Glass fiber reinforced composites have been used to an increasing extent as structural components because of their high strength at relatively low densities. They are more resistant to moisture and weathering than most other structural materials. However, under environments of high humidity and temperature, glass fiber composites with an epoxy or polyester matrix lose a considerable fraction of their strength after a relatively short time. For high strength glass reinforced composites, the glass filaments are mostly of the S-glass and E-glass types. This investigation reports the solvent effect of water on S-glass rovings (filament strands) and powders. S-glass is the strongest silicate glass developed in the past decade, the composition of which in weight percent is: Al,O:,/MgO/SiO, = 25110165. In the temperature range covered (30 to 50°C), analyses ofaluminum, magnesium, and silicon in water after different time periods indicate that magnesium is preferentially leached out of S-glass, either as filaments or as powders, h y water. T h e concentrations of magnesium and silicon in the water reached 2 mgilitre or more depending on the temperature and length of contact time, while the aluminum concentration reached no more than 0.2 mgilitre. Decomposition products of the ingredients present in a composite, including the coupling and curing agents, could further complicate the degradation process. Rate relations are proposed and discussed based on the dissolution data.

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X-ray diffraction data were obtained using a General Electric XRD-5 unit. Copper K a radiation, filtered with nickel, was used to irradiate the samples. The relative intensities of the lines and degrees 28 were obtained from a chart readout of the instrument. ResultsSeveral precipitate fractions could be obtained from the electrolysis of one sample solution. The electrolysis was terminated after the precipitation process became very slow. This last precipitate fraction was extremely gelatinous and difficult to separate from the mother liquor. The solids were dried at 110°C. and analyzed. Yields were 805 or above.The calcium content was found to be less than 1%for all precipitate fractions except the last one, collected from a sample solution. The last fraction showed a considerable increase in calcium content, while the percentage of fluoride present was decreased. A qualitative test for chlorine was made by dissolving the sample in nitric acid and adding silver nitrate solution. Lack of a silver chloride precipitate indicated that the sample contained less than 0.1% chloride.

The transformation of amorphous basic copper carbonate precipitates into the crystalline form in aqueous solutions was experimentally studied. The unique blue-to-green color change and drastic volume reduction of the precipitates in transition made continuous observation and quantitative determination of the transformation process feasible. The transformation, which involves both nucleation and crystal growth proliferation, was autocatalytic. Experimental results are in good agreement with the rate equation formulated on the two-stage kinetics model postulated for the system. Also studied were the effects of temperature and precipitate concentration on the rate of transformation. In the temperature range between 34" and 39"C., the apparent nucleation activation energy was 19.8 kcal./g.-mole.The art and science of crystallization are of interest to a wide range of physical and biological scientists and technologists (1, 6, 11, 16, 20, 30). The vast diversity of interest and objectives calls for the study of mechanism and techniques, such as to grow large perfect crystals, to grow crystals of uniform sizes, and to prevent the formation of crystals. The fundamental forces involved in all types of crystallization, whether in polymers, in organic and inorganic salts, or in metals, are believed to be essentially identical, but various crystallizing systems may show totally different behavior in the course of crystallization under different physical situations.A great amount of work has been done on the various aspects of crystallization with crystallizing systems as diverse as insulin and synthetic zeolites. The effects of physical factors, such as degree of supersaturation, temperature, and cooling rate, on the growth rate of crystals (7, 13, 18, 25), size distribution (4, 15, 17, 29), and crystal morphology (2, 26) have been extensively investigated.It is well established that there are two processes, nucleation and crystal growth, which are instrumental in the crystallization process. Because the elementary kinetic steps are little known and are specific for different systems, only empirical kinetic treatment of individual systems has been advanced by various workers ( 1 0,17,21,23,24,27).The system reported here is a complex inorganic precipitate, basic copper carbonate, formed in an aqueous medium. The stoichiometric relation of the reaction under controlled conditions conforms to the following equations 2NazC03 + 2CuS04 + H 2 0 = CUCO~.CU(OH)Z ( 9 , l Q ) :The initial precipitates formed by mixing aqueous sodium carbonate and cupric sulfate solutions were gelatinous and noncrystalline, but were able to transform themselves into crystalline particles of pure malachite on aging ( 9 , 2 8 ) .The purpose of the present work is to study the kinetics AlChE Journal (Vol. 17, NO. 6) of nucleation and crystal growth inherent in such transformation. Incidentally, this crystallizing system is particularly desirable in that the transformation process can be visually tracked. THEORYCrystal growth can be considered to consist ...

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