Abstract: A hail producing machine includes at least one diffuser for mixing water and carbon dioxide. At least one heat exchanger is in flow communication with the diffuser for receiving the mixture. A refrigeration unit freezes the mixture to form an ice rod in the heat exchanger. The ice rod is ejected from the heat exchanger and is converted into hail stones by a molding station downstream from the heat exchanger.

Abstract: A hail producing machine includes at least one diffuser for mixing water and carbon dioxide. At least one heat exchanger is in flow communication with the diffuser for receiving the mixture. A refrigeration unit freezes the mixture to form an ice rod in the heat exchanger. The ice rod is ejected from the heat exchanger and is converted into hail stones by a molding station downstream from the heat exchanger.

Abstract: Compositions having the general formula (Ca.sub.x Mg.sub.1-x)Zr.sub.4 (PO.sub.4).sub.6 where x is between 0.5 and 0.99 are produced by solid state and sol-gel processes. In a preferred embodiment, when x is between 0.5 and 0.8, the MgCZP materials have near-zero coefficients of thermal expansion. The MgCZPs of the present invention also show unusually low thermal conductivities, and are stable at high temperatures. Macrostructures formed from MgCZP are useful in a wide variety of high-temperature applications. In a preferred process, calcium, magnesium, and zirconium nitrate solutions have their pH adjusted to between 7 and 9 either before or after the addition of ammonium dihydrogen phosphate. After dehydration to a gel, and calcination at temperatures in excess of 850.degree. C. for approximately 16 hours, single phase crystalline MgCZP powders with particle sizes ranging from approximately 20 nm to 50 nm result. The MgCZP powders are then sintered at temperatures ranging from 1200.degree. C. to 1350.