Influence of water type and maturation time on the properties of kaolinite–saponite peloids

We studied the effects of maturation time and water type on the properties of peloids. The peloids were prepared artificially by mixing the same amount of solid phase of kaolin and bentonite (9:1, m:m) with hypersaline mineral water (sodium potassium chloride water) from a spring in La Malahá (Granada, Spain) and bidistilled water (oligometallic water). The liquid/solid ratio was 2:1, m:m, with periodic manual homogenization and maturation time of one to three months. The water content of the peloids was maintained constant during the entire period of maturation.The peloid properties considered were the composition of the liquid phase, the thermal behaviour, the amount of defects in the structure of the main minerals present in the solid phase (kaolinite and saponite) and the ultramicroscopic fabric of the material, determined by scanning electron microscopy (SEM) and image analysis (IA). To date, the latter aspect has been very little studied.The composition of the liquid phases changed with maturation time. Most of the parameters measured showed a tendency to increase with increasing maturation time, as a consequence of releasing ions from the clay minerals into the liquid phase. Thus, the bidistilled water became mineral water. The initial differences between the two waters employed in the mixture were maintained in the liquid phases.The investigation of the thermal behaviour of the peloid revealed that the decrease in temperature followed, with time, a fitted logarithmic curve where R² > 0.9. The maximum change occurred in the first stage, later cooling being slower. A statistic relationship was found between the cooling kinetic and pore size and the size of the particle aggregates measured by SEM-IA. The peloids cooled more rapidly with increasing maturation time, as in the case of saline water.Both the Hinckley index of kaolinite and Integral Breadth index of saponite changed with the maturation time of the peloid. At the end of the maturation process similar values were reached regardless of the water employed.The main effect of maturation time was the increase in the size of the particle aggregates, the formation of a fabric with a more reticular morphology, and the increase in the area occupied by the pores in the SEM micrographs.     

Steam hydration of CFBC ash and the effect of hydration conditions on reactivation

A detailed study has been carried out on how hydration methods and conditions influence the sulphur capture potential of ash from a 165 MWe circulating fluidized bed combustion boiler firing a petroleum coke and coal blend. Both bed ash and fly ash were hydrated with saturated steam at various saturation conditions for different periods of time. Samples of the hydrated residues were then analyzed for free lime and calcium hydroxide content after the hydration process. Some size fractions of the steam-hydrated samples and those hydrated with liquid water in previous work were re-sulphated for 90 min using synthetic flue gas in a thermogravimetric analyzer at 850 °C to investigate how reactivation conditions affect the final sulphur capture behaviour of the ash. This work confirms that either hydration method is effective for reactivating the bed ash fractions tested but not fly ash, which should either be re-injected directly or reactivated in some other manner to improve its sulphur capture potential.     

Effect of grinding on the hydration of hydratable alumina and properties of hydratable alumina-bonded castables

Hydratable alumina (HA) is a superior Ca-free refractory binder, but the quick hydration rate restricts the working time of castables bonded with HA. In this work, HA was grounded for 1 h and 6 h by a rotational ball mill to study the effect of grinding on the hydration of HA and properties of HA-bonded castables. HA samples with and without grinding were cured at 30 °C and then terminated by freeze-vacuum drying. The phase composition and microstructure of the dried HA samples were then examined. Moreover, flow ability and mechanical strength of castables containing ungrounded and grounded HA were also investigated. The results indicate that the specific area of HA particles were decreased by grinding as the micro-pores and micro-cracks on the surface of HA particles were blocked by smaller HA particles, thereby decreasing the hydration rate of HA and increasing the flow ability of castables.     

Effect of hydration on the properties of lanthanum oxide and lanthanum aluminate thin films

The properties of lanthanum oxide films and lanthanum aluminate films were investigated after dipping the films in DI-water. The La₂O₃ film showed rapid dissolution in DI-water and a swift decrease in thickness resulting in an increased leakage current density. The LAO film showed almost no changes in thickness due to the formation of a layer, preventing dissolution. It was revealed that the changes in the films’ oxygen contents during the hydration process affected the films’ dielectric constants. The LAO films showed better hydration resistance characteristics, which are typically more suitable for conventional semiconductor manufacturing processes.     

Effect of CuO on the formation of clinker minerals and the hydration properties

The purposes of this study are to explore the mechanisms of Cu element in clinker burning and hydration processes and to make effective use of waste containing copper in cement production. The effect of CuO on clinker mineral composition, C₃S polymorph and size, Cu element distribution and state, compressive strengths, hydration products, non-evaporable water quantity and hydration heat release rate was analyzed by XRD, SEM, DTA, isothermal heat-conduction calorimetry, etc. Results show that as the amount of CuO increases the formation and growth of C₃S grain are accelerated, R C₃S is gradually transformed into M₃ and the content of C₄AF increases; a small quantity of CuO increases the 3-day and 28-day strengths and the hydration degree of clinker, but excessive CuO has adverse effects. Those effects of CuO on clinker burning process are attributed to the formation of low-melting Cu₂O and the dissolution of CuO in C₄AF which decrease the formation temperature of liquid phase and increase its quantity. The effects on hydration process result from the combined action of the following factors: the induction period is prolonged; the hydration reactions in the initial and acceleration periods are accelerated.     

Thermodynamic modelling of the effect of temperature on the hydration and porosity of Portland cement

The composition of the phase assemblage and the pore solution of Portland cements hydrated between 0 and 60 °C were modelled as a function of time and temperature. The results of thermodynamic modelling showed a good agreement with the experimental data gained at 5, 20, and 50 °C. At 5 and at 20 °C, a similar phase assemblage was calculated to be present, while at approximately 50 °C, thermodynamic calculations predicted the conversion of ettringite and monocarbonate to monosulphate.Modelling showed that in Portland cements which have an Al₂O₃/SO₃ ratio of > 1.3 (bulk weight), above 50 °C monosulphate and monocarbonate are present. In Portland cements which contain less Al (Al₂O₃/SO₃ < 1.3), above 50 °C monosulphate and small amounts of ettringite are expected to persist. A good correlation between calculated porosity and measured compressive strength was observed.     

Gluconate action in the hydration of calcium aluminate cements: Theoretical study,processing of aqueous suspensions and hydration reactivation

Considering the production of stable CAC aqueous suspensions, this work addressed the action of gluconate anion as a Ca²⁺ complexing agent and retarder of CAC hydration. Using quantum simulations, the complexation energy of gluconate complexes was calculated. The pH range of stability for the complexes was estimated and aqueous suspensions containing CAC and sodium gluconate (NaG), stable up to 4 days at room temperature, were prepared. Afterwards, their hydration reactions were reactivated by adjusting the systems’ pH. Results of solidification kinetics and mineralogical characterisation highlighted that, after reactivation, calcium aluminate hydrates were formed. Thermodynamics simulations indicated that using NaG up to 1 wt% would not be deleterious to the systems refractoriness up to 1700 °C. These systems could be applied in less explored processing routes for CAC-based refractory compositions (e.g. slip casting, direct foaming and additive manufacturing), resulting in innovations to produce advanced refractory ceramics.     

Effect of lignosulfonate, calcium chloride and their mixture on the hydration of RHA-blended portland cement

Hydration of 10 wt.% rice husk ash (RHA)-blended Portland cement has been studied in the presence of 2 wt.% CaCl₂, 1 wt.% lignosulfonate (LS) and a mixture of the two admixtures by using different methods. Free lime determinations and differential thermal analysis have shown that CaCl₂ accelerates the pozzolanic reaction of Ca(OH)₂ and RHA. In the presence of mixture of two admixtures, lower amount of water is required for consistency of the paste. IR spectral studies have supported that the mixture of the two admixtures act as a strong accelerator for cement hydration. The compressive strength is highest in the presence of a mixture of the two admixtures at 28 days of hydration. The admixtures did not prevent the deterioration of the blended cement in corrosive atmosphere.     

Effect of hydration temperature on the solubility behavior of Ca-, S-, Al-, and Si-bearing solid phases in Portland cement pastes

The concentrations of Ca, S, Al, Si, Na, and K in the pore solutions of ordinary Portland cement and white Portland cement pastes were measured during the first 28 d of curing at temperatures ranging from 5–50 °C. Saturation indices with respect to solid phases known to form in cement paste were calculated from a thermodynamic analysis of the elemental concentrations. Calculated saturation levels in the two types of paste were similar. The solubility behavior of Portlandite and gypsum at all curing temperatures was in agreement with previously reported behavior near room temperature. Saturation levels of both ettringite and monosulfate decreased with increasing curing temperature. The saturation level of ettringite was greater than that of monosulfate at lower curing temperatures, but at higher temperatures there was effectively no difference. The solubility behavior of C-S-H gel was investigated by applying an appropriate ion activity product (IAP) to the data. The IAP_CSH decreased gradually with hydration time, and at a given hydration time the IAP_CSH was lower at higher curing temperatures.     

Characterization and properties of microarc oxidized coatings containing Si, Ca and Na on titanium

To form bioactive microarc oxidized (MAO) coatings on titanium, the exploration for introducing various elements into the TiO₂-based MAO coatings has been continually noticed. In this work, novel MAO coatings containing Si, Ca and Na (SCN) elements were prepared on titanium. The elemental composition, mechanical properties, corrosion resistance and apatite-forming ability of TiO₂-based MAO coatings containing SCN were investigated. The surface hardness, elastic modulus, elastic recovery and corrosion resistance of the MAO coatings containing SCN were improved obviously by increasing the applied voltages. And the effect of applied voltage on the wetting ability of MAO coatings containing SCN is not significant. The current results indicated that the MAO coating containing SCN possesses good apatite-forming ability. The apatite-bonding structure is highly dependent on the chemical reactivity of the materials surface in simulated body fluid.     

Influence of a fine glass powder on cement hydration: Comparison to fly ash and modeling the degree of hydration

This paper reports the results of an investigation carried out to understand the influence of a fine glass powder on cement hydration. The pozzolanicity of the glass powder and a Class F fly ash for comparison was evaluated using strength activity index over a period of time, and a rapid electrical conductivity based method. Flame emission spectroscopy and electrical conductivity tests were used to quantify the alkali release from glass powder, and gain information on the rate of alkali release. It was found that the glass powder releases only a very small fraction of sodium ions into the solution. It was observed that the glass powder modified pastes show higher non-evaporable water contents than the plain paste and fly ash modified pastes, indicating that glass powder facilitates enhancement in cement hydration. An expression has been developed for the change in non-evaporable water content as a result of enhancement in cement hydration and the hydration of the cement replacement material. The efficiency of any cement replacement material with age in the paste system can be quantified using this parameter. Based on this parameter, a 5% cement replacement with glass powder was found to be effective at the chosen water-to-cementing materials ratio (w/cm), whereas at higher replacement levels, the dilution effect dominates. A model to predict the combined degree of hydration of cement pastes incorporating more than one cementing material is outlined. The measured and predicted combined degrees of hydration agree well.     

Low-temperature sintering,structure transition and dielectrical properties of Ba0.85Ca0.15Ti0.9Zr0.1O3 with Na0.5Bi0.5TiO3 addition

Na_0.5Bi_0.5TiO₃-modified Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃ ceramics were prepared by solid state route and their structural and dielectric properties were investigated. The sintering temperature of BCTZ ceramics has been significantly decreased from 1460 °C to 1280 °C with NBT addition. All samples showed a pure perovskite structure and a stable solid solution has been formed between BCTZ and NBT. Some tetragonal phase gradually transformed to rhombohedral or cubic phase with the addition of NBT. Dielectric peak gradually becomes broader, revealing that the diffuser behavior was enhanced. The prominent superimposed loss peaks related to thermally activated relaxation process. The values of activation energy of the relaxation process are 1.034, 1.285, 1.308 and 1.353 eV, which could be associated with the migration of oxygen vacancies.     

The ion-exchange properties of the Tournemire argillite: I. Study of the H, Na, K, Cs, Ca and Mg behaviour

The main goal of this study is to understand the mechanisms of adsorption of major cations occurring in groundwater on the Tournemire argillite. The Tournemire argillite contains illite, kaolinite, montmorillonite, quartz and calcite and some traces of pyrite. After calcite removal the mineralogical composition is kaolinite 47%, illite 26%, mixed-layer illite/montmorillonite 6%, montmorillonite 4%, chlorite 4% and quartz 13% with some traces of pyrite. The material was conditioned under homoionic form using Na, K, Cs, Ca and Mg. H was taken into account as a competitor ion for each case. For each cation-exchanged argillite, sorption edges were obtained as a function of pH. The “intrinsic” ion-exchange properties of this material, i.e. the concentrations of the different types of sites and the associated selectivity coefficients for H, Na, K, Cs, Ca and Mg were determined. The Tournemire argillite displays four kinds of sorption sites with respective concentrations of 0.04, 0.043, 0.046 and 0.078 mmol g⁻¹. Besides, some sites in very low concentration (5×10⁻⁴ mmol g⁻¹) have been revealed by performing adsorption isotherms of Cs.     

Structural properties,electronic structures and optical properties of WB2 with different structures: A theoretical investigation

The structural, electronic and optical properties of six WB₂ diborides with hP3, hP6, hP12, oP6, hR9 and hR18 structures were systematically investigated using the first-principles calculation based on density functional theory. The optimized atomic coordinates and lattice parameters agree well with the corresponding experimental and theoretical results. All WB₂ are energetically stable, and hP6-WB₂ has the best phase stability and hP3-WB₂ shows the worst phase stability. The results of density of states and the charge density differences indicate that WB₂ have the strong W–B and B–B covalent bonds. The hardness was obtained from the Mulliken population. The predicted values of absorption coefficient α(ω) and reflectivity R(ω) reveal that the laser with a longer wavelength is recommended during the synthesis of WB₂ coatings on the substrate surface using the Nd-YAG laser. Finally, the anisotropy in optical properties for WB₂ was discussed via the polycrystalline and directional static dielectric constants ε₁(0) and static refractive indexes n(0).     

A combination of ESEM, EDX and XRD studies on the fabric of Dutch organic clay from Oostvaardersplassen (Netherlands) and its geotechnical implications

Fabric study, using an environmental scanning electron microscope (ESEM) with a specially designed cooling stage, combined with energy diffraction analysis of X-rays (EDX), has been carried out on organic and calciferous clay from Oostvaardersplassen in the Netherlands for geotechnical engineering research purposes. Three types of clay states have been used: natural, remolded and fractured. ESEM and EDX test results reveal that this clay consists mostly of organic colloid/tissue clothed silt, microfossils, biological remains. Clay minerals were found to be a small fraction. Attention was then drawn to the identification of micro-morphology of calciferous and organic matter present in this clay, by combining these different techniques: ESEM, EDX and optical microscopy. Results indicate the presence of colloid-like film pieces of organic matter throughout the clay which implies the geotechnical properties of this clay, such as strength, could be increased because of cementation.     

Investigation on the comparison of the structural,electrical and optical properties between ZCO:Na and ZCO:(Na,N) films synthesized by RF magnetron sputtering

Sodium doped ZnCdO (ZCO:Na) and sodium-nitrogen co-doped ZnCdO [ZCO:(Na, N)] films have been deposited on quartz substrates by radio frequency (RF) magnetron sputtering followed by a post-annealing treatment. The Hall-effect measurement results emphasized the importance of the dopant and annealing conditions in realizing p-type conversion. The ZCO:(Na, N) film annealed at 655 °C for 30 min (denoted sample F) showed optimal p-type conduction properties, which has the carrier concentration of 7.84 × 10¹⁸ cm^?3. Compared to the best p-type conduction of the ZCO:Na film (sample C), sample F reveals an increased carrier concentration (up from 10¹⁷ to 10¹⁸ cm^?3) owing to the formation of Na_Zn and N_o dual acceptors. Furthermore, the XPS results revealed that sample F has a higher Na_Zn acceptor content than sample C. The ZCO:(Na, N) films exhibited better crystal quality compared to the ZCO:Na films based on comparison of the values of full width at half maximum and intensity. It was found that the band gap (E_g) of all ZCO:Na and ZCO:(Na, N) films were smaller than that of pure ZnO due to Cd doping, and that the E_g increased with the increase of T_ann, which is ascribed to the fact that more Cd atoms were evaporated from the films at higher T_ann. In addition, the E_g of the ZCO:(Na, N) films (samples E-G) are generally larger than that of the ZCO:Na films (samples A-D). This is attributed to the incorporation of N in ZCO:(Na, N), as the N_o acceptor impedes the formation of V_o defects, resulting in a decrease in the formation of the Cd_Zn-V_o complex, which in turn decreased the Cd concentration.     

The effects of Ni-addition on the crystal structure,thermal properties and morphology of Mg-based hydroxyapatites synthesized by a wet chemical method

Four Mg-based hydroxyapatites (HAps) doped with Ni at various amounts of 0, 0.6, 1.2 and 1.8?at% were prepared at the temperature of 870?°C by a wet chemical synthesis. The crystallite size, lattice parameters and crystallinity percent dramatically decreased with adding of Ni. The amount of HAp phase for all the Ni-containing samples is smaller than that of the Ni-free MgHAp. Furthermore, the lattice strain, stress and anisotropic energy density values were affected by the amount of Ni. The differential thermal analysis (DTA) measurements taken in the temperature range from 25 to 1000?°C showed that all the samples are thermally stable. No significant change in the morphology was observed. It was observed that the gradual introduction of Ni caused the Ca-deficiency.     

DRE型发射光谱仪直接测定饱和盐水中的痕量镁、钙、锶和钡

介绍以ＤＲＥ型发射光谱仪及标准加入法测定盐水质量,以便指导生产,保证离子膜电解生产烧碱过程中入槽盐水的高质量。     

Effect of the calcium on the textural, structural and catalytic properties of La1–x Ca x Co1–y Fe y O3 perovskites

In La_1-x Ca _x Co_1-y Fe _y O₃ perovskites, the calcium substitution modifies the crystalline structure toward a pseudocubic one and produces an electronic unbalance, compensated by the formation of oxygen vacancies and Fe⁴⁺ ions. It also increases slightly the ethanol conversion in total combustion, compensating the detriment of catalytic activity caused by the iron substitution and it increases notably the selectivity to total oxidation.     

CaCO3 addition effect on the hydration and mechanical strength evolution of calcium aluminate cement for endodontic applications

Calcium aluminate cement (CAC) hydrates conversion can be inhibited by adding CaCO₃, leading to C₃A·CaCO₃·11H (3CaO·Al₂O₃·CaCO₃·11H₂O) formation. However, despite its benefits, the stability of this monocarbonate hydrate is not fully understood, especially when the samples are kept in contact with liquid during the curing step. Thus, taking into account the increasing interest in the CAC application as a biomaterial in the endodontic area, this work addresses the evaluation of the mechanical strength and phase transformations of a commercial cement (Secar 71) containing 15 or 20 wt% of CaCO₃. Compressive strength, apparent porosity, dimensional linear changes, X ray diffraction and thermogravimetric tests were carried out to evaluate samples immersed in water and kept at 37 °C between 1 and 30 days of curing. According to the collected results, CAH₁₀ and C₂AH₈ formation were inhibited in CaCO₃ containing compositions and the presence of the C₃A.CaCO₃.11H phase led to a significant cement mechanical strength increase. Nevertheless, the partial decomposition of this monocarbonate hydrate was detected at 37 °C in the range of 1-7 days and the continuous hydration of CA and CA₂ also affected the compressive strength behavior of the evaluated samples.