The effect of pressure on tricalcium silicate hydration at different temperatures and in the presence of retarding additives

The hydration of tricalcium silicate (C₃S) is accelerated by pressure. However, the extent to which temperature and/or cement additives modify this effect is largely unknown. Time-resolved synchrotron powder diffraction has been used to study cement hydration as a function of pressure at different temperatures in the absence of additives, and at selected temperatures in the presence of retarding agents. The magnitudes of the apparent activation volumes for C₃S hydration increased with the addition of the retarders sucrose, maltodextrin, aminotri(methylenephosphonic acid) and an AMPS copolymer. Pressure was found to retard the formation of Jaffeite relative to the degree of C₃S hydration in high temperature experiments. For one cement slurry studied without additives, the apparent activation volume for C₃S hydration remained close to ~ ? 28 cm³ mol^? 1 over the range 25 to 60 °C. For another slurry, there were possible signs of a decrease in magnitude at the lowest temperature examined.     

Mathematical modeling of Salmonella typhimurium inactivation under high hydrostatic pressure at different temperatures

Inactivation curves of Salmonella typhimurium under high-hydrostatic pressures (HHPs) (200, 250, 300 and 350 MPa) at different temperatures (15, 25, 35 and 45 °C) in tryptone soy broth were analyzed using the modified Gompertz model. The phase of disappearance (time for inactivation of all cells, λ) and the inactivation rate (μ) of S. typhimurium were inversely related. Inactivation rates of S. typhimurium were higher (P < 0.05) at 45 °C than 15, 25 and 35 °C under HHPs from 200 to 350 MPa. The μ values were ?2.66, ?6.06, ?7.67 and ?7.99 min^?1 at 200, 250, 300 and 350 MPa HHP treatments, respectively, at 45 °C. A negative μ value (always negative) indicates that an increase (become more negative) in μ with increasing pressure or temperature is related to the S. typhimurium inactivation process. The μ values were also increased with increasing temperature from 15 to 45 °C at same treated pressures. Increased pressure and temperature had significant effects on the survival of S. typhimurium. The temperature dependence of the inactivation rate constant was analyzed based on the Arrhenius, linear and square-root models. The pressure sensitivity (low E_μ) determined based on the Arrhenius model was lower at high pressure. E_μ (activation energy) value was 1.94 kJ/mol at 350 Mpa, and 42.88, 12.99 and 3.73 kJ/mol at 200, 250 and 300 MPa, respectively. Results of this study enable the prediction of microbial inactivation exposed to HHPs at different temperatures.     

Ballistic properties and burning behaviour of an ammonium perchlorate/guanidine nitrate/sodium nitrate airbag solid propellant

An experimental investigation on the determination of ballistic properties and burning behavior of a composite solid propellant for airbag application was conducted. The experimental results were obtained using a high-pressure optical strand burner. Steady-state burning rates were determined for a pressure range of 20.8–41.5 MPa and initial propellant temperatures of −30 to +80 °C. For the pressure and temperature ranges tested, the temperature sensitivity was on the order of 1 × 10⁻³ K⁻¹. The pressure exponent was found to be a function of the initial propellant temperature and was 0.75 at 25 °C. The activation energy and the pre-exponential factor of the Arrhenius equation are 2.735 kcal/mol and 15.06 cm/s, respectively. The pressure deflagration limit for this propellant was found to be in the range of 8.37–8.72 MPa. During combustion, small condensed-phase spherical particles were ejected from the burning surface. The size of the particles decreased with either increasing the pressure or the initial propellant temperature. For pressures below 41.4 MPa, average particle size was on the order of 900 μm, and at 84.4 MPa, the bead size was much smaller, on the order of 300 μm. A chemical analysis on these particles using both the ESEM and the X-ray diffraction method indicated that the material of the beads was mostly sodium chloride with a small amount of silicon-containing compounds.     

Mechanical loss,creep, diffusion and ionic conductivity of ZrO2-8 mol%Y2O3 polycrystals

Polycrystalline ZrO₂-8 mol%Y₂O₃ was investigated by combining several experimental techniques on identical materials sintered out of the same high purity powder. The mechanical loss spectrum (damping and elastic modulus) was measured in a large frequency and temperature range (10⁻²Hz–1.5kHz; −150 to 1400°C). Damping due to point defect relaxation at low temperature and to viscoelastic relaxation at high temperature was revealed. The creep resistance was investigated with four-point bending tests (stress and temperature ranges: 20–75 MPa, 1100–1290°C), indicating Nabarro-Herring creep as the main rate-controlling mechanism. Both viscoelastic deformation and creep seem to be controlled by cation diffusion. Measurements of the ⁹⁶Zr tracer diffusivity by secondary ion mass spectrometry at 1125–1460°C yielded an activation enthalpy of 460 kJ/mol. Close values were obtained for creep (440 kJ/mol) and viscoelastic relaxation (530 kJ/mol). Finally, the ionic DC-conductivity of these electrolytes was measured with high accuracy in the range 300–1250°C.     

Effect of curing conditions on the dimensional and thermal stability of calcium phosphate cement for elevated temperature applications

Calcium phosphate cements (CPCs) are attractive materials for elevated temperature applications, like moulds to process thermoplastics up to 300 °C. The CPC resulting from the reaction of wollastonite with phosphoric acid cured at room temperature however contains hydrated phases like brushite, and is thus not stable when exposed to temperatures above 200 °C. A non-contact method based on digital image correlation demonstrated that isothermal curing at 60 °C reduces the thermal shrinkage up to 300 °C by 25%. This curing method results in the direct formation of the more stable monetite in a shorter curing time. The correlated results of TGA, pH of the filtration water, and DSC analysis on partially cured material indicate this. XRD diffractograms and SEM images in combination with EDX show the evolution of the transformation of wollastonite into monetite, and the structure and morphology of the formed material.     

Enthalpy of formation and dehydration of lithium and sodium zeolite beta

Zeolite Li-BEA and Na-BEA with Si/Al = 3–4 were synthesized by alumination and ion exchange, then characterized by XRD, TG–DSC and NMR. The enthalpies of formation and dehydration of Li and Na ion exchanged zeolite beta are investigated by high temperature oxide melt solution calorimetry. For Li-BEA, the formation enthalpies of formation from oxides at 25 °C are 25.6 ± 1.7 kJ/mol TO₂ for the dehydrated zeolite and −8.45 ± 0.94 kJ/mol TO₂ for the fully hydrated zeolite; for Na-BEA they are −2.4 ± 0.6 kJ/mol TO₂ for the dehydrated and −17.8 ± 1.0 kJ/mol TO₂ for the fully hydrated zeolite. The integral dehydration enthalpy at 25 °C is 33.2 ± 1.8 kJ/mol H₂O for Li-BEA and 16.5 ± 1.1 kJ/mol H₂O for Na-BEA. The partial molar dehydration enthalpies of both Li-BEA and Na-BEA are a linear function of water content. Molecular mechanics simulations explore the cation and water molecule positions in the framework at several water contents.     

Modeling the coupled effects of temperature and fineness of Portland cement on the hydration kinetics in cement paste

This paper revisits the coupled impacts of fineness and temperature on the kinetics of Portland cement hydration. The approach consists in i) modeling the impact of fineness on cement dissolution through the hypothesis that the surface dissolution rate of cement particles is independent of their size, in order to, in a second step, ii) model the impact of temperature on the kinetics of cement dissolution. The analysis of the experimental results shows that the effect of cement fineness on the hydration kinetics can be captured by a simple hypothesis: for any age, the reacted thickness of cement grains can be considered independent of the initial cement particle size. In addition, the analysis of the results at different temperatures shows that a constant activation energy can account for the effect of temperature on the hydration kinetics, with an Arrhenius equation applied to the kinetics of surface dissolution. The results from the model give a good agreement with the experimental results in a significant number of combinations (different Portland cements, water/cement ratio from 0.5 to 0.6, cement Blaine fineness from 3500 to 6600 cm²/g, temperature histories between 20 and 60 °C).     

Time-resolved powder neutron diffraction study of the phase transformation sequence of kaolinite to mullite

Mullite formation from kaolinite was studied by means of high-temperature in situ powder neutron diffraction by heating from room temperature up to 1370 °C. Neutron diffractometry under this non-isothermal conditions is suitable for studying high-temperature reaction kinetics and to identify short-lived species which otherwise might escape detection. Data collected from dynamic techniques (neutron diffraction, DTA, TGA and constant-heating rate sintering) were consistent with data gathered in static mode (conventional X-ray diffraction and TEM). The full process occurs in successive stages: (a) kaolinite dehydroxylation yielding metakaolinite in the ∼400–650 °C temperature range, (b) nucleation of mullite in the temperature range ∼980–992 to ∼1121 °C (primary mullite) side by side with a crystalline cubic phase (Si-Al spinel) detected in the ∼983–1030 °C temperature interval; (c) growth of mullite crystals from ∼1136 °C, (d) high (or β) cristobalite crystallization at T > ∼1200 °C and (e) secondary mullite crystallization at T > ∼1300 °C. The calculated activation energy for the kaolinite dehydration was 115 kJ/mol; for the mullite nucleation was 278 kJ/mol and for the growth of mullite process was 87 kJ/mol; finally for cristobalite nucleation the calculated apparent activation energy was 481 kJ/mol.     

Permeability and elastic modulus of cement paste as a function of curing temperature

The permeability and elastic modulus of mature cement paste cured at temperatures between 8 °C and 60 °C were measured using a previously described beam bending method. The permeability increases by two orders of magnitude over this range, with most of the increase occurring when the curing temperature increases from 40 °C to 60 °C. The elastic modulus varies much less, decreasing by about 20% as the curing temperature increases from 20 °C to 60 °C. All specimens had very low permeability, k < 0.1 nm², despite having relatively high porosity, ? ~ 40%. Concomitant investigations of the microstructure using small angle neutron scattering and thermoporometry indicate that the porosity is characterized by nanometric pores, and that the characteristic size of pores controlling transport increases with curing temperature. The variation of the microstructure with curing temperature is attributed to changes in the pore structure of the calcium–silicate–hydrate reaction product. Both the empirical Carmen–Kozeny, and modified Carmen–Kozeny permeability models suggest that the tortuosity is very high regardless of curing temperature, ξ ~ 1000.     

Time-dependent behaviour of hardened cement paste under isotropic loading

The experimental results of isotropic compression tests performed at 20 °C and 90 °C on a class G hardened cement paste hydrated at 90 °C (Ghabezloo et al., 2008, Cem. Conc. Res. 38, 1424–1437) have been revisited considering time-dependent response. Within the frame of a viscoplastic model, the non-linear responses of the volumetric strains as observed in drained and undrained tests and of the pore pressure in undrained tests are analysed. The calibration of model parameters based on experimental data allows to study the effect of the test temperature on the viscous response of hardened cement paste showing that the creep is more pronounced for a higher test temperature. The effect of the hydration temperature on the time dependent behaviour is also studied by evaluating the model parameters for a cement paste hydrated at 60 °C. The time-dependent deformations are more pronounced for hydration at a higher temperature.     

Enhanced fluoride removal from water by non-thermal plasma modified CeO2/Mg–Fe layered double hydroxides

A novel fast and efficient adsorbent based on lamellar compound namely CeO₂/Mg–Fe layered double hydroxide composite has been designed for fluoride removal from water. In order to improve fluoride removal efficiency, non-thermal plasma (NTP) was used to modify the surface state of composites. The prepared composites were characterized by powder X-ray diffraction, thermogravimetric analysis and surface area analyzer. Adsorption equilibrium and kinetics of fluoride on NTP modified composites were investigated. Experimental results indicated that the adsorption capacity was enhanced with NTP surface modification. The maximum adsorption capacity has been found to be 38.7–60.4 mg/g. The kinetic data of adsorption were found to best fit the pseudo-second-order model, while the equilibrium data were found to be well described by Langmuir model. In order to understand the mechanism of adsorption, thermodynamic parameters such as ΔG^θ, ΔS^θ and E_a were calculated. After NTP treatment, the ΔS^θ increased from − 34.7 J/mol·K to − 0.770 J/mol·K, the E_a decreased from 78.8 kJ/mol to 58.9 kJ/mol and the ΔG^θ (25 °C) decreased from − 2.62 kJ/mol to − 3.14 kJ/mol. These values indicate that the fluoride adsorption on NTP modified composites was improved.     

Ettringite decomposition in the presence of barium carbonate

The interaction between cement paste and sulfate-rich solutions or soils induces gypsum, ettringite or thaumasite precipitation. These expansive processes may be mitigated by using BaCO₃ (witherite) as a setting regulator. The present study explored ettringite decomposition in the presence of witherite at different temperatures (25, 40 and 65 °C) and reaction times (up to 90 days) to further the understanding of this process as grounds for developing new sulfate-resistant cements (SR-PC).According to the XRD, FTIR and DSC-TG findings, sulfoaluminate decomposition and barite formation begin in the first 24 h of the reaction, even at ambient temperature (25 °C), and progress rapidly for the first 30 days. The reaction follows a different pathway at 65 °C than at 25 and 40 °C due to ettringite instability at high temperatures.     

Low temperature tensile lap-shear testing of adhesively bonded polyethylene pipe

This work studies the lap-shear strength performance of polyethylene pipeline bonded with acrylic adhesive in the temperature range -10 to +20 °C. Single lap shear test samples were firstly prepared at 20 °C under various clamping pressures and curing times to determine suitable conditions under which to prepare and test further samples at temperatures of -10, -5, 0, +5 and +20 °C. It was found that a decrease in curing/testing temperature to zero degrees resulted in a steady reduction in the lap-shear strength performance of the bonded joints from a mean value of 2.72 MPa at +20 °C to 1.15 MPa at 0 °C. Below zero degrees the strength of the bonded substrates was significantly reduced; no samples bonded at -5 °C had sufficient strength to test and only one sample bonded -10 °C was tested, which had very low strength of 0.105 MPa.     

Transesterification of leather tanning waste to biodiesel at supercritical condition: Kinetics and thermodynamics studies

Catalyst-free transesterification of leather tanning waste with high free fatty acid (FFA) content at supercritical condition was reported in this work. The experiments were performed in batch system at various temperatures (250–325 °C) under constant pressure of 12 MPa and methanol/fatty oil molar ratio of 40:1 for reaction time of 2–10 min. Kinetic modeling of formation of fatty acid methyl esters (FAMEs) that incorporate reversible esterification and non-reversible transesterification simultaneously was verified. The proposed semi-empirical model was fitted against kinetic experimental data over temperature range studied. The kinetic parameters (i.e. k′_TE, k′_E, and k_E′) were determined by nonlinear regression fitting. Thermodynamic activation parameters of the reactions were evaluated based on activation complex theory (ACT) and the following results are obtained: ΔG³ > 0, ΔH³ > 0, and ΔS³ < 0. The activation energy (E_a) of transesterification, forward and reverse esterification reactions was 36.01 kJ/mol, 28.38 kJ/mol, and 5.66 kJ/mol, respectively.     

Onset sintering-coarsening-coalescence kinetics of calcite powders

An onset sintering-coarsening-coalescence (SCC) event based on a significant decrease of specific surface area relative to the dry pressed samples after isothermal firing in the 450–600 °C range in air was determined by N₂ adsorption–desorption hysteresis isotherm for submicron-sized calcite powders. The apparent activation energy for such a rapid SCC event was estimated as 57.5 ± 1.0 kJ/mol based on the time for 50% reduction of specific surface area without appreciable phase change of calcite. The minimum temperature to activate the SCC process, as of concern to industrial CaCO₃ applications and natural limestone formation, is 317 °C based on the extrapolation of steady specific surface area reduction rates to null.     

The effect of temperature on the rate of sulfate attack of Portland cement blended mortars in Na2SO4 solution

Sulfate attack on Portland cement and Portland blended cement concretes is a well-researched field. However, the effect of varying temperature on the rate of sulfate attack requires further attention. This laboratory experiment studied temperatures of 23 °C, 10 °C, 5 °C, and 1 °C. Both Portland and Portland limestone cements were studied in combination with several supplementary cementing materials. The mortar bars were submerged in 5% Na2SO4 (33,800 ppm SO₄^2 −) solution for 15–30 months. At higher temperatures the supplementary cementing materials, particularly the fly ashes, greatly improved the resistance to external sulfate attack. At lower temperatures the metakaolin improved the resistance to sulfate attack; the fly ashes had little to no effect on the low-temperature sulfate resistance. The alterations to sulfate resistance are attributed to: dilution of Portland cement in the presence of supplementary cementing materials; additional nucleation sites provided by finely ground SCMs; and the pozzolanic and hydraulic reactions of the SCMs.     

High-temperature deformation behavior in SrTiO3 ceramics

The high-temperature deformation behavior of a polycrystalline strontium titanate (SrTiO₃) ceramic (6 μm grain size) was investigated at temperatures of 1200–1345 °C in an argon atmosphere. Compressive deformation tests were conducted at strain rates ranging from 5 × 10⁻⁶ to 5 × 10⁻⁵ s⁻¹. Steady-state flow stresses were 0.05–30 MPa and increased with increasing strain rates. Stress exponents of ≈1, at temperatures >1200 °C, indicated a viscous diffusion-controlled deformation with an activation energy of ≈628 ± 24 kJ/mol. Comparison of activation energy with literature data suggests diffusion of cations as the rate-controlling mechanism. Absence of cavitation and grain-shape changes were consistent with grain-boundary sliding as the principal deformation mechanism. The electron back-scattered diffraction (EBSD) technique was used to determine the grain orientation as a function of applied strain. The results indicate that some of the grains rotate with cumulative rotation as large as 7° at a strain of 4%.     

Limiting factors for low-temperature performance of electrolytes in LiFePO4/Li and graphite/Li half cells

Low-temperature performance of LiBF₄ and LiPF₆-based electrolytes in LiFePO₄/Li and graphite/Li half cells was investigated. In the temperature range from 0 °C to ?40 °C, electrochemical impedance spectroscopy (EIS) results show that the charge-transfer resistance (R_ct) of graphite/Li cell decreases, the R_ct of LiFePO₄/Li cell increases, and sum resistance of LiFePO₄/Li and graphite/Li cell decreases when replacing LiPF₆ with LiBF₄. In the temperature range from 25 °C to ?40 °C, energy barrier (W) for Li-ion jump at the solid electrolyte interface (SEI) alters slightly from 16.04 kJ/mol to 13.60 kJ/mol in LiFePO₄/Li cells, but declines greatly from 46.47 kJ/mol to 19.81 kJ/mol in graphite/Li cells when using LiBF₄ instead of LiPF₆, meanwhile, activation energy (ΔG) of electrode reaction is approximately the same (～60 kJ/mol). The above results indicate that the ionic conductivity is the main limiting factor for low-temperature performance of electrolytes in LiFePO₄/Li cell, while factors related with electrolyte-interface are more crucial in graphite/Li cell than in LiFePO₄/Li cell.     

Temperature induced gelation of non–aqueous alumina suspension using oleic acid as dispersant

A novel temperature induced gelation method for alumina suspension using oleic acid as dispersant is reported. Non–aqueous suspension with high solid loading and low viscosity is prepared using normal octane as solvent. Influence of oleic acid on the dispersion of suspension was investigated. There was a well disperse alumina suspension with 1.3 wt% oleic acid. Influence of gelation temperature on the coagulation process and properties of green body was investigated. The sufficiently high viscosity to coagulate the suspension was achieved at −20 °C. The gelation temperature was controlled between the melting point of dispersant and solvent. The gelation mechanism is proposed that alumina suspension is destabilized by dispersant separating out from the solvent and removing from the alumina particles surface. The alumina green body with wet compressive strength of 1.07 MPa can be demolded without deformation by treating 53 vol% alumina suspension at −20 °C for 12 h. After being sintered at 1550 °C for 3 h, dense alumina ceramics with relative density of 98.62% and flexural strength of 371±25 MPa have been obtained by this method.     

Effect of the curing temperature on the creep of a hardened cement paste

Uniaxial creep tests have been performed at ambient temperature on a saturated hardened class G cement paste hydrated at 60 °C and 90 °C. The results have shown that creep is enhanced at higher curing temperature. The visco-damage model of Challamel et al. (2005) has been extended and used to analyze the experimental results. The model parameters have been calibrated on the results of the creep tests performed at different stress levels for both curing temperatures. The model correctly reproduces the effect of the curing temperature on time dependent properties of the material. The enhanced creep at higher curing temperature is attributed to the development of more damage in cement paste and to significant weakening of the mechanical properties.