AIST Stories No1
15/36

Leading the way AIST!13at a glanceTerminologyin order to control humidity over durations of several minutes to several hours.”Maeda and his team investigated natural clay-based materials. They considered what type of material would possess the specific pore size to draw in moisture and simultaneously transfer this moisture in a manner similar to the suction effect of a fiber in order that it accumulate. For example, in the case of a zeolite*2, moisture rapidly reaches a saturated level because of the small size of the pores. Conversely, diatomaceous earth*3 possesses pores that are slightly too large and on this account, adsorption of moisture is difficult unless the humidity is high. Whereas this material is effective for preventing condensation, it was not a suitable material for maintaining a comfortable humidity. Just what type of material has a large pore volume and could adsorb sufficient moisture, but at the same time retain this moisture without immediately releasing it?“The first thing we looked for in a material was whether it could autonomously maintain a humidity of around 50–60%, which is considered comfortable for people. The next point was whether it could respond immediately to fluctuations in moisture levels over a short time span. In addition, even for a material that satisfied this balance, based on the presumption of commercialization, we had to consider options that excluded any materials where the cost was high.”Focusing on the moisture condensation phenomenon, a material that adsorbs vast quantities of moisture was discovered.The research team decided on a natural material called allophane*4, which is weathered volcanic ash soil. Around 1975, allophane had been used in the development of an adsorbent for toxic volatile organic compounds (VOCs) and its properties were well understood. However, while large quantities of allophane are found in a soil for gardening called Kanuma pumice, it causes plant root rot and for this reason, it is treated as industrial waste and disposed of. On this account, it received high marks as a low-cost material that could be reliably procured.“We originally used allophane as a raw material for research of synthesis of synthetic clay*5. In this research process, we found that the pores in allophane of less than five nanometers condensed moisture; moisture adsorption in allophane was high compared with that in diatomaceous earth. From these facts, we believed that we could obtain a material with a high humidity-controlling effect by utilizing the nanopores remaining after low temperature firing of allophane.”Several research findings from the 1970s led to a single idea and joint development of a new material with INAX leading the way towards realization. Further, it was the manufacturer INAX that concretely cleared the practical obstacles that stood in front of commercialization one by one; AIST (at the time the Nagoya Industrial Research Institute) was involved in the research from the standpoint of technology guidance.How does one achieve both moisture-adsorption properties and strength?Days of trial and errorJust what challenges did INAX face on the path to commercialization? Maeda explains as follows:“Ceramics are fired to obtain their final form but this firing process results in shrinkage with the porous structure thereby being lost. Vitrifying and densifying at high temperature is effective for raising strength but this results in the nanopores shrinking and this in turn reduces the quantity of moisture that can be adsorbed. Conversely speaking, strength ends up declining if the nanopores are retained in order to raise the adsorption of moisture. I think the toughest challenge that we faced was to satisfy the dual requirements of possessing a porous structure together with high strength.” After close to one year of trial and error, the conclusion was reached that firing allophane at a low temperature of around 800°C realized a product with a sufficient quantity of pores remaining as well as sufficient strength for use as a construction material.The base technologies were completed in 1994 and 1995 growth era of the 1970s, development of residential areas proceeded rapidly and there were fears that in the future, good quality clays suitable for ceramics would be depleted. Hence, the Nagoya Industrial Research Institute carried out R&D into technology for synthesizing good quality clays. Maeda participated in this project from the start.Moisture adsorption and release mechanismWhen indoor humidity rises, the nanopores in the ceramic adsorb moisture; when the humidity in the room falls, and it dries out, moisture is automatically released.Moisture is adsorbedas room humidity risesHigh humidity Moisture is releasedas room humidity declinesDryingMicroporesSource: LIXILdue to the humidification and deodorization effects of the pores.*4 Allophane: A porous clay mineral present widely in weathered volcanic ash soil. Exhibits high adsorption through moisture condensation in the pores.*5 Synthetic clay manufacture: Japan’s Aichi Prefecture, the location of AIST Chubu Center, is a thriving area for ceramics. In the high economic Leading the way AIST!13at a glanceTerminologyin order to control humidity over durations of several minutes to several hours.”Maeda and his team investigated natural clay-based materials. They considered what type of material would possess the specific pore size to draw in moisture and simultaneously transfer this moisture in a manner similar to the suction effect of a fiber in order that it accumulate. For example, in the case of a zeolite*2, moisture rapidly reaches a saturated level because of the small size of the pores. Conversely, diatomaceous earth*3 possesses pores that are slightly too large and on this account, adsorption of moisture is difficult unless the humidity is high. Whereas this material is effective for preventing condensation, it was not a suitable material for maintaining a comfortable humidity. Just what type of material has a large pore volume and could adsorb sufficient moisture, but at the same time retain this moisture without immediately releasing it?“The first thing we looked for in a material was whether it could autonomously maintain a humidity of around 50–60%, which is considered comfortable for people. The next point was whether it could respond immediately to fluctuations in moisture levels over a short time span. In addition, even for a material that satisfied this balance, based on the presumption of commercialization, we had to consider options that excluded any materials where the cost was high.”Focusing on the moisture condensation phenomenon, a material that adsorbs vast quantities of moisture was discovered.The research team decided on a natural material called allophane*4, which is weathered volcanic ash soil. Around 1975, allophane had been used in the development of an adsorbent for toxic volatile organic compounds (VOCs) and its properties were well understood. However, while large quantities of allophane are found in a soil for gardening called Kanuma pumice, it causes plant root rot and for this reason, it is treated as industrial waste and disposed of. On this account, it received high marks as a low-cost material that could be reliably procured.“We originally used allophane as a raw material for research of synthesis of synthetic clay*5. In this research process, we found that the pores in allophane of less than five nanometers condensed moisture; moisture adsorption in allophane was high compared with that in diatomaceous earth. From these facts, we believed that we could obtain a material with a high humidity-controlling effect by utilizing the nanopores remaining after low temperature firing of allophane.”Several research findings from the 1970s led to a single idea and joint development of a new material with INAX leading the way towards realization. Further, it was the manufacturer INAX that concretely cleared the practical obstacles that stood in front of commercialization one by one; AIST (at the time the Nagoya Industrial Research Institute) was involved in the research from the standpoint of technology guidance.How does one achieve both moisture-adsorption properties and strength?Days of trial and errorJust what challenges did INAX face on the path to commercialization? Maeda explains as follows:“Ceramics are fired to obtain their final form but this firing process results in shrinkage with the porous structure thereby being lost. Vitrifying and densifying at high temperature is effective for raising strength but this results in the nanopores shrinking and this in turn reduces the quantity of moisture that can be adsorbed. Conversely speaking, strength ends up declining if the nanopores are retained in order to raise the adsorption of moisture. I think the toughest challenge that we faced was to satisfy the dual requirements of possessing a porous structure together with high strength.” After close to one year of trial and error, the conclusion was reached that firing allophane at a low temperature of around 800°C realized a product with a sufficient quantity of pores remaining as well as sufficient strength for use as a construction material.The base technologies were completed in 1994 and 1995 growth era of the 1970s, development of residential areas proceeded rapidly and there were fears that in the future, good quality clays suitable for ceramics would be depleted. Hence, the Nagoya Industrial Research Institute carried out R&D into technology for synthesizing good quality clays. Maeda participated in this project from the start.Moisture adsorption and release mechanismWhen indoor humidity rises, the nanopores in the ceramic adsorb moisture; when the humidity in the room falls, and it dries out, moisture is automatically released.Moisture is adsorbedas room humidity risesHigh humidity Moisture is releasedas room humidity declinesDryingMicroporesSource: LIXILdue to the humidification and deodorization effects of the pores.*4 Allophane: A porous clay mineral present widely in weathered volcanic ash soil. Exhibits high adsorption through moisture condensation in the pores.*5 Synthetic clay manufacture: Japan’s Aichi Prefecture, the location of AIST Chubu Center, is a thriving area for ceramics. In the high economic

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