Sintering of Ceramics: Fundamentals The Sintering Process Driving Force for Sintering Defects in Crystalline Solids Diffusion in Crystalline Solids The Chemical Potential Diffusional Flux Equations Diffusion in Ionic Crystals: Ambipolar Diffusion Solid-State and Viscous Sintering Mechanisms of Sintering Effects of Grain Boundaries Theoretical Analysis of Sintering Herring's Scaling Law Analytical Models Numerical Simulation of Sintering Phenomenological Sintering Equations Sintering Diagrams Sintering with an Externally Applied Pressure Stress Intensification Factor and Sintering Stress Alternative Derivation of the Sintering Equations Grain Growth and Microstructure Control General Features of Grain Growth Ostwald Ripening Topological and Interfacial Tension Requirements Normal Grain Growth in Dense Solids Abnormal Grain Growth in Dense Solids Grain Growth in Thin Films Mechanisms Controlling the Boundary Mobility Grain Growth and Pore Evolution in Porous Solids Simultaneous Densification and Grain Growth Fabrication Principles for Ceramics with Controlled Microstructure Liquid-Phase Sintering Elementary Features of Liquid-Phase Sintering Stages of Liquid-Phase Sintering Grain Boundary Films The Basic Mechanisms of Liquid-Phase Sintering Numerical Modeling of Liquid-Phase Sintering Hot Pressing with a Liquid Phase Use of Phase Diagrams in Liquid-Phase Sintering Activated Sintering Vitrification Special Topics in Sintering Inhomogeneities and their Effects on Sintering Constrained Sintering I: Rigid Inclusions Constrained Sintering II: Adherent Thin Films Constrained Sintering III: Multilayers Constitutive Models for Porous Sintering Materials Morphological Stability of Continuous Phases Solid Solution Additives and the Sintering of Ceramics Sintering with Chemical Reaction: Reaction Sintering Viscous Sintering with Crystallization Sintering Process Variables and Sintering Practice Sintering Measurement Techniques Conventional Sintering Microwave Sintering Pressure-Assisted Sintering Appendix A Physical Constants Appendix B SI Units - Names and Symbols Appendix C Conversion of Units Appendix D Ionic Crystal Radii (in units of 10-10m) Appendix E Density and Melting Point of Some Elements and Ceramics

Chapter 17.2.3.5.4 Liquid Phase Sintering M. N. Rahaman, M. N. RahamanSearch for more papers by this author M. N. Rahaman, M. N. RahamanSearch for more papers by this author Book Editor(s):J. J. Zuckerman, J. J. ZuckermanSearch for more papers by this authorJim. D. Atwood, Jim. D. AtwoodSearch for more papers by this author First published: 01 January 1999 https://doi.org/10.1002/9780470145333.ch25Book Series:Inorganic Reactions and Methods AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Inorganic Reactions and Methods: Formation of Ceramics, Volume 18 RelatedInformation

[This corrects the article DOI: 10.1016/j.bioactmat.2020.02.016.].

Borate bioactive glass 13-93B3 converts into an osteoconductive hydroxyapatite-like material in a liquid medium. In this study, 13-93B3 was incorporated into a commercial PMMA (poly(methyl methacrylate)) bone cement, and the conversion of the glass into a precipitate in solution was investigated with scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared (spectroscopy)-attenuated total reflection, and micro-Raman spectroscopy. Glass particles of 5, 33, and 100 mu m diameter were each mixed with the PMMA cement to create 20, 30, and 40% glass-loaded composites. Precipitate formation was found to be a calcium-deficient apatite partially substituted with magnesium ions that resembles native bone material and would ideally encourage bone growth better than stoichiometric hydroxyapatite. Composites of bone cement and 13-93B3 show promise as a means of encouraging bone attachment to the surface of the bone cement.

NOTE: The first page of text has been automatically extracted and included below in lieu of an abstract Session 3464 Undergraduate Laboratory Experience for Ceramics Mohamed N. Rahaman, William G. Fahrenholtz Department of Ceramic Engineering University of Missouri-Rolla Abstract An appreciation for experimental work and the development of laboratory skills are essential parts of undergraduate materials education. To develop effective laboratory courses in materials, the unique characteristics and properties of ceramics must be considered. Normally, ceramics cannot be produced by the methods commonly used for metals and polymers because ceramics are more refractory and brittle than other materials. Ceramics are commonly fabricated by compacting and sintering particulate starting materials. At the University of Missouri-Rolla (UMR), ceramics education is concentrated in the Department of Ceramic Engineering. UMR has an integrated, four-semester laboratory sequence at the sophomore and junior levels designed to provide the specialized training needed for the production of ceramics. The laboratory exercises emphasize a hands-on approach for the students and topics include the use of equipment, selection of raw materials, choice of processing and characterization methods, and statistical design of experiments. The coordination of experiments with topics in other lecture courses is an important part of the undergraduate program. The sophomore and junior classes also provide the necessary foundation for the senior level laboratory courses, a two-semester capstone Senior Design course and a property measurement laboratory. I. Introduction Over the last twenty years, Ceramic Engineering education has been transformed by the emergence of multi-disciplinary materials departments. At several universities, this has resulted in the merging of previously separate departments specializing in metals or ceramics into a single unit that often includes programs in polymers and electronic materials. The new department may be known as Materials Science and Engineering, Materials Engineering, or simply Materials. Examples of merging large, well-established departments include the Ohio State University and the University of Illinois at Urbana-Champaign. More recently, Ceramic Engineering departments at Rutgers University, Alfred University and Clemson University have incorporated a materials component into their ceramics programs. Currently, UMR is the only university where ceramics education and research are housed in a specialized Department of Ceramic Engineering. The predominant situation is, therefore, for ceramics to be taught as part of an undergraduate materials curriculum. Because the application of engineering principles to problems in materials involves a significant amount of experimental work, it is important that undergraduate students develop an appreciation for laboratory practice. Furthermore, it is important that students learn and refine

There is a need for synthetic grafts to reconstruct large bone defects using minimal invasive surgery. Our previous study showed that incorporation of Sr into bioactive borate glass cement enhanced the osteogenic capacity in vivo. However, the amount of Sr in the cement to provide an optimal combination of physicochemical properties and capacity to stimulate bone regeneration and the underlying molecular mechanism of this stimulation is yet to be determined. In this study, bone cements composed of bioactive borosilicate glass particles substituted with varying amounts of Sr (0 mol% to 12 mol% SrO) were created and evaluated in vitro and in vivo. The setting time of the cement increased with Sr substitution of the glass. Upon immersion in PBS, the cement degraded and converted more slowly to HA (hydroxyapatite) with increasing Sr substitution. The released Sr2+ modulated the proliferation, differentiation, and mineralization of hBMSCs (human bone marrow mesenchymal stem cells) in vitro. Osteogenic characteristics were optimally enhanced with cement (designated BG6Sr) composed of particles substituted with 6mol% SrO. When implanted in rabbit femoral condyle defects, BG6Sr cement supported better peri-implant bone formation and bone-implant contact, comparing to cements substituted with 0mol% or 9mol% SrO. The underlying mechanism is involved in the activation of Wnt/β-catenin signaling pathway in osteogenic differentiation of hBMSCs. These results indicate that BG6Sr cement has a promising combination of physicochemical properties and biological performance for minimally invasive healing of bone defects.

Bone cement is used extensively in orthopedics to anchor prostheses to bone and fill voids. Incorporating bioactive glass into poly(methyl methacrylate) (PMMA)-based bone cement could potentially improve its effectiveness for these tasks. This study characterizes the mechanical and degradation properties of composites containing PMMA-based bone cement and particles of borate bioactive glass designated as 13-93B3. Glass particles of size 5, 33, and 100 μm were mixed with PMMA bone cement to create composites containing 20, 30, and 40 wt % glass. Composites and a bone cement control were soaked in phosphate-buffered saline. Compressive strength, Young's modulus, weight loss, water uptake, solution pH, and ionic concentrations were measured over 21 days. The compressive strengths of composites decreased over 21 days. Average Young's moduli of the composites remained below 3 GPa. Weight loss and water uptake of specimens did not exceed 2 and 6%, respectively. Boron concentrations and pH of all solutions increased over time, with higher glass weight fractions leading to higher pH values. Results demonstrated that the composite can sustain glass degradation and ionic release without compromising short-term mechanical strength.

Our aims were to 1) evaluate the capacity of hollow hydroxyapatite (HA) microspheres (212-250 μm) to serve as a delivery system for controlled release of BMP-2 in vitro and 2) examine relaxin as an enhancer of BMP-2 for bone regeneration. Hollow HA microspheres were converted from borate glass microspheres and characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and the Brunauer-Emmett-Teller method. The microspheres loaded with BMP-2 and relaxin were implanted for 6 weeks in Sprague Dawley rats with calvarial defects. BMP-2 alone in the range up to 1 μg per defect exhibited dose-dependent bone regeneration while relaxin alone in the range up to 0.25 μg per defect did not promote bone regeneration. When compared with BMP-2 alone (1 μg per defect), a 50% reduction in the BMP-2 dose was achieved with the addition of 0.05, 0.1, or 0.25 μg of relaxin per defect. These results show that loading HA microspheres with a combination of relaxin and BMP-2 can significantly reduce the BMP-2 dose required to regenerate an equivalent amount of bone.

Bioactive glasses with controllable reactivity and bioactive potential have been created by replacing varying amounts of SiO2in silicate 45S5 glass with B2O3. While these borate and borosilicate glasses formed from 45S5 glass are receiving growing interest for hard and soft tissue repair, their structural characteristics have received little attention. In this study, the structural characteristics of a family of bioactive glasses formed by replacing varying amounts of SiO2 in 45S5 glass with B2O3 were evaluated using multiple spectroscopic techniques. A benefit of this work is the use of multiple spectroscopic techniques and one set of compositional variation for a widely used family of bioactive glasses. The results showed that when compared to 45S5 glass, SiO2 remained the primary network in a borosilicate glass designated 45S5-1B, formed by replacing 33.3 mol. % of the SiO2 in 45S5 with B2O3. The glass network in both glasses was composed mainly of SiO4 tetrahedral units with 2 nonbridging oxygen atoms. In comparison, B2O3 was the primary network former in borosilicate 45S5-2B and borate 45S5-3B glasses, formed by substituting 66.7 mol. % and 100 mol. %, respectively, of SiO2 in 45S5 glass with B2O3. The network in these two glasses was composed mainly of trigonal BO3 structural units (orthoborate or pyroborate groups) and a smaller fraction ∼30%) of tetrahedral BO4 units. The observed structural characteristics are used to rationalize data from a previous study for the reactivity and bioactive potential of this family of bioactive glasses.

This chapter examines the preparation of an aqueous paste composed of Si3N4 powder and sintering additives with the requisite rheology and formed into structures with different shape and architecture by robocasting in an experiment. A commercial powder widely used in the production of structural and medical grade Si3N4 ceramics was used in the experiment. This powder is known to have desirable sintering characteristics but it has been reported to be difficult to disperse in aqueous media to high solids loading. After drying and debinding, the parts were fired using a combination of sintering and hot isostatic pressing (abbreviated sinter HIP) and characterized to evaluate their macrostructure, microstructure and mechanical properties. The optimal amount of PEI was assessed from measurements of the viscosity versus shear strain rate for Si3N4 suspensions containing varying amounts of PEI.

Silicon nitride (Si3N4) has a distinctive combination of material properties such as high strength and fracture toughness, inherent phase stability, scratch resistance, low wear, biocompatibility, hydrophilic behavior, excellent radiographic imaging and resistance to bacterial adhesion, all of which make it an attractive choice for orthopaedic implants. Unlike oxide ceramics, the surface chemistry and topography of Si3N4 can be engineered to address potential in vivo needs. Morphologically, it can be manufactured to have an ultra-smooth or highly fibrous surface structure. Its chemistry can be varied from that of a silica-like surface to one which is predominately comprised of silicon-amines. In the present study, a Si3N4 bioceramic was subjected to thermal, chemical, and mechanical treatments in order to induce changes in surface composition and features. The treatments included grinding and polishing, etching in aqueous hydrofluoric acid, and heating in nitrogen or air. The treated surfaces were characterized using a variety of microscopy techniques to assess morphology. Surface chemistry and phase composition were determined using X-ray photoelectron and Raman spectroscopy, respectively. Streaming potential measurements evaluated surface charging, and sessile water drop techniques assessed wetting behavior. These treatments yielded significant differences in surface properties with isoelectric points ranging from 2 to 5.6, and moderate to extremely hydrophilic water contact angles from similar to 65 degrees to similar to 8 degrees. This work provides a basis for future in vitro and in vivo studies which will examine the effects of these treatments on important orthopaedic properties such as friction, wear, protein adsorption, bacteriostasis and osseointegration.Statement of SignificanceSilicon nitride (Si3N4) exhibits a unique combination of bulk mechanical and surface chemical properties that make it an ideal biomaterial for orthopaedic implants. It is already being used for interbody spinal fusion cages and is being developed for total joint arthroplasty. Its surface texture and chemistry are both highly tunable, yielding physicochemical combinations that may lead to enhanced osseointegration and bacterial resistance without compromising bulk mechanical properties. This study demonstrates the ease with which significant changes to Si3N4's surface phase composition, charging, and wetting behavior can be induced, and represents an initial step towards a mechanistic understanding of the interaction between implant surfaces and the biologic environment. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Introduction: Local delivery of antibiotics using bone cement as the delivery vehicle is an established method of managing implant-associated orthopedic infections. Various fillers have been added to cement to increase antibiotic elution, but they often do so at the expense of strength. This study evaluated the effect of adding a borate bioactive glass, previously shown to promote bone formation, on vancomycin elution from PMMA bone cement.Methods: Five cement composites were made: three loaded with borate bioactive glass along with 0, 1, and 5 grams of vancomycin and two without any glass but with 1 and 5 grams vancomycin to serve as controls. The specimens were soaked in PBS. Eluate of vancomycin was collected every 24 hours and analyzed by HPLC. Orthopedic-relevant mechanical properties of each composite were tested over time.Results: The addition of borate bioactive glass provided an increase in vancomycin release at Day 1 and an increase in sustained vancomycin release throughout the treatment period. An 87.6% and 21.1% increase in cumulative vancomycin release was seen for both 1g and 5g loading groups, respectively. Compressive strength of all composites remained above the weight-bearing threshold of 70 MPa throughout the duration of the study with the glass-containing composites showing comparable strength to their respective controls.Conclusion: The incorporation of borate bioactive glass into commercial PMMA bone cement can significantly increase the elution of vancomycin. The mechanical strength of the cement-glass composites remained above 70 MPa even after soaking for 8 weeks, suggesting their suitability for orthopedic weight-bearing applications.

IntroductionIn total hip arthroplasty (THA), polyethylene (PE) liner oxidation leads to material degradation and increased wear, with many strategies targeting its delay or prevention. However, the...

Silicon nitride (Si3N4) is biocompatible and stable invivo, and these properties, when combined with its superior mechanical properties, make Si3N4 an attractive ceramic implant material in some healthcare applications, particularly in orthopedic surgery. Si3N4 is used in spinal fusion surgery, is under development for use as bearings in joint replacement, and is being considered for use as dental implants. While Si3N4 implants are currently created using conventional ceramic processing techniques, additive manufacturing provides the capacity to create custom implants with the required anatomical shape, precise dimensions, and well-controlled microstructure. Si3N4 can be created with a smooth or microrough surface topography, and its surface chemistry can be varied from a silica-rich to a predominantly silicon-amine composition, which can influence the response of cells, tissues, and bacteria invivo. Si3N4 implants have shown attractive osseointegration and antimicrobial activity invivo, while Si3N4 bearings have shown low wear rates when articulating against itself or against polyethylene. The objective of this article is to review recent developments in the design, processing, and evaluation of Si3N4 implants for healthcare applications.

IntroductionOxide-based alumina (Al2O3) is used to manufacture femoral heads for total hip arthroplasty (THA). Silicon nitride (Si3N4) is a non-oxide ceramic used to make spinal implants. Ceramic m...

Although poly(methylmethacrylate) (PMMA) cements are widely used in orthopaedics, they have numerous drawbacks. This study aimed to improve their bioactivity and osseointegration by incorporating strontium-containing borate bioactive glass (SrBG) as the reinforcement phase and bioactive filler of PMMA cement. The prepared SrBG/PMMA composite cements showed significantly decreased polymerization temperature when compared with PMMA and retained properties of appropriate setting time and high mechanical strength. The bioactivity of SrBG/PMMA composite cements was confirmed in vitro, evidenced by ion release (Ca, P, B and Sr) from SrBG particles. The cellular responses of MC3T3-E1 cells in vitro demonstrated that SrBG incorporation could promote adhesion, migration, proliferation and collagen secretion of cells. Furthermore, our in vivo investigation revealed that SrBG/PMMA composite cements presented better osseointegration than PMMA bone cement. SrBG in the composite cement could stimulate new-bone formation around the interface between the composite cement and host bone at eight and 12 weeks post-implantation, whereas PMMA bone cement only stimulated development of an intervening connective tissue layer. Consequently, the SrBG/PMMA composite cement may be a better alternative to PMMA cement in clinical applications and has promising orthopaedic applications by minimal invasive surgery.