DTA Profiles Research Articles

Structural, thermal and spectroscopic properties of samarium (Sm3+) doped tungsten zinc tellurite glass for application in orange light emitting devices

Using melt quenching method 1 mol% Sm2O3 doped WO3–ZnO–TeO2 glass has been prepared. The structural, thermal, optical and luminescence properties are studied by analyzing the XRD, FTIR, DTA, UV–Vis–NIR absorption, excitation, photoluminescence emission, decay profile, CIE1931 and CIELab diagrams. The DTA profile shows that the glass transition (Tg), crystallization (Tc) and melting temperature (Tm) occur at 384 °C, 559 °C and 810 °C, respectively. The FTIR spectra confirm that the glass has low phonon energy around 666 cm−1. Using absorption spectra the Judd-Ofelt intensity parameters and hence the radiative parameters are determined. The glass emits intense orange light at 600 nm due to 4G5/2 → 6H7/2 transition upon excitation at 403 nm, and the decay profile of the 4G5/2 level shows double-exponential nature. The values of radiative parameters, quantum efficiency (η) and CIE indicate that the glass sample is promising for orange light emitting photonics devices.

Synthesis, X-ray Single-Crystal Structural Characterization, and Thermal Analysis of Bis(O-alkylxanthato)Cd(II) and Bis(O-alkylxanthato)Zn(II) Complexes Used as Precursors for Cadmium and Zinc Sulfide Thin Films.

This work investigates tuning of the molecular structure of a series of O-alkylxanthato zinc and cadmium precursor complexes to enhance production of ZnS and CdS materials. The structures of several bis(O-alkylxanthato) cadmium(II) complexes (8-13) and bis(O-alkyl xanthato)zinc(II) complexes (18 and 19) are reported based on single crystal X-ray diffraction data. CdS and ZnS films were produced by the spin-coating of these metal complexes followed by their thermal decomposition to the corresponding metal sulfides. Thin films of CdS were deposited by spin-coating the bis(O-alkylxanthato) cadmium(II) precursors (7-13) on glass substrates, followed by annealing at 300 °C for 60 min. Thin films of ZnS were deposited by spin-coating bis(O-alkylxanthato) zinc(II) (14-20), followed by annealing at 200 °C for 60 min. The molecular complexes and solid state materials are characterized using a range of techniques including single-crystal X-ray diffraction, pXRD, EDS and XPS, DSC and TGA, UV-vis and PL spectroscopies, and electron microscopy. These techniques provided information on the influence of alkyl chain length on the thermal conditions required to fabricate metal sulfide films as well as film properties such as film quality, and morphology. For example, the obtained crystallite size of metal sulfide films formed is correlated to the hydrocarbon chain length of xanthate ligands in the precursor. The behavior of the complexes under thermal stress was therefore studied in detail. DTA and TGA profiles explain the relationship between hydrocarbon chain length, decomposition temperatures, and the energies required for decomposition. A higher decomposition temperature for complexes with longer hydrocarbon chains is observed compared to complexes with shorter hydrocarbon chains. Band-gap energies calculated from the optical absorption spectra alongside steady state and time-resolved photoluminescence studies are reported for CdS films.

The role of CuO as limiting and luminescent probe for orange red emission of Sm3+ ions in strontium bismuth borosilicate glasses

The properties of glass materials with CuO are suitable for both optical and photovoltaic applications. The role of CuO hinges on the structural properties of glass network. The structural and luminescence properties of melt quenched strontium bismuth borosilicate glasses containing Sm 2 O 3 with varying amounts of CuO (referred as N: SmCu) were studied. Two valence states of Cu ions are possible due to more amount of silica in glass. The amorphous nature of glass was confirmed by XRD and thermal parameters were explained through DTA curves. FTIR spectrum indicated the variation of asymmetric vibrations of SiO 4 units with change in SrO and CuO concentration which influence the valence state of Cu 2+ . The absorption spectra have shown peaks due to 3 d 10 →3 d 9 4s 1 transition of Cu + ions, 6 H 5/2 → 6 P 3/2 transition of Sm 3+ and broad 2 B 1g → 2 B 2g transitions of Cu 2+ ions. The NIR region has peaks of Sm 3+ ions. The Photo Luminescence (PL) spectra of N: SmCu glasses exhibited cyan bluish emission at 485 nm followed by intense emission peaks of Sm 3+ at 312 nm excitation. The emission of N: SmCu10 and N: SmCu12 glasses are quenched due to Cu 2+ ions. Moreover, maximum range of emission is exhibited by ‘N: SmCu8’ glass. The shortening of life time decay observed in ‘N: SmCu’ glasses was inferred to the process of energy transfer. The profiles of life time decay curves are fitted with the help of bi-exponential function. The CIE and CCT values of all glasses are calculated. The white light emission is quite possible in N: SmCu10 glass and the remaining glasses covered Orange - red regions with CCT values ranging from 1892 K–2351 K. The schematic energy level diagram of N: SmCu glasses. • Sm 3+ /Cu 2+ co-doped glasses prepared by melt quench technique. • FTIR show different units of vibrations and DTA profile shows thermal stability. • PL, spectral overlap and life time decay confirms energy transfer. • CIE and CCT value shows white light emission.

Transformation of a Fe–Mn oxide into a ferromagnetic α-Fe2O3

The present investigation concerns synthesis of a ferromagnetic Mn2+-doped α-Fe2O3 following a co-precipitation method. Thus, an aqueous solution containing Fe3+ and Mn2+ ions in a molar ratio of 2:1 was precipitated as hydroxides and then dried at 100 °C. The product was characterized by XRD, TEM and TG–DTA. XRD and TEM analysis revealed that the ‘as-prepared’ material was largely ‘amorphous’ containing mixed-phase nanoparticles of α-FeOOH and MnFe2O4. The TG showed mass loss up to 250 °C while the DTA profile exhibited a broad exothermic peak in the temperature range ~ 300–800 °C, suggesting structural transformation. Additional phases were also synthesized by calcination of the initial product, at various temperatures, which were 200 °C, 450 °C, 600 °C and 750 °C. It was observed that in the temperature interval 600–750 °C, the material was transformed to Mn2+-doped α-Fe2O3 nanorods and nanoparticles having wide oblong shapes. The results were compared with pure α-Fe2O3 which was similarly synthesized without the presence of Mn2+. It was observed that unlike pure α-Fe2O3 which was antiferromagnetic, the Mn2+(α-Fe2O3) sample was ferromagnetic and showed much higher catalytic activity toward decomposition of hydrogen peroxide. The catalytic decomposition of H2O2 could be explained on the basis of Fenton and photo-Fenton effects.

Enhancement of the red emission of Eu3+ by Bi3+ sensitizers in yttrium alumino bismuth borosilicate glasses

Trivalent europium ions doped yttrium alumino bismuth borosilicate glasses (YABiBS) of the composition are synthesized by the melt - quenching method. The structural, thermal and spectral properties of the prepared glasses have been investigated by XRD, EDS, FT-IR, DTA, optical absorption, photoluminescence and decay profiles. XRD indicated the amorphous nature of the samples. From the DTA traces thermal Parameters like ΔT, S and H are evaluated to verify the thermal stability of the titled glasses. FTIR spectra exhibited bands due to various fundamental vibrational units of borate and silicate groups. The optical absorption spectra exhibited the bands due to 7F0 → 5G4, 7F0 → 5L6, 7F0 → 5D2, 7F0 →7F6, and 7F1 → 7F6 transitions of Eu3+ ions. In addition the absorption spectra also exhibited a band due to 1S0 → 1P1 transition of Bi3+ ions. From the absorption spectra, the optical band gap and Urbach energies and also nephelauxetic ratios were evaluated. The emission spectra (excited at 392 nm) exhibited five luminescence bands at 577, 590, 612, 651 and 700 nm assigned to 5D0 → 7F0, 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3, and 5D0 → 7F4 transitions of Eu3+ ions, respectively. The absorption and emission spectra were characterized using Judd-Ofelt (J-O) theory and radiative parameters viz., radiative transition probability (AR), branching ratio (βR), and luminescence quantum efficiency (η), radiative life time (τ), stimulated emission cross-section (σPE) were evaluated. The values of radiative parameters are found to be the highest for the transition 5D0→7F2 of 0.6mol% Eu3+ doped YABiBS glass (BE0.6). The co-doping of Bi3+ ions (10.0mol %) caused a substantial enhancement (nearly three times) in the intensity of this red emission. These results suggested the energy transfer between Bi3+ ions and Eu3+ ions. The energy transfer efficiency has been explained in terms of structural modifications taking place in the glass network.

Li2O[sbnd]LiF[sbnd]ZnF2[sbnd]B2O3[sbnd]P2O5: MnO glasses – Thermal, structural, optical and luminescence characteristics

Here, we present results pertaining to thermal, structural, optical and photoluminescence properties of Li2OLiFZnF2B2O3P2O5: (0.1–1.5mol.%) MnO glasses. DTA profiles revealed a change in glass transition temperature with the addition of MnO suggesting an increase in glass stability. The modifications in structural units are interpreted from FTIR and Raman spectral profiles, which confirm the formation of stable POB bonds. The host Li2OLiFZnF2B2O3P2O5 (labelled as LZBP) glass exhibits emission in the blue region on excitation with 361nm. The red shift in optical absorption edge and decrease in energy of band gap as a function of MnO concentration is analysed from Tauc’s plot. The nature of local symmetry around manganese ions in LZBP matrix has been understood by evaluating the crystal field strength (Dq) and Racah inter-electronic repulsion parameters (B &C) from absorption spectrum and electron-lattice interaction energy (Sħω) factor from emission spectrum. The emission spectra of (0.1–1.5mol.%) Mn2+: LZPB glasses have shown broad band at 613nm assigned to electronic transition 4T1g(G)→6A1g(S) displaying orange-red emission upon excitation at 413nm. Octahedral coordination of Mn2+ ions has been estimated from the position of emission in luminescence spectra. The effect of Mn2+ concentration on emission properties has been discussed from lifetime curves and energy level scheme.

Structural, thermal and optical properties of Tb3+, Eu3+ and co-doped (Tb3++Eu3+): PEO+PVP polymer films

Tb3+ and Eu3+ each ion individually doped and also both these ions doped in PEO+PVP blended polymer films have successfully been synthesized using solution casting method. XRD analyses of these films have demonstrated that those are in semi-crystalline nature. In order to understand their thermal properties, TG–DTA profiles have also been carried out. Fourier transform infrared (FTIR) and Laser Raman Spectra have been used to monitor polymer–salt complex formation, ion–polymer interactions. The polymer films containing Tb3+ and Eu3+ (0.1wt%) ions have displayed green (Tb3+) and red (Eu3+) luminescent colors under an UV source. Their absorption spectra, excitation and emission spectra have also been measured to evaluate their optical properties. For a prominent green emission at 546nm (5D4→7F5) of Tb3+ doped polymer film, and for a prominent red emission at 618nm (5D0→7F2) of Eu3+ polymer film, their emission transition lifetimes have been measured. Eu3+ emission intensity becomes significantly enhanced via an energy transfer from Tb3+ to Eu3+ in co-doped Eu3++Tb3+ polymer films. Thus, based on the results it could be suggested that Tb3+:PEO+PVP, Eu3+:PEO+PVP and (Eu3++ Tb3+):PEO+PVP blended polymer films as potential luminescent optical materials.

Thermally stable blue-emitting NaSrPO 4:Eu 2+ phosphor for near UV white LEDs

A novel blue light emitting NaSr 1 − x PO 4:Eu 2+ x ( x = 0.001 to 0.02) phosphors were prepared by solid-state reaction method to investigate its optical properties and thermal stability for its application in white light-emitting diodes (w-LEDs). The excitation and emission spectra of the prepared phosphor reveal a broad emission peak centered at 460 nm which arises due to 4f–5d transitions of Eu 2+ upon the near ultra-violet (n-UV) excitation wavelength at 380 nm. The effect of Eu 2+ doping concentration and sintering temperature on the emission intensity of NaSrPO 4:Eu 2+ was investigated along with its chromaticity coordinates. The temperature dependent luminescence properties of the prepared phosphor show better results than that of the commercial YAG:Ce 3+phosphor. Besides, their XRD, FT-IR, SEM, TG, and DTA profiles have also been analyzed to explore its structural details.

Host sensitized novel red phosphor CaZrSi2O7 : Eu3+ for near UV and blue LED-based white LEDs

A series of red phosphors Ca1−xZrSi2O7 : Eux (x = 0.5,1,5,10,12 mol%) were prepared by a solid-state reaction technique at various temperatures and their structural and optical properties were investigated. The x-ray diffraction profiles showed that all peaks could be attributed to the monoclinic phase CaZrSi2O7 doped with Eu3+. SEM, FTIR, TG and DTA profiles have also been characterized to explore their structural properties. The luminescence properties of these resulting phosphors have been characterized by photoluminescence spectra. The host matrix itself has shown a strong blue emission which has its maximum intensity at 470 nm. The excitation spectra of CaZrSi2O7 : Eu3+ revealed two excitation bands at 395 and 464 nm which correspond to the sharp 7F0–5L6 and 7F0–5D2 transitions of Eu3+ and matches well with the two popular emissions from n-UV/blue GaN-based LEDs. The prominent red emission was obtained at 615 nm by the excitation transitions 5L6, 5D2 of Eu3+ through the non-radiative energy transfer process from the host to the Eu3+ ion. The effects of charge compensation by monovalent ions on the luminescence behaviour of a red emitting phosphor CaZrSi2O7 : Eu3+ were investigated. The high colour saturation and the low thermal quenching effect of these phosphors make it a potential red component for white light emitting diodes (w-LEDs).

Optical, thermal and dielectric properties of Bi 4(TiO 4) 3 ceramic powders

Bismuth titanate (Bi 4(TiO 4) 3) ceramic powders have been synthesized by using a solid state reaction method. Prominently intense blue emission at 480 nm has been measured with an excitation at 418 nm. The reason for the observance of such a blue emission from this ceramic powder has been explained. The phase formation has been investigated by X-ray diffraction analysis (XRD). The morphology and composition of the ceramic powders have been studied from the measurement of SEM and EDS profiles. FTIR and Raman spectra have also been recorded to analyze the presence of functional groups and Raman active modes in the Bi 4(TiO 4) 3 ceramic powders. The sintering temperature has been optimized to be 1100 °C based on the measured TG–DTA profiles of the as prepared material. Besides these, dielectric properties of ceramic powder in the frequency range of 200 Hz–3 MHz at 300 K have also been carried out.

Powder metallurgy magnesium composite with magnesium silicide in using rice husk silica particles

By using the solid-state reaction of rice husk silica particles with magnesium powder, P/M magnesium based composites dispersed with the magnesium silicide (Mg 2Si) and magnesium oxide (MgO) were fabricated. High-purity silica particles were originated from rice husks, one of the major agricultural wastes, via the citric acid leaching treatment and combustion in air. The effects of the silica particle characteristics such as size, crystalline and porous structures, on the reactivity of silica and magnesium to synthesize Mg 2Si intermetallics were discussed. As the results by DTA and XRD analysis, finer silica particles were more effective for the solid-state reaction at low temperature due to the increase of their surface area contacted with magnesium powder. Amorphous silica was also more useful for this reaction than the crystalline one. The reactivity of rice husk silica was superior to that of the conventional mineral silica particles not only because of its amorphous structure but also the larger specific surface area due to their pore structures. In the case of the green compact of the elemental mixture of silica particles and Mg powder, the silica particle size was not effective on the reactivity because the coarse particles were fractured into fine ones by cold compaction. The distribution of Mg 2Si intermetallics of magnesium powder composites consolidated by SPS process was investigated by XRD and SEM-EDS analysis. When the sintering temperature was over the exothermic temperature of the mixture in the DTA profile, the synthesis of Mg 2Si completely occurred during sintering. The sinterability of the elemental mixture powder was improved when employing the amorphous rice husk silica particles. The density and hardness of their composites sintered over the ignition temperature of the DTA profile were remarkably high because of the good densification by the high reactivity and the distribution of Mg 2Si hard compounds.

Combinations of synergistic interactions and additive behavior during the co-oxidation of chars from lignite and biomass

The aim of this study is to investigate the co-combustion behavior of two different pyrolytic chars. For this purpose, Elbistan lignite and woody shells of hazelnut were pyrolysed in a tube furnace by heating to 900 °C with a heating rate of 40 °C min−1 under dynamic nitrogen flow of 400 mL min−1 to obtain pyrolytic char. These chars were mixed to obtain blends having the biomass char in the ratios of 5, 10, and 20 wt.%. Non-isothermal DTA and TGA profiles of the chars were obtained from ambient to 900 °C with a heating rate of 40 °C min−1 under the static ambient atmosphere. DTA and TGA profiles of the blend chars were interpreted considering the thermal characteristics such as ignition point, burnout at a given temperature, maximum burning rate, the end of combustion etc. Relations between the fraction of the biomass char in the blends and the thermal behavior of the blends were evaluated according to the synergistic approach. It was found that addition of biomass char led to important variations in some thermal properties which can not be explained by the additive behavior. However it can be concluded in general that the combinations of synergistic interactions and additive behavior govern the thermal properties of the blend chars during co-oxidation.

Absorption and emission spectral analysis of Pr3+: tellurite glasses

This paper reports on the results concerning optical absorption and fluorescence properties of 60TeO2–25ZnO–10BaO–4.5La2O3–0.5Pr2O3 (Pr3+: TZBL) glass. Both electronic (αe) and vibrational (αv) band edge cut-off wavelengths of the host glass (TZBL) have been evaluated from the measurement of its UV–Vis and IR transmission spectra. The glass studied has shown 80% transmittance throughout its optical window from 0.366 μm (αe = 3.39 eV) to 6.30 μm (αv = 0.197 eV). The FT-IR transmission spectra of Pr3+ doped and also reference tellurite glasses have demonstrated the presence of TeO4 and TeO3+1 or TeO3 structural units. The thermal properties of this glass have been investigated from the study of DTA profile. The recorded optical absorption spectra of Pr3+: TZBL glass have shown eight absorption bands from 300 nm to 2,500 nm. The fluorescence emission has been observed mainly from 3P1, 3P0 and 1D2 states to the lower lying states and which are assigned to the transitions of 3P0→ 3H4,5,6; 3P0→ 3F2,3,4; 3P1→3H5 & 1D2→3H4,5 upon excitations at three excitation states of 3P0,1,2. From the time resolved spectra, it is found that 3P0 level decays faster than 1D2 level. The fluorescence decay kinetics of 3P0 and 1D2 levels have been measured and the lifetimes are found to be 21 and 39 μs, respectively.

Thermal and kinetic study of corn biodiesel obtained by the methanol and ethanol routes

This work evaluates the thermal and kinetic behaviour of corn biodiesel obtained by the methanol and ethanol routes. As to the TG curves, in air three thermal decomposition steps are for the methanol biodiesel and two steps are for the ethanol biodiesel. These steps are related to the evaporization and/or combustion of the methyl and ethyl esters, respectively. The corn oil presented four thermal decomposition steps in air, and only one step in nitrogen. These steps were attributed to the evaporization and/or decomposition of triglycerides. The TG and DTA profiles of the biodiesel approach the mineral diesel oil ones.

Process Parameters Optimization in Preparing High-Purity Amorphous Silica Originated from Rice Husks

Rice husk, one of the main agricultural disposals in Japan, China, India, and South-east Asian countries, is employed as useful renewable resources to produce energy and high-purity silica (SiO 2 ), because it consists of 70% organics and about 20% SiO 2 . The latter, SiO 2 is obtained by burning rice husks in air. The purity of rice husk ashes, however, is reduced by the remains of both carbon contents originated in organics and original metallic impurities such as K, Na, Ca, P, Al, etc. In the previous works, the utilization of the leaching methods by strong acids with a high concentration for both the remove the metallic impurities and the fragmentation of silica structural network was suggested. As their results, the thermal resolution mechanism of organics was discussed by using TGA showing the mass loss behavior during heating. The objective in this study is to clarify the mechanism of the removal of organic components when applying a dilute H 2 SO 4 leaching treatment with 1∼5% solution concentration. In particular, from a viewpoint of the investigation on molecule structural changes of organics, GCMS (Gas Chromatograph Mass Spectrometer) analysis is carried out on acid-leached rice husks. When using only 1% concentration H 2 SO 4 solution leaching, a change of cellulose of polysaccharides to levoglucosan via glucose of monosaccharide by hydrolysis and condensation reactions occurred. This reaction accompanied with dehydration always served en endothermic heat, which was found in DTA profile of acid leached rice husk materials. It was also clarified that such a low concentration H 2 SO 4 solution was enough to remove alkali metal elements contained in husks. By optimizing the combustion temperature of rice husks after acid leaching, completely amorphous silica ashes, composing of 99.3% SiO 2 and 0.04% carbon, were obtained.

Characterisation of Ca– and Al–pectate gels by thermal analysis and FT-IR spectroscopy

Thermal analysis (TG–DTA) and FT-IR spectroscopy have been performed on calcium–pectate membranes to investigate their structure and the consequent variation caused by aluminium sorption. Calcium–polygalacturonate (Ca–PG) membranes, model systems of the soil–root interface, were exposed to aluminium solutions at different concentrations (25–800 μM). Three different pHs (3.50, 4.00 and 4.50) were chosen to study the influence of different aluminium species, such as [Al(H 2O) 6] 3+, [Al(OH)(H 2O) 5] 2+ and [Al(OH) 2(H 2O) 4] +, on the structure of the Ca–PG membrane. The DTA profiles and FT-IR spectra showed how aluminium sorption induces structural modifications leading to a reorganisation of the chain aggregates and a weakening of the structure. Higher pH, that is, 4.00 and 4.50, and thus hydrolytic aluminium species and related higher calcium content maintain a more regular structure than at pH 3.50. At pH 3.50, both the effect of [Al(H 2O) 6] 3+ and a major calcium release had a greater impact and thus induced a greater weakening of the structure.

Synthesis, characterization, thermolysis and performance evaluation of mercuric-5-nitrotetrazole (MNT)

Mercuric-5-nitrotetrazole (MNT) was synthesized on using a reported method. The product having bulk density of 1.5 g/cm 3, was obtained during this work using mercuric nitrate doped with additives such as cephol/dextrin in the process. Synthesized MNT was characterized by metal content analysis, IR and ESCA. The DTA profile indicated the thermal stability of MNT up to 200 °C. It revealed its higher thermally sensitive [thermal sensitive figure ( S) ∼0.8] in comparison to that of service lead azide (SLA) [ S ∼ 0.4]. Percussion sensitivity data also showed higher sensitivity of MNT. However, it was found less friction sensitive than SLA. The chemical stability of MNT in a carbon dioxide environment was evaluated in comparison to SLA by determining mercury (gravimetrically) and lead azide (volumetrically) contents respectively. Results obtained indicated that no discernable changes occurred in MNT, even after storage for 90 days while in case of SLA, drastic change in lead azide content was observed. IR spectra of MNT sample stored in a closed aluminum dish for 5–10 years could be superimposed on that of the freshly prepared MNT sample. The performance of MNT filled detonator no. 27 assessed in terms of extent of damage on a witness plate was found equivalent to that of the standard ASA (azide, styphynate and aluminium) composition filled detonator.

θ-Crystallite growth restraint induced by the presence of α-crystallites in a nano-sized alumina powder system

The restraint of θ-Al 2O 3 from crystallite growth induced by the presence of α-crystallites in the nano-sized alumina powder system is examined. The θ-crystallite powder was obtained by calcination of boehmite. α-Crystallites present in the θ-powder system, either through addition externally to boehmite or introduced internally by θ-crystallites that transform to α-during θ- to α-phase transformation of the boehmite, affect the rate of θ-crystallite growth. Small amounts of external α-crystallite addition initiates the formation of a subsystem in the boehmite precursor in which the formed θ-crystallite grows faster, bringing about part of the powder system to experience a temperature reduction of θ- to α-phase transformation on DTA profiles. With large amounts of α-crystallite addition, another subsystem in which the rate of θ-crystallite growth slows down occurs. α-Crystallites introduced spontaneously during phase transformation, although with small amounts of the α-crystallite presence, less than 10–20%, whose effect can be eliminated, show similar effects of restraining θ-crystallites from growth. Activation energy calculations demonstrated that, once the α-crystallite appeared, more than ∼100 kJ/mol was required for θ-crystallite growth.

シリカ表面におけるメタノール蒸気の不可逆吸着

Irreversible adsorption of methanol vapor on sillica surface was studied through the measurements of adsorption isotherms and IR absorption as well as differential thermal analysis. Dependencies of irreversible methanol adsorption on the preheating temperature and the vapor pressure was investigated to evaluate the reactivity of silica surface.The irreversible adsorption occurs by two mechanisms, i. e., formation of hydrogen bond and surface methoxylation reaction which forms methoxy groups. DTA profiles of methoxy groups reflects the states of hydroxyl groups on the surface. Isolated methoxy groups exhibited DTA exothermic peaks at higher temperature. They were formed from the isolated hydroxyl groups on the surface preheated at temperatures above 400°C. The surface methoxylation reaction occurred mainly on the isolated hydroxyl groups at a low pressure, while methoxylation of siloxane bridges took place at a pressure higher than that of multilayer formation and was promoted by the methanol vapor condensation in the pores.

Thermal Decomposition of Alkoxides in an Inert Organic Solvent: Novel Method for the Synthesis of Homogeneous Mullite Precursor

Thermal decomposition of a mixture of aluminum iso‐propoxide and tetraethoxysilane (Al/Si = 3) in toluene at 300°C was examined. The reaction completely proceeded and yielded an amorphous product. The DTA profile of the product showed a sharp peak at ∼1000°C which was associated with crystallization of mullite and a small amount of the spinel phase. The mullite prepared by calcination of the product at 1300°C was composed of micro‐crystals having an average diameter of 30 nm and had a large surface area of 41 m2g.