1 / 9

MC Results - Growth Rate

MC Results - Growth Rate. f y /kT = 0.7 kJ mol -1. f y /kT = 1.0 kJ mol -1. MC Results for Dm /kT = 0.2. 0 impurities. Length=10 units. Length = 20 units. Length = 15 units. MC results - summary.

ophrah
Download Presentation

MC Results - Growth Rate

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. MC Results - Growth Rate fy/kT = 0.7 kJ mol-1 fy/kT = 1.0 kJ mol-1

  2. MC Results for Dm/kT = 0.2 0 impurities Length=10 units Length = 20 units Length = 15 units

  3. MC results - summary • Sudden change in slope at Dm/kT = 0.2 signals transition from step growth to island nucleation • glass ceiling for low dosage (kinetic) inhibitors? • For fx/kT = 0.7 • (Dm/kT)* = 0.1 for defects of length = 10 units • (Dm/kT)* = 0.2 for defects of length = 15 and 20 units • decreasing defect width has little effect on growth rate • increasing fx has little effect on growth rate • increasing fy reduces growth rate significantly

  4. Gas Hydrates (Clathrate Hydrates) • Two components • open tetrahedral water lattice • hydrophobic “guest” molecules • Three main crystal structures; • probably two important for environment & industry • Each built from two water polyhedra • diameter 8–9 Å type II type I

  5. Clathrate Hydrates: Guests • hydrophobic (natural gas) • Acid Gases (H2S, CO2) • cyclic ethers (DMO, TMO, THF) • NOT ionic or strongly polar • Size matches/determines structure

  6. Typical of sub-sea pipelines, continental shoulders, tundra Hydrates: Phase Diagram • Favoured by low temperatures and high pressures

  7. Favourable Unfavourable Crystal Nucleation • Activated process: • Favourable “bulk” energy • Unfavourable interfacial energy • Critical “cluster” size • Classical Nucleation Theory • Fundamentally Stochastic • Long and random induction times (~ days)

  8. Nucleation in Other Aqueous Systems • Matsumoto, Saito & Ohmine, Nature 2002 • MD • Mild subcooling (ca 10 K) • Multiple ms trajectories • Critical nucleus built around on long-lived (1-2 ns) hydrogen bonds

  9. Nature of the nucleus • Non-spherical & not compact for ice (from Matsumo et al, Nature 2002)

More Related