让我们的生活更美好——铁的趣闻(3)

我们已经知道了铁的生产量与用量都是无可争议的第一,它又是价格最低廉的金属,在各个领域都得到广泛应用。引领了一个时代的铁对人类文明起了巨大的推动作用。炼铁、炼钢、钢铁材料中的合金元素、钢铁材料加工、热处理等,都具有非常丰富的内涵。但是你知道吗?钢铁还能让我们的生活更美好!现在就让我们走进钢铁的世界里,探究一下钢铁对我们的生活所起到的巨大作用吧。

曾经的贵金属——铝的趣话(1)

如果有人说,铝比金银都贵,你相信吗?是不是觉得这是天方夜谭,不可能的啊,但是,这里告诉你,千真万确,铝曾经比金银都贵。这到底是怎么回事儿呢?现在就让我们走进铝的世界,一看究竟吧。

对人体健康至关重要——铜的趣话(2)

在上一次的内容中,我们已经了解到铜在历史长河中展现出的灿烂辉煌与巨大作用。不仅如此,铜还与人体健康息息相关,说到人体所需要的元素,钙和铁大家一定是不陌生。难道说铜也是人体的必需元素?好的,现在就让我们走进“铜”的世界去看看,在人体健康领域,铜是如何发挥作用的吧。

使用量最大的金属——铁的趣闻(1)

说到钢铁,大家一定不陌生,它与我们的社会发展和日常生活密切相关。然而,你知道钢铁的生产量吗,其产量竟然相当于第2~9名金属产量总和的10倍!而且,中国的钢产量要占到全球的一半以上!钢铁还有非常广泛的用途,在我们的周围无处不在。铁还是最便宜的金属,其价格仅有金的约七万分之一。下面就让我们一起来了解一下我们最“熟悉”的铁吧。

钢铁工业及冶炼工艺发展——铁的趣闻(2)

千年不腐的木乃伊闻名遐迩,千年不锈的铁器存在吗?物美价廉、生活中无处不在的铁质品始于何时,如何演变?钢铁的发展与工业革命和两次世界大战有何相互影响?钢与铁有何区别、如何炼制?除了Fe元素,钢铁中还有哪些元素,作用为何?钢铁冶炼的主要工艺有哪些?钢铁材料的“四把火”是什么?作为金属材料中应用范围最广、种类最多的材料,钢铁的冶炼、加工、热处理等工艺,也是金属材料中最丰富,最成熟的。现在就让我们走进钢铁的世界,领略一下它悠久的历史与精湛的工艺吧。

广泛使用的金属之一——铜的趣闻(3)

铜不仅具有悠久的历史,引领了时代,创造了文明,保障了人体健康,而且还是广泛使用的金属之一。本次我们从成语看铜的影响力说起,讨论一下铜为什么会有如此大的需求,主要应用在哪些领域以及铜资源与中国铜的产业情况。

金属(2):金属密度和熔点的小秘密

贾成厂教授的金属百科系列科普文章之二——"金属(2):金属密度和熔点的小秘密"深入浅出地阐明:密度是物质的特性之一,每种物质都有其密度,不同物质的密度是不同的。金属的密度一般都较大。密度最大的金属是锇,为22.59 g/cm^3。密度最小的金属是锂,仅为0.534 g/cm^3。物质的熔点是在一定压力下固态和液态转化呈现平衡时的温度。熔点最高的金属是钨,熔点高达3410℃。熔点最低的金属是汞,俗称水银,熔点只有–38.87℃。贾成厂教授以细腻而风趣的笔触描述了锇、锂、钨、汞等金属的性能以及应用的"小秘密"。

Fabrication,microstructures,and properties of copper matrix composites reinforced by molybdenum-coated carbon nanotubes

Multiwalled carbon nanotubes （CNTs） were coated by a molybdenum layer using carbonyl thermal decomposition process with a precursor of molybdenum hexacarbonyl. The Mo-coated CNTs （Mo-CNTs） were added into copper powders to fabricate Mo-CNT/Cu composites by means of mechanical milling followed by spark plasma sintering. The Mo-CNTs were uniform dispersion in the Cu matrix when their contents were 2.5 vo1.%-7.5 vol.%, while some Mo-CNT clusters were clearly observed at additions of 10.0 vo1.%-15.0 vol.% Mo-CNTs in the mixture. The mechanical, electrical, and thermal properties of the Mo-CNT/Cu composites were characterized, and the results showed that the tensile strength and hardness were 2.0 and 2.2 times higher than those of CNT-free specimens, respectively. Moreover, the Mo-CNT/Cu composites exhibited an enhanced thermal conductivity but inferior electrical conductivity compared with sintered pure Cu. The uncoated CNT/Cu composites were fabricated by the similar processes, and the measured tensile strength, hardness, thermal conductivity, and electrical conductivity of the CNT/Cu composites were lower than those of the Mo-CNT/Cu composites.

Predicted interfacial thermal conductance and thermal conductivity of diamond/Al composites with various interfacial coatings

The interfacial thermal conductance （ITC） and thermal conductivity （TC） of diamond/Al composites with various coatings were theoretically studied and discussed. A series of predictions and numerical analyses were performed to investigate the effect of thickness, sound velocity, and other parameters of coating layers on the ITC and TC. It is found that both the ITC and TC decline with increasing coating thickness, especially for the coatings with relatively low thermal conductivity. Nevertheless, if the coating thickness is close to zero, or quite a small value, the ITC and TC are mainly determined by the constants of the coating material. Under this condition, coatings such as Ni, TiC, Mo 2 C, SiC, and Si can significantly improve the ITC and TC of diamond/Al composites. By contrast, coatings like Ag will exert the negative effect. Taking the optimization of interfacial bonding into account, conductive carbides such as TiC or Mo 2 C with low thickness can be the most suitable coatings for diamond/Al composites.

Pressure sintering of W-15wt.%Cu alloys prepared by mechanical alloying as a subsequent densification treatment method

The sintered W-15wt.%Cu alloys fabricated by mechanical alloying were re-sintered under pressure to increase the density and improve the properties of these alloys. The pressure was applied vertically along the axis of the sintered sample. Properties such as density, hardness, and bending strength were measured. The microstructures of the sintered bodies were observed. The results showed that the subsequent pressure sintering could increase the density of the sintered W-15wt.%Cu alloys. Their hardness, bending strength, and some other physical properties were also improved by this subsequent densification treatment.

Thermal conductivity behavior of SPS consolidated AlN/Al composites for thermal management applications

A1N/A1 composites are a potentially new kind of thermal management material for electronic packaging and heat sink applications. The spark plasma sintering （SPS） technique was used for the first time to prepare the A1N/A1 composites, and attention was focused on the effects of sintefing parameters on the relative density, microstructure and, in particular, thermal conductivity behavior of the composites. The results showed that the relative density and thermal conductivity of the composites increased with increasing sintering temperature and pressure. The composites sintered at 1550℃ for 5 min under 70 MPa showed the maximum relative density and thermal conductivity, corresponding to 99% and 97.5 W.m-1.K-1, respectively. However, the thermal conductivity of present A1N/A1 composites is still far below the theoretical value. Possible reasons for this deviation were discussed.

Pressure infiltrated Cu/diamond composites for LED applications

Diamond reinforced copper （Cu/diamond） composites were prepared by a pressure infilla＇ation technique. The composites show a super high conductivity of 713 W.m-1.K-1 in combination with an extremely low coefficient of thermal expansion （CTE） of 7.72 × 10-6 K-1 （25-100℃）, which are achieved by modifying the copper matrix with adding 0.3 wt.% of boron to get a good thermal contact between the matrix and the diamond particles. By adopting a series of postmachining techniques the composites were made into near-net-shape parts, and an electroless silver coating was also successfully plated on the composites. Finally, their potential applications in the thermal management of fight emitting diodes （LED） were illustrated via prototype examples.

Change in relative density of WC-Co cemented carbides in spark plasma sintering process

The relative density of WC-Co cemented carbides during spark plasma sintering（SPS） was analyzed.Based on the change in displacement of the ram in the SPS system,the relative densities in the sintering process can be achieved at different temperatures.The results indicated that densification of the samples started at near 900°C,the density rapidly reached its maximum at the increasing temperature stage,in which the temperature was lower than the sintering temperature of 1200°C,and most of the densification took place in the stage.Besides,the theoretical values were consistent with the experimental results.

Friction and wear properties of copper matrix composites reinforced by tungsten-coated carbon nanotubes

Carbon nanotubes （CNTs） were coated by tungsten layer using metal organic chemical vapor deposition process with tungsten hexacarbonyl as a precursor. The W-coated CNTs （W-CNTs） were dispersed into Cu powders by magnetic stirring process and then the mixed powders were consolidated by spark plasma sintering to fabricate W-CNTs/Cu composites. The CNTs/Cu composites were fabricated using the similafprocesses. The friction coefficient and mass wear loss of W-CNTs/Cu and CNTs/Cu composites were studied. The results showed that the W-CNT content, interfacial bonding situation, and applied load could influence the friction coefficient and wear loss of W-CNTs/Cu com- posites. When the W-CNT content was 1.0 wt.%, the W-CNTs/Cu composites got the minimum friction coefficient and wear loss, which were decreased by 72.1% and 47.6%, respectively, compared with pure Cu specimen. The friction coefficient and wear loss of W-CNTs/Cu composites were lower than those of CNTs/Cu composites, which was due to that the interracial bonding at （W-CNTs）-Cu interface was better than that at CNTs-Cu interface. The friction coefficient of composites did not vary obviously with increasing applied load, while the wear loss of composites increased significantly with the increase of applied load.

Spark plasma sintering of high-toughness ZrO_2 materials doped with yttrium

Zirconia powders doped with yttrium prepared by special liquid-phase precipitation method were sintered by spark plasma sintering （SPS） to obtain high performance samples. The microstructure, phase composition, and mechanical properties of the samples were studied. The results of X-ray diffraction （XRD）, Raman spectrum, and transmission electron microscope （TEM） show that the phase is tetragonal. The powders with large surface area and high sintering activity, due to small crystallite size, could be densified at 1100℃. The highest relative density of the sample obtained at 1300℃ is higher than 99% （the tetragonal phase is 6.08 g/cm^3）. The Hv and KIC are 13.76 GPa and 15.4 MPa.m^1/2, respectively.

Dielectric properties of spark plasma sintering AlN-W composite ceramics

In order to develop AlN composites suitable for high average power electronic tube, AlN-W materials were prepared by spark plasma sintering. The effects of manufacture parameters on dielectric loss tangent and permittivity constant were investigated, which include powder-mixed method, milling time of high-energy ball milling, starting powder particle size, sintering temperature and holding time and adding amount of the conductive second phase. The results showed that A1N-W materials sintered at the temperature of 1700℃ holding for 5 min with 10 vol.% W showed the best dielectric loss tangent larger than 0.81 at the frequency 1 kHz-1 MHz. In addition, magnetic stirring mixed powder and lower sintering temperature led to the better propelties because of the higher porosity. The samples sintered from the starting AlN powder with smaller particle size also had the better properties.

Mechanical Behavior and Failure Mechanism of 2.5D(Shallow Bend-joint, Deep Straight-joint) and 3D Orthogonal UHWMPE Fiber/Epoxy Composites by Vacuum-assistant-resin-infused

Ultra-high molecular weight polyethylene（UHMWPE） fiber/epoxy composites were fabricated by a vacuum assisted resin infused（VARI） processing technology. The curing condition of composites was at a cure temperature of 80 ℃ for 3h in a drying oven. The characteristics of 2.5D（shallow bend-joint and deep straight-joint） structure and 3D orthogonal structure were compared. The failure behavior, flexural strength, and microstructures of both composites were investigated. It was found that the flexural property was closely related to undulation angle θ. The flexural strength of 3D orthogonal structure composite was superior to the other two structures composites with the same weave parameters and resin.

Effect of Twisted Fiber on Flexural Property and Microstructure of Woven Fabric Reinforced Composite

Two kinds of 2.5D deep straight-joint structure ultra-high molecular weight polyethylene（UHMWPE）（twisted and original） fibers woven fabric reinforced epoxy resin composites were prepared by the hand lay-up method. Subsequently, the flexural property, microstructures, and failure mechanisms of the composites were also investigated. The average flexural strength of 2.5D deep bend-joint structure twisted fiber and original fiber woven fabric composites were 176.66 MPa and 204.45 MPa, respectively. The results of the characteristics indicated that the twist was the main factor which affected the flexural performance. Flexural property vitally relied on the strength of the fiber itself. Twist decreased the strength of the yarns, which meant that when the mechanical property of woven fabric reinforced composites was improved, the yarns must be kept straight in the woven fabric. The study are extremely valuable to guide the improvement of the mechanical property of the woven fabric reinforced composites.

Influence of process control agents on the performance of Ni_3Al by mechanical alloying

The influence of process control agents （PCAs） on the mechanical properties of Ni3AI intermetallic compounds by mechanical alloying was investigated in order to develop oxide deposition reinforced intermetallics. The PCAs in mechanical alloying were pure ligroin, 75 vol.% ligroin ＋ 25 vol.% alcohol, 50 vol.% ligroin ＋ 50 vol.% alcohol, 25 vol.% ligroin ＋ 75 vol.% alcohol, and pure alcohol. The normal composition is Ni-22.9at.%Al-0.5at.%B, the ball-to-powder weight ratio is 10：1, and the milling time is 30 min. Then, the powders were sintered by spark plasma sintering under 40 MPa for 5 min at 1000℃. The results show that a higher bending strength and a higher hardness were obtained when the PCAs were 75% ligroin ＋ 25% alcohol in mechanical alloying. The bending strength is about 2700 MPa and the hardness （HV） is more than 6 GPa.