<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE article  PUBLIC "-//NLM//DTD Journal Publishing DTD v3.0 20080202//EN" "http://dtd.nlm.nih.gov/publishing/3.0/journalpublishing3.dtd"><article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" dtd-version="3.0" xml:lang="en" article-type="research article"><front><journal-meta><journal-id journal-id-type="publisher-id">AMPC</journal-id><journal-title-group><journal-title>Advances in Materials Physics and Chemistry</journal-title></journal-title-group><issn pub-type="epub">2162-531X</issn><publisher><publisher-name>Scientific Research Publishing</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.4236/ampc.2020.1012024</article-id><article-id pub-id-type="publisher-id">AMPC-106083</article-id><article-categories><subj-group subj-group-type="heading"><subject>Articles</subject></subj-group><subj-group subj-group-type="Discipline-v2"><subject>Chemistry&amp;Materials Science</subject><subject> Physics&amp;Mathematics</subject></subj-group></article-categories><title-group><article-title>
 
 
  Chemical Durability, Structure Properties and Bioactivity of Glasses 48P&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;5&lt;/SUB&gt;-30CaO-(22&amp;#8722;x)Na&lt;SUB&gt;2&lt;/SUB&gt;O-xTiO&lt;SUB&gt;2&lt;/SUB&gt;(With 0 &lt; x ≤ 3; mol%)
 
</article-title></title-group><contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Yassine</surname><given-names>Er-Rouissi</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Sara</surname><given-names>Aqdim</given-names></name><xref ref-type="aff" rid="aff2"><sup>2</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Abdeslam</surname><given-names>El Bouari</given-names></name><xref ref-type="aff" rid="aff2"><sup>2</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Fouzia</surname><given-names>Hmimid</given-names></name><xref ref-type="aff" rid="aff3"><sup>3</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Said</surname><given-names>Aqdim</given-names></name><xref ref-type="aff" rid="aff4"><sup>4</sup></xref><xref ref-type="corresp" rid="cor1"><sup>*</sup></xref></contrib></contrib-group><aff id="aff3"><addr-line>Department of Biology, Faculty of Science, Laboratory Health &amp;amp; Environment, Hassan II University Ain Chock, Casablanca, Morocco</addr-line></aff><aff id="aff2"><addr-line>Faculty of Sciences Ben-M’sik, Laboratory Physical-Chemistry of Applied Materials, Hassan II University, Casablanca, Morocco</addr-line></aff><aff id="aff4"><addr-line>Department of Chemistry, Faculty of Science, Mineral Chemistry Laboratory, Hassan II University Ain Chock, Casablanca, Morocco</addr-line></aff><aff id="aff1"><addr-line>Faculty of Sciences, Laboratory of Materials Engineering for Environment and Valorization, Hassan II University Ain Chock, Casablanca, Morocco</addr-line></aff><pub-date pub-type="epub"><day>24</day><month>12</month><year>2020</year></pub-date><volume>10</volume><issue>12</issue><fpage>305</fpage><lpage>318</lpage><history><date date-type="received"><day>10,</day>	<month>October</month>	<year>2020</year></date><date date-type="rev-recd"><day>21,</day>	<month>December</month>	<year>2020</year>	</date><date date-type="accepted"><day>24,</day>	<month>December</month>	<year>2020</year></date></history><permissions><copyright-statement>&#169; Copyright  2014 by authors and Scientific Research Publishing Inc. </copyright-statement><copyright-year>2014</copyright-year><license><license-p>This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/</license-p></license></permissions><abstract><p>
 
 
  Phosphate glasses of composition 48P
  <sub>2</sub>O
  <sub>5</sub>-30CaO-(22
  &amp;#8722;x)Na
  <sub>2</sub>O-xTiO
  <sub>2</sub> (with 0 &lt; x ≤ 3, mol%) were prepared by direct melting at 1080
  &amp;#176;C &#177; 20
  &amp;#176;C. The chemical durability of these glasses shows an improvement when the Ti
  O
  <sub style="white-space:normal;">2</sub> content varies from 0 to 2 mol%. The measurements of differential thermal analysis and density, both, indicate the increase of the glass transition temperature and the density. The increase of Tg leads to an improvement of glass rigidity. X-ray diffraction analysis of the glasses annealed at 650
  &amp;#176;C for 48 h, indicates the appearance of a mixture of metaphosphate and pyrophosphate phases when the Ti
  O
  <sub style="white-space:normal;">2</sub> content varies from 0 to 2 mol%, the last become majority when the Ti
  O
  <sub style="white-space:normal;">2</sub> content rich 2 mol%. Nevertheless, when the Ti
  O
  <sub style="white-space:normal;">2</sub> content exceeds 2 mol%, the analysis, both, by infrared spectroscopy and X-ray diffraction, reveals a radical change of structure with the formation of majorities isolated orthophosphate groups. SEM micrographs illustrated that the number of crystallites increased in the glass network when the Ti
  O
  <sub style="white-space:normal;">2</sub> content increased at the expense of the Na
  <sub>2</sub>O content. An increase in the TiO
  <sub>2</sub> content beyond 2 mol% led to the formation of a larger number of crystallites of different sizes, dominated by small crystallite sizes assigned to majority isolated short orthophosphate groups. This phenomenon led to a decrease in chemical durability and seems to be the main cause promoting the bioactivity of glasses. The results of the bioactivity, after a test in an SBF physiological solution within 15 days, shows, both, the formation of hydroxyapatite and tricalcium phosphate layers, in addition to the layer Ca
  <sub>2</sub>P
  <sub>2</sub>O
  <sub>7</sub>, known by its bioactivity, in some samples. The results obtained on the glasses studied make them potential candidates for an application in tissue engineering.
 
</p></abstract><kwd-group><kwd>Chemical Durability</kwd><kwd> Phosphate Glasses</kwd><kwd> Titan Oxide</kwd><kwd> Bioactivity</kwd><kwd> SBF</kwd></kwd-group></article-meta></front><body><sec id="s1"><title>1. Introduction</title><p>Several studies have been carried out on phosphate-based glasses as promising materials for various applications in all fields. The properties of phosphate glasses such as low melting point, high thermal expansion coefficient, sealing materials and bioactivity, including the concept of the biomaterials degradation, make them potential candidates for many technological applications [<xref ref-type="bibr" rid="scirp.106083-ref1">1</xref>] - [<xref ref-type="bibr" rid="scirp.106083-ref11">11</xref>]. The bioactivity of phosphate glasses and in particular the property of being completely dissolved in aqueous medium; this degradation concept can be controlled by modifying the intermediate oxides so that the latter are in congruence with the chemical durability and can be used for glasses rich in phosphate and calcium applied as biomaterials [<xref ref-type="bibr" rid="scirp.106083-ref11">11</xref>] - [<xref ref-type="bibr" rid="scirp.106083-ref17">17</xref>]. Calcium phosphate glasses and glass ceramics in the orthophosphate region (CaO/P<sub>2</sub>O<sub>5</sub> = 0.5 - 2) [<xref ref-type="bibr" rid="scirp.106083-ref18">18</xref>] were obtained by using of other oxides such as Na<sub>2</sub>O, Al<sub>2</sub>O<sub>3</sub>, Fe<sub>2</sub>O<sub>3</sub>, ZnO, MgO, TiO<sub>2</sub>, which can easily depolymerize P<sub>2</sub>O<sub>5</sub> oxide from long ultraphosphate (O/P = 2.5) chains to isolated short orthophosphate chains (O/P = 4). Our goal is to develop bioactive glasses, focusing particularly on the effect of the substitution of TiO<sub>2</sub> to calcium phosphate oxide glasses for use in the medical field. The study of composition glasses 48P<sub>2</sub>O<sub>5</sub>-30CaO-(22−x)Na<sub>2</sub>O-xTiO<sub>2</sub> (with 0 &lt; x ≤ 3; mol%) as a function of the TiO<sub>2</sub> content has shown a rigidity of the glass network in congruence with its biodegradability. The increase in the TiO<sub>2</sub> content (with 0 &lt; x ≤ 2; mol%) in the glass network entrained an increase of the chemical durability, and Tg, followed by an important change from metaphosphate (Q<sup>2</sup>) to pyrophosphate structural units (Q<sup>1</sup>). When the TiO<sub>2</sub> content beyond 2 mol%, the chemical durability undergo a slow decrease and the structure evolve toward majority isolated short orthophosphate units (Q<sup>0</sup>), confirmed by IR spectrum and X-Ray diffraction, SEM micrographs illustrated that the number of crystallites increased in the glass network when the TiO<sub>2</sub> content increased at the expense of the Na<sub>2</sub>O content. This indicates that we are near the border between the glass and the crystal [<xref ref-type="bibr" rid="scirp.106083-ref15">15</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref19">19</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref20">20</xref>]. The chemical reactivity of these materials was evaluated after immersion in the simulated body fluid (SBF) at 37˚C for 15 days. The analysis results seem important for the beginning of the glasses bioactivity.</p></sec><sec id="s2"><title>2. Experimental Section</title><p>Phosphate glasses are prepared by direct melting of the (NH<sub>4</sub>)H<sub>2</sub>PO<sub>4</sub>, CaCO<sub>3</sub>, Na<sub>2</sub>O, TiO<sub>2</sub> mixture in suitable proportions. The reagents are intimately crushed then introduced into a porcelain crucible. Then, they are heated initially at 300˚C for 2 h and then at 500˚C for 1h to complete the decomposition. The reaction mixture is then heated at 900˚C. For 40 minutes and finally at 1080˚C. For 30 minutes in order to obtain a homogeneous liquid. Then it is cast in an aluminum plate previously heated to 200˚C to avoid thermal shock. Pellets 5 to 10 mm in diameter and 1 to 3 mm thick are obtained. The samples were then immersed in distilled water at 90˚C for 20 days to determine the dissolution rate evaluated from the mass loss as a function of time. Analysis by IR spectroscopy was done in a frequency range of between 400 and 1600 cm<sup>−1</sup> with a resolution of 2 cm<sup>−1</sup>, using a Fourier transform spectrometer. The vitreous state was first evidenced from the shiny and transparency aspect, which was then confirmed by X-ray diffraction (XRD) patterns. Samples glasses were analyzed by X-ray diffraction after an annealing time of 48 h at 650˚C. Differential thermal analysis (DTA) was performed using a Perkin-Elmer DTA7, at a heating rate of 10˚C/min in a flowing nitrogen atmosphere (30 cm<sup>3</sup>/mn) with alumina crucibles. The Archimedes method was used to measure the density of glasses using orthophthalate as a floating medium. The microstructures of the sample glasses were characterised by scanning electron microscopy (SEM), equipped with a full system micro-analyser (EDX-EDAX). Glass powder of each sample was soaked in SBF solution at 37˚C for 21 days.</p></sec><sec id="s3"><title>3. Results and Discussion</title><sec id="s3_1"><title>3.1. Chemical Durability<sup> </sup></title><p>The glass series 48P<sub>2</sub>O<sub>5</sub>-30CaO-(22−x)Na<sub>2</sub>O-xTiO<sub>2</sub> (with 0 &lt; x ≤ 3 mol%), was approximated by measuring the dissolution rate (DR) which was defined as the weight loss of the glass expressed in terms g∙cm<sup>−</sup><sup>2</sup>∙mn<sup>−</sup><sup>1</sup>. The DR values reported in <xref ref-type="table" rid="table1">Table 1</xref> show a dissolution decrease versus TiO<sub>2</sub> contents between 0.5 and 2 mole %, after their immersion in 100 ml of distilled water, heated at 90˚C for 21 consecutive days (<xref ref-type="fig" rid="fig1">Figure 1</xref>). However, when the TiO<sub>2</sub> content exceeds 2 mol%, there is a relatively significant increase in the dissolution rate. The value</p><table-wrap id="table1" ><label><xref ref-type="table" rid="table1">Table 1</xref></label><caption><title> The composition and some characteristics of the quaternary glasses 48P<sub>2</sub>O<sub>5</sub>-30CaO-(22−x)Na<sub>2</sub>O-xTiO<sub>2 </sub>(with 0 &lt; x ≤ 3; mol%)</title></caption><table><tbody><thead><tr><th align="center" valign="middle"  rowspan="2"  >Glass Sample</th><th align="center" valign="middle"  colspan="4"  >Starting Oxide mixtures mol %</th><th align="center" valign="middle"  rowspan="2"  >[O/P] Ratio</th><th align="center" valign="middle"  rowspan="2"  >log (D<sub>R</sub>) (g∙cm<sup>−</sup><sup>2</sup>∙min<sup>−</sup><sup>1</sup>) (&#177;0.2)</th><th align="center" valign="middle" >Tg (˚C)</th><th align="center" valign="middle" >Tc (˚C)</th></tr></thead><tr><td align="center" valign="middle" >P<sub>2</sub>O<sub>5</sub></td><td align="center" valign="middle" >CaO</td><td align="center" valign="middle" >Na<sub>2</sub>O</td><td align="center" valign="middle" >TiO<sub>2</sub></td><td align="center" valign="middle"  colspan="2"  >(&#177;2)</td></tr><tr><td align="center" valign="middle" >48T05</td><td align="center" valign="middle" >48</td><td align="center" valign="middle" >30</td><td align="center" valign="middle" >21.5</td><td align="center" valign="middle" >0.5</td><td align="center" valign="middle" >3046</td><td align="center" valign="middle" >−4.9</td><td align="center" valign="middle" >405</td><td align="center" valign="middle" >495</td></tr><tr><td align="center" valign="middle" >48T10</td><td align="center" valign="middle" >48</td><td align="center" valign="middle" >30</td><td align="center" valign="middle" >21</td><td align="center" valign="middle" >1</td><td align="center" valign="middle" >3052</td><td align="center" valign="middle" >−5.1</td><td align="center" valign="middle" >449</td><td align="center" valign="middle" >498</td></tr><tr><td align="center" valign="middle" >48T15</td><td align="center" valign="middle" >48</td><td align="center" valign="middle" >30</td><td align="center" valign="middle" >20.5</td><td align="center" valign="middle" >1.5</td><td align="center" valign="middle" >3057</td><td align="center" valign="middle" >−5.7</td><td align="center" valign="middle" >473</td><td align="center" valign="middle" >525</td></tr><tr><td align="center" valign="middle" >48T20</td><td align="center" valign="middle" >48</td><td align="center" valign="middle" >30</td><td align="center" valign="middle" >20</td><td align="center" valign="middle" >2</td><td align="center" valign="middle" >3062</td><td align="center" valign="middle" >−6.05</td><td align="center" valign="middle" >476</td><td align="center" valign="middle" >540</td></tr><tr><td align="center" valign="middle" >48T25</td><td align="center" valign="middle" >48</td><td align="center" valign="middle" >30</td><td align="center" valign="middle" >19.5</td><td align="center" valign="middle" >2.5</td><td align="center" valign="middle" >3067</td><td align="center" valign="middle" >−5.9</td><td align="center" valign="middle" >430</td><td align="center" valign="middle" >490</td></tr><tr><td align="center" valign="middle" >48T30</td><td align="center" valign="middle" >48</td><td align="center" valign="middle" >30</td><td align="center" valign="middle" >19</td><td align="center" valign="middle" >3</td><td align="center" valign="middle" >3072</td><td align="center" valign="middle" >−5.5</td><td align="center" valign="middle" >450</td><td align="center" valign="middle" >496</td></tr></tbody></table></table-wrap><p>of leached pH, for different samples, after 21 days, is represented as a function of the TiO<sub>2</sub> content (<xref ref-type="fig" rid="fig2">Figure 2</xref>), it indicates that the pH of the solution varies in a range between 3 and 7 &#177; 0.5, values which correspond to the leached pH of a bioactive glass [<xref ref-type="bibr" rid="scirp.106083-ref18">18</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref21">21</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref22">22</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref23">23</xref>].</p></sec><sec id="s3_2"><title>3.2. Density and Molar Volumes</title><p>The Archimedes principle was used to measure the density of glasses using orthophthalate as a floating medium. The density of the glasses was obtained by using the relation (1),</p><p>ρ = [ m air m air + m ortho − m ( ortho + glass ) ] ρ ortho (1)</p><p>With: m<sub>air</sub>: the mass of the sample measured in the area.</p><p>m<sub>ortho</sub>: Orthophthalate mass only.</p><p>m<sub>(</sub><sub>ortho+glass</sub><sub>)</sub>: Mass of glass immersed in diethyl orthophthalate.</p><p>ρ<sub>ortho</sub>: 1.11422 g∙cm<sup>−3</sup>.</p><p>The density variation of composition glasses are represented in <xref ref-type="fig" rid="fig2">Figure 2</xref>. The molar volume and the anionic radius of the oxygen in the glass were determined respectively from the relationships (2) and (3):</p><p>V 0 M = M / ρ N A N 0 ∗ (2)</p><p>r c a l ( O = ) = 3 V 0 M / 2 (3)</p><p>With M = molar mass, ρ = density, N<sub>A</sub> = Avogadro number; N 0 ∗ number of oxygen atoms in the molecular formula. The value of the molar volume and the oxygen radius were calculated from the approximate hypothesis of close packing of oxygen anions O<sup>2−</sup>, having r(O<sup>2−</sup>) recapitulated for each composition in <xref ref-type="table" rid="table2">Table 2</xref> [<xref ref-type="bibr" rid="scirp.106083-ref1">1</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref15">15</xref>]. As can be seen from <xref ref-type="fig" rid="fig3">Figure 3</xref>, density increased with TiO<sub>2</sub> content at the expense of Na<sub>2</sub>O. This seems obvious since the molar mass of titanium oxide is greater than that of sodium oxide. However, when the TiO<sub>2</sub> content becomes greater than 2 mol%, a decrease in the density is noted [<xref ref-type="bibr" rid="scirp.106083-ref9">9</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref13">13</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref14">14</xref>].</p><table-wrap id="table2" ><label><xref ref-type="table" rid="table2">Table 2</xref></label><caption><title> Glass composition expressed in terms of quaternary system</title></caption><table><tbody><thead><tr><th align="center" valign="middle" >Glass sample Code</th><th align="center" valign="middle" >Chemical compositions (mol%)</th><th align="center" valign="middle" >Glass compositions inside the ternary diagram</th></tr></thead><tr><td align="center" valign="middle" >48T05</td><td align="center" valign="middle" >48P<sub>2</sub>O<sub>5</sub>∙30CaO∙21.5Na<sub>2</sub>O∙0.5TiO<sub>2</sub></td><td align="center" valign="middle" >0.3173(Na<sub>2</sub>O∙P<sub>2</sub>O<sub>5</sub>)∙0.0096(TiO<sub>2</sub>∙P<sub>2</sub>O<sub>5</sub>)∙0.6731(CaO∙P<sub>2</sub>O<sub>5</sub>)</td></tr><tr><td align="center" valign="middle" >48T10</td><td align="center" valign="middle" >48P<sub>2</sub>O<sub>5</sub>∙30CaO∙21Na<sub>2</sub>O∙1TiO<sub>2</sub></td><td align="center" valign="middle" >0.3077 (Na<sub>2</sub>O∙P<sub>2</sub>O<sub>5</sub>)∙0.0192(TiO<sub>2</sub>∙P<sub>2</sub>O<sub>5</sub>)∙0.6731(CaO∙P<sub>2</sub>O<sub>5</sub>)</td></tr><tr><td align="center" valign="middle" >48T15</td><td align="center" valign="middle" >48P<sub>2</sub>O<sub>5</sub>∙30CaO∙20.5Na<sub>2</sub>O∙1.5TiO<sub>2</sub></td><td align="center" valign="middle" >0.2982(Na<sub>2</sub>O∙P<sub>2</sub>O<sub>5</sub>)∙0.02887(TiO<sub>2</sub>∙P<sub>2</sub>O<sub>5</sub>)∙0.6731(CaO∙P<sub>2</sub>O<sub>5</sub>)</td></tr><tr><td align="center" valign="middle" >48T20</td><td align="center" valign="middle" >48P<sub>2</sub>O<sub>5</sub>∙30CaO∙20Na<sub>2</sub>O∙2TiO<sub>2</sub></td><td align="center" valign="middle" >0.2884(Na<sub>2</sub>O∙P<sub>2</sub>O<sub>5</sub>)∙0.0385(TiO<sub>2</sub>∙P<sub>2</sub>O<sub>5</sub>)∙0.6731(CaO∙P<sub>2</sub>O<sub>5</sub>)</td></tr><tr><td align="center" valign="middle" >48T25</td><td align="center" valign="middle" >48P<sub>2</sub>O<sub>5</sub>∙30CaO∙19.5Na<sub>2</sub>O∙2.5TiO<sub>2</sub></td><td align="center" valign="middle" >0.2788(Na<sub>2</sub>O∙P<sub>2</sub>O<sub>5</sub>)∙0.0481(TiO<sub>2</sub>∙P<sub>2</sub>O<sub>5</sub>)∙0.6731(CaO∙P<sub>2</sub>O<sub>5</sub>)</td></tr><tr><td align="center" valign="middle" >48T30</td><td align="center" valign="middle" >48P<sub>2</sub>O<sub>5</sub>∙30CaO∙19Na<sub>2</sub>O∙3TiO<sub>2</sub></td><td align="center" valign="middle" >0.26923(Na<sub>2</sub>O∙P<sub>2</sub>O<sub>5</sub>)∙0.0576(TiO<sub>2</sub>∙P<sub>2</sub>O<sub>5</sub>)∙0.6731(CaO∙P<sub>2</sub>O<sub>5</sub>)</td></tr></tbody></table></table-wrap></sec><sec id="s3_3"><title>3.3. Infra-Red Spectra</title><p>The infrared spectra of 48P<sub>2</sub>O<sub>5</sub>-30CaO-(22−x)Na<sub>2</sub>O-xTiO<sub>2</sub> series glasses (with 0 &lt; x ≤ 3) are shown in <xref ref-type="fig" rid="fig4">Figure 4</xref>. All the vibration bands of the treated samples are in the frequency range from 1400 to 400 cm<sup>−</sup><sup>1</sup>. Analysis of the infrared spectra obtained for all the glasses shows a wide band at around 510 cm<sup>−1</sup> attributed to the vibration mode of the skeleton δ (P-O-P) [<xref ref-type="bibr" rid="scirp.106083-ref1">1</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref3">3</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref9">9</xref>]. The vibration bands located around 754 - 784 cm<sup>−1</sup> are attributed to the vibration mode Ѵsym (P-O-P)</p><p>of pyrophosphate groups (Q<sup>1</sup>), while the bands at around 1094 cm<sup>−1</sup> and 1267 cm<sup>−1</sup> are respectively assigned to the Ѵsym (PO<sub>2</sub>)/Ѵasy (PO<sub>3</sub>) of pyrophosphate groups (Q<sup>1</sup>) and vibration mode Ѵasy (PO<sub>2</sub>) of metaphosphate groups (Q<sup>2</sup>) [<xref ref-type="bibr" rid="scirp.106083-ref2">2</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref4">4</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref5">5</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref9">9</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref12">12</xref>]. The band at around 1150 cm<sup>−1</sup>, attributed to the stretching vibration Ѵsym (PO<sub>2</sub>) in Q<sup>1</sup> - Q<sup>2</sup> units, appears when the TiO<sub>2</sub> content increased in the glass network [<xref ref-type="bibr" rid="scirp.106083-ref4">4</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref9">9</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref12">12</xref>], while the intensity of the band 1267 cm<sup>−1</sup> attributed to metaphosphates groups (Q<sup>2</sup>) decreased. In the other hand, the band at 880 - 917 cm<sup>−1</sup>, attributed to asymmetric vibration Ѵasy (P-O-P) in the Q<sup>1</sup> unit, shift to high frequencies as the TiO<sub>2</sub> content increased in the network glass [<xref ref-type="bibr" rid="scirp.106083-ref2">2</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref4">4</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref5">5</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref9">9</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref15">15</xref>]. However, the characteristic vibration band of Ѵsym ( PO 4 3 − ) in the Q<sup>0</sup> unit, located around 994 cm<sup>−1</sup>, appeared when the TiO<sub>2</sub> content becomes greater than 1.5 mol%, while the band at 1094 cm<sup>−1</sup>, attributed to the Ѵsym (PO<sub>2</sub>)/Ѵasy (PO<sub>3</sub>) vibration mode of pyrophosphate groups, becomes smaller and smaller [<xref ref-type="bibr" rid="scirp.106083-ref9">9</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref24">24</xref>]. Furthermore, the structure deduced from vibrational spectroscopy is compatible with the localization analysis of the compounds (45T05, 45T10, 45T15) inside the ternary diagram given in <xref ref-type="fig" rid="fig5">Figure 5</xref> and <xref ref-type="table" rid="table3">Table 3</xref>. However, when the TiO<sub>2</sub> content increased beyond 1.5 mole% (45T20, 45T25), we noticed the appearance, in addition to the olygophopshate groups (Q<sup>1</sup> - Q<sup>2</sup>), of isolated short ortho phosphate groups (Q˚) [<xref ref-type="bibr" rid="scirp.106083-ref16">16</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref25">25</xref>] which indicated the approach of the border area between glass and crystal, this can be explained by several factors (high T<sub>f</sub> of TiO<sub>2</sub>, crystallite level in the glass bath, Ti + Ca/P ratio) [<xref ref-type="bibr" rid="scirp.106083-ref15">15</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref20">20</xref>].</p><table-wrap id="table3" ><label><xref ref-type="table" rid="table3">Table 3</xref></label><caption><title> Density and related molar data of the 48P<sub>2</sub>O<sub>5</sub>-30CaO-(22−x)Na<sub>2</sub>O-xTiO<sub>2</sub> system</title></caption><table><tbody><thead><tr><th align="center" valign="middle"  rowspan="2"  >Glass sample code</th><th align="center" valign="middle"  colspan="4"  >Starting oxide mixtures mol %</th><th align="center" valign="middle"  rowspan="2"  >ρ (g∙cm<sup>−</sup><sup>3</sup>) (&#177;0.01)</th><th align="center" valign="middle"  rowspan="2"  >Molar mass (g∙mol<sup>−</sup><sup>1</sup>)</th><th align="center" valign="middle"  rowspan="2"  >Molar volume (&#197;3) Vo<sub>M</sub> = M/[ρ N<sub>A</sub> No*]</th><th align="center" valign="middle"  rowspan="2"  >Calculated oxygen radius (&#197;) r<sub>cal</sub> (O<sup>2</sup><sup>−</sup>)</th></tr></thead><tr><td align="center" valign="middle" >P<sub>2</sub>O<sub>5</sub></td><td align="center" valign="middle" >CaO</td><td align="center" valign="middle" >Na<sub>2</sub>O</td><td align="center" valign="middle" >TiO<sub>2</sub></td></tr><tr><td align="center" valign="middle" >48T05</td><td align="center" valign="middle" >48</td><td align="center" valign="middle" >30</td><td align="center" valign="middle" >21.5</td><td align="center" valign="middle" >0.5</td><td align="center" valign="middle" >2.57</td><td align="center" valign="middle" >98,719</td><td align="center" valign="middle" >21.81</td><td align="center" valign="middle" >1397</td></tr><tr><td align="center" valign="middle" >48T10</td><td align="center" valign="middle" >48</td><td align="center" valign="middle" >30</td><td align="center" valign="middle" >21</td><td align="center" valign="middle" >1</td><td align="center" valign="middle" >2.59</td><td align="center" valign="middle" >98,809</td><td align="center" valign="middle" >21.58</td><td align="center" valign="middle" >1392</td></tr><tr><td align="center" valign="middle" >48T15</td><td align="center" valign="middle" >48</td><td align="center" valign="middle" >30</td><td align="center" valign="middle" >20.5</td><td align="center" valign="middle" >1.5</td><td align="center" valign="middle" >2.60</td><td align="center" valign="middle" >98,898</td><td align="center" valign="middle" >21.52</td><td align="center" valign="middle" >1390</td></tr><tr><td align="center" valign="middle" >48T20</td><td align="center" valign="middle" >48</td><td align="center" valign="middle" >30</td><td align="center" valign="middle" >20</td><td align="center" valign="middle" >2</td><td align="center" valign="middle" >2.61</td><td align="center" valign="middle" >98,988</td><td align="center" valign="middle" >21.40</td><td align="center" valign="middle" >1388</td></tr><tr><td align="center" valign="middle" >48T25</td><td align="center" valign="middle" >48</td><td align="center" valign="middle" >30</td><td align="center" valign="middle" >19.5</td><td align="center" valign="middle" >2.5</td><td align="center" valign="middle" >2.59</td><td align="center" valign="middle" >990,775</td><td align="center" valign="middle" >21.55</td><td align="center" valign="middle" >1391</td></tr><tr><td align="center" valign="middle" >48T30</td><td align="center" valign="middle" >48</td><td align="center" valign="middle" >30</td><td align="center" valign="middle" >19</td><td align="center" valign="middle" >3</td><td align="center" valign="middle" >2.58</td><td align="center" valign="middle" >101,564</td><td align="center" valign="middle" >22.13</td><td align="center" valign="middle" >1403</td></tr></tbody></table></table-wrap></sec><sec id="s3_4"><title>3.4. X-Ray Diffraction and DTA</title><p>As expected, X-ray crystallography confirmed the vitreous nature of all the investigated glass samples studied. In fact, X-ray diffraction pattern (XRD) recordings show the absence of diffraction peaks. DSC of the glasses (<xref ref-type="fig" rid="fig6">Figure 6</xref>) indicates both an increase in the glass transition temperature and the crystallization temperature versus Ti<sub>2</sub>O content. When the Ti<sub>2</sub>O content increases from 0.5 to 2 mol%, the glass transition temperature (Tg) increases in the 405˚C - 476˚C range, whereas the crystallization temperature (Tc) increases in the 495˚C - 540˚C range (see <xref ref-type="table" rid="table1">Table 1</xref>) [<xref ref-type="bibr" rid="scirp.106083-ref24">24</xref>]. Beyond 2 mole %, the glass transition temperature (Tg) and the crystallisation temperature Tc undergo, respectively, a decrease from 476˚C to 430˚C and from 540˚C to 490˚C. The heat treatment of the 48T15, 48T20 and 48T25 glasses at 650, gives the XRD patterns shown in <xref ref-type="fig" rid="fig7">Figure 7</xref>. These spectra show a structural evolution from metaphosphate to pyrophosphate</p><p>and finally to orthophosphates phases. When the 48T15 sample was thermally treated at 650˚C, the amorphous phase partially disappeared and majority Ti(PO<sub>3</sub>)<sub>3</sub> [JCPDS files N˚: 01-082-1178], NaCa(PO<sub>3</sub>)<sub>3</sub> [JCPDS files N˚: 00-23-0669], Na<sub>4</sub>Ca(PO<sub>3</sub>)<sub>6</sub>, [JCPDS files N˚: 00-025-0811] and CaP<sub>2</sub>O<sub>6</sub> [JCPDS files N˚: 00-015-0204] (cyclic metaphosphate O/P = 3), with minor Ca<sub>2</sub>P<sub>2</sub>O<sub>7</sub> [JCDDS files N˚: 00-009-0346] and Na<sub>5</sub>Ti<sub>4</sub>(PO<sub>4</sub>)<sub>6</sub> [JCPDS files N˚: 01-081-2420] phases occurred in the sample. When the TiO<sub>2</sub> content increased in the glass (48T20), the heat treatment at 650˚C caused the formation of NaTiP<sub>2</sub>O<sub>7</sub> [JCPDS file N˚: 01-084-1137-], Ca<sub>2</sub>P<sub>2</sub>O<sub>7</sub> [JCPDS file N˚: 00-009-0346] and TiP<sub>2</sub>O<sub>7</sub> [JCPDS file N˚00-052-1470] with some trace of metaphosphate and isolated short orthophosphates phases, and indicated the increase of pyrophosphate phases (O/P = 3.5). However, when the TiO<sub>2</sub> content exceeded 2 mol% (48T25), the heat treatment, at the same temperature, indicated the majority formation of Na<sub>5</sub>Ti (PO<sub>4</sub>)<sub>3</sub> [JCPDS file N˚: 01-081-2421] and CaTi<sub>4</sub>(PO<sub>4</sub>)<sub>6</sub> [JCPDS file N˚: 00-053-0740] phases to the detriment of the pyrophosphates and metaphosphate phases [<xref ref-type="bibr" rid="scirp.106083-ref23">23</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref25">25</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref26">26</xref>].</p></sec><sec id="s3_5"><title>3.5. SEM Image Analysed</title><p>The SEM micrograph shows the existence of two phases, one crystalline and the other glassy (<xref ref-type="fig" rid="fig8">Figure 8</xref>). It also indicates the formation of crystalline phase agglomerates of different sizes [<xref ref-type="bibr" rid="scirp.106083-ref2">2</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref15">15</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref21">21</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref24">24</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref25">25</xref>]. Thus, a structural change is observed from <xref ref-type="fig" rid="fig8">Figure 8</xref>(a) to <xref ref-type="fig" rid="fig8">Figure 8</xref>(b) which presumably indicates the</p><p>formation of the predominant cyclic metaphosphate phases. However, when looking at <xref ref-type="fig" rid="fig8">Figure 8</xref>(c) there is a structural mixture between cyclic metaphosphates and, presumably, of short pyrophosphate chains. In <xref ref-type="fig" rid="fig8">Figure 8</xref>(d), there is a radical change in the structure from the pyrophosphate groups towards predominantly isolated shorter orthophosphate groups. Consequently, the increase of TiO<sub>2</sub> content in the glassy network leads to a progressive depolymerization of the cyclic metaphosphate groups towards pyrophosphate groups and finally to isolated short orthophosphate groups [<xref ref-type="bibr" rid="scirp.106083-ref24">24</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref25">25</xref>].</p></sec><sec id="s3_6"><title>3.6.In Vitro Bioactivity of Studies Glasses-Surface Analysis Using X-Ray Diffraction</title><p>The study in vitro bioactivity of the prepared glasses was carried out by analyzing X-ray diffraction spectra of the samples after immersion in the simulated body fluid (SBF) for 15 days at 37˚C. The result showed (<xref ref-type="fig" rid="fig9">Figure 9</xref>) that for the majority of studied glasses there is formation, both, of hydroxyapatite and tricalcium phosphate layers on the surfaces of the samples in addition to the Ca<sub>2</sub>P<sub>2</sub>O<sub>7</sub> phase known by its bioactivity [<xref ref-type="bibr" rid="scirp.106083-ref16">16</xref>]. When the TiO<sub>2</sub> content increases in the glass, the HA and tricalcium phosphate phases become more evident. The number of peaks and their intensities increase, while the peak intensity of the CaP<sub>2</sub>O<sub>7</sub> phase decreases. The peaks of tricalcium phosphate appear at 22.84 and 24.10 (2q) are assigned, respectively, to (241) and (132) reflections [JCPDS file N˚00-033-0297], However the peaks of HA located at 26.40, 28 and 32.83 (2q) assign respectively to (002), (102) and (300) reflections [JCPDS file N˚01-074-0566] [<xref ref-type="bibr" rid="scirp.106083-ref27">27</xref>]. The peaks of Ca<sub>2</sub>P<sub>2</sub>O<sub>7</sub> phase appear at 30 and 31.92 (2q) are assigned respectively to (211) and (123) reflections [JCPDS file N˚00-033-0297].</p><p>A deep analysis of the spectra obtained seems to suggest that the tricalcium phosphate layer is more important than the hydroxyapatite phase when the TiO<sub>2</sub> content reaches 3 mol%.</p></sec></sec><sec id="s4"><title>4. Discussion</title><p>Phosphate glasses of composition 48P<sub>2</sub>O<sub>5</sub>-30CaO-(22−x)Na<sub>2</sub>O-xTiO<sub>2</sub> (with 0 &lt; x ≤ 3; mol%) have been investigated. The structure and the chemical durability have been studies using various techniques such IR, XRD, DSC, SEM... Both X-ray diffraction and IR spectroscopy have confirmed the structure change from metaphosphate to olygophosphates when the TiO<sub>2</sub> content increases from 0.5 to 2 mol% in the glass. However, beyond 2 mol% of TiO<sub>2</sub>, the appearance of isolated orthophosphates groups is observed. The scanning electron microscope indicated a morphological changing from one cliche to another as the TiO<sub>2</sub> content increased from 0.5 to 2.5 mol%. This change elucidates the passage from cyclic metaphopsphate groups to olygophosphate (mixture meta and pyrophosphate) and finally to isolated short ortho phosphates groups. The variation of transition temperature versus TiO<sub>2</sub> content indicated an increase in Tg from 405˚C to 430˚C when the TiO<sub>2</sub> content increased from 0.5 to 2 mol%, elucidating an improvement in the rigidity of the glass [<xref ref-type="bibr" rid="scirp.106083-ref26">26</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref28">28</xref>]. Beyond 2 mol% TiO<sub>2</sub>, the transition temperature (Tg) decreased from 430˚C to 395˚C, indicating a slight weakness of the glass due to the radical change of structure by the formation, of isolated ortho phosphate groups, confirmed , both, by IR spectroscopy and XRD [<xref ref-type="bibr" rid="scirp.106083-ref12">12</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref15">15</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref20">20</xref>]. The increase of isolated short orthophosphate chains in the glass network, at the expense of olygophosphate chains, when the Ti<sub>2</sub>O content exceeded 2 mol%, can be explained by the fact that we were close to the border area between crystal and glass [<xref ref-type="bibr" rid="scirp.106083-ref15">15</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref20">20</xref>]. The number of crystallites of different sizes generally increased and exceeded the equilibrium that must be established between the glass bath and the crystallites; hence, we note a significant decrease in chemical durability. At the light of the results obtained, both, for chemical durability, X-ray diffraction and IR spectra analysis (D<sub>R</sub> ≈ 10<sup>−</sup><sup>6</sup> g∙cm<sup>−</sup><sup>2</sup>∙min<sup>−</sup><sup>1</sup>, development of isolated orthophosphate groups ( PO 4 3 − ) [<xref ref-type="bibr" rid="scirp.106083-ref20">20</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref23">23</xref>], the chemical reactivity of these materials studied was evaluated after immersion in the simulated body fluid (SBF) at 37˚C for 15 days. Once in contact with the biological fluids (SBF solution), the bioactive glasses presented the particularity of generating a series of physicochemical reaction to the liquid-glass interface [<xref ref-type="bibr" rid="scirp.106083-ref17">17</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref18">18</xref>] [<xref ref-type="bibr" rid="scirp.106083-ref20">20</xref>]. This series of reactions constitutes the mechanism of bioactivity. The XRD spectra, after test in vitro, indicate the formation of a mixture of hydroxyapatite and tricalcium layers in addition of some traces of calcium pyrophosphate phases, known for its bioactivity [<xref ref-type="bibr" rid="scirp.106083-ref25">25</xref>]. An in-depth analysis of the X-ray spectra obtained, after immersion in the simulated body fluid (SBF), showed that, both, the formation of tricalcium phosphate and of hydroxyapatite layers become more important when the TiO<sub>2</sub> content reached 3 mol%, which, further elucidates that the bioactivity of glasses is like to be greatly successful when once the glass composition is close to the border zone between glass and crystal. In addition, bioactivity appeared in all glasses studied, even those which contain traces of isolated short orthophosphate groups (x ≤ 2 mol%), this, probably, proves that these last ones are the triggers of bioactivity in the glasses.</p></sec><sec id="s5"><title>5. Conclusion</title><p>The influence of TiO<sub>2</sub> on the glass forming characteristics and properties of Na<sub>2</sub>O-TiO<sub>2</sub>-CaO-P<sub>2</sub>O<sub>5</sub> glasses has been investigated. The structure and the chemical durability have been studied using various techniques such IR, XRD, DSC, SEM. The variation of the transition temperature versus TiO<sub>2</sub> content indicates an increase in Tg when the TiO<sub>2</sub> content increases and indicates an improvement in the rigidity of the glass. SEM micrograph indicates the existence of two phases one crystalline and the other vitreous. The morphological of the phase crystalline change from one micrograph to another as the TiO<sub>2</sub> content increases from 0.5 to 2.5 mol% and indicates that the structure moves from cyclic metaphosphate and olygophosphate groups to orthophosphate groups. The chemical reactivity of these materials was evaluated after contacting the different glasses with a synthetic physiological fluid (SBF). The XRD spectra of these glasses, after test in vitro, indicate the formation of a mixture of hydroxyapatite and tricalcium layers with some traces of calcium pyrophosphate phases. The presence of these layers is very interested for an eventual biological application in vivo.</p></sec><sec id="s6"><title>Acknowledgements</title><p>The authors wish to thank National Center for Scientific and Technical Research [Division of Technical Support Unit for Scientific Research (TSUSR) Rabat, Morocco] for their assistance to the realization of this work. We also thank Ms. Pr. R. ELOUATIB (Laboratory physic and chemistry of inorganic materials) for the support that has brought us.</p></sec><sec id="s7"><title>Conflicts of Interest</title><p>The authors declare no conflicts of interest regarding the publication of this paper.</p></sec><sec id="s8"><title>Cite this paper</title><p>Er-Rouissi, Y., Aqdim, S., Bouari, A.E., Hmimid, F. and Aqdim, S. (2020) Chemical Durability, Structure Properties and Bioactivity of Glasses 48P<sub>2</sub>O<sub>5</sub>-30CaO-(22−x)Na<sub>2</sub>O-xTiO<sub>2</sub> (With 0 &lt; x ≤ 3; mol%). Advances in Materials Physics and Chemistry, 10, 305-318. https://doi.org/10.4236/ampc.2020.1012024</p></sec></body><back><ref-list><title>References</title><ref id="scirp.106083-ref1"><label>1</label><mixed-citation publication-type="other" xlink:type="simple">Aqdim, S., Sayouty, E.H., Elouadi, B. and Greneche, J.M. (2012) Chemical Durability and Structural Approach of the Glass Series (40-y) Na2O-yFe2O3-5Al2O3-55P2O5-by IR, X-Ray Diffraction and M&amp;#246;ssbauer Spectroscopy. IOP Conference Series: Materials Science and Engineering, 28, 012003. 
https://doi.org/10.1088/1757-899X/28/1/012003</mixed-citation></ref><ref id="scirp.106083-ref2"><label>2</label><mixed-citation publication-type="other" xlink:type="simple">Aqdim, S. and Ouchetto, M. (2013) Elaboration and Structural Investigation of Iron (III) Phosphate Glasses. Advances in Materials Physics and Chemistry, 3, 332-339.  
http://dx.doi.org/10.4236/ampc.2013.38046</mixed-citation></ref><ref id="scirp.106083-ref3"><label>3</label><mixed-citation publication-type="other" xlink:type="simple">Lai, Y.M., Liang, X.F., Yang, S.Y., Wang, J.X. and Zhang, B.T. (2012) Raman Spectra Study of Iron Phosphate Glasses with Sodium Sulfate. Journal of Molecular Structure, 1013, 134-137. https://doi.org/10.1016/j.molstruc.2012.01.025</mixed-citation></ref><ref id="scirp.106083-ref4"><label>4</label><mixed-citation publication-type="other" xlink:type="simple">Morikawa, H., Lee, S., Kasuga, T. and Brauer, D.S. (2013) Effects of for Calcium Substitution in P2O5-CaO-TiO2 Glasses. Journal of Non-Crystalline Solids, 380, 53-59. https://doi.org/10.1016/j.jnoncrysol.2013.08.029</mixed-citation></ref><ref id="scirp.106083-ref5"><label>5</label><mixed-citation publication-type="other" xlink:type="simple">Chabbou, Z. and Aqdim, S. (2014) Chemical Durability and Structural Proprieties of the Vitreous Part of the System xCaO-(40&amp;#8722;x) ZnO-15Na2O-45P2O5. Advances in Materials Physics and Chemistry, 4, 179-186.  
http://dx.doi.org/10.4236/ampc.2014.410021</mixed-citation></ref><ref id="scirp.106083-ref6"><label>6</label><mixed-citation publication-type="other" xlink:type="simple">Bengisu, M., Brow, R.K., Yilmaz, E., Mogu&amp;#353;-Milankovi&amp;#263;, A. and Reis, S.T. (2006) Aluminoborate and Aluminoborosilicate Glasses with High Chemical Durability and the Effect of P2O5 Additions on the Properties. Journal of Non-Crystallinesolids, 352, 3668-3676. https://doi.org/10.1016/j.jnoncrysol.2006.02.118</mixed-citation></ref><ref id="scirp.106083-ref7"><label>7</label><mixed-citation publication-type="other" xlink:type="simple">Day, D.E., Wu, Z., Ray, C.S. and Hrma, P. (1998) Chemically Durable Iron Phosphate Glass Wasteforms. Journal of Non-Crystalline Solids, 241, 1-12. 
https://doi.org/10.1016/S0022-3093(98)00759-5</mixed-citation></ref><ref id="scirp.106083-ref8"><label>8</label><mixed-citation publication-type="other" xlink:type="simple">Bingham, P.A. and Hand, R.J. (2005) Vitrified Metal Finishing Wastes: I. Composition, Density and Chemical Durability. Journal of Hazardous Materials, 119, 125-133. https://doi.org/10.1016/j.jhazmat.2004.11.014</mixed-citation></ref><ref id="scirp.106083-ref9"><label>9</label><mixed-citation publication-type="other" xlink:type="simple">Shaim, A. and Et-Tabirou, M. (2003) Role of Titanium in Sodium Titanophosphate Glasses and a Model of Structural Units. Materials Chemistry and Physics, 80, 63-67. https://doi.org/10.1016/S0254-0584(02)00087-1</mixed-citation></ref><ref id="scirp.106083-ref10"><label>10</label><mixed-citation publication-type="other" xlink:type="simple">McLaughlin, J.C., Tagg, S.L., Zwanziger, J.W., Haeffner, D.R. and Shastri, S.D. (2000) The Structure of Tellurite Glass: A Combined NMR, Neutron Diffraction, and X-Ray Diffraction Study. Journal of Non-Crystalline Solids, 274, 1-8. 
https://doi.org/10.1016/S0022-3093(00)00199-X</mixed-citation></ref><ref id="scirp.106083-ref11"><label>11</label><mixed-citation publication-type="other" xlink:type="simple">Weiss, D.S.L., Torres, R.D., Buchner, S., Blunk, S. and Soares, P. (2014) Effect of Ti and Mg Dopants on the Mechanical Properties, Solubility, and Bioactivity in Vitro of a Sr-Containing Phosphate Based Glass. Journal of Non-Crystalline Solids, 386, 34-38. https://doi.org/10.1016/j.jnoncrysol.2013.11.036</mixed-citation></ref><ref id="scirp.106083-ref12"><label>12</label><mixed-citation publication-type="other" xlink:type="simple">Brow, R.K., Click, C.A. and Alam, T.M. (2000) Modifier Coordination and Phosphate Glass Networks. Journal of Non-Crystalline Solids, 274, 9-16. 
https://doi.org/10.1016/S0022-3093(00)00178-2</mixed-citation></ref><ref id="scirp.106083-ref13"><label>13</label><mixed-citation publication-type="other" xlink:type="simple">Rajendran, V., Devi, A.G., Azooz, M. and El-Batal, F.H. (2007) Physicochemical Studies of Phosphate Based P2O5-Na2O-CaO-TiO2 Glasses for Biomedical Applications. Journal of Non-Crystalline Solids, 353, 77-84. 
https://doi.org/10.1016/j.jnoncrysol.2006.08.047</mixed-citation></ref><ref id="scirp.106083-ref14"><label>14</label><mixed-citation publication-type="other" xlink:type="simple">Kiani, A., Hanna, J.V., King, S.P., Rees, G.J., Smith, M.E., Roohpour, N. and Knowles, J.C. (2012) Structural Characterization and Physical Properties of P2O5-CaO-Na2O-TiO2 Glasses by Fourier Transform Infrared, Raman and Solid-State Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopies. Acta Biomaterial, 8, 333-340. https://doi.org/10.1016/j.actbio.2011.08.025</mixed-citation></ref><ref id="scirp.106083-ref15"><label>15</label><mixed-citation publication-type="other" xlink:type="simple">Errouissi, Y., Z. Chabbou, N. Beloued, S. Aqdim and Aqdim, S. (2017) Chemical Durability and Structural Properties of Al2O3-CaO-Na2O-P2O5 Glasses Studied by IR Spectroscopy, XRD and SEM. Advances in Materials Physics and Chemistry, 7, 353-363. https://doi.org/10.4236/ampc.2017.710028</mixed-citation></ref><ref id="scirp.106083-ref16"><label>16</label><mixed-citation publication-type="other" xlink:type="simple">Moss, R.M., Abou Neel, E.A., Pickup, D.M., Twyman, H.L., Martin, R.A., Henson, M.D., Barney, E.R., Hannon, A.C., Knowles, J.C. and Newport, R.J. (2010) The Effect of Zinc and Titanium on the Structure of Calcium-Sodium Phosphate Based Glass. Journal of Non-Crystalline Solids, 356, 1319-1324. 
https://doi.org/10.1016/j.jnoncrysol.2010.03.006</mixed-citation></ref><ref id="scirp.106083-ref17"><label>17</label><mixed-citation publication-type="other" xlink:type="simple">Pardini, A. (2007) Laboration et Analyses Structurales de Bioactifs Macroporeux. These de Doctorat, Université de Valenciennes et du Hainaut Cambrés, Valenciennes.</mixed-citation></ref><ref id="scirp.106083-ref18"><label>18</label><mixed-citation publication-type="other" xlink:type="simple">Mullier, C. (2011) Synthese et Caracterisation de biomatériaux phosphocalciques multiphases  dopés ou non avec des inhibiteurs de la Résorption Osseuse, These de Doctorat, Faculté des Sciences &amp; Techniques, Université de Nantes, France.</mixed-citation></ref><ref id="scirp.106083-ref19"><label>19</label><mixed-citation publication-type="other" xlink:type="simple">Makhlouk, R., Beloued, N. and Aqdim, S. (2018) Study of Chromium-Lead-Phosphate Glasses by XRD, IR, Density and Chemical Durability. Advances in Materials Physics and Chemistry, 8, 269-280. https://doi.org/10.4236/ampc.2018.86018</mixed-citation></ref><ref id="scirp.106083-ref20"><label>20</label><mixed-citation publication-type="other" xlink:type="simple">Beloued, N., Chabbou, Z. and Aqdim, S. (2016) Correlation between Chemical Durability Behaviour and Structural Approach of the Vitreous Part of the System 55P2O5-2Cr2O3-(43&amp;#8722;x) Na2O-xPbO. Advances in Materials Physics and Chemistry, 6, 149-156. http://dx.doi.org/10.4236/ampc.2016.66016</mixed-citation></ref><ref id="scirp.106083-ref21"><label>21</label><mixed-citation publication-type="other" xlink:type="simple">Lakhkar, N.J., Park, J.-H., Mordan Vehid Salih, N.J., Wall, I.B., Kim, H.-W., King, S.P., Hanna, J.V., Martin, R.A., Addison, O., Mosselmans, J.F.W. and Knowles, J.C. (2012) Titanium Phosphate Glass Microspheres for Bone Tissue Engineering. Acta Biomaterialia, 8, 4181-4190. https://doi.org/10.1016/j.actbio.2012.07.023</mixed-citation></ref><ref id="scirp.106083-ref22"><label>22</label><mixed-citation publication-type="other" xlink:type="simple">Cédric, B. (2008) Elaboration et Caractérisation d’un Hybride Organominéral à Base de Polycaprolactone et de Bioverre sous Forme de Mousse Macroporeuse Pour la Régénération Osseuse. Thèse d’Université, Specialité Sciences des Materiaux, Ecole Doctorale des Sciences Fondamentales, France.</mixed-citation></ref><ref id="scirp.106083-ref23"><label>23</label><mixed-citation publication-type="other" xlink:type="simple">Melba, N., Ginebra, M.-P., Clement, J., Mart&amp;#305;′nez, S., Avila, G. and Planell, J.A. (2003) Physicochemical Degradation of Titania-Stabilized Soluble Phosphate Glasses for Medical Applications. Journal of the American Ceramic Society, 86, 1345-1352.  
https://doi.org/10.1111/j.1151-2916.2003.tb03474.x</mixed-citation></ref><ref id="scirp.106083-ref24"><label>24</label><mixed-citation publication-type="other" xlink:type="simple">Monem, A.S., El Batal, H.A., Khalil, E.M.A., Azooz, M.A. and Hamdy, Y.M. (2008) In Vivo Behavior of Bioactive Phosphate Glass-Ceramics from the System P2O5-Na2O-CaO Containing TiO2. Journal of Materials Science: Materials in Medicine, 19, 1097-1108. https://doi.org/10.1007/s10856-007-3044-3</mixed-citation></ref><ref id="scirp.106083-ref25"><label>25</label><mixed-citation publication-type="other" xlink:type="simple">El Batal, H.A., Khalil, E.M.A. and Hamdy, Y.M. (2008) In Vitro Behavior of Bioactive Phosphate Glass-Ceramics Fromthe System P2O5-Na2O-CaO Containing Titania. Ceramics International, 35, 1195-1204.  
https://doi.org/10.1016/j.ceramint.2008.06.004</mixed-citation></ref><ref id="scirp.106083-ref26"><label>26</label><mixed-citation publication-type="other" xlink:type="simple">Ali Abou Neel, E., Chrzanowski, W. and Campbell Knowles, J. (2008) Effect of Increasing Titanium Dioxide Content on Bulk and Surface Properties of Phosphate-Based Glasses. Acta Biomaterialia, 4, 523-534.  
https://doi.org/10.1016/j.actbio.2007.11.007</mixed-citation></ref><ref id="scirp.106083-ref27"><label>27</label><mixed-citation publication-type="other" xlink:type="simple">Mathew, M., Schroeder, L.W., Dickens, B. and Brown, W.E. (1977) The Crystal Structure of α-Ca3(PO4)2. Acta Crystallographica Section B, 33, 1325-1333. 
https://doi.org/10.1107/S0567740877006037</mixed-citation></ref><ref id="scirp.106083-ref28"><label>28</label><mixed-citation publication-type="other" xlink:type="simple">Beloued, N., Makhlouk, R., Er-Rouissi, Y., Taibi, M., Sajieddine, M. and Aqdim, S. (2019) Relationship between Chemical Durability, Structure and the Ionic-Covalent Character of Me-O-P Bond (Me=Cr, Fe), in the Vitreous Part of the System 60P2O5-2Cr2O3-(38&amp;#8722;x) Na2O-xFe2O3 (with 3≤ x ≤33 mol%). Advances in Materials Physics and Chemistry, 9, 199-209.</mixed-citation></ref></ref-list></back></article>