粉末注射成型金刚石制品的烧结工艺

对采用粉末注射成型技术制备的金刚石制品的烧结工艺进行了研究。通过观测金刚石制品的形貌、相对密度和抗弯强度,分析了烧结温度、烧结气氛、保温时间及升温速率等对金刚石制品烧结性能的影响,优化了烧结工艺参数。结果表明:随烧结温度的提高或保温时间的延长,金刚石制品的相对密度线性增大后趋于平缓,抗弯强度呈现出先增大后下降趋势;在真空气氛中烧结有利于制品烧结致密化和力学性能的提高;过高的升温速率会引起金刚石制品的烧结变形,过低的升温速率会造成金刚石制品处于加热过程的时间过长,影响制品性能。优化的烧结工艺参数为:烧结气氛为真空烧结,烧结温度为920℃,保温时间为10min,升温速率为5℃/min。     

Role of in-situ Formed Nonoxides Bonded Phases in Property Improvement of Alumina ULC Castables

In order to enhance performance of pre-cast shapes of alumina based castables,the present work explored the approach of forming in-situ bonding phases by incorporating Si powders and then heating in carbon embedded atmosphere. Using tabular alumina as aggregates,tabular alumina,SiC powders,Si powders,calcium aluminate cement,microsilica and ultrafineα-Al₂O₃ powders as matrix, alumina based ultra low cement（ULC） castables were prepared.Influences of Si powder addition at O, 4%,6%,8%and 10%（in mass ） on regular properties, cold modulus of rupture（CMOR）,hot modulus of rupture（HMOR）,thermal shock resistance（TSR） and microstructure of the castables after carbonization were investigated. After incorporation of Si powders and carbon embedded heating,the in-situ mullite and nonoxide phases such as SiAlON and SiC can be formed by oxidation, nitridation or carbonization reaction.HMOR and TSR of the castables with in-situ nonoxides bonding are obviously improved.After carbon embedded heating,the HMOR at 1 400℃increases from 1.6 MPa to 8.3 MPa,and the residual CMOR ratio after thermal shock increases from 64.9%to 137.9%when Si addition increases from 0 to 10%.     

DENSITY DETERMINATION OF WOOD CHIPS USING SILICA POWDER

ABSTRACT

This work reports the application of powder pycnometry in density measurement of granular material instead of the traditional liquid pycnometry. Fine dense silica powder was employed as fluid in an experimental set up to measure the density of wood chips taken as porous media. In order to verify the validity and efficiency of the proposed method, the density of soybean (Glycine max L. Merryl) was also measured. The results of soybean density using ethanol as fluid were compared with the proposed method, obtaining a relative deviation of 7·74%. Relative deviations between the samples of wood chips varied from 1·99% to 7·04%, which indicates that the silica method is efficient in determining the density of porous bodies. Liquid pycnometry technique using paraffin covering did not present satisfactory results.     

Maleated Natural Rubber as a Coupling Agent for Recycled High Density Polyethylene/Natural Rubber/Kenaf Powder Biocomposites

Kenaf powder (KP) was incorporated into recycled high density polyethylene (rHDPE)/natural rubber (NR) blend using an internal mixer at 165°C and rotor speed of 50 rpm. The tensile strength and elongation at break of the composites decreased, while the tensile modulus increased with increasing filler loading. The water absorption was found to increase as the filler content increased. The maleic anhydride grafted natural rubber was prepared and used to enhance the composites performance. The addition of MANR as a coupling agent improved the tensile properties of rHDPE/NR/KP biocomposites. The water absorption was also reduced with the addition of MANR.     

Characterization and Properties of Recycled Polypropylene/Coconut Shell Powder Composites: Effect of Sodium Dodecyl Sulfate Modification

This research work focuses on the utilization of coconut shell powder (CSP) as filler in recycled polypropylene (rPP). Sodium Dedecyl Sulfate (SDS) was used as coupling agent in these composites. The effect of filler content and SDS on tensile properties, thermal properties, water absorption and morphology of rPP/CSP composites were investigated. In this study, modified rPP/CSP composites with SDS show significant increased tensile propertied, thermal stability, crystallinity and low water absorption compared unmodified rPP/CSP composites. Those improvements were contributed by the coupling effect of SDS.     

PROPERTIES OF POLYPROPYLENE/NATURAL RUBBER/RECYCLE RUBBER POWDER BLENDS

Thermoplastic elastomers have been prepared by blending polypropylene (PP), natural rubber (NR), and recycle rubber powder (RRP). The blends were melt-mixed using a Brabender Plasticorder torque rheometer at 190°C and 50 rpm. A fixed 70:30 blend ratio (wt%) of PP and rubber was prepared. The effect of partial replacement of NR with RRP at a fixed rubber content (NR+RRP), 30 wt% on mechanical properties, swelling behavior, torque development, and morphological properties of PP/NR/RRP blends was studied. Results show that the tensile strength, Young's modulus, and swelling resistance increase with increasing RRP content in the PP/NR/RRP blends whereas the stabilization torque and elongation at break exhibit opposite trend.     

Spray Drying of Skim Milk Mixed with Milk Permeate: Effect on Drying Behavior,Physicochemical Properties,and Storage Stability of Powder

The possibility of using milk permeate (MP) to lower the protein level of skim milk powder (SMP) in producing powders of 34% and lower protein is explored. Skim milk suspensions with various levels of MP were prepared by mixing SMP and MP powder (MPP) at the ratios of 1:0, 7:3, 3:7, and 0:1: from 34 to 5.3% protein. The suspensions were dried in a spray dryer with inlet and outlet temperatures of 180 and 80°C, respectively. Increasing permeate concentration in the mixture showed a greater tendency to stickiness manifested by lowered the cyclone recovery of the powder as more powder stuck on the wall of the dryer. Increasing permeate concentration in the resultant powder did not significantly affect the bulk density but led to a reduction in the particle size and also made the powder slight green and yellowish in color. It also found to lower the glass transition temperature (T_g ) of the skim milk powder (SMP) and induce crystallization of lactose at lower water activity (a_w  ≥ 0.328 for SMP:MPP of 3:7 and 0:1 compared to a_w  ≥ 0.0.432 for SMP:MPP of 1:0 and 3:7). Addition of MP in SMP lowered the T_g values of the resulting powders. The permeate fraction in spray-dried SMP/MPP mixtures found to lower the critical a_w and moisture content, suggesting the SMP mixed with MPP is more likely to become sticky than SMP alone (at 34% protein) when stored at a similar water activity and moisture content.     

Characteristics of Milk Powders Produced by Spray Freeze Drying

Skim and whole milk powders were manufactured at lab scale by spray freeze drying (SFD), using liquid nitrogen as the cryogen. The polydispersity of droplet/particle sizes was limited using an encapsulator nozzle to atomize the feed. Particle morphology was examined using a scanning electron microscope. Samples were compared with equivalent spray-dried powders in tests of wettability and dissolution in water. The spray freeze-dried powders were found to be highly porous, with a uniform structure of pores throughout the entire particles. When tested in water, SFD skim milk powders wetted roughly three times as fast as industrially spray-dried agglomerated skim milk powders and were observed to dissolve rapidly by breaking down into smaller particles.     

Effect of Maltodextrin Addition during Spray Drying of Tomato Pulp in Dehumidified Air: II. Powder Properties

This work investigates the effect of maltodextrin addition on the main powder properties during spray drying of tomato pulp in dehumidified air. A pilot-scale spray dryer was employed for the spray-drying process. The modification made to the original design consisted in connecting the spray dryer inlet air intake to an absorption air dryer. 21 DE, 12 DE, and 6 DE maltodextrins were used as drying agents. Tomato pulp was spray dried at inlet air temperatures of 130, 140, and 150°C and (tomato pulp solids)/(maltodextrin solids) ratios of 4.00, 1.00, and 0.25. The tomato powders were analyzed for rheological properties, moisture content, bulk density, solubility, hygroscopicity, and degree of caking. It was found that maltodextrin addition improved powder hygroscopicity, caking, and solubility, whereas it deteriorated slightly its moisture content and density. In addition, analysis of experimental data yielded correlations between powder properties and the above-mentioned variable operating conditions. Regression analysis was used to fit a full second-order polynomial, reduced second-order polynomials, and linear models to the data of each of the properties evaluated. F values for all reduced and linear models with an R ² ≥ 0.70 were calculated to determine if the models could be used in place of full second-order polynomials.     

Optimization of Vacuum Drying Characteristics of Date Powder

Kabkab, Khazravi, and Zark are three varieties of Iranian dates representing high, middle, and low sugar content, respectively. Under the vacuum conditions, powders from these dates were produced and placed in the optimized state for the dehydration reaction. The statistical analyses showed that the moisture reduction range of these three varieties at various conditions (100°C and 15.3 cm Hg, 93°C and 30.4 cm Hg, 84°C and 54.6 cm Hg, 68°C and 60.1 cm Hg) were 17.27±0.16, 20.89±0.19, and 7.61±0.02%, respectively. The analysis of variance (ANOVA) on date variety and thickness (0.2, 1, 2, 2.5, and 3 cm) in drying time indicated that the Zark variety with low moisture and sugar contents exhibited the lowest drying time (about 6 h), followed by Khazravi and KabKab. The optimum condition (85°C, 54.6 cm Hg, and 1 cm thickness during 7 h of drying time) was selected for its favorable effects on the moisture reduction, smell/color quality, energy usage, and economical feasibility.