Re-fluidising the aged gel for high-density alumina green body

A green body with a density as high as possible is critical to diminish the crisis of deformation or cracking when large-size parts are sintered.Here,a new method,i.e.,re-fluidising the aged ceramic gel is developed to prepare the high-density green body.Alumina slurry with 56 vol%solid loading and copolymers of isobutylene and maleic anhydride were aged without vaporisation and re-fluidised by non-intrusive shearing after removing the exuded water.The re-fluidised slurry was re-casted.The resultant wet gel was dried and deboned at a low temperature.The relative density of the obtained green body was 64.6%,1.5%higher than that without aging and re-fluidising.The linear sintering shrinkage of the body decreased by 0.7%.The enhanced green density is explained from the viewpoint of the solid loading and the structure of the slurry.

Liquid drying of BeO gelcast green bodies using ethanol as liquid desiccant

BeO gelcast green bodies were dried by liquid drying method with liquid desiccant ethanol.Effects of ethanol concentration,solids loading and aspect ratio of green body on the moisture and shrinkage of green bodies were studied through measuring mass and dimension.Additionally,liquid drying stress was analyzed and a model of the initial stage drying stress was established.The results show that higher ethanol concentration,lower solids loading and higher aspect ratio of gelcast green bodies increase the drying rate.Increasing the ethanol concentration decreases the shrinkage rate.Liquid drying stress is generated due to a non-uniform drying rate.During the process of liquid drying,the inner drying stress of the green body changes from compressive stress to tensile stress,while the outer drying stress changes from tensile stress to compressive stress.

Effects of Adhesive Composition on Green Joining of CePO_4-ZrO_2 Ceramics

Green bodies of 25%CePO 4/ZrO 2 and ZrO 2 ceramics were joined at 1450℃ for 120 min without applied pressure by using mix ed powders slurries composed of CePO 4 and ZrO 2. The effects of CePO 4/(CePO 4+ZrO 2) ratio of the adhesive on the bond strength of the joints were invest igated. Maximum bond strength of 414MPa was obtained by joining an adhesive wit h the ratio of 0.5. Under the experimental conditions, the grain size of the par ticles grown in the joint was smaller than that in joined ceramics. The microstr ucture of the joint was more homogeneous than that of the matrix and without obv ious cracks, pores and other defects.

Green State Joining ZrO_2/Al_2O_3 Ceramics by Metal Interlayer

Green bodies of Al_2O_3 and ZrO_2 ceramics were joined without applying pressure by using metal slurries of Al as an interlayer according to the mechanism of volume expansion in the oxidation process of Al+O_2→Al_2O_3. The microstructure of the joints was investigated. The results shows that interface cracks are easily produced. With addition of Al_2O_3 and ZrO_2 into the interlayer composition, fine joints could be obtained without obvious cracks, pores and other defects. Under the experimental conditions, the grain size of the particles grown in the joint is smaller than that in the parent material. Therefore, the addition of Al_2O_3 or ZrO_2 can buffer the defect resulting from the volume expansion in the oxidation process. And in the existence of Al_2O_3 or ZrO_2 in the interlayer, active Al_2O_3 can boost the interface reaction.

Joining of ZrO_2/CePO_4 Green Bodies Using Slurries

Ce-ZrO2 and ZrO2/CePO4 ceramic system was joined in the green body by using mixed powder. Three kinds of systems are discussed. The microstructure and bending strengths of the joint were investigated and it is found that the Ce-ZrO2 and 30%CePO4/ZrO2 ceramics can be well joined in the green body. A joint with high mechanical property and good microstructure can be obtained after sintering without applied pressure. Complexly shaped ceramic components can be created by the technique of green state joining. A new way to produce them is provided and the cost is reduced due to the simplicity of the process.

Effects of agarose concentration and addition on the properties of gel-cast 3Y-ZrO2 green and sintered bodies

Using agarose as a gel agent to prepare ceramics is a suitable non-toxic gel-casting method. The effects of agarose concentration and addition amount on gel-cast 3Y-ZrO2 green and sintered bodies were investigated. Green bodies were prepared by gel-casting using an agarose solution of a different agarose mass fraction including 3.0%, 3.5%, 4.0%, 4.5%, 5.0% and 5.5% with an added amount of agarose in the green body at a mass fraction of 0.7%, and using the agarose solution of a mass fraction of 4.5% with a different amount of added agarose including 0.6%, 0.7%, 0.8%, 0.9%, and 1.0% in terms of mass fraction. The green bodies were sintered at I 600 ~C for 4 h. The relative density, linear shrinkage, and bending strength of the green bodies, and L^e density, microstructure, bending strength, and fracture toughness of sintered samples were characterized and analyzed. Results show that comprehensive properties of green bodies made with 4.5% （in terms of mass fraction） agarose solution added to an mass fraction of agarose in the slurry at 0.6% were the best, of which the bending strength was 3.14 MPa, the linear shrinkage was below 4.3%, and the relative density is 57.3%. For sintered bodies, the best fracture toughness was 5.63 MPa m1/2, and the optimal density was 5.88 gcm-3.

Enhanced plasticity of spontaneous coagulation cast oxide ceramic green bodies

In the preparation of large-sized ceramics,the use of a green body with relatively high plasticity is crucial to minimize the risk of cracking during processing.To achieve this goal,glycerol and polyethylene glycol(PEG)were utilized as plasticizers in the shaping of green bodies of oxide ceramics through spontaneous coagulation casting(SCC).This study investigated the effects of plasticizers and particle sizes ranging from the submicron to nanoscale on the slurry viscosity,drying shrinkage of wet gels,and mechanical properties of green bodies.The plasticity of the green bodies was assessed by measuring the impact toughness and flexural stress‒strain curves.By incorporating an appropriate plasticizer,the peak width of the flexural stress‒strain curve for dried green bodies from particles of different sizes was nearly twice that without plasticizers,and the impact toughness was enhanced by approximately 71%,34%,and 41%when the particle size decreased from the submicron scale to the nanoscale(0.45μm,0.18μm,and 50 nm,respectively).The drilling test revealed that there was nearly no cracking around the holes in the green bodies with plasticizers.The plasticity mechanism of the green bodies was examined based on ultraviolet–visible(UV–Vis)spectroscopy and scanning electron microscopy(SEM).It was discovered that plasticizers might mitigate the brittleness of green bodies by adjusting the interactions between molecules and modifying the gel network properly.