Showing papers on "Calcium aluminates published in 2019"

Complex Characterization and Behavior of Waste Fired Brick Powder-Portland Cement System.

Abstract: Two waste fired brick powders coming from brick factories located in Argentine and Czech Republic were examined as alternative mineral admixtures for the production of blended cements. In pastes composition, local Portland cements (Argentine and Czech) were substituted with 8–40%, by mass, with powdered ceramic waste. For the ceramic waste-Portland cement system, workability, the heat released, pozzolanity, specific density, compressive strength, hydrated phases, porosity, and pore size distribution were tested. The relevance of the dilution effect, filler effect, and pozzolanic activity was analyzed to describe the general behavior of the pozzolan/cement system. The properties and performance of cement blends made with finely ground brick powder depended on the composition of ceramic waste and its reactivity, the plain cement used, and the replacement level. Results showed that the initial mini-slump was not affected by a low ceramic waste replacement (8% and 16%), and then it was decreased with an increase in the ceramic waste content. Brick powder behaved as a filler at early ages, but when the hydration proceeded, its pozzolanic activity consumed partially the calcium hydroxide and promoted the formation of hydrated calcium aluminates depending on the age and present carbonates. Finally, blended cements with fired brick powder had low compressive strength at early ages but comparable strength-class at later age.

Modification of oxide inclusions in calcium-treated Al-killed high sulphur steels

Abstract: A study has been carried out to understand the modification of alumina inclusions in Al-killed high sulphur steel with calcium treatment. For calcium treatment to be effective, a general practice is to desulphurise the steel to prevent the formation of solid CaS inclusions that are harmful to steel quality and final properties. To avoid this additional desulphurising step, the authors developed a new approach of calcium treatment of steel at an industrial scale. This approach involves treating the liquid steel with calcium treatment at low aluminium levels which enables formation of liquid calcium aluminate inclusions (C12A7) in the melt and then adding remaining amount of required aluminium. Based on this principle, Al-S diagram has been developed and calcium treatment has been modified accordingly. The inclusion transformation and morphology were studied using scanning electron microscope /energy dispersive spectroscopy analysis and. activity of CaS was calculated.

Study on the modification of inclusions by Ca treatment in GCr18Mo bearing steel

Abstract: The effect of Ca treatment on the modification of inclusions in Al-killed GCr18Mo bearing steel was studied and a thermodynamic and kinetic model was established. The experimental results showed that oxygen content in the steel could be reduced from 120 μg/g to the range 5.5–21.6 μg/g by Al-Ca complex deoxidization at 1 873 K. An appropriate increase in Ca/Al mass ratio is beneficial to reduce the total oxygen content in steel. When the content of dissolved aluminum was in the range of 0.03%–0.3%, with the increase of Ca/Al mass ratio from 0.8–1.6 to 2.4–3.2, the number of inclusions per unit area significantly reduced. In addition, the main types of inclusions were modified from large-sized Al2O3 clusters to plastic or semi-plastic liquid phase calcium aluminates. The experimental results matched well with the thermodynamic analysis.

Synthesis of Calcium Aluminates from Non-Saline Aluminum Dross.

Abstract: The present work examines the synthesis of tricalcium aluminate (for use as a synthetic slag) from the non-saline dross produced in the manufacture of metallic aluminum in holding furnaces. Three types of input drosses were used with Al2O3 contents ranging from 58 to 82 wt %. Calcium aluminates were formed via the mechanical activation (reactive milling) of different mixtures of dross and calcium carbonate, sintering at 1300 °C. The variables affecting the process, especially the milling time and the Al2O3/CaO molar ratio, were studied. The final products were examined via X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The reactive milling time used was 5 h in a ball mill, for a ball/dross mass ratio of 6.5. For a molar relationship of 1:3 (Al2O3/CaO), sintered products with calcium aluminate contents of over 90% were obtained, in which tricalcium aluminate (C3A) was the majority compound (87%), followed by C12A7 (5%).

Synthesis the composites Si 3 N 4 -TiN by hot pressing

Abstract: The Si3N4-TiN composites were obtained by hot pressing at 1600–1800 °C in a nitrogen atmosphere from mixtures of powders of silicon nitride and metallic titanium. The influence of particle morphology, Ti content in the initial charge and synthesis conditions on the microstructure, phase composition, mechanical strength of the samples of ceramic composites Si3N4-TiN was studied. It was established that in the process of sintering, complete nitriding of titanium occurs with the formation of a non-stoichiometric nitride of composition TiN0.9. Samples of composites Si3N4-TiN, obtained from a mixture containing 5-30 % Ti, have a density of 3.02-3.41 g/cm3, water absorption 0.01-0.14 %, open porosity 0.03-0.44 % and flexural strength from 250 to 584 MPa. It is shown that ceramics Si3N4-TiN with a sintering additive of calcium aluminates is characterized by a dense intergrowth of silicon nitride crystals, which provides an increase in the strength of the samples.

Contact strength of C-S-H cement phase

Abstract: The object of the study was the cement phase C-S-H – X-ray amorphous calcium hydrosilicates, obtained by steaming at 80°C together limestone and silica at different molar ratios CaO/SiO2 = 0.5; 1.0; 1.5. The contact strength of the C-S-H phase with additions of portlandite, silica and alumina zols, high-aluminate slag was estimated by hyper-pressing method with subsequent destruction. It was established that the contact strength of the cement phase increases in proportion to the specific pressing pressure, the age of samples and inversely the phase basicity reaching 12 MPa. It was evidenced that additives increase the contact strength of the C-S-H stone. The features of the phase formation during the hydration of calcium aluminates were considered. It was established that there is no negative effect of additional porosity on the strength of the stone, because the restructuring of calcium hydroaluminates takes place during hyper-pressing. The specific behavior of low-basic calcium aluminates in a mixture with the C-S-H phase was established in the case of using high-aluminate slag, which consists in additional formation Al(OH)3 gel during the hydration, that is provide an increase in the contact strength of the compositions.

Газогипсовые материалы с использованием вторичного сырья

Abstract: Purpose: The aim of this work is to investigate compositions and operational procedures for gypsum foamed materials based on acid fluoride and define conditions for the formation of the foamed structure and ways to improve the strength of foamed samples. Materials/Methodology/Approach: A capacity of sulphuric acid to interact with calcium carbonate with release of carbon dioxide is laid for this research. The hallmark of this study is acid fluoride used as a recycled material in which the residual acid adsorbs on anhydrite grains. Also, liquid glass and aluminum oxide nanofibrer are added to the composition. In this research, standard procedures and physicochemical techniques are used for the detection of properties of constructional materials. X-ray diffraction and differential thermal analyses are carried out to study the chemical composition of acid fluoride. The production of heat-insulating material includes preliminary dosage of initial components (acid fluoride, liquid glass, stabilized dispersion of aluminum nanofiber, sodium carbonate and water); blending of these components during 1–2 min followed by the gypsum addition; hardening in chambers for 24 h at 40–60 °C; pouring the ready mixture in divided molds. Standard equipment can be used for this production process. Research findings: The additional use of liquid glass and aluminum oxide nanofiber provides high physical and mechanical properties of samples. The high strength of material is insured by hydration of gypsum and acid fluoride followed by the chemical reaction due to the hardening catalyst. Heat-insulating properties appear due to porosity of product achieved by the release of carbon dioxide and oxygen during the interaction between acid fluoride and sodium carbonate as well as by the dispersion of aluminum oxide nanofiber accompanied by pore formation. Liquid glass and aqueous dispersion of nanofiber are very important for the material composition. The hardness increase occurs due to the formation of calcium silicates of different valency and their hydrates and due to the addition of nanofiber stabilized by sodium hydroxide of aluminum oxide representing a specific proportion of aluminum oxide and AlOOH. As a result of nanoparticle-Ca ion interaction, calcium aluminates and hydrated aluminates form. Calcium silicates and aluminates form the main space frame for the structure of gypsum stone. Additionally, Na 2 SO 4 hardener forms during the interaction of the blend components, i.e. the system is capable to autocatalysis. Also, the appeared non-soluble and slightly soluble products reinforce the stone structure, such that the initial, large gas release which provides low density and pore formation, does not lead to a sharp strength decrease, thereby ensuring the sufficient quality of material. When the oxide film of aluminum fiber is damaged, its violent reaction occurs with aqueous mixture components with hydrogen release. Practical implications: The obtained results can be used in construction of low-rise building and manufacturing partitions for rooms and flats. Originality: Hydration and pore formation processes are described for hardening gypsum materials based on acid fluoride. These processes allow controlling the mixture composition and properties of binding and binding-containing constructional materials. The authors suggest dependencies for control for the composition, structure and properties of composite, heat-insulating materials. The authors show that it is possible to render a targeted effect on the structure formation observed in complex additives which assist in the production of effective walling materials.

Hydraulic composition for additive manufacturing device, and method for manufacturing casting mold

Abstract: The present invention is a hydraulic composition for an additive manufacturing device, the composition having superior dimensional stability and initial flexural strength, and the composition including 1.5-14 parts by mass of a polymer per 100 parts by mass of an inorganic binder. The present invention preferably is a hydraulic composition for an additive manufacturing device, the inorganic binder including 50-100 mass% of calcium aluminates, where the entirety of the inorganic binder is 100 mass%, and more preferably is a hydraulic composition for an additive manufacturing device, the inorganic binder including 0-50 mass% of a rapid-hardening cement, where the entirety of the inorganic binder is 100 mass%.

Impact of the Sintering Additive Al 2 O 3 on the Electrical Conductivity of Proton-Conducting Electrolyte CaZr 0.95 Sc 0.05 O 3 – δ

Abstract: The impact of sintering additive Al2O3 on the electrical conductivity of calcium zirconate-based polycrystalline proton-conducting electrolyte CaZr0.95Sc0.05O3 – δ (CZS) is studied. With the sintering additive Al2O3, ceramic samples synthesized by a combustion technique are denser, and relatively low synthesis temperatures can be used (1470°C). Adding 0.1–0.5 wt % Al2O3 leads to an increase in the grain size from 100 nm to 1–2 μm. Increasing the Al2O3 content up to 0.3 wt % favors a growth in the electrolyte conductivity. For samples containing Al2O3, calcium aluminates are detected at grain boundaries. In samples exposed to humid air, charge transfer both in the grain bulk and at intergrain boundaries is found to be mediated by protons.

Method of processing concrete scrap

Abstract: FIELD: construction.SUBSTANCE: invention relates to the field of construction and the production of building materials and can be used in the manufacture of bricks, paving slabs and other small-piece products, the installation of foundations, including the foundations of roads. Method involves crushing concrete scrap to pieces of 0.01–5.0 mm in size, moistening it to normal molding moisture, adding 5–40 % by weight of low-basic calcium aluminates with a dispersion of 2000–3000 cm/g, mixing wet concrete scrap and low-base calcium aluminates, compaction of the resulting homogeneous mixture at 10–100 MPa.EFFECT: technical result is an increase in the strength of the resulting extruded building material, utilizing waste from the production of concrete.1 cl, 3 tbl