Glasses and glass ceramics in the system xCeO<sub>2·</sub>(50 - x)PbO·50B<sub>2</sub>O<sub>3</sub> (0 ≤ x ≤ 50) have been studied, for the first time, by NMR a...Glasses and glass ceramics in the system xCeO<sub>2·</sub>(50 - x)PbO·50B<sub>2</sub>O<sub>3</sub> (0 ≤ x ≤ 50) have been studied, for the first time, by NMR and FTIR techniques. Effect of CeO<sub>2</sub> substitution with PbO on NMR parameters has been discussed in terms of changing both boron and cerium coordination. The quantitative fraction of four coordinated boron (N<sub>4</sub>) has been simply determined from <sup>11</sup>B NMR spectroscopy. On the other hand, the fraction of total tetrahedral structural units B<sub>4</sub> (BO<sub>4</sub> + PbO<sub>4</sub> + CeO<sub>4</sub>) is obtained from FTIR spectral analysis. It is not possible to get the fraction of cerium oxide directly from the applied spectroscopic tools. Therefore, a simple approach is applied, for the first time, to determine CeO<sub>4</sub> fraction by using the different criteria of both <sup>11</sup>B NMR and FTIR spectroscopy. The fraction of B<sub>4</sub> species is equal to N<sub>4</sub>, within the experimental error, of the same glasses in the composition region of up to 10 mol% CeO<sub>2</sub>. On the other hand, there is a clear difference between both N<sub>4</sub> and B<sub>4</sub> values in glasses of higher CeO<sub>2 </sub>content (>10 mol%). The related difference showed a linear increasing trend with increasing the content of CeO<sub>2</sub> in the glass. This was discussed on the bases of structural role of CeO<sub>2</sub> which acts as a glass former in the region >10 mol%, while, at lower concentration, it consumed as a glass modifier.展开更多
The structure of borosilicate glasses of composition 30Na<sub>2</sub>O-2Al<sub>2</sub>O<sub>3</sub>-25SiO<sub>2</sub>-xFe<sub>2</sub>O<sub>3</sub>...The structure of borosilicate glasses of composition 30Na<sub>2</sub>O-2Al<sub>2</sub>O<sub>3</sub>-25SiO<sub>2</sub>-xFe<sub>2</sub>O<sub>3</sub><sub></sub> (43-x) B<sub>2</sub>O<sub>3</sub> has been investigated in the composition range of 0.5 20 mol% Fe<sub>2</sub>O<sub>3</sub>. <sup>27</sup>Al, <sup>11</sup>B, <sup>29 </sup>Si MAS NMR and FTIR spectroscopies have been used to measure the fraction of different structural species in the glasses. It is evidenced from NMR data that both sodium and Fe<sub>2</sub>O<sub>3</sub> (in low region up to 7 mol%) are the main glass modifier. Structural determination for borosilicate glasses with a high content of (Fe<sub>2</sub>O<sub>3</sub>) was carried out by FTIR spectroscopy, where both <sup>11</sup>B and <sup>29</sup>Si MAS NMR are impossible because of the high quantities of paramagnetic iron (III) species present. NMR analysis was performed on borosilicate glasses containing up to 7 mol% Fe<sub>2</sub>O<sub>3</sub> and the N<sub>4</sub> values obtained by FTIR spectroscopy agree within error with the <sup>11</sup>B NMR results of the same glass samples. Fe<sub>2</sub>O<sub>3</sub> is a main glass modifier in the low-Fe<sub>2</sub>O<sub>3</sub>-content region (≤6 mol%). On other hand, it plays the role of glass former at higher content of Fe<sub>2</sub>O<sub>3</sub>. Increasing both N<sub>4 </sub>of boron tetrahedral units and chemical shift of silicon nuclei to reach maxima at 5 mol% Fe<sub>2</sub>O<sub>3</sub> confirms the role of Fe<sub>2</sub>O<sub>3</sub> as a glass modifier in the low composition region. On the other hand, fast decrease in N<sub>4</sub> with further increasing Fe<sub>2</sub>O<sub>3</sub> contents ≥6 mol%) is an evidence for iron oxide to inter the glass network as a network former.展开更多
A new type of cerium borate glass-ceramic is prepared and studied. The microstructure and crystallization behaviors of the glass samples were investigated by X-ray diffraction (XRD), electron diffraction (ED), and <...A new type of cerium borate glass-ceramic is prepared and studied. The microstructure and crystallization behaviors of the glass samples were investigated by X-ray diffraction (XRD), electron diffraction (ED), and <sup><span style="font-size:12px;font-family:Verdana;">31</span></sup><span style="font-family:Verdana;">P NMR spectroscopy. The microstructures of samples contain <1 mol% CeO</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">are amorphous in nature. More addition of CeO</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> transforms the glass to glass-ceramics without thermal annealing. The morphological change of the microstructure of these materials was followed by transmission electron microscopy (TEM). The obtained results have revealed that the addition of more than 0.8 mol% CeO</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> can promote nucleation and crystallization routes that </span></span><span style="font-family:Verdana;">are </span><span style="font-family:;" "=""><span style="font-family:Verdana;">combined with the establishment of diverse crystalline phases. Glasses with lower contents of CeO</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">showed no tendency to crystallization. The crystals of CeO</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> containing glasses were spheroid like morphology that </span></span><span style="font-family:Verdana;">was </span><span style="font-family:Verdana;">assigned to the three-dimensional fast growth of the well-formed structural species in the boro-apatite phase. In addition, the cerium free glass is characterized by particle-like morphology. Then the growth of spheroid species展开更多
This work is aimed to shed light on <span style="font-family:;" "="">the </span><span style="font-family:;" "="">dielectric behavior of CuO containin...This work is aimed to shed light on <span style="font-family:;" "="">the </span><span style="font-family:;" "="">dielectric behavior of CuO containing glasses, since no publications concerning this issue have been presented before. Different glasses in the binary Na<sub>2</sub>O-B<sub>2</sub>O<sub>3</sub> system<sub> </sub>were prepared by melt annealing technique. XRD spectra have shown that the amorphous structure is dominant in all glasses containing mixed concentrations from CuO and Na<sub>2</sub>O. The crystalline phases appeared only in glass free from Na<sub>2</sub>O. The dielectric spectroscopy is applied to shed some light on the conduction mechanisms in terms of changing both the dielectric constant and the electrical modulus of the investigated glasses. The ac conductivity increases with increasing frequency and decreases with increasing CuO concentration. Both the dielectric constant and dissipation loss </span><span style="font-family:;" "="">is</span><span style="font-family:;" "=""> decreased with increasing frequency. Correlated barrier hopping (CBH) is considered an appropriate conduction mechanism results from the increase of frequency.</span>展开更多
Glasses in the system 24.5Na<sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O·24.5CaO·6P</span>...Glasses in the system 24.5Na<sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O·24.5CaO·6P</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-size:12px;font-family:Verdana;">5</span></sub><span style="font-family:Verdana;">·xSrO·(45-x)SiO</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> have been</span><span style="font-family:;" "=""><span style="font-family:Verdana;"> studied in the composition region of x = 0 - 15 mol%. The as prepared glasses are transparent and have an amorphous network structure. On the otherhand, heat treated glasses are transformed to opaque white glass ceramic characterized by their highly crystalline network structure. Crystalline apatite (calcium phosphate, Ca</span><sub><span style="font-size:12px;font-family:Verdana;">3</span></sub><span style="font-family:Verdana;">(PO</span><sub><span style="font-size:12px;font-family:Verdana;">4</span></sub><span style="font-family:Verdana;">)</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">, wollastonite (calcium silicate, CaSiO</span><sub><span style="font-size:12px;font-family:Verdana;">3</span></sub><span style="font-family:Verdana;">), and strontium calcium phosphate</span></span><span style="font-family:Verdana;"> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">Ca</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">Sr(PO</span><sub><span style="font-size:12px;font-family:Verdana;">4</span></sub><span style="font-family:Verdana;">)</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> </span></span><span style="font-family:;" "=""><span style="font-family:Verdana;">are the main well-formed crystalline species played the major role in m展开更多
Cerium oxide has a great capacity to remove nonbridging oxygen atoms (NBO) from the glass network and serves as glass former units. The well formed CeO<sub>4</sub> units played the role of decreasing NBO f...Cerium oxide has a great capacity to remove nonbridging oxygen atoms (NBO) from the glass network and serves as glass former units. The well formed CeO<sub>4</sub> units played the role of decreasing NBO from the silicate network and cause a reduction in the concentration of tetrahedral boron groups (N<sub>4</sub>). The highest content of NBO in glass of lower CeO<sub>2</sub> (1 mol%) has a dominant role in constructing crystalline clusters in the glass. Higher CeO<sub>2</sub> concentration leads to formation of an amorphous glass network as documented by XRD and TEM-EDP spectra. Coordination of cerium with oxygen atoms gives uniform units of spherical morphology in the pure CeO<sub>2</sub> as well as in cerium rich glass. Clustered species has a great benefit in the field of application, used as a shielding material for ionized radiations.展开更多
文摘Glasses and glass ceramics in the system xCeO<sub>2·</sub>(50 - x)PbO·50B<sub>2</sub>O<sub>3</sub> (0 ≤ x ≤ 50) have been studied, for the first time, by NMR and FTIR techniques. Effect of CeO<sub>2</sub> substitution with PbO on NMR parameters has been discussed in terms of changing both boron and cerium coordination. The quantitative fraction of four coordinated boron (N<sub>4</sub>) has been simply determined from <sup>11</sup>B NMR spectroscopy. On the other hand, the fraction of total tetrahedral structural units B<sub>4</sub> (BO<sub>4</sub> + PbO<sub>4</sub> + CeO<sub>4</sub>) is obtained from FTIR spectral analysis. It is not possible to get the fraction of cerium oxide directly from the applied spectroscopic tools. Therefore, a simple approach is applied, for the first time, to determine CeO<sub>4</sub> fraction by using the different criteria of both <sup>11</sup>B NMR and FTIR spectroscopy. The fraction of B<sub>4</sub> species is equal to N<sub>4</sub>, within the experimental error, of the same glasses in the composition region of up to 10 mol% CeO<sub>2</sub>. On the other hand, there is a clear difference between both N<sub>4</sub> and B<sub>4</sub> values in glasses of higher CeO<sub>2 </sub>content (>10 mol%). The related difference showed a linear increasing trend with increasing the content of CeO<sub>2</sub> in the glass. This was discussed on the bases of structural role of CeO<sub>2</sub> which acts as a glass former in the region >10 mol%, while, at lower concentration, it consumed as a glass modifier.
文摘The structure of borosilicate glasses of composition 30Na<sub>2</sub>O-2Al<sub>2</sub>O<sub>3</sub>-25SiO<sub>2</sub>-xFe<sub>2</sub>O<sub>3</sub><sub></sub> (43-x) B<sub>2</sub>O<sub>3</sub> has been investigated in the composition range of 0.5 20 mol% Fe<sub>2</sub>O<sub>3</sub>. <sup>27</sup>Al, <sup>11</sup>B, <sup>29 </sup>Si MAS NMR and FTIR spectroscopies have been used to measure the fraction of different structural species in the glasses. It is evidenced from NMR data that both sodium and Fe<sub>2</sub>O<sub>3</sub> (in low region up to 7 mol%) are the main glass modifier. Structural determination for borosilicate glasses with a high content of (Fe<sub>2</sub>O<sub>3</sub>) was carried out by FTIR spectroscopy, where both <sup>11</sup>B and <sup>29</sup>Si MAS NMR are impossible because of the high quantities of paramagnetic iron (III) species present. NMR analysis was performed on borosilicate glasses containing up to 7 mol% Fe<sub>2</sub>O<sub>3</sub> and the N<sub>4</sub> values obtained by FTIR spectroscopy agree within error with the <sup>11</sup>B NMR results of the same glass samples. Fe<sub>2</sub>O<sub>3</sub> is a main glass modifier in the low-Fe<sub>2</sub>O<sub>3</sub>-content region (≤6 mol%). On other hand, it plays the role of glass former at higher content of Fe<sub>2</sub>O<sub>3</sub>. Increasing both N<sub>4 </sub>of boron tetrahedral units and chemical shift of silicon nuclei to reach maxima at 5 mol% Fe<sub>2</sub>O<sub>3</sub> confirms the role of Fe<sub>2</sub>O<sub>3</sub> as a glass modifier in the low composition region. On the other hand, fast decrease in N<sub>4</sub> with further increasing Fe<sub>2</sub>O<sub>3</sub> contents ≥6 mol%) is an evidence for iron oxide to inter the glass network as a network former.
文摘A new type of cerium borate glass-ceramic is prepared and studied. The microstructure and crystallization behaviors of the glass samples were investigated by X-ray diffraction (XRD), electron diffraction (ED), and <sup><span style="font-size:12px;font-family:Verdana;">31</span></sup><span style="font-family:Verdana;">P NMR spectroscopy. The microstructures of samples contain <1 mol% CeO</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">are amorphous in nature. More addition of CeO</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> transforms the glass to glass-ceramics without thermal annealing. The morphological change of the microstructure of these materials was followed by transmission electron microscopy (TEM). The obtained results have revealed that the addition of more than 0.8 mol% CeO</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> can promote nucleation and crystallization routes that </span></span><span style="font-family:Verdana;">are </span><span style="font-family:;" "=""><span style="font-family:Verdana;">combined with the establishment of diverse crystalline phases. Glasses with lower contents of CeO</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">showed no tendency to crystallization. The crystals of CeO</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> containing glasses were spheroid like morphology that </span></span><span style="font-family:Verdana;">was </span><span style="font-family:Verdana;">assigned to the three-dimensional fast growth of the well-formed structural species in the boro-apatite phase. In addition, the cerium free glass is characterized by particle-like morphology. Then the growth of spheroid species
文摘This work is aimed to shed light on <span style="font-family:;" "="">the </span><span style="font-family:;" "="">dielectric behavior of CuO containing glasses, since no publications concerning this issue have been presented before. Different glasses in the binary Na<sub>2</sub>O-B<sub>2</sub>O<sub>3</sub> system<sub> </sub>were prepared by melt annealing technique. XRD spectra have shown that the amorphous structure is dominant in all glasses containing mixed concentrations from CuO and Na<sub>2</sub>O. The crystalline phases appeared only in glass free from Na<sub>2</sub>O. The dielectric spectroscopy is applied to shed some light on the conduction mechanisms in terms of changing both the dielectric constant and the electrical modulus of the investigated glasses. The ac conductivity increases with increasing frequency and decreases with increasing CuO concentration. Both the dielectric constant and dissipation loss </span><span style="font-family:;" "="">is</span><span style="font-family:;" "=""> decreased with increasing frequency. Correlated barrier hopping (CBH) is considered an appropriate conduction mechanism results from the increase of frequency.</span>
文摘Glasses in the system 24.5Na<sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O·24.5CaO·6P</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-size:12px;font-family:Verdana;">5</span></sub><span style="font-family:Verdana;">·xSrO·(45-x)SiO</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> have been</span><span style="font-family:;" "=""><span style="font-family:Verdana;"> studied in the composition region of x = 0 - 15 mol%. The as prepared glasses are transparent and have an amorphous network structure. On the otherhand, heat treated glasses are transformed to opaque white glass ceramic characterized by their highly crystalline network structure. Crystalline apatite (calcium phosphate, Ca</span><sub><span style="font-size:12px;font-family:Verdana;">3</span></sub><span style="font-family:Verdana;">(PO</span><sub><span style="font-size:12px;font-family:Verdana;">4</span></sub><span style="font-family:Verdana;">)</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">, wollastonite (calcium silicate, CaSiO</span><sub><span style="font-size:12px;font-family:Verdana;">3</span></sub><span style="font-family:Verdana;">), and strontium calcium phosphate</span></span><span style="font-family:Verdana;"> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">Ca</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">Sr(PO</span><sub><span style="font-size:12px;font-family:Verdana;">4</span></sub><span style="font-family:Verdana;">)</span><sub><span style="font-size:12px;font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> </span></span><span style="font-family:;" "=""><span style="font-family:Verdana;">are the main well-formed crystalline species played the major role in m
文摘Cerium oxide has a great capacity to remove nonbridging oxygen atoms (NBO) from the glass network and serves as glass former units. The well formed CeO<sub>4</sub> units played the role of decreasing NBO from the silicate network and cause a reduction in the concentration of tetrahedral boron groups (N<sub>4</sub>). The highest content of NBO in glass of lower CeO<sub>2</sub> (1 mol%) has a dominant role in constructing crystalline clusters in the glass. Higher CeO<sub>2</sub> concentration leads to formation of an amorphous glass network as documented by XRD and TEM-EDP spectra. Coordination of cerium with oxygen atoms gives uniform units of spherical morphology in the pure CeO<sub>2</sub> as well as in cerium rich glass. Clustered species has a great benefit in the field of application, used as a shielding material for ionized radiations.
