Increase In Sulfur Content Research Articles

The Vulcanization of Elastomers. 20. Sulfur Vulcanization Accelerated with Thiuram Compounds. I

Abstract The present paper deals with the results of an orientating, quantitative investigation of sulfur vulcanization accelerated by thiuram disulfide, with tetramethylthiuram disulfide as the representative example. It was found: In the sulfur cure of natural rubber with tetramethylthiuram disulfide at different TMTD:S ratios, the rates of TMTD decrease and dithiocarbamate formation increase with increasing sulfur concentration, the TMTD content being kept constant. The rates practically do not change any further when the compounds contain 6 gram atoms of sulfur per mole of thiuram disulfide. The peak value of dithiocarbamate formation increases with the increase of sulfur concentration and reaches a constant end value of about 90 mole per cent based on the amount of original thiuram disulfide, when the stocks contain 4 gram atoms of sulfur per mole thiuram disulfide. This end value is identical to the end value of dithiocarbamate formation in the reaction of thiuram disulfide with zinc oxide (in the absence of rubber). The crosslinking, as measured by the change of reciprocal equilibrium swelling per time unit is also a reaction whose rate increases with the sulfur concentration to the point where the compounds contain 6 gram atoms of sulfur per mole of thiuram disulfide. The optimum degrees of crosslinking are roughly proportional to the sulfur concentration; at high sulfur levels the vulcanizates tend to revert. As in the pure TMTD vulcanization, the TMTD decrease as well as the dithiocarbamate formation are always first order reactions. The reversion at higher sulfur levels as well as the complicated course of the increase of combined sulfur during vulcanization render all but impossible an accurate determination of the reaction order for the crosslinking at higher sulfur levels. Nevertheless, in vulcanizations with 1 mole TMTD per 1 or 2 gram atoms of sulfur the crosslinking is a first order reaction.

真空熔解におけるFe-S, Fe-C-S合金の脱硫に関する実験と熱力学的考察

This investigation has been made to ascertain the desulfurization process of cast iron in vacuum-melting. The results of Fe-S and Fe-C-S alloys are summarized as follows: (1) In vacuum-melting at 1600°C, an Fe-S alloy containing 0.075%S is slightly desulfurized and in five minutes a minimum sulfur concentration is obtained. And then the sulfur concentration increases with increasing time. In the case of melting of Fe-C-S alloys in graphite crucibles, considerable desulfurization occurs and after certain times finite sulfur concentrations are obtained. When an alumina crucible is used, although the initial rate of desulfurization of the Fe-C-S alloy containing 3.34%C is much slower than that of melting in a graphite crucible, this rate increases with increasing time and finally the sulfur concentration becomes lower than that of the Fe-C-S alloy melted in a graphite crucible. (2) It may be considered that a slight desulfurization of the Fe-S alloy should occur by oxygen-sulfur reaction and that the increase of sulfur concentration should be due to vaporization of iron. If the desulfurization reactions are approximately in equilibrium during vacuum-melting, it may be said that the Fe-C-S alloy which contains 0.01 to 0.5%S should be most strongly desulfurized by the reactions C+S=CS (g), S=S (g) and C+2S=CS2 (g) in the range of lower sulfur concentration, and by the reaction C+2S=CS2 (g) in the range of higher concentration. The increased rate of desulfurization in the melting of the Fe-C-S alloy in the alumina crucible is considered to be due to entrance of silicon into the melt from the crucible. It may be considered from the thermodynamic equilibrium condition that as far as the carbon concentration is fixed during vacuum-melting the obtainable minimum sulfur concentration should be decreased with increasing carbon concentration of the Fe-C-S alloy used. (3) The sulfur concentration obtained in vacuum-melting of an Fe-C-S-alloy in a graphite crucible for 1/2 hr decreases with increasing emperature, which result consists with the thermodynamic considerations.

半導体に関する研究（第8報）亜酸化銅整流板の特性におよぼす銅素材中の非金属性不純物の影響

In order to supply fundamental data for the production of cuprous oxide rectifiers of high quality, the effects of non-metallic and gaseous elements included in copper on the rectifying properties were studied. In this study, the measurement of the rectifying characteristics, their temperature dependence and the change of forward current at 0.8V and reverse current at 6 V in running test was carried out and the following results were obtained: (1) When the copper contains 0.1% P, it is impossible to make rectifying disks mainly because of nonadherence of the oxide layer. As increasing the phosphorus content is increased from 0.001% to 0.01%, the rectifying resistance increases in the conducting direction, while it decreases in the reverse direction. (2) With the increase of sulphur content from 0.001% to 0.1%, the rectifying re istance decreases in both directions. (3) When copper contains oxygen corresponding to 1.5×102 mm HgO2, the rectifier shows the highest efficiency, in comparison with copper containing various other elements. (4) By increasing the chlorine content from 0.01% to 10%, the rectifying resistance decreases in both directions and on introduction of 0.0002% Cl2 into the first heat treatment furnace improves the rectifying characteristics. (5) The forward current in running test increases in the first few minutes, but afterwards it is kept almost constant. (6) The creeping percentage increases fast in the first few minutes and afterwards gradually. A rectifying disk containing 0.01% P or 10% Cl shows high creeping property.

Liquidus Surface of the Fe-S-O System

The liquidus diagram for the iron field of the Fe-S-O system has been derived experimentally. The solubility of oxygen in molten Fe-S alloys has been measured at several temperatures and found first to decrease slightly and then increase rapidly with increasing sulphur content.

Accelerators in Hard Rubber

Abstract 1. The curve relating the hardness to the time of heating of a high-sulfur stock indicated the presence of two consecutive reactions. The second half of the curve was mainly linear, and its slope might be used as a measure of the second (hard rubber) reaction speed. 2. The straight line when produced downwards passed through or near to the origin. Its position was altered only slightly by normal variations in processing. 3. The straight line may be represented by the equation H=rt+ƒ where H = per cent hardness by Shore's Durometer, t = time of heating in minutes, r = rate of hard rubber formation represented by the tangent of the angle between the curve and the time axis, and ƒ = the intercept along the hardness axis. 4. Influences which are known to increase the speed of chemical reactions increased the slope of the line. Thus, increase of sulfur concentration, rise of vulcanizing temperature, and the presence of catalysts increased the value of r, yielding a “fan” of lines all passing through a point near to or coincident with the origin. 5. The organic accelerators of vulcanization in general were found to act as true accelerators if present in small amounts. With increasing concentration they increased the speed of hardening at 150° C. up to a definite maximum, which appears to be approximately the same for many accelerators. 6. From an investigation of the minimum concentration of accelerator which produced the maximum slope, numbers representing the efficiency of the accelerators have been found. 7. Further addition of accelerator produced no further change in r, but a definite and progressive increase in the value of ƒ. This effect was also produced by the addition of mineral fillers. 8. If the value of H be taken as 100 per cent hardness, the equation H=rt+ƒ may be used for determining the time of cure. r is the rate of cure, dependent upon the nature of the accelerator, and the nature and amount of filler determine the magnitude of ƒ. Values of ƒ referring to some commonly used fillers have been determined. 9. The effect of increasing the temperature of vulcanization on the rate of hardening was examined. It was found that the temperature coefficient of hard rubber formation was not a constant quantity for accelerated hard rubber stocks. In many cases its magnitude increased to a maximum within the temperature range 140–150° C., and then fell at still higher temperatures.

Vacant Positions in the Iron Lattice of Pyrrhotite

PREVIOUS investigations on the solubility of sulphur in iron sulphide (FeS) have led to the conclusion that the solid solutions of sulphur in iron sulphide are formed by substituting some of the iron atoms in the original lattice by sulphur atoms. Assuming that the radius of the sulphur atoms is smaller than that of the iron atoms, this hypothesis explains the fact that the lattice dimensions decrease with increasing sulphur content. It seems, however, doubtful if this relation between the radii of iron and sulphur atoms agrees with reality, and the difficulties are still more increased when one has to explain the analogous (only more pronounced) lattice variations in solid solutions of selenium in iron selenide (FeSe) in the same way, on the assumption that the selenium atoms are smaller than the iron atoms.