Oznaczenia wieku bezwzględnego za pomocą wolumetrycznej odmiany metody K-Ar stosowanej w Instytucie Geologicznym

Abstract

ABSOLUTE AGE DETERMINATION BY VOLUMETRIC VARIETY OF K-Ar METHOD APPLIED IN THE GEOLOGICAL INSTITUTE

Summary

Instruments and methods applied in the Geological Institute in volumetric determination of argon have been discussed. Melting of samples is made by resistance way in a quartz crucible placed in the reaction chamber. The chamber is made of steel and consists of two parts equipped with a knife lock with aluminium gasket. In the chamber lid there are four electrodes inserted through a glass plate. On the electrodes are fastened a heater with a sample and a (Ca-Ti) furnace filled in with metallic calcium and titanium sponge. Both the metallic calcium and titanium sponge are replaced each time when new sample is installed. The instruments and the methods here considered underwent considerable changes. Among them the most important are: 1.Binding of water liberated by burning in the calcium-titanium (Ca-Ti) furnace. In the first version of the instrument, water liberated from minerals was freezed out in a freezer using liquid nitrogen. The investigations have demonstrated that in the freezer water settles with a slight amount of gel substances that at the temperature of liquid nitrogen reveal an ability of argon sorption, like activated coal. Thus the argon loses arising in this way may amount to 100 %. Burning of gases on calcium and titanium allowed the author to eliminate copper oxide commonly used for oxidation of hydrocarbons. The examinations have demonstrated that experimental hydrocarbons are completely burnt by calcium and titanium. 2. Elimination of carbon (C) from the measured volume during the measurements of argon. This results from a fact that in principle there is no possibility of perfect degassing of coal; thus, due to its gasifying, it passes to the measured portion and involves an increased background, difficult for measuring, and resulting in the appearance of considerable errors. Elimination of C from the measured portion, together with an amount of argon falling to this volume, completely does not change the measurement process on Mc Leod vacuometer. Having in view the calculation of the total amount of argon we use a conversion factor that takes into account both volume of coal (C) and quantity of argon included in it. 3. Application of titanium lamp furnace for cleaning of argon during the last phase, shortly before measurements. The furnace contains a titanium wire reeled on a tungsten heating spiral. In this furnace, working at a temperature of 1400° C, the real gases are bound by pulverized titanium that settles in the form of a titanium mirror on the internal wall of the furnace glass bulb. Titanium, like calcium, intensely binds such gases as O², N², CO², CO, hydrocarbons and others at a temperature of 700-800° C. Binding of hydrogen and water takes place already at a temperature of 350-400° C; in this case only hydrogen may again be emitted at a temperature of 800-1000° C. Due to a fact that during the heating of titanium up to 1400° C it undergoes pulverization, and that towards the furnace walls the titanium particles are cooled down to approximately 100° C, we obtain the complete binding of the real gases at the same time, and in all temperature ranges. It should be emphasized here that the furnace has been included in the measurement volume. This allowed the time to be shortened, from the moment of gas burning to the moment of argon measurement, from 120 min. to 15 min. This is highly important, since all these operations are made in static vacuum conditions that change with time due to gasifying of materials. Apart from this, the effects of the gasifying of materials is eliminated by the titanium mirror produced during the process; the mirror absorbs all gases still long after cooling of furnace. This allows the minimum background to be preserved for a long time. It has been experimentally ascertained that when argon is left for 24 hours in the measured portion, its measurement without additional burning of gases in titanium furnace (Ti) is almost identical with the former one. Due to all these changes: 1 – the background of the instrument has considerably been reduced, and its stability has been preserved; 2 - reproducibility of argon measurement has been obtained in a time period considerably greater than that of the whole analytical process, and 3 - potential source of argon losses has been eliminated by binding of water, instead of its freezing out. These changes considerably affect both precision degree and reproducibility of results. Results of check analyses made by foreign laboratories within limits of error coincide with those of the analyses made by the present author.