Olivine and Forsterite Refractories in America FRED A. HARVEY AND RAYMOND E. BIRCH Harbison-Walker Refractories Company, Pittsburgh, Pa.
Commercial refractories in which forsterite (2MgO.SiOz) is the primary constituent were first tested in service about ten years ago. Although development is continuing, the forsterite refractories now available have become established in the United States and Europe. The two papers presented here report the progress on both continents. GoldSchmidt, (page 32) who made the first forsterite refractories without resort to complete fusion of the ingredients, relates the story of this development carried on largely in the laboratory of the Government Raw Material Committee in cooperation with the Norwegian Ministry of Trade and Industry and with Rolf Knudsen of Borgestad Fabrikker. Harvey and Birch have given considerable attention to the performance of forsterite refractories in various industrial furnaces in the United States and Canada. Almost all of the forsterite refractories discussed in the two papers have been made from magnesia and the mineral olivine. Their development marks the first introduction of olivine to the family of industrial minerals. Previously olivine had not been used commercially except as a gem stone.
Forsterite, whose melting point is 1910" C. (3470" F.) is more refractory than many other compounds of importance in refractories, For example silica (cristobalite) melts at 1728' C. (3142' F.), and mullite melts incongruently at 1830' C. (3326' F.). No magnesium silicate other than forsterite is stable a t temperatures above 1562' C. (2844' F.). Forsterite rarely occurs by itself but is common, in homogeneous comlination with fayalite, 2FeO SiOl, as olivine. The term "olivine" covers a wide variety of compositions conforming to the orthosilicate formula 2 R 0 SiO,. The RO molecule may consist of combinations of magnesia, ferrous oxide, calcium oxide, manganous oxide, and similar basic oxides. Olivines in which the RO is made up chiefly of magnesia and ferrous oxide are of main interest as refractories. The olivines are igneous in origin and are believed to be among the first minerals formed from the molten magma. Their separation from later crystallizing minerals may be clean-cut, so that deposits are found which consist almost entirely of olivine. Igneous rock consisting of olivine is called "dunite." The present forsterite refractories consist largely of dunite from deposits occurring near Asheville, X. C. Such a deposit, where olivine is being quarried for use in refractories, is shown in Figure 1. These dunites as now mined may contain as much as 80 to 85 per cent forsterite, but the accessory minerals are mostly of low refractoriness. For this reason, refractories for high temperatures could not be made directly from the rock as mined. As a result of extensive research, corrective measures were worked out which provided for means of treating the crushed natural rock with magnesia so as to convert the major impurities into material at least as refractory as the forsteritic olivine particles of which the rock largely consists. Thus, enstatite (MgO SiOn) was converted into forsterite, as were also the various hydrous magnesium silicates, such as serpentine. Any ferric oxide, present in the natural rock or formed in firing, may combine with the magnesia to form magnesioferrite (higo Fez03). Very little olivine rock is found which does not contain a t least 10 per cent of accessory minerals, and hence the magnesia-enriching treatment has been a necessary step in the production of the present commercial forsterite refractories.
P
URE forsterite is rare in nature but as a major constituent of the magnesium-iron olivines it is a n important rock-forming mineral. The products which have become known as forsterite refractories are made of olivine-bearing rock (dunite) that may contain as much as 85 per cent forsterite. I n addition to olivine, the refractories contain magnesia, added during manufacture, which causes the development of additional forsterite by reacting with accessory minerals such as talc and serpentine that occur with the olivine. Goldschmidt whose pioneering work on forsterite refractories was carried out in Sorway, gives an account of the steps in their development on page 32. Beginning at a later date but without knowledge of Goldschmidt's work, an investigation which reached the same end was carried on independently in the United States. Since details of this development have previously been published ( I ) , the present paper deals principally with the performance of forsterite refractories in various industrial furnaces in the United States and Canada.
Properties of Forsterite Refractories
A complete account of the properties of the commercial forsterite brick has already been given by Harvey and Birch ( I ) . These properties may be summarized briefly as follows: REFRACTORINESS. Their pyrometric cone equivalent is above cone 38. The brick are, therefore, considerably more refractory than silica brick, whose refractoriness expressed in cones is about 32. VOLUMESTABILITY.The brick show from 0.0 to about 0.5 per cent linear shrinkage when heated to 1650" C. (3002" F.) for 5 hours. This is exceptionally satisfactory behavior for any refractory.
27
28
INDUSTRIAL AND ENGISEERING CHEMISTRY
VOL. 30, NO. 1
STREmTH UNDER LOAD. The cold crushing strength of forsterite brick is about 2800 pounds per square inch. In the A. S. T. M. hot load test, the brick will withstand a load of 25 pounds per square inch to a temperature exceeding 1570" C. (2858" F.). This excellent load-carrying ability explains the successful use of forsterite brick in sprung arches of various types of furnaces, particularIy in the copper industry.
furnaces receive molten blister copper from the converters and may Serve as reservoirs or in other modified capacities, In this particular holding furnace, molten blister copper from the converters is introduced by ladle, and the furnace is kept a t a temperature of 2300" to 2400" F. (1260"to 1310" C.) by burning powdered coal. The molten comer is flamed or - * blown to oxidize sulfur, arsenic, iron, and other impurities which are removed from the bath by volatilization, or with the slag. This operation also produces some copper oxide which is then reduced to copper by poling. This consists of introducing several green timbers or poles into the copper; they become charred and serve as the means of reducing the copper oxide. During the poling and flapping operations much copper and many impurities, particularly iron oxide, are boiled and splashed to the underside of the roof. The length of the furnace is 28 feet and the roof span is 14 feet. Previously, 15-inch-thick silica brick had been used with six successive complete roofs giving 8, 8, 9, 7 , 8 , and 8 weeks of life. Splash from the bath produced fluxing which was the chief cause of the roof destruction. The first forsterite roof installed was 12 inches thick in sprung arch construction. It lasted CAROLINA DUNITEQCARRY FROM WHICHREFRACTORY over 28 months without repairing. This reFIGURE 1. KORTH OLIVINEIs OBTAINED markable success was repeated with a second Careful selection is necessary and hand cleaning is practiced t o iemove coatings of roof which lasted about 20 months. Forsterite weitthereh rock products from some of t h e rook. has been adopted as the standard refractory for holding furnace roofs at this plant. SPALLINGRESISTANCE.The brick are more resistant to spalling than ordinary magnesite brick and, in general, may be Roof of Reverberatory Furnace for Smelting compared with the best of the improved new basic brick. Copper THERMAL CONDCCTIVITY. As shown by Figure 2, the thermal conductivity of forsterite brick is even lower than that of silica Forsterite brick was next tried in the larger reverberatory brick at high temperatures. furnaces used for smelting copper ore. Copper smelting furTHERMAL E~PANSIOX. The thermal expansion is of the same order as, but somewhat lower than that of magnesite brick. naces receive the ore after it has been roasted to remove The expansion rate is uniform. combustible and some volatile impurities. These reverberaTYPICAL CHENICAL ANALYSIS. A typical analysis, in per cent, tory furnaces are large-for example, about 115 feet long and is as follows: 25 feet or more wide. Si02 31.7 MgO 57.2 The roasted ore is charged to the furnace through fettling Alios 1.1 CrzOa 0.1 FeO + Fez03 (as FeO) 6 , 4 holes in the roof, together with a slagging agent, commonly cso 2.8 Total 1 0 0 . 0 silica. Since the ore-charging holes are close to the furnace side walls, the charge piles up against these walls and protects Uses of Forsterite Refractories them. The burners, generally using powdered coal or oil, are I n the United States forsterite refractories were first offered located a t the charging end of the furnace. The result is a for sale in 1933. Because there was no background of experismelting action which produces a molten matte consisting of ence for a forsterite brick, the policy followed in supplying the copper and iron sulfides. The matte (later converted t o blisbrick for service test was to proceed slowly and, in general, to ter copper in the converter) and slag are tapped from the end apply them only after weighing all of the theory and other facof the furnace opposite the burner and charging end. tors on which predictions could be based. This has tended to The rate of smelting is determined by the amount by which delay the final determination of the boundaries of the field in the temperature of the furnace exceeds that a t which the which this type of refractory may profitably be used. Howcharge fuses (which may be as low as 2200" F.) (2). Conseever, these limits are now known with what seems to be a fair quently a high rate of copper production, such as has been degree of completeness. Still, there are numerous anomalies in maintained in Canada and some western smelters in the last the field of refractories application, and it may be expected few years, naturally intensifies the severity of service condithat new uses will develop in services where theoretical considtions in the smelter and stimulates attempts to secure better erations would seem to recommend the use of some other type refractories. of refractory. Furthermore, it is anticipated that the field Service conditions are most severe in the charging end of the will be broadened by the introduction of such supplementary furnace where the temperature may approach that of the forsterite refractories as those mentioned in Goldschmidt's basic open-hearth steel furnace. I n a furnace which is probpaper. ably typical of Canadian practice, it may be considered that The industrial uses of forsterite refractories can best be the temperature ranges from about 2900" F. in the charging understood by discussing certain applications in detail. end to perhaps 2500" F. in the tapping end of the furnace. As a result of this temperature difference and of the great Roof of Copper Holding Furnaces amount of fume and dust in the furnace gases, the refractories in the charging end of the furnace require more frequent One of the earliest applications of forsterite refractories was replacement than those in the tapping end. an entire roof installed in a copper holding furnace. Holding A
I
INDUSTRIAL AND ENGIKEERING CHEMISTRY
JANUARY, 1938
A considerable tonnage of forsterite brick is now being used in the roofs of copper reverberatory smelting furnaces. Prior to the period of experimentation with all basic-to-neutral roofs, the standard roof construction was of two types-(a) sprung arches of silica brick and (b) sprung arches of silica brick in combination with magnesite brick. I n the latter construction magnesite shoulders extend upward about sixteen courses from the skew blocks on each side, so that they will reach above the fettling holes. This shoulder construction is used only in the charging end of the furnace. A third type of construction found satisfactory is the use of suspended magnesite brick laid up with steel sheets or cases, following the hletalkase principle. Roofs in the majority of smelting furnaces are built up by one of the first two methods, but the following series of service trials has resulted in establishing a more economic operation in several of the larger smelters through the use of forsterite brick, especially in the roof a t the tapping end of the furnace. One of the first installations of forsterite brick in a copper smelting furnace constituted the entire roof of a furnace 105 feet long. The roof span was 25 feet. The brick were laid up with a chrome ore mortar in sprung arch construction with a rise of 1.33 inches per foot. The thickness of the roof was 15 inches. Previous experience had shown that silica brick with magnesite brick a t the fettling holes would last 100 to 115 days. Within a month the exposed ends of the brick at the charging end of the furnace began to show signs of a peeling action. This consisted of a layer of material about 1 inch thick which separated itself from some of the brick. After 44 days, it was decided to insulate the roof to conserve heat, although it was recognized that this might accelerate the destruction of the brick. About 5 inches of vermiculite insulation were installed. Within 8 hours spalling 2 inches deep began over about 60 feet of the roof a t the hotter end. After a total of 98 days, two 12-foot sections a t the hotter end needed to be replaced after continued spalling or peeling. A third section of 12 feet was repaired within the next month, and a fourth was removed while replacing the third.
I2 IQ
8
0 'C. 572
752
932
1112
1292
1472
1652
1832 *F
TEMPERATURE
FIGURE2. THERhlAL CONDUCTIVITY BRICKS
OF
THREE
The remainder of the roof (about 50 feet) extending forward from the cooler end, about half the length of the furnace, was then about 12 inches thick and in good condition. This portion of the roof gave a long life, and a major part of it was still in place after a year of service. Subsequent use of forsterite brick in smelting furnaces at this plant have established them in the roof in the tapping end of the furnace. Silica brick with magnesite brick shoulders are used in the charging end. Service data indicate that the
29
forsterite in the tapping end of the furnace require replacement only about a fourth as often as the hot end construction. Forsterite brick have also been used successfully in replacement of the magnesite shoulders in the hot-end roof construction. This early complete roof test was made with some of the first forsterite brick produced. Since then the refractory has been improved and modified. Some of these changes have come as a result of experience gained through these early trials. Certain of the causes which terminated the life of the brick in these early roof tests are shown by the photomicrographs of Figure 3C. The normal refractory (Figure 3 A ) consists of large and small olivine grains surrounded by small magnesia particles which have reacted with low-melting silicate impurities to form some secondary forsterite. TABLEI. CHEMICAL ANALYSES O F FORSTERITE BRICK FROM ROOFOF REVERBERATORY FCRSACE FOR SMELTING COPPER
Silica, (SiOn) Alumina ( - 1 1 2 0 3 ) Iron oxide (as FerOs) Lime (CaO) Magnesia ( M g O ) Copper (Cu) Total
L-nused Forsterite Brick 31.3y0 0.8 7.0 1.7 58.5 Trace
__
99.3
Zone 1, Zone 2 , Inner In. of Vltreous Layer Brick (Mostly 1 1 2 I n Back of Slag) Zone 1 11.3v0 30,9y0 3.6 2.5 70.9 14.9 0.6 2.3 3.7 43.4 Prevent b u t not detd. ~
~
90.1
94.0
The brick as altered by heat and vapors at a point inch back of the slag-brick boundary (Figure 3C) in a smelting furnace roof presents a somewhat different appearance. The olivine has recrystallized so that the original grain boundaries are obscured. This has caused a certain increase in density, due to the elimination of the greater part of the pores. Figure 3B shows the method of slag attack. The most interesting feature of this section is that a high iron slag has penetrated the brick by way of the magnesia in the brick. The boundary between the slag and the olivine grains is sharp, but the iron oxide from the slag has gained entrance into the brick through the magnesia. The black grains embedded in the olivine in this photomicrograph are magnesia containing a high percentage of iron oxide. Recrystallisation of the olivine mentioned in connection with Figure 3C has also occurred in this section. The extent to which the composition of forsterite brick in a reverberatory furnace roof may be altered by slag penetration is shown by the analyses in Table I. Petrographic studies show that the solidified slag is mostly magnetite (Fe304). It is highly magnetic. These data and other studies of used brick indicate that iron oxide first attacks the brick by dissolving in the magnesia grains and producing an iron oxide-magnesia solid solution which is soft or plastic a t furnace temperatures. The prolonged exposure to heat and vapors recrystallizes the olivine. The net result of these changes is eventually to give a layer of brick substance modified in density and composition, which could separate from the brick proper to give the type of peeling previously mentioned. This and other studies of forsterite brick from service have served to indicate ways by which the resistance of the brick to destructive agencies has since been improved. Some of the resulting improvements follow: 1. Experience in selecting olivine for use in refractories has made possible the mining of a greatly improved grade of rock. 2. Elimination of the types of olivine rock containing the highest amounts of low-melting impurities has made it possible to reduce the magnesia addition and consequently to obtain an
INDUSTRIAL AND EEGINEERIKG CHEMISTRY
30
increased percentage of forsterite in the fired refractory. This is especially beneficial for those services where iron oxide penetration is most likely to attack the free magnesia in the brick. 3. Steps have been taken to increase the denaity of the brick 8s shipped, in order to minimize volume changes in service as a result of recrystdIimt,ion of the olivine. The principal means of obtaining such modifications have been to burn the brick much harder and to modify the grind so as to give denser packing. Figure 4 shows B thin section of forsterite brick burned to cone 32. The high-temperatwe firing has largely accomplished the same degree of recrystallization of the olivine which had occurred in service with t.hc brick of lighter burn shown in Figure 3C. This result is also indicated by porosity tests which show that the brick &re denser a8 a result of the harder Ering. These improvements can he expected to increase the use of forsterite brick in the reverberatory copper smelting furnace by allowing the extension of their use to sections of the furnace nearer the charging end.
Other Nonferrous Metallurgical Furnaces Following the first successful use of forsterite refractories in a copper holding furnace, their use has extended to other nonferrous furnaces of similar types. Forsterite brick are also being used successfully in the t.op portion of the lining of a converter for blowing scrap brass. These applications have been confined to soctions of the furnace above the slag line. For resistance to slag line attack, it Soon hecanie evident that magnesite brick were superior t o forsterite for these furnaces.
Bulkheads of the Basic Open-Hearth Steel Furnace As the largest single consumer of refractories, it is only natural that the basic open-hearth furnace is one of the first testing grounds for a new or improved refractory. Some portions of tlie furnace last only 2 to 4 weeks and thereby show quickly behavior of the refractories under test. Indetermining thesuitability of forsterite brick for the openhearth furnace, they were teated in some thirty or forty different plants. I n the bulkheads (the exposed walls a t the end of the furnace) they have generally given several times the life of silica brick. Table I1 summarizes a few of these installations. Although for uniformity, comparison is made between forsterite and silica brick in Table 11, other refractories-for example, Metalkme magnesite and chemically bonded chrome
-
A . Thin seetion oi forsterite rdractory shipped for w e I” roof of oopper reverbemtory smelti w furnace. FIGURE
3.
B.
VOL. 30,NO. 1
brick-are also used in bulkheads. Since service conditions vary from plant to plant, and even from furnace to furnace in the same plant, forsterite has not always proved to be the most economical bulkhead refractory even though it may have given several t i e s the life of silica brick. It is, however, justifyingits position as the standard end-wall refractory at R number of plants. OF TEE LIFEOF FOR~TZRITE AND SILICA TAB= 11. COXFARXSDN REPnAcToRIEs IN OPEN-HEAnTA B ~ K I ~ E AATD STEN S T E e t PLANTS Plant
Fuel
NO.
1
1 I 4 4
5 6
;10: 13 13
1s I5
17
19 80
30
Number oi Number of Neste Given Heat3 Given T Y Dof~ Mortar by Foisterite by Silica U s d , with
Brick 200
lYaturn1 gaa Nstllrnl %M Natural sas
Oil
115 98 69
Oil
169
86
Oil Oil
+
Oil tar Coke-oven gam Coke-oven gar ? 7
Producer gsil I’rodueer r,:88 Natural EM Naturnl pss Produoar s . e 8 Producer 8-
m+
229
827 24G
338+ 275 47
so
242-1-
227+ 4Y
16J+ -___
AVerBge
1781
Briok 30 30 30
sn
,523 57 57 100
inn inn inn inn 7 7 57 67 4
15 -.
Forsterite Brick Chrome Chrome Chrome None
Forsterite Forsterite Forsterite Cbrome Chrome Chrome Forstcrite Forsterite lions None
Faisterite Foraterite None Nolle
53
I n addition to the satisfactory service in the end-walls, forsterite brick have given good results in the uptakes, division wall (between the gas and air uptakes), bridge wall, and ports of the open-hearth furnace. Experience with forsterite brick in the open-hearth furnace has shown that two principles inust be observed: 1. Forsterite brick must not, ha used diiectly under silica brick; tho drip from the silica brick is extremely corrosive to forst.erit,ebrick. This generally prevents the use of forsterite in the front, and back walls of the open-hearth furnace with the present silica roof construeiion. 2. Fonterite brick should be kept a reasonable dist,ance from the bath since they are not resistant to the corrosive action of the dag. Flying dust and the vapors Fhich attack the ends snd roof of the open hearth are, however, only moderately corrosive to forsterite brick.
rontaet line between reverherxtuiy iuinace slag and foraterite brick.
PAoToMlCRooRAPAS OF FORSTERTTE REFRACTORY ( X
70,
C. T h i n section of briok 8 / * inch back of the 00”tact boundary between the brck snd tho reverbeistory furnace slag. PLANE POLkRIZED
The mottled light gray *res$ are oiidilc: the black are88 sre niagnezia and slag.
LIGHT)
JANUARY, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
Roof of the Basic Open-Hearth Steel furnace Theoretically there are many reasons for expecting that forsterite would be an ideal refractory for the open-hearth roof; but the one complete roof installation tried was not snccessfnl. The use of silica, an acid refractory, as the roof of a basic furnace seems anomalous, but actually the chief limitation of silica brick in this service is not its acidity but its melting point. Silica brick will begin to drip a t approximately 165Oo to 1675" C . (3002" to 3047" F.), hut they will support a oonsiderable load a t temperatures approaching the lower limit of this range. In load-carrying properties, forsterite brick are approximately the equal of silica brick, but they are much more refractory. These considerations led to the installation of a forsterite sprung-arch roof on a 100-ton open hearth. The roof was 12 inches thiak and laid up without rib construction. The brick were some of the earlier nianufacture and therefore did not incorporate the later improvements in raw material selection and manufacturing method. Perhaps because of the failure to modify the steel work to make allowance for the greater weight and expansion of the forsterite brick (50 per cent more than silica), the main section of the roof soon went out of shape. It buckled and collapsed after fewer heats than are commonly obtained on silica brick. At that time the roof arches in the ends of the furnace and in the slopes leading down to the main section were in excellent condition, but these were also replaced. A small amount of spalling or peeling was observed in the first few heats of this test. This continued progressively, hut even when the main section of the roof collapsed, there were few brick shorter than 9 inches. It is altogether possible that future improvements in forsterite brick may lead to additional trials in the open-hearth roof, For this reason there has been an intensive search into the causes of this behavior. Among the fundamental factors is the relatively high t.herma1 expansion of forsterite brick (and also of magnesite brick) in the open-hearth operating range. The reversible thermal expansion of forsterite and magnesite brick in the range 2000" to 3000" F. (1090' to 1650" C . ) amounts to more than I/,. inch per foot, whereas silica brick show negligible expansion in this range. For this reason it may be that silica has a fundamental advantage over hasic brick where adequate provision for expansion is not ordinarily allowed. The latter keep expanding and contracting between heats, whereas there is little change in silica. However, it is not believed that this factor can stand in the way of the eventual successful use of an improved and modified forsterite brick or some other refmctory of the basic-neutral group in American open-hearth roofs. Within the last few years European steel plants have successfully used a chrome-magnesite brick in this application. However, these furnaces are, in the main, of low tonnage and most of them are prohahly not operated as intensively aa American open hearths.
Portland Cement and Dolomite Rotary Kilns A few years ago only fire clay refractories were used for rotary kiln linings, but these were perhaps adequate for the severity of service then experienced. Later the more refractory high-alumina (diaspore) brick became available, and those in the 70 per cent alumina class became established in a majority of plants as the most economical refractory for the burning zone. Magnesite brick began to be used for this pnrpose only a few years ago, but in many instances involving abnormal severity of service conditions they have become e& tablished as sufficiently superior to high-alumina brick to justify their higher initial cost.
31
Although forsterite brick aregiving splendid results in rotary Portland cement and dolomite kilns, they are newer and consequently not yet so widely nsed as are chemically bonded magnesite brick. The first installation of forsteritc brick in a rotary kiln was a 13-foot section in the burning Bone of a Portland cement kiln. It took a coating from the charge (as is desirable, since the brick are thereby protected), and the brick lasted sufficiently longer than 70 per cent alumina brick to indicate good economy in their use.
FIGURE 4. PE€OTOMICROT-RAPE€ OF TKINSECTION OF FOE~TSRITE REFRACTORY OF CONE 32 BURN ( X 62, PLANE POLARIZED LIQET)
A oertain amount oi reciystallization of the olivine grsina ia w p u e n t .
The kiln was operated continuously for 4 months and was then shut down for repairs to the adjacent high-alumina brick. On restarting the kiln, tho forsterite brick gave no trouble and went on to give much better service than the plant average on 70 per cent alumina brick. A complete burning zone section installed subsequently at another Portland cement plant has recently completed a s u c c e s ~ f ~campaign. l In this campaign forsterite brick established their economy over the considerably less expensive 70 per cent alumina brick. Several additional forsterite linings are now in service in Portland cement kilns. The first installation of forsterite brick in a rotary kiln for calcining dolomite was a section approximately 10 feet long in the burning zone. These kilns, which prepare dolomite clinker for use in the open-hearth furnace, normally operate a t temperatures considerably higher than exist in Portland cement kilns. Again the brick took a satisfactory coating. They were replaced about 3 months later a t the time of a shutdown made necessary by the condition of other parts of the lining. On the basis of this showing, which was two to three times the service secured from 70 per cent alumina, a complete burning-zone lining was installed. These brick gave a highly satisfactory campaign which approximated ten months. This exceeds the average life of magnesite linings a t the same plant, although one of the latter gave a trifle longer service. The future of forsterite refractories for rotary kiln linings may conservatively be regarded as promising. Service records to date indicate that they tend to have several advantages over magnesite brick for this service: 1. The lower thermal conductivity of forsterite brick (as compared with magnesite brick) gives more protection to the
32
INDUSTRIAL AND ENGINEERING CHEMISTRY
steel shell of the kiln. Careful observations by plant men have shown that the shell remains cooler when a forsterite lining is used. This would have been expected in view of the order of thermal conductivity of forsterite and magnesite brick as shown in Figure 2. 2. Kiln shutdowns appear to be less damaging.
Service Experiences The foregoing miscellaneous service records can in most cases be correlated with the physical properties of forsterite brick as shown by laboratory tests. Their successful use in the roofs of copper furnaces is possible mainly because of their high load-carrying capacity a t high temperature. Their relatively low thermal conductivity is apparently a factor of vital value in connection with their use in rotary cement and dolomite kilns. Their successful use in open-hearth bulkheads is attributable to their resistance to the attack of iron oxide in any form, and to their high refractoriness. One other characteristic of forsterite refractories-their volume stability at high temperatures-is being given a practical test a t the Hays Laboratory of the Harbison-Walker Refractories Company. The entire walls and roofs of two furnaces are built of forsterite brick. The larger of these furnaces has a floor area of approximately 6 X 6 feet and a
VOL. 30. NO. 1
height of 5 feet. Approximately seventy heats a t temperatures ranging up to 1710" C. (3110" F.) have been made in the kiln, with excellent results. The ends of the brick show no fusion and in every way indicate that they are well suited for this type of high-temperature service. The fire clay brick previously used gave much shorter life even when the maximum operating temperature did not exceed 1500' C. (2732" F,).
Conclusion The purpose of this paper has been to discuss the application of forsterite refractories in industrial furnaces. Since this type of refractory is only a few years old, a final estimate of their field of application cannot now be made. It is to be expected that new applications will develop due to greater experience in their use and manufacture.
Literature Cited (1) Harvey, F. A.,and Birch, R. E., J. Am. Ceramic SOC.,18 (e), 176-92 (1935). (2) Laist, Frederick, Trans. Am. Inst. Mining M e t . Engrs., 106, 66 (1933). RECEIVED September 23, 1937
Olivine and Forsterite Refractories in Europe
I
N RECEKT years refractories consisting chiefly of mag-
nesium orthosilicate have reached industrial importance. I n the development of such industrial refractories in Europe, forsterite (2MgO.Si02 or Mg2SiOd) has been the object of much research work, both in the laboratory and on an industrial scale, preceding the American work on such refractories by some years. I n 1925 the writer, in cooperation with R. Knudsen, started systematic investigations of forsterite as a refractory. The high melting point of pure forsterite (about 1900" C.) as recorded by the Geophysical Laboratory of Washington made a study of the properties of forsterite as a commercial refractory of interest. Since pure mineral forsterite is rare, synthetic forsterite was made from materials containing magnesium oxide and silica. Jakob (6) was the first to suggest the use of forsterite as a refractory. He proposed that mixtures of serpentine, quartz, and magnesium sulfate be melted in an electric furnace to obtain refractory forsterite. Because of technical difficulties this process is not industrially important a t present. I n 1925 Goldschmidt and Knudsen (3) described the manufacture of refractory forsterite products by a ceramic process from mixtures of talc [Mg3Sid016(OH)z] and magnesium oxide. During the progress of this work it was found that even serpentine and magnesium oxide could be combined to form forsterite a t temperatures below the melting points of any compound involved, and that forsterite products of excellent properties could be made by such a process. During some of the early experiments natural olivine minerals and olivine rocks were found to have valuable refractory properties, despite their ferrous orthosilicate (Fen-
V. M. GOLDSCHMIDT University of Oslo, Norway
SiOd) content. The latter is an extremely fusible substance in the pure state. The melting temperatures of olivines, consisting of about 90 per cent by weight of MgzSiOd and 10 per cent by weight of FezSi04,were stated to be only about 1400" C. by C. Doelter and by J. H. L. Vogt. However, the writer's experiments in 1926 showed that natural olivine rocks, containing as much as 10 per cent FezSiOd,were able to stand underload tests even a t temperatures well above 1700" C., in contradiction to the statements of Doelter and of Vogt. Later it was learned that Doelter's results were due to the fact that he melted his olivine samples in quartz containers, giving fusible clinoenstatite (MgSiOJ by mutual reaction between olivine and silica. The discovery of the valuable properties of olivine and olivine rocks, such as dunites, led to extensive studies on the use of such raw materials for refractories, because Korwsy possesses several important deposits of these rocks. The use of olivine as a refractory was described in 1926 by Goldschmidt and Knudsen (4),and practical work on a larger scale was started to investigate the industrial properties of the new refractory. Soon it was discovered that an addition of moderate amounts of magnesium oxide was valuable in transforming any impurities of the natural rock into refractory substances, such as magnesium orthosilicate and magnesioferrite (MgFez04). The chemical reactions which take place in the burning of
