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Cylinder 1 was entirely filled with liquid metal by evacuat- ing cylinder 1 while simultaneously injecting the metal into the GED through a second plastic tube. Cylinder 2 was filled

to the initial metal height 0 h2 of 3.5 cm (1.378 in). This height

was selected to ensure that the metal level in cylinder 2 was initially higher than the metal level in cylinder 1 (creating a slightly positive pressure in cylinder 1). The mass of the empty and filled GED was measured for all experiments us- ing an Ohaus model EP613C precision balance. The metal mass was found by simply subtracting the metal-filled GED mass from the empty GED mass. The displacement boat was then lowered onto the metal surface in cylinder 2, and the filled GED was placed in the furnace. The thermocouples were set in their locations and the initial height of the dis- placement probe was measured by the laser sensor. The fur- nace was heated at various constant rates ranging from 2°C/ min (3.6°F/min) to 15°C/min (27°F/min) while temperature and expansion measurements were obtained. Multiple tests were performed at each heating rate to ensure that the ex- periments were repeatable. The density of the liquid metal at room temperature (i.e., the initial temperature) was ob- tained by measuring the mass of metal that filled a calibrated volumetric flask. The metal density at room temperature was measured prior to filling the GED for all experiments.

The effective volumetric expansion coefficient of the liquid metal in the GED, eff

culated from m β , as a function of temperature was cal- Eqn. 2

height change in cylinder 2, Tm perature, 0

where D2 is the diameter of cylinder 2, ∆h2 is the measured Tm is the measured initial metal temperature,

is the measured metal tem- is

the density of the liquid metal at room temperature, and mn is the mass of liquid metal in the GED.

sured in the bulb tube). Pure Gas expansion tests

Additional experiments were carried out to determine the true volumetric expansion coefficient of the liquid metal. A spherical borosilicate bulb was fused to a long and nar- row borosilicate tube. The bulb was filled with liquid metal, placed in the furnace, and subjected to a step-heating pro- gram that simulated an “infinitely slow” heating rate. The true volumetric expansion coefficient was calculated using the measurements from the metal-only expansion in the bulb and Equation 2 (with D2 eter and ∆h2

replaced by the bulb tube’s diam- replaced by the metal-only height change mea-

Where: 0 to 0

2 fill

which the molecular weight of a known gas could be mea- sured. Aside from the insertion of a pure gas sample into the GED, the filling and setup procedure followed that of the metal-only tests. Once the GED was filled with metal, a specified volume of argon or hydrogen gas was injected into cylinder 1 of the apparatus through a flexible plastic tube. Liquid metal was simultaneously extracted from cyl- inder 2 to maintain the 3.5 cm (1.378 in) initial height in cylinder 2. Argon gas flowed into cylinder 2 at a rate of 400 cm3

/min (24.410 in3 /min) during the injection of the

gas sample. Once the GED was filled, the remainder of the setup was carried out as previously described. The furnace was heated at low rates of 2°C/min (3.6°F/min) and 3°C/ min (5.4°F/min) while temperature and expansion mea- surements were obtained. These heating rates were chosen based on the results from the metal-only expansion tests and to ensure reasonable isothermality of the gas and the GED. Multiple tests were performed to confirm the repeat- ability of the experiments.

The gas temperature T and initial gas temperature 0 T were

not directly measured. Rather, these temperatures were as- sumed to be the same as the measured metal temperature and measured initial metal temperature, respectively. The reasoning behind this will be discussed later. The measured metal height change in cylinder 2 during heating of the gas samples was used to interpolate the corresponding height change at intervals of 0.1°C (0.18°F) over the measured tem- perature range. This was done to properly match the pure gas measurements with the metal expansion data, as well as to standardize the pure gas expansion measurements and sub- sequent calculations as a function of temperature.

The total gas volume, Vg calculated from

, as a function of temperature was Eqn. 3 volume of the liquid metal. The first term on the right hand g

V is the volume contained by the filled GED (up h ) at the initial temperature and ∆Vm

is the change in

of temperature. The volume change of the liquid metal in the GED corresponding to a given temperature change was determined using29

V (which was verified against the supposed volume of gas injected into the GED), and the second term in Equation 3 corresponds to the change in gas volume, ∆Vg

Eqn. 4

Various volumes of argon and hydrogen gases were heat- ed in the GED in order to observe the nature of the gas expansion in the GED and to determine the accuracy to


As previously stated, the GED acted as a manometer, and the total gas pressure, Pg

, as a function of temperature was calculated from30 International Journal of Metalcasting/Spring 2012

side of Equation 3 corresponds to the initial gas volume, 0

, as a function

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