Silicate Samples Research Articles

Design of a Chiral Mesoporous Silica and Its Application as a Host for Stereoselective Di-π-methane Rearrangements

[reaction: see text] A chiral periodic mesoporous organosilica (ChiMO) was prepared, in which a 1,2-bis-(ureido)cyclohexyl linker (38 wt %) is introduced into the walls of the hybrid organic-inorganic material. This silica was used as a host for 11-formyl-12-methyldibenzobarrelene (2), and the stereoselectivity of the di-pi-methane rearrangement of 2 within this host-guest complex was studied. At low conversions, the only product was the corresponding dibenzosemibullvalene. An enantiomeric excess of 24% at 11% conversion was obtained using the ChiMO as host. These values compare well with those achieved using a system based on conventional faujasites (LiY and NaY) as hosts incorporating a chiral auxiliary. We tested S-phenylglycine, S-proline, S-camphanic acid, and S-mandelic acid as chiral auxiliaries. In contrast to the behavior of the ChiMO material, adsorption of dibenzobarrelene in purely siliceous mesoporous MCM-41 silica (3.2 nm pore size) containing ephedrine failed, a failure that can be explained as arising from the large internal silanol population and high hydrophilicity of the siliceous MCM-41 sample.

Layered amphibolite sequence in NE Sardinia, Italy: remnant of a pre-Variscan mafic silicic layered intrusion?

A banded amphibolite sequence of alternating ultramafic, mafic (amphibolite) and silicic layers, tectonically enclosed within Variscan migmatites, outcrops at Monte Plebi (NE Sardinia) and shows similarities with leptyno-amphibolite complexes. The ultramafic layers consist of amphibole (75–98%), garnet (0–20%), opaque minerals (1–5%) and biotite (0–3%). The mafic rocks are made up of amphibole (65–80%), plagioclase (15–30%), quartz (0–15%), opaque minerals (2–3%) and biotite (0–2%). The silicic layers consist of plagioclase (60–75%), amphibole (15–30%) and quartz (10–15%). Alteration, metasomatic, metamorphic and hydrothermal processes did not significantly modify the original protolith chemistry, as proved by a lack of K2O-enrichment, Rb-enrichment, CaO-depletion, MgO-depletion and by no shift in the rare earth element (REE) patterns. Field, geochemical and isotopic data suggest that ultramafic, mafic and silicic layers represent repeated sequences of cumulates, basic and acidic rocks similar to macrorhythmic units of mafic silicic layered intrusions. The ultramafic layers recall the evolved cumulates of Skaergaard and Pleasant Bay mafic silicic layered intrusions. Mafic layers resemble Thingmuli tholeiites and chilled Pleasant Bay mafic rocks. Silicic layers with Na2O: 4–6 wt%, SiO2: 67–71 wt% were likely oligoclase-rich adcumulates common in many mafic silicic layered intrusions. Some amphibolite showing a strong Ti-, P-depletion and REE-depletion are interpreted as early cumulates nearly devoid of ilmenite and phosphates. All Monte Plebi rocks have extremely low Nb, Ta, Zr, Hf content and high LILE/HFSE ratios, a feature inherited from the original mantle sources. The mafic and ultramafic layers show slight and strong LREE enrichment respectively. Most mafic layer samples plot in the field of continental tholeiites in the TiO2–K2O–P2O5 diagram and are completely different from N-MORB, E-MORB and T-MORB as regards REE patterns and Nd, Sr isotope ratios but show analogies with Siberian, Deccan and proto-Atlantic rift tholeiites. Comparisons with Thingmuli, Skaergaard and Kiglapait rocks and with experimental data suggest that the Monte Plebi intrusion was an open-to-oxygen system with fO2 ≥ FMQ. Mafic and ultramafic samples yielded eNd(460)=+0.79 /+3.06 and 87Sr/86Sr=0.702934–0.703426, and four silicic samples eNd(460)=−0.53/−1.13; 87Sr/86Sr=0.703239–0.703653. Significant differences in Nd isotope ratios between mafic and silicic rocks prove that both groups evolved separately in deeper magma chambers, from different mantle sources, with negligible interaction with crustal material, and were later repeatedly injected within a shallower magma chamber. The spectrum of Sr and Nd isotope data is consistent with a slightly enriched mantle metasomatized during an event earlier than 460 Ma. The metasomatising component was represented by alkali-Th-rich fluids of crustal origin rather than by sedimentary materials, able to modify alkali and Sr–Nd isotope systematics. Monte Plebi layered amphibolites might represent the first example of a strongly metamorphosed fragment of an early Paleozoic mafic silicic layered intrusion emplaced in a thinning continental crust and then tectonically dismembered by Variscan orogeny.

Chemical and phase composition of particles produced by laser ablation of silicate glass and zircon—implications for elemental fractionation during ICP-MS analysis

The chemical and phase compositions of particles produced by laser ablation (266 nm Nd:YAG) of silicate NIST glasses and zircon were studied by SIMS and HR-TEM techniques. The data suggest that the formation of phases of different mineralogy and/or chemical composition from the original sample at the ablation site can result in elemental fractionation (non-stoichiometric sampling) in material delivered to the ICP-MS for quantitative analysis. Evidence of the element fractionation is preserved in chemically zoned ejecta deposited around the ablation pit. The chemical composition and mineralogy of particles varies with particle size so that the efficiency of transport of particles also plays a role in elemental fractionation. During the first 250 pulses in a typical ablation experiment using a 266 nm laser, particle sizes are mainly <2.5 μm; thereafter they decrease to <0.3 μm. Pb and U are fractionated significantly during the ablation of both silicate glass and zircon. During the ablation of glass, both micron-sized, melt-derived, spherical particles, and nm-sized, condensate-derived particle clusters, are produced; the very smallest particles (<0.04 μm) have anomalously high Pb/U ratios. For zircon, both larger (0.2–0.5 μm) spherical particles and agglomerates of smaller (∼0.005 μm) particles produced by ablation are mixtures of amorphous and crystalline materials, probably zircon, baddeleyite (ZrO2) and SiO2. Evidence for thermal decomposition of zircon to baddeleyite and SiO2 is preserved in the wall of the ablation pit, and may lead to the commonly observed increase in Pb/U recorded during laser ablation ICP-MS analysis. It follows that a matrix-matched external calibration is essential for achieving highly precise and accurate laser (266 nm wavelength) ablation ICP-MS analysis of Pb and U in silicate samples.

Heavy-ion elastic recoil detection analysis as a useful tool for tracking experimental modifications in bulk calcium silicates

Chemical modifications carried out on unique amorphous nano-structured calcium silicate have been traced by time-of-flight heavy-ion elastic recoil detection analysis (HERDA). It could be shown that this ion-beam analysis method allows not only surface but also depth analysis of the silicate samples and the modifications effected upon it. While providing a challenge for standard analysis methods, the highly porous, low-density nature of the calcium silicate proved to be an asset for the ion-beam analysis technique chosen. Presented are depth profiles giving elemental compositions and providing the bases for representative chemical formula for the silicates studied. It was proven that a study of the surface composition of this nano-structured silicate is sufficient for indicating the bulk composition of a sample of this material. Copyright © 2005 John Wiley & Sons, Ltd.

Determination of Lithium Contents in Silicates by Isotope Dilution ICP‐MS and its Evaluation by Isotope Dilution Thermal Ionisation Mass Spectrometry

A precise and simple method for the determination of lithium concentrations in small amounts of silicate sample was developed by applying isotope dilution‐inductively coupled plasma‐mass spectrometry (ID‐ICP‐MS). Samples plus a Li spike were digested with HF‐HClO4, dried and diluted with HNO3, and measured by ICP‐MS. No matrix effects were observed for 7Li/6Li in rock solutions with a dilution factor (DF) of 97 at an ICP power of 1.7 kW. By this method, the determination of 0.5 μg g‐1 Li in a silicate sample of 1 mg can be made with a blank correction of &lt; 1%. Lithium contents of ultrabasic to acidic silicate reference materials (JP‐1, JB‐2, JB‐3, JA‐1, JA‐2, JA‐3, JR‐1 and JR‐2 from the Geological Survey of Japan, and PCC‐1 from the US Geological Survey) and chondrites (three different Allende and one Murchison sample) of 8 to 81 mg were determined. The relative standard deviation (RSD) was typically &lt; 1.7%. Lithium contents of these samples were further determined by isotope dilution‐thermal ionisation mass spectrometry (ID‐TIMS). The relative differences between ID‐ICP‐MS and ID‐TIMS were typically &lt; 2%, indicating the high accuracy of ID‐ICP‐MS developed in this study.

The effect of aluminum on the biodeposition of silica in hot spring water: Chemical state of aluminum in siliceous deposits collected along the hot spring water stream of Steep Cone hot spring in Yellowstone National Park, USA

To elucidate the role of aluminum for silica deposition on the surface of microbe, hot spring water and siliceous deposit samples were collected along a stream in the Steep Cone in Yellowstone National Park, USA and were characterized. The SiO 2 content of siliceous deposit samples ranged from 71.86% to 93.68% and the content increased along the stream. Meanwhile, the Al 2O 3 content decreased inversely 6.27% to 0.18% depending on the Al concentration in the hot spring water at each sampling point. Most of the aluminum in the siliceous deposit sample collected at the springhead was present as 4-coordinated Al (Al(4)), showing that the deposit was formed by inorganic reactions between monosilicic acid and aluminum ions. The proportion of 6-coordinated Al (Al(6)) of the siliceous deposit samples increased downstream. As aluminum ions combined on the surface of microbes are present as 6-coordinated Al, it is suggested that aluminum ions are preferentially combined with functional groups on the surface of microbes, and then silicic acids are chemically adsorbed to the aluminum ions that play an essential role as active sites of deposition of monosilicic acid from hot spring water.

Neutron radiography study of water absorption in porous building materials: anomalous diffusion analysis

Dynamic neutron radiography was applied to obtain the experimental data concerning the kinetics of the wetting process in two different types (fired-clay and siliceous brick) of porous construction materials. The technique provides accurate experimental data concerning the first instants as well as the advanced stages of the imbibing process. A significant difference in water absorption parameters, contrasting the materials studied, is found. Both the advance of the wetting front and the time evolution of water content distribution within the sample are analysed. It is shown that for both materials the time dependence of the wetting front position d deviates from the classical square root of time t behaviour. The deviation is analysed in terms of the intercept b in the approximation and the exponent n in the power law d ∼ tn/2. Both materials differ in the sign of the intercept parameter: b > 0 for siliceous brick and b < 0 for fired-clay brick. Two stages of the process with different values of the power law exponent were observed. The advanced period exponents are different for each type of brick: n < 1 for siliceous brick and n > 1 for fired-clay brick. At the initial stages (t < 1000 s) the exponents are substantially less than 1 and smaller than those describing the advanced process. The initial stage exponents are lower for the siliceous brick samples. It is shown that the experimental water content profiles collapse to a single curve when plotted against the variable xt−n/2. The evolution of the distribution of liquid in the porous medium was analysed in terms of the anomalous diffusion equation of Küntz and Lavallée (2001 Experimental evidence and theoretical analysis of anomalous diffusion during water infiltration in porous building materials J. Phys. D: Appl. Phys. 34 2547–54) based on the non-linear generalization of the Fick's law. This approach makes a detailed analysis of the generalized hydraulic diffusivity in the low water content region possible. Successful fitting of experimental data with the diffusivity vanishing at null water content proved the importance of the hypodiffusive component of the process.

Mesoporous tin silicate: an efficient liquid phase oxidative dehydrogenation catalyst

Mesoporous tin silicate materials have been synthesized at room temperature using a self-assembly of cationic surfactant cetyltrimethylammonium bromide (CTAB) and tetraethylorthosilicate (TEOS) and SnCl 4 as Si and Sn precursors, respectively, under mild acidic (pH 4.5–6.5) condition. Si/Sn mol ratios in the product for different mesoporous tin silicate samples were 12.4, 27.2, 48.5 and 74.7 vis-à-vis the ratios 10, 25, 50 and 75, respectively, in the hydrothermal synthesis gels. These mesoporous samples were characterized using powder X-ray diffraction (XRD), N 2 sorption, UV–vis diffuse reflectance (UV DRS), FT-IR spectroscopy, and scanning electron microscopy (SEM) on an instrument with an energy dispersive X-ray (EDS) attachment. Characterization data demonstrated that the samples were moderately ordered, with pore dimension of 2.1–2.4 nm. UV DRS and IR spectral bands suggested the incorporation of tin in the tetrahedral lattice sites of the mesoporous silica network. After calcination, these tin silicate samples retained their mesophase and showed excellent catalytic activity in one-pot liquid phase selective oxidative dehydrogenation of cyclohexane to 1,4-cyclohexadiene using dilute aqueous hydrogen peroxide as oxidant. A very high selectivity for 1,4-cyclohexadiene (83–98%) was observed using different mesoporous tin-silicate samples and acetonitrile solvent. Very little to almost no further oxidation product of the parent and product olefins, i.e. epoxides or cyclohexanone/cyclohexanol was observed.

Dependence of the diffusion coefficients of methane in silicalite on diffusion distance as investigated by 1H PFG NMR

1H PFG NMR was performed to measure the diffusion coefficient of methane in three MFI-type siliceous zeolite silicalite samples, which were synthesized under different hydrothermal conditions resulting in different crystal sizes or intracrystalline defects. Measured diffusivities of methane decreased at the diffusion distance around 7 μm for all samples. The distance almost corresponds with the distance between cracks in the intracrystalline. However, the well-calcined sample, which has no detectable cracks as observed by scanning electron microscope, also showed a drastic decrease in the diffusion coefficient. This result suggests the existence of an intracrystalline transport barrier in the single crystal, the size of which is below the SEM resolution.

Structural and dynamic properties of confined water in nanometric model porous materials (8 Å⩽∅⩽40 Å)

Structural and dynamic properties of confined water have been investigated by ‘‘in situ’’ neutron-scattering experiments. In the medium confinement regime (for MCM-41 host materials: 20 Å⩽∅⩽40 Å) confined water has rather similar properties to bulk (3d) water. The major difference concerns the solidification phase transition. Strong triple-point depression Δ T 3t is observed and Δ T 3t increases when decreasing the pore diameter ∅ (213 K⩽Δ T 3t⩽233 K). Such a confined water behaves as a supercooled liquid phase. The ultra-confinement (AlPO 4-N zeolites: 8 Å⩽∅⩽12 Å), is seen to induce the structuration of the confined water and its stability at room temperature T=300 K due to commensurability effect with the AlPO 4-5 inner surface. No wetting phenomena are observed for both host materials, the silicic MCM-41 samples and the AlPO 4-N zeolite family.

Multiple techniques for mineral identification on Mars:: a study of hydrothermal rocks as potential analogues for astrobiology sites on Mars

Spectroscopic studies of Mars analog materials combining multiple spectral ranges and techniques are necessary in order to obtain ground truth information for interpretation of rocks and soils on Mars. Two hydrothermal rocks from Yellowstone National Park, Wyoming, were characterized here because they contain minerals requiring water for formation and they provide a possible niche for some of the earliest organisms on Earth. If related rocks formed in hydrothermal sites on Mars, identification of these would be important for understanding the geology of the planet and potential habitability for life. XRD, thermal properties, VNIR, mid-IR, and Raman spectroscopy were employed to identify the mineralogy of the samples in this study. The rocks studied here include a travertine from Mammoth Formation that contains primarily calcite with some aragonite and gypsum and a siliceous sinter from Octopus Spring that contains a variety of poorly crystalline to amorphous silicate minerals. Calcite was detected readily in the travertine rock using any one of the techniques studied. The small amount of gypsum was uniquely identified using XRD, VNIR, and mid-IR, while the aragonite was uniquely identified using XRD and Raman. The siliceous sinter sample was more difficult to characterize using each of these techniques and a combination of all techniques was more useful than any single technique. Although XRD is the historical standard for mineral identification, it presents some challenges for remote investigations. Thermal properties are most useful for minerals with discrete thermal transitions. Raman spectroscopy is most effective for detecting polarized species such as CO 3, OH, and CH, and exhibits sharp bands for most highly crystalline minerals when abundant. Mid-IR spectroscopy is most useful in characterizing Si-O (and metal-O) bonds and also has the advantage that remote information about sample texture (e.g., particle size) can be determined. Mid-IR spectroscopy is also sensitive to structural OH, CO 3, and SO 4 bonds when abundant. VNIR spectroscopy is best for characterizing metal excitational bands and water, and is also a good technique for identification of structural OH, CO 3, SO 4, or CH bonds. Combining multiple techniques provides the most comprehensive information about mineralogy because of the different selection rules and particle size sensitivities, in addition to maximum coverage of excitational and vibrational bands at all wavelengths. This study of hydrothermal rocks from Yellowstone provides insights on how to combine information from multiple instruments to identify mineralogy and hence evidence of water on Mars.

04/01169 Recycling process of sodium metaborate to sodium borohydride: Kojima, Y. and Haga, T. International Journal of Hydrogen Energy, 2003, 28, (9), 989–993

A novel method for the rapid dissolution of fused silicates in mineral acid is described. Fusion with 2.5 g of a KBO2-K2CO3 (3:2, w/w) mixture in a platinum crucible at 1000 °C will decompose 0.1 g of silicate samples such as basalt rock, glass sand and powdered glass in 10 min, and the cooled fusion cakes can be completely dissolved by 20 ml of 3 N mineral acids such as hydrochloric, nitric and sulfuric acids in less than 1 min at about 50 °C. Fusion with 5.0 g of a KBO2-K2CO3 (3:2, w/w) mixture can completely decompose 0.1 g of chrome refractory in 20 min and the cooled melt can be dissolved by 80 ml of 3 N hydrochloric or sulfuric acids in less than 30 s.

Highly active disordered extra large pore titanium silicate

A new disordered microporous silica and its titanium silicate analog have been synthesized using a bola-amphiphile surfactant 1,12-diamino dodecane (DADD) as a structure directing agent (SDA). Powder X-ray diffraction, N 2 sorption, 29Si MAS NMR, UV–visible diffuse reflectance, FT-IR spectroscopic tools, and TEM and SEM–EDS were used to characterize this material. Only low angle peak was observed in the XRD for all the samples. TEM images indicated a wormhole-like structure in this material similar to that observed for mesoporous silica HMS, MSU-1, MSU-X, etc. or microporous Si-TMS7. Pore diameter of the micropore estimated from N 2 adsorption isotherms was ≈11.2 Å. Spectroscopic data indicated the incorporation of titanium in the tetrahedral silica network in this material. Three microporous type, Ti-DMS1 titanium silicate samples were synthesized with Si/Ti mole ratios of 24.5, 46.5 and 68.0 in the final solid products. After the removal of the template through calcination this microporous titanium silicate showed an excellent catalytic activity in the ammoximation of bulky ketones using dilute aqueous hydrogen peroxide and aqueous ammonia.

Anthracene as a Non-hygroscopic Diluting Agent for Mössbauer Spectroscopy of Silicate Samples in Moisture-Uptake Studies

Anthracene gained no mass when held in a humid chamber and showed no gamma absorption and so appears to be suitable as a replacement for sugars for dilution of moisture-sensitive 57Fe-Mossbauer spectroscopy samples. Applied to studies of moisture effects on a circumstellar silicate dust simulant, anthracene permitted preparation of sample series for experimental determination of optimal 57Fe-Mossbauer areal density.

Effect of Phosphorus or Boron Addition on Water-Resistance of Water-Glass Adhesives

Water glass adhesives based on sodium silicates have been modified by addition of phosphorous or boron. In the preparation of sodium silicate, mixtures of silica sand and sodium carbonate with the additives was melted at 1400°C. They were dissolved in an autoclave at 180°C, and then concentrated to have a final viscosity for the comparison of their adhesive property and water resistance with the conventional liquid sodium silicates without additives in SiO 2 /Na 2 O molar ratio 2.5∼4.2. Obvious increase of the water resistance was observed for the liquid sodium silicate samples with the 5% P 2 O 5 or B 2 O 3 additives in the solid contents without loosing its adhesive property.

Separation of rare earth elements from scandium by extraction chromatography: Application to radiochemical neutron activation analysis for trace rare earth elements in geological samples

An effective and practical radiochemical separation procedure of radiochemical neutron activation analysis (RNAA) for ultra trace rare earth elements (REEs) in silicate rock samples is presented. The procedure consists of two column separations of anion exchange and extraction chromatography and precipitations as hydroxide and fluoride of REEs. The most seriously interfering nuclide, 46 Sc , is completely separated (<0.005%) from REEs by extraction chromatography using transuranic-element specific (TRU.Spec) resin. Chemical yields were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) and found to be constant within 3% for all REEs, implying that no fractionation occurs among REEs during the radiochemical purification procedure. By means of this procedure, other interfering nuclides than 46 Sc in RNAA of silicate samples were decreased down to <0.02% for 59 Fe , <0.006% for 60 Co and <0.000005% for 51 Cr . The RNAA procedure described in this paper can be one of the most suitable analytical procedures for accurately determining ultra-trace (1–10 pg) REEs in geological and cosmochemical samples.

Immobilization of 12-molybdophosphoric and 12-tungstophosphoric acids on metal-substituted hexagonal mesoporous silica

Hexagonal mesoporous silicate (HMS) materials containing Ti, Zr and Al ions were prepared using the neutral template route. The effect of the cation on the immobilization of 12-molybdophosphoric and 12-tungstophosphoric acids on mesoporous materials was studied. The texture of the samples was studied by the N2 adsorption–desorption isotherms, and their structure by X-ray diffraction (XRD), UV-Vis diffuse reflectance (DRS), infrared (IR) and X-ray photoelectron spectroscopy (XPS), and 1H and 31P nuclear magnetic resonance (NMR). Incorporation of different metals into the framework of HMS led to change in the structural and surface properties of mesoporous silica. All metal-containing samples showed a lower surface area compared to that of pure silica. The introduction of Zr and Al cations led to the development of textural mesoporosity in addition to the framework mesoporosity, characteristic of HMS and Ti-containing mesoporous silica (TiHMS) materials. IR and 1H and 31P NMR spectroscopic data revealed that the species present on the surface of HMS and TiHMS mesoporous materials after impregnation with solutions of 12-molybdophosphoric and 12-tungstophosphoric acid are non-degraded heteropoly anions with a preserved Keggin unit. Partial degradation of the anion was observed for zirconium-containing silicate samples (ZrHMS)-supported acids, the extent of which was stronger for supported molybdophosphoric acid in comparison with that of tungstophosphoric acid.

Efficient oxyfunctionalization of n-hexane by aqueous H 2O 2 over a new TS-PQ™ catalyst

The oxyfunctionalization of n-hexane by aqueous H 2O 2 was found to proceed substantially faster over a titanium-containing pentasil type catalyst denoted as TS-PQ™ (a trademark of PQ corporation for this titanium silicate material), than over other comparable titanium-containing zeolites. This catalyst has an unprecedented >99% efficiency in utilizing H 2O 2 in the oxidation of a paraffin. The effect of temperature, stirring rate, pH, solvent, and reactant ratios on the reaction rate, H 2O 2 efficiency, and product selectivity were evaluated over the TS-PQ™ silicate using a statistically designed catalytic test performed in an atmospheric batch reactor. Accurate reaction times were determined by continuously monitoring H 2O 2 consumption. Hydrated and in situ dehydrated TS-PQ™ titanium silicate samples were studied in a diffuse reflectance (DRIFT) cell by FT-UV and FT-IR spectroscopy. Unlike TS-1 catalysts that mainly contain isolated Ti 4+ ions in tetrahedral lattice positions, TS-PQ™ silicate contains tetrahedral and higher coordination Ti 4+ ions. Slightly acidic conditions affect favorably the reaction rate and C 2 regioselectivity over the TS-PQ™ catalyst. In contrast to TS-1, applying methanol (MOH) as co-solvent had little or negative effect on the reaction rate and the selectivity of TS-PQ™ catalyst for the oxyfunctionalization of n-hexane.

Influence of fringe bending on the enhancement of the diffraction efficiency of bismuth silicate gratings recorded under strong modulation and applied electric fields

The diffraction efficiency of bismuth silicate photorefractive gratings recorded in a nonlinear regime (light modulation depth, ≃1) was numerically calculated; phase coupling and off-Bragg reading conditions were taken into account. We considered gratings recorded with different applied electric dc fields under strong light modulation. We calculated the amplitude and the phase of the refractive-index variation of the gratings by numerically solving first the material rate equations to obtain the phase and the amplitude of the space-charge field and then the wave coupling equations for writing. We also obtained numerical solutions of the wave coupling equations for reading, considering angular deviations from the Bragg condition and bending of the fringes along the thickness of the sample. The diffraction efficiency for a 2-cm bismuth silicate sample recorded with an applied electric field of 2.5 kV/cm and a light modulation depth of 0.9 can be enhanced from 14% to 70% by use of an angular deviation of 3×10-4 rad from the Bragg condition during reading.

Measurement of hydrogen concentration in thick mineral or rock samples

This paper describes an application of a proton–proton elastic recoil coincidence spectroscopy to hydrogen analysis using a proton microbeam at an energy of 20 MeV. This method provides depth profiles of hydrogen over a thickness of 200 μm of silicate samples in a short time. A typical beam size is as small as 27 × 32 μm. The depth resolution is about 10 μm. The present work proves that the proton–proton elastic recoil coincidence spectroscopy is a promising method for measurements of hydrogen in mineral and rock samples with thickness up to 200 μm.