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  • 1
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Six Certified Reference Materials of toxic elements in the concentration range of 1–2 ppm have been prepared in aqueous or HNO3 solution with the participation of fourteen laboratories in India. Various factors affecting the stability of such solutions (hydrolysis, leaching from containers, adsorption, temperature etc.) have been studied and the analytical data for these reference materials have been compiled and certified values have been assigned to them.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 8092-8095 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-resolution diffuse x-ray scattering (DXS) measurements made with a multicrystal x-ray diffractometer have been used to characterize point defect clusters produced by 90-keV and 135-keV BF+2 implantations (fluence=1×1015 cm−2). The specimens were 50-mm-diam (100) silicon single crystals (n type; 4–6 Ω cm resistivity). A highly monochromated and collimated Kα1 is obtained by three-plane (111) silicon single crystals oriented in (+,−,−) setting. The DXS intensity around 400 reciprocal lattice point was measured along [〈sx〉100〈be〉±] directions. Implantation produced a slight broadening of diffraction curves from ∼6 to ∼7 arcsec. From unimplanted regions diffuse scattering was primarily due to isolated interstitial point defects in the investigated volume of reciprocal space. Implantation was found to produce interstitial point defect clusters. Experimental data has been analyzed by using a phenomenological model for dislocation loops by using a curve fitting method. The values of loop size Rcl, volume of the loops Acl, and number of defects per loop Ncl have been determined. For implantation energies of 90 and 135 keV, these are, respectively, Rcl=1.47×10−4 and 1.29×10−4 cm, Acl=2.92×10−16 and 2.27×10−16 cm3, and Ncl=1.46×107 and 1.37×107.
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  • 3
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reactivity of primary and secondary hydroxyl groups of cellulose towards chlorotri(p-tolyl)methane in pyridine was studied in the temperature range of 60 to 100°C. The rate of reaction with the primary hydroxyl groups was found to be 43 times faster than that with the secondary hydroxyl groups of cellulose. The kinetic data showed that the reactivity of chlorotri(p-tolyl)methane towards primary hydroxyl groups of cellulose is higher than that of chlorotriphenylmethane (trityl chloride). The energies of activation for the reaction of primary and secondary hydroxyl groups of cellulose with chlorotri(p-tolyl)methane were found to be 39,6 and 43,1 kJ · mol-1, respectively. The reaction was observed to be pseudo first order.
    Additional Material: 1 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 183 (1982), S. 3003-3017 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the pyrolysis of cellulose and its derivatives (2,2-dichloropropionate and acetate) in nitrogen and air were studied by dynamic thermogravimetry and differential thermal analysis from ambient temperature to 600°C. From the resulting data various thermodynamic parameters could be obtained following the methods of Freeman and Carroll, Broido, and Dave and Chopra. The values of ΔE* for cellulose and its derivatives were found to be in the range 120 to 260 kJ · mol-1. However, the values of the free energy of activation for the degradation of cellulose and its derivatives are almost the same, i. e. 187 to 199 kJ · mol-1, indicating that the basic steps for the thermal degradation of cellulose and its derivatives are the same. Based on Scotney's work on the thermal degradation of cellulose triacetate, a mechanism for the thermal degradation of cellulose 2,2-dichloropropionate is proposed. The IR spectra of the pyrolysis residues of cellulose dichloropropionate indicate that dehydration takes place and a compound containing carbonyl groups is formed.
    Additional Material: 7 Ill.
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  • 5
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The thermal degradation of cellulose and its phosphorylated products (phosphates, diethylphosphate, and diphenylphosphate) were studied in air and nitrogen by differential thermal analysis and dynamic thermogravimetry from ambient temperature to 750°C. From the resulting data various thermodynamic parameters were obtained following the methods of Broido and Freeman and Carroll. The values of Ea for decomposition for phosphorylated cellulose were found to be in the range 55-138 kJ mol-1 in air and 85-152 kJ mol-1 in nitrogen and depended upon the percent of phosphorus contents in the samples. The mass spectrum of cellobiose phosphate indicated the absence of the molecular ion, indicating that the compound was thermally unstable. The IR spectra of the pyrolysis residues of cellulose phosphate gave indication of formation of a compound having C=O and P=O groups. A fire retardancy mechanism for the thermal degradation of cellulose phosphate has been proposed.
    Additional Material: 13 Ill.
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  • 6
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The kinetics of the thermal degradation of cellulose and modified cellulose, namely, cellulose phosphate, cellulose carbanilate, cellulose tosylate, chlorodeoxycellulose, bromodeoxycellulose, and iododeoxycellulose in air were studied by thermogravimetry and differential thermal analysis from ambient temperature to 700°C. The various thermodynamic functions for different stages of thermal degradation had been obtained following the procedure of Broido. The activation energies for the oxidative decomposition of cellulose and modified celluloses were found to be in the range 30-399 kJ mol-1. The infrared spectra of the residues of modified celluloses gave indication of formation of a compound containing P=O, P—O—P (only in the case of cellulose phosphate), C=C, and C=O groups in the final residual char. The EPR signals indicated the formation of trapped and stable free radicals in the thermal degradation of all the compounds, particularly halodeoxycelluloses showed generation of large amounts of trapped free radicals during the oxidative decomposition. Scanning electron micrographs of the thermally degraded cellulose derivatives show changes in the fibrillar structure, evolution of gasesous products, and film formation depending upon the nature of the substituent in the cellulose matrix. The mechanism of thermal degradation of these compounds has been proposed.
    Additional Material: 20 Ill.
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  • 7
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: High-resolution X-ray diffractometry, absolute integrated intensity (ρ) measurements, diffuse X-ray scattering (DXS) and infrared (IR) absorption techniques were used to investigate the influence of oxygen on the structural perfection of high purity (resistivity of the order of 4 kΩ cm) float zone (FZ) grown (111) silicon single crystals. A multicrystal diffractometer set in (+,-,-,+) geometry, with Mo Kα1 radiation, was employed. From the infrared measurements, the oxygen concentration in the sample was determined to be 1.3 × 1017 atoms cm^{-3}. High-resolution X-ray diffraction curves of the as-grown crystal had half-widths of ∼11 arcsec; the ρ value was 3.5 × 10^{-5} rad. To incorporate oxygen in a controlled manner into the specimens, they were annealed under dry oxygen ambient for 8 h in the temperature range 573–1373 K (in eight steps). Up to 723 K there was no appreciable change in oxygen content or in the degree of perfection. Annealing at temperatures (AT) 〉 873 K resulted in considerable increases in the oxygen content, as well as significant improvements in the degree of perfection. For example, as the level of oxygen increased from 1.3 × 1017 to 3.6 × 1017 atoms cm^{-3} for A_T=873 K, the values of half-widths and ρ decreased to ∼7 arcsec and 2.4 × 10^{-5} rad, respectively. However, annealing above 1273 K produced deterioration in lattice perfection. DXS measurements showed remarkable changes in the nature of point defects and their clusters with change in AT. Up to A_T=973 K, the defects were predominantly vacancy clusters. However, with AT in the range 1073–1273 K, the predominent defects were isolated interstitials. Further increase in AT led to interstitial cluster formation, which deteriorated the lattice perfection. This study clearly demonstrates that oxygen concentration in the range ∼3 × 1017 to 13 × 1017 atoms cm^{-3} leads to significant improvement in structural perfection of silicon single crystals.
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  • 8
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: High-resolution X-ray diffraction techniques have been employed successfully to evaluate crystalline quality and long-term stability of coiled membranes. The process of fabrication involves photolithography, implantation by 2 MeV N^{2+} ions in n-type GaAs substrates, followed by selective etching. A five-crystal X-ray diffractometer was employed in (+, −, +) setting with an Mo Kα1 exploring beam for high-resolution X-ray diffractometry and topography experiments. The exploring-beam width was reduced to illuminate different segments of the coiled membrane. Diffraction curves recorded from the bulk crystal surrounding the sensor had a half width of 26 arcseconds, whereas the half widths from sensor segments were in the range ∼58 to ∼166 arcseconds. Different segments (particularly vertical ones) were identified from the observed angular separations between different diffraction peaks as well as from the shape of the diffraction peaks. It was found that different segments of the sensor were tilted with respect to one another and the tilt angles were in the range 15–212 arcseconds. High-resolution X-ray diffraction topographs recorded from (5\bar 11) and (400) diffracting planes revealed that the sides of the trough below the membrane created by etching are not vertical, but tapered. Also, there is a thin strip of crystal freely hanging over the tapered regions as a result of underetching. The surface of the cavity is uneven. The structural perfection of different membrane segments could also be ascertained from the contrast in topographs.
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  • 9
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The critical dark period requirement for flowering of Impatiens balsamina L. cv. Rose, an obligate short day plant, is about 8.5 hours. While GA3 completely substituted for the dark period requirement, Phosfon prolonged it to 9.5 hours.GA3 hastened and Phosfon delayed the initiation of floral buds under all photoperiods.Floral buds opened into flowers only during 8 and 14 hour photoperiods in control and Phosfon-treated plants but during all photoperiods in GA3-treated ones.The delay in floral bud initiation and flowering was correlated with shifting up of the node bearing the first floral bud and flower respectively.While GA3 increased the numher of floral buds and flowers in all photoperiods except 8-hour, Phosfon increased their number in the 14-hour photoperiod only. The number of flowering plants decreased with increasing photoperiod regardless of GA3 and Phosfon application. The effect of Phosfon was completely or partially overcome, depending upon the photoperiod, by simultaneous application of GA3.
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  • 10
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An x-ray traverse topograph of the specimen wafer is recorded with diffracting planes nearly parallel to the straight edge. The scan is adjusted to have the image of the straight edge on one side. A projected image of the diffracting planes is also recorded on the same photographic film in the form of a stationary topograph (a sharp line) at a short distance from the traverse topograph. The angle between the image of the straight edge and the stationary topograph is measured directly. Accuracy of ±3 arcmin is achieved. A multicrystal x-ray diffractometer or a standard x-ray diffraction topography camera can be used. A few illustrative results obtained with silicon wafers are described.
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