Growth Mechanism Of Whiskers Research Articles

Growth mechanism of high-aspect ratio zirconia whisker by molten salt method

Growth mechanism of high-aspect ratio zirconia whisker by molten salt method

Spontaneous growth of Sn whisker on the hot-dipping Al[sbnd]Sn alloy coating on Fe-Cr-B cast steel

Although the MAX phase solid solutions and spontaneous growth of Sn whiskers had been reported widely, the study on the spontaneous growth of whisker at room temperature on the MAB phase was very rare. In our previous work, the periodic layered structure consisted of alternatively arranged Cr-Al-B MAB phase and FeAl3 was formed during the hot-dip aluminizing of Fe-Cr-B cast steel. Herein, the Cr-(Al, Sn)-B MAB phase solid solution was prepared by HDA of Fe-Cr-B cast steel in a AlSn alloy melt and subsequently thermal diffusion treatment. Sn atoms in the Al melt could partially occupy the positions of Al atoms in the Cr-Al-B MAB phase by A-site replacement approach, which resulted in the formation of the Cr-(Al, Sn)-B MAB phase solid solution. Subsequently, spontaneous growth of β-Sn whisker occurred on the Cr-(Al, Sn)-B MAB phase solid solution at room temperature. The original Sn source was the pure Sn phase among the grains of Cr-(Al, Sn)-B MAB phase solid solution. The mass transport pathway for maintaining the spontaneous growth of Sn whiskers was: pure Sn among the grains of Cr-Al-B MAB phase→ Cr-(Al, Sn)-B MAB phase→ SnO2 → Sn whisker. The spontaneous growth of Sn whisker in the air resulted in the deep grooves covered on the surface of whisker, while, growth in the vacuum resulted in the prism structure at the bottom of whisker. The spontaneous growth of Sn whisker could grow from both the bottom and the tip. The findings will expand the family of MAB phase and help well understand the growth mechanism of Sn whisker.

Microstructure characterization and growth mechanism of ZrC whiskers prepared by precursor transformation method

ZrC whiskers were prepared on graphite through precursor transformation method. Effects of heat treatment temperature, catalyst concentration and heat treatment time on phase composition and microstructure of the ZrC whiskers were investigated. Growth mechanism of the ZrC whisker was analyzed. Results indicated that as heat treatment temperature increasing, catalyst activity increased and energy barrier for the carbothermal reduction reaction reduced, resulting in a gradual increase of both production and diameter of the ZrC whiskers. Catalyst could provide nucleation points for the ZrC whiskers, production and diameter of the ZrC whiskers firstly increased as the catalyst concentration increasing. While, when catalyst concentration was over high, length-diameter ratio of the ZrC whiskers decreased and some whiskers were agglomerated. Heat treatment time affected extent of the carbothermal reduction reaction. Production and length-diameter ratio of the ZrC whiskers increased firstly and then decreased with the increase of heat treatment time. When heat treatment temperature was 1600 °C, catalyst concentration was 0.4 mol/L, heat treatment time was 2 h, the ZrC whiskers with diameter of around 130 nm and length of tens of microns were synthesized. The whiskers were composed of a single-crystal ZrC core and an amorphous ZrO2 shell. Growth of the ZrC whiskers was controlled by solid-liquid-solid (S-L-S) mechanism and the Ostwald ripening mechanism.

Microwave-hydrothermal synthesis of calcium borate whiskers: Influencing factors and formation mechanism

The synthesis of whiskers is an important means of high-value utilization of calcium resources. Calcium borate (Ca2B2O5·H2O) whiskers were synthesized by microwave hydrothermal method using CaCl2, Na2B4O7·10H2O and NaOH as raw materials at 140 °C for 2 h. A series of characterizations were conducted on the obtained calcium borate whiskers, including phase identification (XRD and FT-IR), crystal morphology (SEM), crystal structure (TEM and SAED), and thermal stability (TG). Through batch experiments under the control of influencing factors, the effects on product phase and morphology were systematically studied, such as raw material concentration (Ca2+ concentration and the molar ratio of boron/calcium), reaction temperature, holding time and pH value. For the prepared calcium borate whiskers, SAED demonstrated that the whiskers have a single crystal structure, characterized by a sarciniform shape with diameter ranging from 1.2 to 3.1 μm and a length of 50 to 120 μm. And thermal analysis revealed that the calcium borate whiskers remained stable without losing crystalline water at a synthesis temperature of 140 °C, while releasing crystalline water at a temperature range of 383.6 °C to 430.9 °C. The optimal conditions for Microwave-Hydrothermal synthesis were identified based on experimental phenomena, and the solution-liquid–solid (SLS) process of whisker formation was proposed and analyzed. The possible chemical reactions and growth mechanisms of calcium borate whiskers under microwave hydrothermal synthesis were briefly proposed by adjusting the reaction conditions and observing the process of morphological changes.

Surface-Energy-Driven Tin Whisker Growth on Pure Tin

Spontaneous Sn whisker growth, as a reliability issue in electronic assemblies, has drawn much attention in the past several decades. However, the underlying mechanism is still ambiguous. Herein, the growth of Sn whiskers on pure Sn with different specific surface areas was studied to elucidate the effect of surface energy on Sn whisker growth. Though fabricated and cultivated using the same parameters, it was found that Sn whiskers were obtained on the sample of nano-Sn, which possesses excess surface energy, while no whiskers were observed on the sample of micro-Sn, indicating that surface energy plays a significant role in Sn whisker growth. In addition, the whiskering phenomenon is confirmed to be an abnormal recrystallization process according to the microstructure of the whisker root. Therefore, a Sn whisker growth mechanism companied with an abnormal recrystallization process is proposed, which is driven by the excess surface energy. This work provides a new perspective on understanding the long-standing Sn whiskering problem.

The role of stress release in shaping iron whisker morphology during oxygen removal process

Metal growth in materials manufacturing or applications can significantly impact the efficiency and performance of processes. Despite extensive research efforts to understand dendrite and whisker growth mechanisms in various processes like battery charging and metal powder production, the growth of metal during the removal of oxygen from its oxides remains poorly understood. In this study, we investigated the role of stress release in the formation of iron whiskers. Our findings emphasized the significance of the oxygen removal process from hematite (Fe2O3) to wüstite (FeO), as a crucial step in initiating the structure for subsequent iron growth. We observed that, compared to carbon monoxide (CO), hydrogen (H2) exhibited superior stress release capabilities, leading to rapid volume shrinkage in the Fe2O3 to FeO stage. This preferential stress reduction by H2 was attributed to the development of a larger-sized nanoscale hole structure on the surface of iron oxides, effectively inhibiting the growth of filament-shaped whiskers.

Mullite whisker-constructed ceramic membranes prepared from fly ash by in-situ catalytic reaction

The industrial application of ceramic membrane in wastewater treatment is usually inhibited by the high manufacturing cost. Here, a low-cost ceramic membrane with whisker-constructed microstructure was prepared using fly ash as the major material and AlF3 as the catalyst. The influence of AlF3 contents and sintering temperatures on the synthesis of mullite whiskers and consequently the permeance-selectivity of the whisker-constructed ceramic membrane, was investigated. With the increase of AlF3 content, the pore-forming mechanism of the ceramic membrane transformed from particles-packing to mullite whiskers-interlocking. The formation and growth mechanism of mullite whiskers were clarified. The formation of silicate liquid-phase during sintering accelerated the shrinkage of the ceramic membrane and merged the short and fine whiskers. For the ceramic membrane with 10 wt% catalyst sintered at 1100 °C, the porosity and average pore size corresponded to 62.3% and 0.41 μm, respectively. Thus, this work provided a strategy for the preparation of mullite whiskers-constructed ceramic membrane with high porosity at low sintering temperature, which facilitated the high-valuable utilization of fly ash spontaneously.

Formation and evolution mechanism of metal whiskers in extreme aerospace environments: A review

The spontaneous growth and evolution mechanism of metal whiskers have long been scientific problems. With the development of the integration of electronic and electrical productions, short circuits and system failures are raised by metal whiskers continuously. In the meantime, the related theories and mechanisms of whiskering problem are still vague, leading to a deficiency in the studies of environmental factors influencing the whisker phenomenon. Besides, the extreme environments such as aerospace, have been proven the accelerators to the formation of metal whiskers, resulting in a severe threaten to equipment and devices working in such environments including satellite and military equipment. To establish a comprehensive understanding to the whiskering process associated with their applicable control strategies, this study analyzes the growth phenomenon, influencing factors, formation process and evolution mechanism of metal whiskers in extreme service environments, puts forward the corresponding controlling strategies, offers a reference for the establishment of Chinese extreme aerospace strategic environment, and improves the reliability of aerospace systems.

Dynamic growth mechanism of tin whisker driven by compressive stress under thermal-mechanic-electric-diffusion coupling

The dynamic growth mechanism of tin whiskers was studied by combining the phase field method, molecular dynamics simulation, and experiments. The growth driving forces of tin whiskers were defined considering the interaction effects of intrinsic stress, temperature, concentration and current, under the effect of thermal-mechanical-electrical-diffusion coupling. Tin whisker growth is a dynamic stress accumulation and relaxation process.When the stress and stress gradient accumulate to the critical value, tin whiskers start to grow and then decrease until they stop growing. Thereafter, tin whisker growth is triggered again when the stress and stress gradient accumulate to a critical value. The electromigration effect increases the stress caused by the accumulation of anode intermetallics and promotes tin whisker growth. Three-point bending results show that the length and density of tin whiskers in high-pressure stress area are noticeably larger than other areas owing to the superposition and counteraction of stress.

Effect of MoO3 addition on fly ash based porous and high-strength mullite ceramics: In situ whisker growth and self-enhancement mechanism

In this paper, using only high alumina fly ash as raw material and MoO3 as additive agent, the high-strength porous mullite ceramics were achieved by in situ mullite whisker growth via a calcination method. The influence of MoO3 addition on pore structure and mechanical properties of as-prepared mullite ceramics was investigated. The mechanism of MoO3 promoting the formation of mullite whiskers and improving the strength of matrix was elucidated. The porous mullite ceramic reached its best performance with a high porosity of 49.4% and an improved compressive strength of 13.03 MPa with 10 wt% MoO3 addition calcinated at 1300 °C. Specifically, MoO3 facilitated the mullite whisks growth mainly by reducing melting point of amorphous SiO2/quartz and changing crystal structure of Al2O3. The larger aspect ratio of mullite grain at 1300 °C was easier to form an interlocking structure, which enhanced the strength of mullite ceramic while maintaining high porosity.

Research on MgSO4 Whiskers Grown on the Surface of Porous Materials.

The wooden sluice site of the Nanyue Kingdom in Guangzhou, China, is covered with white magnesium sulfate salt whiskers continuously growing from the surface. In this paper, polarizing microscopy, scanning electron microscopy, infrared thermography, Fourier transform infrared spectrometry, and surface tension analysis were utilized to comprehensively analyze the micromorphology of whiskers grown on the surfaces of porous materials collected at the site of Nanyue Kingdom, as well as the change laws of magnesium sulfate solution droplets on the porous hydrophilic matrix, and the migration and crystallization of magnesium sulfate solution in the capillary tube. The diameters of magnesium sulfate salt whiskers grown on the surfaces of porous samples range from 30 to 110 μm. For the first time, it is clear to see that the whisker's structure is hollow and nodular. There are solid crystalline salts in hollow tubes, and some of them are aqueous. The top sections of whiskers are approximately circular and are composed of particles with a size of about 0.4-4.0 μm. Their growth conditions are mainly characterized by the high humidity environment where the porous material is located or locally located, the formation of an annular whisker base, and the pressure difference generated during the formation progress of water-bearing crystals in the capillary of the whisker. The research results expound on the circumstances and mechanism of magnesium sulfate solution-induced whisker development on the surface of porous materials, providing a reference for the study of the whisker growth mechanism.

Study on a eco-friendly and efficient method for growing aluminum nitride whiskers

As the III-V semiconductor with the highest band gap, aluminum nitride (AlN) has broad application prospects in the deep ultraviolet (UVC) field. AlN have unparalleled advantages in the fabrication of nanodevices, making the future of aluminum nitride whiskers bright. The combination of deep-UV selectivity and low-voltage operation makes AlN nanowires the best candidate for developing compact deep-UV photodetectors. In this article, a high-efficiency, eco-friendly AlN whisker preparation technique is introduced on (0001) sapphire substrate without metal catalysts. The as-obtained AlN whiskers have hexagonal wurtzite structure and zigzag morphology, the diameter can reach below 1–10 μm（μm）, and the lengths are tens of microns. The AlN whiskers grows along the [100] direction, but the crystal orientation of growth can be changed by adjusting the V/III ratio. The possible growth mechanism of AlN whiskers is described in the report.

Tin whisker growth from titanium-tin intermetallic and the mechanism

• Tin (Sn) whiskers were observed to grow out of Ti 6 Sn 5 intermetallic particles. • The critical role (as tin atom source) of Ti 6 Sn 5 intermetallic compound in Sn whisker growth is identified. • An atomic diffusion-based whisker growth model is proposed, and a new preparation method of metal nanowires is expected. Spontaneous growth of metal whiskers, represented by tin whiskers, has haunted tin-based platings and solder joints for decades and caused huge losses to the electronics industry. Despite numerous efforts, the underlying growth mechanism has been resisting interpretation, and the whiskering phenomenon even continues to expand its territory. Here, we report the growth of tin whiskers from a Ti 6 Sn 5 intermetallic. These tin whiskers share similar characteristics with those found on the platings or solder joints, but grow more and faster, with finer diameters. After tin whisker growth, Ti 6 Sn 5 retains its crystal structure, implying a dealloying process. Combining experimental and first-principles calculation results, we analyzed the growth mechanism of tin whiskers in detail, and proposed a diffusion-based growth model. The strain energy stored in Ti 6 Sn 5 during deformation provides a driving force for whisker growth, and the short-circuit diffusion paths generated by such deformation accelerate whisker growth. These findings identify the critical role of intermetallic substrate in the whiskering phenomenon, shedding new light for comprehensively understanding the whisker growth mechanisms. Furthermore, the plenty and rapid growth of tin whiskers also means a new method for the preparation of one-dimensional metallic materials.

One-step co-sintering of hierarchical mullite whisker/fiber membranes with gradient pore structures for effective filtration of dust-laden gas

Porous ceramic fiber membranes with high gas permeance have shown great potential for the treatment of dust-laden gas. However, a major challenge is posed by the micro or nano-sized solid particles which can easily block the pore channels of the fiber membranes due to the larger surface pore size. Therefore, in this work, a novel method was proposed for the in-situ growth of mullite whiskers around the surface of the mullite fibers. This method aimed to decorate the pore channels of the fiber membranes by using a layer-by-layer construction strategy. For this purpose, a dry-pressing technique was employed to prepare a “green” mullite fiber support. It was followed by the preparation of another “green” fiber layer with the addition of catalysts on this support. After the co-sintering process, hierarchical mullite whiskers with gradient pore structures were produced. The in-situ growth of mullite whiskers around the fibers decorated the pore structure. As a result, it helped in effectively capturing the solid particles in the dust-laden gas. Additionally, the co-sintering process significantly reduced the sintering consumption and fabrication period. Moreover, a detailed investigation was carried out on the construction parameters including the sintering system atmospheres, Si–Al sol addition content, AlF3 concentration, mechanism of whisker growth and stability. The findings showed that hierarchical mullite whisker/fiber membranes obtained from the proposed method had a mean pore size of 2.7 μm and gas permeance of ∼106 m3 m−2 h−1·kPa−1. The Darcy's permeability coefficient of the membranes was also higher than the membranes prepared from existing methods. Moreover, the optimized membrane showed 99.9% rejection of the solid particles in the dust-laden gas, including micron-size (2.5 μm) and nano-size (300 nm) solid particles. This work provides a novel method for the fabrication of hierarchical mullite whiskers with gradient pore structures having the capability to filter industrial dust-laden gas.

The study on modulable tin whisker growth behaviors and mechanisms on Ti2SnC

The spontaneous growth of tin whiskers has resisted interpretation for more than 70 years. Herein, tin whisker growth behaviours on Ti2SnC bulks cold-pressed under different pressures were studied. It was found that higher whisker growth propensity is reached when Ti2SnC cold-pressed under higher pressure. Several thicker whiskers with diameter more than 3 μm were observed on the samples formed under higher pressure, while the diameter of more than 50% whiskers ranges from 0.5 μm to 1.5 μm for all of the samples. An atomic motion mechanism, in which the element source supplying Sn whisker growth diffuse through the Sn atom layer in Ti2SnC lattice, and the interaction between Ti2SnC and Sn is considered to be the fundamental factor initiating the Sn whisker growth, was employed to understand the phenomena. The findings herein provide new clues to understand the tin whisker growth behaviors and modulable metal whisker fabrication.

Molecular dynamics simulation and experimental study of tin growth in SAC lead-free microsolder joints under thermo-mechanical-electrical coupling

Sn-Ag-Cu system lead-free solders are considered to be promising solder series. The growth of Sn whiskers on the solder surface is an important factor that threatens the reliability of electronic products. In this study, the IMC evolution and whiskers growth of Sn-0.3Ag-0.7Cu (SAC0307) microsolder joints under thermal-mechanical-electrical coupling were investigated by the combination of molecular dynamics simulation and experimental methods. The simulation and experimental results revealed that the electric field intensity had the greatest influence on the atomic diffusion. When the electric field intensity was 0.004 V/Å, the diffusion speed of copper atom to solder reached the maximum, and the intermetallic compounds Cu6Sn5 and Cu3Sn were formed at the interface, which provided the long-term driving force for the growth of tin whiskers at the weak oxide film on the surface. Tin whiskers were inclined to grow at the anode, while holes and cracks were tend to produce at the cathode. When the external pressure stress was 0.03 nN, most of tin atoms were precipitated. When the temperature was 393 K, the whiskers slowly grew to 3.3 µm in length at the growth rate of 0.0182 Å/s. The results can provide the basis for the growth mechanism of tin whisker in real service situations.

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.

Revealing the Pb Whisker Growth Mechanism from Al-Alloy Surface and Morphological Dependency on Material Stress and Growth Environment.

Spontaneous metallic Pb whisker formation from Pb and Bi containing Al-alloy’s surfaces is a newly discovered phenomenon. The whiskers display unique formations, growth and morphology, which give the opportunity to be applied for specialized sensor and electronics applications. Within this work, the impact of environmental conditions (gas composition and moisture) is investigated and correlated with the modification of whisker evolution and growth dynamics. Furthermore, the residual stress state of the aluminum matrix using deep cryogenic treatment is modified and used to further increase whisker nucleation and growth by up to three- and seven-fold, respectively, supported by quantitative results. The results of this paper indicate the possibility to manipulate the whisker not only in terms of their kinetics but also their morphology (optimal conditions are 20% O2 and 35% humidity). Such features allow the tailoring of the whisker structure and surface to volume ratio, which can be optimized for different applications. Finally, this research provides new insight into the growth dynamics of the whiskers through in situ and ex situ measurements, providing further evidence of the complex nucleation and growth mechanisms that dictate the spontaneous growth of Pb whiskers from Al-alloy 6026 surfaces with growth velocities up to 1.15 µm/s.

Carbothermal synthesis of high-aspect-ratio AlN whiskers using graphite felt as carbon source

In this study, aluminum nitride (AlN) whiskers were successfully synthesized via carbothermal reduction nitridation (CRN) method. Graphite felt was used as carbon source and growth substrate, while no any catalyst was introduced. It is found from TEM and SEM analysis that the AlN whiskers grew along [001] direction, presenting uniform morphology and smooth surface with a length of up to microns. The high purity and high crystallinity of the whiskers were confirmed by XRD, XPS and Raman scattering spectrum. In addition, the influence of reaction temperature was systematically investigated, and it was indicated that excessively low or high temperature could both lead to the reduced whisker yield. On basis of the working results, the underlying gas-solid (VS) growth mechanism of AlN whiskers was significantly proposed.

Molecular dynamics simulation of the interfacial evolution and whisker growth of copper-tin coating under electrothermal coupling

With the development of lead-free electronic devices, the failure caused by the growth of tin whiskers poses a potential threat to the reliability of electronic products. In this study, the modified embedded atomic potential proposed by Baskes was used to simulate the interfacial evolution and the whisker growth of copper and tin coatings under electrothermal coupling by using molecular dynamics. Numerical results show that the increase in electric field intensity and temperature can promote the diffusion of Cu atom to Sn atom, and the intermetallic compounds Cu6Sn5 and Cu3Sn are formed successively at the interface of the coating. Compression stress is formed in the coating, and the whisker is shaped at the weak part of the oxide film on the tin layer surface. The increase in electric field intensity and temperature can accelerate the growth of the whisker. This condition is because the increase in electric field intensity or temperature promotes the formation of intermetallic compounds, providing a greater driving force for the growth of tin whiskers. The results can provide a theoretical basis for the growth mechanism of tin whiskers.