Relation between Rheological and Curing Behavior of Inorganic Foam

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Materials and Interfaces

Relation between rheological and curing behavior of inorganic foam slurries in the gel-casting process Xin Wang, Hui Chen, Lei Zhao, Xuan He, Wei Fang, and Weixin Li Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b04908 • Publication Date (Web): 09 Mar 2018 Downloaded from http://pubs.acs.org on March 9, 2018

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Industrial & Engineering Chemistry Research

Relation between rheological and curing behavior of inorganic foam slurries in the gel-casting process Xin Wanga, Hui Chen*a, b, Lei Zhaoa, Xuan Hea, Wei Fanga, Weixin Lia a

The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China

b

HuBei Province Key Laboratory of Coal Conversion and New Carbon Materials, College of

Chemical Engineering and Technology, Wuhan University of Science & Technology, Wuhan 430081, P.R. China *Corresponding author: Hui. Chen, E-mail: [email protected]; Tel/Fax: +862768862833/+862768862833

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Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT: In this work, the procedure for in situ forming process of Al2O3-SiO2 based foams slurry by using diacetin (DAT) and silica sol (SS) as the gelling agent was evaluated, and the rheological behavior of foam slurry was studied. The results showed that the rheological properties played a key role during the curing process of foam slurry. Excellent thixotropy, obvious pseudoplasticity, and large critical strain for the gelling agent contained foam slurries meant a stronger internal three-dimensional network structure which was conducive to shorten the curing time of foam slurry for the further applications. With this technique, we were able to produce porous mullite ceramics with good mechanical and structural properties. After sintering the as-prepared green body at 1350 ºC, the porous ceramics were found with a bulk density of 0.528 g/cm3, the compressive strength of 2.49 MPa, the apparent porosity of 77.9 %, and pores ranged from 100 µm to 500 µm. KEYWORDS: Gel-casting; Foaming method; Rheological; Curing; Porous mullite ceramic.

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1. Introduction

Gel-casting, a novel near net shape forming method for fabricating ceramics green bodies with high mechanical strength and excellent machinability, has received the considerable attention that can be used to prepare large-sized complex-shaped ceramics.1-4 In this process, the powder-solvent suspension is obtained by dispersing the ceramic powders in a premixed water-soluble monomer and initiator. By adding the catalyst and mechanically stirring the colloidal ceramics suspension, cross-linking polymerization occurs to form a three-dimensional network structure, and the slurry is solidified in situ. method

using

5,6

Deng et al.

commercial

7

prepared Al2O3-based ceramics by the gel-casting

α-alumina

powder

as

raw

materials,

N,

N′-dimethyl-acrylamide as gelling monomers and N, N′-methyl-enebisacrylamide as cross-linkers. Their results showed that the as-prepared green bodies exhibited unique bendable and recovery performances after drying treatment at room temperature for 1 h. So, compared with other ceramics forming methods, gel-casting provides a shorter forming cycle and higher green body strength.

In recent years, gel-casting has proven to successfully fabricate porous ceramics combined with foaming method, as well. The foam-gelcasting method has the advantage over both gelcasting processes and direct foaming, which could prepare samples with unique three-dimensional (3D) framework structure, uniformly distributed

3



pores, relatively high strength and porosity. Wu et al.,

8

prepared highly porous

γ-Y2Si2O7 by in situ foam-gel casting methods. The prepared porous γ-Y2Si2O7 has multiple pore structures, high compressive strength (6.22 MPa), and low thermal conductivity (0.230 W/(m•K)). M. Potoczek et al. 9 fabricated Ti2AlC foams with a high porosity of 87 and 93 vol% and relatively high compression strength (1.60 to 2.79 MPa) using foam-gelcasting method. M.F. Sanches et al.

10

also prepared highly porous

cellular ceramics via a versatile method combining emulsification of sunflower oil in alumina suspension. Nevertheless, most of the researches have been focused mainly on the ceramics preparations by the foam-gelcasting method, whilst research on the basic property of foam slurry with gel material has been very limited.

Rheology is the study of flow and deformation of materials under applied forces which is routinely measured using a rheometer. Rheological properties of foam slurry are required to account for the full time needed to produce rigid green bodies. A significant amount of literature is available regarding the correlation between viscosity and shear rate.

11-14

However, very few authors have reported the correlation between thixotropy

and viscoelasticity of ceramics slurries. Continuous changes in the rheological behavior from viscous to viscoelastic and elastic are the essential body-forming step in many of the new shaping processes. And the thixotropy is indicative of the kinetics of the network re-formation over the time period. So, the information of the viscoelastic behavior in the foam-gelcasting process is necessary and essential. In summary, the

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thixotropy and viscoelasticity are closely related to stability, uniformity and curing characteristics of the suspension. Meanwhile, the rheological behavior of ceramics suspensions containing foam and gelation simultaneously by rotational viscometry is inadequate. To address these problems it is necessary to study the rheological properties of ceramics suspensions contained complex components.

As one of the most promising oxide ceramic, mullite (3Al2O3·2SiO2, including natural and synthetic) porous ceramics have received wide attention because of their good chemical and high thermal stability, low thermal expansion coefficient and conductivity, low dielectric constant and high creeps resistance.15 These properties make porous mullite to be widely used in the fields of thermal insulators, catalytic supports, lightweight structural materials and gas/liquid filters.16 In this investigation, the gel-casting combined with direct foaming method was used to prepare mullite porous ceramic. The diacetin (DAT) and silica sol (SS) are jointly employed as the gelling agent during the gel-casting process, combined with direct foaming method to prepare mullite porous ceramics. This article explores the impact of the rheological behavior of aqueous foam slurry before and after the addition of DAT and SS. The internal relation of rheological behavior and curing time is also investigated.

2. Experimental 2.1 Materials

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Calcined clay (CC; ZiBo JinKe Refractory Materials Co., Ltd. Shandong Province, China; d50~74 µm), kaolin clay (KC; China Kaolin Clay Co., Ltd. Jiangsu Province, China; d50~74 µm), kyanite (KY; China XinDATi Xingguo Kyanite Manufacturing Co., Ltd. Hebei Province, China; d50~74 µm), precipitated calcium carbonate (PCC; Jiangxi GuanDATi Chemical Co., Ltd. Jiangxi Province, China; d50~74 µm), silica fume (SF; Elken, Norway; d50~1.50 µm), and ρ-Al2O3 (Almatis Aluminum (Qingdao) Co., Ltd. Qingdao Province, China; d50~1.50 µm) were used as raw materials. Polyacrylic Acid Sodium (Hangzhou Jutao Biochemical Tech. Co., Ltd. Hangzhou Province, China) and sodium lignin sulfonate (Wuhan East China Chemical Co., Ltd, Wuhan Province, China) were mixed together as a composite dispersant with the weight ratio of 1:1. Diacetin (DAT; Shanghai Zuozhou Chemical Technology Co., Ltd. Shanghai Province, China) and silica sol (SS; Shandong Peak-tech New Material Co., Ltd) as gelling agents of the gelcasting process to facilitate the solidification. Foaming agent of previous research was employed in the experiment. 17 SDS (sodium dodecyl sulfate, ≥99% purity), GAC (gum acacia, ≥99% purity) and TDA (1-Tetradecanol, 97% purity) were purchased from Sigma Aldrich and selected as the main foaming agent, the foam stabilizer and the accessory ingredient respectively.

2.2 Gelcasting procedure

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Figure1 Detailed flowchart of the process to prepare porous mullite ceramic

The foams were prepared in two basic steps. 0.1 mol SDS, 0.1 mol GAC and 0.1 mol TDA were added into deionized water and heated at 60 °C for 20 min to ensure all the solutes dispersed uniformly. After cooled down, the solution was stirred rapidly to generate foams for 8-10 min by JJ-1 Numerical Show Precise Power Mixer with speed of 1200-1300 rpm at 25 °C. Foaming expansion of foaming agent bulk solution (V(foam)/V(slurry)) is about 6.

Firstly, homogeneous powder was prepared via mixing 36 wt% CC, 22 wt% KC, 30 wt% KY, 4 wt% PCC, 1 wt% SF and 7 wt% ρ-Al2O3 by cement mixer for 10 min. 1 wt% and 22 wt% deionized water (based on the homogeneous powder) were added into 7



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cement mixer, followed by stirring for 3~5 min. Subsequently, 1200mL/kg (based on the homogeneous powder) foam was added to the inorganic slurry to obtained foam slurry (labeled as PFS). Then 2 wt% DAT and 1 wt% SS (based on the homogeneous powder) were added to the slurry and stirred for 3-5 min to obtain foam slurry (labeled as CFS). Then the CFS was poured into the mold (160 mm × 40 mm × 40 mm). The filled molds were moved into an oven at 25 ºC for a period of time to ensure the low-temperature solidification of the slurry. After consolidation and demolding, the wet green bodies were dried at room temperature for 24 h, and subsequently in an air oven gradually to 110 °C. Finally, the green bodies were heated to 600 °C at 2 °C/min holding for 1.5h, then continue heated to 1350 °C at 2 °C/min holding for 3 h. The detailed process flow diagram was given in Figure 1.

2.3 Measurement Details

The rheological properties of foam slurry related to the addition of DAT and SS were measured using the rotational rheometer (Physica MCR 301, Anton Par GmbH, Germany) equipped with a concentric cylinders geometry (CC17). The test temperature was regulated at 25 °C by Peltier system (H-PTD 200). All viscosity measurements were conducted at shear rates from 1 to 100 s-1. The data obtained from viscosity test were fitted with the Power Law Model show as the following formula: η= k •γ

n -1

(1)

Where η is viscosity of a foam slurry, γ is the applied shear rate, and k and n are the

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consistency factor and non-Newtonian index, respectively. 18,19

The measurement of the thixotropy of foam slurry divided into three stages: the 1st stage, the shear rate was fixed at 1 s−1 for 25 s; the 2nd stage, the shear rate abruptly increased into 3,000 s−1 and held for 10 s; the 3rd stage, the shear rate decreased to 1 s−1 again and held for 50 s. In order to clarify the viscoelasticity, the storage modulus (G’, elastic constituents) was measured via amplitude sweep tests (AST) with controlled shear deformation (CSD, logarithmic ramp γ= 0.01-100%) with the fixed frequency at 1 Hz. The overall test time was 2 h with intervals of 0.5 h. The data of all measurements were recorded by software Rheoplus/32 v2.81 (Anton Paar). Then, a series of samples were cast and seriatim demoulded at regular intervals. The time cycle from cast to demould was defined as curing time when the samples could hold its shape, without collapsed or crazed.

The microstructure of the porous mullite ceramics were obtained using field emission scanning electron microscope (FESEM, Novo 400, FEI Co., USA). Developed crystalline phases of the mullite ceramics were analyzed by XRD (XRD, X'Pert Pro, Philips, Netherlands) with Cu Kα radiation. The compressive tests were performed on cubic samples (40 × 40 ×40 mm3) which were loaded at a crosshead speed of 0.5 mm/min using a universal testing machine (WE-30B, JinLi Technology Co., Ltd, Chian). The load was maintained until the first crack appeared on the foam. Results

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were based on an average of 3 samples.

The porosity of the mullite porous ceramics were measured by Archimedes method (GB/T1966-1996). The apparent or interconnected porosity is determined by weighing the dry ceramics (Wd), then reweighing the ceramics both when it is suspended in water (Ws) and after it is removed from the water (Ww), then the apparent porosity calculated using the equation: Apparent porosity

100

(2)

The true porosity includes both interconnected and closed pores, calculated by the following equation: True porosity

100

(3)

where ρb is the bulk density and ρ is the true density or specific gravity of the ceramics. The true density was tested by the fully automatic true density analyzer (ACCUPYC1330, Micromeritics Instrument CO., USA).

3. Results and discussion 3.1 Viscosity of Foam Slurry

It can be seen from Figure 2(a) that the apparent viscosity of PFS declined with increasing shear rate. And the shear thinning phenomenon was much more obvious over with the time. Meantime, the slurry with gelling agents (Figure 2b) had a higher initial

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viscosity compared with the pure foam slurry. The results implied that all the slurries behaved like pseudoplastic fluid. As the shear rate increased, the internal network of the slurry was gradually ruptured, resulting in a decrease in the viscosity of the slurry. The pseudoplasticity of slurries can be characterized by non-Newtonian index n calculated according to the power low model (Eq. (1)). The non-Newtonian index n represents the strength of the inter-particle network in the slurries. For pseudoplastic slurries, a lower value of n below unity means a stronger inter-particle network which presents highly shear thinning with the increase of shear rate.

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The non-Newtonian index as a

function of time is shown in Figure 3. The two slurry reflected similar variation tendency but different changing degree. For PFS, the n values gradually fallen from 0.39 to 0.30 during two hours. Index n for CFS presented a smaller initial value, and then rapidly declined from 0.27 to 0.11 after 2.0 h. These suggested that stronger network structures were formed in CFS at the very start and the strength of network increased fleetly.

Figure 2 The viscosity-shear rate curves of foam slurries: (a) PFS, (b) CFS

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Figure 3 The parameters n as a function of time

Figure 4 The parameters k as a function of time

The consistency factor k revealed much about the viscosity of the slurry. According to Figure 4, the k values of PFS ranged from 18.07 to 24.78 in 2 hours, and the k of CFS increased from 27.66 to 50.26 during the same time. This behavior pointed that the foam slurry contained gelling agent could obtain a much higher viscosity within given time-frame compared with pour foam slurry. Meanwhile, the evidence for the stronger

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inter-particle network for foam slurry contained gelling agent lies in the significantly higher viscosity of the slurries.

3.2 Thixotropy of foam slurry

In general thixotropy slurry, inorganic particles formed network structure via physical accumulate or electrostatic attraction. Such network structure would change with shearing time under the action of the external force. At given flow conditions, suddenly increase or decrease of the shear rate is a great way to reflect the relationship between viscosity and the change of network structure in the slurry.21 Figure 5 shows the results of the 3-step thixotropy test. The test results indicated that the viscosity of slurries have a sudden decrease when the shear rate increased to 3000 s-1. While the viscosity of slurries could recover again once the shear rate back to 1 s-1. From the observation of Figure 5, it was realized that data pointed toward the same trend of the three-stage thixotropic curves. However, the viscosity recovery rate (the viscosity at random time during the 3rd stage to the viscosity ratio of the end of the 1st stage) and viscosity recovery degree (the maximal viscosity of the 3rd stage to the viscosity ratio of the end of the 1st stage) 22 of PFS and CFS were obvious different.

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Figure 5 The three-stage thixotropic curves of foam slurries: (a) PFS, (b) CFS

Figure 6 The viscosity recovery rate curves of foam slurries: (a) PFS, (b) CFS

Figure 6 shown the viscosity recovery rate curves of PFS and CFS. The recovery degree of PFS had no significant changes during the whole experimentation, about 30% (Figure 6 a). For CFS, maximum viscosity recovery rate of the fresh slurry (initial moment) could achieve in a fairly short time (about 1 s) and then decreased under the action of shear stress, which meant the internal network could be rebuilt within 1 s (Figure 6 b). The viscosity recovery rates could not reach the peak value when the overall test time was over 1 h (Figure 6 b). And the values were almost constant after a

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modest increase that meant the destruction and reconstruction of network structure in a balanced state. On the other hand, the recovery degree gradually declined from 93.3% to 17.7% due to the viscosity continuously increased and the slurry became more and more solid-like. This could lead to an irreversible partial destruction of the internal structure.

3.3 Viscoelasticity of Foam Slurry

The storage module curves of PFS and CFS were reported in Figure 7. For PFS, G’ declined immediately once the strain increased (Figure 7a). It meant that the pure foam slurry had no obvious linear viscoelastic region and the critical strain (γc) of PFS was negligibly small. Once the strain was high enough, the network might be broken and the foam slurry became liquid-like material. G’ immediately declined once the strain increased, the PFS had no obvious linear viscoelastic region which meant the γc of PFS was negligibly small. When the foam slurry contained the gelling agent, the elastic modulus (G’) maintained constant in the linear viscoelastic domain (Figure 7a).

23,24

Indeed, larger γc value implied the more stable internal structure of foam slurry, so the above phenomenon indicated that a three-dimensional network has been built for CFS (Figure 7b). G’ began to decrease when the strain was higher than γc (Figure 7b).

In

conclusion, the network structure built by inorganic particles was very fragile and easy to be damaged compared with the network formed via the gelling agent, even the strong modulus of PFS were larger than the CFS in each experimental stage. Moreover, the curing time of different foam slurry was tested at 25 ºC. The result showed that the

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curing time decreased from 36 h to 10 h with gelling agent adding. It indicated that the addition of DAT and SS could accelerate the curing process to get the demoulded specimen within a short duration.

Figure 7 The storage module curves of foam slurries: (a) PFS, (b) CFS

3.4 Analysis and Discussion

The mechanism of the aforementioned rheological phenomenon of slurries were schematically discussed in Figure 8a. The “micro” three-dimensional network-like structural units were taken shape owing to the DAT molecular (black line). They wrapped the inorganic particles (black ball) and foam (blue ball) to enhance the initial physical accumulation of particles. At the same time, the SS molecular (red line) formed

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a biggish 3D network throughout the system which could twine the “micro” network-like structural mentioned above. These structures also fixed the hydrone molecular by hydrogen bonding according to the hydroxy on the molecular chain that foamed hydrogel-like structure. The liquidity of foam slurry was lost at this moment to get high viscosity as shown in Figure 2 and Figure 4. Although the accumulation of inter-particles in the slurry without gelling agent could cause the pseudoplasticity and thixotropy, the contribution of hydrogel-like structure and a network-like structural unit could improve the pseudoplasticity and thixotropy. The liner viscoelastic domain of slurries containing glycerol triacetin and silica solution could be extended to get a higher value of γc for CFS. The strength of green body became sufficient enough to withstand the body weight to get solidification within a shorter period of time. Figure 8b showed the photograph of the green body from CFS. The wet ceramic green body from CFS can be demoulded after casting for 10 h compared to 36 h for PSF. The demoulded bodies had precise size reproduction and very smooth surface.

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Figure 8 (a) Interaction between inorganic particles foam and gelling agent, (b) Photograph of the green body from CFS

3.5 Phase identification

Figure 9 shows the XRD patterns of the sintered foam samples contained the gelling agent. Mullite, Al2O3 and quartz peaks could be clearly seen in Figure 9. The main crystalline phase is mullite. It could be found that γ-cristobalite phase formed because of the transformation of amorphous SiO2 under high temperature (above 1250 °C). The results indicated that Al2O3-SiO2 based composite powder could prepare mullite porous ceramics via foaming method combining with gel-casting.

Figure 9 XRD patterns of the sintered foam samples contained gelling agent

3.6 Microstructure and physical properties of mullite porous ceramics

Figure 10 shows the typical microstructure of the mullite porous ceramics prepared by 18


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CFS. The microstructures obtained generally consisted of open, spherical-shaped pores with a narrow pore size distribution (Figure 10a). It could be observed that pore walls were sintered between grains to form mullite–whiskers which can be beneficial for the high strength of the porous ceramics, as shown in Figure 10b. After heat treatment at 1350 °C, the ceramics foam has a bulk density of 0.528 g/cm3, apparent porosity of 77.9 % and compressive strength 2.49 MPa. These values were close to those of reticulated porous mullite ceramics25,26. Porous mullite ceramics (1-22 MPa a porosity of 72-83% with 12-1600 °C sintered) were also prepared by Gong et al.

25

by foaming

and starch consolidation. Ding et al.26 fabricated the porous mullite ceramics with a porosity of 88.6 % and a relatively high-compressive strength of 1.52 MPa by a gel freeze-drying process followed by sintering at 1600 °C. Two factors could influence the mechanical strength of porous mullite ceramics prepared in this work: porosity and sintering neck.25 The gel-casting process was so suitable a method to prepare the porous mullite ceramics that there are little dimensional changes and few cracks in samples. Moreover, the relatively high-compressive strength could be also attributed to the complete mullitization and the intensive densification of mullite, which results in dense and tough struts.

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Figure 10 Microstructure of mullite ceramics foam heated at 1350 °C for 3 h

4. Conclusion

In summary, influences of gelling agent on the rheological properties of viscosity, thixotropy, and viscoelasticity for foam slurries during the solidification process were systematically investigated. The “micro” three-dimensional network-like structural units are taken shape owing to the DAT molecular. They wrapped the inorganic particles and foam to enhance the initial physical accumulation of particles. At the same time, the SS molecular formed a biggish 3D network throughout the system which could twine the “micro” network-like structural mentioned above. These structures also fixed the hydrone molecular by hydrogen bonding according to the hydroxy on the molecular chain that foamed hydrogel-like structure. Under these conditions, foam slurries were solid-like to shorten the curing time from 36 h to 10 h. After heat treatment at 1350 °C, the porous ceramics were found with a bulk density of 0.528 g/cm3, the apparent porosity of 77.9 % and compressive strength 2.49 MPa.

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Acknowledgments This work was financially supported by the Natural Science Foundation of Hubei Provincial China (2017CFC829, 2017CFB291), National Natural Science Foundation of China (61604110). This work was also financially supported by the China Scholarship Council for Dr Hui Chen.

Reference (1) Yuan, B.; Wu, H.; Sun, X.; Wang, G.; Li, H. Fabrication of porous alumina green bodies from suspension emulsions by gelcasting. Mater. Let. 2012, 81, 151. (2) Jiang, C.; Gan, X.; Zhang, D.; Xie, R.; Zhou, K. Gelcasting of aluminum nitride ceramics using hydantion epoxy resin as gelling agent. Ceram. Int. 2013, 39, 9429. (3) Brandi, J.; Ximenes, J. C.; Ferreira, M.; Salomao, R. Gelcasting of alumina-chitosan beads. Ceram. Int. 2011, 37, 1231. (4) Zhang, Y.; Xu, J.; Qu, Y.; Xi, X.; Yang, J. Gelcasting of alumina suspension using gellan gum as gelling agent. Cera. Int. 2014, 40, 5715. (5) Omatete, O. O. Gelcasting-a new ceramics forming process. Am. Ceram. Soc. Bull. 1991, 70, 1641. (6) Chen, Y.; Xie, Z.; Yang, J.; Huang, Y. Alumina casting based on gelation of gelatin. J. Eur. Ceram. Soc. 1999, 19, 271. (7) Deng, T.; Wang, Y.; Dufresne, A.; Lin, N. Simultaneous enhancement of elasticity and strength of Al2O3-based ceramics body from cellulose nanocrystals via gel-casting process. Carbohyd. Polym.2018, 181, 111. (8) Wu, Z.; Sun, L.; Wan, P.; Li, J.; Hu, Z.; Wang, J. In situ foam-gelcasting fabrication and properties of highly porous γ-Y2Si2O7 ceramics with multiple pore structures. Scripta. Mater. 2015, 103, 6. (9) Potoczek, M.; de Moraes, E. G.; Colombo, P. Colombo P, Ti2AlC foams produced by gel-casting. J. Eur. Ceram. Soc. 2015, 35, 2445. (10) Sanches, M.; Vitorino, N.; Freitas, C.; Abrantes, J.; Frade, J.; Neto, J. R.; Hotza, D. 21



Page 22 of 24

Cellular ceramicss by gelatin gelcasting of emulsified suspensions with sunflower oil. J. Eur. Ceram. Soc. 2015, 35, 2577. (11) Millán, A. J.; Nieto, M. I.; Moreno, R. Aqueous Gel-Forming of Silicon Nitride Using Carrageenans. J. Am. Ceram. Soc. 2001, 84, 62. (12) Millán, A. J.; Moreno, R.; Nieto, M. a. I. Thermogelling polysaccharides for aqueous gelcasting-Part I: A comparative study of gelling additives. J. Eur. Ceram. Soc. 2002, 22, 2209. (13) Santacruz, I.; Baudı́n, C.; Nieto, M. I.; Moreno, R. Improved green properties of gelcast alumina through multiple synergistic interaction of polysaccharides. J. Eur. Ceram. Soc. 2003, 23, 1785. (14) Millan, A. J.; Nieto, M. a. I.; Baudı́n, C.; Moreno, R.

Thermogelling

polysaccharides for aqueous gelcasting-Part II: Influence of gelling additives on rheological properties and gelcasting of alumina. J. Eur. Ceram. Soc. 2002, 22, 2217. (15) Wang, Y.; Cheng, H.; Liu, H.; Wang, J.

Effects of sintering temperature on

mechanical properties of 3D mullite fiber (ALF FB3) reinforced mullite composites. Ceram. Int. 2013, 39. 9229. (16) Deng, X.; Wang, J.; Liu, J.; Zhang, H.; Li, F.; Duan, H.; Lu, L.; Huang, Z.; Zhao, W.; Zhang, S. Preparation and characterization of porous mullite ceramics via foam-gel-casting. Ceram. Int. 2015, 41, 9009. (17) Du, X.; Zhao, L.; Chen, H.; Qu, W.; Lei, Z.; Li, Y.; Li, S. Synthesis and Properties of Multilayered Films Foams. Colloid. Surface. A. 2013, 436, 599. (18) Teng, W. D.; Edirisinghe, M. J.; Evans, J. R. Optimization of Dispersion and Viscosity of A Ceramics Jet Print Ink. J. Am. Ceram. Soc. 1997, 80, 486. (19) Dhara, S.; Bhargava, P. Influence of nature and amount of dispersant on rheology of aged aqueous alumina gelcasting slurries. J. Am. Ceram. Soc. 2005, 88, 547. (20) Potoczek, M. Gelcasting of alumina foams using agarose solutions. Ceram. Int. 2008, 34, 661. (21) Mewis, J.; Wagner, N. J. Thixotropy. Adv. Colloid. Interfac. 2009, 147-148. 214. (22) Mezger, T. G. The rheology handbook: for users of rotational and oscillatory rheometers. Vincentz Network GmbH & Co KG, 2006. (23) Nachbaur, L.; Mutin, J.; Nonat, A.; Choplin, L. Dynamic mode rheology of cement and tricalcium silicate pastes from mixing to setting. Cem. Concr. Res. 2001, 31, 183. 22


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(24) Schultz, M. A.; Struble, L. J. Use of oscillatory shear to study flow behavior of fresh cement paste. Cem. Concr. Res. 1993, 23, 273. (25) Gong, L.; Wang, Y.; Cheng, X.; Zhang, R.; Zhang, H. Porous mullite ceramics with low thermal conductivity prepared by foaming and starch consolidation. J. Porous Mat. 2014, 21, 15. (26) Ding, S.; Zeng, Y. P.; Jiang, D. Fabrication of mullite ceramics with ultrahigh porosity by gel freeze drying. J. Am. Ceram. Soc. 2007, 90, 2276.

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Relation between Rheological and Curing Behavior of Inorganic Foam

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