The influence of sintering temperature on the properties of compacted bovine hydroxyapatite

On the sintering characteristic of hydroxyapatite (HA), the resulting microstructure and properties are influenced not only by the characteristic and impurities of materials but also are found to be dependent on the thermal history during the fabrication process. This research is concerned with the effect of sintering temperature on the relative density, hardness, and phase purity after sintering process. Bovine HA (BHA) powder obtained from heated local cortical bovine bone at 900 °C for 2 h was uniaxially pressed at 156 MPa into green bodies using a 20 mm cylindrical dies. The compacted green body was pressurelessly sintered in air atmosphere at temperatures ranging from 1000 to 1400 °C, at a furnace ramp rate of 5 °C/min and dwell time of 2 h. The BHA starting powder was characterized using XRD and FTIR. SEM was also used for observing the microstructures of the starting material. The sintered BHA specimens were analyzed using Archimedes method for measuring density; XRD for phase stability; and Vickers method for hardness measurement. The analysis results show that the starting BHA powder and the sintered BHA specimens contain HA. The intensity of the three main peaks of HA decreases with increasing sintering temperature which may be due to decomposition of HA at high temperature. The density and hardness of BHA increases with increasing sintering temperature based on the results obtained.     

Die wall friction and influence of some process parameters on friction in iron powder compaction

Abstract

The coefficient of friction is a system response parameter, which is affected by a number of parameters such as normal load and sliding distance. Experimental results describing the influence of these parameters are presented in this study. These parameters have a crucial role in the modelling of the compaction process and also provide an in depth understanding of the mechanism of friction in powder compaction. The powder surface characteristics change continuously during the pressing, making friction measurement quite difficult. An attempt has been made to identify and separate the powder behaviour during compaction. The experimental results show that the plastic deformation of the surface in contact with the die wall occurs at an early stage of the compacting. At densities above 5 g cm³ the plastic deformation is completed and the variation of the coefficient of friction is minimal. It has been observed that most changes of the powder surface occur at low densities. The nature of the friction has also been discussed.     

A study of magnetic properties of compacted amorphous powder cores

Magnetic properties of compacted cores which are formed from amorphous alloy powders prepared by a rapid quenching water atomization process are studied. The coercivity of the as-compacted core was estimated to beH _c=0.028(/I _s)+1200 with the idea that the coercive force depends on the magnitude of the stress variation. The a.c. magnetic properties are remarkably improved by use of the coupling agent and zinc stearate. The use of the amorphous powder core for choke coils of switching power supplies leads to the decrease of cut-off current, that is, an improvement in the efficiency of power supplies.     

Calcining influence on the powder properties of hydroxyapatite

The effect of different calcination temperatures on the powder characteristics and the sintered density of synthetic hydroxyapatite (HA) powders, produced using two different processing routes, was examined. Powders were produced by either drying, milling and sieving an as-precipitated HA or by spray-drying a slurry of precipitated HA. Calcining the two powders at temperatures between 400 and 1000 °C did not significantly affect the powder particle size. The specific surface areas of the two powders, however, were reduced from 70–80 m²/g for a calcination temperature of 400 °C to approximately 5–7 m²/g for 1000 °C. Analysis of the surfaces of the HA powders using scanning electron microscopy (SEM) illustrated the coarsening and subsequent sintering of the sub-micron crystallites that constitute a powder particle as the calcination temperature increased, corresponding to the decrease in surface area of the powders. The sintered densities of the final ceramics were not significantly affected by calcining the powders. Microhardness measurements of ceramics prepared from powders calcined at different temperatures showed no significant variations with calcination temperature or powder processing method. The results of this study have illustrated that for applications where HA may be used in powder form, for example in plasma-spraying and for the production of HA-polymer composites, calcining the HA will significantly affect the powder properties, namely the surface area and morphology of the powders. For applications requiring HA in a dense ceramic form, for example as granules or blocks, calcining the powders does not significantly affect the properties of the final ceramic.     

The influence of densification temperature and the size of powder particles on the properties of isotropic Nd-Fe-B magnets made of quenched ribbons

The influence of densification temperature and the size of powder particles on magnetization of remanence J _r , coercivity _J H _c of hot-densified Nd-Fe-B magnets made of MQP-A quenched ribbons was investigated. A connection between magnetic properties, parameters of production process and microstructure of the magnet was confirmed. It was found that the remanence of isotropic magnet depends on temperature of hot densification process but is practically independent of the size of powder particles. On the other hand, the temperature of hot densification process and the size of powder particles have a substantial influence on coercivity.     

Relationship between mechanical properties and structure in austempered alloyed compacted graphite cast iron

Abstract

Austempering kinetic measurements and mechanical property measurements are presented for a compacted graphite iron of composition Fe-3.4C-3.5Si-0.25Mn-0.50Mo-0.50Ni (wt-%) austempered at 375°C after austenitising at 890 and 940°C. Analysis of the austempering kinetics shows that alloying elements have a similar effect on the processing window as in ductile irons. The mechanical properties show optimum values at austempering times within the processing window. However, the graphite morphology limits the mechanical property enhancement achieved by austempering. Nevertheless, it is possible to double the strength of the as cast compacted graphite iron without loss in ductility.     

Effect of carbon-fibre powder on friction and wear properties of copper-matrix composites

ABSTRACT

The copper-matrix composite contains carbon-fibre powder which is prepared using a powder metallurgy sintering process in an effort to examine the effects of 50-mesh (270?μm) carbon-fibre powder on the microstructure and, friction and wear properties of copper matrix composites at high speed. When carbon-fibre powder is added within a certain range, the friction coefficient of the composite material is increased and the amount of wear is greatly reduced, When the content of carbon-fibre powder is 0.2wt-%, the hardness, density, friction and wear properties of the copper-based composite material has the best combination.     

The influence of different drying conditions on powder properties and processing characteristics

A water-based suspension of submicron titania particles was dried using a variety of techniques. The resulting powders were fully characterized in order to observe the effect of drying conditions on particle agglomeration. Direct evaporation methods led to quite severe agglomeration, whilst removal of the water by a freeze-drying technique produced powders containing only weak-secondary clusters.

The consequences of the state of aggregation after drying on powder compaction, sintering rates and microstructural development were determined. Although all powders originated from a common starting suspension, samples isolated by freeze drying sintered most rapidly, reaching about 98% of the theoretical density after firing at 1150 °C for 2 h. Agglomerated powders obtained after drying by evaporation, using either a heat lamp or microwave oven to drive off the water, required twice as long to sinter to comparable density. Moreover there was evidence of a much finer-grained microstructure in ceramics fabricated from freeze-dried products.     

Al_2O_3颗粒镀铜对铜基粉末冶金摩擦材料Al_2O_3-Fe-Sn-C/Cu摩擦磨损性能的影响

通过对陶瓷摩擦组元的表面进行化学镀铜来改善铜基粉末冶金摩擦材料中陶瓷相与基体间的结合效果,从而提高材料摩擦磨损性能。分别采用镀铜Al2O3颗粒和未镀铜Al2O3颗粒与铜粉和铁粉等经混合、压制、加压烧结制备Al2O3-Fe-Sn-C/Cu摩擦磨损试样。测试并分析了摩擦材料的微观结构、力学性能及摩擦磨损性能。结果表明:摩擦组元镀铜可使硬质颗粒与铜基体结合紧密;摩擦材料的布氏硬度增加了12%,弹性模量提高了约7%,摩擦系数提高了5%~10%,线磨损量降低了20%~50%;表面镀铜后的Al2O3颗粒不易脱落,摩擦系数稳定性提高了13%~23%。研究结果表明,摩擦组元表面镀铜可提高材料的综合性能。     

氧化石墨结构对电容性能的影响

研究了层状结构氧化石墨的片状尺度、结晶态及不同表面官能团含量对其电化学电容性能的影响.以光谱纯和化学纯石墨为原料,采用改进的Hummer法制备氧化石墨(GO),并将部分氧化石墨球磨.用FT-IR和XPS,对氧化石墨表面官能团进行了分析;XRD、FE-SEM和氮气吸附等温线,对氧化石墨结构和形貌进行了分析.利用恒电流充放...     

On the processing properties and friction behaviours during compaction of powder mixtures

ABSTRACT

Iron-based powder mixtures were prepared by dry and wet mixing method. The friction properties during compaction were tested by measuring the internal and external friction coefficient. The test results showed that the wet mixing process could realise the homogeneity of lubricant and improve the processing properties of the powder mixtures. With 0.6 wt-% lubricants, wet mixing powder mixtures have a flow rate of 29.6 s/50?g, an apparent density of 3.18?g?cm^–3, a repose angle of 35.5°, and the friction coefficient during the compaction is 0.223. An equation to calculate the total (both internal and external) friction forces during the compaction process is proposed, and then the factors influencing the friction coefficient during compaction were quantitatively analysed.     

The change in wettability and structure of silica powder surfaces modified with hexamethyldisilazane

The wettability and surface structure of precipitated silica surface loaded trimethylsilyl groups were investigated. By measuring water and nitrogen adsorptions, it was found that the non- treated sample had micropores. The pores with a diameter less than 0.8 nm were not modified, while the pores with a diameter from 0.8 to 0.9 nm were modified by trimethylsilyl groups and closed by them. From these results, it was assumed that the former pores would become sites for water vapor as surface silanol groups after modification and the latter pores would be independent of water adsorption. The character of the silica bare surface disappeared above a surface conversion rate of 33%. These results are deduced from neopentane adsorption experiments. Furthermore, the water adsorption capacity near saturated pressure, as an index of micro-wettability, did not reach the theoretical monolayer capacity above the same conversion rate (33%). It was also indicated that the preferential dispersion property as an index of macro-wettability drastically changed at a conversion rate of about 33%. From these results, it was demonstrated that the wettability is closely related to the surface structure interfering with the adsorption of water.     

The influence of powder loading and binder additive on the properties of alumina injection-moulding blends

The effects of powder loading and binder additive on the rheology, moulding, and sintered properties of alumina injection-moulding blends were studied. The melt viscosity increased with the powder loading, which enhanced the defect concentration of the moulded parts when the powder loading was higher than 0.54 volume fraction. This transitional powder loading was much smaller than the critical powder loading of 0.65 derived by fitting the rheological data with a mathematical model. The low molecular weight acidic binder additives used in this study effectively reduced the melt viscosity. However, additives that yielded a large quantity of burn-out residue deteriorated the sintered properties. A high powder-loading mixture having a low melt viscosity and good powder dispersion was achieved by eliminating powder agglomerates before mixing, and by using an appropriate binder additive.     

The influence of surface topography on the dynamic friction between acetylsalicyclic acid compacts and steel

The influence of surface topography on the value of the dynamic friction coefficient, _d, for acetylsalicylic acid compacts sliding on steel has been studied using a model system. The value of , an average representative of a range of values of _d, measured during interfacial displacement, was found to be inversely related to the surface roughness of the steel. This indicates the existence of a friction mechanism involving adhesion, deformation and shear components and establishes a potential method for the amelioration of friction problems without recourse to lubricants.     

Effects of plasma flow structure on heat transfer with powder particles

Measurements have been made on the heat transfer to granular material in a plasma reactor having a multijet mixing chamber. The temperature distribution over the cross section has been measured by a spectral method and by calorimetry. The granular-material flow rate affects the heat flux to the walls. The measurements are fitted to an equation in dimensionless parameters.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 5, pp. 824–828, May, 1990.     

Mechanical properties of implosively compacted suspension homopolymer S 57/116 PVC powder

The response of an aggregate of commercially produced particulate polymeric material to static and shock consolidation is described. The presence of interparticle bonding, associated with the explosive process, considerably increases the strength and hardness of the compact, as compared with static processing, and enables a high degree of densification to be attained. The final properties of the compact are influenced by the initial particle size, tap density, and the characteristics of the container. For an aggregate varying in particle size from –150 to 212 m, optimal conditions are reached at shock pressures of between 10 and 11 GPa.     

Variation in electrical properties during chemical reaction between iron powder and concentrated nitric acid

Herein is given the in-situ electrical measurements taken during the chemical reaction between iron powder and concentrated nitric acid. The results show a set of impulsive increases in current in the middle region of the first two seconds of the reaction. This consistent observation is interpreted as indication of intermediate chemical states and is in accord with our previous work showing alternating magnetic anomalies during reactions between iron and sulfur powders initiated by high temperature, and between iron powder and hydrochloric acid. Received: 20 October 2000 / Reviewed and accepted: 23 January 2001     

结合面静摩擦系数的统计模型

基于粗糙表面形貌的统计参数,综合考虑微凸体的完全弹性、弹-塑性和完全塑性三种变形机制,建立了结合面静摩擦系数的统计模型。该模型反映了静摩擦系数是由接触材料性能参数、表面形貌统计参数以及法向载荷共同决定的。通过仿真研究了微凸体高度的随机分布、塑性指数以及法向载荷等因素对静摩擦系数的影响规律。结果表明,修正的指数分布相比简单的指数分布对高斯分布有着较好的近似,且预测值近似等于高斯分布预测结果的均值;静摩擦系数随着塑性指数的增大而减小且变化趋缓;法向载荷增大时,静摩擦系数呈现减小的趋势,但在双对数坐标系下最大静摩擦力仍与法向载荷呈线性正比的关系。     

萃取剂对UHMWPE微孔膜结构与性能的影响

采用热致相分离(TIPS)法制备超高分子量聚乙烯(UHMWPE)微孔膜,研究了分别以正己烷、乙醇和1,2-二氯乙烷作为萃取剂对超高分子量聚乙烯微孔膜结构及其性能的影响.实验表明,当萃取剂依次是正己烷、乙醇和1,2-二氯乙烷时,UHMWPE微孔膜的孔径和孔隙率逐渐减小,但力学性能却逐渐提高.DSC法和WAXD法计算的微孔...