THE HYDRATION OF THE ALUMINATES OF CALCIUM: V. THE HYDROTHERMAL DECOMPOSITION PRODUCTS OF TRICALCIUM ALUMINATE AT 350 °C.

1943 ◽  
Vol 21b (11) ◽  
pp. 236-246 ◽  
Author(s):  
Herbert Johnson ◽  
Thorbergur Thorvaldson
Keyword(s):  
Calcium Hydroxide ◽  
Saturated Steam ◽  
Rectangular Plates ◽  
Hydrated Alumina ◽  
Decomposition Products ◽  
Factors Affecting ◽  
X Ray ◽  
Crystalline Product ◽  
Tricalcium Aluminate ◽  
Lower Temperature

When tricalcium aluminate is treated in saturated steam at 350 °C. hydrolysis occurs with the formation of a crystalline product of the composition 4CaO.3Al2O3.3H2O and calcium hydroxide. The same products result when a 3:1 mixture of calcium hydroxide and hydrated alumina are similarly treated. The calcium hydroxide as well as any hexahydrate of tricalcium aluminate formed at lower temperature may be removed from the hydrothermal product by extraction with a solution of acetic acid buffered with calcium acetate.The 4:3:3 calcium hydroaluminate crystallizes in colourless elongated rectangular plates with parallel extinction, positive elongation, and low birefrigence. The average refractive index is close to 1.627 and the density 2.71 (at 20 °C). The crystals are probably orthorhombic.Appreciable dehydration of the product does not occur on heating below 475° to 500 °C. Dehydration between 650° and 750 °C. in a stream of dry air appears to produce decomposition with the liberation of free alumina and probable formation of the product 12Ca0.7Al2O3.The factors affecting the yield of the 4:3:3 calcium hydroaluminate and the mechanism of the hydrothermal reactions of tricalcium aluminate and its hydrates are discussed. Readings of X-ray powder patterns of the 4:3:3 hydroaluminate and its dehydration products are given.

THE HYDRATION OF THE ALUMINATES OF CALCIUM: IV. HYDROTHERMAL REACTIONS OF TRICALCIUM ALUMINATE AND ITS HYDRATES

1943 ◽  
Vol 21b (4) ◽  
pp. 65-72 ◽  
Author(s):  
G. M. Harris ◽  
W. G. Schneider ◽  
T. Thorvaldson
Keyword(s):  
Calcium Hydroxide ◽  
Rectangular Plate ◽  
Hydrothermal Treatment ◽  
Saturated Steam ◽  
Partial Hydrolysis ◽  
Portland Cement Concrete ◽  
Steam Curing ◽  
Hydrated Alumina ◽  
Hydrothermal Reactions ◽  
Tricalcium Aluminate

A study was made of the hydrothermal reactions of tricalcium aluminate and its hydrates between 120° and 350 °C. Homogeneous samples of the hexahydrate of tricalcium aluminate may be prepared by treatment of the aluminate or its hexagonal hydrate in saturated steam at temperatures up to 150 °C. At temperatures of 250 °C. and above, under conditions favouring rapid hydrolysis, such as the addition of water to the anhydrous aluminate or hydroaluminate before autoclaving and rapid elevation of the temperature of the autoclave, crystals of calcium hvdroxide and of a hydroaluminate of lower lime–alumina ratio appear, usually mixed with the isometric hexahydrate. The new hydroaluminate occurs as rectangular, elongated, prismatic plates of low birefringence, refractive index 1.627, and has a lime–alumina ratio probably lower than 1.5. The hexagonal hydrate of tricalcium aluminate gives on hydrothermal treatment a better yield of the low-limed hydroaluminate than does the anhydrous aluminate. Only partial hydrolysis of the hexahydrate was obtained under any of the conditions used, but the hexagonal hydrate, autoclaved for 12 hr. at 350 °C., gave products composed almost entirely of the rectangular plate hydroaluminate and calcium hydroxide. No free hydrated alumina was found in the hydrothermal products.The rectangular plate hydroaluminate of calcium may also be prepared by the action of calcium hydroxide on hydrated alumina in saturated steam at 350 °C. It is therefore a stable product under those conditions.At temperatures below 250 °C. birefringent crystalline material is also formed on autoclaving tricalcium aluminate or its hydrates under conditions favouring hydrolysis. The experimental evidence indicates that one of the products is the birefringent calcium hydroaluminate formed on autoclaving the lower calcium aluminates at temperatures of 105 to 150 °C. (5).Precast Portland cement concrete products, when subjected to steam-curing, normally contain an excess of water, and the conditions for the formation of these birefringent hydroaluminates of calcium are therefore present. The same applies to the commercial steam-curing of other materials containing free lime and hydrated alumina. The formation of these hydroaluminates may explain the peculiar effect on the tensile and compressive strength of mortar and concrete test pieces produced by hydrothermal treatment at temperatures above 150 °C. (9).

THE HYDRATION OF THE ALUMINATES OF CALCIUM: III. THE HYDRATION OF THE 5:3, 1:1, AND 3:5 CALCIUM ALUMINATES

1943 ◽  
Vol 21b (2) ◽  
pp. 34-42 ◽  
Author(s):  
W. G. Schneider ◽  
T. Thorvaldson
Keyword(s):  
Refractive Index ◽  
Water Absorption ◽  
Anisotropic Material ◽  
Quantitative Estimation ◽  
Saturated Steam ◽  
Hydrated Alumina ◽  
Tricalcium Aluminate ◽  
Calcium Aluminates ◽  
End Products ◽  
Rapid Hydrolysis

The hydration of the aluminates of calcium in saturated steam at 150° and 105 °C. was studied. A method was developed for the quantitative estimation of chemically combined and free hydrated alumina in steam treated mixtures. The rates of hydration at 150 °C. of all the aluminates of calcium were compared. At 150 °C., when conditions favouring- rapid hydrolysis are avoided, the 1:1 and 3:5 lime aluminates are apparently transformed almost quantitatively to the cubic hexahydrate of tricalcium aluminate and hydrated alumina approaching the composition of the monohydrate. The steam treated 5:3 lime aluminate gives lower water absorption and higher content of combined alumina than called for by the above end-products, indicating the formation of a less highly hydrated aluminate of lower lime–alumina ratio than the hexahydrate of tricalcium aluminate. This conclusion is supported by the presence in this product of some anisotropic material with an average refractive index of 1.58. The hydrothermal products obtained on treatment of the three aluminates at 105 °C. all contained larger amounts of this birefringent material and apparently a greater proportion of combined alumina.

Influence of Activating Compounds on Oxidation Mechanisms of Aluminum Powders

2005 ◽  
Vol 896 ◽  
Author(s):  
Curtis Johnson ◽  
Timothy J. Foley ◽  
Kelvin T. Higa
Keyword(s):  
Thermogravimetric Analysis ◽  
Variable Temperature ◽  
Air Oxidation ◽  
Aluminum Powders ◽  
X Ray ◽  
Crystalline Product ◽  
Oxide Phases ◽  
Lower Temperature ◽  
Alpha Alumina ◽  
Oxidation Mechanisms

AbstractThis study involves an investigation of the mechanism underlying activating effects of inorganic additives on the oxidation of aluminum. The oxidation of nano aluminum powders in air was characterized by variable temperature x-ray powder diffraction and thermogravimetric analysis. For a 33-nm aluminum powder the aluminum oxide produced by air oxidation was poorly crystallized until the sample was heated to above 1050°C, where the alpha-alumina phase crystallized. For a mixture of the aluminum with cryolite, crystallization of oxide phases is enhanced, with Na-Al-O phases evident at 550°C and above. Fluorine is lost from the sample between 550 and 850°C, presumably due to reaction with moisture to produce HF. In a similar experiment with aluminum and silver molybdate, the only crystalline product was alpha-alumina, which was observed at 550°C and higher. The general result is that alpha-alumina, the ultimate product in most cases, crystallized at a lower temperature when activating agents were present.

THE HYDRATION OF DICALCIUM SILICATE AND TRICALCIUM SILICATE

1936 ◽  
Vol 14b (1) ◽  
pp. 20-30 ◽  
Author(s):  
N. B. Keevil ◽  
T. Thorvaldson
Keyword(s):  
Calcium Hydroxide ◽  
Tricalcium Silicate ◽  
Dicalcium Silicate ◽  
Crystalline Hydrate ◽  
Saturated Steam ◽  
Partial Hydrolysis ◽  
Hydration Products ◽  
X Ray Diffraction ◽  
Constant Weight ◽  
X Ray

Samples of β-dicalcium silicate, γ-dicalcium silicate, tricalcium silicate, hillebrandite and dehydrated hillebrandite were exposed to saturated steam at temperatures between 50° and 375 °C. After drying to constant weight (usually over calcium oxide) the increase in weight and the amount of free calcium hydroxide were determined. Microscopic examinations and X-ray diffraction patterns of the products were made. The hydration products were then dehydrated and similar studies of the products made. The hydrolysis of the hydration products also was studied.It was found that between 110° and 350 °C. β- and γ-dicalcium silicates may absorb water without hydrolysis to form three crystalline products. Two of these are identical with products already described (20); the third product appears to possess another characteristic crystalline structure as shown by the X-ray pattern, but to have a variable water content with a limiting composition of 2CaO∙SiO2∙H2O. The hydration product may be dehydrated without the liberation of lime.When conditions favoring hydrolyses are avoided, tricalcium silicate hydrates directly to a crystalline hydrate which probably has the limiting composition, 3CaO∙SiO2∙2H2O, although products holding from 1.3 to 2 moles of water give the same X-ray diffraction pattern. When the conditions favor partial hydrolysis, tricalcium silicate decomposes into calcium hydroxide and crystalline hydrated dicalcium silicate. Dehydration of hydrated tricalcium silicate gives one mole of lime along with dicalcium silicate.Hillebrandite exposed to saturated steam at 160 °C. remained unchanged while a sample of dehydrated hillebrandite on hydration gave a product similar to that obtained from β-dicalcium silicate.When treated with a large excess of water, the hydrated silicates hydrolyze to the same extent as the anhydrous silicates, but the final equilibrium is attained more rapidly, especially in the case of hydrated dicalcium silicate.

THE ACTION OF SATURATED STEAM ON DICALCIUM FERRITE AND ON TETRACALCIUM ALUMINOFERRITE

1937 ◽  
Vol 15b (8) ◽  
pp. 331-339
Author(s):  
D. T. Mather ◽  
T. Thorvaldson
Keyword(s):  
Calcium Hydroxide ◽  
Ferric Oxide ◽  
Prolonged Exposure ◽  
Saturated Steam ◽  
X Ray Diffraction ◽  
Similar Treatment ◽  
Rapid Action ◽  
Tricalcium Aluminate ◽  
Water Of Hydration ◽  
Diffraction Patterns

The reactions which occur when dicalcium ferrite and tetracalcium alumino-ferrite are exposed to saturated steam at temperatures between 100° and 300 °C. were studied by determining the water absorbed and the optical properties and X-ray diffraction patterns of the products. The hydration of the probable products of decomposition under the same conditions was also studied. The main results were as follows:Precipitated alumina, treated between 170° and 350 °C. and then dried over calcium oxide or "dehydrite" at 21 °C., gives a monohydrate of alumina. The product is the same whether the initial alumina contains excess combined water or has been dehydrated at any temperature below about 920 °C. On similar treatment between 100° and 170 °C. precipitated ferric oxide loses its water of hydration, giving a material with the crystalline structure of hematite. Tricalcium aluminate at temperatures between 150° and 300 °C. forms the isometric hexahydrate.On prolonged exposure between 100° and 300 °C, dicalcium ferrite is completely decomposed to calcium hydroxide and ferric oxide (hematite). The first step appears to be a rapid direct hydration of the dicalcium ferrite to a dihydrate, followed by a rapid liberation of one mole of calcium hydroxide. Then follows a slow decomposition of the hydrated monocalcium ferrite with the formation of hematite.Similar treatment of tetracalcium aluminoferrite at temperatures from 100° to 300 °C. gives as final products the hexahydrate of tricalcium aluminate, calcium hydroxide, and ferric oxide (hematite). Here again a very rapid action appears to take place, producing the hexahydrate of tricalcium aluminate and hydrated monocalcium ferrite, the latter product then decomposing slowly to calcium hydroxide and ferric oxide as in the case of the dicalcium ferrite.

scholarly journals Urca nuclide production in Type-I X-ray bursts and implications for nuclear physics studies

2020 ◽  
Vol 500 (3) ◽  
pp. 2958-2968
Author(s):  
Grant Merz ◽  
Zach Meisel
Keyword(s):  
Light Curve ◽  
Nuclear Reaction ◽  
Nuclear Physics ◽  
Thermal Structure ◽  
Reaction Rates ◽  
High Mass ◽  
Type I ◽  
Model Calculations ◽  
X Ray ◽  
Lower Temperature

ABSTRACT The thermal structure of accreting neutron stars is affected by the presence of urca nuclei in the neutron star crust. Nuclear isobars harbouring urca nuclides can be produced in the ashes of Type I X-ray bursts, but the details of their production have not yet been explored. Using the code MESA, we investigate urca nuclide production in a one-dimensional model of Type I X-ray bursts using astrophysical conditions thought to resemble the source GS 1826-24. We find that high-mass (A ≥ 55) urca nuclei are primarily produced late in the X-ray burst, during hydrogen-burning freeze-out that corresponds to the tail of the burst light curve. The ∼0.4–0.6 GK temperature relevant for the nucleosynthesis of these urca nuclides is much lower than the ∼1 GK temperature most relevant for X-ray burst light curve impacts by nuclear reaction rates involving high-mass nuclides. The latter temperature is often assumed for nuclear physics studies. Therefore, our findings alter the excitation energy range of interest in compound nuclei for nuclear physics studies of urca nuclide production. We demonstrate that for some cases this will need to be considered in planning for nuclear physics experiments. Additionally, we show that the lower temperature range for urca nuclide production explains why variations of some nuclear reaction rates in model calculations impacts the burst light curve but not local features of the burst ashes.

scholarly journals Transport and Dielectric Properties of Mechanosynthesized La2/3Cu3Ti4O12 Ceramics

Crystals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 313
Author(s):  
Mohamad M. Ahmad ◽  
Hicham Mahfoz Kotb ◽  
Celin Joseph ◽  
Shalendra Kumar ◽  
Adil Alshoaibi
Keyword(s):  
Dielectric Constant ◽  
Sintering Temperature ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Boundary Conductivity ◽  
X Ray ◽  
Giant Dielectric ◽  
Mechanochemical Milling ◽  
Giant Dielectric Constant ◽  
Lower Temperature

La2/3Cu3Ti4O12 (LCTO) powder has been synthesized by the mechanochemical milling technique. The pelletized powder was conventionally sintered for 10 h at a temperature range of 975–1025 °C, which is a lower temperature process compared to the standard solid-state reaction. X-ray diffraction analysis revealed a cubic phase for the current LCTO ceramics. The grain size of the sintered ceramics was found to increase from 1.5 ± 0.5 to 2.3 ± 0.5 μm with an increase in sintering temperature from 975 to 1025 °C. The impedance results show that the grain conductivity is more than three orders of magnitude larger than the grain boundary conductivity for LCTO ceramics. All the samples showed a giant dielectric constant (1.7 × 103–3.4 × 103) and dielectric loss (0.09–0.17) at 300 K and 10 kHz. The giant dielectric constant of the current samples was attributed to the effect of internal barrier layer capacitances due to their electrically inhomogeneous structure.

Pediatric Minor Head Trauma: Factors Affecting the Anxiety of Parents

2021 ◽  
pp. 000992282110096
Author(s):  
Hasan Aldinc ◽  
Cem Gun ◽  
Serpil Yaylaci ◽  
Erol Barbur
Keyword(s):  
Computed Tomography ◽  
Head Trauma ◽  
Pediatric Patients ◽  
Positive Impact ◽  
Cranial Computed Tomography ◽  
Sufficient Information ◽  
Minor Head Trauma ◽  
Computed Tomography Imaging ◽  
Factors Affecting ◽  
X Ray

Managing the anxiety of the parents of pediatric patients with head trauma is challenging. This study aimed to examine the factors that affect anxiety levels of parents whose children were admitted to the emergency department with minor head trauma. In this prospective study, the parents of 663 consecutive pediatric patients were invited to answer a questionnaire. Parents of 600 children participated in the study. The parents who believed they were provided sufficient information and who were satisfied with the service received had significantly more improvement in anxiety-related questions. Cranial X-ray assessment had a significantly positive impact on the anxiety of the parents, whereas cranial computed tomography and neurosurgery consultation did not. In assessing pediatric minor head trauma, cranial computed tomography imaging and neurosurgery consultation should not be expected to relieve the anxiety of the parents. However, adequately informing them and providing satisfaction are the factors that could lead to improvement.

Diffusivity, Solubility and Speciation of Sulphur in Silicate Melts

2006 ◽  
Vol 46 ◽  
pp. 93-97 ◽  
Author(s):  
J. Stelling ◽  
Harald Behrens ◽  
Joachim Deubener ◽  
Stefan Mangold ◽  
Joerg Goettlicher
Keyword(s):  
High Temperature ◽  
Electron Microprobe ◽  
Industrial Production ◽  
Silicate Melts ◽  
Viscosity Data ◽  
Decomposition Products ◽  
X Ray ◽  
Diffusion Couple Technique ◽  
X Ray Absorption ◽  
Diffusion Profiles

Diffusion and solubility of sulphur have important effects on the degassing of silicate melts. Both properties are closely related to the structural incorporation of sulphur in the melt. Depending on the oxygen fugacity, sulphur can be present as sulphide (S2-), sulphite (S4+) or sulphate (S6+). Sulphates play an important role in the industrial production of glasses especially in the fining process. The decomposition products of sulphate amass in bubbles which ascend and homogenize the melt. Structural incorporation of sulphur in glasses is studied by XANES (X-ray Absorption Near Edge Spectroscopy). Diffusion of sulphur is investigated in simple silicate systems using the diffusion couple technique. First diffusion profiles were measured in sodium trisilicate glasses by electron microprobe. The results indicate that sulphur diffusivity in high temperature melts is close to the Eyring diffusivity calculated from viscosity data.

scholarly journals Seasonal changes in Fe species and soluble Fe concentration in the atmosphere in the Northwest Pacific region based on the analysis of aerosols collected in Tsukuba, Japan

2013 ◽  
Vol 13 (15) ◽  
pp. 7695-7710 ◽  
Author(s):  
Y. Takahashi ◽  
T. Furukawa ◽  
Y. Kanai ◽  
M. Uematsu ◽  
G. Zheng ◽  
...  
Keyword(s):  
Fossil Fuel ◽  
Fuel Combustion ◽  
Anthropogenic Sources ◽  
Anthropogenic Activity ◽  
Northwest Pacific ◽  
Pacific Region ◽  
Fossil Fuel Combustion ◽  
Factors Affecting ◽  
X Ray ◽  
Fe Species

Abstract. Atmospheric iron (Fe) can be a significant source of nutrition for phytoplankton inhabiting remote oceans, which in turn has a large influence on the Earth's climate. The bioavailability of Fe in aerosols depends mainly on the fraction of soluble Fe (= [FeSol]/[FeTotal], where [FeSol] and [FeTotal] are the atmospheric concentrations of soluble and total Fe, respectively). However, the numerous factors affecting the soluble Fe fraction have not been fully understood. In this study, the Fe species, chemical composition, and soluble Fe concentrations in aerosols collected in Tsukuba, Japan were investigated over a year (nine samples from December 2002 to October 2003) to identify the factors affecting the amount of soluble Fe supplied into the ocean. The soluble Fe concentration in aerosols is correlated with those of sulfate and oxalate originated from anthropogenic sources, suggesting that soluble Fe is mainly derived from anthropogenic sources. Moreover, the soluble Fe concentration is also correlated with the enrichment factors of vanadium and nickel emitted by fossil fuel combustion. These results suggest that the degree of Fe dissolution is influenced by the magnitude of anthropogenic activity, such as fossil fuel combustion. X-ray absorption fine structure (XAFS) spectroscopy was performed in order to identify the Fe species in aerosols. Fitting of XAFS spectra coupled with micro X-ray fluorescence analysis (μ-XRF) showed the main Fe species in aerosols in Tsukuba to be illite, ferrihydrite, hornblende, and Fe(III) sulfate. Moreover, the soluble Fe fraction in each sample measured by leaching experiments is closely correlated with the Fe(III) sulfate fraction determined by the XAFS spectrum fitting, suggesting that Fe(III) sulfate is the main soluble Fe in the ocean. Another possible factor that can control the amount of soluble Fe supplied into the ocean is the total Fe(III) concentration in the atmosphere, which was high in spring due to the high mineral dust concentrations during spring in East Asia. However, this factor does not contribute to the amount of soluble Fe to a larger degree than the effect of Fe speciation, or more strictly speaking the presence of Fe(III) sulfate. Therefore, based on these results, the most significant factor influencing the amount of soluble Fe in the North Pacific region is the concentration of anthropogenic Fe species such as Fe(III) sulfate that can be emitted from megacities in Eastern Asia.

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