Polymer matrix–clay interaction mediated mechanism of electrical transport in exfoliated and intercalated polymer nanocomposites

We report significant results on charge transport phenomena in the exfoliated and intercalated phase of polymer nanocomposite (PNC). X-ray diffraction and transmission electron microscopy results have provided convincing evidence of exfoliation at lower clay loading (x < 5 wt%) and intercalation at higher clay loading (x > 5 wt%) in the PNC. Fourier transform infrared (FTIR) spectrum indicated lowering of anion symmetry from O_h to C_4ν/C_2ν/C_3ν (depending on mode of cation interaction with counter ion). Substantial jump in electrical conductivity (~110 times) at room temperature has occurred on nanocomposite formation in sharp contrast to that of the polymer salt (PS) complex film. Large conductivity enhancement (10⁻³ S cm⁻¹) is attributed to clay-induced interaction with PS matrix whose origin lies in polymer–ion, ion–ion, ion–clay, and polymer–ion–clay interaction evidenced in the FTIR results. An excellent correlation of conductivity with fraction of free anion and polymer glass-transition temperature agrees well with conductivity enhancement at specific clay loading. A model for charge transport phenomena is proposed to explain clay-induced ion dynamics. The conceptual basis of the model seems consistent with experimental results.     

AC impedance and dielectric spectroscopic studies of Mg<Superscript>2 + </Superscript> ion conducting PVA–PEG blended polymer electrolytes

Polyvinyl alcohol (PVA)–polyethylene glycol (PEG) based solid polymer blend electrolytes with magnesium nitrate have been prepared by the solution cast technique. Impedance spectroscopic technique has been used, to characterize these polymer electrolytes. Complex impedance analysis was used to calculate bulk resistance of the polymer electrolytes. The a.c.-impedance data reveal that the ionic conductivity of PVA–PEG–Mg(NO₃)₂ system is changed with the concentration of magnesium nitrate, maximum conductivity of 9·63 × 10^− 5 S/cm at room temperature was observed for the system of PVA–PEG–Mg(NO₃)₂ (35–35–30). However, ionic conductivity of the above system increased with the increase of temperature, and the highest conductivity of 1·71 × 10^− 3 S/cm was observed at 100°C. The effect of ionic conductivity of polymer blend electrolytes was measured by varying the temperature ranging from 303 to 373 K. The variation of imaginary and real parts of dielectric constant with frequency was studied.     

The comparative influences of structural ordering, grain size, Li-content, and bulk density on the Li+-conductivity of Li0.29La0.57TiO3

The lattice and total Li⁺-ionic conductivity of Li_0.29La_0.57TiO₃ ceramic (LLTO) sintered at 1200 °C were determined as functions of powder calcination temperature and sintering duration, and these results were correlated with the relative degrees of Li⁺-ordering, Li-content, grain size, and bulk density to assess the relative impact of these parameters on material performance. Under all conditions, LLTO formed with a high degree of tetragonal superstructure to its perovskite related framework, and the lattice conductivity closely followed the relative amounts of the superstructure, as evaluated via determination of the sample ordering parameter from X-ray diffraction data. LLTO powders that were calcined at 900 °C for 1 h and sintered at 1200 °C for 6 h gave lattice conductivity values (~1.14 × 10⁻³ S cm⁻¹) comparable within the highest ranges reported in the literature. This coincided with the lowest degree of tetragonal superstructure formation, and it was also found to be largely independent of the values of Li-content measured on sintered ceramic despite significant Li₂O volatilization at longer sintering times (up to 23 % after 12 h at 1200 °C). Samples of LLTO powder that were calcined at 1100 °C and sintered at 1200 °C for 12 h resulted in the highest total Li-ion conductivity value ~6.30 × 10⁻⁵ S cm⁻¹. The total conductivity of LLTO varied inversely with grain size when the grains were <20 μm but was insensitive to that parameter above that size threshold. The strongest influence on total conductivity was primarily the bulk ceramic density. It was estimated from measured values that as the bulk ceramic density approached the full theoretical value for LLTO the total conductivity could near the lattice conductivity of ~1.2 × 10⁻³ S cm⁻¹.     

Investigations on the structural, optical and electrical properties of Nb-doped SnO2 thin films

Niobium-doped tin oxide thin films were deposited on glass substrates by the chemical spray pyrolysis method at a substrate temperature of 400 °C. Effects of Nb doping on the structural, electrical and optical properties have been investigated as a function of niobium concentration (0–2 at.%) in the spray solution. X-ray diffraction patterns showed that the films are polycrystalline in nature and the preferred growth direction of the undoped film shifts to (200) for Nb-doped films. Atomic force microscopy study shows that the surface morphology of these films vary when doping concentration varies. The negative sign of Hall coefficient confirmed the n-type conductivity. Resistivity of ~4.3 × 10⁻³ Ω cm, carrier concentration of ~5 × 10¹⁹ cm⁻³, mobility of ~25 cm² V⁻¹ s⁻¹ and an average optical transmittance of ~70% in the visible region (500–800 nm) were obtained for the film doped with 0.5 at.% niobium.     

Preparation and thermoelectric properties of BP films on SOI and sapphire substrates

The chemical vapor deposited (CVD) BP films on Si(100) (190 nm)/SiO _x (370 nm)/Si(100) (625 μm) (SOI) and sapphire (R-plane) (600 μm) substrates were prepared by the thermal decomposition of the B₂H₆–PH₃–H₂ system in the temperature range of 800–1050 °C for the deposition time of 1.5 h. The BP films were epitaxially grown on the SOI substrate, but a two-step growth method, i.e., a buffer layer at lower temperature and sequent CVD process at 1000 °C for 1.5 h was effective for obtaining a smooth film on the sapphire substrate. The electrical conduction types and electrical properties of these films depended on the growth temperature, gases flow rates and substrates. The thermal conductivity of the film could be replaced by the substrate, so that the calculated thermoelectric figure-of-merit (Z) for the BP films on the SOI substrate was 10⁻⁴–10⁻³/K at 700–1000 K. Those on the sapphire substrate were 10⁻⁶–10⁻⁵/K for the direct growth and 10⁻⁵–10⁻⁴/K for the two-step growth at 700–900 K, indicating that the film on a sapphire by two-step growth would reduce the defect concentrations and promote the electrical conductivity.     

Evaluation of a.c. conductivity behaviour of graphite filled polysulphide modified epoxy composites

Composites of epoxy resin having different amounts of graphite particles have been prepared by solution casting method. Temperature dependence of dielectric constant, tan δ and a.c. conductivity was measured in the frequency range, 1–20 kHz, temperature range, 40–180°C for 0.99, 1.96 and 2.91 wt% graphite filled and unfilled epoxy composites. It was observed that the dielectric constant, tanδ and a.c. conductivity increase with increasing temperature. Near the transition temperature the materials show anomalous behaviour for the observed properties. Peaks of dielectric constant, tan δ and a.c. conductivity were observed to shift towards lower temperature with increasing frequency. Clear relaxation (tan δ) peaks around 169°C were observed in epoxy resin, which shifted to lower temperature side on increasing the frequency. Addition of 2.91 wt% graphite shifted the tan δ peaks towards higher temperature side by creating hindrances to the rotation of polymer dipoles. Addition of 2–91 wt% graphite leads to an increased relaxation time τ of dipoles in polysulphide epoxy from 1.44 × 10⁻⁵− 3.92 × 10⁻⁵ (s) at 90°C by creating the hindrance to the rotation of dipoles.     

Intelligent poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide)-carboxymethyl cellulose full interpenetrating polymeric networks for protein adsorption studies

Poly(N-isopropyl acrylamide) (PNIPAm)–carboxymethyl cellulose (CMC) full interpenetrating polymeric networks (IPNs), based on PNIPAm and CMC, were prepared and investigated for adsorption of biomolecules utilizing a model protein, bovine serum albumin (BSA). N-isopropyl acrylamide monomers were polymerized in the presence of a natural polymer, e.g., carboxymethyl cellulose sodium salt. N,N′-methylenebisacrylamide (CL) was used to crosslink PNIPAm and CMC chains and IPN formed simultaneously. Spectroscopic and thermal characterization of the hydrogels were done with IR spectroscopy and thermogravimetric analysis. The swelling properties of PNIPAm and PNIPAm–CMC hydrogels were investigated as functions of the medium pH, temperature, ionic strength, and BSA. It was observed that the adsorption of protein molecules onto the hydrogels was mainly dependent on temperature and pH of the environment during the experiments. The maximum adsorption capacity (X) was observed at pH 4.7 which is the isoelectric point of BSA and at 40 °C for both hydrogels; and introducing CMC to PNIPAm increased the protein adsorption of the hydrogel. Adsorbed amounts of BSA were 26.70 mg g⁻¹ (4 °C) and 38.70 mg g⁻¹ (40 °C) for PNIPAm–CMC full IPN hydrogels. Adsorbed BSA (up to 80%) was eluted in the elution medium containing 0.1 mol dm⁻³ NaSCN at pH 8.0. Synthesized cylindrically shaped PNIPAm–CMC full IPN hydrogels can be used for adsorption studies related to the removal of proteins in pH- and temperature-sensitive biotechnological areas.     

Microstructure evolution and hardness variation during annealing of equal channel angular pressed ultra-fine grained nickel subjected to 12 passes

The microstructure, thermal stability and hardness of ultra-fine grained (UFG) Ni produced by 12 passes of equal channel angular pressing (ECAP) through the route Bc were studied. Comparing the microstructure and hardness of the as-ECAPed samples with the published data on UFG Ni obtained after 8 passes of ECAP through the route Bc reveals a smaller average grain size (230 nm in the present case compared with 270 nm in 8-pass Ni), significantly lower dislocation density (1.08 × 10¹⁴ m⁻² compared with 9 × 10¹⁴ m⁻² in 8-pass Ni) and lower hardness (2 GPa compared with 2.45 GPa for 8-pass Ni). Study of the thermal stability of the 12-pass UFG Ni revealed that recovery is dominant in the temperature range 150–250°C and recrystallisation occurred at temperatures >250 °C. The UFG microstructure is relatively stable up to about 400 °C. Due to the lower dislocation density and consequently a lower stored energy, the recrystallisation of 12-pass ECAP Ni occurred at a higher temperature (~250 °C) compared with the 8-pass Ni (~200 °C). In the 12-pass Nickel, hardness variation shows that its dependence on grain size is inversely linear rather than the common grain size^−0.5 dependence.     

Investigation of the quasi-ternary system LaMnO3–LaCoO3–“LaCuO3”. II: The series LaMn0.25?xCo0.75?xCu2xO3?δ and LaMn0.75?xCo0.25?xCu2xO3?δ

This paper investigates the crystal structure, thermal expansion, and electrical conductivity of two series of perovskites (LaMn_0.25−x Co_0.75−x Cu_2x O_3−δ and LaMn_0.75−x Co_0.25−x Cu_2x O_3−δ with x = 0, 0.025, 0.05, 0.1, 0.15, 0.2, and 0.25) in the quasi-ternary system LaMnO₃–LaCoO₃–“LaCuO₃”. The Mn/Co ratio was found to have a stronger influence on these properties than the Cu content. In comparison to the Co-rich series (LaMn_0.25−x Co_0.75−x Cu_2x O_3−δ), the Mn-rich series (LaMn_0.75−x Co_0.25−x Cu_2x O_3−δ) showed a much higher Cu solubility. All compositions in this series were single-phase materials after calcination at 1100 °C. The Co-rich series showed higher thermal expansion coefficients (α_max = 19.6 × 10⁻⁶ K⁻¹) and electrical conductivity (σ_max = 730 S/cm at 800 °C) than the Mn-rich series (α_max = 10.6 × 10⁻⁶ K⁻¹, σ_max = 94 S/cm at 800 °C). Irregularities in the thermal expansion curves indicated phase transitions at 150–350 °C for the Mn-rich series, while partial melting occurred at 980–1000 °C for the Co-rich series with x > 0.15. I. Arul Raj—on leave from Central Electrochemical Research Institute, Karaikudi, 630006 India.     

Miscibility and melting properties of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate) blends

The miscibility and melting properties of binary crystalline blends of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate) (PEN/PTT) have been investigated with differential scanning calorimetry (DSC). The glass transition and cold crystallization behaviors indicated that in PEN/PTT blends, there are two different amorphous phases and the PEN/PTT blends are immiscible in the amorphous state. The polymer–polymer interaction parameter, , calculated from equilibrium melting temperature depression of the PEN component was −1.791 × 10⁻⁵ (300 °C), revealing miscibility of PEN/PTT blends in the melt state.     

Interfacial interaction of solid cobalt with liquid Pb-free Sn–Bi–In–Zn–Sb soldering alloys

Dissolution kinetics of cobalt in liquid 87.5%Sn–7.5%Bi–3%In–1%Zn–1%Sb and 80%Sn–15%Bi–3%In–1%Zn–1%Sb soldering alloys and phase formation at the cobalt–solder interface have been investigated in the temperature range of 250–450 °C. The temperature dependence of the cobalt solubility in soldering alloys was found to obey a relation of the Arrhenius type c _s = 4.06 × 10² exp (−46300/RT) mass% for the former alloy and c _s = 5.46 × 10² exp (−49200/RT) mass% for the latter, where R is in J mol⁻¹ K⁻¹ and T in K. For tin, the appropriate equation is c _s = 4.08 × 10² exp (−45200/RT) mass%. The dissolution rate constants are rather close for these soldering alloys and vary in the range (1–9) × 10⁻⁵ m s⁻¹ at disc rotational speeds of 6.45–82.4 rad s⁻¹. For both alloys, the CoSn₃ intermetallic layer is formed at the interface of cobalt and the saturated or undersaturated solder melt at 250 °C and dipping times up to 1800 s, whereas the CoSn₂ intermetallic layer occurs at higher temperatures of 300–450 °C. Formation of an additional intermetallic layer (around 1.5 μm thick) of the CoSn compound was only observed at 450 °C and a dipping time of 1800 s. A simple mathematical equation is proposed to evaluate the intermetallic-layer thickness in the case of undersaturated melts. The tensile strength of the cobalt-to-solder joints is 95–107 MPa, with the relative elongation being 2.0–2.6%.     

Physical Properties of Pyridinium Fluorohydrogenate, [pyridine · H+][H2F3]−

Ionic liquids (ILs), also referred to as molten salts, have found application as electrolytes for batteries and super-capacitors, in electroplating baths, as designer solvents, and as reaction media. A few of the desired properties of a super-capacitor electrolyte are nonflammability, thermal stability, and electrochemical stability. ILs containing aromatic cations have been shown to have low viscosity which results in a high electrochemical conductivity. There is a delicate balance between increasing the thermal stability, or decreasing the melting point, and increasing the electrochemical conductivity of the IL. This study focuses on pyridinium fluorohydrogenate, [pyridine · H⁺][H₂F₃]⁻. Pyridinium fluorohydrogenate has been synthesized by the reaction of pyridine and anhydrous hydrofluoric acid. This IL has a relatively high electrical conductivity (~98 mS · cm⁻¹ at 23 °C), a wide electrochemical window, and a boiling point of 186 °C. A stable gel can also be formed by combining [pyridine · H⁺][H₂F₃]⁻ and a super absorbent polymer such as polyacrylic acid. The gel adds mechanical stability to the matrix while not greatly affecting the conductivity of the IL.     

Sol–gel derived Co<Subscript>3</Subscript>O<Subscript>4</Subscript> thin films: effect of annealing on structural,morphological and optoelectronic properties

Nanocrystalline Co₃O₄ thin films were prepared on glass substrates by using sol–gel spin coating technique. The effect of annealing temperature (400–700 °C) on structural, morphological, electrical and optical properties of Co₃O₄ thin films were studied by X-ray diffraction (XRD), Scanning Electron Microscopy, Electrical conductivity and UV–visible Spectroscopy. XRD measurements show that all the films are nanocrystallized in the cubic spinel structure and present a random orientation. The crystallite size increases with increasing annealing temperature (53–69 nm). These modifications influence the optical properties. The morphology of the sol–gel derived Co₃O₄ shows nanocrystalline grains with some overgrown clusters and it varies with annealing temperature. The optical band gap has been determined from the absorption coefficient. We found that the optical band gap energy decreases from 2.58 to 2.07 eV with increasing annealing temperature between 400 and 700 °C. These mean that the optical quality of Co₃O₄ films is improved by annealing. The dc electrical conductivity of Co₃O₄ thin films were increased from 10⁻⁴ to 10⁻² (Ω cm)⁻¹ with increase in annealing temperature. The electron carrier concentration (n) and mobility (μ) of Co₃O₄ films annealed at 400–700 °C were estimated to be of the order of 2.4–4.5 × 10¹⁹ cm⁻³ and 5.2–7.0 × 10⁻⁵ cm² V⁻¹ s⁻¹ respectively. It is observed that Co₃O₄ thin film annealing at 700 °C after deposition provide a smooth and flat texture suited for optoelectronic applications.     

Low-temperature microwave sintering of TiN–SiC nanocomposites

Densification kinetics study during microwave sintering of titanium nitride-based nanocomposite has been conducted. A series of TiN–SiC compositions with 1, 3, 5 wt% of silicon carbide were microwave sintered at relatively low sintering temperatures (900–1,300 °C) for 0–30 min. The SiC content influenced on heating uniformity and final density and grain-size achieved. Densification process during microwave sintering obeyed the mechanism of grain-boundary diffusion with activation energy of 235 kJ mol⁻¹. Microwave sintering resulted in fine microstructure (~300 nm) and hence high values of micro hardness (~20 GPa).     

Novel bromide anion conducting refractory solid electrolytes based on lanthanum oxybromide

A new type of high bromide anion conducting solid was artificially designed with the solids based on lanthanide oxybromide (LnOBr). LnOBr is selected as it is insoluble in water and also highly stable at temperatures around 800°C. The enhancement of Br⁻ anion conductivity was successfully realized by creating Br⁻ ion vacancies by doping divalent cation in the Ln site of the LnOBr host lattice. The Br⁻ anion conductivity was the highest among the conventional bromide anion conducting solids such as Pb_0.99K_0.01Br_1.99 (373°C) and CsPbBr₃ (500°C) which contain toxic lead in them. The Br⁻ anion conductivity of LnOBr based solid enters into the practically useful region (σ > 10⁻³ Sċcm⁻¹).     

High thermal conductivity composites consisting of diamond filler with tungsten coating and copper (silver) matrix

Tungsten coatings with thickness of 5–500 nm are applied onto plane-faced synthetic diamonds with particle sizes of about 430 and 180 μm. The composition and structure of the coatings are investigated using scanning electron microscopy, X-ray spectral analysis, X-ray diffraction, and atomic force microscopy. The composition of the coatings varies within the range W–W₂C–WC. The average roughness, R _a, of the coatings’ surfaces (20–100 nm) increases with the weight–average thickness of the coating. Composites with a thermal conductivity (TC) as high as 900 W m⁻¹ K⁻¹ are obtained by spontaneous infiltration, without the aid of pressure, using the coated diamond grains as a filler, and copper or silver as a binder. The optimal coating thickness for producing a composite with maximal TC is 100–250 nm. For this thickness the heat conductance of coatings as a filler/matrix interface is calculated as G = (2–10) × 10⁷ W m⁻² K⁻¹. The effects of coating composition, thickness and roughness, as well as of impurities, on wettability during the metal impregnation process and on the TC of the composites are considered.     

Study of the structural and dielectric properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> and PbO addition on BiNbO<Subscript>4</Subscript> ceramic matrix for RF applications

In this paper, the structural and dielectric properties of BNO (BiNbO₄) was investigated as a function of the external RF frequency and temperature. The BNO Ceramics, prepared by the conventional mixed oxide method and doped with 3, 5 and 10 wt. % Bi₂O₃–PbO were sintered at 1,025 °C for 3 h. The X-ray diffraction patterns of the samples sintered, shown the presence of the triclinic phase (β-BNO). In the measurements obtained at room temperature (25 °C) was observed that the largest values of dielectric permittivity (ε′ _r ) at frequency 100 kHz, were for the samples: BNO5Bi (5 wt. % Bi₂O₃) and BNO5Pb (5 wt. % PbO) with values ε′ _r ~ 59.54 and ε′ _r ~ 78.44, respectively. The smaller values of loss tangent (tan δ) were for the samples: BNO5Bi and BNO3Pb (3 wt. % PbO) with values tan δ ~ 5.71 × 10⁻⁴ and tan δ ~ 2.19 × 10⁻⁴, respectively at frequency 33.69 MHz. The analysis as a function of temperature of the dielectric properties of the samples, obtained at frequency 100 kHz, showed that the larger value of the relative dielectric permittivity was about ε′ _r ~ 76.4 at temperature 200 °C for BNO5Pb sample, and the value smaller observed of dielectric loss was for BNO3Bi sample at temperature 80 °C, with about tan δ ~ 5.4 × 10⁻³. The Temperature Coefficient of Capacitance (TCC) values at 1 MHz frequency, present a change of the signal from BNO (−55.06 ppm/°C) to the sample doped of Bi: BNO3Bi (+86.74 ppm/°C) and to the sample doped of Pb: BNO3Pb (+208.87 ppm/°C). One can conclude that starting from the BNO one can increase the doping level of Bi or Pb and find a concentration where one have TCC = 0 ppm/°C, which is important for temperature stable materials applications like high frequency capacitors. The activation energy (H) obtained in the process is approximately 0.55 eV for BNO sample and increase with the doping level. These samples will be studied seeking the development ceramic capacitors for applications in radio frequency devices.     

Preparation, proton conduction, and application in ammonia synthesis at atmospheric pressure of La0.9Ba0.1Ga1– x Mg x O3–α

La_0.9Ba_0.1Ga_1–x Mg _x O_3–α (0 ≤ x ≤ 0.25) was prepared by the microemulsion method. A single phase of LaGaO₃ perovskite structure was formed when x was ≥0.15. Electrochemical hydrogen permeation (hydrogen pumping) proved that La_0.9Ba_0.1Ga_1–x Mg _x O_3–α had proton conduction, and the proton conduction was measured by AC impedance spectroscopy method from 400 to 800 °C in hydrogen atmospheres. Among these samples, La_0.9Ba_0.1Ga_0.8Mg_0.2O_3–α has the highest proton conductivity with the values of 9.51 × 10⁻⁴ to 4.68 × 10⁻² S cm⁻¹ at 400–800 °C. Ammonia was synthesized from nitrogen and hydrogen at atmospheric pressure in an electrolytic cell using La_0.9Ba_0.1Ga_0.8Mg_0.2O_3–α as electrolyte. The rate of NH₃ formation was 1.89 × 10⁻⁹ mol s⁻¹ cm⁻² at 520 °C upon imposing a current of 1 mA through the cell.     

Electrical and thermal conductivities of porous SiC/SiO2/C composites with different morphology from carbonized wood

Porous SiC/SiO₂/C composites exhibiting a wide range of high thermal and electrical conductivities were developed from carbonized wood infiltrated with SiO₂. As a pre-treatment, the samples were either heated at 100 °C or kept at room temperature followed by sintering in the temperature range 1200–1800 °C. The microstructure, the morphology, and the electrical and thermal conductivities of the composites were investigated. Pre-treatment at room temperature followed by sintering up to 1800 °C produced composites exhibiting a greater size of carbon crystallites, a higher ordering of the microstructure of carbon and β-SiC and a smaller amount of SiO₂, resulting in electrical and thermal conductivities of 1.17 × 10⁴ Ω⁻¹ m⁻¹ and 25 W/mK, respectively. The thermal conductivity could be further improved to 101 W/mK by increasing the density of the composite to 1.82 g/cm³. In contrast, the pre-treatment at 100 °C produced composites possessing a lower thermal conductivity of 2 W/mK.     

Distillation Separation of Hydrofluoric Acid and Nitric Acid from Acid Waste Using the Salt Effect on Vapor–Liquid Equilibrium

This study presents the distillation separation of hydrofluoric acid with use of the salt effect on the vapor–liquid equilibrium for acid aqueous solutions and acid mixtures. The vapor–liquid equilibrium of hydrofluoric acid + salt systems (fluorite, potassium nitrate, cesium nitrate) was measured using an apparatus made of perfluoro alkylvinylether. Cesium nitrate showed a salting-out effect on the vapor–liquid equilibrium of the hydrofluoric acid–water system. Fluorite and potassium nitrate showed a salting-in effect on the hydrofluoric acid–water system. Separation of hydrofluoric acid from an acid mixture containing nitric acid and hydrofluoric acid was tested by the simple distillation treatment using the salt effect of cesium nitrate (45 mass%). An acid mixture of nitric acid (5.0 mol · dm⁻³) and hydrofluoric acid (5.0 mol · dm⁻³) was prepared as a sample solution for distillation tests. The concentration of nitric acid in the first distillate decreased from 5.0 mol · dm⁻³ to 1.13 mol · dm⁻³, and the concentration of hydrofluoric acid increased to 5.41 mol · dm⁻³. This first distillate was further distilled without the addition of salt. The concentrations of hydrofluoric acid and nitric acid in the second distillate were 7.21 mol · dm⁻³ and 0.46 mol · dm⁻³, respectively. It was thus found that the salt effect on vapor–liquid equilibrium of acid mixtures was effective for the recycling of acids from acid mixture wastes.