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Eqn. 5


perature, g is gravitational acceleration (9.81 m/s2 s2


where pm


probe and boat. The density of the liquid metal at a given temperature is given by


and Pprobe Eqn. 6


The height difference between the metal surfaces in cylinder 1 and 2 was straightforwardly calculated from


Eqn. 7 Where 0 1


the metal height change in cylinder 1. The metal height change in cylinder 1 of the GED was calculated from


h is the initial metal height in cylinder 1, and ∆h1 Eqn. 8 Where D1,eff


or a gas mixture, can be derived from the ideal gas law, i.e.,31 Eqn. 9


The molecular weight of an ideal gas, Mg Where mg is the total gas mass and R is the universal gas con-


stant (8.314 J/mol/K). Manipulation of Equation 9 gives the ratio of the measured to known molecular weight (or simply the dimensionless molecular weight), ϕ, of a gas i as


Eqn. 10


Where Mi is the known molecular weight of the measured gas i, P is the measured initial gas pressure found by in-


0 g


putting the initial measurement conditions into Equation 5. The accuracy to which the apparatus could measure the mo- lecular weight of a known gas was evaluated through these dimensionless molecular weight measurements.


Where 0 s Binder Gas evolution tests


PUNB bonded sand samples for gas expansion measure- ment were prepared using the same methods as those used for TGA. The bonded sand samples for gas expansion mea- surement were shaped into small cylinders measuring about 0.8 cm (0.315 in) in diameter and 0.5 cm (0.197 in) in height,


International Journal of Metalcasting/Spring 2012


The measured total height change in cylinder 2 was interpo- lated such that the total gas volume and pressure could be determined at intervals of 0.1°C (0.18°F) over the measured temperature range. The total gas volume and pressure were found using the same methods as described for the pure gas volume and pressure calculations. Summation of the partial


29 as a function of temperature is then given by


By conservation of mass, the binder mass lost during thermal decomposition is equivalent to the binder gas mass evolved. The mass of gas evolved from the bonded sand samples, mb


, Eqn. 11 m is the total initial PUNB bonded sand sample mass.


is the effective internal diameter of cylinder 1. , being a single gas


is


is the density of the liquid metal at a given tem- or 32.2 ft/


), ∆H is the height difference between the metal surfaces in cylinders 1 and 2, Patm


is the pressure from the weight of the displacement is atmospheric pressure (101325 Pa),


and the mass of the samples was approximately 0.2 g. The sample mass was measured with the same device used to measure the empty and filled GED. The small sample size helped minimize non-isothermality in the samples during testing, and multiple samples were used in each experiment to achieve the desired total initial sample mass. The bonded sand samples had a porosity of about 33%.26


Therefore, the


bonded sand samples were placed in a plastic bag that was continuously flushed with argon gas and stored in the argon- filled bag for at least 24 hours prior to testing. This ensured that only argon gas occupied the empty space inside the bonded sand samples and that pyrolysis of the bonded sand could occur during the tests.


After purging the GED with argon as previously described, a small amount of metal was injected into cylinder 1 in or- der to create a flat surface of liquid metal at the bottom of cylinder 1. The argon injection tube was withdrawn from the GED, and samples were placed inside the GED such that the samples floated on top of the liquid metal. The argon and metal injection tubes were reinserted into cylinder 2, and the remaining filling and setup were carried out as described for the metal-only tests. The furnace was heated at a rate of 2°C/ min (3.6°F/min) while temperature and expansion measure- ments were obtained. The heating rate was selected based on the results from the pure gas expansion tests (see below). Multiple experiments were performed to obtain the binder gas molecular weight for all temperatures of interest. The total initial sample mass ranged from about 0.4 to 9 g. In ad- dition, measurements were collected as the furnace cooled during some of the tests.


A mixture of argon (from inside the bonded sand samples) and binder gas was present during heating of the PUNB bonded sand samples. The temperatures of the bonded sand samples, argon gas in the bonded sand samples, and evolved binder gas in the GED were not directly measured. These temperatures were assumed to be equivalent to the measured metal temperature. The validity of this assumption will be addressed later in the discussion.


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