Abstract:Techniques for the precise measurement of the P–T melting curves of gases at pressures up to about 12 kbar have been developed. In the method used, a pressure vessel is maintained at a temperature constant to within ± 0.002°K. The pressure in the system is adjusted by manipulation of the pressure generating intensifier until solid–fluid coexistence is obtained within the vessel. The melting temperature is then measured with a platinum resistance thermometer mounted on the vessel, while the corresponding meltin… Show more
“…Table 2 shows the parameters of the simulated graphene nanobubbles. According to this table, all calculated pressures in the trapped substance are considerably lower than the melting pressure of bulk argon at 300 K, which is 1200 MPa 29 , 30 (see Fig. 3 ).…”
Section: Resultsmentioning
confidence: 90%
“…R: radius; H: maximum height; N Ar : number of argon atoms inside the nanobubble; N layers : number of argon layers inside the nanobubble; ρ : argon density; P: argon pressure; L x , L y , L z : final lengths of the simulation box. # R, nm H, nm H/R N Ar N layers ρ , g/cm 3 P, MPa L x , nm L y , nm L z , nm 1 7.8 0.64 0.083 2463 2 1.962 417 43.51 43.60 100 2 7.3 0.95 0.130 2463 3 1.911 398 43.55 43.60 100 3 13.8 1.57 0.114 12952 5 1.859 257 43.43 43.54 100 4 16.9 2.16 0.128 26153 7 1.849 229 78.77 79.17 100 5 24.0 2.77 0.116 73624 9 1.841 197 98.67 98.85 100 6 33.3 3.70 0.111 196331 12 1.837 172 98.55 98.83 100 Figure 3 The melting line of bulk argon 29 , 30 and the thermodynamic state of argon inside the graphene nanobubbles (red dots). …”
Section: Resultsmentioning
confidence: 99%
“… The melting line of bulk argon 29 , 30 and the thermodynamic state of argon inside the graphene nanobubbles (red dots). …”
A two-dimensional (2D) material placed on an atomically flat substrate can lead to the formation of surface nanobubbles trapping different types of substances. In this paper graphene nanobubbles of the radius of 7–34 nm with argon atoms inside are studied using molecular dynamics (MD). All modeled graphene nanobubbles except for the smallest ones exhibit an universal shape, i.e., a constant ratio of a bubble height to its footprint radius, which is in an agreement with experimental studies and their interpretation using the elastic theory of membranes. MD simulations reveal that argon does exist in a solid close-packed phase, although the internal pressure in the nanobubble is not sufficiently high for the ordinary crystallization that would occur in a bulk system. The smallest graphene bubbles with a radius of 7 nm exhibit an unusual “pancake” shape. Previously, nanobubbles with a similar pancake shape were experimentally observed in completely different systems at the interface between water and a hydrophobic surface.
“…Table 2 shows the parameters of the simulated graphene nanobubbles. According to this table, all calculated pressures in the trapped substance are considerably lower than the melting pressure of bulk argon at 300 K, which is 1200 MPa 29 , 30 (see Fig. 3 ).…”
Section: Resultsmentioning
confidence: 90%
“…R: radius; H: maximum height; N Ar : number of argon atoms inside the nanobubble; N layers : number of argon layers inside the nanobubble; ρ : argon density; P: argon pressure; L x , L y , L z : final lengths of the simulation box. # R, nm H, nm H/R N Ar N layers ρ , g/cm 3 P, MPa L x , nm L y , nm L z , nm 1 7.8 0.64 0.083 2463 2 1.962 417 43.51 43.60 100 2 7.3 0.95 0.130 2463 3 1.911 398 43.55 43.60 100 3 13.8 1.57 0.114 12952 5 1.859 257 43.43 43.54 100 4 16.9 2.16 0.128 26153 7 1.849 229 78.77 79.17 100 5 24.0 2.77 0.116 73624 9 1.841 197 98.67 98.85 100 6 33.3 3.70 0.111 196331 12 1.837 172 98.55 98.83 100 Figure 3 The melting line of bulk argon 29 , 30 and the thermodynamic state of argon inside the graphene nanobubbles (red dots). …”
Section: Resultsmentioning
confidence: 99%
“… The melting line of bulk argon 29 , 30 and the thermodynamic state of argon inside the graphene nanobubbles (red dots). …”
A two-dimensional (2D) material placed on an atomically flat substrate can lead to the formation of surface nanobubbles trapping different types of substances. In this paper graphene nanobubbles of the radius of 7–34 nm with argon atoms inside are studied using molecular dynamics (MD). All modeled graphene nanobubbles except for the smallest ones exhibit an universal shape, i.e., a constant ratio of a bubble height to its footprint radius, which is in an agreement with experimental studies and their interpretation using the elastic theory of membranes. MD simulations reveal that argon does exist in a solid close-packed phase, although the internal pressure in the nanobubble is not sufficiently high for the ordinary crystallization that would occur in a bulk system. The smallest graphene bubbles with a radius of 7 nm exhibit an unusual “pancake” shape. Previously, nanobubbles with a similar pancake shape were experimentally observed in completely different systems at the interface between water and a hydrophobic surface.
“…(2); the dash-dotted line (-Á-) is for the melting of the hcp-solid as calculated from equation (2); the dashed lines (---) indicate the possible limits of the fcc and hcp-solid phases. The symbols are: ., reference [31]; Â, reference [32]; h, reference [34]; N, reference [35]; O, reference [36]; d, reference [37]; #, reference [38]; , reference [40]; M, reference [41]; , reference [42]; s, reference [43]; +, reference [44]; , reference [45]; }, reference [7]; , reference [8]; , reference [9]; , is the calculated {s(fcc) + s(hcp) + '} triple-point. …”
The experimental results on the fusion of the heavier rare gases at very high pressures, obtained in the last 20 years, are examined and analysed in conjunction with the measurements made at lower pressures from 1940 onwards. The parameters in the Simon equation for the melting curves of Xe, Kr, and Ar are determined, and the coordinates of a possible high-pressure {s(fcc) + s(hcp) + '} triple-point are identified for each one of these three elements. The enthalpies of transition of the transformations involved are estimated as well as their respective values of the entropies of transition.
“…A[(T/T0)C -1] + P0 and P = A T C + B, where P and T are the pressure and temperature at melting, P0 and T0 are the corresponding triple point values, and ArB, and c are fitted parameters (Hardy et al 1971). Early work on the melting of argon and recent theoretical predictions are summarized in table 3.…”
We discuss the problems associated with the measurement of temperature and the determination of melting in the laser-heated diamond-anvil cell. We also briefly sum marize the main developments of the last three decades in simultaneous highmeasurements and review practical aspects of the technique. The melting curve of argon as a function of pressure has been determined up to 47 GPa, and within ex perimental error, agrees with a Simon relation extrapolation of the melting curve from previous data to only 1.1 GPa. On the basis of currently debated upper and lower limits for the melting curve of pure iron, the argon melting curve can inter sect the melting curve of iron in the range 40-65 GPa. Our experiments suggest that the melting points of iron and argon are equal at 47±1.0 GPa and 2750T200 K. Above this pressure, pure iron would be expected to melt at a lower temperature than solid argon. In a separate experiment, the melting temperature of iron in an argon medium at 57±1 GPa appears greater than 2650T200 K. The intersection of the melting curves for non-interacting materials could serve as standard P -T fixedpoints and offer a route to the standardization of different methods of temperature measurement.
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