Powder Slurry Research Articles

Custom fabrication of reinforced lithium disilicate ceramic ingot.

A method of formulating a reinforcement lithium disilicate ceramic ingot was proposed. The ceramic ingot was broken manually with a mallet to finer particles. The sectioned ingot is ball milled along with 10% of nano zirconia by weight to obtain the desired powder. The reinforced powder is condensed in a 5 ml disposable syringe by powder slurry technique. The compacted ceramic were sintered at 900°C to obtain ceramic ingots. The reinforced ceramic ingots were used in pressable ceramic machines to obtain the desired advantages of zirconia reinforcement and pressable ceramic system.

Synthesis of CuAlO2 from chemically precipitated nano-sized precursors

A study was carried out on the synthesis of CuAlO2 at temperatures below 1000°C, using a simple approach based on mechanical mixing of chemically precipitated CuO and Al(OH)3 nanoparticles. Synthesis of precursor powders was achieved at low temperatures (<100°C) via precipitation from their corresponding aqueous solutions. After drying at room temperature, precursors were mixed in equimolar ratios by a combination of ball milling and sonication. Green pellets were obtained by filtration casting of the mixed powder slurry followed by dry compaction. X-ray diffraction study showed that the single phase CuAlO2 samples with high crystallinity formed only after 5h of firing at 900°C under flowing nitrogen. Electron microscopy images revealed a loosely packed microstructure with high surface area consisting of nanosized grains after the heat treatment. The achieved relative density was 45% of the theoretical density. The crystallite size was estimated to be 39nm and the specific surface area of the sintered sample was measured as 9.67m2/g. The bandgap was calculated as 3.07eV with a transmittance of 60% in the visible region. The measured electrical conductivity was 4×10−3mS/cm at room temperature and showed an increase with increasing measurement temperature, which indicates semiconducting behavior. The conductivity was shown to increase by an order of magnitude with a higher degree of densification by sintering at 1150°C.

Analysis of β-tricalcium phosphate granules prepared with different formulations by nano-computed tomography and scanning electron microscopy.

Among biomaterials used for filling bone defects, beta-tricalcium phosphate (β-TCP) is suitable in non-bearing bones, particularly in dental implantology, oral and maxillofacial surgery. When β-TCP granules are placed in a bone defect, they occupy the void 3D volume. Little is known about the 3D arrangement of the granules, which depends on the nature and size of the granules. The aim of this study was to examine the 3D architecture of porous β-TCP granules. Granules were prepared with different concentrations of β-TCP powder in slurry (10, 11, 15, 18, 21, and 25g of β-TCP powder in distilled water). Granules were prepared by the polyurethane foam method. They were analyzed by nano-computed tomography (nanoCT) and compared with scanning electron microscopy (SEM). Commercial granules of hydroxyapatite-β-TCP prepared by the same methodology were also used. The outer and inner architectures of the granules were shown by nanoCT which evidenced macroporosity, internal porosity and microporosity between the sintered grains. Macroporosity was reduced at high concentration and conversely, numerous concave surfaces were observed. Internal porosity, related to the sublimation of the polyurethane foam, was present in all the granules. Microporosity at the grain joints was evidenced by SEM and on 2D nanoCT sections. Granules presented a heterogeneous aspect due to the different mineralization degree of the sintered powder grains in the β-TCP granules; the difference between hydroxyapatite and β-TCP was also evidenced. NanoCT is an interesting method to analyze the fine morphology of biomaterials with a resolution close to synchrotron and better than microcomputed tomography.

Application of a coating mixture for solid oxide fuel cell interconnects

Due to high operating temperature (800–1000 °C) of SOFC's, limited number of alloys can be employed for the purpose of current collection. The electrical conductivity of these alloys usually decreases during the operation of SOFC because of highly corrosive cathode (air side) environment. Cr evaporation from such alloys is also an important problem of performance degradation. A spinel Mn1.5Co1.5O4 and perovskite La0.60Sr0.40FeO3 mixture is coated on Crofer alloy for corrosion and chromium protection in the cathode side of a SOFC. In study firstly, the performance of the fuel cell with the Crofer 22 APU as interconnect material was measured up to 100 h without any coating. Secondly, using a screen printing method, bare Crofer 22 APU was coated with Mn1.5Co1.5O4 and finally Mn1.5Co1.5O4 + La0.60Sr0.40FeO3 ceramic powder slurries were employed as the coating material. Then, the performances of a SOFC short stack with interconnects coated by two methods were compared with uncoated interconnect. Results show that uncoated interconnect experienced a significant performance lost from 4.5 W to 3.8 W. On the other hand the cells with screen printing coated with a mixture Mn1.5Co1.5O4 and La0.60Sr0.40FeO3 exhibited decreases only from 5.78 W to 5.42 W in the short-term performance tests.

Features of Structure Formation During the Thermal Synthesis of Powders Carbide-Steels from Waste Sludge of Bearing Steels

The peculiarities of structure and phase composition of the briquettes material obtained by thermal fusion of the mixture consisting of a powder slurry obtained by grinding rollers and cone bearings, titanium hydride and graphite. It was shown that after synthesis at temperatures of 1150÷1200 0С phase composition of the obtained alloy includes mainly phases of titanium carbide, cementite and α-Fe. When boron carbide introduced into the mixture too, the last dissociates during thermal synthesis, resulting along with titanium carbide in the alloy significant content boride phases - TiB, TiB2, Ti2B5 and FeB was identified.

Effect of pre-setting pressure applied flexure strength and fracture toughness of new SIFCON + RPC composite during setting phase

Reactive powder concrete (RPC) and Slurry Infiltrated Fiber Concrete (SIFCON) are steel fiber-reinforced cement composites which have superior mechanical properties such as compressive, tensile, shear and flexural strength with extraordinary toughness values. Manufacturing of a new composite material was intended by using superior performance of SIFCON in terms of flexural strength as well as superior performance of RPC in terms of compressive strength. For this reason, fresh SIFCON was filled into the bottom portion of mold by means of specially-designed molds and pre-setting pressure was applied by filling reactive powder concrete on it. For RPC and SIFCON in mold, pre-setting pressure was applied in six different pressures (0, 3, 6, 9, 12, 15MPa). Test results indicated that maximum flexure strength was obtained as 69.70MPa under 15MPa pre-setting pressure. According to control-without pressure, flexure strength was improved by 43.21% with 15MPa pre-setting pressure. Also fracture toughness was increased about 32.03% with 12MPa pre-setting pressure. Prefabricated structural elements can be produced with the composite material, which is built via SIFCON+RPC composite, without needing a steel reinforcement.

Effect of stirring time and sintering temperature on the properties of porous tricalcium phosphate using white particles as pore-creating agent

The present work reports a simple process for fabrication of porous tricalcium phosphate (TCP) ceramics from aqueous powder slurries using wheat particles as pore forming agent. The objective of this research is to learn the effect of stirring time and sintering temperature on the physical properties of porous TCP. Wheat particles incorporated in aqueous TCP slurries and stirred for 1, 2 and 3 hours. Subsequently the slurry was dried in oven at 80˚C for 24 hours and 120˚C for 8 hours. The dried green bodies showed shrinkage in the range 53 -56%. Removal of the pore former followed by sintering at 1000 and 1100˚C produced TCP bodies with porosity 59 – 78% and compressive strength 0.3 - 2.5 MPa.

Emerging technology and techniques.

A technique of fabricating feldspathic porcelain pressable ingots was proposed. A 5 ml disposable syringe was used to condense the powder slurry. The condensed porcelain was sintered at 900΀C to produce porcelain ingots. The fabricated porcelain ingots were used in pressable ceramic machines. The technological advantages of pressable system improve the properties, and the fabricated ingot enhances the application of feldspathic porcelain.

Equivalent Circuit Model Analysis of Microstructure-Controlled LSM/ScSZ Composite Cathodes by Powder Slurry Impregnation Method

Improved electrochemical performance of strontium-doped lanthanum manganite (LSM)/scandia-stabilized zirconia (ScSZ) composite cathodes for solid oxide fuel cells was accomplished by using the powder slurry impregnation (PSI) method where a prefabricated thin porous ScSZ electrolyte layer is impregnated with LSM/ScSZ powder mixture in slurry. The PSI method enabled control of the electrolyte surface roughness, resulting in a decreased electrode polarization resistance despite a tendency of the ohmic resistance to increase due to the added porous ScSZ electrolyte layer. Resistance separation by electrochemical impedance spectroscopy with an equivalent circuit model (ECM) revealed that the proposed composite cathodes exhibited a significant reduction in the oxygen reduction reaction (ORR) resistance at the triple-phase boundary (TPB). Optimization of the electrolyte surface structure is therefore critical so as not to offset the improvement in the ORR resistance. Furthermore, besides the ECM used to separate the resistances, two ECMs that represent the microstructure of actual composite electrodes were evaluated to clarify the electrode structural factors determining the measured impedance spectra. The analysis revealed that impedance response is influenced by the area ratio of the double-phase boundary to the TPB, although cathode performance is mainly determined by the TPB area and the ionic conduction resistance within composite electrodes.

Fabrication of Stainless Steel Foams Using Polymeric Sponge Impregnation Technology

316L stainless steel foams (SSFs) are fabricated successfully by polymeric sponge impregnation technology. The effects of mass fractions of PVA and powder on LOAD in impregnated sponge samples are investigated, and the effects of sintering temperature on apparent density, open porosity and bending strength of SSFs samples are also discussed. The experimental results show that the impregnated sponge samples may hold excellent 3D open-cell network structure and uniform muscles when the mass fractions of PVA and powder in slurry are kept in 9-13 % and 52-75% respectively; with rising the sintering temperature, the apparent density and bending strength of SSFs gradually increases, the open porosity reduces. After the temperature exceeds 1260°C, the bending strength reduces oppositely. A stainless steel foam sample with open porosity of 81.4% and bending strength of about 56.8 Mpa can be obtained after sintering at 1260 °Cfor 30min.

Structure–Property–Processing Relationships for Stainless Steel Foams Made by Mechanical Aeration of Powder Slurries

A simple process, based on the mechanical aeration of a powder slurry, followed by gel casting and sintering, has been used to produce 316L stainless steel metal foams. The foams have spherical pores, with a small size range, connected by windows, to create an interconnected, open cell structure. Despite the simplicity of the process, the foams have good and reproducible foam structures and compressive mechanical properties, although the ability to vary the pore size and density is limited. While foams of this type are more likely to be suited to applications where the connected nature of the porosity is exploited, they demonstrate mechanical properties on a par with foams and porous metals specifically suited to structural applications, where specific strength and energy absorption are paramount. Foams made in this way therefore demonstrate the multi‐functionality that is required of them if they are to be exploited and are thus exciting prospects for further development.

The impact of zinc recycling on the slurry rheology of WC–6 wt.% Co cemented carbides

The slurry rheology of zinc recycled and new WC–6wt.% Co materials has been studied. The impact of polymer molecular weight, particle size distribution, zeta potential and solids loading on slurry rheology has been investigated and correlated with spray dried powder properties. Powders were characterized in terms of granule size distribution, apparent density, flow rate and granule microstructure. Zinc recycled and new powders, produced in both laboratory and production sized mills, were rheologically tested at various particle sizes ranging from 1.3μm to 4.1μm and at 3 different alcohol fractions. Polymer breakdown did not occur during milling, and did not influence slurry rheology. Recycled powders exhibited more consistent zeta potentials compared to new powders however all of the slurries, recycled and new alike, displayed agglomerating tendencies. Grain size distribution was shown to be the dominant factor in the shear response and development of a slurry yield stress, which resulted in solid spray dried granules from slurries possessing finer grain size and a higher yield stress, compared to hollow granules resulting from slurries possessing a coarser grain size and a low yield stress. Finer slurries, regardless of recycling or not, displayed higher settling rates. Zinc recycled slurries settled less quickly than new slurries of similar particle size; however they required longer milling times to achieve the target grain size distribution. Both zinc recycled and new powder slurries can be tailored to produce ideal, solid granules.

Y2O3-BN 복합체의 미세구조 및 내플라즈마 특성

<TEX>$Y_2O_3$</TEX>-BN 세라믹 복합체를 제작하기 위해서, 분말 입도 <TEX>$3{\sim}10{\mu}m$</TEX>인 <TEX>$Y_2O_3$</TEX> 분말을 분산한 슬러리에 pH 조절제인 NaOH를 첨가하였으며 결합제로는 PVA, 가소제로는 PEG를, BN 분말과 혼합하고, 분무건조(spray drying)공정을 거쳐 <TEX>$Y_2O_3$</TEX> 혼합 분말을 제조하였다. <TEX>${\O}14mm$</TEX> 크기의 <TEX>$Y_2O_3$</TEX>-BN 시편을 성형하고, <TEX>$1550^{\circ}C$</TEX> 및 <TEX>$1600^{\circ}C$</TEX>에서 소결하여 <TEX>$Y_2O_3$</TEX>-BN 복합체를 제작하였다. BN 투입량과 소결온도의 변수에 따른 미세구조, 순도, 꺽임강도, 열팽창계수, 밀도, 체적저항, 내플라즈마 특성을 조사하였다. <TEX>$Y_2O_3$</TEX>-BN ceramic composites were fabricated from the slurries of yttria powder with average particle size of 3~10 <TEX>${\mu}m$</TEX>. The slurry was fabricated by mixing PVA binder, NaOH for Ph control, PEG, BN powder and <TEX>$Y_2O_3$</TEX> powder. The mixed <TEX>$Y_2O_3$</TEX> powders were obtained by spray drying process from the slurry. The <TEX>$Y_2O_3$</TEX>-BN composite specimen was shaped in size of <TEX>${\O}14mm$</TEX> and then sintered at <TEX>$1550^{\circ}C$</TEX> and <TEX>$1600^{\circ}C$</TEX>, respectively. The characteristics, microstructure, purities, densities, bulk resistance, thermal expansion, hardness and plasma resistance of the <TEX>$Y_2O_3$</TEX>-BN composites were investigated with the function of BN contents and sintering temperature.

Cathode Powder Surface Treatment Using Atmospheric Pressure Plasma

LiOH, Li2CO3 impurities of NCM (8:1:1) Li ion battery cathode powder were removed by using atmospheric pressure plasma. Specially designed plasma reactor was used for the study. The mixed gas of N2, H2, CH4, SF6 and NF3 was used for dielectric barrier discharge plasma generation. N2-SF6 and N2-NF3 mixed gas plasma showed the best removal performance and when the SF6 or NF3 content was increased, the removal efficiency was also increased with a plateau. Addition of a small amount of hydrogen containing gas such as H2 and CH4 into the plasma enhanced the impurity removal efficiency but the proportional relationship with the content increment with these gases was not shown. It is well known that the fluorine containing gas extinguishes plasma, however the hydrogen containing gas seems attenuated the extinguishing effect of the fluorine containing gas for this case. In the early stage of the study, the cathode powder was treated by direct contact with the plasma, however, it was also observed that the same removal effect was shown by just mixing the powder with the gas passed through the plasma generator. The plasma treatment of 3kW applied power could remove more than 50% of impurities from the NCM powder at 13kg/hr of the treatment speed. In the same impurity removal treatment condition, it was observed that fluorine passivation layer was formed on the surface of the cathode particle at the same time. Other than the impurity removal and fluorine passivation on the cathode active material, the atmospheric pressure plasma powder treatment can offer the solution for enhancement of dispersion property in making powder slurry and carbon adsorption on the active material surface etc.

Pure ZnO and composite ZnO/TiO2 catalyst plates: A comparative study for the degradation of azo dye, pesticide and antibiotic in aqueous solutions

Photocatalytic degradations of azo dye (RR 180), pesticide (2,4-D) and antibiotic (enrofloxacin) in aqueous solutions were performed and compared by using pure ZnO and ZnO/TiO2 composite (at 1:1 ZnO to TiO2 mole ratio) catalysts in a self-supporting plate form. The plates were produced by tape casting of the constituent powder slurries and sintering at 600°C. Photocatalytic degradations of these pollutants were carried out under UVA and UVC irradiations for 120min. Maximum degradation was obtained for 2,4-D solution using pure ZnO plates under UVC. Due to the photolysis effect, UVC wavelength yielded higher efficiency values for all the chemicals than UVA. The discrepancy in the photocatalytic performances of the pure ZnO and the ZnO/TiO2 composite plates were not found to be significant. The plates were found to be effective for the consecutive degradation tests which indicated their potentiality in extended applications.

Electroless Displacement Deposition of Noble Metal on Silicon Powder for Recovering from Urban Mines

Noble metal is not only precious but also crucial for such industries as electronics, catalysts, and jewelry. Recycling noble metals from scrap electronics and industrial wastes, which are called urban mines, is important to preserve natural resources and the environment. In the conventional recycling process, scraps and wastes are dissolved in an aqueous solution and refined chemically. To recover noble metals from a low concentration solution, an ion-exchange resin, activated carbon, electrolysis, or cementation is used. We have been studying electroless displacement deposition of noble metal nanoparticles on silicon (Si) substrates (1) for efficient solar cell production (2) and metal film formation (3). This deposition is a local galvanic reaction expressed by followings:Mn+ → M + nh+ (h+: hole)Si + 4HF2 - + 2h+ → SiF6 2- + 2HF + H2 and/or Si + 6F- + 4h+ → SiF6 2-.Recently, we applied this deposition for recovering noble metals from aqueous solutions (4). Figure 1 shows outline of this recovering process. The first step of the process is addition of hydrofluoric acid (HF) and Si powder into an aqueous solution of noble metal ions. Noble metal particles are deposited on Si powder. The second step of the process is addition of oxidizing agent, such as nitric acid into the solution. Only Si is dissolved into the solution, and only noble metal particles remain in the solid-state. This method is classified into cementation. Features of this recovering are simplicity of process, high efficiency of recovering noble metal, and availability of using waste Si powder and HF provided by electronics industries. Furthermore, this recovering can selectively recover noble metal and copper unlike conventional cementation. In this study, we have investigated recover of noble metal using sawdust Si powder, and replacement of toxic HF by non-toxic agent such as ammonium fluoride (NH4F). 0.2 M (M: mol dm-3) Si powder was added in a mixture solution of metals and 0.15 M HF. The initial concentration of each metal salt in the solution was 1.0 mM. After stirring at 200 rpm at a solution temperature of 298 K, the solution was filtered. The recovery was determined by measurement of change in metal ion concentration of the solution with inductively coupled plasma-atomic emission spectrometry (ICP-AES). Figure 2 shows the recovery plots of noble metals versus treatment time. These recovering uses 350 mesh Si powder or slicing slurry including sawdust Si after using for industrial wefering. Mean diameter of 350 mesh Si powder is 25 μm, and of slicing slurry is 10 μm. Slicing slurry is result in higher efficiency than Si powder. This efficiency of recovery is explained by specific surface area of Si. Figure 3 shows recovery plots of noble metals using 350 mesh Si powder and 0.15 M NH4F instead of HF. Au and Pt were recovered using non-toxic agent under lower rate than that for using HF.ACKNOWLEDGEMENTSThe authors thank Dong Rong Electronics Co., Ltd. for supplying used silicon slurry. The present work was partly supported by Exploratory Research of A-STEP from JST, Grant-in-Aid from Kawanishi Memorial ShinMaywa Education Foundation, and JSPS KAKENHI Grant Number 23560875.REFERENCESS. Yae, N. Nasu, K. Matsumoto, T. Hagihara, N. Fukumuro, and H. Matsuda, Electrochim. Acta, 53, 35 (2007).S. Yae, in: L.A. Kosyachenko (Ed.), Solar Cells - New Aspects and Solutions, InTech, Ch. 11, p. 321, Available from: http://www.intechopen.com (2011).S. Yae, K. Sakabe, N. Fukumuro, S. Sakamoto, and H. Matsuda, J. Electrochem. Soc ., 158(9), D573 (2011).K. Fukuda, S. Yae, N. Fukumuro, S. Sakamoto, and H. Matsuda, ECS Trans., 53(19), 69 (2013).

Sporicidal characteristics of heated dolomite powder against Bacillus subtilis spores.

Dolomite is a double salt composed of calcium carbonate (CaCO3) and magnesium carbonate (MgCO3). The heat treatment of CaCO3 and MgCO3 respectively generates calcium oxide (CaO) and magnesium oxide (MgO), which have antimicrobial activity. In this study, heated dolomite powder (HDP) slurry was investigated for its sporicidal activity against Bacillus subtilis ATCC 6633 spores. The B. subtilis spores used in this study were not affected by acidic (pH 1) or alkaline (pH 13) conditions, indicating that they were highly resistant. However, dolomite powder heated to 1000℃ for 1 h could kill B. subtilis spores, even at pH 12.7. Sporicidal activity was only apparent when the dolomite powder was heated to 800℃ or higher, and sporicidal activity increased with increases in the heating temperature. This temperature corresponded to that of the generation of CaO. We determined that MgO did not contribute to the sporicidal activity of HDP. To elucidate the sporicidal mechanism of the HDP against B. subtilis spores, the generation of active oxygen from HDP slurry was examined by chemiluminescence analysis. The generation of active oxygen increased when the HDP slurry concentration rose. The results suggested that, in addition to its alkalinity, the active oxygen species generated from HDP were associated with sporicidal activity.

슬러리 가압함침에 의한 3D Mullite 섬유 Preform의 알루미나 입자 충전

Well-dispersed slurries of submicron-sized alumina powders were pressure-infiltrated in 3D preforms of mullite fibers and the effects of the particle size and infiltration pressure on the particle packing characteristics were investigated. Infiltration without pressure showed that the packing density increased as the particle size decreased due to the reduction of the friction between the particles and the fibers. The infiltrated preforms contained large pores in the large voids between the fiber tows and small pores in the narrow voids between the individual fibers. Pressure infiltration resulted in a packing density of 77% regardless of the particle size or the infiltration pressure(210 ~ 620 kPa). Pressure infiltration shortened the infiltration time and eliminated the large pores in preforms infiltrated with the slurries of smaller particles. The slurry pressure-infiltration process is thus an efficient method for the packing of matrix materials in various preforms. of the Ti-based hard coatings is attributed to surface cracking and the diffusion of substrate atoms.

Equivalent Circuit Model Analysis of LSM/ScSZ Composite Cathodes Prepared by Impregnating LSM/ScSZ Powder Slurry into a Prefabricated Porous ScSZ Layer

Relationship between microstructure and performance of Sr-doped LaMnO3 (LSM)/Sc2O3-stabilized ZrO2 (ScSZ) composite cathodes was investigated using equivalent circuit models (ECMs) analysis. The cathodes were prepared by impregnating prefabricated porous ScSZ layers with a LSM/ScSZ powder slurry. This method enabled control of the electrolyte surface roughness. Three different ECMs were used for analysis: (i) commonly used ECM in which resistances were connected in series; (ii) ECM consisting of the double-phase boundary (DPB) and the triple-phase boundary (TPB) at the LSM/ScSZ interface; and (iii) ECM representing a three-dimensional electrode. The analysis revealed that impedance response is influenced by the area ratio of the DPB to the TPB although cathode performance is mainly determined by the TPB.

Effect of joining conditions on microstructure and flexural strength of long silicon nitride pipes fabricated by local heat-joining technique

The microstructure and flexural strength of long silicon nitride pipes joined by a local heat-joining technique at different mechanical pressures, temperatures, and holding times were examined. Silicon nitride pipes sintered with Y2O3 and Al2O3 additives were used as the parent material, and a powder slurry of a Si3N4–Y2O3–Al2O3–SiO2 mixture was brush-coated on the rough or uneven end faces of the pipes. The flexural strength gradually decreased with decreasing mechanical pressure from 5 to 1.4 MPa at 1600 °C for 1 h. A large number of small voids measuring less than 1 μm were present in the joint layers of the samples joined with mechanical pressures of 1.4 and 3 MPa at 1600 °C for 1 h, although there were very few voids formed at 5 MPa. When the joining temperature was increased to 1700 °C for 1 h, some voids were observed in both the joint layer and the parent silicon nitride, and the flexural strength decreased to 529 MPa. Furthermore, some voids were formed in the parent silicon nitride when the holding time was increased from 1 to 4 h at 1600 °C and 5 MPa, which indicated slight degradation of the strength from 677 to 644 MPa.