCl2"nH20 have been identified as the cement-forming compounds ( n_, _52^, ^, 83 ) . A similar magnesium oxysulfate cement is used as a binder in many structural materials and for refractory applications. Solutions of MgSO^ react with active MgO to form the cementitious phases, 3Mg(0H) 2'MgS04'nH20 and 5Mg(0H)2 •MgS04*nH20, identified as the stable phases at 25° C, with other phases formed at higher temperatures. Other analogous mixtures , such as zinc and aluminum oxy- chlorides , have also been studied and are used in a limited number of applications. Aluminum oxychlorides are excellent bind- ers for refractory aggregates at tempera- tures to 1,500° C. Oxybromide analogs of magnesium and aluminum oxychlorides have been prepared, but little information is available regarding their properties. Magnesium oxychloride and magnesium oxysulfate cement compositions have been the subject of numerous patents (5,12-13, 15 , 35 ) . In most of the compositions suggested for refractory lining repairs, large quantities of hydrophillic colloids are used to increase the consistency and allow additions of sufficiently concen- trated MgCl2 or MgSO^ solutions to the dry mix, in order to exceed the critical MgCl 2- or MgS04-MgO ratio necessary for the development of a wet mix that can be applied by brushing or troweling. Good chemical bonds have also been obtained using nitrates [NaN0 3 or Ca(N03)2] in quantities of 8 to 20 per- cent by weight of solids, with a variety of constituent combinations of MgO, ilmenite, chromite ore, and Fe , Si, and Al in lesser amounts (4_) . In these com- positions, nitrates react quickly with Fe-Si , forming a silicate bond. Calcium nitrate Ca(N03)2 is preferred to NaNOj since a more refractory silicate is formed. 12 Increasing the high-temperature mechanical strength of cast AljOj refrac- tories by introducing organic additives such as polyvinyl alcohol, sucrose, and flour has not been very successful. The development of an organic film on the AI2O3 particles is thought to mask the intermolecular attraction forces and lower the strength of the cast refractory (44) . Additions of up to 10 percent AI2O3 treated with HCl solutions have significantly improved the strength of AI2O3 castings at temperatures above 1,000° C. It is reported that the forma- tion of aluminum oxychloride bond on the surfaces of y~^12^3 particles treated with HCl solution produces higher strength. The dissolution of >feO from the com- plex is essential in the hardening of both chloride and sulfate cements of mag- nesia. Setting processes involve forma- tion of Mg(0H)2 for sulfate cement and formation of basic MgCl2 for chloride cement. The agglutination of the fine particles in the cement mixture is explained by hydrogen bonds (32) acting directly between the OH groups of the I-lg(OH) 2 in one case and of the basic MgCl2 in the other. The setting of chloride cements can best be illustrated by the following chemical reaction where 3Mg(0H) 2*MgCl2 •nH20 forms as the bonding agent: CI 2 Mg(OH)x (H20)4-x Hx + 3Mg(0H) The use of the so-called "salt phase" as an inherent body component is a new element in the development of manu- facturing procedures for lime-base refractories. The salt phase is mainly CaClj (calcium chloride), which melts at 7 72° C but can be lowered by as much as 400° C in the presence of other salts. The salt phase melts at low temperature, yielding a reactive liquid of low viscos- ity, and leaves the system gradually as a result of high-temperature hydrolysis. The formation of 4CaCl2'CaO upon heating and its effects on the subsequent ceramic processes is thought to be responsible for the development of a unique micro- structure and the high-temperature volume stability (64). The volume stabilization is believed to be helped by the pro- gressive evolution of the HCl resulting from the high-temperature hydrolysis of chloride salts. An even more pronounced effect on volume stabilization has been observed in bodies with CaCOj additions (along with CaCl2), the so-called calcite brick. As more gas phase (CO 2) is cre- ated by the decomposition of the car- bonates, and if the viscosity of the melt is increased (by addition of silicates), a marked expansion of the products may occur. CI 2 Mg(OH) H2O •(MgOH)3'3H20. (7) The strength of unfired refractories containing magnesium oxysulfate, mag- nesium oxysulf ate-H3B03 (boric acid), and sodium polyphosphate bonds has been determined as a function of temperature (74). All the bonding agents develop higher strength in the presence of chro- mite, and the addition of H3BO3 with MgS04*7H20 increased the strength of the refractory in the 400 to 900° C range. Above 1,000° C, the strength of these same refractories was significantly decreased due to incongruent melting of magnesium metaborate (79). One of the problems encountered in the use of MgCOj refractories is the par- tial hydration of MgO in the presence of water. The thermal decomposition of Mg(0H)2 upon heating to 400 to 500° C and the consequent evolution of water vapor cause severe thermal spalling. Additions of approximately 1 percent B2O3, yielding material such as H3BO3, reduce the hydra- tion tendencies of the MgO refractories. In the presence of MgSO^ or MgSO^- yielding material, the addition of H3BO3 is not only ineffective in preventing MgO hydration but actually increases the degree of hydration significantly under certain conditions. An improved chemical 13 bond that at the same time prevents MgO hydration has been described by Martinent (58)« The bonding agent consists of 35 mesh dead-burned MgO, from 0.5 to 5.0 percent magnesixmi sulfate heptahydrate by weight of MgO, and a boron compound yielding B2O3 upon firing, to provide a weight ratio of MgS04:B203 of 2:1 or less. This bonding composition is used in amounts of from 10 to 60 weight- percent of the total refractory composition. A patent by Montague (63) describes a method for obtaining superior chemical bonding in refractory compositions con- taining olivine [(Mg, Fe)2 8104]. The olivine fines are slurried with water, and then H2SO4 is added and mixing is continued. The reaction generated pro- duces large quantities of steam rapidly, and the mixture becomes very viscous and hardens into a solid cake. Ordinarily, the cake is crushed and screened, for convenience. Refractory linings of oli- vine, MgO, and chrome with the described bonding agent were found to be superior to similar compositions using sodium sil- icate bonding. CONCLUSIONS AND RECOMMENDATIONS Chemically bonded brick offers promise in a number of refractory appli- cations for iron and steelmaking, glass manufacturing, high-temperature chemical processes, and energy conversion pro- cesses, as well as in nonref ractory applications. Unfortunately, the efforts to explain chemical kinetics and mechan- ism of bond formations have been limited. With the exception of information on den- tal cements, few data regarding the bond- ing reactions and bond mechanisms are available; in addition, the identified references about bonding mechanisms are very limited. Chemical kinetics and important reaction parameters have not been systematically studied. The possibility of forming a large variety of chemical bonds is great, thereby extending the potential applica- tions for chemically bonded brick in severe environments at moderately high temperatures. Coal gasification and liquifaction present one area of poten- tial applications where the thermal con- ditions are moderately severe (1,100° C), and high chemical durability is required for refractory liners in reducing or oxi- dizing atmospheres with corrosive gases and liquids. The feasibility of using raw mate- rials of marginal purity, such as spent refractory linings and byproduct slags, could be enhanced through the development of chemical bonding agents with various compositions for use in high-temperature environments. Based on the conclusions outlined above, a number of research development projects are recommended: 1. Fundamental research efforts should be devoted to better understanding chemical bond development for various refractory systems. Kinetics and the mechanism of chemical bond formation should be examined. A fundamental under- standing of the processes leading to chemical bond formation will identify opportunities for development of materi- als with new and improved performance, which in turn would help conserve the Nation's mineral resources. 2. Research efforts should be devoted to developing more versatile and inert chemical bonds in chemical binder systems and combinations of binders. Attempts should also be made to determine mechanistically the role of each compo- nent in a binder system. In addition, the effects of important manufactur- ing parameters, such as curing rates, moisture content, and mixing methods for different binder compositions, should be determined. The role of metal powder additions should also be investi- gated, and the use of chemical bonding agents in combination should be explored. 14 3. Research activities for the development of monolithic refractories should continue and be expanded to include chemically bonded compositions in addition to hydraulic bonds. 4. Research should be conducted on the development of chemically bonded refractories from spent refractories, waste linings, and raw materials of mar- ginal purity. 5. Research efforts should be directed at improving the short and unpredictable shelf life of many chemical binders, which would prove very helpful in the development of next-generation chemically bonded refractory products. 6. The opportunities for applica- tion of chemically bonded refractories can be greatly extended by solving certain pressing problems, such as bond migration, bloating, and low hot strengths, which have greatly limited their use. 7. Pitch and tar bonding agents present some health and environmental problems; chemical bonding agents should be developed to substitute for these organic bonding agents. 8. In many cases, the literature evaluation of refractory compositions has not included the service conditions to which the refractory would be subjected. It is recommended that any evaluation program following a development effort should consider the service conditions, and appropriate evaluation procedures should be instituted as part of all refractory development studies. BIBLIOGRAPHY 15 Amirov, R. A., F. Y. Abzgildin, and 9. L. B. Khoroshavin. Refractory Products From Zirconium Dioxide and Metal Powders With Phosphate Binder. Refractories (U.S.S.R.) 10. (Engl. Transl. ), v. 14, No. 11, 1973, pp. 722-729. Cassidy, J. E. Phosphate Bonding Then and Now. Am. Ceram. Soc. Bull., V. 56, 1977, pp. 640-643. Caven, T. U.S. 1934. M. Refractory Article. Pat. 1,949,038, Feb. 27, 2. Baab, K. A., and J. M. Blackwood. Volume Stability of Phosphate- Bonded High-Alumina Brick. Am. Ceram. Soc. Bull., v. 50, 1971, pp. 607-610. 3. Beck, W. R. Crystallographic Inver- sions of the Aluminum Orthophos- phate Polymorphs and Their Relation to Those of Silica. J. Am. Ceram. Soc, V. 32, 1949, pp. 147-151. 4. Belz, F. W. (assigned to Chromium Mining & Smelting Corp., Ltd.). Exothermic Refractory Mixtures for Patching Melting-Furnace Linings. U.S. Pat. 3,082,104, Mar. 19, 1963. 5. Bieda, W., and W. Piatkowsdi (as- signed to Huta im. Lenina) . Alkali-Bonded Unfired Refractories. Polish Pat. 42,602, Jan. 25, 1960. 6. Bobrov, B. S., Y. E. Gorbatyi, and V. N. Nei. (Binders From Blast Furnace Slags and Na Silicate.) Stroit. Mater. Izdeliya Met. Shlakov, 1965, pp. 211-221. 7. Borisov, G. P. (Dependence of the Technological Properties of Sand- Water Glass-Clay Mixtures on the Nature of Interaction of Their Ingredients.) Tekhnol. Svoistva Formovachnykh Smesei, Tr. Soveshch. Teor. Liteinykh Protsessov. , 12th, Moscow, 1966 (pub. 1968), pp. 125-135. 8. Bryantseva, N. F. (Effects of Gypsum and Water Glass on the Hydration of Dolomite Lime and on the Strength of Lime-Sand Article.) Khim. Tekhnol. Vyazhushchikh, Vesh- chestv, 1968, pp. 86-90. 11. 12. 13. 14. 15. 16. 17. 18. Chassevent, L. (Study of the Set- ting of Magnesia Cement.) Chim. & Ind. (Paris), v. 30, 1933, pp. 1020-1076. Chisholm, H. E. (assigned to Food Machinery and Chemical Corp.). Magnesium Oxychloride Cements. U.S. Pat. 2,939,799, June 7, 1960. Council of Scientific and Industrial Research. Improvements Relating to the Production of Chemically Bonded Metal Clad or Unclad Basic Refractories. Indian Ceram. , V. 7, 1960, p. 18. Demediuk, T., and W. F. Cole. A Study on Magnesium Oxysulfates. J. Aust. Chem. Soc, v. 10, 1957, pp. 287-294. Dess, J. M. Structure of Chem- ical Refractories. Belgian Pat. 632,397, Sept. 2, 1963. Doittau Produits Metallurgie S. ar. 1. Refractory Materials. French Pat. 1,317,287, Feb. 8, 1963. Duplin, V. J. U.S. Pat. 1959. , Jr. Refractory Mix. 2,877,125, Mar. 10, 19. Dyno Industrier A.S. Method of Pre- paring Foundry Cores and Moulds and Mouldable Mixture Therefore. British Pat. 1,383,998, Feb. 12, 1975. Emblem, H. G. Ethyl Silicate Binder. British Pat. 1,373,566, Nov. 13, 1974. 16 20. 21. 22. 23. 24. 25. 26. 27. 28. Emblem, H. G. Silicate Gel Binders for Refractories. British Pat. 907,773, Oct. 10, 1962. . Use of Ethyl Silicate as a Binder in Refractory Technology. Trans. J. Brit. Ceram. Soc. , V. 74, No. 6, 1975, pp. 223-228. Emblem, H. G. , and D. J. Cloherty (assigned to Rolls-Royce Ltd.). Binding Liquid for Molds Used in Precision Casting. U.S. Pat. 2,842,445, Jan. 23, 1956. Emblem, H. G. , and C. E. Oxley. Organic Silicate Binders for Refractory Powders. British Pat. 1,009,717, Nov. 10, 1965. . Refractory Binder Compris- ing Organic Silicates. U.S. Pat. 3,329,520, July 4, 1967. Engineering and Mining Journal. Special Correspondence. V. 80, 1905, p. 367. Florke, 0. W. The Structures of AIPO4 and Si02. Ch. in Science of Ceramics, ed. by G. H. Stewart. Academic Press, New York, v. 3, 1967, pp. 13-27. Gitzen, W. J., L. D. Hart, and G. MacZura. Phosphate Bonded Alumina Castables: Some Properties and Application. Am. Ceram. Soc. Bull., V. 35, 1956, pp. 217-223. Gudovich, L. A., B. I. Gurevich, and A. P. Zosin. (Properties of Binder From Slags of Copper- Nickel Production and Water Glass.) Zhelezisto-Magnez. Met. Shlaki Kil'sk. Poluostrova, 1966, pp. 38-58. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. Harbinson-Walker Refractories Co. Basic Refractory Mixtures for Casting or Ramming. British Pat. 963,720, July 15, 1964. Hare, W. A. (assigned to E. I. du Pont de Nemours & Co.). Bonding Sintered Refractory Particles Other Than Oxides. U.S. Pat. 3,296,002, Jan. 3, 1967. Hayek, E., and E. Schnell. (The Chemical Foundations for the Hardening of Magnesia Ce- ments.) Chem.-Ztg., v. 21, 1960, pp. 697-701. Herold, P. G. , and J. F. Burst. Use of Metaphosphates in Refractory Mortar. Univ. Mo. School Mines and Met. Bull., Tech. Ser. , v. 18, No. 2, 1974, pp. 1-34. Heuer, R. P. Furnace Roofs. Brit- ish Pat. 489,680, Aug. 2, 1938. . Refractory Bricks. Belgian Pat. 624,633, Feb. 28, 1963. Heuer, R. P. (assigned to General Refractories Co.). Brick Having Low Modulus Rupture. U.S. Pat. 2,443,424, June 15, 1948. . Chrome-Magnesia Refractory and Method. U.S. Pat. 2,087,107, July 13, 1937. Chrome Refractory Brick and Method of Manufacture Thereof. U.S. Pat. 2,253,620, Aug. 26, 1941. High Pressure Brick Con- taining Magnesia and the Pro- cess of Making the Same. U.S. Pat. 1,992,484, Jan. 9, 1935. 29. Halsey, G. (assigned to Mon- santo Chemicals, Ltd.). Sili- cate Ester Compositions. U.S. Pat. 3,489,709, Jan. 13, 1970. 40. Refractory Brick Process. U.S, Pat. 2,247,376, July 1, 1941. 17 41. Hosokawa, K. (assigned to Harima Refractories Co., Ltd.). Re- fractory Castables. Japanese Pat. 7,903,821, Jan. 12, 1979. 42. Ilenda, F. P., and C. E. Peeler, Jr. (assigned to Diamond Alkali Co.). A Method of Forming a Metal Cast- ing Mold. U.S. Pat. 2,952,553, Sept. 13, 1963. 43. Jelinek, P. (Critical Survey of Moulding and Core Mixtures.) Slevarenstvi, v. 14, No. 8, 1966, pp. 339-341. 44. Kainarskii, I. S., A. G. Karavlov, and G. E. Gnatyuk. Additives for Strengthening Casting of Water- Alumina Slips. Refractories (U.S.S.R.) (Engl. Transl.), No. 5, 1967, pp. 306-310. 45. Kakimoto, N. , T. Ukaji, T. Wakisaka, and Y. Fujita (assigned to Asahi Chemical Industry Co., Ltd.). Waterproof, Refractory Adhesive. Japanese Pat. 10,546, Mar. 11, 1974. 46. Kingery, W. D. Fundamental Study of Phosphate Bonding in Refrac- tories: I. Literature Review. J. Am. Ceram. Soc. , v. 33, 1950, pp. 239-241. 47. . Fundamental Study of Phos- phate Bonding in Refractories: II. Cold Setting Properties. J. Am. Ceram. Soc, v. 33, 1950, pp. 242-247. 48. Kinzie, C. J. Coherent Porous Zirconium Silicates. U.S. Pat. 2,101,947, Dec. 14, 1937. 49. Kovach, B., G. Cacciapuoti, and G. Mendoza. Protective Coating of Refractory Linings. Belgian Pat. 651,112, Nov. 16, 1964. 50. Leframe, J. G. A. Compound Ceramic Products. U.S. Pat. 2,099,367, Nov. 16, 1937. 51. 52. Lipinski, German 1961. F. Fireproof Material. Pat. 974,648, Feb. 23, 53. 54. 55. 56. 57. 58. 59. Lukens, J. S., and N. H. Smith (assigned to Soliden Products, Inc.). Plastic Magnesia Mixture Suitable for Making Articles by Casting. U.S. Pat. 1,838,147, Dec. 29, 1932. Lyon, J. E., T. U. Fox, and J. W. Lyons. Inhibited Phosphoric Acid for Use in High-Aliamina Refrac- tories. Am. Ceram. Soc. Bull., V. 45, 1966, pp. 661-665. . Phosphate Bonding of Mag- nesia Refractories. Am. Ceram. Soc. Bull., V. 45, 1966, pp. 1078- 1081. MacCallxmi, N. E. Furnace Wall Con- struction. U.S. Pat. 1,106,725, Aug. 11, 1914. . Open Hearth Practice With Large Units. Blast Furn. and Steel Plant, v. 8, No. 1, 1920, p. 52. Martaian, D. , and E. Ristea (as- signed to Intreprinderea de Mate- riale de Constructii "7 Novem- bre"). Cold Binder for Refractory Boxes. Romanian Pat. 61,460, July 15, 1976. Martinent, J. R. Bonding Fine- Grained Magnesite Refractories With Sulfate and Boric Acid to Prevent Hydration. British Pat. 1,088,000, Oct. 18, 1967. Matrveeva, F. A., E. A. Plekhanova, and V. E. bforozkova. (Formation of Multi-Layered Refractory Molds for the Lost-Wax Process Using Ethyl Silicate Binder.) Sib. Otd. Akad. Nauk SSSR, Ser. Khim. Nauk, No. 6, 1976, pp. 124-130. 60. 61. 62. 63. 64. 65. 66. 67. 68. Matveev, V. A., and M. A. Khudenko. (Organic Silicate Cements.) Proizvod. Stroit. Izdelli Plast- mass, Mater. Konf. Primen. Plast- mass Stroit., 1963, pp. 209-217. Medvedev, V. M. , B. G. Batrakov, and I. A. Pisarenko (assigned to Scientific-Research Institute of Concrete and Reinforced Concrete) . Acid-Proof Cement. U.S.S.R. Pat. 281,230, Sept. 3, 1970. Menjscikov, F. S. (Experiment in the Use of High Alumina Composi- tions With Phosphate Binding for the Protection of Floors of Annealing Furnaces.) Ogneupory, No. 1, 1974, pp. 35-36. Montague, J. H. , and J. A. Miller (assigned to International and Chemical Corp.). Refractory Com- positions and Method for Prepar- ing Same. U.S. Pat. 3,316,106, Apr. 25, 1967. Morgan, J. D. Refractory. U.S. Pat. 1,809,249, June 9, 1931. Refractory Bonding Method. 69. Nara, K. , and N. Iwase (assigned to Asahi Chemical Industry Co. , Ltd.). Amorphous Acid-Resistant Silicate Refractories. Japanese Pat. 85,110, Aug. 15, 1974. Neely, J. E., J. R. Martinent, and J. Bowman (assigned to Kaiser Alu- minum and Chemical Corp.). Bind- ers for Promoting Adherence of Wet Refractories Blovra Against Ver- tical Furnace Walls. U.S. Pat. 3,262,793, July 26, 1966. 70. 71. 72. 73. Canadian Pat. 387,285, Mar. 5, 1940. 74. Nadachawski, F. T. , L. Rymon, and M. Janiel. Some Refractories Occur- ring in Lime Refractories Contain- ing Calcium Chloride. Ceramurgia Internat., v. 3, No. 1, 1977, pp. 13-17. 75. 76. 77. Newman, E. S. A Study of the System Magnesiimi Oxide-Magnesium Chloride-Water and Heat of Forma- tion of Magnesium Oxy-Chloride. J. Res. NBS, V. 54, No. 6, 1955, pp. 347-355. O'Hara, M. J., J. J. Duga, and H. D. Sheets, Jr. Phosphate Bonding. Am. Ceram. Soc. Bull., v. 51, 1972, pp. 590-595. Ongaro, M. Air-Hardening Cements and Varnishes With a Silicate Base. Italian Pat. 627,266, Oct. 28, 1961. Pirogov, A. A. (Highly Refrac- tory Air-Setting Magnesia Con- cretes.) Ogneupory, No. 10, 1958, pp. 445-454. Pirogov, Y. A., L. A. Babkina, M. I. Kuz'menkov, V. V. Pechkovskii, and G. K. Clerches. Effect of Average Degree of Polymerization of Vitre- ous Sodium Phosphate on the Magnesite Bodies. (U.S.S.R.) (Engl. 14, No. 5, 1973, Strength of Refractories Transl. ) , v. pp. 321-323. Piyanykh, E. G. , and G. I. Antonov. (Strength After Heating of Unfired Refractories Containing Chemical Bonding Agents.) Ogneupory, No. 9, 1979, pp. 48-52. Poegel, H. J. Self -Hardening Water Glass Coating Compositions and Water Glass Cements. German Pat. 2,029,701, Dec. 23, 1971. Preisser, J. Refractory Clay Con- crete Containing Water Glass Binder. German Pat. 2,144,474, Mar. 30, 1972. Quigley Company, Inc. Refractory Composition, Method of Making, and Product. British Pat. 1,383,595, Feb. 10, 1972. 19 78. Rashkovan, I. L. , N. Kuzminkayn, and 86. V. A. Kopeilin. (Thermal Trans- formations in Aluminum Phosphate Binding Agent.) Izv. Akad. Nauk SSSR, Neorg. Mater., v. 2, No. 3, 1966, pp. 464-472. 87. 79. Richardson, J., M. Bester, F. T. Palin, and P. T. A. Hudson. The Effect of Boric Oxide on Some Properties of Magnesia. Trans. Brit. Ceram. Soc. , v. 68, No. 1, 88. 1969, pp. 29-31. 80. Ricker, R. W. (assigned to Aluminum Co. of America) . Castable Refrac- tory Materials Bonded With Calcium Aluminate Cement. U.S. 89, Pat. 2,912,341, Nov. 10, 1959. 81. Rigby, A. J., H. G. Emblem, and E. W. Roberts. Ethyl Silicate Bonded Refractories in a Sliding Gate System. Trans. J. Brit. Ceram. Soc, v. 78, No. 1, 1979, pp. 10-15. Shaw, R. D. Orifice Ring for Glass Moulding Having Non-Uniform Wall Thickness Permitting Varying Ring Sizes in One Cannister. British Pat. 1,394,834, May 21, 1975. Shaw, R. D. , and H. G. Emblem. The Use of Ethyl Silicate in Refrac- tory Technology. Interceram, V. 21, No. 2, 1972, p. 105. Shizuki, R., and U. Takashi. Sili- cate Foam Moldings Sandwiched Between Rubber and Plastic Sheets. Japanese Pat. 4 2,019, June 19, 1973. Terekhovskii, B. I., V. B. Vishnev- skii, and I. N. Godovannaya (assigned to Institute of Problems in Material Management, Academy of Sciences, Ukrainian S.S.R.). Refractory Mixture for Coating and Bonding Ceramic Articles. U.S.S.R. Pat. 509,556, Apr. 5, 1976. Rigby, G. R. The Mechanical Prop- perties of High Alumina Refractor- ies Utilizing Various Bond- ing Agents. Trans J. Brit. Ceram. Soc, v. 70, No. 6, 1971, pp. 199-208. Robinson, W. 0., and W. A. Waggaman. Basic Magnesium Chloride. J. Phys. Chem. , v. 13, 1909, p. 673. Salmanov, G. D. , and V. F. Gulyaeva. (Effect of Finely Ground High- Alumina Additives on the More Important Properties of Concrete Based on Alumina Cements.) Zharostoikie Betony, 1964, pp. 62-71. Scott, J. F., and H. G. Emblem. Some Applications of Ethyl Sili- cate in Refractories. Refract. J. (London), v. 27, No. 7, 1951, p. 286. 90. Terekhovskii, B. I., V. B. Vishnev- skii, S. G. Tresvyatskii, G. V. Plotyan, N. I. Mazur, and A. A. Miroshnichenko (assigned to Insti- tute of Problems in Material Man- agement, Academy of Sciences, Ukrainian S.S.R.). Refractory Adhesive Composition. U.S.S.R. Pat. 539,006, Dec. 16, 1976. 91. Treffner, W. Refractories Technol- ogy. Am. Ceram. Soc. Bull, v. 58, 1979, pp. 215-218. 92. Tresvyatskii, S. G. , B. I. Terek- novskii, V. A. Artemov, V. N. Pav- likov (assigned to Institute of Problems in Material Management, Academy of Sciences, Ukrainian S.S.R.). Refractory Mixture for a Compound of Corundum High-Alumina, Aluminosilicate, and Grog Refrac- tories and Ceramics. U.S.S.R. Pat. 494,371, Dec. 5, 1975. 20 93. Troell, P. T. (assigned to Harbinson-Walker Refractories Co.)« Dry Refractory Bonding Mortar. U.S. Pat. 3,298,839, Jan 17, 1967. 94. Tseitlin, L. A., and A. P. Gubatenko. (Refractory Bodies for Repairing Dinas and Firebrick Structures in Industrial Fur- naces.) Ogneupory, No. 3, 1968, pp. 25-31. 95. Tseitlin, L. A., and A. P. Gubatenko (assigned to Ukrainian Scientific Research Institute of Refractory Materials). Refractory Mass. U.S.S.R. Pat. 196,594, May 16, 1967. 96. Tseitlin, L. A., A. K. Mendelenko, P. D. Orekhov, K. Ya. Neskornniyi, V. I. Zxyagin, N. K. Shabal' , and A. I. Grigor'ev. (Large, Complex Phosphate-Bonded Chamotte Prod- ucts.) Ogneupory, No. 7, 1973, pp. 1-3. 97. Unilever, V. N. Refractory Com- positions. Netherlands Pat. Appl. 6,513,041, Apr. 12, 1966. 98. Union Carbide Corp. Casting Mold. Belgian Pat. 618,036, Sept. 17, 1962. 99. Van Dresser, M. L. , and B. G. Alt- mann (assigned to Kaiser Aluminum and Chemical Corp.). Bonding Basic Refractories for Strength and Hydration Resistance. U.S. Pat. 3,257,217, June 21, 1966. 100. Wainer, E. Ceramic Preparation. U.S. Pat. 2,309,327, Feb. 13, 1945. 101. . Refractory Composition. U.S. Pat. 2,323,951, July 13, 1943. 102. Webber, R. A., J. E. Funk, and V. L. Burdick. Effect of Water Vapor on Gel Formation in Ethyl Silicate Bonded Alumina. Am. Ceram. Soc. Bull., v. 54, 1975, pp. 792-794. 103. Youngman, R. H. Refractory Bricks Formed of Calcined-Magnesite, Chrome Ore, and Sodium Silicate. British Pat. 250,480, Oct. 24, 1925. 104. Yount, J. G. Hot Gunning Materials for Basic Oxygen Furnace Mainten- ance. Am. Ceram. Soc. Bull. , V. 47, 1968, pp. 259-263. 105. Zaikina, V. D. , S. I. Shcheglov, and L. P. Zatsepina. (Studying the Strength of Unfired Phosphate Bonded Forsterite Refractor- ies.) Ogneupory, No. 6, 1968, pp. 50-53. 106. Zhitkova, L. A. (Effect of Methods of Hydrolyzing Ethyl Silicate on the Properties of Refractory Coatings.) Liteinoe Proizvod. , No. 1, 1960, pp. 20-23. GPO 889-493 H 232 ^•^ % '.ft<4JI>