surface discoloration reasons of piezo ceramic elements substrate(2)

The surface of the original piezoelectric discs sensor substrate is pure white, and the surface color is yellow. There are two possibilities, First, since the surface material of the alumina piezo ceramic is yellowe by chemical corrosion, the chemical property of the alumina is stable, and it is difficult to occur at normal temperature. The second is that the contacting material other than the alumina piezo ceramic remains on the surface, or the related material chemically acts and covers the ceramic surface to turn yellow. Since the alumina piezo ceramic substrate is placed between the cast iron grinding discs by a free abrasive, the experimental articles that are in direct or indirect contact with the alumina piezo ceramic surface include slurry and grinding disc.

The pzt disc piezoelectric ceramic substrate has only A1 element and O element on the surface before grinding. After double-side grinding, the surface increases the C element and the Fe element. The C element may come from the diamond abrasive, and the element has stability at room temperature and is difficult to occur chemical action. The Fe element is not an element contained in the alumina piezo ceramic substrate itself, which is derived from the contact of the piezo ceramic substrate. It is a simplified diagram of the double-side grinding system, in which the upper and lower grinding piezo discs are made of cast iron, and the star wheel cage is made of blue steel. From the analysis in the previous section, it is known that the abrasive has no effect on the the surface of the alumina piezo element vibration sensor. Therefore, the iron pollution source has nothing to do with the abrasive, and it comes from a cast iron grinding disc or a blue steel wheel cage. Since the actual gap between the star wheel cage and the grinding disc is relatively large, the abrasive particles between the gaps do not bear the pressure, but only have a mechanical effect on the surface of the star wheel cage with the flow of the slurry. 

The mechanical action has very little iron contamination caused by micro-crushing on the surface of the star wheel. The abrasive particles between the cast iron grinding disc and the ceramic substrate bear the pressure and cause mechanical micro-crushing on the surface of the cast iron grinding disc with the flow of the grinding liquid. Therefore, the iron pollution is mainly caused by the abrasive particles on the cast iron grinding disc surface. Therefore, the surface of the alumina ceramic substrate is grinding, and the reason can be considered as the piezoelectric ceramic element.The substrate is held by the star wheel cage and placed between the upper and lower cast iron grinding discs for star movement.During the processing movement, since the hardness of the abrasive particles is higher than that of the cast iron, the abrasive particles are embedded in the cast iron grinding disc.

Micro-cutting removal of piezo ceramic also causes micro-crushing of the cast iron grinding disc itself, which in turn grinds the cast iron.The surface of the disc is removed. The iron removed on the cast iron grinding disc escapes into the slurry in the dispersed state, and The flow of the slurry migrates to the surface of the alumina ceramic substrate, and the oxygen in the air and water is slowly oxidized. Adsorbed with iron oxide and covered on the piezoelectric ring crystal surface, so that the piezo ceramic surface appears yellowish in color elephant among them, the equations are involved in the chemical action of iron, because alumina piezo ceramics are polycrystalline materials, there are tiny pores between the crystals, and the ion diameter of iron oxide is much smaller than the pores, so it is difficult to clean.