The porosity and morphology properties of ceramic membrane

The success of ceramic membranes as solute separation and filtration makes membrane technology widely used because it has high effectiveness and efficiency as a solute separator and filtration. The solute separation and filtration performances of typical ceramic membranes depend on the porosity properties of the ceramic membrane itself. Membrane porosity indicates the number of porous areas in the membrane. Precipitated silica as filler was added into the ceramic membrane at 0.30 %, 1.01 %, 1.68 %, 2.34 %, and 2.99 % per hundred masses of the membrane. It was revealed that silica acting as a membrane filler increased the porosity of the ceramic membrane. This was confirmed with the SEM (Scanning Electron Microscopy) test and Origin Software. From the test results the highest porosity value is at 2.99 % per hundred masses of membrane.


Introduction
The science and application of ceramic membranes have successfully increased because of their excellent thermal, mechanical and chemical properties [1].Porous ceramic membrane technology offers an important role in environmental separation fields i.e., wastewater treatment and water purification [2].The usage of ceramic membranes has many advantages including excellent chemical and thermal stabilities, pressure resistance, durability, excellent fouling resistance and ease of cleaning [3][4].
Porosity is an important physical property to express the texture and quality characteristics of materials.Porosity is the space between materials and the fraction of empty volume space in the total volume [5].The porosity of ceramic membranes is very dependent on the interaction between the constituent components.The porosity of these membranes is a critical parameter influencing their ability to selectively transport species across the membrane matrix.Morphological features, including pore size, distribution, and surface roughness, significantly impact the membrane's performance in terms of flux, fouling resistance, and mechanical stability [6][7][8].Efforts to composite silica materials with inorganic polymers to minimize the weakness of silica interactions with clay are by adding additives such as PVA and PEG, PVA is useful for harmonizing and greater interactions between other constituent components while PEG functions as a uniform shape and size of pores in the membrane.
The selection of precipitated silica as a filler in ceramic membranes is due to its pore-forming properties, strength, and stability.Precipitated silica can be obtained from various sources, one of which is from fly ash from coal combustion [9][10][11].
Based on this foundation, the present conference paper aims to present a comprehensive analysis of the porosity and morphology properties of ceramic membranes.Through a meticulous examination of fabrication methods, characterization techniques, and the consequential impact on membrane performance, this study contributes valuable insights to the field of ceramic membrane science and engineering.The findings offer practical implications for tailoring ceramic membranes to find the specific requirements of diverse industrial applications, emphasizing the importance of a holistic understanding of porosity and morphology.

Silica recovery process from fly ash
Silica precipitate as the main component of the ceramic membrane was recovered from fly ash from the coal combustion process.The waste fly ash was mixed with 1 N HCl for at least 24 hours.The mixing process produced a slurry type of solution.The fly ash-HCl solution was filtered out while rinsing it with hot water to remove the excess HCl, then was dried using an oven (100 o C) until the constant drying rate was achieved.Next, the dry fly ash was extracted with 3.5 N NaOH and sodium silicate solution filtrate was obtained.Next, the sodium silicate filtrate was dripped with 3 N H2SO4 while stirring with a magnetic stirrer until a white gel and pH 7 were formed.The formed gel was filtered then rinsed with hot water and oven dried until the mass was constant.The chemical reactions are as follows [12][13], SiO2(s) + 2NaOH (aq) → Na2SiO3(aq) + H2O Na2SiO3(aq) + H2SO4 → SiO2(s) + Na2SO4 + H2O

Compounding of silica-based ceramic membranes
Mixing silica with other membrane components by using the recipe of mixing silica precipitates with other ceramic membrane components can be seen in Table 1 as follows, PVA with a mass of 6 grams was mixed with 10 mL of HNO3 1M and 190 mL of distilled water while stirring for 2 hours at 180 o C. The silica that had been obtained previously was added to the 2propanol solution to pass the centrifuge process at 600 rpm for 10 minutes.After the centrifuge, the silica was mixed with ammonium chloride (NH4Cl) and stirred for 1 hour.In addition, 50 millilitres of PVA, 20 millilitres of PEG and 13 grams of clay were mixed into this mixture followed by stirring the mixture at 150 o C (2 hours).Next, the membrane was printed on a petri dish and aerated for 30 hours.The membrane was then sintered in a typical furnace at 700 o C (2 hours).

Morphology testing with scanning electron microscopy of fly ash-based ceramic membrane
SEM or Scanning Electron Microscopy is applied to study the surface part of ceramic membrane objects directly with 10 -3000000x magnifications and, a depth of field of 4 -0.4 mm (resolution of 1 -10 nm).The SEM apparatus had a working principle i.e., an electron gun producing an electron beam which was accelerated by the anode (magnetic lens focused on the electrons towards the ceramic membrane sample), the focused electron beam scans the whole sample directed by the coiled scanning and then the electrons hit the ceramic membranes sample thereby releasing new electrons which will be received by the detector, and sent to the apparatus of a monitor (CRT) [14][15].

Porosity analysis with origin software
SEM testing will produce cross-sectional images of the membrane surface, especially the quality of pores in porous material samples such as ceramic membranes.The cross-sectional image of the surface, referred to as the SEM image, can be used as information to provide the porosity value of the membrane with the help of the origin software.All SEM images of membranes with variations of 0.3%; 1.01%; 1.68%; 2.34%; and 2.99% are entered into the software and provide data that can be used to calculate the porosity value of the ceramic membrane.This test procedure refers to ASTM C20.

The ceramic membrane morphology properties
The properties of the morphology of the ceramic membranes with silica concentration variations were analyzed by SEM test and, the SEM images are shown in Figure 1.From Fig. 1, it was observed that the ceramic membrane structures show some irregularly distributed pores with relatively complex shapes.These images were a peculiarity promoted by the process of getting this material and its characteristics and structural arrangements.It has confirmed the great porous structure with a more homogenous pores distribution.As observed, the pores were randomly shaped.The quality of the surfaces of the ceramic membranes has supported the efficiency of the microfiltration process [16][17][18].
It can be seen from Figure 1(a) that the membrane with 0.3% w/w silica filler has tightly arranged particles with nuclear pores.Figure 1(b) shows a tight particle arrangement like Figure 1(a) so that the space or gap is very minimal.Figure 1(c) shows the morphological structure of the membrane surface which is more regular than the previous two variations of silica filler, the pores in the entire particle arrangement look more numerous and more regular.Figure 1(d) shows a much more harmonious and regular membrane surface morphological structure with smaller sizes.Finally, in Figure 1(e) with a 2.99% w/w silica-filled membrane, the pores produced a further increase in regularity to become more harmonious as seen in the image which has a corrugation.The number of pores becomes more and more dense compared to other membrane variations.The addition of silica concentration will increase the pores in the membrane at the same time the physical addition of PEG will fill the pores [19].

Porosity Analysis of silica-based ceramic membranes
The images of SEM can be used to determine the porosity of a ceramic membrane sample using origin software.The silica-based ceramic membrane porosity was calculated by determining the ratio of pore volume to total ceramic membrane volumes [20].The testing of porosity quality was carried out to study the amount of substance that can be absorbed by the silica-based ceramic membrane [21].SEM images can be used to determine the porosity of a ceramic membrane sample using origin software.The SEM image will be inputted into the origin software, which then provides values that can be applied to determine the porosity properties of each ceramic membrane.Figure 2 shows the contour plot of the SEM images which were analysed using Origin Software.The pore area of the ceramic membrane is the air cavity area separated from the solid unit as shown in Figure 2.With the help of origin software, the matrix integral volume of the SEM image can be known and additional data for calculating porosity can be used with the help of Excel Software.The results of SEM image porosity analysis with origin software are shown in Table 2 below.From Table 2, it was observed that the bigger the concentration of silica precipitated, the higher the degree of the porosity of silica-based ceramic membrane.In the membrane with 0.3 % silica precipitated, the porosity is 59.18 %.The porosity increases successively from membranes filled with 1,01 %; 1,68 %; 2,34 %; and 2,99 %.Namely 67,83 %; 67,99 %; 70,43 %; 71,97 %.
From the obtained porosity results, it can be observed that the greater the mass of precipitated silica filler added to the membrane, the greater the porosity value was obtained.This was because the silica precipitated can reduce the pores sizes and increase the number of pores at the combustion process.

Conclusion
The characterization of all membrane variants shows a tightly arranged particle arrangement that is free of cracks, but the pores formed were not evenly distributed and were relatively complex in shape.The porosity test of all ceramic membranes showed the porosity of the ceramic membrane increases in line with the addition of precipitated silica quantity or concentration.The addition of silica as a filler in the ceramic membrane has increased the pores of the ceramic membrane so that its porosity also e

Table 1 .
Recipe of the silica-based ceramic membrane compound.

Table 2 .
The porosity properties of silica-based ceramic membranes with varied silica concentrations.