Raman microscopy study of basic aluminum sulfate

The tridecameric aluminum polymer [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ was prepared by forced hydrolysis of Al³⁺ up to an OH/Al molar ratio of 2.2. Upon addition of sulfate the tridecamer crystallised as the monoclinic basic aluminum sulfate Na_0.1[AlO₄Al₁₂(OH)₁₂(H₂O)₁₂](SO₄)_3.55. These crystals have been studied using FT-Raman microscopy and compared to the basic aluminum nitrate, Na₂SO₄·xH₂O and Al₂(SO₄)₃·xH₂O. The Raman spectrum of basic aluminum sulfate is dominated by two broad bands which are assigned to the ₁ and ₃ bands at 981 and 1051 cm^{– 1} of the sulfate group in the Al₁₃ sulfate structure. Furthermore the band at 724 cm^{– 1} is assigned to an Al–O mode of the polymerised Al–O–Al bonds in the Al₁₃ Keggin structure. The sharp band at 1066 cm_{– 1} and the minor band at 1384 cm^{– 1} are interpreted to be due to a small amount of nitrate impurity on a different position in the structure than the nitrate present in the Al₁₃ nitrate crystal structure, based on the shift in band position of both the ₁ symmetric stretching and ₃ asymmetric stretching modes.     

Near-infrared spectroscopic study of basic aluminum sulfate and nitrate

The tridecameric Al-polymer [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ was prepared by forced hydrolysis of Al³⁺ up to an OH/Al molar ratio of 2.2. Under slow evaporation crystals were formed of Al₁₃-nitrate. Upon addition of sulfate the tridecamer crystallised as the monoclinic Al₁₃-sulfate. These crystals have been studied using near-infrared spectroscopy and compared to Al₂(SO₄)₃.16H₂O. Although the near-infrared spectra of the Al₁₃-sulfate and nitrate are very similar indicating similar crystal structures, there are minor differences related to the strength with which the crystal water molecules are bonded to the salt groups. The interaction between crystal water and nitrate is stronger than with the sulfate as reflected by the shift of the crystal water band positions from 6213, 4874 and 4553 cm^–1 for the Al₁₃ sulfate towards 5925, 4848 and 4532 cm^–1 for the nitrate. A reversed shift from 5079 and 5037 cm^–1 for the sulfate towards 5238 and 5040 cm^–1 for the nitrate for the water molecules in the Al₁₃ indicate that the nitrate-Al₁₃ bond is weakened due to the influence of the crystal water on the nitrate. The Al-OH bond in the Al₁₃ complex is not influenced by changing the salt group due to the shielding by the water molecules of the Al₁₃ complex.     

XPS study of basic aluminum sulphate and basic aluminium nitrate

Basic aluminium sulphate and nitrate crystals were prepared by forced hydrolysis of aluminium salt solution followed by precipitation with a sulphate solution or by evaporation for the basic aluminium nitrate. X-ray Photoelectron Spectroscopy (XPS) confirms the chemical composition determined by ICP-AES in earlier work. High resolution XPS scans of the individual elements allow the identification of both the central ^IVAlO₄ group and the 12 aluminium octahedra in the [^IVAlO₄Al^VI(OH)₂₄(H₂O)₁₂] building unit by two Al 2p transitions with binding energies of 73.7 and 74.2 eV in both the basic aluminium sulphate and nitrate. Four different types of oxygen atoms were identified in the basic aluminium sulphate associated with the central AlO₄, OH, H₂O and SO₄ groups in the crystal structure with transitions at 529.4, 530.1, 530.7 and 531.8 eV, respectively.     

Regularities of a variation in electrical resistance and deforming stress of ABM-1 alloy and aluminum at 77 K

A resistometric investigation of the onset of plastic flow and the regularities of strain hardening of ABM-1 alloy (Al-Be-Mg) and coarse-grained aluminum at liquid nitrogen temperature is performed. It is shown that plastic flow in the considered materials begins long before the appearance of the yield point. The established regularities of a variation in electrical resistance and deforming stress are explained by the evolution of a structural state characterized by a variation in the coefficient of dislocation interaction.Physics and Technology Institute of Low Temperatures, Academy of Sciences of the Ukraine, Kharkov, Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 3, pp. 321–324, September, 1993.     

Investigation of high-temperature plastic deformation using instrumented microindentation tests. Part IThe deformation of three aluminum alloys at 473 K to 833 K

Constant-load indentation tests were performed on wrought-2024, P/M-2024, and wrought-1100 aluminum alloys to assess the capability of the microindentation testing technique for measuring the high-temperature deformation rate controlling parameters of these alloys. The three alloys all display threshold indentation stress σ_th below which the indentation strain rate ε_ind approaches zero. The nominal inter-obstacle spacing, ℓ*, calculated from σ_th, increases with temperature in a way that is consistent with the known temperature dependence of the inter-particle spacing and dislocation cell size. The measured activation energy ΔG_o of ɛ_ind increases with temperature but remains within the range that is typical of deformation that occurs by dislocation glide limited by weak particles or dislocation/dislocation interactions. The three alloys tested show different trends of ΔG_o versus ℓ* and the trends are consistent with the known temperature dependence of the obstacles to dislocation glide. This study demonstrates that high-temperature indentation tests are sufficiently precise to detect changes in the operative deformation parameters between different alloys of the same general composition. This lays the groundwork for the use of this technique as a general tool for studying the local high-temperature deformation of a wide range of metal-based systems.     

Temperature-compensated sapphire resonator for ultra-stableoscillator capability at temperatures above 77 K

We report on the design and test of a whispering gallery sapphire resonator for which the dominant (WGH_n11) microwave mode family shows frequency-stable, compensated operation for temperatures above 77 K. The resonator makes possible a new ultra-stable oscillator (USO) capability that promises performance improvements over the best available crystal quartz oscillators in a compact cryogenic package. A mechanical compensation mechanism, enabled by the difference between copper and sapphire expansion coefficients, tunes the resonator to cancel the temperature variation of sapphire's dielectric constant. In experimental tests, the WGH₈₁₁ mode showed a frequency turnover temperature of 87 K in agreement with finite element calculations. Preliminary tests of oscillator operation show an Allan Deviation of frequency variation of 1.4-6×10^-12 for measuring times 1 s ⩽τ⩽100 s with unstabilized resonator housing temperature and a mode Q of 2×10⁶. We project a frequency stability 10^-14 for this resonator with stabilized housing temperature and with a mode Q of 10⁷     

Working with non-cryogenic Hall sensors at 77 K

In this work we show the possibility of using non-cryogenic Hall sensors at cryogenic temperatures. To avoid the instabilities at cryogenic temperatures, 9 non-cryogenic Hall sensors are connected to the different channels of a multimeter and the average measurement is obtained as the truthful value. It is demonstrated that the average value is very close to the value obtained for a cryogenic sensor and opens the possibility of using these set of sensors instead of a cryogenic single one.     

α钛合金在室温和低温的冲击韧性

为了考察Al,Sn,Zr,Mo合金元素对α钛合金在室温和77 K低温(液氮)下的缺口冲击韧性(冲击值Ak)的影响,采用示波冲击试验机测试了Ti-2Al,Ti-2Sn,Ti-2Zr和Ti-1Mo 4种α钛合金在室温和77K下的Ak值,并计算了表征其冲击韧性的弹性变形功、塑性变形功和裂纹扩展撕裂功.用扫描电镜观察了4种合金冲击试样断口的形貌.计算数据和显微组织表明,4种合金均显示韧性特征,4种合金元素对冲击韧性贡献的顺序为:Mo＞Zr＞Sn＞Al.     

Trapping and re-emission of deuterium from molybdenum following bombardment at 77 K

The re-emission of deuterium from molybdenum during 7 keV D⁺ bombardment at 77 K has been measured and this data compared with 20 keV D⁺ bombardment. Thermal desorption spectra show an increase in the number of peaks at lower temperatures as the incident ion dose is increased. The results may be interpreted by an increase in the population of trapping (damage) sites created during previous irradiations, in addition to a broadening of the range distribution to intersect the surface. This leads to a diffusion peak much wider than that normally considered for diffusive release.     

Load-carrying capacity of cylindrical high-pressure vessels at 77 and 293°K

Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Problemy Prochnosti, No. 4, pp. 63–66, April, 1988.