No abstract

No abstract

OTH basic investigations into the nature of the glassy state and commercial applications in the field of hermetic sealing have aroused considerable interest in low-melting glassy materials. The purpose of this communication is to report the synthesis of a new group of low-melting inorganic glasses. The glasses thus concerned occur in systems involving the ternary (and quaternary) interactions of the elements arsenic, thallium, sulfur, and selenium.In addition to the low-melting characteristics, application interests lay in synthesizing glasses which would exhibit high fluidities at temperatures less than 400°C. Although binary arsenic-sulfur glasses have softening points of the order of 200'C.. most of the melts are still highly viscous at temperatures in excess of 400OC. Of twenty-four ternary additives studied, three were found to give systems having substantial areas of glass formation characterized by low softening points and high melt fluidities. These are the ternary systems As-TIS, As-TI-Se, and As-Se-S (Fig. 1 ).For the study of these systems, small (20-to 200-gm.) samples were prepared from the elements, by flame heating in lightly corked fused silica test tubes. The melts were allowed to cool slowly in order to emphasize any tendencies toward crystallization or separation of phases. X-ray diffraction methods and visual examination of fracture surfaces were used to determine whether each sample was a homogeneous single-phase glass.The glasses of these three systems have been found to be chemically durable and to exhibit extremely low water solubility. They have shown no tendencies toward devitrification. The resistivities range from 101 to 10'6 ohmcm.. depending on composition; most of the glasses fall in the range lo1* to lOl6 ohm-cm. The dielectric constants vary as a function of heavy metal concentration from 4 to 20.The softening temperatures in the ternary system As-TI-S, as determined by a dilatometer method, range from about 90' to 180'C. compared with the value of 195'C. for the previously reported glassformer AsSa. * However, the most remarkable effect of the addition of thallium to the system A S S is found to be in the lowering of the melt viscosity. The addition of 10 weight 70 (2.5 mole yo) of the metal to arsenic-sulfur mixtures reduces the temperature of 30-poise viscosity (a viscosity similar to that of castor oil a t room temperature) by up to 200OC. Generally, the 30-poise temperatures in this ternary system lie between 250' and 350°C. In the system As-TI-Se this viscosity is reached a t temperatures between 185" and 400°C.. and in the system As-S-Se from 300" to about 400'C., depending on the composition of the glass.The action of thallium in greatly reducing melt viscosities on addition to As-S compositions deserves consideration. By analogy with more conventional glasses it would be expected that 'the addition of large relatively low charged species would reduce melt viscosities, but the results obtained indicate that the action of thallium is unique among twenty-four metal additives...

No abstract

Glass formation has been found to be extensive in the systems As-TI-S, As-Tl-Se, and As-Se-S. Glasses in these systems exhibit unique lowmelting properties; some are highly fluid as low as 185OC. The marked effect of thallium in lowering the viscosity of binary As-S melts was found to be unique among all the metallic additives studied. The glasses are stable, covalent, chemically durable, and dielectric. They exhibit good wetting properties with respect to most metals, and the permeability of the seals formed as well as the volume permeability of the glasses themselves appears to be extremely low. Linear thermal expansion coefficients of some compositions are high, but associated thermal cracking problems are minimized to some extent by the low softening temperatures. The glasses can be evaporated and directly condensed (in uacuo) to form continuous, .grain-free glassy films. The glasses are of considerable interest in the study of the nature of the vitreous state. In addition, their over-all properties make them potentially useful for hermetic sealing of semiconductor and other moisture-sensitive electronic components which might be damaged by high-temperature sealing processes.