Sheila Devasahayam

Effect of electron beam radiolysis on mechanical properties of high performance polyimides. A comparative study of transparent polymer films

The mechanical properties of four optically transparent polyimides prepared from the dianhydrides ODPA and 6FDA and the diamines ODA and DAB were assessed. The property changes when these polymers are subjected to high-energy electron-beam irradiation (1 MeV) for doses up to 18.5 MGy and temperatures up to 523 K were also studied and compared. The corresponding changes on radiolysis of Kapton are reported for comparison with the other polymers. The tensile properties of the four polyimides differed mainly by the nature of the dianhydride, with the ODPA polymers undergoing necking and cold drawing and the 6FDA polymers brittle fracture. The four polyimides were synthesized with the objective of obtaining optimum transparency for space applications where high-energy radiation doses of 15-20 MGy may be expected in geosynchronous orbits over a life span of 20 years. The polyimides were shown to maintain good optical and tensile properties at temperatures up to about 450 K for a dose of 18.5 MGy, but above this temperature the moduli of the polymers began to deteriorate and there was a small decrease in the transmittance of the exposed polymer films.

A comparative study of the radiation resistance of four optically transparent polyimides

A comparative study of the high energy radiation resistance to formation of radicals in two pairs of polymers is reported. In one pair of polymers the phenyl groups containing the imide rings are separated by an ether linkage and in the other pair they are separated by an hexafluoroisopropylidine group. Two of the polymers contained aromatic amine units linked through an ether linkage and the other two polymers contained a trifluoromethyl biphenyl diamine. The polymers were shown to retain a high level of transparency in the visible region following radiolysis to doses as high as 8 Gy. ESR studies of the resistance to radical formation on radiolysis. at 77 K revealed that the polymers containing ether linkages were more stable than their fluorinated analogues, but all were less stable than Kapton (R)

The radiation chemistry of ultem at 77 K as revealed by ESR spectroscopy

Radical formation in ultem following gamma-radiolysis has been reassessed, and the G(R*) values at different temperatures have been determined by ESR spectroscopy. The radical assignment and radical reactivity have been re-examined by photobleaching and thermal annealing studies. Photobleachable radical anions were found to comprise approximate to40% of the total number of radicals formed on radiolysis at 77 K. Spectral subtraction methods, ESR spectral simulations, measurement of g-values and the hyperfine splitting constants were used to identify the other radical intermediates. The principal chain scission radicals are formed due to scission of the main-chain at (i) the ether linkage, (ii) the isopropylidene group and (iii) the imide ring in the main chain. The side chain methyl groups of the isopropylidine units also lose hydrogen to form methylene radicals. The five-line spectrum observed to decay in the temperature range 370-430 K, which has not been assigned previously, has been identified as being characteristic of a di-substituted benzyl radical

Towards identifying the new structures formed on the γ-radiolysis of Ultem

Ultem irradiated up to 10.0 MGy has been analysed using C-13, H-1 and D-2 proton-carbon and proton-proton correlation NMR spectroscopy to shed light on the formation of new structures. Chemical shifts and correlation data were used to determine the structure or partial structures of several new components. The spectra indicated the presence of new groups and structures involving the isopropylidene group, the imide ring, and hydrogen-abstraction reactions. Possible pathways for formation of the new structures are proposed and the G-values for their formation have been estimated

Abrasion Characteristics of Ores

Effects of time and size on t10, the abrasion parameter (fineness indicator) using a calibration model for a given ore type is presented. A model for predicting t10 from a small diameter core material for any ore type is also presented. The ores studied are: Ok Tedi 1, Ok Tedi 2, Red Dome, Alcoa, and Broken Hill. Shape factor of the particles that varies with both the particle size and the ore type affects the abrasion characteristics. Abrasion process in a tumbling mill is described by two mechanisms namely (1) chipping, and (2) abrasion, occurring at different rates. The chipping phenomenon depends on the ore and the shape factor. The abrasion phenomenon is independent of t10° (t10° is the ore-specific t10 at 7 × 10−4 kWh/t tumbling test energy) and the shape factor. Abrasion process occurs at a much slower rate compared to the chipping process. Transition between chipping and abrasion occurs approximately after 2 min of tumbling. The long-term rate is controlled by the abrasion or attrition rather than by the chipping mechanism.

Predicting the Liberation of Sulfide Minerals Using the Breakage Distribution Function

The study validates how the original grain size of the ore influences the propensity of a mineral to be liberated. An Australian zinc ore was investigated for the variation in composition with respect to grain size using QEMSCAN. The breakage patterns of the ore showed that the liberated phases were influenced by the association of various phases in the original ore affecting the size distribution of different species. The combined breakage and the QEMSCAN data were used to predict the effect of grinding which affects the grain size and hence the distribution of grain phases in different size fractions, and relates the latter to the proportions of binary and ternary composite grains in the original ore sample. The study provides a direct correlation between the grain size distribution resulting from grinding to the liberated free minerals, binary and ternary composites. The liberation model parameters determined in the present study are used to predict the liberation of different mineral compositions directly from the size distribution analysis as well as from the t10 parameter. The study has implications for optimizing grinding practice for improved beneficiation, and liberation as over-grinding produces undesirable fines difficult to process as well as incur additional energy input.

Study of microstructure and fracture properties of blunt notched and sharp cracked high density polyethylene specimens

This paper examines the effect of a broad range of crosshead speed (0.05 to 100 mm/min) and a small range of temperature (25 °C and 45 °C) on the failure behaviour of high density polyethylene (HDPE) specimens containing a) standard size blunt notch and b) standard size blunt notch plus small sharp crack – all tested in air. It was observed that the yield stress properties showed linear increase with the natural logarithm of strain rate. The stress intensity factors under blunt notch and sharp crack conditions also increased linearly with natural logarithm of the crosshead speed. The results indicate that in the practical temperature range of 25 °C and 45 °C under normal atmosphere and increasing strain rates, HDPE specimens with both blunt notches and sharp cracks possess superior fracture properties. SEM microstructure studies of fracture surfaces showed craze initiation mechanisms at lower strain rate, whilst at higher strain rates there is evidence of dimple patterns absorbing the strain energy and creating plastic deformation. The stress intensity factor and the yield strength were higher at 25 °C compared to those at 45 °C

G -Values for Scission and Crosslinking on γ — Radiolysis of Ultem at 303 K

The radiation chemical yields G(S) and G(X) for H-linking and Y-linking models for Ultem have been calculated from molecular weight analysis by gel permeation chromatography. These G-values have been compared with the G-values obtained from analysis of soluble fractions above the gel dose, which have been reported in previous works. An analysis of the molecular weight data in terms of H-linking and Y-linking mechanisms yielded values of G(S H ) = 1.0 × 10−3 and G(H) = 6.0 × 10−3 and G(S Y ) = 1.3 × 10−2 and G(Y) = 1.8 × 10−2. The corresponding values obtained from the solubility data were G(S H ) = 0.53 × 10−2, G(H) = 1.39 × 10−2, G(S Y ) = 4.2 × 10−2 and G(Y) = 4.6 × 10−2. The origin of the disagreement between the molecular weight and solubility values is not clear, but it could arise as a result of observed microgel formation below the reported gel dose of 0.13 MGy. Whether the crosslink mechanism proceeds by an H-linking or Y-linking process is also unclear and will require direct observation of the crosslinking structures.

Study of Victorian brown coal dewatering by super absorbent polymers using attenuated total reflection fourier transform infrared spectroscopy

ABSTRACT A simple and useful method to monitor the water content of coal samples using Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy is presented. ATR-FTIR analyses of oven-dried and polymer-dried brown coal samples are discussed. The difference spectra indicate that the drying of as-received coal at room temperature using a Super Absorbent Polymer (SAP) removes only 44% of moisture compared to oven drying at 105 °C. As the SAP does not completely remove the water from the coal the possibility of explosion due to oxidation of the coal powder is greatly reduced. SAP drying is energy and emission efficient compared to oven drying method. At the pH < 5 studied SAP dewatering is dominated by physical processes. The movements in H-bonding observed in ATR-FTIR suggest a physico-chemical process.

Evaluation of coal for metallurgical applications

Abstract: A number of coal parameters are used in coal selection for metallurgical applications. This chapter focuses mainly on coal parameters for use in coke-making and pulverised coal injection for the integrated iron and steel-making process. Parameters for use in alternative iron-making processes such as Corex® and other coal-based smelting reduction technologies are also discussed. This chapter reviews the current status of recent scientific advances in the area to better understand these parameters and thus efficiently utilise coal for various metallurgical applications. Where possible, the international standards related to the critical utilisation parameters identified are listed and discussed.