Heat transfer investigations for in-bed and freeboard vertical U-tubes in a fluidized bed at moderate temperatures

The heat transfer coefficients for a single U-tube immersed vertically in fluidized beds of silica sands ($\text{d}\text{?}{}_{\mathrm{p}}\text{= 222, 488, and 778 μ}\text{m}$) and for a bundle of six hair-pin shaped nested vertical tubes mounted in the freeboard have been measured as a function of fluidizing velocity at bed temperatures ranging from 365 to 535 K. Simultaneous measurements of bed voidage were also made in each case. The effects of bed temperature, fluidizing velocity and particle size on in-bed and freeboard heat transfer coefficients and voidage are examined and explained.     

Electrical potential technique for monitoring subcritical crack growth at elevated temperatures

The electrical potential technique has been successfully used to monitor crack extension under fatigue as well as sustained loading at elevated temperatures in the presence of gross creep deformation. Calibration curves for actual crack extension vs change in electrical potential were determined for two specimen geometries, namely the compact type (CT) and the center crack tension (CCT) type, for an ASTM, grade A470 class 8 steel at 538°C (1000°F) and for a type 304 stainless steel at 594°C (1100°F).

A normalizing factor for expressing crack extension has been derived for the CT specimen. This factor accounts for changes in calibration due to small differences in initial crack length and, it also makes the calibration curve independent of the test temperature and material. Hence, the calibration curves presented herein are applicable to other materials and temperatures provided the specimen geometry and size is the same and the current input and potential leads are also located at the same position.     

Electrometric study on Cu(II), Hg(II) and Ag(I) complexes of isopropylmercaptan and determination of their solubility products

The complexation of copper (Cu⁺²), mercury (Hg⁺²) and silver (Ag⁺) ion with isopropylmercaptan has been studied in 25% (V/V) ethanolic media employing potentiometric, conductometric and amperometric titration techniques. Copper and mercury ions form 1:2 complex while silver ion shows the formation of 1:1 complex. Equilibrium constants and solubility products of these complexes have been evaluated by Ringbom's method at 10°, 20° and 30°C. The overall changes in thermodynamic functions ΔG, ΔH and ΔS accompanying complexation have also been determined at 20°C with the help of an isobar and Gibb's Helmholz equation.     

Monoclonal anti thy 1.2 antibodies from hybridoma HO13-4 do not react with mouse natural killer cells

The susceptibility of NK cells and immune cytotoxic T-cells to treatment with (a) monoclonal anti thy 1.2 antibodies from hybridoma HO13-4, (b) rabbit anti-mouse T-cell antiserum and (c) gamma globulins prepared from AKR/J anti C3H/HeJ antiserum was studied in the presence of rabbit complement. Monoclonal anti thy 1.2 antibody treatment completely abolished the cytotoxic activity of immune T-cells derived from C57BL/6J mice (H-2b) immunized with (C57BL/6J x DBA/2)F1 spleen cells (H-2bd) against P815 (H-2d) target cells. The same treatment had no significant effect on the NK activity of spleen cells from unimmunized mice against YAC target cells. Rabbit anti-mouse T-cell and mouse anti theta antisera also abrogated completely the immune T cell activity of spleen cells. This treatment however also resulted in a partial loss of NK activity. These results indicate that conventional anti theta antisera contain antibodies which recognize antigenic specificities on T-cells as well as on a population of NK cells. The cross reactivity is not a result of thy 1.2 antigen expression on NK cells and T-cells as recognized by the monoclonal antibodies. The specificity recognized by the monoclonal antibody (HO13-4) is only expressed on T-cells.     

The effect of microstructure on the fracture toughness of 300 and 350 grade maraging steels

The fracture toughness of 300 and 350 grade maraging steel that has been given simple heat treatments has been studied. By heating into the austenite region at well-controlled rates and holding for short times, the toughness can be increased significantly above that which is obtained for the standard treatment. It is shown that the toughness increase is due to plastic deformation of the austenite for single-cycled material. When multiple cycles are used, the 300 grade steel undergoes a strain-induced transformation at the crack tip that contributes significantly to the toughness. When singly cycled, 300 grade material is tested at −196°C, its properties approach those obtained for conventionally treated material at room temperature. Models for the toughness improvements are developed that take crack tip phenomena into account, and they are in good agreement with experiment.     

A monitor wafer based controller for semiconductor processes

A monitor wafer based controller is described. The controller can be applied to equipment with or without in-situ sensors. The controller incorporates a novel multivariable adaptation methodology for the feedback controller that employs a layered process/equipment model. The layered model consists of an intrinsic component that corresponds to the initial settings to outputs model and an extrinsic component that transforms the inputs and the outputs of the intrinsic model. The adaptation strategy tunes the extrinsic model only and thus the adaptation strategy is independent of the intrinsic model form. The controller determines whether the process and equipment have changed state by using model based SQC to compare product parameter measurements with the composite model predictions. If a change in state is deduced, a model tuner is activated which adapts the extrinsic model to reflect the new state. To adapt the model, a local experiment design technique is applied that perturbs the equipment settings. Finally, a stepwise optimization technique that permits the specification and utilization of user preference toward changing some process inputs over others is used for determining the new process recipe. We report the controller's application to the plasma enhanced chemical vapor deposition of silicon nitride (PECVD Nitride) process run on Applied Materials Precision Reactor (AMT 5000). The controller has been tested in two ways. First, single and multiple faults were introduced in the process equipment. Second, the controller performance was observed during an extended period of routine use. These evaluations indicate that the controller is able to detect process state change and to adjust the process recipe to keep the process on target     

Diagnosis of semiconductor manufacturing equipment and processes

This paper describes part of the research performed during the Microelectronic Manufacturing Science and Technology (MMST) program on techniques for the diagnosis of equipment malfunctions and misprocessing during semiconductor manufacturing. The main motivation of this work was to investigate techniques for rapid diagnosis. Towards this goal, a number of equipment-level diagnosis techniques are described. These techniques use equipment models to diagnose equipment malfunctions at a given process step. The results obtained by applying these diagnosis approaches are very encouraging. The various approaches were able to diagnose a number of faults that were deliberately introduced to test the algorithms and the equipment faults that developed during the final demonstration of the MMST program. These techniques were applied to a TI-built Advanced Vacuum Processor (AVP) and an Applied Materials Precision reactor AMT 5000     

Heat transfer from an immersed vertical tube to a gas fluidized bed

Fluidization and heat transfer experiments have been conducted in gas fluidized beds of two different sizes, viz., 305 × 305 mm² and 305 × 152.5 mm² and with particles of silica sands ($\text{d}\text{?}{}_{\mathrm{p}}\text{= 167, 488, 504, and 745 μ}\text{m}$), glass beads (d_p = 427 μm) and millet seeds (d_p = 2064 μm) with immersed smooth vertical heated tubes of diameter 12.7, 28.6, and 50.8 mm. Important conclusions are drawn concerning the dependence of heat transfer coefficient on fluidization velocity, bed particle diameter, tube diameter and nature of bed fluidization. The heat transfer data are employed to assess the available literature correlations for heat transfer coefficient and for its maximum value.     

A New Technique for Coating Silicon Carbide Onto Carbon Nanotubes Using a Polycarbosilane Precursor

Multiwalled carbon nanotubes (MWCNTs) have been coated with silicon carbide (SiC) using polycarbosilane as precursor in order to improve their thermo oxidative stability. The polycarbosilane coated MWCNTs were heated to ~1300°C under an inert atmosphere to generate the SiC coating. X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy have confirmed the formation of SiC on the MWCNTs. The retention of the tubular structure of the MWCNTs has been confirmed by transmission electron microscopy. Thermogravimetric analysis has been performed to evaluate the thermo oxidative stabilities of coated and virgin MWCNTs. Sonication studies have shown that the mechanical strength of the MWCNTs was increased after coating with SiC.