Rietveld Quantitative Phase Analysis Research Articles

Clinkering and hydration of alite-belite-ye'elimite cement with increasing ye'elimite percentage

Alite-belite-ye'elimite (ABY) cement is considered to be eco-cements with adequate mechanical properties and fewer CO2 emissions. The phase assemblage and ye’elimite content of ABY cement play a very important role in cement properties. In this study, ABY clinkers with increasing ye'elimite percentage (0.3 wt%-36.4 wt%) were prepared at 1300 °C and the phase composition was characterized by Rietveld Quantitative Phase Analysis combined with energy dispersive X-ray spectrometry. The ye'elimite formed with a calculated composition of Ca3.92Mg0.02Al2.81Fe0.05Si0.04S1.16, incorporating additional sulfur compared to the theoretical value. In addition, the hydration properties of heat evolution, hydration products and compressive strength of ABY cement are studied. The result shows that the increase of ye'elimite content leads to a more intense initial heat release and a higher cumulative heat release. The presence of ye'elimite inhibits the hydration of alite at early ages. ABY mortars with increasing ye'elimite (15.8 wt%) exhibited a higher strength (29.6 MPa) at 3 days by the contribution of ye'elimite hydration, and an increase (47.4 MPa) at 28 days. An adequate proportion of ye'elimite (<15 wt%) is favorable to the performance of ABY cement, and releases 12% less CO2.

Mix and measure - Combining in situ X-ray powder diffraction and microtomography for accurate hydrating cement studies

It is reported an innovative methodology based on in situ MoKα1 laboratory X-ray powder diffraction (LXRPD) and microtomography (μCT) avoiding any sample conditioning. The pastes are injected in 2.0 mm capillaries and the extremes are just sealed. The measurements take place in the same region of the hydrating paste. Thick capillaries are key to avoiding self-desiccation, which dictates the need of high-energy X-ray radiation for the diffraction study. This approach has been tested with a PC 42.5 R paste having w/c = 0.50. μCT data were collected at 12 h and 1, 3, 7 and 79 days. LXRPD data were acquired at 1, 3, 7 and 77 days. In this proof-of-principle research, the same paste was also cured ex situ. Portlandite contents obtained by thermal analysis, ex situ powder diffraction, in situ mass balance calculation and in situ powder diffraction were 13.8, 13.1, 13.1 and 12.5 wt%, respectively. From the μCT study, the grey value histogram evolution with time showed a crossing point which allowed us to distinguish (appearing) hydrated products from (dissolving) unhydrated cement particles. Segmentations were carried out by global thresholding and the random forest approach (one type of supervised Machine Learning). The comparison of the segmented results for the unhydrated cement fraction and the Rietveld quantitative phase analysis outputs gave an agreement of 2 %. The potential of this methodology to deal with more complex binders is also presented.

In-situ laser metal deposition of nitinol and the effect of Ni4Ti3 phase concentration on its pseudoelasticity

Pseudoelasticity is one of the major properties of nitinol. It is highly altered by the presence of nickel-rich Ni4Ti3 phase in the nitinol matrix. Hence it is significant to make an attempt to study the connection between Ni4Ti3-concentration and the matrix-pseudoelasticity. In this work, the connection of pseudoelasticity of nitinol with the concentration of Ni4Ti3 in the matrix was investigated. A 0.5 mm thick preplaced layer of a powder mixture of nickel and titanium (55 % and 45 % by weight, respectively) on a 4 mm thick nitinol substrate was laser scanned with a laser power of 1000 W, scan speeds of 200, 400, 600, 800 and 1000 mm/min and a laser spot diameter of 3 mm under a shielding of argon gas stream. The various phases formed during the process at different scan speeds were quantified by Rietveld quantitative phase analysis. Further, load-displacement curves were obtained with nano-indentation to estimate the pseudoelastic recovery of the matrix and to show the pseudoelastic connection of the matrix with its constituent Ni4Ti3 concentration. The laser scanned tracks (with the scan speeds of 600, 800 and 1000 mm/min) having a higher concentration of Ni4Ti3 showed a higher amount of pseudoelastic recovery. On the other hand, the tracks (with the scan speeds of 200 and 400 mm/min) having a lower concentration of Ni4Ti3 showed a lower amount of pseudoelastic recovery.

Effects of AH3 and AFt on the Hydration-Hardening Properties of the C4A3S¯-CS¯-H2O System.

This study aimed to reveal the effects of the hydration products AH3 and AFt phases on the hydration and hardening properties of calcium sulfoaluminate (CSA) cement. In addition, the effects of anhydrite (CS¯) and gypsum (CS¯H2) on the properties of CSA cement were compared. Calcium sulfoaluminate (C4A3S¯) was synthesized with analytical reagents, and the C4A3S¯-CS¯-H2O system with different molar ratios of CS¯ and C4A3S¯ was established. The phase compositions and contents of AFt and AH3 were determined by X-ray diffraction (XRD), Rietveld quantitative phase analysis, and thermogravimetric analysis (TG). The effects of pore structure and hydration product morphology on mechanical properties were analyzed by mercury intrusion porosity (MIP) and scanning electron microscopy (SEM). The results showed that the compressive strength exhibited a correlation with the AH3 content. In the case of relatively sufficient anhydrite or gypsum, C4A3S¯ has a high degree of hydration, and the AH3 content can be considered to contribute more to the strength of the hardened cement paste. When anhydrite was selected, the combined and interlocked AFt crystals were covered or wrapped by a large amount of AH3. The mechanical properties of the hardened cement paste mixed with anhydrite were better than those of that mixed with gypsum.

Ecotoxicological Properties of Titanium Dioxide Nanomorphologies in Daphnia magna.

In this work, the structural, vibrational, morphological, and colloidal properties of commercial 15.1 nm TiO2 nanoparticles (NPs) and nanowires (NWs, 5.6 thickness, 74.6 nm length) were studied with the purpose of determining their ecotoxicological properties. This was achieved by evaluating acute ecotoxicity experiments carried out in the environmental bioindicator Daphnia magna, where their 24-h lethal concentration (LC50) and morphological changes were evaluated using a TiO2 suspension (pH = 7) with point of zero charge at 6.5 for TiO2 NPs (hydrodynamic diameter of 130 nm) and 5.3 for TiO2 NWs (hydrodynamic diameter of 118 nm). Their LC50 values were 157 and 166 mg L-1 for TiO2 NWs and TiO2 NPs, respectively. The reproduction rate of D. magna after fifteen days of exposure to TiO2 nanomorphologies was delayed (0 pups for TiO2 NWs and 45 neonates for TiO2 NPs) in comparison with the negative control (104 pups). From the morphological experiments, we may conclude that the harmful effects of TiO2 NWs are more severe than those of 100% anatase TiO2 NPs, likely associated with brookite (36.5 wt. %) and protonic trititanate (63.5 wt. %) presented in TiO2 NWs according to Rietveld quantitative phase analysis. Specifically, significant change in the heart morphological parameter was observed. In addition, the structural and morphological properties of TiO2 nanomorphologies were investigated using X-ray diffraction and electron microscopy techniques to confirm the physicochemical properties after the ecotoxicological experiments. The results reveal that no alteration in the chemical structure, size (16.5 nm for TiO2 NPs and 6.6 thickness and 79.2 nm length for NWs), and composition occurred. Hence, both TiO2 samples can be stored and reused for future environmental purposes, e.g., water nanoremediation.

Study on the preparation and properties of high-belite cementitious materials from shield slag and calcium carbide slag

With the continuous increase in subway construction in China, a large amount of shield slag is produced. The piling and transportation of shield slag seriously affect the urban environment. Therefore, it is necessary to study the recycling technology of shield muck to reduce its environmental pollution and realize its resource utilization. Jinan shield muck contains a large amount of calcareous muck and clayey muck. It is feasible to prepare silica-aluminum cementitious materials through the reasonable combination of these mucks. In this study, calcareous slag and clayey slag were used as the main raw materials, and calcium carbide slag, iron powder, silica fume and alum soil were used as correction materials to prepare high-belite cementitious materials based on the residue. By measuring the content of free calcium oxide and using X-ray fluorescence diffraction, scanning electron microscopy and differential thermal analysis, the formation mechanism of high-belite cementified materials under different doping conditions was studied. The results show that the addition of CaSO4 and CF2 can significantly improve the burnability of raw materials when the saturation coefficient of lime holding time has a great influence on the formation of clinker. According to the Rietveld quantitative phase analysis, under the doping state, the content of belite can reach more than 50%. The content of this mineral can effectively overcome the problem of the low short-term strength of high belite cementite materials. Through the above research, it was confirmed that the shield mule of Jinan metro can form high-belite cementitious material.

Hydration characteristics and microstructure evolution of concrete with blended binders from LCD and OLED wastes

The use of pozzolanic waste materials as partial cement replacement is customary in contemporary concretes from the sustainability perspective. In this study, glass wastes from organic light-emitting diode (OLED) and liquid crystal display (LCD) were used waste as supplementary cementing material (SCM) in concrete. For the first time, detailed microstructural and hydration attributes have been studied for such blended concretes. Concretes with 10%, 20%, and 30% substitution of ordinary Portland cement (OPC) by OLED and LCD glass powders were developed. The resulting mechanical properties, hydration attributes, and microstructural features were studied at various ages, up to one year. Superior mechanical properties were shown after 28-day age for blended concretes; however, much profound improvement in compressive and flexural strength was observed at 1-year age. The enhanced mechanical properties of modified concretes are attributed to greater pozzolanic activity and secondary hydrates formation of OLED and LCD glass powders in alkaline cementitious matrix. Greater C-S-H gel formation, lower permeability, and more refined microstructure of the blended concrete were corroborated by thermogravimetric analysis (TGA), Rietveld quantitative phase analysis (RQPA), backscattered electron image analysis (BSE), and mercury intrusion porosimetry (MIP). 20 wt% has been found as the optimal value of cement replacement by either LCD or OLED powder. The results clearly indicate LCD and OLED can be successfully used as SCM for developing concrete with improved properties.

Kinetic model for ye’elimite polymorphs formation during clinkering production of CSA cement

The calcium sulfoaluminate,orthorhombic(OY) and pseudo- cubic(CY) ye’elimitepolymorphs,were synthesized by solid state reaction from SiO2, Al2O3, Fe2O3, CaCO3, Na2CO3, CaSO4·2H2O in specific oxide relationships. Thermal gravimetric analysis (TGA)wasmade before sintering the raw mixes in an electrical furnace.Laboratory X-Ray Powder Diffraction (LXRPD) and Rietveld quantitative phaseanalysis(RQPA) and amorphous and crystalline non-quantified (ACn) quantification were made on each sample. Kinetic were analyzedisothermallybetween 1150 °C and 1300 °C. The kinetic model who best fitted each OY and CY polymorph was the geometrical and diffusional model proposed by Jander (D3 model). The activation energy, Ea (kJ/mol), values obtained for OY and CY were 420 and 275respectively.The activation energy is lower in CY due to the presence of minor elements that reduce the sintering temperature.Thefrequencyfactor or compensation factor A is higher for OY than CY, meaning the need for a higher collisionfrequency. As founded by previous authors, thecoexistenceof both polymorphs must be considered intothekinetic study as a fundamental condition of these results.For this reason, this research proposes the inclusion ofαmodified. OY always is present at the reaction beginning. But as higher the temperature and reaction time, in the presence of some minor elements, CY appears mainly at lower temperatures regarding OY, it means requiring lesser energy. Knowing the kinetic model proposed by this work would allow a better control or tailor of the ratio OY/CY, to produce CSA with different performances.

Exploration of structural, optical, and photoluminescent properties of (1 – x)NiCo2O4/xPbS nanocomposites for optoelectronic applications

The (1 – x)NiCo2O4/xPbS (0 ≤ x ≤ 0.2) nanocomposite samples are synthesized using the hydrothermal and thermolysis procedures. The different phases developed in the obtained nanocomposite samples are accurately determined using the x-ray diffraction technique equipped with a line-detector. The percentage of the formed phases (NiCo2O4 (NCO), PbS, PbSO4), structural and microstructure parameters are determined using Rietveld quantitative phase analysis. The transmission electron microscope (TEM) images and Rietveld analysis reveal almost isotropic particle size in the nano range with a very narrow size distribution. The obtained phase percentage of PbS and PbSO4 are smaller than nominated values (x) suggesting dissolving of some Pb and S ions into NCO which is then confirmed by the analysis of Fourier-transform infrared (FTIR) spectra of nanocomposite samples. The absorption spectra are modified upon doping NCO with PbS. The optical band gaps of the nanocomposites increase as the amount of PbS augments. The effect of alloying on extinction coefficient, refractive index, dielectric constant, optical conductivity, the intensity, and emitted color from the photoluminescence of the nanocomposite samples are also studied. The refractive index value of NCO and NCO–PbS nanocomposite samples exhibit normal dispersions. The photoluminescent measurements reveal that the NCO–PbS nanocomposites can emit a violet color. The improvement in the values of the nonlinear optical (NLO) parameters of pristine NCO at high frequencies or the nanocomposite samples at low frequencies, are made them used in NLO photonic devices.

Phosphorus Substitution Preference in Ye'elimite: Experiments and Density Functional Theory Simulations.

Density functional theory (DFT) simulation has been recently introduced to understand the doping behavior of impurities in clinker phases. P-doped ye’elimite, a typical doping clinker phase, tends to form when phosphogypsum is used to manufacture calcium sulfoaluminate cement (CSA) clinkers. However, the substitution mechanism of P has not been uncovered yet. In this study, the influence of different doping amounts of P on the crystalline and electronic structure of ye’elimite was investigated using backscattered scanning electron microscopy–energy X-ray dispersive spectroscopy, X-ray diffraction tests, Rietveld quantitative phase analysis, and DFT simulations. Furthermore, the substitution preference of P in ye’elimite was revealed. Our results showed that increasing the doping amount of P increased the impurity contents in CSA clinkers, transforming the ye’elimite crystal system from the orthorhombic to the cubic system and decreasing the interplanar spacing of ye’elimite. Based on the calculation results of the defect formation energies, additional energies were required for P atoms to substitute Ca/Al atoms compared with those required for P atoms to substitute S atoms in both orthorhombic and cubic systems of ye’elimite. Combined calculation results of the bond length–bond order and partial density of states showed that the doped P atoms preferably substituted S atoms; the second possible substituted atoms were Al atoms, while there was only a slight possibility for substitution of Ca atoms. The substitution of P atoms for S atoms can be verified based on the elemental distribution in P-doped ye’elimite and the increasing residual CaSO4 contents. The transition of the crystal system and a decrease in the interplanar spacing for ye’elimite can also prove that the substitution of P atoms for Al atoms occurred substantially.

Synthesis and Formation Process of a Typical Doped Solid-Solution Ye’elimite (Ca3.8Na0.2Al5.6Fe0.2Si0.2SO16): Experiments and Kinetic Analysis

Ye’elimite is a dominant phase in calcium sulfoaluminate cement, which is a promising alternative type of cementitious binder. Ca3.8Na0.2Al5.6Fe0.2Si0.2SO16 (abbreviated as ss-C4A3$) is a kind of typical doped solid-solution ye’elimite. In this study, the formation process of ss-C4A3$ was investigated. Clinkers of ss-C4A3$ were sintered at various temperatures for different holding times. X-ray diffraction tests and Rietveld quantitative phase analysis were conducted to determine the phase compositions of the clinkers. Meanwhile, the formation process of ss-C4A3$ was analyzed by kinetic theory. The results show that solid reactions between intermediate phases (calcium aluminate phases) and anhydrite mainly resulted in the formation of ss-C4A3$. In the conditions of 1150–1250 °C, ss-C4A3$ tended to be formed and stable until 4 h. However, when the sintering temperature was 1300 °C, the ss-C4A3$ decreased to generate calcium aluminate phases after 2 h. Compared to other kinetic models, the three-dimensional diffusion model mostly conformed with the formation process of ss-C4A3$, and the fitting results obtained by the Jander model exhibited the highest correlation coefficients. The activation energy of ss-C4A3$ formation equaled 285.6 kJ/mol, which was smaller than that of stoichiometric ye’elimite.

Phase and microstructure evolutions in LC3 binders by multi-technique approach including synchrotron microtomography

Limestone Calcined Clay Cements, LC3, are attracting a lot of attention as it is possible to reduce the clinker factor by 50%, which means a cement CO2 footprint reduction of 40%. This is compatible with maintaining the mechanical strength performances after one week, if the kaolinite contents of the raw clays are above ~40 wt%. Durability properties are also maintained or even enhanced. Here, it is used a multi-technique approach to understand the phase and microstructure developments. From the thermal analysis, partial limestone reactivity is proven. Chiefly, high-resolution synchrotron microtomography has been employed, for the first time in these systems, to characterize their microstructures. The measured total porosities, within our 1 μm spatial resolution (voxel size 0.32 μm), were 16.6, 10.0 and 2.4 vol% at 7, 8 and 60 days of hydration, respectively. Pore connectivity strongly decreases with hydration time due to the chemical reactions producing new phases filling the pores. The 6-connected porosity fractions were 92, 78, and 9% at 7, 8 and 60 days. The reactions filling the pores were investigated by Rietveld quantitative phase analysis and 27Al MAS-NMR.

Lab Case Study of Microbiologically Influenced Corrosion and Rietveld Quantitative Phase Analysis of X-ray Powder Diffraction Data of Deposits from a Refinery.

This paper reports a laboratory-based case study for the characterization of deposits from a crude cooler and reboilers in a Saudi Aramco refinery by microbiologically influenced corrosion (MIC) using microbial, metallurgic, and special analyses and correlates the Rietveld quantitative phase analysis of high-resolution X-ray powder diffraction (XRD) data of scale deposits with microbe compositions. Therefore, rapid in-field microbiological assays could be carried out to assess the potential of MIC. Based on the results, it can be highlighted that the MIC investigation showed that total bacteria and sulfate-reducing bacteria (SRB) were detected in all sampling locations. Methanogens, acid-producing bacteria, and sulfate-reducing archaea were not detected in all samples. Iron-oxidizing bacteria (IOB) were detected in the solid samples from reboilers C and D. Low loads of general bacteria and low levels of microbes with MIC potential were detected in both C and D samples. The trace amount of corrosion products in one sample and the low level of MIC microbes cannot justify the contribution of MIC microbes in the formation of accumulated solids in the system. The findings recommend conducting frequent sampling and analysis including water, oil, and solid from upstream locations to have more decisive evidence of the likelihood of the scale formation and possible contribution of MIC in the formation of deposits in the plant. Subsequently, quantitative phase analysis of XRD data of scale deposits by the Rietveld method revealed that the major phase is calcium sulfate in the form of anhydrate and the minor phases are calcium carbonate in the form of calcite and aragonite, silicon oxide in the form of quartz, and iron oxide corrosion product in the form of magnetite. The results are supported by high-resolution wavelength-dispersive X-ray fluorescence (WDXRF) results. These accurate and reproducible X-ray crystallography findings obtained from Rietveld quantitative phase analysis can guide the field engineers at the refineries and gas plants to overcome the problems of the affected equipment by drawing up the right procedures and taking preventive actions to stop the generation of these particular deposits.

Synthesis and characterization of low-cost zeolite NaA from coal gangue by hydrothermal method

Through this investigation, we have demonstrated a low-cost preparation method of zeolite NaA from coal gangue. The well-developed zeolite NaA of 87.56% crystallinity was successfully prepared by hydrothermal alkali activation method, which required low alkali concentration (1.8 mol/L) compared to other researches (3–6 mol/L). The characterization results of product prepared at different conditions suggest that the purity and crystallinity of zeolite NaA are high at low alkali concentration and longer crystallization time. The Ca2+ exchange value of synthesized zeolite attained 265 mg CaCO3/g compared to commercial zeolite, which is typically 340 mg CaCO3/g. The basic structure parameters and thermal stability have also been studied. The results suggest that the obtained zeolite has a potential to be used as hard water softening agent. Moreover, the result of Rietveld quantitative phase analysis and Box-Behnken's response surface methodology showed that the weight fraction of zeolite NaA in product can reach 71.9%, and the crystallinity can attain 88.14% at the optimal condition of n(SiO2)/n(Al2O3) of 2.60, NaOH(aq) concentration of 1.86 mol/L at 95 °C for 10.08 h.

Quantitative phase analysis and microstructural characterization of Portland cement blends with diatomite waste using the Rietveld method

This paper aims at giving new insights into the impacts of the particle sizes of diatomite waste on the hydration properties of Portland cement from the perspective of quantitative analysis using Rietveld refinements method. XRD identification coupled with Rietveld quantitative phase analysis, as well as isothermal calorimetry and SEM observation, was performed. The results show that the cement hydration during the induction period does not show any significant differences with the decrease in the sizes of the diatomite waste particles; however, hydration during the acceleration period was significantly enhanced. Finer diatomite waste particles (d50 < 1070.9 nm) result in a significant increase in the amounts of ettringite (AFt) and calcium hydroxide (CH) during acceleration period of the cement. Moreover, diatomite waste incorporation contributes to accelerate the early formation of monosulfate (AFm); however, the formation of the AFm was not favorable as the sizes of the diatomite waste particles decrease. The improvement on the hydration of the Portland cement was largely affected by the particle sizes effects of the diatomite waste at the very early stage, and then by the reactivity of diatomite waste at the later stage.

Effect of the Cooling Regime on the Mineralogy and Reactivity of Belite-Sulfoaluminate Clinkers

This study investigated the influence of different cooling regimes on the microstructure and consequent reactivity of belite-sulfoaluminate clinkers. The cement clinkers were synthesized by incorporating secondary raw materials, such as titanogypsum and bottom ash, to the natural raw materials. Clinker phases were determined by Rietveld quantitative phase analysis, while the distribution morphology and the incorporation of substitute ions in the phases were characterized by scanning electron microscopy using energy-dispersive X-ray spectroscopy (SEM/EDS). Clinker reactivity was studied using isothermal calorimetry and was additionally investigated through compressive strength, which was determined for the cement prepared from the synthesized clinkers. X-ray diffraction analysis showed that, as well as the three main phases (belite, calcium sulfoaluminate, and ferrite), the clinkers contained additional minor phases (mayenite, gehlenite, arkanite, periclase, and perovskite), the ratios of which varied according to the cooling regime utilized. Microscopic observations indicated that the cooling regime also influenced the crystal size and morphology of the main phases, which consequently affected clinker reactivity. Furthermore, a smaller amount of substitute elements was incorporated in the main phases when cooling was slowed. Results showed that, in comparison to clinkers cooled at slower rates, air quenched clinkers reacted faster and exhibited a higher compressive strength at 7 days.

Effect of CaO content in raw material on the mineral composition of ferric-rich sulfoaluminate clinker

Ferric-rich calcium sulfoaluminate (FR-CSA) cement is an eco-friendly cement. Fe2O3 exists in different minerals of FR-CSA clinker, e.g., Ca4Al2Fe2O10 (C4AF), Ca2Fe2O5 (C2F), and Ca4Al6-2xFe2xSO16 (C4A3-xFxS-). The mineral composition depends on the chemical composition of the raw materials and significantly determines the reactivity of FR-CSA cement. To optimize the phase composition of the FR-CSA clinker, chemical reagent raw mixtures with different amounts of CaO were used to prepare the FR-CSA clinker. X-ray diffraction (XRD) analysis, Rietveld quantitative phase analysis (RQPA), Fourier Transform Infrared spectroscopy (FT-IR), and scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) were used to identify the mineralogical conditions of the FR-CSA clinker. The results indicated that the amounts of CaO in raw materials greatly affected the iron-bearing phase formation in the FR-CSA clinker. With decreasing CaO content involved in calcination reaction, the amounts of Fe2O3 incorporated in C4A3-xFxS- increased up to 17.72 wt% (where x = 0.36). The findings make it possible to optimize the mineral composition of the FR-CSA clinker by changing the CaO content in raw materials. Furthermore, low CaO content in the raw material is beneficial to the formation of C4A3-xFxS-, which enables the use of solid wastes containing low calcium for producing FR-CSA cement.

Identification of Iron Carbides in Fe(−Na−S)/α‐Al2O3 Fischer‐Tropsch Synthesis Catalysts with X‐ray Powder Diffractometry and Mössbauer Absorption Spectroscopy

AbstractIn Fe‐based Fischer‐Tropsch Synthesis (FTS), the Fe carbides form under the carburizing H2 : CO reaction atmosphere providing the active phases for hydrocarbon synthesis. H2 reduced Fe(−Na−S)/α‐Al2O3 catalyst materials, with and without Na−S promotion, were carburized under CO at 240–440 °C to form Fe carbides. X‐ray Powder Diffractometry (XRPD) with Rietveld Quantitative Phase Analysis (R‐QPA) and Mössbauer Absorption Spectroscopy (MAS) were used to identity and quantify the formed Fe carbide phases. The Fe carbides formed in order of increasing temperature are ϵ‐Fe3C, η‐Fe2C, χ‐Fe5C2 and θ‐Fe3C. θ‐Fe7C3 and a distorted χ‐Fe5C2 phase are formed at 25 bar CO (340 °C) from a Fe oxide precursor. Fe carbide formation was unaffected by Na−S addition, but it did increase Fe oxidation (≤290 °C) and preferred formation of χ‐Fe5C2 over θ‐Fe3C phase (≥390 °C). The results unify the often ambiguous Fe carbide identification and nomenclature and specify the role of Na−S in the carburization process.

Stability and phase transition of 5·1·7 phase in alkaline solutions

5Mg(OH)2·MgSO4·7H2O (5·1·7 phase) is considered to be the main strength phase of magnesium oxysulfate (MOS) cement. In this paper, effect of alkaline solutions on stability of 5·1·7 phase is investigated. Harden pastes containing nearly pure 5·1·7 phase are synthesized and characterized. Compressive strength of 5·1·7 phase, immersed in sodium hydroxide solutions of different pH values for different ages, are compared. X-Ray diffraction (XRD) test and Rietveld quantitative phase analysis (RQPA) are employed to determine phase transition in the harden pastes, meanwhile ion chromatograph (IC) and inductively coupled plasma (ICP) were conducted to confirm ionic concentrations of immersing sodium hydroxide solutions. Moreover, through scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) test, influence of alkaline solutions on microstructure of 5·1·7 phase is analyzed. The results show that, immersed in distill water and relatively low alkaline (pH ≤ 11) solutions, 5·1·7 phase keeps to be stable and the compressive strength tends to be approximately constant with immersing ages prolonging, meanwhile contents of 5·1·7 phase in the harden pastes tended to be almost constant during the immersion and still accounted for over 90 wt% until 28d. In condition of pH ≥ 12, alkaline solutions show negative effects on the mechanical property of 5·1·7 phase, which appears to be more obvious with pH value increasing. Moreover, 5·1·7 phase decomposes to be Mg(OH)2 and MgSO4 when the pH values of immersing solutions exceed 12, which can be reflected by decrement of 5·1·7 phase contents in harden pastes and obvious increasement for concentrations of Mg2+ and SO42- in immersing solutions. Additionally, decomposition of 5·1·7 phase would lead to increasing porosity of the harden pastes.

Rietveld Quantitative Phase Analysis of Oil Well Cement: In Situ Hydration Study at 150 Bars and 150 °C.

Oil and gas well cements are multimineral materials that hydrate under high pressure and temperature. Their overall reactivity at early ages is studied by a number of techniques including through the use of the consistometer. However, for a proper understanding of the performance of these cements in the field, the reactivity of every component, in real-world conditions, must be analysed. To date, in situ high energy synchrotron powder diffraction studies of hydrating oil well cement pastes have been carried out, but the quality of the data was not appropriated for Rietveld quantitative phase analyses. Therefore, the phase reactivities were followed by the inspection of the evolution of non-overlapped diffraction peaks. Very recently, we have developed a new cell specially designed to rotate under high pressure and temperature. Here, this spinning capillary cell is used for in situ studies of the hydration of a commercial oil well cement paste at 150 bars and 150 °C. The powder diffraction data were analysed by the Rietveld method to quantitatively determine the reactivities of each component phase. The reaction degree of alite was 90% after 7 h, and that of belite was 42% at 14 h. These analyses are accurate, as the in situ measured crystalline portlandite content at the end of the experiment, 12.9 wt%, compares relatively well with the value determined ex situ by thermal analysis, i.e., 14.0 wt%. The crystalline calcium silicates forming at 150 bars and 150 °C are also discussed.