Determination Of Boron Research Articles

Prompt gamma activation analysis for boron determination in the tens of milligram range at the HOTNES facility

Boron is an elective element for the Prompt Gamma Activation Analysis (PGAA), due to its exceptionally large neutron capture cross section. This technique, usually performed in nuclear reactors with neutron fluxes as high as 108 cm−2 s−1, can determine quantities of boron as low as tens of nanograms. Some applications, such as the industry of neutron shielding materials, would better benefit from a less sensitive but more portable and accessible boron PGAA, which could be established at construction or fabrication sites. For these purposes ENEA and INFN jointly setup a compact PGAA based on a 0.5 cm3 Cadmium–Zinc–Telluride gamma spectrometer and the HOTNES thermal neutron source. Relying on a series of borated resins with known composition and on comprehensive experimental and Monte Carlo evaluations, this technique features a detection limit in the order of few milligrams in terms of boron mass. As the facility consists simply on a lab-scale neutron source and a polyethylene block with well-established geometry, this simplified PGAA system is suited to be replicated or transported to construction or fabrication sites for QA/QC purposes on borated construction materials for the nuclear sector.

Accurate Boron Determination in Tourmaline by Inductively Coupled Plasma Mass Spectrometry: An Insight into the Boron-Mannitol Complex-Based Wet Acid Digestion Method.

Tourmaline, a boron-bearing mineral, has been extensively applied as a geothermometer, provenance indicator, and fluid-composition recorder in geological studies. In this paper, the decomposition capability of an HF-HNO3-mannitol mixture for a tourmaline sample was investigated in detail for the first time, and a wet acid digestion method based on the boron-mannitol complex for accurate boron determination in tourmaline by inductively coupled plasma mass spectrometry (ICP-MS) was proposed. With a digestion temperature of 140 °C, tourmaline samples of 25 mg (±0.5 mg) can be completely decomposed by a ternary mixture, which consisted of 0.6 mL of HF, 0.6 mL of HNO3, and 0.7 mL of 2% mannitol (wt.), via a continuous heating treatment of 36 h. Following gentle evaporation at 100 °C, the sample residues were re-dissolved using 2 mL of 40% HNO3 solution (wt.) and diluted to about 2.0 × 105-fold by a two-step method using 2% HNO3 solution (wt.). The boron contents in a batch of parallel tourmaline samples were then determined by ICP-MS, and results showed that the boron concentration levels were in a range of 3.20-3.44% with determination RSDs less than 4.0% (n = 5). It was found that the boron concentrations obtained at the mass of 10B were comparable with results from the measurements at the mass of 11B. This revealed that the usage of 2% mannitol with a quantity as high as 0.7 mL in this developed approach did not exhibit significant effect on the quantification accuracy of boron at the mass of 11B. It was also found that the processes including fluoride-forming prevention and fluoride decomposition deteriorated the boron-reserving efficiency of mannitol for tourmaline, causing the averaged boron contents to vary from 2.25% to 3.57% (n = 5). Furthermore, the stability of the boron-mannitol complex under 185 °C by applying the laboratory high pressure-closed digestion method was evaluated, which showed that there existed a 60.36% loss of boron compared to that under 140 °C by using this proposed approach. For this ternary mixture, the tourmaline decomposing efficiency was found to be weakened prominently using 100 °C as the digestion temperature, and tourmaline powders can be observed even after 72 h of continuous heating with B contents within 1.09-1.23% (n = 5). To assess the accuracy of this developed method, the boron recovery of anhydrous lithium tetraborate was studied. It was found that the boron recoveries were within 96.59-102.12% (RSD < 1%, n = 5), demonstrating the accuracy and reliability of this proposed method, which exhibits advantages of high B preserving efficiency, and giving concentration information of both B and trace elements simultaneously. By applying such a boron-mannitol complex-based wet acid digestion method, the chemical composition of boron and trace elements in three tourmaline samples from different pegmatites were quantified, which provided valuable information to distinguish regional deposits and the associated evolution stages.

Rapid in situ determination of boron in irrigated waters using a new colorimetric kit

Boron is an essential micronutrient for normal plant growth. The main objective of this study was the development of a colorimetric kit for the in situ determination of the concentration of boron in irrigation water with a colorimetric scale. Said scale was compared with a boron calibration curve based on the reaction with azomethine-H. The calibration curve of the spectrophotometric method presented a correlation coefficient of 0.998, the detection limit and the quantification limits of the method were 0.1232 and 0.1605 mg/L respectively. It was therefore concluded that the colorimetric kit has potential for the determination of boron in situ in irrigation water.

From nuclear track characterization to machine learning based image classification in neutron autoradiography for boron neutron capture therapy.

Knowledge of the 10B microdistribution is of great relevance in BNCT studies. Since 10B concentration assesment through neutron autoradiography depends on the correct quantification of tracks in a nuclear track detector, image acquisition and processing conditions should be controlled and verified, in order to obtain accurate results to be applied in the frame of BNCT. With this aim, an image verification process was proposed, based on parameters extracted from the quantified nuclear tracks. Track characterization was performed by selecting a set of morphological and pixel-intensity uniformity parameters from the quantified objects (area, diameter, roundness, aspect ratio, heterogeneity and clumpiness). Their distributions were studied, leading to the observation of varying behaviours in images generated by different samples and acquisition conditions. The distributions corresponding to samples coming from the BNC reaction showed similar attributes in each analyzed parameter, proving to be robust to the experimental process, but sensitive to light and focus conditions. Considering those observations, a manual feature extraction was performed as a pre-processing step. A Support Vector Machine (SVM) and a fully dense Neural Network (NN) were optimized, trained, and tested. The final performance metrics were similar for both models: 93%-93% for the SVM, vs 94%-95% for the NN in accuracy and precision respectively. Based on the distribution of the predicted class probabilities, the latter had a better capacity to reject inadequate images, so the NN was selected to perform the image verification step prior to quantification. The trained NN was able to correctly classify the images regardless of their track density. The exhaustive characterization of the nuclear tracks provided new knowledge related to the autoradiographic images generation. The inclusion of machine learning in the analysis workflow proves to optimize the boron determination process and paves the way for further applications in the field of boron imaging.

Determination of boron in borated concrete by means of a simplified prompt gamma activation analysis at the HOTNES facility

Determination of boron in borated concrete by means of a simplified prompt gamma activation analysis at the HOTNES facility

Decay-Associated Fluorescence for Boron Determination in Uranium-Based Nuclear Fuels.

Herein is reported a novel as well as simple, sensitive, and cost-effective method for determination of boron by time-resolved fluorescence spectrometry in uranium-based nuclear fuels. Boron is complexed with fluorescent ligand chromotropic acid, and the complex formed is a measure of boron. Since the steady-state fluorescence spectra of excess ligand and complex are overlapping, the developed method emphasizes the power of time resolution. The signatory fluorescence decay times of ligand and complex are employed to derive their decay-associated spectra (DAS) and, thereby, spectroscopically eliminate the high background of ligand fluorescence. The calibration plot has a wide linear dynamic range of 5-100 ppb with r2 better than 0.998. Precision is better than 5% at the 10 ppb level and 4% at the 50 ppb level (n = 9). The detection limit is 1.5 ppb, and recovery of spiked boron (25 ppb) from the uranium samples was better than 94%. The developed method was validated by analyzing U3O8-based ILCE Standards and applied to enriched uranium fuel samples. The main advantage of the developed method is a reduction in sample size requirement due to better sensitivity and selectivity. This in turn reduces the load of uranium recovery from analytical waste, especially in the case of enriched uranium samples. Additionally, it eliminates the need of organic solvents/medium.

Smartphone digital image colorimetry combined with dispersive solid-phase microextraction for the determination of boron in food samples.

Simple, inexpensive and accurate analytical methods are in high demand. Dispersive solid-phase microextraction (DSPME) was used in combination with smartphone digital image colorimetry (SDIC) to determine boron in nuts as an approach replacing existing costly alternatives. A colorimetric box was designed to capture images of standards and sample solutions. ImageJ software was used to link pixel intensity to the analyte concentration. Under optimum extraction and detection conditions, linear calibration graphs were obtained with coefficients of determination (R2) above 0.9955. Percentage relative standard deviations (%RSD) were below 6.8%. The limits of detection (LOD) ranged between 0.07 and 0.11μgmL-1 (1.8 to 2.8μgg-1), which were sufficient for detection of boron in nut samples (i.e., almond, ivory, peanut and walnut), with percentage relative recoveries (%RR) between 92.0 and 106.0%.

POTENTIOMETRY IN DETERMINING THE CONDITIONS FOR THE FORMATION OF TETRAFLUORBORATE AS AN ANALYTICAL FORM OF BORON

The present paper deals with the research on the optimal conditions for the formation of fluoroborate as an analytical form of boron. Despite numerous scientific publications related to the determination of boron using various methods involving [BF4]ˉ ions as an analytical form, the conditions for obtaining the latter differ significantly. This difference is likely due to the complexity of the H3BO3-F--H3O+ system, where polymolecular forms of hydrofluoric acid can exist. Factors such as the inability to measure pH using a glass electrode, the velocity of the complexation process, and the requirement for specialized labware and equipment resistant to aggressive environments contribute to this complexity. In this study, potentiometry with PVC plasticized [BF4]ˉ - sensors, known for their metrological and operational characteristics, was used as a convenient tool to investigate such systems. The [BF4]ˉ - selective electrode based on the electroactive substance ion pair 2-(N-ethylcarbazole-3)-ethenyl-1,3,3-trimethyl-3H-indole tetrafluoroborate, which retains its metrological characteristics in acidic and strongly acidic environments and exhibits selectivity up to F-(= -4. 0), was employed as a sensor.&#x0D; The sensor allowed for the study of [BF4]ˉ - complex formation under different reaction conditions by recording kinetic curves in EMF-time coordinates. The yield of the analytical form was estimated at different concentrations of acid, fluoride ions, and temperature. The obtained data were used to construct the yield surface of tetrafluoroborate, revealing that the optimal conditions for the formation and stability of tetrafluoroborate at room temperature are a medium of 1 M sulfuric acid and 0. 25 M NH4F. Under these conditions, the yield of [BF4]ˉ reaches 99% within 10 minutes. Although the use of phosphoric acid does not allow for the attainment of an appropriate yield of the analytical form under equilibrium conditions, its low process velocity makes it suitable for kinetic - potentiometric determination of boron. This characteristic was utilized to develop a method for the determination of boron in phosphoric acid using the fixed-time method.&#x0D; Keywords: tetrafluoroborate ion; potentiometric sensor; kinetic determination of boron.

Standardization of the Pharmaceutical Substance of the Silicon-zinc-boron-containing Glycerohydrogel

Introduction. Silicon-zinc-boron-containing glycerohydrogel substance is considered as a pharmaceutical substance for the new drugs creation with antimicrobial action for local, external and intravaginal use. Standardization and validation of the methods determining the quality parameters of the corresponding substances is one of the stages of introducing new pharmacologically active compounds into practice.Aim. Determine the quality parameters of silicon-zinc-boron-containing glycerohydrogel, conduct their approbation. Develop a method for quantitative determination of silicon, zinc and boron. Perform statistical results processing of quantitative determination and provide a validation assessment of the chosen method.Materials and methods. A silicon-zinc-boron-containing glycerohydrogel substance was synthesized at the Institute of Organic Synthesis of the Ural Branch of the Russian Academy of Sciences and was used as the studying object. The studies were performed using a Nicolet 6700 (Thermo Fisher Scientific, USA) spectrometer and an OPTIMA 4300 DV (PerkinElmer, США) optical emission spectrometer with inductively coupled plasma.Results and discussion. The paper describes the results of new pharmacologically active silicon-zinc-boron-containing glycerohydrogel substance qualitative and quantitative tests. The data of statistical processing and validation assessment of the quantitative determination of silicon, zinc, and boron are presented.Conclusion. The quality parameters of silicon-zinc-boron-containing glycerohydrogel were determined. A method of silicon, zinc and boron quantitative determination was developed. Standardization of the investigated pharmacologically active substance was carried out in accordance with the current requirements for pharmaceutical substances in the Russian Federation.

Optimization of Curcumin Method and Usage of Natural Curcumin in Determination of Boron in Steel

Boron containing alloy steels are mainly used in constructional, automotive and many other applications. The presence of even trace amounts of boron affects greatly on the properties of steel such as hardness and machinability. Therefore, it is important to determine it accurately and precisely in the manufacture of these alloys. Due to the drawbacks of common advanced techniques such as Atomic Absorption Spectroscopy (AAS), Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES), the universally accepted method for determination of boron in steel is the spectrophotometric method using curcumin as an auxiliary agent.&#x0D; Although curcumin is the most sensitive spectrophotometric reagent for the above analysis, synthetic curcumin is relatively expensive and it tends to degrade rapidly once it is exposed to air. Furthermore this method is time consuming. Therefore, this study was carried out in order to improve and optimize the available spectroscopic method and to investigate the possibility of using natural curcumin extracted from turmeric in the above analysis.&#x0D; The results of the study implied that natural curcumin extracted and purified from turmeric can be used as accurately and precisely as synthetic curcumin in the analysis of boron in steel. A boron-steel alloy sample found to be containing 0.26±0.01 percent of boron with synthetic curcumin gave a concentration of 0.25±0.00 percent of boron with natural curcumin, indicating no significant difference in the determination. A steel sample found to be containing 0.27±0.01 percent of boron with filter paper ashing step gave a concentration of 0.26±0.01 percent of boron without filter paper ashing step indicating no significant difference. Altering the refluxing step of current procedure significantly changes the concentration of boron indicating that the refluxing step cannot be optimized further.

Comparative determination of atomic boron and carrier concentration in highly boron doped nano-crystalline diamond

Comparative determination of atomic boron and carrier concentration in highly boron doped nano-crystalline diamond

Evidence of the Uyunbulak Salt Lake Water Recharge in the Kumish Basin, Xinjiang, China, from Boron Isotopes

The reserves of nitrate (NO3-) mineral resources in the Turpan-Hami Basin in Xinjiang rank second after those in the Atacama Desert in Chile, South America. Considerable attention has been devoted to nitrogen (N) sources of NO3- deposits in recent years due to the increase in demand for NO3- fertilizers in agriculture and chemical industries. However, although the potassium nitrate (KNO3) deposits in the Uyunbulak salt lake in the Kumish basin, Xinjiang, China, have received increasing attention from numerous researchers in recent years, they all focused on the study of nitrate sources and agreed that the nitrate source in the Kumish basin is mainly atmospheric sedimentation. Studies on their water sources are scarce; for salt lake nitrate deposits, water supply also plays a crucial role in the genesis of the deposit. As a sensitive indicator, a boron isotope is often used to indicate water bodies from different sources. However, the presence of NO3- ions in water will interfere with the determination of boron isotopes, so the research on boron isotopes in nitrate salt lakes has been hindered. In this study, the three-step ion exchange method published by Ma et al. (2020) was used to eliminate the influence of NO3- ions in water on boron isotope determination, so as to reveal the water supply of Uyunbulak Salt Lake in Kumish basin by using boron isotopes which are more sensitive to water types. In this study, ice and snow meltwater, fissure water, groundwater, and surface water samples were collected from the Kumish basin and analyzed for the determination of boron (B) isotopic and hydrochemical compositions during the migration process of water bodies to reveal the recharge relationship between the water bodies from the northwestern margin of the basin and the study area. The obtained hydrochemical composition results showed a gradual increase in the salinity of the water body from 556 to 7372 mg/L from the northwestern to the southeastern parts of the basin, resulting in a gradual change in the hydrochemical facies type of Uyunbulak salt lake to NaCl. This finding suggested that the water body migrates from the northwestern to southeastern parts of the basin. The results of B isotope composition indicated two types of water bodies from different sources, namely, the ice and snow meltwater of the Southern part of the Tianshan Mountains and groundwater of the basin, exhibiting B isotope composition ranges of 26.66–27.26‰ and 12.75–15.19‰, respectively. These two types of water bodies are mixed at the Uzong spring (Q1). The ice and snow meltwater in the mixed water accounted for 46%, while the groundwater accounted for 54%. The mixed water continues to recharge the Uyunbulak Salt Lake in the southeastern part of the basin.

Application of verification and validation procedures depending on the method used

An ICP-AES method with Concentration Ratio Calibration (calibration in relative concentrations) makes it possible to improve significantly the metrological characteristics of certified reference materials (metals, alloys, technical and geological materials). The main reasons for this improvement are the advantages of the ICP-AES in combination with the advantages of the Concentration Ratio Calibration. The errors of sample weighting and the uncertainty of final volume, as well as the error attributed to the addition internal standard aliquot are excluded from the total error of analysis. Lithium hydroxide fusion in silver crucibles has been developed for the complete transfer of the ilmenite and zirconium concentrates, as well as Mg- and Cr- based refractories into solution. Compared with fusion with lithium metaborate in platinum crucibles, the proposed method is advantageous for a significantly lower cost of crucibles, higher solubility of the melt, and possibility of boron determination as an impurity in the analyzed materials. When certifying the reference samples, it is necessary to use the main principle of Concentration Ratio Calibration, i.e., the total amount of certified mass fractions and positive errors of the components to be determined should not exceed 100 % even when the ICP-AES method is not used. While conventional calibration methods use one-dimensional space and one-dimensional traceabihty the concentration ratio calibration works in re-dimensional space and provides higher accuracy of results due to n-dimensional traceabihty It is necessary to develop a theory of re-dimensional traceabihty which will provide a more reliable certification of reference samples in practice than the one-dimensional traceabihty that exists today.

The choice of methods for lithium and boron determination in lithium-boron alloys

A lithium-boron alloy (LBA) with a high lithium content (up to 70%) is used as an anode material for molten salt batteries in chemical sources of current. We present a complex of developed techniques for determining mass fractions of free lithium, total lithium, and total boron in lithium-boron alloys containing lithium mass fractions no more than 70%, boron mass fractions — no less than 26%. Optimal conditions for preparation of LBA samples and subsequent free lithium extraction from them are determined. The developed techniques are intended for i) extraction-titrimetric determination of free lithium in a content range of 20 - 50% (the relative total error no more than 1.1%); ii) determination of the total lithium content using flame atomic emission spectrometry in a content range of 59.0 - 96.0% (the relative overall error no more than 2.7%; iii) determination of the total boron content by two methods, i.e., potentiometric titration within a content range of 5 - 40% (the relative total error no more than 1.3%) and flame atomic absorption spectrometry within a content range of 4.9-50.7% (the relative total error no more than 4.9%). The results of analysis of full-scale LBA samples for the content of free lithium, total lithium and total boron are presented. It is shown that the application of two techniques for the determination of total boron content in lithium-boron alloys makes it possible to get the convergent results within the limits of measurement errors. The developed techniques are certified by the metrological service of the enterprise and can be used for the incoming and process control of the LBA production.

In-Depth Method Investigation for Determination of Boron in Silicate Samples Using an Improved Boron-Mannitol Complex Digestion Method by Inductively Coupled Plasma Mass Spectrometry.

In this paper, a boron-mannitol complex wet acid digestion method proposed for the accurate determination of boron in silicate samples by inductively coupled plasma mass spectrometry (ICP-MS) was investigated in detail for the first time. With the addition of 50 μL of mannitol (2% wt.) into the mixture of 0.6 mL of concentrated HF and 30 μL of concentrated HNO3, the 50 mg of silicate sample was effectively decomposed after being heated overnight with optional pre-ultrasonic treatment. Following fluoride formation prevention by 8% HNO3 (wt.) and fluoride decomposition using 6% HCl (wt.), the samples were fluxed in 2.0 mL of 40% HNO3 (wt.) for 4 h and aged overnight. By diluting 1000-fold using 2% HNO3 (wt.) solution, the samples were directly quantified by an ICP-MS, showing boron recoveries of the standard materials including diabase W-2, basalt JB-2a, and rhyolite JR-2 in the range of 95.5-105.5% (n = 5). For this wet acid method, it was found that the contents of boron had no obvious difference under digestion temperatures of 65, 100, and 140 °C. It was also found that the ICP-MS quantification accuracy deteriorated at the mass of 11B when boron content was about 7250 ng yielding positive bias with average recoveries of 115.5-119.8% (n = 5), while the determination results remained unaffected at the mass of 10B. Furthermore, the digestion efficiency of boron by laboratory high-pressure closed digestion method was assessed. The boron recoveries with samples treated by the high-pressure closed digestion method were found to vary within 49.5-98.0% (n = 5) and even lowered down to 31.1% when skipping pressure relief procedure. The long-term quantification stability study showed that the boron content generally declined in one month for the high-pressure closed digestion method and exhibited no significant changes for the proposed method. By applying such an improved boron-mannitol complex digestion method, the boron concentration in the studied silicate standard materials were accurately determined, providing critical data for further boron isotope analyses and associated geochemical studies. This in-depth method investigation for silicate boron determination demonstrates the feasibility of this boron-mannitol complex strategy under a wide digestion temperature of 65-140 °C, and also sheds light on the extensive applications of boron as a geological tracer.

Separation and determination of boron, chlorine, fluorine and molybdenum in uranium silicide using pyrohydrolysis and ion chromatography

Separation and determination of boron, chlorine, fluorine and molybdenum in uranium silicide using pyrohydrolysis and ion chromatography

Evaluation of Mehlich-3 as a Multi-Element Extractant of Micronutrients and Sulfur in a Soil–Ryegrass System Amended with Varying Biochar Rates from Two Feedstocks

Mehlich-3 (M-3) is used as a universal nutrient extractant due to its ability to simultaneously extract multiple elements. This study aimed to assess M-3 for the simultaneous determination of plant-available zinc (Zn), copper (Cu), iron (Fe), manganese (Mn), boron (B), and sulfate (SO4-S) in a soil amended with switchgrass- (SGB) and poultry litter-derived biochars (PLB), which were used to vary soil pH values (5.7–7.6) and organic carbon (OC) content (2.0–5.5%) in the short-term. Soil and ryegrass (Lolium perenne) were sampled from a growth chamber experiment and analyzed for plant-available and tissue phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), micronutrients (B, Cu, Fe, Mn, and Zn), and sulfur contents. The commonly accepted extractants diethylenetriaminepentaacetic acid (DTPA), for micronutrients, and 0.008 M monocalcium phosphate (MCP), for SO4-S, were used for the evaluation. Relationships between M-3 and DTPA were not reliable for micronutrient availability, although highly significant relationships for Zn and Cu were found. However, M-3-extractable S was highly correlated with S contents in ryegrass tissues regardless of the treatments and provided a 1:1 relationship between MCP and M-3. This offers the potential to eliminate MCP by simply adding S determination after extraction with M-3. Although this research evaluated the d-index for an easier linear relationship between the traditional and proposed methods, more research using several soil samples is needed to establish models and find conversion equations for micronutrients and SO4-S between DTPA-sorbitol, MCP, and M-3.

Critical Quality Control on Determination of Boron Using ICP-OES with Gravimetric Method

Critical quality control on the determination of boron using ICP-EOS with gravimetric method is carried out. This study was conducted to examine the critical aspects which include linearity, LOD, LOQ, precision, and accuracy. Based on the results of the study showed that the determination of boron with the ICP-OES method was following the critical aspects of quality control test results. The linearity of the calibration curve with a concentration range of 0 - 10 mg/L has linearity with a correlation coefficient of 0.9998 and a determination coefficient of 0.9996. The standard solution calibration curve follows the linear regression equation y = 2567.5 x + 23.043. This method has a LOD of 1.24 mg/L and a LOQ of 4.13 mg/L. The ICP-OES method has high precision and accuracy at low, medium, and high concentration levels. The testing precision of low, medium and high concentration levels is 0.44, 0.54, and 0.14%. The accuracy obtained for the three concentration levels was 98.03, 95.05, and 98.61%. Based on the ANOVA test, it was shown that the precision and accuracy at all concentration levels were not significantly different.

Determination of Boron, Lithium and Some Metals in Fly Ash by Laser Ablation ‒ Inductively Coupled Plasma ‒ Optical Emission Spectr ometry

To avoid potentially harmful wet sample preparation is offered to use laser ablation (LA) ‒ inductively coupled plasma ‒ optical emission spectrometry (ICP-OES) as a method for the elemental analysis of fly ash for boron, lithium, and some metals. For this purpose, synthetic samples were prepared by spiking with dissolved standards. As a result, great stability of calibration curves was achieved. It was found that a particle diameter less than 80 μm in fly ash is enough to have a satisfying homogeneity for successful calibration in the method of standard additions. The average recovery test for reference materials used in the study was 16–77% of the certified values for the elements observed. The low results might be the effect of spiking with calibration samples in the liquid state. This type of analysis requires further investigation. According to the results of elemental analysis, the content of boron and lithium was determined for ZUK-2 and SO-1, which was not previously noticed in other papers.

On the crystal-chemistry of meyerhofferite, CaB3O3(OH)5·H2O

The crystal structure and crystal chemistry of meyerhofferite, ideally CaB3O3(OH)5·H2O, was investigated by a multi-methodological approach based on titrimetric determination of boron, gravimetric determination of calcium, determination of fluorine by ion selective electrode, determination of water content by heating, other minor elements by inductively coupled plasma atomic emission spectroscopy, along with single-crystal synchrotron X-ray and neutron diffraction. The concentration of more than 50 chemical elements was measured. The combination of these techniques proves that the composition of meyerhofferite approaches the ideal one (i.e., (Ca1.012Mg0.003) (B2.984Si0.001)O3(OH)5·1.018H2O), with only a modest fraction of Mg (with MgO ≈ 0.03 wt%) replacing Ca, and with Si the only potential substituent of tetrahedral B (with SiO2 ≈ 0.02 wt%). The content of REE and other minor elements is, overall, not significant, including that of fluorine as a potential OH− substituent (i.e., < 0.01 wt%). These findings have some relevant geochemical and technical implications, here discussed. The X-ray and neutron structure model obtained in this study prove that the building units of the structure of meyerhofferite consist of: two BO2(OH)2 tetrahedra and one BO2(OH) triangle, linked by corner-sharing to form [B3O3(OH)5]2− rings, and distorted Ca-polyhedra (with CN = 8, CaO3(OH)4(OH2)), linked by edge-sharing to form infinite chains along [001]. The B3O3(OH)5 rings are connected to the Ca-polyhedra chains by corner- and edge-sharing, on two sides of the chains. These heteropolyhedral chains, made by Ca-polyhedra and B3O3(OH)5 rings, are mutually connected through hydrogen bonding only, giving rise to the tri-dimensional edifice of meyerhofferite. The neutron structure refinement showed no evidence of static or dynamic disorder pertaining to the H sites; their libration regime was found to be significantly anisotropic. At least seven of the nine oxygen sites of the structure are involved in H-bonding, as donors or as acceptors. The role played by the H-bonding scheme on the physical properties of meyerhofferite is discussed.