Study on the Physical and Mechanical Properties of Al-Powder Reinforced Bioactive Glass: Ceramic Composite Material

Glass-ceramic samples, having composition of SiO 2 -35, CaO-45, Na 2 O-10 and P 2 O 5 -10 in weight ratio were prepared through sintering route. Glass powder was reinforced by Al powder. The strength of glass-ceramic composite was found to be temperature dependent, and it varies with the addition of Al powder. Flexural strength increases with the increase of powder addition and sintering temperature, however, decreases with the increase of sintering time. There is an optimum temperature (>1100˚C) above which flexural strength of all samples decreases. Bulk density changes to a higher value as the addition of Al-powder increases up to 3% by weight above which density decreases slowly. On the other hand, apparent porosity and water absorption decrease with the increase of percentage of Al powder added. Porosity and water absorption also showed a dependent characteristic on sintering time and sintering temperature.


Introduction
Biomaterials have been drawn much attention in the recent time due to their extensive medical and non-medical uses [1] [2]. Bioactive materials, when used in a medical device, may interact with the biological systems. They can react in a positive manner with the local cells to form bonds and can transfer loads to and from living cells [1] [3]. Bioactive ceramic is an important biomaterial which is *Contributed equally. mainly used for the replacement of damaged or diseased body parts [4]. The bioactive ceramics can perform their function within the human body without toxicity and can generate a positive reaction in the biological environment of the implants [4] [5]. Bioactive ceramics have two main classes-Bioactive glass (e.g., Bioglass) and Bioactive glass-ceramics (e.g., A/W glass-ceramic). The bioactive glasses are the third-generation biomaterials which can be employed to repair and rebuild damaged tissues, particularly hard tissues [6] [7]. Usually, SiO 2 , Na 2 O, CaO, and P 2 O 5 are the base components of the most common type of bioactive glasses. The bioactive glasses are soft in nature and hence their final shape can be easily given [7]. The main advantage of bioactive glass is the high superficial speed reaction that brings rapid connections to the tissues. But the greater disadvantages are the not optimal mechanical properties and the meager breaking resistance. However, these disadvantages can be overcome by forming bioactive glass-ceramic from the parent bioactive glass through the process of controlled heat treatment above its crystallization temperature [8] [9] [10] [11].
The newly formed bioactive glass-ceramic possesses superior mechanical properties, including greater elastic modulus, failure strength, and hardness, than the parent bioactive glass [8] [12] [13]. However, the brittleness and low fracture toughness of bioactive glass-ceramics sometimes appear as a limitation of their common clinical uses [12]. This discrepancy again can be solved by the addition of a ductile, metallic, secondary phase to the pure glass-ceramic composite structure. Several researchers have already worked with the development of glassceramic matrix composites reinforced with graphite [14] [15], alumina fibers [16], SiC [17], carbon nanotubes [18], etc. In the present research work, pure aluminum (Al) has been selected as the reinforcement material due to its nontoxicity, lower density, and better ductility [19]. The resultant change on the physical and mechanical properties of the prepared glass-ceramic composite samples due to the addition of pure aluminum (Al), and the effect of sintering time and sintering temperature on the samples have been studied through this research work as well.

Experimental Details
The formation and evaluation of Al-powder reinforced bioactive glass-ceramic composite material was performed with six process steps as shown in Figure 1,

Formation of Glass Powder
In order to form glass powder, we took 500 gm glass, 175 gm of SiO 2 , 50 gm of P 2 O 5 , 85.484 gm of Na 2 CO 3 (source of Na 2 O), and 401.786 gm of CaCO 3 (source of CaO) and mixed them properly. After mixing the compounds the mixed batch was annealed at 1135˚C in a globular furnace (heat rate several hundred ˚C per hour) for three hours to form the desired glass-ceramic matrix structure.
The glass was then crushed, and the glassy powder was prepared.

Mixing of Aluminum (Al) Powder
Mixing was a vital part of this experiment. Pure Al powder was mixed homogeneously with the prepared glass powder by varying its weight (wt) percentage (%) of 0%, 3%, and 6%, respectively.

Molding and Pressing
A molding device was used to mold the mixture of Al powder and glass-ceramic powder. In this molding process, polyvinyl alcohol was used as the binder such that five drops of the binder were poured in three grams of the mixture. After then the mixture was pressed with sufficient load of 50 KN, applied by a Weber Pressen Hydraulic Press, to get the desired shape (60.5 mm × 5.5 mm × 4.4 -4.6 mm) of the sample.

Sintering of the Samples
The samples prepared by the Weber Pressen Hydraulic Press were removed and dried properly. Finally, the dried samples were sintered at various temperatures (1050˚C, 1075˚C, 1100˚C) using high temperature furnace.

Characterization of the Samples
In the present work ASTM D790M, 3 points loading technique has been used to where P denotes the load at a given point on the load-deflection curve (expressed in N), L is the distance between the centers of the support span (expressed in mm), b is the width, and d is the depth (both measured in mm) of the specimen. The flexural strain was measured by the following expression [21], Advances in Materials Physics and Chemistry ( ) where D denotes the maximum deflection of the center of the beam (measured in mm). Also, the flexural modulus of the samples was determined by using the following equation [21], where m is the gradient (i.e., slope) of the initial straight-line portion of the load deflection curve (expressed in N/mm).
ASTM C135-762 technique has been used to determine the bulk density (BD) of the samples. The bulk density is given by the following equation [20], where W d determines the weight of the specimen (expressed in gm), and V represents the volume of the specimen under test (measured in mm 3 ).
The apparent porosity (P) of the samples has been determined by employing the evacuation method. The following equation [20] was used to calculate the apparent porosity, where W s denotes the saturated weight, and W d denotes the dry weight of the sample (both measured in mg), V is the volume of the sample (expressed in The water absorption is another important parameter which has been estimated by using ASTM C 67 -91 technique. The following formula [20] provides the water absorption of the samples,    σ f at 1050˚C) at high temperature of 1100˚C. It clarifies that for each temperature/percentage of oxide there is an optimum temperature/percentage of oxide amount above which the strength will be decreased. The cause of this decreasing fusion. The higher amount of Al powder lower is the fusion temperature [22].

Flexural Strength
The effect of sintering time (1.5 h and 3 h) on the σ f for these glass-ceramic samples for different Al powder contents, 0 wt%, 3 wt% and 6 wt% as shown in Figure 3. The values of σ f are shown in Table 2. From Figure 3, and Table 2, it could be revealed that the σ f of the samples increases with increasing the sintering time.

Flexural Strain
The resultant change in the flexural strain (ε f ) of the composite glass-ceramic samples with different sintering temperatures has been shown in Figure 4 and the corresponding data are shown in Table 3. We observed that by increasing the sintering temperature from 1050˚C to 1070˚C, ε f increased from 0.0028 to 0.0036 for Al wt 0%, and 0.0031 to 0.0033 for Al wt 3%, respectively. However, both ε f for 0 wt% and 3 wt% started to be decreased by increasing the sintering temperature to 1100˚C. For Al 6 wt%, ε f (0.029 -0.031) was found to be almost constant at low to high sintering temperature of 1050˚C -1100˚C. Since stress Advances in Materials Physics and Chemistry     Influence of changing sintering time on E f after adding different Al powder (wt%) is exhibited in Figure 6 and the values of E f are shown in Table 5. The E f

Bulk Density
Impact of sintering temperature on the bulk density of the glass-ceramic samples after the addition of different Al wt% is represented in Figure 7 and their corresponding values of bulk density (BD) are summarized in Table 6. It is ob-      Table 7. It is seen that the apparent porosity of glass-ceramics decreased (25.5 to 16 for 0 wt%, 30 to 16.5 for 3 wt%, and 27.5 to 26 for 6 wt% with Advances in Materials Physics and Chemistry  increasing temperature (1050˚C to 1100˚C). However, the apparent porosity is found to be decreased less slowly for the sample with 6 wt% of Al powder. The reason behind the decrease of apparent porosity with sintering temperature is that the surface viscosity of particles of the samples decreases at high temperature and therefore the particles within the ceramic body bond more strongly and the space between the particles gets narrowed [24] [25]. The variation of apparent porosity with the percentage of Al powder at two different sintering times (1.5 h and 3 h) are shown in Figure 10 and Table 8. It elucidates that both higher percentage of Al powder and long sintering time influences to increase the apparent porosity of the samples.

Water Absorptions
Continuous change of water absorption with sintering temperature is represented in Figure 11 and Table 9. The water absorption curves of the composites are found to be decreased (14% to 11% for 0 wt%, 12% to 7% for 3 wt%, and 13.5% to 9% for 6 wt%) gradually with increasing sintering temperature (1050˚C to 1100˚C). This indicates that the increase of sintering temperature decreases the amount of water absorbed by the specimen, keeping the weight of the dry specimen same. Figure 12 shows the effect of sintering time on the water absorption vs percentage of Al powder characters. The corresponding water absorption values are given in Table 10. It is found that the water absorption of Advances in Materials Physics and Chemistry    the sintered glass-ceramic samples increase (7% to 9%, and 7.5% to 15%) with increasing the sintering time from 1.5 hours to 3.0 hours.

Conclusion
We studied physical and mechanical properties of the Al-powder reinforced bioactive glass-ceramic composite material for bio-medical applications. We concluded the results for this investigation. It is observed that the flexural strength of the composites increased with increasing of Al powder added until a certain amount (>3 wt%). Similar results were obtained for the tangent modulus and flexural strain of the composites which increased with temperature for small amount of Al powder added, however decreased for higher amount of powder added (>3 wt%) with high temperature. Apparent porosity and water absorption of the composites decreased with increasing sintering time, temperature, and addition of Al powder. Although it is desirable to minimize the porosity to increase the resistance of the ceramics, the usefulness of this approach is limited.
Therefore, further investigation is necessary in drawing a compromise relation Advances in Materials Physics and Chemistry between the pore size and cellular integration into the materials. Optimization of the physicochemical characteristics for bone reconstruction should then be possible.