Preservation of sub-p.p.b. levels of mercury in distilled and natural fresh waters

Several preservatives, containers, etc. have been suggested in relation to the preservation of mercury samples. This paper reports a comparison of sample containers and of preservatives for synthetic and natural low-level (sub-p.p.b.) mercury samples. It is shown that 1% H₂SO₄+ 0.05% K₂Cr₂O₇ is most advantageous with respect to accuracy, precision and practical aspects such as low detection limits and adaptability to the automated cold-vapor atomic absorption technique. Glass is the best container, and is best washed with concentrated nitric acid or chromic acid. Data from a national interiaboratory quality control study on the determination of mercury show that this preservative is satisfactory for the long-term storage of sub-p.p.b. mercury solutions. The presence of mercury as CH₃Hg⁺³ improves preservation efficiency. The method of total errors is used in comparing the methods.     

Effect of boric acid on properties of high‐alumina phosphate‐bonded plastic refractory materials

The effect of boric acid on the properties of high‐alumina phosphate‐bonded plastic refractory materials at medium temperature is investigated in this work. Powder X‐ray diffraction (XRD), thermogravimetric analysis/differential thermal analysis (TG/DTA), and scanning electron microscopy (SEM) techniques are used to investigate the compositions and microstructures of the Al₂O₃–H₃BO₃ sintering products, in order to study the influence of the generated aluminum borate on the high‐aluminum refractories. Additionally, the effect of the addition of H₃BO₃ on the densification and mechanical strength of high‐aluminum phosphate‐bonded plastic refractories is studied by the permanent linear change, apparent porosity, cold compressive strength, flexural strength, and scanning electron microscopy pattern. The densification and mechanical strength of the refractories can be improved significantly by the optimal addition of H₃BO₃. However, excess H₃BO₃ will bring about a large amount of bound water into the refractories, and superabundant aluminum borate whiskers will be generated by the excess addition of H₃BO₃, both of them resulting in the reduction of the densification and mechanical strength of the refractory. In conclusion, the optimum dosages of H₃BO₃ in the powder system of high‐alumina phosphate‐bonded plastic refractories are 5, 4, and 3 wt%, sintered at 700, 900, and 1100 °C, respectively.     

Preparation and mechanism of polyurethane prepolymer and boric acid co‐modified phenolic foam composite: Mechanical properties,thermal stability,and flame retardant properties

In this work, a new kind of co‐modified phenolic foam was synthesized with polyurethane prepolymer (PUP) and H₃BO₃ by a simple preparation method. Firstly, in order to determine the optimal amount of PUP, the effects of different PUP additions on the mechanical properties, foam microstructure, and pulverization rate of phenolic foam were investigated. Then H₃BO₃ was added to toughened phenolic foam, in order to reduce its fire hazard. The results showed that the mechanical properties of the PFPUP8 phenolic foam composite were the best when the PUP content was 8 wt%. It had a small and regular cell structure, and its pulverization ratio was reduced by 80% compared with that of pristine phenolic foam. Meanwhile, the flame retardant properties of PFPUP8 were improved in different degrees with an increase in the amount of H₃BO₃. Particularly, when the addition of H₃BO₃ was 10 wt%, the peak heat release rate, the total heat release, and the total smoke release values of PFPUP10B were decreased by 35.4%, 42.4%, and 45.2%, respectively, compared with those of PFPUP8. The value of the limit oxygen index was increased by 33.1%. Besides, the addition of H₃BO₃ had no adverse effect on the mechanical properties and pulverization ratio of PFPUP8. In addition, the specific mechanisms of toughening, flame retardant, and smoke suppression are also discussed in this paper on the basis of an investigation into the thermal properties of the toughened flame retardant foam composites by thermogravimetric analysis in N₂ atmosphere.     

The effect of sample preparation on metal determination in soil by FAAS

Different methods for the determination of several metals in soils by flame atomic absorption spectrometry (FAAS) were investigated. Different procedures for total dissolution of soil: I – HF+HClO₄, H₃BO₃, HCl digestion (conventional heating), II – HF+HClO₄, H₃BO₃ digestion followed by fusion with LiBO₂ (conventional heating) and III – HF+HCl+HNO₃, H₃BO₃ digestion (microwave heating), as well as a leaching procedure with HNO₃+HClO₄, HCl were tested and compared. For quality assessment, the certified reference material S-1 soil was used. For most of the investigated metals, the best accuracy and precision were achieved when the procedure I or III were used. The developed procedure was applied to the analysis of soil samples from crude oil refinery and dump of petroleum origin wastes regions.     

The kinetic deuterium isotope effect in the thermal dehydration of boric acid

The kinetic deuterium isotope effect in the thermal dehydration process from H₃BO₃ to HBO₂(III) was determined using simultaneous TG and DSC. The rate constant ratio of H₃BO₃ to D₃BO₃ obtained by the analysis of isothermal TG and DSC curves was found to be smaller than unity. Both activation energy, E, and frequency factor, A, for the dehydration of H₃BO₃ proved to be larger than those of D₃BO₃, using non-isothermal TG and DSC. The origin of the deuterium kinetic isotope effect in the thermal dehydration of boric acid is also briefly discussed.     

A Mechanochemical-Assisted Synthesis of Boron,Nitrogen Co-Doped Porous Carbons as Metal-Free Catalysts

A green and convenient solid-state method assisted by mechanical energy is employed for the synthesis of boron (B) and nitrogen (N) co-doped porous carbons (B,N-Cs). Glutamic acid (Glu) and boric acid (H₃BO₃) are used as the N-containing carbon precursor and boron source, respectively. This method is easy to perform and proved to be efficient towards co-doping B and N into the carbon matrix with high contents of B (7 atom %) and N (10 atom %). By adjusting the molar ratio of H₃BO₃ to Glu, the surface chemical states of B and N could be readily modulated. When increasing H₃BO₃ dosage, the pore size of B,N-Cs could be tuned ranging from micropores to mesopores with a Brunauer–Emmett–Teller (BET) surface area up to 940 m² g⁻¹. Finally, the B,N-Cs were applied as metal-free catalysts for the cycloaddition of CO₂ to epoxides, which outperform the N-doped carbon catalyst (NC-900) and the physically mixed catalyst of NC-900/B₄C. The enhanced activity is attributed to the cooperative effect between B and N sites. X-ray photoelectron spectroscopy (XPS) analysis reveals that BN₃ in the B,N-Cs serves as a critical active site for the cooperative catalysis.     

On tertiary BOx± ions in HF-plasma SNMS

The effect of plasma electron impact on negative secondary ions is investigated by example of a sputtered H₃BO₃/Cu powder pellet. O^–, BO^–, BO⁺, and B⁺ tertiary ions, fractured from strongly forward focussed secondary BO₂ ^– ions, are identified by their kinetic energies. Since most of them are accepted by the ion optics, this process may affect quantification in HF-plasma SNMS.     

The effect of sample preparation on metal determination in soil by FAAS

Different methods for the determination of several metals in soils by flame atomic absorption spectrometry (FAAS) were investigated. Different procedures for total dissolution of soil: I – HF+HClO₄, H₃BO₃, HCl digestion (conventional heating), II – HF+HClO₄, H₃BO₃ digestion followed by fusion with LiBO₂ (conventional heating) and III – HF+HCl+HNO₃, H₃BO₃ digestion (microwave heating), as well as a leaching procedure with HNO₃+HClO₄, HCl were tested and compared. For quality assessment, the certified reference material S-1 soil was used. For most of the investigated metals, the best accuracy and precision were achieved when the procedure I or III were used. The developed procedure was applied to the analysis of soil samples from crude oil refinery and dump of petroleum origin wastes regions. Received: 22 Dezember 1997 / Revised: 9 February 1998 / Accepted: 12 February 1998     

Scale-up of microwave heating process for the production of bio-oil from sewage sludge

A pilot-scale microwave heating apparatus was constructed for the production of bio-oil from sewage sludge, and the effects of important microwave processing parameters and chemical additives on the quality and yield of bio-oils were investigated. It was found that bio-oil was mainly formed at the pyrolysis temperature range of 200–400 °C. A higher heating rate (faster pyrolysis) not only increased the yield of bio-oil, but also improved the quality of bio-oil according to the elemental composition and calorific values. The maximum bio-oil yield was 30.4% of organic fraction, obtained from the pyrolysis of original sewage sludge at microwave radiation power of 8.8 kW and final pyrolysis temperature of 500 °C. All of five simple additives (KOH, H₂SO₄, H₃BO₃, ZnCl₂, and FeSO₄) reduced the bio-oil yield, but the composition and property of bio-oil varied with the additive types greatly. KOH, H₂SO₄, H₃BO₃ and FeSO₄ were found to improve the quality of bio-oils remarkably according to the calorific value, density, viscosity and carbon content of bio-oils, but ZnCl₂ treatment went against that. GC–MS analysis of the bio-oils showed that, alkali treatment promoted the formation of alkanes and monoaromatics, while acid treatment favored the formation of heterocyclics, ketones, alcohols and nitriles. Compared with sulfate slat FeSO₄, chloride salt ZnCl₂ was a better catalyst for selective catalytic pyrolysis of sewage sludge. The addition of ZnCl₂ only promoted the formation reactions of a few kinds of nitriles and ketones remarkably. It is technologically feasible to produce bio-oil form microwave-induced pyrolysis of sewage sludge by optimizing pyrolysis conditions and selecting appropriate additives.     

A New Sodium Borate: Na[B6O8(OH)3]·6H2O·H3BO3

The structure of [B₆H₉NaO₁₄, H₃BO₃, 6H₂O] was determined by single‐crystal X‐ray diffraction and further analyzed by FTIR spectroscopy and differential thermal/thermogravimetric analysis. The asymmetric unit contains Na–O polyhedra (distorted octahedron), [B₆O₈(OH)₃]^– fundamental building blocks, one free water molecule and one free H₃BO₃ molecule. In the hexaborate anion, three B₃O₃ rings are linked by a common oxygen atom with five trigonal and one tetrahedral boron atoms. The hexaborate group is also linked to the oxygenated environment of the sodium atom by three other six‐membered rings, each of which involve two boron atoms, three oxygen atoms, and sodium as the joint atom.     

Valorization of industrial waste lignin via pyrolysis in the presence of additives: Formation,characterization, and application of fuel valued bio-oil and activated char

The annual production of over 50 million tonnes of industrial waste kraft lignin and scant utilization invites environmental concern. To explore the potential of simultaneously produced bio-oil and modified char (Activated char), lignin from industrial effluents was subjected to pyrolytic degradation at 380 °C using various additives, viz., H₃BO₃, ZnCl₂, and KOH yielding encouraging quantities of bio-oils besides substantial quantities of char. Quantitative and qualitative analyses of gaseous products (by GC-TCD) indicated a mixture of CO, CO₂, H₂, and methane, with some variation in volumetric composition suggesting potential for gaseous fuel/syngas. Gaseous products obtained in the presence of H₃BO₃ have the highest methane percentage. The bio-oils obtained in the presence of H₃BO₃, ZnCl₂, KOH, and only pure lignin under otherwise similar conditions were respectively 37%, 21%, 27%, and 11 wt%. In all cases, mainly bio-oils contain phenols, cyclic esters, and carboxylic acids, as indicated by GC-MS analysis. Elemental (C, H, O) Analyses of bio-oils obtained in the presence of (H₃BO₃, ZnCl₂, and KOH) indicated decreasing oxygen content compared to original lignin, suggesting their prima facie potential to lead to fuel additives/supplements. Similarly, the Char obtained in the presence of H₃BO₃, ZnCl₂, KOH, and only pure lignin were respectively, 40%, 53%, 48%, and 33 wt% with a high calorific value. Char obtained from KOH application demonstrated good uptake of Carbofuran (pesticide) from the aqueous solution. Less modified, cost-effective activated char was characterized using FTIR, TG-DTA, XRD, SEM, and BET-BJH, indicating 188.798 m²/g; this explores the role of KOH to form a microporous structure. Pseudo-second-order kinetics explain chemisorption to be dominant in the adsorption process. Thus, pyrolysis at selected temperatures/additives/and further treatments provides a much better way to utilize industrial waste lignin.     

Direct Potentiometric Measurement of NH4H2BO3 Following a Kjeldahl Distillation

Abstract

A method is described for the direct potentiometric measurement of NH₄H₂BO₃, following a Kjeldahl distillation. The NH₃ is distilled into a H₃BO₃ solution, and the activity of the NH₄H₂BO₃ is measured using a cation electrode sensitive to NH₄ ⁺ and an anion electrode sensitive to H₂BO₃. The method has been used to determine nitrogen in dried blood samples with assigned N values, and the potentiometric values agreed with the titrimetric results.     

Bis(tributyltin) oxide as a wood preservative: Its chemical nature in timber

Tributyltin compounds have been used for many years as wood preservatives. This study has provided, for the first time, an explanation for the previously reported dealkylation and/or volatilization of the tributyltin species in, and from, timber. Thus ¹¹⁹Sn NMR studies have shown that, on impregnation into timber, bis(tributyltin) oxide, (Bu₃Sn)₂O, is rapidly converted to other tributyltin species, Bu₃SnOX, and that these subsequently undergo disproportionation to Bu₄Sn and Bu₂Sn(OX)₂ compounds. We have additionally demonstrated that Bu₄Sn, so produced, is not persistent in timber and is lost by volatilization. Since the rate of disproportionation of the Bu₃SnOX species should be dependent upon the nature of the X group, it should be possible to affect significantly, if not to stop, this process by the use of alternative tributyltin fungicides, e.g. tributyltin methanesulphonate. However, tributyltin fungicides have been used successfully in wood preservation for at least 25 years. Therefore, it must be concluded that, even after disproportionation in timber, in service, sufficient preservative action is retained to prevent decay of wood under the conditions of natural exposure.     

Conversion of yttrium-aluminum garnet to soluble forms as a result of mechanochemical treatment

Summary The changes in the solubility and in the phase composition of yttrium-aluminum garnet (YAG) as a result of its mechanochemical treatment for 2 h in a planetary ball mill together with H₃BO₃ and Na₂CO₃ (mole ratio H₂BO₃/Na₂CO₃=4) in ratios (H₃BO₃+Na₂CO₃)/YAG=2,4, and 9 are studied. At a ratio of 9, the yield of yttrium in the water solution obtained upon treatment of the activated mixture at 90 °C (50 cm³ water/g sample) reaches 85%. Its content in the same solution is above 93% relatively to the sum Y+Al.

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Umwandlung von Yttrium-Aluminium-Granat in lösliche Formen durch mechanochemische Behandlung

Zusammenfassung Die Änderungen bezüglich Löslichkeit und Phasenzusammensetzung von Yttrium-Aluminium-Granat (YAG) als Ergebnis einer zweistündigen mechanochemischen Behandlung in einer Kugelmühle zusammen mit H₃BO₃ und Na₂CO₃ (Molverhältnis H₃BO₃/Na₂CO₃=4) bei (H₃BO₃+Na₂CO₃)/YAG-Verhältnissen von 2, 4 und 9 wurden untersucht. Bei einem Verhältnis von 9 erreicht die Ausbeute an Yttrium in der wäßrigen Lösung nach Behandlung der aktivierten Mischung bei 90 °C (50 cm³ H₂O pro Gramm) 85%. Relativ zur Summe Y+Al beträgt der Yttriumgehalt 93%.

     

Thermochemical property of a microporous material for mixed metal borate of Li2Sr4B12O23

A pure mixed alkali–alkaline earth metal borate of Li₂Sr₄B₁₂O₂₃ with microporous structure has been synthesized by high-temperature solid state reaction, and characterized by XRD, FT-IR, TG techniques, and chemical analysis. The molar enthalpies of solution of Li₂Sr₄B₁₂O₂₃ in 1 mol L^?1 HCl(aq), and of SrCl₂·H₂O(s) in [1 mol L^?1 HCl + H₃BO₃ + LiCl·H₂O](aq) have been determined by microcalorimeter at 298.15 K, respectively. From these data and with the incorporation of the previously determined enthalpies of solution of H₃BO₃(s) in 1 mol L^?1 HCl(aq), and of LiCl·H₂O(s) in [1 mol L^?1HCl + H₃BO₃](aq), together with the use of the standard molar enthalpies of formation for SrCl₂·6H₂O(s), LiCl·H₂O(s), H₃BO₃(s), HCl(aq), and H₂O(l), the standard molar enthalpy of formation of ?(11,534.0 ± 10.0) kJ mol^?1 for Li₂Sr₄B₁₂O₂₃ was obtained on the basis of the appropriate thermochemical cycle.     

Boron Doped Carbon Dots with Unusually High Photoluminescence Quantum Yield for Ratiometric Intracellular pH Sensing

Herein we report that boron doping in carbon dots results in increased photoluminescence (PL) quantum yield, which could be used for ratiometric intracellular pH sensing in cancer cell lines. Using a mixture of citric acid monohydrate, thiourea, and boric acid, microwave-assisted synthesis of boron doped blue emitting carbon dots (B-Cdots) with an average size of 3.5±1.0 nm was achieved. For B-Cdots, the maximum quantum yield (QY) was observed to be 25.8 % (11.1 % (w/w) H₃BO₃ input concentration), whereas, the same was calculated to be 16.9 % and 11.4 % for Cdots (synthesized from citric acid monohydrate and thiourea only) and P-Cdots (phosphorus doped carbon dots; synthesized using citric acid monohydrate, thiourea and phosphoric acid) (11.1 % (w/w) H₃PO₄ input concentration), respectively. The observed luminescence efficiencies as obtained from steady state and time-resolved photoluminescence measurements suggest an alternative emission mechanism due to boron/phosphorus doping in carbon dots. We furthermore demonstrated facile composite formation using B-Cdots and another carbon dots with orange emission in presence of polyvinyl alcohol (PVA), resulting in white light emission (0.31, 0.32; λ_ex 380 nm). The white light emitting composite enabled ratiometric pH sensing in the aqueous medium and showed favorable uptake properties by cancerous cells for intracellular pH sensing as well.     

Hydrothermal synthesis and thermodynamic properties of 2CaO·3B<Subscript>2</Subscript>O<Subscript>3</Subscript>·H<Subscript>2</Subscript>O

2CaO·3B₂O₃·H₂O which has non-linear optical (NLO) property was synthesized under hydrothermal condition and identified by XRD, FTIR and TG as well as by chemical analysis. The molar enthalpy of solution of 2CaO·3B₂O₃·H₂O in HCl·54.572H₂O was determined. From a combination of this result with measured enthalpies of solution of H₃BO₃ in HCl·54.501H₂O and of CaO in (HCl+H₃BO₃) solution, together with the standard molar enthalpies of formation of CaO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of −(5733.7±5.2) kJ mol⁻¹ of 2CaO·3B₂O₃·H₂O was obtained. Thermodynamic properties of this compound were also calculated by a group contribution method.     

白硼钙石的合成新方法及其热化学研究(英)

0IntroductionTherearemanykindsofhydratedcalciumbo-rates,bothnaturalandsynthetic.Someofthemarematerialsusedinglass,potteryandporcelainenamelindustry,especiallyinunalkaliglassindustry.4CaO·5B2O3·7H2O,calledpriceite,isacalciumboratemin-eral,notfoundinCaO-B…     

Effects of boric acid on structural and luminescent properties of BaAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:(Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript>) phosphors

Eu²⁺/Dy³⁺-codoped BaAl₂O₄ phosphors were prepared by conventional solid-state reaction with boric acid flux. The effects of boric acid on structural and luminescent properties of BaAl₂O₄:(Eu²⁺, Dy³⁺) were investigated. The crystallinity of BaAl₂O₄ improved with increasing amount of H₃BO₃. Incorporation of Eu²⁺ and Dy³⁺ ions into effective lattice sites was promoted by H₃BO₃ addition. As a result, Eu²⁺ emission in BaAl₂O₄ was greatly enhanced by H₃BO₃, and the duration of persistent luminescence increased with the amount of H₃BO₃. However, the decay lifetime of persistent luminescence was not strongly influenced by the amount of H₃BO₃.     

Iron-catalyzed boration of allylic alcohols with H3BO3 as an additive

A method for the synthesis of allylboronates by iron-catalyzed boration of allylic alcohols with H₃BO₃ as an additive is developed. The introduction of H₃BO₃ promotes the cleavage of C?O bond in allylic alcohols obviously. Functional groups, such as fluoro, chloro, bromo, alkyl, and alkoxy, are tolerated well. Thus, various allylboronates are obtained in acceptable yield.