a Size and metallurgical conditions: 1100 series are wrought samples 1 1/4 in. in diameter, 3/4 in. thick. C1100 series are chill-cast samples 1 1/4 in. square, 3/4 in. thick.

b

C

d

The wrought material for this standard is not available.

Small differences in the copper and zinc contents made necessary the separate analysis of the wrought and chillcast material for this standard.

Other purposely added elements having useful concentration ranges in the cartridge brass standards include: aluminum, antimony, arsenic, beryllium, bismuth, cadmium, silver, and tellurium. Some of these are expected to be certified at a later date.

Values in parentheses are not certified, but are given for information on the composition.

Small differences in the copper and lead contents made necessary the separate analysis of the wrought and chillcast material for this standard.

Bi and Ag also are present in small quantities in the standards, but these elements have not been certified.

Dashes indicate elements present but not certified.

Al, Mn, Ag, and Si also are present in small quantities in the standards, but these elements have not been certified.

Ag, Si, and Mn also are present in small quantities in the standards, but these elements have not been certified.

Ag, As, Sb, and Si also are present in small quantities in the standards, but these elements have not been certified.

Work currently is underway to certify these elements; also,

to provide final certificates for all the copper-base standards wherein the cooperative results will be listed.

Completion

of the work on the copper-base standards is planned for the

fall of this year.

11. PRECAUTIONS FOR APPLICATION

Several precautions are important in the application of these standards to spectrochemical analysis. For the chillcast samples, the NBS number has been stamped on the surface opposite the chill-cast face. For use in calibration by either optical emission or x-ray techniques, analyses always should be made on the chill-cast surface (opposite that which is numbered).

The determination of lead in the free-cutting brass series by x-ray spectrochemical techniques presents the same problem as lead in leaded steel and is highly dependent on proper surface preparation because of the tendency toward smearing or removal of the lead [2]. It may be found necessary to utilize a metallographic polishing technique to minimize the effects of changes in particle size of an undissolved constituent or in the metallurgical structure size [3].

For use by optical emission techniques, the NBS chillcast samples are designed for the analysis of samples prepared in a similar manner. It should be cautioned that samples

for analysis prepared by casting techniques other than that

of unidirectional solification may produce a bias in the spectrochemical results, the magnitude of which will depend

on the excitation parameters.

For wrought material, care should be taken to insure that spectrochemical results obtained on samples relative to the NBS wrought standards are not biased because of differing fabrication techniques or heat treatment.

When the copper content of an alloy is high, 90 percent or more, the heat conductivity, and hence the volatility rate in optical emission analysis, is sensitive to relatively small changes in composition, particularly of copper. At the high copper levels, the heat conductivity also is sensitive to the mass of the samples; therefore, it may be found necessary not only to match samples and standards in terms of size and shape, but also with respect to the positioning of the electrical discharge on the samples. These illustrations serve to emphasize the fact that in order to obtain reliable spectrochemical results, it is imperative to match closely in all aspects the standards and the samples for analysis. Any deviation from this axiom should be investigated thoroughly to insure that a bias has not been introduced.

It is felt desirable to show some examples of analytical curves that can be developed by means of the NBS copper-base standards both by x-ray and by optical emission techniques. These will serve to point to some additional problems that may

be encountered in applications.

The analytical curves cover

only the first three sets of standards originally made

available; viz., cartridge, naval, and the red brass series. Figure 7 shows the analytical curve for zinc by x-ray

analysis.

As might be expected, no significant differences between chill-cast and wrought samples are evident. Although some workers have indicated a nickel correction is necessary for the x-ray determination of zinc, certainly one is not required here where the nickel concentration of the standards is 0.1 percent or less.

The situation depicted in figure 8 for nickel by x-ray determinations is not uncommon; that is, where it is not possible initially to draw a single analytical curve through all the points. A reason must exist. The problem for nickel was resolved when a linear correction for a zinc interelement effect was made, along with a background correction, as shown in figure 9. A reasonable fit of the analytical points for nickel now is evident. The enhancement of nickel by zinc, two mass number higher in the periodic table, is of course predictable. The exact effect over wide concentration ranges of zinc may not be linear and would be more difficult to calculate. However, when the effect is not large and when relatively limited concentration ranges are involved, a linear correction normally is sufficient.

It will be of interest to compare the analytical curves

of the same elements by optical emission analysis.

Figure 10