| As the fast development of the automotive industry in china, more and more problems come out, including the problem of the car-exhaust induced environmental pollution, being highlighted for special attention. Especially as the gradual upgrade of the international emission control regulations , more and more requirements for the oxygen sensor are raised for the detection and control of the car exhaust, resulting in many urgent theoretical and technical problems, meanwhile, the market of oxygen sensor in china is just starting, far behind the international companies. Thus there is not only the academic value but also the economic and strategy value for china in the study of the car oxygen sensor.Nowadays, the chip-style oxygen sensor has dominated the market for the characteristics of the small size, the long life, and the flexibility for tough environments. Materials for the chip-style oxygen sensor include aluminum oxide, titanium carbide, calcium titanate, zirconium oxide and so on, resulting in different characteristics of the oxygen sensor. The zirconium oxide ceramic of 8mol% fraction of Y2O3 stabilize ZrO2 (YSZ) has gain growing concern and has been selected to be the basic material of the oxygen sensor studied in this paper for its advantages of the high oxygen ion conductivity and the stability in oxidation and reduction atmosphere.The manufacture technologies for the zirconium oxide ceramic chip include sol-gel method, extrusion molding method, injection molding method, spray forming method and tape casting method, etc., and the tape casting method is applied broadly for the high efficiency due to the simplicity of equipments, high level of automation, continuity of operation, and for the uniform performance of cast biscuit due to the stable casting process. The tape casting method includes water based method and non-water based method, which having the same technical process. But the non-water tape casting method using a large number of organic solvents, causes great environmental pollution, and its technology has not improved. Therefore, this paper studies the zirconium oxide ceramic slurry using the water based tape casting method, discussing the technical process of the slurry preparation and the tape casting method, giving the standard for the choice of the dispersant, the binder and the plasticizer, while the factors determining the thickness and the quality of the cast film are also analyzed, with the scheme for the enhancement of the quality of the cast film proposed.Considering the high price of the 8mol% fraction of Y2O3 stabilize ZrO2 (YSZ), the cheaper Al2O3 is first chose as the powder to study the specified factor in the water based tape casting process. Referring to the charge ratio in relative references, this paper choosing water as solvent, debugs the composition and dosage of the dispersant, the binder and the plasticizer, and get the best ratio of stable casting slurry. Finally, this paper gets the alumina ceramic slurry which is suitable for the water based tape casting and does the casting. Specifically, this paper prepares the Al2O3 40wt.% slurry for water based tape casting, determines the best value for the amount of the dispersant is 1.0wt.%, chooses dibutyl phthalate plasticizers and polyethylene glycol as the compound with a ratio of 1:1 and a mount of 3.6wt.%, chooses polyvinyl alcohol (PVA) as the binder with the mount of 3.9wt.%. This paper deal the prepared slurry with manual tape-casting operations, and after natural drying for 20h, the relatively flat tape-casting biscuit of Al2O3 is got.Based on the manufacture technology of Al2O3 slurry, this paper replaces Al2O3 with ZrO2 as the powder to prepare the tape casting slurry, and studies the affects of the dispersant, the binder, the plasticizer and other organic additives to the stability of tape casting slurry, getting the formula of the ZrO2 tape casting slurry. Specifically, this paper prepares two different tape casting slurry of the ZrO2 powder with different particle sizes (DA=0.41nm,DB=0.26nm), determines the best ratio of the water-based tape casting slurry as the solid content of ZrO2 A to be 40.0wt.%, determines the amount of the dispersant Ammonium to be 2.0wt.%, uses the PVA as the binder alone with a amount of 3.84wt.%, uses the polyethylene glycol and dibutyl phthalate as the plasticizer with a ratio of 1:1 and a amount of 2.52wt.%. Thus, this paper has prepared the water-based tape casting slurry with good flow properties, and after casting and drying, smooth casting film with scalability is punched, sintering in the conditions of 1550℃, to get the zirconium oxide ceramic with good density, but, the shrinkage of sintering is more than 20% both in the length and width direction, which is not conducive to control the size of zirconium oxide ceramic, and that is due to the low solid content in the slurry. When PVA is used as a binder alone, due to the existence of the organic side chain, after adsorbed on the ceramic surface, PVA increases the viscosity of the slurry, and therefore the solid content of ZrO2 A is very difficult to continue to improve, while when acrylic emulsion S-07 is used as a binder alone, the solid content is enhanced effectively, with the drawback of decreasing the green strength of casting plan films.Considering the factors above, this paper for the first time chooses acrylic emulsion S-07 and PVA as the composite binder, and chooses polyethylene glycol and dibutyl phthalate as the composite plasticizer, increasing the solid content of ZrO2 casting slurry to 45wt.%, thus the Shrinkage in the length direction and the width direction of the sintered samples is reduced by 16.72% and 14.58% respectively, to meet the requirements of production of zirconium oxide ceramic chips. When the ratio of PVA and acrylic emulsion adhesive S-07 is 1.2, the slurry has a good rheological property.In addition, the paper also studies the affects of the first and the second ball mill time to the viscosity of two different zirconium oxide casting slurry with different particle sizes, showing that the ball mill time should get the optimal time, instead as long as possible. For ZrO2 A, the optimal times of the first and the second ball milling time are 10h and 20h, while for ZrO2 B, the optimal times are 8h and 18h. The smaller the particle size of zirconium oxide powder, the shorter the time required for slurry achieving good flow properties. |
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