Interface Compositions Research Articles

Interface characteristics and precipitation during the austenite-to-ferrite transformation of a Ti-Mo microalloyed steel

The complexity of interphase precipitation in a Fe-0.19C-1.54Mn-0.4Si-0.06Al-0.13Mo-0.06Ti (at%) high strength low-alloy (HSLA) steel at an early stage of the austenite-to-ferrite transformation was studied by analyzing the solute distribution across ferrite-austenite interfaces with Kurdjumov-Sachs (K-S) and non-K-S orientation relationships (OR). Structural characterization i.e. ferrite/austenite OR and habit plane characteristics was performed by electron backscatter diffraction (EBSD) and the clustering back-calculation approach, while solute distributions i.e. the solute concentration spikes in the interface regions were studied by atom probe tomography (APT) on the specimens specifically prepared across/near the ferrite/austenite interfaces.It was shown for the first time that interphase precipitation is promoted at both types of interface: (i) a K-S OR and habit plane deviated from ideal (110)α//(111)γ and (ii) a non K-S OR. The key aspect of interphase precipitation is the distribution of solute atoms across the interface, which is pronounced Mn, Ti, Mo and C concentration spikes at the interphase boundary. In contrast, interphase precipitates were not formed at the coherent interface with a K-S OR and habit plane of (110)α//(111)γ. This was correlated with the interfacial condition, where the compositional ratio of substitutional solute and solvent elements remains almost constant across the interface, i.e. Mn and C spikes. Interface compositions in this study did not match with local equilibria (negligible partitioning local equilibrium and paraequilibrium) limits. In addition, it appeared that the interfaces with Mn, Ti, Mo and C concentration spikes form ledges leading to randomly redistributed interphase precipitates.

Optimizing Experimental Conditions for Accurate Quantitative Energy-Dispersive X-ray Analysis of Interfaces at the Atomic Scale.

The invention of silicon drift detectors has resulted in an unprecedented improvement in detection efficiency for energy-dispersive X-ray (EDX) spectroscopy in the scanning transmission electron microscope. The result is numerous beautiful atomic-scale maps, which provide insights into the internal structure of a variety of materials. However, the task still remains to understand exactly where the X-ray signal comes from and how accurately it can be quantified. Unfortunately, when crystals are aligned with a low-order zone axis parallel to the incident beam direction, as is necessary for atomic-resolution imaging, the electron beam channels. When the beam becomes localized in this way, the relationship between the concentration of a particular element and its spectroscopic X-ray signal is generally nonlinear. Here, we discuss the combined effect of both spatial integration and sample tilt for ameliorating the effects of channeling and improving the accuracy of EDX quantification. Both simulations and experimental results will be presented for a perovskite-based oxide interface. We examine how the scattering and spreading of the electron beam can lead to erroneous interpretation of interface compositions, and what approaches can be made to improve our understanding of the underlying atomic structure.

Interface Compositions as Determinants of Resveratrol Stability in Nanoemulsion Delivery Systems.

The incorporation of hydrophobic ingredients, such as resveratrol (a fat-soluble phytochemical), in nanoemulsions can increase the water solubility and stability of these hydrophobic ingredients. The nanodelivery of resveratrol can result in a marked improvement in the bioavailability of this health-promoting ingredient. The current study hypothesized that resveratrol can bind to caprine casein, which may result in the preservation of the biological properties of resveratrol. The fluorescence spectra provided proof of this complex formation by demonstrating that resveratrol binds to caprine casein in the vicinity of tryptophan amino acid residues. The caprine casein/resveratrol complex is stabilized by hydrophobic interactions and hydrogen bonds. Hence, to study the rate of resveratrol degradation during processing/storage, resveratrol losses were determined by reversed-phase high performance liquid chromatography (RP-HPLC) in nanoemulsions stabilized by bovine and caprine caseins individually and in combination with polysorbate-20. At 48 h oxidation, 88.33% and 89.08% was left of resveratrol in the nanoemulsions stabilized by caprine casein (αs1-I)/polysorbate-20 complex and caprine (αs1-II)/polysorbate-20 complex, while there was less resveratrol left in the nanoemulsions stabilized by bovine casein/polysorbate-20 complex, suggesting that oxygen degradation was involved. The findings of this study are crucial for the food industry since they imply the potential use of caprine casein/polysorbate-20 complex to preserve the biological properties of resveratrol.

Analytic description of grain boundary segregation, tension, and formation energy in the copper–nickel system

In this theoretical study, a recently proposed segregation model is applied to segregation data of an exemplary Σ5 grain boundary (GB), which is investigated using a copper–nickel embedded-atom method potential. Segregation in the semi-grandcanonical ensemble is systematically studied by varying the chemical potential in order to explore the full composition range for temperatures from 500 K to 1000 K. As a major thermodynamic feature, the mentioned segregation model avoids the usage of interface compositions, for which an arbitrary volume must be defined, but rather models the thermodynamically unambiguous solute excess. It was shown that the solute excess and the interface formation energy could be described very accurately over a wide range of temperatures and over the entire composition range based on a composition-dependent, but temperature-independent effective energy of segregation. However, the model was initially derived for systems without lattice mismatch so that interface tensions were neglected. Since the copper–nickel system exhibits a moderate lattice mismatch of roughly 2.7%, the copper–nickel system is chosen in this study to further extend the segregation model by a linear-elastic theory to also account for the interface tensions. Using this extended model, it will be shown that the solute excess, GB tensions, and GB formation energies can be derived from the effective energy of segregation for all temperatures and over the whole composition range. As in principle only one single segregation isotherm is sufficient to determine the effective energy of segregation and derived thermodynamic interface quantities, the application of this model is especially interesting for experimental evaluations.

Multicomponent diffusion in a basaltic melt: Temperature dependence

Eighteen successful diffusion couple experiments in 8-component SiO2–TiO2–Al2O3–FeO–MgO–CaO–Na2O–K2O basaltic melts were conducted at 1260 °C and 0.5 GPa and at 1500 °C and 1.0 GPa. These experiments are combined with previous data at 1350 °C and 1.0 GPa (Guo and Zhang, 2018) to study the temperature dependence of multicomponent diffusion in basaltic melts. Effective binary diffusion coefficients of components with monotonic diffusion profiles were extracted and show a strong dependence on their counter-diffusing component even though the average (or interface) compositions are the same. The diffusion matrix at 1260 °C was obtained by simultaneously fitting diffusion profiles of all diffusion couple experiments as well as appropriate data from the literature. All features of concentration profiles in both diffusion couples and mineral dissolution are well reproduced by this new diffusion matrix. At 1500 °C, only diffusion couple experiments are used to obtain the diffusion matrix. Eigenvectors of the diffusion matrix are used to discuss the diffusion (exchange) mechanism, and eigenvalues characterize the diffusion rate. Diffusion mechanisms at both 1260 and 1500 °C are inferred from eigenvectors of diffusion matrices and compared with those at 1350 °C reported in Guo and Zhang (2018). There is indication that diffusion eigenvectors in basaltic melts do not depend much on temperature, but complexity is present for some eigenvectors. The two slowest eigenvectors involve the exchange of SiO2 and/or Al2O3 with nonalkalis. The third slowest eigenvector is due to the exchange of divalent oxides with other oxides. The fastest eigenvector is due to the exchange of Na2O with other oxide components. Some eigenvalues differ from each other by <1/3, and their eigenvectors are less well defined. We define small difference in eigenvalues as near degeneracy. In strict mathematical degeneracy when two eigenvalues are identical, eigenvectors are not uniquely defined because any linear combination of two eigenvectors is also an eigenvector. In the case of near degeneracy, more constraints either in terms of higher data quality or more experiments are needed to resolve the eigenvectors. We made a trial effort to generate a set of average eigenvectors, which are assumed to be constant as temperature varies. The corresponding eigenvalues are roughly Arrhenian. Thus, the temperature-dependent diffusion matrix can be roughly predicted. The method is applied to predict experimental diffusion profiles in basaltic melts during olivine and anorthite dissolution at ~1400 °C with preliminary success. We further applied our diffusion matrix to investigate multicomponent diffusion during magma mixing in the Bushveld Complex and found such diffusion may result in an increased likelihood of sulfide and FeTi oxide mineralization.

Interfacial adhesion of alumina thin films over the full compositional range of ternary fcc alloy films: A combinatorial nanoindentation study

Combinatorial materials design of thin films allows one to investigate fundamental mechanic relationships and optimize films for engineering applications. Using a newly integrated shutter controller, specifically developed for precise control over coating design, ternary alloys with full compositional range can be deposited onto single wafers. Programmable shutters allow one to create multilayered thickness gradients of two or three different materials, which can then be annealed to create films with large compositional gradients. Two 50 nm fcc alloys (AlCuAu, AuAgPd) were magnetron sputtered onto (0001) sapphire wafers. The changing chemical composition across the wafer was investigated with energy dispersive x-ray spectroscopy and transmission electron microscopy. AlCuAu showed multiple phases and intermetallics across the wafer, whereas for AuAgPd a solid-solution was observed. Both alloys were coated with 400 nm Al2O3 (atomic layer deposition, ALD), to investigate their potential as adhesion layers for ALD coatings. Adhesion of the bilayers across the wafer was measured with instrumented nanoindentation, producing well-defined delamination-blisters. Small arrays of indents placed over the surface, each location corresponding to different adhesion layer compositions, illustrate adhesion-promoting properties of numerous interface compositions in single samples. For the two bilayer systems, adhesion mapping revealed the areas of optimum adhesion layer composition for best adhesion properties.

A New Solid-like State for Liquid/Liquid/Particle Mixtures with Bicontinuous Morphology of Concentrated Emulsion and Concentrated Suspension

Research in exploring the microstructures of the ternary liquid/liquid/particle mixture is still a challenging task due to the complex interface properties and compositions of each phase. In this work, we report a new kind of solid-like state for ternary mixtures after the addition of a surfactant, which has the bicontinuous morphology of two phases, that is, the concentrated emulsion and the concentrated noncolloidal suspension. The bicontinuous morphology was justified by optical microscopy and the unique two-step yielding behavior under large oscillatory shear flow, which has the yielding character of a noncolloidal suspension at smaller strain and that of a concentrated emulsion at larger strain. A phase diagram is constructed from the rheological measurements and morphological observations. The boundaries of the new solid-like state can be well predicted from three basic requirements on the glass forming or jamming conditions in the aqueous noncolloidal suspension phase, the aqueous emulsion phase, and the whole ternary mixture.

Optimizing giant dielectric properties via interface composition: A study of rutile-based ceramics

Abstract In this study, the interface compositions, polarization behaviors, and dielectric properties of Ti1-x(Cu0.333Ta0.667)xO2 (x = 5%, 20%, and 45%) ceramics prepared at various sintering conditions are systematically investigated. An analysis of the crystal structure, cation valence state, and element distribution indicates that increasing the sintering temperature and prolonging the sintering time hardly change the lattice symmetry of the bulk phase of the ceramics, but it does alter their interface chemical composition to produce phase separations of Cu and Ta ions and mixed valence states of Ti and Cu cations. Measurement of their dielectric properties further demonstrates that the altered interface composition changes the polarization mechanism of the ceramic samples. For Ti1-x(Cu0.333Ta0.667)xO2 ceramics, increasing the doping level (x) produces larger lattice parameters and more oxygen vacancies and Cu+ ions. Meanwhile, Cu-rich or Ta-rich phases appear at the grain boundary of the highly doped samples. The Ti0.8(Cu0.333Ta0.667)0.2O2 ceramic has giant permittivity (e’ = 65314) due to the competitive coexistence of the internal barrier layer capacitor and surface barrier layer capacitor effects. This study can provide new possibilities for the design of ceramics with desired performance characteristics by purposefully changing the interface features with different preparation conditions.

The Interfacial Characterization and Performance of Cu/Al-Conductive Heads Processed by Explosion Welding, Cold Pressure Welding, and Solid-Liquid Casting

The Cu/Al composites conductive head is widely used in hydrometallurgy as the core component of cathode plate. Its conductive properties directly affect the power consumption, and the bonding strength and corrosion resistance determine the conductive head service life. The Cu/Al conductive head prepared by explosion welding, cold pressure welding, and solid-liquid casting methods were investigated in this paper. The interface microstructure and compositions were examined by scanning electron microscope and X-ray energy dispersive spectrometry. The bonding strength, interface conductivity, and the corrosion resistance of three types of joints were characterized. The Cu/Al bonding interface produced by explosive welding presented a wavy-like morphology with typical defects and many of brittle compounds. A micro-interlocking effect was caused by the sawtooth structures on the cold pressure welding interface, and there was no typical metallurgical reaction on the interface. The Cu/Al bonding interface prepared by solid-liquid casting consisted mainly of an Al-Cu eutectic microstructure (Al2Cu+Al) and partial white slag inclusion. The thickness of the interface transition layer was about 200–250 µm, with defects such as holes, cracks, and unwelded areas. The conductivity, interfacial bonding strength, and corrosion resistance of the conductive head prepared by explosive welding were superior to the other two.

Ferroelectric Polarization in CsPbI3/CsSnI3 Perovskite Heterostructure

Ferroelectricity is believed to be an important origin for the excellent performance of halide perovskite optoelectronic devices, and building halide perovskite heterostructure is an excellent strategy to enhance performance of interfacial ferroelectric polarization. Herein, all-inorganic perovskite CsPbI3/CsSnI3 heterostructures are constructed for disclosing the interfacial electrical contacts and the ferroelectricity via first-principles calculations. In CsPbI3/CsSnI3 heterostructure, there are four kinds of electrical contacts, i.e., PbI2–SnI2, CsI–CsI, PbI2–CsI, and CsI–SnI2 interfaces. Large cation–anion displacements along z-direction are observed for all interface compositions, which indicate a strong ferroelectric field effect in the CsPbI3/CsSnI3 heterostructure. The net polarization displacements of PbI2–SnI2 and CsI–CsI interfaces are smaller than the values of PbI2–CsI and CsI–SnI2 interfaces. The interfacial ferroelectricity drives electron extraction from the perovskite and hinders electron...

Improving Electrocatalysts for Oxygen Evolution Using NixFe3–xO4/Ni Hybrid Nanostructures Formed by Solvothermal Synthesis

Spinel-type oxides have been found to be active electrocatalysts for OER. However, their semiconductor character severely limits their catalytic performance. Herein, we report a facile solvothermal pathway for the synthesis of spinel-type NixFe3–xO4 oxides/Ni metal nanocomposites. The good electrical contact between the metal and semiconductor oxide interface and well-tuned compositions of NixFe3–xO4 spinel oxides are crucial to achieve better OER performance. Specifically, the NixFe3–xO4/Ni nanocomposite sample prepared from a metal precursor ratio of y = 0.15 [y = Fe/(Fe + Ni)] that results in an x value of about 0.36 exhibits catalytic activity with an overpotential of 225 mV to achieve an electrocatalytic current density of j = 10 mA cm–2 and a Tafel slope of 44 mV dec–1 in alkaline electrolyte. This study not only provides new perspectives to designing nanocomposite catalysts for OER but also opens a promising avenue for further enhancing electrocatalytic performance via interface and composition eng...

Microstructure Evolution and Failure Analysis of an Aluminum–Copper Cathode Conductive Head Produced by Explosive Welding

In this paper, microstructure evolution and failure analysis of the aluminum-copper interface of cathode conductive heads during their use were studied. The interface morphologies, compositions, conductivity and mechanical properties were investigated and analyzed. Obvious corrosion was found on the surface of the contact interface, which was more prevalent on an Al matrix. The crack increased sharply in the local metallurgical bonding areas on the interface, with the compound volume having no significant change. The phase transformation occurred on the interface during use, which was investigated using the elemental composition and x-ray diffraction pattern. The microhardness near the interface increased accordingly. An obvious electrical conductivity decrease appeared on the Al/Cu interface of the cathode conductive head after use over a specific time interval. Therefore, the deterioration of the microstructures and corrosion are the primary factors that affect the electrical conductivity and effective bonding, which will lead to eventual failure.

Numerical modelling of moving interfaces under local equilibrium conditions

A new method is presented to simulate moving interfaces during diffusion-controlled growth under local equilibrium conditions. The position and compositions of the interface are obtained directly from the equilibrium state of the subsystem around the moving interface, without iterative calculation between diffusion fluxes and solute balance conditions. The method is applicable to general multi-component systems, and it ensures the consistency in compositions and solute balance at the interfaces; Those are ascribed to the presented consideration of subsystem around the interface region in a discretized form. Explicit equations of interface compositions and position in discretized variables are also presented for the simplified ternary systems of two-solution and compound/solution. The validity and usefulness of the method is demonstrated by simulations of the two important ternary systems; The simulation results illustrate the features of diffusion-controlled growth with different alloy compositions and diffusivities of solutes in both systems.

A new probability method to understand protein-protein interface formation mechanism at amino acid level

Protein-protein interactions and recognitions are essential for organisms to accomplish many cellular processes. The interface compositions of protein-protein complexes are the key to understand the molecular mechanisms of these processes. There are many studies on near native interface recognition for protein-protein interactions, but the formation mechanism of protein-protein interface is still ambiguous. Here, we propose a new probability method to understand protein-protein interface formation mechanism at amino acid level. The probability of two surface residues from two monomers as a true interface residue pair is estimated by their properties in the structures of protein monomers. Estimated residue pairs with interface possibilities combine together to form a protein-protein interface. The possibility values are integrated to discriminate the near native interface from non-near native ones. In this paper, five simple probability based methods are constructed for near native interface recognition based on several geometric and physicochemical descriptors. The performances are comparable to the best results reported previously, which suggests this is a promising way. The idea proposed here will have a certain significance to the future research on protein-protein interactions.

Sulfur passivation for the formation of Si-terminated Al2O3/SiGe(0 0 1) interfaces

Sulfur passivation is used to electrically and chemically passivate the silicon–germanium (SiGe) surfaces before and during the atomic layer deposition (ALD) of aluminum oxide (Al2O3). The electrical properties of the interfaces were examined by variable frequency capacitance–voltage (C–V) spectroscopy. Interface compositions were determined by angle-resolved X-ray photoelectron spectroscopy (AR-XPS). The sulfur adsorbs to a large fraction of surface sites on the SiGe(001) surface, protecting the surface from deleterious surface reactions during processing. Sulfur passivation (a) improved the air stability of the cleaned surfaces prior to ALD, (b) increased the stability of the surface during high-temperature deposition, and (c) increased the Al2O3 ALD nucleation density on SiGe, thereby lowering the leakage current. S passivation suppressed formation of GeO bonds at the interface, leaving the majority of the Al2O3–SiGe interface terminated with direct SiOAl bonding.

SEM-EDX analysis and TOF-SIMS 3D imaging of a textile/rubber interface undergoing fatigue loading

Unidirectional textile⿿rubber composites must exhibit a strong interface to reach admissible lifetime expectancy. Usually, this is achieved by coating the textile with Resorcinol-Formaldehyde-Latex (RFL). Nevertheless, former SEM observations of our composite revealed microcracks at the RFL/rubber interface. They appeared to propagate through fatigue loading, in correlation with hardening of RFL and interfacial rubber, both highlighted by nanoindentation tests. This mechanical damage was not correlated to chemical structure degradation which limited the development of more reliable interfacial materials⿿ formulations. In this perspective, EDX and ToF-SIMS are used in the present study to characterize RFL coated textile and composite's textile/rubber interface compositions, before and after different numbers of cycles of fatigue loading. Those analyses allow the identification of textile contaminants, potentially responsible for composite's initial interfacial microcracks: inorganic grains, polysiloxanes, fatty acids, latex surfactants and esters contaminants, attributed to diffusion from the RFL layer or from textile sizing. Concerning RFL hardening, four potential mechanisms can be raised: VP-latex complexation with metallic ions coming from rubber formulation, RF post-condensation or disproportion, migration of latex surfactants and thermo-oxidative degradations. This last mechanism seems to be the main one responsible for the hardening of interfacial rubber.

Non-equilibrium Solidification and Microsegregation Mechanism Based on Interface Evolution and Discrete Crystal Growth

The interface layer and discrete crystal growth in solidification are traced by analyzing the microsegregation of aluminum alloy. Based on the interface evolution and discrete crystal growth, the non-equilibrium microsegregation mechanism is qualitatively proposed. The solute content of solid is decided by the solidification temperature of interface. And the solidification temperature of interface is further decided by the evolution of interface compositions and interface temperature. The fluctuation of interface compositions and actual interface temperature persists in the whole solidification process.

Determining cooling rates of iron and stony-iron meteorites from measurements of Ni and Co at kamacite–taenite interfaces

Analyses and modeling of Ni zoning in taenite in differentiated meteorites provide metallographic cooling rates at ∼500°C that are inconsistent with conventional formation models. Group IVA iron meteorites have very diverse cooling rates of 100–6600°C/Myr indicating that they cooled inside a large metallic body with little or no silicate mantle (Yang et al., 2007). Wasson and Hoppe (2012) have questioned these diverse cooling rates on the basis of their ion probe measurements of Ni/Co ratios at the kamacite–taenite interface in two group IVA and in two group IIIAB iron meteorites. To investigate their claims and to assess methods for determining relative cooling rates from kamacite–taenite interface compositions, we have analyzed 38 meteorites—13 IVA, 14 IIIAB irons, 4 IAB complex irons, 6 pallasites and a mesosiderite—using the electron probe microanalyzer (EPMA). Ni concentrations in taenite (Niγ) and kamacite (Niα) at kamacite–taenite interfaces are well correlated with metallographic cooling rates: Niγ values increase from 30 to 52wt.% while Niα decreases from 7 to 4wt.% as cooling rates decrease. EPMA measurements of Niγ, Niα, and Niα/Niγ, can therefore be used to provide order-of-magnitude estimates of relative cooling rates. Concentrations of Co in kamacite and taenite at their interface (Coα, Coγ) are controlled by bulk Ni and Co composition, as well as cooling rate. The ratios Coα/Coγ and (Co/Ni)α/(Co/Ni)γ are correlated with cooling rate, but because of significant scatter, these parameters should not be used to estimate cooling rates. Our analyses of 13 group IVA irons provide robust support for diverse cooling rates that decrease with increasing bulk Ni, consistent with measurements of cloudy zone size and tetrataenite width. Apparent equilibration temperatures, which are inferred from Niγ values and the Fe–Ni–P phase diagram and Ni diffusion rates in taenite, show that cooling rates of IVA irons vary by a factor of ≈100, in excellent agreement with the metallographic cooling rates. Similar calculations using Niγ/Niα and Coα/Coγ ratios and phase diagram data give factors that are an order of magnitude lower but have larger uncertainties. Thus we strongly disagree with the conclusion of Wasson and Hoppe (2012) that interface concentrations of Ni and Co are in any way in conflict with the cooling rates of Yang et al. (2008). Our measurements confirm that the IVA irons could not have cooled in an asteroidal core surrounded by a silicate mantle, and also that main-group pallasites cooled slower than IIIAB irons and did not cool at the boundary between the mantle and core from which the IIIAB irons originated. Our data provide additional evidence that mesosiderites, which formed by impact mixing of Fe–Ni melt and crustal rocks, cooled at uniquely slow rates.

Composition pathway in Fe–Cu–Ni alloy during coarsening

In this work the microstructure evolution for a two phase Fe–Cu–Ni ternary alloy is studied in order to understand the kinetic composition paths during coarsening of precipitates. We have employed a quantitative phase-field model utilizing the CALPHAD database to simulate the temporal evolution of a multi-particle system in a two-dimensional domain. The paths for the far-field matrix and for precipitate average compositions obtained from simulation are found to be rectilinear. The trends are compared with the corresponding sharp interface theory, in the context of an additional degree of freedom for determining the interface compositions due to the Gibbs–Thomson effect in a ternary alloy.

Molding Compounds Adhesion and Influence on Reliability of Plastic Packages for SiC-Based Power MOS Devices

Adhesion and interface compositions of epoxy phenolic molding compounds (EMCs) for high-temperature plastic packages are studied. Interfaces are obtained by molding two EMCs onto aluminum oxide-hydroxide surfaces (oxide onto thin film of AlSiCu) and two die passivation layers consisting of fluorinated polyimide and cyclotene. One compound (A) is a “green” type, containing organic phosphorous-based flame retardant, and the other compound (B) is a conventional type containing antimony (III) oxide and bromined resin flame retardants. A high-temperature storage test at 250 °C is employed to study chemical modifications occurring at the previously mentioned interfaces. A high-temperature reverse bias test at 225 °C is employed to study the influences of the EMC chemical formulations on the reliability of plastic packages for SiC-based power MOS devices. Green compound A shows poor adhesion onto Al oxide and high adhesion strength onto both polymer passivations. The failure mechanism is mainly cohesive on the polymer passivations. The conventional compound B shows a high degree of delamination because of poor adhesion compared with the green compound. SiC-based power MOS devices assembled in plastic packages with compound A show better reliability under HTRB test at 225 °C compared with compound B.