General information about ozone and its properties

Ozone is a highly active, allotropic form of oxygen. Under normal temperatures it is a light blue gas with a characteristic sharp smell (it is felt at ozone concentrations of 0.015 mg/m3 air). In liquid phase ozone is indigo-blue and solid - a dense purple-bluish color. Ozone layer of 1 mm thick is practically light not permeable. Ozone is formed from oxygen, absorbing heat and, conversely, if the decomposition goes into oxygen, providing heat (like burning).

Ozone decay mechanism involving homogeneous and heterogeneous systems is complex and depends on the conditions. Ozone decomposition accelerates into homogeneous systems by gaseous additives (nitrogen oxides, chlorine, etc.), and in heterogeneous systems by metals (mercury, silver, copper, etc.) and by oxides of metals (iron, copper, nickel, lead, etc.). At high concentrations of ozone reaction occurs with explosion. At ozone concentration below 9% no explosive decomposition occurs. Low temperatures contribute to the preservation of ozone. At temperatures around -183°C liquid ozone can be stored for long periods of time without significant decomposition. Rapid heating to boiling point (-119°C) or rapid cooling of ozone may cause an explosion. Therefore, knowledge of the properties of ozone and observance of precautionary measures is very important when working with it.

Basic physical qualities of ozone

Parameter	The value
Molecular weight	47.998
The proportion to the air	1.624
Density at STP	2.1415 g / l
The volume at STP	506 cm3 / g
Melting point	- 192,5 ° C
Boiling point	- 111.9 ° C
Critical temperature	- 12.1 ° C
Critical pressure	54,6 atm
Solubility in water at (°C)
0	1.13 g/l
10	0.875 g/l
20	0.688 g/l
40	0.450 g/l
СО	0.307 g/l
Ozone solubility:
in acetic acid (18.2° c)	2.5 g/l
in trichloroacetic acid 0′S)	1.69 g/l
in acetic acid anhydride (0° c)	2.15 g/l
in propionic acid (17.3° c)	3.6 g/l
in propionic acid anhydride (18.2° c)	2.8 g/l
in carbon tetrachloride (21°C)	2.95 g/l

О₃ molecule is unstable and quickly turns into the O₂ producing heat. At low concentrations and without impurities, ozone decomposes slowly, at large — with explosion. Alcohol, in contact with ozone, ignites instantly. Heat and ozone contact even with negligible amounts of substrate oxidation (organic substances, certain metals or metal oxides) dramatically accelerates its decomposition. Ozone can persist for a long time at −78 °C in presence of stabilizer (small amount of HNO₃), as well as in containers from glass and some plastic or precious metals.

Physical properties of ozone are very characteristic: It is easy exploding gas of blue color. Liter of ozone weighs about 2 grams, and the air - 1.3 grams. Therefore, ozone is heavier than air. Ozone melting temperature is -192.7 ºC. Such "melted" ozone is a dark blue liquid. The ozone "ice" has a dark blue color with a violet shade and with thickness exceeding 1 mm becomes opaque. Boiling point of ozone -112 degrees of Celsius.  The gaseous ozone is diamagnetic, i.e. do not have magnetic properties, and in the liquid state is weak paramagnetic.

 

Ozone is toxic to humans, animals and plants; Maximum allowable concentration in the air of working zone is 0.1 mg/m3; in ambient air - 0.16 mg/m3; Median Lethal Dose, LD50 - 0.046 mg/l; (mice, 2 hours), 3 mg/l (mice, 5 min). Small concentrations of ozone in the air creates a feeling of freshness, the inhalation of air with ozone concentrations of more than 0.02 mg/l causes respiratory irritation, coughing, vomiting, dizziness, and fatigue. In presence of nitrogen oxides, ozone toxicity increases 20 times.

Ozone is explosive in all aggregation states, impurities increases its sensitivity. The lower bound for ozone-air mixture is 9%, with higher ozone concentration mixture explodes under the influence of an external pulse, and detonation velocity increases from 880 m/s at a concentration of 9.2% of ozone to 1730 m/s at 77 mol.%.                             

Biological properties of ozone

Despite of large number of studies, the mechanism is insufficiently disclosed. It is known, that at high ozone concentrations lesion of respiratory tract, lungs and mucous membranes are observed. Prolonged exposure to ozone leads to the development of chronic diseases of the lung and upper respiratory tract. Exposure to low doses of ozone has a prophylactic and therapeutic effects and started used actively in medicine - primarily in dermatology and cosmetology. In addition to the great ability to kill bacteria, ozone has high efficiency in destroying spores, cysts (dense shell from around the single-celled organisms, such as flagellates and rhizopods, with their reproduction, as well as in unfavorable for them conditions) and many other pathogenic microbes.

 

Technological application of ozone

In the past 20 years the field of ozone application was significantly expanded and worldwide developments are underway. Such a rapid development of technology using ozone contributes to its environmental friendliness. Unlike other oxidants, ozone in reaction processes decomposes into molecular and atomic oxygen and limited oxides. All these products generally are not polluting environment and did not lead to the formation of carcinogenic substances, such as the oxidation of chlorine or fluorine.

 

Determination of ozone in different dosage units

1 g / m3 = 1000 mg / m3 = 1,000,000 mg / m3 = 0.0208 mol / m3 = 466.4 ppm

1 mol / m3 = 48 g / m3 = 22387 ppm

1 ppm = 2,144 mg / m3

Volume 1% = 10,000 ppm = 21.44 g / m3 = 0.47 mol / m3

1 ppm = 0.8 mg / m3 or 1 mg / m3 = 1.25 ppm

Secure the ozone concentration of 0.1 mg / m3, or about 0,047 ppm

1 mg / l = 1000 mg / m3 = 1 g / m3 = 466.4 ppm = 466.4 ml / m3

Influence of ozone on the human body

Application of ozone in water treatment systems, proven to be highly effective, but same effective and proven safe air treatment systems has not been created so far. Ozonation is considered as non-chemical way of cleaning and is popular among the population. However, chronic effects of micro-ozone concentrations on the human body are not sufficiently studied.

At very low concentrations of ozone, the air feels pleasant and fresh, and unpleasant odors are felt much weaker. In opposite to widespread opinion about the beneficial effect of this gas, which is attributed in some flyers to rich by ozone forest air, in reality ozone at large dilution is a very toxic and dangerous irritant gas. Even small concentrations of ozone can cause irritating effect on the mucous membranes and cause disorders of the central nervous system, which leads to bronchitis and headaches.

Ozone solubility in water

In accordance with Henry’s law, ozone concentration in water increases with increase of ozone concentration in the air mixture, mixed into the water. In addition, higher temperature is, lower the concentration of ozone is. Ozone solubility in water is higher than oxygen, but lower than chlorine (12 times). If we consider 100% ozone, its concentration in water is 570 mg/l at a temperature of 20⁰C. The concentration of gaseous ozone at the outlet of modern ozone devices reaches 14% by weight.

Ozone concentration in the gas mixture	Ozone solubility in water in mg/l in temperature dependence
	50С	100С	150С	200С
1,5%	11,09	9,75	8,4	6,43
2,0%	14,79	13	11,19	8,57
3,0%	22,18	19,5	16,79	12,86

Increased acidity of water reduces the solubility of ozone:

Acidity pH	5,0	6,0	6,5	8,0	9,0
Ozone mg/l	0,68	0,65	0,63	0,62	0,59

 

Ozone decay time in water

Ozone decay time in water (PH 7):

Water temperature° c	Decay Time
+ 150С	30 min
+ 200С	20 min
+ 250С	15 min
+ 300С	12 min
+ 350С	8 min

 

Ozone decay rate in water increases several times in following cases:

1. In presence of impurities in the water, oxidized by ozone.

2. At increased water turbidity.

3. At UV exposure on water.

 

Ozone decay time in the air

Air temperature °C	Decay time
- 500С	3 month
- 350С	18 days
- 250С	8 days
+ 200С	3 days
+ 1200С	1.5 hours
+ 2500С	1.5 sec

 

Ozone decay is accelerated by several orders in presence of catalyst - activated charcoal or special materials based on copper and manganese oxides. Heating of catalyst at +260⁰C in few minutes removes accumulated ozone from catalyst.

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Note: This table of ozone decay in the air is published in various sources, but decay data, particularly at plus temperatures are questionable. In practical recommendations on ozonation of premises it is stated that ozone decay time equals ozonation time + 20 minutes. That is, if ozonation is conducted during of 1 hour, then entrance into the premises (without additional ventilation) is safely after 1 hour and 20 minutes.