THERMOCHEMICAL DESTRUCTION OF INFORMATION MEDIA.

THERMOCHEMICAL DESTRUCTION OF INFORMATION MEDIA.

Boborykin Sergey Nikolaevich,
Ryzhikov Sergey Sergeevich, Candidate of Technical Sciences

THERMOCHEMICAL DESTRUCTION OF INFORMATION MEDIA

The use of high temperatures to destroy information carriers has been known since ancient times. At the dawn of world history, the collections of the Library of Alexandria were burned, causing irreparable and irreparable damage to humanity. Over the centuries, the methods of destroying information on paper carriers have remained virtually unchanged — paper continued to be burned and is still being burned.

At present, confidential information carriers (film and photographic films, magnetic tapes, disks, magneto-optics, permanent memory devices on microcircuits, etc.) subject to periodic destruction have become unusually diverse, compact and sufficiently resistant to physical impacts. Specialists are constantly searching for new methods of destruction. Installations are being created that generate powerful magnetic and electric fields [1, 2], chemical compounds are being developed that decompose the carrier of secrets into their original components at the appropriate moment.

The proposed article examines methods associated with heating the carrier of confidential information to a temperature at which the information on it disappears completely and forever.

Advantages of thermochemical methods of destroying information carriers

By the beginning of the 21st century, a wide variety of carriers had emerged, to which various departments entrusted their secrets. The history of secret services was enriched with examples of how much one had to pay for the low quality of emergency destruction means. There are quite a few examples, of which one can single out the story of the US Embassy in Iran during the anti-Shah uprising, the fate of the archives of the GDR security service during the collapse of the Berlin Wall, and the detention of an American reconnaissance aircraft by China. In all of the above cases, there was an urgent need to destroy secret carriers of all types — paper, magnetic and hardware. And in all three cases (according to the press), efficiency in destruction was precisely what was lacking.

At the same time, there is a fairly universal and effective method, the use of which allows minimizing the damage from a sudden invasion by seekers of other people's secrets. The chemical reactions that underlie it were discovered in the middle of the 19th century by the outstanding Russian scientist N.N. Beketov. Later they were called metallothermy. On their basis, thermite incendiary mixtures were created, which were widely used in the wars of the 20th century. A powerful impetus to the development of this area of ​​chemical science was given by the research of Soviet scientists A.G. Merzhanov, I.P. Borovinsky and V.M. Shkirko, who discovered the phenomenon of self-propagating high-temperature synthesis (SHS) in 1967. Their research allowed them to create a theory of SHS processes and ensure their practical implementation.

Let's consider the advantages of SHS processes in the destruction of information carriers:

• SHS compositions allow for local heating of the carrier to a temperature of 3000 K and higher without the use of special furnaces.
• SHS compositions are self-sufficient, i.e. after initiation, the heat generation process under certain conditions is self-sustaining until the chemical transformation of the components is complete.
• There is a whole class of SHS compositions that, during the heating process, practically do not emit gases and liquid combustion products (a briquette made from such a composition heats up to a temperature of several thousand degrees in a short time, while maintaining its shape and not emitting visible flames).
• Most SHS compositions do not have the connection between mass and properties that is inherent in most explosives. The reaction in a kilogram briquette of SHS composition develops in exactly the same way as in a briquette weighing several grams.
• The combustion of most SHS compositions does not turn into detonation under any conditions.
• SHS compositions, as a rule, have significant chemical stability, which allows them to be built into equipment for the entire service life without periodic replacement.
• The ignition temperature of a significant part of SHS compositions is in the range from 600 to 1200? C, which excludes spontaneous ignition when they are installed on working elements of electronic equipment.
• To start the combustion process of the SHS composition, a very small number of initiation means is sufficient, which allows creating an ignition system on an autonomous power supply, ensuring its energy independence from external sources.
• Using SHS destruction means, it is possible, if necessary, to ensure high targeting of destruction (to a specific microcircuit or group of microcircuits), while preserving the remaining elements and blocks.
• A briquette of SHS composition can be given any shape by pressing or filling with compound, which is especially important when camouflaging means of destroying information carriers.
• Due to the high temperature of the SHS process and the high speed of propagation of the combustion wave (0.5 — 15 cm/sec) [3], existing fire extinguishing means are not capable of interrupting the SHS process.
• Most of the chemical reagents used in SHS processes are quite cheap and accessible, which simplifies their use in special equipment.

Classification and properties of SHS compositions

Depending on the chemical nature of the combustion reaction and the aggregate state of the reagents, four main classes of SHS systems can be distinguished [3]:

• gas-free systems;
• filtration systems;
• gas-emitting systems;
• metal-thermal systems.

The most interesting for use as means of destroying information carriers are the first and fourth class SHS systems.

Gas-free systems

The peculiarity of this class of SHS systems is that both the initial reagents and the resulting substance are in the solid phase. Due to this, the transformation process occurs without gas emission (as the name suggests) and without flame. After the SHS process is initiated, a heating front passes through the sample, without significantly changing its shape and geometric dimensions. Gas emission occurs only due to impurities in the reagents and due to combustion products of the destroyed information carrier.

The processes occurring in SHS reactions of this type can be represented as the following relationship:

A + B = C + Q,

where:
A is a metal in a solid state,
B – metal (non-metal) in solid, liquid or gaseous state,
C – synthesis products (carbides, borides, silicates, oxides, etc.),
Q – thermal energy released during the reaction.

Components A, B and C are given in the table. 1. [4]

Table 1.

The heat of formation of the compound, the melting temperature and the calculated combustion temperature of gasless SHS compositions are given in Table. 2. [4]

Table 2.

* Sublimation temperature

Based on tables 1 and 2, the selection of initial reagents can be made in order to achieve a given temperature for the SHS reaction of destruction of a particular information carrier.

For example, to achieve a temperature of over 3000 K and the absence of liquid slag during combustion, it is necessary to mix titanium and graphite (TiC) or titanium and boron (TiB2) powders, press them into a briquette and set them on fire.

However, it should be taken into account that the efficiency of the SHS reaction is significantly affected by the particle size of the powders of the initial mixture, the ratio of reagents, the quality of thermal insulation and the method of initiation of the process. Some of these factors will be considered in this article, the rest are reflected in [3, 6 – 9].

Metal-thermal systems

This class of SHS systems, also proposed for use in the destruction of information carriers, differs from the previous one in that during the SHS process two reactions occur simultaneously – oxidation and reduction. In general, this process can be written as:

A + B = C + D + Q,

where A is the initial metal,
B is the initial oxide,
C is the resulting metal,
D is the resulting oxide,
Q is the heat released during the reaction.

The efficiency of the metallothermic reaction and its energy characteristics depend on the heat of formation of oxides from the initial elements A and B. These characteristics for some oxides that have practical application are given in Table 3. [5]

Table 3.

In practice, everything is, of course, somewhat more complicated. Some oxides (for example, manganese oxide) are reduced in several stages, and the SHS process may not proceed without an external heat source. Other oxides, on the contrary, react with metals too violently. For example, the combustion process of copper-aluminum thermite is more reminiscent of an explosion than combustion as such [6]. A similar picture is observed when using lead oxides Pb3O4 and PbO2 in a mixture with aluminum or magnesium.

The most widely used compositions are those in which Al or Mg powder is used as the initial metal, and Fe2O3 or Fe3O4 as the metal oxide. The fundamental difference between magnesium and aluminum thermite is that the former, unlike the latter, does not produce liquid slag during combustion. In addition to Mg and Al, a number of metals and metalloids can be used as fuel. The characteristics of mixtures based on them using Fe2O3 as the oxide are given in Table. 4. [6]

Table 4.

Characteristics of thermite compositions based on various oxides and aluminum are given in Table 5.

Table 5.

SHS compositions can also consist of more than two initial components. In some cases, this allows achieving the required combustion characteristics using smaller volumes of the SHS mixture. Examples of such reactions are given in [4]

TiO2 + 2Mg +C = TiC + 2MgO (T ad = 3100 K)

3CrO3 + 6Al + 2C = Cr3C3 + 3Al2O3 (T ad = 4800 K)

MoO3 + 2Al + 2Si = MoSi2 + Al2O3 (T ad = 3800 K)

Methods of initiation of SHS processes

To initiate SHS processes, it is necessary to heat the mixture to a high temperature (depending on the composition of the ingredients, from 600? C to 1000 and higher). If it were necessary to heat the entire sample to initiate the process to such a temperature, then the use of SHS processes in special equipment would hardly be possible. However, SHS compositions have the same property as ordinary gunpowder — the property of local initiation of the process. It is enough to heat a small part of the SHS mixture to the starting temperature, and the combustion wave begins to spread across the sample. So-called step schemes can be used to initiate SHS processes. For example, electric igniter — nitrocellulose — barium peroxide (BaO2) — barium peroxide with aluminum powder — SHS composition (Fig. 1).

Fig. 1.

The following compositions can be used [6]:

• manganese oxide MnO2 (68%), aluminum powder (7.5%), magnesium powder (17%);
• barium oxide BaO2 (88%), magnesium Mg (12%);
• barium oxide BaO2 (31%), iron oxide Fe3O4 (29%), aluminum powder (40%).

The proposed compositions can be initiated using nichrome wire. However, in the case of a large mass of the working SHS composition, it is advisable to introduce an additional transition composition between the igniting composition and the working one, consisting of 40-60% of the igniting composition and 60-40% of the working SHS composition.

Control sensors for sending a signal to destroy information carriers can be very diverse — from a simple button to a complex set of sensors and radio command devices.

Variants of practical implementation of SHS means of destroying information carriers

Given the limited volume of the journal article, only a few typical options for using SHS compounds to destroy currently common confidential information carriers will be considered below.

Paper media.The most traditional type of confidential information carriers usually exists in two states: either stored in safes or transported by couriers. In both cases, the main task in the event of danger is to quickly and, most importantly, reliably destroy documents. Obviously, the most convenient in this case will be special folders (containers) made of heat-resistant material, containing a limited number of paper carriers (for example, A4 sheets of paper). The inner walls of such a folder are made double, between them are placed SVS-briquettes connected by a common destruction initiation system. For transportation by a courier, the folder (or folders) is placed, for example, in a briefcase and connected to an autonomous destruction initiation system in the event of a threat of seizure. In stationary conditions, the folder can be stored in a safe and connected to the general initiation system of the institution. In this case, SHS compositions based on magnesium or aluminum thermite are convenient due to their low cost, availability, and high speed of the SHS process (a thermite briquette weighing 1 kilogram burns in 40 seconds [6]).

Hard and flexible magnetic disk drives, flash cards, and other removable magnetic media.The vast majority of SHS processes are suitable for destroying information on these classes of media, since in the case of magnetic media it is sufficient to heat their entire volume above the Curie point (1000 – 1200 K). Such heating leads to irretrievable loss of information [1, 2]. Structurally, destruction devices can be made either in the form of storage (like the above-mentioned folders for paper media), or in the form of units built into a PC.

Memory chips, encoders, coders, fixed frequency generators.Since all these devices are usually mounted on separate boards, the SVS liquidator can be placed in a ceramic cartridge (to prevent fire) directly above the corresponding microcircuit. A cartridge with several tens of grams of the SVS composition will be enough to completely destroy any microcircuit, and the thermal stability and durability of the mixtures do not create additional problems during the operation of the equipment.

Conclusion

The use of SHS processes is naturally not limited to the destruction of confidential information carriers. The properties of SHS reactions are widely used in various fields of science and technology [3]. SHS processes can be widely used in special equipment, since it is essentially a portable, reliable and effective source of thermal energy. Direct conversion of thermal energy into mechanical energy (for example, into the energy of water vapor) allows creating various drives for emergency closing of doors in shelters, emergency dampers, fire curtains, etc. Such actuators do not require external energy sources and, unlike gunpowder ones, do not emit toxic nitrogen oxides. Triple energy conversion (thermal – mechanical – electrical) allows creating powerful and portable electromagnetic pulse generators, pulse transmitters with high radiation energy with a wide range of applications.

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