Effect cf Nano-ZnO or Nano-Y_2O_3 on Sintering Property of Fused Quartz Ceramics

Fused quartz ceramic was prepared using high purity fused quartz powder as starting material,separately introducing 1%,2% and 3% （in mass,the same hereinafter） nano-ZnO or nano-Y203 as additive,molding at 50 MPa,firing in reduction atmosphere at 1 300,1 350 and 1 400 ℃ for 1 h,respectively.Apparent porosity and cold modulus of rupture were tested and fracture morphology was analyzed by SEM.The results show that adding nano-ZnO or nano-Y2O3 obviously improves sintering of fused quartz; adding nano-ZnO enhances modulus of rupture and decreases apparent porosity; the optimum addition of nano-Y2O3 as sintering aid of fused quartz is 2%.

Preparation and sintering properties of zirconia-mullite-corundum composites using fly ash and zircon

Zirconia-mullite-corundum composites were successfully prepared from fly ash,zircon and alumina powder by a reaction sintering process.The phase and microstructure evolutions of the composite synthesized at desired temperatures of 1 400,1 500 and 1 600°C for 4 h were characterized by X-ray diffractometry and scanning electronic microscopy,respectively.The influences of sintering temperature on shrinkage ratio,apparent porosity and bulk density of the synthesized composite were investigated.The formation process of the composites was discussed in detail.The results show that the zirconia-mullite-corundum composites with good sintering properties can be prepared at 1 600°C for 4 h.Zirconia particles can be homogeneously distributed in mullite matrix,and the zirconia particles are around 5μm.The formation process of zirconia-mullite-corundum composites consists of decomposition of zircon and mullitization process.

Basic characteristics of Australian iron ore concentrate and its effects on sinter properties during the high-limonite sintering process

The basic characteristics of Australian iron ore concentrate (Ore-A) and its effects on sinter properties during a high-limonite sintering process were studied using micro-sinter and sinter pot methods. The results show that the Ore-A exhibits good granulation properties, strong liquid flow capability, high bonding phase strength and crystal strength, but poor assimilability. With increasing Ore-A ratio, the tumbler index and the reduction index (RI) of the sinter first increase and then decrease, whereas the softening interval (Delta T) and the softening start temperature (T (10%)) of the sinter exhibit the opposite behavior; the reduction degradation index (RDI+3.15) of the sinter increases linearly, but the sinter yield exhibits no obvious effects. With increasing Ore-A ratio, the distribution and crystallization of the minerals are improved, the main bonding phase first changes from silico-ferrite of calcium and aluminum (SFCA) to kirschsteinite, silicate, and SFCA and then transforms to 2CaO center dot SiO2 and SFCA. Given the utilization of Ore-A and the improvement of the sinter properties, the Ore-A ratio in the high-limonite sintering process is suggested to be controlled at approximately 6wt%.

Graphene-reinforced aluminum matrix composites prepared by spark plasma sintering

Graphene-reinforced 7055 aluminum alloy composites with different contents of graphene were prepared by spark plasma sintering（SPS）. The structure and mechanical properties of the composites were investigated. Testing results show that the hardness, compressive strength, and yield strength of the composites are improved with the addition of 1wt% graphene. A clean, strong interface is formed between the metal matrix and graphene via metallurgical bonding on atomic scale. Harmful aluminum carbide（Al_4C_3） is not formed during SPS processing. Further addition of graphene（above 1wt%） results in the deterioration in mechanical properties of the composites. The agglomeration of graphene plates is exacerbated with increasing graphene content, which is the main reason for this deterioration.

Effect of Y_2O_3, CeO_2 on Sintering Properties of Si_3N_4 Ceramics

The effect of rare earth oxides Y 2O 3 or CeO 2 on sintering properties of Si 3N 4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results indicate that the best sintering properties appear in Si 3N 4 ceramics with 5% Y 2O 3 or 8% CeO 2. Secondary crystallites are formed at grain boundaries after heat treatment, which decreases the amount of glass phase and contributes to the improvement of high temperature mechanical properties of silicon nitride.

Microstructure and Mechanical Performance of Cu-SnO_2-rGO based Composites Prepared by Plasma Activated Sintering

A novel chemical technique combined with unique plasma activated sintering（PAS） was utilized to prepare consolidated copper matrix composites（CMCs） by adding Cu-SnO2-rGO layered micro powders as reinforced fillers into Cu matrix. The repeating Cu-SnO2-rGO structure was composed of inner dispersed reduced graphene oxide（r GO）, SnO2 as intermedia and outer Cu coating. SnO2 was introduced to the surface of rGO sheets in order to prevent the graphene aggregation with SnO2 serving as spacer and to provide enough active sites for subsequent Cu deposition. This process can guarantee rGO sheets to suffi ciently disperse and Cu nanoparticles to tightly and uniformly anchor on each layer of rGO by means of the SnO2 active sites as well as strictly control the reduction speed of Cu^2＋. The complete cover of Cu nanoparticles on rGO sheets thoroughly avoids direct contact among rGO layers. Hence, the repeating structure can simultaneously solve the wettability problem between rGO and Cu matrix as well as improve the bonding strength between rGO and Cu matrix at the well-bonded Cu-SnO2-rGO interface. The isolated rGO can effectively hinder the glide of dislocation at Cu-rGO interface and support the applied loads. Finally, the compressive strength of CMCs was enhanced when the strengthening effi ciency reached up to 41.

Influence of Yb_2O_3-MgO on Mechanical Properties and Thermal Conductivity of Silicon Nitride Ceramics via Gas Pressure Sintering

In this work,Yb2O3 and Mg O were used as sintering aids in preparing silicon nitride ceramics by gas pressure sintering（ 0. 6 MPa N2atmosphere） to investigate how the amounts of Yb2O3- Mg O influence the mechanical properties and thermal conductivity of silicon nitride ceramics. The total contents of Yb2O3- Mg O added were 1 mol%,2 mol%,4 mol%,6 mol%,8 mol%,10 mol%,12 mol%,14 mol%,keeping the Yb2O3-Mg O molar ratio of 1 ∶ 1 steadily. Curves of the relative density,thermal conductivity and bending strength plotted against the aids content present a ‘mountain＇shape with a maximum at nearly 10 mol% aids. The fracture toughness increased with the amounts of additives up to10 mol% and decreased slightly thereafter. The mechanical properties and thermal conductivity were almost proportional to the amount of the additives before10 mol%. When the content of aids exceeded 10 mol%,it would weaken the mechanical properties and thermal conductivity of the ceramics. The optimum content of Yb2O3- Mg O was 10 mol% by gas pressure sintering（ 0. 6MPa） at 1 850 ℃ for 4 h,which led to a relative density of 98. 9%,a flexural strength of（ 966 ± 38）MPa as well as a fracture toughness of（ 6. 29 ± 0. 29）MPa·m1 /2and thermal conductivity of 82 W /（ m·K）.

Preparation,Structures,Thermal Properties and Sintering Behaviors of B_2O_3-SiO_2-ZnO-BaO-Al_2O_3 Glass

B_2O_3-SiO_2-ZnO-BaO-Al_2O_3 glass with different Al_2O_3 contents（1mol%, 3mol%, 5mol%, and 7mol%） was prepared, and it was intended to be used as lead-free and low-melting glass sealants for solid oxide fuel cells. The effects of Al_2O_3 content on the structures, thermal properties, and sintering behaviors of the B_2O_3-SiO_2-ZnO-BaO-Al_2O_3 glass were investigated in detail. The Al_2O_3 content largely influenced the structures and thermal properties of the glass. When the Al_2O_3 content 5mol%, the transition temperature of the glass decreased with the Al_2O_3 content, while the crystallization temperature increased with the Al_2O_3 content. However, higher Al_2O_3 content degraded the stability of the glass. The B_2O_3-SiO_2-ZnO-BaO-Al_2O_3 glass with 5 mol% Al_2O_3 content exhibits the optimal sintering densification characteristics and can be used as glass sealants for solid oxide fuel cells.

Effect of Sintering Temperature and Zinc Content on Some Properties of Li-Zn Ferrites

Li-Zn mixed ferrites with composition formula ZnxLi0.5-x/2Fe2.5-x/2O4 (0.2≤x≤0.8) were prepared by the usual ceramic method in 1000~1150℃. The effects of Zn substitution and sintering temperature on the formation, densification, microstructure and a.c. electrical conductivity have been studied. Under the effect of changing the firing temperature and Zn content, high sintered Li-Zn ferrite bodies are achieved. More fine structure bodies having high electrical resistance are obtained at high Zn content

Reaction Mechanism and Microstructure Evolution of Reaction Sintered h-BN

Hexagonal boron nitride ceramic（h-BN） based on the nitridation of B powders was obtained by reaction sintering method. The effects of sintering temperature on the mechanical properties and microstructure of the resultant products were investigated and the reaction mechanism was discussed. Results showed that the reaction between B and N2 occurred vigorously at temperatures ranging from 1 000 ℃ to 1 300 ℃, which resulted in the generation of t-BN. When the temperature exceeded 1 450 ℃, transformation from t-BN to h-BN began to occur. As the sintering temperature increased, the spherical particles of t-BN gradually transformed into fine sheet particles of h-BN. These particles subsequently displayed a compact arrangement to achieve a more uniform microstructure, thereby increasing the strength.

Effect of Y_2O_3 Addition on Sintering Properties and Microstructure of Spinel Materials

The effect of Y2O3 addition on the sintering proper- ties and microstructure of spinel was investigated using alumina-rich spinel as the raw material. The phase con- stitution and microstructure of the specimens were charac- terized by XRD and SEM, and the pore structure of the specimens was measured by a mercury porosimeter. The results indicate that a viscous melt forms wrapping around spinel crystals by adding a little Y2O3 powders （1 mass% ）, yttrium alumina garnet will crystallize around spinel crystals by adding more Y2O3 powders （ 3 mass% ） ; the sintering properties of the spinel are sig- nificantly improved by adding Y2O3 powders less than 3 mass%, while they will be relatively weakened by adding Y2O3 powders more than 3 mass%.

Effect of Additive ZrO_2 on Sintering Properties of MgO-CaO Bricks

The effect of electric fused ZrO2,m-ZrO2 and zirconite on the sintering properties of MgO-CaO bricks was studied and the effect of the ZrO2 content and temperature on BD （bulk density）, AP（apparent porosity）and CCS （Cold Crushing strength） of MgO-CaO bricks was investigated.The microstructure of burned specimens was analyzed by SEM. The result shows that the sintering property is best while 5% m-ZrO2 was added at 1 600 ℃.

Rheological and Sintering Properties of Two Kinds of Corundum-spinel Micropowders

For the proper use of micropowders in castables,slurries and fired samples were prepared with two kinds of corundumspinel micropowders(D and G).The effects of the solid content and disperser WSM-R1 on the rheological properties of the slurries were studied.The sintering properties and the slag corrosion resistance of the fired samples were also researched.The results show that:the slurries all show pseudoplastic rheological characteristics.With the same solid content,the slurry with micropowder G has higher initial viscosity than that with micropowder D.Disperser WSM-R1 significantly reduces the initial viscosity of the two slurries and plays a more obvious dispersing effect on the slurry with micropowder G.The fired sample with micropowder G has higher bulk density,lower apparent porosity and better corrosion resistance than that with micropowder D.

Preparation and Thermal Shock Resistance of Mullite Ceramics for High Temperature Solar Thermal Storage

Mullite thermal storage ceramics were prepared by low-cost calcined bauxite and kaolin.The phase composition,microstructure,high temperature resistance and thermophysical properties were characterized by modern testing techniques.The experimental results indicate that sample A3(bauxite/kaolin ratio of 5:5)sintered at 1620℃has the optimum comprehensive properties,with bulk density of 2.83 g·cm^(-3)and bending strength of 155.44 MPa.After 30 thermal shocks(1000℃-room temperature,air cooling),the bending strength of sample A3 increases to 166.15 MPa with an enhancement rate of 6.89%,the corresponding thermal conductivity and specific heat capacity are 3.54 W·(m·K)^(-1)and 1.39 kJ·(kg·K)^(-1)at 800℃,and the thermal storage density is 1096 kJ·kg^(-1)(25-800 mullite ceramics;sintering properties;high-temperature thermal storage;thermal shock resistance).Mullite forms a dense and continuous interlaced network microstructure,which endows the samples high thermal storage density and high bending strength,but the decrease of bauxite/kaolin ratio leads to the decrease of mullite content,which reduces the properties of the samples.

Preparation of SiC Porous Ceramics by Crystalline Silicon Cutting Waste

SiC porous ceramics were prepared at 1 400 ℃ for4 h with crystalline silicon cutting waste and activated carbon as main starting materials and NH4HCO3 as the pore-forming agent. Effects of NH4HCO3 additions( 0,20%,30%,40%,by mass) on the phase composition,microstructure,sintering properties,cold compressive strength and thermal shock resistance of as-prepared Si C porous ceramics were investigated. The results show that:( 1) addition of NH4HCO3 remarkably influences the apparent porosity and cold compressive strength of specimens. The apparent porosity achieves its maximum value( 63. 40%) when 40% NH4HCO3 is added,while the minimum cold compressive strength is 4. 77 MPa;( 2) the specimen with 40% NH4HCO3 has the best thermal shock resistance. The thermal cycling times between1 000 ℃ to room temperature reach 62;( 3) the addition of NH4HCO3 does not remarkably affect the phase composition of the specimens;( 4) the specimens include a large number of SiC particles and a small amount of SiC whiskers.

Effect of nitrogen introduction methods on the microstructure and properties of gradient cemented carbides

Gradient cemented carbides with the surface depleted in cubic phases were prepared following normal powder metallurgical pro-cedures.Gradient zone formation and the influence of nitrogen introduction methods on the microstructure and performance of the alloys were investigated.The results show that the simple one-step vacuum sintering technique is doable for producing gradient cemented carbides.Gradient structure formation is attributed to the gradient in nitrogen activity during sintering,but is independent from nitrogen introduced methods.A uniform carbon distribution is found throughout the materials.Moreover,the transverse rupture strength of the cemented carbides can be increased by a gradient layer.Different nitrogen carriers give the alloys distinguishing microstructure and mechanical properties,and a gradient alloy with ultrafine-TiC0.5N0.5 is found optimal.

Effect of Main Material Ratio on Properties of SiC-Al_2O_3 Porous Ceramics via Polymeric Replication Method

In order to fabricate porous ceramics with good properties and proper production cost,SiC-Al2 O3 porous ceramics were prepared at 1 450 ℃ for 2 h from the powders of commercial silicon carbide and white fused corundum via a polymeric replication method. Effects of the mass ratio of SiC powder to white fused corundum powder（ 1 ∶ 3,1 ∶ 1 and 3 ∶ 1） on the appearance,phase composition,sintering properties and thermal shock resistance were investigated. The research results indicate that the as-prepared Si C-Al2 O3 porous ceramics have uniform pores,and their linear shrinkage ratio,apparent porosity and bulk density reach 4. 70%,67. 17%and 0. 83 g·cm-3,respectively. The thermal shock cycles from 1 400 ℃ to room temperature reach 23 including 15 cycles in air cooling condition and then 8 cycles in water cooling condition. Their main phases areα-Al2 O3 and Al6 Si2 O13 as well as a small amount of SiC and free SiO2. The as-prepared porous ceramic with the ratio of m（ SiC） ∶ m（ Al2 O3） = 1∶ 1 possesses prior comprehensive properties.

Research Progress on Preparation and Properties of Zirconium Carbide Matrix Composites

Zirconium carbide（ZrC） exhibits considerable potential for applications as aerospace thermal protection and the Generation-Ⅳ nuclear fuel inert materials due to its high melting point,exceptional hardness,good ablation resistance and low neutron absorption cross-section.Nevertheless,low sinterability of ZrC powders and poor fracture toughness and reliability of bulk ceramics limit their wide applications in extreme environments.This paper reviews the state of the art of preparation and properties of ZrC composites.Optimizing the sintering process and tailoring the chemical constituents of raw powders and sintering aids could improve sinterability to produce dense bulk ceramics.Different additives such as refractory metals,carbides,silicides,oxides,or carbon fibers are introduced into the ZrC matrix in order to improve fracture toughness,oxidation resistance or thermal shock resistance,etc.Further studies are needed to explore the effects of intrinsic defects（vacancies,dislocations,and grain or phase boundaries,etc.） and additives on microstructure and properties at elevated temperatures.

Sintering Properties and Optimal Blending Schemes of Iron Ores

In order to obtain good sintering performance, it is important to understand sintering properties of iron ores. Sintering properties including chemical composition, granulation and high-temperature behaviors of ores from China, Brazil and Australia. Furthermore, several indices were defined to evaluate sintering properties of iron ores. The results show that： for chemical composition, Brazilian ores present high TFe, low SiOz, and low Alz03 con- tent. For granulation, particle diameter ratio of Brazilian ores are high; particle intermediate fraction of Chinese con- centrates are low; and average particle size and clay type index of Australian ores are high. For high-temperature properties, ores from China, Brazil and Australia present different characteristics. Ores from different origins should be mixed together to obtain good high-temperature properties. According to the analysis of each ore＇s sintering prop- erties, an ore blending scheme （Chinese concentrates 20 ^-1- Brazilian ores 400//oo -k Australian ores 40 ~） was sugges- ted. Moreover, sinter pot test using blending mix was performed, and the results indicated that the ore blending scheme led to good sintering performance and sinter quality.

Influence of Gd_2O_3 and Yb_2O_3 Co-doping on Phase Stability,Thermo-physical Properties and Sintering of 8YSZ

The role of multicomponent rare earth oxides in phase stability, thermophysical properties and sintering for ZrO2-based thermal barrier coatings （TBCs） materials is investigated. 8YSZ codoped with 3 mol% Gd2O3 and 3 mol% Yb2O3 （GYb-YSZ） powders are synthesized by solid state reaction for 24 h at various temperatures. As temperature increases, stabilizers are dissolved into zirconia matrix gradually. Synthesized at 1 500 °C, GYb-YSZ is basically composed of cubic phase. GYb-YSZ exhibits excellent phase stability and sinters lower than 8YSZ by nearly three times. The thermal conductivity of GYb-YSZ is much lower than that of 8YSZ, and the thermal expansion coefficient of GYb-YSZ is comparable to that of 8YSZ. The influence of Gd2O3 and Yb2O3 co-doping on phase stability, thermal conductivity and sintering of 8YSZ is discussed.