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1 MARTIAN CEMENTS Robert J. Milligan 4Frontiers 10th Annual International Mars Society Convention August 30, 2007
© 4Frontiers Corporation2 Robert J. Milligan Aug PORTLAND CEMENT Baseline for the World (Relatively) easy-to-get precursors on Earth Limestone or Calcium Carbonate Sand or Silica Alumina Iron Oxide (Hematite) And finally a dash of Gypsum (Calcium Sulfate)
© 4Frontiers Corporation3 Robert J. Milligan Aug CHEMISTRY The Limestone, Silica, Alumina and Iron Oxide are Pulverized and Mixed in a Rotary Kiln. The temperature is increased to ~1480ºC. The calcium carbonate decomposes to form calcium oxide (quicklime) and carbon dioxide (calcination). The calcium oxide reacts with the other oxides to form: Dicalcium and tricalcium silicates, Tricalcium aluminate, Tetracalcium ferroaluminate. This mass sinters together in what is called “clinker”.
© 4Frontiers Corporation4 Robert J. Milligan Aug FURTHER PROCESSING The Clinker is Removed from the Rotary Kiln and Pulverized. Roughly 5% by Weight Gypsum (Calcium Sulfate) is Added During the Pulverization for Esthetic Effects (It Lightens the Color and Helps Provide a Smooth Surface).
© 4Frontiers Corporation5 Robert J. Milligan Aug NOW LETS TAKE THIS TECHNOLOGY TO MARS Materials: Limestone No Limestone Beds have been Found on Mars. Cement Plants are Operating in Europe in which Gypsum (Calcium Sulfate) has been Substituted for Limestone. The Pyrolysis is Done in the Presence of a Reducing Agent (Carbon Monoxide, Carbon Powder). The Sulfur Dioxide Expelled from the Reaction is Oxidized and Hydrolyzed to Sulfuric Acid. Gypsum has been Identified on Mars.
© 4Frontiers Corporation6 Robert J. Milligan Aug Materials (cont.) Silica Not Known in Any Sort of Concentration on Mars until this Spring. Alumina Not Known in Concentration on Mars. Aluminum Ore Containing Silts (Muds) Have Been Identified. May be Able to Tap The Modified Alkaline Bayer Process for Silica and Alumina. Iron Oxide Hematite is Available Jarosite, KFe 3 (SO 4 ) 2 (OH) 6 Is Also Known
© 4Frontiers Corporation7 Robert J. Milligan Aug MOS SOREL CEMENT A Less Cumbersome Cement to Make on Mars is that Known as Magnesium Oxy-Sulfate (MOS) Sorel Cement. Only One Material, MgSO4H2O (Kieserite), needs to be Beneficiated. Kieserite is Purified, Dehydrated and a Portion is Calcined to Form MgO (Magnesia). Reductive Calcination takes Place at a Lower Temperature than That for Calcium Oxide Magnesia is also useful for the preparation of refractory brick for steelmaking.
© 4Frontiers Corporation8 Robert J. Milligan Aug PREPARATION OF MOS CEMENT An Aqueous Solution of Epsomite, MgSO 4 7H 2 O is Prepared. The Solution is Generally Quite Concentrated With Epsomite Solids Levels From 35 to 65%. Magnesium Oxide is Then Added to the Solution. Care is Taken not to Overheat (Initiate Cure) and External Cooling is Often Used. The Stoichiometry is 5 Moles of MgO for Every Mole of Epsomite. The Final Cement has a Molecular Formula of: 5MgOMgSO 4 8H 2 O
© 4Frontiers Corporation9 Robert J. Milligan Aug DISADVANTAGES OF MOS Mixing the Oxide with the Epsomite The hydroxide may drop out of solution before it reacts with the epsomite. Heat generated may lead to premature cure. Stoichiometry is Critical for Good Concrete. Improper Stoichiometry Causes Exfoiliation. There is a Moisture Problem with the Material. This is Much Less of a Problem on Mars than it is on Earth.
© 4Frontiers Corporation10 Robert J. Milligan Aug MARTIAN GEOLOGIC HISTORY Early Mars had an Atmosphere and Oceans It Also had Volcanic Activity Sulfur Dioxide (SO 2 ) and Basaltic Lava The SO 2 Entered the Early Oceans to Form (in Combination with Oxygen from the Atmosphere) Sulfuric Acid. The Basalt Formed the Major Part of the Beds of these Oceans and was Adding to these Beds During Periods of Volcanic Activity.
© 4Frontiers Corporation11 Robert J. Milligan Aug Acid Rain SO 2 Basalt Flow Steam Martian Ocean CO 2 H 2 O, O 2 Dilute Aqueous H 2 SO 4 EARLY MARS
© 4Frontiers Corporation12 Robert J. Milligan Aug THE CIRCUMSTANTIAL EVIDENCE The Presence of Sulfates Kieserite, MgSO 4 H 2 O, Gypsum, CaSO 4 2H 2 O, Jarosite, KFe 3 (SO 4 ) 2 (OH) 6. The Type of Silica that Spirit Found. Indicated Production at Low Temperature The Lack of Structured Deposits of Carbonates. Oceans were Never Basic Enough to Dissolve Carbon Dioxide
© 4Frontiers Corporation13 Robert J. Milligan Aug CHEMICAL EVIDENCE Dilute Hydrochloric Acid (HCl) Dissolves Olivine and Calcium-Rich Plagioclases Such as Anorthite. The Sodium-Rich Plagioclases Appear to be Unaffected. Hot HCl attacks Iron-Rich Pyroxene. Magnesium Rich Pyroxene Appears to Remain Unaffected. Basalt is Composed of These Three Minerals.
© 4Frontiers Corporation14 Robert J. Milligan Aug RESOLVING THE CHLORIDE- SULFATE DIFFERENCE Sulfate Ions are Larger than Chloride Ions May React Slower with Ions in a Crystal Structure if at All The Martian Oceans Most Likely had Chloride Ions in Solution as Well. The Chloride Ions Could Extract the Metal From the Crystalline Structure, be Replaced by Sulfate and Extract Again (A Catalyst). The Oceans had At Least 10E8 Martian Years to React with the Basalt in the Beds
© 4Frontiers Corporation15 Robert J. Milligan Aug FURTHER MARTIAN GEOLOGIC HISTORY Gradually Volcanism Ceased and the Planet Cooled. Mars Lost its Atmosphere Because of the Lower Mass of the Planet and the Lack of a Magnetic Field. The Sulfate Ions were Eventually Used up and the Ph of the Martian Oceans Increased. As the Oceans Were Not Being Replenished with Water, They Began to Evaporate.
© 4Frontiers Corporation16 Robert J. Milligan Aug THE DEPOSITS Silica is Insoluble and Would have Deposited on the Bed. Gypsum is Soluble in Acid. Depending on the Ph of the Ocean when Evaporated, the Gypsum Could be Found Either Deposited on the Bed (high Ph) or with Kieserite on the Surface (low Ph). Iron and Aluminum Sulfates May be Found Together. Of the Metals Found in Basalt, Aluminum is the Only One So-Far not Identified With a Sulfate. These Deposits or Similar Ores Should be Below the Exposed Kieserite Layer. The Colonists Would Use Hematite and Alumina from the Alkaline Bayer Process for Portland Cement
© 4Frontiers Corporation17 Robert J. Milligan Aug BENEFACTION AND CALCINATION The Gypsum Will Have to be Separated From Whatever Co-Crystallized with It. Solubility Differences It is then Dehydrated and Calcined to the Oxide. This Reductive Calcination will be done Separately as CaO is Needed for Other Operations. Source for Base Ca(OH) 2 for Neutralization of Acid Solution in Gypsum Purification. Base in Alkaline Bayer Extraction of Alumina from Plagioclase
© 4Frontiers Corporation18 Robert J. Milligan Aug SUMMARY In Summary Despite the Fact that All of the Constituents of Portland Cement can be Arrived At, MOS Sorel Cement Appears to be the Material of Choice. Only one Material to Beneficiate. Reductive Pyrolysis can be Carried Out at a Lower Temperature. No Subsequent Grinding Step, the Cement is Formed as a Concentrated Aqueous Solution.
© 4Frontiers Corporation19 Robert J. Milligan Aug CONCRETE FROM PORTLAND CEMENT Portland Cement is Mixed with Sand, Gravel and Water to Form Concrete. The Sand and Gravel is Prewashed to Ensure that no Soluble Species that Could Detract from the Performance of the Concrete is Present in the Mixture. Sand is Primarily Silica on Earth. There is no Silica Sand on Mars. Portland Cement is a Hydraulic Cement Implying that the Cement Adds Water Chemically as it Reacts to Form Concrete. Generally recognized as hydration of calcium oxide
© 4Frontiers Corporation20 Robert J. Milligan Aug CONCRETE MANUFACTURE ON MARS Both Martian Temperature and Pressure Mitigate Against Formation of Concrete From Portland Cement in the Open. Concrete Articles Can Be Built under Near Earthlike Conditions, Cured and then Transported to Where They are Needed. Limits the size and mass of what can be fabricated.
© 4Frontiers Corporation21 Robert J. Milligan Aug CONCRETE MANUFACTURE WITH MOS ON MARS The MOS Concrete Can be Poured on Site Provided the Martian Temperature Initially is Low Enough to Not Allow the Water to Boil. The Freezing Point Depression of the Solution Should be Low Enough to Allow this to Happen. MOS Concretes Can be Used as Grout to Bind Together Pieces of Portland Concrete.
© 4Frontiers Corporation22 Robert J. Milligan Aug REFERENCES
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