Phase change deposition

Movement across a boundary line corresponds to a phase change. The arrows on the figure show six different phase changes sublimation and its reverse, deposition melting and its reverse, freezing and vaporization and its reverse, condensation. 

One interesting question posed by previous researchers (14,19) is why there was asphaltic bitumen deposited at the bottom of the well considering that no phase change or any substantial temperature or pressure changes had taken place. The conclusion was that the question... 

Milliron, D. I Raoux, S. Shelby, R. M. Jordan-Sweet, J. 2007. Solution-phase deposition and nanopatterning of GeSbSe phase-change materials. Nature Mater. 6 352-356. 

Although the concept of phase is well defined thermodynamically, here phase refers to a mechanically separable homogeneous part of an otherwise heterogeneous system. The concept of phase change refers here to a change in the number present or in the nature of a phase or phases as a result of an imposed condition such as temperature or pressure. To clarify and illustrate the topic at hand, we use the specific cases of electrolessly deposited nickel and electrodeposited cobalt. 

A combination of thiosulphate and dimethylthiourea was used in Ref. 48. Using only thiosulphate resulted in slower deposition and, more importantly, poorly adherent films. The resistivity of the as-deposited CuS dropped to 3 X 10 " fl-cm on annealing at 200°C (in N2) without a change in phase or composition. Annealing at 300 and 400°C resulted in loss of S and phase changes. The crystal size was 11 nm (200°C anneal), 19 nm (300°C), and 20 nm (400°C). Presumably no clear XRD pattern was obtained for the as-deposited film of CuS. 

Copper acetate was used in Ref. 38 it was noted that if chloride was used instead of acetate, no deposition occurred, and this was attributed to adsorption of chloride on the substrate (Pt). The berzelianite phase with a small amount of umangite impurity was obtained. The composition and phase of the film could be altered by electrochemical cathodic polarization (in an aqueous K2SO4 solution). Initially, there occurred an increase in lattice parameters and decrease in x (Cu2-A Se). With continued polarization, a phase change occurred until eventually only orthorhombic Cui xSe was present in the film. The umangite phase also disappeared, and it was believed that this impurity phase catalyzed the phase transformation. The change in composition during cathodic polarization was attributed to reduction of zerovalent Se to Se, which was dissolved in the solution. Based on the study of Fohner and JeUinek [41] discussed earlier, this explanation can be interpreted as reduction of Sei ( monovalent Se) to Se (divalent Se). 

At the right combination of pressure and temperature, matter can move directly from a solid to a gas, or vapor. This type of phase change is called sublimation, and it s the kind of phase change responsible for the white mist that emanates from dry ice, the common name for solid carbon dioxide. Movement in the opposite direction, from gas directly into solid phase, is called deposition. 

Another example of phase change is the one exhibited by electrodeposited cobalt. In this case the transformation is from (fee)- to (hcp)-type lattice structure as a result of hydrogen inclusion during deposition on one hand and subsequent out-diffusion on the other hand. 

Like sublimation, deposition plays a lesser role in the water cycle than some other phase changes, but it is no less important to the overall process. Deposition moves gaseous water in the air into the planets water cycle. 

State-of-matter changes, or phase changes, usually depend on the surrounding temperature and pressure. Evaporation, condensation, sublimation, and deposition are examples of common phase changes that often happen naturally on Earth. Chemists can also produce phase changes by manipulating temperatures and pressures in controlled environments. 

Deposition is the opposite of sublimation. It occurs when a gas changes into a solid. In both of these phase changes, the liquid state of matter is skipped altogether. Instead of a solid melting into a liquid and then becoming a gas, as is more common, the solid skips directly to the gaseous state and vice versa. 

The sublimation and deposition phase changes occur when the effects of temperature are combined with pressure. Because gas molecules have a lot of energy, they constantly travel quickly in straight lines until they hit something. When the gas molecules hit the sides of the container in which they are held in, they exert pressure on the container s sides. 

Sublimation and deposition of most molecules does not usually occur on Earth. Scientists can make these phase changes occur in laboratories under controlled conditions, but they are rarely useful or practical. 

Most people have likely never heard of the PVD process, but surely use PVD products. The general concept of putting a protective coating on a surface is not entirely unknown. Paint contains chemicals that deposit a protective layer on the surface of objects. Electroplating uses electricity to deposit a layer of metal on the surface of tableware, jewelry, and coins. The PVD process uses phase changes to deposit layers on the surface of objects. 

Physical vapor deposition is also used to add a clear coat to aluminum balloons and snack bags. The deposition of a specific film made from polyester on the outside of shiny, aluminum balloons gives the balloon added strength while the film remains transparent. The deposition of a similar polyester film on snack bags provides a solid barrier to gases and smells. This industrial phase change is not particularly glamorous or well-known, but it is used in many applications that consumers use in everyday products. 

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