This document is intended to analyse the various problems related to the use of solvents known as chlorine derivatives and to sensitise users to their correct use with the aim of preventing corrosion in the final products.

This section will focus on the characteristics of chlorinated solvents normally used to degrease metals and on the problems that might accidentally follow the inappropriate use of the product.

The second section will concentrate on possible problems arising from the use of uncontrolled solvents.

A thorough analysis of the issue was made necessary by various defective cases registered all over the world in the last two years. Refills manufactured and sold were then rejected by final customers because they just stopped writing. Cases of that kind had never occurred before, nor was the origin of the defect known.

The choice of too volatile solvents like Methylene chloride should be avoided for two main reasons:

1) In certain atmospheric situations, steam contained in the air may condense on the metal surfaces cooled by the quick solvent evaporation and consequently increase water concentration;

2) An excessive solvent evaporation leads to a sudden increase in the water-solvent ratio.

In both cases an azeotropic mixture may be the result.

Solvent drums must not be kept for long in humid places to avoid a possible corrosion of containers and the subsequent solvent contamination.

As far as the storage in tanks is concerned, excellent results are obtained with stainless steel tanks with lined internal walls, so as to avoid any possible corrosion due to moisture.

Before using a container to store chlorinated solvents, one must make sure it is clean, dry and free from rust or metal chips, or from any oil traces that might trigger deterioration processes.

Here are important instructions to be followed in the distillation of chlorinated solvents:

a) Separate the water layer that might possibly cover the solvent before carrying out distillation.

b) Remove possible chips and powders from the solvent before distillation.

c) Collect the contaminated solvent into clean stainless steel or plastic containers, since the presence of rust may catalyse the impoverishment of stabilising agents.

d) Use a system of stabilisers with a boiling point as close as possible to the solvent boiling point so that both go together during distillation.

Inhibitors present in chlorinated solvents play an essential role in reducing the risk of metal oxidation.

An incomplete distillation or insufficient equipment cleaning frequency may lead to an excessive loss of inhibitors during solvents utilisation or distillation.

A regular re-stabilisation of chlorinated solvents is very important to avoid corrosion and oxidation.

For this reason every user must carry out a check at regular intervals to assess the amount of stabiliser necessary to protect chlorinated solvents from acidification.

The purchase of regenerated chlorinated solvents in the market may help you save money but may also cause inconveniences to the user if he is not informed well enough. Indeed it should be remembered that even a chlorinated solvent only partially degraded after distillation may become acid and therefore corrosive, with serious damage both to the equipment and, more frequently, to metal parts.

The best way to avert these risks is refraining from buying regenerated solvents from unknown sources or reckless suppliers.

Even a "home made" regenerating must be carried out with high-quality solvents; it is a simple operation, but it requires some attention and skills.

Remember that washing baths should never contain brass chips or powder (if present they must be promptly removed) since they catalyse the decomposition process.

Regular checks are recommended by all solvent manufacturers to maintain the cleaning system in optimal conditions and to ensure effective degreasing operations.

Some of these checks are very simple and do not require special equipment or chemical know-how; they can be carried out by the operators themselves.

Here are the most well-known control methods:

1. Acid acceptability test
2. Scratch test
3. Aqueous extract pH test

The scratch test is generally used to assess the stability of solvent with aluminium and therefore it does not fall into our scope of analysis; the acid acceptability test is normally used to assess the amount of stabiliser present necessary to protect the solvent from acidification.

The simplest method known is the aqueous extract pH test; the necessary material can easily be found.

To carry out this test put 50 ml of chlorinated solvent in a clean container previously rinsed in distilled water, add the same volume of distilled water previously brought to pH 7 with a normal-hundred HCl solution, and shake for about two minutes.

Leave to separate and finally dip electrodes of the pH-meter into the water and measure.

The pH should be as close as possible to 7. Lower values indicate that the acidification process has already started and that the solvent must therefore be regenerated.

All manufacturers can rely on laboratories with qualified experts at the customers' disposal for technical tests or consultancies; users may even be supplied a "test kit" for a quick and easy assessment of solvent stability.

In November 1992 in Copenhagen, during the fourth Meeting of the European Community, the application rules of the Montreal protocol were modified. The protocol laid down the rules to be followed in production control and use of Chlorofluorocarbons, Hydrochlorofluorocarbons, Carbon Tetrachloride and Trichloroethane.

Trichloroethane had already been included in the group of products regulated by the 2° Review Meeting held in London in June 1990.

Here are Trichloroethane control measures according to the latest application rules:

Production freeze: January 1, 1992 at 1989 levels

50% reduction: January 1, 1994 at 1989 levels

Total elimination: January 1, 1996.

The only derogation still in force apply to Underdeveloped Countries to meet the needs of their domestic markets.

It should be noted that the Montreal protocol provides for general rules only, therefore some countries might decide to set more restrictive rules to accelerate the reduction and elimination of Trichloroethane.