further, the introduction of an internal standard to milligram amounts of sample is difficult. It is thought, however, that the chromium anode spectrum could be used as an internal standard for the determination of titanium in silicates. A series of ancient laterites whose titania content ranges between 0.0 and 8.0% TiOz were analyzed using a method of fusion similar to that described by Rose, Adler, and Flanagan (IO). These rocks, together with NBS refractory standard No. 76 and Milford granite No. 4983, were then used as reference stan(10) H. J. Rose, I. Adler, and F. J. Flanagan, Appl. Spectry., 17, 81 (1963).
dards for the thin film method. The mounts were prepared in the same manner as before. Count rates of TiK, peak and CrK, of the anode spectra were measured, using a LiF (220) analyzing crystal, flow proportional counter, and vacuum. The ratio TiK,/CrK, plotted against concentration of titanium as TiOz is shown in Figure 3. Such a linear trend suggests that further consideration should be given to this method for the determination of other major elements in silicates.
for review October
1967- Accepted November
20, 1967.
A Rotating Oven for a General Sealed-Vessel Sample Decomposition Technique1 Boris Nebesar and David M. Norman Department of Energy, Mines and Resources, Mines Branch, O t t a w a , Canada DECOMPOSITION with acids of analytical samples in sealed glass tubes has been known for over 100 years. Recently, various plastic vessels have been introduced to permit decomposition with hydrofluoric acid. Techniques have been documented in several papers (1-6) and a review (7). In most cases where sealed tubes are employed, the material remains stationary. It is apparent that thorough mixing of a charge, sealed in a long tube, assists decomposition. The rotating oven, described in this contribution, was designed and manufactured specifically for this purpose. DESIGN
The stationary method of decomposition in sealed tubes has suggested design of an apparatus that incorporates the following desirable features : continuous mixing; safe containment of the explosion-like formation of corrosive vapors and provision for their escape in case of failure of a reaction vessel; corrosion resistance of the inside of the oven as well as of the outside construction; compactness for easy placement in a conventional fume hood; good insulation for stabilization of thermal conditions and for close control of temperatures up to 250' C [maximum temperature for continuous heating of Teflon (DuPont)] ; semiautomatic heating and temperature control (or fully automatic if necessary); sufficient capacity for heating of several reaction vessels of various volumes, shapes, and materials simultaneously; simplicity in operation and maintenance; and reasonable cost, kept low by utilizing commercially available materials and parts. A commercially available micro-Carius furnace (A. H. Thomas Co., Philadelphia, Pa.) incorporates several of these features, but it is useful for a different type of sample decomposition. 1
Crown Copyright Reserved.
(1) C. L. Gordon, G. Schlecht, and E. Wichers, J. Res. Natl. Bur. Std., 33, 457 (1944). (2) K. Horeischy, and F. Buhler, Mikrochim. Acfa, 33, 231 (1947). (3) J. Ito, Bull. Chem. SOC.Japan, 35,225 (1962). (4) F. J. Langmyhr, and S. Sveen, Anal. Chim. Acta, 3 2 , l (1965). ( 5 ) F. Wichers, W. R. Schlecht, and C. L. Gordon, J. Res. Nafl. Bur. Std.. 33, 363 (1944). . . (6) Ibid., p..451. (7) H. N. S. Schafer, Analysr, 91, 755 (1966).
APPARATUS
The construction is detailed in Figure 1 and descriptions of its mechanical, electrical, and thermal features follow (numbers in square brackets refer to the assembly drawing, Figure 1). Mechanical. A strong aluminum frame (1.5- X 1.5- X 0.25-inch angle) [I] supports the weight of the oven and driving mechanism and provides stability. The stainless steel outer shell [15], cover [II], and flange [I41are centered by means of a dowel and are joined with socket-head cap screws [13]. They form the outside body of the oven which is held in trunnions [3, I91 and can be continuously rotated on its short axis (instead of its long axis) at 8.75 rpm by means of a reducer [23] (Model VMW-113-100-CS Boston Gear Co., Quincy, Mass.), gears [ZI,221, and a l/s-H.P. electric motor [24]. The inner shell [It?], welded from 16-gauge 302 stainless steel, provides the useful space of the oven in the form of a cylinder measuring inside 13.25 inches long X 37/8 inches. Any pressure is released and vapors can escape through two lls-inch vents [9] in the top insulation [IO] and cover [II]. The remaining inside parts of the oven are sealed by means of a replaceable corrosion and heat-resistant silicone rubber seal [12], cut from 50 or 55 Durometer sheet stock (Armet Industries Ltd., Guelph, Ontario). The free volume makes possible simultaneous treatment of eight reaction tubes, individually enclosed in 12-inch commercially available 0.5-inch galvanized pipe nipples with caps (provided with vents). Within each pipe nipple is placed a glass protective tube and a glass reaction tube which are suitably padded to prevent breakage. Other reaction vessels-e.g., plastic bombs-can be used. Thermal. A cylindrically-shaped refractory heater-core [4 of 4-inch i.d. is available commercially (Norton Co., Worcester, Mass., Model MD-33354). It provides for efficient heating (while also insulating) by means of an electric current. The temperature is measured with a stainless-steel dial thermometer [8] (Cole-Parmer Instrument and Equipment Co., Chicago, Ill,, Model 8123, 9-inch stem), and the required temperature-setting must be established by calibration. This arrangement is only semiautomatic but it is adequate and much less expensive than a fully automatic system, which could be easily incorporated. The top [IO]and bottom [25] insulation boards are solid and made of Transite (Johns Manville CO.) while the center insulating shell [I4is of Micro-Lok 500 (Johns Manville Co.). To have access to the inside of the oven, the top insulation board (as well as the cover) is removable. Woven asbestos cloth or any other suitable heat-resistant material is used for packing the load
[a
VOL 40 NO. 3, MARCH 1968
663
Figure 1. Rotating oven assembly 1. 2. 3. 4. 5.
6. 7.
8. 9.
IO. 11. 12. 13. 14.
Frame and support (aluminum) Slip-ring assembly (phenolite) Trunnion (stainless steel-SS) Heater core (refractory) Thermometer well (SS) Dowel (SS) Thermometer mount (SS) Dial Thermometer (SS) Vents Insulation-top (removable, Transite) Cover [removable, (SS)] Seal (silicone rubber) Socket-head cap screws (SS) Flange (SS)
into the oven to prevent its moving. The oven can be used at temperatures up to 250' C. Electrical. A slip-ring assembly [2] makes possible the continuous supply of heating current while the oven is rotating. The high-resistance heating wire [I71 (8.8 ohms, 1500 watts) is placed into the grooves of the heater core. The power supply (115 V ac) is regulated by means of a variable transformer and an input controller (Cole-Parmer Instrument and Equipment Co., Chicago, Ill., Cat. No. 2018). The input controller incorporates a 10 A relay which has a graduated dial-adjustment that varies the position of the relay's fixed contact. This changes the proportion of each control cycle during which power input can occur, when the relay contacts are closed by the action of the motor-driven cam. This arrangement has a sensitivity of approximately 2" C per division of the controller-dial. Since the heating wire is positioned within the refractory 664
ANALYTICAL CHEMISTRY
15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27.
Outer shell (SS) Insulating shell (Micro-Lok 5 0 0 ) Heating wire (chromel) Inner shell (SS) Trunnion (SS) Bearing block (commercial) Gear (commercial) Gear (commercial) Reducer (commercial) Electric motor (commercial) Insulation-bottom (Transite) Outer shell-bottom (SS) Inner shell-bottom (SS)
heater core, it is completely insulated from any metallic parts. The silicone rubber seal [12], compressed onto the top edge of the inner shell, prevents the escape of acid vapors into the heating-wire area. A simple time clock can be used to switch off the heating current after a specified time. The application of this oven will be reported in a separate communication. ACKNOWLEDGMENT
The authors thank E. K. Swimmings for help with the electrical design and C. Szombathy for drafting.
RECEIVED for review November 6,1967. Accepted December 4,1967. Mention of proprietary products is for identification only and does not constitute endorsement by the Department of Energy, Mines and Resources.
