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Pure hydroxyapatite synthesis originating from amorphous calcium carbonate
Get PDFapplication/pdfWe report a synthesis strategy for pure hydroxyapatite (HAp) using an amorphous calcium carbonate (ACC) colloid as the starting source. Room-temperature phosphorylation and subsequent calcination produce pure HAp via intermediate amorphous calcium phosphate (ACP). The pre-calcined sample undergoes a competitive transformation from ACC to ACP and crystalline calcium carbonate. The water content, ACC concentration, Ca/P molar ratio, and pH during the phosphorylation reaction play crucial roles in the final phase of the crystalline phosphate compound. Pure HAp is formed after ACP is transformed from ACC at a low concentration (1 wt%) of ACC colloid (1.71 < Ca/P < 1.88), whereas Ca/P = 1.51 leads to pure beta-tricalcium phosphate. The ACP phases are precursors for calcium phosphate compounds and may determine the final crystalline phase.journal articl
凝結・硬化過程に凍結を受けたコンクリートの強度増進停滞機構および被害範囲・深さ測定手法に関する研究
Get PDF室蘭工業大学Muroran Institute of Technology博士（工学）application/pdf寒中コンクリート工事で最も留意すべきこととして、初期凍害の防止と強度増進の遅れに対する対応が挙げられる。初期凍害とは、フレッシュ時から硬化初期にかけてコンクリート中の水分が凍結することにより、強度発現の停滞などを引き起こす被害である。初期凍害の防止策は、圧縮強度5.0N/mm2が得られるまでコンクリートを凍結させないような初期養生を行うことである。初期凍害の判定は、実務では温度測定、研究では凍結融解後の養生による強度回復の有無で判定するのが一般的である。しかし、強度回復レベルと被害程度との対応が明らかではないという問題がある。また、実務では厳冬期には万全な凍結防止対策が施されるが、防水押えのコンクリート、部材厚さが薄いスラブ、パラペット等では予期せぬ寒波や養生管理の不備などにより、部材表面を凍結させてしまうという不具合が少なからず発生しているのが現状である。既往研究より、凍結によるセメントペーストの被害程度および回復程度は水セメント比と凍結融解後の養生条件の影響を大きく受ける可能性を報告している。コンクリートを使用した実験に先立ち、セメントペーストおよびモルタルの初期材齢時の凍結による強度増進停滞に関する研究を行った。その結果、凍結前後でセメントペーストの水和反応性は変化しないこと、モルタルでは被害程度の差は凍結を受けた際の凝結性状の影響が大きく、凝結終結前後の凍結が被害の有無を左右する結果になった。そこで、コンクリートについて凝結終結時の凍結が強度増進に及ぼす影響を確認した結果、混和剤による連行空気がないものは、凝結終結時の凍結により強度増進が停滞する結果であった。また、凝結始発前後の凍結を受けた場合には骨材界面にひび割れが生じており、強度低下の要因の一つであることを示した。以上の結果を受け、強度回復が可能となる条件は明らかになったが、実際の施工現場では凝結性状の測定は行っておらず、凝結過程のどの段階で凍結したかは不明である。凍結模様や黒ずみで初期凍害が確認されれば、各々で脆弱と判断した範囲の打ち直し、または補修が行われる。そのため、初期凍害範囲・深さ測定手法の検討を行うために、初期凍害事例が多い土間および防水押え等を対象とし、初期凍害範囲および初期凍害深さ測定として有効になりうる測定手法を選定した。実際の屋外環境で初期凍害を発生させ、それぞれの測定方法について詳細調査により得られた結果との比較と妥当性を検討し、初期凍害範囲・深さ測定手法の一提案を行った。It is important to prevent early frost damage and the response to the delay in strengthening in concrete. Early freezing damage stagnates strength development because of water freezing in the concrete before the early setting stage. Preventive measures against initial frost damage include performing initial curing to avoid freezing concrete until a compressive strength of 5.0 N/mm2 is obtained. In practice, complete antifreeze measures are taken during the winter season. However, frost damage at early ages may occur with unexpected cold waves and inadequate curing management in places where the thickness of the member is small. The authors have investigated the strength enhancement properties of cement paste subjected to initial freezing damage. It is reported that the damage and recovery degree of the frozen cement paste are influenced by the water-cement ratio and the curing conditions after freezing and thawing. In this study, we first confirmed the effects of the water-cement ratio and the curing conditions on the strength enhancement after freezing at the initial age were confirmed by experiments using cement paste and mortar. As a result, it was found that there was no change in the reactivity of cement before and after freezing, and that freezing around the final setting time affected the presence or absence of damage. Next, the compressive strength-enhancing properties of the frozen concrete at the final setting time were confirmed. As a result, the compression strength enhancement of the specimen with a small amount of air in the concrete stagnated due to freezing at the final setting time. In addition, the concrete frozen before and after the first setting time had cracks at the aggregate interface. It was shown that the cracks at the interface of the aggregate are one of the factors that reduce the strength of the concrete that was damaged by the initial frost. However, initial frost damage occurs in an environment where the outdoor temperature changes finely. In the current situation, when initial frost damage occurs, it is dealt with in consultation with the supervisor at each site. Therefore, in order to investigate the optimum initial frost damage range and depth measurement method, an experiment was conducted in which initial frost damage was generated in concrete outdoors in winter. As a result, it was found that the damage range can be specified non-destructively by the degree of repulsion, and the damage depth can be judged by the change in power consumption during core drill drilling. Based on the above experimental results, we proposed a method for dealing with concrete damaged by the initial frost damage.doctoral thesi
落石防護擁壁上に設置された貫通型落石防護柵支柱の曲げが卓越する場合に関する衝撃応答解析の妥当性検討
Get PDF本研究では落石防護擁壁上に設置された貫通型落石防護柵支柱を対象に，支柱に直接重錘による衝撃荷重が作用した場合における動的応答性状を適切に評価可能な解析手法の確立を目的として三次元弾塑性衝撃応答解析を実施した．ここでは，特に支柱の曲げ変形が卓越する場合に着目することとし，重錘の落下高さ H を変化させた 4 ケースの衝撃荷重載荷実験を実施した．また，実験結果と解析結果を比較することによって解析手法の妥当性を検討した．その結果，本解析手法を適用することで，衝撃荷重や重錘衝突後の支柱のひずみ分布性状などの耐衝撃挙動をほぼ適切に再現可能であることが明らかとなった．In order to establish a rational numerical analysismethod for appropriately evaluating the impact resistant behavior of the steel posts for rockfall protection fences installed into the protection walls, 3D elasto-plastic impact response analyses were conducted taking impact velocity of the impacted weight as variables. The applicability of the proposed method was investigated by comparing with the experimental results in the case of the through-type steel posts. From this study, it is confirmed that the impact resistant behavior of the steel posts can be properly simulated by applying the proposed method.journal articl
Effect of a Nitrite/Nitrate-Based Accelerator on the Strength Development and Hydrate Formation in Cold-Weather Cementitious Materials
Get PDFapplication/pdfRecently, there has been increased use of calcium-nitrite and calcium-nitrate as the main components of chloride- and alkali-free anti-freezing agents to promote concrete hydration in cold weather concreting. As the amount of nitrite/nitrate-based accelerators increases, the hydration of tricalcium aluminate (C(3)A phase) and tricalcium silicate (C3S phase) in cement is accelerated, thereby improving the early strength of cement and effectively preventing initial frost damage. Nitrite/nitrate-based accelerators are used in larger amounts than usual in low temperature areas below -10 degrees C. However, the correlation between the hydration process and strength development in concrete containing considerable nitrite/nitrate-based accelerators remains to be clearly identified. In this study, the hydrate composition (via X-ray diffraction and nuclear magnetic resonance), pore structures (via mercury intrusion porosimetry), and crystal form (via scanning electron microscopy) were determined, and investigations were performed to elucidate the effect of nitrite/nitrate-based accelerators on the initial strength development and hydrate formation of cement. Nitrite/nitrate-AFm (aluminate-ferret-monosulfate; AFm) was produced in addition to ettringite at the initial stage of hydration of cement by adding a nitrite/nitrate-based accelerator. The amount of the hydrates was attributed to an increase in the absolute amounts of NO2- and NO3- ions reacting with Al2O3 in the tricalcium aluminate (C(3)A phase). Further, by effectively filling the pores, it greatly contributed to the enhancement of the strength of the hardened cement product, and the degree of the contribution tended to increase with the amount of addition. On the other hand, in addition to the occurrence of cracks due to the release of a large amount of heat of hydration, the amount of expansion and contraction may increase, and it is considered necessary to adjust the amount used for each concrete work.journal articl
反応焼結法による希土類単硫化物 RESx (RE = Gd, Ho)の合成
Get PDF室蘭工業大学Muroran Institute of Technology博士（工学）application/pdf希土類単硫化物はNaCl型の結晶構造をもち，光学デバイス，太陽電池，フォトダイオード，磁気記録デバイスなどのエレクトロニクス分野における応用に不可欠な材料である。しかし，希土類金属と硫黄の蒸気圧が大きく異なる点，単体の希土類金属が極めて酸化しやすい点，これまでの試料作製方法が非常に多くの反応プロセスを伴う複雑なものであることなどから，純良な希土類単硫化物試料の合成は困難であった。本研究では，これまで研究例のほとんどない，Gd, Ho を含む希土類単硫化物に着目し，CS2ガス硫化法により作製した希土類三二硫化物（α-Gd2S3, δ-Ho2S3）と希土類単体（Ho）もしくは希土類水素化物（GdH2）を出発物質とし，放電プラズマ焼結（SPS）装置を用いた反応焼結法により，物性測定が可能である大きなサイズの希土類単硫化物GdS, HoSの純良な単一相焼結体の合成に成功した。また，出発原料の希土類と硫黄の比率を変えることにより，非化学量論比組成のGdSx，HoSxの単一相焼結体を広い組成範囲で合成することにも成功した。さらに，得られた試料について，結晶構造解析，元素組成分析，微量に含まれる不純物の同定を行い，熱物性，電子物性を詳細に調べた。その結果，格子定数，融点，電気伝導率の変化が，希土類と硫黄の組成比（x）と密接に関係していることを確認した。本研究では，従来の方法よりも単純なプロセスで不純物の少ない純良な希土類単硫化物の大型焼結体の合成が可能であることを示した。さらに，出発原料の比率を変えることで，非化学量論比組成の希土類単硫化物における希土類と硫黄の組成比（x）を制御することが可能であることを示した。さらに，希土類と硫黄の組成比（x）を変えることで電気伝導率などの物性を大きく変化させることが可能であることから，今回得られた結果は，物性値の最適化を行う上でも重要な知見であると考えられる。これらの結果は，Gd, Ho以外の希土類単硫化物にも応用が可能であると考えられ，今後の希土類単硫化物の設計の幅を広げることにつながり，次世代の高性能デバイスに不可欠な材料開発の発展に寄与するものであると考えられる。Rare-earth monosulfides RES (RE=rare earth element) with NaCl structure have various practical and potential applications in the electronics field, such as optical devices, photovoltaics, photodiodes, and magnetic recording devices. However, the synthesis of high-quality RES samples remains a challenge because RE is easily oxidized, large difference between the vapor pressures of RE and S, and the complexity of the previous synthesis methods. In this study, we focused on rare-earth monosulfides containing Gd and Ho, on which few studies have been done so far. Using rare-earth sesquisulfides (-Gd2S3, -Ho2S3) prepared by the CS2 gas sulfurization process and Ho metal or GdH2 as a starting material, we have succeeded in synthesizing single-phase GdS and HoS compacts of large size that we can measure their physical properties, by reaction sintering method using a spark plasma sintering (SPS) device. We have also succeeded in synthesizing single-phase GdSx and HoSx compacts with non-stoichiometric ratio composition in a wide composition range by changing the ratio of Gd (or Ho) and S as starting materials. Furthermore, for the obtained samples, crystal structure, elemental composition, identification of impurity phases, thermal properties and electronic properties were investigated in detail. As a result, it was confirmed that changes in lattice constant, melting point, and electrical conductivity are closely related to the composition ratio (x) of RE and S. In this study, we showed that it is possible to synthesize large compacts of pure rare-earth monosulfides with less impurities by a simpler process than the conventional method. Furthermore, it was shown that the composition ratio (x) of RE and S in rare-earth monosulfides with non-stoichiometric ratio composition can be controlled by changing the ratio of starting materials and we can significantly change physical properties such as electrical conductivity by changing the composition ratio (x) of RE and S. Therefore, the results are important for optimizing physical properties. These results are also considered to be applicable to rare-earth monosulfides other than Gd and Ho, which will lead to a wider range of designs for rare-earth monosulfides. It is considered to contribute to develop materials for next-generation high-performance devices.doctoral thesi
低速度衝撃を受けるFRPシート接着曲げ補強RC梁に関する弾塑性衝撃応答解析手法の開発研究
Get PDF室蘭工業大学Muroran Institute of Technology博士（工学）application/pdf近年，RC 構造物の耐衝撃性向上法の１つとして，高強度重量比や高耐食性および高施工性を有する FRP 材料を用いた補強方法に着目し，種々の実験的検討が行われている。しかしながら，耐衝撃設計法を確立し実構造物への適用を早期に実現するためには，実験とともに数値解析的検討も併用して効率的に研究を推進することが重要である。このような観点より，本研究では，FRP シート接着曲げ補強 RC 梁の耐衝撃挙動を適切に評価可能な数値解析手法の開発を目的として，シートの補強効果に直接影響を与えるひび割れ幅や分布特性を精度よく再現するために，コンクリートの軸方向要素長を数ミリ程度まで小さくし，かつ仮想引張強度を導入し弾性域のみを考慮した引張ひずみエネルギー等価の概念に基づく手法を提案した。また，提案手法を適用した三次元弾塑性衝撃応答解析を実施し，実験結果と比較することによってその適用性を検証した。本論文の構成は，以下の通りである。第１章は本論文の序論であり，本研究の背景や既往の研究，および目的について述べている。第２章では，本研究で対象とした試験体や重錘落下衝撃荷重載荷実験法の概要について述べている。第３章では，本研究において実施した FRP シート接着曲げ補強 RC 梁に関する重錘落下衝撃荷重載荷実験について述べている。検討の結果，シート補強 RC 梁は，シート剥離，破断あるいは載荷点近傍上縁コンクリートの圧壊のいずれかによって終局に至ることを明らかにしている。第４章では，本研究で適用した材料構成則の概要を述べるとともに，提案のコンクリート要素に関する引張ひずみエネルギー等価の概念について述べている。第５章では，単一衝撃荷重載荷を受ける無補強および AFRP シート接着曲げ補強 RC 梁を対象に，提案手法および国内外で広く用いられている２つのモデルを用いた三次元弾塑性衝撃応答解析を実施し，各モデルの適用性について述べている。検討の結果，３つのモデルの中で提案手法が最も精度よく実現象を再現可能であることを明らかにしている。第６章では，本研究で開発した提案手法の汎用性に関する検討を行うために，AFRP シート接着曲げ補強 RC 梁に関する重錘の落下高さを漸増させる場合や一定落下高さでの繰り返し衝撃荷重載荷実験を対象に，再現解析を実施している。検討の結果，提案手法を用いることによって，FRP シートの目付量や載荷方法によらずシート剥離や破断現象も含めた RC 梁の耐衝撃挙動を適切に評価可能であることを明らかにしている。 第７章は本論文の結論であり，本研究で得られた知見を整理している。In recent years, to investigate applicability of the strengthening method using fiber-reinforced polymer (FRP) composite materials on existing reinforced concrete (RC) structures under impact loading, the experimental researches and development have been conducted both in and out of Japan. Because the FRP materials have the advantages of light weight, non-corrosiveness, high ratio of strength to weight, and relatively easy installation. To apply the method in practice, the design specification has to be established smoothly by conducting not only experimental but also numerical research works efficiently. However, the numerical analysis method precisely evaluating FRP sheet debonding and/or fracture has not been developed yet. From this point of view, in this study, the numerical analysis method to better simulate the strengthening effects of the FRP sheets considering the sheet debonding and fracture was developed. To accomplish this, an equivalent tensile fracture energy concept for concrete elements under consideration of the elastic tensile strain energy and introduction of a fictitious tensile strength of concrete was proposed. The applicability was considered comparing with the experimental results of the RC beams strengthened in flexure with Aramid FRP sheets under drop-weight impact loading tests varying drop height of the weight and sheet volume. The test results in the cases of iterative impact loading with a constant energy and gradually increasing energy were also considered. From the comparison among two models frequently used worldwide and the proposed method based on the experimental results, it is confirmed that the proposed method can most precisely simulate the test results among them.thesi
Novel Scattering Operator for Arbitrary Finite Element Models in Optical Waveguides
Get PDFapplication/pdfAn efficient finite-element-method-based scattering operator (FEM-SO) is proposed. Utilizing field based propagation operators as boundary conditions, arbitrary light waves including radiation and evanescent waves can be treated at input and output ports. In contrast to conventional scattering operator techniques, the FEM-SO is applicable to arbitrary structures by using finite element models. In addition, considering structural discontinuities at the connecting boundary of scattering operators, an interface matrix to satisfy the boundary conditions between unit structures is introduced. To verify the present approach, numerical examples are shown for propagation characteristics of high-index-contrast waveguide facet and power spectrum of a photonic-crystal Fabry-Perot (FP) cavity filter.journal articl
Characteristics of thickness-vibration-mode PZT transducer for acoustic micropumps
No full textapplication/pdfThe characteristics of a thickness-vibration-mode PZT transducer for acoustic micropumps are evaluated with a U-shaped tube structure. The phenomenon in which the height of the water level can be increased in a U-shaped tube due to the acoustic driving force was used to develop measurement methods for the output pressure and flow rate of the acoustic micropump driven by a PZT transducer. The measurement results showed that the output pressure increases from 22.6 to 37.6 Pa and the flow rate increases from 3.6 to 6.4 ml/min when input voltages of 68-105 V-pp are applied to the PZT transducer and the height of water level is 30 cm above the PZT transducer. To discuss the effect of backpressure, the output characteristics of pressure and flow at water height levels of 31 and 32 cm were measured for comparison with those at 30 cm. (C) 2021 Elsevier B.V. All rights reserved.journal articl
Footsteps of International Co-learning between Muroran IT and RMIT
Get PDFapplication/pdfThis paper serves two purposes; 1) outlining the value and potential of language study tours and 2) documenting the footsteps of collaborative co-learning that has been implemented between Muroran Institute of Technology and RMIT university over 20 years. The value of the study tours is discussed with emphasis on intercultural communication in the 21st century, while unwrapping what has been organised and implemented between these two universities in order to provide students with learning opportunities that feed into their ever-changing worldviews.特集departmental bulletin pape
European Study Tour Learning English in Germany - A window to the outside
Get PDFapplication/pdfWhat led to study trips to Europe/Germany? For what reason are they in English? How did the partnership with the WSH Zwickau originate? Which essential role did the ESP (Europa Studienprojekt) play? From which experiences did the students gain and how did they react? Answer to these questions will be given in the following report.特集departmental bulletin pape