J.I. Escalante-García

Nonevaporable water from neat OPC and replacement materials in composite cements hydrated at different temperatures

Pastes of two neat OPC and three blended cements using GGBFS (60%), PFA (30%) and a volcanic ash (23%), were cured for up to 1 year at five temperatures. The degree of hydration of the OPCs was estimated by quantitative X-ray diffraction analysis and by measurements of nonevaporable water by thermogravimetry. A correlation between the results from these techniques is presented for the neat OPCSs. The correlation was used to estimate the contribution to the nonevaporable water from the cement replacement material fraction for the blended cements. According to the estimated data, the slag displayed a hydraulic nature retaining significant amounts of water in its hydrates, the slag nonevaporable water values as function of time varied with temperature and the patterns were similar to those of degree of hydration of the neat cement. The data estimated for the two pozzolanic materials indicated that their hydrates retained small amounts of water in spite of the CH consumption.

Glass–ceramic materials with regulated dielectric properties based on the system BaO–PbO–TiO2–B2O3–Al2O3

Vitrification and crystallization properties of glasses of the system BaO-TiO 2 -PbO-Al 2 O 3 (B 2 O 3 ) were investigated. The fields of vitrification based on ternary diagrams of BaTiO 3 -PbTiO 3 -(TiO 2 +Al 2 O 3 +B 2 O 3 ) with varied contents of Al 2 O 3 (10, 13, 16 mol%) and B 2 O 3 (3, 15 mol%) were identified. The glass compositions obtained had relatively low melting temperature (1450°C). These stable glasses could be thermally treated to produce glass-ceramics characterized by fine-crystalline structures and regulated permittivity associated to the contents of ferroelectric phases. The phase composition of such glass-ceramics included different Pb x Ba 1-x TiO 3 solid solutions depending on the starting chemical composition. Permittivity of the obtained materials (f=800 kHz, T=25°C) varied from 20 to 680 relatively to the time of crystallization.

Alkali-activated slag-metakaolin pastes: strength, structural, and microstructural characterization

Pastes of granulated blast furnace slag (GBFS) and metakaolin (MK) at GBFS/MK mass ratios of 100/0, 50/50, and 0/100 were activated with sodium silicate with modulus (Ms) SiO2/Na2O of 1, 1.5, and 2, and with 5, 10, and 15% Na2O, relative to the mass binder. Samples were cured at 20 °C for up to 720 days, compressive strength, structural, and microstructural characteristics were investigated. Binders of 100% GBFS developed the highest strength of 120 MPa with 5% Na2O, while those of 100% MK required 15% Na2O to develop high strength. The composites 50% GBFS/50% MK required 10% of Na2O to reach up to 88 MPa. In general, the best Ms was 1–1.5. Structural and microstructural examination of the formulation 50/50 indicated the combined formation of a matrix of reaction products of crystalline C–S–H, an Al-substituted alkali charge-balanced calcium silicate hydrate C–N–(A)–S–H–type gel and geopolymeric gel (N–A–S–H), while 100% GBFS binders showed a 9 Å tobermorite-type calcium silicate hydrate (Ca5Si6O16(OH)2) intermixed with an amorphous C–N–(A)–S–H gel.

EFFECT OF GEOTHERMAL WASTE ON STRENGTH AND MICROSTRUCTURE OF ALKALI-ACTIVATED SLAG CEMENT MORTARS

Abstract Mortars of blast furnace slag replaced with 10% of a geothermal silica waste were cured for 90 days. The binder was activated by 6 wt.% Na 2 O equivalent of NaOH and water glass. The presence of the silica enhanced the formation of hydration products as shown by nonevaporable water (NEW) results. Backscattered electron images indicated that the microstructures of blended slag had less porosity than those of neat slag mortars and the interfacial zone between aggregate and hydration products was dense and of homogeneous composition similar to the matrix of hydration products. The main hydration products were C-S-H and for NaOH a hydrotalcite type phase was found as finely intermixed with the C-S-H.

Inorganic wastes in manufacturing of glass-ceramics: slurry of phosphorous fertilizer production and oil shale ash

The use of bicomponent raw material mixtures of industrial wastes to produce pyroxene glass ceramics was investigated. It is shown that oil shale ash from heat power stations can promote the production of crystalline phases and the slurry from phosphorous fertilizer production can provide sufficient concentration of nucleating agents. Mechanical and chemical properties, as well as the structure and crystallization mechanism were characterized. An increase of phosphorous oxide and fluorine concentrations leads to a change of the crystallization mechanism.

Synthesis and structural characterization of Ba(LnIII2/3BVI1/3)O3 (LnIII=Dy, Gd and Sm; BVI=Mo or W) complex perovskites

Abstract We describe in this work the synthesis and crystal structure of five rare earth and Mo(VI) or W(VI) containing complex perovskites. The compounds studied are Ba(Dy 2/3 Mo 1/3 )O 3 , Ba(Dy 2/3 W 1/3 )O 3 , Ba(Gd 2/3 Mo 1/3 )O 3 , Ba(Gd 2/3 W 1/3 )O 3 and Ba(Sm 2/3 W 1/3 )O 3 and were prepared starting from solutions, by the polymeric precursors method. Structural characterization by HREM, SAED and powder XRD revealed the five compounds to be ordered cubic perovskites, SG Fm -3 m (225), with a cell parameter double of that of a simple perovskite cell and increasing as the size of the trivalent lanthanide ion increases (Dy

Preparation and magnetic properties of Zn–Ti subtituted Ba-ferrite powders

Abstract Zn–Ti-substituted barium ferrite powders were prepared by the sol–gel method and characterized. The room temperature magnetic properties were evaluated for different levels of dopant, Fe/Ba ratios, and heat-treatment temperatures. The results showed that M s was not very much influenced by the substitution level up to 0.6 at.%. Contrarily, H ci did show a marked decrease, owing to the reduction of the magnetocrystalline anisotropy of the BaM phase. On the other hand, an excess of Ba led to the decrease of M s and the increase of H ci . Additionally, Zn–Ti substitutions were effective in decreasing crystallite sizes below 100 nm.

Modification of the float-glass surface by treatment with urea aqueous solution

Abstract The thermo-chemical modification of float-glass surface structure and properties by the aerosol of aqueous solution of urea was investigated. It is shown that the character of the modification depended on the temperature of treatment. The chemical interaction of urea and water vapor with the soda–lime–silicate glass yielded different products under various treatment conditions; the effects of such products on the glass properties were also analyzed. For industrial application of the investigated treatment, the temperature range of 140–160 °C has been identified as optimal, promoting increased mechanical strength and enhanced adhesion of glass surface to poly(vinyl butiral); also this is not related to atmosphere contamination. The effectiveness of the proposed method was tested and confirmed under industrial conditions of float-glass production.