Mechanical properties and electrochemical behavior of borosilicate glass system

N. Elkhoshkhanya, Fatma Mahgoub a, Ahmed Hefnawya, Mohamed E. Hussein a

a Department of Material Science, Institute of Graduate Studies and Researches, Alexandria University, 163 Horreya Avenue, Shatby 21526, Egypt.

*Corresponding Author:

E-Mail: [email protected]:

New synthesis borosilicate glass in the molar percentages of 50 B2O3 – (14-x) SiO2 – (20+x) Li2O –15 Na2CO3 –1Al2O3, where X=0,1,2,3,4,5 mol % prepared by melt quenching technique .the amorphous nature for the samples of glass has been confirmed by X-ray diffraction (XRD). Fourier transform infrared spectroscopy (FTIR) carried out to explore the glass structural characterization to resolve the problem of the local arrangement structure in all glass samples. Their densities have been determined by the method of Archimedes using toluene as buoyant liquid. Then the molar volume values and the oxygen packing density values were calculated. The ultrasound wave velocities (longitudinal and shear) were measured at room temperature through using the pulse-echo technique and It is used to calculate the experimental elastic moduli of all glass samples. Theoretical models (bond compression and Makishima–Mackenzie models) were calculated to interpret the behavior of experimental elastic moduli. Apply the impedance spectroscopy to follow up the behavior of a borosilicate glass system and deduce the conductance for all samples of a glass system.

Keywords:

Borosilicate glass; Mechanical properties; electrochemical properties; impedance spectroscopy.

Introduction:

The propagation of acoustic waves in bulk glasses has the importance to understand the mechanical properties where some information is given about the microstructure and the dynamics of glasses 1, 2.

The effect of increasing Li2o content and reduction of Sio2 content according to the gradient (From x=0: x=5 mol %) for 50 B2O3 – (14-x) SiO2 – (20+x) Li2O –15 Na2CO3 –1Al2O3 glass system on ultrasonic velocity has been investigated.

Borosilicate glass has many properties of which very low thermal expansion coefficient, resistant to thermal shock, chemically resistant and high softening point 3.

Many authors have studied the structure and the mechanical properties of borosilicate glasses Because of its various physical and chemical properties;inwhich has a wide range of uses including: pharmaceuticals industry, industrial chemical process plants, laboratories, bulbs for high powered lamps, domestic kitchens and in the semiconductor industry through the development of micro electro mechanical systems (MEMS) 4,5 .

The main aim of this work is studying of the mechanical properties and electrochemical behavior of the following glass system:

.50 B2O3 – (14-x) SiO2 – (20+x) Li2O –15 Na2o – 1 Al2O3

Where=0,1,2,3,4,5 mol % to complete the previous studies for a borosilicate glass.

Through measuring both the Longitudinal velocity and the shear velocity and measuring the density , will be evaluation of the longitudinal ,shear, bulk and Young’s moduli, Poisson’s ratio,micro hardness , acoustic impedance , thermal expansion coefficient ,Mean Velocity , Softening Temperature and Theta Debay temperature which will give more information about the structure and rigidity of the glass system6after adding the Li2o content and dropping the Sio2 content at the same time according to the gradient from (X=0 : X=5 mol % ) as will be detailed .

The structure and elastic moduli of a glass system can be evaluated based on initially experimental measurements and then through the theoretical models such as Makishima and Mackenzie model as well as Bond compression model which interpreted qualitatively in terms of the average stretching force constant , the average cross-link density, and the average atomic ring size of the network 1.

In addition to apply the impedance spectroscopy technique to measure the changes and follow up the electrochemical properties of the glass system and exploring the conductance for all glass samples after those structural modifications have occurred 7, 8.

Experimental procedure:

2.1. Preparation of glasses:

Preparation of a borosilicate glass system: 50 B2O3 – (14-X) SiO2 – (20+X) Li2O –15 Na2o – 1 Al2O3 , where X=0,1,2,3,4,5 mol % by weighed the required quantities according to table 1 using a single digital balance of 0.1 mg accuracy ( its type SHIMADZU AX 200 ) , then mixed the chemicals components and repeat the grinding using the mortar to ensure the homogeneity of the mixture which is placed in a platinum crucible and placed in an electric oven to procedure the melting quenching technique at 1040oCfor 20 minutes for each sample from the following samples listed in table 1The molten caste onto a rectangular slab from a preheated stainless-steel mold which has a diameter of 12 mm and a length of 6 mm, then transferred to the annealing furnace at 400oC for two hours to avert the mechanical strains developed during the quenching technique.

After switched off the furnace, allowed the glass samples to cool inside until a room temperature.

By using a lapping machine with 600 grade SiC powder, make the glass surfaces as a parallel opposite faces and polished them by a polishing machine.

2.2. X-ray diffraction study (XRD):

X-ray Diffraction (XRD) used to detect the amorphous nature of glasses 2,9.

An X-ray diffractometer its kind (PW1700: Philips Eindhoven, the New Netherlands) using CuK as a radiation source at a temperature between 20o and 80o

2.3. Spectroscopic study (FTIR):

FTIR spectroscopy carried out to explore the glass structural characterization to resolve the problem of the local arrangement structure in all glass samples.

FTIR spectra are recorded by the Bruker infrared spectrum model Vertex 70V (KBr Beam Spliter). The samples were milled in a mortar to fine powder and well mixid with KBr and pressure to shape transparent pellets which used to get the infrared spectra of the glass samples at room temperature, in range 4000–400 cm–1 wavenumber in absorbance mode. 9,10.

2.4. Density, molar volume and Oxygen Packing Density calculations:

The density (?) of all glass samples was calculated using Archimedes’s Principle through using the toluene as an immersing liquid by the displacement method 11 and applying the following relation:

? =Wawa-wt*?t…… (gcm-3) (1)

Where wa is the weight of a glass sample in air.

, wt is the weight of a glass sample in toluene.

and ?t is the toluene density = 0.864 (g cm-3).

For more accuracy, the measurement was repeated three times

and the densities of all samples were measured to the fourth decimal

(± 0.0004 g/cm3).

Measuring the molar volume (Vm) of the all samples 11 was calculated from the following relation: Vm = M? (2)

Where ? is the density of the glass, and M is the glass molecular weight which equal ? xiMi

Where xi is the mole fraction for the component oxide i.

and Mi is molecular weight for the component oxide i.

As well as are calculated the Oxygen Packing Density {O.P.D} as a relation:

OPD=no. of oxygen atoms in glass sampleVm …… (mol/cm3) (3)

Where (OPD) is oxygen packing density and Vm is the molar volume.

2.5. Ultrasonic velocities measurements:

By using the conventional pulse-echo technique at the room temperature by utilizing the use of 2.25 MHz X-cut and Y-cut adapters , we were obtained The ultrasonic wave velocities through measuring the elapsed time between initiate and receive pulse which appearing on the screen of an ultrasonic flaw detector called USM2 (Krautkramer) , The velocity calculated according to the relation:

U=2X?t (4) Where X is the thickness of a glass sample and ?t is the time interval.

All velocity measurements carried out at 25oC, 298oK and a frequency of 4 MHz with repeated measurements three times for data accuracy 4.

2.6. Determination of elastic moduli:

At room temperature and by using the longitudinal velocity (?l) , the shear velocity (?s) and the measured density (?) which through can be calculate the elastic constants of each glass sample taking into account the following definitions 6:

The Longitudinal Modulus (L):

The ratio between the longitudinal stress and the longitudinal strain for the propagation of the longitudinal wave as given by the relation:

L=??l2 (5) Shear Modulus (G):

Can be calculated from the shear velocity directly as,

G=?vs2 (6)

Bulk Modulus (K):

Can be calculated from the ultrasonic velocities (?land ?s ), and It is the ratio between the volumetric stress and volumetric strain as given by the relation:

K=L-43 G 7

Young’s Modulus (E):

It is the ratio between tensile stress to tensile strain; it is often called the elastic modulus and given by the relation:

E=21+?G (8)

Poisson’s Ratio (?):

It is the ratio between the transverse contraction strain to longitudinal extension strain in the direction of the tensile force applied as given by the relation:

?=( L-2G )2 (L-G) (9)Where ? is the density of a glass sample, and ?land ?s are the longitudinal and shear ultrasonic velocities that have been measured respectively.

2.7. Calculation of other mechanical properties:

Also with taking into account the following definitions 6:

Mean sound velocity ?mean:

The velocity of traveling waves is a physical constant for any particular medium under pressure and temperature specific and it is given by:

?mean =1vl3+1vs33-1 3 (10)Debye temperature ?D:

Is an experimental parameter in the Debye’s heat formula, for solids represent the temperature at which all the vibrational modes are excited almost as given by the relation:

.

?D=hKB9N4?V13*?mean (11) Micro-hardness H?:

Provide the necessary data about the microstructures and the hardness of a material and calculated by the relation:

H?=1-2?E6(1+?) (12) Softening temperature Tsm:

The temperature at which a material softens under a fixed pressure and various standard conditions and given by:

Tsm =M.wt.?C*vs2 (13)Acoustic impedance Z:

Determines the reflection and transmission of sound energy in the glass material and can be obtained as:

Z=vmean ? (14)

Thermal expansion coefficient ?P:

A property of properties of materials which describes the volume change due to a change in temperature and can be calculated from the relation:

?p =23.2 vl- 0.57457 (15)Knowing that (h) is Plank’s constant, (kB) is Boltzmann constant, (N) is the vibrating atoms number per unit volume, (?) is the density of sample, (M.wt.) is the molecular weight and (C) is a constant which equal ( 0.5074×105 cm/k1/2s ).

2.8. Theoretical elastic moduli and Poisson’s ratio:

2.8.1. Makishima and Mackenzie model:

A theoretical model to calculate the elastic moduli of oxide glasses (Young’s modulus Em, bulk modulus Km and shear modulus Gm) and Poisson’s ratio ?m which depends only on both of the dissociation energy per unit volume (Gi) of the oxide constituents and the packing density (Vt) as the following equations:

Em=2VtGt 16

Km=5.862 Vt2Gi xi (17)

Gm=3EmKm9Km-Em (18)

?m=Em2Gm-1 (19)

Knowing that

1) Gt: The dissociation energy per unit volume for glasses

Gt= i(Gixi ) ……..( 20 ) Where Gi is the dissociation energy per unit volume.

xi is the mole fraction for the component oxide i.

2) Vt: The packing density of the glass.Vt=?MVi Xi ………..(21 ).Where Vi is the packing factor for the component oxide i

, M is the molecular weight for the glass

and ? is the density. 1,12,13,14,15,16,17.

Bond compression model:

The behavior of experimental elastic moduli can be interpreted quantitatively by the bond compression model.

According to the relations ( 22 , 23 , 24 and 25 ) Respectively ,the average stretching force constant F, the number of network bonds per unit volume nb , the estimated bulk modulus Kbc, the average atomic ring size of the network l were calculated as the following:

F= (xnff)i(xnf)i 22nb=(NAVM)infxi (23)Kbc=(nbr2F 9) (24) l=0.0106 FKe0.26nm 25Where r is the bond length where =17r02 , NA is Avogadro’s number, VM is the molar volume, nf is the coordination number of the cation, xi is the mole fraction of the component oxide that denoted by i, f is the stretching force constant of the oxide and Ke is the experimental bulk modulus 11,14 ,18,19, ,20,21,22.

Also, The average cross-link density of the glass per unit formula nc , the theoretical Poisson’s ratio ?bc , the calculated shear modulus Gbc , the calculated Longitudinal modulus Lbc and the calculated Young’s modulus Ebc were calculated from the relations (26, 27, 28, 29 and 30) respectively

nc=ixinciNCiixiNci (26) ?bc=0.28(nc)-0.25 (27) Gbc =1.5 Kcal1-2?bc1+ ?bc (28) Lbc = Kcal+1.33 Gbc (29) Ebc=21+2?bcGbc (30) Where Nc is the number of cations per glass formula unit and the component oxide 1,19,21,22 .

2.9. Electrochemical behavior of a borosilicate glass system:

2.9.1. Impedance Spectroscopy:

Impedance spectroscopy considered as an effective way to study the electrical properties of glasses generally, through presented impedance data in the Nyquist diagram in which the real part (Zreal) as X-axis and the imaginary part (Zimag) as Y-axis, in which each point corresponds to a different frequency from others 23.

Impedance spectroscopy investigated by using the electrochemical system (GAMRY PCI4G750) at room temperature and a typical-two electrode was used in an electrochemical test with reference electrode (saturated calomel electrode), a platinum wire as the counter electrode (auxiliary electrode) and the sample as the working electrode , after coating both the glass samples faces by applying carbon paste as an electrical conductive material, then dried the coated samples for 1 hour at a temperature between 100 -120oC, then placed the samples between two parallel surfaces inside the two-electrode cell which connects to the gamry instruments framework in the frequency range between 0.1 Hz–30kHz which is controlled by a computer 24.

III.9.2.Conductance Measurement:

Complement to the study of the electrochemical properties of the present glass samples, the conductance (G) of glasses were measured using HIOKI 3532-50 LCR HITESTER by applying DC current across two electrode at the frequency range between 50 Hz–5 MHz 25, 26 and have been obtained the values of the average conductance (Gav) which have been captured by a personal computer for a glass system from (X=0: X=5 mol %).

Results and Discussion:

3.1. XRD:

The amorphous nature of a glass samples confirmed by doesn’t appear any sharp peaks in the XRD spectrum as shown in Figure 12.

3.2. FTIR Spectroscopy:

FTIR bands of the glass system samples appear in the regions between 400 and 2000 cm-1 at room temperature as shown in Figure 2.

Notice that the observed FTIR bands of six samples are similar with a slight shift and the FTIR wavenumbers and their assignments are summarized in the Table (2) and exhibit distinct Frequency regions as the following:

1-The band from 400 to 420 cm-1 is assigned to Stretching vibration of Li–O bonds in the glass network 27.

2-The band around 444 cm-1 is assigned to bending vibration of O–B–O bonds and specific vibration of Na–O bonds 28.

3-The band from 470 to 600 cm-1 is assigned to bending vibration of Si-O-Si and O–Si–O of bridging oxygens (Q4) and overlap with B–O–B linkages or Al–O–Al or Al–O–Si bonds 4,5,29.

4-The band from 690 to 720 cm-1 is assigned to B–O–B bending vibrations of BO3 triangles 5.

5-The peaks around 900 cm-1 (from 830 to 1190 cm-1) is assigned to Stretching vibrations of B–O bonds in the tetrahedral BO4 plus to appearance of peaks for stretching vibration of BO4 units in various structural groups and notice that these peaks shifted to right with the gradient from (X=0:X=5) Indicating an increase of BO4 with the same gradient 4,5.

6-The broad band around 1300 cm-1 is set to Non Bonding Oxygen of asymmetric stretching vibrations of tetrahedral SiO4–(Q3) 4,30.

7-The band from 1400 to 1500 cm-1 is assigned to B–O antisymmetric stretching vibration of trigonal BO3 units only 4.

8-The broad band from 1530 to 1560 cm-1 is assigned to Stretching modes of Si–O and B–O bond of the tetra hedral BO4 units 31.

9-The band around 1650 cm-1 is assigned to presence of B–O– bonds in isolated pyroborate 30.

3.3. Density, molar volume and Oxygen Packing Density:

All the density (?), the molar volume (V), Oxygen Packing Density O.P.D for each sample of the glass system are given in Table 3.

As shown in table 3 It is clear that the measured density (?), and Oxygen Packing Density O.P.D Increases with the variation of the mol % (from X=o:X=5 mol %) of all glass samples in which the Densities varied from 2.3787 to 2.3907 (g/cm3) which can be explained due to the increase in theO.P.D varied from 0.0863 to 0.0870 (g/cm3) which due to the increase number of oxygen atoms per a sample causing more linkages in the glass network making the glass structure more compact thus increasing the glass density. as well as BO3 conversion into BO4 led to the density of glass increases, while the molar volume (V) decreases from 25.0193 to 24.2622(cm3/mol) due to the bond length or an interatomic spacing between atoms of the glass decreases and led to compact in the structure and the value of average boron-boron separation is found to decrease with the gradient (From X=0: X=5 mol %) of a glass system which indicates an increase in the density and a decrease in the molar volume for the same gradient of a glass system 32.

3.4. Ultrasonic velocities:

Figure 3 shows the variation of the longitudinal and the shear ultrasonic velocities increasingly for all glass samples of the system

50 B2O3 – (14-x) SiO2 – (20+x) Li2O –15 Na2CO3–1 Al2O3 (from x=o: x=5 mol %) and have been shown in Table 3.

From Fig. 3, It is clear that the Longitudinal Velocity varies from 6,146 to 7,060(m/s) and the Shear Velocity varies from 3,772 to 3,828(m/s) with a gradient (From X=0: X=5 mol %) of the present glass system, meaning that the change in oxides content plays an essential role in increasing the waves propagation through the glass, with the knowledge that the ultrasonic velocity increment linked to the packing density increment as a result of the transformation of Boron ions coordination6.

Because of this packing density increment, the rigidity increases for a glass system with the gradient (From X=0: X=5 mol %) due to the creation of bridging oxygens and hence the ultrasonic velocities increases as mentioned and in addition to increase elastic moduli (longitudinal L, shear G, bulk K and Young’s E) 6.

3.5. Determination of elastic moduli:

Figure 4 Shows that the variation of Elastic moduli were increasingly (longitudinal (L) varies from 89.8504 to119.1592 GPa, shear (G) varies from 33.8437 to 35.0318 GPa, bulk (K) varies from 44.7254 to 72.4502 GPa and Young’s (E) varies from 81.0801 to 90.5076 GPa with the gradient (from X=o:X=5 mol%)of a glass system and the results have been shown in Table 3.

The elastic moduli increment as a result of the rigidity of glass samples increases , Because the rigidity may refer to create the bridging oxygens from the formation of Li+ and BO4 in the glass network32.

Poisson’s ratio is a good tool to measure the Cross-link density of the glass network and when its increases The degree of the cross-link density increases 2, so Poisson’s ratio ? calculated by applying relation (9) and through Figure 5 shows that Poisson’s ratio ? increased from 0.1979 to 0.2918 according to a gradient (from X=0: X=5) mol % for a glass system as a result of that the glass network become more tightly packed with the same gradient and the results have been shown in Table 3.

3.6. Calculation of mechanical properties:

The values as shown in table 3 shows that Micro-hardness H increases from 4.7889 to 6.8170 (Gpa), Acoustic impedance Z varies from 9.9031 to 10.2114 (x10-6 Kg. m-2.s-1) , Thermal expansion coefficient ?p varies from 142,574 to 163,779 (K-1) , Mean sound velocity Vmean varies from 4,163 to 4,271 (m/s), softening temperature Ts varies from 693.56 to 700.69 (ºK) and Debye Temperature ?D varies from 569.40 to 590.20 (ºK) and all the above are increased with the variation of the mol % (from X=o: X=5 mol %) of all glass samples of system .

Debye temperature which obtained directly from measured velocities , increases with the gradient from (X=0:X=5 mol %) and This due to the formation of stronger rings in a glass system as a result of creation of bridging oxygen which means that the atoms number increases in the glass chemical formula with the same gradient 32.

Same case, the mean ultrasonic velocity increases due to the reinforcement in the glass structure as a result of the bridging oxygens creation which leds to an increase in the glass rigidity with the same gradient 32.

Moreover both of acoustic impedance and thermal expansion coefficient are increases due to the rigidity of the structure of the glass system increases with the same gradient 6.

Micro-hardness represents the required stress to eliminate the free volume of the glass and softening temperature is the temperature point which changes the viscous flow to the plastic flow and determines the temperature stability for a glass and when increases the softening temperature, improves the stability of its elastic properties.

That is, the increase in both the micro-hardness and the softening temperature,

Can be attributed to the increase the rigidity of the glass system with the same gradient 32.

3.7. Theoretical elastic moduli and Poisson’s ratio:

3.7.1. Makishima and Mackenzie model:

The results of calculated elastic moduli of a glass system(from X=o: X=5 mol %) by using Makishima and Mackenzie model were illustrated in table 4 and show the same trend as that of the previously measured experimental values as shown in fig. 6, in which Young’s Modulus Em varies from 41.7735 to 42.8263(GPa), Bulk Modulus Km varies from 65.5812 to 68.0644 (GPa) , and Shear Modulus Gm varies from 14.9851 to 15.3485 (GPa ) , while Poisson’s Ratio ?m varies from 0.3938 to 0.3951 .

As the results that illustrated in table 4, the increment in the packing density of the glass (Vt) from 0.5356 to 0.5422 which is related to the decrease in the molar volume (as shown in table 3) 33.

In another direction, the dissociation energy per unit volume for glass (Gt) increases from 38.9950 to 39.4900 KJ/cm3 with the gradient (from X=0: X=5 mol %) of a glass system. This led to that the molar volume clearly depends on the elastic moduli through calculation both of the packing density and the dissociation energy per unit volume of the glass 33.

3.7.2. Bond compression model:

The results that illustrated in Table 5 shows that the variation of Elastic moduli of a glass system from (X=0: X=5 mol %) which were calculated by a bond compression model has the same trend as that of the previously measured experimental values Which were compatible with the values have been calculated by using a Makishima and Mackenzie model as shown in fig. 6 as mentioned before ,in which The estimated bulk modulus (kbc) varies from 46.6453 to 46.7731 (Gpa),The calculated shear Modulus (Gbc) varies from 27.3687 to 27.5252 (Gpa) , The calculated longitudinal Modulus (Lbc) varies from 83.0456 to 83.3816 (Gpa) and The calculated Young’s Modulus (Ebc) varies from 82.6119 to 83.0172 (Gpa) , while The theoretical Poisson’s ratio (?bc) varies from 0.2548 to 0.2537 .

The estimated bulk modulus (kbc) varies from 46.6453 to 46.7731 (Gpa), this increase in (Kbc) can be explained on basis of reliance of the (Kbc) on the number of the network bonds per unit volume (nb) and the average bond lengths , Which depends on the calculation of the first-order stretching-force constant (F) 33.

Consequently, the gradient from (X=o: X=5 mol %) of a glass system causes increase in the number of the network bonds per unit volume (nb) from 8.4150 to 8.6990 (m-3×1028), while the average bond stretching force constant (F) gradually decreases from 360.0500 to 349.2500 (N/m) 33.

The ratio (Kbc/Ke) is a measure of the extent of the bending bonds is subject to the formation of network bonds, this ratio is supposed that be proportional directly to the average ring size (?) and proportional inversely to the elastic moduli which specified experimentally .The (Kbc/Ke) values are decreases from 1.0429 to 0.6456 and the values of the average ring size (?) are decreases from 0.5273 to 0.4615 (nm), this decrease in the values of (Kbc/Ke) and (?) prove the increase in the elastic moduli and hence the network structure becomes more stiff and less open 33.

The calculated average cross-link density per unit formula nc are very gradually increases from 1.4624 to 1.4764 is a result of the replacement of Sio2 atoms which have crosslink density nc=2 per unit cation with Li20 atoms which also have crosslink density nc=2 per unit cation 33.

(The effect of increasing the Li2o content and reducing the Sio2 content of a glass system simultaneously) or the effect of the gradient (from X=0: X=5 mol %) on the elastic moduli of a glass system 50 B2O3 – (14-x) SiO2 – (20+x) Li2O –15 Na2CO3 –1Al2O3 where x=0,1,2,3,4,5 as shown (Tables 3, 4 and 5) was proved by Makishima–Mackenzie model through increasing the total packing density of the glass (Vt) from 0.5356 to 0.5422 and increasing the dissociation energy per unit volume for glass (Gt) from 38.9950 to 39.4900 KJ/cm3 33.

Also, The effect of the gradient (from X=o: X=5 mol %) for a glasses can be interpreted by bond compression based on decreasing the average stretching-force constant (F) from 360.0500 to 349.2500 (N/m) and increasing the number of the network bonds per unit volume (nb) from 8.4150 to 8.6990 (m-3×1028)that indicates the increase in bulk modulus (kbc) which calculated by bond compression from 46.6453 to 46.7731 (Gpa) which leads to the increase of all elastic moduli according to the gradient (from X=o: X=5 mol % ) 33.

3.8. Electrochemical measurements of a borosilicate glass system:

3.8.1. Impedance Spectroscopy measurements:

The impedance spectroscopy data of a glass system leading to a series of semi-circles in the Nyquist diagram as shown in Fig.7 ,It can be observed the increase in impedance as a result of the increase in the O.P.D which varied from 0.0863 to 0.0870 (g/cm3) with the gradient from ( X=0:X=5 mol % ) ( as table 3 ) due to the increase number of oxygen atoms per a sample causing more linkages in the glass network making the glass structure more compact , thus impeding the movement within the glass network due to increased the glass density from 2.3787 to 2.3907 (g/cm3) with the same gradient from ( X=0:X=5 mol % ) as table 3 34,35.

From Fig. (7) can be concluded the values of polarization resistance (Rp) in which used to measure the rates of instantaneous corrosion 36 , through the resulting spectra illustrated that the polarization resistance increases ascending with the gradient from (X=0: X=5 mol %) of a glass system and the results have been illustrated in Table 6 .

The values of a polarization resistance (Rp) which illustrated in table 6 varies from 3.30*104 to 1.42*108 (?.cm2), this increase confirms presence abundance of bonds formed and the increase in the number of bridging oxygen through appearance of peaks for stretching vibration of BO4 with the gradient from (X=0: X=5 mol %) as illustrated in FTIR spectroscopy (Fig. 2)

, This leads to that the interstices are filled result of the incorporation of Li ions with the same gradient and thus impeding the propagation of waves within the glass networks more.

IV.8.1. Conductance Measurement:

The conductance (G) was measured at a different frequencies and have been obtained the values of the average conductance (Gav) of each sample and the results illustrated in Table 6.

The results showed that the average conductance (Gav) varies from 1.74*10-4 to 6.28*10-6 (S or ?-1) of a glass system from (X=0: X=5 mol %), as observed , the conductivity reduces with addition of Li2o to the glass system with the same gradient , which indicates a drop in the electronic contribution due to the changes in the glass network such as formation of bridging oxygens in the form of BO4 units in various structural groups and the formation of various structural oxides as illustrated in FTIR spectroscopy ( Fig. 2 ) , these changes causes the intervalence transfer restriction and the electron mobility reduction within the glass network and hence the conductivity decreases with the gradient from ( X=0 : X=5 mol % )37,38.

CONCLUSION:

The mechanical and electrochemical properties of a glass system : 50 B2O3 – (14-X) SiO2 – (20+X) Li2O –15 Na2o – 1 Al2O3, where x=0,1,2,3,4,5 mol% have been measured and showed the following conclusions:

(1) The observed increase in the density of the glass system with the gradient from (X=o: X=5 mol %), while the molar volume (V) decreases with the same gradient.

(2) The longitudinal ultrasonic and Shear ultrasonic velocities are increased with the gradient from (X=o: X=5 mol %) of a glass system due to the packing density increment as a result of the transformation of Boron ions coordination.

(3) The increase in the elastic moduli, micro hardness , acoustic impedence , thermal expansion coefficient, softening temperature and theta Debay temperature values with the gradient from ( X=o: X=5 mol %) of a glass system confirms increased the rigidity of glass network .

(4) Makishima and Mackenzie model and Bond compression model appears to be valid for interpretation of elastic moduli quantitatively for the investigated glasses, which showed that the values of the elastic moduli and Poisson’s ratio which have been calculated by using the two models are compatible with the experimental values

(5)From the analysis of impedance data illustrated that increase occured in impedance beside increase in a polarization resistance of tha glass system due to the increasing number of bonds formed within the glass structure with a gradient from (X=0: X=5 mol %) which have been followed by a decrease in electrical conductivity of the glass system with the same gradient.

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