Calcium sulfate an unusual property: when mixed with water at normal (ambient) temperatures, it quickly reverts chemically to the preferred dihydrate form, while physically "setting" to form a rigid and relatively strong gypsum crystal lattice: This reaction is exothermic and is responsible for the ease with which gypsum can be cast into various shapes including sheets (for drywall), sticks (for blackboard chalk), and molds (to immobilize broken bones, or for metal casting). Mixed with polymers, it has been used as a bone repair cement. Small amounts of calcined gypsum are added to earth to create strong structures directly from cast earth, an
Blackboard Inc. United States Court of Appeals for the Federal Circuit. A ruling was made by the Court of Appeals on July 27, 2009 that the 38 patent claims made by Blackboard in its suit against Desire2Learn were invalid. The dispute was resolved, when Blackboard and Desire2Learn announced on December 15, 2009 that each company was settling all ongoing litigation between them and had made a cross-licensing agreement. In April 2010, the firm abandoned patent 6,988,138, and in November that year the company's legal counsel announced the patent's "official termination" and stated that Blackboard had ended its appeals. Blackboard Inc. Blackboard Inc.