Binary Powder Mixtures Research Articles

Experimental study of the deformation behaviour of compacted metal powders used in a new rapid tooling process

To examine the feasibility of a newly proposed rapid tooling process based on the backing of a metal shell with metal powders, the compressive deformation behaviour of selected metal powders and metal shells was investigated. It was found that the mechanical properties of the powder material and the mixing ratio of powders of different sizes had a significant effect on the compressive deformation behaviour of the compacted powders. Softer metal powders with the same compressive stress tended to produce greater plastic deformation and formed a block under a stress of 138 MPa. Mixing two or more powders of different sizes could significantly increase the deformation resistance of the compacted powders. Minimum plastic deformation was achieved when the fraction of the coarse powder in a binary powder mixture reached 0.77. Initial loading at a higher stress could minimize or eliminate the plastic deformation in subsequent loading cycles. This feature could be used advantageously in powder packing for the proposed new rapid tooling process. Some elastic properties of the compacted metal powders were also determined from the compression experimental data.

Effect of random internal structure on combustion of binary powder mixtures

Combustion of a mixture of two solid reactants is considered. A combined geometrical and physicochemical model of mixing of these reactants is proposed. The model takes into account random distribution of reactants and voids over the system. This allows description of incomplete burning of reactants. The model is used for studying the combustion wave propagation in a binary heterogeneous mixture. The obtained results are compared with those calculated from the perfect-mixing model, which implies that the deficient (with respect to the stoichiometry) component burns completely. It is shown that micrononuniformity of mixing not only reduces the combustion wave temperature and velocity but also can lead to a shift of the maximal wave velocity away from the stoichiometric composition of the mixture. The results of this study allow us to suggest that one of the main reasons for such a shift, which was observed in a number of experimental works, is structural disorder of binary mixtures.

Influence of Compacted Hydrophobic and Hydrophilic Colloidal Silicon Dioxide on Tableting Properties of Pharmaceutical Excipients

The effect of noncompacted and compacted hydrophilic as well as hydrophobic colloidal silicon dioxide (CSD) on tableting properties of three different pharmaceutical excipients used for direct compression, namely, Avicel® PH 101, Starch 1500®®, and Tablettose® 80, was investigated. Binary powder mixtures containing 0.5% CSD and 99.5% excipient were compressed on an instrumented single-punch tablet press, and the radial tensile strength/compaction load profiles were examined. The Ryshkewitch-Duckworth relationship shows that the influence of CSD on tablet strength was dependent on the hydrophobic and hydrophilic nature of the CSD and on the compaction characteristics of the excipients. Tablets from each excipient with and without CSDs were subjected to different levels of relative humidity at 20°C for 7 days. The sorption isotherms and the radial tensile strengths of the tablets after the storage period showed that neither hydrophilic nor hydrophobic CSD influenced the tablet properties of Avicel® PH 101, Starch 1500®®, and Tablettose® 80. Moreover, ternary powder mixtures containing magnesium stearate as a third component were compressed in order to study the influence of CSD on the deleterious effect of magnesium stearate on the interparticle bonding. The radial tensile strength/compaction load profiles and the residual and ejection forces of tablets made from ternary mixtures showed that CSD eliminated the negative effect of magnesium stearate on interparticle bonding while maintaining the lubrication action, in a manner that was affected by its hydrophobicity/hydrophilicity and by the particle deformation properties of the excipient upon compression.

Effect of glidants in binary powder mixtures

The intention of this study is to investigate on a particulate level the flow properties of dry powder mixtures consisting of cornstarch and a second nanoscaled material. Special attention is paid to the question on the working mechanism of glidants. In 1974, Rumpf showed that a roughness on the surface of a smooth particle leads to a reduction of its forces of interaction with another particle. The interaction forces are reduced as the surface roughness increases the distance between the centers of gravity of the two interacting particles. Agglomerates as well as the primary particles of materials used as glidants are characterized by diameters in the lower nanometer range. In consequence they are strongly adsorbed at the surface of larger particles and act as a surface roughness. If the effect of a glidant would be due to its ability to act as a surface roughness then all nanoparticles being small enough to reduce the net interaction forces could be used as glidants almost irrespective of their chemical nature. Indeed we have been able to demonstrate that nanoparticles of titanium dioxide, aluminum oxide, silicon dioxide or of carbon black act as glidants. Mixing time directly influences the efficiency of a nanomaterial to act as a glidant. Due to increasing ratio of adhesive force to particle weight with decreasing particle radius, nanomaterials tend to aggregate and agglomerate. With increasing mixing time the size of agglomerates decreases. At the same time the number of primary particles available for adsorption on the surfaces of the cornstarch particles increases. An optimum in flow properties is achieved at a characteristic mixing time. At a further increase in mixing time, the size of agglomerates decreases and the coverage of the cornstarch particles by nanoparticles increases. Eventually cornstarch particles are obtained being completely coated with nanoparticles. The surfaces of these coated particles are smooth. Accordingly they show a poor flow behavior. The property of the nanomaterial to act as a glidant is lost.

Methodology for Determination of the Maximum Packing Fraction for Particle-Filled Polymer Suspensions

An analysis technique was developed on the basis of a modified version of Sudduth's model for calculating maximum packing fraction (MPF). Calculated MPF values were compared with experimental values obtained with rheological methods. By analysis of MPF data for three commercial titania powders dispersed in low molecular weight polyethylene, a large difference was observed between the experimental and calculated MPF values. For instance, a TiO 2 P25/VF sample had an experimental MPF of 0.15 while the calculated value was ~0.8. To address this issue, f was incorporated as a variable that would influence the packing fraction. By studying the behavior of three different types of submicron titania, an empirical equation was devised, that correlated f with particle size, particle size distribution, and packing structure. This overall treatment appeared to be relevant for predicting the f for binary millimeter steel powder mixtures. Thus, the form of this empirical function may guide us towards developing a derivation of a quantitative expression based on first principles.

Damping and elastic properties of binary powder mixtures

Damping and elastic properties of binary powder mixtures were investigated by a dynamic measurement method using vibration. Experiments were performed on a range of binary powder mixtures comprised of glass sphere, sand, polyethylene and rubber powders. Loss factor and Young's modulus of binary mixtures were calculated from the experimental data. The calculated loss factors were dependent upon the mixing fraction, but almost independent of compressive stress and packing conditions. In order to describe the properties of binary mixtures, a simple two-phase model has been developed and compared with experimental data. Reasonable agreement between the model and the experimental data was obtained.

Experimental study of the mixing kinetics of binary pharmaceutical powder mixtures in a laboratory hoop mixer

As increasingly commented by the literature during the last 5 years, estimating the homogeneity of a powder mixture and following powder mixing processes is not a simple task. In this paper, we present the development and statistical validation of a sampling methodology for defining the number of samples required to provide a reasonable estimation of the homogeneity attained in a laboratory scale tumbler mixer. This method is then used to follow the mixing kinetics of a dilute binary powder mixture in a hoop mixer. Special attention is paid to the statistical meaning of the values obtained and the influence of the physical characteristics such as particle size and shape. The role of the particle shape of the majority powder is particularly emphasised and it is quantitatively demonstrated that spherical particles are harder to mix and more ready to segregate than particles with irregular shapes. The different mixing mechanisms at play are identified; the practical limits of use of such tumbler mixers with pharmaceutical powders are discussed.

Effective mass of powder beds subjected to low magnitude vibration and its application to binary systems: Part 2—comparison of segregated and well-mixed binary powder mixtures

This paper presents an investigation of segregated and well-mixed binary powder mixtures in terms of the effective mass of the powder beds, when subject to low magnitude vibration (<0.1 g) . An experimental system, developed in Part 1 of the present series of papers, was used to measure the effective mass of powder beds. Segregated systems were produced from materials of different densities, by layering materials. Tests were performed with both segregated and well-mixed systems with changing the mixing ratio. There was a significant difference in the effective mass between segregated and well-mixed systems, indicating that the effective mass of binary powder mixtures is dependent upon the dispersion of composition and the quality of mixing. The effective mass of well-mixed systems was in agreement with Rayleigh's theory, whilst the segregated systems showed significant deviations from the theory. A simplified model based upon Rayleigh's energy method was proposed to predict effective mass for segregated systems, and compared to experimental data. Results showed a reasonable agreement between the model and experimental data. The application of this technology to mixing has been examined, and the effective mass has been measured as a function of mixing time in a number of mixing situations. The effective mass indicates not only the deviation from an ideal mix, but also the direction of segregation.

Interactions of a La 0.9Sr 0.1Ga 0.8Mg 0.2O 3− δ electrolyte with Fe 2O 3, Co 2O 3 and NiO anode materials

In this study, the interactions of a Sr- and Mg-doped lanthanum gallate (LSGM with composition La 0.9Sr 0.1Ga 0.8Mg 0.2O 3− δ ) electrolyte with Fe 2O 3, Co 2O 3 and NiO as the anode starting materials were investigated. It was found that the order of reactivity of the LSGM with the three oxides was Co 2O 3>NiO>Fe 2O 3, and La-containing oxides were detected in these binary powder mixtures after firing. The anode performance was greatly influenced by the interaction. The Fe 2O 3–LSGM anode, mixed with 40 vol.% LSGM powder and sintered at 1150°C, exhibited the highest initial performance in comparison with NiO–LSGM and Co 2O 3–LSGM anodes. It seems that Fe 2O 3 is a possible anode starting material for a LSGM-based solid oxide fuel cell.

Energy dissipation of binary powder mixtures subject to vibration

Abstract This paper presents an investigation of energy dissipation of vibrating binary powder mixtures packed naturally at low acceleration levels. A model based upon both viscoelastic and two-phase theories has been developed to predict the dissipation energy of binary mixtures packed naturally. Two experimental systems including open-top and top-cap systems were used to measure the properties of the mixture beds subject to vibration. The open-top system provides the dissipation energy rate of a powder bed packed naturally. On the other hand, the top-cap system produces the elastic and damping properties of a powder bed with a top-cap mass as a loading weight. The model developed uses the elastic and damping properties of the powder bed deduced from the top-cap data to predict the properties of beds packed naturally. Comparison between the model and experimental data obtained by the open-top system has been made, and good agreement between the model prediction and the experimental data was obtained. This has implications for the damping mechanisms and dynamics of binary powder mixtures packed naturally under vibration.

高エネルギー遊星ボールミルによるＡｌ９５−ｘＦｅｘＣｒ５混合粉末のメカニカルアロイング過程

Al95–xFexCr5 (X=10, 25, 35, 50) ternary powder mixtures and Al–(10, 25, 35, 50) at%Fe binary powder mixtures were mechanically alloyed by high-energy ball milling using a ball-to-powder weight ratio of 238: 10. The structural evolution during milling was investigated by X-ray diffraction techniques and transmission electron microscopy. The solid solutions of α–Al(Fe, Cr) and α–Fe(Cr) were formed in the early stage of milling for Al–Fe–Cr powder mixtures. In the case of Al–10 at%–5 at%Cr powder mixtures, the Al80Cr13.5Fe6.5 compound was formed and disappeared during milling, and Al5(Fe, Cr)2 and Al(Fe, Cr) were detected after longer time milling. In Al–25 at%–5 at%Cr powder mixtures, Al5(Fe, Cr)2, Al(Fe, Cr) and amorphous phases were consecutively formed during milling. In milling process of Al–35 at%–5 at%Cr and Al–50 at%–5 at%Cr powder mixtures, only the Al(Fe, Cr) compound was found and it finally became an amorphous phase. Retardation of amorphization was recognized in the Al–Fe–5 at%Cr ternary system, and the composition range of amorphous formation was almost in agreement with the results of enthalpy calculation for the solid solution and amorphous phase in the systems.

Quantitative analysis of polymorphs in binary and multi-component powder mixtures by near-infrared reflectance spectroscopy

Near-infrared reflectance spectroscopy was employed to quantify polymorphs in binary and multi-component powder mixtures. Sulfamethoxazole (SMZ) forms I and II were used as model polymorphs for this study. The instrument reproducibility, method error, precision, and limits of detection and quantification of the method were assessed. Physical mixtures of the polymorph pair were made by weight, ranging from 0 to 100% SMZ form I in II. Near-infrared spectra of the powder samples contained in glass vials were obtained over the wavelength region of 1100–2500 nm. A calibration plot was constructed by plotting SMZ form I weight percent against a ratio of second derivative values of log(1/ R′) (where R′ is the relative reflectance) versus wavelength. The coefficients of determination, R 2, were generally greater than 0.9997 and standard errors were low for all the systems. Instrument error was assessed by analyzing a sample 10 times without perturbation. Method error was assessed in the same manner except the sample was re-mixed between analyses. A precision study was conducted by analyzing aliquots from a larger homogeneous sample. Limits of detection (LOD) and quantification (LOQ) were determined from the standard deviation of the response of the blank samples (100% SMZ form II, undiluted or diluted with 60% lactose). These limits were subsequently validated with independent samples. The results show that polymorphs can be quantified in binary and multi-component mixtures in the 2% polymorph composition range. These studies indicate that NIRS is a precise and accurate quantitative tool for determination of polymorphs in the solid-state, is comparable to other characterization techniques, and is more convenient to use than many other methods.

Interface reactions in the NiO–SDC–LSGM system

The reactivity of NiO–SDC (samaria-doped ceria) anode material with a Sr- and Mg-doped lanthanum gallate (LSGM) electrolyte was studied by X-ray diffraction (XRD) and electrical measurements. It was found that a LaNiO 3-based compound in hexagonal structure formed in binary powder mixtures of NiO and LSGM after firing at 1150°C. Reaction between SDC and LSGM was also observed. Several SDC peaks merged with the adjacent LSGM peaks during firing, and a SrLaGa 3O 7 compound was identified as a reaction product. Reaction between LSGM and SDC could cause more than 50% loss in the ionic conductivity of LSGM–SDC electrolytes sintered at 1350°C. The measured conductivity of an LSGM electrolyte with a NiO–LSGM anode prepared at 1350°C was extremely low, indicating that the LaNiO 3-based new phase is highly insulating. The reaction between NiO and SDC was not so obvious in comparison with NiO–LSGM and SDC–LSGM binary mixtures.

Quantitative determination of content in binary powder mixtures using diffuse reflectance near infrared spectrometry and multivariate analysis

A simplified methodology for development of calibrations for binary powder mixtures using near infrared (NIR) spectroscopy is presented. It is demonstrated that multivariate calibration can be performed using only a small calibration dataset of two to five samples. The intrinsic heterogeneity of the powder mixtures at the sample size effectively measured using standard fibre-optic probes prevents the assignment of a true reference content value to each obtained spectrum. Instead, the nominal mixture content of the sample is used as reference value. To obtain a spectrum more representative of each sample, a mean spectrum is computed from several spectra collected from different sample sub-fractions. Two principally different powder mixtures were used in this study: one composed of two fine powders ( d<300 μm) and the other mixture composed of one fine ( d 50=170 μm) and one coarse ( d 50=590 μm) powder. In the case of mixing fine powders, the calibration model is obtained by PLS regression using two PLS components after spectral data pre-treatment with multiplicative signal correction (MSC). Furthermore, it is demonstrated that the powder content variation determined by NIR is wavelength dependent due to the dependence of effective sample size on radiation wavelength. In the case of mixing one fine and one coarse powder, the large difference in particle size between the two powder components cause a non-linear X– Y relationship, which can be handled by means of spectral averaging and a non-linear (QPLS) regression. In both cases, the first PLS loading vector was interpreted as describing the difference between the spectra of the two pure components. The presented methodology should be useful for applications of NIR spectroscopy in processes involving powder mixtures.

Investigation on Multi-Layer Direct Metal Laser Sintering of 316L Stainless Steel Powder Beds

Research and development of laser based sintering technology has occurred at a rapid pace since its invention in the 1980s'. A wide range of materials have been developed including polymers, metals and ceramics. The ultimate goal for this technology is to provide manufacturing industries with fast and flexible means of producing parts that are truly functional. Step by step this active research area is leading towards rapid manufacturing solutions which will be significantly different from the rather limited rapid prototyping solutions of today. In processing metallic materials, porosity is still a major problem although a number of notable solutions such as infiltration with low melting point alloys or direct fusing with binary powder mixtures have been proposed. Neither of these solutions allows one to build components without compromising part strength and functionality. A process route is required that will allow solid parts to be built from a single powder component without requiring time consuming downstream processes. The surface quality must be consistent with those attainable by modern machining techniques. To this end, the present work examines the feasibility of using low energy high peak power laser pulses from a Q-switched Nd:YAG laser to melt stainless steel powder fractions whilst examining the melt displacement and the effects of rapid vaporisation of the powder layer.

Prediction of the Hiestand Bonding Indices of Binary Powder Mixtures from Single-Component Bonding Indices

ABSTRACTA priori predictions of the bonding indices of binary powder mixtures from the single-component indices were attempted. The binary mixtures were classified according to the mechanism of deformation of the single-components as plastic–plastic, brittle–brittle, and plastic–brittle. When the components of a binary mixture consolidated by the same mechanism (plastic–plastic and brittle–brittle mixtures), a straight line could be fit to a plot of bonding index versus composition. This linearity indicates that the bonding index can be reliably estimated by interpolation between the two single-component bonding indices. When the mixtures were such that one component was brittle while the other was plastic, a linear function did not fit the data. For these cases, a second-degree polynomial equation could befit to a plot of bonding index versus composition. A combination of multiple linear regression and trial and error was used to generate a single generalized equation. For pairs of compounds wherein each compound has a different compaction mechanism, this new equation appears to allow satisfactory predictions of the bonding indices of mixtures with varying compositions using only the single-component bonding indices.

Prediction of the Hiestand Bonding Indices of Binary Powder Mixtures from Single-Component Bonding Indices

Prediction of the Hiestand Bonding Indices of Binary Powder Mixtures from Single-Component Bonding Indices

Tribochemical Applications of High-Intensity Ultrasound: Sonochemical Production of Intermetallic Coatings in Heterogeneous Media

An energy-dispersive X-ray (EDX) study of binary mixtures of mixed composition metal powders exposed to high-intensity ultrasound in decane indicates that metal particles are fused by the action of ultrasound and develop intermetallic coatings. The principal mechanism behind both processes is interparticle collision caused by the rapid movement of particles propelled by shockwaves generated at cavitation sites. By examination of systems with differing metallurgical compatibilities (Ni/Co, Cu/Cr, and Cu/Mo), it has been determined that the intermetallic coatings are generated by both adhesive wear and direct impact. The mechanisms of ultrasound-induced coatings are discussed.

Detecting powder mixture segregation for multicomponent mixtures

Rollins et al. (1995, Powder Technol. 84, 277–282), showed the superiority of the analysis of variance technique (ANOVA) over the mixing index approach in the detection of segregation in binary powder mixtures. In industry, a common problem is determinating the level of segregation in a multicomponent mixture. This article compares the performance of multivariate analysis of variance (MANOVA) technique to that of multivariate indices. Using a Monte-Carlo simulation study, the techniques performances are evaluated for varying levels of segregation, between species (intra) correlation, level of measurement error and level of test significance.

Effect of driving force on pressure slip casting of silicon carbide bodies

Binary silicon carbide powder mixtures with the particle size distribution designed to maximise the particles packing density were dispersed in aqueous medium in the absence and in the presence of different amounts of a deflocculant. The solid loading was fixed at 70 wt% and correspond to the conditions that most facilitate homogeneously and high packed structures to be obtained. The influence of the amount of deflocculant and applied pressure on the kinetics of the pressure slip casting process and on the microstructure of the green bodies was investigated. It was found that the pressure promotes a slightly increasing trend of green density of bodies obtained from suspensions with no or low amounts of deflocculant. The structures obtained from wellstabilised slurries are pressure independent. However, the maximum packing densities were always lower than that obtained by slip casting and required higher concentrations of deflocculant. Further, for a given applied pressure, it was found that the green density was time dependent. This results could be interpreted in terms of different particle rearrangement mechanisms.