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Query: EC:4.1.2.42 (DTA)
 1,693 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Reaction process in the equimolar mixtures of MgO-MgNH4PO4.6H2O and MgO-NH4H2PO4 were investigated by TG-DTA and X-ray diffraction. In the MgO-MgNH4PO4.6H2O system, MgNH4PO4.6H2O was changed by heating in the following way. The formation of MgNH4PO4.H2O by dehydration about 100 degrees C and of amorphous Mg2P2O7 by dehydration and removal of NH3 above 200 degrees C and the crystallization of Mg2P2O7 above 600 degrees C. A part of the amorphous Mg2P2O7 reacted with MgO to form Mg3(PO4)2 above 600 degrees C. The crystallized Mg2P2O7 also reacted with MgO to form Mg3(PO4)2 at higher temperature. In the MgO-NH4H2PO4 system, MgNH4PO4.H2O was formed by the reaction between them, which was corresponded to an exothermic peak about 140 degrees C in the DTA curve. MgNH4PO4.H2O, an unknown phase Y and an amorphous phase were formed at 200 degrees C. The crystalline phases almost disappeared and another unknown phase X appeared at 300 degrees C. The phase X also disappeared and Mg(PO3)2 appeared at 400 degrees C. In the TG-DTA curve for this system, an exothermic peak, which was corresponded to crystallization of Mg(PO3)2, was observed about 550 degrees C and the decomposition of NH4H2PO4 ceased after the crystallization. Mg(PO3)2 reacted with MgO to form Mg2P2O7 at higher temperature.
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PMID:[Thermal behavior of phosphate-bonded investment. Part 2. Reactions in the systems of MgO-MgNH4PO4.6H2O and MgO-NH4H2PO4 (author's transl)]. 695 99

It is known that the organic molecules can provide an effective means to manipulate the surface properties of the biodegradable ceramic. There are two ways to modify the surface of the biodegradable ceramic by organic molecules. The first one is through surface adsorption but organic molecules will easily be washed out in the physiological environment. The second approach is to graft organic molecules through covalent bond to the hydroxyl groups that are available on the surface of the ceramics. Isocyanate group has been reported as a coupling agent for hydroxyapatite and organic molecule. The studies showed that the isocyanate could react with hydroxyl groups of hydroxyapatite and form a covalent bond between isocyanate and hydroxyapatite. In the study, hexamethylene diisocyanate (HMDI) was used as coupling agent and calcium hydrogenphosphate (CaHPO4, CHP) was the candidate ceramic. CHP will react with HMDI at the temperature of 20 degrees C, 30 degrees C, 40 degrees C, 50 degrees C, 60 degrees C, and 70 degrees C for 4h. Dibutyltin dilaurate and hydroquinone were used as catalyst and inhibitor, respectively. The effect of reaction temperature on the grafted yield will be described. The linkage between CHP and HMDI will be characterized by DTA, TGA, FTIR, XRD, and 31P, 13C liquid state NMR. From the results, we successfully modified the surface of CHP with coupling agent of HMDI. The grafted yield of HMDI on CHP was increasing with the reaction temperature. The best temperature for CHP modified by HMDI is around 50 degrees C. The linkage between HMDI and the surface of CHP is a urethane linkage as CHP-O-CO-NH-(CH2)6-N=C=O. After further treatment, the terminal group of CHP treated with HMDI (MCHP) will be converted into a primary amine group as the formula of CHP-O-CO-NH-(CH2)6-NH2. If reaction temperature is 60 degrees C, long extension chain will occur with a urea linkage between the isocyanate groups as the formula of CHP-O-CO-NH-(CH2)6-(NH-CO-NH-(CH2)6)n-NH2. At reaction temperature higher than 60 degrees C, the HMDI will become prepolymerized forms in solution. The prepolymerized forms such as allophanate, biuret, uretidione and urea linkage will turn the solution into gel type mixture, which will lead to low grafted yield of HMDI on CHP. When MCHP prepared at the temperature 20 degrees C, there is no evidence of long extension but the grafted yield is the lowest only 0.9 wt% around.
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PMID:A study on grafting and characterization of HMDI-modified calcium hydrogenphosphate. 1160 90

The intercalation of Co(2+), [Co(NH(3))(6)](3+), and [Co(NH(3))(5)Cl](2+) ions into layered manganese oxide (birnessite) was studied by chemical, XRD, SEM, IR, and DTA-TG analyses. The intercalation reaction progressed by a 2:1 or 3:1 ion-exchange mechanism depending on the valence of the starting ions. The oxidation state of cobalt did not change with the intercalation reaction. The intercalation of [Co(NH(3))(6)](3+) ions resulted in an increase of basal spacing from 0.716 to 0.956 nm, giving a layered structure material consisting mainly of platelike particles. The chemical analysis results showed that the structure of [Co(NH(3))(6)](3+) ions was maintained in the interlayer. On the other hand, an H(2)O/NH(3) ligand exchange reaction progressed for the intercalation of [Co(NH(3))(5)Cl](2+) ions, resulting in an increase in the basal spacing from 0.716 to 0.956 nm.
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PMID:Intercalation of cobaltammine complex ions into layered manganese oxide. 1292 72

Tungsten-promoted zirconia (WO(3)/ZrO(2)) nanoparticles were synthesized in reverse micelles of water/sodium bis(2-ethylexyl) sulfosuccinate/isooctane, which were compared with WO(3)/ZrO(2) prepared by incipient wetness impregnation and sol-gel method. The control of particle size was achieved by varying the process variables, such as water-to-surfactant molar ratio and reagent concentration. Their sizes, appearances, crystal structures, and thermochemical behavior were characterized by UV-vis, TEM, XRD and TG-DTA. NH(3)-TPD and Hammett indicator measurement were also employed to study the acidity of samples. The results revealed that samples prepared in reverse micelles had higher percentages of T-ZrO(2) and greater acid strength than those of other samples. The alkylation of butene with isobutane on WO(3)/ZrO(2) was carried out in a fixed-bed reactor. Samples synthesized in reverse micelles had better reaction performance than others. A parallel relationship could be drawn between the catalytic activity and the acid amounts as well as the acid strength of the catalysis.
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PMID:Controllable synthesis, characterization and catalytic properties of WO(3)/ZrO(2) mixed oxides nanoparticles. 1295 87

This paper reports the synthesis of high energy materials (HEMs) viz. 3,3'-diamino-4,4'-azoxyfurazan (DAAF), 3,3s'-azobis(6-amino-1,2,4,5-tetrazine) [DAAT] and 1,4-dihydrazino tetrazine (DHTz). The products obtained were characterized by IR, 1H NMR, 13C NMR and mass spectra. Thermolysis of these compounds carried out by applying TG-DTA and DSC techniques indicated that the thermal stability of DAAF and DAAT was in the temperature range of 230-250 degrees C, whereas that of DHTz was up to approximately 140 degrees C. TG-FTIR of gaseous products of these compounds suggests the evolution of NH2CN/NH3 and HCN as major decomposition products. The impact and friction sensitivity data revealed that DAAF is insensitive to mechanical stimuli whereas DAAT and DHTz are vulnerable to impact stimuli. The cyclic voltammetric studies brought out that, DAAF, DAAT and DHTz are electroactive compounds and thereby can be detected at even low concentration at pH 7 and 13. The theoretical predictions of explosive power of DAAF, DAAT and DHTz alone and their combinations with well-known insensitive high explosives using Becker-Kistiakowsky Wilson (BKW) code as well as that of propellants based on them by NASA-CEC-71 suggest their potential in specific systems.
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PMID:Synthesis, characterization and thermal studies on furazan- and tetrazine-based high energy materials. 1536 10

A mesoporous hybrid gel is prepared with tetraethoxysilane (TEOS) and bis(trimethoxysilyl)hexane (TSH) as precursors without using any templating agent. Nitrogen sorption, TG-DTA, FTIR, and point of zero charge (PZC) measurement are used to characterize the gel. The gel has a specific surface area of 695 m(2) g(-1) with a pore size of 3.5 nm, a pore volume of 0.564 cm(3) g(-1), and a point of zero charge (PZC) of 6.2. The kinetics and thermodynamics of bromophenol blue (BPB) adsorption by the gel in aqueous solution are investigated comprehensively. The effects of initial BPB concentration, pH, ionic strength, and temperature on the adsorption are investigated. Kinetic studies show that the kinetic data are well described by the pseudo-second-order kinetic model. Initial adsorption rate increases with the increase in initial BPB concentration and temperature. Adsorption activation energy is found to be 62.5-67.5 kJ mol(-1) depending on the initial BPB concentration. Internal diffusion appears to be the rate-limiting step for the adsorption process. The equilibrium adsorption amount increases with the increase in the initial BPB concentration, solution acidity, and ionic strength, but decreases with the increase in temperature. The thermodynamic analysis indicates that the adsorption is spontaneous and exothermic. The adsorption isotherms can be well described with Freundlich equation indicating the heterogeneity of the hybrid gel surface. Electrostatic and hydrophobic interactions are suggested to be the dominant mechanism for adsorption.
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PMID:Kinetics and thermodynamics of bromophenol blue adsorption by a mesoporous hybrid gel derived from tetraethoxysilane and bis(trimethoxysilyl)hexane. 1672 50

Amorphous mesoporous aluminophosphates (AlPO) with P/Al molar ratio in the range 0.8-1.15 are synthesized by using the citric acid (CA) route and are systematically characterized using N(2)-adsorption, XRD, SEM, solid-state CP-MAS NMR, FT-IR, TG-DTA, CO(2)-TPD, and NH(3)-TPD. The characterization studies show that the change in P/Al ratio could affect the structure, texture, thermal stability, and surface acid-base properties of AlPO. Samples with a relatively low P/Al ratio (< or =1.0) exhibit uniform amorphous mesoporous character and high thermal stability (up to 1173 K). Partial crystallization of the AlPO framework easily occurred on the sample with higher P/Al ratio (> or =1.1), thus leading to significant decrease of surface area and formation of particle pile mesopores. Both weak acid and weak base sites are observed over AlPO materials, and the amounts of acid-base sites can be effectively controlled by adjusting the P/Al ratio. The presence of suitable interaction between citric acid and AlPO framework is critical for the formation of mesoporous structures. Both CA and PO(4) units are considered to be ligands to coordinate with aluminum ions, forming relative uniform complexes (such as CA-Al-PO(4)) in the as-synthesized AlPO materials. The mesoporous structure of AlPO materials is obtained after the rapid decomposition of citric acid. Vapor phase selective O-methylation of catechol with methanol reaction is carried out to investigate the catalytic performances of AlPO materials with different P/Al ratios. Among them, AlP(1.1)O shows the highest activity (88.4% conversion of catechol) and the highest yield of guaiacol (74.3%). The presence of suitable weak acid-base pairs may play an important role on the title reaction.
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PMID:Thermally stable amorphous mesoporous aluminophosphates with controllable P/Al ratio: synthesis, characterization, and catalytic performance for selective O-methylation of catechol. 1692 87

The present and future relationship between the metallurgical development of new steels and the determination of second-phase compounds in these steels is emphasized on the basis of recent developments in the quantitative determination of these phases. Results of the application of DTA-EGA methods are presented as an example of this analytical approach, and the method used to measure the amounts of gases evolved from the reactions of second-phase compounds with O(2) is described in detail. The DTA-EGA method has also revealed phases that had not been found earlier in steels. Smaller amounts of second-phase compounds can be more accurately determined by this method than by any other procedure. Examples are cited for the reaction of O(2), H(2), steam, and NH(3) with second-phase compounds in the isolated residue, and the use of these reactions for the determination of second phases is discussed. A disadvantage of the DTA-EGA method is that it is dependent on the quantitative chemical separation of the second phase from the matrix steel by one of several methods. The relative merits of isolating second-phase compounds by electrochemical dissolution, by dissolution in halogen and alcohols or aliphatic esters, and by use of dilute acids are discussed in terms of their effect on the DTA-EGA determination.
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PMID:Second phases in steel. 1775 52

Nitrogen-doped nanosize TiO2 was prepared by sol-gel method with TBT and EDA as forerunner body, ethanol as solvent and glacial acetic acid as inhibitor. The crystalline structure and spectrum character were characterzed. According to the curves of differential thermal gravimetric analysis (TG/DTA), the crystal transformation temperature and the best calcining temperature of the obtained samples were determined. According to the ultraviolet-visible diffuse reflection spectrum (UV-Vis/ DRS), the spectral absorption characteristic of the obtained samples was characterized; According to the X-ray diffraction spectrum (XRD), the particle size and crystalline phase structure of the prepared samples were determined; and according to the X-ray photoelectron spectrum (XPS), the superficial composition of the prepared samples was analyzed. The relations between the red shift degree of absorption band and the proportion of EDA/TBT and calcining temperature were investigated in this experiment. The results indicate that the crystal phase of the obtained nitrogen-doped TiO2 is anatase, and the absorption band has a red shift obviously. Both the proportion of EDA/TBT and the calcining temperature have an evident effect on the spectral absorption of the prepared samples. When the mol proportion of EDA/TBT is 1 : 10 and the calcining temperature is 600 degrees C, the spectral absorption of the prepared samples is the strongest.
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PMID:[Preparation of N-doped nanosize TiO2 and spectral analysis]. 1847 25

The method co-precipitation was applied to preparation the zirconium hydroxide as a type drinking-water defluoridation adsorbent. The effect of the preparation conditions on the adsorptive capacity was studied. The optimization of preparation condition for zirconium hydroxide concludes that co-precipitation time is 10 h, pH value is 7.0, drying time is 72 h, calcination temperature is below 100 degrees C. Also, the adsorbent samples were characterized. SEM measurements reveal that zirconium hydroxide powder are constructed by several small particles, with a diameter about 20-30 microm. XRD and TG/DTA measurements show that the zirconium hydroxide samples have amorphous phase and converse to tetragonal phase when calcined at 600 degrees C. Nitrogen adsorption/desorption measurements show that samples have large surface areas of 138.4 m2/g and a 2 nm average pore size distribution in the mesopore region. The performance of zirconium hydroxide regeneration process was investigated. The results show that the regeneration techniques are very suitable to restore the fluorine-removal ability for zirconium hydroxide.
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PMID:[Preparation and characterization of zirconium hydroxide powder for fluoride adsorption]. 2082 20


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