Kiyohisa Eguchi

Application of nuclear magnetic resonance pore structure analysis to porous silica glass

The internal pore structure of a series of porous silica glasses has been investigated using nuclear magnetic resonance (NMR). Longitudinal and transverse relaxation of protons in deionized water confined to the pores of the samples has been measured and interpreted to provide pore size distributions. Two sets of leached, phase‐separated porous glasses were used: the first nominally bimodal, the second with a more uniform pore space with pore sizes varying from 32 to 1350 A. Our results provide a stringent test of NMR relaxation as a method for pore size analysis. NMR relaxation experiments were performed on one sample as a function of the amount of water imbibed confirming the validity of the theoretical model used to interpret the magnetic resonance data.

NMR study of the solidification and melting of3He in porous glasses

TheP-T phase diagrams of the liquid-solid phase transition of3He in three porous glasses with different pore sizes have been determined from spin-lattice relaxation measurements in the temperature range 0.5–4.2 K. The onset of solidification of3He in the pores occurs at excess pressure over the bulk phase transition. The excess pressure depends on the pore size. A model of the phase transition in small pores which takes into account the contribution of the surface energy to the free energy is described and compared with experimental results. TheT1 relaxation mechanism of3He in the pores is found to be due to the surface relaxation when3He is in the liquid phase and due to the relaxation of bulk solid3He when it is in the solid phase.

Study of Self-Diffusion Process of Water Molecules in Porous Glass by Stimulated Spin Echo Method with Pulsed Field Gradients

The self-diffusion process of water molecules through high-silica porous glass has been studied for three samples with different pore diameters using a stimulated echo method with pulsed field gradients. It was found that the diffusion process over a large distance can be described as a Gaussian diffusion process and that the effective diffusion constant is proportional to the porosity of the high-silica glass sample.

Measurements of surface relaxation time of solid, liquid and adsorbed 3He in porous glasses

Abstract The surface relaxation time T ls has been investigated in solid, liquid and adsorbed 3 He in porous glasses for a wide frequency range by using pulsed SQUID-NMR. ALL T ls agreed with each other and were proportional to the frequency at least at low frequencies. A model is proposed to explain the above results of T ls .

Solidification of 3He in a porous glass

Abstract NMR relaxation measurements of 3 He in porous high silica glass within a temperature range of 0.5 to 4.2 K at various applied pressures up to 14.6 MPa are reported. The onset of solidification of 3 He in the pores was observed at excess pressures ≈ 2.3−4.7 MPa above the bulk melting pressure between 1.3 and 2.1 K. The specific heat of 3 He in the porous glass was measured to supplement the NMR measurements and the result confirmed the solidification.

Study of surface relaxation mechanism of liquid3He in porous glass by using SQUID NMR

Nuclear spin relaxation of liquid3He in porous glass has been studied. In addition to measurements of the longitudinal spin relaxation timeT1 by a usual pulsed SQUID NMR, measurements of the transverse spin relaxation timeT2 have been performed by using a newly developed SQUID NMR method to observe a spin echo signal. Temperature and frequency dependences ofT1 andT2 have been measured. A simple model is proposed which explains the main features of the experimental results.

Solid-Liquid Phase Diagrams of 3He in Porous Glasses

Solidification and melting phenomena of 3He in restricted geometries were investigated by measuring the magnetization, Mz, and the spin lattice relaxation time, T1 of 3He with SQUID-NMR technique. Two porous glasses were used whose average pore diameters were 4 nm and 18 nm, respectively. Measurements were made at various pressures between S.V.P. and 9 MPa in the temperature range between 20 mK and 4 K. The melting curve minimum in the P-T phase diagram was observed for 18 nm porous glass, but not for 4 nm. We attributed this to the depression of Fermi temperature, in addition to the large hysteresis between solidification and melting, for 3He in the small pores.

Frost Heaving Phenomena in Helium

The frost heaving phenomena was studied by using a combination of 4He and porous glass. We were able to set up a perfect ice segregation condition such that the frost heave occurred at the boundary between bulk solid and supercooled liquid in the pores below the bulk freezing temperature. The frost heave was observed both in the super fluid and normal regions. The frost heaving pressure in the normal fluid region agreed well with the modified Clausius-Clapeyron equation.

Ion Exchange Ability of Porous Glass

The ion exchange abilities of two kinds of porous glasses with pore diameters of 4 and 48nm was studied in the aqueous solutions of M(NO3)n (M=Li, K, Mg, Ca, Mn, Co, Ni, Cu, Zn, Cr, Fe), and NiX (X=Br2, I2, SO4, (NO3)2, (ClO4)2, C2O4, (CH3CH(OH)COO)2). The ion exchange ability of Fe3+ was high, but that of the other chemical species were also the same. Porous glasses were modified by treatment with trimethylchlorosilane (TMS), γ-aminopropyltriethoxysilane (γ-APTES) and 1, 3-propanesultone (PS). The porous glass treated with TMS had no ion exchange ability. The ion exchange ability of glass treated with PS was three times and by γ-APTES was ten times as high as that of the untreaded glass.

Distribution of Impregnated Component and Nonuniformity of Colloidal Silica in Porous Glass

Porous glass prepared by acid leaching of phase separated glass contains colloidal silica, resulting in the nonunif ormity in the porous glass. Porous glass rods were impregnated with aluminum nitrate solutions, and some of them were treated subsequently with ammonia to precipitate aluminum hydroxide. Then the porous glasses were sintered to form nonporous glasses. The concentration profile of aluminum in the sintered glasses was studied with reference to the nonunif ormity. The aluminum concentration in the impregnated and ammonia-treated specimens was high at the surface region and decreased toward the center. This fact coincides with the distribution of porosity which is high at the surface region. The concentration difference between the as-impregnated and impregnated and ammonia-treated specimens was large at the center and decreased toward the surface, in good correlation with the distribution of the surface area which is high at the center. A narrow gap with a low aluminum concentration was observed at the center of the impregnated specimen and was ascribed to the very densely deposited colloidal silica.