首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Thermal behaviour of melamine   总被引:4,自引:0,他引:4  
Melamine undergoes condensation on heating with elimination of ammonia and formation of insoluble products. Thermogravimetry and infrared characterisation show that two products of successive condensation can be reproducibly obtained upon heating atT}<500 °C and then at 600 °C. Above 620 °C, the melamine condensate undergoes thermal degradation with quantitative formation of volatile products.
Zusammenfassung Melanin geht beim Erhitzen eine Kondensation unter Abgabe von Ammoniak und Bildung unlöslicher Produkte ein. Durch Thermogravimetrie und Infrarotspektroskopie wird gezeigt, daß beim Erhitzen zwei Produkte von aufeinanderfolgenden Kondensationsreaktionen beiT}<500 °C undT= 600 °C reproduzierbar erhalten werden. Oberhalb 620 °C wird das Melaminkondensat vollständig unter Bildung flüchtiger Produkte thermisch zersetzt.

. , . , 500°, — 600°. 620° .


The authors wish to thank Dr. N. Del Fanti of Mantefluos, Italy for most helpful discussion.

This work has been supported by the Consiglio Nazionale delle Ricerche through the Progetto Finalizzato Chimica Fine e Secondaria.  相似文献   

2.
From the thermal decomposition curves of riboflavin at various heating rates in static air atmosphere, the stages of thermal decomposition of this compound were established. The following kinetic parameters were calculated for the first decomposition stage of this process: activation energy (E a ), reaction order (n), preexponential factor (A) and reaction rate constant (k). A mechanism of the changes is proposed.
Zusammenfassung Die Stadien der thermischen Zersetzung von Riboflavin wurden aus den Kurven der thermischen Zersetzung in Luftatmosphäre bei verschiedenen Aufheizgeschwindigkeiten ermittelt. Für den ersten Zersetzungsschritt dieses Prozesses werden die Werte für die Aktivierungsenergie (E a ), die Reaktionsordnung (n), den präexponentiellen Faktor (A) und die Reaktionsgeschwindigkeitskonstante (k) berechnet. Für die Umwandlungen wird ein Mechanismus vorgeschlagen.

, , . , (E a ), (n), (A) (k). .
  相似文献   

3.
Voltammetric studies revealed that under transient conditions in the pH range 3.7 to 5.0, the deposition of zinc from ZnSO4 solutions involves the formation of adsorbed monovalent zinc. The conversion of divalent zinc to monovalent is a slow step. In the presence of gluconate, the reduction of divalent complex involves the monovalent zinc complex and the second electron transfer is slow. In the pH range 10 to 12.5, the zinc complex may be [(Zn(GH4)4]2- and is found to vary with gluconate and OH- ions. The conversion of [Zn(GH4)(OH)abs -] to Zn(OH)2 or Zn(GH4)2 is the slow step in the reduction of the complexes. In strong alkali solutions sodium gluconate forms zinc hydroxy gluconate complexes. [Zn(OH)3(GH4)]2- to adsorbed [Zn(OH)(GH4)]- is the slow step in the reduction.  相似文献   

4.
5.
Thermal behaviour of some minerals (kaolinite, halloysite, two montmorillonites, quartz and calcite) for different sample amounts and heating rates has been investigated using differential thermal analysis. On the basis of the DTA analysis carried out, the PA curves of each mineral have been obtained for different heating rates. These diagrams can be employed in the semiquantitative evaluation of identical substances contained in uncharacterized polymineral samples.  相似文献   

6.
A novel benzoxazine monomer (Bz-C) based on agrochemical renewable resource—cardanol (by-product of cashew nut tree, Anacardium occidentale) was synthesized. Bz-C, a liquid monomer, was used as reactive diluent for the solventless synthesis of bisphenol-A benzoxazine monomer (Bz-A). Benzoxazine monomer based on cardanol and bisphenol-A in 3:1, 1:1 and 1:3 blend ratio were prepared by this method. The resins had Brookfield viscosity at 316 K in the range of 145–81,533 mPa s. The resins were characterized by 1H-NMR, FTIR and elemental analysis. Curing characteristics were studied by DSC analysis. Thermal stability of cured resins was found to improve with increase in Bz-C content in the blends.  相似文献   

7.
Thermal decomposition characteristics of thallous perchlorate are investigated in nitrogen and in air using TG and DTA techniques. Isothermal studies at 380°, 400°, 420° and 440° in air and in nitrogen showed that the relative amounts of the decomposition products, namely, thallic oxide and thallous chloride, depend upon both the temperature and the atmosphere around the sample. At low pressures (5×10–1 mm/Hg) there is volatilization of thallous perchlorate even at 200°.
Zusammenfassung Die thermischen Zersetzungscharakteristika von Thallium(I)-perchlorate wurden in Stickstoff und in Luft unter Anwendung der TG- und DTA-Techniken untersucht. Isotherme Studien bei 380°, 400°, 420° und 440° in Luft und in Stickstoff zeigten, daß die relativen Mengen der Zersetzungsprodukte, Thallium(III)oxid und Thallium(I) Chlorid, sowohl von der Temperatur als auch von der das Muster umgebenden Atmosphäre abhängen. Bei niedrigen Drücken (5×10–1 mm/Hg) verflüchtigt sich Thallium(I)perchlorat bei 200°.

Résumé On a étudié par TG et ATD les caractéristiques de la décomposition thermique du perchlorate de thallium(I) dans l'azote et dans l'air. Des études isothermes à 380, 400, 420 et 440°C dans l'air et dans l'azote ont montré que les taux relatifs de produits de décomposition, c'est-à-dire l'oxyde de thallium(III) et le chlorure de thallium(I), dépendent de la température ainsi que de l'atmosphère autour de l'échantillon. Sous faible pression (5 · 10–1 torr) le perchlorure de thallium(I) se volatilise même à 200°.

. , 380°, 400°, 420°, 440° , , , , , . (5 · 10–1 . .) 200°.


One of us (A.S.G.) is thankful to the Council of Scientific and Industrial Research, India for the award of a fellowship.  相似文献   

8.
9.
10.
The purpose of this work was to investigate the effect of several factors (anion type in the copper salt, pH and concentration of the salt solution) on the structure and thermo-oxidative degradation of the polyacrylamidoxime-copper chelates, by using elemental analysis, IR spectroscopy and dynamic thermogravimetry. The chelates containing copper ions as sulphate exhibit a better initial thermal stability than the polyacrylamidoxime fibre presumably due to the crosslinking generated by the intermolecular complexation of the ions; the removal of the sulphate anions takes place concomitantly with the second step of polymeric chain decomposition. The initial thermal decomposition of the chelates formed by copper ions as nitrate begins at lower temperatures as compared to the polyacrylamidoxime fibre, probably by the nitrate anion release, which partly overlaps the initial decomposition of the copper ion-crosslinked polymeric chains. Copper ions as either sulphate or nitrate catalyse the reactions involved in the main step of polyacrylamidoxime fibre decomposition; the higher the copper amount, the stronger the catalytic effect.  相似文献   

11.
Fourier-transform infrared (FTIR) spectroscopy has been applied in combination with wide-angle X-ray diffraction and measurements of strength, fluidity, yellowness, birefringence, and moisture regain to detect microstructural changes in lyocell fibres, a regenerated cellulose fibre, subjected to direct heat and annealing treatments. TMA, and SEM were used to show the effect of direct heat and annealing on lyocell fibres. The FTIR spectroscopy results show that a decrease in intermolecular hydrogen bonding occurs at 70 and 80 °C for annealed and directly heated samples, respectively. The results demonstrate increase of the intensity of O–H stretching vibrations, this associated with hydrogen bonds reforming around 130 °C. Lyocell fibres shrink with direct heating in the temperature range 130–160 °C. The crystallinity decreases gradually with increasing temperature. There is no significant change in colour of the samples annealed up to 150 °C. A continuous increase in the fluidity occurs for the annealed samples in the range 150–230 °C. The tenacity and breaking extension of heated samples decrease with increasing temperature. The lower annealing temperatures cause no observable change in the smooth and void-free surface, but in the annealing temperature range 170–230 °C, substantial non-uniformity is apparent on the surface of the fibres.  相似文献   

12.
A derivatograph was used to follow the modification of the skeleton structure and thermal stability of zeolites in sodium and ammonium forms. Analogous investigations were carried out by independent methods such as IR and X-ray. Comparison showed good agreement between the results. The controlled dealumination of the Y-type zeolite enhanced the thermal stability  相似文献   

13.
The thermal decomposition under argon of the boracites M3B7O13X (M=divalent metal ion, X=halogen ion or OH?) has been studied by thermogravimetry (TG) and differential thermal analysis (DTA) for the compositions MgCl, MgOH, CrC1, CrBr, CrI, MnCl, MnBr, MnI, FeCl, FeBr, FeI, CoCl, CoBr, CoI, NiCl, NiBr, NiI, CuCl, CuBr, ZnCl, ZnBr, ZnI, CdCl, CdBr and CdI. The lithium boracites Li4B 7O12X, with XCl and Br, have also been studied. The stability of the boracites systematically decreases in the order MCI>MBr>MI. The most stable boracite is CrCl (1% weight loss at 1242°C) and the least stable one studied here is MgOH (1% weight loss at 717°C).  相似文献   

14.
Thermal behaviour of natural vermiculite (Santa Olalla, Huelva, Spain) was investigated by TG, DTA, emanation thermal analysis (ETA) and high temperature XRD on heating in the temperature range from 30 to 1100°C before and after vibratory mill grinding. Microstructure changes of natural and ground vermiculite samples were characterized by using ETA under in situ conditions of heating. By comparing the ETA and XRD results it was demonstrated that a decrease of radon release rate measured by ETA characterized the decrease in the interlayer spacing of the vermiculite samples that followed the dehydration. Dedicated to the memory of Professor Dr. Ferenc Paulik who passed away on October 12, 2005.  相似文献   

15.
Thermal decomposition of zinc carbonate hydroxide   总被引:3,自引:0,他引:3  
This study is devoted to the thermal decomposition of two zinc carbonate hydroxide samples up to 400 °C. Thermogravimetric analysis (TGA), boat experiments and differential scanning calorimetry (DSC) measurements were used to follow the decomposition reactions. The initial samples and the solid decomposition products were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and laser particle size analyzer. Results showed that zinc carbonate hydroxide decomposition started at about 150 °C and the rate of decomposition became significant at temperatures higher than 200 °C. The apparent activation energies (Ea) in the temperature range 150–240 °C for these two samples were 132 and 153 kJ/mol. The XRD analyses of the intermediately decomposed samples and the DSC results up to 400 °C suggested a single-step decomposition of zinc carbonate hydroxide to zinc oxide with not much change in their overall morphologies.  相似文献   

16.
The isothermal decomposition of zinc hydroxy azides, Zn(OH)2-x(N3)x: follows deceleratory kinetics throughout the temperature range studied. The initial part of the decomposition fits into unimolecular decay law, log (1-a) = -kt. The contracting volume law satisfactorily describes the data at higher degrees of decomposition. The maximum value ofa upto which the slow decomposition could be recorded was 0.75. The aged form of zinc hydroxy azide decomposes with much lower rates and slightly different topochemical characteristics. The decrease in the rate of decomposition on ageing has been attributed to the formation of carbonate on the surface of the compound during storage. The change in topochemical behaviour is traced to the reported layer structure of zinc hydroxy azide. The effect of pre-heating on subsequent thermal decomposition has also been discussed.  相似文献   

17.
18.
Summary Zinc may be determined polarographically in acetate buffered solutions of PH 4 to 5.6.
Zusammenfassung Die polarographische Bestimmung von Zink ist möglich in mit Acetat gepufferten Lösungen vom PH 4 bis 5,6.

Résumé On peut doser le zinc par polarographie dans des solutions de pH 4 à 5,6 tamponnées à l'acétate.
  相似文献   

19.
PEEK is characterised by high impact and fatigue resistance andT g of 145C. Blends of PEEK and PEI have been made and scanning electron micro-graphs of the broken specimen show that the two polymers are completely miscible in all proportions. The study also shows that PEEKPEI 5050 blend, can be used as matrix for composite applications with appreciable enhancement ofT g to 177C.  相似文献   

20.
《Liquid crystals》2000,27(8):1029-1033
We have investigated the electro-optical performance of switchable nematic emulsions as a function of temperature. The electro-optical properties of nematic emulsions are highly dependent on temperature because several parameters such as droplet size, number density, viscosity, surface free energy, elastic constant, refractive indices, dielectric anisotropy, and liquid crystal/monomer solubility are affected by temperature. In particular, both ON state transmittances and decay times show a decreasing behaviour with increasing temperature. On the contrary, the OFF state transmittances increase, and the rise times do not change in an appreciable way.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号