Abstract
Rayon fibers treated respectively with ammonium sulfate, diammonium hydrogen phosphate and ammonium chloride were heated and carbonized in a nitrogen atmosphere at the rates of 1 to 5°C/min to various temperatures up to 1000°C. Changes in the physical properties in this process were investigated. In this range of heating rate, the carbonized rayon fibers obtained from the untreated one were so brittle that their strength properties could not be measured.
The tensile strength of the carbonized fiber varied depending on the kind of ammonium salts used for the treatment, the texture of starting material and also the heating rate. The results obtained suggest that; 1) ammonium sulfate serves for strengthening the carbon fibers, while neither diammonium hydrogen phosphate nor ammonium chloride bring about such an effect; 2) the higher degree of molecular orientation of the rayon precursor gives the greater strength to the resulting carbonized fiber; 3) the lower the heating rate, the stronger the resultant carbonized fiber.
Further, density, X-ray diffraction and elementary composition were measured of the samples heated at various temperatures. Based on these results, the effect of ammonium sulfate on the yield and the strength properties of the carbonized fiber has been discussed.
