The Application of Ion Concentration Measurements to the Control of Industrial Processes

1922 Journal of Industrial & Engineering Chemistry  
395 The tensile strength curves, Fig. 20 , show values for this property which are nearly the same for all the compounds, probably within the experimental error due to slight differences in the state of cure. The same is true of the tensile values after accelerated aging. After the 60-day weathering test, however, it is observed that the stocks containing the larger proportions of zinc oxide show definitely better aging qualities than those containing larger proportions of magnesium carbonate,
more » ... gnesium carbonate, as a result, of the greater surface cracking tendency of rubber heavily compounded with magnesium carbonate. This again seems to be related in a degree to the crystalline character of the magnesium carbonate particles, since the plane surfaces and sharp edges of the crystals would be expected to favor the development of cleavage planes in the rubber itself when stressed, or perhaps even under the influence of changes in temperature, producing alternate expansion and contraction of the rubber matrix around each particle. The hardness and permanent set (Fig. 21) of these compounds both show increasing values with increasing proportions of magnesium carbonate. The permanent set, however, does not exceed 16 per cent until half the zinc oxide has been replaced by magnesium carbonate. The total resilient energy capacity and energy absorbed a t 300 per cent elongation (Fig. 22 based on data in Table VI) both shorn a marked increase with successive increments of magnesiuh carbonate replacing zinc oxide in the $ompound. For the absorbed energy at 300 per cent elongation this increase is linear, as is also true of the curve showing stress at 300 per cent elongation for the same compounds (Fig. 20) .
doi:10.1021/ie50149a009 fatcat:hnm3nengeraorb2qsfe2ut4mmu