Direct Reading Spectrometer Research Articles

Rivet Sample Holder for Spectrochemical Analysis

Recently, this laboratory was faced with the problem of analyzing steel and aluminum rivets using a Jarrell-Ash Direct Reading Spectrometer. The small size of these rivets prevented the direct use of the electrode holders in the arc stand. It would be necessary to melt the rivets into a briquette large enough to fit in the stand. Melting these rivets was time consuming, and the number of rivets necessary to make a sufficiently large briquette made it expensive.

Analysis of human tissue ash with a direct reading spectrometer.

Analysis of human tissue ash with a direct reading spectrometer.

A method of uranium isotope analysis by direct reading emission spectroscopy

A special-purpose direct reading spectrometer has been developed for the determination of U235, U236 and U238, using the spectral lines at 4244.12, 4244.22, and 4244.37 Å, respectively. The parallel-channel integrating method is used, in which the ratios of U235 and U236 to U238 are determined simultaneously. A 5 A 2400 Å a.c. are is used, the sample (uranium oxide) being held in a graphite crater. The three spectral lines are separated by optical means; exact optical alignment is maintained automatically. At 3 per cent concentration of U235, a coefficient of variation of 1 per cent of the amount present is achieved. The sensitivity for U236 is better than 0.1 per cent. Sample preparation is simple and straightforward. Less than 3 min is required for an analysis.

A method of uranium isotope analysis by direct reading emission spectroscopy

A special-purpose direct reading spectrometer has been developed for the determination of U235, U236 and U238, using the spectral lines at 4244.12, 4244.22, and 4244.37 Å, respectively. The parallel-channel integrating method is used, in which the ratios of U235 and U236 to U238 are determined simultaneously. A 5 A 2400 Å a.c. are is used, the sample (uranium oxide) being held in a graphite crater. The three spectral lines are separated by optical means; exact optical alignment is maintained automatically. At 3 per cent concentration of U235, a coefficient of variation of 1 per cent of the amount present is achieved. The sensitivity for U236 is better than 0.1 per cent. Sample preparation is simple and straightforward. Less than 3 min is required for an analysis.

Direct Reading Spectrometer Combined with Spectrograph

Direct reading spectrometer combined with spectrograph has been devised for both quantitative and qualitative spectrochemical routine analyses.Paschen and Runge mounting of 2.2m concave diffraction grating is used, and 10 exit slits and photomultipliers for direct reading analysis of alloying constituents of steel, and 100 feet roll film camera for qualitative analysis are provided for the spectrometer. Fundamental investigation of high alloy steel analysis by the fully automatic high precision process is described.

Der Einsatz eines lichtelektrischen Gerätes zur serienmässigen Durchführung von Mikroanalysen bei der Untersuchung von Stahlgefügebestandteilen

The investigation of the non-metallic constituents of steel after electrolytic isolation is a problem of microchemistry that requires systematic and organized procedures in addition to highly sensitive methods because of the large number of samples. The weights of the samples available for investigation are usually < 1 mg, very often only 50 μg. These have to be quantitatively analysed for five to ten elements. For solving these problems, determinations have been developed which are combinations of microanalytical methods and spectrochemical methods with internal standard. For the spectrochemical analysis the inclusions of oxides are melted with borax and the melt is dissolved in citric acid which contains cobalt as internal standard. For the subsequent spectrographic method which uses the above solution, the resolving power of the quartz-spectrograph Qu 24 of Zeiss is sufficient. By using the spectrochemical method the time required for analysis is reduced to one tenth of the time required by usual chemical methods. This has already been published in a paper. Just a few months ago it has been found possible by using a direct reading spectrometer, the “Spectro-Lecteur automatique” of the Cameca, Paris, to materially shorten the time required for analysis, as compared with the above method. The change from the internal standard method, which uses the photoplate and which has been used till now, to the direct reading method can be done easily without interruption of the routine work. Such a rapid change was only possible because of the special construction of the “Spectro-Lecteur automatique” and after a short time the analysis of iron, manganese, chromium, aluminium, silicon; titanium, calcium, and magnesium in the isolated oxide inclusions of steels can be made by the direct reading method. Generally the same lines as in the spectrographic method are used. The sensitivity is sufficient even for the last elements which are iron and silicon in the sequence of direct reading.

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The intention of this introductory paper is to give a base for the following papers on details by reviewing our knowledge about the physical processes in spark discharges and about their qualities. The discharges have to volatilize the samples and to excite the vapour to produce radiation. Further development may lead to separation of these two functions. A suitable source should fulfil three requirements: o (a) definability of discharge conditions (b) stability and reproducibility (c) spectral character adapted to the analytical problem. The paper will first consider electrotechnical questions, among them the electric phenomena occurring in the discharge circuit and being either a damped oscillation or an aperiodic process. It is important to keep in mind that an oscillatory spark is nothing else than an a.c. arc of high frequency having high current, but low voltage across the gap. For the production of sequences of uniform sparks the problems of the charging circuit are to be considered. By “controlling” the spark generator it is possible to produce sequences of sparks all having the same character independent of the variable physical conditions in the analytical gap. Different possibilities of control will be discussed. There are a good many of electrical parameters of the discharge circuits which may be varied. But the spectral character of a spark is essentially determined by the energy used in the spark gap (not in the circuit) and the duration of the spark, roughly speaking by the shape of the curve enveloping the graph of current versus time. Another question will be discussed, the description of a spectrochemical source by its optical parameters, a question of some importance for general methods of spectrochemical calibration. The data of the electric circuits are by no means sufficient to fix the type of a spark discharge. The manner in which the material is being volatilized influences the radiation of light essentially. The results of some investigations on this will be discussed, but further experiments using a large variety of substances are necessary. A definite relationship between the amount of material released and the electric charges passing the gap seems to exist. The excitation of light does not mainly occur in the positive column of the discharge but in clouds of vapour exploding from the electrodes and carrying their energy from there. Hence, for the radiation it is of importance what happens to these vapour clouds after their release from the electrodes. In particular the losses of energy by the cooling effects of the surrounding gas and the surfaces of the electrodes are to be considered. The origin of spark lines and of the continuous background will be discussed in the light of new experiments on the time development of radiation during the life of a single spark. The influence which the statistical distribution of spark strokes over the surfaces of the electrodes has on the radiation and on the volatilization has in general not yet received the attention which it deserves. Examples will be given, the importance of the concept of a “natural shape” of the electrodes will be pointed out. This helps in understanding and describing the phenomena, in spite of the fact that these shapes are not suited for practical work. But it is possible to understand the working of those shapes which are used in practice. Remarks will be made on the influence of air currents and some explanations given for the shape and reproducibility of sparking-off curves. These curves are useful means in studying discharges with the aim of finding spectrochemical working directions. It will be discussed how the sparking-off curves depend on the area of the electrodes, on their temperature and-on their composition and metallographic history. It seems most probable that many of these factors may act via chemical reactions at the surface of the electrodes. Of particular interest is the formation of slags. Pressed electrode tablets allow the investigation of these influences by adding compounds as fluxes or buffers. Experiments made with direct reading spectrometers demonstrate an amazing reproducibility of the complicated sparking-pff processes if suitable working conditions are strictly observed. In some cases sparking curves showing regular periodic oscillations of the intensity ratio occur which may be explained by some kind of subsequent release of layers from the ele trodes. The qualities of special types of discharges will be considered, such as discharges at low pressure, with high currents or of long duration. This will give an opportunity to discuss the question of when the concept of temperature can be used for the radiant plasma of spark discharges.

Electronics in automatic direct reading spectrometers for the analysis of metals

After first discussing the fundamentals of photoelectric spectrometry, the basic essentials of automatic direct reading instruments are reviewed, reference being made to a 3-metre direct reading spectrometer with 30 channels which has been developed as a rapid routine production control unit in the making of non-ferrous alloys. The circuit employs features not previously used in this type of equipment, including a ‘dekatron’ counter circuit and a printing recorder to register the counts corresponding to the intensity ratios of the selected spectral lines of the constituent elements being measured. The con centrations are then determined from working curves established experimentally for each measuring channel to give the concentration as a function of the count for the corresponding element.

The Design and Construction of a 22 Foot Direct-Reading Optical Spectrometer

To meet a number of spectrochemical problems involving relatively complex spectra, a versatile grating spectrometer having high resolution and dispersion and using photomultiplier tubes to measure the intensities of the spectral lines was constructed. A concave diffraction grating having a radius of curvature of 21 feet 10 inches and ruled with 15,000 lines per inch over a 5 inch surface was used in an Eagle mounting designed to cover continuously the range from 2000 Ångstrom Units in the first order to 5800 Ångstrom Units in the fourth order. Five feet of spectrum are available at any setting of the instrument. To minimize backlash and spurious motion, kinematic principles were used in the design of the adjustments. Vibration absorbers and dampeners were used to minimize the effects of vibration, and constructing the instrument in a completely enclosed room located within an air-conditioned area minimized the effects of temperature changes. Either visual or photographic means may be used to position the exit slits and to adjust the optics. Both scanning and integration techniques are available.

Direct-reading metal spectroscopy with a d.c. arc

A d.c. globule arc that hisses vigorously has been developed in conjunction with a direct-reading spectrometer built on a wavelength spectrometer and measuring intensity ratios by the null indication of a symmetrical cathode-follower bridge circuit. Self-electrodes are held in massive brass supports with the anode uppermost and the arc run until large molten globules form and stabilize on both electrodes. The relationship between the manganese concentration in carbon steels and the intensity ratio of manganese 4754 A to iron 5455.6 A is linear in the range 0.3% to 1.3% manganese, and standard deviations of 2% of content have been obtained. Standard deviations of 4% have been obtained by ordinary photographic photometry using manganese 4754 A and iron 4707.281 A. A method of preparing a working curve from a knowledge of the background intensity of the manganese line and a single standard sample is suggested. There is a discontinuity in the volt-ampere characteristic of the arc, but the curve is nearly parallel to the current axis at the operating point.

Analysis of Some Metals with the Direct Reading Spectrometer

Analysis of Some Metals with the Direct Reading Spectrometer

Direct-Reading Spectrometer for Ferrous Analysis

The direct-reading spectrometer, previously described by Saunderson, Caldecourt, and Peterson of the Dow Chemical Company, has been adapted for ferrous analysis. Data is given on reproducibility of analytical results obtained for Ni, Cr, Si, Mn, Cu, Mo, Al, and Sn in steel. The inherent accuracy of the instrument is discussed with respect to both the electronic and photometric systems employed. Errors introduced are shown to be small compared with spectrochemical uncertainties inherent in the source.

A Photoelectric Instrument for Direct Spectrochemical Analysis

A direct reading spectrometer for spectrochemical analysis, combining great speed, simplicity of operation, and exceptionally good analytical results, is described. The grating spectrometer is equipped with eleven electron multiplier photo-tubes allowing the determination of ten elements using the internal standard method. The light intensities are integrated over a sparking period of 20 seconds by storing the photo-currents in suitable condensers. Direct-current amplifiers of novel design perform the function of measuring the stored charges, and the results are recorded on a strip chart of electrical marking paper. A method is discussed for making a background correction which materially increases the sensitivity and accuracy for trace elements. Analytical results having a standard deviation of the order of 2 percent of the amount present on alloying constituents are regularly obtained by routine operators.