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Liquidus determinations in the 25% SiO2 plane of the quaternary system CaONb2O5TiO2SiO2
Journal of’the Less-Common Metals Elsevier Sequoia S.A., Lausanne - Printed
349 in The Netherlands
LIQUIDUS DETERMINATIONS IN THE 25% SiOz PLANE OF THE QUATERNARY SYSTEM Ca0-Nb20,-Ti02--SiO**
A. JONGEJAN
and A. L. WILKINS
Mineral Sciences Division, Department of Energy, Mines and Resources, Mines Branch, Ottawa (Canada) (Received
March
24th, 1972)
SUMMARY
Liquidus temperatures in the 25% SiOz plane ofthe CaO-Nb,O,-TiO,-Si02 phase tetrahedron have been determined using the customary quench technique as well as hot-stage microscopy. The boundaries between the phase fields of CaO .TiOz, CaO *TiOz*SiO,, TiOz, SiOz, CaO*Nb,Os, CaOe SiO,, 10 CaO*Nb,O,*6 SiOz (niocalite) and 2 CaO . SiOz have partly been outlined. This 25% SiOz plane probably also includes phase fields for 3 CJaO - SiOz and CaO. A phase field of CaO * SiOz is wedged in between those of CaO. NbzOs and 10 CaO . Nbz05. 6 SiOz (niocalite), instead of a field of 2 CaO * Nb,Os, as is found in the 20% SiOz plane. This would be expected from the known CaO-Nb,O,-SiO, phase diagram. All three compounds, 2 CaO.Nb,O,, CaO. NbzOs and 10 CaO. Nb,O, .6 SiOz, apparently occupy similar phase volumes between the CaO-Nb,O,SiO, side and the large phase volume of CaO .TiO, (perovskite), in the quaternary system. A summary of the phase relationships studied in the CaO-Nbz05-Ti02-Si02 system is given, and also some discussion of the mineralogical implications of these studies.
INTRODUCTION
Studies of the phase equilibrium relationships in the CaO-Nb,O,-TiO,-Si02 phase tetrahedron, reported previously ’ - ’ , have been extended to include those in the 25% SiOz plane. The location of this plane in the phase tetrahedron and its relation to the other planes previously studied are shown in Fig. 1**. If, in the tetrahedron, the CaO.SiO,CaO .Nbz05-2 CaO .Nb,O, boundary, starting from the relevant eutectic in the CaGNbz05-SiOz side6a7, bends slightly upwards towards the SiOz apex, it is possible that the 25% SiOz plane would intersect the 2 CaO. Nb,05 phase space * Crown Copyrights reserved. Division Report MS-PP72-12. ** The abbreviations commonly used in literature dealing with the chemistry used in this paper, viz., C=CaO, N =NbZOs, T=TiO, and S=SiO,. J. Less-Common Metals, 29 (1972)
of ceramic
oxides will be
A. JONGEJAN, A. L. WILKINS
Ti 0, Fig. 1. The quaternary system CaO-NbzO,-TiOiSiO, relation to the planes studied in previous work.
NY% showing the location of the 25%SiO, plane in
inside the tetrahedron and form there a small CzN field. The CaO.SiO,-&aO. Nb,O,-2 CaO.Nb,O, eutectic is approximately 1% SiOz below the 25 % SiOz plane ac(;ording to the CaO-Nb,O,-SiOz phase diagram. Although several aspects of the quaternary system, such as the extent of any solid-solution phenomena and the exact location of the quaternary eutectics have not been studied, the objective to provide sufficient data to give a general impression about the shape and size of the phase spaces of various compounds in the tetrahedron has been fulfilled. The series ofstudies is, therefore, te~inated with this present paper.
The experimental methods for the liquidus determinations were the same as those described for the 15% and the 20% SiO, planes4*5. Mixtures of the required compositions were prepared from Mallinckrodt’s “Analytical Reagent”-grade calcium carbonate, 99.5% pure niobium pentoxide from Alfa Inorganics, Inc., Beverley, Massachusetts, heated to 125@C, Baker’s “Analytical Reagent”-grade titanium dioxide, and silicon dioxide, prepared from Baker and Adamson’s silicic acid, dehydrated overnight at 1250°C. A quantity of the chemicals, sufficient to yield 4 g of the required composition, was mixed in an agate mortar. These mixtures were heated in platinum crucibles overnight at looo” C to sinter them and partly to decompose the calcium carbonate. They were then heated to 17OO’C in a gas-fired muffle furnace for one hour. The mixtures were ground for one minute in appropriate grinders (Wig-L-Bug grinders No. 6 and 3A from Crescent Dental Mfg. Co., Lyons, Illinois.) to produce fine-grained powders of which the small quantities used in the liquidus determinations were representative of the bulk compositions. After cleaning the powders magnetically, reproducible results were obtained with this technique. J. Less-Common Metals, 29 (1972)
THE QUATERNARYSYSTEMCa@Nb,O,-TiO,-Si02
351
Liquidus temperatures, which all lay below 17O@C, were measured initially using a Griffin-Telin hot-stagemicroscope equipped with a Pt : 5% Rh ZIS.Pt : 20% Rh the~ocouple. The use of this instrument has been described previously’. The liquidus temperatures of samples having compositions near field boundaries and piercing points were measured with the customary quench technique, in which a small sample (3 mg) in a Pt envelope was kept at an elevated temperature until equilibrium conditions were obtained and then quenched in water. The thermocouples used in measuring those temperatures were calibrated against the melting points of gold (1063*(Z) and palladium (1549’C). The accuracy of the determinations using the quench techniques was + l”C, but that of the determinations using the hot-stage microscope was + s” C. RESULTSAND DISCUSSION The compositions of the mixtures for which the liquidus temperatures determined are indicated in Fig. 2, together with the field boundaries.
/ T,Oz
”
to
” 20
”
so
25%SiO*
” 40
V
” 60
50
wei(lhtPer
”
70
” 80
were
”
cent $O
2x&
Fig. 2. The compositions of the mixtures used in the liquidus determinations in the 25%SiO, plane of the CaO-Nbz05-Ti02-Si02 system. Liquidus temperatures determined by the quench technique are indicated by l ; those determined using a hot-stage microscope equipped with a Pt :5%Rh OS.Pt :20%Rh thermocouple are indicated by 0. f. Le.~~s-C~~~on Mefols, 29 (1972)
352
A. JONGEJAN, A. L. WILKINS
20
TiO;!
30
lo
25xsio2
v
v 40
50 wei@
V 60
”
70
80
Pa cent Qc
Fig. 3. Field boundaries (heavy lines) and isotherms (thin lines) in the 25%Si02 plane of the CaO-Nb20,TiO&%O, system. Dashed lines are inferred.
The results of the liquidus dete~inations on these mixtures are listed in Table I and are shown in Fig. 3. In both figures, the compositions in the 25% SiOz plane have been expanded to loo%, although they actually represent (lOO-25%)=75x of the aggregate composition of the CaO, NbzOs, TiOs, and SiOz contents. The com~sitions, therefore, correspond to those listed in the three columns of Table I under the heading “Compositions in the 25% SiO, Plane”. The fields are similar to those in the 20% Si02 plane, except for the presence ofafield ofCaO*SiO, insteadofone of2 CaO*Nb,O,.Asin the 15% and20’4 SiOz planes, the compositions in the TiOz and SiOz fields containing less than 20-25x CaO either did not quench or quenched to opaque glasses, notwithstanding the increase of SiOs in the compositions. It is certain, however, that the TiOrSiOz boundary in the tetrah~ron gradually moves towards the CaO-Ti02--SiOz side with an increase in the SiOz content, when its position in the 25% SiOz plane is compared with that in the 20% SiOs plane. This observation would agree with the inference from the Ca&TiOs-SiOz phase diagram” that the rutile (TiO,) phase space probably extends in the CacT J. Less-Common Metals, 29 (1972)
353
THE QUATERNARY SYSTEM CaQ-NbZ05-TiO,-SiO, TABLE I LIQUIDUS SYSTEM Reference
DETERMINATIONS
Compositions in 25%Si02 plane (wt.%)
Composition (wt.%)
numbers
CaO
Ti02 primary 70-345 25CNTS 7G344 25CNTS 7G343 25CNTS 7&342 25CNTS 7G341 25CNTS
IN THE 25%SiO, PLANE OF THE CaGNb,O,-TiO,-SiO,
Nb,O,
-~ TiO,
QUATERN~Y
Methods*
Liquidus temp. eC)
1445 1405 1390 1365 1337
SiOz cao
Nb,Os
Ti02
89 88 87 86 85
18.75 19.50 20.25 21.00 21.75
14.25 15.00 15.75 16.50 17.25
42.00 40.50 39.00 37.50 36.00
25.00 25.00 25.00 25.00 25.00
25 26 21 28 29
19 20 21 22 23
56 54 52 50 48
H.S. H.S. H.S. H.S.
SiOz primary 7%212 25CNTS 13 7&538 25CNTSl29 7G314 25CNTS 66 7&540 25CNTS131 7C-317 25CNTS 69 70-322 25CNTS 74 7&318 25CNTS 70 7&347 25CNTS 91 7&293a 25CNTS 55 7c-293 25CNTS 54 7G211 25CNTS 12 70-321 25CNTS 73 7&349 25cNTs 93 7%348 25CNTS 92 7&201 25CNTS 2 7G-200 25CNTS 1
18.00 18.00 18.75 18.25 19.50 20.25 21.00 21.00 21.00 21.00 21.75 21.75 22.50 22.50 24.00 24.00
27.00 18.75 30.00 21.00 33.00 28.50 31.50 27.00 21.00 19.50 30.00 28.50 25.50 24.00 33.00 30.75
30.00 38.25 26.25 35.25 22.50 26.25 22.50 27.00 33.00 34.50 23.25 24.75 27.00 28.50 18.00 20.25
25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.Oil 25.00 25.00 25.00
24 24 25 25 26 27 28 28 28 28 29 29 30 30 32 32
36 35 40 28 44 38 42 36 28 26 40 38 34 32 44 41
40 51 35 4-l 30 35 30 36 44 46 31 33 36 38 24 27
H.S. H.S. H.S. H.S. H.S.
CaO . TiOz *SiO, primal‘Y 7&215 25CNTS 16 22.50 70-292 25CNTS 53 22.50 7U476 25CNTSl22 22.50 70-200 25CNTS 1 24.00 24.00 7G216 ZSCNTS 17 24.00 7&478 25CNTSl24 24.00 7W77 25CNTSl23 70~202 25CNTS 3 25.50 7%217 25CNTS 18 25.50 27.15 70469 25CNTSll5 21.75 7(r535 25CNTS126 70-221 25CNTS 22 28.50 29.25 7&222 25CNTS 23 29.25 7Ck288 25CNTS 49
22.50 18.00 14.25 30.75 21.00 13.50 11.25 29.25 26.25 30.75 9.75 16.50 24.00 10.50
30.00 34.50 38.25 20.25 30.00 37.50 39.75 20.25 23.25 16.50 37.50 30.00 21.75 35.25
25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00
30 30 30 32 32 32 32 34 34 37 37 38 39 39
30 24 19 41 28 18 15 39 35 41 13 22 32 14
40 46 51 27 40 50 53 27 31
CaO ’ iVb,O, primary 7%207 25CNTS 8 7&475 25cNTs121 70-205 25CNTS 6
37.50 40.50 34.50
13.50 9.00 15.00
25.00 25.00 25.00
32 34 34
50 54 46
18 12 20
24.00 25.50 25.50
Q
Q H.S. H.S. z H.S.
Q H.S. z
Q
1550 1455 1500 1453 1480 1430 1410 1385 1383 1387 1370 1353 1315 1314 1260 1281
1312 1337 1345 1281 1330 1356 1360 1293 1305 1272 1372 1348 1302 1358
22” 50 40 29 47
Q H.S.
Q
1310 1320 1285
-. (Continued) J. Less-Common Metals, 29 (1972)
354
A. JONGEJAN, A. L. WILKINS
TABLE I (continued)
-
CaO
70-203 70-471 70-469 7&351
25CNTS 4 25CNTS117 25CNTSllS 25CNTS 95
CaO 7SiUz priory 70-309 25CNTS 70-298 25CNTS 70-352 25CNTS 70-233 25CNTS 7(r234 25CNTS 7s3.53 25CNTS 10 CaO. 7&235 70-313 70-354 70-240 70-355 7&356 7&115
Compositions in 25%Si02 plane (wt.%)
Composition (wt.%)
Reference numbers
61 60 96 34 35 97
TiO,
SiOz CaO
Nb;?O,
Ti02
25.50 27.75 27.75 30.75
31.50 33.75 30.75 33.00
18.00 13.50 16.50 11.25
25.00 25.00 25.00 25.00
34 37 37 41
42 45 41 44
24 18 22 15
31.50 31.50 33.75 34.50 34.50 34.50
33.00 31.50 31.50 28.50 30.00 32.25
10.50 12.00 9.75 12.00 10.50 8.25
25.00 25.00 25.00 25.00 25.00 25.00
42 42 45 46 46 46
44 42 42 38 40 43
14 16 13 16 14 11
30.00 27.75 27.75 26.25 26.625 25.50 25.50
9.00 9.00 7.50 9.00 7.50 7.50 5.25
25.00 25.00 25.00 25.00 25.00 25.00 25.00
48 51 53 53 54.5 56 59
40 37 37 35 35.5 34 34
12 12 10 12 10 10 7
30.00 28.50 26.25 24.75 22.50 15.00 30.00 28.50 24.75 27.00 28.50 27.00 25.50 18.00 24.00 16.50 26.25 24.75 15.00 23.25 13.50 21.75 24.75 23.25 21.75
15.00 16.50 18.75 20.25 22.50 30.00 13.50 15.00 18.75 15.00 12.00 13.50 15.00 22.50 15.00 22.50 11.25 12.75 22.50 12.75 22.50 12.75 9.00 10.50 11.25
25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.90 25.00 25.00 25.00 25.00 25.00 25.00 25.00
40 40 40 40 40 45 42 42 42 44 46 46 46 46 48 48 50 50 50 52 52 54 55 55 56
40 38 35 33 30 20 40 38 33 36 38 36 34 24 32 22 35 33 20 31 18 29 33 31 29
20 22 25 27 30 40 18 20 25 20 16 18 20 30 20 30 15 17 30 17 30 17 12 14 15
Nb,Os*6 SiO, primary 25CNTS 36 36.00 25CNTS 65 38.25 25CNTS 98 39.75 25CNTS 41 39.75 25CNTS 99 40.875 25CNTSlOO 42.00 25CNTS133 44.25
CaO mTiO, primary 7(r228 25CNTS 29 7&227 25CNTS 28 70-225 25CNTS 26 70-224 25CNTS 2.5 7(r223 25CNTS 24 7@-220 25CNTS 21 70-297 25CNTS 59 7%229 25CNTS 30 70-226 25CNTS 27 70-230 25CNTS 31 7&233 25CNTS 34 7@232 25CNTS 33 70-231 25CNTS 32 70-330 25CNTS 77 70-236 25CNTS 37 7!%331 25CNTS 78 70-311 25CNTS 63 70-237 25CNTS 38 7&332 25CNTS 79 7&238 25CNTS 39 7&333 25CNTS 80 711-239 25CNTS 40 70-241 25CNTS 42 70-334 25CNTS 81 7Ck335 25CNTS 82
Nb,Os
30.00 30.00 30.00 30.00 30.00 30.00 31.50 31.50 31.50 33.00 34.50 34.50 34.50 34.50 36.00 36.00 37.50 37.50 37.50 39.00 39.00 40.50 41.25 41.25 42.00
Methods*
Liquidus temp. CC)
1273 1290 1272 1252
Q :: ::
H.S.
Q H.S.
Q Q
H.S. ;
Q
H.S. H.S.
Q
H.S.
Q
KS. H.S. H.S. H.S.
Q
H.S. H.S. H.S. H.S. H.S.
Q
H.S. H.S. H.S. H.S. H.S. H.S. H.S. H.S.
1269 1217 1310 1314 1310 1322
1324 1345 1360 1352 1375 1372 1397
1260 1279 1292 1302 1310 1356 1285 1300 1325 1328 1314 1345 1362 1430 1390 1470 1358 1400 1510 1425 1565 1450 1400 1430 1450 (Continued)
J. Less-Common Metals, 29 (1972)
THE QUATERNARY
355
SYSTEM CaO-Nb,Os-TiO,-SiO,
TABLE I (continued) Composition (wt.%)
Reference numbers
cao
Nb,Ol
-.____ TiO,
Compositions in 25x%0, plane (wt.%)
Methods*
SiOz CaO
Nb,O,
TiO,
70-242 25CNTS 43 70-468 25CNTS114 7@467 25CNTS113 70-465 25CNTSlll 7&464 25CNTSllO 70-357 25CNTSlOl 70-336 25CNTS 83 70-360 25CNTS103 70-358 25CNTS102 70-337 25CNTS 84 70-243 25CNTS 44 70-244 25CNTS 45 70-282 25CNTS 47 70-361 25CNTS104 7iX-463 25CNTS109 70-365 25CNTS108
42.15 42.75 42.75 42.15 42.75 43.50 43.50 44.25 45.00 45.00 45.00 45.00 4.5.00 46.50 46.50 48.00
23.25 18.00 16.50 13.00 12.00 24.00 20.25 21.75 22.50 18.75 16.50 15.00 12.00 18.00 10.50 10.50
9.00 14.25 15.75 18.75 20.25 7.50 11.25 9.00 7.50 11.25 13.50 15.00 18.00 10.50 18.00 16.50
25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00
57 57 57 57 57 58 58 59 60 60 60 60 60 62 62 64
31 24 22 18 16 32 27 29 30 25 22 20 16 24 14 14
12 19 21 25 27 10 15 12 10 15 18 20 24 14 24 22
2 CaO. SiO, pTima~y 71-115 25CNTSi33
44.25
25.50
5.25
25.00
59
34
7
Liquidus temp. CC)
H.S. H.S. H.S. H.S. H.S.
H.S. H.S. H.S. H.S. H.S.
1425 1512 1530 1575 1595 1389 1480 1460 1428 1496 1541 1560 1595 1510 1645 1650
Q
1397
Q H.S. H.S.
Q H.S.
Q
* Q = quench technique. H.S. = hot-stage microscope (Pt : 5%Rh us. Pt : 20’dRh thermocouple).
Nb20,-Ti02--Si02 tetrahedron up to approximately 32% SiO,. Also, the gradual increase in size of the intersection of the sphene (CaO *TiOz* SiOz) phase space with increasing SiOt content could be expected from the CaO-TiO,-SiO, diagram. REVIEW
OF THE RELATIONS
IN THE CaC&Nb,O,-TiO,-SiO,
SYSTEM
Because of the complexity of the phase relations in the C-N-T-S system, a three-dimensional drawing of the tetrahedron containing the spatial relationships between the phase volumes of the various compounds could not be used satisfactorily for illustration purposes. Therefore, the three parallel planes, studied respectively at 15x, 20% and 25% SiOz, have been sketched in Fig 4 as parts of the C-N-T-S tetmh~ron using the C-N-T ternary system as the base. Several sections and details have been omitted for clarity. The phase fields have been indicated by their mineral names rather than by their chemical compositions, because solid-solution phenomena were not studied in these investigations, but could be expected to be present. Although the Nb,O,-TiOz--SiO, system has not been studied in this series, it can be expected to be composed, for the greater part, of a two-liquid area, except for a small SiOz field near the SiOt corner, and for a strip connected with the N-T edge and containing the fields of TiOz, the niobium titanates, and NbzO,. The extent of the two-liquid phase space in the quaternary system can & estimated from the CaO-Nb,0S-Si0,6, CaO-TiO,-SiO,“, and CaO.NbzO,CaO . Ti02-Si022 phase diagrams. The intersections of the 15x, 20x, and 25% SiO, J. Less-Common
Metals, 29 (1972)
356
A. JONGEJAN. A. L. WILKINS 75%CaO 25XSlOz
Fig. 4. Parts of the Ca(TNb,O,-TiOz-SiOZ and 20% SiOz planes.
phase tetrahedron
shown as blocks separated by the 15%
planes with the two-liquid phase space have been inferred and are indicated only at the sides of these planes. The two-liquid phase space is separated from those of the CaO-containing binary compounds by a TiOz phase space at one side of the tetrahedron and by the cristobalite-tridymite phase space on the other side. Figure 4 shows that the compounds that occur within the C-T-S system extend into the quaternary C-N-T-S system either a long way towards the C-N-S face (e.g., perovskite and sphene), or, alternatively, completely to that face (e.g., C,S and C2S). The niocalite (3 C&*CN) phase space forms an extension of the small, thin layer of rankinite (C&S,), not shown in Fig. 4, and is wedged, for the greatest part, in between the CS and C2S phase spaces, as is shown in the 25% SiOz plane of Fig. 4. Its NbzO,-rich side is connected with the C2N space, as is shown in the 20% SiOz plane of Fig. 4. Although the 25% SiOz plane includes only a small field of pseudo-wollastonite (CaO . SiOz), and this compound does not appear at either the 20% SiOz or the 15% SiOz level, it does, however, occupy a medium to large volume in the quaternary system, extending from the C-T-S face to the C-N-S face. An impression of the size of this volume can be gained from the extent of its field in the CN-CS-T plane studied previously3. The CaO-Nb,O,-SiO, phase diagram’ indicated that the spaces of the calcium niobates richer in CaO than C2N would not be expected to intersect the 15% SiOz plane. The information on the phase relations in the CNCST plane3 indicated that the C8N,Ts phase space extends from the C-N-T base up to approximately 1% below the 15% SiOz plane, so that this phase occupies a space larger than might be expected from its metastable properties. It is probable, however, that solid-solution phenomena make the relations in this part of the tetrahedron very complex. J. Less-Common
Metals, 29 (1972)
THE
QUATERNARY
SYSTEM
Ca@Nb,O,-TiO,-SiO,
351
The high-lime part of the quaternary system has not been studied extensively ; hence, the presence of the calcium titanates, and also of the phases &NT, and “X”, as described previously’, is uncertain at the 15% SiOz level. The existence of these phases had to be inferred from the shape of the isotherms in the CaO-Nb,O,-TiO, system because no optical or X-ray crystallographic properties were obtained. It is very probable, therefore, that solid-solution phenomena, involving the perovskite structure, will also make the relationships in this part of the tetrahedron more complicated than shown. The small pyrochlore field, however, formed a space in the tetrahedron that extended from the C-N-T base to SiOz contents of over 15%. Also, the C2N’ phase appeared to be still present at that level, while it could not be detected at the 20% level. From the available data, locations of some quaternary eutectics may be inferred. Abbreviations for chemical compositions of compounds, rather than their mineralogical names, have been used in the following discussion for the sake of brevity. There are four ternary eutectics in the CaC&Nb,O,-SiO, system, formed, respectively, by C& CS and C,ONS,, by CS, CN and S, by CS, CN and C2N, and by C2S, C2N and ClONS,. In the CaO-TiO,-SiO, system, in addition to the eutectic formed by C& CS and CT, there are four formed by CTS with CS and S, with CS and CT, with CT and TiOz, and with TiOz and SiOz, respectively. It is probable that a quaternary eutectic is formed in the compatibility tetrahedron of the relevant compounds by C&, CS, CT and C,,NS, at approximately 50% CaO, 10% Nb,O,, 8% TiO, and 32% SiOz. The compatibility relationships developed in previous work’ are shown again in Fig. 5. It is also probable that a quaternary eutectic is formed by CTS, CS, CN and S in the compatibility tetrahedron of these compounds. The location of that eutectic is St02
Fig. 5. The quaternary system Ca@NbzO,-TiO,-Si02 showing the location of the binary and pseudobinary systems for which liquidus temperatures were determined in previous work, together with the relevant joins in the limiting ternary systems. J. Less-Common
Met&,
29 (1972)
358
A. JONGEJAN,
A. L. WILKINS
more difficult to estimate, but it might be near the 32% CaO, 26% NbzOs, 13% TiOz and 29% SiO, composition. One invariant point will probably be formed by CS, CN, C2N and CT and another by CS, CN, CT and CTS. At least one of these points, probably the former, can be expected to be a quaternary eutectic. Both will be located near the CS, CN, CT piercing point in the 25% SiOZ plane, and near the CS-rich boundary of the perovskite field in the CS-CN-T plane3. The C2S, C2N’, CT, CloNSs invariant point is possibly a eutectic, located slightly below the C2S, CT, C,,NS, piercing point in the 20% SiOZ plane and, therefore, close to the 44% CaO, 31% Nb,O,, 5% TiO,, and 20% SiOZ composition. The quaternary eutectic, possibly formed by CTS, CT, C3NT3 (pyrochlore) andT, willbenearthe20°/o CaO,32% Nbz05,35’A TiO,and 13% SiOzcomposition. This composition is slightly below the CTS, C,NT,, CT piercing point in the 15% SiOZ plane and close to that of CTS, C,NT, and TiOz in the CS-CN-T plane. Finally, the location of an invariant point formed by a boundary originating in the CTS-T-S eutectic is difficult to visualize because at least the beginning of that boundary is located in the CTST-S-CsN,T, compatibility tetrahedron. The location of that point could, therefore, be close to the foregoing eutectic, below the 15% SiOZ level and near the CN-T-S piercing point in that level. However, because of the metastable nature of the CsN,T, compound, it is more probable that a eutectic will be formed with CN in the same area. MINERALOGICAL
IMPLICATIONS
Because the work on the phase relationships of niobia in relation to lime, titania and silica originated in problems concerning the processing of the niobium ore from Oka, Quebec, and the occurrence of the mineral niocalite”“*“) in the paragenesis of this ore, a few observations on the relevant mineral assemblage’2*‘3 will be discussed. Although, according to the following notes, it may seem possible to indicate some relations between the paragenesis of the niobium minerals and the results of the phase equilibrium studies, these relations refer to geological conditions in which pressure is involved as a variable. This variable was not included in the phase equilibrium studies as the work was primarily concerned with a possible heat treatment of the ore. The following is, therefore, only tentative. One of the most important results ofthemineralogical analysis is the occurrence of a niobium-containing perovskite, associated with pyrochlore, in a matrix of carbonate minerals. The Nbz05 :TiO, ratio in the composition of both minerals varied directly with that in the composition of the ore. Although SiO, has been included in the studies, instead of COZ, because of the composition of the niocalite, viz., 10 CaO . Nb,O, .6 SiOZ, the combination of perovskite and pyrochlore is based on the compatibility relationships between these two minerals as indicated in Fig. 5. In spite of the ore representing a multi-component system and both minerals having complex compositions, this compatibility relationship apparently persists in nature. Similarly, sphene was not present, because of a shortage of TiOz in the mineral assemblage studied”. The observations that CT in the sub-solidus condition probably forms exJ. Less-Common Metals, 29 (1972)
THE QUATERNARY
SYSTEM
Ca0_Nb,O,-TiO,-SiO,
359
tensive solid solutions along the CN-CT join’, and the possibility that this also takes place along the C,N-CT join in a multi-component system containing fair amounts of NazO, MgO and Fe,O,, make the association of perovskite and pyrochlore with CaO . (CO,) feasible. However, the geology of the Oka area shows13 that the niobium-bearing minerals do not occur to any large extent in the same type of rock, and that they are formed in different stages of the formation of the complex. Hence, any relationships between them should be considered to exist locally only. The Oka geology indicates that carbonaceous rocks have been affected by intrusion and by later metasomatic and hydrothermal activity, which resulted in the formation of secondary minerals among which are the niobium-bearing minerals. Local conditions will, therefore, control the type of paragenesis in which any particular niobium-bearing mineral occurs. The mineral, niocalite, occurs in an association with garnet, altered melilite (2 CaO . MgO .2 SiOz), apatite, magnetite and biotite, strongly suggesting metasomatic activity during the formation. The succession of the various generations of minerals has not been studied, but it will probably be complex and dependent on the composition and conditions in each location. The formation of niocalite could be expected in bulk compositions that are comparatively rich in CaO and SiOz, but the Nb,O, content should exceed that of TiOz significantly. The absence of sphene and minerals comparable with pseudo-wollastonite (CaO 1SiOz) in SiOz content, and particularly the presence of melilite (2 CaO . MgO . 2 SiOz) and nepheline (Na,O. Al,O,. 2 Si02) suggests a surplus of CaO and Na,O over SiOz. This observation agrees with the predominance of the niobium-bearing minerals, pyrochlore and perovskite, over niocalite which occurs in compositions having appreciable Si02 contents, according to the phase diagram of the quaternary system shown in Figs. 4 and 5. The preference of niobium to concentrate with sodium rather than with potassium minerals has been described recently by Aleksandrov et a1.14.
The conditions are complicated by the varying contents of MgO (dolomite) in the composition of the limestone before the intrusive and metasomatic activity; these are reflected in the occurrence of minerals such as monticellite (CaO * MgO . SiOz), and by the presence of iron in minerals such as iron sulphides, magnetite, soda pyroxene [Na,O*(Al,Fe),0,.4 SiOz] and biotite [K,0.6(Mg,Fe)0.(Al,Fe),03. 6 Si02.4 HzO]. Nevertheless, most of the conditions favour a high CaO and low SiOz content, thus keeping the composition within the CaO-C,SC,N-CT compatibility tetrahedron, as shown in Fig. 5 ; hence, the occurrence of niocalite can be expected only in rare SiOz rich locations. ACKNOWLEDGEMENTS
The authors wish to express their thanks to Drs. N. F. H. Bright and D. A. Reeve for critically reading and editing the manuscript and to E. J. Murray for the preparation of X-ray diffraction powder patterns. The first and last mentioned are members of the staff of the Mineral Sciences Division, and Dr. Reeve is a member of the Metals Reduction and Energy Centre, Mines Branch, Department of Energy, Mines and Resources. J. Less-Common Metals,
29 (1972)
360
A. JONGEJAN, A. L. WILKINS
REFERENCES 1 A. Jongejan and A. L. Wilkins, J. 2 A. Jongejan and A. L. Wilkins, J. 3 A. Jongejan and A. L. Wilkins, J. 4 A. Jongejan and A. L. Wilkins, J. 5 A. Jongejan and A. L. Wilkins, J.
Less-Common Metals, 24 (1971) 445.
Less-Common Met&,
25 (1971) 109.
Less-Common Metals, 25 (1971) 345. Less-Common Metals, 26 (1971) 89. Less-Common Metals, 27 (1972) 101. 6 A. T. Prince, M. Ibrahim and A. L. Wilkins, Min. Sci. Div. Rept. MS 63-52, Mines Branch, Dept. Energy,
Mines Resources, Ottawa, Canada, 1963. 7 A. Jongejan and A. L. Wilkins, J. Less-Common Metals, 19 (1969) 203. 8 A. Jongejan and A. L. Wilkins, J. Less-Common Metals, 21 (1970) 185. 9 A. Jongejan and A. L. Wilkins, J. Less-Common Metals, 21 (1970) 225. 10 R. C. de Vries,R. Roy and E. F. Osbom, J. Am. Ceram. Sot., 38 (1955) 161, 11 (i) E. H. Nickel, Am. Mineralogist, 41 (1956) 785. (ii) E. H. Nickel, J. F. Rowland and J. A. Maxwell, Can. Mineralogist, 6 (1958) 264. 12 E. H. Nickel, Mines Branch best. Rept. IR 61-146, Mines Branch, Dept. Energy, Mines Resources, Ottawa, Canada, 1961. 13 R. B. Rowe, &on. Geot, Ser. No. 18, Geo~~icu~ Survey, Dept. Energy, Mines Resources, Canada, 1958. 14 I. V. Aleksandrov, T. A. Trusikova and B. P. Tupitsin, GeocAem. Intern&, 8 (1971) 229. J. Less-Common Metals, 29 (1972)
349 in The Netherlands
LIQUIDUS DETERMINATIONS IN THE 25% SiOz PLANE OF THE QUATERNARY SYSTEM Ca0-Nb20,-Ti02--SiO**
A. JONGEJAN
and A. L. WILKINS
Mineral Sciences Division, Department of Energy, Mines and Resources, Mines Branch, Ottawa (Canada) (Received
March
24th, 1972)
SUMMARY
Liquidus temperatures in the 25% SiOz plane ofthe CaO-Nb,O,-TiO,-Si02 phase tetrahedron have been determined using the customary quench technique as well as hot-stage microscopy. The boundaries between the phase fields of CaO .TiOz, CaO *TiOz*SiO,, TiOz, SiOz, CaO*Nb,Os, CaOe SiO,, 10 CaO*Nb,O,*6 SiOz (niocalite) and 2 CaO . SiOz have partly been outlined. This 25% SiOz plane probably also includes phase fields for 3 CJaO - SiOz and CaO. A phase field of CaO * SiOz is wedged in between those of CaO. NbzOs and 10 CaO . Nbz05. 6 SiOz (niocalite), instead of a field of 2 CaO * Nb,Os, as is found in the 20% SiOz plane. This would be expected from the known CaO-Nb,O,-SiO, phase diagram. All three compounds, 2 CaO.Nb,O,, CaO. NbzOs and 10 CaO. Nb,O, .6 SiOz, apparently occupy similar phase volumes between the CaO-Nb,O,SiO, side and the large phase volume of CaO .TiO, (perovskite), in the quaternary system. A summary of the phase relationships studied in the CaO-Nbz05-Ti02-Si02 system is given, and also some discussion of the mineralogical implications of these studies.
INTRODUCTION
Studies of the phase equilibrium relationships in the CaO-Nb,O,-TiO,-Si02 phase tetrahedron, reported previously ’ - ’ , have been extended to include those in the 25% SiOz plane. The location of this plane in the phase tetrahedron and its relation to the other planes previously studied are shown in Fig. 1**. If, in the tetrahedron, the CaO.SiO,CaO .Nbz05-2 CaO .Nb,O, boundary, starting from the relevant eutectic in the CaGNbz05-SiOz side6a7, bends slightly upwards towards the SiOz apex, it is possible that the 25% SiOz plane would intersect the 2 CaO. Nb,05 phase space * Crown Copyrights reserved. Division Report MS-PP72-12. ** The abbreviations commonly used in literature dealing with the chemistry used in this paper, viz., C=CaO, N =NbZOs, T=TiO, and S=SiO,. J. Less-Common Metals, 29 (1972)
of ceramic
oxides will be
A. JONGEJAN, A. L. WILKINS
Ti 0, Fig. 1. The quaternary system CaO-NbzO,-TiOiSiO, relation to the planes studied in previous work.
NY% showing the location of the 25%SiO, plane in
inside the tetrahedron and form there a small CzN field. The CaO.SiO,-&aO. Nb,O,-2 CaO.Nb,O, eutectic is approximately 1% SiOz below the 25 % SiOz plane ac(;ording to the CaO-Nb,O,-SiOz phase diagram. Although several aspects of the quaternary system, such as the extent of any solid-solution phenomena and the exact location of the quaternary eutectics have not been studied, the objective to provide sufficient data to give a general impression about the shape and size of the phase spaces of various compounds in the tetrahedron has been fulfilled. The series ofstudies is, therefore, te~inated with this present paper.
The experimental methods for the liquidus determinations were the same as those described for the 15% and the 20% SiO, planes4*5. Mixtures of the required compositions were prepared from Mallinckrodt’s “Analytical Reagent”-grade calcium carbonate, 99.5% pure niobium pentoxide from Alfa Inorganics, Inc., Beverley, Massachusetts, heated to 125@C, Baker’s “Analytical Reagent”-grade titanium dioxide, and silicon dioxide, prepared from Baker and Adamson’s silicic acid, dehydrated overnight at 1250°C. A quantity of the chemicals, sufficient to yield 4 g of the required composition, was mixed in an agate mortar. These mixtures were heated in platinum crucibles overnight at looo” C to sinter them and partly to decompose the calcium carbonate. They were then heated to 17OO’C in a gas-fired muffle furnace for one hour. The mixtures were ground for one minute in appropriate grinders (Wig-L-Bug grinders No. 6 and 3A from Crescent Dental Mfg. Co., Lyons, Illinois.) to produce fine-grained powders of which the small quantities used in the liquidus determinations were representative of the bulk compositions. After cleaning the powders magnetically, reproducible results were obtained with this technique. J. Less-Common Metals, 29 (1972)
THE QUATERNARYSYSTEMCa@Nb,O,-TiO,-Si02
351
Liquidus temperatures, which all lay below 17O@C, were measured initially using a Griffin-Telin hot-stagemicroscope equipped with a Pt : 5% Rh ZIS.Pt : 20% Rh the~ocouple. The use of this instrument has been described previously’. The liquidus temperatures of samples having compositions near field boundaries and piercing points were measured with the customary quench technique, in which a small sample (3 mg) in a Pt envelope was kept at an elevated temperature until equilibrium conditions were obtained and then quenched in water. The thermocouples used in measuring those temperatures were calibrated against the melting points of gold (1063*(Z) and palladium (1549’C). The accuracy of the determinations using the quench techniques was + l”C, but that of the determinations using the hot-stage microscope was + s” C. RESULTSAND DISCUSSION The compositions of the mixtures for which the liquidus temperatures determined are indicated in Fig. 2, together with the field boundaries.
/ T,Oz
”
to
” 20
”
so
25%SiO*
” 40
V
” 60
50
wei(lhtPer
”
70
” 80
were
”
cent $O
2x&
Fig. 2. The compositions of the mixtures used in the liquidus determinations in the 25%SiO, plane of the CaO-Nbz05-Ti02-Si02 system. Liquidus temperatures determined by the quench technique are indicated by l ; those determined using a hot-stage microscope equipped with a Pt :5%Rh OS.Pt :20%Rh thermocouple are indicated by 0. f. Le.~~s-C~~~on Mefols, 29 (1972)
352
A. JONGEJAN, A. L. WILKINS
20
TiO;!
30
lo
25xsio2
v
v 40
50 wei@
V 60
”
70
80
Pa cent Qc
Fig. 3. Field boundaries (heavy lines) and isotherms (thin lines) in the 25%Si02 plane of the CaO-Nb20,TiO&%O, system. Dashed lines are inferred.
The results of the liquidus dete~inations on these mixtures are listed in Table I and are shown in Fig. 3. In both figures, the compositions in the 25% SiOz plane have been expanded to loo%, although they actually represent (lOO-25%)=75x of the aggregate composition of the CaO, NbzOs, TiOs, and SiOz contents. The com~sitions, therefore, correspond to those listed in the three columns of Table I under the heading “Compositions in the 25% SiO, Plane”. The fields are similar to those in the 20% Si02 plane, except for the presence ofafield ofCaO*SiO, insteadofone of2 CaO*Nb,O,.Asin the 15% and20’4 SiOz planes, the compositions in the TiOz and SiOz fields containing less than 20-25x CaO either did not quench or quenched to opaque glasses, notwithstanding the increase of SiOs in the compositions. It is certain, however, that the TiOrSiOz boundary in the tetrah~ron gradually moves towards the CaO-Ti02--SiOz side with an increase in the SiOz content, when its position in the 25% SiOz plane is compared with that in the 20% SiOs plane. This observation would agree with the inference from the Ca&TiOs-SiOz phase diagram” that the rutile (TiO,) phase space probably extends in the CacT J. Less-Common Metals, 29 (1972)
353
THE QUATERNARY SYSTEM CaQ-NbZ05-TiO,-SiO, TABLE I LIQUIDUS SYSTEM Reference
DETERMINATIONS
Compositions in 25%Si02 plane (wt.%)
Composition (wt.%)
numbers
CaO
Ti02 primary 70-345 25CNTS 7G344 25CNTS 7G343 25CNTS 7&342 25CNTS 7G341 25CNTS
IN THE 25%SiO, PLANE OF THE CaGNb,O,-TiO,-SiO,
Nb,O,
-~ TiO,
QUATERN~Y
Methods*
Liquidus temp. eC)
1445 1405 1390 1365 1337
SiOz cao
Nb,Os
Ti02
89 88 87 86 85
18.75 19.50 20.25 21.00 21.75
14.25 15.00 15.75 16.50 17.25
42.00 40.50 39.00 37.50 36.00
25.00 25.00 25.00 25.00 25.00
25 26 21 28 29
19 20 21 22 23
56 54 52 50 48
H.S. H.S. H.S. H.S.
SiOz primary 7%212 25CNTS 13 7&538 25CNTSl29 7G314 25CNTS 66 7&540 25CNTS131 7C-317 25CNTS 69 70-322 25CNTS 74 7&318 25CNTS 70 7&347 25CNTS 91 7&293a 25CNTS 55 7c-293 25CNTS 54 7G211 25CNTS 12 70-321 25CNTS 73 7&349 25cNTs 93 7%348 25CNTS 92 7&201 25CNTS 2 7G-200 25CNTS 1
18.00 18.00 18.75 18.25 19.50 20.25 21.00 21.00 21.00 21.00 21.75 21.75 22.50 22.50 24.00 24.00
27.00 18.75 30.00 21.00 33.00 28.50 31.50 27.00 21.00 19.50 30.00 28.50 25.50 24.00 33.00 30.75
30.00 38.25 26.25 35.25 22.50 26.25 22.50 27.00 33.00 34.50 23.25 24.75 27.00 28.50 18.00 20.25
25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.Oil 25.00 25.00 25.00
24 24 25 25 26 27 28 28 28 28 29 29 30 30 32 32
36 35 40 28 44 38 42 36 28 26 40 38 34 32 44 41
40 51 35 4-l 30 35 30 36 44 46 31 33 36 38 24 27
H.S. H.S. H.S. H.S. H.S.
CaO . TiOz *SiO, primal‘Y 7&215 25CNTS 16 22.50 70-292 25CNTS 53 22.50 7U476 25CNTSl22 22.50 70-200 25CNTS 1 24.00 24.00 7G216 ZSCNTS 17 24.00 7&478 25CNTSl24 24.00 7W77 25CNTSl23 70~202 25CNTS 3 25.50 7%217 25CNTS 18 25.50 27.15 70469 25CNTSll5 21.75 7(r535 25CNTS126 70-221 25CNTS 22 28.50 29.25 7&222 25CNTS 23 29.25 7Ck288 25CNTS 49
22.50 18.00 14.25 30.75 21.00 13.50 11.25 29.25 26.25 30.75 9.75 16.50 24.00 10.50
30.00 34.50 38.25 20.25 30.00 37.50 39.75 20.25 23.25 16.50 37.50 30.00 21.75 35.25
25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00
30 30 30 32 32 32 32 34 34 37 37 38 39 39
30 24 19 41 28 18 15 39 35 41 13 22 32 14
40 46 51 27 40 50 53 27 31
CaO ’ iVb,O, primary 7%207 25CNTS 8 7&475 25cNTs121 70-205 25CNTS 6
37.50 40.50 34.50
13.50 9.00 15.00
25.00 25.00 25.00
32 34 34
50 54 46
18 12 20
24.00 25.50 25.50
Q
Q H.S. H.S. z H.S.
Q H.S. z
Q
1550 1455 1500 1453 1480 1430 1410 1385 1383 1387 1370 1353 1315 1314 1260 1281
1312 1337 1345 1281 1330 1356 1360 1293 1305 1272 1372 1348 1302 1358
22” 50 40 29 47
Q H.S.
Q
1310 1320 1285
-. (Continued) J. Less-Common Metals, 29 (1972)
354
A. JONGEJAN, A. L. WILKINS
TABLE I (continued)
-
CaO
70-203 70-471 70-469 7&351
25CNTS 4 25CNTS117 25CNTSllS 25CNTS 95
CaO 7SiUz priory 70-309 25CNTS 70-298 25CNTS 70-352 25CNTS 70-233 25CNTS 7(r234 25CNTS 7s3.53 25CNTS 10 CaO. 7&235 70-313 70-354 70-240 70-355 7&356 7&115
Compositions in 25%Si02 plane (wt.%)
Composition (wt.%)
Reference numbers
61 60 96 34 35 97
TiO,
SiOz CaO
Nb;?O,
Ti02
25.50 27.75 27.75 30.75
31.50 33.75 30.75 33.00
18.00 13.50 16.50 11.25
25.00 25.00 25.00 25.00
34 37 37 41
42 45 41 44
24 18 22 15
31.50 31.50 33.75 34.50 34.50 34.50
33.00 31.50 31.50 28.50 30.00 32.25
10.50 12.00 9.75 12.00 10.50 8.25
25.00 25.00 25.00 25.00 25.00 25.00
42 42 45 46 46 46
44 42 42 38 40 43
14 16 13 16 14 11
30.00 27.75 27.75 26.25 26.625 25.50 25.50
9.00 9.00 7.50 9.00 7.50 7.50 5.25
25.00 25.00 25.00 25.00 25.00 25.00 25.00
48 51 53 53 54.5 56 59
40 37 37 35 35.5 34 34
12 12 10 12 10 10 7
30.00 28.50 26.25 24.75 22.50 15.00 30.00 28.50 24.75 27.00 28.50 27.00 25.50 18.00 24.00 16.50 26.25 24.75 15.00 23.25 13.50 21.75 24.75 23.25 21.75
15.00 16.50 18.75 20.25 22.50 30.00 13.50 15.00 18.75 15.00 12.00 13.50 15.00 22.50 15.00 22.50 11.25 12.75 22.50 12.75 22.50 12.75 9.00 10.50 11.25
25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.90 25.00 25.00 25.00 25.00 25.00 25.00 25.00
40 40 40 40 40 45 42 42 42 44 46 46 46 46 48 48 50 50 50 52 52 54 55 55 56
40 38 35 33 30 20 40 38 33 36 38 36 34 24 32 22 35 33 20 31 18 29 33 31 29
20 22 25 27 30 40 18 20 25 20 16 18 20 30 20 30 15 17 30 17 30 17 12 14 15
Nb,Os*6 SiO, primary 25CNTS 36 36.00 25CNTS 65 38.25 25CNTS 98 39.75 25CNTS 41 39.75 25CNTS 99 40.875 25CNTSlOO 42.00 25CNTS133 44.25
CaO mTiO, primary 7(r228 25CNTS 29 7&227 25CNTS 28 70-225 25CNTS 26 70-224 25CNTS 2.5 7(r223 25CNTS 24 7@-220 25CNTS 21 70-297 25CNTS 59 7%229 25CNTS 30 70-226 25CNTS 27 70-230 25CNTS 31 7&233 25CNTS 34 7@232 25CNTS 33 70-231 25CNTS 32 70-330 25CNTS 77 70-236 25CNTS 37 7!%331 25CNTS 78 70-311 25CNTS 63 70-237 25CNTS 38 7&332 25CNTS 79 7&238 25CNTS 39 7&333 25CNTS 80 711-239 25CNTS 40 70-241 25CNTS 42 70-334 25CNTS 81 7Ck335 25CNTS 82
Nb,Os
30.00 30.00 30.00 30.00 30.00 30.00 31.50 31.50 31.50 33.00 34.50 34.50 34.50 34.50 36.00 36.00 37.50 37.50 37.50 39.00 39.00 40.50 41.25 41.25 42.00
Methods*
Liquidus temp. CC)
1273 1290 1272 1252
Q :: ::
H.S.
Q H.S.
Q Q
H.S. ;
Q
H.S. H.S.
Q
H.S.
Q
KS. H.S. H.S. H.S.
Q
H.S. H.S. H.S. H.S. H.S.
Q
H.S. H.S. H.S. H.S. H.S. H.S. H.S. H.S.
1269 1217 1310 1314 1310 1322
1324 1345 1360 1352 1375 1372 1397
1260 1279 1292 1302 1310 1356 1285 1300 1325 1328 1314 1345 1362 1430 1390 1470 1358 1400 1510 1425 1565 1450 1400 1430 1450 (Continued)
J. Less-Common Metals, 29 (1972)
THE QUATERNARY
355
SYSTEM CaO-Nb,Os-TiO,-SiO,
TABLE I (continued) Composition (wt.%)
Reference numbers
cao
Nb,Ol
-.____ TiO,
Compositions in 25x%0, plane (wt.%)
Methods*
SiOz CaO
Nb,O,
TiO,
70-242 25CNTS 43 70-468 25CNTS114 7@467 25CNTS113 70-465 25CNTSlll 7&464 25CNTSllO 70-357 25CNTSlOl 70-336 25CNTS 83 70-360 25CNTS103 70-358 25CNTS102 70-337 25CNTS 84 70-243 25CNTS 44 70-244 25CNTS 45 70-282 25CNTS 47 70-361 25CNTS104 7iX-463 25CNTS109 70-365 25CNTS108
42.15 42.75 42.75 42.15 42.75 43.50 43.50 44.25 45.00 45.00 45.00 45.00 4.5.00 46.50 46.50 48.00
23.25 18.00 16.50 13.00 12.00 24.00 20.25 21.75 22.50 18.75 16.50 15.00 12.00 18.00 10.50 10.50
9.00 14.25 15.75 18.75 20.25 7.50 11.25 9.00 7.50 11.25 13.50 15.00 18.00 10.50 18.00 16.50
25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00
57 57 57 57 57 58 58 59 60 60 60 60 60 62 62 64
31 24 22 18 16 32 27 29 30 25 22 20 16 24 14 14
12 19 21 25 27 10 15 12 10 15 18 20 24 14 24 22
2 CaO. SiO, pTima~y 71-115 25CNTSi33
44.25
25.50
5.25
25.00
59
34
7
Liquidus temp. CC)
H.S. H.S. H.S. H.S. H.S.
H.S. H.S. H.S. H.S. H.S.
1425 1512 1530 1575 1595 1389 1480 1460 1428 1496 1541 1560 1595 1510 1645 1650
Q
1397
Q H.S. H.S.
Q H.S.
Q
* Q = quench technique. H.S. = hot-stage microscope (Pt : 5%Rh us. Pt : 20’dRh thermocouple).
Nb20,-Ti02--Si02 tetrahedron up to approximately 32% SiO,. Also, the gradual increase in size of the intersection of the sphene (CaO *TiOz* SiOz) phase space with increasing SiOt content could be expected from the CaO-TiO,-SiO, diagram. REVIEW
OF THE RELATIONS
IN THE CaC&Nb,O,-TiO,-SiO,
SYSTEM
Because of the complexity of the phase relations in the C-N-T-S system, a three-dimensional drawing of the tetrahedron containing the spatial relationships between the phase volumes of the various compounds could not be used satisfactorily for illustration purposes. Therefore, the three parallel planes, studied respectively at 15x, 20% and 25% SiOz, have been sketched in Fig 4 as parts of the C-N-T-S tetmh~ron using the C-N-T ternary system as the base. Several sections and details have been omitted for clarity. The phase fields have been indicated by their mineral names rather than by their chemical compositions, because solid-solution phenomena were not studied in these investigations, but could be expected to be present. Although the Nb,O,-TiOz--SiO, system has not been studied in this series, it can be expected to be composed, for the greater part, of a two-liquid area, except for a small SiOz field near the SiOt corner, and for a strip connected with the N-T edge and containing the fields of TiOz, the niobium titanates, and NbzO,. The extent of the two-liquid phase space in the quaternary system can & estimated from the CaO-Nb,0S-Si0,6, CaO-TiO,-SiO,“, and CaO.NbzO,CaO . Ti02-Si022 phase diagrams. The intersections of the 15x, 20x, and 25% SiO, J. Less-Common
Metals, 29 (1972)
356
A. JONGEJAN. A. L. WILKINS 75%CaO 25XSlOz
Fig. 4. Parts of the Ca(TNb,O,-TiOz-SiOZ and 20% SiOz planes.
phase tetrahedron
shown as blocks separated by the 15%
planes with the two-liquid phase space have been inferred and are indicated only at the sides of these planes. The two-liquid phase space is separated from those of the CaO-containing binary compounds by a TiOz phase space at one side of the tetrahedron and by the cristobalite-tridymite phase space on the other side. Figure 4 shows that the compounds that occur within the C-T-S system extend into the quaternary C-N-T-S system either a long way towards the C-N-S face (e.g., perovskite and sphene), or, alternatively, completely to that face (e.g., C,S and C2S). The niocalite (3 C&*CN) phase space forms an extension of the small, thin layer of rankinite (C&S,), not shown in Fig. 4, and is wedged, for the greatest part, in between the CS and C2S phase spaces, as is shown in the 25% SiOz plane of Fig. 4. Its NbzO,-rich side is connected with the C2N space, as is shown in the 20% SiOz plane of Fig. 4. Although the 25% SiOz plane includes only a small field of pseudo-wollastonite (CaO . SiOz), and this compound does not appear at either the 20% SiOz or the 15% SiOz level, it does, however, occupy a medium to large volume in the quaternary system, extending from the C-T-S face to the C-N-S face. An impression of the size of this volume can be gained from the extent of its field in the CN-CS-T plane studied previously3. The CaO-Nb,O,-SiO, phase diagram’ indicated that the spaces of the calcium niobates richer in CaO than C2N would not be expected to intersect the 15% SiOz plane. The information on the phase relations in the CNCST plane3 indicated that the C8N,Ts phase space extends from the C-N-T base up to approximately 1% below the 15% SiOz plane, so that this phase occupies a space larger than might be expected from its metastable properties. It is probable, however, that solid-solution phenomena make the relations in this part of the tetrahedron very complex. J. Less-Common
Metals, 29 (1972)
THE
QUATERNARY
SYSTEM
Ca@Nb,O,-TiO,-SiO,
351
The high-lime part of the quaternary system has not been studied extensively ; hence, the presence of the calcium titanates, and also of the phases &NT, and “X”, as described previously’, is uncertain at the 15% SiOz level. The existence of these phases had to be inferred from the shape of the isotherms in the CaO-Nb,O,-TiO, system because no optical or X-ray crystallographic properties were obtained. It is very probable, therefore, that solid-solution phenomena, involving the perovskite structure, will also make the relationships in this part of the tetrahedron more complicated than shown. The small pyrochlore field, however, formed a space in the tetrahedron that extended from the C-N-T base to SiOz contents of over 15%. Also, the C2N’ phase appeared to be still present at that level, while it could not be detected at the 20% level. From the available data, locations of some quaternary eutectics may be inferred. Abbreviations for chemical compositions of compounds, rather than their mineralogical names, have been used in the following discussion for the sake of brevity. There are four ternary eutectics in the CaC&Nb,O,-SiO, system, formed, respectively, by C& CS and C,ONS,, by CS, CN and S, by CS, CN and C2N, and by C2S, C2N and ClONS,. In the CaO-TiO,-SiO, system, in addition to the eutectic formed by C& CS and CT, there are four formed by CTS with CS and S, with CS and CT, with CT and TiOz, and with TiOz and SiOz, respectively. It is probable that a quaternary eutectic is formed in the compatibility tetrahedron of the relevant compounds by C&, CS, CT and C,,NS, at approximately 50% CaO, 10% Nb,O,, 8% TiO, and 32% SiOz. The compatibility relationships developed in previous work’ are shown again in Fig. 5. It is also probable that a quaternary eutectic is formed by CTS, CS, CN and S in the compatibility tetrahedron of these compounds. The location of that eutectic is St02
Fig. 5. The quaternary system Ca@NbzO,-TiO,-Si02 showing the location of the binary and pseudobinary systems for which liquidus temperatures were determined in previous work, together with the relevant joins in the limiting ternary systems. J. Less-Common
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more difficult to estimate, but it might be near the 32% CaO, 26% NbzOs, 13% TiOz and 29% SiO, composition. One invariant point will probably be formed by CS, CN, C2N and CT and another by CS, CN, CT and CTS. At least one of these points, probably the former, can be expected to be a quaternary eutectic. Both will be located near the CS, CN, CT piercing point in the 25% SiOZ plane, and near the CS-rich boundary of the perovskite field in the CS-CN-T plane3. The C2S, C2N’, CT, CloNSs invariant point is possibly a eutectic, located slightly below the C2S, CT, C,,NS, piercing point in the 20% SiOZ plane and, therefore, close to the 44% CaO, 31% Nb,O,, 5% TiO,, and 20% SiOZ composition. The quaternary eutectic, possibly formed by CTS, CT, C3NT3 (pyrochlore) andT, willbenearthe20°/o CaO,32% Nbz05,35’A TiO,and 13% SiOzcomposition. This composition is slightly below the CTS, C,NT,, CT piercing point in the 15% SiOZ plane and close to that of CTS, C,NT, and TiOz in the CS-CN-T plane. Finally, the location of an invariant point formed by a boundary originating in the CTS-T-S eutectic is difficult to visualize because at least the beginning of that boundary is located in the CTST-S-CsN,T, compatibility tetrahedron. The location of that point could, therefore, be close to the foregoing eutectic, below the 15% SiOZ level and near the CN-T-S piercing point in that level. However, because of the metastable nature of the CsN,T, compound, it is more probable that a eutectic will be formed with CN in the same area. MINERALOGICAL
IMPLICATIONS
Because the work on the phase relationships of niobia in relation to lime, titania and silica originated in problems concerning the processing of the niobium ore from Oka, Quebec, and the occurrence of the mineral niocalite”“*“) in the paragenesis of this ore, a few observations on the relevant mineral assemblage’2*‘3 will be discussed. Although, according to the following notes, it may seem possible to indicate some relations between the paragenesis of the niobium minerals and the results of the phase equilibrium studies, these relations refer to geological conditions in which pressure is involved as a variable. This variable was not included in the phase equilibrium studies as the work was primarily concerned with a possible heat treatment of the ore. The following is, therefore, only tentative. One of the most important results ofthemineralogical analysis is the occurrence of a niobium-containing perovskite, associated with pyrochlore, in a matrix of carbonate minerals. The Nbz05 :TiO, ratio in the composition of both minerals varied directly with that in the composition of the ore. Although SiO, has been included in the studies, instead of COZ, because of the composition of the niocalite, viz., 10 CaO . Nb,O, .6 SiOZ, the combination of perovskite and pyrochlore is based on the compatibility relationships between these two minerals as indicated in Fig. 5. In spite of the ore representing a multi-component system and both minerals having complex compositions, this compatibility relationship apparently persists in nature. Similarly, sphene was not present, because of a shortage of TiOz in the mineral assemblage studied”. The observations that CT in the sub-solidus condition probably forms exJ. Less-Common Metals, 29 (1972)
THE QUATERNARY
SYSTEM
Ca0_Nb,O,-TiO,-SiO,
359
tensive solid solutions along the CN-CT join’, and the possibility that this also takes place along the C,N-CT join in a multi-component system containing fair amounts of NazO, MgO and Fe,O,, make the association of perovskite and pyrochlore with CaO . (CO,) feasible. However, the geology of the Oka area shows13 that the niobium-bearing minerals do not occur to any large extent in the same type of rock, and that they are formed in different stages of the formation of the complex. Hence, any relationships between them should be considered to exist locally only. The Oka geology indicates that carbonaceous rocks have been affected by intrusion and by later metasomatic and hydrothermal activity, which resulted in the formation of secondary minerals among which are the niobium-bearing minerals. Local conditions will, therefore, control the type of paragenesis in which any particular niobium-bearing mineral occurs. The mineral, niocalite, occurs in an association with garnet, altered melilite (2 CaO . MgO .2 SiOz), apatite, magnetite and biotite, strongly suggesting metasomatic activity during the formation. The succession of the various generations of minerals has not been studied, but it will probably be complex and dependent on the composition and conditions in each location. The formation of niocalite could be expected in bulk compositions that are comparatively rich in CaO and SiOz, but the Nb,O, content should exceed that of TiOz significantly. The absence of sphene and minerals comparable with pseudo-wollastonite (CaO 1SiOz) in SiOz content, and particularly the presence of melilite (2 CaO . MgO . 2 SiOz) and nepheline (Na,O. Al,O,. 2 Si02) suggests a surplus of CaO and Na,O over SiOz. This observation agrees with the predominance of the niobium-bearing minerals, pyrochlore and perovskite, over niocalite which occurs in compositions having appreciable Si02 contents, according to the phase diagram of the quaternary system shown in Figs. 4 and 5. The preference of niobium to concentrate with sodium rather than with potassium minerals has been described recently by Aleksandrov et a1.14.
The conditions are complicated by the varying contents of MgO (dolomite) in the composition of the limestone before the intrusive and metasomatic activity; these are reflected in the occurrence of minerals such as monticellite (CaO * MgO . SiOz), and by the presence of iron in minerals such as iron sulphides, magnetite, soda pyroxene [Na,O*(Al,Fe),0,.4 SiOz] and biotite [K,0.6(Mg,Fe)0.(Al,Fe),03. 6 Si02.4 HzO]. Nevertheless, most of the conditions favour a high CaO and low SiOz content, thus keeping the composition within the CaO-C,SC,N-CT compatibility tetrahedron, as shown in Fig. 5 ; hence, the occurrence of niocalite can be expected only in rare SiOz rich locations. ACKNOWLEDGEMENTS
The authors wish to express their thanks to Drs. N. F. H. Bright and D. A. Reeve for critically reading and editing the manuscript and to E. J. Murray for the preparation of X-ray diffraction powder patterns. The first and last mentioned are members of the staff of the Mineral Sciences Division, and Dr. Reeve is a member of the Metals Reduction and Energy Centre, Mines Branch, Department of Energy, Mines and Resources. J. Less-Common Metals,
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Mines Resources, Ottawa, Canada, 1963. 7 A. Jongejan and A. L. Wilkins, J. Less-Common Metals, 19 (1969) 203. 8 A. Jongejan and A. L. Wilkins, J. Less-Common Metals, 21 (1970) 185. 9 A. Jongejan and A. L. Wilkins, J. Less-Common Metals, 21 (1970) 225. 10 R. C. de Vries,R. Roy and E. F. Osbom, J. Am. Ceram. Sot., 38 (1955) 161, 11 (i) E. H. Nickel, Am. Mineralogist, 41 (1956) 785. (ii) E. H. Nickel, J. F. Rowland and J. A. Maxwell, Can. Mineralogist, 6 (1958) 264. 12 E. H. Nickel, Mines Branch best. Rept. IR 61-146, Mines Branch, Dept. Energy, Mines Resources, Ottawa, Canada, 1961. 13 R. B. Rowe, &on. Geot, Ser. No. 18, Geo~~icu~ Survey, Dept. Energy, Mines Resources, Canada, 1958. 14 I. V. Aleksandrov, T. A. Trusikova and B. P. Tupitsin, GeocAem. Intern&, 8 (1971) 229. J. Less-Common Metals, 29 (1972)