INDUSTRIAL AND ENGINEERING CHEMISTRY
1060
CONCLUSIONS The experimental results reported in this paper indicate : 1. Expansion of cement pastes stored in water is a function of the content of 3Ca0.AleOs (or ratio of alumina to ferric oxide), sulfur trioxide, magnesia, and free calcium oxide. The effect of the 3CaO.AlnOs content has been found to be slight when present in computed amounts of 7 per cent or less. (In the cements used, this corresponds to a ratio of alumina to ferric oxide of about 1.3.) The influence of sulfur trioxide is slight when present in amounts not exceeding 2 per cent, and larger quantities are ineffective provided the 3Ca0.AlZOa content is low. The magnesia may produce excessive expansions at ages beyond 3 months when present in amounts above about 5 per cent. The free calcium oxide may result in excessive expansions during the first week when present in amounts above about 2 per cent. 2. Contraction of cement pastes stored in air increases with increasing 3CaO.Al~03content (or ratio of alumina to ferric oxide). 3. Susceptibility to attack by solutions of sodium and magnesium sulfate is found to be determined primarily by the 3Ca0.A1203content (or ratio of alumina, to ferric oxide) of the cement. When the 3CaO.Al2Oais present in amounts computed to be 7 per cent or less (ratio of alumina to ferric oxide of about 1.3 in the cements studied), the specimens show high resistance to sulfate solutions, but the resistance diminishes rapidly as the 3Ca0.AlzOacontent (or ratio of alumina t o ferric oxide) increases above the amounts given previously. The presence of magnesia in amounts above about 5 per cent increases slightly the susceptibility to attack by sulfate solutions. 4. Chan es in the 3CaO8iOt and 2CaOSiOn contents of the cement fave been found not t o alter the order of magnitude of the volume changes or resistance to sulfate solutions except that very low 3CaO.SiOz cements o‘f high 3Ca0.A1203content ma be attacked more rapidly by sulfate solutions than cements of Lgher 3CaO8i02 content containing the same percentage of 3CaO.Al208. 5. Specimens of the cements prepared of lean mix and high water-to-cement ratio were found to be less resistant to the action of sulfate solutions than those made of a rich mix and low water-to-cement ratio. However, certain changes in cement composition were found to have a greater effect upon resistance to sulfate attack than changes in the richness of the mix and water-to-cement ratio, within the limits studied.
analysis of the experimental findings has led to the following interpretation of effects:
1.
Vol. 26, No. 10
VoIume changes in some constituents of the cement may
be caused by: (a) the direct hydration of the cement compounds
to form crystalline or amorphous products of increased volume; ( b ) the colloidal swelling and contraction of the amorphous hydrated calcium silicates and calcium ferrite with changes in the water concentration of the environment; (c) the combination of 3CaO.AI203 and water with the calcium sulfate added as a retarder to form calcium sulfoaluminate; or ( d ) the formation of addition products due to the reaction of some of the constituents of the cement with salts in the solution surrounding the specimen. 2. Weakening and disintegration may furthermore be caused by a loss of cementing materials by chemical actions of base exchange and a consequent leaching out of essential hydraulic components of the structure. 3. The rate with which the reactions enumerated above take place may be governed by: (a) the composition of the cement or ( b ) the nature of the paste.
LITERATWRE CITED (1) Am. SOC.Testing Materials, Proceedings, 28, Pt. 1, 233 (1928).
(2) Am. SOC. Testing Materials, Standard Spec. for Portland Cement C 77-32; Federal Spec. for Portland Cement SS-C-191. (3) Ashton and Wilson, A m . J. Sci., 13, 209 (1927). (4) Bates, Eng. News-Record, 110, 492 (1933). (5) Bates, Proc. A m . SOC.Testing Materials, 33, Pt. 2, 462 (1933). (6) Bogue, IND. ENG.CHEM.,Anal. Ed., 1, 192 (1929). (7) Carlson and Bates, Eng. News-Record, 107, 130 (1931). (8) Fleming, Eng. J., 16, 215, 260 (1933). (9) Hughes, Proc. Am. SOC.Testing Materials, 33, Pt. 2 , 511 (1933). (10) International Critical Tables, Vol. I, McGraw-Hill Book Co., New York, 1926. (11) Johnson, “Materials of CoMtruction,” 6th ed., p. 384, John Wiley & Sons, New York, 1925. (12) Klein and Phillips, Bur. Standards, Tech. Paper 43 (1914). (13) Lerch, Ashton, and Bogue, Bur. Standards J . Research, 2, 715 (1929); reprint 54. (14) Lerch and Bogue, IND.ENG.CHEX, Anal. Ed., 2, 296 (1930). (15) Lerch and Bogue, J. Phys. Chem., 31, 1627 (1927). (16) Merriman, Eng. News-Record, 104, 62 (1930). (17) Miller and Manson, U. S. Dept. Agr., Tech. Bull. 358 (1933). (18) Shelton, IND.ENO.&EM., 17,589 (1925); 18,854 (1926). (19) Thorvaldson, Vigfusson, and Lamour, Trans. Roy. Soc. Caanado. 111, [3] 21 (1927); Thorvaldson, Wolochow, and Vigfusson, Can. J . Research, 6 , 485 (1932). (20) Wells, Bur. Standards J . Research, 1, 951 (1928); reprint 34. RBCEIYEDJune 13, 1934. Publication by permisaion of the Direator, National Bureau of Standards. This is Paper No. 28 of the Portland Cement Association Fellowship at the Bureau of S t a n d a r b .
Liberation of Fluorine in Fluoride Glass Manufacture HENRY H. BLAU,Macbeth-Evans Glass Company, Charleroi, Pa., AND ALEXANDER SILVERMAN, University of Pittsburgh, Pittsburgh, Pa.
T
HE behavior of fluorine during the formation of glasses,
glazes, and enamels has long evoked controversies. These discussions have involved not only the role of the fluorine retained in the resulting products but also the possible ways in which i t may be liberated during the melting processes. Unfortunately, in many of these publications the conclusions have been derived from limited data b y the application of orthodox but not fully warranted hypotheses.
PASTINCONSISTENCIES Most of the earlier workers ascribed the liberation of fluorine to the formation of silicon tetrafluoride by reactions of the type: 2CaF2 9iO2-+ 2Ca0 SiFl
+
+
Vogt (16) stated that all of the fluorine introduced in porcelain glazes was evolved in this way. Bock (2) and Poste and Rice (16) similarly reported that all of the fluorine was liberated as silicon tetrafluoride from the enamels which they investigated. Griinwald (7) and Eyer (S), while retaining the view that the fluorine was evolved as silicon tetrafluoride, maintained that only part of the fluorine was retained in finished enamels. Muschiol (12) confirmed their views as to the partial loss of fluorine in the commercial production of enamels. Mayer and Havas (IO) upheld the theory of partial loss of fluorine for enamels but attributed the loss to the evolution of silicon tetrafluoride and boron fluoride. Musiol (IS), using Vogt’s percentage compositions and the assumptions that fluorine and the alkalies alone were lost from the melts, concluded that fluorine was liberated as such or as sodium fluoride, potassium fluoride, or aluminum fluoride, without the forma-
ENGINEER Ii Y G C H E M I S T R 1-
I K DUSTR I A L A N D
October, 1934
tion of silicon tetrafluoride. Hansen (8) in a contributed discussion refuted Musiol’s contentions and showed from similar data that the loss as silicon tetrafluoride and boron fluoride was more probable for enamels. Agde and Krause (1) investigated the materials actually evolved from enamels and found no fluorine or silicon tetrafluoride. They concluded that the sublimation of fluorides in the early stages of fusion explained the volatility losses. Otremba (14) reported that the losses occurred as silicon tetrafluoride from enamels made from sodium fluosilicate. Gehlhoff, Iialsing, and Thomas (6) concluded that the evolution fronl ghSSeS OCcurred as silicon tetrafluoride and sodium fluoride, depending upon the preponderance of silica and sodium oxide in the composition employed. They stated that with technical glasses containing 65 Per cent 01 more silica, the fluorine would be lost mostly aS silicon tetrafluoride and to Only a slight extent as sodium fluoride. A detailed review of the literature not only revealed these inconsistencies but showed that percentage compositions had been used without the coincident initial and h a 1 weights. Assumptions also were frequently made that tlie content of certain constituents remained constant throughout the melting processes. The situationis further complicated by the fact that not only were certain constituents liberated, but that silica, alumina, etc., are gained as a result of the solution of the refractory containers in which the fusions are carried out commercia~y and in most experblental work. To eliminate these difficulties, the melting processes of the present investigation were carried out with materials of unusually high purity in platinum receptacles under wellcontrolled and predetermined conditions.
SIMPLE GLASSES Two series of glasses have been prepared in which the compositions of the syntheses are as shown in Table I. TAB-
I.
GUssEe
COMPOSITIONS OF
.Series A: Silica Calcium fluoride Sodium carbonate Sodium fluoride SiOn NatO CaO
1
2 100.0 100.0 20.0 20.0 36.0 28.7 6.0 100.0 100.0 20.6 20.6 14.1 14.1 9.6 11.8 14.6 11.9 1 2 100.0 100.0 6.0 7.8 7.8 21.6 21.6 26.6 19.2 100.0 100.0 20.6 20.6 14.1 14.1 9.6 12.1 14.6 11.7
...
F
COl Series E: Silica Calcium fluoride Sodium carbonate Sodium fluoride Calcium carbonate SiOn NazO CaO
...
F
coz
3 4 100.0 100.0 20.0 20.0 22.4 16.1 10.0 16.0 100.0 100.0 20.6 20.6 14.1 14.1 14.1 16.3 9.3 6.7 8 4 100.0 100.0 10.0 16.0 7.8 7.8 21.6 21.5 12.8 6.4 100.0 100.0 20.6 20.5 14.1 14.1 14.6 16.9 8.9 6.1
All of the compositions have the same contents of silica, sodium oxide, and calcium oxide, and the fluorine is progressively increased. In series A this is accomplished by additions of sodium fluoride with coincidental adjustment of the sodium carbonate. In series B this progression is brought about by addition of calcium fluoride with the compensation of the calcium content by the reduction of the cal-
1061
cium carbonate. (The association of the sodium and calcium with oxygen in this tabulation is made on an entirely arbitrary basis without attempt to adjust the oxygen content for its fluorine equivalent.) The variation in carbon dioxide content is merely coincidental. On a basis of comparison, neglecting the carbon dioxide content, syntheses A1 and Bl are identical.
Raw MATERIALS AND MELTING PROCEDURES These syntheses were made from chemically pure, analyzed materials. The silica was a purified quartzite with a ferric oxide content of slightly less than 0.005 per cent, The talcium fluoride contained small amounts of magnesium and alkalies as impurities. The melting technic closely resembles that employed by Faraday (4, 6)in his early but monumental work on optical glass : s
t
~
~
~
e
(~ $ $~ o$l s ~~~~ ~~ ~ ~ ~ ~ g G~ ~ ~ ~ ~
re,Snforced by fitting them into small holders hollowed out of Babcock & Wilcox NO. 80 refractory. This refractory not only served as reenforcement for the platinum vessel but also provided a means of readily introducing and removing it from the furnace with the assurance that the materials of the fusion did not come in contact with any foreign substances such as refractory, metallic tongs, etc., other than the platinum pan itself. Each fusion had a total weight of approximately 30 grams and an area of 6 X 6 cm. with a depth of 1.25 cm. The melting was carried out in an electric furnace employing silicon carbide (Globar) resistors as heating elements. Prior to melting, the batches were dried overnight at 110’ C. Approximately two-thirds of each batch was placed in its platinum receptacle and brought up to 1425” C. at the rate of 10’ per minute. On attaining this temperature, the balance of the batch was added, and the fusion maintained at 1425’ C. for one hour. After this period the fusion was complete. The glasses were then removed from the furnace and permitted to cool quickly to room temperature. Table I1 sets forth the losses in weight occurring during the drying and fusing processes. Glasses A2-2, B1, and B2 were melted simultaneously, whereas A2-3 was of identical composition with A2-2 but was fused in a aecond independent melting operation. The satisfactory agreement of the losses for these duplicates is noteworthy.
ANALYSESOF GLASSES The resulting glasses were ground in a clean agate mortar to a size of less than 100 mesh, and samples were analyzed to determine the contents of silica, calcium oxide, sodium oxide, and fluorine. This was done by applying the Hoffman and Lundell modification (9) of the Berzelius method. Spectrographic analyses were also made covering the wave length range from 2400 to 6700 1. These revealed the presence of small amounts of lithium and magnesium, together with mere traces of aluminum, iron, chromium, and titanium. Table I11 sets forth the analytical data together with values derived from it by using the weights of the batches and resulting glasses. The items in Table I11 under “unaccounted fluorine” indicate the fluorine lost to the melt, for which there have been no equivalent losses of silica, sodium oxide, or calcium oxide. These values were obtained by deducting from the total fluorine loss, the sum of the fluorine equivalents corresponding to the silica, sodium oxide, and calcium oxide
TABLE11. LOSSESIN WEIGEITDURING DRYING AND FUSING WBIQBTS(in grama)
r
Before GLMS drvinn A2-2” 30.725 A2-3 80.727 B1 30.901 B2 30.658 B3 30.403 B4 30.151 Number after dash indicates
- -
a
Total after drvine 30.602 30.607 30.865 30.615 30.345 30.084 the number of the melt of -
I
PERCENTAGE^
Total after meltine 26.680 26.675 26.818 26.744 26.643 26.394 batch A2.
-
Melting 1088
3.922 3.932 4.047 3.871 3.702 3.690
Drying loss 0.4 0.4 0.1 0.1 0.2 0.2
iMelting loss 12.8 12.8 13.1 12.6 12.2 12.3
COT ID
bat.& 7.7 7.7 9.4 7.7 5.9 4 2
-_____
1.oaaaa
other than theoretical
cog 6.1 5.1
3.7 4.9 6.3 8.1
1062
INDUSTRIAL AND ENGINEERING CHEMISTRY
losses on the respective bases of silicon tetrafluoride, sodium fluoride, and calcium fluoride. The results of these calculations indicate that more than half of the fluorine introduced has been lost in some form other than these fluorides and that the conventional conceptions of these losses apparently account for relatively small percentages of the total losses. AMOUNTS PERCENTOF CONh e. A.R RS OP -S E- -s . -. . PER- COMPN.STITUENTB AMOUNTS IN EACH CON- CENTAQES CALCD. RETAINED L o s ~ EQVIVA-CONA2
Si02 NarO CaO
F B1
FROM
ANALYSIS BATCH 74.1 100.0 14.5 20.5 10.0 14.1 2.6 11.8
Si09 NazO CaO
74.2 14.2 10.4 2.1
100.0 20.5 14.1 9.6
Si02 Nag0 CaO
74.2 13.9 10.4 2.7
100.0 20.5 14.1 12.1
F B2
BY
F
IN
IN
GLASS MELTINQ 99.1 0.9 19.3 1.2 13.3 0.8 3.5 8.3 Unaccounted F 99.6 0.4 19.1 1.4 14.0 0.1 2.8 6.8 Unaccounted F 99.3 0.7 18.6 1.9 13.9 0.2 3.6 8.5 Unaccounted F
LENTS STITUENT
OFF 1.1
0.7 0.5
6:O 0.5 0.9 0.1
i:3 0.9 1.2 0.1
6:3
LOST 0.9 5.9 5.7 70.4 50.9 0.4 6.8 0.7 70.8 55.2 0.7 9.3 1.4 70.2 52.0
There are indications that a small amount may be evolved as silicon tetrafluoride, sodium fluoride, and calcium fluoride. There are even definite indications that the more sodium fluoride or calcium fluoride introduced as such, the greater is the loss of sodium or of calcium. The data even suggest the probability that both sodium fluoride and calcium fluoride are lost as a result of the individual vapor pressures of these compounds during the earlier stages of melting, but that some sodium fluoride is evolved from the fusion during the more advanced stages or even after the subdances are in solution. It is also noteworthy that the total fluorine loss was found to be an almost constant percentage of the amounts introduced.
MECHANISM OF FLUORINE LIBERATION The possible explanations of the losses of fluorine, for which there are no equivalent losses of more electropositive elements, are not entirely satisfying. Perhaps the most tenable hypothetical reactions for this purpose are of the following types:
+ 2CaF2 + O2+2CaO&O, + 2Ft +CaFz 4NaF + Oz ---t 2Na?O.S102 + 2F1 + == Ca08i02 + FzO + 2NaF ++O2 0, NazO+liOz + FzO + CaFz + HzO CaOSiOz + 2HF + 2NaF + HzOz==t Na20.Si02+ 2HF + 3HzO 6HF +
2Si02 2Si02 Si02 SiO; Si02 Si02 3Fz
08
It seems improbable that silicon tetrafluoride is first formed and then, before leaving the melt, reacts with water so that the fluorine is evolved as hydrogen fluoride in accordance with the reaction: SiFa
+ 2H20 a SiOl + 4HF CONCLUSIONS
TABLE111. ANALYTICALDATA
STITVGLASS ENTS
Vol. 26, No. 10
(1A)
(a (2Bj (3A)
(3B) (4)
The extremely electronegative character and great reactivity of fluorine, as well as the well-known difficulties of oxidizing the fluorides to form the element, hardly favor the acceptance of reactions of type 1. On the other hand, the anomalous liberation of fluorine on the mere pulverizing of certain fluorites has been reported by Becquerel and Moissan (11)and others, Reactions of type 2 are possible but hardly probable. Reactions of type 3 may be looked upon as a sumfnation of reactions 1 and 4. They may be considered as being in better agreement with conventional chemical views. The roles of silica and water in these reactions offer interesting fields for further investigation. The great reactivities of fluorine and hydrogen fluoride would have prevented the identification of these substances in the reaction products in the work of Agde and Krause (1). Similarly, it is entirely possible that reactions 1, 2, or 3 are primary reactions in the commercial melting of glasses and that these highly reactive products are evolved only to react or dissolve as they pass through the bed of melting materials, which is ordinarily much deeper than was the case in the present experiments.
Accordingly, i t may be concluded that: 1. Relatively small percentages of the total fluorine are evolved as silicon tetrafluoride, sodium fluoride, or calcium fluoride from fluoride glasses. 2. Appreciable amounts of calcium are lost, particularly when the fluorine is introduced as calcium fluoride. 3. The loss of fluorine is almost a constant percentage of the amounts of fluorine introduced in the batches investigated, irrespective of its introduction as sodium fluoride or calcium fluoride. 4.1 Most of the fluorine loss may be attributed to its liberation from the melt in the elemental form, as the oxide of fluorine, or as hydrogen fluoride.
LITERATURE CITED Agde, G . , and Krause, H. F., 2. angew. Chem., 40, 886-95 (1 927). Bock, B.,Chem.-Ztg., 32, 730 (1908). Eyer, G., “Emaille-Wissenschaft,” p. 50, Verlag “Die Glashutte,” Dresden, 1913. Faraday, M., “Experimental Researches in Chemistry and Physics,” F. 231,Richard Taylor & Wm. Francis, London, 1859. Faraday, M., Phil. Trans., 120, 1 (1830). Gehlhoff, G.,Kalsing, H., and Thomas, M., 2. tech. Physik, 12, 326-7 (1931). Grunwald, J., “Abhandlungen aus der Eisenemail und Verzinnungstechnik,” pp. 146,153,154,F. Stoll, Jr., Leipzig, 1910. Hansen, J. E.,J. Am. Ceramic SOC.,7 , 115-17 (1924). Hoffman, J. I., and Lundell, G . E. F., Bur. Standards J. Research, 3 , 581-95 (1929). Mayer, M., and Havas, B., Chem.-Ztg., 33, 758 (1909). Moissan, H.,“Traite de chimie min6rale,” Vol. I, p. 64,Masson et Cie, Paris, 1904. Muschiol, E., Keram. Rundschau, 34, 4 (1926). Musiol, C., J. Am. Ceramic Soc., 7 , 105-15 (1924). Otremba, A.,Keram. Rundschau, 33, 343-5 (1925). Poste, E. P.,and Rice, B. A., J. Am. Ceramic SOC.,1, 221-34 (1918). Vogt, G . , Sprechsaal, 42,345-6 (1909). RECEIVBD August 6, 1934. Presented before the Division of Industrial and Engineering Chemistry a t the 88th Meeting of the American Chemical Society, Cleveland, Ohio, September 10 t o 14,1934. This paper is Contribution 288 from the Department of Chemiatry, University of Pittsburgh. 1 Similar conclueions seem t o have been reached recently by the Russian investigators I. I. Kitaigorodski and S. M. Kurouskaya in work not aa yet available in this country.
In the paper by Clark, Flege, and Ziegler on CORRECTION. “Surgical Catgut Ligatures’’ [IND.ENG. CHEM., 26, 440-5 (1934)] it was by no means the intention of claiming originality or priority in depicting the general theory of protein structure (for example, in the sentences under the formula, first column, page 442, and two paragraphs under Figure 2, page 443). Full credit for the generalized theory and even for many of the phrases which have come into general use is due W. T. Astbury, the present paper being a confirmation of his ideas although specifically concerned with ligatures with which Astbury has not worked. Although specific reference is made to Astbury in the third line and near the center of the first column on page 442, in the paragraphs above mentioned his name was omitted through unfortunate oversight during condensation. In these places and others dealing with proteins in general it should be understood that the ideas of Astbury are directly stated and utilized in interpreting these new experimental results on ligatures. G. L. CLARK
