Fraction Of Boron Research Articles

Effect of carbon codoping on boron diffusion in amorphous silicon

The effect of carbon codoping on boron diffusion in amorphous silicon is investigated during low temperature annealing. The diffusivity of boron is unaffected by carbon codoping, but the fraction of mobile boron is observed to increase with increasing carbon concentration. A concomitant reduction in boron clustering is also observed at higher carbon coimplant concentrations, consistent with a change in the local trap concentration. This is consistent with carbon possibly acting as a trap site for boron and thereby changing the size and dynamics of the boron cluster formation.

Formation behavior and refining approach of TiB2 particles synthesized by combustion reaction

Titanium boride (TiB2) particles were synthesized in aluminum matrix by a combustion reaction of Ti–B–Al preform, aiming at synthesizing nano-scale fine particles. The formation behavior of TiB2 particle was observed by Combustion Front Quenching Method (CFQM) , in which self-propagating combustion wave was terminated by heat absorption of metallic mold. At the earliest stage of the reaction, the reaction between aluminum and titanium took place, and boron was not involved in the reaction. The nucleation site of TiB2 was a peripheral area of boron particles. TiB2 particles synthesized at the early stage of the reaction was very fine (~200 nm) , and the growth of particles occurred during a high-temperature stage of the combustion reaction. The effect of powder blending ratio on the size of TiB2 particle was examined. The combustion temperature was reduced by increasing aluminum fraction in the preform. The synthesized TiB2 particle was effectively refined by increasing the blending ratio of aluminum. By using finer boron particles or by increasing boron fraction in the preform, TiB2 particle was also refined effectively.

Probing alkali coordination environments in alkali borate glasses by multinuclear magnetic resonance

Five series of binary alkali borate glasses were prepared to compare the alkali dependence of network and modifier short-range order. 11B magic-angle spinning (MAS) NMR reveals that the fraction of four-coordinate boron depends strongly upon alkali type at high-alkali concentrations: heavier alkalis favour the formation of non-bridging oxygens, whereas lithium borates contain a much higher concentration of tetrahedral boron units. The alkali modifiers were observed directly by MAS NMR to measure the change in chemical shift with composition. All alkali peaks shift to higher frequency with increasing loading, indicative of decreasing average coordination numbers. Relative to their known chemical shift ranges, the heavier alkalis exhibit the greatest shifts, whereas the lithium shifts are subtle. This is interpreted in terms of the availability of charged and partially charged coordinating oxygens in the network. Moreover, the 133Cs chemical shifts plateau at 40 mol%, implying that the Cs + coordination number reaches a lower limit at this composition. This work demonstrates that NMR instrumentation and methodology have reached a level where even challenging nuclei like 39K and 87Rb can be probed to yield structural information in glasses.

Structure of single and mixed alkali Li–Rb borate glasses by neutron diffraction

We have compared the local structure of Li–, Rb– and Li–Rb diborate glasses using neutron diffraction and reverse Monte Carlo simulations. The fraction of tetrahedral boron decreases as the Rb content increases, but is similar in the single and mixed alkali glasses at diborate compositions. Rb borate glasses exhibit an extensive cation ordering with Rb–Rb correlations at 4.7 and 7 Å. The environment of alkalis is slightly modified between the single and mixed glasses while their relative distribution is essentially random. This indicates that the alkali environment is affected by the presence of a different alkali and this cation–cation interaction could be a fundamental mechanism, together with the site mismatch, to explain the mixed alkali effect.

Structure of Alkali Borate Glasses at High Pressure: B and LiK-Edge Inelastic X-Ray Scattering Study

We report the first in situ boron K-edge inelastic x-ray scattering (IXS) spectra for alkali borate glasses (Li2B4O7) at high pressure up to 30 GPa where pressure-induced coordination transformation from three-coordinated to four-coordinated boron was directly probed. Coordination transformation (reversible upon decompression) begins around 5 GPa and the fraction of four-coordinated boron increases with pressure from about 50% (at 1 atm) to more than 95% (at 30 GPa) with multiple densification mechanisms, evidenced by three distinct pressure ranges for (d[4]B/dP)T. The lithium K-edge IXS spectrum for Li-borate glasses at 5 GPa shows IXS features similar to that at 1 atm, suggesting that the Li environment does not change much with pressure up to 5 GPa. These results provide improved understanding of the structure of low-z glass at high pressure.

Effect of structure change on thermal and dielectric characteristics in low-temperature firing Bi2O3–B2O3–ZnO glasses

In a Bi2O3–B2O3–ZnO glass system, glass structure change, sintering behavior and resultant physical characteristics of the glass were examined when various amounts of Bi2O3 and ZnO mixture were added. When the total amount of Bi2O3 and ZnO was below 30 mol%, a phase separation occurred and homogeneous glass was not obtained. The fraction of four-coordinated borons (BO4) was highest when the total amount of Bi2O3 and ZnO was 50mol%. Further addition over 50 mol% induced a borate anomaly phenomenon in the glass, which resulted in the decrease in BO4 fraction. The sintering temperature and glass transition temperature decreased as the amount of Bi2O3 and ZnO increased. The thermal expansion coefficient and dielectric constant of the specimens were also examined.

An unusual isotopic fractionation of boron in synthetic calcium carbonate precipitated from seawater and saline water

Inorganic calcium carbonate precipitation from natural seawater and saline water at various pH values was carried out experimentally. The results show the clear positive relationships between boron concentration and δ 11 B of inorganic calcium carbonate with the pH of natural seawater and saline water. However, the variations of boron isotopic fractionation between inorganic calcite and seawater/saline water with pH are inconsistent with the hypothesis that B(OH) 4 - is the dominant spe-cies incorporated into the biogenic calcite structure. The isotopic fractionation factors a between synthetic calcium carbonate precipitate and parent solutions increase systematically as pH increases, from 0.9884 at pH 7.60 to 1.0072 at pH 8.60 for seawater and from 0.9826 at pH 7.60 to 1.0178 at pH 8.75 for saline water. An unusual boron isotopic fractionation factor of larger than 1 in synthetic calcium carbonate precipitated from seawater/saline water at higher pH is observed, which implies that a substantial amount of the isotopically heavier B(OH) 3 species must be incorporated preferentially into synthetic inorganic carbonate. The results propose that the incorporation of B(OH) 3 is attributed to the formation of Mg(OH) 2 at higher pH of calcifying microenvironment during the synthetic calcium carbonate precipitation. The preliminary experiment of Mg(OH) 2 precipitated from artificial seawater shows that heavier 11 B is enriched in Mg(OH) 2 precipitation, which suggests that isotopically heavier B(OH) 3 species incorporated preferentially into Mg(OH) 2 precipitation. This result cannot be applied to explain the boron isotopic fractionation of marine bio-carbonate because of the possibility that the unusual environment in this study appears in formation of marine bio-carbonate is infinitesimal. We, however, must pay more attention to this phenomenon observed in this study, which accidentally appears in especially natural environment.

Nanocomposite Ti–B–N coatings synthesized by reactive arc evaporation

Nanocomposite Ti–B–N coatings have been prepared by reactive arc evaporation from Ti–B compound targets. The highly ionized flux of film-forming species was utilized to synthesize a promising nanocrystalline metastable supersaturated solid solution of boron in TiN at lower nitrogen fractions. The combined results from elastic recoil detection, X-ray photoelectron spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy and selected area electron diffraction indicate that the additional nitrogen incorporated at higher partial pressures triggers the formation of a separate amorphous BN matrix phase surrounding the 6–8 nm sized face-centered cubic crystallites. A maximum in the hardness is obtained for the strained TiBN crystallites surrounded by a small fraction of boron synthesized at a nitrogen fraction of 0.1, while the formation of the amorphous BN phase leads to lower values.

Al-alloyed MgB2: correlation of superconducting properties, microstructure and chemical composition

Al-alloyed MgB2 was prepared by solid state reaction of Mg1-xAlx alloy and crystalline B powder particles. The nominal composition of the samples was Mg1-xAlxB2, with x = 0, 0.1, 0.2, 0.3. Residual resistivity (ρ0) of the samples measured by four-probe technique is comparable to the single crystals, indicating the excellent quality of these samples. The lattice parameters c and a decrease at a rate of 1.15 pm and 0.17 pm per at.% Al, respectively. Superconducting transition temperature (Tc) determined by measuring the resistive superconducting transition, decreases with increasing Al alloying at a rate of 1.56 K/at.% Al. Microstructure and chemical composition have been investigated by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). Al is incorporated into MgB2 grains of ∼1 µm size by substitution of Mg lattice sites with Al. Al was found to be distributed inhomogenously which partially explains the broadening of the superconducting transition width (ΔTc) with increasing Al mole fraction. Al alloyed samples contain large (∼15 µm) and small (∼ 2 µm ) secondary phases embedded in the (Mg, Al)B2 matrix. The composition of large secondary phases is found to be (Mg, Al)B7+δ, with the mole fraction of excess boron (δ) increasing from 0.99 at.% in pure sample to 4.14 at.% in highest alloyed sample. The Al to Mg mole fraction ratio in these large secondary phases is about half of that in the matrix. The size and density of the large secondary phases increased with increase in Al mole fraction. The secondary phases constitute less than 4% of the total sample volume and are thus not likely to affect the bulk superconductivity.

Resonant laser-SNMS of boron for analysis of paleoceanographic samples

Calcite shells of foraminifera, which are accumulated in the ocean sediment, are an important object of paleoceanographic studies to reconstruct environmental parameters of the past. Foraminifera are unicellular organisms living in almost all parts of the ocean during the entire paleoceanographic time scale. The isotope ratio of boron incorporated in the calcite shell delivers information about the pH-value of the ocean at the time the shell was formed. Since the boron fraction of such a shell is about 5 ppm, an extremely sensitive technique is necessary for an exact boron isotope ratio determination. Resonant laser secondary neutral mass spectrometry (r-laser-SNMS) was used to measure boron isotope ratios in calcite shells. Analysis was carried out with a time-of-flight mass spectrometer equipped with an electron impact gun for sputtering and a Ga + primary ion source. Resonant ionization of sputtered boron neutrals was performed via a three-step ionization scheme accomplished with two tunable dye lasers and the fundamental wavelength of a Nd:YAG laser. After optimizing the boron ionization and detection process, boron isotope ratios were directly measured on single foraminiferal shells after removing contaminants by Ar + ion beam sputtering.

Experimental Study and Monte Carlo Modeling of Calcium Borosilicate Glasses Leaching

AbstractDuring aqueous alteration of glass an alteration layer appears on the glass surface. The properties of this alteration layer are of great importance for understanding and predicting the long-term behavior of high-level radioactive waste glasses. Numerical modeling can be very useful for understanding the impact of the glass composition on its aqueous reactivity and long-term properties but it is quite difficult to model these complex glasses. In order to identify the effect of the calcium content on glass alteration, seven oxide glass compositions (57SiO2 17B2O3 (22−x)Na2O xCaO 4ZrO2; 0 < x < 11) were investigated and a Monte Carlo model was developed to describe their leaching behavior. The specimens were altered at constant temperature (T = 90°C) at a glass-surface-area-to-solution-volume (SA/V) ratio of 15 cm 1 in a buffered solution (pH 9.2). Under these conditions all the variations observed in the leaching behavior are attributable to composition effects. Increasing the calcium content in the glass appears to be responsible for a sharp drop in the final leached boron fraction. In parallel with this experimental work, a Monte Carlo model was used to investigate the effect of calcium content on the leaching behavior. The glass structure was built with a random distribution of silicon and boron on the lattice points of a diamond lattice with sodium atoms located in interstitial position. The model was upgraded to take into account the effect of zirconium and calcium. Zirconium atoms are placed in interstitial position (with cations acting as charge compensators) and interact with six lattice atoms (Si or B) by decreasing their dissolution probability. Acting like sodium but with less effect, calcium atoms increase the dissolution probability of atoms placed in their neighborhood. Monte Carlo simulations performed with this model are in good agreement with the experimental results. The dependence of the dissolution rate on the calcium content can be described by a quadratic function: fitting the simulated points gives a minimum alteration rate at about 7.4 mol% calcium. This value is consistent with the figure of 8.0 mol% obtained from the experimental work. The model was also used to investigate the role of calcium in the glass structure and it pointed out that calcium act preferentially as a network modifier rather than a charge compensator in this kind of glasses.

Reactive magnetron sputtering of hard Si–B–C–N films with a high-temperature oxidation resistance

Based on the results obtained for C–N and Si–C–N films, a systematic investigation of reactive magnetron sputtering of hard quaternary Si–B–C–N materials has been carried out. The Si–B–C–N films were deposited on p-type Si(100) substrates by dc magnetron co-sputtering using a single C–Si–B target (at a fixed 20% boron fraction in the target erosion area) in nitrogen-argon gas mixtures. Elemental compositions of the films, their surface bonding structure and mechanical properties, together with their oxidation resistance in air, were controlled by the Si fraction (5–75%) in the magnetron target erosion area, the Ar fraction (0–75%) in the gas mixture, the rf induced negative substrate bias voltage (from a floating potential to −500V) and the substrate temperature (180–350°C). The total pressure and the discharge current on the magnetron target were held constant at 0.5Pa and 1A, respectively. The energy and flux of ions bombarding the growing films were determined on the basis of the discharge characteristics measured for the rf discharge dominating in the deposition zone. Mass spectroscopy was used to show composition of the total ion fluxes onto the substrate and to explain differences between sputtering of carbon, silicon and boron from a composed target in nitrogen-argon discharges. The films, typically 1.0–2.4μm thick, possessing a density around 2.4gcm−3, were found to be amorphous in nanostructure with a very smooth surface (Ra⩽0.8nm) and good adhesion to substrates at a low compressive stress (1.0–1.6GPa). They exhibited high hardness (up to 47GPa) and elastic recovery (up to 88%), and extremely high oxidation resistance in air at elevated temperatures (up to a 1350°C substrate limit).

Network connectivity in aluminoborosilicate glasses: A high-resolution 11B, 27Al and 17O NMR study

O-17 enriched calcium and potassium aluminoborosilicate glasses with compositions similar (or analogous) to commercial E-glass were made and studied by 11B, 27Al and 17O NMR in order to explore the network speciation and mixing. Fractions of non-bridging oxygens associated with silicon and boron can be obtained simply from 17O magic angle spinning (MAS) NMR, while bridging oxygen populations result from complete peak assignment of high-resolution 17O triple quantum magic angle spinning (3QMAS) NMR spectra. Dramatic differences between the two samples in boron and oxygen speciation demonstrate a large effect of the charge of the modifier cation on mixing behavior and on the stabilization of non-bridging oxygens. The observed oxygen speciation is compared with that calculated from two models: random mixing of Si, B, and Al, and mixing with avoidance of linkages between tetrahedral aluminum and tetrahedral boron groups. Mixing of B and Al in the K-containing glass tends to follow the latter, while the network speciation in the Ca-containing glass is closer to the random model. The effects of Al and Si on boron speciation are discussed, and indicate that the maximum fractions of four-coordinated boron observed in a wide range of glass compositions are closely related to tetrahedral B and Al ‘avoidance’. A modified ‘Dell and Bray’ model is proposed which seems to accurately approximate boron speciation in many alkali aluminoborosilicate glasses. The higher field strength modifier cation (Ca2+ vs. K+) promotes the formation of non-bridging oxygen, trigonal over tetrahedral boron, and at least minor amounts of five-coordinated aluminum.

Boron isotopic fractionation between minerals and fluids: New insights from in situ high pressure-high temperature vibrational spectroscopic data

Equilibrium boron isotopic fractionations between trigonal B(OH) 3 and tetragonal B(OH) 4 − aqueous species have been calculated at high P- T conditions using measured vibrational spectra (Raman and IR) and force-field modeling to compute reduced partition function ratios for B-isotopic exchange following Urey’s theory. The calculated isotopic fractionation factor at 300 K, α 3/4 = 1.0176(2), is slightly lower than the formerly calculated value of α 3/4 = 1.0193 ( Kakihana and Kotaka, 1977), due to differences in the determined vibrational frequencies. The effect of pressure on α 3/4 up to 10 GPa and 723 K is shown to be negligible relative to temperature or speciation (pH) effects. Implications for the interpretation of boron fractionation in experimental and natural systems are discussed. We also show that the relationship between seawater-mineral B isotope fractionation and pH can be expressed using two variables, α 3/4 on one hand, and the pK a of the boric acid-borate equilibrium on the other hand. This latter value is given by the equilibrium of boron species in water for the carbonate-water exchange, but could be governed by mineral surface properties in the case of clays. This may allow defining intrinsic paleo-pHmeters from B isotope fractionation between carbonate and authigenic minerals. Finally, it is shown that fractionation of boron isotopes can be rationalized in terms of the changes in 1) coordination of B from trigonal to tetrahedral in both fluids and minerals; and 2) the ligand nature around B from OH − in the fluid and some hydrous minerals to non-hydrogenated O in many minerals. Relationships are established that allow predicting the isotopic fractionation factor of B between minerals and fluid.

Matrix effect and partitioning of boron isotopes between immiscible Si-rich and B-rich liquids in the Si–Al–B–Ca–Na–O system: A SIMS study of glasses quenched from centrifuge experiments

The results of a study of isotopic fractionation of boron between silica-rich (LS) and borate-rich (LB) immiscible liquids in the system Si–B–Al–Ca–Na are reported. Partitioning experiments were performed on glasses produced by quenching immiscible coexisting Si-rich and B-rich borosilicate melt pairs that had been equilibrated at high temperature and separated with the aid of a high temperature centrifuge furnace [Veksler, I.V., Dorfman, A.M., Dingwell, D.B., Zotov, N., 2002. Element partitioning between immiscible borosilicate liquids: a high-temperature centrifuge study. Geochim. Cosmochim. Acta 66, 2603–2614]. Here B/Si and 11B/ 10B ratios have been determined using secondary ion mass spectrometry (SIMS). The determinations encountered unexpectedly strong matrix effect (up to 12‰) due to contrasting chemical compositions of the immiscible melts. Employment of − 60 V high-voltage offset (not used during routine SIMS B isotope measurements) effectively eliminated the initially observed matrix effect. With this improved SIMS technique, we obtained the result that the coexisting quenched immiscible liquids have the same 11B/ 10B ratio within ± 1.2‰ (2 σ) analytical uncertainty. Thus little or no significant two-liquid fractionation of 10B and 11B isotopes was observed in the temperature range between 950 and 1350 °C. This is despite the observation that significantly different proportions of trigonal vs. tetrahedrally coordinated B in these immiscible liquids have been determined by Raman spectroscopic analyses. The essential observations (i.e., a strong matrix effect and a lack of significant B isotope fractionation between the glasses) were both supported by independent thermal ionization mass spectrometry (TIMS) analyses of one selected centrifuged pair. Those glasses showed no difference in B isotopic composition within the quoted 2 σ analytical error of ± 1.0‰.

The effect of Cs 2O additions on HLW wasteform glasses

Physical parameters and structural characteristics are reported for the mixed alkali borosilicate glass system, xCs 2O(100 − x)(MW) (0 ⩽ x ⩽ 9.66) where MW is the BNFL wasteform glass (10.29 mol% Li 2O, 10.53 mol% Na 2O, 18.57 mol% B 2O 3, 60.61 mol% SiO 2). Glass density was found to increase with x whilst the glass transition temperature ( T g) decreased. The fraction of four-coordinated boron (N 4) determined from 11B magic angle spinning nuclear magnetic resonance (MAS NMR) increased with x in a manner consistent with previous reports on the sodium–lithium–borosilicate system and contrary to the Dell model. 29Si MAS NMR was used to identify the fraction of Q 4 (B) and Q 3 units as a function of x. Raman spectra indicated the presence of reedmergnerite and danburite superstructural units. Mass loss measurements showed a non-linear variation with x, having a maximum between 7 and 8 mol% Cs 2O and a correlation was found between the amount of Q 3 units in the solid and the volatilization loss from the melt.

Structure ofB2O3Glass at High Pressure: AB11Solid-State NMR Study

We report spectroscopic evidence for the pressure-induced structural changes in B2O3 glass quenched from melts at pressures up to 6 GPa using solid-state NMR. While all borons are tri-coordinated at 1 atm, the fraction of tetra-coordinated boron increases with pressure, being about 5% and 27% in the B2O3 glass quenched from melts at 2 and 6 GPa, respectively. The fraction of boroxol ring species increases with pressure up to 2 GPa and apparently decreases with further compression up to 6 GPa. Two densification mechanisms are proposed to explain the variation of boron species with pressure.

Structural studies in the BaO–B 2O 3–TiO 2 system by XAS and 11B-NMR

The structure of barium–titanium–metaborate xBaO– xB 2O 3– yTiO 2 ( y=0%, 4%, 8%, 16% and x=50– y/2) amorphous and crystallized powders, obtained using a polymeric precursor method, was investigated by Ti and B K-edge X-ray absorption spectroscopy (XAS) and 11B-NMR high-resolution techniques. XANES study of amorphous samples shows that Ti 4+ ions exist as [4]Ti species associated to [6]Ti and [5]Ti species in a practically equivalent amount. After crystallization, titanium environment is predominately composed by [6]Ti species. According to XANES results obtained at the B K-edge, the fraction of boron in tetrahedral sites ( [4]B) reduces as the amount of TiO 2 is increased from x=0% to 4%, with a consequent increase of boron in trigonal sites ( [3]B). By a combination of 11B-NMR spin-echo and triple quantum magic angle spinning (3Q-MAS) techniques, the detailed borate speciation was determined as consisting in [4]B and two kind of trigonal sites, [3]B A and [3]B B , corresponding, respectively, to borates sharing three and two O atoms with other boron units. NMR results reveal not only the reduction in boron coordination also seen by XANES but also the simultaneous reduction in the condensation degree of trigonal units, when the Ti content is increased in the glass. In crystallized samples, β-BaB 2O 4 and BaTi(BO 3) 2 phases were identified and quantified by 11B-NMR.

Chemical fractionation of boron and heavy metals in soils irrigated with wastewater in central Mexico

Abstract The aim of the present work was to evaluate the accumulation of selected trace elements (boron, cadmium, chromium, mercury, lead and arsenic) in agricultural soils of the Zone 1 of the Irrigation District 03 (DR03) in the State of Hidalgo, Mexico. The soils of Zone 1 have, on average, been irrigated with raw wastewater for about 20 years (range 6–41 years). A clear positive correlation between the organic carbon contents in soils and the irrigation time was found. The total concentrations of the elements analysed were 0.51–1.89 mg Cd kg−1, 11.59–27.42 mg Cr kg−1, 3.99–47.08 mg Pb kg−1 and 9.2–123.8 mg B kg−1. Samples of topsoils (0–30 cm) were extracted using a modified Tessier method according to a six fraction scheme: easily soluble (F0), exchangeable (F1), bound to carbonates (F2), associated with oxides of iron and manganese (F3), bound to organic matter and sulphides (F4), and the residual fraction (F5). In general, the elements were distributed in the fractions F0, F4, and F5. The concentrations of total arsenic and mercury were below the detection limits (0.03 and 0.01 mg kg−1, respectively) except for 0.77 mg Hg kg−1 in one soil. The concentrations of total Cr and Pb did not exceed the maximum permissible levels set by the regulations of the European Union whereas total Cd was on the verge. A linear increase between the total metal concentrations and the irrigation time was found. In this study several crops harvested from soils showed Cd and Pb contents higher than those recommended by the Dutch and German guidelines. It can be concluded that the soils may pose a potential risk to the trophic chain and effective restrictions for the cultivation of crops that are sensitive to or known to accumulate heavy metals (i.e. nopal, onions, garlic, lettuce, potatoes, beets, and turnips) should be considered.

The use and usefulness of boron isotopes in natural silicate–water systems

Boron and its two stable isotopes 10B and 11B are considered powerful tracers in low temperature regimes like ocean waters and subduction zones, while very little is known about the isotopic fractionation in high pressure–temperature (PT) regimes. However, recent studies indicate that boron fractionation in silicate–water systems may follow a systematic relationship with temperature, regardless of the geological regime. In this paper we review previous B isotope studies and test the empirical relationship proposed by Williams et al. [Boron isotope geochemistry during diagenesis. Part I. Experimental determination of fractionation during illitization of smectite, Geochim. Cosmochim. Acta 65 (2001a) 1769–1782; Boron isotope geochemistry during diagenesis. Part II. Applications to organic sediments, Geochim. Cosmochim. Acta 65 (2001b) 1783–1794; Application of boron isotopes to the understanding of fluid–rock interactions in a hydrothermally stimulated oil reservoir in the Alberta Basin, Canada, Geofluids 1 (2001c) 229–240] by comparing it with the wealth of earlier data from studies of different geological scenarios. Our main conclusion is that, given the large variations of B isotope fractionation patterns in natural silicate–water systems, the majority of these systems are not represented by the proposed relationship. Factors more complex than temperature alone appear to control B isotope geochemistry, which include species of the silicate mineral, starting fluid, pH, geological setting, fluid/rock ratio (i.e. porosity), or time for equilibration between the solid and fluid phase.