Structure and magnetic behavior of Zn doped NdMnO3 manganite: Neutron diffraction study

Effect of Zn doping on the structural and magnetic properties of NdMnO₃ has been investigated by neutron diffraction and dc magnetic susceptibility measurements. The partial replacement of Mn³⁺ by Zn²⁺ results in the decrease in T_N. In the temperature dependent magnetization measurements, a broad hump and a sharp peak has been observed around ~ 50 K and 10 K respectively for both the samples. Thermal hysteresis in magnetization between cooling and heating runs indicate first-order phase transition. Magnetization measurements on NdMn_0.95Zn_0.05O₃ sample clearly show that, 5% Zn-doping in NdMnO₃ results in the suppression in magnetism which is evident from the weakening of Nd–Mn interaction below T_N, and resulting in antiferromagnetic coupling of Mn³⁺ ions along x-axis with Mn³⁺ moments oriented parallel or antiparallel to the x-component of Nd³⁺ moments.     

Synthesis and thermal performance of polymer precursor for ZrC ceramic

A novel ZrC preceramic precursor (PZC) was compounded via liquid phase chemical reaction without any organic solvent choosing ZrOCl₂·8H₂O and polyvinyl alcohol as Zr source and C source, respectively. The composition and structure of ZrC precursor were analysed through XRD, FT-IR, XPS and SEM. The results showed both Zr-O-C bonds and Zr-O bonds existed in the precursor. The results observed by SEM showed that many irregular particles were generated, whose particle sizes were mainly in the range of 0.2–3 μm. In addition, particle aggregation can be easily observed. Besides, the thermal property and pyrolysis process of PZC were studied. In accordance with XRD, the initial temperature of the earliest detection of ZrC in pyrolysis products of PZC was 1300 °C. Monoclinic ZrO₂ and tetragonal ZrO₂ can be observed at this temperature as well. Ulteriorly, when the pyrolysis temperature was risen up to 1500 °C, only ZrC ceramic can be found.     

Synthesis and color properties of the TiO2@CoAl2O4 blue pigments with low cobalt content applied in ceramic glaze

The TiO₂@CoAl₂O₄ complex blue pigments with low cobalt content were synthesized through calcinations of the precursor obtained from coprecipitating Co²⁺ and Al³⁺ to form Co‐Al LDHs (layered double hydroxides) on the surface of TiO₂ particles. The structure and the properties of the synthesized pigments were characterized by XRD, SEM, TEM, UV‐Vis spectroscopy, XPS, and colorimeter. The precursors of the blue TiO₂@CoAl₂O₄ complex pigments were consisted of LDHs shell layer encapsulated TiO₂ microsphere. After calcinations at 1100°C, the LDHs shell layer were absolutely transformed to the spinel CoAl₂O₄, and the pigments presented a core‐shell structure and uniform sphere morphology (the diameter of microsphere was about 780 nm). The absorption bands at around 547, 584, and 624 nm in the Uv‐Vis absorption spectra of the TiO₂@CoAl₂O₄ complex pigments were corresponded to the characteristic absorption bands of the spinel CoAl₂O₄, revealed the pigments with a bright blue hue. In addition, as the mass ratio of CoAl₂O₄/TiO₂ increased to 0.4, the blue component of the pigments reached to 27.89 and slight color variation with the increase in the CoAl₂O₄ content in a range, possessed low cobalt content and exhibited a stabile performance in commercial low‐temperature ceramic glazes. The XGT results showed that the TiO₂@CoAl₂O₄ complex pigments with low cobalt content presented bright color in ceramic glaze. Especially, the synthesized pigments reduced the usage and toxicity of cobalt, which were efficiency for economy and environmental protection.     

Solution combustion synthesis of (Co,Ni)Cr2O4 pigments: Influence of initial solution concentration

Initial solution concentration effect was studied on the synthesis of mixed spinels Co_1-ΨNi_ΨCr₂O₄ (0≤Ψ≤1) obtained by Solution Combustion Synthesis. Fd-3m spinel structure was developed in all range of compositions analysed, regardless of the concentration. However, structural characteristics such as ion rearrangement and crystal size showed a noticeable dependence on the initial concentration, being the spinel network more ordered and with higher crystallite size as the concentration increased. Cell parameter, however, presented dependence on composition but not on initial solution concentration.All as-synthesized pigments showed a significant colouring power in ceramic glazes without any significant influence of initial solution concentration. Therefore, a second thermal treatment was not needed. The coloured glazes covered a broad range of tones in the green section of colour space, which evolved as a function of composition.     

Assessment of zirconia fluorescence after treatment with immersion in liquids,glass infiltration and aging

This study evaluated the fluorescence of white zirconia immersed in coloring and fluorescence liquids, subjected to glass infiltration and aging. Sixty zirconia discs were machined and divided into groups. Ten discs received no treatment before sintering (Group NT), ten discs were immersed in a coloring liquid (Group A2), and ten discs were immersed in a fluorescent liquid (Group F). The other thirty discs were infiltrated with glass after the previous treatments (Groups NT + I, A2+I, and F + I). The composition of the liquids was characterized by X-Ray fluorescence. Additional superficial roughness and X-Ray diffraction measurements were made. Diffuse reflectance and total fluorescence were evaluated before and after aging, performed in an autoclave at 134 °C for 4 h. By X-Ray fluorescence analysis, a high concentration of Fe₂O₃ (80.7 at%) was found in the composition of the coloring liquid; Bi₂O₃ (54.2 at%) and Cl (45.2 at%) were found in the fluorescence liquid. Greater reflectance was observed in the glass infiltrated groups, in particular Groups NT + I and F + I. Mean values found for arithmetic average roughness (Ra) varied around 0.2 μm. The 3D Fluorescence maps of the groups submitted to immersion showed a higher total fluorescence value than Group NT, except for Group A2. Group F showed the highest fluorescence value that was 12.8 times higher than the value of Group NT. Fluorescence emission occurred in the region between 350 and 550 nm after excitation ranging between 290 and 360 nm. The presence of the glass infiltrated layer protected the samples from hydrothermal degradation.     

Post-fire residual mechanical properties of concrete made with recycled concrete coarse aggregates

This paper presents results of an experimental study on the residual mechanical performance of concrete produced with recycled coarse aggregates, after being subjected to high temperatures. Four different concrete compositions were prepared: a reference concrete made with natural coarse aggregates and three concrete mixes with replacement rates of 20%, 50% and 100% of natural coarse aggregates by recycled concrete coarse aggregates. Specimens were exposed for a period of 1 h to temperatures of 400 °C, 600 °C and 800 °C, after being heated in accordance with ISO 834 time–temperature curve. After cooling down to ambient temperature, the following basic mechanical properties were then evaluated and compared with reference values obtained prior to thermal exposure: (i) compressive strength; (ii) tensile splitting strength; and (iii) elasticity modulus. Results obtained show that there are no significant differences in the thermal response and post-fire mechanical behaviour of concrete made with recycled coarse aggregates, when compared to conventional concrete.     

NaV2O5 nanoplates: Hydrothermal synthesis,characterization and study of their optical and electrochemical properties

Plate-like nanocrystalline NaV₂O₅ has been synthesized hydrothermally via a simple and elegant route. The morphology, the structure, the crystallinity and the composition of the samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, nitrogen adsorption/desorption isotherms and photoluminescence. Electrochemical measurements have revealed reversible redox behavior with doping/dedoping process corresponding to reversible cation intercalation/deintercalation into the crystal lattice of the nanoplates. This process is easier in propylene carbonate than in aqueous solvent and is easier for the small Li⁺ cation than larger ones K⁺. This is attributed to probable presence of two different tunnel cavities in the NaV₂O₅ lattice.     

Changes in microstructures and physical properties of polymer-modified mortars during wet storage

The decrease in strength of tile adhesive mortars during wet storage was investigated. In a first approach, the water resistance of the polymer phases was tested on structures isolated from the mortar and in situ. It was observed that cellulose ether and polyvinyl alcohol structures are water-soluble. Subsequent investigations on polymer mobility within the mortar showed that the migrating pore water transports cellulose ether and polyvinyl alcohol during periods of water intrusion and drying. This leads to enrichments at the mortar-substrate interface. In contrast, latices interacting with the cement are water-resistant, and therefore, immobile in the mortar. Further experiments revealed that the mortar underwent considerable volume changes depending on the storage condition. Cracking occurred mainly close to the mortar-tile interface, cement hydrates grew within these shrinkage or expansion cracks. Test results revealed that the strength decrease of wet stored tile adhesives is caused by different mechanisms related to cement hydration, volume changes of the mortar, and reversible swelling of latex films.     

Synthesis and properties of conductive B4C ceramic composites with TiB2 grain network

High electrical resistance and low fracture toughness of B₄C ceramics are 2 of the primary challenges for further machining of B₄C ceramics. This report illustrates that these 2 challenges can be overcome simultaneously using core‐shell B₄C‐TiB₂&TiC powder composites, which were prepared by molten‐salt method using B₄C (10 ± 0.6 μm) and Ti powders as raw materials without co‐ball milling. Finally, the near completely dense (98%) B₄C‐TiB₂ interlayer ceramic composites were successfully fabricated by subsequent pulsed electric current sintering (PECS). The uniform conductive coating on the surface of B₄C particles improved the mass transport by electro‐migration in PECS and thus enhanced the sinterability of the composites at a comparatively low temperature of 1700°C. The mechanical, electrical and thermal properties of the ceramic composites were investigated. The interconnected conductive TiB₂ phase at the grain boundary of B₄C significantly improved the properties of B₄C‐TiB₂ ceramic composites: in the case of B₄C‐29.8 vol% TiB₂ composite, the fracture toughness of 4.38 MPa·m^1/2, the electrical conductivity of 4.06 × 10⁵ S/m, and a high thermal conductivity of 33 W/mK were achieved.     

Mechanical and fracture properties of cement-based bi-materials after thermal cycling

This study investigates the effect of thermal cycles on the fracture properties of the cement-based bi-materials. Sixty eight cubes were exposed to a varied number of 24-hour thermal cycles ranging from 0 to 90 and subsequently were tested in a wedge splitting configuration. The mechanical and fracture properties of normal strength and high strength concretes are substantially improved after 30 thermal cycles, but less so after 90 thermal cycles both in isolation and when bonded to an ultra high-performance fibre-reinforced cement-based composite.     

Wavelet-based analysis of ultrasonic longitudinal and transverse pulses in cement-based materials

Ultrasonic pulse velocity has been used for decades to detect localized damage and to estimate concrete properties. More recent applications aim at diffuse damage characterization, such as environmental and mechanical damage. In most applications the methodology to calculate pulse speed is a very important issue. This work, applying continuous wavelet transform (CWT) to construct time-frequency signal representations, calculates frequency-dependent velocity of longitudinal and transverse ultrasonic pulses using wavelet scales. The method is applied to a total of 14 specimens of 5 different mixes and frequency-dependent velocities are calculated using four wavelet families. The CWT capability to decompose the inquiring pulse spectrum and analyze phase velocities is discussed with regard to wavelet, pulse type, and mixture. Frequency-dependent velocity of longitudinal pulses at lower frequencies (from 100 kHz up to 250 kHz) was proven to be much more sensitive to mix proportions than transverse pulses.     

Experimental investigation and modelling of the Na+ mobility in NaLnTiO4 (Ln = La,Nd) ceramics

In NaLnTiO₄ (Ln = La, Nd) layered perovskite-like compounds, the mobility of sodium ions was studied using impedance spectroscopy and simulated by the molecular dynamics approach. NaLnTiO₄ was prepared via a high-temperature solid-state reaction with final annealing at 900 °С. The conductivity was measured using the complex impedance technique between 1 MHz and 100 Hz in the temperature range of 523–923 K. Using the DFT (Density Functional Theory) method, the charges of atoms in the crystal structure were calculated and applied to simulate the sodium atom mobility in NaNdTiO₄ and NaLaTiO₄ crystals using classical molecular dynamics in the temperature range of 523–923 K. Based on these calculations, the dependence of the diffusion coefficients of sodium atoms on temperature was studied. The mobility of sodium ions in NaLaTiO₄ is demonstrated to be higher than that in NaNdTiO₄ because of the more ionic characteristic of its bonds.     

Assessment of the long-term stability of cementitious barriers of radioactive waste repositories by using digital-image-based microstructure generation and reactive transport modelling

Cement-based grout plays a significant role in the design and performance of nuclear waste repositories: used correctly, it can enhance their safety. However, the high water-to-binder ratios, which are required to meet the desired workability and injection ability at early age, lead to high porosity that may affect the durability of this material and undermine its long-term geochemical performance.In this paper, a new methodology is presented in order to help the process of mix design which best meets the compromise between these two conflicting requirements. It involves the combined use of the computer programs CEMHYD3D for the generation of digital-image-based microstructures and CrunchFlow, for the reactive transport calculations affecting the materials so simulated. This approach is exemplified with two grout types, namely, the so-called Standard mix 5/5, used in the upper parts of the structure, and the “low-pH” P308B, to be injected at higher depths.The results of the digital reconstruction of the mineralogical composition of the hardened paste are entirely logical, as the microstructures display high degrees of hydration, large porosities and low or nil contents of aluminium compounds.Diffusion of solutes in the pore solution was considered to be the dominant transport process. A single scenario was studied for both mix designs and their performances were compared. The reactive transport model adequately reproduces the process of decalcification of the C-S-H and the precipitation of calcite, which is corroborated by empirical observations. It was found that the evolution of the deterioration process is sensitive to the chemical composition of groundwater, its effects being more severe when grout is set under continuous exposure to poorly mineralized groundwater. Results obtained appear to indicate that a correct conceptualization of the problem was accomplished and support the assumption that, in absence of more reliable empirical data, it might constitute a useful tool to estimate the durability of cement-based structures.     

Incorporation of trace elements in Portland cement clinker: Thresholds limits for Cu, Ni, Sn or Zn

This paper aims at defining precisely, the threshold limits for several trace elements (Cu, Ni, Sn or Zn) which correspond to the maximum amount that could be incorporated into a standard clinker whilst reaching the limit of solid solution of its four major phases (C₃S, C₂S, C₃A and C₄AF). These threshold limits were investigated through laboratory synthesised clinkers that were mainly studied by X-ray Diffraction and Scanning Electron Microscopy. The reference clinker was close to a typical Portland clinker (65% C₃S, 18% C₂S, 8% C₃A and 8% C₄AF). The threshold limits for Cu, Ni, Zn and Sn are quite high with respect to the current contents in clinker and were respectively equal to 0.35, 0.5, 0.7 and 1 wt.%. It appeared that beyond the defined threshold limits, trace elements had different behaviours. Ni was associated with Mg as a magnesium nickel oxide (MgNiO₂) and Sn reacted with lime to form a calcium stannate (Ca₂SnO₄). Cu changed the crystallisation process and affected therefore the formation of C₃S. Indeed a high content of Cu in clinker led to the decomposition of C₃S into C₂S and of free lime. Zn, in turn, affected the formation of C₃A. Ca₆Zn₃Al₄O₁₅ was formed whilst a tremendous reduction of C₃A content was identified. The reactivity of cements made with the clinkers at the threshold limits was followed by calorimetry and compressive strength measurements on cement paste. The results revealed that the doped cements were at least as reactive as the reference cement.     

On the roles of HEC in Pechini sol-gel method: Enhancement of stability,wettability of the sol and surface roughness of Bi2212 film

Bi2212 superconducting thin film was prepared through a modified Pechini sol-gel method called surfactant assisted Pechini. Nitrates were used as reactors, ethylenediamine tetraacetic acid (EDTA) and hydroxyethyl cellulose (HEC) was adopted as chelating agent and surfactant respectively to prepare sol for Bi2212 film. The effects of HEC on the phase formation, crystallization behavior, morphology and superconductivity of the samples were characterized using X-ray diffraction, field emission scanning electron microscope, atomic force microscope and the standard four-probe method. C-axis epitaxial Bi2212 thin film with high Bi2212 phase purity was obtained through the modified method, and the sample had good crystallization properties, smooth surface and excellent electrical transport properties. Furthermore, a model is proposed to clarify the roles of surfactant in the preparation of Bi2212 films.     

Investigation into relations among technological properties, hydration kinetics and early age hydration of self-leveling underlayments

Technological properties such as flow value, setting times, compressive strength and early age dimensional stability as linear shrinkage and expansion have been studied for two types of self-leveling underlayments (SLU) in which the kind of calcium sulfates was varied. The influence on hydration kinetics has been measured by isothermal heat flow calorimetry. The results obtained for the technological properties change significantly when different kinds of calcium sulfates are used. The basic trend for the results changes when the composition changes from a calcium aluminate cement system to a Portland cement system. Additionally, there was an interesting relationship to final dimensional stability and shape of heat evolution curve. Moreover the time to reach plateau of dimensional stability was related to the development of compressive strength. In the meanwhile, using hemihydrate in Portland cement systems caused low compressive strength and significant expansion. On the other hand, in the results of XRD measurements, the first genesis of Ettringite corresponded to the first shrinkage of SLU. Interesting results related with technological properties and hydration kinetics or the results of XRD other than these above results were obtained.     

Synthesis and characterization of titanium complex with a dithiolate ligand for green LCD color filter dyes

Three green compounds for color filter dyes based on bis(cyclopentadienyl) titanium complexes including dithiolate ligand were synthesized. Physical properties by the change of the substitution groups of the synthesized materials were systematically examined. UV-visible absorption spectrum of the synthesized materials showed maximum absorbing wavelengths of 427 to 430 nm and 632 to 635 nm in solution state, and 434 to 438 nm and 637 to 651 nm in film state, indicating green and black colors. It was observed that the extinction coefficient values (log ε) of all the synthesized materials are very high at 4.0 or above. In addition, it was shown that since the T_d values of three synthesized materials show thermal stability higher than 240°C, they possess high potential to be applied as dyes for LCD color filter and black matrix addictive.     

Upscaling quasi-brittle strength of cement paste and mortar: A multi-scale engineering mechanics model

It is well known from experiments that the uniaxial compressive strength of cementitious materials depends linearly on the degree of hydration, once a critical hydration degree has been surpassed. It is less known about the microstructural material characteristics which drive this dependence, nor about the nature of the hydration degree–strength relationship before the aforementioned critical hydration degree is reached. In order to elucidate the latter issues, we here present a micromechanical explanation for the hydration degree–strength relationships of cement pastes and mortars covering a large range of compositions: Therefore, we envision, at a scale of fifteen to twenty microns, a hydrate foam (comprising spherical water and air phases, as well as needle-shaped hydrate phases oriented isotropically in all space directions), which, at a higher scale of several hundred microns, acts as a contiguous matrix in which cement grains are embedded as spherical clinker inclusions. Mortar is represented as a contiguous cement paste matrix with spherical sand grain inclusions. Failure of the most unfavorably stressed hydrate phase is associated with overall (quasi-brittle) failure of cement paste or mortar. After careful experimental validation, our modeling approach strongly suggests that it is the mixture- and hydration degree-dependent load transfer of overall, material sample-related, uniaxial compressive stress states down to deviatoric stress peaks within the hydrate phases triggering local failure, which determines the first nonlinear, and then linear dependence of quasi-brittle strength of cementitious materials on the degree of hydration.     

Improvements in microstructural,mechanical, and biocompatibility properties of nano-sized hydroxyapatites doped with yttrium and fluoride

Hydroxyapatite was doped with Y³⁺ (2.5, 5 and 7.5 mol%) and F⁻ (2.5 mol%) ions (2.5YFHA, 5YFHA, 7.5YFHA, respectively) to compare its structural and mechanical properties and cellular response with pure-hydroxyapatite. No second phases were observed by X-ray diffraction spectra of 2.5YFHA. Doped hydroxyapatites had F⁻ bonds in addition to OH⁻ bonds. Hydroxyapatites sintered at 900 and 1100 °C were in nano-size. 7.5YFHA sintered at 1300 °C had the highest microhardness value. 2.5YFHA sintered at 1100 °C had the highest fracture toughness value. MTT viability assays showed high cell attachments on 2.5YFHA. Cell proliferation on 2.5YFHA and 5YFHA sintered at 1100 and 1300 °C was comparable with the control after 5-day culture. The highest ALP production and calcium deposition were observed on all hydroxyapatites sintered at 1100 °C. 2.5YFHA sintered at 1100 °C can be an alternative for hydroxyapatite in orthopedic applications.     

Microstructure and mechanical properties of hot-pressed SiC/(W,Ti)C ceramic composites

SiC/(W, Ti)C ceramic composites with different content of (W, Ti)C solid-solution were produced by hot pressing. The effect of (W, Ti)C content on the microstructure and mechanical properties of SiC/(W, Ti)C ceramic composites has been studied. Densification rates of the SiC/(W, Ti)C ceramic composites were found to be affected by addition of (W, Ti)C. Increasing (W, Ti)C content led to increase the densification rates of the composites. The sintering temperature was lowered from 2100 °C for monolithic SiC to 1900 °C for the SiC/(W, Ti)C composites. Results show that additions of (W, Ti)C to SiC matrix resulted in improved mechanical properties compared to pure SiC ceramic. The fracture toughness and flexural strength continuously increased with increasing (W, Ti)C content up to 60 vol.%, while the hardness decreased with increasing (W, Ti)C content.