Serviceability and reinforcement of low content whisker in portland cement

In order to explore the serviceability and reinforcement of CaCO₃ whisker in portland cement matrix, the durability of CaCO₃ whisker and effect of low whisker content(0%–4.0%) on the working performance and mechanical properties of portland cement were investigated. The experimental results show that CaCO₃ whiskers have a good stability and serviceability in cement, and should not significantly alter the rheological properties of the cement paste. The flexural and compressive strength of portland cement reinforced by CaCO₃ whiskers was increased by 33.3% and 12.83%, respectively.     

The Mechanical Properties of Polyurethane Elastomer Reinforced and Toughened By CaSO4—Whisker

CaSO4 whisker reinforcing and toughening mechanisms for polyurethane elastomer were studied.The effects of dispersity of CaSO4 whisker and interfacial bonding state on reinforcement and toughness were discussed.The microanalyses showed that CaSO4 whisker reinforcing mechanism for polyurethane elastomer mainly was load transferring and its toughening mechanism involved crack deflection and whisker pullout.The results indicated that composites with 5%-10% CaSO4 whisker exhibited the best mechancal properties,Good bonding in terface was formed between whisker and matrix after the surface of CaSO4 whisker was treated by silane coupling agent.The fairly improved strength and toughness are attributed to the better interfacial bonding state.     

Mechanical Properties and Microstructure of CaSO_4 Whisker Reinforced Cement Mortar

Calcium sulfate whisker(CaSO_4 whiskers), a new type of microfiber material, was used in cement matrix to increase the strength of the cement based composites. Effect of CaSO_4 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% CaSO_4 whiskers. Also, the chemical composition and structural transformation of the hardened cement matrix with CaSO_4 whiskers were identified by X-ray diffraction(XRD) and scanning electron microscope(SEM). Conclusion can be drawn that CaSO_4 whiskers can effectively retard the formation and restrict the coalescence of micro-crack expansion. The interaction mechanism of CaSO_4 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.     

多尺度纤维复合增强水泥基材料的力学性能

为改善水泥基材料抗拉强度低、韧性差以及易开裂等性能缺陷,采用微米级碳酸钙晶须和厘米级短切耐碱玻璃纤维复合增强高性能水泥基材料,并对不同纤维增强水泥基材料的基本力学性能进行研究.结果表明:微观碳酸钙晶须和宏观耐碱玻璃纤维均有利于水泥基材料力学性能的提高,且提高程度与纤维(或晶须)掺量及长度相关;采用碳酸钙晶须和耐碱玻璃纤...     

Tensile properties of an aluminum matrix composite reinforced by SnO<Subscript>2</Subscript>-coated Al<Subscript>18</Subscript>B<Subscript>4</Subscript>O<Subscript>33</Subscript> whisker

Al18B4O33 whisker was coated by SnO2 particles using a chemical precipitation method, and an aluminum matrix composite reinforced by the coated whisker was fabricated by squeeze casting technique. It is found that the SnO2 coating can react with aluminum matrix during squeeze casting process, and Sn particles are induced near the interface between Al18B4O33 whisker and matrix. The tensile test at room temperature indicated that the tensile strength of Al18B4O33 whisker reinforced aluminum matrix composite can be enhanced by suitable content of SnO2 coating. The composites with various whisker coating contents exhibit maximum tensile plasticity at about 300 ℃, and the composite with a suitable whisker coating content could enhance its tensile plasticity evidently, which suggest that an Al18B4O33 whisker-Al composite with both high strength at room temperature and high formability at elevated temperature can be designed.     

Fabrication and Characterization of Nano- CaCO3/Polypropylene Foam Sheets

By applying the reinforcing and toughening effect of calcium carbonate （CaCO3） nanoparticles on polypropylene, foam sheets of good performance were successfully fabricated by extrusion. The equipment and conditions of the extrusion were explored. The mechanical properties of the produced foam sheets were tested. The effect of CaCO3 nano-particles on the mechanical properties and the cellular structure of the sheets was comprehensively studied. The experimental results show that the optimum content of CaCO3 nano-particles in the composite material was -4wt%. At this content, the nano-particles were well dispersed in the substrate, and the composite material had maximum tensile strength and impact strength. Surface treatment of the nano-particles only affected the impact strength of the composite material. CaCO3 micro-particles, on the other hand, showed little effect on the properties of the composite material when the micro-particles content was less than 5 wt%. At a content higher than 5wt%, the properties of the composite material significantly worsened.     

Effect of Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> and CaCO<Subscript>3</Subscript> on coreduction roasting of blast furnace dust and high-phosphorus oolitic hematite

Iron was recovered from blast furnace dust and high-phosphorus oolitic hematite in the presence of Na₂CO₃ and CaCO₃ additives. The functions of Na₂CO₃ and CaCO₃ during the coreduction roasting process were investigated by XRD and SEM-EDS analyses. Results indicate that these additives not only hinder the reduction of fluorapatite, CaCO₃ also decreases the P content of direct reduced iron (DRI) by increasing the reduction alkalinity. P remains as fluorapatite in the slag, which can be removed by grinding and magnetic separation under optimal conditions. The Na₂CO₃ promotes hematite reduction and improves the iron recovery (ε_Fe) by replacing the FeO from fayalite, which results in quick growth and aggregation of metallic iron and improvement of ε_Fe in DRI. A DRI with 91.88 mass% Fe, and 0.065 mass% P can be achieved at a recovery of 87.86 mass% under the optimal condition.     

Fabrication and microstructure of C<Subscript>a</Subscript>TiO<Subscript>3</Subscript> coating by laser cladding

In order to explore the way to improve the adhesion of the calcium phosphate bioceramic coating to Ti substrate, the CaTiO3 coating was fabricated on Ti substrate by laser cladding (LC) using powders of CaCO3 and CaHPO4, and then the composition and microstructure of the coatings were investigated. During LC, CaCO3 can hardly react with Ti, and the coating fabricated using CaCO3 powder is mainly composed of the process of CaO, the decomposition product of CaCO3. Moreover, the coating has a loosened structure and part of it has peeled off from the substrate. CaHPO4 reacts vigorously with Ti, and the coating fabricated using CaHPO4 mainly consists of CaTiO3 which is one of the reaction products between Ti and CaHPO4. Chemical bonding is formed at the interface between coating and substrate, which may enhance the adhesion of the CaTiO3 coating to Ti substrate. Furthermore, CaTiO3 dendrite and eutectic of CaTiO3 and Ca2P2O7 are found on the surface of the coating, implying that a transition can be formed between CaTiO3 and some calcium phosphate bioceramic. So CaTiO3 coating fabricated using CaHPO4 can be a potential candidate to improve the adhesion between calcium phosphate coating and Ti substrate. However, there are also pores and cracks existing in the coating, which may degrade the mechanical properties of the coating.     

Fabrication and properties of degradable PPC/EVOH/starch/CaCO<Subscript>3</Subscript> composites

Thermally stable and biodegradable composites from poly （propylene carbonate） （PPC）, poly （ethylene-co-vinyl alcohol） （EVOH）, starch and CaCO3 were fabricated by melt blending. Differential scanning calorimetry （DSC）, differential thermal analysis/thermal gravimetric analysis （DTA/TGA）, tensile test and scanning electron microscope （SEM） were performed to investigate the miscibility, thermal behavior and tensile properties of the PPC/EVOH/Starch/CaCO3 composites. DSC results indicate that the introduction of EVOH could improve the compatibility between PPC and starch to some extent because of the interfacial interaction between PPC and EVOH, leading to an increase in tensile strength. The tensile strength began to decrease when more starch was added due to the aggregation of starch particles. SEM examination showed the good interracial bonding between the fillers and polymeric components. The incorporation of both EVOH and fillers can greatly increase the thermal stability of PPC matrix. The PPC/EVOH/Starch/CaCO3 composites can be melt processed and can be used as a common biodegradable material for a wide application.     

Effect of Cold-rolling on Hardness of SiCw／Al Composite

A SiCw|A| compostie was fabricated through a squeeze cast route and cold rolled to about 30%,50% and 70% reduction in thickness.respectively.The length of whiskers in the composite before and after rolling was examined using SEM.Some of the rolled composites were annealed by recrystallizing to remove the work hardening of the matrix alloy.The hardness of the rolled and annealed SiC A SiCw|A| composites was examined and then associated with the change of the whisker length and the work hardening of the matrix alloy.It was found that the hardness was a function of the degree of cold rolling .For the cold rolled composites .with the increase in the degree of cold rolling .the hardness increases at first,and decreases when the degree of cold rolling excecds 50%.For the annealed ones .however,the hardness monotonously with the increase in rolling degree.The different changes in hardness beticeen the rolled and annealed composites coukl be attributed to a result of the competition benceen the work hardening of the matrix resulting from the cold rolling and the work softening arising from the change of whisker length.     

Composition Design for High C3S Cement Clinker and Its Mineral Formation

A new composition of Portland cement clinker was studied, in which KH, SM and IM was 0.98,2.4 and 2.4 respectively as well as its meal added 1%CuO （in mass）. Fired at 1 200℃,1 350℃,1 400℃ and 1 450℃ for 30 min, the resultant mineral phases component and mineral morphology were analyzed. The performances of the cement which was made of clinker burned at 1 450℃ and fly ash were determined. By means of QXRD, XRD and optical microscopy, it is shown that the clinker burnt at 1 450℃ has the larger size crystals and distinct crystal interface, in which the C3S content is 73.37% and the mineral phases is dominantly C3S, following by minor C2S, C3A and tetracalcium aluminoferrite. The results reveal that a new type of high C3S content clinker can completely be made by traditional temperature-time schedule. The performances of the cement produced from this clinker with addtion of 50% fly ash and 5% gupsum were in agreement with the 32.5 strength grade of Portland fly-ash cement. The results also show that the clinker has a significant effect of saving energy and utilizing waste slag.     

Effect of Grain Size of CaCO3 and SiO2 on the Formation of C3S Under Different Conditions

The effect of grain size of CaCO3 and SiO2 on the formation of C3S under various conditions, such as rapid heating rate（800 ℃/min）, normal heating rate（30 ℃/min） and in the presence or absence of ZnO, was studied. The results show that the decomposition temperature of CaCO3, the temperature of appearance of liquid phase and the f-CaO content descend when the grain size of CaCO3 and SiO2 becomes smaller, which attributes to the reactive activity enhancement of powders due to the decrease of the particle size. When the grain size of CaCO3 and SiO2 is below 1 μm, the rate of the formation of C3S is greatly raised. A rapid sintering rate and the presence of ZnO have an important effect on the formation of C3S and can lower the temperature of the formation of C3S by about 50 ℃.     

Fabrication and mechanical properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiAl composites

Al₂O₃/TiAl composites were successfully fabricated by hot-press-assisted exothermic dispersion method with elemental powder mixtures of Ti, Al TiO₂ and Nb₂O₅, and the microstructure and mechanical properties were investigated. The results indicate the fine Al₂O₃ particles tend to disperse on the grain boundaries. The grain size of TiAl matrix decreases and the hardness increases with increasing Nb₂O₅ content. The bending strength and fracture toughness reach to a maximum when Nb₂O₅ content is 6 wt%, under 642 MPa and 6.69 MPa·m^1/2, respectively. Based on the fractography and the observation of crack propagation path, it is concluded that the strengthening and toughening of such composites at room temperature can be attributed to the refinement of the TiAl matrix, the deflection behavior in the crack propagation and the dispersion of Al₂O₃ particles.     

Effect of diatomite additive on the mechanical and dielectric properties of porous SiO<Subscript>2</Subscript>-Si<Subscript>3</Subscript>N<Subscript>4</Subscript> composite ceramics

Porous SiO₂-Si₃N₄ composite ceramics with high porosity and excellent mechanical properties were fabricated by pressureless-sintering at relatively low temperature of 1 500 °C using diatomite as pore forming agent. The effects of diatomite on flexural strength, fracture toughness, shrinkage, porosity and phase transformation of the porous ceramics were investigated in detail. Compared with that of the ceramic without adding diatomite, the porosity of the ceramic with 10% diatomite is increased by about 27.4%, the flexural strength and fracture toughness reaches 78.04 MPa and 1.25 MPa·m^1/2, respectively. As the porosity increases, the dielectric constant of porous SiO₂-Si₃N₄ ceramic decreases obviously from 3.65 to 2.95.     

Effect of aluminum addition on microstructure and properties of SiO<Subscript>2</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO vitrified bond

Influence of aluminum addition on the structures and properties of SiO₂-B₂O₃-Al₂O₃-CaO vitrified bond at low sintering temperature and high strength was discussed. FTIR and XRD analyses were used to characterize the structures of the basic vitrified bond with different contents of aluminum. The bending strength and the thermal expansion coefficients were also tested. Meanwhile, the microstructures of composite specimens at sintering temperature of 660 °C were observed by scanning electron microscope (SEM). The experimental results showed that the properties of vitrified bond with 1wt% aluminum were improved significantly, where the bending strength, Rockwell hardness, and thermal expansion coefficient of the vitrified bond reached 132 MPa, 63 HRB, and 6.73×10^-6 °C^-1, respectively.     

Microstructure and mechanical properties of TiB<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites

Effects of Al2O3 and Ni as the additives on the sinterability, microstructure and mechanical properties were systematic studied. The experimental results show that only a relative density about 96.2% of hot-pressing TiB2-30%Al2O3 can be attained due to the plate-like TiB2 particle and its random orientation and excessive Al2O3 grain growth. When sintering temperature is higher than 1 700 ℃, TiB2 grain growth can be found, which obvious improves flexural strength of TiB2 matrix but decreases toughness. It seems that mechanical properties of TiB2-Al2O3 composites are mainly depended on relative density besides grain growth. otherwise, they will be determined by relative density and TiB2 matrix strength together. Anyway, Al2O3 addition can weaken the grain boundary and thus improve the toughness of the materials. A flexural strength of 529 MPa, Vickers hardness of 24.8 GPa and indentation toughness of 4.56 MPa·m1/2 can be achieved inTiB2-30vol% Al2O3.     

Activation of anhydrate phosphogypsum by K<Subscript>2</Subscript>SO<Subscript>4</Subscript> and hemihydrate gypsum

Lime pretreated phosphogypsum(PG) was calcined at 500 ℃ to produce anhydrate gypsum cement. Due to the slow hydration of anhydrate gypsum, additives, K2SO4 and hemihydrate gypsum were selected to accelerate the hydration of anhydrate. The hydration characteristics, the resistance to hydrodynamic water, and the mineralogical studies were investigated. The experimental results suggest that activated by K2SO4 and hemihydrate, anhydrate PG hydrates much more rapidly than that in the presence of only K2SO4 or in the absence of additives. The binder has proper setting time, good strength development, and relatively better resistance to water. The hardened binder has hydrated products of rod or stick like shaped dihydrate gypsum crystals.     

Thermal shock resistances of FeMnCr/Cr<Subscript>3</Subscript>C<Subscript>2</Subscript> coatings deposited by arc spraying

Arc spraying with the cored wires was applied to deposit FeMnCr/Cr₃C₂ coatings on low carbon steel substrates, namely FM1, FM2 and FM3. Thermal shock resistances of the coatings were investigated to assess the influence of Cr₃C₂ content on thermal shock resistance. Characteristics of the coatings under thermal cycling test were studied by optical microscopy, field emission scanning electron microscope (FE-SEM) and energy dispersion spectrum (EDS), X-ray diffraction (XRD). The experimental results show that hardness of the coatings increases, bonding strength decreases slightly with increase of the Cr₃C₂ content of the coatings. As a result, FM2 coating possesses the best thermal shock resistance, attributing to its better thermal expansion matches and wettability than those of FM3 coating, less oxide rate than that of FM1 coating restraining from cracks formation and propagation in coatings.     

The Influence of Yttrium Isopropoxide on the Mechanical Properties of SiCw-reinforced AlN Ceramics

By using self-made metal-alkoxide yttrium isopropoxide as a sintering additive and disperser of whisker, the SiC whisker reinforced AlN ceramics was prepared. Its apparent density is 99.5 percent of the theoretical density; its flexural strength and fracture toughness are 681 MPa and 5.21 MPa·m^1/2 respectively. Comparing the result with that by applying Y₂O₃ powder as a sintering additive, the flexural strength is increased by 25% and the fracture toughness is increased by 33%. The dispersity of whisker by increased yttrium isopropoxide is significantly better than that by Triton X-100. CHEN Yong-xi: Born in 1945     

Improved Breakdown Strength in (Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>)<Subscript>0.85</Subscript>Bi<Subscript>0.1</Subscript>TiO<Subscript>3</Subscript> Ceramics with Addition of CaZrO<Subscript>3</Subscript> for Energy Storage Application

(Ba_0.6Sr_0.4)_0.85Bi_0.1TiO₃ ceramics doped with x wt%CaZrO₃ (x= 0-10) were synthesized by solid-state reaction method. The effects of CaZrO₃ amount on the dielectric properties and structure of (Ba_0.6Sr_0.4)_0.85Bi_0.1TiO₃ ceramics were investigated. X-ray diffraction results indicated a pure cubic perovskite structure for all samples and that the lattice parameter increased till x=5 and then slightly decreased. A homogenous microstructure was observed with the addition of CaZrO₃. Dielectric measurements revealed a relaxor-like characteristic for all samples and that the diffusivity γ reached the maximum value of 1.78 at x=5. With the addition of CaZrO₃, the dielectric constant dependence on electric field was weakened, insulation resistivity enhanced and dielectric breakdown strength improved obviously and reached 19.9 kV/mm at x=7.5. In virtue of low dielectric loss (tan δ<0.001 5), moderate dielectric constant (ε_r >1 500) and high breakdown strength (E_b >17.5 kV/mm), the CaZrO₃ doped (Ba_0.6Sr_0.4)_0.85Bi_0.1TiO₃ ceramic is a potential candidate material for high power electric applications.