Increasing B2O3 Content Research Articles

Influence of B<sub>2</sub>O<sub>3</sub> on Phosphate Ion Released from SiO<sub>2</sub>-B<sub>2</sub>O<sub>3</sub>-P<sub>2</sub>O<sub>5</sub>-Na<sub>2</sub>CO<sub>3 </sub> Glass in Synthetic Seawater

Phosphates have been receiving important attention in various fields and one of the fundamental sources of nutrients required to be used as source of nutrients for plankton growth. The objective of this study is to determine the effect of boron oxide on phosphate ion released from the system SiO2-B2O3-P2O5-Na2CO3 glasses. The compositions of this glass system [wt%: (55-x)% SiO2- (15+x)% B2O3- 5% P2O5- 25% Na2CO3] where 15≤x≤40 % have been prepared with the different amount of B2O3 (30-55wt%) and P2O5 with Na2CO3 were fixed. The glass has been prepared by melting in the alumina crucible within 2 h of soaking time at 1300 °C in the furnace and cooled to room temperature. The obtained glass samples were crushed and sieved at mean size of 2 mm – 4 mm. The dissolution studies were determined through the immersion of the glass samples in 50 mL synthetic seawater for 30 days under static condition. The results were obtained and analyzed using Discrete Auto Analyzer. Fourier Transform Infrared (FTIR) with Attenuated Total Reflectance (ATR) method was used to determine the functional group sample of glasses and the glass phase was characterized by X-Ray diffraction (XRD) techniques. Dissolution studies showed that, the concentration of phosphate ion released decreased with increasing B2O3 content whilst, increased with immersion time. The obtained experimental data indicated that, the optimum concentration of phosphate ion (10.27 ppm) was achieved at 35 wt% of B2O3 at week three.

Effect of compositions and additives content on crystallization behavior of Ti-rich phase from Ti-bearing blast furnace slag

The precipitation behavior of Ti-rich phases from high Ti-bearing blast furnace (Ti-BF) slag was studied with (Mg + Al)/(Ca + Si) ratio and B2 O3 concentration range from 0.37 to 0.67 and from 0 to 4%, respectively. Scanning Electron Microscope (SEM) and Electron probe X-ray microanalysis (EPMA) were used for determining crystal behavior of the slags quenched from high temperatures and the compositions of the crystals. The results showed that two main phases, which were perovskite and anosovite can precipitate during the experimental process. Specifically speaking, when the content of B2 O3 was 2.0% and (Mg + Al)/(Ca + Si) ratio was 0.47, the precipitated crystals of the melt slags transformed from perovskite to anosovite at the temperature of 1320 °C. With the increase of B2 O3 content from 0 to 4.0%, the volume fraction of anosovite enhanced from 0 to 8.3% correspondingly. The increasing of (Mg + Al)/(Ca + Si) ratio and B2 O3 were favorable to form anosovite while decrease (Mg + Al)/(Ca + Si) ratio was beneficial to precipitate perovskite.

Thermal expansion and structural complexity of strontium borates

Thermal expansion of four strontium borates has been studied by high-temperature powder X-ray diffraction. Strong anisotropy of thermal expansion is observed for the structures of Sr3B2O6 (0D) and SrB2O4 (1D) based on triangles BO3 only: The high expansion occurs perpendicular to the BO3 plane, i.e. along the direction of the less strong bonds in the crystal structure. The monoclinic Sr2B16O26 (3D) borate expands dramatically due to shear deformations in monoclinic plane: Monoclinic β′ angle changes significantly because it is not fixed by symmetry. In contrast to these borates, SrB4O7 (3D) borate built up from tetrahedra only expands almost isotropically. Average value of volume expansion is 36 × 10−6 K−1 for studied Sr-borates. Tendency of slight decrease in the volume thermal expansion and sharp decrease in the melting points is observed with an increase in B2O3 content as a result of the degree of polymerization increase. As the B2O3 content grows in Sr-borates, the structural complexity increases in the SrO–B2O3 system due to more complex anionic structure. Inverse “melting temperature decrease—structural complexity increase” correlation is revealed.

Structural investigation of BaO[sbnd]B2O3[sbnd]P2O5 glasses by NMR and Raman spectroscopy

Glasses of the ternary system BaOB2O3P2O5 were prepared and studied in broad concentration limits covering the whole vitrification domain: 20–50 mol% BaO, 0–40 mol% B2O3 and 20–60 mol% P2O5. Their structure was studied with combinations of Raman spectroscopy, 31P MAS NMR spectroscopy and 11B MAS NMR spectroscopy. The obtained results are discussed in several compositional lines A: (100-x)Ba(PO3)2xB2O3, B: 40BaOyB2O3(60-y)P2O5, C: (50-z)BaOzB2O350P2O5, D: (60-w)BaOwB2O340P2O5 and E: uBaO40B2O3(60-u)P2O5. Boron oxide incorporates into the phosphate network in the form of BO4 and BO3 groups and increases their glass transition temperature. Nevertheless, the increase in Tg is only steep within the region of 0–20 mol% B2O3 reaching a maximum at the glasses with ∼30 mol% B2O3. In the lines A, B and E a decrease in the P2O5 and an increase of B2O3 content results in the shortening of phosphate chains with decreasing P2O5 content; these changes are most pronounced in line B with a constant BaO content. In lines C and D with a constant P2O5 content a decrease in the BaO content results, in contrast, in the reverse transformation of phosphate structural units in the direction Q1 → Q2 → Q3 as detected from Raman spectra and 31P MAS NMR spectra. 11B MAS NMR spectra revealed that only BO4 units are present in the glasses with 0–20 mol% B2O3. In the glasses of the E series the fraction of BO3 units increases with a decreasing P2O5 content. By the decomposition of the 11B MAS NMR spectra it is possible to estimate the fractions of basic structural units formed by boron - B(OP)3O, B(OP)2O2 and BO3 in all the glasses of the glass forming region.

Formation of Mixed Bond‐Angle Linkages in Zinc Boromolybdate Glasses

The short and medium range structure of glassy MoO3–ZnO–B2O3 has been studied by neutron diffraction and reverse Monte Carlo simulation. The partial atomic pair correlation functions and coordination numbers are presented that are not yet reported for this system. We have established that the first neighbor distances do not depend on concentration within limit of error, the actual values are rB‐O = 1.38 Å, rMo‐O = 1.72 Å, and rZn‐O = 1.97 Å. It is found that ZnO takes part in the glassy structure as network former, as ZnO4 tetrahedral are linked both to MoO4 and to BO3 and BO4 groups. It is revealed that BO4/BO3 increases with increasing B2O3 content. We have found that only small amount of boroxol ring is present, BO3 and BO4 groups are organized into superstructure units, and a small part is in isolated BO3 triangles. The BO3 and BO4 units are linked to MoO4 or ZnO4 forming mixed [4]Mo‐O‐[3]B, [4]Mo‐O‐[4]B, [4]Mo‐O‐[4]Zn, [3]B‐O‐[4]Zn, [4]B‐O‐[4]Zn bond linkages.

Tailoring order–disorder temperature and microwave dielectric properties of Ba[(Co0.6Zn0.4)1/3Nb2/3]O3 ceramics

The order–disorder temperature (To–d) of Ba[(Co0.6Zn0.4)1/3Nb2/3]O3 ceramics was determined via X-ray diffraction, Raman spectroscopy and differential thermal analysis, respectively. To–d was determined to be between 1425 and 1450 °C by a quenching method. The endothermic peak in the DTA curve shows the order–disorder transition. B2O3 was applied to tune the densification temperature (Ts) and tailor the microwave dielectric properties. The ordering degree and unloaded quality factor (Qf) are improved when Ts is reduced to 1400 °C at B2O3 content of 0.25 mol%. Ts is further decreased and the ordering degree and Qf are decreased when B2O3 content is increased to 0.5 mol%. The dielectric constant (εr) and temperature coefficient of resonant frequency (τf) decrease slightly with increasing B2O3 content. The optimum microwave dielectric properties (i.e., εr = 34.0, Qf = 50,400 GHz, τf = 5.5 × 10−6/°C) are obtained for the Ba[(Co0.6Zn0.4)1/3Nb2/3]O3-0.25 mol% B2O3 ceramics sintered at a lower temperature.

Thermal behavior and the properties of BaO–B2O3–P2O5 glasses

Borophosphate glasses of the BaO–B2O3–P2O5 ternary system were prepared and studied within the large glass-forming region of the system. Fourteen investigated glass samples of barium borophosphate glasses were discussed for a comparison of the compositional trends in their properties in four compositional series such as A: (100 − x)Ba(PO3)2–xB2O3, B: 40BaO–yB2O3–(60 − y)P2O5, C: (50 − z)BaO–zB2O3–50P2O5, and D: (60 − w)BaO–wB2O3–40P2O5. Changes in glass density and molar volume primarily depend on the BaO content in the glasses. The thermal properties were studied with a differential thermal analysis, hot-stage microscopy, and dilatometry. Glass transition temperature increases with a rising B2O3 content most rapidly in the glass series A and B. It reaches its maximum in these series for the glasses containing 20–30 mol%, where the glass network represents a 3D structure interlinked with P–O–B, P–O–P, and B–O–B bridges. The thermal expansion coefficient decreases, in contrast, with the increasing B2O3 content in these ternary glasses as well as their chemical durability. The crystallization of these glasses, in the samples with a low B2O3 content, results in the formation of barium metaphosphate BaP2O6. Certain crystallized samples also contain a small amount of BPO4, and diffraction lines of ternary compounds BaBPO5 and Ba3B(PO4)3 were revealed in a number of samples. A new compound of the composition Ba5B2P8O28 was identified in the crystallized glass 50BaO–10B2O3–40P2O5.

Modification of the Structure of Ti-Bearing Mold Flux by the Simultaneous Addition of B2O3 and Na2O

The present paper mainly focused on how B2O3 and Na2O additions influenced the structure of the Ti-bearing fluoride-free mold flux and investigated how the boron-related units were affected by Na2O. Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, 11B magic angle spinning-nuclear magnetic resonance (MAS-NMR), and X-ray photoelectron spectroscopy (XPS) were utilized to identify different structural units and to analyze the overall modification of the network by additives. It was found that BO3 was more abundant than BO4 in the flux. In addition, the addition of B2O3 and Na2O was proved to promote conversion from non-ring BO3 to tetrahedral BO4, and this was confirmed by FTIR and 11B MAS NMR analysis. BO3 was a two-dimensional structure unit and contributed to construct a less stable network. With increasing B2O3 content, degree of polymerization of the flux was increased as confirmed by increased fraction of Q 3 in Raman spectra and non-bridging oxygen in XPS. By contrast, the addition of Na2O, which is a strong network breaker, brought about more non-bridging oxygen by breaking the Si-O-Si linkage which was verified by XPS results. Consequently, a less polymerized network was observed by decreasing content of Q 3 from Raman spectra.

Effect of boron oxide addition on the viscosity-temperature behaviour and structure of phosphate-based glasses.

In this study, nine phosphate-based glass formulations from the system P2 O5 -CaO-Na2 O-MgO-B2 O3 were prepared with P2 O5 content fixed as 40, 45 and 50 mol%, where Na2 O was replaced by 5 and 10 mol% B2 O3 and MgO and CaO were fixed to 24 and 16 mol%, respectively. The effect of B2 O3 addition on the viscosity-temperature behaviour, fragility index and structure of the glasses was investigated. The composition of the glasses was confirmed by ICP-AES. The viscosity-temperature behaviour of the glasses were measured using beam-bending and parallel -plate viscometers. The viscosity of the glasses investigated was found to shift to higher temperature with increasing B2 O3 content. The kinetic fragility parameter, m and F1/2 , estimated from the viscosity curve were found to decease with increasing B2 O3 content. The structural analysis was achieved by a combination of Fourier transform infrared spectroscopy and solid state nuclear magnetic resonance. 31 P solid-state magic-angle-spinning nuclear magnetic resonance (MAS-NMR) showed that the local structure of the glasses changes with increasing B2 O3 content. As B2 O3 was added to the glass systems, the phosphate connectivity increases as the as the Q1 units transforms into Q2 units. The 11 B NMR results confirmed the presence of tetrahedral boron (BO4 ) units for all the compositions investigated. Structural analysis indicates an increasing level of cross-linking with increasing B2 O3 content. Evidence of the presence of P-O-B bonds was also observed from the FTIR and 31 P NMR analysis. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 764-777, 2017.

Influence of B2O3and Basicity on Viscosity and Structure of Medium Titanium Bearing Blast Furnace Slag

The effects of B2O3and basicity (CaO/SiO2) on the viscous behavior and structure of medium titanium bearing blast furnace slag (MTBBFS) were investigated. High temperature viscosimeter was applied to measure the viscosities of CaO-SiO2-MgO-TiO2-Al2O3-B2O3slag system and X-ray diffraction (XRD), NBO/T ratio, and structure parameterQwere employed to analyze its network structure. The results showed that the viscosity decreased and break point temperature increased with increasing basicity to 1.20. However B2O3addition gave rise to a decrease in slag viscosity and break point temperature inspite of basicity. The more B2O3content leads to the more pronounced variation, especially for the slag with larger basicity. The conventional NBO/T formula was revised to predict the structure variation of relatively complicated medium Ti bearing slag based on the work of Yanhong Gao and other researchers. The increase of B2O3content in slag made parameterQturn fromQ2toQ1, suggesting that network structure became simpler. It was also noticed that the addition of B2O3could suppress the formation of perovskite.

Short-range and Medium-range Structural Order in CaO–SiO<sub>2</sub>–TiO<sub>2</sub>–B<sub>2</sub>O<sub>3</sub> Glasses

The present study aimed to provide a deep insight of short-range and medium-range structural order for CaO-SiO2-TiO2-B2O3 glasses. From various prospects, four techniques, FTIR, Raman, XPS and NMR, were simultaneously employed and only the direct evidences indicated from the spectra were used for structural analysis. The FTIR and Raman spectra proved that the main silicon-related units were Q(0)(Si), Q(2)(Si) and Q(3)(Si) and the results of Raman fittings revealed that a B2O3 addition resulted in an increase of Q(1)(Si) and Q(3)(Si) at the cost of Q(0)(Si) and Q(2)(Si), thus inducing an increasing Degree of Polymerization (DOP). An enhanced DOP generally implied a lower abundance of non-bridging oxygen in the networks, which was further demonstrated by the O1s XPS fittings. Additionally, the B-11 NMR spectra indicated that the dominant boron-related groups were BO3 trigonal comprising ring and non-ring BO3 as well as BO4 tetrahedral comprising BO4(1B,3Si) and BO4(0B,4Si). Furthermore, it was clarified that an increase of B2O3 content promoted the ratios of BO4(1B,3Si) to BO4(0B,4Si) and BO4 tetrahedral to BO3 trigonal, which undoubtedly identified the occurrence of an equilibrium reaction between NBO, BO4 tetrahedral and BO3 trigonal in the glass.

Effects of B2O3 content and sintering temperature on crystallization and microstructure of CBS glass–ceramic coatings

Borosilicate glass–ceramics precursors with varying compositional ratios in the CaO–SiO2–B2O3 (CBS) system were synthesized by sol–gel method. The precursors were calcined at 1200°C for 2h to form glass powders. The glass–ceramics were prepared by overlaying glass slurries on the substrates before sintering at different temperatures. The as-prepared glasses and glass–ceramics were characterized by differential scanning calorimetry and X-ray diffraction. The crystallization activation energies (Ec) were calculated using the Kissinger method from DSC results. The morphology and crystallization behavior of the glass–ceramics were monitored by scanning electron microscopy. Both glass transition and crystallization temperatures decreased, however, the metastable zone increased. The Ec values of CBS glasses and glass–ceramics were 254.1, 173.2 and 164.4kJ/mol with increasing B2O3 content, whereas that of the calcined G3 glass was 104.9kJ/mol. Finally, the coatings were prepared at a low temperature (700°C). The crystals that grew on the surface of multilayer coatings demonstrated heterogeneous surface nucleation and crystallization after heat-treatment from 700°C to 850°C for 4h.

Crystallization and properties of B2O3 doped LZAS vitrified bond for diamond grinding tools

The effects of B2O3 on the crystallization and properties of Li2O–ZnO–Al2O3–SiO2 (LZAS) vitrified bonds were investigated for diamond grinding tool application. The results show that the [BO3] in the glass structure increased with increasing B2O3 content. The glass transition temperature and the first crystallization peak temperature decreased, while the second crystallization peak temperature increased with increasing B2O3 content. The increase in B2O3 content has a little influence on the value of Avrami exponent (n), keeping two-dimensional crystal growth mechanism. Realized composite with 8mol% B2O3 of LZAS vitrified bond has a higher crystal volume fraction and a uniform sphere-shaped microstructure. Moreover, vitrified bond B8 exhibits a high bending strength (198MPa), a good chemical durability (20days, DR=3.1×10−9g/cm2min), an appropriate TEC (4.63×10−6/°C) and a good wettability to diamond abrasives, suggesting that it would be a promising material for diamond grinding tool.

Processing and characterization of novel borophosphate glasses and fibers for medical applications

In this paper, we investigate the effect of P2O5 substitution by B2O3 in the (50−x)P2O5·20CaO·20SrO·10Na2O·x B2O3 glass system (x from 0 to 5mol%) on the thermal and structural properties and also on the glass reactivity in simulated body fluid. The goal is to develop new glass candidates for biomedical glass fibers. The addition of B2O3 at the expense of P2O5 increases the refractive index of the glass and also the thermal stability of the glass indicating that these glasses are promising glasses for fiber drawing. Thus, within such glass composition, the core of a core–clad fiber has a larger concentration of B2O3 than the clad of the fiber to enable the light to propagate inside the core. All the investigated glasses form a calcium phosphate layer at their surface when immersed in simulated body fluid. It was found that small addition of B2O3 (1.25mol%) leads to a decrease in the initial dissolution rate and a delayed layer formation. However, with increasing B2O3 content, the chemical durability decreased slightly but was higher than for the B-free glass. In addition, formation of the calcium phosphate layer was further delayed. This suggests that small contents of B2O3 led to formation of P–O–B bonds and only few BO4 units, increasing the chemical durability. At higher B2O3 contents, the amount of BO4 units increases which makes the glass network slightly more prone to be hydrolyzed. Thus, formation of BO4 units induced by the addition of B2O3 at the expense of P2O5 reduces the reactivity of the glass in SBF. Borophosphate fibers were successfully drawn from preform. As expected from the bioresponse of the bulk glasses in simulated body fluid, the reduction in the intensity of the light transmitted is less and slower in a borophosphate fiber than in a phosphate fiber upon immersion.

Grain growth kinetics for B2O3-doped ZnO ceramics

Abstract Grain growth kinetics in 0.1 to 2 mol % B2O3-added ZnO ceramics was studied by using a simplified phenomenological grain growth kinetics equation Gn = K0 · t · exp(-Q/RT) together with the physical properties of sintered samples. The samples, prepared by conventional ceramics processing techniques, were sintered at temperatures between 1050 to 1250 °C for 1, 2, 3, 5 and 10 hours in air. The kinetic grain growth exponent value (n) and the activation energy for the grain growth of the 0.1 mol % B2O3-doped ZnO ceramics were found to be 2.8 and 332 kJ/mol, respectively. By increasing B2O3 content to 1 mol %, the grain growth exponent value (n) and the activation energy decreased to 2 and 238 kJ/mol, respectively. The XRD study revealed the presence of a second phase, Zn3B2O6 formed when the B2O3 content was > 1 mol %. The formation of Zn3B2O6 phase gave rise to an increase of the grain growth kinetic exponent and the grain growth activation energy. The kinetic grain growth exponent value (n) and the activation energy for the grain growth of the 2 mol % B2O3-doped ZnO ceramics were found to be 3 and 307 kJ/mol, respectively. This can be attributed to the second particle drag (pinning) mechanism in the liquid phase sintering.

Cation Diffusivity and the Mixed Network Former Effect in Borosilicate Glasses

Understanding the structural origins of cationic diffusion processes in silicate glasses is important for high-tech applications of silicate glasses. For glasses with more than one network former, transport properties such as diffusivity are often nonlinear functions of the particular distribution of these network formers, a phenomenon known as the mixed network former effect. Here, we investigate the sodium-potassium interdiffusion (D̅Na-K) and the calcium inward diffusion (DCa) in soda lime borosilicate glasses with varying silica/borate ratio but constant modifier content. Indeed, the structural organization of borosilicate glasses results in a pronounced nonlinear composition dependence of D̅Na-K and DCa (i.e., the mixed network former effect). Initial addition of B2O3 to the glass system results in a significant decrease in both diffusivities, whereas the change in diffusivity per mole of added B2O3 decreases with increasing B2O3 concentration. Besides the influences of water content and atomic packing degree, we find that 99% of the composition dependence of log D̅Na-K can be ascribed to the change in concentration of tetrahedral boron groups. This indicates that the formation of BO4/2 groups slows down diffusion processes of alkali and alkaline earth ions. Therefore, the mixed network former effect of the studied glass series is linked with the change of the concentration of tetrahedral boron groups, which is caused by the interactions between the different types of network formers.

Structural Roles of Boron and Silicon in the CaO-SiO2-B2O3 Glasses Using FTIR, Raman, and NMR Spectroscopy

The present paper provided not only a deep insight of network structures of borosilicate glasses but also a basic linkage between the network structures and the viscous flow behaviors of many borosilicate melts. The structures of a ternary system of CaO-SiO2-B2O3 were characterized using Fourier transformation infrared (FTIR), Raman, and magic angular spinning nuclear magnetic resonance spectroscopy. The results of FTIR and Raman spectra complementally verified that the main Si-related units were SiO4 tetrahedral with zero, one, two, and three bridging oxygens [Q0(Si), Q1(Si), Q2(Si), and Q3(Si)]; the added B2O3 leaded to an increase of Q3(Si) at the cost of Q0(Si) and Q2(Si), and therefore an increasing degree of polymerization (DOP) was induced. Additionally, the 11B NMR spectra demonstrated that the dominant B-related groups were BO3 trigonal and BO4 tetrahedral, while an increasing B2O3 content facilitated the existence of BO4 tetrahedral. Moreover, there was a competitive effect between the enhanced DOP and the presence of BO3 trigonal and BO4 tetrahedral in the networks, which therefore resulted in a decreasing viscosity of borosilicate melts in numerous studies.

Physical, structural and optical characterizations of borate modified bismuth–silicate–tellurite glasses

Quaternary bismuthate glasses with compositions xB2O3–(80−x) Bi2O3–15SiO2–5TeO2 have been prepared by melt-quench technique. X-ray diffraction studies were performed to ascertain the amorphous nature of samples. The density, molar volume and crystalline volume decrease with increase in B2O3 content whereas the glass transition temperature shows the reverse trend. The Raman and FTIR spectra of the studied glasses indicate that B2O3 has been found to exist in the form of BO3 trigonal and BO4 tetrahedral structural units and vibrations corresponding to these structural units increase with increase in B2O3 content. SiO2 is present in the form of SiO4 tetrahedral structural units and TeO2 in the form of TeO3 structural units. Bismuth plays the role of network modifier [BiO6 octahedra] as well as network former [BiO3 pyramids] for all the glass compositions. The optical band gap energy has been calculated from the fitting of both Mott and Davis’s model and Hydrogenic excitonic model with the experimentally observed absorption spectra. A good fitting of experimental data with HEM indicates the excitonic formation in the studies glass system. The values of optical band gap energy show nonlinear behavior due to the structural changes that take place in the present glass samples. The Urbach energy calculated using Urbach empirical formula for studied glass samples suggest the possibility of reduction in defect concentrations. The metallization criterion of the presently studied samples suggests that the prepared glasses may be potential candidates for nonlinear optical applications.

Influence of B2O3and TiO2on Viscosity of Titanium-Bearing Blast Furnace Slag

The viscous behavior of CaO–SiO2–MgO–TiO2–Al2O3–B2O3 blast furnace (BF) slag system was studied. The effects of the B2O3 and the TiO2 on the viscosity and break point temperature, as well as the correlations of the properties with the slag structure were analyzed. According to the experiment results, an increase in the TiO2 content tended to enhance the slag viscosity and break point temperature of the slag due to the formation of perovskite, whereas B2O3 had an opposite effect on them. In addition, increasing B2O3 content seems to be more effective in affecting the viscosity compared to TiO2 additions. Depolymerization of the slag after adding B2O3 should be attributed to decrease in the quantities of perovskite.

In vitro bioactivity evaluation, mechanical properties and microstructural characterization of Na2O–CaO–B2O3–P2O5 glasses

Na2O–CaO–B2O3–P2O5 glasses have been prepared by the melt-quenching method. B2O3 content was systematically increased from 5 to 30mol%, at the expense of P2O5, in the chemical composition of these glasses. Density, Vickers microhardness and fracture toughness of the prepared glasses were measured. In vitro bioactivity of the glasses was assessed by soaking in the simulated body fluid (SBF) at 37±0.5°C for 3, 7, 14 and 30days. The glasses were tested in the form of glass grains as well as bulk slabs. The structure and composition of the solid reaction products were analyzed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The kinetics of degradation of the glass particles were monitored by measuring the weight loss of the particles and the ionic concentration of Ca, P and B in the SBF solution using inductive coupled plasma-atomic emission spectroscopy (ICP-AES). The obtained results revealed the formation of a bioactive hydroxyapatite (HA) layer, composed of nano-crystallites, on the surface of glass grains after the in vitro assays. The results have been used to understand the formation of HA as a function of glass composition and soaking time in the SBF. It can be pointed out that increasing B2O3 content in glass composition enhances the bioactivity of glasses. The nanometric particle size of the formed HA and in vitro bioactivity of the studied glasses make them possible candidates for tissue engineering application.