High-Temperature Strength of MgO Refractories, Report of lnvestigations 8732

8/12/2019 High-Temperature Strength of MgO Refractories, Report of lnvestigations 8732

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Report of lnvestigations 8732

lnfluence of Selected Additivesand CaO:Si0 Ratioon High-Temperature Strengthof MgO Refractoriesy Nancy S Raymon

UNITED STATES DEPARTMENT OF INTERIORJames G Watt SecretaryBUREAU OF MINESRobert C Horton DirectorResearch at the Tuscaloosa Research Center is carried out under 1 e m o r a n d u of agreement between theureau of Mines U.S. O e p a r t m e t of lhe lnterior and the U n i e r s i t y of Alaba ma.


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h i s publ cation has been cataloged s follows :

Ra ymon, o f ; a Uni red n of

r io r, 1\ur eau o f Mines ; 8732)d c > ; i o a l rc fe re n cs .of ) : s 11 . : 28 . 23:87 3

r a : Magnc 3. O x i l e s 4 .a l s T i l ll. Se ri e s: Hcpo rt of ; : :

l ' < Bure>tu o f Mi11 cs) ; 8 732.

2 3 . U43 [ 4 t8. 26] 622 6 6 6 72\ R2 H 00 2 4


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CONTENTS

AbstractIntroduct ion 2Tes t procedures 2

Sample p r ep a r a t i o n 2Modulus o f rupture tests 3Factorial ly designed e x p e r im e n t 3esults and discuss ion 4In i t i a l screening t e s t s 4Factorial ly designed e x p e r im e n t 5

Conclus ions 8TABLES

1. Source location and chemical composition of periclase mater ials used in2.3.4.5.6.

i n i t i a l screening t e s t s Factorial program variables Chemical composition of periclase mater ials used in fac tor ia l ly designed

33

experiments 4Effect of oxide additions on hot OR values of three commercial periclasegrains at 1 550 CEffect of oxide additions on hot OR values of commercial periclasegrains at 1 550 CAnalysis of variance data reported as F-ratios 67


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INFLUENCE OF SELECTED D D i i V E S AND CaO:Si0 2 R i O HIGH TEMPERATURESTRENGTH OF MgO REFRACTORIESBy Noncy S Roymon 1

BSTR CTThe Bureau of Mines i n e s t i g a t e d the effect of controlled additions ofselected metal oxides as well as the adjustment of the calcia-to-si l ica

rat io on the high-temperature strength of refractory-grade periclase.Increases in the hot flexural strength of some periclase materials inthe range of threefold to fourfold were obtained with additions of Zr0 2and by adjustment of the CaO:Si02 rat io to the 2.5 to 3.0 l e e l . Results show that for each periclase refractory raw material there existsa combination of l e e l of Zr02 addition and an adjustment to theCaO:Si02 rat io that optimizes the hot flexural strength of each ofthese materials. Data also indicate that the i m p r o e d hot strengths canbe attr ibuted to the high-temperature secondary phases formed betweenthe different l e e l s of periclase impurities and the a d d i t i e s resul t ing in i m p r o e d intergranular high-temperature bond strength.

1Meta l lurg is t formerly with u s c l o o s Research Center Bureau of Mines u s c -Ala. ; now r es ides in Blacksburg va.


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2

INTRODUCTIONThe re f rac to r i e s indust ry has an impact

on a l l steelmaking processes , as well ason the production of aluminum, glasscopper, cement, and other commodities.With the emphasis today on the impact ofengineering mater ia ls on increas ing pro

d u c t i i t y a need ex i s t s to i m p r o e thehigh-temperature performance of re f rac tory l in ing mater ia ls . The ref rac toryproper t ies of domestic raw mater ia ls andproducts must be optimized to meet imp r o e d performance demands tha t h a e re sul ted from new processing d e e l o p m e n t sin hydrometal lurgical and pyrometal lurgical operat ions. I t i s espec ia l ly important to i den t i fy subs t i tu t e s for theimported c h r o i t e ore tha t i s used in theproduction of basic re f rac to r ies .

The ref rac tory industry uses 16 pct ofthe to ta l chromite consumed in the UnitedStates .2 The s tee l indust ry i s by fa rthe la rgest s ingle consumer of re f rac t o r i e s u t i l i z in g o e r 60 pct of thet o t a l tonnage produced annual ly.3 Thesteelmaking furnaces predominantly usebasic l in ings produced from MgO in the

f o r n of dead-burned grain and chromite.Although there are adequate resourcesof MgO in the world today, espec ia l ly the synthet ic MgO d e r i e d from

seawaters and br ines the United Stateshas no s ign i f i can t domestic chrome oreresource, so tha t a l l of the chromiteconsumed in the United States i simported.4

As par t of the Bureau of Mines missionto encourage and as s i s t the d e e l o p m e n tof the Nat ion s mineral resources and toi den t i fy domestic subs t i tu te mater ia l sexploratory i n e s t i g a t i o n s were conductedon the e f fec t s of a d d i t i e s on the hots t r eng th of per ic lase raw mater ia ls . Thes tudies c o e r e d in th i s repor t i n v o l e de x t e n s i e screening t es t s to i den t i fypo ten t i a l ly promising metal oxidea d d i t i e s . Select ion was predominantlybased on the e f fec t s of these oxides onthe s in te r ing of MgO as reported by Layden and McQuarrie.S They hypothesizedtha t to ce r t a in l imi ts addi t ions of Feand Mn ions enter the MgO crys ta l l a t t i c eand promote s in te r ing while addi t ionsof other ions such as T i Zr, and Taaid s in te r ing by unident i f iable mechanisms. The main effec t s and i n t e rac t ioneffec t s of metal oxides and CaO:Si02(C/S) ra t ios on high-temperature f lexura ls t r eng th of the ref rac tory-grade 1-1g0 weredetermined through f ac to r i a l l y designedexperiments .

TEST PROCEDURESSample Prepara t ion

The mater ia l s e a l u a t e d werecommercial-grade, dead-burned per ic lasegrains tha t are used in the production ofbasic re f rac to r ies . The samples were

d e r i e d e i ther from seawater, lake andwel l br ines or na tura l magnesite andcame from I s rae l Japan, or the UnitedStates . Par t i a l chemical analyses in cluding the C/S ra t ios of the 11

2Peterson, c. Chromium. BuMinesMinerals Yearbook 1980, v. 1, 1981.3oickson, h u.s. Refractor iesIndustry--A Progress Report . Indus t r i a lMiner. , . 148, 1980, 59.

mater ia l s used in the i n i t i a l screeningt e s t s are g i e n in tab le 1. The fol lowing reagent-grade oxides were evaluatedas a d d i t i e s : CaO Fe 2o 3 MnO Sc 2o3 Si0 2 Ta 2o5 Ti0 2 Zro 2 These oxideswere chosen because of t h e i r high melt ingpoints and because the cat ion atomicrad i i are e r y s imilar to tha t of MgOal lowing so l id so lu t ion development a thigh temperatures.

4work c i ted n footnote 2.SLayden, G. and c.

Effect of Minor Additions onMgO. J . Am. Ceram. Soc. ,1959, 89-92.

McQuarrie.Sinter ing ofv . 2, . 2,


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3TABLE 1. - Source, location, and chemical composition of periclase materialsused in in i t i a l screening testsSource and sample Locationnumber MgOBrine:

1 Is rae l 99.2 - 2 United States 97.6 - 3 o 94.5 - 4 do 93.7Magnesite: 2 do . . . . 92.2Seawater:S 1 Japan 97.6S-2 o 96.4S 3 United States 96.2S 4 o 94.5S 5 o 93.5S 6 Israel 93.3

N Not detected.The as-received periclase grain materiwere crushed, then ground to passa 200-mesh sieve in a tungstenmill . The dif -metallic oxides in the form of325-mesh, reagent-grade powdersto the ground periclase mateAfter thoroughly mixing the drythe admixtures were i sos tat -pressed to 20,000 psi and subsefired to 1,600 C in an elect r icwith molydisilicide heating ele-adjust the C/S rat io of sameither CaO or S i O ~ was added. Therate was 200 C/hr followed by asoaking time of 1 hr. The f iredwere reground to pass 200 meshpressed at 2,000 psi into 3/8- by- by 2-in briquets. These were f ired toC in the previously described manand cut into 1/4- by 1/4- by 2-in

for modulus of rupture MOR)Modulus of Rupture Tests

The MORc. tes ts were performedThe specially designedand test ing procedurein a previous publication.6at

MORare

6McLendon, J . . . s. Raymon, and .Relationship of MineralogicalChemical Composition of Refractoryto Modulus of Rupture a tto 1,600 c. BuMines RI 8386,

Chemical analyses, wt-pctCaO Si0 2 Alz03 Bz03 Fe 2o3 C/S0.68 0.10 0.04 N 0.08 6.8.63 .90 .23 0.09 .18 .72.40 .90 .26 .09 .19 2.72.80 1.90 .26 .03 .25 1.52.90 1. 70 .34 .02 .82 1.7

.53 .60 .26 .03 .53 .9.90 2.10 .26 .01 .27 .41.10 .80 .34 .06 .45 1.41.10 1.90 .38 .23 .70 .41.20 2.70 .34 .19 .56 .41.20 3.30 .26 .33 .54 .4Factorial ly Designed Experiment

establ ish the interaction effects ofoxide additions and C/S rat io adjustments, single replicates of 3- by 3- by4-factorial experimen ts of completelyrandom design were performed. Table 2shows the levels at which each factor wasexamined. Finely ground 85 pct minus200-mesh domestic periclase raw materials were obtained for these tes ts .

TABLE 2. - Factorial program variablesFactor Level1 2 3 4HnO mole-pct 0.25 0.50 NDZr0 2 mole-pct 1. 2.0 NDC/S mole rat io 5 2.0 2.5 3.0

ND Not determined.Although the periclase materials weresimilar to ones used in the in i t i a lscreening tes ts the chemical composit ions of the new shipments of the per i clase materials differed from those inthe ear l ier s tudies , as shown in table 3.The samples were renumbered to include asubscriptSamples were prepared by blending the85 pct minus 200-mesh periclase with ad

ditives in a slurry of water. After drying th is mixture, the material waspressed into 1- by 2- by 1/4-in briquetsand f ired for 2 hr in a gas-fired fur


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4

This higher f ir ing temperature is morerepresentative of industrial practiceand eliminates the necessity of regrinding and refir ing the samples. The

sintered slabs1/4- by 2-in1,550 c.were cut into 1/4- bybars for MOR testing at

TABLE 3. Chemical composition of periclase materials usedin factorial ly designed experimentsSample Analysis, wt-pctMgO CaO Si02 Al203 2 0 3 Fe 23 C/S

B 2n 95.3 0.61 0.64 0.20 0.11 0.61 1.0B 3 n 95.9 2.30 .56 .13 .02 .40 4.1M 2n 93.5 3.30 1.30 .44 .02 .64 2.5S 3 n 97.4 .89 .60 .12 .05 .46 1.5S 4n 93.9 .96 1.80 .41 .13 .68 .5

RESULTS ND DISCUSSIONni t ia l Screening Tests

Table 4 presents the hot MOR data obtained at 1,550 C for periclase materials - 1 - 4 and - 2 with oxide additions at levels of 1/4, 1/2, 1, and 2mole-percent. For the in i t ia l evaluation

of the effectiveness of the metal oxideaddit ives, these three periclase materials were chosen because their MgOcontents ranged broadly from a high of99.2 to a low of 92.2 pct as shown intable 1.

TABLE 4. Effect of oxide additions on hot MOR valuesof three commercial periclase grains at 1,550 CHot MOR psi 2.0

Zr02 4,500 1,850 2,250 2,650 3,475Ti0 2 4,500 N 1 700 600 650Ta 2o5 4,500 N 1,600 1 7 50 2,250Sc 2o3 4,500 N 675 5,47 5 5,550Fe 2o3 4,500 N 3,000 2,000 1,275 4,500 N 6,175 4,625 4,350

SAMPLE - 4 93.7 w P C T MgOZr0 2 4,610 7,650 8,700 1,125 750Ti0

2 4,610 1,825 7,550 6,050 125Ta 2o5 4,610 N 375 200 NSc2o3 4,610 N N N NFe 2o3 4,610 N 1,000 225 725nO 4,610 N 3,650 5,875 2,325

SAMPLE - 2 92.2 w - P C T ~ 0Zr0 2 1,800 N 1,350 725 750Ti02 1,800 N 350 250 100Ta 2o5 1,800 N 300 225 350Sc 2o3 1,800 N 2,725 2,525 NFe 2o 1,800 1,37 5 2,250 750 375nO 1,800 N 1,27 5 1,87 5 1,900ND Not determined.


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In general , the 93.7-pct-MgO per ic lasedoped and undoped, produced samof the highes t s t rength . The re

of the per ic lase grainsi s re la ted to the to t a l impurcontent, but the type of impuri t ies

be more important .Additions of Zr0 2 in amounts ofand 0.50 mole-pct wereto increase the s t rength of

sample - 4 93.7 wt-pctby 66 pct and 89 pct respecHowever, addi t ions of Zr0 2 in0.5 mole-pct resul ted ins t rength for samples - 2 - 1

- 4 . Additions of Ti0 2 decreaseds t rength of peric lase samples - 2 - 1 but increased the s t rengthsample - 4 when added in amounts0.25 and 2.00 mole-pct. DopingTa 2o5 decreased the hot s t rengtha l l three samples. Additions of

2o3 increased the s t rength of per i sample ~ 1 2 by about 45.0 pct andf sample - 1 by about 22.0 pct a t theand 2.0-mole-pct addit ion; samplewas not evaluated. Additions of

2o3 decreased the s t rength of samplesand - 4 whereas 0.5-mole-pct addi increased the s t rength of sample

Additions of MnO appeared to in hot s t rength values in severa l

The ef fec t s of the selected metal oxideZr0 2 Ti0 2 and MnO addi t ions and C/Sadjustments to 2:1 on f l exura l

a t 1,550 C on a l l 11 per ic laseare shown in tab le 5. St a t i s

analyses of the data indicated tha tof Zr0 2 s igni f icant ly improved

5

hot s t rengths of s ix of the peric lasemater ia l s especial ly those derived fromseawater , whereas addit ions of 0.5-mole-pct MnO improved hot f lexuralstrengths of two of the peric lasemater ia ls . Additions of Ti0 2 resul ted indecreased s t rength values. As noted inprevious s tudies 7 adjust ing C/S ra t iosto 2:1 s igni f icant ly improved hot MORvalues of most of the re f rac tor ies .These s tudies a lso demonstrated the deleter ious ef fec t of high levels on hotstrengt11 of commercial per ic lases . Thehot s t rengths in tab le 5 for peric lasesamples S-4, S-5, and S-6, which have thethree highes t contents , were thethree lowest values measured.

Results from th is phase of the studyindicated that a C/S ra t io and metaloxide addi t ion combination should be establ ished for each individual peric lasemater ia l . Of the meta l l i c oxides s tudiedin th i s inves t igat ion addi t ions ofMnO and Zr0 2 appeared to be the mostpromising.

Fac tor ia l ly Designed Experiment

Analyses of variance as applied tothe resu l t s of the f ac to r i a l experimentident i f ied main ef fec ts and in te rac t ionef fec ts for each of the per ic lase materials . The concentrations of MnO and Zr0 2and the C/S ra t io were chosen as the facto rs and hot MOR as the response, forthe 4-level f ac to r i a l experiment designout l ined ea r l i e r . Table 6 l i s t s the Fra t ios for each factor and for secondorder in te rac t ions between fac to rs .

w o r k ci ted in footnote s.


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TABLE 5. - Effect of oxide additions on hot OR values of 11 commerical periclase grains at 1,550 CSample - 3 - 4 S-1 S-2 S-3 S-4 S-5 S-6Source Israel United United United United Japan Japan United United United IsraelStates States States States States States StatesgO wt-pct 99.2 97.6 94.5 93.7 92.2 97.6 96.4 96.2 94.5 93.5 93.3B2o3 wt-pct 0.09 0.09 0.03 0.02 0.03 0.01 0.06 0.2 0.20 0.3C/S ratio ,as-received 7 0.7 2.7 1.5 1.7 .9 .4 1.4 0.4 0.4 0.4MOR psi:As-received 4,550 220 6,520 4,610 1,800 490 240 450 210 170 180

Zr0 2 , wt-pct: 5, 7305 2,250 220 6,360 860 310 510 250 130 190 1,000 370 700 1,220 300 920 450 450 300 130 210

2 1,040 600 6,830 960 750 980 540 710 410 150 410Ti0 2 , wt-pct:5 330 100 490 490 350 270 130 190 230 50 180

360 80 230 140 160 250 280 210 90 60 502 . . . . . . . . . . 650 110 125 50 100 260 130 80 120 110 140MnO wt-pct:

5 1,040 170 3,650 6,620* 1,275 620 230 490 220 120 2301 . . . . . . . . . . 4,950 160 5,480 5,760 1,380 420 210 400 190 140 1302 4,350 160 2,325 3,690 1,900 540 160 460 230 130 150

C/S ratio 2 440 530 1 100 2,420 580 1 , 4 5 2 ,420 900 680 1,190* 710I -OR improvement sign1ficant at 99 pct confidence level (Student s t test . IIMiller, and J. Freund. Probabili ty and Stat is t ics for Engineers. Prentice Hall, Englewood Cliffs,N.J. , 1965, 136-39, 168-70.


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TABLE 6. - Analysis of a r i a n c e datareported as F-ra t ios B-3n S-4n S-3n B-2n M-2n

0.6 1.1 1.7 0.4 1.8 23.1 .9 50.5 9.08 61.4c. . . . . 11.88 7.6 20.07 .04 64.1 1. 4 .4 1.6 .9 .66AC 1. 4 1.0 1. 3 1.2 1.04BC 7.14 2.01 19.27 1. 5 115.5= MnO = ZrO2 c = C/S.The C/S ra t io had a s ign i f ican t e f fec t

the ho t s t rength of sample M-2n, thena tu ra l magnesite per ic l a se , soaddi t ion of Zr0 2 The i n t e rac of C/S ra t io and Zr0 2 had a highlyon hot st rength ofper ic lase mater ia l , with the most

i n t e rac t ion occurr ing a t Zr0 2of 1.0-mole-pct and a C/S r a t i o

Additions of Zr0 2 also had s ign i f ican ton the hot s t r eng th of samplea b r i n e - d e r i e d 95-pct-MgO p er i

of Zro2 content andra t io were found to be ins ign i f ican t .sample contains subs tan t ia l boronreportedo be extremely dele ter ious to the

of per ic lase .8 Thera t io adjustment was found to befor sample . S-3n, a 97-seawater per ic lase .

The effec t of C/S ra t io was found to befor sample S-4n, a seawatercontaining 94 pct MgO and 0.13Interac t ions between fac were shown to be unimportant . The

BGilpin, . c., and D. R. F. Spencer.D e e l o p m e n t s in Dead-Burnt Magnesite

Dead-Burnt Dolomite. Refrac. J . ,47, . 4, Apri l 1972, 4-16.

C/S ra t io was found to befac to r in determining hotsample B-3n, a 96-pct-MgOr i e d from br ine .

7

a s ign i f ican tst rength of

per ic lase de-

Phase i d en t i f ica t io n r e su l t s by X-rayd i f f r ac t io n in the optimized per ic l a semater ia ls containing MnO addi t ions,samples S-3n and B-3n, indica ted t ha tt race amounts of CaMn03 , C and aspine l were present in both of thesespecimens .

x-ray d i f f r ac t io n analys is indica tedt ha t CaZr03 was presen t in both samplescontaining Zr0 2 addi t ions, samples M-2nand B-2n. h e only other secondary phasein sample M-2n was a t race amount of C Sample B-2n, a high-boron per i clase 0.11 pct contained a minoramount of cubic Zr0 2 Also detected inth i s specimen were t race amounts of mont i c e l l i t e and merwinite , which mayaccount for i t s r e l a t i e l y low hotst rength when compared wi th tha t of someof the other doped samples. I t has beenwell documented tha t the low melt ingpoints of mont ice l l i t e 1,487 C andmerwinite 1,577 C lead to lower hots t rengths for per ic lase tha t containthese s i l i c a t e s as secondary phases.Thus, in the case of a l l per ic l a se mater i a l , a C/S r a t i o of a t l eas t 2.5 i sdes ired in order to p r o i d e more r e f rac tory dicalcium s i l i c a t e tha t melts a t2,130 C, or t r ica lc ium s i l i c a t e tha td i ssoc ia te s a t 1,900 C. Similar ly , addi t ions of Zr0 2 resul ted in the formationof CaZr03 , a e r y ref rac tory secondaryphase melt ing point of 2,340 C).

The only secondary phases iden t i f ied insample S- 4n, another high-boron per ic lase0.13 pct was h i s samplea l so exhibi ted l ess i m p r o e m e n t in hotst rength than other doped per ic lasemater ia ls .


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8

ON LUSIONS

Additions of Zr0 2 and C/S ra t io ad jus t ments were determined to be effec t ive inincreasing the hot MOR of calcined p er i clase gra in mater ia l s . The most e f fec t ive addit ive tes ted was Zr 0 2 The l eve lof addi t ion of Zro 2 and the C/S r a t i oadjustment required to yie ld maximum hots t rength varied among per ic lase re f rac tory raw mater ia l s . In the case of asreceived per ic lase samples having hotstrengths of 1,500 psi or over , the

GOVERNMENT PRINfiNG OFFICE: 1982- 605 015/97

use of oxide addtions or C/S ra t ioadjustments had littl posi t ive e f fec t onhot s t rength. The fac to r i a l ly designedexperiment was judged to be usefu l inevaluat ing the i n t e rac t ion e f fec t s between fac tors and in es tabl ishing thecombination and l eve l s of fac tors yie lding optimum resu l t s . Research to developsuperior fu l l - s i ze br ick from domesticper ic lase gra in mater ia l s using thesere su l t s methods i s continuing

IN T B U OF MINES PGH . 2644

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High-Temperature Strength of MgO Refractories, Report of lnvestigations 8732