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Two-dimensional (2D) transition metal carbides and nitrides (MXenes) possess a unique combination of properties, such as metallic conductivity combined with hydrophilicity and surface redox activity, that are important for energy storage, printed electronics, biomedical, catalytic and other applications. However, the use of many MXene chemistries beyond titanium carbides is limited by the cost of MAX phase precursors, which are usually produced from pure elements, involving expensive transition metals. Herein, we demonstrate a low-cost rapid aluminothermic combustion synthesis of MAX phases from an inexpensive oxide precursor, producing V2AlC in seconds, with low energy input. A reactor for self-propagating high-temperature synthesis (SHS) was designed and manufactured for this study. The V2CTx MXene produced from the SHS MAX is similar to MXene from conventional pressureless sintered MAX in terms of oxidation resistance, environmental stability, conductivity, and electrochemical performance, but has a larger flake size. This work demonstrates an alternative, low-cost and scalable approach to the synthesis of MAX phases and, subsequently, MXenes without sacrificing their properties.

Rigid, solid-state components represent the current paradigm for electronic systems, but they lack post-production reconfigurability and pose ever-increasing challenges to efficient end-of-life recycling. Liquid electronics may overcome these limitations by offering flexible in-the-field redesign and separation at end-of-life via simple liquid phase chemistries. Up to now, preliminary work on liquid electronics has focused on liquid metal components, but these devices still require an encapsulating polymer and typically use alloys of rare elements like indium. Here, using the self-assembly of jammed two-dimensional titanium carbide (Ti

Despite the recent advances in bottom-up synthesis of different kinds of atomically precise graphene nanoribbons (GNRs) with very diverse physical properties, the translation of these GNRs into electronic devices remains challenging. Among other factors, the electronic characterization of GNRs is hampered by their complex synthesis that often requires custom-made organic precursors and the need for their transfer to dielectric substrates compatible with the conventional device fabrication procedures. In this paper, we demonstrate that uniform electrically conductive GNR films can be grown on arbitrary high-temperature-resistant substrates, such as metals, Si/SiO

Narrow atomically precise graphene nanoribbons hold great promise for electronic and optoelectronic applications, but the previously demonstrated nanoribbon-based devices typically suffer from low currents and mobilities. In this study, we explored the idea of lateral extension of graphene nanoribbons for improving their electrical conductivity. We started with a conventional chevron graphene nanoribbon, and designed its laterally extended variant. We synthesized these new graphene nanoribbons in solution and found that the lateral extension results in decrease of their electronic bandgap and improvement in the electrical conductivity of nanoribbon-based thin films. These films were employed in gas sensors and an electronic nose system, which showed improved responsivities to low molecular weight alcohols compared to similar sensors based on benchmark graphitic materials, such as graphene and reduced graphene oxide, and a reliable analyte recognition. This study shows the methodology for designing new atomically precise graphene nanoribbons with improved properties, their bottom-up synthesis, characterization, processing and implementation in electronic devices., Atomically precise graphene nanoribbons are a promising platform for tailored electron transport, yet they suffer from low conductivity. Here, the authors devise a strategy to laterally extend conventional chevron nanoribbons, thus achieving increased electrical conductivity and improved chemical sensing capabilities.

Synthesis of quantum dots is a valuable experiment for demonstration and discussion of quantum phenomena in undergraduate chemistry curricula. Recently, a new class of all-inorganic perovskite quantum dots (QDs) with a formula of CsPbX3 (X = Cl, Br, I) was presented and attracted tremendous attention. Here we adapt the synthesis of CsPbX3 QDs for implementation in inorganic chemistry laboratory class. Perovskite QDs have a number of advantages: they exhibit bright photoluminescence in the visible range of spectrum with a narrow bandwidth, and their emission wavelength can be changed by tuning both size and composition of nanoparticles. The described experiment provides a discussion point on many important concepts of inorganic chemistry, materials science, and nanotechnology, such as colloidal synthesis of nanoparticles, perovskite crystal structure, quantum size effect, as well as photovoltaics and renewable energy.

The MXene field continues to grow and expand as more research groups begin to study this fascinating and very large class of 2D materials. While synthesis and applications of MXenes have been widely discussed in literature, characterization is often overlooked. Due to the large variety of MXene structures and compositions, it is often necessary to use multiple advanced characterization techniques within a single study, and each characterization technique has its own quirks, pitfalls, and benefits when applied to MXenes. This review focuses on the utilization of X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, electron microscopy/spectroscopy and a number of other techniques to understand if the precursor (MAX phase) is suitable for MXene synthesis, confirm successful synthesis of MXene, and finally determine its composition, structure and properties. Researchers should look to this review article as a guide to help them understand which techniques to use for characterization of their MXene samples and leverage the best characterization practices developed to date.

Solution bottom-up approaches can be used to prepare bulk quantities of narrow atomically precise graphene nanoribbons (GNRs) with various widths and geometries. These GNRs are often considered as promising materials for electronic and optoelectronic applications. However, the handling and processing of nanoribbons for practical applications can be difficult because of their entanglement and aggregation, and thus poor solubility in conventional solvents. In this work, we studied the aggregation-dependent properties of solution-synthesized chevron GNRs in a variety of solvents. We demonstrate that the spectroscopic features observed in the experimentally measured absorbance spectra of chevron GNRs are in a good agreement with the theoretically predicted excitionic transitions. We also show that the absorbance spectra of GNRs evolve with aggregation time, which is important to consider for the spectroscopic determination of optical bandgaps of nanoribbons. We discuss two types of GNR assemblies: bulk aggregates of π–π stacked nanoribbons that form in a solution and rather long one-dimensional (1D) structures that were observed on a variety of surfaces, such as Au(111), mica and Si/SiO2. We demonstrate that the few-μm-long 1D GNR structures can be conveniently visualized by conventional microscopy techniques and used for the fabrication of electronic devices.

Because of their intriguing electronic and optical properties, atomically precise graphene nanoribbons (GNRs) are considered to be promising materials for electronics and photovoltaics. However, significant aggregation and low solubility of GNRs in conventional solvents result in their poor processability for materials characterization and device studies. In this paper, we demonstrate a new fabrication approach for large-scale uniform thin films of nonfunctionalized atomically precise chevron-type GNRs. The method is based on (1) the exceptional solubility of graphitic materials in chlorosulfonic acid and (2) the original interfacial self-assembly approach by which uniform films that are single-GNR (∼2 nm) thick can be routinely prepared. These films can be transferred to various substrates including Si/SiO2 and used for the streamlined fabrication of arrays of GNR-based devices. The described self-assembly approach should be applicable to other types of solution-synthesized atomically precise GNRs as wel...

Graphene nanoribbons (GNRs) attract much attention from researchers due to their tunable physical properties and potential for becoming nanoscale building blocks of electronic devices. GNRs can be synthesized with atomic precision by on-surface approaches from specially designed molecular precursors. While a considerable number of ribbons with very diverse structures and properties have been demonstrated in recent years, there have been only limited examples of on-surface synthesized GNRs modified with functional groups. In this study, we designed a nanoribbon, in which the chevron GNR backbone is decorated with phenyl functionalities, and demonstrate the on-surface synthesis of these GNRs on Au(111). We show that the phenyl modification affects the assembly of the GNR polymer precursors through π-π interactions. Scanning tunneling spectroscopy of the modified GNRs on Au(111) revealed that they have a band gap of 2.50 ± 0.02 eV, which is comparable to that of the parent chevron GNR. The phenyl functionalization leads to a shift of the band edges to lower energies, suggesting that it could be a useful tool for the GNR band structure engineering. We also investigated lateral fusion of the phenyl-modified GNRs and demonstrate that it could be used to engineer different kinds of atomically precise graphene nanopores. A similar functionalization approach could be potentially applied to other GNRs to affect their on-surface assembly, modify their electronic properties, and realize graphene nanopores with a variety of structures.

Titanium trisulfide (TiS3) is a promising layered semiconductor material. Several-mm-long TiS3 whiskers can be conveniently grown by the direct reaction of titanium and sulfur. In this study, we exfoliated these whiskers using the adhesive tape approach and fabricated few-layered TiS3 field-effect transistors (FETs). The TiS3 FETs showed an n-type electronic transport with room-temperature field-effect mobilities of 18-24 cm(2) V(-1) s(-1) and ON/OFF ratios up to 300. We demonstrate that TiS3 is compatible with the conventional atomic layer deposition (ALD) procedure for Al2O3. ALD of alumina on TiS3 FETs resulted in mobility increase up to 43 cm(2) V(-1) s(-1), ON/OFF ratios up to 7000, and much improved subthreshold swing characteristics. This study shows that TiS3 is a competitive electronic material in the family of two-dimensional (2D) transition metal chalcogenides and can be considered for emerging device applications.

We demonstrate that layered carbon black nanoparticles can be oxidatively peeled via the reaction with potassium permanganate in sulfuric acid. As a result of this reaction, outer layers of carbon nanoparticles “peel” off due to high levels of oxidation while the less oxidized inner cores, though they exhibit remarkable solubility in water, remain mostly intact.

Atomically precise graphene nanoribbons (GNRs) of two types, chevron GNRs and N = 7 straight armchair GNRs (7-AGNRs), have been synthesized through a direct contact transfer (DCT) of molecular precursors on Au(111) and gradual annealing. This method provides an alternative to the conventional approach for the deposition of molecules on surfaces by sublimation and simplifies preparation of dense monolayer films of GNRs. The DCT method allows deposition of molecules on a surface in their original state and then studying their gradual transformation to polymers to GNRs by scanning tunneling microscopy (STM) upon annealing. We performed STM characterization of the precursors of chevron GNRs and 7-AGNRs, and demonstrate that the assemblies of the intermediates of the GNR synthesis are stabilized by π–π interactions. This conclusion was supported by the density functional theory calculations. The resulting monolayer films of GNRs have sufficient coverage and density of nanoribbons for ex situ characterization by spectroscopic methods, such as Raman spectroscopy, and may prove useful for the future GNR device studies.

Bottom-up fabrication of narrow strips of graphene, also known as graphene nanoribbons or GNRs, is an attractive way to open a bandgap in semimetallic graphene. In this chapter, we review recent progress in solution-based synthesis of GNRs with atomically precise structures. We discuss a variety of atomically precise GNRs and highlight theoretical and practical aspects of their structural design and solution synthesis. These GNRs are typically synthesized through a polymerization of rationally designed molecular precursors followed by a planarization through a cyclodehydrogenation reaction. We discuss various synthetic techniques for polymerization and planarization steps, possible approaches for chemical modification of GNRs, and compare the properties of GNRs that could be achieved by different synthetic methods. We also discuss the importance of the rational design of molecular precursors to avoid isomerization during the synthesis and achieve GNRs that have only one possible structure. Significant attention in this chapter is paid to the methods of material characterization of solution-synthesized GNRs. The chapter is concluded with the discussion of the most significant challenges in the field and the future outlook.

Resorbable monophase ceramics and ceramic composites based on calcium pyrophosphate (CPP, Ca2P2O7), tricalcium phosphate (TCP, Ca3(PO4)2), and hydroxyapatite (HAp, Ca10(PO4)6(OH)2) were prepared via thermal treatment of a HAp (Ca/P = 1.67) and CPP (Ca/P=1) mixture. High-temperature solid-state reaction between HAp and CPP leading to TCP formation was studied within the range 700–800 °C. The metastable α-TCP phase was observed in this range as a product of the solid-state reaction. The reaction had been completed before sintering of the powders started. The microstructure of CPP/TCP composites was found to be duplex-like, consisting of large CPP grains with smaller TCP grains among CPP ones. In the case of the monophase ceramics with starting HAp/CPP ratio corresponding to TCP, grain size was less than 300 nm.

The properties of Ca-deficient hydroxyapatite powder synthesized from calcium nitrate and ammonium hydrophosphate at 60°C, pH = 7, and Ca/P = 1.67, 1.61, and 1.48 are presented. After sintering at 1100°C for 6 h the phase composition of the ceramic based on these powders was represented by tricalcium phosphate (Ca/P = 1.48) or tricalcium phosphate hydroxyapatite (Ca/P = 1.67 and 1.61). The grain size of the ceramic was 100 – 1000 nm.

Photoactive perovskite quantum dot films, deposited via an inkjet printer, have been characterized by x-ray diffraction and x-ray photoelectron spectroscopy. The crystal structure and bonding environment are consistent with CsPbBr3 perovskite quantum dots. The current-voltage (I-V) and capacitance-voltage (C-V) transport measurements indicate that the photo-carrier drift lifetime can exceed 1 ms for some printed perovskite films. This far exceeds the dark drift carrier lifetime, which is below 50 ns. The printed films show a photocarrier density 109 greater than the dark carrier density, making these printed films ideal candidates for application in photodetectors. The successful printing of photoactive-perovskite quantum dot films of CsPbBr3, indicates that the rapid prototyping of various perovskite inks and multilayers is realizable.

The present work is aimed at the elucidation of the role played by CaCl 2 and NH 4 NO 3 (the latter is a by-product of the solution synthesis of hydroxyapatite, hereinafter referred to as HAp) in the densification of nano-sized HAp powder in the course of the pressureless sintering. Nanocrystalline HAp powder was fabricated via the wet-precipitation technique by the dropwise addition of an (NH 4 ) 2 HPO 4 solution to a Ca(NO 3 ) 2 mother solution at a pre-adjusted pH at 60 °C. The pH of the aqueous mixture was maintained at a constant value (either 7 or 9) by the addition of an appropriate amount of NH 4 OH. The Ca/P ratio was set to 1.67, 1.61, and 1.48; 10 wt% of CaCl 2 was added to dry HAp powder. NH 4 NO 3 remaining in unwashed HAp powder can act as a fluxing agent that promotes partial melting at a relatively low temperature (150–250 °C) thus allowing the particles to rearrange into a denser packing. Several mechanisms of the CaCl 2 action as a densification additive might be envisaged: (i) a decrease in the melting temperature; (ii) the surface wetting of grains; (iii) a change in the growth morphology owing to the high-temperature surfactant properties; (iv) a possible reaction with HAp on the surface of grains giving rise to the decomposition of HAp and yielding chlorapatite (ClAp), which can convert back to HAp over a wide temperature range and at any level of H 2 O.

Calcium phosphate powders for manufacturing bioceramics were synthesized via precipitation from stock solutions of (NH4)2HPO4 and Ca(NO3)2, or CaCl2 or Ca(CH3COO)2 with [Ca2+]/[PO 43−] = 1, without pH regulation. Properties of powdered samples, including density and microstructure of ceramics sintered at 900, 1000, 1100°C, were studied. The following pairs of precursors such as Ca(NO3)2/(NH4)2HPO4, CaCl2/(NH4)2HPO4, Ca(CH3COO)2/(NH4)2HPO4 gave both insoluble calcium phosphates and the corresponding by-products of synthesis — NH4NO3, NH4Cl, NH4CH3COO. These by-products were released from the calcium phosphate precipitates in the course of heating to the temperature of sintering. Owing to specific buffer properties of the solutions being formed during synthesis, the pH value varied in a wide range during the precipitation process leading to different final values of pH and, thus, to different target phase(s) after annealing at 900–1100°C. After sintering, the samples based on the powders synthesized from Ca(NO3)2/(NH4)2HPO4 consisted of β-Ca2P2O7, whereas the samples based on the powders derived from CaCl2/(NH4)2HPO4 were composed of β-Ca2P2O7 and β-Ca3(PO4)2, and the samples based on the powders synthesized from Ca(CH3COO)2/(NH4)2HPO4 contained only β-Ca3(PO4)2. All the powders can be considered as the precursors for fabrication of bioceramics with enhanced resorption.

The properties of powder synthesized from calcium nitrate and ammonium hydrophosphate phosphate hydrophosphate hydrophoshydroin the presence of polyvinyl alcohol are investigated. It is established that the presence of 0.25–0.50% PVC strongly influences the rheological and thermal properties of the powder. A tendency toward anomalous growth of grains appears in the microstructure of ceramic based on hydroxyapatite synthesized with PVA.

Hydroxyapatite, Ca10(PO4)6(OH)2, powders with enhanced sinterability have been synthesized through precipitation from calcium nitrate and ammonium hydrogen phosphate solutions at pH 9, t= 60°C, and a Ca/P atomic ratio of 1.67, and their properties have been studied: phase composition, particle size distribution, loose density, and green density. The initial solution concentration is shown to influence the properties of the powders and the ceramics fabricated from them. Comparison of the particle size distributions in disaggregated powders and the grain size distributions in the ceramics indicates that the ceramics inherit the structure of the corresponding powders. Optimizing the synthesis conditions in order to enhance the sinterability of the powders, we obtained green compacts with the highest shrinkage rate in the range 850–950°C and shrinkage onset at 600°C, which is 100–150°C lower in comparison with powders synthesized in earlier studies from calcium nitrate and ammonium hydrogen phosphate.

A worldwide search is now underway for materials which are suitable for introducing into the human body for purposes of diagnostics, medical treatment, or replacement of bone tissue. Physicians are especially interested in ceramic materials whose chemical composition is close to that of natural bone tissue. This is a ceramic based on calciumphosphate compounds, primarily hydroxyapatite (HAP) — a material which is identical to the biomineral of human bones. Together with biocompatibility and bioactivity, materials for bone implants must exhibit bioresistance (resistance to dissolution in the body) or bioresorbability (capability of gradually or completely dissolving in water in the body as the new bone accumulates) depending on the medical treatment being used.

Hydroxyapatite ceramics technology is examined. Disperse systems and their evolution in each process state are determined. Data from gravimetric and dilatometric analysis and scanning microscopy are reported. The aggregate distribution by size in the initial powder and the grain distribution by size in the sintered ceramic are compared. The inheritance of the properties of the initial powders by the structure characteristic of ceramic materials is demonstrated. The evolution of modern materials science is related to the creation of new materials with unique properties. Production of such materials implies improvement of existing technologies or creation of new schemes. Considering different materials as disperse systems (DS) with defined properties allows applying the general principles of the existence of DS in technologies for different ceramic materials. An examination of preparation of the initial materials [1], molding [2, 3], and high-temperature treatment [4, 5] in materials technology with consideration of the existence of disperse system and surface phenomena makes it possible to perfect existing technologies [6] and develop new materials [7], including nanoceramics [8, 9]. The basic stages in fabrication of ceramics are preparation of the initial components and molding and firing [10] or, in other words, preparation of the initial material in the form of powder or slip and consolidation [11]. Without any doubt, according to many determinations in ceramics, this concerns transforming the material from a granulated state to a monolithic state. Technology for ceramics, like many other highmelting nonmetallic and silicate materials, is a set of processes of creation, evolution, and in some cases destruction of DS consisting of disperse phase and dispersion medium. The most important distinctive features of DS are the continuity of the dispersion medium, state of comminution of the disperse phase, and presence of phase boundaries, which is due to their heterogeneity [12, 13]. The classification of disperse systems by the aggregate state of the substance of the disperse phase and dispersion medium is the most popular. According to this classification, most existing ceramic materials can be assigned to solid-insolid (SS), gas-in-solid (GS), or solid, gas-in-solid (S, GS) disperse systems. The real materials are unconditionally more complex DS and can contain more than one disperse phase, as well as more than one dispersion medium. With respect to all formal features, many ceramic materials that are DS (SS, GS, or S, GS) can be assigned to composite materials (CM) formed by bulk combination of chemically heterogeneous components with different physical and mechanical properties with a distinct interface between them. CM are characterized by properties that none of their components individually have [14, 15]. In other words, such composite materials as DS can be polymatrix or polyfilled. According to the traditional approach to composite mate

Narrow graphene nanoribbons (GNRs) constructed by atomically precise bottom-up synthesis from molecular precursors have attracted significant interest as promising materials for nanoelectronics. But there has been little awareness of the potential of GNRs to serve as nanoscale building blocks of novel materials. Here we show that the substitutional doping with nitrogen atoms can trigger the hierarchical self-assembly of GNRs into ordered metamaterials. We use GNRs doped with eight N atoms per unit cell and their undoped analogues, synthesized using both surface-assisted and solution approaches, to study this self-assembly on a support and in an unrestricted three-dimensional (3D) solution environment. On a surface, N-doping mediates the formation of hydrogen-bonded GNR sheets. In solution, sheets of side-by-side coordinated GNRs can in turn assemble via van der Waals and π-stacking interactions into 3D stacks, a process that ultimately produces macroscopic crystalline structures. The optoelectronic properties of these semiconducting GNR crystals are determined entirely by those of the individual nanoscale constituents, which are tunable by varying their width, edge orientation, termination, and so forth. The atomically precise bottom-up synthesis of bulk quantities of basic nanoribbon units and their subsequent self-assembly into crystalline structures suggests that the rapidly developing toolset of organic and polymer chemistry can be harnessed to realize families of novel carbon-based materials with engineered properties.

The contact angles of molten NaCl and CaCl2 on hydroxyapatite (HAp) in air at 866 and 880 °C are close to zero. Wettability and the kinetics of spreading in the NaCl/HAp system were not affected by the reaction product presaturation of a melt or by substrate density and roughness; the rate of spreading for NaCl/HAp was described by the De Genes model of viscous dissipation, while it slowed down significantly in case of CaCl2/HAp due to the interfacial reaction resulting in a surface tension gradient.

Graphene nanoribbons (GNRs) have received a great deal of attention due to their promise for electronic and optoelectronic applications. Several recent studies have focused on the synthesis of GNRs by the bottom-up approaches that could yield very narrow GNRs with atomically precise edges. One type of GNRs that has received a considerable attention is the chevron-like GNR with a very distinct periodic structure. Surface-assisted and solution-based synthetic approaches for the chevron-like GNRs have been developed, but their electronic properties have not been reported yet. In this work, we synthesized chevron-like GNRs in bulk by a solution-based method, characterized them by a number of spectroscopic techniques and measured their bulk conductivity. We demonstrate that solution-synthesized chevron-like GNRs are electrically conductive in bulk, which makes them a potentially promising material for applications in organic electronics and photovoltaics.

According to theoretical studies, narrow graphene nanoribbons with atomically precise armchair edges and widths of2 nm have a bandgap comparable to that in silicon (1.1 eV), which makes them potentially promising for logic applications. Different top-down fabrication approaches typically yield ribbons with width10 nm and have limited control over their edge structure. Here we demonstrate a novel bottom-up approach that yields gram quantities of high-aspect-ratio graphene nanoribbons, which are only ~1 nm wide and have atomically smooth armchair edges. These ribbons are shown to have a large electronic bandgap of ~1.3 eV, which is significantly higher than any value reported so far in experimental studies of graphene nanoribbons prepared by top-down approaches. These synthetic ribbons could have lengths of100 nm and self-assemble in highly ordered few-micrometer-long 'nanobelts' that can be visualized by conventional microscopy techniques, and potentially used for the fabrication of electronic devices.

Hydroxyapatite (HAp), tricalcium phosphate (TCP) and calcium pyrophosphate (CPP) are known to be among calcium phosphates used in clinical medicine due to their biocompatibility. HAp and other complex calcium phosphate salts are the end-products of the biological mineralization process. Calcium pyrophosphate Ca2P2O7 (β-CPP) is one of the intermediate products involved in this process. The biological response with respect to new bone formation is quite similar for CPP and HAp. Sintered CPP has better biological responses, and, thus, a great potential as a biodegradable bone substitute. The rate of biodegradation depends on: (i) material texture (porosity type and level), (ii) quality of biodegradation phase (phase composition, grain size, properties of grain boundaries). Several sources for CPP phase in ceramics can be assumed. CPP phase may come from frit (CaO-P2O5, Ca/P=0.2-0.75) used as a sintering additive. Ceramics can be fabricated from powder of CPP with Na4P2O7 as sintering additive, via interaction between H3PO4 or (NH4)2HPO4 and porous HAp at high temperature after soaking it in the former solutions. The aim of the present work was focused on fabrication of multiphase ceramics with enhanced resorptivity due to presence of CPP phase and investigation of processes leading to formation of the multiphase ceramics based on HAp and CPP originated from CaHPO4. Ceramic materials have been made from mixtures of powders of stoihiometric HAp (Ca/P=1.67) and monetite (CaHPO4, Ca/P=1). Powders of HAp and monetite were synthesized by means of wet chemical precipitation from aqueous solutions of Ca(NO3)2*4H2O and (NH4)2HPO4 at 60 °C and pH=9 for HAp and pH=4-5 for monetite. Component ratio HAp:monetite was varied from 0:100 to 100:0 % with a step of 20%. Powders of raw materials and the mixtures were tested by means of XRD, TG, DTG, SEM, dilatometry. Linear shrinkage, density and microstructure of samples of ceramic materials sintered at 900, 1000, 1100°C with isothermal holding during 6 hours were tested. Complicated consequence of phase transformations took place during heating the the mixtures from 20 to 1200 C. The CPP (Ca/P=1, converted from CaHPO4 at 400-500°C ) reacts with HAp (Ca/P=1.67) causing additional weight loss in the region of 600-1050°C due to solid state reaction leading to TCP (Ca/P=1.55) formation. Linear shrinkage of HAp at 1100°C after 6 hours was found to be about 21%; for Ca2P2O7 formed from monetite, and for the mixtures - less than 11%. Resulted ceramics with the phase composition of HAp, CPP and TCP, i.e. with a different content of degradable phase and different ratio of CPP/TCP, can be treated as a biocompatible bioactive material with a tunable rate and limit of biodegradation.

Bioceramics based on hydroxyapatite (HAp) is known to be a prospective material for biomedical applications. However, sintering of HAp is still understudied in sense of reasonable selection of controlling parameters. In particular, the role of impurities and co-products of powder fabrication is still questionable. The data concerning the role of ammonium nitrate coming to precipitated HAp from the mother liquor, its effect on powder compaction and subsequent sintering, are not available.Nanosized powders of HAp were fabricated via conventional wet-precipitation technique by dropwise adding of Ca(NO3)2 solution (0.25 -1.67 M) to the stock solution of (NH4)2HPO4 (0.15-1.00 M) with pre-adjusted pH at 60°C in presence of polyvinyl alcohol (PVA). PVA was added to the stock solution in order (i) to block crystal growth during synthesis , (ii) to improve stability of Hap suspension to sedimentation, (iii) to regulate an aggregation of HA nanoparticles during synthesis and in the stage of drying.NH4NO3 – a by-product of the precipitation reaction, presented in as-precipitated powder in amount of 30%, was evaluated as an additive affecting a compaction of the powder and the initial stage of a sintering. The powder samples were tested by XRD, FTIR, light-scattering , TEM and SEM/EDX to get particle sizes, morphology and chemical composition, dilatometry. Ceramics were sintered at 700-1250°C and evaluated with SEM/EDX and density measurements.Addition of PVA to the stock solution in the course of HAp precipitation is a promising technique to control an aggregation of HAp nanoparticles in the stages of drying and sintering. PVA acting as a surfactant in the solution and as a binder in dry powder can keep highly reactive small HAp particles within large agglomerates providing better molding of the powder and controllable densification of ceramics. The effect of PVA on microstructure of the HAp powder and their sintering behaviour is discussed in terms of self-organisation concept and synergetics.