A vehicle steering assembly comprising a vehicle steering system, a wheel assembly including a pivotal wheel hub for supporting a wheel, a knuckle mounted to the hub, and a pivot arm extending outward from the knuckle. The solubility of the source of magnesium is smaller than 100 gL. In addition, the conductive layer between the gate electrodes can relax the electric field applied to the corner of the gate electrode. Applications: contrast agent for MRI. A barrel-polishing method is also disclosed.