EFFECT OF OTHER OXIDES ON THE MICROSTRUCTURE OF PERICLASE (MgO) ABOVE STEEL MELTING TEMPERATURES by Otto K. Riegger, Gerald Io Madden, and Lawrence H. Van Vlack ABSTRACT: The microstructures developed by periclase (MgO) in the presence of calcium-silicate, calcium-aluminate, and calcium-ironaluminate liquids were examined after firing at temperatures up to 1800~C (5270~F). This study led to the following results pertaining to growth of the individual crystalline grains, liquid phase distribution, and second-solid-phase bonding in these microstructureso The rate of periclase crystalline grain growth is controlled by the energy of the solid/liquid interface, and increases with the square root of time and temperature. It is also influenced by the composition of both the liquid and the solido The distribution of the liquid phase among the individual crystalline grains is controlled by the composition of the liquid. Solid-to-solid bonding is more effective in the presence of a liquid when there are two solid phases present rather than one. This last finding may lead to useful generalizations in formulating refractory compositions with improved high-temperature strength. July 18, 1962 Submitted to the American Iron and Steel Institute by the Department of Chemical and Metallurgical Engineering The University of Michigan Ann Arbor, Michigan

I. INTRODUCTION This report presents the results of a study of the effect of other oxide liquids on the microstructure of periclase (MgO) at temperatures up to 1800~C (3270~F). The purpose of the study was to learn more about the effects of such service factors as (1) time, (2) temperature, (3) liquid composition, and (4) liquid content upon the crystalline grain* growth, liquid-phase distribution, and solid-phase bonding, This study was prompted by the fact that present-day service conditions for basic refractories demand higher temperatures than those previously reported.,2 These reports indicated that balanced compositions might lead to more solid-to-solid contact in periclase (MgO) microstructures. A summary of previous work on microstructures and equilibrium phase relationships is presented in Appendix A. Details of the experimental procedures used in the present study are presented in Appendix B. In brief, these include heat treatments of prescribed compositions which contain the solid periclase (MgO) and a liquid composed of various oxides. After heat treatment the compositions were subjected to quenching and microscopic examination. The results of the study are discussed in Section II in terms of (A) the crystalline grain growth of the solid oxide, (B) the effect of liquid composition upon microstructural geometry, which includes the distribution of the liquid among the solid oxide grains, and (C) the effectiveness of the presence of a second solid phase in providing more solid-to-solid contact. The second consideration, (B), is illustrated in Fig. 1, which shows the effect of lime (CaO) additions in promoting solid-to-solid contact between magnesiowustite grains. The effectiveness of a second solid phase in providing more solid-tosolid contact is illustrated in Fig. 2. II. RESULTS AND DISCUSSION The microstructure of periclase was examined after it had been exposed to calcium-silicate, calcium-aluminate, and calcium-iron-aluminate liquids, over the temperature interval 1400~C (25500F) to 1800~C (3270~F). In addition to *Because "grain" as used in the steel industry bears two connotations, in this report a separate term will be used for each. "Grog grain" denotes the refractory raw material particle, and "crystalline grain" denotes the conventional grain of a microstructure. 2

temperature and composition of the liquid, the variables included time and the amount of liquid. A limited number of magnesiowistite compositions with an MgO/FeO ratio of 80/20 were examined to establish the relationship between magnesiowUstite and periclase microstructures. The complete data are presented in Table IV. A. Growth of Individual Crystalline Grains 1. Time. —The crystalline grain size of periclase was found to increase with the square root of time for all of the conditions of temperature and time studied. A typical set of data for periclase in the presence of a calciumsilicate liquid is shown in Figs. 3 and 4. A similar correlation between crystalline grain size and time has previously been reported for both magnesiowUstite and magnesiomagnetite.l,2 This correlation indicates that the rate of growth at constant temperature is controlled by the energy of the interface between the solid and the liquid. 2. Temperature -The periclase crystalline grain size was found to increase markedly with temperature at constant composition over the interval 1400~C (2550~F) to 1800~C (3270~F). Examples of this growth are shown in Figs. 5 and 6. The increased growth rates at higher temperatures may be attributed to two factorso First, the mobilities of the diffusing magnesium and oxygen ions are expected to be higher, which would allow for faster transport from small crystalline grains through the liquid and onto growing crystalline grains. Second, at higher temperatures the solubility of MgO is higher in the 4CaO. A1203Fe203 liquids, as shown in Figo 13o This would contribute to a higher diffusion rate. However, this second effect may be partially offset by an increase in liquid content, which is shown to retard grain growth. 3. Amount of Liquid —As was previously reported for the magnesiowUstites and magnesiomagnetites,1s2 the amount of liquid has an effect upon the rate of crystalline grain growth. Although this effect is to be considered secondary to those of time and temperature, it is a measurable one, The rate of crystalline grain growth has been found to decrease as the liquid content is increased, with typical results for periclase and several oxide liquids as shown in Fig. 7. In this and earlier studies the amount of liquid was controlled through the amount of fluxing oxide added to it, and actual liquid contents were measured on the microstructures, A definite explanation for the decreased growth rate cannot be given at this time, but possible explanations have already been offerede1 4. Liquid Composition.-The composition of the liquid was found to have an effect upon the growth rate of periclase crystalline grains. It was found that in general, the growth rate was highest in calcium-iron-aluminate liquids, 5

intermediate in calcium-aluminate liquids, and lowest in calcium-silicate liquids. Specific comparisons can be made for samples which have comparable liquid contents and have been fired at 16000C for 64 hours. Several examples of this comparison (other factors constant) are presented in Table I. TABLE I CRYSTALLINE GRAIN SIZE VS. LIQUID COMPOSITION Liquid Mean Diameter Liquid Composition (mm) Content (%) C4AF*.091 14 CaO/A1203-56/44 o075 13 CaO/A1203-42/58.076 19 CaO/Si02-53/47.058 13 CaO/Si02-39/61.076 13 *C4AF = 4CaO-Al203-Fe203 The higher growth rate for the CaO/Si02-59/61 liquid as compared with the CaO/Si02-55/47 liquid may be explained in terms of the known phase relationships, which are reproduced in Fig, 12. As the CaO/Si02 ratio decreases along the 1600CC isotherm, the solubility of MgO in the liquid increases quite markedly. This would allow for a faster diffusion rate of MgO through the liquid. Changing the CaO/A1203 ratio from 56/44 to 42/58 does not produce a change in the growth rate in the CaO-MgO-A1203 system. From the known phase relationships, which are reproduced in Fig~ 11, it can be seen that changing the CaO/A1203 ratio in the liquid along the 1600~C isotherm does not change the solubility of MgO; therefore the growth rate would be expected to remain constant. The increase in growth rate with the addition of iron oxide to calciumaluminate liquids cannot be definitely explained at this time. It should be noted, however, that there might be some solid solution of iron in the periclase, and that this would lead to a higher rate of crystalline grain growth. 5. Solid Composition._ —The addition of FeO to the periclase solid to produce an over-all MgO/FeO ratio of 80/20 was found to increase the crystalline grain growth rate. After sintering for 4 hours at 1700~C (3190~F) the comparison shown in Table II were made (other factors constant).

TABLE II CRYSTALLINE GRAIN SIZE VS. SOLID COMPOSITION Solid Liquid Mean Diameter Liquid Composition Composition (mm) Content (%) 80/20 MgO/FeO 50/50 CaO/Si02.085 5.7 80/20 MgO/FeO 50/50 CaO/Si02.074 10 MgO 15/85 CaO/SiO2.057 5 MgO 65/35 CaO/SiO2.035 8 For comparable liquid contents it is seen that the crystalline grain growth rate for the 80/20 MgO/FeO solid solution is appreciably faster than that for pure periclase (MgO). This observation agrees with the results reported for magnesiowustite, where it was found that the growth rate decreased with increasing MgO contents in the solid.1 B. Liquid Phase Distribution The effect of lime (CaO) additions to silicate liquids in promoting solidto-solid contact in magnesiow-Ustite microstructures is illustrated in Fig. 1. Silicate liquids completely penetrate the solid grain boundaries. However, lime (CaO) additions to these liquids modify the solid/liquid interface energy so that the penetration is restricted to definite angular shapes, thus providing for increased solid-to-solid contact Microstructures similar to those for magnesiowCustite in the presence of calcium-silicate liquids were found for periclase in the presence of various liquids. Three typical microstructures for periclase in the presence of calcium-silicate, calcium-aluminate, and calcium-iron-aluminate liquids are shown in Fig. 8. The liquid phase distribution in these microstructures can be characterized by the dihedral angle, which is the angle of penetration of the liquid along the solid grain boundaries. The median of a number of randomly measured angles provides a convenient index for comparing microstructures.3 A summary of dihedral angle measurements for periclase microstructures is presented in Table III. 5

TABLE III DIHEDRAL ANGLES IN PERICLASE MICROSTRUCTURES AFTER 64 HOURS AT 1600~C (2910~F) Liquid Dihedral Angle Composition (Degrees) CaO/SiO2-39/61 22 CaO/Si02-53/47 24 CaO/Al203-42/58 31 CaO/Al203-56/44 29 C4AF* 30 *C4AF = 4CaO.Al203 Fe203 Within a given system there is essentially no change in microstructure with the composition of the liquid. In the CaO-MgO-SiO2 system this behavior can be explained in terms of the structure of the liquid. The 1600~C isotherm closely parallels and lies almost directly above the orthosilicate join. The structure of liquids in this region of the diagram is controlled by the Si04 = tetrahedra concentration, which is essentially constant in this case. The amount of solid-to-solid contact is higher for calcium-aluminate liquids than for calcium-silicate liquids, as indicated by the larger dihedral angle. The most probable explanation for this behavior would note that calcium-aluminate liquids dissolve very little of the solid periclase, which may be in part responsible for the greater dihedral angle. This situation differs from that of silicate liquids in contact with magnesiowfustites, where the solubility of the solid is much higher. The addition of iron oxide to calciumaluminate liquids has very little effect on the dihedral angle. C. Solid Phase Bonding As previously reported,l 2 the presence of a second solid phase is beneficial in promoting solid-to-solid contact. It was found that such contact is also promoted in periclase base refractories when forsterite (Mg2SiO4) and spinel (MgA1204) are present as the second solid phase. The compositions studied were chosen as illustrations of the surface energy relationships in a system containing two solids and a liquid, and do not reflect possible direct applications in formulating refractory compositions. 6

If the CaO/SiO2 ratio is decreased below 39/61 in the CaO-MgO-SiO2 system at 1600~C, a second solid-forsterite (Mg2SiO4) -will form as an equilibrium microconstituent. The distribution of this phase can be controlled through heat treatment. If the forsterite is formed on cooling from a higher temperature where only periclase and liquid are present, it will be precipitated in the liquid which is present as a film between the periclase grains. When formed under these conditions, the second solid phase is most effective in promoting solid-to-solid contact. An example of bonding with forsterite is shown in Fig. 9. With a 15/85 ratio of CaO/SiO2, only periclase and liquid will be present at 1800~C (3270~F). On cooling to 1600~C (2910~F), forsterite will be precipitated to form an intergranular bridge in the liquid between periclase grains. This treatment is effective in producing extensive solidto-solid contacto Spinel (MgA104) can provide another example of second-solid-phase bonding in the CaO-MgO-A1203 system. With a CaO/A1203 ratio of 30/70 in this system, only periclase and liquid will be present at 1800~C (3270~F). On cooling to 1600~C (2910~F), spinel will be precipitated in the intergranular liquid and thus provide solid-to-solid contact, Figure 10 shows the microstructure produced under these conditions. These two examples provide supporting evidence for a conclusion drawn earlier:l,2 the energy of the boundary between two unlike solid phases is lower than the energy of the boundary between like solids. This conclusion is reached by noting that the liquids present in the two examples cited above do not penetrate periclase-forsterite or periclase-spinel boundaries as extensively as they do periclase-periclase boundaries. This result could prove to be useful in formulating refractory structures with high-temperature properties. III. CONCLUSIONS The microstructures which are developed by periclase (MgO) in the presence of calcium-silicate, calcium-aluminate, and calcium-iron-aluminate liquids have been described. The major conclusions which can be drawn from this study are: 1. Growth of Individual Crystalline Grains,-The rate of crystalline grain growth of periclase was found to be controlled by the relative solid/ liquid interface energy. It was found to increase with the square root of time and with temperature, but to decrease where liquid contents were increased. The growth rate was also found to be influenced by the composition of the liquid and, when solid solution occurred, by the composition of the solid. 7

2. Liquid Phase Distribution. -The degree of liquid penetration along boundaries between adjacent crystalline grains was found to be slightly sensitive to the composition of the liquid. Calcium-silicate liquids were found to penetrate the boundaries most deeply, whereas calcium-aluminate and calcium-iron-aluminate liquids provided for the most solid-to-solid contact. 35. Solid Phase Bonding.,-Solid-to-solid bonding is more effective in the presence of a liquid when two solid phases are present rather than one. 8

TABLE IV Sample Figure Composition Temperature TimeMean Liquid Dihedral iNo. No. Solid ~)i(u s) Diameter Content Angle* (C),Sd(Hours) (mm) (%) (Degrees) 239 MgO CaO/A1203-50/50 1400 60.0570 7 240 MgO CaO/Al203-50/50 1400 6o.0410 16 241 MgO CaO/A1203-50/50 1400 60.0377 30 253 MgO CaO/A1203-56/44 1500 4.0259 254 MgO CaO/A1203-56/44 1500 4.0273 265 MgO CaO/A1203-56/44 1500 16.0428 266 MgO CaO/A1203-56/44 1500 16.0381 279 MgO C4AF** 1400 16.0473 281 MgO C4AF** 1400 4.0353 282 5(a) MgO C4AF** 1400 4.0287 283 MgO C4AF** 1400 36.0636 284 MgO C4AF** 1400 36.0689 285 Mg C4AF** 1400 36.0677 286 MgO C4AF** 1400 64 o0816 287 MgO C4AF** 1400 64.0715 288 MgO C4AF** 1400 64.0663 361 MgO CaO/A1203-56/44 1500 64.0567 12 362 MgO CaO/A1203-56/44 1500 64.0568 19 363 MgO CaO/A1203-56/44 1500 64.0560 25 364 MgO CaO/A120342/58 1500 64.0672 12 365 MgO CaO/A1203-42/58 1500 64.0510 18 366 MgO CaO/A1203-42/58 1500 64.0449 23 392 MgO CaO/Si02-39/61 1600 4.0341 7 393 MgO Ca0/Si02-39/61 1600 4.0392 12 394 MgO CaO/Si02-55/47 1600 4.0322 13 395 3 (a) MgO CaO/Si02-53/47 1600 4.0282 17 396 MgO CaO/Si02-39/61 16oo 16.0524 5 397 MgO CaO/Si02-39/61 1600 16.0511 12 398 MgO CaO/Si02-53/47 1600 16.0395 7 399 3(b) MgO CaO/Si02-53/47 16oo 16.0383 12 402 5(b) MgO C4AF** 1600 4.0524 430 MgO CaO/Si02-39/61 16oo 64.0795 6 23 431 2(a) MgO CaO/Si02-39/61 1600 64.0761 13 21

TABLE IV (Concluded) Sample Figure CompositionTemperature Time Mean Liquid Dihedral No, W No, ISolid Liquid I (~C) (Hours) Diameter Content Angle* (mm) (%) (Degrees) 452 MgO CaO/Si02-53/47 16oo 64 o0588 10 22 433 5(c) MgO CaO/Si02-553/47 600 64.0575 13 25 437 MgO CaO/A1203-42/58 1600 64-.0902 5 30 438 8(a) MgO CaO/A1203-42/58 1600 64.0759 19 31 439 MgO CaO/A1203-56/44 1600 64.o86o 6 440 8(b) MgO CaO/A1203-56/44 1600 64.0748 13 441 MgO C4AF** 1600 64.0814 4.6 28 442 MgO C4AF** 1600 64.0970 9.5 31 443 8(c) MgO C4AF** 1600 64.0909 14 51 456 MgO C4AF** 1700 1.0462 458 MgO CaO/A1203-50/50 1700 1.0499 462 MgO CaO/A1203-65/35 1700 1.0382 H 464 MgO CaO/Si02-15/85 1700 1.0374 0 466 MgO CaO/Si0-65//3 5 1700 1.0258 476 MgO C4AF** 1700 4.0724 5 478 MgO CaO/A1203-50/50 1700 4.0562 9 480 MgO CaO/A1203-30/70 1700 4.0614 13 482 MgO CaO/A1203-65/35 1700 4.0512 11 484 MgO CaO/Si02-15/85 1700 4.0568 5 486 MgO CaO/Si02-65/35 1700 4.0346 8 518 5(c) MgO C4AF** 1800 4.0879 520 MgO CaO/A1203-50/50 1800 4.0660 522 MgO CaO/A1203-30/70 1800 4.0684 524 MgO CaO/A1203-65/3 5 1800 4.0784 526 MgO CaO/Si02-15/85 1800 4.0711 528 MgO CaO/Si02-65/355 1800 4.0659 5530*** 10 MgO CaO/A1203-30/70 1800 4 5534*** 2(b),9 MgO CaO/Si02-65/355 1800 4 558~MgO/FeO CaO/Si02-50/50 1700 4.0852 6 80/20 559 l(b) MgO CaO/Si02-50/50 1700 4.0741 10 560 MgO CaO/SiO2-50/50 1700 4.0608 15 *The angle of p6netration of the liquid phase between two grains of the solid phase. **C4AF = 4CaO.A1203-Fe203 ***The two samples were refired at 1600~C for 16 hours.

ACKNOWLEDGMENTS The financial support of the American Iron and Steel Institute is gratefully recognized by the authors. 11

APPENDIX A, REVIEW OF LITERATURE Since a review of the pertinent literature concerning ceramic microstructures was included in an earlier report on magnesiowustites [(Mg, Fe)O], this appendix includes only a summary of that report, a summary of a subsequent report on the microstructures of magnesiomagnetite (MgxFe3-xO4),2 and a discussion of the phase relationships studied in the present investigation. (a) Microstructures of MagnesiowUstite [(Mg,Fe)O] in the Presence of Si02 An investigation of the effect of time, temperature, amount of liquid, and ratio of MgO to FeO was carried out on periclase-type oxides. Results indicated that the magnesiowUstite crystalline grain size increases as the time and temperature of firing are increased. The crystalline grain size was found to decrease slightly as the amount of liquid was increased for a given firing time and temperature. The growth rate was found to decrease as the MgO/FeO ratio was increased and also to decrease in the presence of a second solid phase. The location of the liquid phase was also an important consideration in this investigation. The liquid phase was found to penetrate as a film between the individual magnesiowtistite grains under all the conditions studied. When spinel-type phases were present, however, they were found to provide a solid-to-solid "bridge" between magnesiowUstite grains. (b) Microstructures of Magnesiomagnetite (MgxFe3-x04) in the Presence of Si02 An investigation similar to that described above was carried out on magnesiomagnetite, with results indicating the same effects on crystalline grain growth as were found for magnesiowistite. With respect to the location of the liquid phase, it was found that silicate liquids do not penetrate magnesiomagnetite grain boundaries as fully as in magnesiowUstites. However, the amount of solid-to-solid contact is limited. Over the range studied, the degree of liquid penetration was not found to be sensitive to the composition of the solid, but the presence of olivine as a second solid phase was found to provide a means of bridging magnesiomagnetite grains and of providing for more solid-to-solid contact (c) Phase Relationships In the CaO-MgO-A1203 ternary shown in Fig. 11 there is very little change 12

in the solubility of MgO with composition or with temperature along either the 1500 or 1600~C isotherm, This situation is changed considerably in the CaO-MgO-Si02 ternary system shown in Fig. 12. The solubility of MgO in the liquid changes significantly with liquid content along the 1600~C isotherm. However, this isotherm is parallel to and almost directly above the join from forsterite (2MgO.Si02) to di-calcium silicate (2CaO.Si02) with the compounds monticellite (CaOMgOSi02) and merwinite (3CaO.MgO~2SiO2) between, which would indicate that the structure of the liquids along the 1600oC isotherm are very similar, The pseudo-binary C4AF-MgO is shown in Fig. 13. The solubility of MgO is limited in the liquid phase in this system. 13

APPENDIX B. EXPERIMENTAL PROCEDURE Samples were obtained by sintering reagent-grade raw materials at selected temperatures for various times. This heat treatment was followed by subsequent preparation of the samples for microscopic examination by reflected light. (a) Sample Preparation Reagent grades of Fe203, MgO, CaO, SiO2 and A1203 powders were weighed and mixed in the desired amounts. The respective mixtures were then pressed into pellet-size samples. Presintering and regrinding were not necessary for structures which contained a liquid phase during heat treating. (b) Heat Treatments For the sintering temperatures up to and including 1600~C (2910~F), a tube furnace heated by SiC heating elements was used. The furnace temperature was controlled by means of a thermocouple placed near the heating elements. Sample temperatures were determined by a separate Pt-PtRh thermocouple placed in the tube close to the sample. The tube was open at both ends to allow the sample composition to come to equilibrium with an atmosphere of air. The samples were water-quenched after being fired at these temperatures. The samples run at 1700 and 1800~C were fired in an oxy-acetylene fusion test furnace. Sample temperatures were determined by sighting directly on the sample with an optical pyrometer. The desired temperature was maintained by manually adjusting the gas flow rate. (c) Microscopic Examination Standard reflected light metallographic procedures were used in preparing the samples for analysis. This included grinding, impregnation, mounting, and polishing. Grain sizes were determined by measuring the mean diameter of a number of randomly selected grains in a two-dimensional microsection. Although this dimension will be smaller than the true mean diameter by a factor of approximately 0.86, this index is a consistent means of comparing the grain size of similar microstructures. 3 14

Liquid contents were measured using a point counting technique on a number of randomly selected areas in a two-dimensional microsection. The dihedral angles were measured using an ocular rotating-stage combination on a two-dimensional cut of the sample.4 15

REFERENCES 1. Lo H. Van Vlack and 0. K, Riegger, Microstructure of Magnesiowtistite [(Mg,Fe)O] in the Presence of SiO2, The University of Michigan, ORA Report 03683-5-T, Ann Arbor, April, 1961. 2. Lo H. Van Vlack, 0. K. Riegger, and G. I. Madden, Microstructure of Magnesiomagnetite [MgxFe3,x04] in the Presence of SiO2, The University of Michigan, ORA Report 03683-8-T, Ann Arbor, November, 1961. 3. L. H. Van Vlack, Physical Ceramics for Engineers, Ann Arbor, Malloy Printing, p. 49 (1960). 4. 0. K. Riegger and L. H. Van Vlack, "Dihedral Angle Measurement," Trans. AIME, 218 (1960), 933. 5. R. B. Sosman and Olaf Andersen, Phase Equilibrium Diagrams of the Refractory Oxides, Research Laboratory, U.S. Steel Corp. (1946), Plate 4. 6 G. A. Rankin and H. E. Merwin, "Das Ternare System: Calciumoxyd-Aluminiumoxyd-Magnesiumoxyd," Z. anorg. u. allgem. Chem., 96 (1916), 309. 7. E. F. Osborn and A. Muan, Phase Equilibrium Diagrams of Oxide Systems, The American Ceramic Soc., Columbus (1960), Plate 2. 8. R. W. Ricker and Eo F. Osborn, "Additional Phase Equilibrium Data for the System CaO-MgO-Si02," J. Am. Ceram. Soc., 37 (1954), 133. 9. J. R. Rait, "Basic Refractories," Iron and Steel, 23 (1950), 90. 16

0 0. ---------------- ---------- k~ ~ ~~~~~~~~~~~...............................................SZ...-........... 0)'-4~~~~~~~~~~~~~~~~~~~~~~~......................................................... 0 0 O Nvng o ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~~~~................. 0.......... HOC HHC) 0 00~~~~~~~~~~~~~~~~~~~............................o.. O ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~~~.................. 0....................................... 6.........I...H.......0. 0~~~~~~~~~~~,ZH~~~~~~~~~~.........................i..................................................40 O t4' H....................... ( ) 4 Q~~~~~~~~~~~~~~.................o..... HOC a ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~ H' U 0........... O N U "'~~~~~~~~~~~<~~~....0 C t 0.... 0~~~Q~~ U), 0a~~~~~~'.,...... 0 U)... 00 H0) 4000'~~~~~~~~~~~~~~~~~~~~........... 000) Orb~~~~~~~~~~~~~~.......................................... Q~~~~~~~~~o \)0~~~~~~~...................................................... _ ho...................t...........'....... C O ~~~~~~~~s' U t 0 U UH~~~................................................. I....................................... H' ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~~~~~..........c t.................... H 0 U''-'0 Z 0 U~~~~~~~~~~~~~~~........................0..... 0 ) 0.......'..0 0 0....0.....> U' 00 0 0)0 t~~~~~~~~~~~~~....... 00 ~~~~~~~~~~~~~~~~~~~~~'-' ctU~~~~~~~~~~~~~~~~~~~~~~~~~........ o ~~~~~~~~~~~~~~~-'- ~ 00't~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~........'-'~~~~~~~~~~~~~~~~~~~~~~~~~' ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~.............H H..............'0;"~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~~~~~~~~~~~~~~~~~~~...................... 0.............................O.. 0-i H............Z "~~~~~~~~~~~~~~~~~~~~~~~~~~~-0 ~ ~ ~ ~ ~~~~~~~~.................................. ~ ~ ~ ~ ~ ~ ~ ~ 4 0~ 0 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~........ 0~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~........... O H ~ ~ ~ ~ ~ ~ ~~~~~~~~~......... C............ U......s........O.. r~~~~~~~~~~~~~~~~~4 ~ ~ ~ ~ ~ ~~...............r....... H O O tt A~~~~~~~~~~~~~~~~~~~~~~~~~~...............................................H a.......................................d........................... ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~,'~

Ad Hi r (a) (b) (c) 41 hours 16 hours 64 hours F"ig n). Effeet of time on Crystal.]ine grain size X250. Microstructures are periclase in the presence of a liquid with a CaO/SiOp ratio of 55/47. Fired at l16000C. Etched with 5e HF......0....~ W.........10....020.. 0......... F... i).C ta me Grain Si ev...... ime. ( a e....aml..es......... ) 4 506 ig 4. d C rysta.]._lXi, e Gran Size. rs............ Time tt*.................. (Sam [.e exmple as. i icgX 3 5.)..........t C OS0p r ti T 74 7 ird a............ehd i~ ~~- KP.......... ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~'s............................. j,O~ ~~~~~~~~~~~~~~~~~~~~.............................................................. —~C~) $~~~~~~~~~~~C;cz"~~~~~~~~~~~~~~~~~~~~~................................~ ~ ~~ ~ ~ ~~ ~ ~ ~ ~ ~ ~ ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ]xxxxxxxx Z:j.......... ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~~ Q........... ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ r ~~~~~~~ ~~~~~~~~~~~~~O~~~~~~~~~~~~~b~...........................- (H UR )' Mirotucuesar er-lae nth resec o

(a) (b) (c) l40000 1600~C 18000c Fig..g 5. Crystalli:ne grain growth of peric ]ase as a function of temperature after 4 hours in the presence of a 4CaO. A1205.Fe205-ri eh Iiquiid. Etched with 5. HI.f. 250X Y t.... >: jai,i: /IUI"/ /.08 M / -AO / Ass^~~~~ /~A ^ ~~~~~~~/ / IU / *f> / Z04A O ox / TEMPERATURE -0G as in Fig. 5.) Affiato t'o o ii, ~. J:.~. ( S a m e example.s as in Fi g. 5.)iiiiiii (Et) (b) (C)~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~7...... 1400XX.XxC1800 F`3.g, fii, Crystall.~~~~~~~~~~~~~~~~~~.ne gra~~~~~~~ln grow-i~~~~~~~~ft of per~~~~~~~~~i~~ctar~~~~~e as a func-l;;ion o-I:`~~~~~~~~~~....... temperature tltP~~~~~~~~~~~~~~~~ter 4 hours in the psesenec ~~~~~~~~~~~~~~~~................... S~~~nO. R~~~~~~p~~~g.Pe O -rict~~~~~~~......................e wit.tO~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.............. C~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~L~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~...... Q/~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.......oa:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..... 1200 iSBO I~~~~~~~~~~~~~~~~oo taco sdsoo~~~~~~~~~~~~~~~~~~~~; ~~~~~~~ troo ~~~~~~~~~~~~~~~~~~~~~~~sai~~~~~-.4.............

.10.080.06a. Z.04- 0- — 0-.02 - 01 5 10 15 20 25 30 LIQUID CONTENT - % Fig. 7. Crystalline Grain Size vs. Liquid Content. Periclase (MgO) plus other oxide liquids. Curve ta): liquid composition 50/50 CaO/A1203, temperature 1400 C (2550~F), and time 60 hours. Curve (b): liquid composition 42/58 CaO/AL203, temperature 1500~C (2730~F), and time 64 hours.

......................... X........... Xx........................................................................................................................... X............................................................................................................:X............................................................... X............................................... X X:x A,........... X.,...................... X.:........................................................... X.................................................................................. X....................................................................................................................... iurri-si icate liquid.......................................................................................................................................................-...............................................................-................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... 1-1-...................................................................................................................................................................................................................................................................................................... I1-1.11..................................1............................................................................................................................................................V............................................................................................................................................................................................................................................................................................................................................................................................................... --.......................................................................-...........................................................................................................-.............................................................................-..................................................................................................................................................................................................................................................................................................................................-.......................................................-...............................................................................................-....................................................-............................... *.................................................................................................................................................................................................................................................................................................................... -— %........................................................................................................................................................................................................................................................................................................................ "I.,"..".......................-........................................................................................................................................................................................................................................................................................ —:::: 4:X:....................................................................................................................................................................................................................................................................0...........................................................................................................................................................................................................................................................................................-.......................................................................................................................I..........................................................................................................................................................IY —. --............. I.".....,........,.,.............,...............,....................I..................... 11...............................................................................................-........................................................................................................................................................................................................................................ W.............................-..........................................................................................................................................................................................................................-................................................ b) Cal-cium-aluminate liquid.............................-.............-.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................-........................................................................................................................................................................................................................................................................I............................................................................................................................................. 111-1..............................................................................................................................................................................................................................................................................................................................................................................................................................................................-.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................-............................................... ---.................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................I...............................................................................-.................... 1....................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................-............................................. X.....................................:xj Calc'luai-.1'.ron-alum'-'Lnate liquid. I -

Brig. 9. Forsteritc (Mg2Si04}) bondi~ng. 250OX. CaO/SiO~ ratio 15/8:5. Sinterwed 4i hours at 1+800~C (3270~F) followed 5y i46 hours a-t 1600~C (291+0~F). This treatment produced extensive so~id~to. solid contact. Etched with [~ HF. Fig. 10. Spine]. (MgACO,) bonding. 250X.' CaO/AI O~ ratio 30/70. sintered 4s hotr~: at 1800~0C ()2'"[0~F)3 followed by. 1[6 hours at ^6000 2;9t F *Etched with'jf LF.

A 3CAO.A5ALL \ / FO ~^^ ^MGO. AL203 CAO.ALC3 52 \ SPINEL 5CA0.3 AL203 7/1600 o, \, 1800~C 3 CA 0.AA L203 X / LIME \ ~/.~~~ l PERICLASE E s 2 —v v VI v __S _v\/ CAO MoO Fig. 11. System CaO-MgO-4lO. (After Sosman and Andersen(5) and Rankin and Merwin 0 )

S o102 3CAO.MG0.2S102 a, ~ / ^~ ~FORSTERITE LIME ~~~/ X\~ ~PERICLASE \ z V V \ \.___ V V \ V V CA0 MOO Fig. 12. System Ca8-MgO-SiO2. (After Osborn and Muan(7) and Ricker and Osborn )).

2800 2400 0 I/ w 2000 2) 1 1600 1200 20 40 60 80 QAF WEIGHT % MoO Fig. L3. System 4C9O A1203.Fe203-MgO; C=CaO, A=A1203, F=Fe2O3. (After Rait(9 ).