Showing papers by "Michio Inagaki published in 1994"

Self‐Combustion Reactions Induced by Mechanical Activation: Formation of Aluminum Nitride from Aluminum–Graphite Powder Mixture

Abstract: The powders of aluminum metal and natural graphite mixed in various molar ratios (Al/C = 7/0–0/7) were ground in a planetary ball mill. When the mixtures thus activated mechanically were exposed to air, exothermic reactions spontaneously occurred in two successive steps, evolving red heat initially and then white heat. The main product was aluminum carbide in the first step and aluminum nitride as well as carbide in the second step. From the measurements of XPS spectra and the lattice constants, it was concluded that the aluminum nitride obtained is solid solution with the composition of (Al2OC)1–x(AlN)x. The effects of mixing ratio of Al to C, grinding time, and gas atmosphere on the formation of aluminum nitride are discussed.

Criteria for the Intercalation of Sulfuric Acid

Abstract: The criteria for the intercalation of sulfuric acid were studied. The intercalation reaction was found to be governed by the relation between the onset potential values for each stage structure and the upper limit of the saturated potential. It was also shown clearly that the intercalation of sulfuric acid was possible on the hosts with the crystallite thickness along the c-axis above 20 nm and also with positive magnetoresistance at room temperature.

Carbonization of polyimide films: Effect of cold‐drawing and chemical structure

Abstract: Polyimides of various chemical structures were prepared from pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), oxydianiline (ODA), and p-phenylenediamine (PDA). The cold-drawn polyimide films were prepared and carbonized. The electrical conductivity of the carbonized films enhanced linearly with the draw ratio. The effect of cold-drawing on the electrical conductivity is more remarkable with the rigid polyimides such as PMDA/PDA and BPDA/PDA than the flexible polyimides such as PMDA/ODA and BPDA/ODA. The tendency is well in accord with the effect of cold drawing on the improvement of modulus of polyimides. With the rigid polyimides, the higher alignment of polymer chain is supposed to be achieved by the cold-drawing. © 1994 John Wiley & Sons, Inc.

Structural strain in pyrites evaluated by X-ray powder diffraction

Abstract: Two parameters for measuring the structural strain, the effective Debye-Waller parameter, B eff, and lattice strain, ɛ, were evaluated on a natural pyrite (FeS2) after grinding. The effective Debye-Waller parameter, B eff, which depends on the displacement of atoms in the crystal, was calculated for the overall crystal, B eff(FeS2), and for sulphur, B eff(S), from the intensities of the X-ray diffraction lines. The B eff(S) increased markedly with increasing grinding time, while B eff(FeS2) did not change significantly. The lattice strain, ɛ, was not recognized. These observations suggest that the displacement of sulphur atoms preferentially takes place by grinding. The relations between these B eff values and crystallite size, L, were observed to be common for two different methods of grinding. This tendency was considered to be an inherent property of pyrite. The value of B eff(S) is a useful index to estimate mechanically caused strain in pyrite.

Single-crystal study of topotactic changes between NH4VO3 and V2O5

Abstract: In the thermal decomposition of NH4VO3 to V2O5, the changes in crystallographic orientation were studied by using single crystals of NH4VO3 prepared by recrystallization from aqueous solution. X-Ray diffraction (XRD) measurements clearly showed that a shrinkage took place along b axis of NH4VO3 up to 180 °C and V2O5 sheets started to be formed in parallel to ab plane of NH4VO3 above 205 °C. These changes in crystallographic orientation were confirmed through the reverse reactions to NH4VO3. Crack formation during the decomposition, observed with scanning electron microscopy (SEM), was consistent with the topotactic changes observed.

Lithium Secondary Battery Based on Intercalation in Carbon Fibers As Negative Electrode

Abstract: Lithium secondary batteries using carbon as negative electrode with intercalated Li have been developed. Various kinds of carbon fibers with different crystallographic and macroscopic structure are applied as a negative electrode for the lithium secondary batteries with 1 mol LiClO4/propylene carbonate electrolyte. The battery performances of the fibrous electrode are evaluated as a function of the structure of the carbon fibers. Not only the crystallographic structures but also the morphology of the fibers affect the battery performances. It was shown that Li is stored to form electrochemically the 1st stage compounds in well-ordered and even in disordered carbon fiber electrodes.

Coating of SiC-Gradient Carbon Material with Mullite Film and Its Oxidation Resistance

Abstract: The optimum conditions for mullite coating on SiC-gradient carbon substrates and its oxidation resistance were studied. A homogeneous precursor solution with the composition of Al/Si=3 was prepared by refluxing an ethanol solution of Al(NO3)3 and silicon ethoxide (TEOS) of 0.1mol/l at its boiling point for 12h. A mullite film with a thickness of 1.0μm without any cracks was obtained under the following conditions; the drawing up the substrate from the precursor solution at a rate of 0.05cm/s, keeping at room temperature for 24h and at 100°C for 48h in air, and then heating up to 1300°C at a rate of 200°C/h. The SiC-gradient carbon substrates coated with the mullite film showed the excellent oxidation resistance; no appreciable weight loss by oxidation at 1000°C for 15h was observed.

Formation and structure of ternary graphite intercalation compounds with two metal chlorides

Abstract: The formation processes of the «bi-intercalation» type compounds in the systems of AlCl 3 -FeCl 3 -graphite and AlCl 3 -CuCl 2 -graphite were studied by using three different reaction paths. By structural refinement the «mixed» type compounds were found to have more defective intercalate layers than the «bi-intercalation» type

A Study on Dehydration Behavior of CaCrO4 by the AE and TG-DTA-MS Methods

Abstract: 物質 の加熱 に伴 う重量変化 お よび熱的変化 を追跡す る 手法 と して, 熱 重量(TG), 示差熱(DTA)分 析が広 く用 い られてお り, 最 近では, このTG-DTA測 定 に加 えて ガ ス状物 質の質量 をその場で計測するために質量分析(MS) が利用 される ようにな っている。一方, アコーステ ィッ ク ・エ ミッシ ョン (Acoustic Emission, AE) とは 「音 響の 放 出」 の ことを言い,「 固体 材料 内部の微小 な破壊あ る いはそれ と同様 なエネルギー開放過程 によって発生す る 弾性 波動現象 」 と定 義で き, このAE波 は可 聴域 以上 の 周波 数(kHz~MHz)を 持つ超音波 である。 このAEを 計測 するAE法 はコ ンクリー ト構造 物の破壊 検査, 炭素繊維 を含 む複合材料 などの破壊機構 や金属 中での転位 の研究 な どに用 い られてお り, 速いメカニカルな変化 を追跡す るのに非常 に適 した技法 であ る1)。AE法 を熱分析 として 利用 しよ うとする試 みは最初 にLonvikに よってなされ, 彼 に よってThermosonimetry(TS)と 呼 ばれている2),3)。嶋 田は, AE法 をDTA法 と組 み合 わせ て同時測定 す ること に よ り, NaClO4, KClO4お よびKNO3な どの無機 固体の 相 転移, 融解, 熱分 解過程 を追 跡 している4)-10)。しか し, 酸化反応 などを含め た広義の固体 反応 を調べ る手段 としてのAE法 は未 だ確 立 されて いる とは言 えず, 多 く の事 例 を集 めてい る段 階 にあ る。 CaCrO4粉 末 はLaCrO3の 焼結助剤 と しで用 い られ る が, その熱的挙動を詳細 に検討 した報告はない。CaCrO4 は固体 表面 もしくは固体 中に微 量な水 を含み, その水 は 525°Cま でに非 可逆的 に脱離 する と言 われて いる11)。し か し, どの ような形 の水が含 まれ, どの ような過程 で脱 水 するのか明 らかにされていない。 そ こで, 本研究 では AE法 と他 の熱分析 手法であ るTG-DTA-MS法 を使 って 北海道大 学工学部応用 化学科: 札 幌市 北区北13条 西8丁 目 〒060 Department of Applied Chemistry, Faculty of Engineering, Hokkaido University, Kita-ku, Sapporo 060, Japan

Oxidation of zirconium carbide powders and single crystals accompanying deposition of carbon

Abstract: The oxidation of the powder and single crystal samples of ZrC was carried out below 450 °C at an oxygen pressure of 2.6 kPa. The formation of carbon was confirmed in both samples by Raman spectroscopy. The ZrO2 phase formed on the surfaces of ZrC single crystal was found to be divided into two regions, zones 1 and 2, the former being adjacent to the ZrC and containing the 14 – 23 atomic % carbon in contrast to the 7 – 10 atomic % in the latter.

Coating of Carbon Materials with Silica by Sol-Gel Method.

Abstract: The optimum conditions for silica coating on carbon materials by using an ethanol solution of tetraethoxysilane (TEOS) were studied. A homogeneous film of silica with a thickness of 0.2 pm without any cracks was obtained by dip-coating process under the following conditions; the ethanol solution containing TEOS of 0.1 molg, the pulling-out velocity of the carbon substrates at 2.0 cm/s, the gelation in the air for 48 h, and the heating at 70 °C for 1 h and then up to 1000 °C by 5 °C/min. From the SEM observation of the cross-section of the substrates with silica, it was shown that the silica coating film adhered excellently to carbon substrate.

Synthesis of aluminum nitride in air by the self–combustion of mechanically activated aluminum–graphite powders

Abstract: The powders of aluminum metal and natural graphite mixed in various molar ratios(Al/C=7/0∼0/7) were ground in a planetary ball mill. When the mixtures thus activated mechanically were exposed to air, exothermic reactions spontaneously occurred in two successive steps, evolving red heat initially and then white heat. The main product was aluminum carbide in the first step and aluminum nitride as well as carbide in the second step. From the measurements of XPS spectra and the lattice constants, it was considered that aluminum nitride obtained is solid solutions with the composition of (Al2OC)1-x(AlN)x. The effect of mixing ratio of Al to C, grinding time and gas atmosphere on the formation of aluminum nitride are discussed.