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 magnesium 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
INDUSTRIAL AND ENGINEERING CHEMISTRY
JANUARY, 1938
a mixture of olivine rock and burnt magnesite in an oxidising atmosphere may be described by the equation:
+
18Mg,SiO' 2Fe.Si0' olivine
+ Op+ 6Mg0 = 20Mg2Si04+ 2MgFe10+ iorsterite
magnesioferrite
33
way, forming lenticular masses in gneissic rocks of granitic or granodioritic composition. The individual deposits of olivine rock are sometimes 3 km. long and attain a thickness of several hundred meters. Often the olivine rock is accompanied by eclogites. The leases for production from the principal deposits are controlled by the Norwegian Govern-
Other reactions taking place are, for example, the transformation of enstatite into forsterite according to the eqnation: MgSiOs
+ MgO = Mg$iO,
A description of these reactions was given by Borgestad Fabrikker and Goidschmidt in 1929 ( 1 ) .
Suitable gradings of the raw materials made it possible to manufacture products with exceptionally low shrinkage during the process of burning; this shrinkage was restricted to fractions of one per cent of the linear dimensions of the bricks, and even exact ruaintenance of the dimensions of molded articles coiild be secured.
THE first experimental manufacture of forsterite products was started in 1925-26, and tests of the forsterite bricks were made in reheating furnaces and ceramic kilns and in gas-fired furnaces in Xorway with promising results. The special advantages of the natural olivine rock cousists in its high melting point and in the absence of any iindesirable transformations during heating, giving an unsurpassed degree of volume stability up to very high temperat,ures as compared with other natural refractory materials. The olivine has the unique advantage that no previous calcining is required. The chemical analysis of a typical shipment of SO tons of rather pure olivine rock made by 0. Roer of Oslo in 1927 is as follows:
The rock is a duuitc and contains, besides olivine, small amounts of enstatite, magnesian amphibole, chromite, and traces of magnetit.e, phlogopite, corundum, and some secondary serpentine. Other varieties contain such minerals as diopside. Coniuion secondary minerals are serpentine, talc, and chlorite. .The dunite, analyzed above, contains 90 per cent by weight of olivine, 6 per cent enstatite, 1 per cent iron ores (chromite and mametite). and 3 Der cent seruentiiie. The chemical
If such a rock isheated in an oxidizing atmosphere-for grayish or green olivine becomes example, in a kilt-the bright reddish broum This transforniation is due to the oxidation of ferrous iron (in the Fe,SiO, component) to ferric iron, a compound of u-hich is segregated as brown translucent grains and flakes regularly orientated along the cleavage planes of the olivine, as sh0u.n in Figure 1. The brown ferromagnetic crystals are either MgFelOl or the cubic form of ferric oxide (u-Fe70s) or, niost probably, an isomorphous mixture of these two compounds, leaving an excess of silica in the silicate phase. The same phenomenon is sometimes seen in the olivines of volcanic racks as a natural process of oxidation at elevated teniperatures. The specific gravity of the dunite is ahout 3.3. The underload refractoriness of the purest natural olivine rock is very high; the varieties of olivine rock that contain some serpentine as product of hydration are somewhat less refractory. T h e olivine rocks are situated at the west coast of Nor-
Photomiciopcwh b i E . P . Rczlord
FIounp: 1. OLIYINEIN Wnicii TINY GRAINSAND Fums OF A N IRONBEAKING Coupomin HATESEPARATED UPON HEATING TO 2500" F. IN AN 0x1DIZLNG ATMOSPHERE( X 200, PLANE POLARIZED LIGHT) ment. The resources of these fields are estimated at about 2 billion tons, which can be producedinopen qnarries. Some of the deposits are located on the seacoast and steamers can thus be loaded direct from the quarries, as shown in Figure 2. The great extent and high degree of purity of several of the Norwegian olivine deposits and their favorablo location near ice-free harhors give the new refractory a great advantage. Several thousand tons of olivine rock have already been shipped.
THE industrial use of olivine refractories from 1928 to 1931 was largely developed in Germany. Refractories were made according to the writer's methods by transforming olivine rock into a mixture of forsterite and magnesium ferrite. The products were tried for various purposes. Successful use of the forsterite bricks was made in ceramic kilns for high-temperature work; where temperatures above 1600' C. could be attained, the chamber walls and roofs were lined with forsterite brick. Also successful experiments were made by German manufacturers in the use of an olivine ramming mass as the lining of induction fnrnaccs for melting nonferrous alloys. Copper-nickel alloys could also be melted successfully in these furnaces. Forsterito bricks were successfully used in 1930 and 1931 for the arched roofs of copper refining furnaces fired either with gas or with powdered coal; the life of the olivine roof is about three times that of a silica roof. Somewhat conflicting evidence was obtained in the iron and steel industry. I n some cases the material was used successfully, but nu the whole the olivine bricks of that period did not satisfy requirements. During 1932 some use was made of olivine, under the writer's licenses in the construction of kilns for burning magnesite refractories in Germany and as a ramming mass in the bottoms of electric steel furnaces in Italy. Experiments are now being carried out in Germany on the use of forsterite refractories in rotary cement kilns. The use of forsterite bricks in the hearths of forging furnaces has
34
INDUSTRIAL AND ENGINEERING CHEMISTRY
been introduced successfully in other countries; this success
is due essentially to the exceptional resistivity of the forsterite products to the corrosive action of iron oxides. In Germany synthetic forsterite is being made from mixtures of serpentine and magnesium oxide (7) under patents of the writer. This process makes it possible for forsterite prodacts to be manufactured without importing raw material from Norway, even though the manufacturing costs are increased. I n England forsterite bricks have been used successfully in the forging and reheating furnaces of steel works. This use may open important markets in several countries, since forsterite bricks are extremely resistant to the fluxing action of iron compounds. Of special importance to European manufacturers and users of olivine refractories is the olivine mortar, invented by Harvey and Birch (5) which not only joins forsterite bricks, but magnesite, chromite, and many other refractories as well. Further important improvements have been made by them in the field of chromite-magnesite-forsterite refractories. I n Europe recently refractories have been made even from impure:olivine rocks, and very important results have been attained with improved forsterite products. These refractories are being tested industrially at the present time.
THE f o r s t e r i t e r e f r a c tories manufactured on a large s c a l e h a v e shown superior properties in certain fields of applicationfor example, i n c e r a m i c kilns, in certain induction f u r n a c e s , i n t h e arched roofs of copper s m e l t i n g and refining furnaces, and in the hearths of forging and r e h e a t i n g furnaces. Other uses are still in the experimental stage, such as in rotary c e m e n t k i l n s . The introduction of olivine r e f r a c t o r i e s into certain other fields is limited a t present by the comparative w e a k n e s s of forsterite a g a i n s t t h e a c t i o n of metallurgical slags (with the remarkable e x c e p t i o n of slags very rich in iron) ; also the strength of forsterite brick after sudden changes of temperature is not as satisfactory as is desired. These difficulties h a v e been surmounted, however, by a n improved process. The following table gives comparative data on the present European forsterite brick and the new improved forsterite brick made in the writer's l a b o r a t o r i e s in N o r w a y . The temperatures ( C e n t i g r a d e ) are given for underload tests of 2 kg. per sq. cm. (28.4 pounds per square inch) :
Forsterite Brick Normal Improved
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Softening 1% 2% Temp. Compression Compression 1560 1630 1660 1640 1710 1725
3% Compression 1675 1730
Failure 1687 1737
Results of the spalling test (number of quenchings, by a cold air blast, until breakdown) from 1100" C., are: Normal forsterite brick Improved forsterite brick
7-8 20
The improved forsterite brick is also superior to the earlier brick in its resistance to slag and fused salts. Improved resistance to spalling is obtained by making the refractory from two different components. The granular material is one refractory substance and the cementing material is another. Such a composition prevents the accumulation of thermal strains over larger areas of the brick; an internal adjustment takes place around any single grain of the granular material and the possibility of spalling is thereby reduced. When such a heterogeneous refractory i8 made, care must be taken that the mechanical underload strength is provided for by a compact crystalline granular material (in this case, olivine) and that the chemical resistivity is provided for by a very insoluble ground mass in which the olivine grains are embedded. I n the present case the ground massmay be made from a spinel mineral, rich in magnesium and chromium. I n this way the new heterogeneous forsterite refractory is made from granular olivine and a cementing mass, essentially magnesium chromium spinel (for example, the refractory may comprise 70 per cent olivine and 30 per c e n t g r o u n d mass). P a t e n t s for this type of forsterite refractory have been applied for in all industrial countries. A summary of the European research work on olivine is given by the writer's French patents (2).
Literature Cited (1) Borgestad Fabrikker and Goldschmidt, Norwegian Patent 50,149 (1929). (2) G o l d s c h m i d t , French Patents 623,573 (1926); 643,638(1927); 721,545 (1931): 790,877 (1935); 811,237,811,659 (1936); additions 34,049 (1929) and 37,785 (1931). (3) Goldschmidt and Knudsen, Norwegian P a t e n t 45,083 (1925). (4) Ibid., 47,407 (1926). ( 5 ) Harvey and Birch, U. S. Patent 2,077,792 (1937). (6) Jakob, J., German Patent 417,360(1924). (7) Pieper, L., Ber. Keram. Ges., 18,41-64 (16871. RECEIVED September 23, 1937.
FIGURE2 .
LOADIXG OLIVINE
ON A
700-TON STEAMER
NORWEGIAN QUARRY
AT A
