Sol-gel coated polarization vessels

Details Sol-gel coated polarization vessels Sol-gel coated polarization vessels

2000-02-11

2003-04-22

Soderquist, Arlen (Department: 1743)

Chemical apparatus and process disinfecting, deodorizing, preser

Control element responsive to a sensed operating condition

C215S012200, C427S376200, C427S397700, C428S034600

Reexamination Certificate

active

06551559

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to methods and apparatus for hyperpolarizing noble gases. More particularly, the invention relates to methods for manufacturing glass apparatus useful for hyperpolarizing noble gases.
The number and variety of applications of noble gases, particularly
3
He and
129
Xe, polarized through spin-exchange optical pumping (Bhaskar et al. 1982; Happer et al. 1984) have grown rapidly over the past few years. Most recently, the enhanced NMR signals of laser-polarized
129
Xe, which are about five orders of magnitude larger than those from thermally polarized
129
Xe, have made possible the first high-speed biological magnetic resonance imaging (MRI) of a gas (Albert et al. 1994), opening many new avenues of research. Historically, polarized
129
Xe has been used for fundamental symmetry studies (Chupp et al. 1994), nuclear spin relaxation studies of solids (Gatzke et al. 1993), high resolution nuclear magnetic resonance spectroscopy (NMR) (Raftery et al. 1991), and cross-polarization to other nuclei (Gatzke et al. 1993; Driehuys et al. 1993; Long et al. 1993). Polarized
3
He is an important nuclear target (Anthony et al. 1993; Middleton, unpublished; Newbury et al. 1991; Newbury et al. 1992) and has also been shown to be an excellent nucleus for gas-phase MRI (Middleton et al. 1995).
All of these applications require that the highly non-equilibrium polarizations of the noble gas nuclei be long-lived, i.e., the decay of polarization to thermal equilibrium level must be slow. However, interactions of the polarized noble gas nuclei with surfaces can cause rapid relaxation, often resulting in relaxation times T
1
that are undesirably short. Understanding these mechanisms, and devising methods of inhibiting relaxation, is vital for continued progress in a large variety of experiments using polarized noble gases.
Bouchiat and Brossel identified relaxation of hyperpolarized rubidium on coatings of paraffin on the walls of glass resonance cells (Bouchiat et al. 1966). This relaxation was attributed to adsorption of rubidium on the coatings leading to depolarizing interactions such as dipole-dipole interaction between electron spin of the rubidium atom and the nuclear spin of the protons in the coating. This paper reports a diminution of such interactions upon substituting (CD
2
)
n
paraffins for (CH
2
)
n
paraffins, i.e., deuterating the paraffins. Bouchiat and Brossel, however, do not extrapolate on this work and make no inferences concerning potential interactions of other elements with paraffins or the reduction thereof. Nor does this paper indicate whether any other polymeric materials exhibit depolarizing properties.
Zeng and co-workers made substantial progress in reducing
129
Xe surface relaxation by introducing the use of the silicone coating agent SurfaSil (Zeng et al. 1983). Relaxation times of order T
1
~20 min are now routinely attained using such coatings. Nonetheless, these relaxation times are still approximately two orders of magnitude shorter than what is ultimately possible for gaseous
129
Xe at standard temperatures and pressures. It has been thought that continuing inability to improve nuclear spin lifetimes is attributable to paramagnetic impurities in the coating compositions. Efforts to reduce relaxation by removing such impurities, however, have met with little success. Accordingly, it is evident that better understanding of the
129
Xe surface interactions has been needed.
Driehuys et al. identified polymeric coatings which further improved the properties of containers with respect to polarized noble gases. See, for example, U.S. Pat. No. 5,612,103. The polymers were modified to limit depolarizing interaction with the container surfaces. For example, contact with protons was limited by providing substituents having non-zero spin, e.g., substituting deuterium for protons. Alternatively, permeability was controlled by suitable selection of polymeric coating materials.
As a result, there exists a need for improving the yield and efficiency of noble gas hyperpolarization processes by reducing the depolarizing interactions of the noble gas with surfaces in the hyperpolarization system.
The manufacture of sol-gel materials is well known in the art. See, for example, Brinker et al. (1990). In particular, methods for manufacturing sol-gel glasses are known. See, e.g., U.S. Pat. Nos. 5,637,507, 5,008,219, and 4,385,086, the complete disclosures of which are incorporated herein by reference. Such materials can be applied as coatings. However, none of the art of which Applicants are presently aware discloses any utility for such materials in the context of preserving noble gas polarization.
There is also a need for increasing the total amount of hyperpolarization in a noble gas by reducing or counteracting depolarizing interactions between the noble gas and its surrounding physical system.
Moreover, there is a need for improving the duration of storage of hyperpolarized noble gas by reducing depolarizing interactions of the noble gas with the storage container.
In addition, there is a need for improving the efficiency of magnetic resonance imaging methods which require the use of hyperpolarized noble gas nuclei by decreasing the amount of physical interaction of the noble gas with physical systems.
SUMMARY OF THE INVENTION
In one embodiment, the invention is a polarization cell for hyperpolarizing a noble gas, wherein the polarization cell has an interior surface coated with a glass coating deposited from a sol-gel.
The noble gas is preferably
129
Xe or
3
He. The glass coating is preferably substantially impermeable to the noble gas and/or to ions in the material from which the polarization cell is manufactured. The polarization cell is preferably made of at least one material selected from the group consisting of glasses, ceramics, composites, metals. The glass coating is preferably alkali resistant. Also, the glass coating is preferably substantially free of paramagnetic or other depolarizing impurities. An especially preferred glass coating is an aluminosilicate glass.
In another embodiment, the invention is a method for hyperpolarizing a noble gas, comprising:
spin polarizing a noble gas in a polarization cell having an interior surface coated with a glass coating deposited from a sol-gel.
In another embodiment of the invention, in an apparatus for hyperpolarizing a noble gas, comprising:
a) a source of laser energy; and
b) a polarization cell;
the improvement consists of a glass coating deposited from a sol-gel onto an interior surface of the polarization cell.
In still another embodiment, the invention is a method of reducing depolarizing interaction between a hyperpolarized noble gas and a surface of a container, comprising providing on the surface of the container a glass coating deposited from a sol-gel. Preferably, the container is a polarization cell, a conduit for transferring the hyperpolarized noble gas, an accumulation reservoir for accumulating the hyperpolarized noble gas, or a storage reservoir for storing the hyperpolarized noble gas.
In yet another embodiment, the invention is an apparatus for containing a hyperpolarized noble gas, wherein the apparatus has an interior surface coated with a glass coating deposited from a sol-gel. Preferred apparatus includes, for example, a polarization cell, a conduit for transferring the hyperpolarized noble gas, an accumulation reservoir for accumulating the hyperpolarized noble gas, or a storage reservoir for storing the hyperpolarized noble gas. Also included, is a transport or storage container having an interior surface coated with a glass coating deposited from a sol-gel suitable for transport or storage of the hyperpolarized noble gas.
As a result the invention provides a method and apparatus for substantially improving the production and storage of hyperpolarized noble gases. The glass coatings substantially reduce depolarizing interactions of polarized noble gas nuclei with surfaces of containers such as polarization cells, and decrease losses to permeabili

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