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Innovation Technology in Aerogel Synthesis

#G-906


Elaboration of Controlled Aerogel Synthesis Technologies and Formation of Pilot Plant

Tech Area / Field

  • CHE-SYN/Basic and Synthetic Chemistry/Chemistry
  • CHE-POL/Polymer Chemistry/Chemistry

Status
3 Approved without Funding

Registration date
12.07.2002

Leading Institute
Institute of Cybernetics, Georgia, Tbilisi

Supporting institutes

  • Joint Institute of Nuclear Research, Russia, Moscow reg., Dubna

Collaborators

  • Argonne National Laboratory (ANL), USA, IL, Argonne

Project summary

Analyzing the development of areas of physical and chemical research, a change in the character of such research can be noted. Whereas in the past objects of natural origin (atom, ion, molecule) served as the main subject of research, objects of artificial origin are now placed at the forefront. Clusters, quantum dots, superlattices, endohedral structures, high-temperature superconductors etc. are typical examples. This situation can be characterized as a transition from analysis to the synthesis of natural objects, which should undoubtedly be considered as an indicator of the qualitative development of science and technology. The present project concerns aerogel materials, one of the most significant examples of an artificially designed object. They have an extremely fascinating and unique set of properties and hence find applications in perse fields. Aerogel consists of more than 96% air. The remaining four percent is a wispy matrix of metal oxides, although they are most commonly made out of silica (silica dioxide). Carbon aerogels have recently been synthesized using organic precursors. According to their physical parameters (density, index of reflection, etc.) aerogels occupy an intermediate position between solid and gas. For example, the density of aerogel might be a hundred times less than the density of substances it is synthesized from and, sometimes, heavier than air. Besides being the best thermal, electrical and acoustic insulators known, aerogels find application as filters for seawater desalination, micrometeoroid collectors, and subatomic particle detectors. In future, aerogels could be used in windows, building insulation, automobile catalyst converters, and high-efficiency battery electrodes. Also, Stardust spacecraft will use aerogel to capture particles from comet Wild 2 in 2004. NASA used aerogel for thermal insulation on the Mars Exploration Rover, and it may assist in a proposed fundamental-physics-testing mission and the Mars Scout Program. One of the first developments of aerogels was most strongly promoted by their utility in detectors of Cerenkov radiation. The speed of light in a given medium is determined by the medium's index of refraction, and the index of refraction for aerogels happens to be in a range that can be covered neither by compressed gases nor by liquids. Aerogels have already been incorporated in several Cerenkov detectors worldwide. Indeed, this is currently the widest practical application of the material.

Aerogels have better insulation properties than the polyurethane foam currently used to insulate refrigerators, containers and buildings. The main aim of silica aerogel research is currently to develop and investigate the preindustrial production and application of monolithic or granular aerogel in fireproof glass (such as oven doors), solar collectors, insulating glass and air-conditioning equipment. Of these potential applications, thermal insulation is the most significant. While cooler regions use such heating energy, air conditioning systems are heavily used in countries with a hot climate. The consequence is that large quantities of fossil fuels are used in the household sector, both reducing natural energy resources and producing considerable environmental pollution. This can be improved only by means of alternative energy sources and more effective thermal insulation. The aim is to reduce thermal losses by very good insulation. Besides ecological aspects there is an enormous potential for energy savings. Monolithic sheets or granules of silica aerogel as a spacer between glass panes have good insulating properties and an economic potential for large windows. The optical quality, stiffness, strength, permeability and a decrease in the duration of the drying process need to be further developed. To this end, the main objective of the research project is to develop and produce new precursors, to replace the ones currently used.

Silica aerogel, composed mainly of silicon dioxide, is nonflammable, nontoxic, transparent, environmentally safe and has one of the lightest weights among known solid materials. Most of the properties that aerogels exhibit can be related to the intriguing structure of the delicate gel body. It is very important to explore how this structure can be altered in the course of synthesis, to optimize the performance of aerogels in practical aims.

It was obvious to researchers working on aerogels that they were ideal for use in composite materials. However, this area required considerable fundamental research for aerogel preparation and research of their properties, so it has begun to develop rapidly only lately.

Expensive and time-consuming processes like supercritical drying are required to protect the gel structure against drying stress. Production of transparent, non-fragile samples is difficult. These obstacles have limited the utility of aerogels. Therefore, much research has been devoted to seeking technological solutions, to make stiffer, more transparent, stronger and cheaper aerogels, which is also the objective of given project.

Abundant and valuable information on the properties of aerogel can be extracted from the analysis of oscillations propagating in it. It is well known that sound propagates in aerogels at speeds of 100 to 300 meters per second. This is surprising in a material made of the same components as ordinary glass, which can transmit sound waves at speeds of 5,000 meters per second. So, extensive studies of the acoustic properties of aerogels are of great interest.

Organic aerogels can be converted into pure carbon aerogels while still retaining many properties of the original aerogel, and at the same time becoming electrically conductive. This unique material with a large surface area, controllable pore size, and high purity is responsible for revolutionary developments in supercapacitors and in capacitive deionization. In order to minimize the thermal conductivity and maximize the electric conductivity of aerogels, one has to know how the porosity and the skeletal structure of the aerogels influence these properties. The structure of aerogels is generally dominated by sol-gel polymerization conditions, such as catalyst concentration. In this project the dependence of thermal and electric conductivity on density and catalyst concentration will be analyzed to determine the optimum polymerization conditions to obtain aerogels with high thermal resistance and high electric conductivity. Carbon aerogel can be used to create more efficient electrochemical devices. In particular, given the simplicity of production and relatively undemanding operation of a gas accumulator, inventors and rationalizers should improve these current sources to bring the characteristics and constructions to acceptable practical applications. The known methods of synthesis are very promising, yet neither is preferable for the production of large, stiff, strong, transparent and waterproof aerogel sheets for use as thermal insulation spacers in windows and electrochemical devices.

So, according to the above facts, the ways of attaining the objectives and the expected results are as follows:

1a. To improve the sample transparency a special method of deep purification will be elaborated. Silica organic raw material will be purified of metal action traces with a low-concentrated (0.05-0.5%) aqueous solution of ammonium with subsequent rapid drying to prevent the formation of hydrate shapes. Thus, the purified raw material will be affected by fractional distillation in an atmosphere of inert gas.

1b. Also, we shall be able to optimize the process of synthesis by varying:

a) the degree of hydrolysis at the first stage;


b) the content of the catalyst;
c) the catalyst concentration. This is necessary in aerogel application both as a window thermal insulator and as a radiator of Cerenkov detectors in physical experiments.
2. To increase the strength and to improve elastic characteristics of aerogels, the influence of copolymers - alkicoxilanes will be studied. We will also study the influence of aging in different media upon the strength of gels. Such aerogels with low density are advantageous for utilization in thermal insulation systems and electrochemical devices.
3. In our opinion, shrinkage of samples of insufficient density dried by a traditional method is caused by uncontrolled polycondensation of the surface alcogel hydroxide groups at high temperature. To decrease shrinkage, a method of drying in the presence of trimethylalkoxisilane will also be elaborated. We will decrease linear shrinkage by using trimethylmetoxilane.
4. Ttrimethylsilyl-groups formed on the gel surface in the presence of trimethylmetoxilanes help the finished aerogel to acquire sufficient hydrophoby. The effectiveness of fluorine-substituted trimethyltoxisilanes will be studied.
5. To increase the light output, optimal multicomponent wave-shifting components on the basis of organic luminophores will be selected. Special attention will be paid to the stability of the doped aerogels for light and oxidation by air. If necessary, luminophors of a relevant color will be chosen for ornamentation.
6. With the synthesis of high-density aerogels, the main objective will be to reduce product cost by using cheaper raw materials (polymer ethylsilicate) and by making the process as cheap as possible. High-density materials can be used effectively as catalyst carriers. High-density aerogels can also be used for the synthesis of homogeneous glass where they are preferred to traditional ones due to their low level of shrinkage.
7. With the derived characteristics and through the study of the influence of each parameter we will be able to gain considerable knowledge of the material. For example, the structure and properties of carbon aerogels vary with the synthesis parameters, and through our understanding of the influence of each parameter it is possible to produce a specific material for given applications (including light-transmitting or dull organic aerogels).
8. The theory of propagation of elastic weaves in porous media filled with a superfluid is to be developed and the velocity and attenuation of propagating waves is to be calculated.
9. Light scattering in aerogels may be measured by laser methods. Thermal and electric conductivity will be measured by well-known methods. Besides the improvement of large-scale aerogel, we will produce laboratory specimens of a gas accumulator on the basis of carbon aerogel, to make them suitable for application as a current source.
10. Synthesis will be a continuous and closed process using a liquid/solvent separator, where supercritical solvents are decompressed and returned to a gaseous state. In parallel solvent cleaning and continuous purity control are planned. The compressed solvent will be heated above its critical temperature, making it supercritical. This closed and continuous drying process might decrease the preparation time without consuming a large amount of the solvent and will make a good start for a more effective industrial process.

Implementation of the project is an alternative for scientists engaged in the defense industry and will allow the re-establishment of relations between the scientific centers of Russia and Georgia for co-operation in solid state physics organic and inorganic chemistry. The project fully corresponds to the goals and tasks of the ISTC. The basis for fulfilling the project is an accumulation of methodological, experimental and inpidual potential and the experience of the project participants, working in solid-state physics, organic and inorganic chemistry. The majority of the scientists involved in the project are highly skilled.

Project implementation will support basic and applied research in solid-state physics and chemistry, which have been traditionally carried out at a high level at the Institute of Cybernetics (Tbilisi, Georgia) and the Joint Institute for Nuclear Research (Dubna, Russia). Eleven scientists, earlier involved in weapons activity, will participate in the project. Participation of foreign collaborators is foreseen. It will promote international scientific contacts. Elaboration of the present program requires an improved approach and modern methodology.

Combination of the theoretical approach with empirical analysis and numerical modeling will be used as a technical approach. Scientific seminars and workshops will be held, and reports and scientific articles will be prepared during project fulfillment. Quarterly, annual and final scientific technical reports will also be prepared for the Center.


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