Length Of Whiskers Research Articles

Refining whisker size of 2024Al/Al18B4O33w composite through extrusion and its effects on the material's micro-structures and mechanical properties

Hot extrusion is used to improve the distribution of whiskers and refine the whisker sizes of 2024Al/Al18B4O33w composite. The grain size and the ultimate tensile strength of the extruded 2024Al/Al18B4O33w composite are analyzed. The results show that the average length of whiskers decreases due to the whisker breakage. The nonuniform distributions of stress and velocity along the whisker lead to whisker breakage. The microcrack between the broken whiskers can propagate into the interface or the matrix, related to the wedge angle of the broken whisker. The extrusion is beneficial to the whisker staggered and makes it easy for the microcracks filled with matrix. The whisker breakage and the whisker staggered result in the decreasing distance between the neighboring whiskers. Due to the dislocation motion constrained by matrix and the overlap of the deformation areas, the decreasing distance between the neighboring whiskers promoting the recrystallization results in the smaller grain size. During tensile tests, due to the smaller resistance with the smaller distance between the neighboring whiskers, the cracks between the progressive broken whiskers are easy to coalesce resulting in the lower ultimate tensile strength of the extruded composite.

Deformation behavior and microstructure evolution of a Ti/TiB metal-matrix composite during high-temperature compression tests

A Ti/TiB metal-matrix composite (MMC) was produced by spark plasma sintering (SPS) using a Ti-10wt.%TiB2 powder mixture at temperatures of 850 or 1000°C, corresponding to the α or β phase fields of Ti, respectively. The structures of both conditions were similar; however, a higher fraction of unreacted TiB2 and finer TiB whiskers were observed after sintering at 850°C. The mechanical behavior and microstructural response of the MMC to uniaxial compression in the temperature range from 500 to 1050°С was studied. At low temperatures of 500–700°C, the MMC sintered at 1000°C had a greater strength and lower ductility. At higher temperatures of 850–1050°C, the MMC sintered at 1000°C was compressed to a 70% strain without cracking, whereas surface cracks were observed in the specimen sintered at 850°C. Microstructure evolution of the Ti matrix was associated with the i) formation of a cell microstructure at 500°C, ii) continuous dynamic recrystallization at 700°C, and iii) discontinuous dynamic recrystallization at temperatures ≥850°C. A considerable decreasing the length of the TiB whiskers, which occurred much slower in the β phase, was observed during deformation. The mechanisms governing the mechanical behavior in different temperature regions were established using activation energy analysis.

Effect of ZnAl2O4 coating on the compressive behaviors of aluminum borate whiskers-reinforced aluminum composites at elevated temperatures

Aluminum borate whiskers (ABOw) with or without ZnAl2O4 coating reinforced pure aluminum composites (ABOw/Al, ABOw/ZnAl2O4/Al) were fabricated by squeeze casting. The effects of ZnAl2O4 coating on the compressive behaviors, microstructures, and matrix textures of the composites were investigated at different temperatures and strain rates. The results indicate that the maximum compressive flow stress of the composites almost linearly decreases with the increase in temperature. The maximum compressive flow stress of ABOw/ZnAl2O4/Al composite is higher than that of ABOw/Al composite at the same temperature when the strain rate is larger, however, it is reversed when the strain rate is smaller. It is more serious for the fracture of whiskers in ABOw/ZnAl2O4/Al composite than that in ABOw/Al composite at the high compressive strain rate. However, the average length of whiskers in ABOw/ZnAl2O4/Al composite is larger than that in ABOw/Al composite at the low compressive strain rate. The strong matrix texture in ABOw/ZnAl2O4/Al composite appears at the high compressive strain rate, however, it is observed in ABOw/Al composite at the low compressive strain rate.

Preparation and characterization of α-chitin whiskers, chitosan nanoparticles and chitosan nanoscaffold from Parapenaeus longirostris

The α-chitin whiskers were prepared by acid hydrolysis of α-chitin from Parapenaeus longirostris shells from Moroccan local sources. A chitosan nanoscaffold in the form of a colloidal solution was obtained from the deacetylation of α-chitin whiskers under alkaline conditions. Chitosan-based nanoparticles were prepared through ionic cross-linking and gelation of chitosan by tripolyphosphate. The chemical structure and physicochemical properties of α-chitin whiskers, chitosan nanoparticles and chitosan nanoscaffold were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The length of the as-prepared whiskers ranged between 90 and 620 nm, while the width ranged between 9 and 63 nm, with the average values being about 354 and 25 nm, respectively. The obtained chitosan nanoparticles were consistently spherical with an overall diameter of approximately 32 nm. Chitosan nanoscaffold possessed an interconnected pore network with an average pore size of 200 nm.

Phenotypic analysis of parents and their reciprocal F1 hybrids in Phalaenopsis

In this study, we studied the phenotypic and breeding efficiency of Phalaenopsis reciprocal hybrids and their parents. For reciprocal hybridization, Phalaenopsis ‘KS Little Gem’ and ‘1747’ from Taiwan were used as parents. After crossing ‘KS Little Gem’ × ‘1747’ in 2010, 34 individuals from ‘KS 1059’ hybrids were developed. The crossing between ‘1747’ × ‘KS Little Gem’ resulted in the development of 63 individuals from ‘KS 1076’ hybrids. Detailed morphological characteristics of newly developed hybrids; ‘KS 1059’, ‘KS 1076’ and their parents were collected according to guidelines determined by the Korea Seed and Variety Service (KSVS). The leaf characteristics were similar in reciprocal hybrids and their parents, except in number of leaves, which as were maximal in ‘KS 1059’. In terms of flower characteristics including number of flowers, inflorescence length, pedicel length and pedicel diameter, features of the parents were combined in the hybrids. By contrast in case of flower length, both hybrids showed similarity to ‘KS Little Gem’, and a similar pattern was observed in flower width. The petal length in hybrids and parents were similar, but the petal width of hybrids was more closer to that of ‘KS Little Gem’. The length of whiskers was long in both parents, but very short whiskers were recorded in hybrids. The length and width of the apical lobe were similar in parents and hybrids, but hybrids were closer to ‘1747’. In the case of duration of of flowering, the maximum value of 123 days was recorded in ‘KS Little Gem’ similar to ‘KS 1059’, whereas ‘1747’ and ‘KS 1076’ had almost identical values. It can be concluded that to generate Phalaenopsis with a longer shelf life, ‘KS Little Gem’ might be selected as the female parent during hybridization.

Fine-scale whisker growth measurements can reveal temporal foraging patterns from stable isotope signatures

Stable isotope analysis of slow-growing, metabolically inert tissues is a common method for investigating foraging ecology in migratory animals, as direct observations of feeding are often not possible. Using tissue growth dynamics to interpret foraging timelines can maximize the utility of foraging data; however, applying inappropriate growth models is problematic, and high-resolution growth measurements are seldom made. We used photogrammetry to repeatedly measure the length of whiskers in 93 follicles over 670 d in a trained, captive northern elephant seal Mirounga angustirostris. We developed and optimized a follicle-specific growth model to describe the 18 000 whisker length measurements. Whiskers from the captive seal exhibited asymptotic growth that was described by the von Bertalanffy growth function. Applying the growth model to serially sampled whiskers from 4 free-ranging adult female northern elephant seals resulted in alignment of peaks in δ 15 N along the length of whiskers with the breeding haul- out period, when seals are not feeding. Our study provides a high-resolution whisker growth model and is the first to use whisker growth dynamics to improve temporal interpretation of iso- topic ratios.

Effect of forging on the microstructure and tensile properties of 2024Al/Al18B4O33w composite

The hot forging of the 2024Al/Al18B4O33w composite fabricated by the squeeze casting technique was carried out at 450°C to improve the ductility. The microstructure and tensile properties of the as-cast and forged 2024Al/Al18B4O33w composites are studied. Non-homogeneous distribution of the reinforcement whiskers was revealed in the as-cast composite. The forging led to significant variations in the average length and distribution of the reinforcement whiskers in comparison with the as-cast composite. After forging, the tensile tests showed an increase in the ultimate tensile strength at room temperature and a decrease at elevated temperature. The forging highly increased the ductility both at room and elevated temperature.

Studying Pressure Induced Whiskers Formation from Sn-Rich Surfaces

Whiskers formed on the lead-free tin surfaces pose a serious risk to small electronic devices causing a short circuit and leading to the component/device failure. The present research was focused on the investigation of tin whisker formation on a motor control unit sockets made of tin coated copper, applying to the specimen mechanical load alone or together with heat treatment/electric current. Scanning Electron Microscopic (SEM) imaging was applied in order to study the microstructure of tin whiskers obtained, their length and number at the boundary of each imprint. If the mechanical stress increases from 1000 to 5000 MPa, the average number of whiskers and possible formation spots also increase from 570 to 1300. The length of whiskers varied from 3 μm after 0.5 h to 5.5 μm after 3 hours of exposition. It has been found that heat treatment at 150°C for 1 hour significantly reduces the number of whiskers (on average 6 times as few) formed. Therefore, the threat of failure of the electronic equipment is reduced.

In situ synthesis of porous ceramics with a framework structure of magnesium borate whiskers

New porous ceramics with a framework structure of magnesium borate (Mg2B2O5) whiskers with the diameter of 0.3–0.4μm and length of 2–5μm were synthesized in situ by use of [(MgCO3)4·Mg (OH)2·5H2O] (BMC)–H3BO3 mixture at 900°C. With the addition of Ni(NO3)2, the diameter and length of Mg2B2O5 whiskers decreased to 0.2–0.3μm and increased to 4–8μm, respectively, while the strength of porous ceramics increased from 4.72 to 15.72MPa. The formation mechanism of the Mg2B2O5 whiskers is considered to be the solution–liquid–solid (SLS) growth.

Growth behaviors of tin whisker in RE‐doped Sn‐Zn‐Ga solder

PurposeThe purpose of this paper is to investigate the growth behavior and mechanism of Sn whisker induced by RE addition in Sn‐Zn‐Ga‐Pr solder at ambient condition.Design/methodology/approachBy means of aging treatment, FIB and SEM microstructure analysis, the whisker growth behavior was investigated.FindingsIt was found that the morphologies of tin whisker are changed during air exposure. After 60 days aging, the average length of the longest whiskers could reach up to 70 μm, some whiskers even can grow to a length of 100 μm. It was discussed that the oxidation of Pr‐Sn intermetallics provides driving force for whisker growth.Originality/valueTin whisker growth is a complex reliability issue for lead‐free solder. The current research can be helpful in re‐understanding the issue of tin whisker growth as well as an enriched understanding on the effects of REs on lead‐free solders.

Thermal stress driven Sn whisker growth: in air and in vacuum

Whisker growths from matte tin electroplating have been observed during thermal cycling up to 1,000 cycles either in air or in vacuum. The density, length, and width of thermal stress whiskers depend on the plating thickness of 2 and 5 μm in the present study. Whiskers grown on the 2 μm plating are longer and thinner than those on 5 μm plating. In both cases, whiskers grow thinner and faster in vacuum than in air. These apparent variations come from the grain sizes and the thermal stress distributions in the electroplating, intrinsically different in 2 and 5 μm thick films. The grain structure of whisker root, particularly grain boundary cracks oxidized in air, determines the stress concentration to drive the whisker growth. Cracking caused by oxidation was rarely observed in vacuum hence causes thin and straight whiskers even from thick plating. Our results indicate that the stress concentration at whisker root grain is essential for controlling whisker growth morphology, and has a critical impact on various electronic applications.

Elastic modulus of rat whiskers—A key biomaterial in the rat whisker sensory system

Nanoindentation tests were carried out to measure the elastic modulus of rat whisker, which is used as a high-acuity sensor for exploring the world and discriminating object distance, size and surface texture. The measured load–depth curves show that the biomaterial of rat whisker exhibits obvious visco-elastic characteristic, such as load relaxation and displacement creeping. The measured indentation modulus of rat whiskers decreases with indentation depth at the same location. The mean value of the measured indentation moduli of 24 major whiskers varies from 0.33GPa to 4.92GPa. The elastic modulus is independent of the freshness of the whisker sample. It is also found that the length and diameter of whiskers have no direct relationship to the indentation modulus at the base. Based on the measured elastic modulus, the bending stiffness at the base of a whisker is predicted in the range of 0.58–134.79mNmm2 and the rotational stiffness at the middle of a whisker is within 0.06–10.93mNmm/rad. These results can be used to study the mechanical behavior of the rat whisker sensor system.

Effects of sodium dodecyl sulfate on the oriented growth of nesquehonite whiskers

In this study, nesquehonite MgCO3·3H2O whiskers with long length and high aspect ratio were synthesized through reactive crystallization, in which MgCl2 and Na2CO3 precipitated in the presence of sodium dodecyl sulfate (SDS). The effects of SDS concentration, reactive temperature and reactants concentration were investigated. SEM, XRD and FT-IR were used to character morphology and structure of the products. It was found that the presence of SDS in the mixed aqueous solution was an important parameter for the morphology and size of nesquehonite crystals. The morphology of nesquehonite crystals changed from rod-like to bundle-like with increasing SDS concentration. The average length of nesquehonite whiskers was about 87–180μm while the aspect ratio was 18–45. The longest length reached 250μm and the biggest aspect ratio was about 100. The reactive temperature and reactant concentration also affect the size even the crystal type. It is concluded that SDS was beneficial for oriented growth of one-dimensional nesquehonite whiskers based on the formation process of the nesquehonite whiskers. The possible mechanism of SDS in nesquehonite whiskers precipitation was ascribed to physical adsorption of SDS on the individual amorphous nanoparticles or crystallites. The critical point of oriented growth occurred when the SDS concentration was about 4.33mM.

An investigation of the growth of bismuth whiskers and nanowires during physical vapour deposition

Bismuth thin films of thickness in the region of 500 nm have been prepared by planar magnetron sputtering onto glass, silicon and GaAs substrates. Electron microscopy of these films reveals that bismuth whiskers grow spontaneously when the substrate is heated to temperatures between 110 and 140 °C during deposition and the optimum temperature for such growth is largely independent of substrate. Depositing films under similar conditions using thermal evaporation does not, however, produce the whisker growth. X-ray diffraction has been employed to investigate film texture with temperature and it has been shown that the film crystallites are predominantly [1 1 0] and [1 1 1] oriented. The [1 1 0] orientation of the crystallites dominates at deposition temperatures above 110 °C for sputter deposition and the [1 1 1] at lower temperatures. The optimum temperature for whisker growth coincides with the temperature for the change between predominant orientations. While sputter deposition appears to favour films with crystallite orientation of [1 1 0], thermal evaporation favours [1 1 1] and has a higher change-over temperature. The whiskers that grow from the film emerge at off-normal angles between 43.3° and 69.2° with a mean of 54 ± 3°. The projected length of whiskers on a 500 nm film on a GaAs substrate shows a wide distribution to a maximum of more than 100 µm. The mean projected length for this sample was 16 ± 1 µm and the diameter is around 0.5 µm. Measurements of the electrical properties of the whiskers at room temperature reveals ohmic behaviour with an estimated resistivity of 2.2 ± 0.2 µΩ m. Detailed examination of scanning electron micrographs, eliminates all growth mechanisms except tip growth by a non-catalysed vapour–solid/vapour–liquid–solid method. By depositing thinner films it is shown that this spontaneous growth of whiskers offers a route to fabricate high quality bismuth nanowires of lengths exceeding 10 µm.

Effects of Annealing on Sn Whisker Formation Under Temperature Cycling and Isothermal Storage Conditions

The global move toward reducing the usage of lead in electronics manufacturing industry is driving the industry to switch from tin-lead alloys to pure tin (Sn) for its component plating process. This transition has resulted in a reliability concern due to the formation of conductive Sn whiskers, which can grow from the component after the plating process within a few hours to months, with their length ranging from 10 micrometers up to several millimeters. The conductive Sn whiskers may cause current leakage or short circuits, leading to catastrophic failure in the field. This paper presents the results of an experimental study on Sn whisker formation based on the effects of annealing for 1 h at 150°C and environmental test conditions from the joint electron devices engineering council standards. This paper consisted of one temperature cycling test and two isothermal storage tests. The characterization results obtained confirm that temperature cycling and isothermal storage favor the formation of whiskers on Sn-plated copper lead frames. The average maximum length of the whiskers increased with the number of temperature cycles and duration of isothermal storage. It is also shown that annealing for 1 h at 150°C of the samples is effective in reducing the average maximum length of whiskers. Growth mechanisms of the Sn whiskers due to the effects of annealing and without annealing are also discussed.

Influence of Die Angle on the Extrusion Behavior of 6061Al Matrix Composite Reinforced with SnO<sub>2</sub>-Coated Aluminum Borate Whisker

The 6061Al matrix composites reinforced with SnO2-coated aluminum borate whisker were fabricated using squeeze casting method. The composite were extruded successfully at 350°Cwith different die angles. The experiment results illustrate that the die angle have important influences on the extrusion process. The surface quality of extruded composites was improved and the extrusion load was reduced with die angle increasing from 30 to 60 degree. The <111> and <100> textures for aluminum matrix were formed in all extruded composites. The dispersion degree of the <111> texture, the alignment degree and the average length of whiskers increases with die angle increasing. There is a suitable die angle for the optimization of the extrusion process of the present composite.

Study on Synthesis of the High Aspect Ratios Nesquehonite Whiskers

In this paper, nesquehonite whiskers were synthesized by low-temperature aqueous solution method, and the impacts of reaction temperature, reaction time and surfactant dosage and other factors on the maximum whisker length and high aspect ratios of nesquehonite whiskers were also investigated. Results showed that under the conditions that the reaction temperature was 40 – 50 °C the reaction time was 50 – 60min and the amount of surfactant dosage was 1% (by mass), high aspect ratios nesquehonite whisker products can be synthesized. On this basis, growth mechanism of the nesquehonite whiskers was discussed.

Sexual Traits as Quality Indicators in Lekking Male Great Bustards

AbstractWe studied the development of two sexual traits, whiskers and neck plumage, in relation to sexual selection in 41 free‐living great bustard, Otis tarda, males radio‐tracked at nine leks in central Spain in 1998–2001. During the pre‐breeding male–male competition period (Feb.) prior to female arrival, number and length of whiskers correlated with weight, but not with body size or age. Whiskers may thus have evolved as an intrasexual indicator of weight, which in the absence of other weapons in this species is decisive in male–male combats. Signalling through whiskers contributes to minimizing dangerous aggressive interactions in the lek. During the mating period (Apr.), both whisker and neck development were correlated with weight and age. Males reaching higher expression of both traits exhibited higher display intensity, a more prolonged display period through the mating season, and a higher estimated mating success. Moreover, interannual changes in a male’s expression of both traits were associated with changes in its display intensity and estimated mating success. Our results resolve earlier debates and contradictory results from previous authors, suggesting that these two secondary sexual traits, whiskers and neck, may function as reliable indicators of age and weight, the two main factors determining social rank of males in great bustard leks, during both rival assessment and mate choice. Their dual functions provide support for the pre‐existing trait and redundant signal hypotheses and suggest that multiple ornaments functioning as redundant signals might be more widespread than previously acknowledged.

ZnO Nanoarrays Film Grown by Forced-Hydrolysis-Initiated-Nucleation Technique and its Photo-Induced Electrical Property

Anhydrous zinc acetate pre-coated on the FTO substrate was served as a template layer, and ZnO nanowhisker arrays were simply and successfully fabricated by its forced-hydrolysis-initiated-nucleation of the layer in an aqueous solution at low temperature below 100 °C. The technique doesn’t need any expensive metal catalyst and high-temperature treatment. The density, diameter and length of whiskers were controllable by changing the deposition time. As-grown ZnO nanoarrays showed photo-induced electrical property. Enhanced photo-induced current (2.0~3.0  10-5 A) was detected under laser irradiation after DNA molecules labeled with dye molecules were loaded on the ZnO nanowhisker arrays.

A technique for production of nanocrystalline cellulose with a narrow size distribution

Nanocrystalline cellulose (NCC) was prepared by sulfuric acid hydrolysis of microcrystalline cellulose. A differential centrifugation technique was studied to obtain NCC whiskers with a narrow size distribution. It was shown that the volume of NCC in different fractions had an inverse relationship with relative centrifugal force (RCF). The length of NCC whiskers was also fractionized by differential RCF. The aspect ratio of NCC in different fractions had a relatively narrow range. This technique provides an easy way of producing NCC whiskers with a narrow size distribution.