Compacted Powder Mixtures Research Articles

Consolidation and compaction of powder mixtures: III. Binary mixtures of different particle size fractions of different types of crystalline lactose

Tablets were compacted from a coarse fraction (250–315 μm), a fine fraction (32–45 μm) and from binary blends of a coarse and a fine fraction of different types of crystalline lactose. The results showed differences in consolidation and compaction between the granular lactose types i.e., roller-dried β-lactose and anhydrous α-lactose, and the non-granular lactose types, namely, crystalline β-lactose and α-lactose monohydrate. Equal particle size fractions of the granular types of lactose exhibited greater specific powder surface areas, less fragmentation on compression, and higher binding capacities than the non-granular types. Slight increases in consolidation were demonstrated on compression of binary blends of the coarse and fine fraction of the different types of lactose. Differences in morphology between the lactose types were shown by increasing true densities of the granular types when examined on tablets compacted with increasing compression force. No change in true densities on compaction were demonstrated by the non-granular types.

In situ microfusion process in Al—Fe alloys

An exothermic reaction in the Al—Fe alloy system was utilized in the sintering of compacted powder mixtures. The reaction occurs during the heating period, and the heat generated in the reaction provides a small liquid volume. The liquid is necessary for densification, and full densification requires an optimum amount of liquid based on suitable processing conditions, such as the particle size, the compaction pressure, and the lifetime of liquid. Some parameters, such as the furnace temperature, the iron addition, the reaction temperature and the heating rate, affect the sintering mainly through their influence on the liquid volume. Others affect the compact viscosity, the distribution of liquid and the spreading of liquid during sintering. The optimum processing conditions given are based on the experimental work, and the interaction effects between the parameters are also discussed, leading to a suggested mechanism for the process.

Consolidation and compaction of powder mixtures: II. Binary mixtures of different particle size fractions of α-lactose monohydrate

Binary mixtures of different particle size fractions of α-lactose monohydrate were compacted into tablets. The results showed decreased crushing strengths and decreased internal specific surface areas of the tablets as compared with the values calculated by linear interpolation of the data obtained for the corresponding single powder fractions. The extent of decreased strength and decreased surface area of the tablets was found to depend upon the weight ratio of the finer sieve fraction in the blend and to increase with the diameter ratio between coarse and finer particles. These results indicate an interaction with respect to consolidation and compaction which is explained by decreased fragmentation potentials, caused by increased packing densities of the binary mixtures of different particle size fractions of crystalline lactose. All data on crushing strength and internal specific surface area of the tablets fitted the unique linear relationship between these parameters, as found previously for tablets compressed from binary mixtures of equal particle size fractions of different types of crystalline lactose.

Sintering Property of Green Compacts of Si and TiC Mixed Powders in Nitrogen

The sintering property of powder mixture compacts of TiC and Si in a nitrogen atmosphere at 1350°C is discussed. TiC formed TiN and free carbon on reaction with nitrogen, and a small portion of this free carbon was converted into β-SiC on reaction with Si. A large portion of the Si formed Si3N4 on reacton with nitrogen. Approximately half of the TiC remained unreacted when heated for 10h at the final sintering temperature of 1350°C. Thus, composite ceramics having a composition of TiC⋅TiN⋅Si3N4⋅C⋅β-SiC were obtained. The porosity of this composite was much smaller than that of ordinary Si3N4 bonded ceramics because of the volume increase caused by the conversion of Si to Si3N4 and additionally of TiC to TiN, C and β-SiC. Carbon, in particular, seemed to have a remarkable effect on reducing the number of pores in the sintered body. The sample dimensions increased in the sintering stage partly because TiC particles formed porous clusters of TiN by reacting with nitrogen.

Reaction Sintering Property of Green Compact of Si and TiC Mixed Powders in Nitrogen

ABSTRACTWe have developed a new type of near net shape sintering process using nitridation of Si and other inorganic powders. In this report, the sintering property of powder mixture compacts of TiC (10μm or 0.9μm) and Si (0.9μm) in a nitrogen atmosphere at 1350°C was investigated.A large portion of the Si formed Si3N4 on reaction with nitrogen, while TiC formed TiN and free carbon. A small portion of this free carbon was converted into β-SiC on reaction with Si and about 98% of the free carbon remained in the sintered body. Thus, composite ceramics having a composition of Si3N4·TiC·TiN·C·β-SiC were obtained. The porosity of this composite was much smaller than that of ordinary Si3N4 bonded ceramics, because of the large volume expansion for formation of free carbon. The pore size under 5μm can be got using TiC powder with an avarage size of 0.9μm.

Consolidation and compaction of powder mixtures. I. Binary mixtures of same particle size fractions of different types of crystalline lactose

Binary powder mixtures of four different types of crystalline lactose: α-lactose monohydrate, anhydrous α-lactose, roller-dried β-lactose and crystalline β-lactose, were compressed into tablets. The results showed a proportional intercorrelation of the crushing strength and internal specific surface area of the tablets, respectively, with the composition of the powder blend, when compressed from binary mixtures of same particle size fraction. All data were found to fit the unique relationship between the crushing strength and the internal specific surface area of crystalline lactose tablets. It is concluded that binary mixtures of same particle size fractions of different types of crystalline lactose exhibit no interaction between the components during consolidation.

Preparation of ductile NbAl powders for the fabrication of Nb 3Al superconductors

The influence of rapid quenching and hydrogenation on the structure and phase composition of niobium-rich NbAl alloys was investigated. Starting ingots were prepared by conventional arc melting of compacted powder mixtures. The phase diagram for NbAl, presented by Jorda et al., was confirmed in the examined concentration range up to about 30 at.% aluminium. Specimens were quenched with cooling rates not less than 10 4 K s −1, both from the solid and liquid state. A metastable extension of the niobium solid solution up to 27 at.% aluminium was obtained after quenching small droplets from temperatures T ⩾ 2200 °C. Contrary to previous publications, it is shown that rapid quenching of solids (19–24 at.% aluminium) from 1750 °C in a eutectic GaIn bath does not lead to the formation of metastable states in the region of the Nb 3Al phase. Ductile Nb-Al powders of an average composition “Nb 3Al” were prepared with a combined hydridingdehydriding process. The retransformation of the metastable powders was determined to occur in the temperature range between 710 and 860 °C depending on the aluminium concentration. Based on these findings, a new perspective results for the powder metallurgical fabrication of Nb 3Al superconductors.

焼結鋼におけるモリブデンの拡散合金化過程 Ｉ 鉄‐モリブデン‐炭素系圧粉体拡散対における合金化過程

In order to reveal the diffusion processes of molybdenum in sintered steels, diffusion couples prepared from powder mixture compacts were heated in vacuum at 1523K for 3.6ks, and the diffusion zones were examined mainly by means of EPMA.Carbon in the iron-molybdenum diffusion couples intensively affected the diffusion layer formation through the carbide layers formation. In the diffusion couples containing carbon, the molybdenum diffusion in iron was considerably enhanced by using Mo2, C powder compacts as the coupling partner for iron powder compact or iron-carbon powder mixture compact, as compared with the use of molybdenum and graphite powder mixture compacts of the same composition. The difference in the degree of molybdenum diffusion was attributed to the iron-molybdenum-carbon ternary liquid phase formation in the interface of diffusion couple, as well as the diffusion in the solid phase.

Production of titanium nickelide from compacted nickel-titanium powder mixtures by sintering with interdiffusion but without the formation of a liquid phase

Porous titanium nickelide exhibiting the shape “memory” effect has been produced from pressed titanium and nickel (carbonyl and electrolytic) powder mixtures of equiatomic composition by high-temperature vacuum sintering resulting in interdiffusion of its components without the formation of a liquid phase. Use of a carbonyl rather than an electrolytic powder in the starting mixture enables sintered TiNi of better physicomechanical properties to be obtained. Sintered TiNi can find practical application not only as a semifinished product in the manufacture of nonporous parts by hot working but also for the production of parts whose thermomechanical recovery characteristics are their key service properties.

Observations on the compaction of binary thermite powder mixtures

Observations on the compaction of binary thermite powder mixtures

Energy relations in the compaction of binary powder mixtures

1. In the compaction of powder mixtures, energy absorption takes place as in the case of pure metals. Relative absorption at first increases, attains a maximum, and then falls off. At high degrees of densification, differential relative absorption becomes negative because of a marked strength loss experienced by materials being compacted. 2. Energy absorption is not an additive function of concentration. This finding is supported by a hypothesis postulating the formation of surface solid solutions in the contact zones of powders being compacted. 3. Additions of Fe, Cu, and Zn in Al lower energy absorption. 4. Additions of Al in Fe, Cu, and Zn increase energy absorption owing to the high absorptive capacity of Al. 5. The thickness of the surface solid-solution layers, as calculated from the drop in energy absorption, is of the order of 0.4μ.

Reflectance of Compacted Powder Mixtures

The spectral reflectance of compacted powder mixtures in the 0.23 to 2.65 μ range was calculated from the reflectances of the components. Accurate control was maintained over particle size and compaction pressure. Mixtures could be classified into three categories according to the opacities of the powder particles: opaque–opaque, opaque–transparent, and transparent–transparent. The reflectances of opaque–opaque mixtures were always intermediate to those of the components. However, mixtures of opaque–transparent powders could have reflectances either intermediate or considerably lower than those of the components. On the other hand, transparent–transparent mixtures had reflectances intermediate to those of the components, or at most three percent above or below. Equations were developed for calculation of the reflectances of mixtures for the three cases. The equations involved parameters such as the spectral reflectances of the components, their percent surface areas in the mixture, the relative transparencies of the powders, and the single-particle reflectances. Good agreement was obtained in most cases between calculated and experimental data.

The thermal conductivity of compacted powder carbons and mixtures of carbon powders with uranium carbide particles

Measurements of thermal conductivity and electrical resistivity have been undertaken over the temperature range 20°–200°C for a series of compacted graphite powder matrices and a series of matrix materials mixed with different volumes of coated uranium carbide particles. The temperature range has been extended to 1000°C for particular samples. Results indicate that the manufacturing process produces homogeneous materials whose measured transport properties are affected markedly by variations of several parameters including the initial compacting pressure, the volume of added particles and the amount of pyrolytic carbon deposited in the pores. Large variations in both physical properties are obtained at the lower temperatures for changes in each of these parameters. For the pressure variable the thermal conductivity is found to change linearly with increase of pressure over the range 6–1000 psi. At higher temperatures the differences are much reduced and the materials behave in a manner similar to other carbons and graphites having similar properties at the lower temperatures.

130. The thermal conductivity of compacted powder carbons and mixtures of carbon powders with uranium carbide particles

130. The thermal conductivity of compacted powder carbons and mixtures of carbon powders with uranium carbide particles