I S D C S T R I A L A S D ENGINEERING CHE;MISTRY
December, 1926
No silicon was detected in melt 2827, although it was sparingly present in melt 2828. The loss in strength and the gain in ductility peculiar to the annealed specimens are accounted for by the expulsion of Mg2Si and silicon from solution during slow cooling (compare Figure 5 with Figure 4). Melt 2831 (8.91 Mg, 4.95 Si, 0.60 Fe est.) was the only other alloy examined metallographically. It is nearly of eutectic (Al-MgBi) composition (Figure 6). Besides the abundant binary eutectic (Figures 11 and 12) duplex needles (Figure 13) and skeletons of the iron-bearing compounds, the blue-gray constituent, binary AI-Si eutectic (Figure 13) were the structural features. In the cope part of the tension specimen liquation caused the appearance of pri-
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mary Mg&i (Figure 7). The cross section of one of these large hexagonal plates of primary magnesium silicide is shown in Figure 14. Fan-shaped ternary areas containing silicon, such as obtained in melts 2827 and 2828, were absent in melt 2831. Binary AI-Si eutectic in the last melt was always associated with segregated, duplex iron-bearing needles (Figure 13). After having been quenched and aged melt 2831 had no abnormal characteristics. The iron-bearing particles tended to roundness, as did the excess MgzSi (Figure 8); and while the silicon was retained in solution, the blue-gray constituent was unaltered. The annealed specimen showed even more ostensible rounding of MgzSi and a small quantity of particles of silicon (Figure 9).
The Rate of Polymerization of Perilla Oil' By Maximilian Toch and T. T. Ling TOCHBROTHERS, NEW YORK,N. Y.
ERILLA oil is obtained from the seeds of perilla plants which grow in China, Japan, and India. The seeds average 38 per cent of oil. Aside from its edible value, the oil is used in the manufacture of varnishes in the oriental countries. During recent years perilla oil has been imported into the United States. Early investigators'?* reported perilla oil as a valuable raw material for the manufacture of paints and varnishes, but its scarcity and high price have prevented it from being widely used. However, the present demand for the oil has already created a market and there is no doubt that it will be employed more extensively in the future. The analytical constants of perilla oil are very close to those of linseed oil. However, the former is characterized by its high iodine number, 196 to 206, which is the highest among all known drying oils. Many investigators2J have reported different results with regard to the drying properties of perilla oil. Some have found such phenomena as formation of droplets, running into streaks, tendency to creep, and slow drying as compared with linseed oil, while others have not noticed these condit,ions and have taken opposite views. These different results may be due to factors such as the source and species of the seeds, the methods of extraction, and the treatment of the oil. From a number of samples the writers have found that perilla oil generally dries twelve hours sooner than linseed oil, and produces a satisfactory film. I t has been observed that the dried film turns yellow more quickly than that of linseed oil. This is natural on account of the greater degree of unsaturation, as indicated by the iodine number, so that more oxidation products are formed. The chemical composition of perilla oil has not been thoroughly investigated. Bauer4 states that it consists of the glycerides of 88 per cent unsaturated acids and 12 per cent saturated acids. They are chiefly linoleic, isomeric linolenic, palmitic, and oleic acids.
P
Previous Work
Perilla oil is often used by manufacturers of paints and varnishes in the form of "bodied" oil. Bodied perilla oil, like all other bodied drying oils, is obtained by heating the oil at an elevated temperature. The effect of heat upon linseed oil and China wood oil has been thoroughly investi1
Received June 18, 1926.
* Numbers in text refer to bibliography at end of paper.
gated.'-9 In the case of linseed oil there is an increase in specific gravity, refractive index, and acid number and a decrease in iodine number, while in the case of China wood oil there is an increase in specific gravity and a decrease in refractive index, acid number, and iodine number. I n both instances the molecular weights have increased and it is therefore considered as being a polymerization process. Lewkowitsch states that no doubt polymerization also takes place on the heating of perilla oil. GardnerlO heated perilla oil to 300", 400", and 500" F. separately in open beakers for 10 minutes. After cooling, the results of his analysis showed a slight increase in specific gravity and saponification number and a decrease in acid number and iodine number. Bodying of Perilla Oil
The laboratory experiment by Gardner did not attempt to produce a bodied oil which was used by varnish makers. Practically no data on either laboratory or commercial production of bodied perilla oil have been reported. The authors have tried various methods of bodying perilla oil, both in the laboratory and on a commercial scale. A sample of raw perilla oil studied in the laboratory showed the following analytical constants : Specific gravity (20' C.) Refractive index (25' C.) Acid number Iodine number
0.9134 1.4812 3.10 201
Three hundred cubic centimeters of raw perilla oil were heated in a 500-cc. Erlenmeyer flask at a temperature of 580"F. To another lot heated in the same way air was blown through. The rate of the polymerization was checked by the determination of the refractive index of a drop of oil drawn out at quarter-hour intervals. Indices (25" C . ) of Perilla Oil Heated Alone at 580' F. a n d Air-Blown after Heating Time
Table I-Refractive Hours
2'2L / r 2 1' 1 23/4
3
Heat alone 1.4812 1.4819 1.4826 1.4839 1.4849 1.4860 1.4869 1,4879 1.4887 1.4892 1.4898 1.4904 1.4909
Heat and air 1.4812 1.4817 1.4827 1.4845 1.4861 1.4873 1.4885 1.4896 1.4904 1.4913 1.4919
....
....
IXDCSTRIAL A X D E N G I S E E R I S G CHEMISTRY
1286
The final analytical constants of these two samples of bodied oil were: Specific gravity ( Z O O C.) Refractive index (25' C . ) Acid number Iodine number
Heat alone 0.9672 1.4914 13.62 141
Heat and air 0,9722 1.4923 12.22 138
Evidently, air shortens the time of perilla oil to reach its desirable consistency and produces a bodied oil of lower acid number. Whether air acts merely as an oxidizing agent or a catalytic agent on the polymerization of perilla oil requires further investigation. The air-blown oil is, however, much darker in color than the one bodied by heat alone. The dark color was probably due to the presence of decomposition products caused by the oxidation of the oil which could not be avoided when air was bubbled through it a t such elevated temperature. If air is blow711 through the oil at a lower temperature, a lighter oil can possibly be obtained. Polymerization
One hundred gallons of raw perilla oil were charged into a 150-gallon monel kettle. The kettle was then set over a coke fire. After 3 hours' heating the temperature reached 580" F., a t which point the oil was bleached to a pale yellow and remained so throughout the heating process. The temperature was kept constant a t 580" F. for 4 hours before the kettle was removed from the fire and allowed to cool. It was noticed during the heating that considerable volatile matter was given off. This volatile matter attacked the membrane of the eyes and throat and had the odor of acrolein. There were also present combustible gases and moisture. The total loss due to the volatile matter was approximately 5 per cent by volume. Samples of oil were drawn out with a dipper a t the end of the first hour and a t half-hour intervals thereafter. These samples were kept in 500-cc. bottles, tightly corked and sealed for examination. Methods of Examination
During the course of polymerization of perilla oil, the changes in specific gravity, refractive index, acid number, iodine number, and molecular weight were examined. The resulting data are given in Table 11. Tat,le 11-Changes i n Properties of Peril la Oil duriing Pol)rmerizatiaIn Temper- Specific Refractive MolecAcid ature gravity index Iodine iilar Time O F. (20' C . ) (25' '2.) number number weight 7:OO Start 0.9316 1.4808 0.85 205.3 753 8:OO 200 0.85 0.9317 1.4809 759 204.6 204.5 8:30 300 0.85 0.9318 1.4809 766 9:00 380 1.00 0.9319 1.4809 204.6 780 204.1 9:30 480 1.09 800 0.9320 1.4810 196.5 1O:OO 570 84 1 1.57 0.9332 1.4815 186.5 10:30 580 1.4832 867 2.67 0.9384 172.9 11:OO 580 0.9450 1.4848 994 3.59 1133 4.43 161.1 11:30 580 0.9506 1.4863 0.9554 1.4875 5.54 1234 12:OO 580 154.0 1312 147.4 6.57 12:30 580 0.9598 1.4885 1432 7.58 1:OO 580 146.0 0.9630 1.4895 144.6 1:30 580 1540 0.9659 1.4903 8.34 2:00 580 143.0 1586 0,9687 1.4909 9.85 10.37 1612 141.5 2:30 530 0.9700 1.4915 1650 10.65 139.7 3:OO 480 0.9711 1.4915
The specific gravity was determined by the use of a 25-cc. pycnometer at 20" C. The refractive index was measured by means of a Zeiss ,4bb6 refractometer a t 25" C. The acid number was obtained by refluxing about 10 grams of oil in 50 cc. of a neutral benzene-alcohol mixture for a half hour and titrating against a 0.1 N alcoholic sodium hydroxide solution. The iodine number was determined by the Wijs method. Approximately, 50 per cent excess of Wijs' solution was added and the absorption allowed to proceed for 2 hours in each determination. The molecular weight was determined by the freezing point method in benzene. The portion of redistilled benzene which
Vol. 18, No. 12
was used came over between 79.8" and 80.3" C. under a barometric pressure of 765 mm. By means of pure naphthalene the freezing constant of this benzene was found to be 51.04. I n each determination 12 to 13 grams of benzene and 0.5 to 0.6 gram of oil were used. Discussion of Results
SPECIFICGRAVITY-There was very little change in the specific grarity for the first 2.5 hours while the oil was heated below 500" F. As soon as the oil reached 580" F. there was a rapid increase in specific gravity. The greatest increase occurred between the third and fifth hour, then it became slower toward the completion of the process. After 8 hours' heating the total increase in specific gravity over that of the raw oil was 0.0395. REFRACTIVE IsDEx-The change in refractive index is directly proportional to the change in specific gravity. The total increase in refractive index was 0.0107. 4 s the measurement of refractive index requires but a moment, it offers a convenient method for controlling the process of boiling the oil. ACID NuMBER-Jvhen the polymerization of perilla oil took place, there was a rapid increase in acid number, which followed more or less in the same rate as the increase in specific gravity and refractive index. Fichandlerll boiled linseed oil under practically the same conditions as the authors and found that there ~7~a.salso an increase in acid number. The increav in acid number for both oils is almost identicalfrom 0.92 to 11.3 for linseed oil, and from 0.85 to 10.37 for perilla oil. The increase in acid number, as explained by Coffey,lZis due to the direct hydrolysis of the glycerides by water. The glycerol produced by hydrolysis would also decompose at high temperature into acrolein and water, which formed part of the constituents of the volatile matter. IODINE SUhfBER-The iodine number decreased as the oil polymerized. Below 500" F. the iodine number remained almost unchanged, but on reaching 580" F. there was a rapid drop and this continued for 2 hours, after which it dropped more slowly. I n comparison with the change in linseed oil, determined by Fichandler, perilla oil showed a much slower drop in iodine number when it was first heated, but when it reached 580" F. the rate of decrease in iodine number was much more rapid. This indicates that a t comparatively lower temperatures linseed oil polymerizes more quickly than perilla oil, while at comparatively higher temperatures the reverse is the case. MOLECULAR WEIGHT-The rate of increase of the apparent molecular weight of perilla oil has presented some interesting facts which may serve as a criterion for testing the prevailing theories of the mechanism of polymerization. The increase of the molecular weight took place simultaneously with the changes of the other constants. The rate varies directly with the changes in specific gravity, refractive index, and acid number, and inversely with the iodine number, This shows that the degree of polymerization can be checked up by any one of the other constants. Theory of Polymerization
According to Salway,13 the polymerization of drying oil begins with a liberation of one or more fatty-acid radicals, which condense with the unsaturated linkages of the fatty oil, forming a diglyceride. Then there is a further condensation of the diglyceride to form a polyglyceride. Salway's theory is supported by the fact that the decrease in iodine number is accompanied by a decrease in acid value. However, he could not furnish any evidence as to the formation of the polyglyceride. Long and Wentz'4 determined the rate of molecular weight in the boiling of linseed oil and were inclined to confirm Salway's theory. The results of laboratory experiments have not always
INDUSTRIAL AND ENGI.VEERIh'G CHEMISTRY
December, 1926
agreed with those from the factory method of boiling drying oils. As discussed under acid number, in both thch boiling of linseed oil and perilla oil there was an increase in acid number, which is contradictory to some of the laboratory experiments. The presence of a minute amount of water in the oil would hydrolyze the glycerides, forming glycerol and free fatty acids. Some of these free fatty acids probably condense a t the unsaturated linkages of the oil as explained by Salway. Some may volatilize, while others remain in the oil. It was shown that the air-blown oil has a lower acid number than straight heat-bodied oil, for the air would increase the speed of the evaporation of the free fatty acids. Conclusion
1-The polymerization of perilla oil, like that of linseed oil and China wood oil, takes place at high temperature (above 500" F.) with the evolution of volatile matter. This is shown by the increase of molecular weight of perilla oil during the course of heating. 2-The figures for iodine number curve show that the higher the temperature, the more rapidly perilla oil polymerize$. However, perilla oil does not begin to polymerize as soon as linseed oil, but on reaching comparatively higher temperatures the polymerization proceeds more rapidly.
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3-Although viscosity test is a common pract'ice among varnish makers, the rate of polymerization of perilla oil can also be followed by examining the increase in specific gravity and refractive index, and the decrease in iodine number. 4-When perilla oil is heated in the laboratory and on a large scale, there is always an increase of acid number, which disagrees with the result of some previous invest'igators. Bibliography I-Proc. A m . Soc. Testing Materials, 16, Pt. I , 275 (1916); Paint Mf7s. Assoc. U . S.,Circ. 52, 106, and 257. 2-Lewkowitsch, "Chemical Technology and Analysis of Oils, F a t s , and Waxes," 1922, Val. 11, p. 42. 3-Morrell a n d Wood, "Chemistry of Drying Oils," 1925, p. 56. 4--Bauer, Farben-Zlg., 27, 2766 (1922). 5-Lewkowitsch, "Chemical Technology and Analysis of Oils, F a t s and Lvaxes," 1923, Val. 111, p. 134. 6-Morrell and Wood, "Chemistry of Drying Oils," 1926, p. 158. 7-Ingle, J . SOL.Chem. I n d . , 30, 344 (1911). 8-Krumbhaar, Chem.-Ztg., 40, 937 (1916). 9-Schapringer, Dissertation, Karlsruhe, 1912. 10-Gardner, "Paint Researches and Their Practical Applications," 1917, p. 321. 11-Fichandler, Ind. Eng. Chem., 17, 478 (1925). 12-Coffey, J . SOC.Chem. Ind., 40, 19T (1921). 13-Salway, I b i d . , 39, 3241' (1920). 14-Long and \Ventz, I n d . Eng. Chem., 17, 905 (1923).
The Fixation of Nitrogen as Aluminum Nitride' By H. J. Krase, J. G. Thompson, and J. Y. Yee FIXEDN I T R O G E S RESEARCH LABOR4TORY,
T
HE different aluminum nitride processes which h a v e been proposed consist essentially in bringing in contact a t high temperatures a mixture of bauxite, carbon, and nitrogen, when reaction occurs with formation of aluminum nitride and carbon monoxide, as represented by the equation: A1203
+ 3C + NzAl,N? + 3co =
2
3 4
D.
c
The history of the aluminum nitride process from the standpoint principally of the patent literature, together with the chemistry of the process, is briefly reviewed. Experiments on the reduction of low-grade bauxite in the electric furnace gave sufficiently encouraging results to warrant the further investigation of this question with larger equipment. Nitrification experiments on the ferro-aluminum alloys showed that practically all the aluminum in the alloys could be nitrified if small amounts of such substances as cryolite, magnesium, aluminum, calcium fluoride, or chloride were added to the pulverized alloy before nitrification.
This reaction is commonly assumed to go through the stage wherein aluminum carbide is formed and then nitrified. I n fact, the first United States patent, granted t o Serpelq2 whose name has been rlosely associated with the dwelopment of the aluminum nitride process in Europe, was granted for the reaction of aluminum carbide with nitrogen at a red heat yielding aluminum nitride. After the granting of the first patent in 190?, development of the process proceeded rapidly and many new patents appeared. By 1911 Serpek had developed and patented what has since been known as the Serpek process.3 The technical difficulties encountered in the economic operation of this process were undoubtedly very great, for it was afterwards a b a n d ~ n e d . ~Beginning with U. S. Patent 1,155.840 (1915) a new process is disclosed which is radically different from the others. This process consisted in making a ferro-aluminum a loy in much the same manner as was done by the Cowles brothers in 1885. The development of the ferro-alloy in1
n'ASHIh.GTON.
Received June 4, 1926 U. S P a t e n t 867,615 (19Oi). U S Patents 987.408, 996,032 (1911) Chem -Zfg , 38, 1266 (1914).
dustry since then, however, s h o u l d , according to Richa r d ~ ,make ~ it possible to produce aluminum as ferroaluminum cheaper than by the electrolytic process. This new process, however, did not progress as far as commercial d e v e l o p m e n t , undoubtedly because of the difficulty experienced in obtaining suita b 1e f'erro-aluminum alloys by the e l e c t r i c - f u r n a c e method.
The Chemistry of Aluminum Nitride
FORMATIOX OF ALUMIKUM NITRIDEFROM THE ELEMEXTSThe formation of this compound from aluminum and nitrogen was first observed by Briegleb and Gauther,6and later studied by Rlallett,? Fichter and Spengel and \1701f.9 By heating aluminum in nitrogen to 820' and 1000" C., aluminum nitride is formed. By heating aluminum powder quickly to a high temperature in nitrogen, Wolf1o succeeded in preparing a small quantity which contained 33.9 per cent nitrogen (theory for AlX = 34.08 per cent K) though he was unable to reproduce this result. filost of the preparations contained 32.8 per cent nitrogen The reaction of aluminum with nitrogen is exothermic, according to Fichter and Jenny," to the extent of 62,000 Chem M e t . Eng , 19, 502 (1918). A n n . , 123, 238 (1862). J Chem Soc (London) 2, 349 (1676). * Z anorg. Chem , 82, 192 (1913) 9 I b z d , 83, 159 (1913) 1 0 Zbrd , 87, 123 (1914). 1 1 Heloetzca Chim. .4cta, 5, 448 (1922). 6
7
