Rutile

Chemical Properties

Rutile has a chemical formula of TiO₂, although it is in fact not purely titanium dioxide. In reality there is a minimum of 94.0 % TiO₂ in rutile and the rest is made up of impurities such as Fe, Ta, Nb, Cr, V and Sn.

As an oxide of titanium, rutile can thus be classified chemically as a metal oxide, but is more specifically a member of a small group of metal oxides known as the rutile group.

The Rutile Group

The rutile group also contains minerals such as Cassiterite (Tin Oxide), Plattnerite (Lead oxide), Pyrolusite (Manganese Oxide) and Stishovite (Silicon Oxide). All members of the group have the formula MO₂ and a 4/m 2/m 2/m symmetry (see Crystal Structure of Rutile).

Like rutile, the other members of the rutile group are often important ores of their respective metals.

Physical Properties

The table below shows physical constants and characteristics of rutile, including its optical properties.

Specific Gravity/Density (g/cm³)	4.2 – 4.3
Mohs Hardness at 20^oC	6.5
Dielectric Constant	6.7
Birefringence	Maximum (0.285 – 0.296)
Luster	Submetallic to adamantine
Diaphaneity	Opaque to translucent
Fracture	Concohidal to uneven
Steak	Pale Brown
Pleochroism	Weak to moderate
Refractive Index	- 2.60 to 2.89
Reflective Power	~21%

Looking at the table, we can see that with a Mohs Hardness of 6.5 at 20^oC, rutile is a brittle material. This coincides with its crystal structure (see Crystal Structure of Rutile).

Optically, rutile is transparent in thin crystals otherwise it is found to be opaque. It’s refractive index is relatively high, 2.60 – 2.89, giving it a greater sparkle than diamond.

Metaphysical Properties

On a slightly different note, some people believe that rutile has metaphysical properties. It is said to one more forgiving towards both oneself and others, and to give a general sense of tranquillity. Rutile is also said to stimulate one's problem solving capabilities by providing a more in-depth understanding of the details involved.

In the field of complimentary medicine, rutile is used to help strengthen the immune system and to help in the treatment of pulmonary and circulatory disorders.

Titanium Dioxide

As rutile has a defective crystal structure, very little spectroscopic or thermo-chemical data has been collected for it. However, for pure titanium dioxide of which a minimum of 94 % of rutile is made up, there is a reasonable amount. Some of this data is shown below.

Gas Phase Thermochemistry Data

Quantity	Value	Units	Reference
Δ_fH°_gas	-305.4324	kJ/mol	Chase, 1998
S°_{gas,1 bar}	260.14	J/mol*K	Chase, 1998

Gas Phase Heat Capacity (Shomate Equation)

C_p° = A + B*t + C*t² + D*t³ + E/t²
H° - H°_298.15= A*t + B*t²/2 + C*t³/3 + D*t⁴/4 - E/t + F -Δ_fH°_f,298
S° = A*ln(t) + B*t + C*t²/2 + D*t³/3 - E/(2*t²) + G
    C_p = heat capacity (J/mol*K)
    H° = standard enthalpy (kJ/mol)
    Δ_fH°_298.15 = enthalpy of formation at 298.15 K (kJ/mol)
    S° = standard entropy (J/mol*K)
    t = temperature (K) / 1000.

Temperature (K)	4000. - 6000.
A	63.82818
B	-4.418178
C	1.080707
D	-0.058816
E	-5.216235
F	-336.0739
G	323.0094
ΔH°_f,298 (kJ/mol)	-305.4324
Reference	Chase, 1998

Gas Phase Ion Energetics Data

Ionization energy determination

IE (eV)	Method	Reference
9.5 ± 0.5	EI	Balducci, Gigli, et al., 1985
9. ± 0.5	EI	Balducci, Gigli, et al., 1985, 2
10.4 ± 1.0	EI	Banon, Chatillon, et al., 1982
9.54 ± 0.10	EI	Hildenbrand, 1976
10.2 ± 0.2	EI	Rauh and Ackermann, 1974
11.56 ± 0.14	EI	Wu and Wahlbeck, 1972
8.5 ± 0.5	EI	Balducci, De Maria, et al., 1972
9. ± 0.2	EI	Mesnard, Uzan, et al., 1966

Appearance energy determinations

Ion	AE (eV)	Other Products	Method	Reference
OTi⁺	13.7 ± 0.5	O	EI	Banon, Chatillon, et al., 1982
Ti⁺	14.6 ± 0.5	O₂	EI	Banon, Chatillon, et al., 1982
Ti⁺	20. ± 0.2	?	EI	Mesnard, Uzan, et al., 1966
TiO⁺	8. ± 0.5	O	EI	Mesnard, Uzan, et al., 1966

Vibrational and Electronic Spectra

State: unknown

Energy (cm^-1)	Med.	Transition	λ_min (nm)	λ_max(nm)	References
T_o = 18880	Ne		529	621	McIntyre, Thompson, et al., 1971

State: a

Energy (cm^-1)	Med.	Trans.	λ_min (nm)	λ_max (nm)	References
T_o= 15800 ± 800	gas				Wu and Wang, 1997

State: X

Vib. Sym.	No.	Approx. type of mode	cm^-1	Med.	Method	References
a₁	1	Sym. stretch	965 {T}	gas	IR	DeVore and Gallaher, 1983 Wu and Wang, 1997
	1	Sym. stretch	962.0	Ne	IR	McIntyre, et al., 1971
	1	Sym. stretch	946.9	Ar	IR	Chertihin and Andrews, 1995
b₂	3	Asym. stretch	944	gas	IR	DeVore and Gallaher, 1983
	3	Asym. stretch	934.8	Ne	IR	McIntyre, et al., 1971
	3	Asym. stretch	917.1	Ar	IR	Chertihin and Andrews, 1995

Notes

T Tentative assignment or approximate value.

T_o Energy separation between the v = 0 levels of the excited and electronic ground states.

Infrared Spectrum of TiO₂

Technique:	FT-IR Spectrum	Phase:	Solid
MF:	TiO2	MW:	79.88
MP:	1855	BP:	2900
X Axis	Wavenumber (cm-1)	Y Axis	Absorbance