Investigation of Residue and Coating Stoichiometry on 120-mm Combustible Cartridge Cases
Abstract : An investigation was conducted to determine the cause of coating residue found in the test gun chambers during qualification firing of 120-mm combustible cartridge case (CCC) ammunition for the MlAl/A2 main battle tank. The CCC is coated with a clear epoxy- polyamide topcoat and a highly pigmented aluminum epoxy basecoat. A laboratory analysis was performed on actual residues; parts of the CCC retain samples of actual coatings and laboratory control samples. Since there are six different resins used in this two-component coating system, production errors and deviations from correct mixing prior to application could have caused the residue. Any variation from the specified stoichiometry could also result in films with lower cross-link densities and lower glass transition temperatures (Tg). Rounds fired at 120 C have more residues than identical rounds fired at ambient temperature; additional weeks of cure lower the amounts of residue. A differential screening calorimeter (DSC) analysis of the various samples revealed that a suspect lot of ammunition with higher levels of residue had lower Tg values. Fourier-transform infrared (FTIR) was effective in monitoring the degree of cure of the epoxy coating system. Analyzing the residue from actual firings showed similar features. Koenig hardness values showed variations caused by dry film thickness, but also showed insignificant changes caused by transformations in the stoichiometry of the clear topcoat from 52.5 to 45 phr (pounds per hundred of resin).
Thermal characterization of polymeric materials
Thermoanalytical instrumentation, techniques and methodology, P.K. Gallagher the basis of thermal analysis, B. Wunderlich thermoplastic polymers, R.P. Chartoff polymer blends and block copolymers, H.E. Bair and A. Hale elastomers, A.K. Sircar thermosets, R.B. Prime fibres, M. Jaffe, J.D. Menczel, and W.E. Bessy films, M. Jaffe, J.D. Menczel, and W.E. Bessy thermal characterization of composites, R.J. Morgan thermal analysis of additives in polymers, H.E. Bair.
A new technique for decalcifying thin ground specimens of adult human enamel.
Abstract A new decalcification technique is described for the recovery of the organic matrix from thin ground specimens of adult human enamel. An aqueous solution of chromium sulphate which has both fixing and decalcifying properties is used. The results are compared with those obtained when an adjacent part of the same ground specimen was decalcified with the hydrochloric acid solution of Brain (1962). Dependent on slight differences in pH of the chromium solutions, two different appearances of the recovered matrix are obtained: above pH $ 3.2 a structural matrix which is positively birefringent at refractive index 1.55, whereas below this pH a matrix which is homogeneous and non-birefringent and almost similar to the matrix obtained after hydrochloric acid decalcification. The two types of matrices are discussed and the one favoured on morphological grounds, the chromium sulphate structural matrix, is related to present concepts of the structure of the native enamel matrix.