Aqueous Washing

The principle of this method of conservation is to immerse the artefact in a tank containing a suitable solution. The chloride ion dissolves from the rust him into the solution that is changed, initially, every week and subsequently every month. The chloride content of the solution is analyzed at the end of each changeover. The process is continued until there is no more chloride detected. At this point, the artefact is deemed to be conserved. This can take up to 5 years for marine artefacts with high levels of chlorides buried within deep rust layers. Even after this length of time, one is not absolutely certain that all the deleterious ions have been removed from the rust/metal interface. 

A relatively simple method is to dissolve out the chloride by immersion in distilled or de-mineralised water. Most of the common metals and alloys will continue to corrode in this solution although at a slower rate due to the lower conductivity of these solutions compared to seawater. This can be serious if the artefact is to be immersed for periods up to 5 years, but has been employed if the immersion times are relatively short. A small copper alloy sheave recovered from the Mary Rose was soaked in running demineralised water for 27 days and the chloride levels dropped from 106 to 10 ppm over this period. 

By using boiled water, the dissolved oxygen is expelled and hence, there should be no corrosion as the cathode reactant has been eliminated from the electrolyte. Unless the boiled water is kept in sealed containers, air (oxygen) will slowly dissolve into the water and corrosion of the metal or alloy will re-commence. As an alternative, using hot demineralised or distilled water will reduce the concentration of dissolved oxygen and hence corrosion, but this must be counter-balanced by the rise in reaction rates with temperature. In open conservation tanks, a temperature of 70°C is required to notice a significant reduction in rates of corrosion of metals. Small copper alloy artefacts from the Mary Rose were treated in this way using water at 80°C for 30 days. At the end of this period, the chloride levels in the water dropped to below 1 ppm. 

Some conservators have alternated between tanks of boiled and cold water for their artefacts. They claimed that the expansion and contraction of the artefact, will assist in the removal of the deeply-buried chlorides from the rust layers. One must be careful that this does not cause the rust to spall off the underlying metal due to the difference in expansion coefficients between the two classes of materials. 

By altering the pH of the solution, it may be possible to dissolve out the chlorides without corroding the metal. This is achieved by the formation of a thin, passive film, approximately 10 nm thick on the exposed uncorroded metal. The pH required to passivate any given metal or alloy can be determined by inspection of the relevant E-pH diagram. For wrought iron, a passive film will form above a pH value of 9.5. This would be a disaster for aluminium artefacts 

---

Method 2. Place 0-2 g. of cupric acetate, 10 g. of ammonium nitrate, 21 2 g. of benzoin and 70 ml. of an 80 per cent, by volume acetic acid -water solution in a 250 ml. flask fitted with a reflux condenser. Heat the mixture with occasional shaking (1). When solution occurs, a vigorous evolution of nitrogen is observed. Reflux for 90 minutes, cool the solution, seed the solution with a crystal of benzil (2), and allow to stand for 1 hour. Filter at the pump and keep the mother liquor (3) wash well with water and dry (preferably in an oven at 60°). The resulting benzil has m.p. 94-95° and the m.p. is unaffected by recrystallisation from alcohol or from carbon tetrachloride (2 ml. per gram). Dilution of the mother liquor with the aqueous washings gives a further 1 Og. of benzil (4). 

Combustible masking materials such as organic char may be partially or completely removed by periodic elevations of the catalyst bed temperature. Noncombustible masking materials may be removed by air lancing or aqueous washing generally with a leaching solution (20,21). 

The following day the acid liquid is filtered with suction through a large Buchner funnel, to remove large quantities of humus which are produced. The humus on the filter is washed with two 350-cc. portions of water and finally with two 300-cc. portions of benzene. The filtered liquid and aqueous washings have a volume of approximately 10 1. The s-methylfurfural is... 

In a 2-1. flask fitted with a total-reflux, variable-take-off distillation head is placed a solution of 53 g. (0.472 mole) of dihydroresorcinol (Note 1), 2.3 g. of -toluenesulfonic acid monohydrate and 250 ml. of absolute ethanol in 900 ml. of benzene. The mixture is heated to boiling and the azeotrope composed of benzene, alcohol, and water is removed at the rate of 100 ml. per hour. When the temperature of the distilling vapor reaches 78° (Note 2), the distillation is stopped and the residual solution is washed with four 100-ml. portions of 10% aqueous sodium hydroxide which have been saturated with sodium chloride. The resulting organic solution is washed with successive 50-ml. portions of water until the aqueous washings are neutral and then concentrated under reduced pressure. The residual liquid is distilled under reduced pressure. The yield of 3-ethoxy-2-cyclohexenone (Note 3), b.p. 66-68.5°/0.4 mm. or 115-121°/11 mm., Mq 1.5015, is 46.6-49.9 g. (70-75%). 

The combined aqueous washes are acidified with dilute hydrochloric acid and extracted with ethyl acetate. Evaporation of this extract yields 86 mg of 3a-hydroxy-ll-oxo-5j -etianic acid, mp 291-293° (dec.). 

The reaction takes place at low temperature (40-60 °C), without any solvent, in two (or more, up to four) well-mixed reactors in series. The pressure is sufficient to maintain the reactants in the liquid phase (no gas phase). Mixing and heat removal are ensured by an external circulation loop. The two components of the catalytic system are injected separately into this reaction loop with precise flow control. The residence time could be between 5 and 10 hours. At the output of the reaction section, the effluent containing the catalyst is chemically neutralized and the catalyst residue is separated from the products by aqueous washing. The catalyst components are not recycled. Unconverted olefin and inert hydrocarbons are separated from the octenes by distillation columns. The catalytic system is sensitive to impurities that can coordinate strongly to the nickel metal center or can react with the alkylaluminium derivative (polyunsaturated hydrocarbons and polar compounds such as water). 

The ionic liquid process has a number of advantages over traditional cationic polymerization processes such as the Cosden process, which employs a liquid-phase aluminium(III) chloride catalyst to polymerize butene feedstocks [30]. The separation and removal of the product from the ionic liquid phase as the reaction proceeds allows the polymer to be obtained simply and in a highly pure state. Indeed, the polymer contains so little of the ionic liquid that an aqueous wash step can be dispensed with. This separation also means that further reaction (e.g., isomerization) of the polymer s unsaturated ot-terminus is minimized. In addition to the ease of isolation of the desired product, the ionic liquid is not destroyed by any aqueous washing procedure and so can be reused in subsequent polymerization reactions, resulting in a reduction of operating costs. The ionic liquid technology does not require massive capital investment and is reported to be easily retrofitted to existing Cosden process plants. 

Chemical and physical properties of the contaminant should also be investigated. Solubility in water (or other washing fluids) is one of the most important physical characteristics. Hydrophobic contaminants can be difficult to separate from the soil particles and into the aqueous washing fluid. Reactivity with wash fluids may, in some cases, be another important characteristic to consider. Other contaminant characteristics such as volatility and density may be important for the design of remedy screening studies and related residuals treatment systems. Speciation is important in metal-contaminated sites. 

---