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Synchronized activity plays an important role in sensory coding and memory and is a hallmark of functional network connectivity. However, the effect of sensory activation on synchronization and cortical functional connectivity is largely unknown. In this study, we investigated the effect of whisker activation on synchronization and functional connectivity of the primary (wS1) and secondary (wS2) whisker somatosensory cortices at the single-cell level. The results showed that during the spontaneous pre-stimulus state, neurons tended to be functionally connected with nearby neurons which shared similar tuning characteristics. Whisker activation using either ramp-and-hold stimulation or artificial whisking against sandpaper has significantly reduced the average overall pairwise synchronization and functional connectivity within the wS1 barrel and wS2 cortices. Whisker stimulation disconnected approximately a third of neuronal pairs that were functionally connected during the unstimulated state. Nearby neurons with congruent tuning properties were more likely to remain functionally connected during whisker activation. The findings of this study indicated that cortical somatosensory networks are organized in non-random small world networks composed of neurons sharing relatively similar tuning properties. Sensory whisker activation intensifies these properties and further subdivides the cortical network into smaller more functionally uniform subnetworks, which possibly serve to increase the computational capacity of the network.

Studies using functional magnetic resonance imaging assume that hemodynamic responses have roughly linear relationships with underlying neural activity. However, to accurately investigate the neurovascular transfer function and compare its variability across brain regions, it is necessary to obtain full-field imaging of both electrophysiological and hemodynamic responses under various stimulus conditions with superior spatiotemporal resolution. Optical imaging combined with voltage-sensitive dye (VSD) and intrinsic signals (IS) is a powerful tool to address this issue. We performed VSD and IS imaging in the primary (S1) and secondary (S2) somatosensory cortices of rats to obtain optical maps of whisker-evoked responses. There were characteristic differences in sensory responses between the S1 and S2 cortices: VSD imaging revealed more localized excitatory and stronger inhibitory neural activity in S1 than in S2. IS imaging revealed stronger metabolic responses in S1 than in S2. We calculated the degree of response to compare the sensory responses between cortical regions and found that the ratio of the degree of response of S2 to S1 was similar, irrespective of whether the ratio was determined by VSD or IS imaging. These results suggest that neurovascular coupling does not vary between the S1 and S2 cortices.

Since the use of the most stable Pb-based materials in the electronic industry has been banned due to human health concerns, numerous research studies have focused on Pb-free materials such as pure tin and its alloys for electronic applications. Pure tin, however, suffers from tin whiskers’ formation, which tends to endanger the efficiency of electronic circuits, and even worse, may cause short circuits to the electronic components. This research aims to investigate the effects of stress on tin whiskers’ formation and growth and the mitigation method for the immersion of the tin surface’s finish deposited on a copper substrate. The coated surface was subjected to external stress by micro-hardness indenters with a 2N load in order to simulate external stress applied to the coating layer, prior to storage in the humidity chamber with environmental conditions of 30 °C/60% RH up to 52 weeks. A nickel underlayer was deposited between the tin surface finish and copper substrate to mitigate the formation and growth of tin whiskers. FESEM was used to observe the whiskers and EDX was used for measuring the chemical composition of the surface finish, tin whiskers, and oxides formed after a certain period of storage. An image analyzer was used to measure the whiskers’ length using the JEDEC Standard (JESD22-A121A). The results showed that the tin whiskers increased directly proportional to the storage time, and they formed and grew longer on the thicker tin coating (2.3 μm) than the thin coating (1.5 μm). This is due to greater internal stress being generated by the thicker intermetallic compounds identified as the Cu5Sn6 phase, formed on a thicker tin coating. In addition, the formation and growth of CuO flowers on the 1.5 μm-thick tin coating suppressed the growth of tin whiskers. However, the addition of external stress by an indentation on the tin coating surface showed that the tin whiskers’ growth discontinued after week 4 in the indented area. Instead, the whiskers that formed were greater and longer at a distance farther from the indented area due to Sn atom migration from a high stress concentration to a lower stress concentration. Nonetheless, the length of the whisker for the indented surface was shorter than the non-indented surface because the whiskers’ growth was suppressed by the formation of CuO flowers. On the other hand, a nickel underlayer successfully mitigated the formation of tin whiskers upon the immersion of a tin surface finish.

Bio-inspired robotic whisker touch sensors exist, although the shape of the whisker is often overlooked, despite it affecting whisker mechanics and resulting whisker movements. We demonstrate here in three Carnivora species that whisker shape affects tactile interactions. We recommend that whisker shape needs to be designed specifically for a task, and suggest that this is a good area for future research.

The investigation on tin (Sn) whiskers formation has been widely applied in the field of lead-free electronic packaging. This is due to the fact that use of the Sn–Pb finishes has converted to Pb-free finishes in the electronic industry. Sn whiskers can grow long enough to cause a short circuit, which affects electronic devices’ reliability. This study investigates Sn whiskers’ formation in the thin Sn–0.7Cu–0.05Ga Pb-free solder under the influence of electromigration and thermal ageing for surface finish applications. The samples were stored in ambient conditions for 1000 h before being exposed to electromigration and thermal ageing to study the corresponding whiskers’ growth. A scanning electron microscope (SEM) was used to study the Sn whiskers’ microstructure, while an optical microscope (OM) was utilized to investigate the IMC layers in the samples. The results show that the addition of 0.05 wt.% gallium (Ga) decreased the Sn whisker’s length and growth density while simultaneously refining the IMC layers. Synchrotron micro-XRF (µ-XRF) shows the existence and distribution of Ga addition in both electromigration and thermal ageing samples. The shear test was used to determine the solder alloys’ mechanical properties. As a result, the addition of Ga to the Sn–0.7Cu solder improved the fracture morphology of solder joints. In conclusion, Ga’s addition resulted in decreasing Sn whisker formation and refining of the IMCs while also increasing the shear strength of the Sn–0.7Cu solder by ~14%.

Fly ash is a by-product from burning of coal. Utilization of fly ash by carbothermic reduction is an effective way to recover aluminum, silicon, and iron to enhance product-added value. This work is focused on the phase transformation of Al2O3, SiO2 and Fe2O3 during carbothermic reduction of fly ash in air. A comparative analysis of carbothermic reduction of fly ash in air and in nitrogen was made. Thermodynamics analysis was performed to illustrate the possible reactions for residue and condensate. X-ray diffraction (XRD), scanning electronic microscope (SEM), and energy dispersive spectrometry (EDS) were employed to characterize the phase composition, surface morphology, and microstructure of the reduced products. Results show that Fe3Si and Fe2Si appear sequentially with increasing of temperature. Al5O6N is an intermediate compound. Residue of Al9FeSi3, Al, and Si, and condensate of SiC, AlN and C are obtained. β-SiAlON was not found in the residue. Nitrogen is involved in the reduction of Al2O3 but not in the reduction of SiO2 and Fe2O3. Carbothermic reduction of fly ash in air did not behave the same as fly ash in nitrogen.

As it becomes possible to simulate increasingly complex neural networks, it becomes correspondingly important to model the sensory information that animals actively acquire: the biomechanics of sensory acquisition directly determines the sensory input and therefore neural processing. Here, we exploit the tractable mechanics of the well-studied rodent vibrissal ("whisker") system to present a model that can simulate the signals acquired by a full sensor array actively sampling the environment. Rodents actively "whisk" ∼60 vibrissae (whiskers) to obtain tactile information, and this system is therefore ideal to study closed-loop sensorimotor processing. The simulation framework presented here, WHISKiT Physics, incorporates realistic morphology of the rat whisker array to predict the time-varying mechanical signals generated at each whisker base during sensory acquisition. Single-whisker dynamics were optimized based on experimental data and then validated against free tip oscillations and dynamic responses to collisions. The model is then extrapolated to include all whiskers in the array, incorporating each whisker's individual geometry. Simulation examples in laboratory and natural environments demonstrate that WHISKiT Physics can predict input signals during various behaviors, currently impossible in the biological animal. In one exemplary use of the model, the results suggest that active whisking increases in-plane whisker bending compared to passive stimulation and that principal component analysis can reveal the relative contributions of whisker identity and mechanics at each whisker base to the vibrissotactile response. These results highlight how interactions between array morphology and individual whisker geometry and dynamics shape the signals that the brain must process.

Si whiskers grown by Ni-Metal-Induced-Lateral-Crystallization (Ni-MILC) were grown at 413 °C, intentionally below the threshold for Solid State Crystallization, which is 420 °C. These whiskers have significant common characteristics with whiskers grown by the Vapor Liquid Solid (VLS) method. The crystalline quality of the whiskers in both methods is the same. However, in VLS, a crystalline substrate is required, in contrast to the amorphous one in Ni-MILC for the growth of single crystalline whiskers. Moreover, whiskers grown by VLS have a polygonal cross-section with their diameter determined by the diameter of the hemispherical metallic catalysts. On the other hand, in the Ni-MILC, the cross-section of the whiskers depends on the size of the NiSi2 grain from which they are emanated. This was confirmed by observing the crossing whiskers and the rotational Moiré patterns in the crossing area. The structure of disturbed short and thin nonlinear branches on the side-walls of the whiskers was studied. In the whiskers grown by the VLS method, significant contamination occurs by the metallic catalyst degrading the electrical characteristics of the whisker. Such Si whiskers are not compatible with the current CMOS process. Whiskers grown by Ni-MILC at 413 °C are also contaminated by Ni. However, the excess Ni is in the form of tetrahedral NiSi2 inclusions which are coherent with the Si matrix due to the very low misfit of 0.4% between them. These whiskers are compatible with current CMOS process and Thin Film Transistors (TFTs).

The addition of CaF2@SiO2 and SiC whiskers to ceramic tools can improve their flexural strength and fracture toughness, reduce surface damage, and improve their cutting performance. The cutting experiments showed that under the same cutting conditions, the surface roughness of the workpiece processed with the Al2O3/TiC/SiC/CaF2@SiO2 (ATSC10) tool was significantly lower than that of the workpiece processed with the Al2O3/TiC/ SiC (ATS) tool. Additionally, the main cutting force and cutting temperature when cutting with the ATSC10 tool were lower by 30 and 31.7%, respectively. These results were attributed to the precipitation of CaF2 from the nanocoated particles during cutting and the formation of a uniform and continuous lubricating film on the surface of the tool. The wear on the front surface of the ATS tool was mainly adhesive, and that on the back tool surface was mainly abrasive. For ATSC10, the main forms of wear on the tool front surface were adhesive and abrasive, whereas the main form of wear on the tool back surface was abrasive with slight adhesive wear. The addition of nano-coated particles and whiskers improved the mechanical properties of the cutting tool while maintaining good cutting performance.

Materials and processes currently used for 1st level interconnects are reviewed, and possible options for achieving significant reductions in temperatures to which the processor is exposed during packaging are considered. While the low melting point tin-bismuth alloys that are being introduced to board level assembly are potential candidates for 1st level interconnect, it has yet to be confirmed that other properties of these alloys are consistent with the requirements of materials needed to make fine pitch connections in close proximity to the processor. Of particular concern is the possibility of alpha emissions, microstructural stability, susceptibility to electromigration, whisker growth, and the possibility of polymorphic transformation of the tin phase at the cryogenic temperatures to which some processors might be exposed. For high frequency circuitry the inductance and the capacitance properties of the interconnect material also have to be taken into account. Consideration has to be given to whether the low melting point indium alloys that are used in the attachment of IR Focal Plane Arrays could be used for 1st level interconnects. Where the mechanical properties of low melting point alloys might not be sufficient to cope with possible service conditions, there are methods for forming a bond that is substantially comprised of intermetallic compounds at temperatures lower than the process temperatures required for reflow of conventional lead-free solders.

It is eagerly required to prevent external stress type Sn whisker generated from Sn plating film on connecter joints because it causes short circuits. We evaluated a variety of Sn plating films using various current waves and conducted external stress type whisker test. The results showed that Sn plating film using periodic reverse (PR) current was most effective to suppress the whisker growth. We analyzed the plating films by XRD to investigate the mechanism of the whisker suppression. The plating film using PR current had large numbers of Sn crystal orientations than other current waves. We believe that controlling Sn crystal orientations is a key factor to suppress Sn whisker growth.

One of the hardly predictable issues in the case of solder joints are tin whiskers. Tin whiskers are electrically conductive crystals that spontaneously grow on a surface. This article deals with tin whiskers growth on the three types of metallization (pure tin, SnCu1 and SnCu3 solder alloy) of the copper substrate. Two stressing factors were considered in the experiment – temperature ageing (three temperature conditions were chosen: 20 °C, 50 °C and 80 °C) and mechanical stress via bend of wire before and after the soldering process. The incidence of whiskers on the surfaces was observed by confocal microscopy. The results show that the major influence on whiskers incidence has two factors, mechanical stress followed by the influence of temperature. Whereas the other factor – copper content in used materials showed a minor influence on whiskers incidence.

Tactile sensing can provide sufficient cues concerning the geometry and texture of the contact in unknown environments. This paper proposes a semi-flexible triboelectric bionic whisker sensor (TBWS) as a novel scheme for robotic tactile perception. To be specific, it comprises power generation units (38mm in length, 18mm in width, and 10mm in thickness), octagonal plate, carbon fiber shaft (300mm in length, 1.5mm in diameter), shape memory alloy, and supporting parts. The octagonal plate hit the power generation units resulted from the carbon fiber shaft subjected to the external force, allowing to gene rate signals from the principle of via triboelectric and electrostatic induction. One another feature of the proposed sensors is that it is inspired by the structure of rat whisker follicles characterized by complex higher-order dynamics. Experimental result shows that TBWS can help robots accomplish autonomous work in complex environments. There is no doubt that the invention of sensor TBWS provides a new direction for robots’ future research.

This research aims to study the corrosion rate and characteristics of corrosion products of carbon steel due to exposure in the environment of Banda Aceh, Indonesia. The ASTM G50 was used as the basis for the specifications of the specimens for corrosion rate calculation. The corrosion rate was calculated based on ASTM G1. The features of corrosion products studied are morphological features, types, and chemical compounds of the rust. These characteristics were identified using scanning electron microscopy (SEM) and x-ray diffractometer (XRD). The corrosion rate of carbon steel was obtained using the weight-loss method. The study was conducted for twelve months, i.e. January to December of 2018. After one year of exposure, it was found that the highest corrosion rate occurred in the March–April period which was 0.024 mpy and falls into outstanding category of relative corrosion resistance. Various morphological features of corrosion products found during the period of exposure, including worm nest, bird's nest, globular, cotton ball, laminar, lath, bar, needle-shaped, and whisker structures. These structures were lepidocrocite (γ-FeOOH) and goethite (α-FeOOH). During twelve months of exposure, corrosion products formed were dominantly lepidocrocite and goethite. It was found that the lepidocrocite might transform into goethite through prolonged exposure time., Atmospheric Corrosion, Banda Aceh, Corrosion Product, Carbon Steel, SEM, XRD

Neurons in the barrel cortex respond preferentially to stimulation of one principal whisker and weakly to several adjacent whiskers. Such integration exists already in layer 4, the pivotal recipient layer of thalamic inputs. Previous studies show that cortical neurons gradually adapt to repeated whisker stimulations and that layer 4 neurons exhibit whisker specific adaptation and no apparent interactions with other whiskers. This study aimed to study the specificity of adaptation of layer 2/3 cortical cells. Towards this aim, we compared the synaptic response of neurons to either repetitive stimulation of one of two responsive whiskers or when repetitive stimulation of the two whiskers was interleaved. We found that in most layer 2/3 cells adaptation is whisker-specific. These findings indicate that despite the multi-whisker receptive fields in the cortex, the adaptation process for each whisker-pathway is mostly independent of other whiskers. A mechanism allowing high responsiveness in complex environments.

Nearly all mammals have a vibrissal system specialized for tactile sensation, composed of whiskers growing from sensor-rich follicles in the skin. When a whisker deflects against an object, it deforms within the follicle and exerts forces on the mechanoreceptors inside. In addition, during active whisking behavior, muscle contractions around the follicle and increases in blood pressure in the ring sinus will affect the whisker deformation profile. To date, however, it is not yet possible to experimentally measure how the whisker deforms in an intact follicle or its effects on different groups of mechanoreceptors. The present study develops a novel model to predict vibrissal deformation within the follicle sinus complex. The model is based on experimental results from a previous ex vivo study on whisker deformation within the follicle, and on a new histological analysis of follicle tissue. It is then used to simulate whisker deformation within the follicle during passive touch and active whisking. Results suggest that the most likely whisker deformation profile is “S-shaped,” crossing the midline of the follicle right below the ring sinus. Simulations of active whisking indicate that an increase in overall muscle stiffness, an increase in the ratio between deep and superficial intrinsic muscle stiffness, and an increase in sinus blood pressure will all enhance tactile sensitivity. Finally, we discuss how the deformation profiles might map to the responses of primary afferents of each mechanoreceptor type. The mechanical model presented in this study is an important first step in simulating mechanical interactions within whisker follicles., Author summary Many mammals rely on whiskers as a mode of tactile sensation, especially when exploring in darkness. Active, rhythmic protraction and retraction of the whiskers, commonly referred to as “whisking,” is observed among many whisker specialist animals. During whisker-based sensing, forces and moments generated by external stimuli are transmitted to the base of the whisker shaft inside the follicle. Within the follicle, the interaction between the whisker’s deformation and the surrounding tissue determines how different groups of mechanoreceptors will deform, thereby transducing the mechanical signals into electrical signals. However, it is not yet possible to experimentally measure this interaction in vivo. We therefore created a mechanical model of the follicle sinus complex to simulate whisker deformation within the follicle resulting from external whisker deflection. Our results provide the first estimate of whisker shape as it deforms in the follicle, during both passive touch and active whisking. In turn, these shape estimates allow us to predict how the whisker will deform against different types of mechanoreceptors at different locations within the follicle. In addition, we find that both intrinsic muscle contraction and an increase in blood pressure will improve the tactile sensitivity of the whisker system.

The features of nucleation and the mechanisms of further growth of nano- and microsized filamentary crystals (so-called whiskers) of fullerene in the volume of an isolated evaporating drop of a C60 molecular solution in ortho-xylene on a smooth surface of silicon and glass substrates have been studied for the first time. The morphological features and the exact dimensional characteristics of nanostructured mC60 fullerene filamentary crystals (where m is the number of spherical C60 macromolecules in the synthesized whisker) that are promising for the creation of nano- and micro-dimensional photoelectric converters in solar energy were determined by high-resolution scanning electron microscopy. When a drop of a molecular solution of C60 in ortho-xylene is transferred onto the surface of an optically smooth glass substrate, filamentary crystalline structures (nanowhiskers) with sizes of ∼250–700 nm in length and ∼50 nm wide were synthesized in the process of natural thermal evaporation of an organic solvent at room temperature (T ≈ 25°С). In this case, the surface of the resulting mC60 nanowhiskers is molecularly smooth, and the roughness does not exceed ∼5 nm. It has been found that at a temperature of silicon substrate T ≈ 35°С, not only the nucleation and growth of crystalline structures of filamentary nanocrystals in a volume of evaporating drop of C60 solution are accelerated, but there is also a significant (more than two orders of magnitude) increase in the final geometric dimensions of the synthesized whiskers. The ratio of the length (L ≈ 80 μm) to width (D ≈ 7.0 μm) of the filamentary crystals is approximately 11 : 1. A nanostructured organic semiconductor coating with a thickness of 10 μm, consisting of closely spaced mC60 filamentary crystals and a molecular layer of fullerene C60 on the smooth surface of a plane silicon substrate has been obtained for the first time.

Spray drying, binder jetting and chemical vapor infiltration (CVI) were used in combination for the first time to fabricate SiC whisker-reinforced SiC ceramic matrix composites (SiCW/SiC). Granulated needle-shaped SiCW was spray dried into SiCW spherical particles to increase flowability and thereby increase printability. Then, binder jetting was employed to print a novel SiCW preform with two-stage pores using the SiCW spherical particles. The subsequent CVI technology produced pure, dense, and continuous SiC matrix with high modulus and strength. Consequently, SiCW/SiC with appropriate mechanical properties was obtained. Finally, the challenges of the novel method and the ways to improve the mechanical properties of SiCW/SiC are discussed.

This paper presents the results of a research program set up to evaluate atomic layer deposition (ALD) conformal coatings as a method of mitigating the growth of tin whiskers from printed circuit board assemblies. The effect of ALD coating process variables on the ability of the coating to mitigate whisker growth were evaluated. Scanning electron microscopy and optical microscopy were used to evaluate both the size and distribution of tin whiskers and the coating/whisker interactions. Results show that the ALD process can achieve significant reductions in whisker growth and thus offers considerable potential as a reworkable whisker mitigation strategy. The effect of ALD layer thickness on whisker formation was also investigated. Studies indicate that thermal exposure during ALD processing may contribute significantly to the observed whisker mitigation.

A commercial carbon whisker reinforced polylactic acid composite made by a type of three-dimensional (3D) printing known as material extrusion additive manufacturing is investigated. The primary ob...

Ultrasonic vibration–assisted drilling (UVAD) can significantly improve the quality of the hole while reducing the axial force of drilling, which has important application prospects. In order to reveal the variation law of drilling force under the joint action of ultrasonic vibration and cutting heat, and to guide the optimization of high-efficiency UVAD process, titanium matrix composites TiBw/TC4 (TiB whisker volume fraction of 8.5%) is taken as the research object. Firstly, based on the theory of fracture indentation and the theory of ordinary drilling (OD), the comprehensive softening coefficient of the material under the action of ultrasonic impact and cutting temperature is introduced, and the model of axial drilling force considering the softening effect is established. Secondly, the experiment of UVAD was carried out, and the interaction mechanism about drilling force and vibration impact and drilling temperature was analyzed. Finally, the experimental data was used to establish the softening coefficient response surface, which described visually the variation law of the softening coefficient. The feasibility of the drilling force model was verified, and the trend between the drilling parameters and the drilling force was analyzed. The results show that the error between experimental axial drilling force value and prediction value of UVAD is less than 10%, and the maximum axial drilling force is about 23.1% lower than OD.

Sn Cu alloy electrodeposits have found a wide range of applications in the electronics, automotive and aerospace industries. In the current research, the electrodeposition of Sn Cu alloy coatings produced from an electrolyte based on fluoroboric acids was thoroughly studied. The cathode current density was found to have a significant impact on the appearance and the surface morphology of Sn Cu alloy electrodeposits. Our experimental results suggested that deposition current density, magnetic agitation and pulsed current parameters (pulse frequency and duty cycle) were all found to be crucial factors significantly affecting the chemical composition of the Sn Cu alloy electrodeposits. In addition, the employment of pulsed current techniques significantly improved the edge effect and the surface roughness. Whisker growth on the Sn Cu alloy electrodeposits was assessed. All the samples subjected to different electroplating condition were prone to develop Sn whiskers after a few weeks of storage at room temperature.

In this study, composite ceramics with tunable electromagnetic properties were developed based on SiC-Si3N4 hybrids. First, SiC-Si3N4 whisker preforms with various SiC whisker (SiCw) concentrations were prepared by the nitridation of Si in SiCw-Si powder compacts. The in-situ-grown Si3N4 whiskers (Si3N4w) were dispersed uniformly in the voids inside the interconnected network formed by SiCw. The whisker reinforcements effectively toughened the SiBCN matrix through interface debonding, crack deflection and whisker pullout mechanisms. The electromagnetic properties of the composite ceramics can be tuned by adjusting the composition of (SiC-Si3N4)w preforms. The composite ceramic with 31.9 vol% SiCw exhibited the broadest effective absorption bandwidth (EAB) of 2.9 GHz in X band. Furthermore, a multilayer radar absorbing structure (RAS) composed of ceramic composites with gradient electromagnetic parameters was constructed to further improve the absorption properties. By adjusting the structure of the RAS, the resulting EAB of the RAS covered the entire X band.

Tin whisker growth, which may lead to short circuits and current leakage, is a serious issue in electronics components. Polyurethane-based conformal coatings have been seen as an effective candidate to mitigate the tin whisker growth. To better understand the effect of such coatings, this study exposed the tin-plated copper coupons coated with i) moisture cured polyurethane (PU) and ii) dual UV/moisture cured polyurethane acrylate (PUA), for long-term (up to 5000 h) high-temperature and high-humidity (HTHH) storage (85 °C and 85%RH, respectively). After HTHH storage, microstructural developments in the tin layer, coating degradation, tin surface reaction, and coating adhesion to tin surface were analyzed to compare the tin whisker mitigation behavior. In order to improve the coating adhesion, tin surface was also treated with a silane adhesion promoter before coating was applied. Furthermore, the effect of electron beam irradiation was investigated as it degraded the coating properties and adhesion. The results show that maintaining good adhesion and suppressing the degradation of mechanical properties of conformal coatings during various environmental exposures are essential for enhanced tin whisker mitigation.

High-strength insulating ceramic materials were prepared using lightweight mullite microspheres with dense surfaces and high internal porosity as the main raw material and silica sol as a binder. The effects of AlF 3 ·3H 2 O content on the in situ formation and growth of mullite whiskers were analyzed by X-ray diffraction and scanning electron microscopy. The obtained results showed that mullite whiskers were formed in large quantities at 1200 °C using AlF 3 ·3H 2 O and V 2 O 5 as additives; their optimal growth was observed at 4 wt% AlF 3 ·3H 2 O and 1 wt% V 2 O 5 . The apparent porosity of the produced specimens was 39%; the MOR and CCS of the specimens were 31 and 152 MPa, respectively; the HMOR at 1300 °C was 11.32 MPa; and the thermal conductivity at 900 °C was 0.783 W m −1 K −1 . The staggered whisker network structure formed between mullite microspheres not only improved the mechanical properties of the material, but also refined its pore size, reduced the thermal conductivity, and enhanced the thermal insulation properties.

Spontaneous tin whisker growth has been mysterious and catastrophic for more than half century. The difficulty in the research on this topic consists of the randomness of the whisker growth, the slow growth rate and many other tricky factors. Herein, with Ti2SnC-Sn as a new platform, fast tin whisker growth is realized to facilitate the research. The whisker morphology is found to be modulated by oxide film. A striated whisker morphology forms as growing in air, whereas a faceted morphology forms in vacuum. Furthermore, the evolution to the faceted morphology is attributed to the reconstruction of the whisker surface driven by surface energy reduction. The findings might open a new avenue to uncover the myths of this long-standing issue, and thus develop a long-awaited lead-free tin whisker mitigation strategy.

The crack healing properties of Si3N4 composite ceramic reinforced by SiC whiskers (Si3N4/SiCw) was studied. Six kinds of pre-cracks were introduced on the center of the tensile side of the specimens, and the relationship between the crack area and crack healing properties was studied. The results show that the healing effect of strength recovery is similar with that of smooth specimens for pre-cracked specimens with crack depth less than 60 μm. As for the propagated crack and the central through crack, the strength recovery rapidly decreases due to the increase of crack depth. It could be concluded that it is difficult to heal pre-cracked specimens with the crack depth over 90 μm. The main reason is considered to be that the melted glass phase blocked in the surface, and prevented the oxidation reaction in the inner of crack.