TIlE J O U R N A L OF I N D C S T R I A L A N D ENGINEERING CHEMISTRY
Nov., 1916
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ORIGINAL PAPERS THE COMMON REFRACTORY OXIDES‘ By ROBERTB. SOSxAh. Received July 26, 1916
I n discussing t h e “common refractory oxides” we will confine ourselves t o t h e common rock-forming oxides: silica, alumina, magnesia, lime, a n d t h e oxides of iron, These taken together make u p practically 90 per cent b y weight of t h e accessible outer shell of t h e e a r t h , while soda, potash, a n d v a t e r make u p most of t h e remaining I O per cent. I n comparing t h e properties of t h e individual oxides a n d i n discussing their important compounds a n d mixtures, 1 hope t o bring out certain general principles t h a t will serve t o classify a n d correlate in our minds some of t h e facts which have already been discovered, a n d at t h e same time show where additional research is needed. THE PURE OXIDES
One property of t h e oxides which is of primary importance is t h e melting point. T h e melting points of t h e common oxides are listed in Table I : TABLEI-MELTING POINTS OF Silica.
THE COXMON REFRACTORY OXIDES
. . . . . . . . . . . . . . . . Si02 (quartz)
(cristobalite)
..
.
Ferric oxide. . . . . . . , FezOa Ferrosoferric oxide. . . . . . FeaOa Ferrous oxide . . . FeO
Below 1470’ 16251 2050 2800‘ 2570’ Unknown 1580’
Unknown
SILICA~-TWO melting points are given for silica. The explanation of these introduces t h e very interesting set of allotropic forms t h a t silica exhibits. I have a t t e m p t e d t o give a graphic statement of t h e relations of these forms in one of t h e diagrams of Fig. 11. Silica possesses t o a n unusual degree t h e property of responding very slowly t o changes of temperature as regards its melting point a n d its transitions from one principal form t o another. Each of these principal forms, on t h e other h a n d , has one or two inversion points of its own, which respond very promptly t o temperature change. The principal forms are q u a r t z , tridynzite, a n d cristobalite. Quartz has as reversible inversion a t j 7 j”, tridymite has inversions a t 1 1 7 a n d 163’; cristobalite is peculiar i n having a n inversion point whose temperature varies from about 2 0 0 to 2 7 j 0 , depending upon t h e previous history of t h e crystal. By rapid heating, quartz can be melted before it has h a d time t o transform into tridymite o,r cristobalite. The atomic or molecular basis for these interesting relations remains t o be worked out. ALUMIn-A3-Two allotropic forms of Alz03are known. T h e common form, known as a, is t h e same as t h e mineral corundum. It was t h e only form which appeared in t h e lime-alumina-silica investigation b y Rankin a n d Wright. The magnesia-alumina-silica s t u d y (by Rankin a n d Merwin) brought out a second P a r t of a paper presented before a joint meeting of the local sections Chemical and American Electrochemical Societies a t Niagara Falls, April 4, 1916. C . N. Fenner, A m . JOUV.Sci., 36 (1913), 331-384. * Rankin and Merwin, J . A m . Chem. SOL.,38 (1916), 568-588. 1
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or form. A t first i t was thought possible t h a t i t might be a compound corresponding t o magnetite, with t h e formula Alsoq, b u t a chemical analysis b y H. S. Washington shows i t t o be pure Al2O3. I t s relation t o t h e o! form is not yet known. X A G K E S I A - O ~one ~ ~ crystalline form of MgO is known: it is t h e same as t h e mineral periclase. Magnesia has t h e highest melting point of a n y of t h e oxides here described (2800 ”). LI&m-There is only one crystalline form of CaO known a t high temperatures. It seems t o possess a n inversion point, however, a t about 4 2 0 ” ~ which is similar t o t h e j 7 j O reversible inversion point of quartz. T h e exact location of this point will require further investigation. Pure CaO is, however, obtainable i n t w o forms.2 T h e first, which is probably amorphous, results from t h e dissociation of calcium carbonate at low red temperatures, On heating for a considerable time a t higher temperatures, i t changes gradually into t h e cubic crystalline lime of refractive index 1.83. The latter forms directly from silicate melts or from fused calcium nitrate, a n d is t h e stable form a t high temperatures. T h e porous lime ought not, perhaps, t o be called a distinct “form,” as i t is probably not such i n t h e sense i n which cristobalite is a “form” of silica. T h e porous, probably amorphous, form of CaO is much more reactive t h a n t h e crystalline. It unites readily with dry carbon dioxide or with water, whereas t h e crystalline CaO unites only slowly with these compounds. T h e fundamental reason for this difference is yet t o be found. OXIDES OF I R O N ~ - Toxides ~~ of iron offer a research problem quite different in character from t h a t of t h e other oxides described above, b y reason of t h e fact t h a t their compositions a n d properties a t high temperatures depend upon t h e pressure of oxygen in cont a c t with t h e m . Ferric oxide, F e 2 0 3 ,which occurs i n nature as hematite, begins t o dissociate, as t h e temperature rises, into oxygen a n d a solid solution containing ferrous iron; this may b e considered as a solid solution of FeaOl in Fe203. At a given temperature t h e initial dissociation pressure is high, b u t i t drops rapidly as t h e percentage of FeO in t h e solid increases, passing through a range i n which t h e pressure falls rather. slowly with chapge of composition, a n d finally falling rapidly t o t h e dissociation pressure of FesOq, which is very low (less t h a n 0.04 mm. of mercury, a t I Z O O ~ ) . Fe304, in t u r n , dissociates into oxygen a n d a mixt u r e of oxides whose character has not yet been deter mined. The properties of FeO are still practically unknown. T h e most of t h e recorded methods for preparing “ferrous oxide” yield only a mixture of metallic iron
of the American
3
1198.
Rankin and Wright, Am. Jour. Sci., 39 (1915), 1-79. Sosman, Hostetter and Merwin, J . Wash. Acad. Sci., S (1915), 563-569. Sosman and Hostetter, J . A m . Chem. Soc., 38 (1916), 807-833, 1188-
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THE JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Vol. 8, No.
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FIG. I
(or iron carbide) with a n oxide whose composition falls between FeO and Fea04. Ferric oxide has a n inversion point a t 678’, which is s h a r p and reversible, like t h e 5 7 5 ” inversion of quartz. This point is marked b y a n absorption of heat, as t h e temperature passes 6 7 8 ” , and also b y a sudden drop in magnetic susceptibility. According t o Honda there is a similar inversion a t -40’. FeaOa is said t o have a similar magnetic inversion point a t about j30’, when i t suddenly changes from a “ferromagnetic” t o a “paramagnetic” condition. We have not yet investigated this inversion thermally. T h e relations of these inversions t o one another, and t o t h e similar inversions in pure iron and in steel, offer a n interesting field for future study. T W O - A S D THREE-.CONPONENT S Y S T E Y S O F T H E OXIDES
I n order t o give a comprehensive and concise view of t h e relationships of t h e compounds and mixtures which can be made u p from a n y two or three of t h e refractory oxides, I have compiled t h e accompanying diagrams (Figs. I and 11). T h e facts are expressed in t h e form of phase rule diagrams of all t h e possible two- and three-component systems which can be made u p from t h e 6 oxides SiO,! &Os, MgO, CaO, F e 2 0 3 and FeO. From these 6 oxides there can be made 15 two-component systems and 2 0 three-component systems, making a total of 3 j, all of which are included in t h e two diagrams.
T h e larger p a r t of t h e d a t a upon which the compilation is based are from t h e results of researches made in t h e Geophysical Laboratory, individual references t o which will be omitted. The dotted curves showing the expansion of tridymite and cristobalite are from measurements b y Le Chatelier. The melting points of &OB, SIgO and CaO were determined b y Kanolt a t t h e Bureau of Standards. All of t h e compositions have been recalculated t o a molal percentage basis, in order t o bring out more clearly t h e regularities and analogies. The temperature scales of t h e two-component diagrams are all alike, and t h e base of each diagram is a t 1000’. I n t h e three-component diagrams the principal tempera. tures (quintuple points, etc.) are given in figures opposite t h e curve-intersections t o which they apply. The three-component triangles are of course only projections upon a horizontal plane of t h e space model oE t h e fusion surface, in which temperature is laid of€ vertically. Inversion points in t h e solid phases therefore do not appear; it is also not practicable, on account of t h e small size of the diagrams. to show t h e primary phases in each field, and various other important facts for which reference must be made t o t h e original papers. The triangular projections do, however, give a good comparative view of the different systems. Vnfortunately, many of t h e three-component triangles must be left nearly bare of information, b u t i t
Nov., 1916
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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is t o b e hoped t h a t t h e next few years will see m a n y of these gaps filled. I n these cases, as well as i n t h e completed diagrams, I have indicated b y letters t h e compositions of t h e principal natural minerals belonging in t h e system. A s t u d y of t h e composition of t h e binary compounds of these oxides brings out a n important generalization which may be s t a t e d as follows: T h e stable oxygenated compounds of t h e elements silicon, alumin u m , magnesium, lime and iron with one another
It is interesting t o note also t h a t t h e majority of t h e compounds which are unstable a t their melting points contain a larger number of t h e individual molecules t h a n do t h e stable compounds. A generalization similar t o t h e one s t a t e d above for binary compounds applies t o t h e ternary compounds, as far as these are known. It m a y be s t a t e d t h u s : t h e ternary compounds of t h e common refractory oxides are made u p of t h e more stable binary compounds (usually I : I compounds) in simple propor-
are all made u p of t h e refroctory oxides of these elements in s i m p l e p r o p o r t i o n s , usually I : I or 2 : I. This seems t o be t r u e quite regardless of what might b e expected from valence relations of t h e elements concerned. T h e validity of this rule will be evident from Table 11, a list of all of t h e known binary compounds of t h e common refractory oxides, separa-
tions, usually I : I . This fact is illustrated b y Table 111, which contains all of t h e known compounds in two of t h e ternary systems which have been more or less completely studied:
TABLE 11-BINARY CONPOUNDS OF THE COMXON REFRACTORY OXIDES SYSTEM
COMPOUND
MINERALNAME
RATIOO F OXIDES
Stable Compounds SiOz-AlzOs SiOz-MgO SiOz-Ca0 A1nOs-MgO AlzOs-Ca0 FezOa-FeO SiOz-FeO AlzO3-FeO FezOa-MgO
AlzSiOs MgnSiOa CaSiOa CazSiOd MgAlzOa Ca A 1204 CaaAl~aOis Car Ah014 pea04
Sillimanite Forsterite Wollastonite
FeSiOa FetSiOi FeAh03 MgFezOa
Griinerite Fayalite Hercynite Magnesioferrite
spinel'
....
....
Magnetite Mineval Compounds, Stability Unknown
1: 1 2 : 1 1 : l
2 : 1: 1 : 3:
1
1 1
5
5 : 3 1: 1
1: 2 : 1 : 1:
1
1
1 1
Compounds Unstable at Melting Point SiOz-MgO SiOn-CaO AlzOs-Ca0 Pen&-CaO FezOa-FeO
MgSiOs CaaSiOs CasSinO? Ca3AlzOr CaFeaOa CasFezOr 2FeO.dFezOs
Enstatite
.... ....
.... .... ....
....
1 : 3: 3 : 3 : 1 : 2:
1 1 2 1 1 1
2:3
t e d into two classes: ( I ) those which are stable a t their melting points a n d below, ( 2 ) those which dissociate at temperatures below their melting points. Certain mineral compounds, whose properties are not yet well known, are also included.
TABLE111-TERNARYCOMPOUNDS O F THE COMMON REFRACTORY OXIDES SYSTEM TERNARY COMPOUNDSMINERAL OXIDE RATIOS SiOz-Alz03-CaO SiOz-Mg0-Ca0
CaSi0a.AlzSiOr CaSiOa.CaA1204 CaSiOa.MgSiOs CanSiOc.MgzSiO4
Anorthite Gehlenite Diopside Monticellite
(1 : 1) : (1 : 1) : (1 : 1) : (2 : 1) :
(1 (1 (1 (2
: 1) : 1) : 1) : 1)
An excursion into t h e field of t h e alkali silicates furnishes other interesting examples of this principle, as shown i n Table I V : TABLE IV
SYSTEM CONPOUND SiO~-A1~08-P\Taz0 1\TazSi03.AlzSiOj NazSiOs.AlzSiOs.2SiOz hJazSiOa.AlzSiOr.4SiOn SiOz-AlzOaKzO
MINERAL Nephelite Jadeite Albite (feldspar) KzSiOa.AlzSiOr Kaliophilite KzSiOa.AlzSiOr.2SiOz Leucite KzSi03.AlnSiOs.4SiO~ Orthoclase (feldspar)
THE SILICATES AS "MOLECULAR
OXIDE RATIOS (1 : 1) : (1 : 1) : 0 (1 : 1) : (1 : 1) : 2 (1: 1 ) : (1: 1 . 4 (1 : 1) : (1 : 11 I 0 (1 : 1) : (1 : 1) : 2 (1 : 1) : (1 : 1) : 4
CO>IPOUNDS1l
T h e whole impression left b y a review, such as t h a t outlined above. of t h e silicates a n d other compounds of t h e refractory oxides, is t h a t these compounds are really " m o l e c u l a r compouiads" of t h e oxides-in Werner's terminology, compounds of second and third order. Students of t h e history of chemistry will recognize in this viewpoint something similar t o t h e dualistic system of Berzelius, which flourished over I O O years agp. But i t differs radically f r o m Berzelius's system,
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I7ol. 8 , XO.
11
in t h a t the idea t h a t there must be a positive and exactly the compound t h a t does form. I t s small negative part t o every molecule is dropped. Long margin of existence, furthermore, is indicated b y the after its electrical basis was shown t o be false, Ber- very slightly pronounced maximum in t h e melting zelius’s system persisted because of its convenience curve (see Fig. I ) . and b y the appearance of crystals in t h e classification of chemical substances. T h e of its constituent oxides in its melt, suggesting rise of t h e idea of valence, however, and the remark- dissociation very near its melting point. able growth of organic chemistry with its basis in the Are the “molecular compounds” drawing us away, structural formulas of organic compounds, drove then, from the atomic theory and the structural formula? Rerzelius’s system into the background. I t would be a misfortune if such were the result. The Of late years the importance of so-called “molecu- atomic theory need no longer be looked upon as a lar compounds” has been gaining increased recogni- theory, b u t rather as an assemblage of well-proved tion. It has been realized t h a t the valence theory facts, and all chemical theory must rest on t h e atom. and t h e structural formulas based thereon have been The structural formula, furthermore. has proved too inadequate t o represent vast numbers of compounds 1-aluable in organic chemistry t o bc lightly laid aside. between individual molecules within each of which Ait t h e same time there must be somcthing behind the valences seemed t o be completely “satisfied.” the regularities which appealed t o Hcrzelius, and which It was these compounds t h a t called forth Werner’s form so simple a basis for t h e understanding of t h e coniimportant work on t h e ammonia complexes, and his pounds of t h e refractory oxides. theory of principal and secondary valences, which he There exists a considerable 1-aricty of facts which has applied t o a great number of complex compounds, lead unavoidably toward t h e belief t h a t the simpler including crystalline hydrates. molecules retain n certain degree of individuality I n t h e meantime, however, t h e structural formula when they enter into t h e more complex compounds and fixed valence idea had been extended t o t h e in- Water of crystallization, for instance, shows t h e same organic compounds, including even the little-known spectral absorption bands as water in solid solution silicates. Inorganic chains and rings were more and as liquid water itself. It is not necessary t o supcommon in t h e textbooks twenty years ago t h a n they pose, however, t h a t there is any sharp division bcare now, but they still survive. Severtheless, I think tween “molecular” and “atomic” compounds, or b e i t is a fair statement t h a t little or no good resulted tween compounds of different “orders.” We may from t h e inorganic structural formulas, certainly rather expect t h a t there is a continuous gradation from nothing comparable with their yield in the organic compounds in uThich t h e physical properties of the field. The most of t h e m represented no real facts constituents have almost complctcly disappeared, about t h e substance. This is especially true of tlie over t o the “weakest” of molecular compounds, wherc silicates, where t h e attempt t o extend t h e organic t h e physical properties of the constituent molecules idea resulted principally in confusion. Perhaps t h e are almost completely retained. THE STRCCTURE O F C R Y S T A L L I S E COXPOUNDS climax was reached in a recent book b y W. and D. Xsch, in which we are provided with structural forBut no sooner have we convinced ourselves t h a t mulas for window glass and Portland cement. certain molecules (such as t h e refractory oxides) F. W. Clarke’s recent Geological Survey Bulletin retain a considerable degree of their individuality in on “ T h e Constitution of t h e Natural Silicates” is crystalline compounds, t h a n we are informed by t h e based on t h e structural idea, and some of his formulas X-ray analysis of crystal structure t h a t i n - a crystal do have a defensible basis of fact. But the variance t h e molecule has completely disappeared, or rather, between t h e facts and t h e predictions t h a t one might we should say, t h e crystal itself is one huge molecule. reasonably make from these structural formulas is The X-ray spectra of a crystal reveal t o us that, i t very wide. One can sit down with a pencil and paper consists only of atoms, arranged in space in an orderly and construct on t h e valence basis a number of alumi- manner. A crystal of sodium chloride, for instance, n u m silicates, for example, of various empirical for- is only an assemblage of row upon row and layer upon mulas and rarious constitutions for each formula, layer of sodium and chlorine atonis,in which no parand any one of these would seem just as likely t o oc- ticular sodium atom is united t o a n y particular chlorinc cur as another. Yet t h e o n l y aluminum silicate t h a t atom. The word “molecule,!’ in the case of crystalline forms at high temperatures, namely, sillimanite, Al?SiOj! sodium chloride, therefore, no longer represents a n y has t o be laid aside b y Clarke as possibly a “basic meta- concept, as it does in t h e case of a gas. This a p p a r silicate,” a t e r m t h a t calls t o mind t h e unassorted d u m p ently unavoidable deduction has been hard for some heap of ferric hydrates, lead carbonates, and other of t h e chemists t o swallow, and they have sought ways muddy mixtures inherited from the days of “basic salts.” of preserving the molecule in the crystal. Barlow.’ This case of aluminum silicate, from t h e point of for instance, believes t h a t a sufficient degree of symview t h a t I a m trying t o set forth, is comparatively metry t o explain the X-ray patterns can be obtained simple. A1203and S O 2 , being alike in forming many in a sodium chloride crystal by an arrangement of stable compounds with h I g 0 , CaO and other bases, the atoms which still permits a given sodium atom t o may be expected t o form no very stable compounds lie nearer t o one particular chlorine atom t h a n t o a n y with each other. If any compound is formed, the other chlorine, so t h a t these pairs may still be considone most t o be expected is t h a t d i i c h contains the ered real molecules in the crystal. simplest ratio of t h e o x i d e s , namely, I : I . This is 1 Puor. R o y . Soc., 9 1 (1914!, 1-16.
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T17E J O C R W A L O F I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Whether our familiar concept of t h e molecule will survive, when applied t o t h e crystalline s t a t e , is for t h e future t o determine. For t h e present we may content ourselves with t h e conviction t h a t t h e molecule is a t least p o t e n t i a l l y present, for let t h e crystal of sodium chloride be heated $0 its melting point, then each sodium a t o m will seize upon a chlorine a t o m a n d go whirling away with i t into t h e liquid, like t h e individuals in a ballroom who have been sitting quietly on orderly rows of chairs until t h e music s t a r t s , when t h e y suddenly group themselves into pairs which go circling about t h e room. There is considerable evidence, on t h e other hand, t h a t certain compounds t h a t exist in t h e crystalline s t a t e are entirely dissociated in t h e liquid state. T h e concept of molecule, as applied in t h e liquid a n d gaseous states, can therefore have no meaning a t all in t h e case of these compounds. Their formation must be controlled b y forces which come into play only when t h e atoms arrange themselves in orderly patterns; t h e y may b e considered t o be not t h e result of chemical affinities or valences between atoms, as we ordinarily understand such forces i n :t liquid or gaseous molecule, b u t merely t h e result of t h e fact t h a t a n orderly arrangement of atoms has been brought about. I n other words, t h e occurrence of a melting point maxim u m a n d t h e other indications of one of these compounds i n t h e phase-rule diagram might have been predicted, not b y chemistry, but b y geometry. The silicate diopside, CaSiOs. MgSiOs, for instance, m a y be such a compound. Fig. I11 gives t h e curves of specific x-olume against composition for all mixtures of CaSiOi a n d MgSiOs, both i n t h e glassy a n d i n t h e crystalline state. There is no indication of t h e existence of a compound in t h e liquid (unordered or glassy) state. Only when t h e glass is crystallized does t h e sharp maximum of condensation appear a t t h e composition
T h e restilt is a troublesome shrinkage a t temperatures far below t h e melting point of t h e alumina. which is t h e principal constituent of t h e ware; this shrinkage is caused b y t h e combining of SiOz with AI2O3 a n d perhaps with other impurities present, a n d t h e flowing of t h e resulting viscous liquid. An instance of t h e refractoriness of a pure compound is furnished b y t h e very successful “ M a r q u a r d t Porcelain” made b y t h e Royal Berlin Porcelain Works. T h e mineral kaolinite, Al2O3.2Si02.z H 2 0 , t h e principal constituent of fire clay, is not t h e hydrate of a n y hightemperature compound, and when i t is heated i t breaks up. At high temperatures i t becomes t h e n simply a mixture of AlzSiOs a n d SiOn, which if heated for a long time will soften a n d flow a t t h e temperature of t h e eutectic between A12SiOj a n d SiOZ, which is lower even t h a n t h e melting point of SiOn or below 1625’. But if A1203 is added t o a pure kaolin t o make a mixture equivalent in composition t o A12Si05,which is t h e pure compound sillimanite, t h e n a t a high
20
I : 1. PRACTICAL ASPECTS
There are certain principles of practical importance which may be deduced f r o m t h e facts presented in Figs. I a n d 11. In t h e first place it will be observed t h a t t h e maximum melting points i n all of t h e twoa n d three-component systems are t h e melting points of pure stable compounds, a n d t h e highest melting points of all are those of t h e pure oxides AlzOa, CaO a n d MgO. This fact is of particular importance t o t h e maker of refractory mixlures. I n general, it may be said t h a t the addition of , m y substance t o a refractory will t e n d t o lower i t s melting point. One principal line of progress i n refractories must lie, therefore, in t h e direction of greater chemical purity in t h e materials. Of course, high melting point is not t h e only desirable feature of a refractory, nor is i t always t h e most desirable. The ram material must be easily molded or cast a n d easily bonded, a n d t h e product must be mechanically strong. I n order t o get t h e material bonded a n d t o give it strength a n d resistance t o abrasion, i t is customary t o a d d a bonding material. T h e Norton Company’s alundum wares. for instance, contain a variable quantity of a siliceous cement.
989
5
ub
30
M o l per cenf
40
50
4
.&
;.3
9
FIG.111
temperature this compound will form. Once formed, i t will not melt or flow below 181 j o . This is n o t , of course, t h e whole story of Marquardt porcelain. Grinding, mixing, molding, drying, and burning all introduce their difficulties, b u t t h e fundamental principle remains t h a t all these processes are directed toward t h e building of a pure high-melting compound. An interesting phenomenon exhibited b y t h e refractory oxides is t h a t k n o y n as sintering. Any finely powdered substance if held slightly below its melting point will sinter together more or less solidly. T h e nearer t o its melting point a n object made of a pure refractory oxide can be burned, therefore, t h e less binder it will require. There is no reason why a perfectly pure oxide, such as A120s, cannot be made into a dense h a r d refractory without t h e aid of a n y bond, provided only t h a t t h e temperature is under good contro1.l 1 I n the discussion of t h e paper, Mr. Landis stated t h a t in attempting t o carry out the Car0 process for the oxidation of ammonia, catalyzers of cerium oxide, of thorium oxide, and of various mixtures of these oxides had been tried, and t h a t a t a temperature below 800‘ all of these oxides sintered t o an impervious mass on long-time runs.
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Another method of bonding a refractory has been already hinted a t in t h e description of Marquardt porcelain. If a pure high-melting compound of two or more oxides be selected as t h e refractory. it may be made u p b y thoroughly mixing t h e component oxides in finely poxT-dered form. T h e mixture is then molded in the usual way, dried and burned. A t a temperature well below t h e melting point of the compound, the oxides will begin t o unite t o form t h e compound, and this chemical reaction will bind the mass together even more effectively t h a n could be accomplished b y sintering. T h e best example of such a product is magnesium aluminate or spinel, Mg0.A1208. J t has been occasionally used b y individual investigators in Germany for crucibles, tubes. and the like, and a similar mixture, probably impure, has also been made up into forms by the Royal Berlin Porcelain Works. A s is shown in Fig. 1: its melting point is unusually high and its eutectics v i t h its tnvo component oxides melt not much lon-er (192, and Z O ~ O ’ ) . Particular care need not be taken. therefore. t o malie it up in the exact proportion t o form lIgO.Al2O3. I t is t o be regretted t h a t it is not yet available in this country in forms similar t o those of Norton alundum. Amoiig the other facts represented o n the diagrams of Pigs. I ant1 IT, which find appiications in industrial science, wc ma)- mention somc of the properties of the polymorphic forms of the pure oxides. One of the diagrams of Fig. I1 represents t h e volume curves of the forms oE silica. T h e inversion of quartz a t ,?, - a is accompanied by a sudden change of volume, _ r
an expansion in passing from t h e l o n - t o the hightemperature form; so a granite vall in 2 burning building. if it becomes heated t o s;jo, is seriously shattered by t h e inversion of t h e quartz which makes so large a proportion of t h e stone. T h e silica brick cap of a glass furnace. as t h e temperature passes 5 s 5 ’, changes so rapidly in d mensions t h a t a man must be kept a t hand with a wrench t o “follow u p ” the cap. K O ordinary force is able t o resist t h e change; a pile of 4 or j tons of pig iron failed t o keep t h e cap from rising a t 57 j O . 1 Another practical effect is t h e disintegration of silica brick. Brick made of quartz is likely t o be “rotted” or n-eakened by disintegration if heated and cooled repeatedly past t h e 57:’ point. Fused silica, or “quartz glass,” i s only stable above the melting point of cristobalite ( 1 6 2 5 ’ ) . If used a t temperatures below this, i t strives constantly t o crystallize, and t h e speed of crystallization is greater, t h e higher t h e temperature. Hence t h e well-known “devitrification” of silica glass. But it happens that t h e high.-temperature f o r m of cristobalite has practically t h e same density as t h e glass itself, so t h a t if held at a high temperature the material retains its transparency and homogeneity. Only when it passes the a-p in\-ersion point a t zoo t o 2 7 jO does it break up into t h e familiar chalky, devitrified mass. T h e t h e r the cristobalite retains the strength of the glass a t high temperatures I do not know, b u t for some purposes, a t least, it might be interesting t o see whether the 1
Trans, A m . Ceramic Soc., 16 (1913), 519
Val. 8, XO. T I
original advantageous properties of t h e glass mould not be preserved if t h e furnace were not allowed t o cool below 300’. In 1914Mr. F. J. Tone, of the Carborundum Company, sent us what seemed t o be a new crystalline form of silica, consisting of a chalky mass of fine parallel fibers. T h e microscope showed t h a t it was really amorphous, and was in fact a jibrous glass probably deposited from a vapor. This tendency of amorphous silica t o deposit in various fibrous forms is very marked. Crystalline alumina is now used b y t h e hundreds of tons in grinding-JTheels. The crystals are for t h e most part corundum or a-alumina, b u t a certain proportion of p-alumina is also found in t h e artificial abrasi\Tes. One use of this fused alumina which is familiar t o all chemists is in t h e Norton Company‘s “aiundum” articles. We have observed recently t h a t boats made of alundum are extraordinarily constant in weight a t high temperatures, much more so t h a n platinum.’ Platinum steadily loses weight in osygen a t rIoo--Tzoo’> especially when iron oxide is heated in i t , mhereas an alundum boat is constant mithin 0 . I mg. The reason is simple and ob\-ious: platinum is an oxidizable metal and forms a volatile oxide, 17-hile alumina is a completely saturatc:d a n d non-1-olatilc: oxide. At I IOO--IZOO’ the platinum is oxidized b y the oxygen of the air, and the oxide is carried remains ~ unchanged. a v a y > while t h e B l ~ O l I a n y other facts with their practical applications could be brought out b y going through t h e diagrams in detail, but I beliere t h a t enough has been said t o show t h a t future progress in t h e application of our knoTT-ledge of the common refractory oxides must follow two principal lines: (I) c o n t r o l o j t h e pzgrity o/ Tnatesials, and ( 2 ) a c c u r a t e control oJ high t e f n p e r a tzrres. Cmxnysic.ik LABORATORY CARNEGIE I N S T I T U T i O N O F \\‘,ASIIINGTOX LVASHINGTOK,
D. C
SOME EXPERIMENTS ON THE CONCENTRATION OF RADIUM 1N CARNOTITE ORES By &BERT
G.
L O O M I S A N D HERM.4N SCHLUNDT
Received June 24, 1916
The investigations2 of t h e United Sta.tes Bureau of Alines have emphasized the fact t h a t t h e carnotite deposits of Colorado and Ctah constitute t h e principal source of radium in the United States. I n recent years these ores h a r e also become one of t h e main sources of t h e radium produced abroad. Abouz a year ago the Standard Chemical Company published the’statement3 t h a t in the year 1914it had produced 18 grams of hydrous radium bromide, equivalent t o 9.6 grams of radium element, and t h a t its total production up t o 1Iarch I , 191j, had reached t h e handsome figure of 2 4 . 3 gra.ms of the bromide. Hostetter and Sosman, J . A m . Chem. Soc., 58 (1916), 118X-Il‘iX Moore and Kithil, “ A Preliminary Report on Uranium, Radium and Vanadium,” Bureau of Mines, Bull. 70 (1913); Parsons, Moore, Lind and Schaefer, “Extraction and Recovery of Radium. Uranium and \’anadium from Carnotite,” Bureau of Mines. Bull. 104 (1915). 3 Viol. “The Radium Situation in America,” Radium, 4 (19151, 106 1
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