Study on the relationship between the particle size distribution and the effectiveness of the K‐powder fire extinguishing agent

The relationship between the particle size distribution and the extinguishing effectiveness of the new K‐powder fire extinguishing agent has been studied experimentally, to explore the reason of the great extinguishing efficiency exhibited by the new K‐powder fire extinguishing agent on Class B fire (liquid fuel fire). The results of the experiment showed that the extinguishing effectiveness increased along with the decrease of the particle size distribution. In addition, a sharp discontinuity appeared around the limiting size, about 40 μm. The powder with the particle size below 40 μm exhibited highly effective extinguishing with the minimum effective extinguishing concentration C_xr = 23 g·m^?3, while the powder with the particle size above 40 μm exhibited little fire extinguishing efficiency. Compared with other fire extinguishing agents produced by different substances, the new K‐powder fire extinguishing has the bigger limiting size. That means, in the same particle size distribution, the new K‐powder fire extinguishing agent contains more highly effective powder than others contain, and is more effective.     

硅渣和玻璃粉直接烧结制备多孔材料的气孔结构与力学性能

以硅渣和玻璃粉为原料,采用粉体直接烧结法制备多孔材料,研究了烧结温度(700~900℃)、烧结时间(15~120min)和升温速率(10~100℃·min^-1)对多孔材料表观密度、气孔率、物相组成、抗压强度的影响。结果表明:气孔结构均匀性随烧结温度的升高而降低;表观密度随烧结温度的升高先减小后增大,随保温时间的延长而增大,随升温速率的增大而减小,气孔率的变化趋势与表观密度的相反;多孔材料的主要物相为玻璃相和硅、SiC、SiO2、Ca2Al2SiO7等结晶相,且结晶度随烧结温度的升高而降低;抗压强度随烧结温度的升高呈先增大后减小的趋势;当烧结温度为750℃,升温速率为30℃·min^-1,烧结时间为30 min时,多孔材料的主晶相为硅和Ca2Al2SiO7,抗压强度最大(1.60MPa),表观密度为0.43g·cm^-3,气孔率为80%。     

户内热转印粉末涂料用混合型聚酯树脂的合成研究

通过分析热转印性能的影响因素合成了不同结构的聚酯树脂，研究了树脂酸值对热转印性能的影响，同时研究了部分单体对聚酯树脂热转印性能的影响。采用 DSC热分析法研究了固化促进剂对粉末涂料固化行为的影响，结果表明：选择合适的固化促进剂对涂层转印性能的提高有至关重要的作用。     

TiC含量对TC4合金激光熔覆层组织和性能的影响

采用激光熔覆工艺在TC4钛合金基体表面制备了添加不同质量分数(0%、2%、4%、6%)TiC的Ni60A复合熔覆层,通过光学显微镜、显微硬度计、X射线衍射仪、摩擦磨损机分析了不同TiC含量对熔覆层组织及性能的影响。结果表明:未添加TiC的熔覆层组织以树枝晶为主,添加TiC后出现了花瓣状物相;XRD分析发现熔覆层中出现了AlCCr₂、Al_0.24B_0.01Ni_0.75等硬质增强相,这些能够显著提高熔覆层的硬度。显微硬度及摩擦磨损试验结果表明,添加TiC的熔覆层平均硬度均较基体硬度有大幅提高,摩擦因数显著降低,且随TiC含量的增加,熔覆层硬度先增加后降低,摩擦因数先降低后增加,4%TiC熔覆层的硬度最大,相比基体提高了213.3%,摩擦因数最小,为0.309 774。     

Fabrication of composites from different carbon content ferrous powders adopting thermomechanical processes

In this research, deep consolidation technique is utilized for processing of low and high carbon content ferrous powders to manufacture composite material. High carbon content ferrous powders were used as reinforcing material. The powder particles were allowed to mix with low carbon content ferrous powders in 50:50 weight percent for fabrication of composites. The composites were heat treated at three different temperatures (i.e., 800°C, 900°C, and 1000°C). The changes in microstructure, microhardness, the grain size, and bonding among powder particles were studied. Refinement of grains was observed and this led to improved hardness enabling the processed material to be used as a suitable composite. Abrasive wear tests were carried out using a laboratory tribometer in dry reciprocating sliding contact against Sic abrasive paper. The outcomes demonstrate that the abrasive wear resistance was notably affected by the treatment temperature and hardness of the composites.     

Hydrogen generation from the hydrolysis of aluminum promoted by Ni–Li–B catalyst

In this study, the high activity Ni–Li–B catalysts were fabricated through wet chemical reduction method. Their morphological structures, crystallinity, surface area and composition were examined by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) method and energy-dispersive X-ray spectroscopy (EDS). The aluminum-water reaction tests were explored in the range of temperatures from 35–75 °C. It was found that water could react with aluminum to generate hydrogen gas. The yield and hydrogen generation rate were significantly increased when all prepared catalysts were added into the reaction. The Ni–Li–B (X_LiCl = 0.1 g) catalyst exhibited the highest cumulative hydrogen volume of 201.3 ml with an average hydrogen production rate of 0.50 ml min⁻¹ at 55 °C. This phenomenon could be pointed to the emergence of the micro galvanic cell formed by the Ni–Li–B, Li/Ni–Li–B, Li and Al, which accelerated aluminum to rapidly react with water.     

Effects of different drying methods on the physicochemical property and edible quality of fermented Pyracantha fortuneana fruit powder

In this study, hot air drying (HAD), hot air-/microwave-assisted vacuum drying (HAMAVD) and hot air-assisted microwave drying (HAAMD) were applied to lactic acid-fermented Pyracantha fortuneana fruit (PFF). Influences of different drying methods on fluidity and dispersion, microstructure, hygroscopicity, rehydration, colour change, sourness and energy consumption were investigated. Results showed that HAAMD had the best overall performance on the quality of the PFF powder. HAAMD PFF powder had higher expansion force (1.65 mL g⁻¹) and water-holding capacity (2.68 g g⁻¹), lower degree of compression (9.09%) and energy consumption, smaller colour change and better taste. Organic acids (mainly malic acids) of all drying powders decreased, but HAAMD and HAMAVD could better improve the acidity characteristics of PFF powders, which may be related to the drying time and the temperature change processes. Consequently, this study can provide references for the utilisation of fresh PFF, the design and commercialisation of PFF-related products.     

Improving the homogeneity and properties of ferrous powder mixes by a novel powder mixing process

Fe-2Cu-0.8C powder mixes were prepared by a wet mixing and spray-drying process using iron, copper, graphite and zinc stearate as main raw materials, and stearic acid, alcohol wax and amide wax as binders. The properties of the as-prepared binder treated powder mixes were investigated. The bonding efficiency of the binders was tested by measure the retention of graphite and copper in the powder mixes after dusting resistance test. The test results show that the wet mixing and spray-drying process can realise the bonding of different particles and improve processing properties of the powder mixes. A flow rate of 30.6?s/50?g and an apparent density of 3.18?g/cm³ were obtained for powder mixes with alcohol wax as binder. The results of dusting resistance test demonstrated that alcohol wax and amide wax have better bonding effect for Cu and graphite powders, respectively, which was reflected by the difference value of electronegativity between Fe, Cu, C elements and functional groups. Compared with mechanically mixing powder mixes, using binder treated powder mixes can also reduce the friction coefficient during compaction by 0.012–0.026. The addition of different binders also has a great influence on the properties of sintered parts.     

High-entropy alloys fabricated via powder metallurgy. A critical review

High-entropy alloys (HEAs) have attracted a great deal of interest over the last 14 years. One reason for this level of interest is related to these alloys breaking the alloying principles that have been applied for many centuries. Thus, HEAs usually possess a single phase (contrary to expectations according to the composition of the alloy) and exhibit a high level of performance in different properties related to many developing areas in industry. Despite this significant interest, most HEAs have been developed via ingot metallurgy. More recently, powder metallurgy (PM) has appeared as an interesting alternative for further developing this family of alloys to possibly widen the field of nanostructures in HEAs and improve some capabilities of these alloys. In this paper, PM methods applied to HEAs are reviewed, and some possible ways to develop the use of powders as raw materials are introduced.