Hydrophobic and Physical Properties of the Two Step Processed Ambient Pressure Dried Silica Aerogels with Various Exchanging Solvents

The experimental results by using various exchanging solvents in the preparation of two step (acid and base) processed ambient pressure dried hydrophobic silica aerogels, are reported. Silica alcogels were prepared by hydrolysis with oxalic acid and condensation with NH₄OH of ethanol diluted tetraethylorthosilicate (TEOS) precursor and hexamethyldisilazane(HMDZ) methylating agent. The exchanging solvents used were: hexane, cyclohexane, heptane, benzene, toluene and xylene. The physical properties such as % of volume shrinkage, density, pore volume, % of porosity, thermal conductivity, % of optical transmission, surface area, pore size distribution and contact angle (θ) of the silica aerogels with water, were measured as a function of EtOH/TEOS molar ratios (R) for all the exchanging solvents. It was found that the physical and hydrophobic properties of the silica aerogels strongly depend on the nature of the solvent and R. Heptane solvent resulted in highly transparent (≈90% optical transmission at 700 nm for 1 cm thick sample), low density (≈0.060 g/cm³), low thermal conductive (≈0.070 W/m·K), high % of porosity (97%), high surface area (750 m²/g), uniform porosity and hydrophobic (θ ≈ 160°) aerogels compared to other solvents. On the otherhand, xylene resulted in aerogels with higher hydrophobicity (θ ≈ 172°) among other solvents.     

Synthesis and physical properties of TEOS-based silica aerogels prepared by two step (acid–base) sol–gel process

The experimental results on the synthesis and physical properties of tetraethoxysilane- (TEOS) based silica aerogels produced by two step (acid–base) sol–gel process, are reported. The oxalic acid (A) and NH₄OH (B) concentrations were varied from 0 to 0.1 M and from 0.4 to 3 M, respectively. Monolithic and transparent aerogels have been obtained for the values of A=0.001 M and B=1 M. The effect of time interval (t) before the base catalyst (NH₄OH) addition to the acidic sol was studied from 0 to 72 h. The time interval at t=24 h of NH₄OH addition was found to be the best, in terms of low volume shrinkage, high optical transmission and monolithicity. The molar ratio of EtOH/TEOS (S) was varied from 3 to 7.5. Monolithic and transparent aerogels were obtained for an S value of 6.9. Also, the effects of molar ratio of acidic water, i.e., H₂O/TEOS (W₁) and basic water, i.e., H₂O/TEOS (W₂) on the physical properties of the aerogels have been studied. Highly transparent (∼90%) and monolithic aerogels with lower volume shrinkage (<10%) were obtained for the molar ratio 1:6.9:3.5:2.2 of TEOS:EtOH:acidic (H₂O):basic (H₂O). The results are discussed by taking into consideration the hydrolysis and polycondensation reactions. The aerogels were characterized by scanning electron microscopy (SEM), optical transmission, bulk density, volume shrinkage and porosity measurements.     

Low-Temperature Sol-Gel Synthesis of Single-Phase ZrTiO4 Nanoparticles

Ceramic ZrTiO₄ powders were prepared by a sol-gel method using zirconium oxychloride and titanium tetraisopropoxide. In situ high temperature X-ray diffraction results show that crystallization of the amorphous gel starts at 400 ^∘C. Single-phase ZrTiO₄ nanoparticles were obtained after heat treatment at 450 ^∘C for one hour. An average particle size of 46 nm has been determined by nitrogen adsorption analysis. After pressing these sinteractive powders, pellets with controlled pore size distribution were obtained by sintering at temperatures as low as 400 ^∘C. The analysis of pores by mercury porosimetry gives an average porosity of 45%. The electrical resistivity, determined by impedance spectroscopy measurements at 24 ^∘C under different humidity environments, shows the ability of these pellets to adsorb water vapor in the porous surfaces. Pellets fabricated with the nanosized powders prepared by the sol-gel technique are proposed as good candidates to be used in humidity sensing devices.     

Influence of molar ratios of precursor,catalyst, solvent and water on monolithicity and physical properties of TMOS silica aerogels

In continuation to our earlier work on aerogels, the experimental results on the monolithicity and physical properties of silica aerogels as a function of the molar ratios of tetramethoxysilane (TMOS) precursor, catalyst (NH₄OH), methanol (MeOH) solvent and water, are reported. The molar ratios of NH₄OH/TMOS, MeOH/TMOS and H₂O/TMOS were varied from 7.1 × 10^–6 to 9.6 × 10^–1, 1 to 90 and 1 to 18 respectively. It has been found that larger molar ratios of NH₄OH/TMOS (10^–2), MeOH/TMOS (13 to 60) and H₂O/TMOS (>10) resulted in transparent but cracked aerogels, and very low molar ratios of these combinations gave monolithic but less transparent or opaque aerogels. The best quality silica aerogels, in terms of monolithicity, transparency and low density, have been obtained with TMOS:MeOH:H₂O:NH₄OH in the molar ratio of 1:12:4:3.7 × 10^–3 respectively. The aerogels have been characterized by density, optical transmission, surface area and porosity measurements. The results have been discussed by taking into account the hydrolysis and condensation reactions, and syneresis effects.     

Low thermalconductive,transparent and hydrophobic ambient pressure dried silica aerogels with various preparation conditions using sodium silicate solutions

The experimental results on the preparation of low thermal conductivity and transparent ambient pressure dried silica aerogels with the sodium silicate solution, TMCS silylating agent with methanol, isopropyl alcohol, hexane and xylene solvents, are reported. This study is focussed on the effect of preparation conditions such as varying the number of preparation steps, pH of the hydrosol and hydrogel ageing temperature, for the production of the low thermal conductive silica aerogels and the results are analysed. Density, thermal conductivity, % of optical transmission and contact angle of the aerogels were measured. The Fourier Transform Infrared Spectroscopy (FTIR) studies revealed the presence of Si–C and C–H along with the Si–O–Si and OH bonds and their intensities strongly depend on the processing steps, pH of the hydrosol and gel ageing temperature. The UV–Visible spectra indicated the % of optical transmission of the aerogels decreased with increasing the number of processing steps, increase in the pH of the hydrosol from 3 to 8 and decreased for ageing temperature up to 50 °C. Further increase in temperature >50 °C, the % of optical transmission of the aerogels increased. The TGA-DTA data showed the thermal stability of the aerogels with respect to hydrophobicity is 325 °C. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) analyses revealed the nanostructure of the aerogels. The porosity of the aerogels was studied using the pore size distribution. Silica aerogels with low density (0.051 g/cc), low thermal conductivity (0.049 W/m K), optical transmission (65%), high hydrophobicity (159°) and resistance to humid atmosphere >1 year was obtained in the present studies.     

Optically transparent silica aerogels based on sodium silicate by a two step sol–gel process and ambient pressure drying

Interest in improving the optical transmission of sodium silicate-based aerogels by ambient pressure drying led to the synthesis of aerogels using a two-step sol–gel process. To produce optically transparent silica aerogel granules, NH₄F (1 M) and HCl (4 M) were used as hydrolyzing and condensation catalysts, respectively. The silica aerogels were characterized by their bulk density, porosity (%), contact angle and thermal conductivity. Optical transmission of as synthesized aerogels was studied by comparing the photos of aerogel granules. Scanning electron microscopic study showed the presence of fractal structures in these aerogels. The degree of transparency in two step sol–gel process-based aerogels is higher than the conventional single step aerogels. The N₂ adsorption–desorption analysis depicts that the two step sol–gel based aerogels have large surface areas. Optically transparent silica aerogels with a low density of ∼0.125 g/cc, low thermal conductivity of ∼0.128 W/mK and higher Brunauer, Emmett, and Teller surface area of ∼425 m²/g were obtained by using NH₄F (1 M), HCl (4 M), and a molar ratio of Na₂SiO₃::H₂O::trimethylchlorosilane of 1::146.67::9.46. The aerogels retained their hydrophobicity up to 500 °C.     

Study of Optical Properties of <Emphasis Type="Italic">Macrophomina phaseolina</Emphasis> Impregnated Sol-gel Derived Silica Matrices

In the present frame of work, Macrophomina phaseolina is encapsulated in silica matrices at various concentrations by low temperature sol-gel technique using tetraethylorthosilicate (TEOS) as precursor. The optical and photophysical properties of these samples have been studied by second harmonics of Nd:YAG laser at 532 nm. UV-visible absorption spectra of samples have been recorded and it is found that the absorption increases with increase in concentration of fungus. Further, a decrease in output transmission intensity of the laser has been observed with increase in fungus concentration. The temporal response of these samples has also been examined. The results show that the fungus concentration can be measured within ∼15–20 min. This method of optical sensing of fungus in test sample is faster than other techniques, such as the conventional colorimetric method which takes about 1 h.     

Nb-Doped PZT Material by Sol-Gel Combustion

Nanocrystalline niobium doped lead zirconate titanate powders (PZTN) were prepared by a citrate-nitrate sol-gel combustion technique. The technique involves three steps: preparation of stable and homogeneous sol, formation of gel, combustion of gel. The sol was prepared by mixing stable solutions of Zr-oxynitrate, Pb-citrate, Nb- and Ti-peroxo-citrate precursors. The heat induced auto ignition leads to the decomposition of precursors and formation of pure perovskite phase after soaking at 400^∘C for 4 h. The particles were found to be irregular aggregates of nanosized primary particles (crystallite size about 30 nm). Different milling treatments were performed in order to improve the sinterability. Ball milled (100 h with PEG) powders were sintered at 1100^∘C for 2 h in air showing 97% relative density at a densification T 100^∘C lower than following the conventional mixed oxide route. The stoichiometry of the system was determined at each stage of the process and no fluctuation was detected.     

Organic Surface Modification of TEOS Based Silica Aerogels Synthesized by Co-Precursor and Derivatization Methods

The experimental results on the organic modification of tetraethoxysilane (TEOS) based silica aerogels synthesized by co-precursor and derivatization methods are reported and discussed. In order to obtain silica aerogels with better physicochemical properties in terms of higher hydrophobicity, optical transmission and thermal stability, eight organosilane compounds (hydrophobic reagents) of the type R _n SiX_4–n have been used. The molar ratio of tetraethoxysilane (TEOS), ethanol (EtOH), water (0.001 M oxalic acid catalyst) was kept constant at 1:5:7 respectively. The organically modified silica aerogels were produced by two different methods: (i) Co-precursor method and (ii) Derivatization method. In the former method, the molar ratio of hydrophobic reagent (HR) to TEOS was varied from 0.1 to 0.6. In the later method, derivatization of the wet gels was carried out using 20% hydrophobic reagent in methanol. The merits and demerits of both these methods have been presented. The organic surface modification of the aerogels was confirmed by the Fourier Transform Infrared (FTIR) spectroscopic studies and the contact angle measurements. In the co-precursor method, with the increase in hydrophobic reagent/TEOS molar ratio, the hydrophobicity increases ( = 136°) and the optical transmission decreases (5%), whereas in the derivatization method the optical transmission is very high (T 85%) but the hydrophobicity is low ( = 120°). The thermal stability of the hydrophobic aerogels (the temperature up to which the hydrophobicity is retained) was studied in the temperature range of 25–800°C. The aerogels based on the co-precursor method retained the hydrophobicity up to a temperature as high as 520°C and on the other hand, the derivatized aerogels are hydrophobic only up to a temperature of 285°C. For the first time, TEOS based hydrophobic silica aerogels have been obtained with negligible volume shrinkage using the trimethylethoxysilane (TMES) co-precursor. The aerogels were characterized by Fourier transform infrared spectroscopy (FTIR), optical transmittance, Scanning Electron Microscope (SEM), thermogravimetric (TG) and differential thermal (DT) analyses and the contact angle measurements.     

Physico-chemical properties of ambiently dried sodium silicate based aerogels catalyzed with various acids

Experimental results on the physico-chemical properties of ambiently dried sodium silicate based aerogels catalyzed with various acids are reported. The aerogels were prepared by hydrolysis and polycondensation of sodium silicate followed by subsequent washings, surface chemical modification and ambient pressure drying using 10 various acid catalysts consisting of strong and weak acids. The strength and concentration of acids have the major effect on the gelation of sol and hence the physico-chemical properties of the silica aerogels. Strong acids such as HCl, HNO₃ and H₂SO₄ resulted in shrunk (70–95%) aerogels whereas weak acids such as citric and tartaric acids resulted in less shrunk (34–50%) aerogels. The physical properties of silica aerogels were studied by measuring bulk density, volume shrinkage (%), porosity (%), pore volume, thermal conductivity, contact angle with water, Transmission Electron Microscopy (TEM), Atomic Absorption Spectroscopy (AAS), Fourier Transform Infrared Spectroscopy (FTIR), Thermo Gravimetric-Differential Thermal (TG-DT) analyses and N₂ adsorption–desorption BET surface analyzer. The best quality silica aerogels in terms of low density (0.086 g/cm³), low volume shrinkage (34%), high porosity (95%), low thermal conductivity (0.09 W/m K) and hydrophobic (148°) were obtained for molar ratio of Na₂SiO₃:H₂O:citric acid:TMCS at 1:146.67:0.72:9.46 with 20 min gelation time. The resulting aerogels exhibited the thermal stability up to around 420 °C.     

Effective preparation of crack-free silica aerogels via ambient drying

Effective ambient-drying techniques for synthesizing crack-free silica aerogel bulks from the industrial waterglass have been developed. Silica wet gels were obtained from aqueous colloidal silica sols prepared by ion-exchange of waterglass solution (4–10 wt% SiO₂). Crack-free monolithic silica aerogel disks (diameter of 22 mm and thickness of 7 mm) were produced via solvent exchange/surface modification of the wet gels using isopropanol/trimethylchlorosilane/n-Hexane solution, followed by ambient drying. The effects of the silica content in sol and the molar ratio of trimethylchlorosilane/pore water on the morphology and property of final aerogel products were also investigated. The porosity, density, and specific surface area of silica aerogels were in the range of 92–94%, 0.13–0.16 g/cm³, and ∼675 m²/g, respectively. The degree of springback during the ambient drying processing of modified silica gels was 94%.     

Effect of iron acetylacetonate on physico-chemical properties of waterglass based aerogels by ambient pressure drying

The effect of iron acetylacetonate on the physico-chemical properties of waterglass based silica aerogels by ambient pressure drying has been investigated. Doping the gels with iron acetylacetonat (FeAA) facilitates in the diminution of the density of the aerogels. The well established silica network provides effective confinement of FeAA nanoparticles which resists the collapse of silica network during ambient pressure drying. Therefore, in the present paper, the effects of FeAA on the physico-chemical properties of the aerogels have been studied by varying the FeAA:Na₂SiO₃ molar ratio from 3 × 10⁻⁴ to 6 × 10⁻⁴. The aerogels were prepared via ambient pressure drying and characterized by the bulk density, thermal conductivity and water contact angle. The aerogel’s surface morphology, elemental analysis and pore structure were characterized by means of EDAX and FTIR, TEM and N₂ adsorption- desorption analyzer. The high temperature hydrophobicity of these aerogels was checked by heating them in temperature controlled furnace. Silica aerogels with low density ~0.050 g/cc have been obtained using the molar ratio of Na₂SiO₃:H₂O:FeAA:Citric acid:TMCS at 1:146.67:3 × 10⁻⁴:0.54:9.46, respectively. EDAX and FTIR studies show that the iron species are entrapped in the mesoporous framework and not took part in the bonding with silica.     

Study of thermal conductivity and effect of humidity on HMDZ modified TEOS based aerogel dried at ambient pressure

The experimental results on the study of thermal conductivity and effect of humidity on HMDZ modified TEOS based aerogels dried at ambient pressure, are reported. Silica sol was prepared by keeping the MeOH/TEOS molar ratio, Acidic water (Oxalic acid) and basic water (NH₄OH) concentrations constant at 16.5, 0.001 and 1 M, respectively throughout the experiments and the HMDZ/TEOS molar ratio (h) was varied from 0.34 to 2.1. Finally, the surface modified wet gels were dried at an ambient pressure. The thermal conductivity of the aerogel samples was measured. Further, the humidity study was carried out in 80% humid surrounding at 30 °C temperature over 80 days. The best quality aerogels in terms of low bulk density, thermal conductivity and durability (no moisture absorption) with an only 2% of weight gain were obtained for TEOS: MeOH: Acidic H₂O: Basic H₂O: HMDZ molar ratio at 1:16.5:0.81:0.50:0.681, respectively. The thermal stability and hydrophobicity of the aerogel have been confirmed with Thermo gravimetric and Differential Thermal (TG–DT) analyses and Fourier Transform Infrared Spectroscopy (FTIR), respectively. Microstructural studies were carried out by Scanning Electron microscopy (SEM).     

Effect of post-treatment (gel aging) on the properties of methyltrimethoxysilane based silica aerogels prepared by two-step sol–gel process

The properties of silica aerogels are highly dependent on the post-treatment steps like gel washing, gel aging and gel drying. The experimental results of the studies on one of the post-treatment steps i.e. gel aging effect on the physical and microstructural properties of methyltrimethoxysilane (MTMS) based silica aerogels, are reported. These hybrid aerogels were prepared by two step sol–gel process followed by supercritical drying. The molar ratio of MeOH/MTMS (M) was varied from 7 to 35 by keeping the H₂O/MTMS (W) molar ratio constant at 4. The as prepared alcogels of different molar ratios were aged from 0 to 5 days. It was observed that 2 days of gel aging period is the optimum gel aging period for good quality aerogels in terms of low density, less volume shrinkage and high porosity. The well tailored network matrix with low density (0.04 g/cm³), less volume shrinkage (4.5%), low thermal conductivity (0.05 W/mK) and high porosity (98.84 %) was obtained for 2 days of gel aging period of M = 35. Further, the gelation time varied from 8 to 1 h depending on the M values. The gelation time was being more for lesser M values. The aerogels were characterized by bulk density, porosity, volume shrinkage, thermal conductivity, Scanning Electron Microscopy and the Fourier Transform Infrared spectroscopy.     

Influence of thermal process on microstructural and physical properties of ambient pressure dried hydrophobic silica aerogel monoliths

The experimental results of thermal process on the microstructural and physical properties of ambient pressure dried hydrophobic silica aerogel monoliths are reported and discussed. With sodium silicate as precursor, ethanol/hexamethyldisiloxane/hydrochloric acid as surface modification agent, the crack-free and high hydrophobic silica aerogel monoliths was obtained possessing the properties as low density (0.096 g/cm³), high surface area (651 m²/g), high hydrophobicity (~147°) and low thermal conductivity (0.0217 Wm/K). Silica aerogels maintained hydrophobic behavior up to 430 °C. After a thermal process changing from room temperature to 300 °C, the hydrophobicity remained unchanged (~128°), of which the porosity was 95.69% and specific density about 0.094 g/cm³. After high temperature treatment (300–500 °C), the density of final product decreased from 0.094 to 0.089 g/cm³ and porosity increased to 96.33%. With surface area of 466 m²/g, porosity of 91.21% and density about 0.113 g/cm³, silica aerogels were at a good state at 800 °C. Thermal conductivities at desired temperatures were analyzed by the transient plane heat source method. Thermal conductivity coefficients of silica aerogel monoliths changed from 0.0217 to 0.0981 Wm/K as temperature increased to 800 °C, revealed an excellent heat insulation effect during thermal process.     

Hydrophobic silica aerogels prepared via rapid supercritical extraction

Hydrophobic silica aerogels have been prepared using the rapid supercritical extraction (RSCE) technique. The RSCE technique is a one-step methanol supercritical extraction method for producing aerogel monoliths in 3 to 8 h. Standard aerogels were prepared from a tetramethoxysilane (TMOS) recipe with a molar ratio of TMOS:MeOH:H₂O:NH₄OH of 1.0:12.0:4.0:7.4 × 10⁻³. Hydrophobic aerogels were prepared using the same recipe except the TMOS was replaced with a mixture of TMOS and one of the following organosilane co-precursors: methytrimethoxysilane (MTMS), ethyltrimethoxysilane (ETMS), or propyltrimeth-oxysilane (PTMS). Results show that, by increasing the amount of catalyst and increasing gelation time, monolithic aerogels can be prepared out of volume mixtures including up to 75% MTMS, 50% ETMS or 50% PTMS in 7.5–15 h. As the amount of co-precursor is increased the aerogels become more hydrophobic (sessile tests with water droplets yield contact angles up to 155°) and less transparent (transmission through a 12.2-mm thick sample decreases from 83 to 50% at 800 nm). The skeletal and bulk density decrease and the surface area increases (550–760 m²/g) when TMOS is substituted with increasing amounts of MTMS. The amount of co-precursor does not affect the thermal conductivity. SEM imaging shows significant differences in the nanostructure for the most hydrophobic surfaces.     

Synthesis of MWCNTs doped sodium silicate based aerogels by ambient pressure drying

The successful incorporation of multiwalled carbon nanotubes (MWCNTs) into silica aerogels prepared by sol–gel method is reported herein. Pure silica aerogels prepared using sodium silicate precursor by ambient pressure drying are so fragile that they cannot be used easily. MWCNTs were used as reinforcements to improve the mechanical properties of silica aerogels. Results show that inserting small amounts of MWCNTs in the gels causes enhanced dimensional stability of silica aerogels. The silica aerogels were prepared by doping MWCNTs in silica matrix before gelation. The influence of MWCNTs on some microstructural aspects of silica matrix has been studied using nitrogen adsorption–desorption isotherms. From SEM study it is confirmed that the silica particles get capped on the surface of MWCNTs suggesting an enhanced toughness. Further, FTIR, Raman, EDAX, thermal conductivity and hydrophobicity studies of these doped aerogels were carried out. By addition of MWCNTs, silica aerogels were formed with 706 m²/g BET and 1,200 m²/g Langmuir surface areas and 149^o contact angle. Low density (0.052 g/cc) and low thermal conductivity (0.067 W/m K) MWCNTs doped silica aerogels were obtained for the molar ratio of Na₂SiO₃::H₂O::MWCNTs::citric acid::TMCS at 1::146.67::2.5 × 10⁻³::0.54::9.46 respectively with improved mechanical strength.     

Preparation and characterization of SiO2 two-step aerogels

Aerogels are well suited as transparent insulation materials in solar architecture and collector systems. Their nanoporous structure provides a high solar transmittance and a low thermal conductivity, generally below 0.02 W m^–1 K^–1. Transparent aerogels with densities above 80 kgm^–3 can easily be prepared at room temperature via a one-step sol-gel process with subsequent supercritical drying. Separating hydrolysis and condensation via a two-step method allows the preparation of transparent ultra-low density SiO₂-aerogels. To optimize the optical properties, characterized by the scattering coefficient of the gels, we have investigated the influence of preparation parameters, such as pH-value of the sol-gel starting solution and macroscopic density, on the gel structure. To determine the nanostructure we performed spectral light scattering as well as small angle X-ray scattering (SAXS) measurements.     

Fabrication of Ordered TiO2 Porous Thin Films by Sol-Dipping PS Template Method

Monolayer polystyrene spheres (∼400 nm) array templates were assembled orderly on clean glass substrates by dip-drawing method from emulsion of PS and porous TiO₂ thin films were prepared by using sol-dipping template method to fill TiO₂ sol into the interstices among the close-packed PS templates and then annealing to remove the PS templates. The effects of TiO₂ precursor sol concentration and dipping time in sol on the porous structure of the thin films were studied. The results showed pore size of the ordered TiO₂ porous thin film depended mainly on PS size and partly on TiO₂ sol concentration. The shrinkage of pore diameter was about 10% for 0.2 M and 20% for 0.4 M TiO₂ sol concentrations. X-ray diffraction (XRD) spectra indicated the porous thin film was anatase structure. The transmittance spectrum showed that optical transmittance of the porous thin film kept above 70% beyond the wavelength of 430 nm. Optical band-gap of the porous TiO₂ thin film (fired at 550^∘;C) was 3.12 eV.     

Critical Evaluation of Protonation Constants. Literature Analysis and Experimental Potentiometric and Calorimetric Data for the Thermodynamics of Phthalate Protonation in Different Ionic Media

The protonation constants of phthalate were determined in aqueous NaCl (0.1 ≤ I ≤ 5,mol⋅L⁻¹) and in aqueous Me₄NCl (0.1 mol⋅L⁻¹ ≤ I ≤ 3,mol⋅L⁻¹) at t = 25,^∘C. Experimental data were employed in conjunction with literature data from studies in different ionic media (Et₄NI: 0 ≤ I ≤ 1,mol⋅L⁻¹; NaClO₄: 0.05 mol⋅L⁻¹ ≤ I ≤ 2,mol⋅L⁻¹)to study the dependence on ionic strength using different models, such as the SIT and Pitzer equations, and an Extended Debye-Hückel type equation. Experimental calorimetric data in NaCl and protonation constants at different temperatures in Et₄NI (5 ≤ t ≤ 45^∘C) and in NaClO₄ (15 ≤ t ≤ 35 ^∘C) were also used to study their dependence on temperature. Recommended equilibrium data are reported together with a short discussion of a prospective protocol for drawing these data.