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Procedía Engineering
ELSEVIER
Procedía Engineering 46 (2012) 45 - 53
www.elsevier.com/locate/procedia
1st International Symposium on Innovation and Technology in the Phosphate Industry
[SYMPHOS 2011]
The Development of Phosphate Materials with High added value: a
Researcher Viewpoint.
High value material including phosphates can result from: (i) major efforts to maintain and possible improve the quality of education, (ii) cross disciplinary approach (Chemistry, Physics, Geology, Biology etc.), (iii) implementation of new concepts which are able to push back the technological frontiers. In this context four examples of high value phosphate materials are analyzed in detail in this publication:
• LaPO4 composites used at high temperatures and in oxygenated environment.
• Cement for cold areas,
• Phosphate Materials for inertial confinement fusion,
• Photonic component for permanent storage of information.
In all the previous examples the creation of new materials results from an overlapping between the basic functions of the phosphate groups and the new concepts related to various scientific fields e.g. electrochemistry, optics, mechanics, etc., and / or the use of new technologies to the elaboration of materials. The result is a representation of phosphate materials completely new compared to traditional views.
© 2012 The Authors.PublishedbyElsevierLtd. Selectionand/orpeer-reviewunderresponsibilityof the Scientific CommitteeofSYMPHOS2011
Keywords: High value phosphates, cements , photonic materials.
1. Introduction
The exploitation of phosphates is fundamentally centered on the production of fertilizer and phosphoric acid which represents the most important economic targets. A priori the production of phosphate with high added value is not yet an activity sector which can seem strategically interesting in terms of exploitation, processing and consequently valuation. However, in the second part of the XXth century and even more at the beginning of the XXlst century, the developments of the chemistry, physics medicine and biology revealed in numerous domains the potentialities of phosphates. Two "general public" examples illustrates this tendency: (i) at the frontier of the biological and inorganic worlds, biomaterials such calcium phosphates for evident medical reasons which require sophisticated method of elaboration, (ii) the remarkable scientific and industrial breakthrough of lithium phosphates LiMPO4( M = Iron, Manganese, Cobalt, Nickel) as positive electrodes in the batteries of type " Lithium ion " used specifically in electric motor cars and in many other systems. These two examples, connected respectively with the fields of medicine and energy, are typical of the potential contribution of
* Corresponding author.
E-mail address: leflem@icmcb-bordeaux.cnrs.fr
Gilles Le Flema *
Institute of Chemistry of Condensed Matter of Bordeaux (ICMCB), CNRS-UPR 9048 Avenue du Dr. Schweitzer, 33608 Pessac (France). (leflem@icmcb-bordeaux.cnrs.fr)
Abstract
1877-7058 © 2012 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Scientific Committee of SYMPHOS 2011 doi: 10.1016/j .proeng.2012.09.444
phosphates with high added value for new major economic objects.
Clearly any strategy leading to new technological frontiers based primarily on the quality of training of the actors of this development. This training must take place within a multidisciplinary context that is becoming increasingly necessary: for example the development of biomaterials requires the meeting of competences in chemistry, biology, medicine and mechanics.
Such formation leads to consider progressively scientific concepts which are constantly updated for the development of new techniques or new materials. By focusing on innovation in solid materials - including phosphate-, several of these new approaches can be emphasized:
• the notion of composite which a combination of several phases needed to create a specific property in a material,,
• the role of the final size of the particles obtained in a preparation process (aggregates, nano, micro), and also the influence of their porosity and their surface on the property of the final product,
• the new methods of synthesis may involve either low temperatures - e.g. soft chemistry methods - either high temperatures or high pressures or reactions in a supercritical fluid,
• the fact that the desired property can involve either volume of the particle or its surface,
• the systematic study of aging processes of materials in their operating conditions.
Table 1 summarizes a number of phosphate materials at different stages of development by introducing the competences required to their creation.
Table 1: Examples of phosphate materials at different stages of development
High Value Phosphates
Required Competences
Composites for high temperature uses with LaPO4
Chemical bonded phosphate ceramics : cement for low temperature environments and radioactive waste storage Positive electrodes for batteries ( LiFePO4)
Phosphate glass laser for fusion energy
Phosphates for second harmonic generation Photonic components for information storage
Biomaterials
Waste storage_
Geology, Chemistry, Mechanics , High Temperature, Aging process
Chemistry, Mechanics, Aging process
Composite, Chemistry, Electrochemistry, Surface reaction, Nano
Physics and Chemistry of Glasses, Optics, Mechanics
Chemistry, Crystal growth, Nonlinear optics Chemistry: Redox process, Materials laser processing, Optics
Chemistry, Biology, Mechanics, Medicine, Ceramics Chemistry, Geology, Mechanics , Aging process_
This list is not exhaustive: it does not include all current research on zeolites (heterogeneous catalysis, membranes), the zero expanding ceramics, solid electrolytes, sensors etc..
2. LaPO4 composites used at high temperature and in oxygenated environment.
2.1. What is a composite ?
A composite may be defined as a material with at least two components whose respective characteristics form a new system with improved overall performance or even with a new property. The concept of a composite needs a synergy between the properties of the constituents: this concept is therefore beyond the simple addition of mixture of these constituents.
The notion of composite was first imposed for structural and thermostructural materials in relation to their mechanical properties. They generally consist of a matrix (carbon, polymer, ceramic, metal) and a reinforcement (fiber: carbon, silicon carbide etc..; particle: silicon carbide, oxide, etc..). Between the reinforcement and the matrix, the connecting region (interface) will play a key role in the mechanical and thermomechanical properties.
2.2. Composites Alumina-Lanthanum Phosphate (Fig.1)
One of the parameters governing the mechanical properties of a composite is the interaction between the different phases (e.g. matrix - reinforcement) which can be more or less strong. This interaction may be altered by the presence of one (or
more) phase (s) resulting from a chemical reaction between the components and / or a propagation of defects at this interface. The strengthening of mechanical properties of a ceramic composite will be linked to the nature of this interface. One of the functions of such interface is to prevent the spread of random cracks in the composite.
In this context various materials were developed in the Al2O3-LaPO4 system for developing resistant ceramic matrix composites which can operate in critical conditions : for example thousands of hours at high temperatures in oxidizing environments. There are many applications: thermal insulators, components of nuclear reactors, turbines, protection of SiC fibers etc. The origin of these new composites is due to the remarkable properties of lanthanum monophosphate LaPO4.
2.3. Properties LaPO4
LaPO4 is very refractory with a melting point above 2000 ° C. It is stable in a wide variety of environments: air, water vapor, CO2 and slightly reducing atmosphere. It does not react, at least below 1600 ° C, with many other refractory oxides: Al2O3 (alumina), ZrO2 ( zirconia), Y3Al5O12 (yttrium aluminium garnet) Al6Si2O13 (mullite). For example the composite Al2O3 / LaPO4 have good decoupling properties which can inhibit the propagation of defects. All these characteristics have led to three types of materials:
• porous ceramics,
• machinable ceramics,
• composites stable at high temperature
2.4. Porous Ceramics
Porous ceramics can be prepared using the reaction : 3 La2 (CO3) 3, xH2O + 2Al(H2PO4) 3 + [y Al2O3] ^ Al2O3 + 6 LaPO4 + 9 CO2 + (6+3x) H2O + [y Al2O3].
The additional alumina (y) can be added to adjust the final ratio Al2O3/LaPO4. This reaction is used to make ceramics with open porosity since the evolved gases are pore-forming agents. Materials can be obtained with a uniform distribution of the pore size centered around 200 nm [1].
2.5. Machinable Ceramics
The alumina being difficult to machine, mixtures of alumina and lanthanum phosphate in increasing proportion were evaluated to increase the machinabilty of the final material. These mixtures are sintered at 1600 ° C to obtain a composite with the theoretical density (no pores). Even at this temperature, there is no reaction between the two phases but the gradual introduction of LaPO4 provokes a marked decrease of mechanical properties such as the Vickers hardness or the Young's modulus. As an example, the composites containing 40 wt% LaPO4 can be easily drilled with tungsten carbide tools [2].
Porous Ceramics
Machinable Ceramics
High temperature Ceramics
Figure 1. Composites of the Al2O3/LaPO4 system
2.6. Ceramics stable at high temperatures
Alumina fibers can be characterized by their tensile strength, in the absence or presence of the matrix component. A woven of alumina fiber (two-dimensional structure) is infiltrated with a solution of precursors of the matrix LaPO4. This solution contains phosphoric acid, lanthanum nitrate and the alumina powder. After drying carried out in a hydraulic press, under a pressure of 0.2 MPa at 60 ° C, composites are annealed for 1 h. at 1100 ° C. A clear increase in tensile strength is observed, compared to the resistance of the fiber-free matrix system. This property is related to the fact that the fibers are covered with a layer of LaPO4, the rest of the matrix being composed of a mixture of lanthanum phosphate and alumina. These composites are also more resistant than those where the matrix is a pure lanthanum phosphate [3].
3. Cement for cold areas
The development of these cements is based on the concept of "Chemically bonded phosphate ceramics (SCLC)." This concept introduced by W. D. Kingery [4] by analysing the reaction products of inorganic oxides in solutions of phosphoric acid and has been clearly defined by R. Roy: "Inorganic solid consolidated by chemical reactions in place of conventional heat treatments at high temperature" [5]. These materials have been studied and developed by the group A. S. Wagh [6] at Argonne National Laboratory (United States) in particular for the storage and stabilization of radioactive waste. Another possible application was also investigated for the development of cements for oil installations working in cold areas. The objectives of this latest application are numerous: repair of road infrastructure, consolidation of concrete and, more recently, equipment installations in the oil industry in very cold areas such as Alaska (permafrost).
Bore hole
Drilling
Permafrost
Ca si ng steel
Cernen t
Figure 2. Details of drilling in permafrost and use of chemically bonded phosphate ceramics as cement. The specifications for these cements require:
• a formation at very cold temperatures (<0 ° C) and slightly exothermic to avoid the melting of permafrost,
• the absence of pores to avoid any damage resulting gels cycles - thaws,
• a thermal conductivity as low as possible,
• a very good mechanical properties for use as a support for the pipeline,
• a very good adaptability with both steel tubes and the fields where the drilling is made,
• a perfect insolubility in water (offshore installations).
In the particular case of a well drilling where the role of the cement is to stabilize the central steel tube, the temperature may rise up to 120 ° C and the cement can also be subject to a pressure gradient. Figure 2 shows one of these applications: cementing around a drill pipe.
3.1. Principle of formation of a SCLC
Considering the example of the reaction products of potassium dihydrogen phosphate KH2PO4 with magnesia MgO for illustrating the formation of SCLC.
1) Reaction of a basic oxide such as magnesia in an acid solution. When the acidity of solutions decreases the reactions are successively:
• MgO + 2H+ = Mg2+ (aq) + H2O (aq symbolizes the dissolved species)
• MgO + H + = [Mg (OH)]+ (aq)
• MgO + H2O = Mg2+ (aq) + 2OH"
The reactions of magnesia with the phosphoric acid is very exothermic which can lead to rapid reactions producing soluble species such as Mg (H2PO4)2.
2) Formation of a cement
From this approach the Argonne group has developed a new phosphate cement based on the reaction:
MgO + KH2PO4 + 5 H2O = KMgPO4, 6H2O.
The resulting slurry becomes a very hard ceramic after a few hours. For the particular case of use in cold areas, the initial concentration of potassium acid phosphate is higher than the saturation concentration. As a result, after shaking the mud, when all the magnesia is consumed, an amount of KH2PO4 is dissolved in water which has the effect of lowering the freezing point of water, thus, this solution does not freeze at the permafrost temperatures [6].
3.2. Production of cement for cold regions
Cements developed under the name "ceramicrete" contain a number of additives to optimize their performance: they are 20% lighter than conventional cements, their porosities are less than 1% which makes them invulnerable to cycles gels thaws and they have a thermal conductivity about half that of comparable materials [7]. They are also stable in the marine environment.
Typical compositions and some of the corresponding properties are given in Table 2.
Table 2. Typical composition of cement for permafrost. (Ashes are particles resulting from the combustion of carbon. The composition of the C and F class is normalized as a function of the calcium, silica, alumina and iron concentrations).
Components
Individual component (w %)
Total in slurry
Binder components
MgO KH2PO4 Ash mixtures
Class C Class F Boric acid Water
Physical properties of the cement
density (g/cc) 1,8
9,93 29,8
19,87 19,87 0,5 20
Open Porosity (vol. %)
Compressive strength
0,5 20
Specific heat J/g.K
Thermal conductivity (W/mK)
4. Phosphate Materials for inertial confinement fusion.
4.1. Principle of fusion by inertial confinement.
The fusion power plants are designed to use the energy released by fusion of two light atoms. For example nuclear fusion of deuterium D and tritium T leads to the formation of 4He by the reaction:
D + T —> a + n + 17.5 Mev (n is a neutron)
In inertial confinement this reaction proceeds, under the impact of laser beam power, by the implosion of a target containing a mixture of deuterium and tritium.
The development of these plants is dedicated in a distant future to the energy production, perhaps replacing the fossil fuels but the current development is mostly related to military applications with multiple scientific benefits, such as better knowledge of plasma physics. Whether in the American project NIF (National Ignition Facility) or in the French LMJ (Laser Megajoule), the optical properties of phosphates are essential.
The principle of the experiment is as follows: a target filled with deuterium and tritium is subject to the illumination of very intense laser beams radiating in the near ultraviolet (351nm). The target is a microballoon mixture where the Deuterium - Tritium mixture was solidified at 20K. The energy absorbed by the electrons at the periphery of the target generates a plasma with very high temperatures and pressures (20 million K and few hundred M bars). The plasma expands outward by reaction type "rocket", and compresses the target centripetally causing the trigger of fusion reactions.
The irradiation time, the configuration of the experiment, the nature of the target, the number of beams arriving on this target (NIF: 192, LMJ: 240) and the energy delivered by these beams (LMJ: 1.8 Mega joule) are the parameters determining the fusion reaction. The system is very complex can be divided into four modules:
• the initial laser source: the emission wavelength of 1.06 microns
• the chains of amplification of the intensity of the beam
• the conversion rate: 0.351 1.06 |m
• the combustion chamber of the target.
Figure 3. Simplified scheme of fusion experiment by inertial confinement.
Phosphates are involved in the steps of amplification and frequency conversion.
4.2. Phosphate glasses for amplification [8]
The initial laser source delivers a beam light (A=1.06 |m -exactly 1.053 | m in the case of LMJ) with a low energy (=1 joule LMJ) which is introduced into a "pilot" for "shaping" this initial radiation in time and space.
The amplifier systems are designed to boost the energy at about 15 - 20 kJ. They consist of plates of neodymium-doped phosphate glass whose dimensions can be very large (46x81x3, 4 cm in the NIF project).
Among all types of possible materials glasses were selected because they can be produced as large pieces. The composition is dictated by very precise and complex specifications:
• a good optical characteristics of Nd3 + ion in these glasses,
• a great homogeneity of refractive index in each piece which implies a very uniform composition,
• a low attenuation at the working wavelength,
• a high resistance to the formation of color centers by the optical pumping,
• a low nonlinear index to avoid the problem of self-focusing of the beam,
• a relatively easy making to avoid the formation of bubbles, inclusions such as metal and crystal nuclei.
The optimization of the optical properties and thermo-optical is possible by modulating the composition. The selected glasses are close to the metaphosphate composition (mol%): P2O5 55-60, Al2O3 8-12%, K2O 13-17%, BaO 10-15% and an amount less or equal to 2% of Nd2O3.
Continuous melting of phosphate laser glass is used to supply such meter-scale
laser amplifier. The elaboration of these glasses is carried out in large vessel plate by a continuous casting process at about 1000-1300°C. Two key factors for melting these glasses successfully are the elimination of damage induced by Pt-inclusions and the dehydroxylation of the glass to concentrations less than100 ppmw OH. The former problem was overcome by working in an oxidizing environment leading to the dissolution of platinum in the form of Pt4+ ions which seem to have a negligible impact on the laser properties [9].
4.3. Phosphates as frequency converters [10].
The use of short wavelengths is due to the optimization of the deposition of laser energy on the target: energy penetrates more in the heart of this target and therefore is more efficient.
The wavelength of the amplified beam is 1.06 | m. It must be converted in to a wavelength of 0.351 |m i.e. a triple frequency ( ro^3ra).
The crystals used are the potassium dihydrogen phosphate KH2PO4 (KDP) and the deuterated compound KD2PO4 (DKDP). The growth technique is crystallization from a solution of phosphate. Very recently a "faster" growth technique has been developed: the large sizes of crystals are obtained in two months instead of two years. This requires
the control of the stability of the solution during the continuous cooling from the onset of spontaneous nucleation centers to the final size of large crystals. The crystals can have the following dimensions 55x55x30cm.
Frequency conversion which is attached to the fact that the crystals are non centro symmetric, occurred sequentially:
• in a first step , two-thirds of the incident light (ra) are converted by a crystal of KDP into the second harmonic (2
• in a second step the residual fundamental beam are converted to third harmonic (ra + 2ra = 3ra) by a DKDP crystal in a configuration of specific polarization.
5. Photonic component for permanent storage of information.
5.1. The object of the investigation.
The media currently used for the magnetic or optical storages of information, have the disadvantage of having a limited life of five to ten years. On the other hand the media such as DVD, Blu ray are, in essence, two-dimensional. Designing a new system of information storage, through the implementation of a truly three dimensional space (3D) multiplies the storage capacity. The objective is to find an "ideal" photonic component with a high temporal stability with such a capability. In this context new materials have recently been identified on the basis of the optical properties of phosphate glasses containing stable Ag+ ions. This study, typically multidisciplinary, is the result of very close cooperation between chemists at the Institute of Materials Chemistry of Condensed Matter of Bordeaux (ICMCB) and physicists of the Center for Molecular and Optical Physics of the University of Bordeaux (CPMOH)[11,12].
5.2. Design of the material: an illustration of material laser processing
The phosphate glasses may contain important rate in Ag + ion. This is the case, for example of glasses of the system Ag2O - ZnO - P2O5 that can be stabilized by gallium oxide Ga2O3. Subjected to an excitation light wavelength equal to 260 nm they have a broad emission centered around 365 nm. This fluorescence is due to isolated Ag+ ions in the glass.
However if the excitation occurs at X = 425 nm in the near ultraviolet a white light emission is observed, the origin of which is attributed to the presence of Agmx+ aggregates where m (< 10) is the number of atoms in the aggregate and x the degree of ionization. This intensity is very strong with high efficiency.
Figure 4. Design of silver phosphate glasses as photonic components. A near infra red high repetition -rate femtosecond laser is focused into a silver phosphate glass which can be moved in 3D by translation to make sequential silver aggregates[11,12].
When the radiation dose is adjusted properly, the fluorescence intensity of these aggregates can be controlled and a grayscale coding can be created as in the case of silver photographic film: by specifying the conditions of excitation, a scale of 256 levels of fluorescence intensity could be established. On the other hand, by playing with the intrinsic optical properties of these glasses, a three-dimensional registration of these fluorescent centers is possible [12].
5.3. How the phosphate works? (Fig 4)
The operation of such a glass is shown schematically in Figure 4 and can be described in two steps:
• The step of writing. Under the illumination of the infrared beam ( X = 1030 nm), Ag+ initially present in the glass become Agmx+ aggregates which are in the form of small cylinders. These aggregates are the voxels. The optical properties of glass allow a voxel (volumetric pixel)inscription in three dimensional space (3D).
• The step of reading. The luminescence of these voxels is detected under illumination by a laser (X =524 nm). This luminescence is collected by a photodiode.
This brief overview of some phosphate materials of high technology, leads to the conclusion that phosphate chemistry covers a wide variety of scientific and industrial fields in addition to traditional production such as phosphoric acid and fertilizers. Common to all these examples is the basic structural entity [PO4] which has two functions:
• a structural function: phosphate entities involved in the organization of the material structure but have little impact on its properties,
• -an inductive function: the covalency of the P - O bond is the direct or indirect source of the considered properties. Its role is important in the case of positive electrodes for batteries and for all parameters related to the optical properties.
Images stored in 3D Space
Silver aggregates in the glass
6. Conclusion.
In all the previous examples the creation of new materials results from an overlapping between the basic functions of the phosphate groups and the new concepts related to various scientific fields e.g. electrochemistry, optics, mechanics , etc., and / or the use of new technologies to the elaboration of materials. The result is a representation of phosphate materials completely new compared to traditional views.
References
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[3] J. B. Davis, D. B. Marshall and P. E. D. Morgan, "Monazite-containing oxide/oxide composites "J. Eur. Ceram. Soc., 20 (2000) 583
[4] W. D. Kingery. « Fundamental Study of Phosphate Bonding in Refractories: Cold-setting properties » J. Am Ceram. Soc., 33[5](1950)242.
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[8] B. Le Garrec, D. Taroux et S. Bouillet « Les verres lasers de la Ligne d'Intégration Laser et du Laser Mégajoule » Le Verre 14 N°5 (2007) 11.
[9] J. H. Campbell, T. I. Suratwala, C. B. Thorsness, J. S. Hayden, A. J. Thorne, J. M. Cimino, A. J. Marker III, K. Takeuchi, M. Smolley, G. F. Ficini-Dorn. , «Continuous melting of phosphate laser glasses», J. NonCrystalline Solids 263&264 (2000) 342.
[10] V.G. Dmitriev, G.G. Gurzadyan and D.N. Nikogosyan, Handbook of Nonlinear Optical Crystals, Springer Verlag, Berlin-Heidelberg (1991).
[11] A. Royon, K. Bourhis, M. Bellec, G. Papon, B. Bousquet, Y. Deshayes, T. Cardinal and L. Canioni, « Silver clusters embedded in glass as a perennial high capacity optical recording medium », Adv. Mater. 22(2010)5282; Nature 468(04 november) 2010.
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