Effect of Sintering Temperature on Properties of Zirconia Ceramic Grinding Ball

Since the 1970s, Professor Gavrie from Australia discovered the phase change toughening mechanism of zirconia ceramics, which have been widely used in a variety of structural and functional ceramics. It has become second only to alumina ceramics, the amount of structural ceramics in the second. Zirconia ceramic grinding ball is a kind of zirconia ceramics with a large amount of products, widely used in ceramics, building materials, chemical, coating, electronics, machinery, food, medicine, cosmetics and many other industries. Because the zirconia material itself has excellent high hardness, high strength, high toughness, high wear resistance, high corrosion resistance and high volume density, grinding efficiency higher characteristic, therefore zirconia ceramic grinding ball in addition to used in great quantities in zirconia ceramic powder grinding, in other electronic ceramics powder, magnetic powder, high technology structure and functional ceramics powder, ceramic pigment and glaze , chemical and all kinds of coatings, mechanical polishing powder, medicine and food powder ultrafine grinding also plays a very important role in reducing the introduction of impurities in the grinding material and improve the grinding and dispersion effect is incomparable to other grinding media. At the same time in some special ultrafine powder grinding equipment such as mixing mill, sand mill, high-speed vibration mill and other new equipment in the zirconia beads have become the only available products. Although its price is very high, but because of its very low abrasion, the grinding and dispersion effect of the grinding material is good, there is no need to often add material, so the comprehensive use cost is still relatively low, the use of the field is also expanding. In many fields are gradually replacing alumina, silicic acid, agate and other grinding media ball.

Sintering process is one of the key links in the production of ceramic products, which plays an important role in the microstructure and properties of ceramic materials. After sintering, the physical and chemical properties of ceramic body change, which determines the properties of the final product. The most important technological parameter in sintering process is the determination of sintering temperature. The influence of sintering temperature on volume density and wear resistance of grinding ball of rolling zirconia ceramics was studied.

I. Preparation and performance test method of zirconia ceramic grinding ball

1. Preparation of zirconia ceramic ball billet

Zirconia ceramic grinding ball was prepared by rolling forming method with submicron 3%YZO ceramic powder with median diameter (mole fraction)3.75. The preparation process is as follows: put a certain amount of prefabricated zirconia ball core (size less than 0.5mm) in the ball rolling machine, start the ball rolling machine, and make it rotate continuously and smoothly at a speed of 40/min under the collar Angle. Firstly, a certain amount of 0.3% polyvinyl alcohol aqueous solution was sprayed on the surface of the ball core in the ball rolling machine, and then a certain amount of zirconia powder was added to the ball core, and the ball core was rolled for 1min to make the powder adhere firmly to the ball core. Repeated this process makes the ball rolling machine in the zirconia sphere size gradually increased. When the size of the ball increases to about coin 7mm, spray the right amount of water and stop spraying powder, continue to roll for about 30min to polish the surface of the ball body, and get a smooth surface and good roundness of zirconia ceramic grinding ball body after stopping. The body is naturally dried for 24h, and then fully dried in an oven at 80℃. After measuring the diameter of ten balls to calculate its total volume, and weighing its total weight, calculated that the specific gravity of the dried ball body is 4.29 C /m3.

2. Sintering process of zirconia ceramic ball billet

The zirconia ceramic spheres were divided into four groups and fired according to the following sintering process: room temperature to 1000℃, heating rate of 100℃/h; 1000℃ to firing temperature, the heating rate is 50℃/h, the firing temperature of the four groups of samples are respectively set as 1450℃, 00℃,1550℃,1600℃. After holding for 2 hours with the furnace cooling, the diameter of about 6mm zirconia ceramic grinding ball.

3. Test method for performance of zirconia ceramic spheres

Measurement of volume density:
The dry weight and water weight of sintered zro2 ceramic grinding ball were measured on the scale of 1/10,000 accuracy, and the volume density of zro2 ceramic grinding ball was calculated by Archimedes method.

Measurement of self-wear rate:
Each group of zirconia ceramic grinding balls to be measured was weighed at about 1kg, denoted as M (accuracy 0.019, same below), and loaded into a poly vinegar tank with 220mm and 220mm inner diameter and added with 500mL deionized water. The balls were ground for 48h at 60r/min speed on a ball grinding test machine. The sample was cleaned with water, dried in an oven at 80℃ and weighed as mZ. The self-wear rate was :(m: 1mz)/(m,*48), and the unit was 10-6 /h,(millionth /h).

Ⅱ. Results and discussion

1. Effect of sintering temperature on volume density of zirconia ceramic grinding ball

Figure 1 shows the variation curve of volume density with sintering temperature measured by Archimedes method after the zirconia grinding ball body obtained by rolling molding method was burned according to the specified sintering process. It can be clearly seen that with the increase of firing temperature, the volume density of zirconia ball increases gradually, the volume density increases sharply between 1500℃ and 1550℃, but the temperature range of 1450 ℃ to 1500℃,1550 ℃ to 1600℃ curves are flat. Obviously, after sintering at 1450℃ and 1500℃, zirconia ceramic grinding balls are not completely sintered and densified, and the volume density is low, at the level of 5.7-5.75 g/cm^-3. After sintering at 1550℃, the volume density of zRO2 ceramic grinding ball increases sharply and densification is obvious. The volume density reaches 5.91g/cm^-3. When the temperature rises to 1600℃, although the volume density still increases slightly (the relative density is 97.2%), the sintered sphere has basically reached densification, with very little room for rise.

 

2. Effect of sintering temperature on self-wear rate of zirconia ceramic grinding ball

Figure 2 shows the curve of self-wear rate of zirconia ceramic grinding ball changing with firing temperature. It can be seen from Figure 2 that the self-wear rate of zirconia ceramic grinding ball decreases first and then increases with the increase of firing temperature, and the self-wear rate of grinding ball fired at 1550℃ is the lowest. This is because under the condition of lower than 1550℃, the densification effect of porcelain sintering is poor, at this time, the volume density of zirconia ceramic grinding ball is the main factor affecting its self-wear rate. The higher the density of the sphere is, the closer the grain bond is, and the lower the self-wear rate is. At this time, the self-wear rate decreases with the increase of volume density. When the sintering temperature reaches 1550℃, the grinding ball of zirconia ceramic is basically densified. At this time, the content of tetragonal zirconia, which can undergo stress-induced phase transformation of zirconia at room temperature, should be the main factor affecting the true wear resistance. At 1550℃, although the volume density is not the maximum, the content of tetragonal zirconia which can undergo phase transformation is the maximum, so the self-wear rate is the minimum at this time. When the sintering temperature rises to 1600℃, the volume density of zirconia ceramic grinding ball increases slightly, but the excessive sintering temperature leads to the abnormal growth of some grain sizes.

Since the grain size of zirconia ceramics controls the possibility of partially stable tetragonal zirconia phase transition, When the grain size of more than four phase zirconium oxide into monoclinic zirconia of phase transition critical value, the big grain square phase of zirconia in cool to room temperature will occur in the process of transformation into a monoclinic phase, cause the zirconia ceramic ball at room temperature can occur in the four corners of the phase transformation toughening phase of zirconia content reduced, wear resistance, so the wear rate began to rise again.

Ⅲ. Conclusion

  • Zirconia ceramic ball billet prepared by rolling forming method has the characteristics of smooth surface, good roundness and high volume density. At 1550~1600℃, the relative volume density of ceramic can reach 97%.
  • The wear resistance of zirconia ceramic grinding ball is mainly affected by its volume density and tetragonal zirconia content. Under the conditions of this test, the zirconia ceramic ball body formed by rolling method can be fired at 1550℃, and the best wear resistance can be obtained.
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