A method having the following steps: running a circulation valve
comprising a reactive material into the well bore on the casing;
reverse-circulating an activator material in the well bore until the
activator material contacts the reactive material of the circulation
valve; reconfiguring the circulation valve by contact of the activator
material with the reactive material; and reverse-circulating a cement
composition in the well bore until the reconfigured circulation valve
decreases flow of the cement composition. A circulation valve for
cementing casing in a well bore, the valve having: a valve housing
connected to the casing and comprising a reactive material; a plurality
of holes in the housing, wherein the plurality of holes allow fluid
communication between an inner diameter of the housing and an exterior of
the housing, wherein the reactive material is expandable to close the
plurality of holes.