Crystal Grain Size Research Articles

Preparation and Application of Self-Curing Magnesium Phosphate Cement Concrete with High Early Strength in Severe Cold Environments.

The early strength of magnesium phosphate cement (MPC) decreases sharply in severe cold environments ≤−10 °C, with the 2 h compressive strength falling to 3.5 MPa at−20 °C. Therefore, it cannot be used as a repair material for emergency repair construction in such environments. In this study, MPC is adapted for use in such cold environments by replacing part of the dead-burned magnesia (M) in the mixture with a small amount of light-burned magnesia (LBM) and introducing dilute phosphoric acid (PA) solution as the mixing water. The heat released by the highly active acid–base reaction of PA and LBM stimulates an MPC reaction. Moreover, the early strength of the MPC significantly improves with the increase in the Mg2+ concentration and the initial reaction temperature of the MPC paste, which enables MPC hardening in severe cold environments. Although the morphology of the reaction products of the MPC is poor and the grain plumpness and size of the struvite crystals are remarkably reduced, the early strength of MPC prepared in the severe cold environment is close to that of MPC prepared under normal temperature. Furthermore, the increases in the early reaction temperature and early strength of magnesium phosphate cement concrete (MPCC) are significantly improved when the PA concentration in the mixing water and the LBM/M ratio are 10% and 4–6% at −10 °C and 20% and 6–8% at −20 °C, respectively. Moreover, self-curing of MPCC can be realized even at −20 °C, at which temperature the 2 h and 24 h compressive strength of MPCC reach 36 MPa and 45 MPa, respectively.

Effect of pH on the activity of ice-binding protein from Marinomonas primoryensis.

The ability of an ice-binding protein (IBP) from Marinomonas primoryensis (MpIBP) to influence ice crystal growth and structure in nonphysiological pH environments was investigated in this work. The ability for MpIBP to retain ice interactivity under stressed environmental conditions was determined via (1) a modified splat assay to determine ice recrystallization inhibition (IRI) of polycrystalline ice and (2) nanoliter osmometry to evaluate the ability of MpIBP to dynamically shape the morphology of a single ice crystal. Circular dichroism (CD) was used to relate the IRI and DIS activity of MpIBP to secondary structure. The results illustrate that MpIBP secondary structure was stable between pH 6 and pH 10. It was found that MpIBP did not interact with ice at pH ≤ 4 or pH ≥ 13. At 6 ≤ pH ≥ 12 MpIBP exhibited a reduction in grain size of ice crystals as compared to control solutions and demonstrated dynamic ice shaping at 6 ≤ pH ≥ 10. The results substantiate that MpIBP retains some secondary structure and function in non-neutral pH environments; thereby, enabling its potential utility in nonphysiological materials science and engineering applications.

G-C3N4@PMo12 composite material double adjustment improves the performance of perovskite-based photovoltaic devices

At present, reducing the defect density at grain boundaries is still the main method to improve the performance of perovskite photodetectors. The increase of grain size can also improve the performance of perovskite photodetectors. In this work, we added POM @ g-C3N4 as a dopant into the perovskite precursor solution for the first time. The doping of g-C3N4 can control the crystallization rate of perovskite, thereby passivating the charge recombination center at the grain boundary to reduce the defect density. However, the conduction band energy level of g-C3N4 is higher than that of perovskite, which is not conducive to electron transmission. Polyoxometalate (POM) H3PMo12O40 (PMo12) has very good ultraviolet–visible light absorption. Adding it to perovskite can improve the ultraviolet–visible light absorption of the perovskite layer. Furthermore, the energy level of the polyoxometalate PMo12 matches the perovskite layer, which promotes the electron transport. Adding the composite material to the perovskite precursor solution not only increases the grain size of the perovskite crystals from 100 nm to 300 nm, but also increases the light absorption of the perovskite layer. Consequently, the photocurrent increased from 4.5 μA to 11.5 μA under the double regulation of the composite material, which is 2.6 times of the photocurrent of the reference group. This work provides a method of double adjustment of composite materials to increase the photocurrent of photodetectors.

Investigation of rheological behavior for commercial mold slags

Rheological behaviors of several commercial mold slags, which were designed for continuous casting of high-carbon steel, peritectic steel, and high-Al steel were studied using rotational viscometer with various rotating speeds. The crystallization rates, which were correlated with rheological behaviors, were detected by in-situ observation. The effect of steel-slag interface reaction between high-Al steel and CaO–Al2O3-based slag on the non-Newtonian fluid behaviors was also discussed. The main results demonstrated that these mold slags all belonged to pseudoplastic fluid and exhibited shear thinning characteristics. The index of flow characteristics in high temperature zone was less than 1 and fluctuated around 0.9, while in low temperature zone, n rapidly decreased from 0.9 to 0.3. The results show that the low temperature zone is more obvious than the high temperature zone for the shear thinning characteristics of the mold fluxes below the break temperature. The shear thinning was closely related to the crystallization rate and grain size of crystals precipitated within melts. Steel-slag interface reaction decreased the content of glass formers, such as SiO2 and B2O3. The crystallization capacity was enhanced, followed by a reduction of lubrication ability. It is found non-Newtonian behaviors of commercial mold slag are closely associated with their crystallization capacity, and the discussion range of viscosity temperature is more in line with the actual temperature drop range of molten flux during continuous casting, which is of great significance to understand the mechanism of shear thinning and optimize the comprehensive performances of commercial mold slags.

Improvement of Nb/Cu adhesion and increase of Nb crystal size by laser radiation

Adhesion of Nb thin film to Cu substrate and size of Nb crystal grains for RF cavities were studied depending on laser intensity and dose. Structures of Nb/Cu, obtained by magnetron sputtering with 500 ˚C (Nr.1) and 700 ˚C (Nr.2) deposition temperature, were irradiated by pulsed Nd:YAG laser. Four areas, irradiated with doses D1 = 5.6x1020, D2 = 8.8x1020, D3 = 1.76x1021 and D4 = 1.76x1022 phot/cm2, were studied. Delamination was investigated by scratching method using conical diamond indenter with force increased from 10 mN to 3.0 N. Characterization of the structure before and after the irradiation was performed using an optical microscope, AFM, SEM and XRD. Comparing with the non-irradiated area, the critical delamination force increased by 10% for sample Nr.2 and by 36% for sample Nr.1 at laser doses D2 and D4, respectively. It means that Nb coating layer of sample Nr. 1 is better than that of sample Nr.2. The decrease of average roughness of Nb layer by an order of magnitude was observed after the laser irradiation. The improvement of the structure adhesion was also observed and explained by the diffusion of Nb atoms into Cu through dislocations. The increase of Nb crystallites size from 20 to 35 nm was calculated using XRD data.

Fabrication of mullite nano ceramic through addition of long-chain carbohydrates

Compared to common coarse-grained ceramics, nano-scaled mullite ceramics exhibit unique microstructures and mechanical properties. However, fabrication of homogeneous and ultra-fine ceramic crystals still remains a major challenge. In this study, fine-grain mullite nanocrystals with uniform particle distribution have been successfully synthesized by addition of agarose, which is a long-chain carbohydrate to the precursor. The effect of length of the carbohydrate chain on the size of mullite crystals has been investigated. The results show that long-chain carbohydrate agarose results in smaller grain size of mullite crystals as compared with glucose. Moreover, nano-scaled mullite ceramics with high hardness (18.36 GPa) and fracture toughness values (3.7 MPa m1/2) were obtained owing to the high relative density and small grain size. The present work highlights its potential application as long-chain carbohydrate in producing high-performance nanoceramics.

Synthesis of silica-rich zeolite using quaternary ammonium-based templates

In this study, silica-rich zeolite was made at a ratio Si/Al = 30. The template used was cationic surfactant from quaternary ammonium, tetrapropylammonium bromide (TPAB) and cetyltrimethylammonium bromide (CTAB). The CMC for TPABr (n – C3H7)4N is 10−3 M, and spherical micelle of CTAB is 8.9x10−4 M. The concentration of the TPAB and CTAB which used in this study were 0.0325; 0.125; 0.25 and 0.5 M. The results show that the type of synthesized zeolites are silica-rich sodalite with the crystal size 216 A°. The use of quaternary ammonium-based templates can increase crystallinity and reduce the size of silica-rich sodalite crystal grains but remain in the mesopore material size range. The concentration of the tetrapropylammonium bromide (TPAB) template is very influential on surface area and pore volume, whereas for cetyltrimethylammonium bromide (CTAB) it affects surface area but not on pore volume. The largest surface area and pore volume of 96 m2/g and 3.4×10−2 obtained for silica-rich sodalite using a landfill template at small concentrations.

Effect of Cooling Rate on Crystallization Behavior of CaO-SiO2-MgO-Cr2O3 Based Slag

AbstractIn order to improve the recycling efficiency of stainless-steel slag resources, the effect of different cooling rates on the crystallization behavior of CaO-SiO2-MgO-Cr2O3 based system was studied by using FactSage 7.1, XRD, SEM and IPP 6.0. The results indicated that the spinel is a high-temperature precipitated phase and the cooling rate had less effect on the final grain size of spinel crystals, but had greater influences on the nucleation of spinel crystals and the crystallization of silicates such as α-C2S.When the cooling rate was 12∘C/min, the spinel crystals was the unique precipitation. However, the spinel crystals and α-C2S could produce during the slag cooling process as the cooling rate was1∘C/min. Chromium in silicate phase is inclinable to leaching with the dissolution of silicate phase, so the formation of silicate phase should be controlled. According to the influence of the cooling rate on the formation of spinel crystals and the erosion of spinel crystals by α-C2S, it is suggested that the cooling rate of the stainless-steel slag in industrial treatment should not be lower than 12∘C/min.

Stable Efficient Methylammonium Lead Iodide Thin Film Photodetectors with Highly Oriented Millimeter-Sized Crystal Grains

The size of crystal grains in lead halide perovskite thin films remains a vital design feature for durable optoelectronic devices. With larger crystals and reduced grain boundaries per surface area...

γ-ray shielding features and crystallization of TiO2 borotellurite glasses

Glasses of composition (60B2O3 –10 Na2O – 20TeO2 – (10-x) CaO) + xTiO2 where x ranged from 0.5 to 3 mol% have been prepared and coded as BTNCT0.0 (x = 0), BTNCT0.5 (x = 0.5), BTNCT 1.0 (x = 1.0), BTNCT2.0 (x = 2.0), and BTNCT3.0 (x = 3.0). Glass transition temperature (Tg) and crystallization temperature (Tc) have been determined for the prepared samples. The addition of small concentration of TiO2 leads to change both of Tg and Tc. The glassy temperature of this glass is about 435 °C and the crystallization temperature at about 505 °C. Heat treatment has done for the glasses to obtain the crystalline phase. This action studied by both XRD, SEM, TEM, and EDAX pictures. Results proved that the glass phase performs as interconnecting amorphous zones between the crystals and the size of crystal grains is changed from 1 μm to 20 μm. The capability of using the investigated glasses as radiation shielding glasses has been evaluated. The mass attenuation coefficient (µ/ρ) has been calculated by using WinXcom software program in the range of 0.01–15 MeV photon energy. The related shielding parameters such as linear attenuation coefficient (µ), half value layer (HVL) and mean free path (MFP) were evaluated and compared with those of commercial γ-ray shielding concrete. Results reveal that the HVL values for all investigated glasses increased except for BTNCT1.0 sample. Thus, BTNCT1.0 glass sample has the lowest HVL compared to other samples.

The effect of cooling rate on immiscible silicate liquid microstructure: an example from the Palaeogene dykes of Northeast England

AbstractThe migration and accumulation of immiscible silicate liquids may play a significant role in the differentiation of crustal magma bodies and the formation of some economic mineral deposits. However, our understanding of the processes that control the segregation of these liquids is currently limited by the short timescales of petrological experiments. Detailed microstructural investigations of Palaeogene basaltic dykes from Northeast England, coupled with simple 1D thermal models, constrain the effects of cooling rate on the microstructure of unmixed immiscible silicate liquids under natural conditions. The size of unmixed Fe-rich droplets within a continuous silicic phase is related to the cooling rate by a power law, with droplet diameter increasing with decreasing cooling rate, accompanied by an increase in the number of droplets. Fe-rich droplet coarsening is a result of diffusion-controlled growth. The average apparent aspect ratio and grain size of matrix plagioclase crystals indicate that nucleation and growth of these grains probably occurred in a static (or only weakly convecting) fluid dynamical regime.

Room-Temperature Cubic Phase Crystallization and High Stability of Vacuum-Deposited Methylammonium Lead Triiodide Thin Films for High-Efficiency Solar Cells.

Methylammonium lead triiodide (MAPI) has emerged as a high-performance photovoltaic material. Common understanding is that at room temperature, it adopts a tetragonal phase and it only converts to the perfect cubic phase around 50-60 °C. Most MAPI films are prepared using a solution-based coating process, yet they can also be obtained by vapor-phase deposition methods. Vapor-phase-processed MAPI films have significantly different characteristics than their solvent-processed analogous, such as relatively small crystal-grain sizes and short excited-state lifetimes. However, solar cells based on vapor-phase-processed MAPI films exhibit high power-conversion efficiencies. Surprisingly, after detailed characterization it is found that the vapor-phase-processed MAPI films adopt a cubic crystal structure at room temperature that is stable for weeks, even in ambient atmosphere. Furthermore, it is demonstrated that by tuning the deposition rates of both precursors during codeposition it is possible to vary the perovskite phase from cubic to tetragonal at room temperature. These findings challenge the common belief that MAPI is only stable in the tetragonal phase at room temperature.

Effect of Zr and Sc on microstructure and properties of 7136 aluminum alloy

We have linked experimental results to theoretical calculations and discussed the precipitation behavior of Zr and Sc in 7136 alloy and the influence of precipitation on the microstructure and mechanical properties of the alloy. The experimental results show that the added Sc atom can replace the Zr atom in the cubic Al3Zr phase with a lattice constant of a = 0.4417 nm, and form Al3(ScxZr1-x), which is also cubic and has a lattice constant of a = 0.4212 nm. A heterogeneous nucleation core promotes crystal-grain refinement, and the average size of the as-cast crystal grains is reduced from 82.4 μm to 51.7 μm. The valence electron structure and strongest bond energy of the Al3Zr phase with different structures was analyzed by the empirical electron theory. For Ll2-Al3Zr, the covalent electron number and bond energy of the strongest bonds are 0.3226 and 52.8 kJ/mol, respectively, and for DO23-Al3Zr, the numerical values are 0.4471 and 71.0 kJ/mol, respectively. Combined with the ab initio calculation, Ll2-Al3Zr has a good stability. Under suitable conditions, Ll2-Al3Zr will transform into the more stable DO23-Al3Zr. Quantitative analysis of the effect of strengthening mechanism such as fine grain strengthening and dispersion strengthening caused by the addition of Sc element on the yield strength of the alloy. The calculation results show that 0.2% elemental Sc addition can increase the alloy strength by 36.63 MPa, which is very similar to the measured result of 38.61 MPa.

Fabrication of PbO2/SnO2 composite anode for electrochemical degradation of 3-chlorophenol in aqueous solution

In present work, SnO2 nanoparticles were synthesized using simple hydrothermal process, and then a novel PbO2/SnO2 electrode was successfully fabricated using obtained SnO2 nanoparticles for electrochemical oxidation of 3-chlorophenol (3-CP). The microstructure, element distribution, crystal structure and chemical composition of samples were characterized by the analytical techniques including SEM, EDS, XRD and XPS. The electrochemical performances of electrodes were evaluated using LSV and CV measurements. The ·OH radicals generation capacity of electrodes was determined using terephthalic acid as trapping agent. Moreover, the PbO2/SnO2 electrodes were applied in the electrochemical degradation of 3-CP in aqueous solution. The results show that the doping of SnO2 nanoparticles reduced the grain size of PbO2 crystal and improved the content of Oads on the surface of electrode. In contrast with the pure PbO2 electrode, the PbO2/SnO2-1.0 electrode (the concentration of SnO2 in electroplating solution was 1.0 g/L) exhibited higher oxygen evolution potential, stronger direct oxidation capacity and ·OH radicals generation capacity, and superior electrochemical activity for degradation of 3-CP. The intermediates formed in electrochemical degradation of 3-CP were revealed by HPLC and a plausible degradation pathway was proposed. Furthermore, PbO2/SnO2-1.0 electrode also showed a high reusability for 3-CP degradation.

The effect of the minor Al addition on microstructure and soft magnetic properties for (Fe0.5Co0.5)73.5Si13.5Nb3Cu1B9 nanocrystalline alloy

(Fe0.5Co0.5)73.5Si13.5Nb3Cu1B9-xAlx (x = 0.2, 0.4, 0.6, 0.8) nanocrystalline alloys were investigated with the aim of improving the soft magnetic properties and keeping thermal stability of initial permeability. The temperature dependence of initial permeability (μi - T) was measured from room temperature up to 720 °C for all the alloys. The differential scanning calorimetry and X-ray diffractometry were performed for analyzing crystallization process and microstructure. Experimental results pointed out that the partial replacement of B with Al significantly decreased onset temperature of the primary crystallization (Tx1) from 498 °C to 466 °C and slightly increased the crystallized interval temperature (ΔTx) from 210 °C to 226 °C. μi of alloys annealed at 600 °C maintained a relatively stable value from ambient temperature up to 650 °C. Moreover, μi showed a slight increase with the increase of Al content from 0.2 to 0.6, which could be ascribed to the formation of the uniform nanostructure with small grain size and high volume fraction of crystals. As a result, (Fe0.5Co0.5)73.5Si13.5Nb3Cu1B8.4Al0.6 nanocrystalline alloy annealed at 600 °C exhibited excellent soft magnetic properties at high temperature.

New viewpoint about the effects of boric acid on luminous intensity of Sr2MgSi2O7: Eu, Dy

In this work, high temperature solid phase method was applied to prepare Sr2MgSi2O7:Eu, Dy blue light long-persistence materials with different contents of H3BO3. Under the condition of low H3BO3 content, it was difficult for Eu and Dy to enter Sr2MgSi2O7 lattice, impurity phase of Sr3MgSi2O8 was observed, and initial afterglow luminance of the sample was very low. With the increase of H3BO3, Sr3MgSi2O8 phase disappeared, Eu and Dy entered Sr2MgSi2O7 lattice smoothly, and the grain size as well as initial afterglow luminance of samples increased significantly. The initial afterglow luminance of the sample reached the maximum while the H3BO3 content was 10% (molar ratio). As H3BO3 content increased further, the initial afterglow luminance reduced rapidly. After detailed analysis, we consider that the key factors influencing the afterglow luminance of samples are the formation and the density of luminous unit, which is greatly determined by the Eu and Dy’s entering Sr2MgSi2O7 lattice as well as the grain size of Sr2MgSi2O7 crystal.

Effect of Mg-Based of Multi-Layered Structure on Hydrogen Desorption Properties

This study proposed the new method of preparing Mg-based composite by mixed powder Ni and Ti onto the surface of pure Mg ingot. The prepared method caused that hydrogen absorbing phase Mg2Ni and catalytic phase NiTi generated and distributed regularly. The pure Mg ingot as the center and the powder Ni and Ti as cladding material on the surface were formed and sintered, in which the temperature range of generated alloy phase Mg2Ni and NiTi was confirmed at first; according to the temperature range, the size of Mg2Ni and NiTi crystal grains at 650°C and 850°C were analyzed and compared, respectively; The size of Mg2Ni alloy phase at the surface and center was calculated by comparing the atomic radius of Ni, Ti to confirm that Mg2Ni distributed on the surface due to the atom Ti replaced the atom Ni in Mg2Ni to generate the alloy phase NiTi; the capacity of the hydrogen desorption reached 4wt% within 5min. The disadvantages that easy to chalking and difficult to activate in the conventional method were avoided and achieved the application of the multilayer composite material in hydrogen storage field.

Influence of SiO2 contents on the microstructure and mechanical properties of lithium disilicate glass-ceramics by reaction sintering

Preparation of lithium disilicate glass-ceramics was attempted via solid-state reaction between Li2SiO3 crystals and SiO2 glass. By addition of 0.5 mol Li2Si2O5 glass as binding, the mixtures were hot-pressing sintered at 840 °C for 1 h. The effect of SiO2 contents (1–2 mol) on the reaction sintering behavior, microstructure and mechanical properties of Li2Si2O5 glass-ceramics was studied. Part of SiO2 glass crystallized to quartz so that at least 1.5 mol SiO2 was needed for the complete reaction with the 1 mol LM crystals. The grain size of Li2Si2O5 crystals increased with increasing the SiO2 content depending on the degree of reaction. The flexural strength and fracture toughness of the samples both increased firstly then decreased with the increasing SiO2. After reaction, rod-like Li2Si2O5 crystals of tens microns long could be obtained, which were several times longer than the directly crystallized ones from the parent glass. Such reaction formed large Li2Si2O5 crystals apparently had an effective toughening effect without sacrificing other properties. Due to the complete reaction of 1 mol Li2SiO3 crystals by 1.5 mol SiO2 glass in the specimens of M1S1.5D0.5, high flexural strength of 373 ± 12 MPa and improved fracture toughness of 3.35 ± 0.12 MPa∙m1/2 were obtained. The improved properties were attributed mainly to crack deflexion and grain-bridging toughening mechanisms.

Effects of Starting Materials on Preparation and Properties of Pure SiC Ceramics via the HTPVT Method

The method of high temperature physical vapor transport (HTPVT) is an available approach to prepare silicon carbide (SiC) ceramics with high density and high purity. In the present work, α-SiC (6H-SiC) and β-SiC (3C-SiC) powders were used as starting materials respectively to fabricate SiC ceramics with HTPVT process, and the effects of starting materials on nucleation, density, microstructure and mechanical properties of SiC ceramics were investigated. It showed that at high temperature, the decomposition rate of β-SiC was higher than that of α-SiC, and at the initial nucleation stage, the average grain size of SiC crystal obtained with β-SiC starting materials was smaller than that with α-SiC starting materials, because higher vapour pressure of gas phase which decomposed by β-SiC starting materials facilitated nucleation and growth of SiC grains. Density of the resulted SiC ceramics using α-SiC and β-SiC as starting materials was 3.16 g·cm-3 and 3.17 g·cm-3, indicating close values, while, using β-SiC as the starting materials, the grain size was smaller, consequently, the flexure strength was higher. Increasing growth temperature from 2200°C to 2300°C, the densities and the flexure strength of the SiC ceramics using either α-SiC or β-SiC were decreased.

Microstructure and properties of CVD coated Ti(C, N)-based cermets with varying WC additions

In this paper, multilayer coatings of TiN/TiCN/Al2O3/TiN are deposited on the Ti(C, N)-based cermets containing WC, and the effect of WC on the growth and adhesion strength as well as the mechanical properties of the coating are investigated. The multilayer coatings deposited by chemical vapor deposition (CVD) are uniform and dense. TiN coating exhibits a dense fine-grained structures and the Ti (C,N) on TiN coating shows dense columnar structure. The α-Al2O3 layer deposited on transition coating presents coarse grains with limited voids. The grain size of the columnar crystals deposited on the substrates gradually decreases with WC addition. The Al2O3 layer shows a preferred growth orientation of (104) plane. For TiN/TiCN phase, a change in orientation from (111) to (200) is observed. Generally, the (200) preferred orientation enhances and (111) preferred orientation diminishes with increasing WC addition. Strong adhesion of the CVD coating is obtained due to a sufficient amount of chemical elements, especially tungsten, diffusing from the substrate to the interfacial layer. Scratch tests show that the adhesion strength of TiN/TiCN/Al2O3/TiN films gradually increases firstly, and then decreases. With the addition of WC, the hardness, elastic modulus and plasticity index increase at the beginning, and then decrease. The change in nanohardness and elastic modulus is related to the grain size, elemental diffusion, and preferred orientation of the coating.