ICE CRYSTALS OF WATER MIXED WITH ORGANICS
Combining water vapor and organic vapors produces crystals with a different physical appearance than are produced from any of the vapors individually. Some organic compounds are totally incompatible with water, and their interactions can be quite interesting. In one case, the combined inorganic/organic crystals would alternately form and dissolve. In some cases, no crystals formed.
Bromoform and water
Bromoform is barely soluble in water. A mixture of bromoform (m.p. = 7.5°C) and water (m.p. = 0°C) was allowed to evaporate, condense, and crystallize on a tungsten substrate at -20°C.
Dimethyl carbonate and water
Dimethyl carbonate decomposes in water. Here, DMC (m.p. = 2 - 4°C) and water are seen crystallizing.
Dichloropropanol (C3H6Cl2O), a liquid with an ethereal odor, and water
1,3 -Dichloro-2-propanol is used as a solvent for hard resins and nitrocellulose. Here an evaporating mixture of dcp (m.p. = -4°C) and water condense and crystallize.
AMMONIA ICE CRYSTALS
Finally, here is a look at the crystallization of an interesting gas. Ammonia is a gas until it reaches a temperature of approximately -33.4°C or is placed under 6 atmospheres pressure at 10°C. It begins to crystallize at -77.7°C at atmospheric pressure. The ammonia found in the household kitchen is a mild solution of the gas in water (ammonium hydroxide). A more concentrated solution also finds multiple uses in the laboratory as a source of ammonia in chemical reactions and was used here to produce ammonia ice. But first, an out-of-this-world view of ammonia ice.
Titan is Saturn's largest moon and is the second largest moon in our solar system, exceeded only by Jupiter's Ganymede. With a diameter of 5150 km, icy Titan is about 6% larger than the planet Mercury. Its thick atmosphere of nitrogen, argon, methane, ethane, hydrogen cyanide, carbon dioxide, water, and many other trace organics blankets Titan, making it appear larger than it is.
In Titan's distant past, ammonia was much more available; however, perhaps as a result of decomposition by incoming radiation, the ammonia broke down into nitrogen, which remains, and hydrogen, which escaped into space. At the low surface temperature of -179°C, any ammonia still remaining at the surface is probably trapped in ethane ice, water ice, and in pools of liquid ethane and methane (as seen here). Snow falling from a smoggy, orange sky probably consists of ethane, liquid methane, and multiple other organics (including trace amounts of ammonia ejected from below the surface of Titan). In Titan's earlier days, mixed or, perhaps, nearly pure ammonia snowfalls might have been very common. If so, a brisk walk along the banks of an ethane lake could have offered views as shown.
Lying somewhere between "Titan in a bottle" and the world's most elaborate snow globe, my ammonia ice experiment is shown here in action. At the extreme left is a flask partially filled with a 30% solution of ammonium hydroxide. The flask is placed within a heating mantle connected to a powerstat to allow gentle warming to drive out the ammonia. The flask is equipped with a two-hole stopper with two glass tubes. One tube has a red balloon (color not overly critical) that acts both as a safety relief and a squeeze bulb. The other tube is connected to a U-tube immersed in a freezing mixture of water ice and salt. This step removes much of the moisture that passes over from the ammonium hydroxide. Next, a tube filled with calcium oxide completes the drying of the ammonia gas. This tube connects directly with the lucite microscope chamber centered in a large, lucite disc to cover and lightly seal the liquid nitrogen dewar. A styrofoam block with white-light LEDs inserted surrounds, illuminates, and insulates the top of the chamber. The lower part of the chamber (below the disc) sits snugly on a solid aluminum cylinder resting in the liquid nitrogen. All this is being viewed with my trusty Meiji stereo microscope and a CCD camera. The focusing monitor is just visible at the extreme right in the photograph.
The rubber tube seen on the right connects to a tube filled with activated charcoal to adsorb excess ammonia. On one occasion, that tube got quite hot in operation! And, yes, solid or liquid ammonia is hazardous to the skin, causing burning and blistering which, apparently, heals very slowly, to hear my wife tell it. It is even more hazardous to breathe as lung edema is possible.
This video begins with a flurry of ammonia snow. Then, crystals of solid ammonia are seen growing and billowing on a substrate of silicon fragments used to simulate Titan's surface. Following this, a tungsten wire with rapidly growing mixed crystals of ammonia is shown. Even with the drying procedure, small amounts of moisture will get in and produce mixed ice crystals of ammonium hydrates, ammonia, and water ice. However, that is acceptable since there most probably is water ice on Titan. Finally, crystals of ammonia growing on the wall of a copper tube are seen being blanketed by an ammonia snowfall. That final view was photographed in real time, whereas the other views in this video were recorded in time lapse.
Mixed crystals of ammonia with ethane and, possibly, methane and other organic compounds may be very common on the surface of Titan and other moons beyond the planet Mars. Some even speculate the existence of asteroids made of solid ammonia. This type of crystal formation should also be expected to occur in the atmospheres of the outer planets (e.g., Jupiter, Saturn and its rings, etc.) as well. The glittering crystals would alternately upwell and then cascade downwards, producing an unimaginably beautiful sight in the lower realms of the churning planetary atmospheres, landing on any exposed surfaces, if such there be.
WHAT NEXT?
After experimenting with multiple combinations of liquids and gases, there are many other possible directions to go in pursuing the subject of crystal formation by vapor phase condensation. Employing polarized light to study crystal growth is one useful direction. Developing three-dimensional video/film techniques for recording growth would be a real plus. All of my work displayed above involved studying materials initially at room temperature and crystallizing below room temperature.
A well-trodden path complementary to the above is to study crystals formed from materials initially at above-ambient temperatures and allowed to cool slowly while being observed. Exposing naphthalene to an elevated temperature and allowing the vapor to sublime while examining the crystals forming under the microscope is an example. Experiments along these lines would require the construction of a temperature-controlled hot stage. My design for the construction of a very inexpensive hot stage suitable for microscopy is described in one of the references.
Now for the explanation of the Titan video: I created the image of Titan using several computer graphics software programs listed in the "Credits" section of the "References" page. However, the snowfall was generated in the ammonia ice apparatus described above. I recorded a particularly good ammonia snow flurry occurring in the setup and overlayed the sequence on the computer image of Titan.
