Search Results
Summary Two hydrated and aged cement pastes from India (NCB), w/c=0.4, of a similar chemical composition but of a different specific surface and different strength (OPC, C-33 and C-43), hydrated at w/c=0.4 for 1 month, were studied by XRD after 1 year and 5-6 year ageing on contact with air. They were tested by static heating (SH) in fresh state, and by DTA/DTG/TG, IR and mass spectrometry (MS), after ageing, presented elsewhere. The main XRD peaks of (i) portlandite were decreasing with T and disappearing about 450°C, (ii) calcite peak at room T was small and broad, it increased gradually, especially after portlandite disappearance; above 600°C it was lowered and it was lost above 700°C. Important variation in the d(001) of portlandite with ageing was observed, exceeding the standard value of d(001)=4.895 Å (72-0156). It was higher in the paste C-33 (4.925-4.936 Å), containing more carbonates, than in the paste C-43 (4.916-4.927 Å). Small variations only were found in the value of d(101), i.e. 2.627-2.635 Å (nominally 2.622 Å), whereas the d(104) of calcite could be used as internal standard and other calcium carbonates (vaterite and aragonite) showed a small variation only. The increase ind(hkl) with temperature was straight linear (in portlandite ?d(001)=0.095 Å, at 30-400°C) and the thermal expansion coefficient estimated thereform was high (4.75-4.95·10-5 K-1). Close to the T of decomposition the ?d/?T became steeper. The thermal variation of d(104)=3.035 Å of calcite (?d=0.015 Å at 30-400°C) was smaller than that ofd(101) of portlandite (?d=0.025 Å at 30-400°C) and was similar in C-33 and C-43. The thermal expansion coefficient was 1.54 10-5 K-1, thus higher than the reported aa=0.65·10-5 K-1.
Abstract
Sintering processes in the Y2O3–Al2O3–B2 O3 system and its subsystems (Y2O3–B2O3 and Al2 O3–B2O3) have been investigated by using combined DTA and XRD measurements to get a better understanding of solid state chemical changes resulting in the formation of yttrium aluminum borate (YAl3(BO3)4, YAB) phase and to study the possible role and contribution of various simple borates formed also in the former processes. Two new exothermic heat effects of YBO3 formation have been detected by DTA in the Y2O3–B2O3 system between 720 and 980C. In the Al2O3–B2O3 system a new experimental XRD profile of Al4B2O9 was observed. Formation of these borates seems to promote the nucleation of double borate YAB below 1000C. Conversion of Al4B2O9 to Al18B4 O33 was observed after a long term (10 h) sintering at 1050C. Similarly, an increased formation of YAB has been observed as a product of the sintering reaction between YBO3 and Al18B4O33 at 1150C. The two latter single borates are found to be identical with the high temperature decomposition products of YAB.
Abstract
Nifedipine complexes with β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD), 2-hydroxypropyl-β-cyclodextrin (2HP-β-CD), randomly methylated-β-cyclodextrin (RM-β-CD) and heptakis(2,6-O-dimethyl)-β-cyclodextrin (DM-β-CD) have been prepared by both kneading and heating methods and their behaviour studied by differential scanning calorimetry (DSC), diffuse reflectance mid-infrared spectroscopy (FTIR) and X-ray diffractometry (XRD). DSC revealed the nifedipine melting endotherm with onset at approximately 171°C for the kneaded mixtures with β-CD, γ-CD and 2HP-β-CD, thus confirming the presence of nifedipine in the crystalline state, while some decrease in crystallinity was observed in the DM-β-CD kneaded mixture. With RM-β-CD, however, broadening and shifting of the nifedipine endotherm and reduction in its intensity suggested that the kneading could have produced an amorphous inclusion complex. These differing extents of interaction of nifedipine with the cyclodextrins were confirmed by FTIR and XRD studies.
Abstract
We studied the removal process of excessive free carbon in the nano-SiC powder by TG-DTA-MS, XRD and TEM three methods. The studies showed that the temperature of removing excessive free carbon in the nano-SiC powder should be about 750°C in air.
Abstract
Emanation thermal analysis (ETA), thermogravimetry, DTA and XRD were used in thermal characterization of natural vermiculite (Santa Olalla, Huelva, Spain) and of Na+- and - exchanged vermiculite samples during heating in air in the range 25-1100C. A good agreement between the results of these methods was found. Changes in the radon release rate measured by ETA, which reflected the decrease and collapse of the interlayer space after the release of water as well as the formation of new crystalline phases were evaluated using a mathematical model. The model used for the evaluation was found suitable for the quantitative characterization of microstructure changes during in situ conditions of heating of vermiculite samples.
Abstract
The effect of magnesium bromide hexahydrate [MgBr2·6H2O] as a nondurable finish on the flammability of 100% cotton fabric, (woven construction, massing 150 g m−2) has been investigated. The laundered bone-dried, massed fabrics were impregnated with various concentrations of the aqueous above-mentioned salt solutions by means of squeeze rolls and drying in an oven at 110°C for 30 min. The specimens were then cooled in a desiccator, re-massed with an analytical balance and kept under standard conditions before the fulfillment of the vertical flame spread test. After several experiments the optimum add-on values to impart flame-retardancy expressed in g anhydrous magnesium bromide hexahydrate per 100 g fabric were determined to be about 5.6%. The ashes of the treated specimens were subjected to X-ray diffraction analysis (XRD), and the result was compared with data for pure MgO powder and/or MgBr2 specimens. Consequently the existence of MgO was detected in the ashes.
Abstract
Metal carboxylato-hydrazinates are very good precursors for the synthesis of metal as well as mixed metal oxides as these decompose to nanosized oxides with high surface area most of the times at comparatively lower temperatures. In the present study one such novel precursor nickel manganese fumarato-hydrazinate (NiMn2(C4H2O4)3·6N2H4) has been prepared and characterized by XRD, FTIR and chemical analysis. The thermal decomposition of the precursor has also been studied by isothermal, differential thermal and thermogravimetric analysis. The precursor shows two-step dehydrazination followed by decarboxylation to form NiMn2O4. The infrared spectra show N-N stretching frequency at 965 cm−1, which confirm the bidentate bridging hydrazine. XRD confirms the formation of single phase NiMn2O4.
Abstract
The swelling properties of Al-pillared clays, obtained from five different smectites, were studied using X-ray diffraction. These clays, the dioctahedral beidellite and montmorillonite and the trioctahedral saponite, hectorite and laponite differ in source of isomorphic substitution and represent a series of decreasing basicity along the siloxane plane. An Al oxyhydroxy cation was inserted between the layers to form the respective pillared clays and these clays were heated incrementally to 600°C. The XRD peaks at each stage of heating were recorded as well as the same samples subsequently wetted. Basal spacings of each clay at each stage of dehydration ↭d rehydration indicated that the swelling of tetrahedrally substituted saponite and beidellite was indeed restricted, compared with the other three clays. This was attributed to greater basicity of the oxygen plane of beidellite and saponite due to tetrahedral substitution of Si by Al, resulting in an increase in the strength of hydrogen bonds between either water or the interlayer polyhydroxy cation and the clay. The data from the XRD analyses helped in addition, to clarify the thermal transformations of the Keggin ion itself. According to the changes in thed-spacings of the pillared clays it was concluded that the Keggin ion lost its structural water at ∼200°C and dehydroxylated in a range beginning at 350°C. Between 500 to 600°C this polymer cation, which is thought to form the Al2O3 oxide, did not rehydrate.
Abstract
Galena is the principal ore mineral for lead industry and the production of lead and its alloys. The industrial processing of galena includes its oxidized roasting to lead oxide, followed by reduction smelting of lead oxide agglomerate with coke in the blast furnace to commercial lead. The present work reports a thermal analysis study of oxidized roasting of Egyptian galena using a derivatograph. The reaction products were identified microscopically and by using a Siemens Crystalloflex diffractometer. On roasting of galena (heating in the air flow), its oxidation to lead sulphate was shown by a wide and small exothermic DTA peak at 460C. The reaction between galena and lead sulphate, produced PbSO4PbO at 580C, is shown by a small exothermic peak. A large and sharp exothermic tripple maximum at 730, 740 and 765C was due to the intensive oxidation of galena, accompanied by an increase in mass (TG). This mass increase is attributed to the formation of different sulphates. The mass loss is observed at temperature higher than 900C due to the dissociation of the sulphates to lead oxide and evolution of sulphur dioxide. The standard free energy (ΔG) and equilibrium constant (K) of the reaction of oxidation of galena to lead oxide at 800C are –167.102 kcal mol–1 and 1.091034, respectively. These values reflect the irreversibility of the reaction. The products of the oxidized roasting of galena are different, depending upon the temperature of roasting such as anglesite at 300C, basic lead sulphates of specified compositions: (PbSO4PbO at 600C, PbSO42PbO at 800C and PbSO44PbO at 900C) and lead oxide at 1000C.
Powder XRD pattern of the DGCC single crystals Table 1 2θ, d , hkl , Height of the peak, area of the peak and FWHM of DGCC crystals
