Crystal Whiskers Research Articles

Infrared Transmission Spectra of TiS3: Fundamental Absorption Edge, Phonons, and Excitons

Transmission spectra of TiS3 single crystal whiskers in the infrared and optical bands have been studied at various light polarizations in the temperature range from room to liquid helium. The absolute absorption coefficients have been determined. Previously unknown phonon modes have been observed in the far infrared region. The study of the temperature dependence of the band gap width has shown that it increases by 50 meV under cooling from 300 to 5 K. The comparison of spectra measured at different polarization directions indicates that the optical gap is anisotropic. A 1.28-eV absorption peak has been detected below ~150 K and has been attributed to the excitation of excitons.

Improved length of calcium sulfate crystal seeds and whiskers via ball milling and hydration treatment

Elucidating the effect of growth periods on the quality of calcium sulfate whiskers (CSWs) prepared from calcium sulfate dihydrate (DH) is imperative. Herein, crystal seeds and whiskers were prepared from DH in a water–glycerol system. Longer whiskers were obtained from crystal seeds prepared via hydration of DH for 30 s than via ball milling for 5 min followed by hydration for 20 s. The attachment of cetyltrimethyl ammonium bromide and glycerol additives to the whisker tops promoted whisker growth. The whisker sponges exhibited good thermal barrier properties and compression cycle stability.

Exploring Greenockite: Occurrences and Geological Setting

Greenockite, mineral containing cadmium, is of significant scientific interest owing to its remarkable properties and potential applications in the field of science. It commonly forms in hydrothermal ore deposits as a secondary mineral due to complex cadmium-sulfur interactions influenced by temperature. Typically, it replaces zinc minerals like sphalerite, depending on the abundance of cadmium and zinc in hydrothermal fluids. Solid solubility in the ZnS CdS system occurs at high temperatures, with immiscibility observed under specific conditions. Greenockite forms at relatively low temperatures (100°C to 200°C) and is influenced by factors such as oxygen fugacity, hydrogen sulfide activity, and chloride ion content. Its hexagonal zinc blende structure results in diverse crystal forms, including rods, wires, and whiskers, often adorned with bismuth drops. Experimental studies have identified factors affecting its formation, such as solid solubility, precipitation mechanisms, pH levels, and fluid composition. Its vibrant coloration, attributed to cadmium concentration, varies from pale yellow to deep orange-red. Geologically, it is present in diverse settings, including metamorphosed zinc oxide mineralization, granites, fumaroles, pegmatites, and sediment-hosted Pb-Zn deposits, with a unique occurrence in gabbroic rock at the Babbitt deposit. In India, Greenockite has been identified in the Bagada orogenic gold prospect, situated within the Paleoproterozoic Mahakoshal belt, Central Indian Tectonic Zone (CITZ). Additionally, it is found in hydrothermal deposits of Pb-Zn mines of Zawar. It is exclusively encountered within specific geological settings, primarily as a secondary product. This paper provides a comprehensive exploration of its geological occurrences, distribution, associations, and exceptions.

Microwave-enhanced selective leaching calcium from steelmaking slag to fix CO2 and produce high value-added CaCO3

The abundant resources of steel slag make it an intriguing prospect for long-term CO2 storage by mineral carbonation. Herein, the dissolution of steel slag in an acetic acid (HAc) solution and the fixation of CO2 in the leachate of steel slag to synthesize high-value CaCO3 were investigated. Results show that the microwave water bath condition is beneficial for improving the leaching rate of Ca and Mg elements in steel slag, while the low-concentration HAc solution displays high selectivity for Ca + Mg. In a water bath reaction enhanced by microwave, the leaching rate and selectivity of Ca + Mg can be increased by elevating the reaction temperature, extending the leaching time, lowering the concentration of HAc solution, and increasing the stirring rate. The kinetic parameters of the calcium element, including the apparent activation energy, were determined to be 14.51 kJ·mol−1, suggesting control by surface chemical reactions. Finally, high-purity CaCO3 crystal whiskers can be synthesized under 400 W ultrasonic conditions with a reaction temperature of 70 ℃, reaction time of 15 min, and a solution pH at 9.1 by introducing 20 % CO2 into the leachate. This strategy facilitates the concurrent utilization of dilute CO2 flue gas and voluminous solid steel slag waste, thereby improving the economic and environmental performance of the steel industry.

Development of healthier and industrially applicable oleogel with low saturated fatty acid content using a small amount of high-melting fat

We aimed to develop a low-saturated fat oleogel with a small amount of high-melting fat and elucidate its gelation mechanism. Fully hydrogenated rapeseed oil rich in behenic acid (FHR-B), fully hydrogenated rapeseed oil rich in stearic acid (FHR-S), fully hydrogenated fish oil extracted from sardines (FHF), fully hydrogenated beef tallow (FHBT), fully hydrogenated palm oil (FHP), and fully hydrogenated hard palm mid-fraction (FHHPMF) were used as oleogelators. The gelation ability, chemical composition, crystal morphology, polymorphism, and melting properties of the prepared samples were evaluated. FHR-B, FHF, FHP, and FHHPMF formed gels with 2 wt% or lower concentrations. High-melting fat with a high gelation ability formed fibrous crystals with a high aspect ratio, that is, whisker crystals, in canola oil. The crystal morphology was affected by the triacylglycerol composition. Moreover, high-temperature storage caused the separation of TAGs, affecting the crystal morphology. Hence, high-melting fats with complex TAG compositions showed different gelation behaviors depending on the storage temperature. We confirmed that FHHPMF exhibited exceptionally high gelation ability, forming a gel at only 0.5 wt%. Therefore, FHHPMF may be a suitable oleogelator for industrial use with a controllable saturated fatty acid content and waxy mouthfeel.

Microstructure and evolution of hafnium carbide whiskers via polymer-derived ceramics: A novel formation mechanism

Polymer-derived ultra-high-temperature ceramic (UHTC) nanocomposites have attracted growing attention due to the increasing demands for advanced thermal structure components in aerospace. Herein, hafnium carbide (HfC) whiskers are successfully fabricated in carbon fiber preforms via the polymer-derived ceramic (PDC) method. A novel carbon nanotube (CNT) template growth mechanism combined with the PDC method is proposed in this work, which is different from the conventional vapor–liquid–solid (VLS) mechanism that is commonly used for polymer-derived nanostructured ceramics. The CNTs are synthesized and proved to be the templates for fabricating the HfC whiskers, which are generated by the released low-molecular-weight gas such as CO, CO₂, and CH₄ during the pyrolysis of a Hf-containing precursor. The formed products are composed of inner single crystal HfC whiskers that are measured to be several tens of micrometers in length and 100–200 nm in diameter and outer HfC/HfO₂ particles. Our work not only proposes a new strategy to prepare the HfC whiskers, but also puts forward a new thinking of the efficient utilization of a UHTC polymer precursor.

Polarization analysis of terahertz emission from Bi-2212 cross-whisker intrinsic Josephson junction devices and their refractive index

Polarization analyses of the terahertz (THz) emission from Bi2Sr2CaCu2O8+δ whisker crystals used for superconducting THz emitters were conducted. The THz emission mode was estimated by a simple polarization measurement, and a simulation study was conducted to examine the validity of the polarization analysis. The refractive index of whisker crystals revealed through the polarization analyses was greater than that of bulk single crystals and agreed well with our previous THz emission report. The simulation study suggested the complex plasma excitation mode of the THz emission, and an interpretation of the refractive index obtained in this study is provided.

Dynamical Models of Plasticity with Nonmonotonic Deformation Curves for Nanomaterials

Nanomaterials are widely used in different fields, such as microelectronics, industry, and nanocomposites, and they can exhibit unstable deformation behaviour depending on the strain rates. Under strain rates of 10−4–10−1 s−1, the deformation of nanomaterials, unlike the quasi-static deformation of micromaterials, is characterized by the presence of the rate sensitivity as a possible scale phenomenon in dynamic plasticity. In this paper, the relaxation model of plasticity for the prediction of deformation curves at different strain rates is used. It allows us to comprehensively study the effects of strain hardening in a wide range of deformation conditions for coarse-grained materials and nanomaterials. Considering the plastic deformation of the nanosized samples in the early stages, dynamical softening, associated with a generation of new defects, and dynamic hardening, are crucial. The proposed model, using one parameter or the classical hardening law as an example of nanosized gold whisker crystals, tungsten single-crystal pillars, and single-crystalline Au-Ag alloy nanowires, is verified. Calculated sets of parameters of characteristic time, as a parameter of rate sensitivity of a material, and hardening parameters for different nanomaterials are compared. It is shown that the characteristic relaxation times for the single-crystal nanomaterials (100–103 s) are greater than for the nanostructured materials (10−6–10−4 s). Despite the manifestation of dynamics at different strain rates of nanomaterials, single crystal and nanostructured materials, the proposed model can be successfully applied to materials with different degrees of hardening or softening.

Filamentous crystal growth in organic liquids and selection of crystal morphology

Filamentous crystals such as whisker crystals are often seen not only in metallic liquids, but also in organic liquids and solutions. They are interesting as reinforce materials. However, it remains challenging to induce filamentous crystals due to an incomplete understanding of the mechanisms behind their formation. In this paper, we investigate filamentous crystal growth in viscous organic liquids. It is found that filamentous crystals grow via an extraordinary dynamical path, where the molecules locally evaporate to bubbles and then redeposite to the tip of growing crystalline filaments. We also succeeded in controlling whether filamentous or faceted crystal growth is selected by inducing or suppressing the bubbles.

Growth and characterization of Bi2Sr2Ca1–x Y x Cu2O8+δ single-crystal whiskers

Substitution of Y for Ca in the Bi2Sr2CaCu2O8+δ (Bi-2212) system is known to effectively change the hole carrier density. In this paper, we report the growth and characterization of Y-substituted Bi-2212 whisker crystals. The evaluated Y content in the whiskers increased as we increased the nominal Y-ratio in the Bi–Sr–Ca–Y–Cu–Te precursor. The X-ray diffraction patterns of whiskers aligned on a glass plate only showed (00l) Bragg peaks of the Bi-2212 phase, indicating that the grown whiskers are single crystalline. The c-axis lattice parameter showed a monotonic decrease with Y-substitution. The resistivity of Y-substituted whiskers showed a systematic decrease in superconducting transition temperature and an increase in normal resistivity, suggesting that the hole carrier density was controlled via Y-substitution. Based on these results, we propose that Bi-2212 with various carrier concentrations can be easily obtained by growing Y-substituted whiskers. Furthermore, such whiskers with controlled T c might be useful for microelectronic applications such as terahertz oscillators.

Composition and structure of calcium-phosphate coatings on Ti3AlC2 produced by sol-gel synthesis

Calcium phosphate materials have been widely used in medical practice for decades. Due to their bioactivity and integration with human hard tissues. They have been produced in the form of dense and porous ceramics, powders and needle-like crystals (whiskers). Despite the high mechanical properties (hardness, compressive strength), calcium phosphate ceramics are mainly used in medicine mainly as the fillers for bone defects formed due to injuries or diseases because they have high fragility and low crack resistance. These circumstances do not allow using them in the sites that have high mechanical loads (e.g. hip surgery). To solve these problems metal implants are used. Among them, Ti-based alloys are the most widely used due to its high mechanical properties, biocompatibility and high corrosion resistance. Recently, the data on the use of MAX phases as medical materials to create the composites based on Ti3SiC2 have appeared in the literature. Calcium phosphate coatings were obtained on Ti3AlC2 substrate by the sol-gel method. The effect of temperature, holding time, chemical compositions of reactants on the phase composition and structure of the samples are discussed. XRD measurements have revealed that the initial coatings consists of nanoparticles sized 10-50 nm. Light and scanning electron microscopy (SEM) were applied to study the morphology of the coatings. It have been shown that the coatings had thickness in an interval 40-100 mm and had the homogenous structure. It has been established by X-ray phase identification that the coating after heating at 1000oC during 1 hour contained b-tricalcium phosphate (b-TCP). It was found, that the thickness and phase composition of coatings depend on the time of coating in calcium phosphate solution. The optimal conditions for the formation of coatings are established.

Dual Mechanism of Natural Polyphenols on crystal whiskers formation on calcium oxalate monohydrate crystal surface

Designing (macro)molecules controlling crystallization is an essential approach to regulate structure and properties of crystalline materials and circumvent detrimental mineralization in nature, biological, and synthetic systems. Here we discovered four novel, natural polyphenols, including gallic acid, ellagic acid, punicalagin, and tannic acid, as a new class of inhibitors for nucleation and crystal growth of calcium oxalate (CaOx), a primary constitution of kidney stones. Study of time-resolved growth reveals that polyphenols regulate the kinetics of crystal-liquid interface acting as a dual role of growth promoter and inhibitor which displays a new record of growth promotion up to 75% or complete suppression, dependent upon the modifier concentration. Time-elapsed in situ atomic force microscopy measurements unveil these modifiers regulate the growth mode from spiral-mediated to generation of two-dimensional (2D) islands and layer spreading mechanism, leading to formation of step bunches growing out of (010) surface and forming macroscopically crystal whiskers. The governing regime between growth promotion and inhibition is determined by inhibitors concentration but can be influenced by crystallization driving force. Such unique growth mechanism of crystal whiskers may also provide potential implications for understanding and synthesizing branched and hierarchical structures of biomimetic materials.

Nanostructuring of Mn(II)Pc thin films by vacuum deposition in a weak magnetic field

Manganese phthalocyanine, Mn(II)Pc, is a disc-like paramagnetic molecule whose unusual electronic structure have been studied for decades. However, no credible results on the direct impact of intrinsic molecular magnetism on the solid state properties of Mn(II)Pc are known. In this work, the Mn(II)Pc films were deposited by thermal vacuum evaporation with and without applying an external static magnetic field with a strength of a few tenths of a Tesla to the growth zone. Evolution of the microstructure of the thus formed films was documented using XRD, SEM, AFM and optical methods. In the field-free conditions, the Mn(II)Pc films deposited on the hot substrate are rather smooth, continuous and strongly textured. Large needle-like crystals (whiskers) grow when magnetic field is turned on, without noticeable correlation with the direction of field lines. However, the density of whiskers per unit area increases with increasing field strength. Possible explanations of the growth mechanism include molecular surface diffusion, adsorption energy lowering and Lorentz force but none of them is yet internally consistent.

On the Possibility of Obtaining Titanium Nitride Whisker Crystals from the Gas Phase

On the Possibility of Obtaining Titanium Nitride Whisker Crystals from the Gas Phase

Joining of Al2O3 to ZTA using a B2O3–Al2O3–SiO2 glass with in-situ precipitated whiskers

A novel B2O3–Al2O3–SiO2 (BAS) glass filler was first developed to join Al2O3 and zirconia toughened alumina (ZTA) ceramics. The microstructure, crystallization products, and interfacial reaction layer of the joint were all studied. Detailed growth process and the microstructural evolution mechanism of aluminum borate (Al18B4O33 and Al4B2O9) crystal whiskers were revealed through controlling the joining temperature and the holding time. The results showed that the Al18B4O33 and Al4B2O9 whiskers formed at the interfaces and in the joining seam, owing to the reaction between the substrates and the BAS glass system, and the precipitation out of the glass, respectively. Finally, bonded with this BAS glass filler at 1400 °C for one hour, the joints exhibited a maximum shear strength of 42 MPa at room temperature and good mechanical performance after thermal cycling.

Analysis of the Microstructure and Mechanical Properties of TiBw/Ti-6Al-4V Ti Matrix Composite Joint Fabricated Using TiCuNiZr Amorphous Brazing Filler Metal.

TiB crystal whiskers (TiBw) can be synthesized in situ in Ti alloy matrix through powder metallurgy for the preparation of a new type of ceramic fiber-reinforced Ti matrix composite (TMC) TiBw/Ti-6Al-4V. In the TiBw/Ti-6Al-4V TMC, the reinforced phase/matrix interface is clean and has superior comprehensive mechanical properties, but its machinability is degraded. Hence, the bonding of reliable materials is important. To further optimize the TiBw/Ti-6Al-4V brazing technology and determine the relationship between the microstructure and tensile property of the brazed joint, results demonstrate that the elements of brazing filler metal are under sufficient and uniform diffusion, the microstructure is the typical Widmanstätten structure, and fine granular compounds in β phase are observed. The average tensile strength of the brazing specimen is 998 MPa under room temperature, which is 97.3% of that of the base metal. During the high-temperature (400 °C) tensile process, a fracture occurred at the base metal of the highest tensile test specimen with strength reaching 689 MPa, and the tensile fracture involved a combination of intergranular and transgranular modes at both room temperature and 400 °C. The fracture surface has dimples, secondary cracks are generated by the fracture of TiB whiskers, and large holes form when whole TiB whiskers are removed. The proposed algorithm provides evidence for promoting the application of TiBw/Ti-6Al-4V TMCs in practical production.

THz emission from a Bi2Sr2CaCu2O8+δ cross-whisker junction

Cuprate superconductor Bi2Sr2CaCu2O8+δ (BSCCO) has been a promising candidate of a coherent, continuous, and compact THz light source owing to its intrinsic Josephson junction (IJJ) inside the crystal structure. In this paper, we utilized BSCCO cross-whisker (CW) junctions to produce THz emitter device using the whisker crystals which can be easily obtained compared with single crystals. As a result, we have successfully observed the emission from the CW IJJ at the frequency of ∼0.7 THz, which is the first observation of a THz emission from whiskers to our knowledge. Our findings would enlarge the applicability of BSCCO superconductors for compact THz emission sources.

Large thermoelectric power factor in whisker crystals of solid solutions of the one-dimensional tellurides Ta4SiTe4 and Nb4SiTe4

One-dimensional tellurides Ta4SiTe4 and Nb4SiTe4 were found to show high thermoelectric performance below room temperature. This study reported the synthesis and thermoelectric properties of Ta4SiTe4-Nb4SiTe4 solid solutions and Mo- or Ti-doped (Ta0.5Nb0.5)4SiTe4. Thermoelectric power of the solid solutions systematically increased with increasing Ta content, while their electrical resistivity was unexpectedly small. Mo- and Ti-doped (Ta0.5Nb0.5)4SiTe4 showed n- and p-type thermoelectric properties with large power factors exceeding 40 μW cm−1 K−2, respectively. The fact that not only Ta4SiTe4 and Nb4SiTe4 but also their solid solutions showed high performance indicated that this system is a promising candidate for thermoelectric applications at low temperatures.

High-Temperature Ceramic Composites (SiC/SiCw)

The prospects for using ceramic composite materials in place of metallic materials in heat-loaded units in advanced aircraft are examined. The manufacture of silicon carbide based ceramic composite materials, reinforced with filamentary crystals (whiskers), by means of hot-pressing and spark plasma sintering using oxide and nitride sintering additives was investigated. A complex of physical-mechanical and thermal properties of composites was investigated.

Hole-doped M4SiTe4 (M = Ta, Nb) as an efficient p-type thermoelectric material for low-temperature applications

Solid-state thermoelectric cooling is expected to be widely used in various cryogenic applications such as local cooling of superconducting devices. At present, however, thermoelectric cooling using p- and n-type Bi2Te3-based materials has been put to practical use only at room temperature. Recently, M4SiTe4 (M = Ta, Nb) has been found to show excellent n-type thermoelectric properties down to 50 K. This paper reports on the synthesis of high-performance p-type M4SiTe4 by Ti doping, which can be combined with n-type M4SiTe4 in a cooling device at low temperatures. The thermoelectric power factor of p-type M4SiTe4 reaches a maximum value of approximately 60 μW cm−1 K−2 at 210 K and exceeds the practical level in a wide temperature range of 130–270 K. A finite temperature drop by Peltier cooling was also achieved in a cooling device made of p- and n-type Ta4SiTe4 whisker crystals. These results clearly indicate that M4SiTe4 is promising to realize a practical thermoelectric cooler for use at low temperatures, which is not covered by Bi2Te3-based materials.