R. Mossadegh

Determination of the mass fraction of crystals in partly frozen hydrocarbon fuels

Abstract The per cent by mass of crystalline solid in a partly frozen hydrocarbon fuel cannot be determined by a filtration experiment alone because the precipitate retained by the filter entraps large amounts of the liquid phase. A technique has been developed which augments the filtration experiment with an independent determination of the amount of liquid in the precipitate and hence allows calculation of the true value of the mass percent of crystalline solid, % S . This method involves the addition to the initial fuel of a small amount of a non-crystallizing dye as a tracer and the determination of the amount of entrapped liquid in the precipitate fraction by a spectrophotometric comparison of the dye concentrations in the precipitate and filtrate. The technique has been tested at several temperatures on both a diesel and a jet fuel. % S increased with decreasing temperature below the melting point. The % S values for the jet fuel were in good agreement with results obtained in another laboratory using a filtration/g.c. analysis method. Precipitates obtained by filtration of the partly frozen fuels were found to contain 50–80% entrapped liquid.

DSC studies of melting behavior of heavy metal fluoride glass compositions

Abstract Differential scanning calorimetry (DSC) studies of a number of heavy fluoride glasses have been carried out while heating from below the glass transition up to 950K. The glasses first crystallize and then remelt. The final stage of melting is generally marked by a small, high temperature endotherm, whose location allows assignment of a liquidus temperature TL to the glass composition. The ratio T L T g of the liquidus to the glass transition temperature is roughly constant and equal to about 1.5 for a wide variety of glass compositions.

Sub-Tg relaxations in heavy metal fluoride glasses

Structural relaxation studies during annealing of a series of ZrF4-based glasses below the glass transition temperature have been carried out. Indications are that no property changes due to structural relaxation are likely to occur at ambient temperature over periods of tens of years. Some of the lower Tg glasses, however, did exhibit detectable structural relaxation on annealing at temperatures as low as 100°C over roughly a one year time period.

Structural Relaxation in Fluoride Glasses

Structural relaxation studies during annealing of a series of ZrF4-based glasses below the glass transition temperature have been carried out. Indications are that no property changes due to structural relaxation are likely to occur at ambient temperature over periods of tens of years. Some of the lower Tg glasses, however, did exhibit detectable structural relaxation on annealing at temperatures as low as 100°C over roughly a one year time period.

Crystallization And Viscosity Of Heavy Metal Fluoride Glasses

Shear viscosity data for a glassforming ZrF4-BaF2-LaF3-A1F3 composition covering the range from the highly fluid melt down to the glass transition (10-1 to 1013 P) have been collected from five sources. The viscosity temperature dependence is highly non-Arrhenius and cannot be described by three parameter expressions such as the Fulcher equation. The four parameter Cohen-Grest equation, however, does give a good fit to the data, possibly allowing interpolation in the range of intermediate viscosity important for fiber drawing where data is currently lacking. The viscosity data are compared with crystallization temperatures obtained by DSC during heating and cooling at 10K/min.