Abstract: There is provided a glass-ceramic substrate for an information storage medium usable in an information storage device of the ramp loading system. The glass-ceramic substrate has Young's modulus (GPa)/specific gravity of 37 or over and includes 0 to less than 10 weight percent (expressed on oxide basis) of Al2O3. The glass-ceramic substrate has, as its predominant crystal phases, lithium disilicate (Li2O.2SiO2) and &agr;-quartz (&agr;-SiO2), has a coefficient of thermal expansion within a range from 65×10−7/° C. to 130×10−7/° C. wtihin a temperature range from −50° C. to +70° C. and has a surface roughness (Ra) (arithmetic mean roughness) of 9 Å or below.

Abstract: A ceramic restoration based on a leucitic glass-ceramic, which is characterized in that the glass-ceramic includes by way of components 40-95 wt.-% SiO2 5-25 wt.-% Al2O3 5-25 wt.-% K2O 0-25 wt.-% Na2O 0-20 wt.-% CaO 0-8 wt.-% B2O3 0-0.5 wt.-% P2O5 0-3 wt.-% F, in that it contains, as sole crystalline phase, leucite in a total proportion from 20 to 45 wt.-%, at least 80% of the theoretically producible quantity of leucite being present, and in that it exhibits a linear coefficient of thermal expansion &agr;(20-500° C.) from 12.5·10−6 to 15.5·10−6 K−1. This glass-ceramic is particularly suitable for processing as pressed ceramic and can be advantageously faced with dental ceramic that exhibits a linear coefficient of thermal expansion &agr;(20-500° C.) from 13.5·10−6 to 17.0·10−6 K−1.

Abstract: A method for producing a machinable feldspathic porcelain comprising leucite is presented. Machinability is imparted to feldspathic porcelains by achieving homogeneous distribution of fine crystalline constituent comprised of at least one of the following leucite phases: potassium tetragonal leucite, rubidium leucite, cesium stabilized cubic leucite, rubidium stabilized cubic leucite, and pollucite. The porcelains produced in accordance with the present invention are readily machinable by using available diamond tooling techniques. Furthermore, the porcelains are especially useful for the fabrication of dental restorations using CAD/CAM technology.

Abstract: A dental porcelain composition, comprising a glassy matrix and leucite crystallites embedded therein, and having maturing temperatures in the range from about 600.degree. C. to about 885.degree. C. and CTEs in the range from about 11 to about 19, more preferably in the range from about 11.5 to about 18, and most preferably in the range from about 12 to about 17.5.times.10.sup.-6 /.degree.C. (measured from 25.degree. C. to 500.degree. C.). The tetragonal leucite is preferably both fine-grained (i.e, having average diameters of less than about 7 microns) and uniformly-sized. Preferably, the average diameters are less than about 1 to about 3 microns.

Abstract: A magnetic disc substrate is provided, which includes a magnetic disc substrate body made of glass and is characterized in that a metal element capable of absorbing light is present in at least a surface portion of the magnetic disc substrate body, and a texture is formed on a surface of the magnetic disc substrate body. Ions of the metal element are dispersed in the surface portion of the magnetic disc substrate, or the metal element is contained in a composition of the glass constituting the magnetic disc substrate in the form of an oxide. The glass is preferably a crystallized glass a Li.sub.2 O--Al.sub.2 O.sub.3 --SiO.sub.2 based crystallized glass, which particularly preferably contains 65 to 85 wt % of SiO.sub.2, 8 to 15 wt % of Li.sub.2 O, 2 to 8 wt % of Al.sub.2 O.sub.3, 1 to 5 wt % of P.sub.2 O.sub.5 and 1 to 10 wt % of ZrO.sub.2 and has lithium disilicate (Li.sub.2 O.multidot.2SiO.sub.2) as a main crystalline phase.

Abstract: A dental porcelain composition, comprising a glassy matrix and rubidium leucite crystallites embedded therein, and having maturing temperatures in the range from about 650.degree. C. to about 800.degree. C. and CTEs in the range from about 13 to about 17, more preferably in the range from about 13.5 to about 16, and most preferably in the range from about 14 to about 16.times.10.sup.-6 /.degree. C. (measured from 25.degree. C. to 400.degree. C.). The tetragonal rubidium leucite is preferably both fine-grained (i.e., having average diameters of less than about 5 microns) and uniformly sized. Preferably, the average diameters are less than about 1 to about 2 microns.

Abstract: The invention relates to a glass ceramic in which mica and ZrO.sub.2 are present in crystallized form, containing:K.sub.2 O: 0-9% by weightNa.sub.2 O: 0-9% by weight with the condition that Na.sub.2 O and K.sub.2 O together make up at least about 4% by weight,SiO.sub.2 : 35-60% by weightMgO: 10-25% by weightAl.sub.2 O.sub.3 : 7-30% by weightZrO2: 4-12% by weightF.sup.- : 2-10% by weight which is essentially free of lithium, calcium, strontium and barium, to a process for its production and to its use as a tooth replacement.

Abstract: A feldspathic porcelain composition is provided which comprises a continuous glassy matrix phase and a discontinuous, substantially uniformly dispersed cubic leucite crystalline phase, said composition possessing a fusion temperature of from about 800.degree. to about 1200.degree. C. Methods of making the feldspathic porcelain composition are also provided, said methods comprising the steps of forming an alkali aluminosilicate powder comprising SiO.sub.2, Al.sub.2 O.sub.3, K.sub.2 O and Na.sub.2 O and at least one metal salt of rubidium, cesium, calcium, strontium, barium or thallium; heating the powder to effect an exchange of alkali cations with metal cations derived from said metal salt to provide a feldspathic porcelain composition which comprises a continuous glassy matrix phase and a discontinuous crystalline phase comprising cubic leucite.

Abstract: A porcelain composition for dental restorations comprising a leucite crystallite phase and a glass matrix phase, wherein the leucite crystallites possess diameters not exceeding about 10 micron. Preferably, the porcelain composition has a maturing temperature from about 750.degree. to about 1050.degree. C. and a coefficient of thermal expansion from about 12.times.10.sup.-6 /.degree. C. to about 17.5.times.10.sup.-6 /.degree. C., and comprises:______________________________________ Component Amount (wt. %) ______________________________________ SiO.sub.2 57-66 Al.sub.2 O.sub.3 7-15 K.sub.2 O 7-15 Na.sub.2 O 7-12 Li.sub.2 O 0.5-3.

Abstract: A ZrO.sub.2 -containing glass ceramic is described, the main crystalline phase of which is formed by ZrO.sub.2 and which has at least one further crystalline phase, and which can be used in particular in dentistry.

Abstract: A glass-ceramic composite which has forsterite in an amount of 40 to 60% by weight is included in crystallized glass having a coefficient of thermal expansion of 100.degree. to 200.times.10.sup.-7 /.degree.C. is used to configure a package, to the electrode pads of which a quartz crystal is directly soldered, without any supporting material. A quartz crystal piece is included within a flat package that use a glass-ceramic composite according to the present invention, thereby greatly limiting the variation in resonance characteristics with respect to heat treating done when the package is sealed, as compared to previous packages.

Abstract: Multilayer green tape stacks having sufficient layers so that the fired stack is at least 2 millimeters in thickness on a metal support substrate are made by interleaving two types of green tapes comprising a low dielectric loss glass of a first type including at least 5% of an oxide filler and a green tape of a second type comprising a low dielectric loss glass and a higher amount of an oxide filler than the green tape of the first type, on a metal support substrate. These fired green tape stacks shrink on firing only in the thickness dimension.

Abstract: A crystallizable ceramic composition for forming a ceramic dielectric body having a dielectric constant in the range of 4.8-5.3 at 1 MHz and a linear thermal expansion coefficient of 4.0-5.1.times.10.sup.-6 K.sup.-1 in the temperature range of 25.degree.-200.degree. C. The dielectric composition comprises a mixture of finely divided particles of 10-90 wt % Mg-Al-Si glass and 10-90 wt % Ca-Al-B-Si glass. The dielectric composition can be used with organic solvents, polymeric binder and plasticizer to produce an unfired green tape which is cofirable with high electrical conductivity metallurgies such as gold, silver, silver-palladium and copper.

Abstract: This invention is directed at the makings of glass-ceramic which is uniquely suited for use as a disc substrate for utilization in a magnetic memory storage device. The glass ceramic material exhibits a crystal phase assemblage comprised predominately of a mixture of lithium disilicate and tridymite which are uniformly interspersed with a residual glass phase and form an interlocked microstructure with the glass. The composition consists essentially, expressed in terms of weight percent on the oxide basis, of 75-95% SiO.sub.2, 3-15% Li.sub.2 O, 0-6% Al.sub.2 O.sub.3, and 0-6% K.sub.2 O. The nucleating agent for this glass-ceramic is selected from the group consisting of 0-0.1% Pd and 0-5% P.sub.2 O.sub.5 ; however if Pd is absent the P.sub.2 O.sub.5 amount is at least 0.5% and if P.sub.2 O.sub.5 is absent then the Pd amount is at least 0.005%. Additionally, up to 15% of optional ingredients may be added, including, B.sub.2 O.sub.3, Na.sub.2 O, ZnO, MgO, CaO, SrO, ZrO.sub.2, TiO.sub.2, F, Sb.sub.2 O.sub.3, As.

Abstract: A ZrO.sub.2 -containing glass ceramic is described, the main crystalline phase of which is formed by ZrO.sub.2 and which has at least one further crystalline phase, and which can be used in particular in dentistry.

Abstract: A leucite-containing phosphosilicate glass-ceramic is described which, in addition to a leucite crystalline phase and at least one further crystalline phase, also contains one or more glass phases.

Abstract: A two-phase porcelain composition for dental restorations comprising a leucite crystallite phase dispersed in a feldspathic glass matrix, a maturing temperature of from about 750.degree. to about 1050.degree. C. and a coefficient of thermal expansion of from about 12.times.10.sup.-6 /.degree.C. to about 17.5.times.10.sup.-6 /.degree.C., said porcelain composition comprising:______________________________________ Component Amount (wt. %) ______________________________________ SiO.sub.2 57-66 Al.sub.2 O.sub.3 7-15 K.sub.2 O 7-15 Na.sub.2 O 7-12 Li.sub.2 O 0.5-3 CaO 0-3 MgO 0-7 F 0-4 CeO.sub.2 0-1 ______________________________________wherein the leucite crystallites possess diameters not exceeding about 10 microns and represent from about 5 to about 65 weight percent of the two-phase porcelain composition.

Abstract: Chemically derived leucite is claimed. The chemically derived leucite is obtained from a stable dispersion of a potassia precursor, an alumina precursor and a silica precursor having a specified dry weight solids content. Chemically derived tetragonal leucite is particularly useful as a component of a dental porcelain.

Abstract: Alkali-zinc-silicate glass ceramics and glasses are described which have a linear thermal expansion coefficient in the range from 8.0 to 18.7.times.10.sup.-6 K.sup.-1, an excellent chemical resistance and other advantageous optical properties and can be used in particular as dental material.

Abstract: A ceramic circuit board comprises a ceramic substrate having a glaze film formed thereon, the glaze film being overlaid with a functional thin film such as a ferromagnetic film serving as a magnetic sensor, for example. The ceramic substrate is made of a low-firing ceramic material such as a glass ceramic material which can be sintered at a temperature below 1000.degree. C. by co-firing with the glaze film. Preferably, the ceramic substrate has a recess on its top surface, and the glaze film is embedded in the recess such that the difference in level between the ceramic substrate and the glaze film is 20 .mu.m or less.

Abstract: Conductive via fill inks for green tapes to be stacked and bonded to a support substrate, the glass used for the green tape having a firing temperature from 850.degree.-950.degree. C., wherein the glass used for the via fill ink has a glass transition temperature that is higher than that of the glass used to make the green tape, preferably does not crystallize at the maximum firing temperature of the green tape and comprises from 30-75 percent by volume of the glass-conductive metal powder mixture of the via fill ink. These conductive via fill inks will not shrink until the green tape shrinkage has commenced during firing of the composite circuit board and they will flow slightly during firing, forming good bonds to the glass in the walls of the vias, thereby ensuring good integrity of the vias and good connections to the circuitry on the fired ceramic multilayer circuit board.

Abstract: A dental porcelain material free of yellow coloring or opacification upon firing is produced. A powder mixture is prepared by adding 0.1 to 2.0 wt % of antimony trioxide and 0.01 to 5 wt % of nitric acid or its salt or salt, to a porcelain starting material. The powder mixture is heat-treated at a temperature not lower than the softening temperature of the powder mixture to produce a fused mass which is pulverized and water-washed. 0.01 to 5 wt % of nitric acid or its salt or salts may be added again during the pulverizing step.

Abstract: Novel oxide coatings which can be conveniently applied to reinforcing fibers such as silicon carbide fibers, and which when introduced as a fiber coating into fiber reinforced ceramic matrix composites provide composites exhibiting improved resistance to embrittlement at high temperatures, are described. Oxides effective to provide the improved composites in accordance with the invention include CeO.sub.2 and ZrO.sub.2.

Abstract: A granular material which includes an inorganic substrate and a ceramic coating shows improved adhesion to bituminous surfaces, decreased alkalinity, and, when formulated as a three coated algae-resistant granule, exhibits improved algae-resistance over previously known granules. The ceramic coating comprises the reaction product of an alkali metal silicate and an aluminosilicate, the ceramic coating further including a borate compound and zinc oxide having a particle size less than about 0.13 micrometer. It has been found that the use of a borate compound and zinc oxide having the stated particle size allows the granules to be adhered to a substrate for longer periods of time, thus producing a surface which retains its original color for a longer period of time. Methods of producing such ceramic-coated granular materials, and composite sheets including the granules are also presented.

Abstract: A glass-ceramic for a magnetic disk substrate in which the grain size can be controlled and the surface roughness after polishing is within the range from 15 .ANG. to 50 .ANG. is provided by heat treating a base glass including in weight percent:______________________________________ SiO.sub.2 65-83% Li.sub.2 O 8-13% K.sub.2 O 0-7% Mgo + ZnO + PbO 0.5-5.5% in which MgO 0.5-5.5% ZnO 0-5% PbO 0-5% P.sub.2 O.sub.5 1-4% Al.sub.2 O.sub.3 0-7% As.sub.2 O.sub.3 + Sb.sub.2 O.sub.3 0-2% ______________________________________The glass-ceramic contains lithium disilicate (Li.sub.2 O. 2SiO.sub.2) and alpha-quartz (SiO.sub.2) as the main crystal phases.

Abstract: There is provided a composite oxide represented by the formulaiR.sub.2 O.jAl.sub.2 O.sub.3.kTiO.sub.2.mSiO.sub.2.nH.sub.2 Owherein R denotes an alkali metal, i is 0.3 to 1, k is 0 to 0.9, j+k=1, m is 7 to 70 and n is 0.2 to 0.4, said composite oxide being amorphous, and its cumulative specific pore volume of pores having a pore radius of 10.sup.4 A or less being 2.0 to 3.0 cc/g. This composite oxide can be produced by a process which comprises a first reaction step of adding an acid aqueous solution capable of forming a silicate by reaction with an alkali silicate to 7 to 10% by weight, calculated as silica, of an alkali silicate aqueous solution in the presence of a salt at 10 to 45.degree. C. such that a neutralization ratio becomes 20 to 40%, and a second reaction step of heating the reaction solution obtained in the above reaction at temperature of 90.degree. C.

Abstract: A vestibule block or interior furnace wall utilized in a diffusion furnace for manufacturing semi-conductors, integrated circuits and the like, and which is made of refractory or ceramic material, is treated on its surface with a suspension of fine particulate of a glass frit composition comprising an alkali earth metal alumino silicate, and is thereafter heated above the transition temperature of the alkali earth metal alumino silicate. Vestibule blocks and interior surface walls which have been treated in the above-described manner are highly abrasion resistant on their surface, generate virtually no particulate matter under conditions of ordinary use in the semi-conductor manufacturing processes, and generate significantly less particulate matter when tested in an abrasion test against vestibule blocks of the prior art.

Abstract: A ceramics composite material containing crystallized glass as the matrix and fibers or whiskers of ceramics as a reinforcement material, is obtained by melting original glass to form crystallized glass, compounding the same with fibers or whiskers of oxide ceramics and thereafter crystallizing the original glass. This ceramics composite material does not form any voids and can easily contain at least 50 volume percent of the reinforcement material, whereby a good mechanical strength and fracture toughness are achieved. In the compounding step, the content of the reinforcement can be further increased by forcing out any excess part of the original glass from the reinforcement material by applying pressure to a substance obtained by mixing the original glass with the reinforcement. Further, the ceramics composite material can be efficiently formed into a desired configuration by heating because the original glass flows viscously.

Abstract: There is provided a composite oxide represented by the formulaiR.sub.2 O.jAl.sub.2 O.sub.3.kTiO.sub.2.mSiO.sub.2.nH.sub.2 Owherein R denotes an alkali metal, i is 0.3 to 1, k is 0 to 0.9, j+k=1, m is 7 to 70 and n is 0.2 to 0.4,said composite oxide being amorphous, and its cumulative specific pore volume of pores having a pore radius of 10.sup.4 A or less being 2.0 to 3.0 cc/g. This composite oxide can be produced by a process which comprises a first reaction step of adding an acid aqueous solution capable of forming a silicate by reaction with an alkali silicate to 7 to 10% by weight, calculated as silica, of an alkali silicate aqueous solution in the presence of a salt at 10.degree. to 45.degree. C. such that a neutralization ratio becomes 20 to 40%, and a second reaction step of heating the reaction solution obtained in the above reaction at a temperature of 90.degree. C.

Abstract: A ceramics composite material containing crystallized glass as the matrix and fibers or whiskers of ceramics as a reinforcement material, is obtained by melting original glass to form crystallized glass, compounding the same with fibers or whiskers of oxide ceramics and thereafter crystallizing the original glass. This ceramics composite material does not form any voids and can easily contain at least 50 volume percent of the reinforcement material, whereby a good mechanical strength and fracture toughness are achieved. In the compounding step, the content of the reinforcement can be further increased by forcing out any excess part of the original glass from the reinforcement material by applying pressure to a substance obtained by mixing the original glass with the reinforcement. Further, the ceramics composite material can be efficiently formed into a desired configuration by heating because the original glass flows viscously.

Abstract: This invention relates to a process for preparing a lithium containing ceramic article. The process provides a ceramic article that is substantially crack free and has as its principal crystalline phase a beta-eucryptite phase, a beta-spodumene phase, or a mixture thereof. The process comprises calcining a powder of a lithium-exchanged zeolite up to its collapse temperature for a time sufficient to collapse the zeolite framework and provide an amorphous powder. The amorphous powder is now formed into a shaped article and sintered at a temperature of about 700.degree. to about 1150.degree. C. for a time of about 1 to about 12 hours. The zeolites which can be used are those having a SiO.sub.2 Al.sub.2 O.sub.3 ratio of about 2 to about 8.5 and include zeolite B, zeolite ZK-19, zeolite W, phillipsite, hormotome, gismondine and mixtures thereof and have a sodium content less than about 1 weight percent. It is preferred that the lithium-exchanged zeolite have an average particle size of less than about 10 microns.

Abstract: Alkali metal- and alkaline earth metal-oxide aluminosilicate amorphous glass articles can be strengthened by providing such glass with a cerium dioxide sensitizer and a nucleating agent, irradiating the article with electromagnetic radiation, heating the irradiated article to a temperature between about the annealing and softening points of the glass, and cooling the heated, irradiated glass article. The treated article has a thick lower layer of the amorphous glass, but a thin layer of this glass at the surface of the article has been converted to a crystalline state. In this surface layer, some of the cerium has been converted from a +3 to a +4 ionic state and some of the metal element in the nucleating agent has been changed to a metallic state. The adjacent location of the lower and surface layers creates large compressive stresses at the surface layer which imparts great strength to the glass article.

Abstract: The present invention is directed to a method for synthesizing highly crystalline pollucite articles at temperatures not exceeding 1650.degree. C. The method comprises two general steps:(a) a glass frit is prepared having a composition varying from approximately the stoichiometry of Cs.sub.2 O.2SiO.sub.2 to approximately the stoichiometry of Cs.sub.2 O.4SiO.sub.2 with, optionally, up to 5% Al.sub.2 O.sub.3 ; and(b) that glass frit is reacted at a temperature between about 1000.degree.-1650.degree. C. with an Al.sub.2 O.sub.3 -containing material in sufficient amounts to yield a final product having a stoichiometry approximating that of pollucite.

Abstract: A wear-resistant alumina material is disclosed, as is its preparation by liquid phase sintering a mixture of about 70 to 95 percent by weight of crystalline Al.sub.2 O.sub.3 particles and about 30 to 5 percent by weight of glass phase-forming components in a nitrogenizing atmosphere from which oxygen is substantially excluded. Generally, the resulting material has a 5 Kg Vickers hardness which is at least about 5 percent greater than the hardness of a corresponding alumina material sintered in air.

Abstract: A ceramic material suitable for packaging of large scale integrated circuits is produced by the process of forming a mixture of a powdered glass ceramic material which is a glassy precursor to cordierite ceramic material, formed by the steps which are as follows:a. Mix tetragonal phase material selected from the group consisitng of zirconia or hafnia powder containing a stabilizing oxide compound selected from the group consisting of MgO, CaO and Y.sub.2 O.sub.3 and a glass frit powder or frit of a glassy precursor of cordierite glass ceramic to yield a suspension of solids. Preferably, a binder is included.b. Disperse the suspended solids to yield a dispersion of the zirconia or hafnia with the stabilizing oxide compound and the glassy precursor.c. Densify the dispersion of zirconia or hafnia with the stabilizing oxide compound and the glassy precursor by a sintering heat treatment at a temperature of about 840.degree. C.

Abstract: Translucent feldspathic dental porcelain compositions and dental restoration made therefrom exhibiting a crystalline leucite content of at least about 45% by weight, wherein said leucite crystallites exhibit a size of less than about 35 microns, comprising:______________________________________ Component Percentage (by weight) ______________________________________ SiO.sub.2 55-70 Al.sub.2 O.sub.3 16-20 CaO 0.5-5.0 MgO 0.5-5.0 Li.sub.2 O 1.0-5.0 Na.sub.2 O 2.0-5.0 K.sub.2 O 12.5-22.5 Ce.sub.2 O.sub.3 0-1.0 ______________________________________said dental restorations exhibit a compressive strength of at least about 125,000 p.s.i., a flexural strength of at least about 16,000 p.s.i., and a diametral tensile strength of at least about 6,000 p.s.i., thereby obviating the need for metal as ceramic supports.

Abstract: Porcelain compositions, especially dental porcelain compositions, which contain leucite crystals in controlled amounts in a glassy phase matrix to permit selective adjustment of the thermal coefficient of expansion of the porcelain compositions, including methods of preparing and using same and products derived therefrom.

Abstract: There is disclosed a single-frit porcelain powder, suitable for use as a porcelain layer on metal-base dental restorations, and having a fired coefficient of thermal expansion within the range of from about 12 to about 14.times.10.sup.-6 in./in. .degree.C., wherein said single frit porcelain is of the following composition:______________________________________ Component Weight Percent ______________________________________ SiO.sub.2 651/2 .+-. 4 Al.sub.2 O.sub.3 15 .+-. 2 K.sub.2 O 121/2 - 1, + 2 Flux 4 .+-. 1 MO 2 .+-. 1 ______________________________________wherein M represents calcium, magnesium, or a mixture thereof, and Flux represents sodium oxide or lithium oxide, or a mixture thereof, and, optionally, may also contain boron oxide.

Abstract: There are disclosed glass-ceramic materials characterized by a nepheline crystal phase and optionally having a secondary celsian or hexacelsian crystal phase. In addition to the SiO.sub.2, Al.sub.2 O.sub.3, Na.sub.2 O, and TiO.sub.2 as a nucleating agent, the materials contain K.sub.2 O and/or Li.sub.2 O in limited amount, and preferably also contain BaO. These additives provide microwave compatibility, a thermal coefficient of expansion below 95.times.10.sup.-7 /.degree.C., and suitability for application as glazed table or ovenware.

Abstract: This invention is concerned with the production of glass-ceramics especially suitable for incorporating radioactive wastes. The inventive glass-ceramics contain at least two crystal phases selected from the group of pollucite, mullite, monazite, and, optionally, tetragonal or cubic zirconia as the predominant crystal phases and consist essentially, expressed in weight percent on the oxide basis, of 5-40% Cs.sub.2 O, 15-50% Al.sub.2 O.sub.3, 0-30% La.sub.2 O.sub.3 +CeO.sub.2, 0-20% P.sub.2 O.sub.5, 0-30% ZrO.sub.2, 12-65% La.sub.2 O.sub.3 +CeO.sub.2 +P.sub.2 O.sub.5, and 15-50% SiO.sub.2.

Abstract: The present invention is concerned with glass-ceramic articles which are extremely resistant to impact and spontaneous delayed breakage, are capable of being sawn with a diamond wheel to a depth of over one-third the cross section thereof without breakage, and exhibit modulus of rupture values of at least 150,000 psi. The articles consist of a body portion and an integral surface compression layer having a depth of at least 0.005". The body portion consists essentially, in weight percent, of about 8-13% Na.sub.2 O, 7-13% K.sub.2 O, 30-36% Al.sub.2 O.sub.3, 35-43% SiO.sub.2, and 6-10% RO.sub.2, wherein RO.sub.2 consists of 6-10% TiO.sub.2 and 0-4% ZrO.sub.2, wherein the molar ratio Al.sub.2 O.sub.3 :SiO.sub.2 is >0.5 but <0.6 and the molar ratio K.sub.2 O:Na.sub.2 O is >1:3 but <1 and contains nepheline solid solution crystals corresponding to the formula Na.sub.8-x K.sub.x Al.sub.8 Si.sub.8 O.sub.32, with x varying from 0.25-4.73, as the predominant crystal phase.