Retarding intermetallic compounds growth of Zn high-temperature solder and Cu substrate by trace element addition

Since the thickness of layers of intermetallic compounds (IMCs) at the joining interface has an apparent effect on the joint reliability, understanding the growth mechanisms of IMCs is important for die-attachment applications. In the present study, the interfacial reaction between elements (Ca, Mn, Cr, and Ti) added to Zn alloys and Cu substrate were investigated in detail, focusing on IMCs grown by isothermal aging at 150 °C. The reaction layers included two types of Cu–Zn IMCs i.e., γ-Cu₅Zn₈ and ε-CuZn₅ phases. The joining interface with trace elements containing Zn solder reduced the growth rate of the IMCs. In particular, the addition of 0.1 wt% Cr to pure Zn solder decreased the growth rate of the IMCs by approximately 50 %. The mechanism we propose assumes that a phase containing the small Cr atoms exists between the solder and ε-CuZn₅, which suppresses the diffusion of metal atoms. To summarize, the Cr additive showed beneficial effects in terms of suppressing the growth of IMCs during the solid-state isothermal aging.     

Optimal Total Planning for Incinerator Plants in an Urban Area

This paper proposes optimal total planning for incinerator plants (IPs) in a typical urban area, which includes a method of determining the number of plants and the capacities of the IPs. Burnable municipal refuse is disposed of sanitarily by high‐temperature incineration at the IPs. At the same time, power generation from waste (PGW) is being performed at many IPs to recover energy. At present, the amount of energy generated by PGW is greater than that of wind power or photovoltaic power generation. However, PGW has a limited generation efficiency and low generation output due to the smaller capacity of IPs. To overcome the above weakness, highly efficient PGW is necessary with total integration and scaling up of IPs. Regarding total integration and scaling up, operation in larger areas is favorable from the point of view of refuse volume and collection. In the planning stage, both the cost of IPs and refuse collection, which is important for refuse disposal, should be taken into account comprehensively. Optimal total planing for IPs can be performed in two stages. First, the disposal capacity G_k of an IP versus the number of plants K is decided by constraints. G_k is about the same for all K because of maintenance and refuse collection, and is greater than 300 tons per day in steps of 100 tons per day. G_k should be decided not only by refuse volume but also by cessation of operation at plants due to maintenance or faults. Second, the cost of each value of K is calculated based on the construction and operating costs of the IPs, income from selling the energy of PGW, and refuse collection costs. Therefore, the value of K with the minimum cost is selected as the optimal number of IPs. A numerical simulation of an area with a population of 3 million indicates that the optimal plant number is 4. At present there are eight or nine IPs in cities of 3 million people. The above cost reduction effect will be about 15% from the present value. Considering the situation of aging IPs, a decreasing trend in refuse volume, and the stringent financial conditions of local governments, the proposed method is very effective and realistic.     

Whole abdominal irradiation for peritoneal dissemination of alimentary tract cancers

Between January 1986 and August 1991, 19 patients with alimentary tract cancers complicated by peritoneal dissemination received whole abdominal irradiation combined with intraperitoneal chemotherapy postoperatively. Using a moving-strip technique of irradiation, 12.0 Gy was delivered in three fractions to the entire abdominal contents with partial liver and kidney shielding. The primary tumor sites were the stomach in 12 patients, the colorectum in five, and the gall bladder in two. Nine patients with gross residual disease also received a limited field boost of 30.6 Gy in 17 fractions after completion of treatment to the whole abdomen. None of the patients failed to complete the planned dose despite acute gastrointestinal toxicity (nausea and vomiting, 84%, diarrhea and cramping, 78%) and acute hematologic toxicity (leukocytopenia, 84%, thrombocytopenia, 68%). Our follow-up study revealed that the actuarial one-year survival rate was 28.4% and the median survival time was 9.0 months. Survival rates at one-year for patients with colorectal and gastric cancer were 75.0% and 16.7%, respectively. Patients with gastric cancer (n = 12) had a poorer outcome than those with colorectal cancer (n = 5) in the present study. One reason for this difference may have been the presence of cancerous pleuritis, which was frequently observed in patients with gastric cancer. Therefore, more intensive treatment to prevent cancerous pleuritis seems to be necessary to improve the efficacy of whole abdominal irradiation.     

Physicochemical properties of Ba(Zr,Ce)O3-δ-based proton-conducting electrolytes for solid oxide fuel cells in terms of chemical stability and electrochemical performance

To enhance the power generation efficiency of solid oxide fuel cells (SOFCs), the use of proton-conducting solid solutions of doped BaCeO₃ and doped BaZrO₃, with formulas of the Ba(Zr_0.1Ce_0.7Y_0.1X_0.1)O_3-δ (X = Ga, Sc, In, Yb, Gd), was investigated as SOFCs electrolyte materials with respect to both chemical stability and electrical conductivity. Regarding chemical stability, the weight changes of each material were measured under a CO₂ atmosphere in a temperature range of 1200 °C–600 °C.Higher chemical stability was observed for dopant ions with smaller radii. Regarding conductivity, the dependences of the total conductivities on the oxygen partial pressure and temperature were measured in the temperature range of 600 °C–900 °C. In each material, the total conductivity was proportional to the oxygen partial pressure to the 1/4 power at high oxygen partial pressures, as previously observed for accepter-doped proton-conducting perovskite-type oxides. The derived conductivities for each type of charge carrier showed that the hole conductivity increased with the ionic conductivity. Based on the measured data, the leakage current densities were calculated for SOFCs with each of the investigated electrolyte materials and an area-specific resistance of 0.383 Ωcm². BZCYSc showed the minimum leakage current density, with a value of 3.7% of the external current density at 600 °C. Therefore, this study indicates that BZCYSc is the most desirable among the materials investigated for use as SOFCs electrolyte. However, for BZCYSc to be used as SOFCs electrolyte material, a protective layer is needed to ensure its chemical stability.     

Conversion Process of Strontium–Titanium Bimetallic Methoxyethoxide Precursor into SrTiO3 via Hydrolysis/Calcination

The conversion of a Sr–Ti bimetallic methoxyethoxide precursor into SrTiO₃ via hydrolysis and/or calcination was investigated. Hydrolysis with various water/metal molar ratios ( r _H; r _H= 0.5, 2, 4, 6, 8, 10) in tetrahydrofuran at reflux resulted in a decrease in the amount of the methoxyethoxyl groups, and the hydrolyzed products were soluble with r _H≤ 2. At r _H≥ 8, SrTiO₃ was crystallized without calcination. Both the hydrolyzed and unhydrolyzed precursors ( r _H= 0, 0.5, 2) were calcined in dry air at 550°–800°C. SrTiO₃ was crystallized on calcination at ≥550°C from amorphous materials with a considerable loss of carbon, which was present as both chars and carbonate ions.     

Icosahedron cage occupancy of structure-H hydrate helped by Xe -1,1-, cis -1,2-, trans-1,2-, and cis-1,4-dimethylcyclohexanes

Four mixtures of 1,1-, cis-1,2-, trans-1,2-, and cis-1,4-dimethylcyclohexanes (hereafter abbreviated DMCH) including H₂O and Xe have been investigated in a temperature range over 274.5 K and a pressure range up to 2.7 MPa. The 1,1-DMCH and cis-1,2-DMCH generate the structure-H hydrate in the temperature range up to 295.2 and 280.2 K, respectively. Especially, very large depression of equilibrium pressure has been observed in the structure-H 1,1-DMCH hydrate system. On the other hand, neither trans-1,2-DMCH nor cis-1,4-DMCH generates the structure-H hydrate in the present temperature range. It is an important finding that the cis-1,4-DMCH does not generate the structure-H hydrate in the presence of Xe, while the mixture of cis-1,4-DMCH and methane generates the structure-H hydrate.