Preparation and properties of bimodal porous apatite ceramics through slip casting using different hydroxyapatite powders

A bimodal porous hydroxyapatite (HAp) body with high flexural strength was prepared through slip casting. The effect of different particle sizes on the flexural strength and microstructure of three different types of hydroxyapatite (HAp) powders was studied. The powder characteristic of laboratory-synthesized HAp powder (L-HAp) was obtained through a wet-milling method, drying and heating of a mixture of calcium hydrogen phosphate di-hydrate and calcium carbonate. The median particle size of L-HAp was 0.34 μm, and the specific surface area was 38.01 m²/g. The commercial HAp had median particle sizes for the K-HAp (Kishida chemical Co. Ltd., K-HAp) and T-HAp (Taihei chemical Co. Ltd., T-HAp) of 1.13 and 3.65 μm, and specific surface areas of 11.62 and 6.23 m²/g, respectively. The different powder characteristics affected the slip characteristics, and the flexural strength and microstructure of the sintered porous HAp bodies were also different. The flexural strengths of the porous HAp ceramics prepared by heating at 1200 °C for 3 h in air were 17.59 MPa for L-HAp with a porosity of 60.48%, 3.92 MPa for commercial K-HAp with a porosity of 79.37%, and 4.55 MPa for commercial T-HAp with a porosity of 76.46%.     

Fractal properties of boundary surfaces in zircon powders prepared by plasmochemistry methods

Translated from Steklo i Keramika, No. 3, pp. 20–21, March, 1992.     

Sintering and mechanical properties of MgO-doped nanocrystalline hydroxyapatite

Hydroxyapatite (HA) has been extensively studied for its exceptional ability in promoting osseointegration as in bone graft substitute and biomimetic coating of prosthetic implants. However poor mechanical properties of HA, in particular its low fracture toughness, has made its widespread adaption in a number of biomedical applications challenging. Here we employ an optimized wet precipitation method to synthesize nanocrystalline HA with significantly improved mechanical properties. In addition doping by MgO is found to effectively suppress grain growth and enhance fracture toughness by nearly 50% while good densification and phase stability in all samples regardless of concentration of dopant are fully maintained. Microstructural analysis further suggests that the exceptionally superior mechanical properties can be explained by migration of MgO to grain boundaries where they transform the more common transgranular fracture into an intergranular mode. Our biodegradation tests also confirm that MgO-doped HA is indeed a suitable candidate for load bearing implants.     

Sintering behavior of Ni–Zn ferrite powders prepared by molten-salt synthesis

Ni_0.5Zn_0.5Fe₂O₄ powders were prepared by a novel molten-salt synthesis method. The effects of calcination processes of the powders on their sintering behaviors were investigated. Compared with the synthesis by traditional solid-state reaction, the proposed molten-salt method can significantly reduce the synthesis temperature of Ni_0.5Zn_0.5Fe₂O₄ from 800 to 550°C below, and the prepared powders have relatively high sintering activity at low temperature, which can thus decrease the sintering temperature. However, the abnormal growth of grains is easy to occur during sintering, thus resulting in uneven grain size. In particular, during the molten-salt synthesis, the holding time for calcination is a dominant factor affecting the activity and crystallization degree of the resultant powders. From the point of view of increasing the density of sintered bodies, the optimal conditions for synthesizing Ni_0.5Zn_0.5Fe₂O₄ powder by the proposed molten-salt synthesis is 400°C for 6 h. In addition, the saturate magnetization of the finally obtained ferrite ceramics has nothing to do with the preparation processes, while their coercivity depends on their densification and grain size caused by their different processing routes.     

Sintering of nanostructured powders

Results are provided for a study of the internal structure of submicron spherical particles in ZrO₂–Y₂O₃ aerosol powders synthesized by ultrasonic atomization pyrolysis. It is shown the sintering potential for these powders is determined mainly by their internal nanostructural parameters, and not the degree of starting powder fineness. It is detected that the activity of submicron nanostructured powders is commensurate with the activity of ultrafine powders. In contrast to the latter, these powders consist of individual particles not joined in stable multiparticle formations, i.e., agglomerates. This simplifies considerably their practical application without loss of quality for the material obtained.     

Sintering of active powders

Conclusions An analysis was carried out of the properties of powders produced by calcining salts and grinding them in a planetary mill. Short-term grinding (2–3 min) increases the bulk density of the powders and the density of the green molding, improves the sinterability, and results in less firing shrinkage. With a longer grinding time the open porosity of the specimens usually remains high after firing.Short-term grinding in a planetary mill results in a significant improvement in the technological properties of active powders and renders them suitable for the production of ceramics.Translated from Ogneupory, No. 8, pp. 54–57, August, 1978.     

不同方法制备高吸水性树脂性能的研究

以玉米秸秆为主要原料,除杂改性得羧甲基纤维素。然后以N,N’-亚甲基双丙烯酰胺为交联剂,分别采用传统加热聚合、微波辐照聚合和超声辐照法合成高吸水性树脂,并对吸水树脂的吸水倍率、吸盐水(质量分数为0.9%NaC l水溶液)倍率及保水能力进行测试。结果表明,同一比例下,超声辐照法制得的吸水性树脂的吸水倍率及保水能力均高于其它两种方法;超声功率为60%的条件下,吸水倍率可达635 g/g。微波辐照法制得的吸水性树脂的吸盐水倍率较高,微波功率为320 W时制得的吸水树脂吸盐水倍率可达65 g/g。     

Comparative study of dielectric properties of geopolymer matrices using different dielectric powders

Due to their interesting properties, geopolymers have found various applications in different domains. The evaluation of the dielectric properties of a geopolymer matrix for RF applications is innovative. In this context, this paper focuses, first, on the evaluation of the suitability of a geopolymer matrix with dielectric materials, and then on the improvement of the real permittivity value of the obtained material. For this purpose, the precursors either dielectric powder or aluminosilicate powder were first characterized. Then, the feasibility of the geopolymer matrix was investigated. Based on the feasibility test, it was shown that these kinds of materials can be successfully filled with various types of dielectric materials, such as ZrO₂, BaTiO₃ and Y₂O₃. Moreover, the optimized parameters of the synthesis process, which included a small amount of water in the formulation, were 20 °C for the synthesis temperature, 85% for the humidity level and 7 days for the setting time. The measurement of the dielectric properties evidenced, first, that the real part of the relative permittivity strongly depends on the formulation and storage process. Then, the incorporation of a high percentage of BaTiO₃ (60%) induced an increase in the real part of the permittivity value and a decrease in the loss tangent. Finally, the mixing law of Maxwell-Garnet was applied to compare the theoretical and measured values of the permittivity. It was deduced that the small difference detected at low percentages whatever the dielectric materials can be explained by the preponderant effect of the geopolymer matrix compared to ZrO₂ or BaTiO₃, it seems that the mixing law well functioned with BaTiO₃ than ZrO₂. This is in accordance with the better dielectric properties for samples containing BaTiO₃.     

Multilayer structure of molybdena/γ-alumina catalysts prepared using different methods

The apparent surface coverage by molybdena in three series of$\text{MoO}{}_3\text{γ-Al}{}_2\text{O}{}_3$ catalysts prepared by different methods was determined by electrophoretic migration. These methods were designed to vary the extent of clustering (polymerization) in the solutions and on the wet catalysts. The combined use of electrophoretic migration and molybdenum extraction measurements showed that in alumina-supported molybdena catalysts with content below 14 wt%, molybdenum is present in both monolayer and multilayer forms over the entire range of molybdenum loading studied, irrespective of the method of catalyst preparation used.     

两种电化学方法对制备羟基磷灰石涂层的差异性研究

通过恒电流和脉冲电流技术在钛基表面制备磷酸钙,然后经热碱处理得到羟基磷灰石(HAP)涂层。利用X射线衍射(XRD)、红外光谱(FT-IR)和扫描电镜(SEM)等手段对涂层的结构及形貌进行了表征,并对涂层的耐腐蚀性进行了研究。结果表明,恒电流与脉冲电流技术均可在钛基表面电沉积羟基磷灰石涂层,所得的2种涂层均具有良好的生物相容性;与恒电流方法制得的涂层相比,脉冲电流技术制得的涂层更均匀、致密,与基体结合强度较高,在模拟体液中表现出较好的耐腐蚀性。     

Efficiency of different compaction methods for corundum-zirconia powders

Acomparative analysis for different methods of compacting corundum-zirconia powders of different fineness, and also the effect of a plastifier on compaction efficiency are presented. It is shown that the most dense compacts are prepared with two-directional magnetic-pulse pressing. In view of this it is proposed to use two-directional magnetic-pulse pressing of oxide powders as the main compaction method in the production of corundum-zirconia nanoceramics. Translated from Novye Ogneupory, No. 10, pp. 51–56, October 2008.     

High-performance polypropylene film prepared from reactor powders having different characteristics

Ultra-high molecular weight isotactic polypropylene (UHMW-iPP) reactor powders have been successfully ultra drawn below melting temperature (T_m) by a combination of calendar rolling and tensile drawing techniques. Two UHMW-iPP reactor powders having different MWs were synthesized by using the same Ziegler-Natta catalyst system at 70 °C in hexane. The resultant tensile properties increased with increasing draw ratio, due to orientation-crystallization during tensile draw, which was indicated by DSC and WAXD measurements. The film drawn under optimum conditions exhibited the maximum tensile modulus of ∼25 GPa, independent of sample MW, corresponding to 70% of the ultimate modulus of iPP crystal. However, the higher maximum tensile strength of ∼1.0 GPa was achieved for the reactor powder having the higher MW, which is three times as high as those of commercial high-strength iPP tapes. Such a fact that high performances have been achieved by processing from reactor powder state below T_m implies that crystallization with less entanglement occurs during polymerization. When drawability and resultant properties were compared among different iPP reactor powders prepared under different conditions, it was clarified that they were predominantly affected by not only MW but also by the reactor powder morphology, especially surface smoothness.     

Constitution and morphology of hydroxyapatite whiskers prepared using amine additives

Currently-available HA particle-reinforced composites are not suitable for use in large stress-bearing restorations and biomedical substitution due to low strength and poor durability. HA is the most promising because of good biocompatibility and bioactivity, and since reinforcement efficacy is greatly affected by length and aspect ratio, the preparation of long HA whiskers could be important for biomedical applications. Acetamide, formamide, and carbonyl diamide were tested as precipitation agents to modify crystal growth habit. The morphology and composition of the whiskers showed a sensitive dependence on the additive used. Carbonyl diamide and formamide led to contaminated HA; crystals were needle-like but contained carbonate or formate, respectively. In comparison, acetamide showed a low hydrolysis rate under hydrothermal conditions, giving rise to a rapid growth of HA crystals at a low supersaturation. Furthermore, the hydrolysis products of AA affected neither the composition nor the growth habit of the HA.     

Study of dielectric properties of polypyrrole prepared using two different oxidizing agents

Polypyrrole samples that have been prepared in a conducting state by a chemical method using two different oxidizing agents, ferric chloride and potassium persulphate, in different concentrations have been transformed to a dielectric state by heating at 333 K for 7 days and then at 353 K for 4 days more. Then the frequency and temperature 32 dependence of the dielectric constant ε′, loss tangent tan δ and AC conductivity σ′ were investigated using a complex impedance technique. It has been found that the concentrations of the reactants used in the preparation have a noticeable effect on the dielectric properties. It has been concluded also that heating at constant temperature has enhanced the resistivity of the samples, which can be considered as a simple method of obtaining polypyrrole (PPy) in a dielectric state rather than more complex electrochemical methods which may be useful in some future applications such as the manufacture of supercapacitors. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99:3370–3379, 2006     

Sintering behavior and mechanical properties of hydroxyapatite ceramics prepared from Nile Tilapia (Oreochromis niloticus) bone and commercial powder for biomedical applications

In this work, Nile tilapia (Oreochromis niloticus) bone was calcined at 800 °C for 5 h in an air atmosphere to obtain hydroxyapatite powder (FB powder). The elemental composition, phase structure, and morphology of the FB powder were investigated and compared with commercial hydroxyapatite powder (SM powder). The FB-powder exhibited 1.01 at. % of Mg while the SM-powder showed Mg in ppm-level. Carbonate groups were detected in the two powders. Both HAp and β-tricalcium phosphate (β-TCP) structures were found in the FB powder, but the SM powder exhibit only the HAp phase. Irregular-shaped particles were observed in the FB powder. After the two HAp powders were sintered at 1200 °C and 1250 °C for 2 h (FB-1200, FB-1250, SM-1200, and SM-1250), the β-TCP intensity peaks of the FB-ceramic samples significantly increased with increasing sintering temperature. The highest relative density, well-packed grains, and β-TCP stabilization by Mg at the Ca5 site of the FB-1250 structure were the dominant factors governing the highest mechanical properties. Although high density was observed in the SM-1200 sample, Vickers hardness of the SM-1200 sample is lower than the FB-1250 sample. This may be attributed to the partial decomposition of HAp into β-TCP, α-tricalcium phosphate (α-TCP), and Ca₁₀(PO₄)₆O phases. In addition, the increase of grain size was the main factor that governs the increasing compressive strength and Young's modulus instead of density and phase decomposition of the SM-ceramic samples.     

Sintering behaviour and properties of zirconia ceramics prepared by pressureless sintering

Improvements in the sintering process and powder quality can lead to wider application of zirconia in ceramics. In this study, the effects of different temperatures on the stability, relative content of the tetragonal phase, and composition of Al₂O₃–ZrO₂ ceramic powders were explored using pressureless-assisted sintering. The crystallinity of the sintered Al₂O₃–ZrO₂ samples was significantly improved. The content of the tetragonal-phase ZrO₂ in sintered ceramic powders was 52.07%, 52.46%, 56.16%, 63.99%, and 64.90%, respectively, which was significantly higher than those of the raw materials. The average particle size of the sintered samples decreased from 1.07 μm to 0.17 μm with an increase in temperature, indicating that the ceramic powder particles were refined. The sample that was subjected to pressureless-assisted sintering at 1200 °C and held for 1 h exhibited the best stability and more uniform particle distribution compared to other samples. The particle size distribution data were closer to the standard line, satisfying the requirements of the normal distribution law. The results revealed that a high temperature was more favourable to the solid solution, and the formation of an Al₂O₃–ZrO₂ solid solution can diminish the influence of the volume expansion of ceramic powders on the sample properties during sintering. Therefore, the addition of the sintering aid Al₂O₃ significantly promotes the densification of the powders, and the pressureless sintering technique reduces the sintering temperature of the solid solution, thus imparting a crystalline structure and excellent mechanical properties to the material.     

A comparative study on hygroscopic and physiochemical properties of chicken powders obtained by different drying methods

Abstract

Different drying methods (spray drying (SD), vacuum drying (VD), microwave vacuum drying (MVD), and infrared vacuum drying (IFVD)) were applied in order to compare the hygroscopicity behavior of chicken powders. The hygroscopicity curves and glass transition temperature were used to evaluate the influence of ambient humidity and temperature on moisture absorption of powders. The results showed that the chicken powder dried by MVD had the lowest moisture absorption, followed by IFVD, VD, and SD. The hygroscopicity of SD chicken powders was different from other three kinds of chicken powders due to the physical properties of particles and the changes of protein secondary structure as detected by the Fourier transform-infrared spectrometer. For the three vacuum drying methods, the difference of protein secondary structure was the main reason of differences in hygroscopicity. Although MVD chicken powders were slightly inferior to SD chicken powders in taste, MVD chicken powders were the best in terms of smell and color as suggested by instrumental sensory parameter evaluations. It was found that MVD had a positive effect on reducing moisture absorption and maintaining sensory quality of chicken powders.     

Enhancement of mechanical properties of hydroxyapatite coating prepared by electrophoretic deposition method

The addition of bio-inert ceramics such as alumina and zirconia can significantly improve the mechanical properties of hydroxyapatite bioactive coatings and increase their biocompatibility. In the present study, the surface of a titanium substrate was coated by the electrophoretic deposition method (EPD). Moreover, the reaction bonding process has been used to precipitate the nanocomposite containing the hydroxyapatite (HA), alumina, yitteria-stabilized zirconia (YSZ). The coating process was performed by an electrical power supply and a suspension of hydroxyapatite, aluminum, and YSZ nanopowders. For preparing a suspension consisting of 50% isopropanol and 50% acetone, 0.6 g/L of iodine was used as a stabilizer. Green and sintered coatings were analyzed by FE-SEM and XRD. In addition, the mechanical properties such as bonding strength, hardness, and toughness were measured. The hardness, bonding strength, and toughness of the HA coating were 107 ± 10.3 HV, 10.8 ± 3.2MPa, and 0.72MPa√m, respectively, while those of the HA-Al₂O₃-YSZ nanocomposite coating were 213 ± 1.8 HV, 35 ± 1.6MPa, and 1.6MPa√m, respectively.     

Characterization and catalytic properties of mesoporous CuO/SBA-16 prepared by different impregnation methods

CuO/SBA-16 catalysts were prepared by two different routes – the conventional impregnation method and the modified impregnation method with pH adjustment. These catalysts were characterized by X-ray diffraction (XRD), atomic absorption spectrometry (AAS), N₂ physisorption and hydrogen temperature programmed reduction (H₂-TPR) measurements which reveal that the cubic cage-like (Im3m) pore structure of the parent SBA-16 molecule sieves was well maintained throughout the synthesis. After introduction of Cu, a different CuO dispersion exists on these catalysts. The CuO/SBA-16 prepared by modified impregnation method has a single highly dispersed CuO which is considered as a highly efficient species for hydroxylation of phenol with H₂O₂. CuO/SBA-16 prepared by the conventional impregnation method shows the presence of bulk CuO species which is undesirable for this reaction.