PubMed · 199297
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P Carta, F Sanna-Randaccio. [Experimental emphysema].. https://pubmed.ncbi.nlm.nih.gov/199297/
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Aspirin and four salicylate impurities of aspirin (salicylic acid, acetylsalicylsalicylic acid, acetylsalicylic anhydride, and salicylsalicylic acid) were resolved by silica gell TLC and by high-pressure liquid chromatography (HPLC) on a reversed-phase C18 column. Care was necessary in the choice of a column because of similar column failed to resolve these five compounds. Salicylsalicylic acid was isolated from aspirin tablets by extraction followed by reversed-phase C18 HPLC. The structure of this compound was confirmed by comparison with an authentic sample of salicylsalicylic acid by HPLC, TLC, IR and UV spectrophotometry, and mass spectrometry. Two other compounds, acetylsalicylic anhydride and acetylsalicylsalicylic acid, which had been previously identified by chromatography as impurities in aspirin, were isolated and further characterized.
The cause of the three shrinkages in the thermal expansion curves of gypsum bonded investments, which were characterized in the previous study, was examined mainly by means of TG-DTA method, X-ray diffraction method and SEM observation. The main results were as follows: 1. The first shrinkage between 100 degrees C and 200 degrees C was caused by the dehydration of gypsum. 2. The second shrinkage between 300 degrees C and 400 degrees C was due to the transformation of soluble anhydrite to insoluble anhydrite. 3. The third shrinkage beginning at the temperature range 700 degrees C approximately 800 degrees C is considered to be related to the sintering of insoluble anhydrite.
The sintering kinetics of insoluble anhydrite were studied by measuring the isothermal shrinkage of compacts of insoluble anhydrite powders in air. The sintering process of insoluble anhydrite powders consisted of two stages for the temperature range from 630 degrees C to 720 degrees C. The first shrinkage could be described as a bulk diffusion model and followed the equation delta L/Lo infinity t 0.5l +/- 0.08, where delta L/Lo is fractional shrinkage and t is the sintering time. The apparent activation energy of the shringage was 130 kcal/mole. The second shrinkage followed the equation delta L/Lo infinity t 1.83 +/- 0.30, but could not be explained with reasonable model. However, the SEM observations of the fractured surface of compacts suggested that the second shrinkage corresponded to the grain growth of insoluble anhydrite.