Surface properties of cement hydration products. I. Pore structure of calcium silicate hydrates prepared in a suspension form

Adsorption–desorption isotherms of water vapour at 30° were determined on preparations of calcium silicate hydrates of different molar ratios of lime/silica before and after free lime and free silica extractions. From these isotherms specific surface areas were measured and total pore structure analysis was evaluated. A surface layer thickness (t) curve for the adsorption of water vapour on calcium silicate hydrates was constructed, based on experimental curves previously published for the number of layers adsorbed on a variety of non-porous solids with the same heat of adsorption as the calcium silicate hydrates. The existence of both wide pores and micropores was detected in the calcium silicate hydrates. When the samples were free from uncombined lime and silica the micropores were estimated to have an average hydraulic radius of 4–5 Å, whereas the wide pores had an average size of 10 Å. Wide pores up to 200 Å also exist. The pores were predominantly parallel plates.     

The interrelation between structure and mechanical properties of CNx (0 ≤ x ≤ 0.5) coatings obtained by graphite arc sputtering

Hardness, elastic modulus, internal stresses and friction coefficients were measured in CN_{0 ≤ x ≤ 0.5} coatings (1–3 μm). The dependence of these parameters on nitrogen concentration can be applied in the practical coatings. The structure investigations show that the domain amorphous matrix mixture consists of CN_{x ≤ 0.1} and CN_0.5. Such structure allows understanding the dependence of the CN_{0 ≤ x ≤ 0.5} coatings properties on nitrogen concentration. Through the structure, the coating properties of CN_{0 ≤ x ≤ 0.5}, depend on the nitrogen concentration.     

Deformation of nonfired refractories based on phosphate binders. 6. Deformation under heating and creep in corundum composites

The results of studying heating deformation and creep are described for two systems: electrocorundum — α-Al₂O₃ — phosphate binder and electrocorundum — pyrophyllite — phosphate binder. It is shown that composites with H₃PO₄ experience less deformation than composites with the alumochromium-phosphate binder, whereas using pyrophyllite instead of aluminum oxide increases creep deformation due to the presence of the liquid phase in the material. The effect of technological factors is investigated. __________ Translated from Novye Ogneupory, No. 6, pp. 58–62, June, 2007. Continuation. See beginning in Vol. 48, Nos. 1–2, 2007.     

Thermal decomposition,structural changes and surface properties of chromium oxide gel

Structural and phase changes of a prepared sample of chromium oxide gel were explored by differential thermal analysis and X-ray diffraction analysis. Dehydration products were obtained at various temperatures up to 740 °C, by heating in air for 3 hours. Samples obtained by heating below 320 °C were amorphous to X-rays whereas those obtained at 320 °C, and between 320 and 510°C proved to be a mixture of α- and γ-Cr₂O₃. However, at temperatures above 510 °C, only one form, the stable α-Cr₂O₃ exists. The glow phenomenon is attributed to the presence of excess oxygen, resulting from the reduction of Cr(VI) to Cr(III), just prior to the conversion of the amorphous gel to the crystalline γ-Cr₂O₃, which is accompanied by a release of energy. Surface area measurements were carried out by cyclohexane, methanol and water adsorption at 35 °C, and the areas were compared with those measured by nitrogen at liquid nitrogen temperature. Pore structure analysis for both micro- and mesopores were carried out. The low temperature samples are characterised by the presence of both types of pores, with the micropore fraction predominating acquiring thus the property of molecular sieves; the pores being accessible to water and nitrogen but not to cyclohexane or methanol. At temperatures above 320 °C, the microporosity collapses with the production of a heterogeneous assembly of mesopores. In the mean time the surface changes to be hydrophobic in nature; accordingly it cannot be measured from water adsorption.     

Ways Toward Increasing Endurance of the Lining of Rotary Kilns

A brick mortar (the chromite-periclase filler, CPF) for the hot-face lining of rotary kilns for calcination of magnesite and its mixtures has been developed and tested. The CPF is based on a periclase-chromite mixture with the addition of aluminum and ferrophosphorus. The use of CPF makes it possible to increase the lining endurance of 90 and 170-meter rotary kilns by a factor of 2.5 and 1.5, respectively.     

Navigation waterway for Lake Nasser/Nubia on the Nile River

The High Aswan Dam is one of the largest dams in the world. Completion of the dam in 1970 resulted in the formation of Lake Nasser/Nubia (LNN). LNN has a highly irregular shape and dimensions. Its total length is about 500 km (335 km in Egypt, known as Lake Nasser; 165 km in Sudan, known as Lake Nubia). It has an average width of 12 km, an average depth of about 25 m and a maximum depth of 90 m. Large quantities of sediment are deposited in the lake, which complicates accurate knowledge of its navigational routes. Moreover, the sediment deposition and lowering of water levels has resulted in the creation of shallow areas that navigation bottlenecks. Furthermore, this problem is expected to increase in the future because of climate change impacts, and the effects of upper Nile River projects. The objective of this study was to identify a sustainable channel for navigation purposes in Lake Nasser/Nubia. A numerical model (Delft‐3D) was used to simulate the navigation waterway along Lake Nasser/Nubia. Calibration and verification of the model for flow and sediment deposition were performed during the period of 2009–2012. There was a good agreement between the observed and modelled results for the whole domain. The model was used to evaluate the designed navigation waterway, based on different scenarios. The calculated volume of the needed dredging, based on time series for the years 2002–2006 (‘which represents a minimum flood’), was 5.94 million m³ (mcm); the calculated volume of the dredging using time series for the years 1992–1996 (‘which represents an average flood’) was 6.64 mcm; and the calculated volume of the dredging using time series for the years 1996–2000 (‘which represents a maximum flood’) was 8.46 mcm. The modelling approach proved to be a useful tool for monitoring the future navigation waterway in Lake Nasser/Nubia.     

The use of airfoil and Chebyshev polynomials methods for solving fuzzy Fredholm integro-differential equations with Cauchy kernel

In this paper the airfoil and the Chebyshev polynomials methods to solve the fuzzy Fredholm integro-differential equation with Cauchy kernel under generalized \(H\) -differentiability are discussed. The existence and uniqueness of the solution and convergence of the proposed methods are proved in details. Finally some examples show the accuracy of these methods.     

Strength level of high-strength complex fibre from stiff-chain polymers

The discrete strength levels for ultrahigh-modulus Terlon, Armos, and SVM fibre were found. Small-angle x-ray scattering and the calculation procedure known as the method of tangents were used to estimate the radii of submicrocracks. The limiting and actual values of the average strength levels of these types of fibre were calculated for two characteristic radii of inertia R₁ and R₂. The agreement of the results with the published data confirms the accuracy of the method of tangents.Ukrainian Scientific-Research Institute of Fibre, Kiev. Translated from Khimicheskie Volokna, No. 6, pp. 33–35, November–December, 1992.     

Towards combinatorial evolution of composite systems

The paper describes combinatorial evolution of composite systems. The approach consists of the following stages: (i) design of general hierarchical structure of the examined system; (ii) design of structures for several series system generations; (iii) extraction of changes between the system generations as a set of change items and their evaluation (multicriteria analysis including usage of interval multiset estimates, binary relations over the items: compatibility, complementarity, precedence); (iv) combinatorial synthesis of system forecast(s) as selection of prospective change items while taking into account total constraint(s) (multiple choice problem) or morphological design while taking into account compatibility between the selected change items; (v) aggregation of the obtained system forecast into a resultant forecast. The approach was used for modeling of combinatorial evolution in several applications: (1) DSS COMBI for multicriteria ranking, (2) electronic equipment for image processing, (3) standard for transmission of multimedia information (MPEG, MPEG 2, MPEG 4), and (4) ZigBee communication protocol for wireless sensor network. In the article, the suggested approach is illustrated by evolution of three author courses on multicriteria decision making and modular system design. The following is presented: (a) hierarchical structures of the courses, (b) change items between the courses, (c) combinatorial design of prospective forecasts, (d) aggregation of the forecast into a resultant one.