Showing papers in "American Ceramic Society Bulletin in 1993"

Bioceramics : from concept to clinic

Abstract: Ceramics used for the repair and reconstruction of diseased or damaged parts of the musculo-skeletal system, termed bioceramics, may be bioinert (alumina, zirconia), resorbable (tricalcium phosphate), bioactive (hydroxyapatite, bioactive glasses, and glass-ceramics), or porous for tissue ingrowth (hydroxyapatite-coated metals, alumina). Applications include replacements for hips, knees, teeth, tendons, and ligaments and repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jaw bone, spinal fusion, and bone fillers after tumor surgery. Carbon coatings are thromboresistant and are used for prosthetic heart valves. The mechanisms of tissue bonding to bioactive ceramics are beginning to be understood, which can result in the molecular design of bioceramics for interfacial bonding with hard and soft tissues. Composites are being developed with high toughness and elastic modulus match with bone. Therapeutic treatment of cancer has been achieved by localized delivery of radioactive isotopes via glass beads. Development of standard test methods for prediction of long-term (20-year) mechanical reliability under load is still needed.

Cordierite glass-ceramics for multilayer ceramic packaging

Abstract: Sinterable cordierite glass-ceramics developed for use in fabricating copper-glass-ceramic multilayer substrates have been studied to understand the important role of the composition in sintering, crystallization, and microstructural development

BaTi4O9/Ba2Ti9O20-based ceramics resurrected for modern microwave applications

Abstract: Ceramics based on BaTi 4 O 9 and Ba 2 Ti 9 O 2 0 have been largely ignored over the past decade by manufacturers of high Q, high dielectric constant, temperature compensated materials for commercial wireless communications at elevated frequencies. When processed correctly, these ceramics yield properties that rival if not exceed those of ZrTiO 4 -based products currently used. Materials incorporating ZnO/Me 2 O 5 (Me = Ta, Nb) and their properties are described.

Calcium aluminate cements

Abstract: 1.1. Name of substance Calcium Aluminate Cements GORKAL 40, GORKAL 40M,GORKAL 50 1.2. Purpose production of concretes and refractory mortars as well as ingredient of construction chemistry products 1.3. Data concerning manufacturer Manufacturer Gorka Cement Sp. z o.o. Street 22 Lipca 58 Postal code/city 32-540 Trzebinia Country Poland Telephone no. ++48 32 758 10 99 Fax ++48 32 623 34 50 e-mail sekretariat@gorka.com.pl website www.gorka.com.pl

Reliability and reproducibility of ceramic sensors. I: NTC thermistors

Abstract: Reliability and reproducibility of ceramic sensors depends on a number of factors including manufacturing parameters. Part I of this three part series takes a closer look at these factors for thermistors with negative temperature-coefficient.

Influence of ZnO evaporation on microwave dielectric loss and sinterability of Ba(Zn1/3Ta2/3)O3 ceramics

Abstract: Evaporation of ZnO caused an inhomogeneous and complicated densification process for Ba(Zn 1/3 Ta 2/3 )O 3 ceramics. Densification near the surface was retarded by ZnO evaporation. It was found that homogeneous densification was obtained by sintering with ZnO powder muffling. Formation of an extraphase was suppressed by ZnO muffling. The sinterability of these ceramics was sensitive to preparation conditions. Small deviations in composition from the stoichiometric composition had a significant influence on sinterability. SiO 2 additions were found to improve sinterability.

Preparation and evaluation of sinterable silicon nitride powder by imide decomposition method

Abstract: A chemical synthesis process for producing high-quality Si[sub 3]N[sub 4] powder was developed by applying an imide decomposition method and well-controlled heat-treatment to the crystallization process. Si[sub 3]N[sub 4] powder produced by this process had superior characteristics, such as high purity, fine particle, high [alpha]-content, and good sinterability. Highly dense Si[sub 3]N[sub 4] ceramics were fabricated by both high-pressure hot-pressing of Si[sub 3]N[sub 4] without additives and pressureless sintering of oxide-doped Si[sub 3]N[sub 4], and their excellent mechanical properties were demonstrated. [alpha]/[beta]-SiAlON ceramics were fabricated by sintering the mixture of [alpha]-Si[sub 3]N[sub 4] and Ln-[alpha]-SiAlON powders (where Ln = Y and lanthanide elements), and the thermomechanical properties of SiAlON-based ceramics were much improved by selecting Tm or Yb as the lanthanide elements.

Preparation and characterization of ceramic fine powders produced by the emulsion process

Abstract: The driving forces for this research were the need to produce simple and complex ceramic fine powders with high chemical purity, uniform particle size in the range of 0.1 to 1.0 [mu]m, and the ability to manipulate the composition to meet certain physical and electrical properties. An emulsion process has been developed for producing fine, uniform powders with sizes ranging from 200 to 100nm. The process is ideal for preparing both simple and complex compounds, including titanates, oxides, and superconductors.

Magnesia-spinel brick for cement rotary kilns

Abstract: The evolution of cement rotary kilns with regards to changes in fuel and operating conditions has significant impact on refractory lining performance. Raw materials and properties of magnesia-spinel brick, which may be a solution, are described and compared

The economics of advanced self-propagating high-temperature synthesis materials fabrication

Abstract: The self-propagating, high-temperature synthesis (SHS) process enjoys inherent economic advantages It also is often the most feasible means to produce certain materials This article compares production costs of several materials prepared using SHS and conventional processes The results are presented of calculations for Si[sub 3]N[sub 4] powder production, AlN tile production, and SiC tile production

A new synthesis process for AlN

Abstract: Aluminium powders are mixed with lithium salts which are easily synthesized into pure alminium nitride by heating the mixed powders in nitrogen at temperatures ranging from 800°C to 1200°C.

The potential of fly ash for cement manufacture

Abstract: The fly ash from fluidized bed combustion is normally not suitable as a raw material for cement manufacture, because of high sulfur content. Calcium sulfoaluminate belite cement clinkers may provide a way to make this fly ash usable as a cement raw material. A well-known computational technique can be used to identify mixture/phase composition relationships for the raw materials. This article therefore analyzes binary mixtures composed of high-sulfate, fluidized bed combustion ashes. Emphasis is given to creating suitable raw mixtures from by-products of the same fluidized bed reactor unit. If feasible, the mixture components would then be mutually corrective and there would be no need to transport either component for long distances when used in the manufacture of proposed cements. The examples chosen also illustrate the use of the computation method, which may be applied broadly.

Baghouse and cartridge dust collectors: A comparison

Abstract: Increased demands are being placed on air filtration systems. The particular application will determine whether a baghouse or cartridge type is best. Baghouse and cartridge dust collectors both have their place in modern air filtering systems. Baghouses have been in use much longer, but cartridge types offer significant advantages for particular applications. The task facing the site engineer is to match the requirements of the specific application with the inherent characteristics of the dust collector. This article presents basic information about both types of dust collectors that can help provide the best solution to that problem.

Designing ceramic components for durability

Abstract: Successful application of advanced ceramics depends on proper characterization of material properties and the use of a probabilistic brittle material design methodology. Ceramic properties have progressively improved due to advances in both processing and composition. This has reduced the number and size of defects, led to the development of tougher materials that better tolerate the presence of flows, and improved understanding and control of microstructural composition. However, ceramics are inherently brittle, and the lack of ductility leads to low strain tolerance, low fracture toughness, and large variations in observed fracture strength caused by the variable severity and random distribution of flaws. Described here is a computer program for predicting the probability of a monolithic ceramic component's failure as a function of its time in service.

Synthesis and properties of high-purity alumina

Abstract: High-purity alumina is intended primarily for the high-pressure sodium-vapor lamp envelope market and other specialty alumina applications such as abrasives, catalysts, and structural ceramics. High-purity alumina must calcine to Al[sub 2]O[sub 3] with minimal metal impurities ([>=]99.99% Al[sub 2]O[sub 3]). Sulfate and chloride impurities are also undesirable. High-purity alumina should have less than 20ppm alkali and alkaline-earth metals, and less than 10 ppm each in transition-metal impurities. A process for synthesizing alumina by converting pure aluminum metal to aluminum hydroxide and the resultant alumina properties are described.

Ceramic-ceramic composites for dry sliding in closed tribosystems

Abstract: Engineers have always dreamed of dry-running machine elements, ie, moving parts that require no lubrication However, because of heavy friction losses and wear, high-performance machinery can only maintain full operational reliability with the aid of sophisticated lubricants The latest environmental legislation in Germany classifies liquid lubricants as pollutants requiring special disposal Environmental legislation may someday require the elimination of lubricants Preliminary results indicate that ceramic-ceramic composites may be a solution

Wear and machining of engineering ceramics by abrasive waterjets

Abstract: The purpose of this investigation was to simulate a machining front from an abrasive waterjet and its movements in a ceramic material Wear factors affecting the abrasive waterjet nozzle were also to be established Therefore, a low inclination angle (9[degree]) was used between the nozzle and test sample, simulating a moving machine front A standard nozzle with an inner diameter of 076 mm was used in the test, and it was placed close to the samples The outer diameter of the abrasive nozzle was 95 mm The high wear rate from abrasive waterjets makes it possible to machine hard ceramics-including dense alumina, titanium boride, silicon nitride, and composites-at high machining speeds

Statistical process control of glass manufactured for nuclear waste disposal

Abstract: Construction of the nation's first, and the world's largest, facility to immobilize high-level nuclear waste has recently been completed at the Savannah River Site (SRS) in Aiken, SC Liquid, high-level nuclear waste that has accumulated from over 35 years of reprocessing of nuclear fuels for national defense purposes will be immobilized in durable borosilicate glass in the SRS Defense Waste Processing Facility (DWPF) A ceramic, slurry-fed, Joule-heated electric melter will be used in the DWPF to reliably melt the borosilicate nuclear waste glasses at approximately 1150[degree]C The glass melt from the DWPF will be poured into stainless steel canisters for eventual disposal in a geologic repository Process and product quality models based on glass composition have been developed which simplify the fabrication of the glass while ensuring glass processibility and quality These models help to form the foundation of the statistical process control system used to monitor and control glass composition

Economic comparison of continuous and batch sintering of silicon nitride

Abstract: It is generally agreed that Si[sub 3]N[sub 4]-based compositions can be produced with reliable properties that are suitable for some automotive components. The major barrier to extensive application of Si[sub 3]N[sub 4] components is cost. Continuous sintering has recently been investigated as a means for cost-effective sintering of selected Si[sub 3]N[sub 4] compositions. Factors related to the cost of sintering in both belt furnaces and batch furnaces of increasing capacity - to allow sintering of the large number of parts required by the automotive industry - have been considered.

Injection moldable ceramic-ceramic composites: Compounding behavior, whisker degradation, and orientation

Abstract: During the past decade, enhanced processing has produced ceramic materials with improved mechanical properties and reliability. However, ceramic materials are still inherently brittle. Therefore, whisker-reinforced ceramic composites have recently received significant attention because of their attractive mechanical properties. In addition, the discrete nature and moderate aspect ratio of the short whiskers allow them to be processed into complex-shaped components, using automated fabrication methods, such as injection molding. Here, the compounding behavior of injection moldable silicon powder - SiC whisker formulations, for toughened reaction-bonded Si[sub 3]N[sub 4] composites, was examined as a function of the binder system. The effect on whisker degradation and orientation was also studied.