The loss tangent and storage modulus of cement mortar containing treated silica fume and styrene-acrylic are measured. Shaking table tests on three groups of 1/4 models of high damping concrete frames are conducted to compare the effects of reducing vibration. A relationship between the viscosity coefficient of high damping concrete and the damping coefficient of structure is established by analyzing dynamic parameters like damping ratio and frequency, and comparing responses of relative displacement and absolute acceleration. Surface treatment of silica fume and styrene-acrylic emulsion prior to incorporation in a cement mortar increases the loss tangent of the resulting composite by 40–400% as compared to the cement mortar without any admixtures, and the damping ratio of the reinforced concrete is raised by 7%–9%. In addition, a theoretical method of determining the viscosity coefficient of the material on the basis of shaking table test results is put forward.
Experiments were carried out to design polyvinyl alcohol (PVA) fiber reinforced cementitous composites (PVA-FRCCs) holding high ductility and energy consumption ability. Besides, the properties of each ingredients in composites, mixing method and technology for fresh mixture were described in detail. Then, the pseudo-strain-hardening (PSH) behavior was investigated in uniaxial tension test. As a result, the maximum ultimate tensile strain can reach 0.7 percent. On the other hand, the single edge notch (SEN) thin sheet specimens were employed to gain the normal tensile load via crack mouth opening displacement (CMOD) curves, which can show obvious PSH behavior. In addition, the curves can be divided into four zones whose fracture toughness calculation methods were discussed. The wedge splitting (WS) test method can be applied to discuss the fracture toughness. Moreover, fracture energy of SEN and WS specimens were both approximately evaluated.
The effects of activated coal gangue on compressive strength, porosity and pore size distribution of hardened cement pastes were investigated. Activated coal gangue with two different kaolin contents, one higher and one lower, were used to partially replace Portland cement at 0%, 10%, and 30% by weight. The water to binder ratio(w/b) of 0.5 was used for all the blended cement paste mixes. Experimental results indicate that the blended cement of activated coal gangue mortar with higher kaolin mineral content has a higher compressive strength than that with lower kaolin mineral content. The porosity and pore size of blended cement mortar were significantly affected by the replacement of activated coal gangue.
The influence of silica fume, slag and fly ash on alkali-silica reaction under the condition of 70 °C is studied. The results show that silica, slag and fly ash may inhibit alkali-silica reaction only under suitable content. When the content is less than 10%, silica fume does not markedly influence the expansion of alkalisilica reaction. When the content is 15%–20%, silica fume only may delay the expansion of alkali-silica reaction. When the content is 30%–70%, slag may only delay the expansion of alkali-silica reaction, but cannot inhibit the expansion of alkali-silica reaction. When the content is 10%, fly ash does not markedly influence the expansion of alkali-silica reaction. When the content is 20%–30%, fly ash may only delay the expansion of alkali-silica reaction, but cannot inhibit the expansion of alkali-silica reaction. When the content is over 50%, it is possible that fly ash can inhibit effectively alkali-silica reaction.
The photoluminescence (PL) characteristics of Eu3+ and Li+ co-doped ZnO PL materials against heat-treatment temperature were discussed. The PL xerogel and powder samples were prepared by solgel process. The emission spectra of all samples showed two broad bands peaking at 590 nm and 620 nm under UV-Vis excitation. But the relative intensity of red PL (620 nm) was much greater than that of green PL (590 nm) of the same sample, that’s to say, the red color was the main luminescence. With heat-treatment temperature increase, the two kinds of colors PL intensity decreased, and both the red and green PL intensity of the xerogel samples was much greater than those of powder samples respectively. The XRD patterns revealed that Eu3+ ions were successfully incorporated in ZnO crystals in xerogel samples. When heat-treatment temperature reached 350 °C, the Eu3+ began to separate out of the ZnO crystals and Eu2O3 crystals came into being. When the powder sample was subjected to UV-Vis excitation, the energy transfered from the host ZnO emission to Eu3+ became weaker than the xerogel sample.
Although helical and twisted reinforcement has been used to reinforce concrete for more than two decades, its rationale still remains unclear. With a brief review of current researches on the helical and twisted reinforcement properties, this paper describes some new phenomenon of the helical and twisted reinforcement in concrete and other matrix by experimental studies, and then discusses on mechanism of “helical effect of strengthening”. This paper also discusses the mechanism of “accessional helical effect of strengthening” and its significance in industrial practice. Extensive tests indicate that twisting is the most effective way to improve reinforcement mechanical properties. The main results are: (1) They can greatly enhance bond anchorage in base material. In some pull-out tests, the pull-out resistance increases with reinforcement slip within the specimens, which results not only in a higher pull-out load but also a larger slip up to 70%–80% of reinforcement embedded length. (2) Concrete reinforced by twisted bars demonstrates certain ductility at failure. (3) The bond strength depends on the pitch space directly. (4) The twisted effect on material strengthening is from a three-dimensional interlocking force which is formed from material untwisting when they were pulled out from base specimens.
The hot deformation experiments of ultra-low carbon steel in ferrite range were carried out in a hot simulator in order to research hot deformation behaviors of ultra-low carbon steel in ferrite range at low temperature. The results show that the influences of deformation parameters on flow stress are different to those in austenitic deformation. The deformation characteristic parameters were calculated for ultra-low carbon steel in ferrite region. The flow stress equation for ultra-low carbon steel in ferritic deformation at low temperature was obtained.
Different compositions of yttrium silicates coatings were deposited on SiC-C/C by plasma spraying and an outer borosilicate glass was applied on the yttrium silicates coatings surfaces. The structure of the multi-layer coatings was characterized by XRD and SEM analyses. High temperature oxidation behavior of the multi-layer coatings coated C/C composites was investigated. Results show that SiC/2SiO2·Y2O3/1.5SiO2·Y2O3/ SiO2·Y2O3/glass multi-layer coating has better high temperature oxidation resistance, protecting carbon/ carbon composites from oxidation at 1 773 K in air for 164 h with the weight loss of 1.65%. The oxidation weight loss of the coated C/C with time accorded with parabolic rule in the temperature range 1 573 K–1 873 K; and the corresponding oxidation activation energy of the coated carbon/carbon composites is 132.2 kJ/mol.
The dielectric properties of (AgxNa1−x)(NbyTa1−y)O3 were investigated, and its dielectric loss and capacitance were measured. The dielectric properties of nanometer (AgxNa1−x)(NbyTa1−y)O3 ceramic prepared by liquid method were better than that by conventional solid method. The average grain size of the nanometer powder(34 nm) obtained by citrate-gel method was small near 500 nm and homogeneous and the microstructure was dense and uniform. In addition, the sintering temperature had a great effect on properties. The dielectric properties of resultant samples were as follows: ɛ>500, tgδ<6×10−4, a c< 10 ppm /°C, ρ v>1 012 Ω·cm.
The prepolymer polyurethanes (PUs) based on isophorone diisocyanate (IPDI), poly(propylene glycol) (PPG), 1,4-butanediol (BDO) and dimethylopropionic acid (DMPA) were synthesized at 75–80 °C for 7–8 hours, using dibutyltin dilauate (DBTDL) as catalyzer, and polyurethane-acrylate hybrid emulsion was prepared after methyl methacrylate (MMA) was polymerized, using potassium persulfate and azobisisobutyronitrile (AIBN) as initiator, respectively. The influences of these factors such as the kind of initiator, the feed method of initiator and the addition of initiator on properties of polyurethane-acrylate were studied. The FTIR and GPC of aqueous polyurethane were analyzed. The FTIR spectra show that the degree of microphase-separate between the soft segments and rigid segments is high. The analysis of molecular weights stated that molecular weights increased most significantly after amine was added. The experimental results reveal that the appearance of emulsion is excellent, the film is harder and the water absorption radio of the film is less when oil-solubility AIBN is used as initiator. The semi-continuous can increase the molecular weight of polymer and the optimum amount of the initiator was 3% for MMA.
As a potential artificial cartilage material, the friction and wear properties of nano-hydroxy apatite (HA) particles filled poly (vinyl alcohol) hydrogel (PVA-H) composites sliding against stainless steel disk under water lubrication condition were studied by using a four ball tester. The worn surfaces were investigated by using a scanning electron microscope (SEM) to determine the wear mechanisms. Experimental results show that filling HA to PVA-H will slightly increase the friction coefficient of composites with the increasing of HA content under water lubrication condition. Meanwhile, HA particles can greatly reduce the wear mass loss of the PVA-H composites and enhance the load carrying capacity, the wear loss of the 1 wt% HA reinforced PVA-H composites can be decreased by 30 percent under 2.0 MPa to 50 percent under 0.5 MPa contact pressure. We also found that 2 wt% HA content of composites increase the wear mass loss under the same condition. SEM examination shows that the worn surface of low HA containing (1 wt%) composites are much smoother than that of pure PVA-H or high HA containing (2 wt%) composites under 1.5 MPa contact pressure. It is also found that there are big hole and big reunited HA particles in the surface of 2 wt% HA containing composites, which leads to deterioration of the surface of samples under higher loads in water lubrication. These results may be useful in the tribological design of artificial articular cartilage material.
Interpenetrating polymer networks (IPNs) based on fluoroelastomer/ butadiene-acrylonitrile rubber (FKM/NBR) by molten blending at a high temperature and chemical cross-linking of two components were prepared. The influence of the two networks component on the mechanical properties and thermostabilities was studied. The experimental results show that the mechanical properties of the IPNs are superior to those of the individual FKM and NBR networks due to forming the case of interpenetrating and intercross-linking between the two networks, the mechanical properties and thermal resistance exhibit higher values when 80/20 (w/w) FKM and NBR is blended and respectively cured simultaneously. The co-continuous morphology of the IPNs in the blends of 80/20 (w/w) FKM/NBR is found by transmission electron microscopy (TEM), the differential scanning calorimetry (DSC) determination shows that the blends of 80/20 (w/w) FKM/NBR have better compatibility, and the glass transition temperature of the elastomer is −21.5 °C.
A new rheocasting process, Low Superheat Pouring with a Shear Field (LSPSF), was developed to produce semi-solid slurry for the rheo-forming process. The LSPSF process is one of controlled nucleation and limited growth techniques in which effective nucleation rate is controlled by passive mixing and localized rapid cooling near the liquidus temperature; dendrite growth is limited by a much slower cooling process. The experimental results of rheocast Al-Cu alloy 201 and secondary diecasting alloy A380 demonstrate that LSPSF process is capable of producing high-quality slurry in a matter of seconds. It is concluded that maximizing nucleation and nuclei survival directly lead to the grain refinement of the rheocasting microstructure, and high nuclei density combined with a slower cooling afterwards leads to a globular structure of primary phases.
A technology for electroless Ni-P deposition on AZ91D from a low cost plating bath containing sulfate nickel was proposed. The seal pretreatment was employed before the electroless Ni-P deposition for the sake of occluding the micro holes of the cast magnesium alloy and interdicting the bubble formation in the Ni-P coating during plating process. And pickling pretreatment can provide a better adhesion between the Ni-P deposition and AZ91D substrate. The deposition speed of the Ni-P coating is 29 μm/h. The technology is employed to AZ91D magnesium alloy automobile parts and can provide high hardness and high wear-resistant. The weight losses of Ni-P plated and heat-treated Ni-P plated magnesium alloy specimen are only about 1/6 and 1/10 that of bare magnesium alloy specimen after 10 min abrasion wear, respectively. The hardness of the electroless Ni-P plated brake pedal support brackets is 674.1 VHN and 935.7 VHN after 2 hours heat treatments at 180 °. The adhesion of Ni-P coatings on magnesium alloy substrates meets the demands of ISO Standards 2819. The technology is environment friendly and cannot cause hazard to environment because of absence of chromate in the whole process.
Styrene-acrylate latex with high glass transition temperature (T g), low minimum film forming temperature(MFT) and good stability was prepared via core-shell emulsion polymerization. With semicontinuous process, high conversion rate of monomer and low gel rate were achieved. The weight ratio of core monomer to shell monomer was approximately 1.35. It is found that many factors such as emulsifiers, initiators, reaction temperature, pH value and polymerization technology have influences on the permormance of styrene-acrylate latex. The prepared latex was characterized by TEM and FTIR. The obtained latex with T g of 20.57 °, MFT of 5.0 °, and good stability, had good stability of film forming.
2A12 Al alloy was suffered from equal-channel angular pressing(ECAP) in this experiment. The influence of ECAP pass number on ultimate strength(UTS), hardness and elongation was studied. The results show that during ECAP the number of sample passing through the channels is very important for mechanical properties and microstructure refinement. ECAP not only increases their plasticity and hardness but also leads to refined grain. But the elongation reduces from 17.5% to11.8 % after 1 pass ECAP, then almost tends to be unchanged with the increasing of pass number. The value of ultimate strength of 2A12 Al alloy increases by 135%, hardness by 51%, and ultra fine grains of about 200 nm can be observed after 8 passes.
Influence of hot rolling conditions on the mechanical properties of hot rolled TRIP steel was investigated. Thermomechanical control processing (TMCP) was conducted by using a laboratory hot rolling mill, in which three different kinds of finish rolling temperatures were applied. The results show that polygonal ferrite, granular bainite and larger amount of stabilized retained austenite can be obtained by controlled rolling processes. The finer ferrite grain size is produced through the deformation induced transformation during deformation rather than after deformation, which affects the mechanical properties of hot rolled TRIP steel. Mechanical properties increase with decreasing finish rolling temperature due to the stabilization of retained austenite. Ultimate tensile strength (UTS), total elongation (TEL) and the product of ultimate tensile strength and total elongation (UTS×TEL) reaches optimal values (791 MPa, 36% and 28 476 MPa%, respectively) when the specimen was hot rolled for 50% reduction at finish rolling temperature of 700 °C.
La0.6Sr0.4Co1−yFe yO3 (y=0−1.0) powders were synthesized by a citrate method, and the structure and mixed electronic-ionic conducting properties of the resulting ceramics were investigated. The synthesized La0.6Sr0.4Co1−yFe yO3 powders have a pure perovskite structure and consist of uniform and fine particles. A perovskite structure with rhombohedral symmetry was certified for the La0.6Sr0.4Co1−yFe yO3 ceramics. The increase of Co/Fe ratio significantly promoted the grain growth and microstructural densification. The La0.6Sr0.4Co1−yFe yO3 compositions with relatively higher Co/Fe ratio exhibit superior mixed conducting properties. The electronic structure and microstructure of the ceramics are responsible for the variation of the mixed conducting properties with Co/Fe ratio.
The test of fast-freezing method is employed to research the freezing resistance of C60 and C80 high-performance concrete with nanometer-SiO2, and XRD and SEM are employed to analyze the mechanism of its influence. The experimental results show that the freezing resistance of high-performance concrete has been effectively improved. The compressive strength of C60, C70 and C80 high-performance concrete added with nano-SiO2 can be improved by 8%, 6% and 5% respectively, the weight loss can be reduced by 1%, 0.6% and 0.3% respectively and the relative dynamic elastic modulus can be improved by 7%, 4% and 6% respectively after the 300 times freeze-thaw cycle.
Wear-resistant laser-induced thermite reaction Al2O3 ceramic coatings can be fabricated on pure Al and AA7075 aluminum alloy by laser cladding (one-step method) and laser cladding followed by laser re-melting (two-step method) using mixed powders CuO-Al-SiO2 in order to improve the wear properties of aluminum and aluminum alloy, respectively. The microstructure of the coatings was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The wear resistance of the coatings was evaluated under dry sliding wear test condition at room temperature. Owing to the presence of hard α-Al2O3 and γ-Al2O3 phases, the coatings exhibited excellent wear resistance. In addition, the wear resistance of the coatings fabricated by two-step method is superior to that of the coatings fabricated by one-step method.
Antimony doped tin-oxide powders were prepared by controlled precipitation. Surface compositions were determined by X-ray photoelectron spectroscopy (XPS). The results indicate that enrichment of dopant at the surface of nanoparticles depends on total doping concentration and annealing temperature. Doped antimony shows the tendency to diffuse to surface when annealing at high temperatures. But same amount of Sb atoms are retained on the surface for powders annealing at different temperatures. The higher enrichment at higher temperature is caused by the decreasing of surface areas. Variation of the conductivities of SnO2 powders is also discussed.
The plastification modification of poly (vinyl chloride) (PVC) with the long-chain linear polyester (LP) synthesized by linear dodecanedioic acid (DC12) or tetradecanedioic acid (DC14) with different diols is investigated. The processing characteristics, mechanical properties and extraction property of the PVC/LP blends in different solvents (xylene, cyclohexane, ethanol) were also studied in detail. All results were compared with that of the PVC plasticized with dioctyl phthalate (DOP). The results show that the molecular weight, molecular structure and loading of LP greatly influence the mechanical properties of the PVC/LP blends. The processability and the mechanical properties of PVC plasticized by LP are comparable to those of the corresponding PVC/DOP blends. However, the PVC/LP blends posses much better migration resistance property than the corresponding PVC/DOP blends, which makes the long-chain linear polyester become a very good plasticizer candidate for PVC industry.
In order to achieve higher density of P/M steels using the die wall lubrication compacting method or powder lubricant in warm compaction process, the influence of different process parameters on the green density of warm compacted samples was studied. According to the orthogonal test method, the authors systematically study the influence of the different compaction pressure, condition of lubrication and compaction temperature on the green density of the sample in the warm compaction process, and put forward the optimal process parameter of warm compaction experiment. It is found that, a high compaction pressure (≥700 MPa), die wall lubrication combined with a small amount of internal lubricants, and fitting compaction temperature by different condition of lubrication, are the optimal parameters in warm compaction process.
Iridium thin films have been deposited on Si3N4(100 nm)/Si(100) substrates by magnetron sputtering. And then iridium film micro-patterns were fabricated by ion milling technique. The atomic force microscopy (AFM) measurements reveal that there is a very flat and smooth surface with an average roughness of 0.64 nm for the iridium films. The X-ray diffraction also reveals that the deposited iridium films have a polycrystalline microstructure with (111) plane preferential orientation. The electrical resistivity of the iridium films was also measured and discussed.
The electrochemical characteristic of antimicrobial stainless steel bearing copper NSSAM3 in sulfate reducing bacterial (SRB) was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The results show that inoculation of SRB into the culture medium significantly affects the anodic polarization behavior of NSSAM3 and accelerates anodic depolarization process, however, it has little effect on cathodic polarization curves of NSSAM3. Under the same exposure time, the anodic polarization curves of NSSAM3 in culture medium with SRB are in anodic active dissolution state when anodic polarization potential value is below 0 V(SCE), whose anodic polarization current density is bigger than that of in culture medium without SRB. Moreover, when the concentration of Cu2+ in SRB medium increases, anodic polarization current density of NSSAM3 decreases and polarization resistance increases with increasing time. Scanning electron microscope (SEM) observations indicate that SRB unevenly attaches on the surface of NSSAM3, and induces the sensitivity to local corrosion.
CdS nanowire arrays were synthesized by altering current(AC) electrodeposition in the porous anodic alumina film prepared by aluminium anodizing in oxalic acid. These nanowires have a uniform diameter of about 45 nm corresponding to the pore size of the films used and length up to several microns. The X-ray diffraction(XRD) pattern indicates that the CdS nanowires crystallize in an hcp structure. Besides, photoluminescences(PL) of CdS nanowire arrays, characterized by spectrophotometer show that CdS nanowries embedded in porous alumina template increases the light-emitting intensity and induces a red shift of PL band.
It is very difficult to prepare full-densified aluminum nitride-boron nitride (AlN/BN) composite ceramics with homogeneous microstructure and high thermal conductivity. Spark plasma sintering (SPS) was used to fully densify the AlN/BN composites in this work. Microstructure, mechanical properties and thermal conductivity of the SPS sintered AlN/BN composites with 5–30 vol% BN were investigated. The results show that the microstructure of composites is fine and homogenous, and the AlN/BN composites exhibit high mechanical properties. To promote the growth of AlN grains and modify the distribution of grain boundary in AlN/BN composites, a heat treating methodology was introduced through gas pressure sintering (GPS). This processing was significantly beneficial to enhancing the thermal conductivity of the specimen. The thermal conductivity of AlN/BN composites with 5–30 vol% BN reached 60 W/m·K after the samples were treated by GPS.
Water blown rigid polyurethane foams with different functionality were prepared. The physical properties of rigid foams were measured with rotational viscometer (NDJ-1), universal testing machine (Instron3365), scanning electron microscope (SEM) and differential scanning calorimeter (DSC). The results show that the viscosity of polyether polyol increases exponentially from 62 mPa·s to 6 000 mPa·s with the increase of functionality from 2 to 5.6, respectively. The overall density of foam increases slightly from 31.7 kg/m3 to 37.4 kg/m3 with increasing functionality while core density exhibited little difference. Compressive strength of foam shows the similar behavior with density except for 2-functional sample. At the same time, dimensional stability becomes better with increasing functionality except for 5.6-functional foam that has worse stability than 4.8-functional foam. From the SEM results, the functionality is not an important factor in determining distribution of cell size of foam. According to the results of thermal analysis, the glass transition temperature (T g) shifts to a higher temperature from 128.9 ° to 166.3 ° for the 2 to 5.6 functional foam, respectively.
The composition, microstructure, mechanical and frictional properties of PTFE and its fillers were represented and analyzed by XRD, SEM, DSC, XPS and large-scale polarizing microscope. The results show that PTFE has a flocculent structure with high melt temperature and decomposition temperature, big contact angle and crystallinity, and low surface hardness, compression strength, friction coefficient, wearing capacity and surface energy. Cooling rate influenced the friction coefficient and wear resistance. Graphite and molybdenum disulfide have a flake structure, and molybdenum disulfide has a big contact angle and low surface energy. Copper powder has a globular structure and its chief component is Cu-Pb alloy, and there is a loose layer on the surface. Carbon fiber has a rod structure and there are C=O and C-O-C polar groups on the skeleton surface. The decreasing order of water absorption capacity is graphite, carbon fiber, molybdenum disulfide, PTFE and copper powder.
To reuse roller waste as a raw material of high performance green ceramic balls, three kinds of white alumina ceramic balls whose wear resistance were 2–3 times of the best high alumina ceramic ball with 90% Al2O3 were prepared, and the Al2O3 content of the prepared balls was 75%. It is found that the effect of calcia and magnesia on the wear resistance of ceramic balls is contrast to the accepted one: the wear rate of the ceramic balls prepared in CaO-Al2O3-SiO2 system is the lowest and the wear rate of the ceramic balls prepared in MgO-Al2O3-SiO2 is the highest. The main crystal phase of the ceramic ball is mullite and corundum. The ceramic ball granular is uniform and fine with 4–5 μm average size. The pore diameter is about 2 μm. The wear way of the ceramic balls is mainly transcrystalline fracture.
By means of ultrasonic dispersion, carbon nanofibers reinforced epoxy resin composite was prepared in the lab, the electrical conductivity of composite with different carbon nanofibers loadings were studied, also the voltage-current relationship, resistance-temperature properties and mechano-electric effect were investigated. Results show that the resistivity of composite decreases in geometric progression with the increasing of carbon nanofibers, and the threshold ranges between 0.1 wt%–0.2 wt%. The voltage-current relationship is in good conformity with the Ohm’s law, both positive temperature coefficient and negative temperature coefficient can be found at elevated temperature. In the course of stretching, the electrical resistance of the composites increases with the stress steadily and changes sharply near the breaking point, which is of importance for the safety monitor and structure health diagnosis.