80 APPLIED SPECTROSCOPY

FIG. 1. VARIABLE TEMPERATURE SPECIMEN MOUNT IN DIFFRACTOMETER HOLDER

where beam penetration becomes appreciable. An even greater advantage of this system hes in the fact that the jet of dry gas streaming over the specimen surface prohibits ice formation even m fairly humid conditions. For extensive use it is best to use the specimen holder m some sort of an enclosure so that one may take advantage of a positive pres- sure o{ dry gas within the vessel as a further deterrent to ice formation. For the specimen mount described, the stan- dard Norelco can-type scatter shield, changed only slightly, served nicely as an enclosure. This scatter shield may be pre- pared for work at low temperatures by drilling one or two small holes In the front to accommodate incoming gas and thermocouple leads, and covering the can slit which permits beam entry and exit with a material nearly transparent to x-rays. One to two md Mylar® has been found satisfactory for this purpose. Naturally, a specially constructed double wall Dewar type vessel is preferable as an enclosure but adds considerably to the expense and complexity of the apparatus.

Methods of controlhng the temperature of the gas passed through the mount naturally vary considerably de- pending on the exact effect desired. Varying the flow of dry mtrogen through a copper coil immersed in hquid nitrogen functions well, as does coohng with mtrogen va- porized from the hqmd state. In the latter case, the tem- perature is controlled by changing the rate of hquld mtro- gen vaporization with a closely controlled immers,on heater. The liqulfied gases themselves may be run through the specimen mount to obtain the lowest temperature for that liqmfied gas. The flow may be carefully adjusted to insure that the hquld vaporizes beneath the sample, resulting in a gas temperature on the sample surface approximately that of the hqmfied gas. The delivery tube to the specimen mount normally is a double wall tube of Teflon, or rubber, further insulated with cotton, glass wool, or foamed low density plastic. The Mylar slit covering may be kept clear of frost by passing dry air over the slit. This is usually necessary only when operating at very low temperatures and when using soft radiation such as chrommm. For normal use with copper radiation frost is usually allowed to form on the sht covering since it acts as an insulator for that area and does not attenuate the beam excessively.

Although designed for low temperature work, the specimen mount may be used as it is up to 200°C and even h~gher with a change in construction materials. For use at higher temperatures the mount has been constructed in two pieces using copper and fired lavlte as construction materials. The mount also may be fabricated entirely of lavite using the same design as that used with Teflon. Lawte, a mixed silicate, is ideal for this use since m the unfired state ~t is soft and almost soap-like, while m the fired state it is stable, hard, and refractory.

Only one minor change was made on the x-ray gon- iometer itself. Two threaded holes wele placed in the gon- lometer mounting head to match two holes in the rear of the Teflon block. This allows the specimen mount to be bolted rigidly to the diffractometer rather than relying on the small spring normally used to secure the sample in No relco dlffractometers. This change was necessary because feed tube drag at low temperatures caused some sample dis- placement. Attaching the specimen mount m this way minimized displacement.

The specimen mount described has proven valuable for investigating all types of materials at low temperatures and up to 200°C. Phase changes and other thermal effects have been observed m pressed sohd organic and inorganic ma- terials. Diffraction patterns have been recorded and phase changes observed from sohd]fied organic liquids with the mount changed to accept hquld samples. Coefficient of thermal expansion is obtained easily and in much less time than w~th film techniques. However, it is recogmzed that there are inherent weaknesses m th,s s,mple mount that preclude its use with the same precision and accuracy as with film methods. The coefficient of thermal expansion for aluminum determined with th,s mount is 19.4 x 10-¢~/- °C (-196 to 75°C) which compares favorably with early data (3) for a slightly different temperature range.

Literature Cited

1. S. C. Abrahams, R . L. Collin, W. N. Llpscomb and T. B. Reed, Rev. Sc~. Inslr. 21, 396 (1950)

2. W. Hume-Rothery and D. J. Strawbridge, Ibid. 24, 89 (1947)

3. International Crthcal Tables, McGraw-Hill Book Co., New York, 1927, Vol. 2, p. 459

Submitted April 17, 1959

Improvement of Brown Recorders Equipped with Ball Point Pens

Bernard M. Mitzner

van Amengen Haebler, Division of Internahonal Flavors and Fra- g rances , Un ion Beach, N e w Jersey

L : _ CORDER POINTER BALL POINT PEN SHAFT

;. 2

I --PEN HOLDER

FIc. 1. SIDE VIEW OF PEN HOLDER

The Brown Recorder which has been factory equipped with a ball point pen functions very poorly as the pefi skips and at times does not write at all. The holder that contained the pen was weighted with several heavy ~ in. iron bolts, as shown m Figure 1, with the result that the pen performs very satisfactorily. This device has been successfully employed on our recorder for several months. Submitted April 17, 1959