Potential of thermal analysis in preparation and characterization of solid catalysis

Supported catalysts contain often only small amounts of active component(s) which renders their characterization difficult, particularly because they usually contain a substantial amount of water. Thermal analysis (TA) coupled with mass spectrometry (MS) offers an interesting potential for characterizing such material, various steps of catalyst preparation as well as crucial properties of fresh and used catalysts can be investigated. Some examples illustrating the versatility of TA-MS in catalysis research, such as solid-state reactions occurring upon exposure of the precursors or catalysts to reducing, oxidizing or inert atmosphere, are presented in this study. The combined use of TA and MS allows in many cases a much more detailed interpretation of the observed phenomena than could be achieved by one of these methods alone.     

Microstructural control of b-silicon nitride ceramics to improve thermal conductivity

An advanced silicon nitride material with high isotropic thermal conductivity (149 W m^-1 K^-1) has been developed. This high thermal conductivity was achieved with a process that combines high-quality seed crystals with a suitable additive system to promote grain growth. In this process, the addition of β-Si₃N₄ seed crystals was found to be effective in improving thermal conductivity due to their low defect and impurity concentrations. The seed crystals seem to work as nuclei for controlling grain growth during the sintering process. Controlling the growth of elongated grains so that they do not interact with each other seems important for suppressing the generation of new defects inside the grains. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal behavior of polyazomethine-ethers having phenanthrene moiety in the main chain

Eleven types of polyazomethine-ethers were prepared from 2,7-diaminophenanthrene as the amine and 4,4'-diformyl- α,ω -diphenoxyalkanes, 4,4'-diformyl-3,3'-methoxy- α,ω -diphenoxyalkanes and 4,4'-diformyl-3,3'-ethoxy- α,ω -diphenoxyalkanes as the dialdehydes. The polymerization was carried out by stirring the monomers in a mixture of m-cresol/o-chlorophenol (1:1) for 3 h at room temperature in the dark. The reduced viscosities of polymers were 0.49 to 1.61. The melting temperature (Tm) of the polymer without substituent group was 281°C from 4,4'-diformyl-1,3-diphenoxypropane and then showed a characteristic odd-and-even alternation between even- and odd-numbered carbon chain length in the ethers. The Tm's of the polymers with substituent groups were lower than the linear polymers because of the loose packing as observed for the lower crystallinity. The 10% mass-loss temperatures were 430 K for linear polymers and the lower temperatures were attained for the polymers with substituent groups. This revised version was published online in July 2006 with corrections to the Cover Date.     

氮化硅纳米线制备过程中反应条件的影响

采用X 射线衍射和扫描电子显微镜技术, 考察了溶胶-凝胶法制备氮化硅纳米线过程中反应条件(添加剂种类和含量、反应时间以及反应温度)对碳热还原产物组成和形貌的影响. 结果表明, 碳化后铁含量为5%(w)的凝胶, 在1300 ℃下反应10 h, Si₃N₄纳米线产率较高. 添加剂的种类和含量不同, 所得产物的组成和形貌也不相同.随着反应温度的升高或反应时间的延长,产物经历了一个从SiO_x到Si₂N₂O 再到Si₃N₄的转变过程. 在有金属组分存在时, Si₃N₄纳米线由气-液-固过程形成.     

Trace analysis of microcontaminations in compliance with ISO 9001: monitoring and diagnostics in large-scale silicon manufacturing

 Severing principles are reported concerning the certification of and quality assurance in a trace-analysis laboratory that handles a large number of real samples, about 60 000 analyses/year with 50 validated methods. ISO 9001 emphasizes monitoring rather than diagnostics. For monitoring purposes the trace-analysis methods must be highly selective and of high precision, with high throughput and uptime within a justifiable economic framework in the analytical range of interest. All trace-analysis methods must be cross-checked using independent analytical tools. The analytical laboratory must be fully integrated in the total quality management of the plant. The analyst must know not only the performance of the trace-analysis tools but also the materials and processes involved in manufacturing. Received: 19 October 1995 Accepted: 15 November 1995     

Curing and thermal behaviour of epoxy resin in the presence of a mixture of imide-amines

The curing behaviour of diglycidyl ether of bisphenol-A (DGEBA) was investigated by the dynamic differential scanning calorimetry using varying molar ratios of aromatic imide-amines and 4,4′-diaminodiphenylsulfone (DDS). The imide-amines were prepared by reacting 1 mole of naphthalene 1,4,5,8-tetracarboxylic dianhydride (N) and 4,4′-oxodiphthalic anhydride (O) with 2.5 moles of 4,4′-diaminodiphenyl ether (E) or 4,4′-diaminodiphenyl methane (M) or 4,4′-diaminodiphenylsulfone (S) and designated as NE/OE or NM/OM or NS/OS. The mixture of the imide-amines and DDS at ratio of 0:1, 0.25:0.75, 0.5:0.5, 0.75:0.25 and 1:0 were used to investigate the curing behaviour of DGEBA. A single exotherm was observed on curing with mixture of imide-amines and DDS. This clearly shows that the two amines act as co-curing agents. Curing temperatures were higher with imide-amines having sulfone linkage irrespective of anhydride. Curing of DGEBA with mixture of imide-amines and or DDS resulted in a decrease in characteristic curing temperatures. The thermal stability of the isothermally cured resins was also evaluated using dynamic thermogravimetry in a nitrogen atmosphere. The char yield was higher in case of resins cured imide-amines based on N and E. The activation energy of decomposition and integral procedural decomposition temperature were also calculated from the TG data.     

Comparison ofE a values obtained by thermal analysis with energy of ‘charge-transfer’ spectra for potassium and silver permanganates

The activation energy,E _a taken from the thermal decomposition of KMnO₄ and AgMnO₄ was compared with the energy of the longest wavelength O→Mn ‘charge transfer’ (CT) transition. TheE _a and CT correlation was found in these systems. However, such relationship can be valid when in the dissociation process the electron transfer is assumed to be the rate determining step. Thus, the permanganates as well as the previously studied chromates, are positive examples showing that in some cases, the energies derived from both methods can be comparable.     

Synthesis and cytotoxic properties of 7α-chloro-3-methyl-1,1-dioxoceph-3-ems, substituted with amide or keto group at position 4

7α-Chloro-3-methyl-1,1-dioxoceph-3-ems with amide or keto group at position 4 have been synthesized by structural modification of 7α-chloro-3-methyl-1,1-dioxoceph-3-em-4-carboxylic acid. Screening of these compounds for cytotoxic activity revealed compounds with specific activity against cancer cells in vitro, capable of effective inhibition of the growth of sarcoma S-180 in vivo. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, 1849–1859, December 2007.     

Monitoring of the evolved gases in apatite-ammonium sulfate thermal reactions

Summary Thermal reactions in natural fluorapatite or fluorcarbonate apatite and ammonium sulfate mixtures with mole ratio 1:4 at calcination up to 500°C were studied by simultaneous thermogravimetry and FTIR analysis of the evolved gases. The composition of natural apatite has little impact on the release of NH₃. Upon the evolution of NH₃ nitrous oxides were found in minor amounts. The release of SO₂ at temperatures above 400°C is more intensive and occurs at lower temperatures in the case of fluorapatite than of carbonate containing apatites. Evolution of CO₂ starts at 250°C with maximum at 350-360°C.     

Applicability of the Kissinger equation in thermal analysis

Pt/WO_x–ZrO₂ bifunctional catalysts were synthesized using impregnation and polymeric precursor methods. After the synthesis process the samples were calcined at 600, 700 and 800°C and characterized by X-ray diffraction, nitrogen adsorption and temperature programmed reduction study by thermogravimetry. DTG-TPR profiles showed between three and five reduction events at different temperatures attributed to platinum reduction and to different stages of tungsten species reduction. A comparative study of the synthesis method influence on the DTG-TPR curves was accomplished.     

Effects of doping on the thermal stability of spindle-shaped γ-Fe2O3 particles

Spindle-shaped α-FeOOH particles were synthesized using the chemical coprecipitation method in Fe(CO₃)_x(OH)_2(?x) suspensions system by adding metallic ions. The spindle-shaped γ-Fe₂O₃ particles were obtained by dehydration of α-FeOOH, and subsequent reduction and oxidation. Its thermal stability was investigated by differential thermal analysis (DTA). It was found that the transition temperature of γ-Fe₂O₃→α-Fe₂O₃ of samples doped with metallic ions is higher than that of the pure γ-Fe₂O₃ and increasing with increase of the size of the metallic ions, and γ-Fe₂O₃ by doping with two or more different metallic ions together has even higher thermal stability. The origin of the improved thermal stability was discussed. Additionally, the magnetic properties of γ-Fe₂O₃ were measured.     

Thermal analysis of environmentally compatible polymers containing plant components in the main chain

Environmentally compatible polymers such as poly(ε-caprolactone) (PCL) and polyurethane (PU) derivatives from PCL's were synthesized from saccharides, polysaccharides and lignins such as glucose, fructose, sucrose, cellulose, cellulose acetate, alcoholysis lignin, kraft lignin and sodium lignosulfonate. Flexible and rigid PU sheets and foams were also prepared by the reaction of OH groups of saccharides and lignins with isocyanates such as toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). Glass transition temperatures (T_g's), cold-crystallization temperatures (T_cc's) and melting temperatures (T_m's) of saccharide- and lignin-based PCL's and PU's were determined by differential scanning calorimetry (DSC), and phase diagrams were obtained. Methods of controlling mechanical properties such as stress and elasticity of PU's through changing thermal properties such as glass transition temperature were established. Thermogravimetry (TG) and TG-Fourier transform infrared spectrometry (FTIR) were also carried out in order to analyze the degradation temperature and evolved gases from the above obtained polymers. This revised version was published online in July 2006 with corrections to the Cover Date.     

Application of neural networks in analysis of thermal decomposition of CoSO4·7H2O

Thermal decomposition of CoSO₄·7H₂O was investigated by simultaneous DTA-TG techniques and XRD method. Neural networks were used for DTA-TG curves analysis. Additionally, the network architecture (GRNN - Generalized Regression Neural Networks) and its statistical parameters were calculated. This method permits to generate DTA-TG curves without using kinetic models. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study on thermal decomposition kinetics of N,N′-bis(5,5-dimethyl-2-phospha-2-thio-1,3-dioxan-2-yl)ethylenediamine in air

The thermal decomposition kinetics of the N,N′-bis(5,5-dimethyl-2-phospha-2-thio-1,3-dioxan-2-yl) ethylenediamine (DPTDEDA) in air were studied by TGDTG techniques. The kinetic parameters of the decomposition process for the title compound in the two main thermal decomposition steps were calculated through the Friedman and Flynn-Wall-Ozawsa (FWO) methods and the thermal decomposition mechanism of DPTDEDA was also studied with the Coats-Redfern and Achar methods. The results show that the activation energies for the two main thermal decomposition steps are 128.03 and 92.59 kJ·mol⁻¹ with the Friedman method, and 138.75 and 106.78 kJ·mol⁻¹ with the FWO method, respectively. Although there are two main thermal decomposition steps for DPTDEDA in air, the thermal decomposition mechanism of DPTDEDA in the two steps are the same, i.e. f(α) = 3/2(1 − α)^4/3[(1 − α)^−1/3 − 1]⁻¹. __________ Translated from Acta Chimica Sinica, 2008, 66(9) (in Chinese)     

Preparation,characterization and thermal decomposition of phenylenediammonium sulfate salts Part. XVI

Polyaniline/α-Al₂O₃ (PANI/α-Al₂O₃) composites were synthesized by in situ polymerization through ammonium persulfate ((NH₄)₂S₂O₈, APS) oxidized aniline using HCl as dopant. XRD and FTIR were used to characterize the PANI/α-Al₂O₃ composites. The thermal stabilities and glass transition temperature (T _g) of PANI/α-Al₂O₃ composites were tested using thermogravimetric (TG) method and modulated differential scanning calorimetry (MDSC) technique. The results of TG showed that the thermal stability of PANI/α-Al₂O₃ composite increased and then decreased with the increase in α-Al₂O₃ content. The derivative thermogravimetry (DTG) curves showed one step degradation of PANI when the α-Al₂O₃ content was lower than 52.5 mass%, and exhibited two steps degradation when the α-Al₂O₃ content was higher than 63.6 mass%. The MDSC curves showed that the T _g of PANI/α-Al₂O₃ composites increased and then decreased with the augment of α-Al₂O₃ for the interaction between PANI chains and the surface of α-Al₂O₃.     

CsF–Si(OEt)4 catalyzed addition of (hetero)aromatic amides to ethyl acrylate

The conjugate addition of some (hetero)aromatic amides to an α,β‐unsaturated ester (ethyl acrylate) proceeds efficiently in the presence of an equimolar amount of the CsF–Si(OEt)₄ system to afford the corresponding ethyl esters of N‐substituted β‐amino acids. Copyright © 2001 John Wiley & Sons, Ltd.     

New trend of radiation application to polymer modification — irradiation in oxygen free atmosphere and at elevated temperature

Polycarbosilane (PCS) fiber as a precursor for ceramic fiber of silicon carbide was cured by electron beam (EB) irradiation under oxygen free atmosphere. Oxygen content in the cured PCS fiber was scarce and the obtained silicon carbide (SiC) fiber with low oxygen content showed high heat resistance up to 1973 K and tensile strength of 3 GPa. Also, the EB cured PCS fiber with very low oxygen content could be converted to silicon nitride (Si₃N₄) fiber by the pyrolysis in NH₃ gas atmosphere, which was the new processing to produce Si₃N₄ fiber. The process of SiC fiber synthesis was developed to the commercial plant.

The other application was the crosslinking of polytetrafluoroethylene (PTFE). PTFE, which had been recognized to be a typical chain scission polymer, could be induced to crosslinking by irradiation at the molten state in oxygen free atmosphere. The physical properties such as crystallinity, mechanical properties, etc. changed much by crosslinking, and the radiation resistance was much improved.     

“<Emphasis Type="Italic">ortho</Emphasis>-Effect” in thermal curtius rearrangement of alkylbenzoyl azides into isocyanates: A quantitative interpretation

The reasons for abnormally high reactivity of ortho-alkylbenzoyl azides in thermal Curtius rearrangement were established by the density functional method (PBE/TZ2P approximation). The key factor responsible for the rearrangement rate is the destabilization of the conjugated structure of arylacyl azide through steric effects of the ortho-substituents. Additional intramolecular hydrogen bonding, as in o-hydroxybenzoyl azide molecule, stabilizes the conjugated structure and increases the energy barrier to the reaction. Quantitative interpretation of the “ortho-effect” is given based on the dependence of the reactivity of ortho-alkylbenzoyl azides on the dihedral angle, which characterizes the extent of coplanarity of the acyl azide group and benzene ring. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 7–13, January, 2007.     

Synthesis,characterization and thermal analysis of polyaniline (PANI)/Co<Subscript>3</Subscript>O<Subscript>4</Subscript> composites

Conducting polyaniline/Cobaltosic oxide (PANI/Co₃O₄) composites were synthesized for the first time, by in situ deposition technique in the presence of hydrochloric acid (HCl) as a dopant by adding the fine grade powder (an average particle size of approximately 80 nm) of Co₃O₄ into the polymerization reaction mixture of aniline. The composites obtained were characterized by infrared spectra (IR) and X-ray diffraction (XRD). The composition and the thermal stability of the composites were investigated by TG-DTG. The results suggest that the thermal stability of the composites is higher than that of the pure PANI. The improvement in the thermal stability for the composites is attributed to the interaction between PANI and nano-Co₃O₄.     

Reactions of 3-hydroxytetrahydropyrimidin-4-ones with electrophilic reagents

The reactions of nonsubstituted or 2-aryl-substituted 3-hydroxytetrahydropyrimidin-4-ones (HTHP) with carboxylic acid chlorides, tosyl chloride, or aryl isocyanates afford mainlyN,O-diacylated,N,O-ditosylated, orN,O-diarylcarbamoylated HTHP, respectively.N,O-Diacylated HTHP are also formed in the reactions of acid chlorides with Schiff's bases based on β-aminopropionohydroxamic acid.N-Acylated HTHP can be obtained by treatingN,O-diacylated HTHP with ammonia. The reactions of 2,2-dialkyl(alkylene)-substituted HTHP with acid chlorides or phenyl isocyanate giveN,O-diacylated orN,O-diphenyl-carbamoylated β-aminopropionohydroxamic acid, respectively. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2327–2332, December, 1999.