Mechanical processing of cotton causes two types of damage: the first type is physical in nature, resulting from the breaking and bruising of fibers; the second type is chemical in nature, as shown by a decrease in D.P. This change in D.P. is brought about by a mechanical-chemical rupture of molecular bonds and not through a thermal mechanism. A quantitative estimate of the relative damage occurring in each mechanical operation investigated is presented. A loss in D.P of 30 percent was measured as a result of the mechanical operations which converted an Empire seed cotton into yarn.

of the surface in sufficient quantity to assure its involvement in the propagation of the reaction. The etch rates thus seem to be the result of a balance struck between the autocatalytic factors, which are explosive in nature, and some rate limiting mechanism. Since the rates are the result of the difference between these two large quantities, the system may be inherently unstable, and this may cause the measured etch rates to be nonreproducible. ConclusionsThe role of acetic acid in the etchant is primarily that of a diluent. As such it is able to provide control over the rate of the reaction by reducing the concentration of the kinetically important species. However, this function also can be performed with nitric acid as diluent in the compositions rich in nitric acid, or with hydrofluoric acid in the compositions rich in hydrofluoric acid. Excessive addition of acetic acid can cause the etch rates to become erratic and extremely critical with respect to small changes in composition. Water also can be used as a diluent, except that in the high hydrofluoric acid region the system is critical with respect to the addition of diluent.The kinetics in the acetic acid diluted system are governed by the same factors that operate in the CHEMICAL ETCHING OF SILICON 111water diluted system. Thus the reaction rates are determined by the rate of diffusion of the kinetically important species to the surface of the specimen. The autocatalytic factors that operate in the water diluted system play the same role in the acetic acid diluted system. The quantitative differences between the two systems can be explained on the basis of the difference in the basicity and dielectric constant of the two diluents.ABSTRACT Silicon tetraiodide is formed from commercial silicon and iodine in a fluidbed reactor. Impurities are rejected by solvent recrystallization followed by fractional distillation. High-purity silicon is formed by thermal decomposition of the iodide on a silicon surface. Silicon made this way has a resistivity over a 1000 ohm-cm. Reproducible results are obtained which suggest the product quality is controlled by back-contamination from the decomposition and crystal growing steps. Data from the decomposition of silicon tetraiodide at 1000~ and low pressure are correlated by the relation:where p ~ lb SiL vapor feed/hr/ft 2 heated surface and m = fraction of SiL~) converted to SLs>. It is postulated that this reaction reaches equilibrium.Iodide chemistry was developed by Van Arkel and de Boer (1) into a useful method for reducing the oxygen, nitrogen, or carbon content of such refractory materials as titanium, zirconium, hafnium, and silicon. Other impurities, aluminum, beryllium, boron, iron, and copper, are not rejected effectively by this simple iodide cycle and, as a result, further

An equation, for the calculation of the counterpart of viscosity for a pseudoplastic (or dilatant) liquid exists from the relationship existing between 1/ t and ΔP. Evaluation of ζ and Z defines the liquid property as completely as does η alone for a Newtonian liquid. The counterpart of viscosity-ratio, which is independent of the rate of shear and viscometer dimensions, can be used to determine the intrinsic viscosity, [η]. The general character of the change in Z with the concentration is indicated.