非连续体吸波平板的设计制备及吸波机理分析

通过吸波体内导电媒质的“孤岛”化设计, 制备了单层非连续体平板吸波材料, 并分析了不同炭黑含量和不同试样厚度对吸波效能的影响以及电磁波的损耗机理。发现随着CB/ ABS 颗粒中炭黑含量和试样厚度的增加, 在8～18 GHz 频段内, 非连续体试样的反射损耗增加。当炭黑质量含量达到30 %时, 平板的反射损耗在8. 5～18 GHz 宽频范围内都超过- 10 dB , 在15～18 GHz 均高于- 15 dB。当试样厚度达到20 mm 时, 其反射损耗在8～18 GHz 频率范围内超过- 15 dB。结果表明, 非连续体试样较热压致密试样吸波效能有较大提高, 是很有潜力的吸波结构。      

二氧化锰涂覆EPS方法与效能分析

采用直接涂覆法将二氧化锰涂覆在EPS表面制成吸波球体。实验证实，这种方法有能力涂覆大密度导电粉末，且效果良好。在反射阻抗的测试中，当试样厚度为10mm时，其反射损耗在8～18GHz频率范围内为-7～-15dB，发现随着吸波颗粒中二氧化锰含量和试样厚度的增加，在8～18GHz频段内，试样的反射损耗增加。二氧化锰层吸波球体效能略低于同等导电层厚度的炭粉层吸波球体。     

天然尖晶石型铁氧体(铁砂)基复合吸波涂料特性研究

天然尖晶石型铁氧体（铁砂）与聚氨脂粘结剂制成的吸波涂料在7～12GHz频段有两个吸收峰，涂层厚度1．25mm时，吸收量5．2～8．5dB，在基础吸波材料(铁砂)中添加尖晶石型铁氧体、顺磁性稀土材料和六角铁氧体制成复合吸波涂料，使其吸收量达18～25aB，匹配厚度1．1～1．2mm，两吸收峰间距＞4．4GHz，它加工简单，价格低廉。     

镍锌铁氧体的制备及其吸波性能的研究

利用溶胶直接自蔓延反应制备了镍锌铁氧体纳米粉末，采用XRD分析了其结构。以聚乙烯醇为基体（PVA）制备了炭黑，镍锌铁氧体复合材料吸波平板；采用矢量网络分析仪测量了其在2～18GHz频带上的吸波性能。结果表明：具有双层结构的炭黑，镍锌铁氧体复合材料具有较好的吸波效果，试样厚度为3mm；当面层镍锌铁氧体的质量分数为40％，底层炭粉的质量分数为20％时，在8～18GHz的测试频段范围内，复合材料最大吸收峰值为-15．7GHz，优于-6dB的有效带宽为6．4GHz；当底层炭粉的质量分数为15％时，复合材料最大吸收峰值为-13．6GHz，优于-6dB的有效带宽为8．2GHz。     

掺杂 TiO2水泥的吸波性能与力学性能研究

研究了纳米吸波材料与硅酸盐水泥复合材料的吸波性能和力学性能,讨论并分析了纳米氧化钛的用量、分散方式、试样厚度对电磁波反射衰减的关系和纳米氧化钛对水泥基复合材料的力学性能影响。实验结果表明：在8-18GHz频率范围内,纳米氧化钛与水泥制成的复合材料的反射率均小于-7dB,在16．24GHz时其反射率达-16．34(m,反射率小于-10dB的带宽达4．5GHz,且其力学性能明显优于水泥净浆。     

水泥基吸波材料的性能研究及微观分析?

通过双层设计使水泥基吸波材料尽可能与空间波阻抗相匹配,同时具有良好的电磁波损耗特性,实验测试了水泥基吸波材料的吸波与力学性能,并对吸波材料进行了微观分析.研究结果表明,水泥基吸波板在2~18 GHz频率范围内低于－10 dB的有效带宽分别为3．7和10．8 GHz,水泥基吸波材料的力学性能优于基准材料,掺入0．5％碳纳米管可有效提高水泥净浆的抗压强度.     

掺石墨/碳纤维电磁屏蔽砂浆的研究

以石墨和碳纤维为电磁屏蔽功能基元材料,将其添加到砂浆中,部分取代砂浆中的砂,调节电磁屏蔽功能材料的含量,使砂浆对电磁波具有屏蔽和吸收功能。研究了电磁屏蔽功能基元材料含量对砂浆电磁屏蔽效能的影响。结果表明添加石墨和碳纤维电磁屏蔽功能基元材料的电磁屏蔽砂浆,在30～200MHz频率范围内,电磁屏蔽效能SE较大,随着频率增加,屏蔽效能SE迅速降低。在200MHz～1.8GHz频率范围内,电磁屏蔽效能SE值趋于平缓,屏蔽效能较低。在1.8GHz附近,碳纤维电磁屏蔽砂浆的SEmin最大,为10dB。     

吸收剂形状对雷达吸波材料性能的影响研究

以片状铁、针状多晶铁纤维、球形羰基铁粉吸收剂为原材料分析探讨了磁性吸收剂形状对其微波电磁参数的影响。结果表明，2GHz时磁导率实部最大的为片状，其次是针状，最小的为球形吸收剂，片状铁吸收剂磁导率实部在2GHz时可达4．65，磁导率虚部2～18GHz均高于多晶铁纤维和羰基铁粉。模拟其吸波性能发现片状铁吸收剂吸波性能在2～9．6GHz优于多晶铁纤维和羰基铁粉，可用于提高吸波材料的低频吸波性能。     

单向取向碳基气凝胶的制备及电磁屏蔽性能研究

碳基气凝胶具有自支撑的三维导电网络,是开发新型高性能电磁屏蔽及吸波材料的研究热点。通过单向冷冻干燥法制备了具有单向取向结构的碳纳米管/壳聚糖(CNT/CS)气凝胶,考察了不同CNT/CS浓度及配比对气凝胶冷冻速率、线性收缩率、微观结构、电导率和电磁屏蔽效能的影响,研究了取向方向对气凝胶导电性能和电磁屏蔽效能的影响。结果表明：CNT/CS气凝胶具有显著的各向异性,取向方向上的电导率最高可达14.34S/m,是垂直于取向方向上的1.5～3.0倍。CNT/CS气凝胶具有优良的电磁屏蔽效能,在12GHz的频率下屏蔽效能最高可达20.3dB。气凝胶在垂直于取向方向上的电磁屏蔽效能高于取向方向。     

碳纳米管加载量对复合材料吸波性能的影响

将不同质量分数的碳纳米管和环氧树脂充分混合，制成复合吸波涂料并涂覆在铝板上制成吸波涂层。采用TEM对碳纳米管的形貌进行观察。使用反射率扫频测量系统HP8757E标量网络分析仪检测复合材料的吸波性能。结果表明，复合材料在2GHz～18GHz均有良好的吸波性能。碳纳米管加载质量分数为8％和10％时，复合材料吸波性能最佳。8％碳纳米管加载量，峰值最大，达到～22．55dB，波峰出现在12．32GHz，带宽分别为2．56GHz（R〈-8dB）和4．00GHz（R〈-5dB）。10％碳纳米管添加量，带宽最大，分别达到2．80GHz（R〈-8dB）和7．00GHz（R〈-5dB），波峰出现在13．67GHz，峰值为-14．59dB。     

The effects of ground granulated blast-furnace slag blending with fly ash and activator content on the workability and strength properties of geopolymer concrete cured at ambient temperature

Inclusion of ground granulated blast-furnace slag (GGBFS) with class F fly-ash can have a significant effect on the setting and strength development of geopolymer binders when cured in ambient temperature. This paper evaluates the effect of different proportions of GGBFS and activator content on the workability and strength properties of fly ash based geopolymer concrete. In this study, GGBFS was added as 0%, 10% and 20% of the total binder with variable activator content (40% and 35%) and sodium silicate to sodium hydroxide ratio (1.5–2.5). Significant increase in strength and some decrease in the workability were observed in geopolymer concretes with higher GGBFS and lower sodium silicate to sodium hydroxide ratio in the mixtures. Similar to OPC concrete, development of tensile strength correlated well with the compressive strength of ambient-cured geopolymer concrete. The predictions of tensile strength from compressive strength of ambient-cured geopolymer concrete using the ACI 318 and AS 3600 codes tend to be similar to that for OPC concrete. The predictions are more conservative for heat-cured geopolymer concrete than for ambient-cured geopolymer concrete.     

Electromagnetic wave absorbing characteristics of carbon black cement-based composites

Electrical resistivity, compressive strength, and the electromagnetic absorbing effectiveness of carbon black (CB) cement-based composites (CBCC) with different contents of high-structure CB were studied in this paper. The results indicate that the resistivity of CBCC versus the concentration of CB curves has typical features of percolation phenomena: CBCC in the percolation threshold zone contains 0.36–1.34 vol.% of CB. Thus, the conductive network can be formed in CBCC by using small amount of high-structure CB. Compressive strength of CBCC decreases with CB content increasing. Especially, compressive strength decreases substantially when CB content is more than 3.0 wt.%. CBCC exhibits good performance of absorbing electromagnetic waves in the frequency range of 8–26.5 GHz. For CBCC containing 2.5 wt.% of CB, the minimum reflectivity reaches ?20.30 dB. The frequency bandwidth in which the reflectivity is less than ?10 dB was from 14.9 GHz to 26.5 GHz. The filling of CB has improved the dielectric constant and the loss factor of the cement material remarkably. The loss factor of CBCC increases with the CB content increasing.     

镀镍碳纳米管的微波吸收性能研究

用竖式炉流动法制备了碳纳米管,碳纳米管的外径40nm～70nm,内径7nm～10nm,长度50μm～1000μm,呈直线型,用化学镀法在碳纳米管表面镀上了一层均匀的金属镍。碳纳米管吸波涂层在厚度为0.97mm时,在8GHz～18GHz,最大吸收峰在11.4GHz(R=-22.89dB),R<-10dB的频宽为3.0Hz,R<-5dB的频宽为4.7GHz。镀镍碳纳米管吸波涂层在相同厚度下,最大吸收峰在14GHz(R=-11.85dB),R<-10dB的频宽为2.23Hz,R<-5dB的频宽为4.6GHz。碳纳米管表面镀镍后虽然吸收峰值变小,但吸收峰有宽化的趋势,这种趋势对提高材料的吸波性能是有利的。碳纳米管作为偶极子在电磁场的作用下,会产生耗散电流,在周围基体作用下,耗散电流被衰减,从而雷达波能量被转换为其它形式的能量。     

Production and properties of foamed reservoir sludge inorganic polymers

The feasibility of using reservoir sludge as a raw material in the production of foamed inorganic polymers with different densities is investigated in this work. Reservoir sludge is first crushed, ground down and then calcined at the temperature of 850 °C for 6 h to become calcined reservoir sludge (CRS) powders. A mixture of 30% blast furnace slag and 70% CRS powders is alkali-activated by mixing with different alkaline activating solutions of water, sodium hydroxide and sodium silicate. The viscosities and compressive strengths of the resulting inorganic binders are measured and compared with each other. Furthermore, the inorganic binder paste that has the maximum compressive strength and best workability is mixed with various amounts of preformed air bubbles to produce foamed reservoir sludge inorganic polymer (FRSIP) specimens with different densities. The effects of density on the water absorption, pore size distribution, compressive strength, bending strength and transmission loss of the FRSIP specimens are evaluated.     

不同粘结剂对碳纳米管红外吸收涂层性能的影响

碳纳米管涂层已在低温工作环境中大量应用,所选用的粘结剂在很大程度上影响其红外吸收性能及与基体的结合性能。分别用水玻璃粘结剂和磷酸盐粘结剂与碳纳米管、镍粉混合制成涂料,并将其涂覆在铜基体表面。采用XRD和SEM对涂层的红外吸收性能、物相、晶体结构及形貌进行了表征;测试了涂层的抗热震性能。结果表明:当粘结剂为磷酸盐、含量为90%~85%时,1 400~3 570 cm~(-1)(2.80~7.14μm)波段内涂层的平均光吸收度达1.992~2.084,红外吸收性能最佳,抗热震次数可达35次(25~120℃),满足了用户要求(10次)。     

Evaluation of critical binder properties affecting the compactibility of binary mixtures

The aim of this study was to identify essential physical and mechanical properties of various binders and to investigate their influence on the tensile strength and porosity of tablets made from binary mixtures with sodium bicarbonate. The binders were characterized according to axial and radial tensile strength after compression into tablets, yield pressure and minimum porosity during compression, and elastic recovery after compression. The addition of a binder generally resulted in an increase in the tensile strength and a decrease in the porosity of the sodium bicarbonate tablets. The location of the binder in the voids between the sodium bicarbonate particles thus decreasing the porosity of the tablet seemed to be an important consideration. Consequently, the addition of binders with a low yield pressure value and a relatively small elastic recovery value (e.g., polyethylene glycol 3000 and polyvinylpyrrolidone) resulted in tablets of low porosity and high tensile strength, especially in the axial direction. The tensile strength of the pure binder also seemed to be important, especially for binders with a lower degree of deformability (e.g., microcrystalline cellulose and pregelatinised starch). The results also indicated the value of using both axial and radial tensile strength measurements in assessing the effect of a dry binder and showed that the importance of different binder properties varied according to the direction of the tablet strength measurements. The results demonstrated that the applied characteristics of the binders used in this study may serve as a useful tool in evaluating the effectiveness of binders.     

Chemical activation of hybrid binders based on siliceous fly ash and Portland cement

The hydration of Portland cement (PC) blended with a high amount of a siliceous fly ash (70% fly ash, 30% PC) has been examined. The fly ash contributes significantly to the long-term strength development, when compared to a reference sample with quartz powder. However the long setting time and the poor early strength prevent the use of such binders. Therefore the effect of different activators (sodium carbonate, potassium sodium silicate, potassium citrate and sodium oxalate) on the setting, the hydration kinetics and the strength development of the fly ash-PC blend has been investigated.The addition of the activators increases the pH and decreases thus the calcium concentrations in the pore solution, which leads to a faster reaction of alite and thus to early setting and increased early strength. On the long term, the high alkali concentrations lower the compressive strength and lead to a (partial) destabilization of ettringite.Sodium oxalate and potassium sodium silicate accelerate both the setting of the fly ash-PC blend and increase the early compressive strength. Furthermore, they show better compressive strengths at later ages compared to the other activators. Based on these findings, they can be considered as the most suitable accelerators among the investigated activators.     

Evaluation of Critical Binder Properties Affecting the Compactibility of Binary Mixtures

The aim of this study was to identify essential physical and mechanical properties of various binders and to investigate their influence on the tensile strength and porosity of tablets made from binary mixtures with sodium bicarbonate. The binders were characterized according to axial and radial tensile strength after compression into tablets, yield pressure and minimum porosity during compression, and elastic recovery after compression. The addition of a binder generally resulted in an increase in the tensile strength and a decrease in the porosity of the sodium bicarbonate tablets. The location of the binder in the voids between the sodium bicarbonate particles thus decreasing the porosity of the tablet seemed to be an important consideration. Consequently, the addition of binders with a low yield pressure value and a relatively small elastic recovery value (e.g., polyethylene glycol 3000 and polyvinylpyrrolidone) resulted in tablets of low porosity and high tensile strength, especially in the axial direction. The tensile strength of the pure binder also seemed to be important, especially for binders with a lower degree of deformability (e.g., microcrystalline cellulose and pregelatinised starch). The results also indicated the value of using both axial and radial tensile strength measurements in assessing the effect of a dry binder and showed that the importance of different binder properties varied according to the direction of the tablet strength measurements. The results demonstrated that the applied characteristics of the binders used in this study may serve as a useful tool in evaluating the effectiveness of binders.     

Study on compressive mechanical properties of nanohydroxyapatite reinforced poly(vinyl alcohol) gel composites as biomaterial

Nanohydroxyapatite reinforced poly(vinyl alcohol) (nano-HA/PVA) gel composites has been proposed as a promising biomaterial to replace diseased or damaged articular cartilage. In this paper, nano-HA/PVA gel composites were prepared by in situ synthesis nano-HA particles in PVA solution and accompanied with freeze/thaw method. The influence of nano-HA content, PVA concentration and freeze/thaw cycle times on the compressive mechanical behavior of nano-HA/PVA gel composites were evaluated using mechanical test equipment. The results showed that the compressive mechanical behavior of nano-HA/PVA gel composites was similar to that of natural articular cartilage, which held special viscoelastic characteristics. Both the compressive strength and modulus of the composites improved correspondingly with the rise of freeze/thaw cycle times and PVA concentration. The compressive strength and modulus of nano-HA/PVA gel composites firstly increased and then presented decreasing trend with the rise of nano-HA content. Furthermore, the compressive modulus of the composites improved exponentially with the rise of compressive strain ratio.     

Hydrolytic stability and acid resistance of porous silicate ceramics

Different inorganic binders (sodium aluminate, silicate, and aluminosilicate) have been used to engineer porous silicate ceramics, and the effect of the binder on the hydrolytic stability and acid resistance of the ceramics has been assessed. Only the ceramics based on the aluminosilicate binder are found to be hydrolytically stable, with an insignificant strength loss (≃6%) in 20% sulfuric acid, and can therefore be used as filtering materials for removing mechanical impurities from sulfuric acid solutions. A key role in the structural degradation of the porous silicate ceramics is played by the solution acidity rather than by the nature of the acid or its concentration.