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.

Morphology and optical properties of tetrapod-like zinc oxide whiskers synthesized via equilibrium gas expanding method

The zinc oxide whiskers were synthesized by the equilibrium gas expanding method at the temperature of 700 C with metallic zinc as the main raw material without any catalysts. The effects of the growth time on microstructure and photoluminescence properties were investigated. The results show that the as-grown samples are composed of uniform tetrapod-like ZnO whiskers. The length and diameter of the arms of the tetrapod-like ZnO whiskers increase obviously with the increase of the growth time. The strong single ultraviolet （UV） emission centering 385-391 nm without any accompanying deep-level emission is observed in the room temperature photoluminescence （PL） spectra of the whiskers. The intensity of UV emission increases markedly with the increase of growth time.

Effect of SiC whiskers on the oxidation protective properties of SiC coatings for carbon/carbon composites

In order to effectively employ the unique high temperature mechanical properties of carbon/carbon composite substrates, SiC coatings reinforced by SiC whiskers were prepared by pack cementation method. The effect of SiC whiskers on the oxidation resistance properties of the single-layer coating and double-layer coating was investigated. SiC whiskers in the single-layer SiC coating have little effect on the anti-oxidation property but obviously improve the thermal shock property. The double-layer coating with inner-layer reinforced coating exhibits more perfect anti-oxidation ability than the double-layer coating with SiC inner-layer coating.

Preparation of Mullite Whiskers and Their Enhancement Effect on Ceramic Matrix Composites

Mullite whiskers were facilely prepared by sintering kyanite at high temperature, with the addition of AlF3·3H20. The as-prepared whiskers have been characterized systematically in terms of phase composition, morphology, and structure. Results showed that the morphology and size of mullite whiskers were strongly depended on the content of AlF3·3H20 and sintering temperature. At temperatures in the range of 1 100 to 1 500 ℃ with 4 wt% addition of AlF3·3H20, the well-shaped mullite whiskers were obtained. For an instance, the mullite whiskers with 5-10 μm in length and 0.1-0.2 μm in cross-section could be formed at 1 400 ℃, with 4 wt% addition of A1F3·3H20. Moreover, results showed that the addition of mullite whiskers into ceramic matrix enhanced its fracture toughness significantly.

Preparation, Characterization, and Formation Mechanism of Calcium Sulfate Hemihydrate Whiskers

Calcium sulfate hemihydrate whiskers were synthesized successfully via one-step hydrothermal crystallization method using phosphogypsum at 130 °C for 240 min with an initial slurry mass fraction of 2.5 wt%. The phase compositions, microstructures, thermal properties and molecular structures of asprepared samples were analyzed by XRD, ESEM, EDS, TG-DTA, and FT-IR. The influence of raw materials’ ball-milling time on the morphologies of whiskers was investigated. The effects of impurities on crystallization morphologies and length to diameter ratio(L/D) of calcium sulfate hemihydrate whiskers were studied. The results indicated that the calcium sulfate dihydrate crystalline could be translated directly into fibrous calcium sulfate hemihydrate whiskers. It was beneficial to form fine fiber structure when the ball-milling time of the raw material was 15 min. Aspect ratio of calcium sulfate hemihydrate whiskers decreased with increasing content of impurities. Moreover, the relative growth mechanism of whisker crystals via one-step hydrothermal crystallization method was discussed in detail.

Photocatalytic performance of K2Ti6O13 whiskers to H2 evolution and CO2 photo-reduction

K2Ti6O13 whiskers were synthesized by conventional sol-gel method, sono-chemical assisted and microwave assisted sol-gel method in order to obtain catalysts with different particle sizes and to modify their optical, textural and electrochemical properties. These modifications improved their photocatalytic activity for H2 evolution and CO2 photo-reduction. Long K2Ti6O13 whiskers prepared by ultrasound assisted sol-gel method are the most active photocatalysts for the hydrogen evolution reaction using pure water as reactant (U-SG, 10,065 μmol g^-1). In contrast, an opposite behavior was observed using a mixture of ethanol-water, where the highest activity was achieved by the shortest and less crystalline K2Ti6O13 whiskers (C-SG, 3,2871 μmol g^-1). In case of CO2 photo-reduction, long whiskers that were also prepared by the sono-chemical assisted sol-gel method were the most active to transform CO2 to formaldehyde, methane, methanol and hydrogen. The EFB value of this catalyst is located very close to the potential for formaldehyde production and favors the selectivity to this organic product.

Synergistically Toughening Effect of SiC Whiskers and Nanoparticles in Al_2O_3-based Composite Ceramic Cutting Tool Material

In recent decades, many additives with different characteristics have been applied to strengthen and toughen Al2O3-based ceramic cutting tool materials. Among them, SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties. While no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening effects of them have not been studied. An Al2O3-SiCw-SiC np advanced ceramic cutting tool material is fabricated by adding both one-dimensional SiC whiskers and zero-dimensional SiC nanoparticles into the Al2O3 matrix with an effective dispersing and mixing process. The composites with 25 vol% SiC whiskers and 25 vol% SiC nanoparticles alone are also investegated for comparison purposes. Results show that the Al2O3-SiCw-SiCnp composite with both 20 vo1% SiC whiskers and 5 vol% SiC nanoparticles additives have much improved mechanical properties. The flexural strength of Al2O3-SiCw-SiCnp is 730＋ 95 MPa and fracture toughness is 5.6 ± 0.6 MPa.m1/2. The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination. It is indicated that when SiC whiskers and nanoparticles are added together, the grains are further refined and homogenized, so that the microstructure and fracture mode ratio is modified. The SiC nanoparticles are found helpful to enhance the toughening effects of the SiC whiskers. The proposed research helps to enrich the types of ceramic cutting tool and is benefit to expand the application range of ceramic cutting tool.

Rigid polyurethane foam reinforced with cellulosewhiskers: Synthesis and characterization

A novel nanocomposite of rigid polyurethane foam was prepared by the polymerization of a sucrose-based polyol, a glycerol-based polyol and polymeric methylene diphenyl diisocyanate in the presence of cellulose whiskers. The cell morphology of the resulting foams was examined by scanning electron microscopy which showed both the pure foam and the nanocomposite foam had homogeneous cell dispersion and uniform cell size of approximately 200 μm. Analysis of the foams by Fourier transform infrared(FT-IR) spectroscopy indicated that both samples exhibited signals attributed to the polyurethane including the NH stretching and bending vibrations at 3320 cm^(-1) and 1530 cm^(-1), the OC=O vibration at 1730 cm^(-1) and the CO-NH vibration at 1600 cm^(-1). FT-IR analysis of the nanocomposite indicated that cellulose whiskers were crosslinked with the polyurethane matrix as the signal intensity of the OH stretch at 3500 cm^(-1) was significantly reduced in comparison to the spectral data acquired for a control sample prepared from the pure polyurethane foam mixed with cellulose whiskers. According to ASTM standard testing procedures, the tensile modulus, tensile strength and yield strength of the nanocomposite foam were found to be improved by 36.8%, 13.8% and 15.2%, and the compressive modulus and strength were enhanced by 179.9% and 143.4%, respectively. Dynamic mechanical analysis results testified the improvements of mechanical properties and showed a better thermal stability of the nanocomposite foam.

Synthesis of Mg_2B_2O_5 whiskers via coprecipitation and sintering process

Mg2B2O5 whiskers with high aspect ratio were synthesized by coprecipitation and sintering process using MgCl2-6H2O, H3BO3, and NaOH as raw materials and KCl as a flux. Their formation process was investigated by thermogravimetry and differential scanning calo- rimetry （TG-DSC）, X-ray diffraction （XRD）, and scanning electron microcopy （SEM）. It is found that the products synthesized at 832℃ are monoclinic Mg2B205 whiskers with a diameter of 200-400 nm and a length of 50-80 μm. Transmission electron microscopy （TEM） and selected area electron diffraction （SAED） analyses show that the whiskers obtained at 832℃ are single crystalline and grow along with the [010] direction. The growth mechanism of Mg2B2O5 whiskers was also presented.

Synthesis of potassium hexatitanate whiskers using hydrothermal method

High quality potassium hexatitanate whiskers were hydrothermally synthesized in one step under moderate temperature and pressure conditions. Effects of the titanium source and reaction conditions on the hydrothermal reaction rate, product phase component, and morphology of whiskers were investigated. The results show that the reactivity of hydrated titania, anatase TiO2, and rutile TiO2 with KOH decreases in turn, and with hydrated titania as titanium source, it is difficult to obtain potassium hexatitanate whiskers with good morphology. In contrast, uniform potassium hexatitanate whiskers with a length of 10-20 μm and a diameter of 200-700 nm were obtained using anatase TiO2 as titanium source. The investigation demonstrates that the initial KOH concentration, annealing temperature and time, molar ratio of K2O/TiO2, etc. significantly affect the morphology of the as-synthesized whiskers. The optimized synthesis condition is as follows： anatase as a titanium source 10 wt.% KOH solution; annealing temperature and time of 300℃ and 5 h, respectively; K2O/TiO2 molar ratio of 5, etc. A rhombic potassium hexatitanate was prepared under the optimum condition and the whisker grew along the [110] direction. The reaction mechanism was discussed.

Synthesis of ZnO whiskers via hydrothermal decomposition route

ZnO whiskers with a length of 30-40μm and a diameter of about 1μm were synthesized by co-precipitation of ZnSO 4 and Na2CO3 solution at room temperature followed by hydrothermal treatment of the as-prepared Zn5(CO3)2(OH)6 precursor at 160 ℃for 6 h.The increase of the initial solution pH promotes the hydrothermal conversion of the particulate Zn5(CO3)2(OH)6 to ZnO whiskers.The presence of minor amount of EDTA in the hydrothermal solution promotes the one dimensional growth of ZnO whiskers,leading to the formation of ZnO whiskers with a length of 50-60μm and a diameter of 1-2μm.

Fabrication and properties of aluminum silicate fibrous materials with in situ synthesized K2Ti6O13 whiskers

To improve their mechanical and thermal insulation properties, aluminum silicate fibrous materials with in situ synthesized K_2Ti_6O_(13) whiskers were prepared by firing a mixture of short aluminum silicate fibers and gel powders obtained from a sol–gel process. During the preparation process, the fiber surface was coated with K_2Ti_6O_(13) whiskers after the fibers were subjected to a heat treatment carried out at various temperatures. The effects of process parameters on the microstructure, compressive strength, and thermal conductivity were analyzed systematically. The results show that higher treatment temperatures and longer treatment durations promoted the development of K_2Ti_6O_(13) whiskers on the surface of aluminum silicate fibers; in addition, the intersection structure between whiskers modulated the morphology and volume of the multi-aperture structure among fibers, substantially increasing the fibers' compressive strength and reducing their heat conduction and convective heat transfer at high temperatures.

Removal and utilization of calcite existed in scheelite by preparation of calcium sulfate whiskers

In order to eliminate the effect of calcite associated with scheelite on the scheelite flotation, hydrochloric acid was used to dissolve the calcite, and the soaking solution was used to prepare CaSO_4 whiskers by hydrothermal reaction with sulfuric acid at ambient pressure. First, the condition experiments of preparing CaSO_4 whiskers by using CaCl_2 and H_2SO_4 were carried out to optimize reaction parameters of the crystallization process. The optimal conditions were: at 102 ℃ reaction temperature, 0,5 mol/L reactant concentration and 60 min reaction time. Then based on the condition experiments and considering keeping acid concentration stable for achieving HCl recycling, Calcium sulfate whiskers with the average diameter of 1.41 μm and the average aspect ratio of 109 were prepared by the soaking solution after evaporating to half of its volume and 1.0 mol/L H_2SO_4 at 102 ℃ for 60 min: After ion exchange processing,the filtrate could be used as HCl in the process of HCl dissolution.

Growth and Photoluminescence Properties of Tetrapod-Shaped ZnO Microcrystals-Whiskers and Microrods

Tetrapod-shaped ZnO microcrystals in forms of whiskers and microrods have been grown in the same crucible by thermal evaporation of Zn/C mixtures at a temperature of 930℃ in air without using any catalyst. The tetrapod-shaped ZnO microrods were capped by hexagonal pyramids. It is for the first time observed that the tetrapod-shaped ZnO whiskers and microrods have quite different morphologies, and this is believed to be a result of different growth behaviors associated with these two forms of ZnO microcrystals. The octa-twin model has been used to discuss their growth behaviors. Photoluminescence properties of these two forms of tetrapod-shaped ZnO microcrystals have been investigated using different excitation wavelengths. Both of the two forms of ZnO microcrystals showed strong green emission and weak ultraviolet emission behaviors. The excitation spectrum of the tetrapod-shaped ZnO whiskers showed a strong excitation peak at 395 nm, which was not observed for the tetrapod-shaped ZnO microrods.

Direct synthesis of single-phase α-CaSO4·0.5H2O whiskers from waste nitrate solution

Single-phaseα-CaSO4·0.5H2O whiskers were directly synthesized from waste Ca(NO3)2 solution using a hydrothermal method,and HNO3 was synchronously regenerated.The effects of reaction temperature and Ca^2+concentration on the phase composition and morphology of products were determined by X-ray diffraction and optical microscopy.On the basis of the experimental results,the formation diagram ofα-CaSO4·0.5H2O was plotted within the range of 5–35 g·L^-1 Ca^2+and 115°C–150°C.In addition,the conditions of the direct synthesis ofα-CaSO4·0.5H2O were determined.Well-crystallized,single-phaseα-CaSO4·0.5H2O whiskers with high aspect ratios(length,1785μm;diameter,10.63μm;aspect ratio,168)and HNO3(70.25 g·L^-1)were obtained at the optimal conditions of 25 g·L^-1 Ca^2+and 125°C.

Preparation of Layered Potassium Titanate Whiskers with Large Length-diameter Ratio by KDC Method

Pure K2Ti4O9 whiskers were prepared by KDC（Kneading-Drying-Calcination） method with TiO2 and K2CO3 as raw materials. The influences of TiO2/K2CO3 molar ratio（RT/K）, calcination temperature（TC） and cooling process on phase composition and morphology of the whiskers were investigated by TG-DSC（thermo gravimetric-differential scanning calorimeter）, XRD（X-ray diffraction）, and SEM（scanning electron microscope）. Pure K2Ti4O9 potassium titanate whiskers with large length-diameter ratio（r）（over 250） can be obtained at RT/K = 2.9 and TC = 950 ℃.

Liquid precipitation and microstructure of Mg6Al2(OH)15NO3CO3·4H2O whiskers

High-quality LDH-NO_3-CO_3 whiskers were synthesized via a liquid precipitation method using Mg(NO_3)_2·6H_2O and Al(NO_3)_3·9H_2O as raw materials and Na_2CO_3-NaHCO_3 buffer solutions as precipitant. The whiskers were characterized by X-ray diffraction, transmission electron microscope, and Brunauer-Emmett-Teller N_2 surface area measurement. The influence of buffer solution concentration on the characteristics of the sample was investigated. The results show that the buffer solution concentration has significant impact on whiskers with intercalated structure. Overall, LDH-NO_3-CO_3 whiskers with well-defined geometry, distinct intercalated structure, high quality, and good dispersion capability can be obtained under the following conditions: buffer solution volumetric ratio of 60%, reaction temperature of 55°C, and reaction time of 269 h.

The Absorption Behavior of Tetrapod Shaped ZnO Whiskers

The infrared absorption spectrum of zinc oxide whiskers with tetrapod shape was recorded and compared with ZnO powder. The absorptions of microwave and sound were investigated with a result showing that the ZnO whiskers are of excellence as absorbents of microwave and soundproofing. The results of vibration damping tests of polyvinyl chloride indicate that the material containing the tetrapod shaped ZnO whiskers appears superior damping characteristics.

Synthesis of Calcium Chloroborate Whiskers Via Sedimentation and Sintering Process

Single crystalline calcium chloroborate（Ca2B5O9Cl） whiskers with uniform diameter have been fabricated by a two-step process. The precursor was firstly prepared by the sedimentation reaction between CaCl2, H3BO3 and Na OH aqueous solutions, and then sintered at different temperatures for 6 h with KCl as flux. The XRD indicates that the product synthesized at 600 °C is Orthorhombic Ca2B5O9Cl. SEM and TEM results show that the Ca2B5O9Cl is whisker with the diameter about 0.2-0.5 μm and the length up to 15 μm. SAED analysis shows that the whisker is single crystalline and grows along [001] direction. The possible formation process and growth mechanism were proposed.

ZnO whiskers growth on the surface of Sn9Zn/Cu solder joints in concentrator silicon solar cells solder layer

ZnO whiskers observation on the surface of SnZn/Cu solder joints in concentrator silicon solar cells solder layer is reported. In the experiment,SnZn/Cu samples are left in laboratory after reflow soldering for two years before an examination by SEM,then ZnO whiskers can be observed obviously,which grows out from the rich-Zn phase of the samples and causes electrical short circuit in the electronics appliances,which demonstrates that the SnZn solder shows a risk for the short circuiting failure of an electronic device. Moreover,the growth mechanism of ZnO whiskers is researched based on cracked oxide theory,which provides the reference support for SnZn solders application.