Mechanical Properties and Microstructure of CaSO4 Whisker Reinforced Cement Mortar

Calcium sulfate whisker(CaSO4 whiskers), a new type of microfiber material, was used in cement matrix to increase the strength of the cement based composites. Effect of CaSO4 whiskers on the mechanical properties of the resulting cement mortar was also studied. The results showed that the flexural strength and compressive strength of the mortar specimen was improved as high as 28.3% and 8.5% by incorporating 5 wt% CaSO4 whiskers. Also, the chemical composition and structural transformation of the hardened cement matrix with CaSO4 whiskers were identified by X-ray diffraction(XRD) and scanning electron microscope(SEM). Conclusion can be drawn that CaSO4 whiskers can effectively retard the formation and restrict the coalescence of micro-crack expansion. The interaction mechanism of CaSO4 whisker on the reinforcement is mainly on three aspects: whisker pullout, crack deflection, and crack bridging. Mercury intrusion porosimetry(MIP) tests have confirmed that for 28 d cement mortar, the harmless pores increased from 9.33% to 10.62%, and the harmful pores decreased from 2.08% to 1.90%. Therefore, the whisker can optimize the pore size distribution of the resulting cement mortar.

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.

Exploration of As(Ⅲ)/As(V) Uptake from Aqueous Solution by Synthesized Calcium Sulfate Whisker

Although common calcium-containing minerals such as calcite and gypsum may fix arsenic, the interaction between modified calcic minerals and arsenic has seldom been reported. The uptake behavior of As(Ⅲ)/As(V) from aqueous solutions by calcium sulfate whisker(CSW, dihydrate or anhydrite) synthesized through a cooling recrystallization method was explored. A series of batch experiments were conducted to examine the effect of p H, reaction time, whisker dosage, and initial As concentration. X-ray diffraction(XRD) and scanning electron microscopy(SEM) were used to characterize the samples prepared. The results showed that p H of the aqueous solution was an important parameter for As(Ⅲ)/As(V) uptake, and an excellent removal efficiency could be achieved under strongly alkaline condition. The data from batch experiments for reaction of As(V) with calcium sulfate dihydrate whisker(CSDW) and calcium sulfate anhydrous whisker(CSAW) were well described with extended Langmuir EXT1 model, from which theoretic maximum adsorption capacity of 46.57 mg As(V)·(g CSDW)-1and 39.18 mg As(V)·(g CSAW)-1were obtained. Some calcium arsenate solids products,such as Ca As O3(OH)(weilite, syn), Ca3(As O4)2(calcium arsenate), Ca O–As2O5, Ca–As–O, Ca5(As O4)3OH·x H2O(calcium arsenate hydroxide hydrate), and Ca H(As O4)·2H2O(hydrogen calcium arsenic oxide hydrate), were detected at p H = 12.5 through XRD analysis. This indicates that the interaction mechanism between As(V) and CSW is a complex adsorption process combined with surface dissolution and chemical precipitation.

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.

Effect of Environmental Conditions on Tin (Sn) Whisker Growth

This research focuses on tin whisker growth under two different environmental conditions namely hygrothermal and a salt solution. Tin coated brass coupons were used for this study to analyze the growth of tin whiskers over time. Their growth rates were examined periodically using optical and scanning electron microscopy. The physical characteristics of the tin whiskers were identified for each environmental condition. It was discovered that submersion of tin coated brass substrates in 5% salt solution considerably increased the density (number of whiskers per unit area), and the length of the whiskers. In addition, it was found that the geometry and aspect ratio of tin whiskers were different for each environment.

Study on Preparation and Separation of SIC Whiskerand Particle from Rice Hulls

The growth mechanism of paramorphic SiC whisker (SiCw) and SiC particle (SiCp) produced from rice bulls under the catalytic actions is studied. The results indicate that the growtb mechanism of the SiCw is vapour-liquid-solid (VLS) , while the crystalline structure of the SiCw is β-SiC. Some SiCp will be formed during the production of the SiCw. Under the pilot-plant condition, the grade of SiCw is over 20%, and SiCp is over 50%. The micron-grade of SiCw and SiCp are separated successfully by flotation and other traditional mineral separation and purification technology. So the grade of the high purity SiCw is over 95 %.

Preparation of MgO whisker from magnesite tailings and its application

Magnesium carbonate whisker as precursor was prepared from the low-grade magnesite tailings by the route of calcination, hydration, carbonation and thermal decomposition, and then MgO whisker was prepared by calcining the precursor. In addition, the effect of MgO whisker addition on sintering and thermal shock resistance of refractory was also investigated. The results show that the thermal decomposition product is MgCO3·3H2O and its morphology is remarkably influenced by the types of additives, and magnesium carbonate whisker with the length of 10-60 μm and length-diameter ratio of 10-20 is successfully prepared when a type of soluble magnesium salt is added. MgO whisker with the length of 10-40 μm is derived from precursor with the heating rate of 1 ℃/min. The thermal shock resistance of refractory is significantly improved by the addition of MgO whisker due to its effect on binding and preventing crack expanding, and the proper amount of whisker addition is around 3%.

Grinding Characteristics Of Directionally Aligned SiC Whisker Wheel - Comparison With A12O3 Fiber Wheel

A unique SiC whisker wheel was invented,in which the whiskers were aligned normally to the grinding wheel surface.In this paper,grindabilities of the SiC whisker wheel are investigated and compared with those of other wheels of SiC grains,Al2O3 grains,as well as Al2O3 long and short fibres which were also aligned normally to the grinding wheel surface,respectively.The main research contents concern grinding characteristics of a directionally aligned SiC whisker wheel such as material-removal volume,wheel-wear rates,integrity of the ground surfaces,grinding ratios and grinding efficiency.Furthermore,grinding wheels of whiskers and fibres have a common disadvantage:they tend to load easily.The authors have proposed a simple method of loading-free grinding to overcome this propensity and investigate some related grinding characteristics under loading-free grinding conditions.

Development of an Experimental Phosphate-Calcium Cement with a Whisker-Like Structure

In a previous study, the authors tried to synthesize dental materials from dental waste, which was accomplished with alginate impression materials and gypsum. A powder was set by mixing it with phosphate solution. Fibrous curled crystals were found through SEM observation. The present study shows a detailed analysis of the crystals. XRD analysis indicated the crystals are Brushite. A unique profile of the crystal shows it can be a good apatite precursor or cell scaffold;however, this hypothesis requires further examination.

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.

Reduced graphene oxide porous films containing SiC whiskers for constructing multilayer electromagnetic shields

Developing lightweight and flexible thin films for electromagnetic interference(EMI)shielding is of great importance.Porous thin films of reduced graphene oxide containing SiC whiskers(SiC@RGO)for EMI shielding were prepared by a two-step reduction of graphene oxide(GO),in which the two steps were chemical reduction by HI and the solid phase microwave irradiation.A significant increase of the film thickness from around 20 to 200μm was achieved due to the formation of a porous structure by gases released during the 3 s of solid phase microwave irradiation.The total shielding effectiveness(SET)and the reflective SE(SE_(R))of the SiC@RGO porous thin films depended on the GO/SiC mass ratio.The highest SET achieved was 35.6 dB while the SE_(R) was only 2.8 dB,when the GO/SiC mass ratio was 4∶1.The addition of SiC whiskers was critical for the multi-reflection,interfacial po-larization and dielectric attenuation of EM waves.A multilayer film with a gradient change of SE values was constructed using SiC@RGO porous films and multi-walled carbon nanotubes buckypapers.The highest SET of the multilayer films reached 75.1 dB with a SE_(R) of 2.7 dB for a film thickness of about 1.5 mm.These porous SiC@RGO thin films should find use in multilayer or sand-wich structures for EMI absorption in packaging or lining.

Hillock Sn whiskers growth behaviors in Sn0.3Ag0.7Cu/Cu solder joints during corrosion

Hillock Sn whiskers in Sn0.3Ag0.7Cu solder are investigated in 20 seconds in corrosive climate(95% methanol and 5% nitric acid),and the growth mechanism of hillock Sn whiskers is studied.The results indicate that hillock Sn whiskers are formed near the interface of Sn0.3Ag0.7Cu/Cu solder joints,and small corrosion pits provide conceive sites for Sn whiskers. Moreover,compressive stress induced by IMC reaction and oxidation for the whisker growth may be suggested as the driving force.

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.

Characteristic Studies on Whisker-Reinforced Borosilicate Glasses

Glass composition of fixed values of the structural factor R(CdO/B2O3) = 0.5 and K(SiO2\B2O3) = 0.5 in borosilicate glass modified by CdO has been studied by different techniques. The amorphous structure of as prepared glass was confirmed by both XRD and EDP spectroscopy. The amorphous samples were treated thermally to be transformed to suitable type of crystalline glass ceramic. Based on SEM and TEM data, the bulk crystallized network was developed by treating the glasses at high treatment route (950°C - 1100°C) for a specific time (8 hours). Crystalline Al4B2O9 and Al18B4O33 whisker phases are simply detected by X-ray diffraction spectroscopy. The scanning and transmission electron microscopes (SEM and TEM) have confirmed that aluminum borate crystalline phases in the form of whiskers (rods) species are the main formed type. Both size and concentration of the whisker species were increased with increasing temperature of thermal heat treatment. Formation of this type of crystals (whiskers) leads to interlocking microstructure and as a direct result, an increase in hardness number, glass transition temperature is simply evidenced. Glass-ceramics synthesized in this study can be applied as high temperature resistant materials because their microstructures can resist micro-cracking upon indentation. The crack length due to indentation process is reduced by increasing concentration of crystalline road or whisker like structure.

Preparation of Phosphogypsum-Based Calcium Sulfate Hemihydrate Whiskers by Hydrothermal Method

Calcium sulfate hemihydrate (CaSO4·0.5H2O, HH) is one of the three most commonly phases of gypsum observed in natural precipitates. Calcium sulfate hemihydrate whisker is a kind of fibriform single crystal with the mean diameter of 1-3 μm and the mean aspect ratio of 30–80. HH whisker was the most promising reinforcement seemed to be calcium sulfate-based due to its high intensity, high corrosion-resistance, good thermal stability, non-poisonous and low price. Thus, HH whiskers combine both reinforcement and low price, may be both effective in improving mechanical performance and extending application area.

Dual Convergence of Facial Nerve Branches Innervating Whisker Pad in Rats

The precise anatomy of the facial nerve branches innervating rat whisker pad and the distribution of their corresponding motor neurons in facial nucleus area were investigated.The extratemporal facial nerves of 6 rats were anatomically observed under a surgical microscope,and then the nerve specimens of facial nerve branches at 7 anatomical sites were taken and examined for the axons and myelin sheath using Luxol fast blue staining.The distribution of facial motor neurons innervating the facial branches was observed in 12 rats by retrograde labelling.The distal pes,a fusing architecture of the buccal and marginal mandibular branches,was found to furcate into superior,middle and inferior branches to innervate whisker pad.Histologically,the myelin sheath of each branch was morphologically consistent,and the nerve fiber bundles of facial nerve branches became increasingly thinner and scattered,particularly after crossing the distal pes site and innervating the whisker pad.The facial motor neurons innervating the buccal and marginal mandibular branches were clearly distributed in similar regions in facial nucleus.This study confirmed the highly spatial synergy between the buccal and marginal mandibular branches innervating the whisker pad from extratemporal anatomy and distribution of facial motor neurons.

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.

Microstructure,mechanical and wear properties of aluminum borate whisker reinforced aluminum matrix composites

The microstructural features and the consequent mechanical properties were characterized in aluminium borate whisker(ABOw)(5, 10 and 15 wt.%) reinforced commercially-pure aluminium composites fabricated by conventional powder metallurgy technique. The aluminium powder and the whisker were effectively blended by a semi-powder metallurgy method. The blended powder mixtures were cold compacted and sintered at 600 ℃. The sintered composites were characterized for microstructural features by optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), transmission electron microscopy(TEM) and X-ray diffraction(XRD) analysis. Porosity in the composites with variation in ABOw contents was determined. The effect of variation in content of ABOw on mechanical properties, viz. hardness, bending strength and compressive strength of the composites was evaluated. The dry sliding wear behaviour was evaluated at varying sliding distance at constant loads. Maximum flexural strength of 172 MPa and compressive strength of 324 MPa with improved hardness around HV 40.2 are obtained in composite with 10 wt.% ABOw. Further increase in ABOw content deteriorates the properties. A substantial increase in wear resistance is also observed with 10 wt.% ABOw. The excellent combination of mechanical properties of Al-10 wt.%ABOw composites is attributed to good interfacial bonds, less porosity and uniformity in the microstructure.

Mg_(2)Sn-induced whisker growth on the surfaces of Mg/Sn/Mg ultrasonic-assisted soldering joints

In this paper,the phenomena of Mg_(2)Sn-induced Sn whisker growth were explored on the surfaces of Mg/Sn/Mg ultrasonic-assisted soldering joints after aging treatment.The in-situ observation and thermal analysis confirmed that the formation and the corrosion of Mg_(2)Sn nanoparticles were the dominant reason of Sn whisker growth.The Mg_(2)Sn accumulation at the grain boundaries would pin the dislocation slip and affect the continuity of whisker growth,and the boundary angle would thus play a decisive role in the growth shape of Sn whiskers due to the pining effect of Mg_(2)Sn.This study might be conducive to elucidating the growth behavior of Sn whiskers and provide the exploration strategy to further improve the bonding strength of Mg/Sn/Mg ultrasonic-assisted soldering joints.

Study on Microstructures of Micron Si_3N_4 Composite Ceramic with Addition of Nano SiC and SiC Whisker

The microstructures and crack propagating characteristic of Si 3N 4 (μ)/SiC (n, w) composite ceramic were studied with AEM. The Si 3N 4 (μ)/SiC (n, w) composite ceramic consists of β Si 3N 4, β SiC, a small amount of α Si 3N 4 and α SiC, and amorphous phase. Most of Si 3N 4 grains were equiaxed crystal and also there were some bulky columnar ones. Most of SiC particles and SiC whiskers distributed at the Si 3N 4 grain boundaries and a few of smaller SiC particles in the Si 3N 4 grains. Most of amorphous structure was in the junction of several Si 3N 4 grains and thin amorphous layer was observed only at a few of Si 3N 4 boundaries. Failured cracks propagated mainly along the boundaries of the Si 3N 4 grains and partially passed through Si 3N 4 grains. The path of crack propagating might change, branching and twisting of the cracks might occur when the expanding crack meet the SiC particle and/or SiC whisker. Effect of the microstructure on strength and toughness of the composite ceramic was briefly discussed.