温室墙体用蓄热新材料的发展

温室大棚在现代设施农业中得到广泛的发展,温室墙体的蓄热性能是影响温室大棚室内温度的关键因素之一。由于传统温室墙体多采用黏土、砖块等急剧消耗性的材料,且对土地资源造成严重破坏,此类传统农业设施会逐渐被淘汰。随着农业技术的发展,环保高效蓄热新材料的开发及其在设施农业中的应用成为发展的趋势。本文将蓄热材料分为显热、潜热及化学蓄热三类,分别阐述了其研究发展现状,分析了各自的优缺点。详细论述了相变蓄热材料在国内外的研究进展,指出了研究过程中存在的问题,最后对温室墙体蓄热材料的发展前景进行了展望。

Research on Copper Matte Corrosion to Periclase-spinel Refractories

Effects of TiO2 or ZrO2 addition on corrosion resist; ance of periclase -spinel refractories to copper matte at different temperatures were investigated using static crucible method, and the results were compared with those of fused rebonded magnesite -chrome bricks. The chartges in chemical compositions and microstructure in different zones of the specimens after corrosion tests were studied by means of EDAX and SEM. The results show that ： （ 1 ） the reaction between periclase - spinel refractories and copper matte is very weak with the reaction layer thinner than 1 mm. Penetration is the main cause of copper matte corrosion and the penetration depth increases with temperature rising. When temperature exceeds 1200 ℃ , the penetration depth increases significantly; （2） appropriate TiO2 addition can improve penetration resistance （even better than that of magnesia chrome brick）, the optimum addition is 2 %. But ZrO2 has no remarkable effect on penetration resistance to copper matte of periclase - spinel refractories ; （ 3 ） SEM and EDAX analysis indicates that, Cu2S penetrates much further into the specimens than FeS.

High-temperature dielectric and microwave absorption performances of TiB2/Al2O3 ceramics prepared by spark plasma sintering

TiB_(2)/Al2O3 ceramics reinforced with Mg O are prepared by spark plasma sintering(SPS).The dielectric and microwave(MW)absorption properties are discussed.The results indicate that both the commercial TiB_(2)(C-TiB_(2))content and preparing temperature play important roles in the dielectric properties.Simultaneously,TiB_(2)/Al2O3 composite shows the best MW absorption property when the C-TiB_(2)content and preparing temperature are 9 wt%and 1400°C.To further improve the MW absorption properties,the composite containing 9 wt%synthesized TiB_(2)(S-TiB_(2))has been sintered at 1400°C.Its high-temperature complex permittivity is greater than that of TiB_(2)/Al2O3 composite with 9 wt%C-TiB_(2)sintered at 1400°C and is directly proportional to the temperature.Besides,TiB_(2)/Al2O3 composite with 9 wt%S-TiB_(2)possesses a better MW absorption at 25–500°C,its effective absorption bandwidth(RL<-5 dB)can reach 4.2 GHz at 25–500°C.And the minimum reflection loss(RLmin)value reaches-43.41 dB at the temperature of 800°C with a thickness of 1.45 mm for TiB_(2)/Al2O3 composite with 9 wt%C-TiB_(2).Consequently,the satisfying absorbing layer(d<1.75 mm),flexural strength,heat stability and considerable high-temperature MW absorption ability grant TiB_(2)/Al2O3 ceramics practical applications as high-temperature microwave absorption materials(MAMs).

Temperature-insensitive microwave absorption of TiB2-Al_(2)O_(3)/MgAl_(2)O_(4) ceramics based on controllable electrical conductivity

The design of the high-temperature microwave absorbing materials (MAMs) with temperature-insensitive and considerable microwave absorption (MA) capacity is a tremendous challenge.Ti B2-Al_(2)O_(3)/Mg Al_(2)O_(4) MAMs are prepared by the spark plasma sintering (SPS).Further,the influences of the Al_(2)O_(3) content on the flexural strength,thermal stability,high-temperature electrical conductivity,dielectric and MA properties are discussed.The results show that the Al_(2)O_(3) content is associated with flexural strength,high-temperature thermal stability,electrical conductivity,dielectric and MA properties.Meanwhile,the temperatureinsensitive and considerable MA properties with the minimum reflection loss (RLmin) ranging from -19.4 to -14.3 dB and the effective absorption bandwidth (EAB,RL<-5 dB) of 3.19–3.55 GHz are attained at 25°C–700°C in 8.2–12.4 GHz as the Al_(2)O_(3) content increases from 70.6 wt%to 80.6 wt%.This is ascribed to the compensating effect of the positive and negative temperature coefficient materials on the high-temperature electrical conductivity as well as the co-play of the dipolar and interfacial polarization at elevated temperatures.Consequently,Ti B2-Al_(2)O_(3)/Mg Al_(2)O_(4) ceramics exhibit the ideal prospect as the high-temperature MAMs.