Fig. 3.63  Viscosity measurement experimental setup

Exothermic Reaction

Certain products, in contact with water, react and release corrosive products. This reaction develops more or less violently according to the involved chemical agent. This rise of temperature may aggravate the burn. Some examples:

•The powerful reducing agents such as sodium and lithium

•The anhydrous form of the acids such as the icy acetic acid or the sulfuric acid when concentrated beyond 96%

•Alkylaluminums

Fig. 3.64  Titanium tetrachloride

•Titanium salts (TiCl4) (Fig. 3.64)

•Chlorosilanes (trichloromethylsilane)

•Bore (BF3)

Titanium Tetrachloride

When in contact with water or any other aqueous solution, TiCl4 releases some hydrochloric acid (Fig. 3.64).

An in vitro manipulation helps to objectify the variations of pH and of temperature when we add to 1 mL of tetrachloride of titanium, an increasing volume of water then, in comparison, an increasing volume of Diphoterine®.

The reaction instantaneously generates a release of energy and an increase of temperature. Very quickly, when adding 5 mL of water or Diphoterine®, this exothermic effect decreases, because of dilution, and the temperature returns to 20°C.

On this purely physical aspect water and Diphoterine® have the same effect. However, there is a big difference on the chemical side. From this point of view, Diphoterine®, with a very low volume added, restores the pH toward the acceptable physiologic zone very quickly, while water maintains a very corrosive pH (Fig. 3.65).

Fig. 3.66  Titanium tetrachloride experimental washing (zoom on first 5 mL)

Fig. 3.67  Titanium tetrachloride experimental washing (zoom on first 300 mL)

−3

−5

0

−1

−3

−5 0

Beginning of the experiment: first five milliliters

Volume (mL)

Moreover, the speed of washing is a factor that is not as decisive for thermal burns as it is for chemical burns.

For the latter, on the other hand, the fundamental element of aggressiveness is the persistence of pH values out of the physiological zone.

Let us look closer at the very beginning of the manipulation, for more precision on the look of curves by zoom effect on the first 5 mL (Fig. 3.66).

In the same way, let us look at the first 300 mL (Fig. 3.67).

Trichloromethylsilane

Like titanium tetrachloride, when in contact with water or any other aqueous solution, trichloromethylsilane releases some hydrochloric acid (Fig. 3.68).

Cl

Cl

Fig. 3.68  Trichloromethylsilane

The same release of energy occurs with trichloromethylsilane than with titanium tetrachloride. We observed the same conclusions than in the previous paragraph using water compared Diphoterine® (Fig. 3.69).

Boron Trifluoride

In contact with water, BF3 forms some boron hydroxide (B(OH)3) and releases some hydrofluoric acid (Fig. 3.70).

Fig. 3.69  Trichloromethyl­ silane experimental washing

pH

7

6

5

4

3

2

1

0

−1

−2

−3

0

Evolution of the pH of 1 mL of 98% trichloromethylsilane with an increased volume of water versus Diphoterine®

Diphoterine

water

Physiologically accepted pH

Volume (mL)

BF3 + 3H2O B(OH)3 + 3HF

Fig. 3.70  Boron trifluoride

In the following experiment of dosage, we can observe that water has only an effect of passive dilution with a pH and a pF, which remain low in spite of the increasing addition of a big quantity of water (Fig. 3.71).

On the contrary, the increasing addition of Hexafluorine® very quickly restores both the pH and the pF toward the physiologically acceptable level.

Other types of chemicals, as concentrated corrosives and particularly the acids, may react with water by a release of heat.

The heating produced during the contact of a concentrated corrosive and water can be experimentally observed in a beaker. The effect can be observed in statics or in dynamics during a simulation of wash.

Sulfuric Acid

With the example of very concentrated sulfuric acid (H2SO4) in contact with water, the solvation releases a very big heating of more than 90°C (Fig. 3.72).

Fig. 3.71  Boron trifluoride experimental washing

Evolution of the pH and the pF of a mixture of BF3 in acetic acid with an increased volume of water or Hexafluorine®

Volume (ml)

Fig. 3.72  Sulfuric acid experimental washing

Evolution of the temperature

during the dosage of 1 ml 95% sulfuric acid by Tap water

Time (s)

If during a static dilution, the temperature is very high, it is no more the same there during a dynamic wash.

In dynamics (Fig. 3.73), the external wash enables the measurement of the effect of mechanical draining of the wash associated with the effect diminution of the temperature, which is exponential, and thus very fast (Fig. 3.74).

We then observe that, thanks to the wash, temperature reaches no more than 50 degrees over a few seconds. Usually considered as “icy,” this very concentrated, even totally anhydride, acid reacts with water via the formation of hydrogen bonds, which cause an exothermic reaction, a sign of a molecular excitement and a variation of entropy (Fig. 3.74).

This heating is not as big with soda (Fig. 3.75): When in contact with some skin or an eye, the very

concentrated corrosives, dissolve the water of tissues. Before they really lead to a chemical burn, or simultaneously, these very concentrated corrosives can cause a burn by dehydration and/or by thermal effect.

Once more, this justifies the necessity of beginning the wash as soon as possible.