Borate Form Research Articles

Thermal storage achievement of paraffin wax phase change material systems with regard to novolac aerogel/carbon monofilament/zinc borate form stabilization

Recently, the development of thermal conductive phase change composites (PCCs) to overcome the limitation of low thermal conductivity and easy leakage of organic phase change materials (PCMs) has led to the wide application of these materials. In this study, a novolac aerogel-based composite was employed as porous support for the encapsulation of paraffin to fabricate a new class of high-performance PCCs. Carbon monofilaments and zinc borate were incorporated into the aerogel as the heat conduction network. Furthermore, zinc borate can act as a flame retardant and nucleation agent. The nanocomposite aerogels were synthesized using the sol-gel technique and then the molten paraffin was impregnated into systems. The structure and thermal properties of the nanocomposite aerogels and PCCs were characterized. Fortunately, no shrinkage was observed during aerogel synthesis. SEM images showed the formation of novolac colloids on the surface of carbon fiber. The presence of conductive fillers results in an enhancement of the thermal conductivity of novolac aerogel. Moreover, the thermal conductivity of fabricated aerogels was predicted using a modified series-parallel model for porous composite structures. Furthermore, more porosity and larger pore size of aerogels by incorporation of filler have led to a significant increase in paraffin absorption capacity. So that the highest impregnation was reached to 364.5 wt% that belongs to AC15Z15 sample. The form-stable PCMs had negligible paraffin leakage upon phase change process (less than 1.4 wt%). In addition, the leakage of PCMs composite was less than 2.59 wt% after heating for 10 h showed outstanding cycle stability of synthesized PCCs. The phase transition temperature and phase change enthalpy of PCCs were in the range of 85–96 °C and 33.94–41.85 J/g, respectively. Moreover, the latent heat of PCCs is in the range of pure paraffin, achieving high energy storage capacity. This type of PCMs system in nanostructure can be used in electrical industry for free cooling of electrical coils in this temperature range.

Removal of boron by boron selective resin-filled electrodeionization

Boron exists in the earth’s crust mainly in the form of borates or boric acid. Boric acid is a weak electrolyte and does not completely dissociate in aqueous solutions. Due to such features, it is not always possible to remove it efficiently by conventional water treatment technologies. In this work, it is the first time of the usage of boron selective resin-filled electrodeionization (EDI) to remove boron from aqueous solutions. While the experiments were carried out in constant voltage mode, however it was revealed that the applied potential and feed flow rate have significant effects on boron removal. On the other hand, variation in the electrolyte conductivity did not result in any notable changes in the boron removal efficiency. The removal performance of the boron selective resin-filled EDI cell was evaluated by calculation of flux, mass transfer coefficient, and power consumption. The results demonstrated that the feed flow rate has a significant effect on the mass transfer coefficient and flux of boron. The mass transfer coefficient of boron is found to be 7.78 × 10−4m∕s which is much higher than previously reported values in the literature. The energy consumption of boron selective resin-filled-EDI was in the range of 6.64 × 10−3–1.11 × 10 −1 Wh/g. The boron concentration in the solution decreased from 5 mg/L to 0.3 mg/L with a boron removal rate up to 94%.

Reaction Mechanism and Kinetics of Boron Removal from Metallurgical-Grade Silicon Based on Li2o-SiO2 slags

Slag refining is generally considered as one of the most optimal options for boron removal from metallurgical-grade silicon. Therefore, finding an effective refining agent to eliminate boron from metallurgical-grade silicon is of great importance. In this work, a new Li2O-SiO2 slag system was chosen as a promising agent to remove boron impurity from metallurgical-grade silicon at the conditions of holding time, slag composition and mass ratio of slag to silicon. To lower the production cost and achieve industrial application, slag treatments were carried out under an air atmosphere rather than under protective gas atmosphere. The boron concentration in metallurgical-grade silicon was successfully reduced from 8.6 ppmw to 0.4 ppmw after slag refining for 0.5 h at 1973 K when the mass ratio of the 60wt.% Li2O-40wt.% SiO2 slag to metallurgical-grade silicon was 3. This figure is significantly close to the required boron purity of SOG-Si (below 0.3 ppmw). It was proposed that the addition of CaF2 decreased the activity of silica, which brings about a negative effect on the boron removal capacity of Li2O-SiO2 slags. Moreover, the reaction mechanism and kinetics of boron removal were further investigated. Analysis of the boron concentration in the resulting slag after refining revealed that the primary boron removal approach was that a large amount of boron was oxidized and then volatilized to the atmosphere in the form of gaseous borates. Based on the two-film theory, the total mass transfer coefficient of boron was determined to be 2.3×10-2 μm s-1.

Structure and thermal pyrolysis mechanism of poly(resorcinol borate) with high char yield

Boron-containing organic polymers have excellent thermal stability and flame retardancy. Hyperbranched polymers, in which boron atoms are introduced in the form of borates, exhibit superior performance and have more applicability. This work focuses on the boron-containing polymer poly (resorcinol borate) (PRB). The chemical structure of PRB and its structural evolution at high temperatures are investigated in order to clarify the reason for its high char yield. The results indicate that the molecular skeleton of PRB mainly consists of aromatic structures, borates, BOB structures, and a small number of boron hydroxyl groups and phenolic hydroxyl groups. During pyrolysis, boron oxide is formed by the cleavage of borate OC bonds at about 400 °C. This process effectively avoids the formation and release of volatile carbon dioxide, reducing carbon loss. A large fraction of the carbon from aromatic rings is converted to amorphous carbon via pyrolysis, which possesses higher thermal stability. These results can guide the design and synthesis of novel boron-containing polymers and can provide a strategy for modifying the thermal properties of phenolic resins in order to broaden their applicability in the field of ablative-resistant composites and coatings.

Stable Phase Equilibrium and Phase Diagram of the Quinary System Li+, K+, Rb+, Mg2+//Borate-H2O at T = 348.15 K

The stable phase equilibrium of mixed aqueous electrolyte system Li+, K+, Rb+, Mg2+//borate-H2O has been studied using the isothermal dissolution method at T = 348.15 K. The space diagram, the planar projection diagram (saturated with Li2B4O7), water content diagram, and diagrams of the physicochemical properties (densities and refractive indices) have been constructed based on the Janecke method. The crystallographic form of the solid phase at the quinary system invariant point was identified by the X-ray diffraction method. Results show that the quinary system belongs to a simple type without solid solution or double salt formed. The crystallographic form of borates formed in this work are Li2B4O7·3H2O, K2B4O5(OH)4·2H2O, RbB5O6(OH)4·2H2O, and MgB4O5(OH)4·7H2O. Under the condition of Li2B4O7 saturated, the crystallization area of salts decrease in the order of RbB5O6(OH)4·2H2O > MgB4O5(OH)4·7H2O > K2B4O5(OH)4·2H2O.

Reaction Mechanism and Kinetics of Boron Removal from Metallurgical-Grade Silicon Based on Li2O-SiO2 Slags

Boron removal from metallurgical-grade silicon by Li2O-SiO2 slag refining under an air atmosphere was experimentally investigated to explore the potential of this method for achieving high boron removal. The boron concentration in the refined silicon was studied under different conditions of holding time, slag composition, and mass ratio of slag to silicon. The boron concentration in metallurgical-grade silicon was successfully reduced from 8.6 ppmw to 0.4 ppmw after slag refining for 0.5 h at 1973 K when the mass ratio of the 60 wt.% Li2O-40 wt.% SiO2 slag to metallurgical-grade silicon was 3. It was proposed that the addition of CaF2 decreased the activity of silica, which brings about a negative effect on the boron removal capacity of Li2O-SiO2 slags. Moreover, the reaction mechanism and kinetics of boron removal were further studied. Analysis of the boron concentration in the resulting slag after refining revealed that the primary boron removal approach was that a large amount of boron was oxidized and then volatilized to the atmosphere in the form of gaseous borates. Based on the two-film theory, the total mass transfer coefficient of boron was determined to be 2.3 × 10−2 μm/s.

Dietary Supplementation of Boron Differentially Alters Expression of Borate Transporter (NaBCl) mRNA by Jejunum and Kidney of Growing Pigs

Inorganic boron (B), in the form of various borates, is readily absorbed across gastrointestinal epithelia. Although there is no stated B requirement, dietary B supplementation is thought to positively affect animal growth and metabolism, including promotion of bone strength and cell proliferation. Because of effective homeostatic control of plasma B levels, primarly by renal excretion, B toxicity in animals and humans is rare. The mechanisms responsible for improved animal performance and borate homeostasis are incompletely understood. Although a Na+-coupled borate transporter (NaBC1) has been identified, the effect of dietary B supplementation on expression of NaBCl has not been evaluated. An experiment was conducted with growing pigs to determine if NaBC1 mRNA was expressed by small intestinal epithelia and kidney of growing barrows and whether dietary B (as borate) supplementation would affect expression of NaBC1 mRNA. A concomitant objective was to test the hypothesis that B supplementation of a phosphorus (P)-deficient diet would improve calcium, phosphorus, or nitrogen retention. Twenty-four crossbred growing barrows (body weight=74.0±9.8 kg) were selected and used in a randomized complete block design experiment with a total of eight blocks and three B supplementation treatments (n=8/treatment). A typical corn-soybean meal basal diet (calculated to contain 41 mg intrinsic B/kg) was formulated to meet or exceed nutrient requirements, except for P, and fed to all pigs for 12 days. The basal diet plus 0, 50, or 100 mg/kg of B (prilled sodium borate pentahydrate, Na₂B₄O₇·5H₂O) was then fed for 18 more days. Feces and urine were collected during days 6 to 16 of the B supplementation, and pigs were killed for collection of jejunal and ileal epithelia and kidney tissue. Real-time reverse transcription-PCR analysis revealed that NaBC1 mRNA was expressed by these tissues, a novel finding for jejunal and ileal epithelia. Boron supplementation increased jejunal, but decreased, renal NaBC1 mRNA expression, relative to the 0 mg/kg treatment. The finding that NaBC1 mRNA is regulatable by dietary B is novel. That B supplementation evoked opposite effects on jejunal and kidney NaBC1 mRNA expression indicates that transcriptional regulation of NaBC1 expression may constitute a part of the homeostatic control of B metabolism. In contrast to its effect on NaBC1 mRNA expression, B supplementation did not affect total tract digestibility or retention of phosphorus, calcium, or nitrogen.

An Overview on Preparation and TL Characterization of Lithium Borates for Dosimetric Use

Boron that appears in borate form in nature is an essential additive to a variety of industrial products. Recently, certain boron compounds have attracted attention in high technology utilization areas owing to their special crystal and optical characteristics. Thermoluminescent (TL) dosimetry that is used to record amount of radiation exposure is one of such areas. Two borates searched for candidacy in TL dosimetry are lithium tetraborate and lithium triborate. These materials are synthesized and metal doped by numerous researchers to be tested for thermoluminescence response. Lithium tetraborate has aroused interest of scientists since 1960s by the courtesy of the thermoluminescence (TL) property. However, lithium triborate is rather new in this area. This study compromises a broad overview including synthesis methods employed for the production of these two materials. Furthermore, the TL properties that have significant effect on the TL dosimetry potential of a compound are noted along with the detailed information on TL measurement procedure specifications.

Optimization of an isotope dilution gas chromatography/mass spectrometry method for the detection of endogenous estrogen metabolites in urine samples

A gas chromatography/mass spectrometry (GC/MS) method for the simultaneous quantitation of ten estrogen metabolites in human urine was optimized. The method consists of initial enzymatic hydrolysis of the estrogen conjugates using beta-glucuronidase followed by solid-phase extraction (SPE) on Sep-pak C18 columns and further sample purification by ion-exchange chromatography on QAE-Sephadex cartridges in the acetate form. QAE-Sephadex cartridges in the borate form were used to separate estrogens into two fractions: one fraction containing estrogens lacking vicinal cis-hydroxyls (Fr 1) and another containing estrogens possessing vicinal cis-hydroxyls (catecholestrogens; Fr 2). Finally, following O-trimethylsilyl ether derivatization, the estrogens were analyzed by GC/MS in the selected ion monitoring mode. Estrogens were quantitated using deuterated internal standards, which were added to the samples at the initiation of the work-up procedures. After addition to estrogen-low male human samples the standards showed good chromatographic linear response and reproducibility. A reduction in the number of steps and improvements in the robustness of the work-up procedures were achieved. The modified method described is less complex, amenable to use with commercially available SPE columns and fulfils all the reliability criteria, resulting in highly specific and accurate results.

GC-MS method for detection of endogenous estrogens in urine samples

Breast cancer is the most common cause of death due to malignancy among women worldwide and the majority of the established risk factors are linked to estrogens as the case maybe the endogenous estrogen metabolism. The identification of specific alterations in endogenous estrogen metabolism as risk factor for breast cancer is a topic of extensive research. For simultaneus quantitation of all estrogens and estrogen metabolites of interest, an aforementioned gas-chromatography mass spectrometry method was optimised. After enzymatic deconjugation of estrogen conjugates using β-glucuronidase, solid-phase extraction on Sep-pak C18 columns and further sample purification by ion exchange chromatography on QAE-Sephadex cartridges in the acetat form, QAE-Sephadex cartridges in the borate form were used to separate estrogens into two fractions: one fraction containing estrogens without vicinal cis-hydroxyls and a second fraction containing estrogens with vicinal cis-hydroxyls (=catecholestrogens). After derivatisation estrogens were analysed by gas-chromatography mass spectroscopy in the selected ion monitoring mode.

Synthesis in vitro of novel nucleic-acid-like polymers of Ehrlich ascites tumor cells.

1 When cytoplasmic particles isolated from Ehrlich ascites tumor cells were incubated with [14C]ribose, es and inorganic phosphate in the presence of MgCl2 and Tris/HCl (pH 7.0), radioactivity was incorporated into trichloroacetic-acid-insoluble materials. 2 Radioactive products, extracted and purified by DEAE-cellulose column chromatography, were hydrolyzed in i M HCl at 100°C for 1 h and the resultant radioactive neutral sugar components were purified and identified as ribose, glucose and rhamnose by gas chromatography and mass spectrometry. 3 When [14C]glucose was incubated in the same reaction system, radioactivity was also incorporated into trichloroacetic-acid-insoluble materials. Purified radioactive products were hydrolyzed in 1 M HCl at 100°C for 1 h and the resultant radioactive neutral sugar components were also shown to be ribose, glucose and a little rhamnose, as was the case with the products synthesized from [14C]ribose. 4 When [14C]deoxyribose was incubated in the same reaction system, little incorporation was observed. 5 The radioactive products were incubated with venom phosphodiesterase and the digests were analyzed by Dowex lX4 column chromatography. The results suggest that the radioactive products contained ribo-nuclcotides and ‘nucleotides’ containing glucose (glucose ‘nucleotides’). 6 When the radioactive products were incubated with both venom phosphodiesterase and alkaline phosphatase, ribonucleosides and glucose ‘nucleosides’ were detected. In Dowex 1X4 (borate form) chromatography, tibonuclcosides were eluted coincidentalhy with ribonucleoside markers (Cyd Ado Urd and Guo), whereas the elution profiles of glucose ‘nucleosides’ were totallydifferent fromfacto of ribonucleosides.

A review of boron effects in the environment.

Boron (B) is a naturally occurring element that is found in the form of borates in the oceans, sedimentary rocks, coal, shale, and in some soils. Borates are released naturally into the atmosphere and aquatic environment from oceans, geothermal steams, and weathering of clay-rich sedimentary rocks. B is also released to a lesser extent from anthropogenic sources. B concentrations in air range from <0.5 to 80 ng/m3 with an average of 20 ng/m3, and in soils from 10 to 300 mg/kg with an average of 30 mg/kg. Concentrations of B in surface freshwaters are typically <0.1-0.5 mg/L; much higher concentrations are measured in a few areas, depending on the geochemical nature of the drainage catchment. B accumulates in both aquatic and terrestrial plants, but it does not appear to be biomagnified through the food chain. No observed effect concentrations (NOECs) for aquatic invertebrates tend to be in the range of 6-10 mg B/L with lower values of 1-2 mg/L for community studies. No effect concentrations for fish in natural waters are around 1 mg/L, although lower values have been recorded in reconstituted water. Comparing no effect concentrations with the general ambient environmental levels indicates that the risk to aquatic ecosystems from B is low. In a few B-rich areas, natural levels will be higher; however, there is some indication that organisms may be adapted to the local conditions. B is an essential micronutrient for higher plants with interspecies differences in the levels required for optimum growth. In general, there is a small concentration range between deficiency and toxicity; however, toxicity owing to excess B is much less common in the environment than B deficiency. Levels of B in aquatic plants growing in areas receiving B-rich runoff from irrigated fields are higher than dietary concentrations, which cause effects on the growth of young birds in the laboratory; however, the bioavailability in the field of such plant-accumulated B is uncertain.

Quantification of 1,5-anhydro- d-glucitol in urine by automated borate complex anion-exchange chromatography with an immobilized enzyme reactor

HPLC using a borate form of a strongly anion-exchange resin column and an immobilized enzyme reactor for colorimetric detection was used to quantify urinary 1,5-anhydro- d-glucitol. Urine samples were introduced into the system every 7 min without any pretreatment, and after separation of interfering substances in the column, 1,5-anhydro- d-glucitol was successively detected. Quantitative determination of urinary 1,5-anhydro- d-glucitol was possible within the 1.2–300 μmol/l range. The coefficient of variance was less than 3% and the correlation between results obtained with our system ( y) and those obtained by gas chromatography–mass spectrometry ( x) was y=0.983 x−1.287 μmol/l ( n=42, r=0.998).

Sorption of glucose by an anion-exchange membrane in the borate form. Stability of the complexes and the facilitated transport of glucose

The reaction of glucose with the borate ion has been studied in an anion exchange membrane. Two complexes, BL − and BL 2 −, form in the membrane, and their corresponding stability coefficients β 1 ∗ and β 2 ∗ have been determined. The results have revealed that the BL − complex is much more stable in the membrane than BL 2 −, and the stability coefficient β 1 ∗ varies as a function of the relative proportions of the borate ion and the BL − complex. The facilitated transport of glucose was performed through an anion exchange membrane by using the borate ion as carrier; the content of the latter was fixed by the concentration of boric acid in solution. The permeance of the membrane was measured in two cases. In the first case, the boric acid concentration was fixed and the concentration of glucose varied. In the second case, the glucose concentration was fixed and the influence of boric acid concentration was examined.

Conductance study of the borate form of an anionic homogeneous membrane by impedance spectroscopy

Abstract To improve our understanding of the mechanism of boron extraction from B(OH) 3 aqueous solutions by means of electrodialysis across a homogeneous anionic ADP/216 membrane, the conductivity of the borate form of the membrane was investigated using impedance spectroscopy. Measurements were carried out for concentrations ranging from 0.02 to 0.51 mol kg −1 at four temperatures between 5 and 40°C. The marked decrease in the membrane conductivity at higher concentrations was attributed to the formation of univalent polyborate anions, the mobilities of which decrease with increasing number of boron atoms. Equilibrium constants for the formation of tri- and pentaborate species were estimated. For this membrane, the specific conductivities at 25°C of the mono- and triborate counter-ions were found to be (30 ± 1) Ω −1 cm −1 and (0.30 ± 0.05) Ω −1 cm −1 respectively. The activation energies for migration of these two species were proportional to the number of boron atoms.

Carrier-mediated, thermal energy coupled, non-isothermal membrane transport: Part 1. Transfer of the solute boric acid

The study of the influence of temperature on the carrier-mediated transport through synthetic ion-exchange membranes has been undertaken. Quantitatively, the effects of temperature on the concentration gradient dependent facilitated transport of boric acid through an anion-exchange membrane (IONAC 3475 XL) in its borate form has been investigated. It has been observed that there is an enhancement in transport when the temperature of the two compartments under study is increased uniformly (isothermal systems), and for a given average temperature, when the temperature of the downstream compartment is increased relatively to the uphill compartment (non-isothermal systems). Transport is diminished when the temperature gradient is reversed. These results have been explained on the basis of membrane conductivity and boron capacity variations with temperature thanks to the Van't Hoff law, which is encountered in classical thermodynamics. The conclusion is that the enhancement of transport is due to the facilitation of the decomposition of polyborate complexes as the temperature rises.

Separation of Neutral Glycoasparagines According to Their Content of cis Diol Groups.

A procedure for obtaining pure glycoasparagine specimens was developed. This method constitutes ion-exchange chromatography in a DEAE-Sephadex A-25 (borate form) column, using a linear gradient of borate buffer as the eluent. With no conversion, almost all the individual glycoasparagines, including some new ones, derived from ovalbumin could be isolated in pure form. By the borate-ion exchange chromatographic technique presented here, different types of neutral glycoasparagnes having a differing ability to form a complex with borate ions.

Nuclear grade resins: kinetics of isotopic and ionic exchanges for borate and chloride anions

An experimental study of borate anion fixation on nuclear grade exchangers is presented. Such resins are characterized by a very low chloride content. The increase of the resin capacity with the concentration of the external solution has been determined in the range 0.05 to 0.13 mol dm −3. The kinetics of both isotopic exchanges and conversion from the hydroxyl to the borate form have been measured. Similar investigations are reported for chloride ion fixation on the resins, for comparison. From the experimental results, the rate determining steps were generally ionic diffusion processes in the resin. More precisely, self diffusion obeys Fick's equations strictly; chloride fixation on the OH − form resin involves the Nernst-Planck equation; borate exchange seems to follow a shell progressive model.

Influence of acute metabolic acidosis on the monomer and polymer forms of renal phosphate-dependent glutaminase

Phosphate-dependent glutaminase (PDG) was measured in kidney cortex homogenates and mitochondria from control and acutely acidotic rats. The effect of plasma from acutely acidotic rats on PDG activity in homogenates from normal rats was also studied. Acidosis or incubation in acidotic plasma enhanced enzyme activity when measured at 1.0 mM but not at 20.0 mM glutamine. This effect was not due to increased mitochondrial permeability since similar results were obtained after solubilization of the enzyme with Triton X-100. Increased enzyme activity was observed with either the Tris (monomer) form or the borate (polymer) form of the enzyme, indicating that enhanced activity is not due to polymerization but probably to a conformational change in the enzyme such that the Km for glutamine is lowered.

Sorbitol determination by liquid chromatography: application to red blood cells of diabetic rats.

This report describes an application of liquid chromatography to the determination of sorbitol in red blood cells. The chromatograph employed in the present study was made up of sub- and main-separation systems and a detector portion. The sub-separation system was for concentration of polyols and involved two small columns, each containing the same anion exchange resin. The first was a tiny column which, in borate form, served as the concentrator of polyols and sugars charged in a large volume, while the second, in acetate form, separated the carbohydrates from the borate. The main system was for the fine separation of each carbohydrate and employed cation exchange columns. The detector part utilized a flow fluorometric method comprising two successive reactions: periodate oxidation followed by the Hantzsch reaction. The resulting whole chromatographic system was applied to the determination of sorbitol in red blood cells obtained from normal rats and rats made diabetic by the administration of streptozotocin; a part of the latter group had also received an aldose reductase inhibitor. Our results supported the concepts that a prolonged duration of high blood glucose level induces an elevated level of sorbitol inside red blood cells and that aldose reductase inhibitors are effective in reducing this level.