Morphology of Barium Sulfate as Seen through Electron Microscopy S H I N 2 0 OKADA
and SABURO MAGARI
Engineering Research Inrtitute, Kyoto University, Kyoto, Japan
This investigation was undertaken to determine the morphology of barium sulfate, whioh is pmipitated from barium chloride and sulfurio aoid a t various concentrations and temperatures. The morphology of barium sulfate is affected by the reaotion temperature and the concentration of hoth reagents. Barium sulfate has been studied by the use of an electron microsoope, employing the replica method, which is of value in studying powdery substances. The results are shown i n photovaphs. Generally speaking, the smaller the concentration of each reagent, the simpler is the form of the preoipitate, and the higher the reaction temperature, the greater is the rate of growth of the precipitate. The precipitate from a definite concentration and temperature has a definite characteristic shape.
The arrow in Figure 1, c, indicates how it was peeled off. As some of the precipitates adhered to the resin, to obtain a good replica the authors were obliged to peel the resin many times. Then the resin, placed in a vacuum evaporator, was coated with aluminum and shadowed with chromium in the usual manner.
T""
study of the precipitate of barium sulfate has a considerable history, going back nearly half a century. More recently eleotron microscopical studies have been published (1, S), and the authors have reported on the mechanimn of precipitation of barium sulfate (a, S). I n this paper they describe the morphology of barium sulfate, which is precipitated from various concentrations of barium chloride and sulfuric acid a t room and near-boiling temperatures. EXPERIMENT
Barium chloride and sulfuric acid were mixed directly to cause precipitation. Concentrations of hoth reagents were 0.1, 0.05, 0.01, 0.005, and 0.001M. The chemicals used in this experiment were C.P. barium chloride from Merck in Germany and C.P. sulfuric acid for battery use. The barium chloride solution was filtered after ~bfew days' aging. Two milliliters of barium chloride of a definite concentration were poured drop by drop into 2.5 ml. of sulfuric acid of the same concentration. Each time the sulfuric acid waa in excess it prevented the crystdlization of barium chloride. After 24bour aging, the precipitates were washed several times with distilled water. To examine the ureciuitate. the authors employed the replica method of electron &icrdscopv. As a study on the replica of a powdery substance has been published (4), only a brief description is given here.
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Figure 2. SUSPENSION P.V.4.
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SLIDE GUSS
Electronmiemgraphs of harium sulfate
From 2 "1. of 0 . l M barinm(I1) plus 2.5 ml. of 0.1M sulfate at room tomDerature A . Transmission imam B . Replica
(C)
Figure 1. Technique used in replica method
the poli(viny1 alcohol) sheet (Figure 1,%). 'Then a benzene solution of poly(methy1 methacrylate) was poured over it (Figure 1, c). After drying, the poly(metby1 methacrylate) was peeled offthe poly(viny1 alcohol) sheet.
Figure 3.
Replica of barium sulfate
From 2 ml. of 0.05.M barium(II1 plus 2.5 ml. of 0.05 Y s u l f a t e a t room temperDtUPe
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ANALYTICAL CHEMISTRY
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direct. trsnsmisfiian method of electron microscopy in Figure 2. Figure 2, 11, shows sn image, obt.ained bj- tho direct method, of barium sulfate preripit.ated from 0.lM solution while Figure 2, B , shows the surface of the barium sulfate. (In ail this work 2 ml. of barium ohlaridr solution were poured droprise into 2.5 ml. of sulfuric acid.) Figure 2, A , does not show definitely that each precipitate has L: crystalline structure composed of flaky crystals not highly aggregated, hut t h k is confirmed by Figure 2, B. In a previous paper ( 3 )the authors expressed the opinion that n large. irregularly shaped particle of barium sulfate is an aggregate of a-sggrcgates, -and designated it as @-aggregate. but Figure 2, B , shows that an irregularly shaped particle is not always an aggregate of a-aggregates but may he an araggregate in a growing state. This fact is recognized everywhere in this experiment.
Figure 7.
Replioas of barium sulfate
From 2 ml. of 0.lM barium(I1) ulus 2.6 ml. of 0.111 sulfate a t boiling
V O L U M E 27, N O . 9, S E P T E M B E R 1955
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a long a i s , 60 that the axis grow pnrallrl to t longer than thP branc Tho precipitslc socn
Figure 9.
Replica of barium sulfate
From 2 ml. of 0.01.Mbs*rium(ll) "1"s
2.5 ml. of 0.0111 sulfate
at boiling noli
From 2 ml. of 0.001M ba,rium(IIl plus 2.5 ml. of 0.001M sulfate s t boiling point
Precipitates from 0.134 solution have two shapes, its seen in Figure 7. The preoipitates oonsist of a regular combination of
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powder on the right side. I n the same experiment they were also able to compare the replica image with the direct transmission image. It is clear that without the replica image it would scarcely be possible to deduce the regular structure of the precipitate from the direct image alone. The shape in Figure 8, A , has some branches stemming from the V-axis. The branches have an almost uniform width of about 1 micron, or rather slightly Fidei at, the farther ends of the V-axis. This V-shaped precipitate is, in the authors' opinion, one side of an X-shaped axis, the branches appearing only within the acute angle of the V-axis, so that it also seems to belong to a cross-shaped type. Figure 9 shows precipitates from 0.0131 solution. They are similar to those in Figure 8, A , but not so large in size, and the mosaic blocks are not so clear. Figure 10 shows precipitates from O.OO5M solution. They have a butterfly shape, and the authors believe that they grow to an X-axis, with branches both inside and outside of the acute angle. Figure 11 shows the simplest type of precipitates obtained in this experiment. They are also similar to a cylindrical lens as are those in Figure 6, but they are not so large, and they are uniform in size. Were it not, for the replica method, one might suppose that these precipitates have rectangular and spindle shapes. But the work reported here confirmed that they have only one shape, and that the convex surface of the precipitate is not round like a lens. but is composed of four planes.
Mixed a t the boiling point, the size of the precipitates is proportional to the concentration throughout this experiment, and the velocity of growth is increased, so perfectly shaped precipitates can be seen even a t 0.1M. Independent of the mixing temperature, precipitates from higher concentrations have a complex crystal shape, and precipitates from 0.OOlM have the simplest shape and are small. Generally speaking, the large precipitate is easy to filter and the simply shaped precipitate is free from contamination. I n the case of barium sulfate, the larger precipitates have a complex shape and a large surface area. The size of the precipitate from 0.001.M solution a t the boiling point is small (about 2 microns) and its shape is the simplest, so the authors feel that these precipitates are the most free from contamination. The predominant shape of precipitates a t room temperature is a perpendicular cross shape (Figure 4), and that at the boiling point is an oblique cross shape. From this experiment it is clear that precipitates from a definite concentration have a definite characteristic shape, so one can deduce the conditions of the precipitation from the shape of the precipitates. It is obvious that the replica method is of value in the study of powdery substances, because the surface of the powder is shomn by the use of the replication, and no attention need be given to specimen change through electron bombardment.
DISCUSSION
(1) Fischer, R. B., ANAL.CHEM., 23, 1667-71 (1951). Bull. Eng. Researchlnst. Kyoto Univ., 1, 37-43 (1952). (2) Nagari, S., (3) Okada, S., Kawane, ll.,and l l a g a r i , S., Mem. Fac. Eng. Kyoto C'n~t..13. 198-208 11951). (4) Okada, S. a n d l l a g a r i , S . , Bull. Eng. Research Inst. Kyoto Univ., 3, 59-63 (1953). (5) Suito, E., a n d Takiyama, K., Proc. J a p a n Acad., 28, 133-8 (1952). RECEIVED for review August 9, 1954. Accepted March 22, 1955.
In the case of the direct miying of both reagents a t room temperature. the size of the precipitates is smallest a t the highest conrentration (O.lM), and is largest a t medium concentration (0.01.11). Below O . O l M , the size of the precipitate is proportional to the concentration and the precipitate has a definite shnpc tlt.lwnding upon the concentration.
LITERATURE CITED
Flame Photometric Determination of Manganese WILLIAM A. DIPPEL' and C L A R K E. BRICKER D e p a r t m e n t of Chemistry, Princeton University, Princeton,
A rapid method for the flame photometric determination of manganese in a variety of materials is described. The intensity of the emission of the manganese line at 403.3 mp is measured for this determination. Any enhancement or inhibition of this intensity by other ions present can be corrected by a standard addition technique. General background radiation in the vicinity of 403.3 mp can be detected from the intensity of the emission at 400 and 406 mp, respectively. Correction for such interference can be applied without any adverse effect to the standard addition procedure.
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LTHOUGH several authors (8,5, 7-9) have reported that manganese can be determined by means of flame spectroscopy, the details of the procedures, in most cases, have not been reported, and the instruments used have been homemade adaptations of Lundegirdh's apparatus employing photographic recording of intensities. -411 of the previously reported methods have been concerned with the determination of manganese in organic matter or in minerals or rocks. After preliminary studies confirmed that several parts per million of manganese could be determined easily by flame photometry, a n investigation was undertaken in order to establish 1
Present address, E. I. du Pout de Semours & Co., Carney's Point, N. J.
N. 1. rapid procedures for the determination of this element in complex materials such as rocks and alloys. ris Kuemmel and Karl ( 5 ) have pointed out, the application of flame photometry in the metallurgical field has not been very widespread. I n addition to their paper on the determination of alkali and alkaline earth metals in cast iron, the only other metallurgical analyses employing flame photometry previously described are the determination of sodium and potassium in lithium metal ( d ) , the analysis of lithium in magnesium-lithium alloys (IO), the determination of traces of sodium in aluminum ( I ) , and the determination of indium in aluminum (6). This paper describes rapid procedures for the determination of manganese and presents simple techniques for reducing the errors in this determination caused by interference phenomena encountered with complex solutions containing a number of different chemical components present in the original samples or introduced by the dissolution procedure. APPARATUS
Measurements of emission intensities were made with a Beckman Model DU spectrophotometer equipped with a Model 4030 atomizer-burner employing an oxygen-acetylene mixture. The regular blue-sensitive phototube in the spectrophotometer was replaced by the Model 4300 photomultiplier accessory furnished bv the manufacturer. The manganese emission intensities were measured a t a wave length of 103.3 mp employing a slit width of 0.06 mm.
