Aqueous Nitric Acid Solutions Research Articles

In English

The synthesis and characterization of heterostructure por-Ga2O3/GaAs represent a crucial advancement in nanomaterials, particularly in optoelectronic applications. Employing a two-stage electrochemical etching methodology, this research has elucidated the precise conditions required to fabricate such a heterostructure. The initial stage involves etching monocrystalline gallium arsenide (GaAs) using an aqueous nitric acid solution as the electrolyte. This process is governed by the redox reactions at the crystal-electrolyte interface, where GaAs are partially oxidized and selectively etched. The second stage introduces ethanol into the electrolytic solution. This chemical addition serves a dual purpose: Firstly, it modulates the electrochemical environment, allowing for controlling pore morphology in GaAs. Secondly, it facilitates the etching of the resultant oxide layer, which predominantly consists of gallium oxide (Ga2O3). The formation of this oxide layer can be attributed to the oxidation of GaAs, driven by the electrochemical potentials and resulting in the deposition of reaction by-products on the substrate surface. The fabricated nanocomposite was comprehensively characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDX), and Raman Spectroscopy. SEM imaging revealed a range of agglomerated nanostructures dispersed across the surface, with dimensions ranging from 8–25 μm, 1–1.5 μm, and 70–100 nm. These observations suggest a hierarchical pore structure indicative of a complex etching mechanism modulated by the electrolyte composition. Raman spectroscopic analysis corroborated the presence of various phases in the heterostructure. Signals corresponding to bulk GaAs, serving as the substrate, were distinguishable. In addition, peaks indicative of porous GaAs and porous Ga2O3 were observed. A cubic phase in the Ga2O3 layer was particularly noteworthy, suggesting a higher degree of crystallinity. Notably, the absence of Raman-active modes associated with internal stresses implies that the fabricated heterostructure is of high quality.

Improved determination of nitrate isotopes in irrigated agricultural areas and Bayesian mixing model quantification of nitrate sources and fate

Technological advancements in isotope techniques have been widely utilized in environmental pollution research, particularly for the monitoring of nitrate pollution in water. The utilization of pretreatment with an aqueous nitric acid solution offers numerous advantages in analyzing isotopic composition; however, there is still room for improvement regarding conversion efficiency, reduced reaction time, and cost control. In light of this, this study proposes an enhanced chemical conversion method that involves mitigating the interference caused by the nitrogen azide reaction during the pretreatment process, optimizing the purge gas to remove interfering factors, and improving the inlet device for measuring nitrous oxide. The improved method was applied to determine nitrate isotopes in the Ulansuhai Basin, Inner Mongolia and its reliability was verified through analytical results obtained from bacterial denitrification methods. The mean δ15N-NO3- and δ18O-NO3- values determined using the chemical transformation method were 4.85‰ and 23.44‰, respectively. Compared with the previous method, the improved method enhanced the maneuverability of precise control, the pretreatment time was reduced from 2 to 3 hours to 1.5 hours, and the experimental cost was scaled down to half of the original one. In addition, the contribution of each source was calculated by combining nitrate isotopes with a Bayesian stable isotope mixing model. It was found that manure sewage accounted for (50.1±22.6) % while soil nitrogen sources contributed (25.1±20.4) % to nitrate levels in Ulansuhai Lake's water. The chemical conversion methods successfully improved within this study can also be applied to other watersheds or regions. These research findings provide a valuable theoretical foundation for managing nitrogen sources within watersheds.

ENVIRONMENTALLY SAFE TECHNOLOGY OF STARCH NITRATE PRODUCTION

This article is devoted to development of an environmentally safe technology for production of an explosive substance – starch nitrate. The aim of the development was to create the technology for starch nitrate production, which reduces the man-made burden on the environment, due to the absence of acidic wastes discharged into the environment, and also ensures the chemical stability of starch nitrate. This is achieved by starch nitration with highly concentrated nitric acid without adding sulfuric acid. To work out this process in laboratory conditions, nitration of starch was carried out with 98 %, 90 % and 85 % nitric acids. Obtained starch nitrate was precipitated from the solution in nitric acid into the aqueous solution of nitric acid of lower concentration, separated from the precipitation medium, washed with water, dried, and its chemical stability was determined. The following portions of starch nitrate were precipitated in media prepared from drains formed after washing previous portions of starch nitrate by adding 98 % nitric acid to them. Concentrations of nitric acid in the initial and spent precipitation media were determined. Based on the results of the experimental studies, the modes of the technological process were established, which allows effective regeneration of the presipitation medium after presipitation of starch nitrate, which excludes the ingress of acid waste into the environment, and ensure high chemical stability of the obtained starch nitrate. The technological scheme for the continuous production of starch nitrate according to environmentally safe technology using a drum vacuum filter was developed, in which all starch nitrate stabilization operations are combined.

Primary photophysical and photochemical processes for cerium ammonium nitrate (CAN) in acetonitrile.

Cerium ammonium nitrate (CAN) is an important photolytic source of NO3• radicals in aqueous nitric acid solutions and in acetonitrile. In this work we performed the study of primary photochemical processes for CAN in acetonitrile by means of ultrafast TA spectroscopy and quantum chemical calculations. Photoexcitation of CAN is followed by ultrafast (< 100fs) intersystem crossing; the vibrationally cooled triplet state decays to pentacoordinated Ce(III) intermediate and NO3• radical with the characteristic time of ca. 40ps. Quantum chemical (QM) calculations satisfactorily describe the UV-vis spectrum of the triplet state. An important feature of CAN photochemistry in CH3CN is the partial stabilization of the radical complex (RC) [(NH4)2CeIII(NO3)5…NO3•], which lifetime is ca. 2μs. The possibility of the RC stabilization is supported by the QM calculations.

The distribution coefficients of Nd3+ and Y3+ between 0.1 and 2.1 M HNO3 and HDEHP at 298.15 K

Rare earth metals are considered to be some of the most critical raw materials on the planet due to their use in many products and technologies, the difficulty in isolating the individual elements from ores and each other, and the market restrictions that threaten their supply. However, despite this, the recycling rates for rare earth metals remain low. Hydrometallurgy has been proposed to hold the greatest potential for the recovery of rare earth metals from waste materials. However, the design of hydrometallurgical processes for the recovery of rare earth elements from waste requires a good understanding of the behaviour of the rare earth metals between different phases.In this study, the distribution coefficients of two rare earth metals, yttrium, and neodymium, between an organic solvent; bis(2-ethylhexyl) phosphate, diluted in n-dodecane at between 0.25 M and 1 M; and an aqueous nitric acid solution at concentrations of between 0.1 M and 2.8 M were measured. Distribution measurements were performed using a series of liquid–liquid extraction cells at a constant temperature of 298.2 K. The concentration of the rare earth metals was measured using ICP-OES analysis. The distribution coefficients and the acid concentration were found to be inversely related to each other. Conversely, the distribution coefficients were directly proportional to the concentration of the solvent in the organic phase.The data reported in this paper will be used to design a counter-current liquid–liquid extraction column for the recovery of neodymium from waste permanent magnet powder.

Pilot-scale Validation of the Modeling of NOx Reactive Absorption Process Using Aqueous Solutions Containing Nitric Acid and Hydrogen Peroxide

NOx are harmful pollutants emitted by many industries and must be removed before the gases are released into the atmosphere. Among the various techniques used for NOx removal, reactive absorption by hydrogen peroxide in a packed column has the advantage of being able to transform NOx into nitric acid which can be recycled and reused in the plants. This work aimed at modeling the NOx absorption by means of aqueous solutions of hydrogen peroxide and nitric acid, applied in a packed column operating under different representative conditions. The model established using the Aspen software considers the equilibrium and the kinetics of the reactions taking place both in the gas phase and in the liquid phase as well as the thermodynamic properties of the chemical (molecular and ionic) components estimated using the Electrolyte NRTL model. It allows predicting NOx absorption performances in terms of efficiency and selectivity. The model was validated by comparing simulation results with experimental ones obtained in a pilot-scale absorption column and published previously. The predicted values are in satisfactory agreement with the experimental data showing a deviation between 5 and 8%. Therefore, the model developed in this work could be advantageously used to design industrial-scale reactive NOx absorption columns.

Triflimide Effect in Solvent Extraction of Rare-Earth Elements from Nitric Acid Solutions by TODGA

ABSTRACT Outer-sphere interactions play an important role in the liquid-liquid extraction and separation of metal ions and they could be used to tune the efficiency and selectivity of recovery. Here, we report the extraction behaviour and separation of trivalent rare-earth elements from aqueous nitric acid solutions with N,N,N’,N’-tetra-n-octyl diglycolamide (TODGA), which was preliminarily contacted with an aqueous solution of N-H acid bis[(trifluoromethyl)sulfonyl]imide (triflimide, HTf2N; Tf = CF3SO2) resulting in an adduct TODGA⋅HTf2N. We examined in detail the extraction system composed of TODGA acidified with HTf2N and 1,2-dichloroethane as diluent. The effect of various experimental conditions such as the nature of diluent, aqueous nitric acid concentration, and TODGA⋅HTf2N concentration in the organic phase was studied. It has been found that the distribution coefficient values for metal ions are much greater, especially at low aqueous acidity in the extraction systems with the acidified organic solvent phase. Furthermore, the heavier lanthanides were effectively extracted and the intergroup lanthanide selectivity was greatly improved (separation factors for the Lu/La pair increased by 40 and 2 times for the two systems under study, respectively).

Synergistic Extraction of Lanthanides(III) from Acidic Aqueous Solutions with Mixtures of Bis(Diphenylcarbamoylmethylphosphine Oxide) Ligands and Dinonylnaphtalene Sulfonic Acid

ABSTRACT The extraction of lanthanides(III) from aqueous nitric acid solutions with mixtures of bis(diphenylcarbamoylmethylphosphine oxides) (L) and dinonylnaphthalene sulfonic acid (HDNNS) in organic diluents is studied. It is established that the efficiency of extraction of Ln(III) ions increases significantly when HDNNS is added to the organic phase containing L. The synergistic effect arises due to the higher hydrophobicity of the extractable Ln(III) complexes formed by the L ligand and DNNS− anions compared to those containing NO3 − ions as counteranions. The stoichiometry of the extracted complexes is determined, and the influence of the composition of the aqueous phase, the nature of the organic solvent, and the structure of the bis-CMPO ligands on the efficiency of the extraction of metal ions into the organic phase is considered. The synergistic effect during the extraction of Ln(III) from aqueous nitric acid solutions with mixtures of L and HDNNS weakens with increasing the acidity of the aqueous phase; however, it also holds in acidic media.

Isotropic coal tar pitch-based carbon fibers: Effect of nitric acid towards elimination of air-stabilization step

The remarkable properties exhibited by carbon fibers have generated considerable interest in seeking alternative approaches to replace time-consuming, energy-intensive, and multi-step procedures for their synthesis. Among the various stages involved in carbon fiber synthesis, the stabilization step plays a crucial role as it necessitates an extended duration to transform thermoplastic pitch-fibers into thermosetting fibers, thus preventing them from melting during high-temperature treatments. In this study, isotropic coal tar pitch (ICTP) was transformed into pitch fibers through melt-spinning process and subsequently subjected to chemical treatment for stabilization using varying concentrations (ranging from 5% to 50% v/v) of aqueous nitric acid (HNO3) solutions. The objective was to determine the optimal concentration for effective stabilization. Consequently, this research eliminates the conventional, time-consuming air-stabilization process by treating the pitch fibers with nitric acid prior to carbonization. To produce carbon fibers, all chemically stabilized pitch fibers were directly carbonized at 1000 °C. Comprehensive characterizations including Rheology, Elemental analysis, FTIR, TGA, FE-SEM, XRD, Raman, and XPS were conducted to investigate the chemical and structural transformations occurring during the fiber processing. It was observed that aqueous nitric acid solutions ranging from 15% to 30% (v/v) exhibited superior structural, morphological, and mechanical properties compared to other concentrations of HNO3.

Extraction of Lanthanides(III) from Aqueous Nitric Acid Solutions with Tetra(n-octyl)diglycolamide into Methyltrioctylammonium Bis(trifluoromethanesulfonul)imide Ionic Liquid and Its Mixtures with Molecular Organic Diluents

The extraction of lanthanides(III) from aqueous nitric acid solutions with tetra(n-octyl)diglycolamide into methyltrioctylammonium bis(trifluoromethanesulfonul)imide ([N1888][Tf2N]) ionic liquid and its mixtures with molecular organic diluents is investigated in this study. This study also investigates the effect of HNO3 concentration in the aqueous phase on the extraction of Ln(III) ions. Subsequently, the stoichiometry of the extracted complexes is determined, and the mechanism of Ln(III) extraction in a system with [N1888][Tf2N] is discussed. It is shown that the intragroup selectivity of the extraction of Ln(III) ions is significantly higher when using [N1888][Tf2N] than when using the imidazolium-based ionic liquid [C4mim][Tf2N].

Efficient separation of americium by a mixed solvent of two extractants, a diamideamine and a nitrilotriacetamide.

The Japan Atomic Energy Agency (JAEA) has proposed the Solvent Extraction from Liquid waste using Extractants of CHON-type for Transmutation (SELECT) process by solvent extraction as a new separation technology to recover minor actinides (MA) from high-level liquid waste (HLLW) produced by spent fuel reprocessing. The MA separation in the SELECT process comprises the recovery of MA and rare earths (RE) from HLLW, MA/RE separation, and Am/Cm separation. Three highly practical extractants are used in the MA separation. Furthermore, this flow configuration facilitates the preparation of nitric acid concentrations in the aqueous phase. However, the separation factor between Cm and Nd in the MA/RE separation is small (SFCm/Nd = 2.5), requiring many extraction stages for continuous extraction in a mixer settler. Therefore, this study investigated the separation of only Am from an aqueous nitric acid solution containing MA (Am and Cm) and RE using an organic phase mixed with two extractants alkyl diamideamine with 2-ethylhexyl alkyl chains (ADAAM(EH)) and hexa-n-octylnitrilotriacetamide (HONTA) used in the SELECT process. Under high-concentration nitric acid conditions, Am and La, Ce, Pr, Nd (light lanthanides) were extracted in the ADAAM(EH) + HONTA mixed solvent, whereas Cm, medium, and heavy lanthanides, and Y were partitioned in the aqueous phase. Subsequently, only light lanthanides could be back extracted from the ADAAM(EH) + HONTA mixture solvent containing Am and light lanthanides in low nitric acid concentrations. Furthermore, Am could be easily stripped with 0.2M or 5M nitric acid. This method does not require the mutual separation of Cm and Nd, which have low separation factors. Am can be efficiently separated by one extraction and two back extractions, reducing the number of steps in the SELECT process.

MODIFICATION OF THE SURFACE OF COPPER ALLOYS WITH ALUMINUM IN THE CONDITIONS OF SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS

The influence of the technological parameters of the SHS process (temperature, holding time and alloying of B, Cr, Ti) on the corrosion resistance of brass with a surface alite layer, which effectively resists β-radiation, was studied. The research was carried out in 30% aqueous solutions of HNO3, HCl, H2SO4. Aluminized coatings doped with silicon, which are obtained under optimal parameters, have 1.7-2.1 times higher corrosion resistance than doped B and Ti. Alloyed coatings have phases CuSi, CuAl, CuAl2, CuTi, Ti2Cu3, CuCr, Cu3Al, Cu2Al, Al3Si, and α-phase doped with Cr, Al, Si, B, Ti. When tested in a 30% aqueous solution of nitric acid, the coating doped with titanium and silicon shows a weight loss of 32 and 37 g/m2, respectively.

Patterns of the process of starch nitration with nitric acid

The article presents the results of the experimental study on the starch nitration process with aqueous solutions of nitric acid. This nitrating medium has a number of advantages over the nitric and sulfuric acids mixture commonly used in industry, in particular it concerns the chemical stability of resulting starch nitrate. The aim of this work is to establish the dependence of nitration degree of starch on the nitration process parameters, taking into account changes in the chemical composition of its macromolecules. The experimental research method involved the use of ferrous sulfate method to determine the nitration degree of starch and IR-Fourier spectroscopy to analyze the macromolecules chemical composition. The parameters of the nitration process were changed in the following ranges: the mass fraction of water in acid solution of 0 to 35%, the temperature of 3.4 to 800С, the nitration module, as the ratio of the mass of the acid solution to the mass of potato starch of 1 to 40, and the nitration time of 1 to 180 min or 24 h. Based on the experimental results, it was found that the maximum degree of starch nitration is achieved with a water mass fraction in the nitrating solution of about 2%; a further increase in its content leads to a decrease in the starch nitration degree. The increase in the starch nitration degree to the maximum value in this case indicates the nucleophilic mechanism of starch nitration. It is shown that the temperature has a weak effect on the starch nitration degree, and nitrates of oxidized starch are formed under the conditions of high temperature. Increasing the nitration modulus leads to an increase in the starch nitration degree. The effect of nitration time on the starch nitration degree is related to the starch property to dissolve in nitric acid. The initial stage of starch nitration process proceeds at a high rate, which is a consequence of the acid intense penetration into the starch amorphous regions and their dissolution. In the following stages, the nitration process is slowed down due to the acid diffusion into the starch crystalline regions. If nitration is continued, a practically stable value of the nitration degree is achieved in the resulting starch nitrate. The obtained results allow choosing rational conditions for preparation of starch nitrate, which is a powerful explosive.

Cover Feature: Gamma Radiation‐Induced Degradation of Acetohydroxamic Acid (AHA) in Aqueous Nitrate and Nitric Acid Solutions Evaluated by Multiscale Modelling (ChemPhysChem 5/2023)

The Cover Feature represents acetohydroxamic acid degradation in used nuclear fuel reprocessing cycles, where it is broken down by hydrolysis and radiation in aqueous nitric acid to form acetic acid, hydroxylamine, nitrous oxide, and hydrogen gas. Designed by Rett Longmore. More information can be found in the Research Article by Jacy K. Conrad, Gregory P. Horne and co-workers.

Radiolytic evaluation of acetohydroxamic acid (AHA) under biphasic (HNO3:n-dodecane and TBP/DEHBA/DEHiBA) used nuclear fuel reprocessing conditions

Acetohydroxamic acid (AHA) has been proposed as a substitute for hydrazine-stabilized reductants for the selective separation of plutonium and neptunium from co-extracted uranium during the reprocessing of used nuclear fuel. However, limited information exists for the chemical behavior of AHA in ionizing radiation fields, especially under representative biphasic reprocessing solvent system conditions. Here we present a systematic gamma irradiation study on the radiolytic integrity of AHA in aqueous nitric acid solutions (0.2 M HNO3) in contact with an organic phase, comprising current (tri-butyl phosphate) and next generation (N,N-di-(2-ethylhexyl)butyramide and N,N-di-(2-ethylhexyl)isobutyramide) reprocessing ligands dissolved in n-dodecane diluent. Biphasic AHA irradiations exhibited negligible effect of the organic phase on the rate of AHA radiolysis—affording an average pseudo dose constant of d' = (−58.66 ± 6.10) × 10−4 kGy−1—and subsequent formation of the predominant degradation products (hydroxylamine and acetic acid), relative to complementary single-phase systems. The radiolysis of AHA was found to have negligible impact on ligand degradation rates: G(TBP) = −0.038 ± 0.002 μmol J−1, G(DEHBA) = −0.117 ± 0.004 μmol J−1, and G(DEHiBA) = −0.102 ± 0.003 μmol J−1. These observations demonstrate that the radiolytic transients and steady-state degradation products generated in either phase have limited capacity for migrating across the aqueous-organic interface to undergo subsequent chemistry within the investigated dose range (≤110 kGy). These findings support the substitution of AHA into advanced reprocessing flowsheets.

Chemoconvection of miscible solutions in an inclined layer

This paper presents an experimental and numerical investigation of the chemoconvective flow of two miscible reacting solutions that generate a plain layer oriented at some angle to the gravity field. In the experiments, the aqueous solutions of nitric acid and sodium hydroxide were used. The system evolves from an initial state, in which each homogeneous solution occupies half of the layer, and the contact surface between the layers is flat. When the reacting solutions come into contact with each other, an acid-base neutralization reaction occurs, forming salt and water. The system configuration is chosen so that the acid solution of lower density rests on top of the denser base. This excludes the development of the Rayleigh–Taylor instability. The experiments were performed for such initial concentrations of the reagents at which a wave regime is realized in the system. The wave comprises a density jump rapidly advancing in the direction of gravity and separating the immobile alkali solution and the layer of acid and salt mixture, the convective motion of which feeds the frontal reaction with fresh acid. The visualization of the flow in the experiments was performed using a Fizeau interferometer. The numerical study of a complete three-dimensional problem was carried out using the ANSYS CFX hydrodynamic simulation program. We studied the flow evolution at a gradual increase in the angle of inclination from 0° to 70°. We found that the layer inclination leads to a significant change in the structure and intensity of the convective motion. Already at small inclination angles (up to 30°), the flow becomes three-dimensional, which makes the Hele-Shaw approximation inapplicable to this case. We show that there is a spontaneous stratification of salt and acid concentration fields in the cocurrent wave flow. With an increase in the angle of inclination, the wave velocity decreases, and chemoconvection in the cocurrent flow becomes less intense and acquires a certain vortex structure. At larger angles (from 50° to 70°), the wave front is strongly deformed or the wave breaks up. We demonstrate that an up-and-down fluid flow develops in the layer above the density jump. This flow eventually loses its stability with respect to the vertical rolls of solutal Rayleigh convection. There is a good agreement between the experimental measurements and the results of numerical simulation of the 3D problem.

Statistical Optimisation of Chemical Stability of Hybrid Microwave-Sintered Alumina Ceramics in Nitric Acid.

The goal of this research is the statistical optimisation of the chemical stability of hybrid microwave-sintered alumina ceramics in nitric acid. The chemical stability of ceramic materials in corrosive media depends on many parameters, such as the chemical and phase composition of the ceramics, the properties of the aggressive medium (concentration, temperature, and pressure), and the exposure time. Therefore, the chemical stability of alumina ceramics in different aqueous nitric acid solution concentrations (0.50 mol dm-3, 1.25 mol dm-3, and 2.00 mol dm-3), different exposure times (up to 10 days), as well as different temperatures (25, 40, and 55 °C), was investigated, modelled, and optimised. The chemical stability of high purity alumina ceramics (99.8345 wt.% of Al2O3) was determined by measuring the amount of eluted ions (Al3+, Ca2+, Fe3+, Mg2+, Na+, and Si4+) obtained by inductively coupled plasma atomic emission spectrometry. The changes in the density of alumina ceramics during the chemical stability monitoring were also determined. The Box-Behnken approach was employed to reach the optimum conditions for obtaining the highest possible chemical stability of alumina at a given temperature range, exposure time, and molar concentration of nitric acid. It was found that an increase in exposure time, temperature, and nitric acid concentration led to an increase in the elution of ions from hybrid microwave-sintered alumina. Higher amounts of eluted ions, Al3+ (14.805 µg cm-2), Ca2+ (7.079 µg cm-2), Fe3+ (0.361 µg cm-2), Mg2+ (3.654 µg cm-2), and Na+ ions (13.261 µg cm-2), were obtained at 55 °C in the 2 mol dm- 3 nitric acid. The amount of eluted Si4+ ions is below the detection limit of inductively coupled plasma atomic emission spectrometry. The change in the alumina ceramic density during the corrosion test was negligible.

Gamma Radiation-Induced Degradation of Acetohydroxamic Acid (AHA) in Aqueous Nitrate and Nitric Acid Solutions Evaluated by Multiscale Modelling.

Acetohydroxamic acid (AHA) has been proposed for inclusion in advanced, single-cycle, used nuclear fuel reprocessing solvent systems for the reduction and complexation of plutonium and neptunium ions. For this application, a detailed description of the fundamental degradation of AHA in dilute aqueous nitric acid is required. To this end, we present a comprehensive, multiscale computer model for the coupled radiolytic and hydrolytic degradation of AHA in aqueous sodium nitrate and nitric acid solutions. Rate coefficients for the reactions of AHA and hydroxylamine (HA) with the oxidizing nitrate radical were measured for the first time using electron pulse radiolysis and used as inputs for the kinetic model. The computer model results are validated by comparison to experimental data from steady-state gamma ray irradiations, for which the agreement is excellent. The presented model accurately predicts the yields of the major degradation products of AHA: acetic acid, HA, nitrous oxide, and molecular hydrogen.

Ceramic molds based on yttrium oxide for the casting of titanium alloys

The effect of various binding agents based on aqueous solutions of nitric acid, yttrium nitrate and orthophosphoric acid and yttrium hydroxide gel on the physical and mechanical properties of casting molds based on Y2O3 has been studied. It is shown that the most promising binding agent for yttrium oxide casting molds is a phosphate bond. The data describing the curing mechanism of phosphate-bonded molding mass is presented. The influence of the concentration of binding agent solutions on the strength characteristics of molding materials after curing and heat treatment is shown. Information about the interaction of yttrium oxide powder molds with phosphate-binding with titanium melt of VT1-0 and VT6 grades is presented. The obtained data allowed us to describe the advantages and disadvantages of the developed molding compound. A method for producing casting molds based on yttrium oxide powder with a yttrium phosphate-binding agent was developed based on this research.

Water-stable, strong, biodegradable lignocellulose straws replacement for plastic straws

The mechanical properties and uncontrollable deformation of paper straws in water limit their potential to replace plastic straws. In this study, a simple and effective approach was developed for processing biomass and making water-stable, strong, biodegradable lignose cellulose straws (LCSs). Chemical pretreatment in an aqueous solution of nitric acid and hydrogen peroxide was used to activate residual lignin and increase the levels of phenolic hydroxyl (0.79 mmol/g) and carboxyl groups (0.54 mmol/g) in the biomass to enhance adhesion between fibers. A mechanical treatment was used to refine and branch the fibers, so that the fibers resembled thick trunks with thin branches. LCSs were made by rolling wet paper made from the fibers that contained thick trunk fibers, thin branched fibers and activated residual lignin. The residual lignin and thin branched fibers filled the voids between adjacent thick trunk fibers to form a dense structure. In the subsequent heat treatment process, residual lignin softened and penetrated the gaps between adjacent fibers, and acted as a polyphenol binder to enhance the mechanical strength and water resistance of the LCSs. The LCSs exhibited outstanding tensile strength (127 MPa), flexural strength (62 MPa) and durable water stability for more than 150 d. The LCSs were safe and fully biodegradable, and they are a sustainable alternative to plastic straws.