Rubidium
Rubidium is a soft, silvery white metal which is easily oxidized in air. It has only one stable form. Rubidium is the second most electropositive and the second most alkaline element. It also has the lowest ionization potential. Current uses of rubidium are limited but include such applications as vacuum tubes and photoelectric cells. Potential applications include use as a heat transfer medium and as a fuel for ion propulsion engines. The chemical behavior of rubidium is similar to that of potassium; it reacts vigorously with air or water and should be handled and stored in a dry, inert environment.
PHYSICAL PROPERTIES:
Crystal Structure: Body-centered cubic, A2; a = 0.562 + 0.003 nm at -173 oC;
a = 0.570nm at 0 oC.
Atomic Weight: 85.467
Density:
oC g/cc
20 1.532
39 1.475
50 1.47
150 1.46
220 1.45
Density for Liquid Range: ρ = 1.48 - 4.5 (T - Tm), where density is in g/cc and Tm is the
melting point.
Volume Change on Melting: 2.5% increase
THERMAL PROPERTIES:
Melting Point: 38.89 oC
Boiling Point: 688 oC
Coefficient of Thermal Expansion:
Linear: 90 μm/m ⋅ K at 20 oC; 340 μm/m ⋅ K at 40 to 100 oC.
Volumetric: 3.38 x 10-4 m/m ⋅ K
Specific Heat: 0.33489 kJ/kg ⋅ K at 0 oC; 0.3797 kJ/kg ⋅ K at 50 oC.
Enthalpy: Solid: HT - H298 = 160.16 T + 0.32080 T2 - 76,259.
Liquid: HT - H298 = 384.47 T - 88,846. T is in K and HT - H298 is in J/kg.
Entropy: Solid: S = 885.45 log T - 1297.9. T is in K and S is in J/kg.
Latent Heat of Fusion: 25.535 kJ/kg
Latent Heat of Vaporization: 887.46 kJ/kg.
Thermal Conductivity:
oC Phase W/m ⋅ K
0 Solid 58.3
25 Solid 58.2
38.89 Solid 58.1
38.89 Liquid 33.3
Vapor Pressure:
oC kPa
294 0.1333
387 1.333
519 13.33
569 26.66
628 53.33
Saturated Vapor Pressure:
log P = (-4688/T) - 1.76 log T + 15.195, where P is in Pa and T is in K.
Critical Temperature and Pressure:
Tc = 2083 + 20 K and Pc = 14.54 + 0.5 MPa
ELECTRICAL PROPERTIES:
Electrical Resistivity:
Temperature Resistivity
oC K nΩ ⋅ m
0 273 115.4
20 293 128.4
39.9 312.1 137(a)
39.9 312.1 220(b)(c)
100 373 274.7(c)
(a) Solid. (b) Liquid. (c) Equation for resistivity between 312.1 K and 373 K:
ρ = 0.086T - 4.8, where T is in K.
Temperature Coefficient: 0.06 nΩ ⋅ m per K
Electrochemical Equivalent:
Valence Equivalent, mg/C
1 0.8858
2 0.4429
3 0.2214
4 0.1107
Electrolytic Solution Potential: Versus H2: -2.924 V at 25 oC
Work Function: 2.09 eV (0.335 aJ)
Photoelectric Threshold: 7.3 x 10-4 C
MAGNETIC PROPERTIES:
Magnetic Susceptibility: Volume: 2.6 x 10-3 mks at 30 oC
CHEMICAL PROPERTIES:
General Corrosion Behavior: Rubidium is very active. It ignites in air at room temperature and will react explosively in oxygen. Rubidium can easily dissociate water to form the hydroxide and will react spontaneously with gaseous chlorine and fluorine and explosively with liquid bromine.
MECHANICAL PROPERTIES:
Hardness: 0.3 Mohs
Modulus of Elasticity: 2.35 GPa
Kinematic Liquid Viscosity:
oC mm2/s
38 0.4573
39 0.4561
40 0.4528
50 0.4267
99.7 0.3359
140.5 0.2904
179 0.2586
220.1 0.2332
Liquid Surface Tension:
oC N/m
39 0.0847
100 0.080
550 0.051
632 0.0468
Speed of Sound: At melting point: v = 1260 m/s